Critical Materials (Materials Today) 9780128187890, 9780128187906

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Critical Materials

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Materials Today

Critical Materials

Alexander King

Elsevier Radarweg 29, PO Box 211, 1000 AE Amsterdam, Netherlands The Boulevard, Langford Lane, Kidlington, Oxford OX5 1GB, United Kingdom 50 Hampshire Street, 5th Floor, Cambridge, MA 02139, United States © 2021 Elsevier Inc. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein. Library of Congress Cataloging-in-Publication Data A catalog record for this book is available from the Library of Congress British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library ISBN: 978-0-12-818789-0 For information on all Elsevier publications visit our website at https://www.elsevier.com/books-and-journals

Image Credit: Trevor M. Riedemann. This photograph has been authored, in whole or in part, under Contract No. DE-AC02-07CH11358 with the U.S. Department of Energy.

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Contents

Acknowledgments Abbreviations and acronyms Preface 1

2

3

ix xi xv

What happened to the rare earths? Monopoly, price shock, and the idea of a critical material The essentiality of the rare earths Rare earth sources Rare earth supply challenges—2005–15 After the price spike Lessons learned: The price spike in hindsight Coda: Every challenge is also an opportunity References

1 2 7 9 13 14 15 17

This is not new. A short history of materials criticality and supply-chain challenges Copper and the end of the Bronze Age (~ 1200 BCE) The Venetian monopoly on glass Cordite in World War I (1914–18) Silk and nylon (the 1930s and 1940s) World War II (1939–45) Old lead (1978) Cobalt (1978) Niobium (1979) Molybdenum (1980 and 2004) Tantalum (1997, 2000, and 2008) Photovoltaic silicon (mid-2000s) Rhenium (2006–08) Lessons learned References

19 19 21 23 24 24 38 40 41 42 43 44 47 47 50

Assessing the risks Defining critical materials Assessments of materials criticality Consistency and contrast Variation of criticality over time Regional perspectives on criticality

53 53 54 57 60 73

vi

Contents

Indicators of criticality What does criticality mean? Consequences of criticality Tipping points. What takes us from criticality to crisis? Lessons learned What will we need? References

75 86 87 87 91 91 92

4

What changed after the rare earth crisis? Impacts of the rare earth crisis Conflicts and conflict resolution The supply side The demand side Postcrisis rare earth prices and utilization Lessons learned References

95 95 97 99 101 120 121 121

5

Mitigating criticality, part I: Material substitution The challenge of inventing materials on demand Improving the forecast Using existing materials Increasing the speed of new material discovery and deployment Lessons learned References

123 123 124 126 129 159 159

6

Mitigating criticality, part II: Source diversification How are mines developed? Conventional mines Unconventional sources Coproduction Progress since the rare earth crisis Lessons learned References

161 162 165 179 184 198 199 199

7

Mitigating criticality, part III: Improving the stewardship of existing supplies Urban mines versus conventional mines Regulatory versus economic drivers Reducing manufacturing waste In-process recycling End-of-life recycling Recycling as a response to criticality: Successes and failures What fraction of current need can be met by recycling? Emerging targets for recycling Potentially viable recycling technologies

205 205 206 208 210 212 215 218 221 228

Contents

8

vii

Lessons learned References

233 234

Tactics and strategies for the future What have we learned? Time is the biggest challenge Summary Epilog: Criticality in the time of coronavirus References

235 235 236 252 253 253

Index

255

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Acknowledgments

This book is an attempt to summarize what I have learned in the process of setting up and running the Critical Materials Institute for its first 5 years, and I have had many teachers. The late Karl Gschneidner, Jr. was my mentor on all things related to the rare-earth elements, and he is greatly missed. All of the people of CMI have contributed to my education but especially its leadership team, which has included Iver Anderson, Gretchen Baier, Joni Barnes, Deb Covey, Rod Eggert, Cynthia Feller, Yoshiko Fujita, Dan Ginosar, Chris Haase, Carol Handwerker, the late Scott Herbst, Ed Jones, Tom Lograsso, Scott McCall, Bruce Moyer, Eric Peterson, Brian Sales, Adam Schwartz and Eric Schwegler. Others have provided notable input, specific contributions, and moments of enlightenment or levity, including Jenni Brockpahler, Steve Constantinides, Bill McCallum, Ikenna Nlebedim, Duane Johnson, Richard LeSar, John Ormerod, Ryan Ott, Orlando Rios, Sadas Sadasivan, Alok Srivastava, Stan Trout, Patrice Turchi, Jeff Wang, David Weiss, and probably a few others who have slipped my memory. The US Department of Energy supported the learning phase of this work by funding the Critical Materials Institute through the Division of Energy Efficiency and Renewable Energy’s Advanced Manufacturing Office. This book was written with the support of the Iowa State University of Science and Technology. Finally, my wife, Christine, has provided steadfast forbearance and stability amid the chaos, along with some timely professional consultation on information resources.

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Abbreviations and acronyms

ACREI AI AIM AIST ALMR AMD AMR ASTM ASX At. No. BCE BFR BGS CAGR CALPHAD CAPEX CENRS CES CFL CMI COVID-19 CPU CRIRSCO CRM CRT DARPA DfD DFS DFT DHS DKB DOE DRAM DRC EC EEZ EU EV FOB

Association of Chinese Rare Earth Industries artificial intelligence accelerated insertion of materials The National Institute of Advanced Industrial Science and Technology (Japan) Association of Lamp and Mercury Recyclers acid mine drainage anisotropic magnetoresistance American Society for Testing and Materials Australian Stock Exchange atomic number before the Christian (or common) era brominated flame retardant British Geological Survey compound annual growth rate calculation of phase diagrams capital expenditures Committee on Environment, Natural Resources, and Sustainability (of NSTC) Cambridge Engineering Selector (from Granta Design) compact fluorescent lamp Critical Materials Institute coronavirus disease 2019 central processor unit Committee for Mineral Reserves International Reporting Standards critical raw material cathode ray tube Defense Advanced Research Projects Agency (the United States) design for disassembly definitive feasibility study density functional theory Department of Homeland Security of the United States designer knowledge base Department of Energy of the United States dynamic random-access memory Democratic Republic of the Congo (since 1997), formerly Zaire European Commission exclusive economic zone European Union electric vehicle free on board at shipping point (means that ownership is transferred to the purchaser when goods leave the named shipping point)

xii

GM GMR GPS GRS GTP HD HDD HDDR HEU HEV HREE HSLA IC ICE ICME iNEMI IR ISO JCG JORC LCO LENS LEU LIBS LME LREE MD MESS MGI MRI MRT MSX NASA NEDO NI-43101 NIST NMC NORM NRC NSTC NYMEX OPEX PEA PFS PGM ppm

Abbreviations and acronyms

General Motors giant magnetoresistance global positioning system government rubber styrene Global Tungsten and Powders Corporation hydrogen decrepitation hard disk drive hydrogenation, disproportionation, desorption, and recombination high-enriched uranium hybrid electric vehicle heavy rare-earth element high strength, low alloy (of steels) integrated circuit internal combustion engine integrated computational materials engineering International Electronics Manufacturing Initiative infrared International Standards Organization Japan Coast Guard Joint Ore Reserves Committee (produces the Australasian code for reporting of exploration results, mineral resources, and ore reserves) lithium cobalt oxide laser engineered net shaping low-enriched uranium laser-induced breakdown spectroscopy London Metal Exchange light rare-earth element molecular dynamics multiple elements from a single source materials genome initiative magnetic resonance imaging molecular recognition technology membrane solvent extraction National Aeronautics and Space Administration New Energy and Industrial Technology Development Organization (Japan) National Instrument 43-101 (Canadian resource assessment and reporting standard) National Institute of Standards and Technology (the United States) lithium nickel manganese cobalt oxide naturally occurring radioactive material National Research Council (of the US National Academies of Sciences, Engineering, and Medicine) National Science and Technology Council (of the United States) New York Mercantile Exchange operating expenditures preliminary economic assessment preliminary feasibility study platinum group metal parts per million

Abbreviations and acronyms

PRC PV PVC QP R&D RAM REE REO REPM REY ROI ROW SAMREC SCSMSC SOFC SX TBC TREO TRL TSX US, USA UV WTO WWI WWII XRF YSZ

Peoples’ Republic of China photovoltaic polyvinyl chloride quench and partition research and development random-access memory rare-earth element rare-earth oxide rare-earth permanent magnet rare earths plus yttrium, i.e., the lanthanides plus yttrium return on investment Rest of World, i.e., all countries except China South African Mineral Reporting Codes Subcommittee on Critical and Strategic Mineral Supply Chains (of NSTC) solid oxide fuel cell solvent extraction thermal barrier coating total rare-earth oxide, i.e., the sum over all of the rare-earth elements technology readiness level Toronto Stock Exchange The United States (of America) ultraviolet World Trade Organization World War I World War II X-ray fluorescence yttria-stabilized zirconia

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Preface

I did not set out to write this book. In 2010 a group of researchers gathered to design an agenda for research and development that aimed at alleviating the challenges to rare-earth supplies that were then emerging. In 2013 the Critical Materials Institute was stood up, and I served as the director for its first 5 years. As we and others around the world pursued various lines of research, we learned a lot of things that did not work and also found a few that did. This volume is an attempt to summarize that knowledge, as logically and methodically as such recent hindsight allows, to create a guide for others working threats to materials supply chains. This is not a book about materials science. Although a certain amount of materials science is included, it is usually only described at the level of an introductory college class, and much more detailed texts are available if you want to read deeply into that subject. This book is about the intersections of materials science, manufacturing and public policy. My goal has been to include just enough about each of these topics to enable the practitioners of the others to understand each other and have enough vision into their different worlds to recognize where their efforts may or may not align. When they align, impact is possible; when they do not, all effort is for naught. I draw on historical and recent examples of R&D efforts that have helped to alleviate material shortages, along with cases where they have failed to have any impact despite the excellence of the research. Lessons learned from these case studies are used to identify the traits of successful programs and the pitfalls that should be avoided in creating research-based solutions to material supply challenges. Alexander King Ames, IA, United States

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What happened to the rare earths? Monopoly, price shock, and the idea of a critical material

1

Every manufactured thing is made of some kind of material. In some cases manufacturers are free to choose among different materials that can meet their needs, and they make selections according to the cost or properties of the available materials, to optimize profit or performance. In other cases there is only one material that meets the needs of the manufactured object. Thomas Edison’s incandescent electric lightbulb famously depended on the identification of a material to use for the hot, glowing filament, and after testing hundreds or maybe thousands of possible materials, tungsten was identified as the only one that met the needs: It could be heated by an electric current, and it did not melt at the elevated temperatures where it would glow and provide light. Materials that are necessary for a particular product, like tungsten in lightbulbs, are regarded as essential. You can’t make the product without them, and there are no ready substitutes to use if you can’t get them. Today’s technologies are full of essential materials: All of our smart devices rely on data processing enabled by silicon and several ancillary materials; nuclear reactors need uranium to produce heat that is eventually converted to electricity; early photocopiers and laser printers were enabled by the particular properties of selenium sulfide print drums; electrical energy storage is dominated by rechargeable batteries made with lithium; and despite increasing use of carbon fibers, the aviation industry still depends very heavily on aluminum-based structures. Essential materials have particular properties that make them work: Tungsten has a very high melting point, silicon is a semiconductor, uranium’s atomic nucleus can be fissile, selenium sulfide is a photoconductor that only transmits electricity when it is exposed to light, lithium is easily ionized and transported between the electrodes of batteries, and aluminum has high strength relative to its weight and cost. Because of their properties, these (and many other) materials are, or have been, essential. As will be clear from some of these examples, essentiality is not a permanent property of a material: Incandescent lighting has been replaced by other more efficient technologies, nuclear power is increasingly unpopular in many parts of the world, selenium sulfide has been replaced by amorphous silicon in laser printers, and aluminum is being replaced by carbon fiber composites in some airplanes. The rare earths are a particular set of chemical elements whose properties make them essential to a wide range of products. These once-obscure substances started to gain attention in the late 2000s because they are essential to many technologies, and their supplies were perceived to be threatened.

Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00001-3 © 2021 Elsevier Inc. All rights reserved.

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When an essential material has a risk of supply disruptions, it is considered a critical material, and when supply concerns erupted about the rare earths, they sparked broader interest in the general issue of critical materials. A decade after the rare earth price shock, we have learned a great deal about criticality, materials supply crises, and how best to manage them.

The essentiality of the rare earths The rare earths comprise 17 chemical elements including all of the lanthanides, the 15 elements from lanthanum (atomic number 57) to lutetium (At. No. 71). Scandium (At. No. 21) and yttrium (At. No. 39) are usually included in the set of rare earth elements (REEs), because they also belong to Group 3 of the periodic table and are closely related to the rare earths in terms of their chemical behavior. All of the rare earth elements are shown in Fig. 1.1. The definition of the set of elements that belong to the rare earth category is not always consistent. Some authors exclude or ignore scandium, and some authors refer to the “rare earths plus yttrium” (REY) implying that they only consider the lanthanides to be “true” rare earths. Distinctions are frequently drawn between “light” and “heavy” rare earths, based upon their atomic weights, but the borderline between light and heavy is variable, and some people apply the label “medium” to an intermediate group, also of variable membership. Despite this variability, distinctions between light and heavy rare earths are useful. Rare earth mines are typically described as being

Fig. 1.1 The rare earth elements include all of the lanthanide series along with scandium and yttrium.

The rare earths and the idea of a critical material

3

richer or poorer in one or other category—and yttrium is more often associated with heavy rare earths in this context, so it is considered a “heavy rare earth,” despite its relatively low atomic weight. The first rare earths were discovered in 1787, in the form of a black mineral from a quarry in Ytterby, Sweden, near Gothenburg. From this rock the Finnish chemist Johan Gadolin extracted an oxide (or “earth”), which he named ceria, after Ceres, the Roman goddess of agriculture, grain crops, fertility, and motherly relationships. He published the discovery in 1794 [1]. Only later were the various rare earths separated from each other and reduced into elemental metals, but as they were successively isolated, uses for them also developed. A newly discovered rare earth bearing mineral was named gadolinite in 1800, in Gadolin’s honor. When element number 64 was discovered in 1880, it was named after him, too—gadolinium—even though it is not extracted from gadolinite. Like gadolinium, most of the rare earths were discovered in the late 19th and early 20th centuries, following the development of the periodic table by Mendeleev, in 1867 [2]. The systematic organization of the chemical elements predicted the existence of elements that were not yet known, and a large part of chemical science of that time was devoted to finding them. It was assumed that the lanthanides must be rare because they were not found very easily, and the term “rare earth” stuck. In fact the rare earth elements are not so much rare as they are elusive. Except for promethium (At. No. 61), which decays radioactively, has no stable isotopes, and is not found in nature, the rare earths are fairly abundant in the crust of the Earth with cerium being the most abundant rare earth and the 25th most-abundant element of all. Overall, elemental abundance in the Earth’s crust are shown in Fig. 1.2, but this does not tell the whole story: the REEs are neither commonly found in isolation nor in very high concentrations. While significant geologic concentrations of iron, nickel, and other elements exist as ores in many places on Earth, the rare earths are rather more uniformly distributed, and where they are locally concentrated, they tend to be found in mixtures and are very hard to separate from each other and also from oxygen. Their chemical similarity is responsible for both their colocation and the difficulty of separating them. Their high affinity for oxygen not only makes it hard to produce metal from their ores but also drives some of their essential uses. Some of the earliest uses were pioneered by Carl Auer von Welsbach [3]. In many cases former uses have ceased, either because the application became obsolete or alternative materials were identified, but some of Auer’s inventions have had a surprising persistence. Lanthanum, cerium, and yttrium oxides, combined with magnesium oxide, formed the first commercial rare earth material, and it was used for gas-lamp mantles. Auer’s 1885 patent on “Actinophor” was the basis of a business that he started in 1887. Although the material had good emissive power for light and it glowed brightly when heated, the color spectrum was greenish and not considered very attractive, so in 1890 Auer and Haittinger patented an improved gas mantle comprising 99% thoria and 1% ceria [3]. This produced a whiter light, and it became the dominant gas mantle material worldwide, lasting until electric lighting eventually replaced gas: it remains in use today for some gas lanterns such as those used by recreational campers. Thoria is

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Fig. 1.2 The abundance of the elements in the earth’s crust, relative to the abundance of silicon. Despite their name the rare earths are not exceptionally scarce. From G.B. Haxel, J.B. Hedrick, G.J. Orris, Rare Earth Elements—Critical Resources for High Technology” (fact sheet), US Geological Survey. https://pubs.usgs.gov/fs/2002/fs087-02/ fs087-02.pdf .

not a rare earth since thorium is an actinide element, not a lanthanide, but the need to find a source for thoria had a profound impact on the production of rare earths. Among other uses for the rare earths, carbon arc lamps, especially those used in large movie projectors, were significantly enhanced by additions of lanthanum and other rare earth elements to the carbon electrodes, but like gas lamps, this technology is largely a thing of the past. Mischmetal was originally developed by Auer as a mixture of 30% iron and 70% rare earths and today typically contains roughly 50% cerium, 25% lanthanum, and small amounts of neodymium and praseodymium. It is used as a spark generator for cigarette lighters and welding torch igniters—an enduring use over many decades [3] made possible by the highly exothermic reaction of the rare earths with atmospheric oxygen, when a fresh surface is exposed by scraping. In the 1920s praseodymium began to be used as a yellowish-orange stain for ceramics and remains in use for this application today. Around the same time, neodymium started to be used to tint glass for both decorative use and for industrial goggles for glassworkers and welders. It also remains in use for this purpose. General Electric’s premium Reveal incandescent lightbulb line used neodymium-tinted glass envelope to provide an improved color balance relative to other incandescent lamps,

The rare earths and the idea of a critical material

5

but this application has been replaced by a new LED version of the Reveal product line, which develops its characteristic spectrum through different means. All of these uses of rare earths (with the possible exception of welding goggles) may now be considered to be somewhat inessential, optional, or “boutique” applications that are either small in volume, are easily replaced, or have otherwise been made obsolete. The 1960s, however, saw two new applications for rare earth elements, in which unique benefits emerged from the electronic orbital structure of the lanthanides. These are the first large-scale, initially nonsubstitutable uses for rare earth materials. Zeolite catalysts for crude oil cracking, known as fluid cracking catalysts, or FCCs, are stabilized by the addition of rare earths and achieve significantly longer life as a result of the addition of yttrium and other REEs. The first generation of color televisions suffered from poor color saturation because of the low output of the available red phosphors and the resulting need to “mute” the green and blue phosphors to maintain a reasonable color balance. This all changed with the discovery of a brighter red phosphor, europium-doped yttrium orthovanadate, which was first adopted by Zenith Electronics, and then industry wide. Truly essential uses for the rare earths were in place for the first time, at least if you believe that color TVs are essential. Cerium oxide, or ceria, is used in powder form as a chemical-mechanical planarization medium for silicon wafers and as “optician’s rouge” for polishing glass, combining excellent abrasive properties with a mild chemical attack of the target materials. It also has widespread applications in catalysis, being used in some automotive catalytic converters and in the coatings of self-cleaning ovens. Yttrium oxide, or yttria, has a range of uses including the tough structural ceramic yttria-stabilized zirconia (YSZ) that has many uses including protective coatings on the turbine blades of jet engines, allowing them to run at higher temperatures where they are more efficient. Yttria is the host material for europium and terbium dopants that make red and green phosphors. It is used in dental porcelain and is an essential component in YBa2Cu3O7 high-temperature superconductors. Yttrium is frequently added to metallic alloys to improve their oxidation resistance. Other uses of rare earths have come and gone over time. Gadolinium gallium garnet single crystals, for example, were used as substrates for permanent memory chips based on the technology of magnetic bubbles in IBM computers of the 1970s and 1980s. Major new uses for rare earth elements emerged in 1967 with the discovery of highpowered permanent magnets based on samarium and cobalt [4] and again in 1982 with the discovery of even stronger magnets based on neodymium, iron, and boron [5, 6]. Today a large fraction of the permanent magnet market depends on the Nd-Fe-B formulation and its derivatives. Current uses of the rare earths tend to focus particularly on the properties imparted by their 4f electrons, which are unique to the lanthanides and result in applications related to optical properties, magnetic properties, catalysis, and to some extent mechanical properties. Rare earths are sometimes used to modify the microstructures of major metal products, appearing as grain refiners for castings of aluminum, for example. A partial list of current applications is provided in Table 1.1. In each of these

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Table 1.1 Principal current uses of the rare earths. Element

Current uses

Scandium Yttrium

Structural alloys, medical lasers, metal halide lamps Phosphors, catalysts, propane gas mantles, oxygen sensors, structural metal alloys, structural ceramics, thermal barrier coatings, microwave filters, transducers, gemstones, pharmaceuticals, high-temperature superconductors Ni-M-H rechargeable batteries, lighter flints, electron emitters, fiberoptic glasses, scintillators for radiation detection, high-refractive index optics, abrasives, steels, welding, phosphors, phosphate control Structural metal alloys, polishing, fuel cracking catalysts, self-cleaning ovens, automotive catalytic converters, phosphors, pigment stabilization Pigments, magnets, structural metal alloys, lighting, welders’ goggles, fiber-optic amplifiers, catalysts, lighter flints Pigments, magnets, lasers, cryocoolers, fertilizers, automobile rear-view mirrors

Lanthanum

Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium

Holmium Erbium Thulium Ytterbium Lutetium

Magnets, cancer treatment, nuclear reactor control rods, IR absorbers Phosphors Cancer treatment, neutron radiography, MRI contrast agents, neutron shielding, structural metal alloys Phosphors, magnets (vs Dy), magnetostrictive actuators, SOFCs (vs Y) Magnetostrictive actuators, thermal neutron absorbers, lasers, IR sources, metal-halide lamps, radiation dosimeters, catalysts, adiabatic refrigeration Magnetic flux concentrators, neutron absorbers, lasers, fiber-optics, pigments, magnets (vs Dy) Lasers, optical amplifiers, medical lasers, neutron absorbers, vanadium alloys, pigments for artificial gemstones, cryocoolers Portable X-ray sources, lasers (especially in surgery), radiation dosimeters, fluorescent anticounterfeiting banknote dyes Gamma-ray sources, stainless steels, lasers, fiber-optics Metal alloys, catalysts, cancer treatment

applications, rare earth elements are considered to be difficult or impossible to substitute. Particularly important and persistently unsubstitutable uses for the rare earths include europium, for red light-emitting phosphors, terbium for green light-emitting phosphors, erbium for fiber-optics and medical lasers, and samarium, neodymium, and dysprosium for high-strength permanent magnets. Gadolinium is also important in the control systems of some nuclear reactors, because the uniquely high neutron capture cross section of its nucleus makes it a very effective neutron flux moderator. Despite the challenges of maintaining a supply chain for rare earth materials, new potential uses continue to emerge, and a partial list of these is provided in Table 1.2. It is possible or even likely, of course, that many of these technologies will fail to

The rare earths and the idea of a critical material

7

Table 1.2 Potential and emerging uses of the rare earths. Element

Potential and emerging uses

Scandium Yttrium Lanthanum Cerium

Lightweight high-strength structural materials Increasing concentrations in next-generation YSZ Hydrogen storage Solid oxide fuel cells, electronic applications (in fullerines), magnets, structural metal alloys, catalysts Magnetic refrigeration Downconversion of UV light to improve the efficiency of silicon solar cells

Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium

Quantum computing, X-ray lasers, thermoelectrics Quantum computing Magnetic refrigeration, solid oxide fuel cells SOFCs

Lasers and optics, cryocoolers, vanadium alloys, pigments Pigments Ultra-high-precision clocks, military pyrotechnics Pigments, lithographic lenses, X-ray phosphors

penetrate the market as a result of the usual barriers to commercialization (often characterized as the “valley of death”), but the challenges are increased in cases where an essential material is known to be critical in the sense described in this book, since this tends to deter interest from investors.

Rare earth sources As uses for the rare earths emerged around the beginning of the 20th century, sources for them were developed in a variety of places. From 1900 to about 1960, most of the supplies came from monazite ores in “placer deposits,” associated with alluvial sand. Monazite is nominally either cerium or lanthanum phosphate, but the cation is actually a mixture of different rare earths, and the anion can also be a mixture of phosphate and silicate ions. The mineral can include thorium in addition to the rare earths. Monazite exists as isolated crystals in igneous rocks such as granite, zircon, or ilmenite, and these crystals are released as grains of sand when the rocks weather. The potential of extracting REEs from monazite was identified by Carl Auer von Welsbach, who discovered it in ballast sand in the bilges of a Brazilian ship, as a source of thorium to provide the material for his lamp mantles. While thorium was the initial target of monazite mining, rare earths such as cerium and lanthanum could be extracted, too. Brazil and India dominated the market for monazite until the outbreak of World War

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II, when South Africa also began production. Australia and the United States (particularly in North Carolina) have also been producers of this ore from time to time. New uses for the rare earths that emerged in the years after World War II generated growing demands, and concerns about the radioactivity of thorium created the need to find a different source. A rare earth deposit at Mountain Pass, California, had entered small-scale production in 1952 after being discovered in 1949: this deposit includes both monazite and bastnaesite embedded along with other minerals in a carbonatite matrix. Bastnaesite, bearing rare earths with a much lower thorium content than monazite, became the primary target for rare earth extraction. The Molybdenum Corporation of America, later known as MolyCorp, expanded the production of the bastnaesite ore in the 1960s to meet the growing demand for europium, which was required for the latest consumer electronics sensation—color televisions—and Mountain Pass’s bastnaesite ore body quickly became the world’s dominant source of rare earths. Bastnaesite is a fluorocarbonate mineral based on the formula (REE)CO3F, where “REE” refers to any rare earth element. The Mountain Pass bastnaesite’s rare earth content is dominated by cerium and lanthanum, with decreasing amounts of neodymium, praseodymium, samarium, and other elements with higher atomic number, as shown in Fig. 1.3. In 1977 MolyCorp and its Mountain Pass mine were acquired by Union Oil (Unocal), which became part of Chevron Corporation in 2005. Rare earth demand continued to grow with the development of neodymium-iron-boron permanent magnet alloys in 1982 [5, 6], but the Mountain Pass processing facility was plagued by leaks from its wastewater system, with as many as 60 spills of radioactive waste occurring between 1984 and 1998. In 1984 rare earth production also started at a bastnaesite mine in the Bayan Obo iron mining district near the city of Baotou, Inner Mongolia, in the People’s Republic of China (PRC), and it ramped up very quickly. Production ceased at Mountain Pass in 2002 under the combined pressure of market competition from Baotou and the cost of coping with the challenges of working with hazardous materials in an environmentally sensitive location. Fig. 1.3 Relative concentrations of different rare earth elements contained in the Mountain Pass bastnaesite ore.

The rare earths and the idea of a critical material

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While bastnaesite provided light rare earths such as lanthanum, cerium, praseodymium, and neodymium, it did not meet the demand for heavy rare earths such as europium, dysprosium, and terbium. These are needed in smaller quantities but are crucial in a range of high-tech applications including efficient lighting, where europium is used to generate red light and terbium emits green light. Dysprosium is added to Nd-Fe-B magnets to improve their performance at elevated temperatures. These heavy rare earths, along with a few others, are mostly obtained from deposits of ion-adsorption clays (also known as lateritic clays) that are fairly widespread in Southern China, although the individual deposits are relatively small. The heavy rare earths are extracted by leaching these clay deposits with acid. By 2008 almost 98% of the world’s rare earth supplies came from China. The output of the leading producers at this time is shown in Fig. 1.4.

Rare earth supply challenges—2005–15 In 2005 the Chinese government began imposing annual export quotas on rare earths and reduced the quotas particularly sharply in 2010, as Chinese domestic industries increased their utilization of these materials. In 2005 the export quota represented about 55% of the total Chinese production, and this proportion fell at an accelerating pace until 2010 when the quota was only 23% of the total production, as shown in Fig. 1.5. The actions taken by China were hard to interpret without a clear view of the operation of Chinese commodity markets, so analysts and pundits in the rest of the world ascribed a variety of agendas or goals to China based on the reported actions, leading to concerns about security of supply and a high degree of market nervousness. One impact of the quotas was a marked differential between the prices of rare earths in China and the rest of the world, and the attention of various governments was drawn to

Fig. 1.4 The global distribution of rare earth oxide production in 2008. Data from the USGS Mineral Commodity Summary, 2009. https://s3-us-west-2.amazonaws. com/prd-wret/assets/palladium/production/mineral-pubs/mcs/mcs2009.pdf.

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Fig. 1.5 Chinese rare earth oxide production (in green) and export quotas (in red) from 2005 to 2015. The export quotas ended in 2016.

Price per kilogram of representative rare earth oxides, FOB China, in US$

6000 Neodymium Europium Dysprosium

5000 4000 3000 2000 1000

15 20

20 14

13 20

12 20

11 20

20 10

09 20

20 08

07 20

20 06

0

Fig. 1.6 The prices of three representative rare earths from 2006 to 2016. Source of raw price data: Argus Media Inc. (direct.argusmedia.com).

the issue as the prices of imported rare earths began to increase and delivery times lengthened. The price history of the rare earths from the mid-2000s to the mid2010s is illustrated in Fig. 1.6. In 2008 rare earth industry authorities including Dudley Kingsnorth [7] projected that China’s internal demand for rare earths would outstrip its own production by about 2012, and total world demand would be met only if production outside of China (the so-called “rest of the world” or ROW) were to increase substantially.

The rare earths and the idea of a critical material

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By this time, concerns about rare earth supplies had already reached high government circles worldwide. Japan is a major importer of rare earths for use in its electronics and electric vehicle industries, and it reacted quickly with government-supported programs to ameliorate potential shortages. Notably a major research and development program to enable recycling of rare metals was started in the summer of 2008, under the banner of “Urban Mining” [8]. The European Commission recognized the risks posed to the EU’s economy and issued a communication the EU Parliament in November [9]. Following various informal consultations, the US Congress held a formal hearing about rare earth supplies, in the Space, Science and Technology Committee of the House of Representatives in March 2010. In September 2010 a Chinese fishing vessel collided with a Japanese Coast Guard patrol boat near a group of disputed islands in the East China Sea, known as Senkaku in Japan, and Diaoyu in China. According to China the ship was operating in Chinese waters, but Japan claims the territory, too. The Chinese vessel, its captain, and crew were arrested by the Japanese Coast Guard, resulting in a diplomatic incident between the two nations. While it was widely reported that China cut off rare earth exports to Japan in an effort to win the release of its citizens, the truth may be more complicated. Some diplomatic meetings were canceled at this time, as often occurs in the wake of such incidents between nations, but China officially denies that any embargo was imposed. The reports of an embargo against Japan may have stemmed from the actions of local officials in refusing to allow a single ship to sail, with or without any approval from the central government in Beijing. While the details of the various government actions are unclear, their interpretation was quite definite. Around the time of the fishing boat incident, much was made about an earlier (1992) remark by Deng Xiaoping: “The Middle East has oil. China has rare earths.” Deng had been the paramount leader of the People’s Republic of China from 1978 to 1989, and his comment was taken by many to indicate that China had plans dating back at least to the time of his leadership, to use its rare earth supply monopoly for geopolitical leverage. While China often appears to be a single, centrally controlled rare earth source from viewpoints in the rest of the world, it actually has a diverse group of suppliers that can be categorized in a number of different ways. At the time of the crisis, the Association of Chinese Rare Earth Industries (ACREI) counted about 350 corporations among its membership, across a spectrum of light and heavy rare earth producers and end users. Many of the mines in China at this time were unlicensed operations, falling outside the control of the government, and referred to as “illegal.” By some estimates, up to 40% of China’s production was illegal at the time of the price spike, but foreign sales from illegal mines still appeared to count toward the export quotas, so there is some ambiguity about the extent of Chinese central government control. Following the lead taken by Japan and the European Commission, governments of consumer nations elsewhere in the world began to develop reports, policies, and strategy documents identifying essential materials that might be at risk and defining the approaches that might be adopted to maintain supplies to meet their economic and/ or strategic needs. As the uses of the rare earths were studied, it became clear that they had a particularly essential role in enabling clean energy technologies, whose

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imminent expansion was an attractive economic opportunity. Rare earth use was growing as a result of increasing market penetration of wind energy and electric vehicles, requiring neodymium and dysprosium for high-strength permanent magnets, and efficient lighting was producing new demands for europium, terbium, and yttrium. The US Department of Energy’s 2010 Critical Materials Strategy [10] considered 14 chemical elements essential for four clean energy technologies: magnets, batteries, thin-film photovoltaics, and fluorescent lighting. Also in 2010 the European Commission (EC) issued a report on critical raw materials for the European economy [11]. Although the EC report was broader in scope than the DOE report, most of the materials that it identified as critical arose through their essentiality to the clean energy sector of the economy. Among the many others that were issued around the world, these two reports set a tone and a standard approach for the discussion of critical materials. l

l

l

They both looked at the problem in the light of an analysis suggested in 2008, in a study by the US National Academies of Science [12], considering both the essentiality and the supply risk for any particular material. They both looked at the problem as a general concern that could apply to any essential material, rather than focusing only on the rare earth elements. They both suggested a set of approaches to ameliorate materials criticality.

Late in 2010 the EU, the United States, and Japan agreed to form a trilateral working group on critical raw materials, which meets annually to discuss and coordinate research and development efforts aimed at reducing criticality. With all of this government attention and the perception that China had, indeed, imposed an embargo against Japan, buyers of rare earths, already nervous about the increasingly stringent export quotas, drove the prices to new highs. Neodymium prices eventually peaked in 2011, at around 10 times their precrisis prices and dysprosium prices multiplied by a factor of 25, around the time that the United States and the EU began funding large-scale R&D efforts focused on their own needs and perceptions of the problem. In 2012, not long after rare earth prices began to fall back from their peaks, the United States, the European Union, and Japan jointly filed a complaint with the World Trade Organization (WTO), asserting that China’s rare earth quotas were illegal. China countered that the quotas were put in place as a means of environmental protection, presumably by reducing production at the most heavily polluted mines, but the WTO’s Dispute Settlement Body found in favor of the US-led coalition. China appealed the finding, repeating the claim that the export quotas were needed to curtail production while the environmental challenges associated with mining were addressed—and these were gaining widespread media attention, but it is more likely that falling demand in response to the price spike had, by this time, made reductions in production more palatable, or even necessary. WTO rejected the Chinese appeal, and the quotas were eventually dropped in 2015. The removal of the quotas, however, had little observable impact on rare earth prices, which had by then returned mostly to within two to four times their precrisis levels.

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Whether or not the Chinese government had specific geopolitical goals, it is clear that its growing economy generated internal needs for rare earths and other minerals. China also has well-recognized ambitions to become a global provider of high-tech devices and other goods, most recently formalized through its “Made in China 2025” policy, which was announced in 2015.

After the price spike

Annual world production in tonnes of REO and thousands of tonnes of Al and Cu

From the earliest industrial extraction of rare earths in 1950 until the 2010 price spike, global production had grown at a compounded annual growth rate (CAGR) of about 13%, reflecting steadily increasing demand, considerably outstripping the growth in production of copper (3% CAGR) and aluminum (6% CAGR). Over this period the production of all of these commodities typically only flattened or declined modestly during recessions, as shown in Fig. 1.7, although their prices may have fallen more considerably in response to the economic conditions. One exception is that the production of rare earths dropped noticeably during the two recessions of the early 1970s, because these were related to energy crises, and fluid cracking catalysts (FCCs) for oil refineries were the dominant use of rare earths at the time. In contrast the production of rare earths was barely affected by the global recession of 2008 but in 2011, immediately following the price spike, world production—meaning primarily Chinese production—dropped by 17% from its level the year before, settling at about 30% below the level that would have been expected if not for the price spike. 250,000

REO

Aluminum

Copper

200,000

150,000

100,000

50,000

0 1950

1960

1970

1980

1990

2000

2010

Fig. 1.7 Global production of rare earth oxide (REO), aluminum, and copper from 1950 to 2018. Although the absolute quantities for REO are smaller, the growth rate of REO production is the largest. The gray bands represent the approximate dates of worldwide economic recessions. Production data are taken from the annual USGS Mineral Commodity Summaries for the relevant years.

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Critical Materials

If we ignore the impact of additions or subtractions to end users’ or speculators’ inventories and assume that production is driven primarily by current industrial demand, this production drop would represent a dramatic and immediate destruction of demand in response to the price spike. A more realistic scenario is that end users of rare earths drew down their existing inventories rather than acquiring new material when the prices spiked, and they used that cushion (if they had the luxury) to buy some time to work on reducing their usage. We will describe in some detail how demand was reduced, in later chapters, but for now, we note that much of the demand drop relates to usage reductions that were relatively easy to achieve. Following the dramatic production decline in 2011 and two more years of similarly low production in 2012 and 2013, growth has resumed and world production regained its 2010 level in 2017. Inventories have been depleted, and the easy reductions in rare earth usage—the “low-hanging fruit”—have now been taken, and further reductions will be more challenging. The prior underlying trends have resumed and will likely continue to drive demand upward. The eventual crossover of the supply and demand lines projected by Dudley Kingsnorth has been delayed by several years, but not yet completely averted.

Lessons learned: The price spike in hindsight One purpose of this book is to identify lessons from the rare earth crisis so that they can be applied if similar supply challenges occur in the future. As the rare earth crisis unfolded, several different responses were implemented, most of which can be categorized as efforts to increase supplies or, conversely, reduce demand. We will analyze the effectiveness of these approaches in detail and develop specific lessons in subsequent chapters. Regarding the influence of scientific advice to policy-makers: the National Academies in the United States and their corresponding organizations in other countries have a role of providing high-quality, objective advice on science, engineering, and health matters. The Academies strive to address some of society’s toughest challenges and their peer-reviewed reports present the evidence-based consensus of these committees of experts. Even though the quality of these reports is uniformly high, their impacts vary. The 2008 report on Critical Materials had a very significant influence on the approaches adopted in response to the rare earth price spike largely because of the following: l

l

l

It was prescient, appearing shortly before the rare earth crisis fully emerged. Accurate predictions are more highly respected than post hoc explanations. It was timely, appearing only a year or so before policy-makers became engaged in the issue. It was clearly relevant to the events at hand and its application was, on the face of it, straightforward.

Regarding the impact of world events on the production of industrial metals: l

l

Recessions have relatively small impact on the production of metals in most cases, although prices may rise or fall with changing demand. A dramatic price spike, however, results in immediate demand destruction.

The rare earths and the idea of a critical material

15

Coda: Every challenge is also an opportunity Concerns about the availability of rare earth elements stimulated a boom in research and development efforts and associated activities, worldwide. They also provided a rich source of inspiration for fictional diversions, the arts and, less benignly, investment fraud. Prior to the rare earth price spike, references to the term “rare earth” in novels were restricted to the genre of science fiction, where it relates not to the rare earth elements but to the scarcity of planets like Earth, capable of supporting life. In the immediate aftermath of the price spike, there was a surge in the publication of thrillers that relate in one way or another to heroic efforts to thwart the intentions of evil nations, corporations, or individual masterminds to control the world’s supply of rare earths or other critical materials. A short (and possibly incomplete) list of these is provided in Table 1.3. In almost all cases the plots are flawed by bad science, including the pervasive misidentification of other elements as rare earths. In some the rare earths show up only as an abstract concept, possibly added to a plot at the last minute to capitalize Table 1.3 Works of fiction based on the rare earth crisis. Death on the Silk Road by Russell Miller, illustrated by Robert Banis. Beach House Books, 2011 The Bourne Dominion by Eric Van Lustbader. Grand Central Publishing 2011 Rare Earth by Paul Mason. OR Books, 2011 Rare Earth by Davis Bunn. Bethany House, 2012 Poseidon’s Arrow by Clive Cussler, with Dirk Cussler. G.P. Putnam’s Sons, 2012 The Eighteenth Element by David W. Cowles, Hadley V. Baxendale & Co., 2012 Rare Earth by Harry Marku. Mohyla, 2012 The Descent from Truth by Gaylon Greer. 1 edition, 2012 Dead End at Port Royal by P.D. Saracin. CreateSpace Independent Publishing Platform, 2012 Rare Earths (The Armageddon Conspiracy) by Burt Webb. Cybercon, 2013 Yukon Fever by Bob Neir. CreateSpace Independent Publishing Platform, 2014 Blood Profit$ by J. Victor Tomaszek and James N. Patrick. Roundfire Books, John Hunt Publishing, 2014 Tucker’s Discovery by Jed O’Dea. PELL Resources, 2014 Rare Earth Element by G.A. Chamberlin. Crown Eagle Publishing, 2014 From TIMNA to MARS: Searching for Rare Earth Metals by Avraham Y. Anouchi. CreateSpace Independent Publishing Platform, 2014 Amazon Burning (A James Acton Thriller) by J. Robert Kennedy. CreateSpace Independent Publishing Platform, 2014 Dysprosium Deception by Graham Holt. Amazon Digital Services LLC, 2014 Tom Clancy’s Full Force and Effect (A Jack Ryan Novel) by Mark Greane. Michael Joseph Ltd., 2014 The Accidental Courier by Harley Sachs. IDEVCO Intellectual Properties, 2014 Rare Earth by Michael Asher. Endeavour Press, 2015 Rare Earth by Clive Barnett Hewitt. PublishNation, 2015 Rare Earth by Reid Ridgway. Watershed Communications, 2015 Against the Current by Barry Cole. GoodDog Publishing, LLC, 2015 Continued

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Table 1.3 Continued A Death in the Family: A Detective Kubu Mystery by Machael Stanley. Minotaur Books, 2015 Terms of Use by Scott Allan Morrison. Thomas & Mercer, 2016 Point of Control by L.J. Sellers. Thomas & Mercer, 2016 Mohave Murder: A Dan Ballantine Mystery by Mark Travis. Amazon Digital Services LLC, 2016 Rare Mettle by Ann Bridges. Balcony 7 Media and Publishing, 2016 The Rare Earth Exchange by Bernard Besson (Author), Sophie Weiner (Translator). Le French Book, 2016 The Mine by Peter Watermeyer. Amazon Digital Services, LLC, 2016 Rare Earth by Damien Ayres. Amazon Digital Services LLC, 2016 No Return by Rob Sangster. Bell Bridge Books, 2018 Red Metal by Mark Grealey and Hunter Ripley Rawlings. Berkley, 2019 Rare Earth: a Luke Dodge Adventure Novel by C.F. Goldblatt. Independently published, 2019 Ascending Power by Michael Gibson. Independently published, 2019 The Umbrella Men by Keith Carter. Neem Tree Press, 2019 Anwei’s Diamond by Robert Ogden. Independently published, 2019 Kim Jong Un’s Atomic Bomb by Keith Suek, illustrated by Zak Pullen. Independently published, 2019 The Bluebird Plan by Bob J Quinn. Independently published, 2020

on the marketing potential of the headlines of the day. In many cases the writing, editing, and fact-checking are, frankly, awful, but some of the better-crafted ones are at least amusing to read. The thread of “good versus evil” runs through all of them, however, and this is not a helpful framework in which to solve the real-life challenges of imminent supply-chain failure for any material. In a similar good-versus-evil vein, though perhaps with less clarity on which characters represent either side, Netflix released the second season of its political drama House of Cards, in February 2014 with a significant plot thread relating to a political wrangle over the control of a Chinese rare earth mine, both mirroring and extrapolating from the real-life events. Less sensationally but still reflecting the headlines of the time, the ThyssenBornemisza Museum of Art in Madrid, Spain, ran an exhibition entitled RARE EARTHS, from February to May 2015, featuring 17 commissioned works, one for each rare earth element. The artists included representation from many countries that had existing or potential rare earth interests, including China’s Ai Wei Wei. Rare earths also made it into the widely syndicated Dilbert cartoon strip in February 2011 and July 2014 and were briefly and obliquely referenced in June 2012. Another oblique reference occurred in the Cul de Sac strip, which appears in the Washington Post, in August, 2010. A different approach to capitalizing on the headlines of 2009 and 2010 arose in the form of schemes in which credulous investors were sold “rare earths” in various forms, on the promise that the prices would continue to rise and they would realize huge

The rare earths and the idea of a critical material

17

profits. Even if they were sold actual rare earths, this would have been an unwise investment as the price history clearly demonstrates: nothing that goes up in price that fast can maintain the momentum. In at least a few cases, it was also unwise for the scammers, some of whom have been convicted and sent to prison. Phony investments aside, there were many anecdotal reports of accelerated buying of rare earths in various forms, both by individuals and corporations, during the price run-up, and this may have contributed to the inflation of rare earth prices. We will discuss the nature of trading in the rare earths in more detail, in Chapter 3.

References [1] J. Gadolin, Unders€okning Af En Svart Tung Stenart Ifra˚n Ytterby Stenbrott I Roslagen, vol. 15, Vetenskaps Academiens Nya Handlingar, Kongl, 1794, pp. 137–155. € [2] D. Mendeleev, Uber Die Beziehungen Der Eigenschaften Zu Den Atomgewichten Der Elemente, Z. Chem. 12 (1869) 405–406. [3] E. Greinacher, K.A. Gschneidner Jr. (Ed.), History of Rare Earth Applications, Rare Earth Market Today, ACS Symposium SeriesAmerican Chemical Society, Washington, DC, 1981, pp. 3–17. [4] K. Strnat, G. Hoffer, J. Olson, W. Ostertag, J.J. Becker, A family of new cobalt-base permanent magnet materials, J. Appl. Phys. 38 (1967) 1001. [5] J.J. Croat, J.F. Herbst, R.W. Lee, F.E. Pinkerton, Pr-Fe and Nd-Fe-based materials—a new class of high-performance permanent-magnets, J. Appl. Phys. 55 (1984) 2078–2082. [6] H. Onodera, Y. Yamaguchi, H. Yamamoto, M. Sagawa, Y. Matsuura, H. Yamamoto, Magnetic-properties of a new permanent-magnet based on a Nd-Fe-B compound (neomax) I: M€ossbauer study, J. Magn. Magn. Mater. 46 (1984) 151–156. [7] D.J. Kingsnorth, Rare earths at the crossroads-Dudley J Kingsnorth looks at the world market and sees how the industry is coping with present and future demands, Ind. Miner. (2008) 66. [8] M. Frid, Urban Mining: The Hunt for Rare Metals, https://www.treehugger.com/corpo rate-responsibility/urban-mining-the-hunt-for-rare-metals.html, 2008 (Accessed 28 December 2018). [9] European Commission, The Raw Materials Initiative—Meeting Our Critical Needs for Growth and Jobs in Europe, European Commission, Brussels, 2008. [10] U.S. Department of Energy, Department of Energy (Ed.), Critical Materials Strategy, DOE, Washington, DC, 2010. [11] Ad Hoc Working Group on Defining Critical Raw Materials, Report on Critical Raw Materials for the EU, European Commission, Brussels, 2010. [12] National Research Council (U.S.). Committee on Critical Mineral Impacts on the U.S. Economy., National Research Council (U.S.). Committee on Earth Resources., National Research Council (U.S.). Board on Earth Sciences and Resources., National Research Council (U.S.). Division on Earth and Life Studies., Ebrary Inc., Minerals, Critical Minerals, and the U.S. Economy, National Academies Press, Washington, DC, 2008 p. xvi, 245 p. ill. (some col.), col. map 23 cm.

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This is not new. A short history of materials criticality and supply-chain challenges

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The term “critical material” emerged in 2008, and it refers to materials that are at risk of supply-chain failures that could have disruptive consequences. Supply crises have affected materials, however, almost since mankind started using them so it is safe to assume that there must have been a risk of supply-chain failure prior to any actual occurrence. There have, therefore, been critical materials for many centuries, even if they were not so named. Historical examples of supply-chain failures and the circumstances surrounding them can help us to identify the traits of critical materials and the effects of their shortages. The insights that we gain from these case studies should guide our identification of materials that are critical before they enter a full-fledged crisis and our approaches to prevent them and deal with crises if they still occur. The examples in this chapter are historical, but they are not complete representations of history. In all cases we will look at historical incidents through the lens of materials supply chains, and it should be recognized that stories written from this or any other particular viewpoint run the risk of overemphasizing its impact relative to other issues that might also have changed the course of events. Events affect materials and technologies at least as much as materials and technologies affect events.

Copper and the end of the Bronze Age (1200 BCE) The early development of humankind is categorized in eras defined by the materials used at the time. The time period of each era varies with location, particularly from the stone age until the time when widespread communication and trade allowed for technologies to be shared around the globe, sometime during the Iron Age. The dates for the Bronze Age, in particular, differ considerably between the civilizations that emerged in the Eastern Mediterranean and those that grew up in China. The end of the Bronze Age in the Eastern Mediterranean is particularly instructive so we focus our attention there, even though the Chinese and Indian bronze ages are also subjects well worth studying. The Stone Age started about 2,500,000 years ago, when our ancestors began to use tools made of wood, bone, hide, plant fiber, and stone. It is divided into three eras: the Paleolithic, or Old Stone Age, lasted until about 10,000 BCE; the Mesolithic, or Middle Stone Age, lasted until about 4000 BCE; and the Neolithic, or New Stone Age, lasted until about 3300 BCE. Agriculture emerged in the Neolithic era, leading to the establishment of permanent settlements, but the tools used in the Neolithic age were still the same as those of the ancients. Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00002-5 © 2021 Elsevier Inc. All rights reserved.

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The Copper Age, or Chalcolithic era, is considered to be something of a transitional period lasting from around 5500 to 2300 BCE, in Europe and the Eastern Mediterranean. It overlaps the Stone Age and the Bronze Age and is often omitted from timelines, which suggest that the Bronze Age directly replaced the Stone Age, but copper was clearly found to be superior to stone for many purposes, before the widespread emergence of bronze. The Bronze Age lasted from 3000 BCE to about around 1200 BCE in the Eastern Mediterranean, but it lasted much longer—until roughly 300 BCE—in Europe and Asia. Bronze was made by alloying tin with copper, and it initially emerged where both metals were found in close proximity, notably in Sumer, between the Tigris and Euphrates rivers in what is now Southern Iraq. Bronze production spread widely around the Eastern Mediterranean region, providing a technological base that underpinned the development of increasingly sophisticated nation-states and civilizations that left extensive records of their wars, treaties, and trading [1]. As trade developed, production also became concentrated where it was most efficient. Copper production, in particular, eventually came to be dominated by the island of Cyprus, whose name refers directly to copper because of its rich deposits of copper ore. Without a single dominant source, tin production remained widely dispersed, extending well beyond the areas with the most advanced civilizations. Cyprus’s dominance of copper production came quite late, after many other Bronze Age advances. Writing, record keeping, money, city-states, and nations with formal governments, shipping, and trade were all in place—and, indeed, necessary for Cyprus to become the center of copper production. Sunken Cypriot trading ships from the era have been discovered, with large copper cargoes in place, and material from Cyprus has been identified in artifacts found as far away as Sweden. Around 1200 BC, there was a sudden and widespread breakdown of civilization in the Eastern Mediterranean that is referred to as the Bronze Age Collapse [2]. Kingdoms that had thrived heretofore ceased to exist, and others saw great changes in their power and influence. Once-dominant civilizations like those of the Assyrians, Hittites, Medes, Mycenaeans, Spartans, and Trojans are never heard of after the Dark Age that followed the collapse. The causes of the Bronze Age Collapse are debated [3], but they probably include natural disasters including documented volcanic eruptions, earthquakes, and droughts, along with wars and revolts. Events such as these had occurred before however, and it is not clear why this case was different. One possibility is that Cyprus was invaded by a shadowy group known as the Sea Peoples, making copper unavailable and impacting the availability of bronze for tools of agriculture and weapons of war, alike. What is certain is that the Bronze Age did not collapse because of the emergence of a new technology. Stone had given way to copper and bronze because the newer materials provided better performance in key applications such as tools and weaponry. Bronze effectively gave way to nothing, as the Eastern Mediterranean civilizations collapsed around it. At the time of the collapse, iron was actually an inferior material in many regards: l

Bronze was harder and held a sharp edge better than iron, because no methods for hardening iron had yet been developed.

History of materials criticality and supply-chain challenges l

l

l

21

Bronze had better corrosion resistance than iron. Many Bronze Age objects still exist in excellent condition today, while much newer iron objects have corroded away. Bronze was easier to manufacture: it can be melted at around 1200°C, while iron requires around 1550°C, a temperature that can only be reached in a fire through the use of bellows, which had not yet been invented. Bronze was cheaper: ancient records indicate that iron was as much as nine times more expensive than gold.

Following the Bronze Age Collapse, the Eastern Mediterranean region entered a Dark Age during which some of the Bronze Age civilizations persisted for a while, somewhat diminished, relying largely on recycling to ensure their supplies of the one essential technology material of the time. The region eventually began to recover in around 1000 BCE, when the technology of iron-making emerged, and this is the period in which ancient Rome emerged as a major power. We do not know to what extent a lack of bronze contributed to the Bronze Age Collapse, but it seems likely that it was a factor. The lack of bronze was caused by a shortage of copper, which occurred because copper production had become concentrated in essentially one place—Cyprus—creating the world’s first supply-chain vulnerability and, perhaps, the world’s first critical material.

The Venetian monopoly on glass Venice was founded on an island in a lagoon on the northeast coast of Italy as the Roman Empire declined and a succession of barbarian invasions created the need for safer places to live. By the 11th century AD, it had grown into a thriving city-state and trading center dominating commerce between Europe, North Africa, and the Middle East, and its continuing fame as a trading port made it a natural setting for Shakespeare’s play The Merchant of Venice, first published in 1600. Glassmaking had been discovered independently in ancient Sumer and Egypt around 3500 BCE, during the Bronze Age, but a series of circumstances led to Venice’s emergence as the dominant producer and technology leader. Glass production began in Venice in about AD 450, with the arrival of glassmakers from Aquileia, a town northeast of Venice, on the route of many of the barbarian invaders from the north. Glassmakers subsequently arrived from further afield as their homes were overrun by the barbarians, so a once-distributed industry became concentrated in Venice. Glass production grew and spread around the city, and as Venice became increasingly densely populated with no options to expand its area, the glass furnaces began to present a significant fire hazard. In AD 1291 the city leaders enacted a law that relocated glass production to the neighboring island of Murano, effectively creating the world’s first zoning regulations and also its first technology incubator, in the interest of protecting high-valued residential property from the hazards and general disagreeability of being too close to industrial production. The concentration of glassmakers on Murano enabled collaborations that led to technical developments, including the clearest transparent glass of its time

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(cristallo) and several forms of decorative glass, variously used for windows, mirrors, beads, and jewelry. By the end of the 15th century, Venice was the Western world’s dominant center of glassmaking, and it exported glassware throughout Europe, the Middle East, and North Africa. The city derived a significant fraction of its wealth from its mastery of glassmaking and expertise in trade. In some ways the situation of Venetian glass in the middle of the second millennium AD parallels the situation of Chinese rare earths at the beginning of the third: we often discuss Venice and China, respectively, as if they were single producers, but the reality is that both of them hosted multiple individual concerns that benefitted from coordination and control by trade associations and the government. In the 15th and 16th centuries, glass had become critical to Venice’s economy and influence in the World, and the city-state sought to protect its primary industrial product. The glassmakers’ guild banned its members from divulging their secrets and even restricted their travel, with penalties up to death. Glassmakers also enjoyed some social benefits, including the right for their daughters to marry into the city’s nobility. Recognizing the power of innovation, Venice created the world’s first patent system in 1474, providing protection against competition for inventors and the right for the government to use their creations. Venice continued to dominate and benefit from glass production for three more centuries, expanding the product line to include luxury goods including sophisticated art objects, chandeliers, decorative containers, and drinkware, but by the end of the 17th century, glassmakers in England, Prussia, and Bohemia developed alternatives to Venice’s clear cristallo glass. Competition from these reduced the market for Venetian glass, which then saw its sphere of trading dominance shrink to a more local region, serving customers primarily in the Italian city-states and the Turkish Empire. Venice’s economy also suffered from the loss of its dominance as a trading hub for cotton, silk, and other commodities, including slaves, as trade routes to the New World and the Far East opened up. Financially weaker and with its once-dominant navy reduced to just four galleys and 11 smaller galliots, the city was attacked and conquered by Napoleon Bonaparte in May 1797, and the Venetian Republic came to an end. Venetian glassmaking withered under the control of Napoleon’s empire as a result of taxes and tariffs that further undercut its profitability. Glassmaking had helped to sustain the city of Venice from before the 10th century to the end of the 18th century. The localization of production and development into a single hub had produced technical advances that entrenched the material as a cornerstone of the city’s economy, and recognizing its economic criticality the city had taken pains to protect its monopoly. Technical advances elsewhere eventually broke Venice’s monopoly, weakening the city’s economy and diminishing its ability to defend itself against Bonaparte’s marauding armies. Glass had been a key part of the Venetian economy for 800 years, and the loss of Venice’s monopoly on glass production had catastrophic consequences: from the Venetian perspective then, glass had long been a critical material.

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Cordite in World War I (1914–18) Historians debate the causes of the World War I (WWI), but there is no question that it was the first “total war” and it was enabled by large-scale industrial production. The stage had been set by the industrial revolution that had transformed much of Western Europe half a century earlier. Germany’s strategy at the beginning of WWI was to focus on the Western Front, with a plan to invade France via Belgium and capture the French industrial region adjacent to the Belgian border before moving on to Paris. Much of Belgium was quickly captured, but the war stagnated with the opposing armies dug into trenches running from the English Channel to the border of Switzerland. Neither side gained or lost more than about 30 miles at any point on this front, for the remaining three-and-a-half years of the war, but that was not for lack of effort. Major battles took place between the entrenched forces at the Marne (1914), Ypres (1914 and 1915), Verdun (1916), the Somme (1916), Passchendaele (1917), and Cambrai (1917) in addition to an attempted invasion by Allied Forces at Gallipoli (1915–16) and the naval Battle of Jutland (1916). Several new technologies were deployed during this war, including air power, battleships, submarines, tanks, machine guns, and poisonous gas, but the main tools used to deliver destruction were bullets and artillery shells, both of which were propelled by cordite. Cordite was an excellent propellant for bullets and shells. It was smokeless, and it burned slowly compared with other explosives, generating gas at a rate that is high enough to accelerate a projectile but not so high as to damage the barrel of a gun. It was formed into strands or filaments that were cut to length and bundled, making them easy to measure out and load into cartridges. Early in WWI, cordite was in short supply for both sides. In March 1915 the British artillery had fired more shells in a single bombardment lasting only 35 minutes than it had used in the entire Boer War of 1899–1902, but by May of that year, they were restricted to firing four shells per gun per day. Germany lacked some of cordite’s raw materials including cotton, camphor, pyrites, and saltpeter, but Britain had a different problem: cordite production required large quantities of acetone. Industrial acetone was made by the dry distillation of wood, and the United Kingdom was not a timber-producing country having been deforested in favor of agriculture centuries before. Lacking an indigenous source of wood, Britain imported acetone from the United States and other timber producers, but it wasn’t coming fast enough. The British government turned to Chaim Weizmann, a senior lecturer in chemistry at Manchester University (who later became the first President of Israel). Weizmann found an efficient method to produce acetone from grains and starches that was quickly industrialized, unleashing the production of cordite using Britain’s indigenous resources. The feedstock for Weizmann’s process was mainly agricultural products and waste, but they also included the seeds of the horse-chestnut tree, which are closely related to the American buckeye and inedible. In Britain, horse chestnuts are collected and used for a schoolyard game known as “conkers,” and their diversion into acetone production brought many schoolchildren into the war effort, at least during the weeks in the early autumn when the nuts fall from trees across the nation.

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Germany had held the advantage in artillery shell production in 1914, outproducing Britain by a factor of nearly two, but after Britain solved its acetone problem, the Allies would eventually outproduce Germany by a factor of three. At the outset of hostilities, imported acetone was the weak link in Britain’s cordite supply chain leaving it unable to keep up with the growing demand from the munitions industry. Scientific research provided a new indigenous source for acetone, enabling the country to meet its demand for cordite and prevent the German forces from meeting their initial objectives. WWI was ultimately a battle of resources—a siege on a large scale—with neither side gaining or losing territory but both sides using up their essential supplies. Britain, France, and Russia were joined by a global alliance including Australia and the United States and had access to extensive resources. Hemmed in on land in both the East and the West and defeated at sea, Germany ran out of soldiers, food, and war materiel first.

Silk and nylon (the 1930s and 1940s) In the 1930s 75%–80% of the silk used in the United States went into ladies’ stockings, with much smaller amounts going into parachutes, ropes, and a few other uses, and the United States imported 90% of its silk from Japan. What is claimed to be the world’s first synthetic fiber was invented in 1937 by Wallace Carothers in the laboratories of E.I. DuPont de Nemours and Company in Delaware, and it was initially named Fiber-66. Seeking uses for the new material, the company sought relatively low-volume products whose users would be prepared to pay substantial prices that could generate a rapid returns on the company’s investment, and they settled on hosiery. Nylon stockings were introduced to the market in 1939, and by 1941 they held 30% of the market. Nylons did not initially replace silk stockings because there was a silk shortage, but after Japan attacked Pearl Harbor on December 7, 1941, nylon did replace silk in all of its military applications, including glider towropes, aircraft fuel tanks, flak jackets, shoelaces, mosquito netting, hammocks, and parachutes. Having proven itself as a substitute in hosiery, the synthetic material became the go-to replacement in all of silk’s applications, and all of the available production was diverted to military use. Nylon consequently became a shortage material for stockings until the war ended. Silk became a critical material because of the US’s reliance on a single source. While nylon had begun to make inroads into its market by the time the war started, it emerged from the war as the foremost material in all of the applications that silk had once dominated.

World War II (1939–45) Raw materials were a concern for almost all of the major industrial nations for much of the 20th century, and well into the middle of the century, a nation’s production of steel was one of its most important measures of economic power. So emotive was the need

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to produce steel that in 1912 a 34-year-old Russian revolutionary dropped his birth name, Iosif Djugashvili, to become Joseph Stalin—drawing on the Russian word for steel: stal (сталь). Critical materials had played a role in the prosecution of WWI, but they were a significant part of the cause of World War II (WWII) in addition to playing multiple roles in the outcome of the conflict. WWII was more geographically widespread than WWI, and it was also more disconnected, with the war in Europe taking place almost entirely separately from the war in the Pacific: these were effectively two separate wars taking place at the same time and being waged for somewhat different reasons. The Axis powers of Germany, Italy, and Japan had different agendas, and there was little coordination of war efforts between its European and Asian participants. The Allies all fought together in Europe and in parts of the Pacific, but Japanese forces never took the field alongside Germans or Italians. The two conflicts even ended on separate dates: the Allies declared victory in Europe on May 8, 1945, and in Japan 4 months later, on September 2. During WWI, Japan had been a member of the Allies opposed to Germany, and it had gained some of Germany’s territories in the Far East when the war ended and the Treaty of Versailles was signed. In the great depression of the 1930s, Japan’s population and politics became intensely nationalistic, and the country began building up its military, as did much of Europe. The global surge in military-related industries helped many of the World’s economies to recover, but Japan’s home islands are not richly endowed in geological resources, so it needed to seek them elsewhere. It had long relied on the United States for coal, oil, and iron, but now started a process of colonization to assure its resources. Manchuria, an industrial region of northeastern China, was annexed in 1932, providing Japan with sources for iron and coal. Taking advantage of the communist uprising led by Mao Zedong, Japan further expanded its territories in China to include Beijing and several resource-rich regions in 1937 and 1938. By 1939 it controlled most of the eastern coast of China from Russia’s southern border to Shanghai, along with all of Korea and Taiwan. Japan had initially avoided annexing regions that would have caused clashes with any of the European powers, but its occupation of Manchuria, on the border between China and Russia, led to conflict with Russia, so in 1936 Japan joined with the original Axis powers of Germany and Italy in the Anti-Comintern Pact that opposed Russia’s postrevolution communist government. When WWII broke out in Europe, in 1939, Germany and Russia were bound by a mutual nonaggression pact, and soon after the war began with Germany’s invasion of Poland, Russia successively invaded its western neighbors. Despite the nonaggression pact, Germany eventually invaded Russia in June 1941 in pursuit of oil to fuel its forces, and Russia joined the Allies led by the United Kingdom, in opposition to the Axis powers. Through the Anti-Comintern Pact, then, Japan effectively entered the war as an opponent of Britain and its Allies, which now included its old foe, Russia. Japan then expanded its colonization efforts further south, attacking British and French interests in Southeast Asia and taking control of the World’s leading rubber producing region. It also expanded into the Pacific island nations, gaining control of the Philippines, which provided it with a source of copper.

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The involvement of Japan in WWII was a result of its need for raw materials and Germany’s need for oil. Almost all industrial feedstocks were critical materials for Japan, because of its lack of indigenous resources. Japan eventually drew the United States into the war when it launched a preemptive strike on the American fleet at Pearl Harbor, on December 7, 1941. Around the world the WWII became very largely a sequence of maneuvers, invasions, and battles that were pursued for control of critical materials and other resources.

Oil As with WWI, the WWII was a conflict whose outcome depended on resources. While WWI had been a static siege-like war, WWII was a much more mobile affair, so oil and rubber played more significant roles. Germany was determined not to repeat the endgame of WWI, and its strategy was driven by the need to assure its supplies of oil and other key materials while denying the same resources to its enemies. Germany’s armed forces, collectively known as the Wehrmacht, had developed a synthetic fuel industry, but it could not meet the demands of a major war, so the army seized control of Romania’s Ploesti oil fields in 1940, and then in 1941, breaching the mutual nonaggression pact, it tried, unsuccessfully, to invade Russia to take advantage of its enormous oil and mineral resources.

Rubber Germany also had no supplies of natural rubber, so it developed synthetic alternatives, and almost all of the rubber that it used during WWII was synthetic. Russia also developed its own synthetic rubber, but Britain relied on its natural rubber plantations in Southeast Asia until they were captured by Japan, whereupon the US government launched a large interdisciplinary, interinstitutional research and development program that resulted in the deployment of GRS (or Government Rubber-Styrene), a copolymer of butadiene and styrene similar to the German synthetic rubber. By the end of the war, the US production of GRS was about twice the world’s production of natural rubber, and synthetic rubber continues to be produced in much larger quantities than the natural material, to this day.

Steel Supplies of steel for ships, guns, and armor were a concern for both sides during the war, and all participating nations had some form of control over its allocation. Its use for making automobiles, appliances, and many domestic products was restricted or banned resulting in a culture of “make do and mend,” and recycling programs to boost supply were widespread. Scrap collection boomed, and wrought iron fences were torn down around the world to feed the steel furnaces. As in the case of acetone production during WWI, children were often involved in collecting raw materials such as steel and iron scrap. Germany had internal iron sources that fed its steel industry, but the supply was not enough to maintain the war effort, so imports of iron ore from neutral Sweden were ramped up.

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Nickel Nickel is added to steel to make it stronger and tougher, and nickel steel was used during WWII primarily for armor plate and in gearboxes. Stainless steel was also in great demand during the war, and it relies on more significant additions of nickel and chromium to the iron base metal. The war created large demands for nickel, and Canada increased production from its mines to support Britain after it declared war on Germany. The US government underwrote the operation of a nickel mine in Cuba by the Freeport Nickel company, which quickly became uneconomical soon after the war ended and was shut down. The United States replaced the traditional copper-nickel alloy in its 5-cent “nickel” coins with a silver-copper-manganese formulation between 1942 and 1945. It is not clear how much nickel this actually contributed to the war effort, however, because the prewar alloy was only 25% nickel, with the remaining 75% being copper. A more significant contribution probably came from the development of high-manganese stainless steels, which use lower concentrations of nickel, although these involve more complicated processing and are not as highly corrosion resistant. The Allies’ solution to meeting the growing nickel demand, then, was a combination of ramping up existing capacity, diversifying sources, and substituting for nickel in less essential or demanding applications. The Wehrmacht obtained nickel from mines in Finland, which had sided with Germany to protect itself from Russia. This strategy worked until Russia began to gain the upper hand later in the war and Finland switched its allegiance, leaving Germany’s forces without a reliable source of nickel for the last few months of the war.

Molybdenum Molybdenum had also been developed as an alloying addition in steel, providing some of the same benefits as nickel. With good indigenous sources of molybdenum, German steel makers had developed molybdenum-chromium steels for use in their artillery pieces during WWI, while the Allies had perfected nickel-chromium steels. The German strategy on nickel was therefore a combination of source diversification and material substitution.

Chromium Chromium is an essential component of stainless steel. Lacking indigenous sources, Germany stockpiled chromium aggressively in the years leading up to WWII, importing up to five times as much as it consumed, but once the war started, many of the world’s leading suppliers, who were under British control, stopped providing material to Germany. With military uses growing the German stockpile was projected to last only a little more than a year, even with tough restrictions on the use of this critical strategic material. Russia had major chromium resources, but even early in the war while it was still allied with Germany, it withheld its chromium from the Wehrmacht to meet its own needs. Neutral Turkey became the largest single contributor to Germany’s supplies. Turkey had about 20% of the world’s production capacity, but it provided roughly a third of all German imports after the beginning of the war, at

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steadily increasing prices, while maintaining a precarious neutral position between Germany and its neighbor and traditional enemy, Russia. Germany eventually gained access to other sources of chromium in Romania, Bulgaria, and Greece, when it invaded the Balkan Peninsula in 1940 and 1941.

Tungsten Tungsten had emerged as a strategic material in Germany, where its use in high-speed machining steels had been pioneered for munitions production during WWI. The Second World War brought more applications for tungsten, notably tungsten carbide armor-piercing shells, which gave the German forces an advantage in tank battles early in the war. It was only later that US armorers were able to provide similar munitions to the Allied forces to level the playing field. Tungsten was also crucial for electric lamp filaments and, more significantly, for cathodes in vacuum tubes that were essential for the many electronic devices that were developed during the war, including radar. The United States had indigenous tungsten sources, and the metal could be extracted as a by-product from the tin mines in southwestern England. Japan had access to tungsten from China and Indo-China, but Nazi Germany depended entirely on Portugal and Spain for its supplies. Portugal remained neutral throughout the war and was able to profit by selling this strategic material to both sides, at ever-increasing prices. Recognizing that Portugal was Germany’s primary supplier and despite their access to other sources, the Allies bought as much tungsten as they could from Portugal, in an effort to reduce the amount available to Germany and force up its price, applying economic heft to control its enemy’s access to a critical material.

Copper Copper was needed for electric wire as more and more of the war effort depended on electrical devices with radios and radar playing prominent roles and also for alloying with zinc to make brass for cartridge casings. The US government responded to the war-related needs for copper by suspending its use in currency. The nation’s 1-cent penny coins were traditionally made of bronze, 95% of which was copper, and in 1943 and part of 1944, it issued pennies made from zinc-coated steel. The wartime steel pennies, however, were prone to corrosion, so production quickly returned to bronze at the end of the war. Belgium also issued steel 2-franc coins during WWII, to conserve supplies of copper for its war efforts. When the Manhattan Project needed 4500 tonnes of copper wire to make electromagnets, it used silver instead.

Aluminum Aluminum was used widely during the war for aircraft and also in various internal combustion engine blocks, particularly for tanks. For the most part, however strategically important it was, it did not become a supply concern for Germany, which was the world’s leading producer at the beginning of the war. Prior to its entry into the war, the United States had sufficient deposits at its disposal and enough electric

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power to reduce them to metal to meet its domestic needs, but the single American production company, Alcoa, was reluctant to boost production in support of war efforts until it came under intense political pressure to help the Allies. With increased production and the eventual entry of the United States into the war, Russia ultimately obtained roughly half of the aluminum necessary to meet its wartime needs from the United States. Britain also benefitted from US production capacity, and it mounted extensive recycling efforts to assure its own supplies.

Polyethylene Polyethylene had been developed in England a few years before the outbreak of WWII, but there were few uses for it, and it was something of a boutique material, mostly used for novelties. When radar was developed, however, the electronic systems had new requirements for wiring to transmit high-frequency signals without interference, so coaxial cables were developed and used extensively. Early coaxial cable designs used natural materials to insulate the copper core from the sheath layer, but these suffered from too much electrical permittivity, allowing cross talk between the conductors. Some of the most closely guarded secrets of the war were cable designs that overcame this problem through the use of polyethylene insulators. This was the first use for which polyethylene was truly essential, transforming it almost overnight from a boutique material into a critical material.

Materials for atomic weapons Nuclear fission was observed shortly before the outbreak of WWII in December 1938 when Otto Hahn and Fritz Strassmann found that barium was produced by bombarding uranium with neutrons. This was explained by Lise Meitner and Otto Frisch, in January 1939, who postulated that a neutron could be absorbed by the nucleus of 235U converting it to 236U, which is unstable and divides spontaneously to form one atom of 92Kr, one atom of 141Ba along with the release of three highenergy neutrons. Physicists quickly recognized the possibility of generating chain reactions in which the neutrons emitted in the fission process are absorbed by other 235 U atoms in a self-sustaining process, releasing enormous amounts of energy. Nuclear weapon development efforts began very soon afterward in both Germany and the United States. Germany obtained uranium in sufficient quantities for its research efforts from at least three places. The initial source was a stock of waste material from which radium had been extracted for use in gas mantles, by Carl Auer von Welsbach’s rare earth company, Auergesellschaft, located near Berlin. After the invasion of Belgium, Germany gained access to a second stockpile that had been mined in the Congo and was being used by a company in Olen, near Antwerp, for the same purposes as Auergesellschaft. The third source was a silver mine in Joachimsthal, Czechoslovakia, that produced uranium oxide as a by-product: the mine is estimated to have had the capacity to produce about 1 tonne of uranium oxide per month after Germany annexed Czechoslovakia.

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The United States obtained most of its supplies of uranium from the same African mine that had produced the Belgian stockpile. Located near the village of Shinkolobwe in the Congo’s Katanga province, this mine had started production in 1921 to provide radium, primarily for gas lamp mantles and luminescent dials for watches, clocks, and other instruments. Production had ceased in 1935 and was only restarted in 1944 with the help from the US Army Corps of Engineers—too late to contribute to winning WWII but certainly sustaining the subsequent Cold War arm race. The Manhattan Project’s uranium oxide came from an existing ore stockpile at Shinkolobwe, with an initial shipment of 1200 tonnes in 1940 and regular monthly deliveries of about 400 tonnes starting in 1942, under tight security, which included removing Shinkolobwe’s location from maps. Despite the long journey across land and sea from Shinkolobwe to the United States, only two shipments of the African uranium were lost during the war. The United States also obtained about 180 tonnes of uranium ore per month from the Eldorado Mine at Port Radium on the Great Bear Lake near the Arctic Circle in Canada’s Northwest Territories. Atomic weapons depend on fissile atoms and the concept of a “critical mass.” A fissile atom can undergo radioactive decay when a free-moving neutron strikes its nucleus. The atom is split, producing two lighter elements and a few energetic neutrons. Small amounts of fissile materials do not sustain chain reactions, because the neutrons that they emit escape from the volume before they can stimulate the decay of other fissile atoms. Larger volumes of material increase the chance of a chain reaction occurring, in which a neutron produced by the decay of one atom causes the fission of another. At some particular volume of concentrated fissile matter, enough of the neutrons are captured to cause a “prompt critical” chain reaction with all of the fissile atoms involved, generating a sudden release of energy. Below this critical mass the radioactive decay does not sustain a chain reaction, but at or above the critical mass, the fissile matter explodes. Bombs can be made using 235U or 239Pu as the fissile material, but the design of the bomb and the means of producing the material are different. Uranium bombs can be made using two subcritical charges held at the opposite ends of a cylinder: these are forced together by conventional explosive charges to form a critical mass and trigger the device. The mechanism is essentially a gun that shoots one subcritical slug of uranium into another to form the critical mass, as shown in Fig. 2.1A. Around 15 kg of 235U is needed to achieve critical mass, but this is diluted by 238U in highly enriched uranium (HEU), so the total mass of the uranium charge is larger. Plutonium bombs are a little more complicated. The fission of 239Pu produces more neutrons than 235U, and this means that the critical mass for plutonium is smaller— only about 5 kg. Unfortunately the nucleus of 239Pu can occasionally absorb a neutron rather than undergoing fission, resulting in the formation of 240Pu, which decays more rapidly than 239Pu. As the 240Pu concentration builds up, a subcritical plutonium charge can gradually become more critical, increasing the chain reaction rate and building up enough heat to melt—an outcome known as a “fizzle” that renders the bomb inoperable. Plutonium bomb designs overcame this possibility by using a single subcritical plutonium “pit,” presumably so-named because it is located in the bomb

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Fig. 2.1 Two schematic designs used for WWII atomic bombs: (A) gun-type design used in bombs made with enriched uranium and (B) implosion-type design used in bombs made with plutonium. In both cases, conventional explosives were used to merge subcritical charges into critical masses that underwent prompt-critical explosions driven by nuclear fission chain reactions.

like the pit of a peach, as shown in Fig. 2.1B. The pit is uniformly compressed by highexplosive shaped charges that concentrate the fissile material into a critical mass. WWII plutonium bombs were more complicated than uranium bombs because of the challenges involved in assuring a symmetrical implosion. They can be easily distinguished by their more nearly spherical shape than uranium bombs, which are more cylindrical, as illustrated in Fig. 2.1. The initial raw material for either type of bomb is uranium. Natural uranium is a mixture of isotopes with stable 238U being the most common, and the fissile 235U is present at a concentration of only about 0.72%. Various processes can be used to enrich uranium to the level of 3%–5% (“low-enriched uranium” or LEU) for use in conventional reactors or greater than 20% (“high-enriched uranium” or HEU), which can be used in fast reactors. “Weapon-grade uranium” has more than 80% 235U. The residue of uranium enrichment is a large quantity of “depleted uranium,” which is nearly pure 238U. Uranium enrichment relies on finding ways to discriminate between atoms or molecules containing 238U and 235U, which are chemically identical and differ only slightly in mass. The mass difference means that the lighter isotope, 235U, will accelerate slightly faster when a force is applied to it by electrolysis or in a centrifuge. It will also diffuse slightly faster through another material. All enrichment processes,

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however, are limited by the small difference in mass between the two isotopes, so they are not highly selective and must be repeated iteratively until the desired level of enrichment is achieved. It is a long and tedious process, involving large facilities and a great deal of energy. The production of 239Pu is achieved by converting the dominant natural isotope of uranium, 238U, through neutron irradiation, in a reactor. 238U becomes 239U when its nucleus absorbs a neutron, and 239U quickly decays into 239Np (with the emission of a β-particle) and then 239Pu (with the emission of a second β-particle). When enough of the 238U is converted and the concentration of 239Pu builds up to a high enough level, the plutonium can be extracted using chemical methods. The trick is to slow the neutrons moving through a uranium reactor to a speed where they are efficiently captured by the 238U nuclei, and this is achieved through the use of a “moderator,” which absorbs energy from fast neutrons without reacting with them.

German efforts German scientists opted to try to develop a plutonium bomb, judging that the complex process of enriching uranium to the level needed for a bomb would be too slow and too costly. Their first task was to build a reactor to convert uranium to plutonium. At first, they tried to use graphite as the moderator but found that they could not sustain a controlled chain reaction with that design, so they focused their efforts on heavy water instead. The problems that they encountered with graphite were almost certainly related to impurities like boron that absorb neutrons rather than just slowing them down, so their decision to use heavy water was driven by the lack of suitably pure graphite. Heavy water differs from regular water in the isotopes of hydrogen that it contains. Hydrogen nuclei can contain one, two, or three neutrons, giving the isotopes 1H, 2H, and 3H. 2H is also known as deuterium, D, and 3H commonly goes by the name tritium, or T. Natural water is a mixture of H2O, D2O, and T2O, along with HDO (half-heavy water) and presumably HTO and DTO: HDO is the most abundant heavy variant, with a natural concentration of about 0.00003%. Heavy water molecules freeze and boil a few degrees Celsius above the freezing and boiling points of light water, and they have a slightly higher pH. Heavy water is harder to ionize than light water. When water is ionized, the H+ ions are 33% lighter than D+ ions, so they move more quickly in response to an electric field. Electrolysis of water affects a smaller fraction of deuterium atoms, because fewer of them are ionized, and it transports them more slowly than hydrogen ions, so it results in the preferential release of hydrogen gas over heavy hydrogen gas, and heavy water accumulates in the electrolyte as electrolysis proceeds. Heavy water is not radioactive. Its value is that it absorbs energy from fast neutrons through elastic collisions. A neutron moving through heavy water can collide with a deuterium nucleus, transferring momentum to the heavy water molecule. The water is heated by this process, and the neutron is slowed, but no radiochemical reactions occur that could absorb the neutron. Slower-moving neutrons, however, are more likely to be absorbed by 238U nuclei as they pass through the reactor’s fuel, so they are more efficient at producing 239Pu after they have passed through some heavy water.

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Heavy water was available to the German team from only one source: it was produced for use in scientific research as a by-product of the manufacture of ammonia via electrolysis, by Norsk Hydro at the company’s Vemork hydroelectric plant. Norway had been invaded by the Nazi forces in 1940, and the Vemork facility was under German control. When its use in producing heavy water became known to the allies, the plant was a target of heroic sabotage efforts, and later when the Allies had established sufficient air superiority, bombing raids. With the plant sustaining damage faster than it could be repaired, the Wehrmacht eventually decided to move all of the remaining stock of heavy water to Germany, in steel drums. The route included crossing Lake Tinn on a ferry, which was sunk by a bomb planted in the ship by a saboteur, and the last remaining supply of heavy water was lost. Germany’s reliance on a single source for its neutron moderator was clearly a supply-chain risk. Even without the Allied efforts to destroy the heavy water production facility in Norway, however, it is not clear that it could ever have produced sufficient amounts of heavy water for a reactor capable of producing enough 239Pu to make a bomb: some drums from the sunken ferry were recovered in 2005, and the concentration of the heavy water in them was found to be too low to have been useful. Eventually, realizing that the effort was progressing too slowly to have any impact on the outcome of the war, the Wehrmacht sidelined its nuclear weapon program.

Allied efforts Allied efforts focused on creating both uranium and plutonium bombs, through a massive effort known as the Manhattan Project, involving a virtual army of scientists and support staff with facilities across the United States. The first step was the construction of a reactor to prove that controlled chain reactions could occur. Enrico Fermi built a prototype reactor at the University of Chicago, using unenriched natural uranium oxide and uranium metal as fuel and pure graphite as the moderator. The reactor needed to have very low concentrations of neutronabsorbing contaminants (commonly called “neutron poisons”) like the ones that had stymied German efforts to use graphite as a moderator, but uranium oxide ore and most commercial graphite were quite rich in boron. The head of the Manhattan Project’s Metallurgy Laboratory at the University of Chicago tried to recruit Frank Spedding from Iowa State College to join the Project to lead the work on removing neutron poisons from uranium, but he declined to move to Chicago. Early in 1942 Spedding was allowed to organize a group of scientists in the Chemistry Department at Iowa State College in Ames, Iowa, to begin work on developing a process for producing high-purity uranium metal. Their process converted uranium oxide to uranium tetrafluoride, leaving the impurities behind, then reduced the fluoride with magnesium metal. This method is still used to produce highpurity uranium and is commonly referred to as the Ames process. After Spedding demonstrated the purity of the uranium and the possibility of producing it in sufficient quantities, the necessary equipment to expand the work was provided to the college in Ames, and the top-secret program known as the Ames Project was established [4, 5].

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The Ames Project eventually shipped more than 2 million pounds of pure uranium metal, in used whiskey barrels, from its small building on the Iowa State College campus to the University of Chicago for Fermi’s experimental reactor and subsequently to other Manhattan Project reactors. This is a rare case of a major wartime manufacturing effort taking place under top-secret conditions on an academic campus, and the Ames Project was recognized with the award of an Army-Navy E-Flag for excellence in materiel production, an honor more commonly accorded to manufacturing corporations. In September 1942 high-purity uranium dioxide began arriving in large quantities at the University of Chicago from the Mallinckrodt company in St. Louis, at around the time that the first purified uranium metal arrived from Iowa State College. A new, high-purity form of graphite was developed by the National Carbon company in Cleveland, Ohio, in a close collaboration with the University of Chicago team, beginning in late 1940. Two hundred fifty tonnes of this material were delivered to Chicago by November 1942, forming the bulk of the carbon used for the reactor known as Chicago Pile-1. The reactor was constructed with the new pure carbon and a mixture of unenriched uranium dioxide and uranium metal, and it achieved a self-sustaining chain reaction on December 2, 1942. With a power output of only 200 W, it worked without a cooling system. Construction started on a larger pilot-scale reactor in February 1943 at Oak Ridge, Tennessee, using natural uranium metal as the fuel, high-purity graphite as the moderator, and light water as its coolant. This reactor achieved criticality on November 4, 1943, and it produced its first plutonium within the same month, generating enough material for testing and providing essential data to allow bomb design to begin at Los Alamos early in 1944. Based on the success of the Oak Ridge reactor, three additional units were built in Hanford, Washington, with the first of them coming on line in September 1944, eventually providing the plutonium for the bomb that the US Army Air Force dropped on Nagasaki on August 9, 1945. While its initial reactors were graphite moderated, the United States continued the development of heavy water-moderated reactors as a backup in case graphite reactors failed to meet their goals. As in Europe, North America had only one facility that was capable of producing heavy water: an ammonia plant located in Trail, British Columbia, but this factory was not yet being used to produce heavy water. It produced large quantities of hydrogen through electrolysis, but this is just one of the steps required for separating heavy water from normal water. The US government leased adjacent land from the company and from the Canadian government and began to adapt the facility for heavy water production. Construction began on September 1, 1942, and production began in the summer of 1943. Three additional heavy water plants were built during 1943 to speed up construction and cut costs, at military establishments in Morgantown, West Virginia; Newport Indiana; and Sylacauga, Alabama. These facilities all concentrated heavy water using a distillation method, exploiting the slightly different boiling points of heavy and light water.

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Combined the four facilities were intended to produce 2.6 tons of heavy water per month, but all of them struggled to reach their targets. By the end of 1944, it was clear that their output was not needed for backup reactors since Hanford’s graphitemoderated reactors were shipping plutonium to Los Alamos in sufficient quantities. The three US heavy water facilities were shut down in the summer of 1945, but the Canadian plant stayed in operation until 1956. Although heavy water reactors did not ultimately contribute to the Manhattan Project, more than 80,000 pounds of heavy water were separated by the four facilities, and this was used in reactors built later, at the University of Chicago and in Chalk River in Canada. Increasing the 235U concentration in nuclear fuel makes reactors more efficient, so even at low enrichment levels, it contributes to the production of plutonium, and weapon-grade uranium for direct use in bombs requires more than 80% of 235U. However, in 1942, there was no proven method of separating 235U from 238U. It was clear that any method that relied upon the difference in atomic mass, at around one-half of 1%, would only discriminate very poorly between the isotopes. In the era of commercial nuclear power that emerged after WWII, centrifuges have been used with great success to separate uranium hexafluoride gas molecules containing different uranium isotopes, but efforts to develop the yet-unproven technology for the Manhattan Project were dogged by engineering challenges associated thousands of units of large-scale high-speed rotating machinery, required to run continuously for long periods of time. Development work on the technology lasted until November 1942, when the disappointing extraction rate and persistent mechanical failures resulted in a decision to abandon this method. Electromagnetic separation is simpler in concept and uses no large moving parts but is less efficient than centrifugal separation: it uses an electromagnetic force acting on ions rather than a mechanical force acting on molecules, and ions that include lighter isotopes have lower mass, so they accelerate more rapidly. A machine called a calutron was selected for the job, and this was basically a large mass spectrometer based on the cyclotron developed at Berkeley. This system forms a beam of uranium tetrachloride ions, which is deflected through 180° by a series of electromagnets. The lighter ions of 235UCl4 are deflected a little more than the heavier ones of 238UCl4, and they can be captured in a separate collector, as shown in Fig. 2.2 [6]. In February 1943, construction began on electromagnetic separation plant at Oak Ridge, a few miles from the graphite reactor that had produced the first plutonium. The calutrons were large devices, and several of them were needed, each with several large electromagnets. It was determined that the windings would require about 4500 tonnes of copper, which was already in short supply for the war effort, so the design was modified, and about 5000 tonnes of silver was released from the US treasury to be used instead of copper. The last of the silver was returned to the treasury when the plant was finally decommissioned in 1970. The electromagnetic separation plant at Oak Ridge was built without the benefit of a pilot-scale test facility, and much was learned about ion beams during its operation. The production rate was slow, the separation rate was low, and there were large losses of material from ions that missed the collectors and ended up elsewhere in the system, particularly the walls of the vacuum chambers. Nevertheless, the plant began to

36

Critical Materials ORNL-LR-DWG 42951

Magnet coils

M2 Heavier isotope M1 Lighter isotope Magnetic field normal to plane of diagram

Ion receiver Manifold

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20-in. Diffusion pump

Hev =

mv2 R

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Kinney pump

Fig. 2.2 Archival engineering drawing showing the principal components of the calutrons that were used to separate 235UCl4 from 238UCl4 in the Manhattan Project. The ion beams comprising the lighter radioactive isotope travel through a magnetic field in a circular path of smaller radius than the beams made up of the heavier isotope, allowing them to be collected in separate receivers. The magnetic fields that deflected the ion beams were created by electromagnets with silver windings, because of the wartime shortage of copper. Reproduced with permission from A.L. Yergey, A.K. Yergey, Preparative scale mass spectrometry: a brief history of the calutron, J. Am. Soc. Mass Spectrom. 8, 1997, 943–953, copyright Elsevier, 1997.

deliver enriched uranium with about 13%–15% 235U in March 1944, and it was used for the final stage in the production of weapon grade-enriched uranium later the same year. A third method of enrichment is based on the effect of molecular mass on gaseous diffusion: the rate of diffusion of a gas through a membrane depends on the square root of its molecular weight. Lighter molecules pass through more quickly, and they are slightly enriched on the output side. After several successive diffusion stages, the

History of materials criticality and supply-chain challenges

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enrichment can build up to a significant level, but the square root dependence on mass makes this a less selective process than electromagnetic separation, so it requires a huge number of separation stages. With very little of the basic technology even developed to the “proof-of-concept” stage, the Manhattan Project began the construction of a gaseous diffusion enrichment plant, at Oak Ridge in May 1943. It would be the largest building in the world when it was complete. Major challenges included the development of pumps and motors that could handle the highly corrosive UF6 gas and the development of a suitable effusion membrane to separate it. The membrane had to be strong enough to withstand the pressure difference that drove the gas through it; it had to be porous, with a very narrow channels for the gas to pass through; and it also had to withstand chemical attack from the UF6 gas. Nickel was believed to have the necessary corrosion resistance, and two different approaches were tested for making the barriers from it. A powder metallurgical method was selected in January 1944. Six separation stages were ready for operation in April 1944, and based on their performance, some significant changes were made to the design of the facility, which was already well along in its construction. As separation stages were added, the enrichment level increased, and the facility eventually had 2892 stages in operation by August of 1944. A third separation facility was built at Oak Ridge, using yet another principle. In a temperature gradient, lighter gases tend to accumulate in the hotter region and the heavier ones in the cold zone as a result of their different convection rates. The Manhattan Project had initially rejected this “thermal diffusion” approach, and as an effort led by the US Army, its leaders were not aware of the research being conducted on this method by the Naval Research Laboratory. When they eventually learned of the successes of the Navy researchers, the Manhattan Project began to work on its own thermal diffusion plant, using UF6 gas. Construction began in July 1944, and partial operation started by September. After the plant was complete in March 1945, it had 2142 separation columns. As a result of the rapid pace of construction, many problems arose during commissioning, and the plant had a lot of leaks, but after these were resolved in about June 1945, it was able to produce nearly 6 tons of uranium per month, modestly enriched to 0.852% 235U. By mid-1945, then, the Manhattan Project had three uranium enrichment facilities operating in parallel, but it was still not meeting its goals for this critical material, either in terms of the volume or the fissile material concentration in the product. The problem was solved by operating the three methods in series. The thermal diffusion plant was used as the first stage, taking natural uranium from 0.71% to 0.89% 235U, in the form of uranium hexafluoride. This became the input for the gaseous diffusion plant, which took the enrichment level up to about 23%, and that output was converted into UCl4 that was used to feed the calutrons in the electromagnetic separation plant, which boosted the concentration to 89%. About 50 kg of uranium, enriched to 89% 235U, was delivered to Los Alamos by July 1945. This was blended with some 50%-enriched material yielding an average of around 85%, to provide the material used for the uranium bomb that was dropped on Hiroshima, on August 6, 1945.

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The story of nuclear weapons development during WWII is a tale of material supply chains. German efforts fell victim to the lack of sufficiently pure carbon for use as a neutron moderator and their reliance on a single source for their only alternative, heavy water. Allied efforts successively overcame material challenges including the exclusion of neutron poisons from their uranium fuels and graphite moderators and the substitution of silver for copper in the calutrons. They developed multiple sources of materials wherever possible, and they pursued multiple—often unproven—technologies to make the materials that they needed, essentially fostering and benefitting from competition among them. The project benefitted from the efforts of scientists at a wide range of different organizations, and it built a remarkably focused and successful collaborative team. The only obvious organizational shortcoming of the effort was the isolation of efforts led by the US Army from those led by the Navy. Rivalries among the Manhattan Project’s participants, however, would increasingly affect nuclear research in the years that followed the war. While the scientific community had clearly seen the potential of nuclear weapons and were impressively focused on delivering on that while avoiding being its victims, they unfortunately had little understanding of the environmental and health risks of the work that they were doing.

Old lead (1978) Lead is an abundant element in the crust of the earth and has been used by humanity since before the time of the Roman Empire. It is a heavy metal with many isotopes including 204Pb, 206Pb, 207Pb, and 208Pb, all of which have stable nuclei, and these atoms are mostly primordial, having existed in the universe before planet Earth was formed. These isotopes are considered to be “old” lead, and they are present at concentrations of 1.4%, 24.1%, 22.1%, and 52.4%, respectively, in terrestrial deposits. While 204Pb is exclusively primordial, 206Pb, 207Pb, and 208Pb, along with several other isotopes, may also be formed by the radioactive decay of other naturally occurring elements such as uranium or thorium. Lead formed by this process is considered to be “radiogenic” or “new” lead, having been formed in the crust of the earth. 206Pb is the final stable product of the decay of 238U. 207Pb is the end of the decay chain of 235U, and 208Pb is the end product of 232Th. While these are all stable end products of radioactive decay, many other isotopes are intermediate products that undergo radioactive decay resulting in the emission of α- or β-particles. These isotopes are typically present at trace levels in lead deposits that are associated with uranium or thorium, and the low levels of radioactivity that they cause are of little concern in most applications. Most of the particles that they emit are captured within the lead object in which they are generated. In 1978, Intel Corporation discovered that α-particles could cause so-called “soft errors” in dynamic random-access memory (DRAM), by generating electron-hole pairs that can charge or discharge the tiny capacitors that make up individual bytes of memory, changing their status from 0 to 1 or vice versa [7]. As the devices grew smaller, they would become more susceptible to α-particles, which were thought to come from the radioactive decay of atoms in the lead-tin solder that was used to

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connect memory chips to the circuit boards in memory units. Logic devices relying on transistors were also susceptible to errors caused by α-radiation when they became very small, and concerns arose about “flip-chip” systems that were developed to reduce the size and increase the robustness of electronic devices. These were connected directly to their circuit boards by balls of lead-based solder, placing the source of radiation very close to the active elements of the processors. Two solutions to the soft error problem were considered. Shielding the DRAM and CPU chips from the source of radiation proved impractical because of the small spaces involved and the amount of shielding that would be required. The other possibility was to eliminate new lead from the system, making old lead, or low-α lead, into a critical material for mounting semiconductor chips. Microelectronics manufacturers such as IBM and Intel began to seek sources for low-α lead, and the price of this material, critical for their products, rose dramatically. Low-α lead can be obtained from ore bodies that are not associated with uranium or thorium deposits, so they are made up of primordial lead without any radiogenic components. Pre-Cambrian deposits, more than 520 million years old, are the preferred sources. Modern recycled lead cannot be used because it is always a mixture of material from different sources, but older lead objects such as ships’ ballast and certain architectural objects can be single-source material, which may be low-α if the original source was made up of old lead. Where the original source is not primordial lead, the decay of radioactive lead eventually results in stable isotopes, but the half-lives of some of the intermediate products are in the tens or hundreds of thousands of years, so merely aging a stockpile does not result in low-α lead in a reasonable time frame. Ancient lead objects do, however, produce measurably less α-particles than newer ones, and this phenomenon can be used to measure their age, but they still do not reach the low levels needed for microelectronics and certain particle-physics measurements. Among a few other sources, low-α lead was found in the Polaris zinc mine that opened on Little Cornwallis Island in Canada’s far north, in 1982. The lead ore, galena, found in certain parts of this mine was found to be exceptionally low in radiation, and this was smelted separately from the rest to be sold to Intel at a premium price. The mine ceased production in 2002 when its zinc ore body was exhausted: the value of the coproduced low-α lead was not sufficient to sustain its operation. Information about other methods used to acquire low-α lead is shrouded in corporate secrets. It is rumored, for example, that IBM surveyed the output of all of the world’s lead mines to find which of them had low-α output and that Intel actually bought one such mine. IBM is rumored to have acquired low-α lead from the joints of stainedglass windows in European cathedrals, paying for them to be replaced with conventional lead. Uses of low-α lead in scientific research projects tend to be more openly documented, and it is known that certain particle-physics experiments have been shielded with low-α lead acquired from archeological finds. The urgency of finding low-α lead for the microelectronics industry effectively came to an end in 2006 when the use of lead was banned in electronics for environmental reasons, and lead-tin solder was replaced by a lead-free alloy made from copper, tin, and silver. Concerns continue for other applications and other low-α materials, including tin.

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Cobalt (1978) In the 1970s, about 65% of cobalt traded in the world came from the Kolwezi district in the southwest of the African nation of Zaire, a country with great mineral wealth but beset by political instability. The country had been a colony owned and directly ruled by King Leopold II of Belgium from 1885 to 1908, when it was known as the Congo Free State. It then passed to the control of the Belgian government, becoming a colony called the Belgian Congo. The country was in this status through the WWII, when it was a source of uranium for the Allied nuclear weapons program. With the end of WWII, a fervor for independence from colonialization swept across Africa, and Belgium granted independence to the Congo in 1960. The nation was almost immediately plunged into a civil war with various players, some with and some without external allies, vying for power. It eventually came under the control of Mobutu Sese Seko in 1965, and he changed the name of the country to Zaire in 1971. Zaire was under Mobutu’s dictatorial rule at the time of the cobalt crisis, but it was not at peace. In 1977 and 1978, rebellions afflicted the southwest of the country in a province that Mobutu had renamed from Katanga to Shaba, which contained the country’s uranium and cobalt resources. Rebels from this province were based in neighboring Angola, a communist state heavily supported by Cuba at that time, and the conflict become one of the hot spots in the Cold War. Concerns arose about the effects of this conflict on the availability of resources from this region of Zaire. In the 1970s cobalt was used primarily in superalloys for jet engines and chemical processing plants. When high-strength samarium-cobalt permanent magnet alloys emerged in the early 1970s, there was initial reluctance to adopt them because of concern about the supply of the rare earth element samarium, but General Motors (GM) eventually opted to use a Sm-Co permanent magnet starter motor in some of its vehicles, taking advantage of the weight and volume advantages of these motors over their traditional counterparts. Unfortunately, for GM, the supply of cobalt (rather than samarium) became problematic, with prices rising abruptly from about US$5/lb in 1976 to US$25/lb in 1978 because of the threat to the Kolwezi district posed by rebel forces. Interestingly the price spike coincided with increasing global production, as seen in Fig. 2.3, and the rebels never directly impacted the output from Kolwezi’s cobalt mines. Nevertheless, price spikes like this had never been seen before, and cobalt consumers sought alternative suppliers and substitute materials. Cobalt-based superalloys were displaced from many uses by their nickel-based counterparts, despite their poorer performance at high temperatures, and research and development efforts focused more on nickel than cobalt-based alloys for many years. GM and other users of high-strength magnets tried to find alternatives to Sm-Co, one result of which was the development of the neodymium-iron-boron magnet alloy, which first appeared in about 1984 [8] and was in commercial use by 1986. Since the 1970s, world cobalt production has grown very significantly, going from a peak of 31.5 kt/year at the end of the 1970s to 140 kt/year in 2018. Much of the additional production is generated through coproduction from copper mining and goes into lithium-ion batteries, which first appeared in the market in 2002 and have grown into a major product in their own right. Growth in the production of cobalt is largely driven

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History of materials criticality and supply-chain challenges

Fig. 2.3 Global cobalt production levels (left ordinate axis) and annual average cobalt prices (right ordinate axis) between 1980 and 2012. Gray bands represent the approximate dates of global recessions. Price and production rise and fall in-phase or out of phase at different times. Original data from the USGS Mineral Commodity Summaries for the relevant years.

by this application, and because battery manufacturers see cobalt availability as a potential challenge to the growth of their industry, they are working hard to reduce the amount that they use. The cobalt crisis began with a lack of source diversity. It resulted in demand destruction in the element’s existing uses while stimulating the development of new sources, freeing up supplies for emerging uses. Mobuto Sese Seko would eventually be forced out by a rebellion based in Zaire’s eastern provinces, adjacent to Rwanda, which had recently suffered its own genocidal rebellion. Laurent-D
esir
e Kabila replaced Mobutu in 1996, and he changed the name of the country from Zaire to the Democratic Republic of the Congo (DRC) in the following year. Control of mineral production in the country continues to be questionable.

Niobium (1979) Niobium underwent a significant price spike in 1979. A rare refractory metal, once also known as columbium, was used mostly as an alloying element in high-strength low-alloy (HSLA) steels and in certain superalloys. Alloyed with tin, it also found a niche use in superconductors, which were used for high-strength electromagnets in particle colliders: Nb3Sn has a superconducting critical temperature of around 18.3 K and was the best superconductor in the world at the time of the price spike, at least in terms of its superconducting transition temperature. Most of the world’s niobium consumption, however, went into high-strength, low-alloy (HSLA) steels for automobiles and pipelines, and smaller amounts went into superalloys. Production was dominated by Canada, along with Nigeria, Brazil, and a few other minor contributors.

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The primary reason for the niobium price spike was a worldwide switch from the use of cobalt-based superalloys to nickel-based superalloys for gas-turbine engines in aircraft and land-based applications and also in cryogenic tanks. The most popular superalloy that emerged for these purposes was Alloy 718, comprising 55%Ni, 21%Cr, 5%Nb, and 3%Mo, with the niobium addition overcoming the propensity of the alloy to crack during welding. Ironically, part of the reason for this switch from cobalt- to nickel-based superalloys was the cobalt crisis of 1978, and the sudden increase in demand for niobium created an imbalance of supply and demand for that material, which was quickly resolved as Brazil ramped up its production. Brazil is now the dominant producer of niobium, providing as much as 85% of the world’s needs, dwarfing Canada’s current contribution of about 10%. The niobium price spike was effectively a “knock-on” effect from the cobalt crisis, but there was no corresponding downstream impact from niobium on other elements.

Molybdenum (1980 and 2004) In 1979 and 1980 demand for molybdenum significantly outstripped supply, generating a brief price spike. About 70% of the molybdenum available to free markets came from the United States with the rest coming in approximately equal amounts from Canada and Chile. Sources of molybdenum included primary molybdenum mines and coproduction from copper anode sludge, and softness in the copper market suppressed molybdenum production from the latter source since the revenue earned from molybdenum was not sufficient to drive the production and stockpiling of excess copper. Increases in output from the United States were offset by reductions caused by labor disputes in Canada, and world production levels were static (excluding China, which did not export any molybdenum at the time). Despite the relatively constant supply, demand for molybdenum was growing, largely as a result of its use in HSLA steels, which were being used increasingly in the bodies of cars and trucks as a means of reducing their weight to improve their fuel efficiency. By 1979 virtually all existing inventories of molybdenum were depleted, and although new mines were in development in response to the increasing needs, demand outpaced the available production. The price spike abated in 1982, with the onset of a global recession and consequent fall in demand for new vehicles. As the market for copper recovered in the wake of the depression, supplies of molybdenum also improved [9]. A second molybdenum price spike occurred in 2004. Demand for molybdenum was again recovering following an economic recession that had begun in 2002, but production was growing, too. China was by then the third largest producer, a major exporter, and meeting about 23% of the world’s molybdenum demand [10]. In the first quarter of 2004, however, China abruptly halted its exports of molybdenum without any warning or explanation, causing great concern among consumers and driving prices up abruptly. Although Chinese exports returned to their normal levels in the next quarter, the sudden cut had left commodity traders nervous, and prices continued

History of materials criticality and supply-chain challenges

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to rise. The increasing prices brought more producers into the market, with the result that by the end of 2004, with Chinese exports restored and supplies meeting or exceeding demand, prices fell back to their earlier levels [11].

Tantalum (1997, 2000, and 2008) Tantalum is a rare, corrosion-resistant refractory metal with uses in alloy production, nuclear reactors, vacuum systems, and electronics. One of its most important applications is in large-capacity capacitors that are used in a wide range of electronics devices. Those who peer inside their electronics will easily identify the tantalum capacitors soldered onto their circuit boards from their characteristic yellow color. A new use for tantalum emerged in 1997 when IBM announced the first integrated circuit (IC) using copper interconnects. Up to this time the preferred material for electrical connections between individual devices within ICs had been an aluminumcopper alloy with about 4% of copper that IBM had invented in 1970, but with shrinking device sizes and conductor linewidths, a material with greater conductivity was needed. Pure copper interconnects swept through the semiconductor industry very rapidly after IBM had proven them effective. One of the challenges that they had overcome in this process was isolating the copper interconnects from the silicon substrates. Copper atoms can diffuse into silicon where they change the electrical properties on which the device depends, so a thin but effective diffusion barrier is required between the copper and the silicon. The materials selected for this job were tantalum and tantalum nitride, sometimes separately, depending on the need for an electrical conductor or an insulator, but frequently together in two-layer barriers. These diffusion barriers are very thin—just a few atomic layers wide—so they do not create a large ongoing demand for tantalum. As the new interconnect technology rolled out, however, the semiconductor industry had to retool, and large stocks of tantalum were acquired over a short period of time causing a small but discernable one-time spike in demand. World production of tantalum is shown by country of origin in Fig. 2.4. The switch from aluminum to copper interconnects, along with the rapid growth of the microelectronics industry, led many to conclude that demand for tantalum would grow continuously and a price spike occurred in 1997 despite that tantalum production was increasing in both Australia and Brazil, which accounted for the majority of the world’s supply. A second spike occurred in 2000, while output from Australia and Brazil was growing even more quickly, and Rwanda started to export tantalum after recovering from the aftermath of its 1990–94 Civil War. The worldwide recession of 2008 severely impacted tantalum demand, and several mines, including the Wodgina mine in Australia, were placed in “care and maintenance” status. Australia’s contribution to the world’s supply of tantalum was eventually replaced by output from Rwanda and the Democratic Republic of the Congo (DRC) despite concerns about the use of coerced labor and suspicions of illicit trade in the materials from these sources. Several electronics manufacturers, especially in Japan and Korea, searched for ways to meet their tantalum needs, and a variety of recycling methods were developed, particularly by automating the process of recovering tantalum capacitors from used

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Fig. 2.4 Global tantalum production by source country, between 1994 and 2017. Price spikes occurred in 1997 and 2000 and a price collapse accompanied the recession of 2008.

electronics. As these recycling tools began to be commissioned, however, manufacturers also reduced their use of tantalum capacitors through improved design and substitution with ceramic capacitors. In this case the perceived urgency of the need spurred three approaches to solving the shortage: substitution, reduction, and recycling. As the use of tantalum capacitors dropped through the reduction and substitution efforts, it grew more difficult for recycling efforts to be cost-effective because of the smaller amounts available for recovery. So far, at least, there has been little return from efforts to recover tantalum from end-of-life electronics.

Photovoltaic silicon (mid-2000s) Silicon is the second most abundant element in the Earth’s crust, and yet the solar photovoltaic industry suffered from a supply shortage that curtailed solar-electric growth in the mid-2000s. Photovoltaic energy was not cost-competitive with conventional electric power, but it was encouraged with government incentives around the world for several reasons, including the following: l

l

l

l

concerns about carbon emissions the ability of solar PV to serve regions not reached by power grids, particularly in emerging economies aspirations to establish leadership in an emerging industry the expectation that costs would decline as more units were manufactured

The world’s photovoltaic generating capacity had grown by 19% between 1999 and 2000, and the pace of growth increased steadily, reaching 41% between 2004 and

History of materials criticality and supply-chain challenges

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2005. From 2005 to 2007, however, the growth rate fell back to around 35%. Although the growth was still impressive by most standards, the solar photovoltaic industry was clearly suppressed between about 2004 and 2008 and also afflicted by soaring raw material costs. This was because of insufficient supplies of polycrystalline silicon (or “polysilicon”), which is the active constituent of most solar photovoltaic systems. Prices spiked from about $30/kg for photovoltaic-grade polysilicon in 2004 to $475 in 2008, and the increasing cost of the raw material outweighed the government subsidies in many places. The raw material for polysilicon is the same as that for silicon wafers and glass— they all start life as silicon dioxide in the form of quartz, which can be found in sand, but better starting purity is obtained from rock quartz. The process of making microelectronic-grade and solar-grade silicon starts with the production of metallurgical-grade silicon, which is relatively impure at about 98.5% Si and is obtained by carbothermic reduction of molten quartz. Solar cells and integrated circuits require much higher levels of purity—99.999% (“five nines” or 5N) for solar cells and 99.9999999% (9N) for integrated circuits. Integrated circuits also require large single crystals from which individual wafers are cut. PV silicon wafers are sliced from polycrystalline silicon ingots. Various purification methods are used to achieve the necessary purity levels, but the processes used to produce PV polysilicon and IC single-crystal silicon are different, and they are not carried out in the same facilities. Polysilicon production is driven entirely by the solar industry, and single-crystal silicon is driven entirely by the microelectronics industry. Polysilicon demand grew rapidly with the emerging solar industry, but polysilicon producers were initially reluctant to invest in new factories. A polysilicon facility typically takes about 3 years to build and has costs in the range of a billion dollars. The growth of the PV industry was perceived to be driven by government incentives, which could vanish at any time, so investors were reluctant to commit large amounts of capital with long payback times. The supply of polysilicon was unable to keep up with the rapidly increasing demand, largely because of uncertainty in the investment community. The lag in polysilicon supply opened doors for alternative technologies, and solar cells made of cadmium telluride benefitted considerably. At the time of the polysilicon shortage, CdTe was nearly as efficient a solar energy converter as silicon, but it had other challenges, including its reliance on tellurium, which has significant supply risks of its own, and the fact that cadmium is highly toxic. Despite these problems, large numbers of CdTe solar cells were installed, notably in Germany, which had very aggressive clean energy goals and incentives. First Solar Corporation launched production of commercial CdTe solar cells in 2002 and reached an annual production of 25 MW of energy production capacity in 2005. By the end of 2009, it was the largest solar cell manufacturer in the world, with an annual production rate of 1 GW, and the efficiency of its cells slightly exceeded the efficiency of the best commercial polysilicon units. With the establishment of new production capacity in Europe, Asia, and North America, the polysilicon shortage eased after 2008, and polysilicon prices eventually fell to $17/kg in 2014. The price decline may have been accelerated by overproduction of PV silicon in government-subsidized factories in China, and accusations of illegal

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dumping of low-priced PV units were made by the United States in 2014. With low prices and high availability, the year-on-year growth of the installed PV base rose above 60% in 2009, peaking in 2011 when a near-doubling over the previous year occurred. The low polysilicon prices also had an impact on cadmium telluride sales. First Solar remains a powerful player, but it was forced into significant restructuring as it came under price pressure from the newly resurgent polysilicon sector and its aggressive sales tactics. In 2011 General Electric announced plans to enter the CdTe PV market with a new factory to be built in Aurora, Colorado, but in 2013 it reversed course and sold the facility to First Solar. Cadmium telluride PV units are more expensive than their polysilicon counterparts, but they have greater output: purchasers who are impacted by the initial cost are more likely to buy polysilicon units, while those who focus on the long-term return on their investment tend to consider cadmium telluride more favorably. Critical materials significantly impacted the market penetration of a much-needed clean-energy technology just as it was emerging. Government incentives helped to create the growth that resulted in material demands that could not be met and also complicated the market response. The shortage of polysilicon helped to open the door for a substitute material, cadmium telluride. In retrospect the long-term impact of the polysilicon shortage was small: the installed base of solar PV generating capacity has continued to grow as seen in Fig. 2.5, and polysilicon costs have declined with negative effects on the CdTe market share, but the PV industry as a whole and the CdTe component in particular could quite easily have fallen out of contention. The solar photovoltaic industry, as well as the demand for its specialized materials, continues to be at the mercy of government policy, but it is rapidly approaching price parity with electrical generation based on fossil fuels. Once solar energy becomes consistently cheaper than fossil energy, the sensitivity to government policy may be expected to diminish.

Fig. 2.5 Annual growth rates of the global installed solar-PV capacity, between 1994 and 2016. The industry’s growth outstripped the global production capacity for solar-grade polycrystalline silicon in the mid-2000s, despite the high crustal abundance of silicon.

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Rhenium (2006–08) Among all of the elements, rhenium is one of the rarest, least widely utilized, and least substitutable. It is slightly less abundant in the earth’s crust than platinum. The market for rhenium is one of the smallest, with only about 45 or 50 tonnes being used worldwide each year. More than 80% of this goes into superalloys for jet engines, where it imparts strength at high temperatures, allowing the engines to run hotter and thus more efficiently. Rhenium is produced as a by-product of copper, specifically when the ore contains molybdenite: it is a by-product of molybdenum production, in operations where molybdenum is a by-product of copper. The largest single producer is Chile, which commands a little more than half of the world’s supply [12, 13]. As new generations of passenger aircraft came on line in the mid-2000s, with new and more efficient engines stipulated by the airlines, demand for rhenium grew, threatening to outstrip supply. Although prices rose rapidly starting in 2006, supplies did not respond proportionately because of the negligibly small impact on the revenues of copper producers. Prices continued to rise through 2007 and into 2008, abating only with the onset of the worldwide economic recession, that year. This is a case in which the economics of coproduction combined with the vulnerability of a small market to demand fluctuations to create a criticality. The aeroengine industry responded with refinements in alloy design to reduce the need for rhenium and changes in the business model to allow for greater recovery and recycling of end-of-life components. With the postrecession recovery in aeroengine production, rhenium prices recovered to some degree, but did not return to the levels of the 2008 peak. Rhenium remains vulnerable to changes in demand as jet engines continue to evolve and supplies are essentially unresponsive to price.

Lessons learned The examples described in this chapter show that industrial materials have always been subject to supply-chain failures. The details vary from case to case, and there is no fixed pattern to the nature of the supply-chain weaknesses, their consequences, or the most effective solutions to them. There are, however, some recurring themes that fall into different categories.

Failures of supply Excessive reliance on single sources or highly localized production is a significant supply-chain risk, as seen in the cases of copper during the Bronze Age, heavy water in Germany’s WWII nuclear weapons efforts and cobalt in 1978. Trade between remote partners enables localization of production wherever it is most economical, as exemplified by the dominance of copper production by Cyprus in the late Bronze Age. This creates single sites of potential failure and increases the risk of supply-chain disruptions.

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Lack of market transparency can lead to false inferences about future supplies of materials, such as the case of molybdenum in 2004. Political instability increases market uncertainty or causes actual shortages as seen in the cobalt crisis in 1978. Wars separate supply chains along lines of allegiance, and neutral countries such as Turkey and Portugal, in WWII, can benefit, provided they avoid the risk of invasion.

Changes in demand Technical progress can relieve or exacerbate the criticality of a material by reducing demand or increasing it. The need for low-α lead was essentially eliminated by the development of lead-free solder. The demand for PV-grade silicon rose rapidly as solar technology emerged. High-tech devices like nuclear reactors and integrated circuits can result in new demands on the performance of materials, resulting in the criticality of specific grades or purities of materials that are otherwise abundant and highly available. Responses to one critical material can have impacts on others. Reductions in demand for cobalt following the Zairian uprising of 1978 resulted in increasing demand for niobium required in nickel-based superalloys. The challenges of PV-grade silicon supply in the mid-2000s increased demand for cadmium and tellurium, with a converse effect taking place when silicon supplies improved. Increasing access to air travel caused increasing demand for jet engine superalloys in the mid- to late-2000s, challenging the supply of rhenium.

Grade dependence of criticality In some cases criticality is restricted to a particular grade of a material, rather than applying to its entire supply. For example, highly transparent glass was much more important to Venice than all other grades. Boron- and cobalt-free uranium was required for the Manhattan Project’s nuclear reactors, along with boron-free graphite. Nuclear technologies depend on specific isotopes of elements like uranium and plutonium. Heavy water has distinct properties from light water. Low-α lead was briefly critical for the electronics industry, despite the high availability of all other grades. High-purity, PV-grade silicon was in short supply, while lower purity metallurgical silicon and higher-purity electronic-grade silicon material were both easily accessible. Grade-dependent criticality is most likely to arise in the most advanced (or the most rapidly advancing) technologies of their time, as these can be especially dependent on the properties of specific materials.

Consequences of supply-chain failures The unavailability of a material can have particularly large consequences when it is coupled with other events such as natural disasters or wars (e.g., the Bronze Age Collapse, WWI, and WWII).

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The Venetian glass industry reveals how production monopolies are extremely important to those who own them, and that they can be expected to strive to keep them intact. The decline of Venice also shows us that materials needed to make its goods may be particularly critical to societies whose economies are dominated by a single product. The loss of Venice’s monopoly on glass production shows that technical advances around the world are threats to local production monopolies. Changes in demand can affect supply chains. The supplies of cobalt have diversified as its use has grown and where the DRC was once its dominant producer it now just the largest of several. Tantalum has seen the replacement of one dominant producer (Australia) by two others (Rwanda and DRC) as demand shrank and then recovered. A supply shortfall that is solved through the adoption of an alternative material can result in a permanent loss of market share for the original material. This is how natural rubber was displaced by synthetic rubber, silk was replaced by nylon, and tantalum was replaced by ceramics in capacitors. Other examples have emerged in the aftermath of the rare earth crisis, as we shall see later in this book.

Solutions to supply failures Increasing production at existing facilities is usually the quickest way to respond to increasing demand, but it tends to reduce source diversity. Expansion of production is not always easy in a free market, even where excess capacity exists. The ability to derive economic benefit is essential. Source diversification is an effective strategy for dealing with a shortage, but it takes longer than increasing production at existing facilities because it requires the construction of new production facilities. It has long-term benefits for supply stability. Material substitution is an effective strategy and sometimes results in materials that outperform the ones that they were developed to replace, as seen in the case of Nd2Fe14B substituting for Sm-Co magnets. Materials that succeed as substitutes for critical materials may be vulnerable to reverse substitution when the supply chain of the original material is strengthened, as seen in the case of CdTe substituting for silicon in photovoltaic cells. The use of substitute materials can involve significant adaptations of the technologies that use them, as in the case of neutron moderators in nuclear reactors: Graphite cannot be directly substituted by heavy water, so switching between the two materials requires a complete system redesign. Recycling is an effective strategy for materials where widespread use provides for a significant stock of recyclable material, as in the case of iron during WWII, provided that it is coupled with efforts to restrict the use of the material to its most critical applications. The case of rhenium in superalloys shows that recycling is also effective for singleuse materials, which can be recaptured at the end of life and used without separating the individual elements in the material.

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Germany’s efforts to assure supplies of chromium during WWII show that stockpiling is not an effective strategy for needs extending beyond very short terms. Competition for critical resources may result in temporary advantages for individual consumers, but does not solve the global problem, and it has other consequences. Nations have repeatedly resorted to annexation and/or invasion of lands rich in particular resources, only to find themselves in expanding conflicts. Competition for resources is also engaged through “economic warfare,” as in the case of the Allied efforts to prevent Nazi Germany from acquiring tungsten from Portugal during WWII. The focus of competition for resources has generally shifted in the direction of economics and away from armed conflict since the end of WWII, but it continues to be fierce, as seen in the case of the rare earth elements. Supply challenges are almost always solved through combinations of approaches rather than single strategies. GE used a combination of approaches to solve its problems with rhenium supply, for example. The Manhattan Project succeeded because it used multiple approaches to provide fissile material (using both uranium and plutonium) and neutron moderators (maintaining efforts to produce both high-purity graphite and heavy water). It also worked on four different approaches for uranium enrichment, eventually abandoning one of them and combining the remain three. It had multiple sources for most of its most critical materials. German efforts were more narrowly focused and suffered from poorer material source diversity. Overcoming supply-chain crises requires multiple approaches and significant duplication of effort. Open and even aggressive competition to create solutions is helpful, but coordination is also required, as in the case of the Manhattan Project’s uranium enrichment efforts. Leadership counts. Scientific research and technological development are essential and highly effective tools for developing supply-chain solutions, and they are most effective when they are closely linked together.

Further observations Price spikes are generally short lived, typically lasting between 1 and 2 years, but they are also usually singularities that occur when the tension between supply and demand—whether real or perceived—becomes too great. Most responses to shortages take significantly longer than the timespan of a price spike, so it is necessary to pay attention to signs of growing tensions in the supply-chain to be aware of the materials that might undergo crises and prepare accordingly. Despite our best efforts to predict supply shortfalls, the possibility of a technological surprise or a natural catastrophe always exists. Efforts aimed at reducing the response time have great value in dealing with unpredicted supply-chain crises.

References [1] M. Otte, Vers La Pr
ehistoire: Une Initiation, De Boeck, Brussels, 2007. [2] O.T.P.K. Dickinson, The Aegean Bronze Age, Cambridge World Archaeology, Cambridge University Press, Cambridge. 1994. xxii, 342 p.

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[3] E.H. Cline, 1177 B.C.: the year civilization collapsed, in: Turning Points in Ancient History, Princeton University Press, Princeton, 2015, p. 264. [4] J.A. Goldman, National Science in the Nation’s Heartland—the Ames Laboratory and Iowa State University, 1942-1965, Technol. Cult. 41 (2000) 435–459. [5] C.S. Payne, The Ames Project: Administering Classified Research as a Part of the Manhattan Project at Iowa State College, PhD Dissertation, Department of Education, Iowa State University, 1992, pp. 1942–1945. [6] A.L. Yergey, A.K. Yergey, Preparative scale mass spectrometry: a brief history of the calutron, J. Am. Soc. Mass Spectrom. 8 (1997) 943–953. [7] T.C. May, M.H. Woods, Alpha-particle-induced soft errors in dynamic memories, IEEE Trans. Electron Devices 26 (1979) 2–9. [8] H. Onodera, Y. Yamaguchi, H. Yamamoto, M. Sagawa, Y. Matsuura, H. Yamamoto, Magnetic-properties of a new permanent-magnet based on a Nd-Fe-B compound (Neomax).1. M€ossbauer study, J. Magn. Magn. Mater. 46 (1984) 151–156. [9] R.Q. Barr, Molybdenum statistics and technology 1979, J. Met. 32 (1980) 60–63. [10] U.S. Geological Survey, Mineral Commodity Summaries, http://minerals.usgs.gov/ minerals/pubs/mcs/2004/mcs2004.pdf, 2004. (Accessed 23 June 2016). [11] Molybdenum’s Perfect Storm, Casey Research, Delray Beach, FL, 2005. [12] G. Gunn, Critical Metals Handbook, Wiley, Chichester, England, 2014. [13] U.S. Geological Survey, Mineral Commodity Summaries, http://minerals.usgs.gov/ minerals/pubs/mcs/2016/mcs2016.pdf, 2016. (Accessed 23 June 2016).

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Defining critical materials After the rare-earth price spike, the term “critical material” rapidly gained currency and is now applied quite widely. It is, however, potentially misleading because the word “critical” has multiple meanings, several of which could apply to materials, in different contexts. According to the Oxford English Dictionary, “critical” means (among other things): (Of a situation or problem) having the potential to become disastrous; at a point of crisis: having a decisive or crucial importance in the success, failure, or existence of something. extremely ill and at risk of death. (In Mathematics or Physics) relating to or denoting a point of transition from one state to another. (Of a nuclear reactor or fuel) maintaining a self-sustaining chain reaction. l

l

A critical material must be decisive or crucial important to the success, failure, or existence of something, that is, it must be an essential material, but it may or may not actually be at a point of crisis. However, essentiality, although necessary, is not sufficient to assign the label critical material. This term is reserved for materials that are essential and also have significant supply-chain uncertainties. Materials criticality in this sense does not relate to phase transformations or nuclear fission, although the terms “critical” and “criticality” are also applied to materials, for different phenomena, in those contexts. In context of this book, the declaration that a material is critical is statement that supply risks exist and significant consequences might ensue from a supply-chain disruption. It is not a statement that a supply crisis currently exists or a prediction that one ever will: it is a warning that scenarios are conceivable in which shortages could occur, rather than a cause for immediate alarm. It identifies a need for contingency planning regarding supplies and the development of strategies to apply, should a crisis actually arise. It is common to refer to materials criticality in a binary sense—materials are either considered to be or not to be critical—but in reality, there is a spectrum of criticality: some materials are more or less critical than others, and it is important to quantify their criticality, even if it can only be done in an approximate manner.

Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00003-7 © 2021 Elsevier Inc. All rights reserved.

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Assessments of materials criticality The current attention to critical materials is only the most recent episode in an ongoing series of outbreaks of concern about the availability of mineral resources and other necessities of life dating back to the Industrial Revolution [1–6]. Although some of these use specific commodities, such as coal [3], to make their points, most of the alarms sounded in these works are rather general warnings that population growth threatens to outstrip the availability of resources. Even if it is accepted that we might, one day, run short of certain materials, we will not run out of all of them at the same time. The varying criticality of different commodities was first described in the sense used in this book and applied systematically to different minerals, in the 2008 NRC study “Minerals, Critical Minerals, and the US Economy” [7]. Critical minerals can encompass substances such as petroleum or helium that may not be considered to be materials, but, for the purposes of this book, “critical mineral” and “critical material” can be used interchangeably wherever the mineral in question is the major source of a material. The goal of criticality analysis is to identify and rank materials according to the risk of a supply disruption, where “risk” includes the likelihood and the consequences of such a disruption. Materials identified as critical can then be the subject of mitigation efforts to reduce the likelihood or the impact of a supply-chain failure, or both. The combination of functional essentiality and supply-chain fragility was identified as the defining feature of criticality in the NRC study, following from which the criticality of a material is commonly depicted in a plot shown schematically in Fig. 3.1.

Increasing essentiality

D A

B

C

Increasing supply risk

Fig. 3.1 Classification of materials according to their supply risk and their importance to a particular application. Material A has greater supply risk, and greater consequences ensue from a supply disruption, so it is considered more critical than Material B. Material C has the same level of essentiality as Material B, but a greater supply risk than either Material A or Material C. Material D has a greater level of essentiality than Materials A, B, or C but a lower supply risk than any of them. It is not clear how Materials C and D should be ranked against Materials A and B in terms of their criticality, or if that is even a useful question.

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Supply fragility is depicted on one axis and the level of essentiality on the other. The ad hoc committee that prepared this study applied the methodology to 11 minerals and identified indium, manganese, niobium, platinum group metals (PGMs), and rare-earth elements (REEs) as critical materials in the context of the US economy. When concerns about supplies of rare-earth elements began to emerge a year or so after the publication of the NRC study, interest in materials criticality grew rapidly, and a number of efforts were undertaken with a view to identifying other materials potentially at risk, and these all follow the same general approach. While some studies assign the vertical axis to “essentiality” and the horizontal axis to “supply risk” as in the NRC study, others reverse the assignment. Nevertheless, materials that plot in the top right corner of the diagram are more critical than those in the bottom left. Criticality, assessment efforts have been mounted by government agencies, corporations, and academic researchers, and they vary in several particulars, notably the methods used for quantifying essentiality and supply risk. In some cases, additional information is considered in criticality analyses. For example, environmental risks associated with the extraction of materials have been added on a third, orthogonal axis in some analyses [8, 9]. Other concerns may be applied in some corporate applications of the methodology: for example, a company’s annual expenditures on each material may be depicted, or they may show profit generated by products that contain the material [10]. These additional considerations really amount to supply-chain risks, in the case of environmental issues, and consequences of supply-chain failures in the case of costs, so it is arguable that they could be included in the parameters that go into the respective axes of a two-dimensional criticality diagram, including them as a third axis has the effect of drawing special attention to them, which may be useful in some settings. The US Department of Energy’s 2010 Critical Materials Strategy [11] is a twodimensional, forward-looking analysis with time horizons up to 15 years. It considered 14 chemical elements in the context of their essentiality to four clean energy technologies and identified six of them—all of which are rare-earth elements—as critical materials, and three as near-critical elements, two of which are rare earths. This report only addressed materials needs for magnets, batteries, thin-film photovoltaics, and fluorescent lighting. DOE updated its Critical Materials Strategy in 2011 [12], this time including 16 elements in the analysis and considering a wider range of projections of supply and demand, while addressing the same suite of technologies as in the 2010 report. Five rare-earth elements were found to be critical in both the 5- and 15-year time frames, and a shifting set of elements was found to be near critical between the two timeframes, with lithium appearing as a near-critical material in the 15-year scenario. The European Commission (EC) issued a report on critical raw materials for the European economy, in 2010 [13]. This study addressed 41 minerals and metals, counting both the platinum group metals and rare-earth elements as single items. Of the 41 materials considered, 14, including the PGMs and the REEs, were identified as being critical. All but two of the critical materials are chemical elements, the exceptions being fluorspar and graphite. Baseline data for 2006 were used in the analysis, and projections were made out to 2030, considering changes in demand anticipated on

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the expectation of some specific technology developments. The report did not consider any increase in primary material production, because mine development takes up to two decades and is unlikely to affect the supply picture by 2030. While the study focuses on impact to the economy as a whole, rather than any specific technology or industry sector, the list of technologies that drive up criticality in this study is dominated by clean energy, communication, computation, and medical devices, so there is some overlap with the DOE studies. A follow-up to the 2011 EC report was issued in 2014 [14]. Following the same methodology as the 2011 report, this study considered 54 nonenergy, nonagricultural materials. It also split the REEs into three distinct materials or groups of materials: scandium was treated separately, and the grouped light REEs (defined here as lanthanum, cerium, praseodymium, neodymium, and samarium) and heavy REEs (including europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and yttrium) were plotted as single materials. Although the distinction is often made between light (i.e., low atomic weight) REEs and heavy (high atomic weight) REEs, as in the 2014 EC report, the location of the dividing line is not universally agreed so detailed comparisons are not always possible. In addition to several mineral compounds, the 2014 EC report also included three biotic materials: natural rubber, pulpwood, and sawn softwood. The report identifies 20 critical materials, and the increase from 14 in the 2011 study cannot be attributed entirely to the increased number of materials that were considered. In 2017 the EC issued a new review of the list of critical raw materials [15]. In this work, nine new materials were added to the assessment, and individual analyses were made for some REEs and PGM elements, so that 78 materials were considered. A modified methodology was applied, and average production data for the previous 5-year period were used for the assessment, which is now more a snapshot of the most recent status than a forward-looking assessment of criticality. Twenty-six individual materials or material groups were found to be critical, and three materials that were found to be critical in the 2014 report—chromium, coking coal, and magnesite—were not identified as critical in the 2017 report. It is not clear to what extent the changes in the list of critical materials result from changes in the assessment method, versus actual changes in the supply or essentiality of the individual materials, or the inclusion of new data that were not previously available. In addition to its triennial reports on materials critical to the European economy, the EC has sponsored two reports on materials that are specifically critical to decarbonization of the EU’s energy sector, published in 2011 [16] and 2013 [17]. The focus of these reports is similar to the US DOE Critical Materials Strategy, and they consequently make an interesting counterpoint to it. The second and more comprehensive of the European decarbonization studies assessed 32 materials for their impact on clean energy technologies, with scenarios projected out to 2020 and 2030. Eight materials were assessed to have high criticality and six more were in the “medium-high” category. Six of the eight highly critical materials were REEs. Addressing the same end uses in the clean energy sector, a 2011 study produced by the American Physical Society’s Panel on Public Affairs and the Materials Research Society’s Government Affairs Committee [18] is more qualitative than the DOE and

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EC reports, but it identifies 29 chemical elements as energy-critical. Thirteen of these are REEs, and six are PGMs; the balance is being made up of helium, lithium, cobalt, gallium, germanium, selenium, silver, indium, tellurium, and rhenium.

National lists of critical materials Adopting a different approach, the British Geological Survey (BGS) has issued “Risk Lists” in 2011 [19], 2012 [20], and 2015 [21] for chemical elements or groups of elements. The BGS Risk Lists are based primarily upon the likelihood of supply disruption and do not take any significant account of the consequences of supply-chain failures—or essentiality—so they only address one of the two dimensions of materials criticality. The BGS assessments consider concentration of production, reserve distribution, recycling rate, substitutability, governance (of the top producing nation), governance (of the top reserve-hosting nation), and (in the 2015 assessment, for the first time) the companion metal fraction. The BGS Risk Lists do not consider the specific uses of the materials (except, perhaps, in terms of the assessment of substitutability, which can only be assessed with respect to specific uses) so they can be considered global and economy wide, but not complete criticality assessments. Each element is assigned a numerical risk level, from zero to 10, with 10 representing the highest risk. For 2011 the BGS list was led by antimony, PGMs, mercury, tungsten, REEs, and niobium, in declining order of risk, down to 8.0. For 2012 the elements achieving the same levels of risk were REEs, tungsten, antimony, molybdenum, strontium, mercury, barium, graphite, beryllium, and germanium, and for 2015 the top of the list included REEs, antimony, bismuth, germanium, vanadium, gallium, strontium, tungsten, molybdenum, cobalt, and indium. In the United States the White House National Science and Technology Council developed a multifactor screening methodology for critical minerals in 2016 [22] and the US government issued its first comprehensive list of critical materials in 2018 [23], based on this methodology applied to minerals data up to 2013—the most recent year for which complete data were then available. The list identified 34 distinct materials as critical, grouping all of the lanthanides under the title “rare earths” and all of the PGMs as a single item. The study was subsequently updated with minerals data for 2014 [24], and it was concluded that over the 1-year interval: “Overall, potential criticality… decreased since the last report, but a number of minerals saw an increase in potential criticality.” The majority of minerals for which criticality declined fell in the lower two quartiles in both analyses, while the top three minerals, yttrium, rare earths and gallium, all saw their criticality potentials increase.

Consistency and contrast The detailed results of criticality assessments are sometimes only of local interest or consequence, but their similarities and differences can be very informative. In some cases, boundaries are drawn at specific points on each axis of a criticality plot to separate critical from noncritical materials, but these are always somewhat arbitrary.

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Criticality assessments vary in their conclusions for a variety of reasons; examples are as follows: l

l

The quantification methods for essentiality and supply risk are not standardized, and methodological variations can lead to differences in the results. There is greater variation in the way that essentiality is assessed than the way in which supply risk is, and the differences reflect differing priorities among the organizations conducting the studies. All analyses assign numerical values to the essentiality and the supply fragility of each material, based on a selection of factors, summarized in Table 3.1. Different analyses may quantify the individual factors differently and may assign different weights to each factor that reflect the agendas or opinions of the various analysts. In most cases the contributing factors are based on actual data, but the reliability of the data can vary. In a few cases, “expert opinion” is also gathered and included in the analyses, the value of which is variable depending on the breadth of input that is collected. There is no clear consensus on what factors should be considered or how individual components of the assessment should be weighted in measuring either the essentiality or the supply risk for any particular material. Some of the studies assess criticality at a single point in time—usually the most recent year or years for which complete information is available—while others attempt to look into the future, based upon projections of supply and/or demand for each material considered. Current or recent assessments of the state of criticality are essentially academic exercises but they also help to establish a historical record which can have value in establishing the validity of the assessment method. Forward-looking assessments are usually intended to guide policy-making for corporations or governments. Current or recent assessments have the advantage of greater reliance on actual data, while forward-looking assessments are, of course, fraught with uncertainties and are frequently made obsolete by changing circumstances: they are best understood as possible scenarios, rather than predictions, and their reliability declines sharply as the time-horizon increases. Table 3.1 Factors considered in assessing criticality. Essentiality

Supply risk

Impact resulting from loss of access Low substitutability Time required to develop alternatives Consumption volume Diversity of use Cost of developing alternatives Expert opinion

Lack of supplier diversity Lack of geographic diversity of reserves Large demand growth Small supply growth Fraction of world production required Low recycling rate High import reliance Trade restrictions Supply-chain weak links and bottlenecks Small market size Governance index of host nation High companionality, coproduction High ecological impact Expert opinion

Individual studies consider different subsets of these considerations, weight their contributions differently, and quantify them in different ways. Some of the factors listed here are not independent from each other, which raises the possibility of “double counting” some contributors to a criticality assessment.

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l

l

l

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Most studies only address a finite number of materials and effectively score them against each other. Many studies only consider chemical elements, while others consider specific allotropes of elements such as graphite or diamond, compounds such as phosphates, or biotic materials such as wood. The presence or absence of a material in a study obviously not only has an impact on whether it is determined to be critical, but also may be indirect effects on the assessment of other materials—materials A, B, C, or D may score differently, depending on whether material E is included in a study. Although it is less likely that the relative ranking of A, B, C, and D will be significantly affected, the location of the threshold for criticality can be affected by the inclusion of material E. The identification of a critical material depends on the technological context. What is essential for a manufacturer of automobiles may differ from what is essential for a manufacturer of medical instruments. The identification depends on location. What is unavailable in one country or region may be readily available in other parts of the world, so, for example, the United States which produces 85% of the world’s beryllium does not regard it as a critical material, while many other nations do. The essentiality of the material to the economy also varies by nation and region as their industrial bases vary. Some economies are sustained more by mineral extraction; others are sustained by materials consumption in manufacturing. Australia, Canada, Brazil, and the Democratic Republic of the Congo (DRC) are examples of economies that are more dependent on mineral extraction and can be characterized as materials producers, while the economies of western Europe are driven more by manufacturing and therefore are therefore materials consumers. The interests of materials producers are better served by assessing materials essentiality on a global basis, while the interests of materials consumers call for a more local determination of essentiality. These two different types of economy see the materials supply chain from the opposite ends, but there are others that are more equally invested in production and consumption. Responses to criticality may vary according to these designations, in addition to the determination of which materials are critical. The identification of criticality is time dependent. What is a critical material today may not be critical tomorrow, as technological applications and materials availability evolve. This is particularly noticeable for the assessments that have been repeated or updated with only minor changes in methodology or scope, where the changes can be ascribed with moderate confidence to actual changes of underlying criticality. The identification of a critical material tends to impact its patterns of use, as we shall see in subsequent chapters, so the most critical materials also tend to exhibit the greatest time dependency of their assessments.

With all of the uncertainties associated with quantifying essentiality and supply-chain fragility, there is some risk of creating the illusion of quantitativity in criticality assessments, and they should be considered to be approximate guides rather than precise measurements. Small differences in the plotted locations of different materials within a single study are probably insignificant, but large differences, such as those between materials “A” and “B” in Fig. 3.1 represent real differences in risk for the users of the materials. DOE’s reports acknowledge this by assigning materials only within quartiles on the two axes of the criticality chart, rather than plotting precise locations. With all of the variations of methodology for criticality analyses, there is no global consensus on what materials are actually critical, because of the differences of analytical method, focus, location, and time, as noted in the preceding text. For the same reasons, nearly all of the studies need to be considered with a degree of caution, and

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readers should take care to ensure their understanding of the parameters within which any analysis was performed. Bearing these cautions in mind, some legitimate conclusions may be made by comparing the results of different studies.

Variation of criticality over time Despite all of the variability among the different studies, the repetition of essentially identical or similar studies over time provides an outlook on the general directions of materials criticality. Changes in criticality are reflected in two effects: (a) Increasing or decreasing criticality levels of individual materials. (b) Increasing or decreasing numbers of materials that are considered to be critical.

It is not clear that a change in either indicator or any combination of them can be used as a meaningful guide to the general trend or probable path of criticality overall, especially for variations over short time periods, but the trends are still worth noting. The EU studies focusing on economic impact identified 14 critical materials in 2011, 20 in 2014, and 26 in 2017. These increases may be attributed, at least in part, to increases in the scope of the studies and changes in the methodology, but it is also possible that materials criticality is actually increasing. The BGS studies are also repeated over time, and although they are not assessments of criticality, they provide a numerical assessment of supply risk. Of the 41 elements listed in the 2015 BGS report, 34 had seen increased supply risk over the levels assessed in 2011, with gallium showing the largest increase; one material was unchanged; and only six had seen their risks decline. The average risk increased by 1.2 on a scale of 0–10, and the largest changes are illustrated in Fig. 3.2. This report suggests that the majority of the materials that were considered saw increases in their supply risk. The NSTC critical mineral assessments show increases in overall criticality from 1996 to 2013 but a decline from 2013 to 2014, which may or may not represent a new trend. These reports concur with the BGS studies’ conclusion that the criticality of gallium, in particular, increased dramatically. It remains to be determined whether or not there is a persistent trend of increasing or decreasing criticality over time. Available data suggest that criticality has increased over some timespan but that the trend may also have recently reversed in the aftermath of the rare-earth crisis, particularly for some of the less-critical minerals. There are some persistent societal trends that tend to increase criticality levels over time and some that tend to reduce it, but regional and/or short-term effects may have more significant impacts than overall trends.

Global trends and their impacts on criticality Increasing levels of criticality may result from several factors, but predictions about mineral availability have a poor record of accuracy so we need to learn from their failures. A particularly relevant case is the prediction of widespread commodity shortages

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Fig. 3.2 Changes of supply risk over time, as measured by the British Geological Survey. The 10 largest changes are included in this graph.

made by Paul Ehrlich, its refutation by Julian Simon, and the wager between them about its accuracy, that is nicely captured in Paul Sabin’s book The Bet: Paul Ehrlich, Julian Simon, and Our Gamble over Earth’s Future (Yale University Press, 2013). Ehrlich had become famous in the 1970s by modernizing and propounding the arguments initially proposed by Thomas Malthus in his 1798 Essay on the Principle of Population [1]. In short the populationist view holds that since the world’s human population grows geometrically, the supplies of food and other necessities only grow arithmetically and planet Earth will eventually run out of resources. Ehrlich suggested that we would start to see signs of this within 10 years, in the form of tightening supplies and increasing prices of commodities. Simon took the view that technological advances would emerge in response to market forces, to overcome any such shortages and hold prices down. In 1980 the two men struck a wager on the 1990 price, adjusted for inflation, of a hypothetical “basket” of metals containing initially equal values of copper, chromium, tin, nickel, and tungsten: if it went up, Ehrlich would win; if it went down, Simon would get the bragging rights. When the bet came due, the world’s population had grown by nearly 20%, but the cost of the basket of metals on the open market had declined by 58%, and the price of every single metal in the basket had also declined. Simon had bet that technological advances would prevail over increasing demand, and he had won convincingly. The reasons for Simon’s win are more complicated and nuanced than typically depicted. Technological advances have, indeed, consistently reduced the inflationadjusted cost of metals ever since the industrial revolution, despite some significant challenges, and some interesting principles can be seen at work in this information.

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Also the increase in the population, predicted more-or-less accurately by Ehrlich, did not result in a corresponding increase in demand for metals because the population growth mostly swelled the ranks of the poor so it did not significantly increase the number of consumers for the metals covered by the bet. Both of these facts have an impact on materials criticality, so they are worth examining in a little more detail: one of them persists, but the other has changed significantly.

Commodity prices and the impact of technological advance Fig. 3.3 shows the inflation-adjusted price of a different market basket of metals than the one used for the Ehrlich-Simon bet, but this choice allows for a consistent measure dating from 1845 (roughly two decades after the end of the industrial revolution) almost to the present day. A quick look reveals an almost linear decline in the commodity prices, persisting for a century and a half. A closer examination reveals some major departures from the straight line, corresponding to major wars (1914–18 and 1939–45) and the Great Depression (1930), and other smaller excursions related to other events, but still the trend is unmistakable. This overall decline in metal prices is, perhaps, all the more surprising when we consider the growth in demand over the same period of time, reflected in the production levels exemplified in Fig. 3.4 and the decline in ore grades illustrated in Fig. 3.5 [25]. Comprehensive views of these trends across different materials have also been presented in a separate report by Mudd [26]. When a mine first opens, production

Fig. 3.3 The Economist’s industrial metal price index includes aluminum, copper, nickel, zinc, tin, and lead. In this figure the inflation-adjusted cost index is normalized to the value of these metals in 1845, and it shows a steady long-term decline, with significant excursions from the trend corresponding to events such as World War I (1914–18), the Great Depression (1929–39), and World War II (1939–45). Reproduced with permission from The Economist, https://www.economist.com/free-exchange/ 2011/10/14/hitting-our-limits. © 2011, The Economist.

Fig. 3.4 Australian mining production trends for selected minerals from the Industrial Revolution to the 2006. This illustrates the general trend that can be assumed to apply to the whole world. Reproduced with permission from G.M. Mudd, The environmental sustainability of mining in Australia: key mega-trends and looming constraints, Resour. Policy 35 (2010) 98–115. © Elsevier, 2010.

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Fig. 3.5 Trends in the grades of ores mined in Australia, from the Industrial Revolution to 2006. This reflects the general trend that applies to the whole world. Reproduced with permission from G.M. Mudd, The environmental sustainability of mining in Australia: key mega-trends and looming constraints, Resour. Policy 35 (2010) 98–115. © Elsevier, 2010.

typically focuses on the richest ore grade that can be identified within the property and, as the deposit is worked out, leaner and leaner grades are accessed until the mine becomes uneconomical. When new mines are contemplated, the richest available ore deposits are preferred, but when old mines are abandoned and replaced by new ones, the next deposit to be accessed is likely to be less rich than the original content of the most recently abandoned mines. The global trend is for production to come from poorer and poorer ore grades over time, in some cases dramatically. In the 1849 gold rush, the recoverable ore was gold flakes and nuggets—effectively an ore grade of 100%. Today, gold is extracted from ores with parts-per-million concentration levels. The impacts on major commodities are less dramatic, but more impactful because of

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Unit production cost

the larger quantities involved. Major steel producers have seen the average ore grade of their feedstocks that have declined by as much as 10% over the last decade. While the challenges of economic extraction from poorer grades are successively overcome, some of the environmental impacts of extraction continue to increase because of the need to transport increased quantities of ore to produce the same amount of metal and dispose of the increasing amounts of waste material at the end of the process. The long-term price decline is an illustration of Henderson’s law, which is obeyed for almost every industrial product that has been analyzed. The phenomenon was first observed in 1936, in a study of aircraft manufacture [27], and formalized by T.P. Henderson in a series of reports published by the Boston Consulting Group, in the late 1960s and 1970s [28]. Henderson defines the manufacturing experience curve as the cost to produce an item plotted against the cumulative number of items produced, and it shows that costs decline as manufacturing experience accumulates. The decline in cost is sustained by a mix of economies of scale, practical experience in the manufacturing plant, product redesign, and appropriately focused R&D. Henderson’s law says that the fractional decline in production cost is approximately constant for each doubling of the cumulative production volume, so plotting cost versus the logarithm of the cumulative production yields a straight line, as shown in Fig. 3.6. Different products and processes have differing slopes, and it is now common to refer to “a 90%” or a “95%” experience curve, meaning that making the product costs 10% or 5% less, respectively, for every doubling of the total amount produced. The experience curve is a powerful tool for strategic planning in the manufacturing sector, allowing for projection of prices into the future and the measurement of performance against expectations. Moore’s law, concerning the regular doubling of semiconductor device density, translates into Henderson’s law if we consider the unit cost of production of a single transistor. Fig. 3.3 is effectively an experience curve, because the production of metals increased geometrically over time, so the time axis is approximately equivalent to a logarithmic axis in terms of cumulative production. The pattern that displayed by this diagram was clearly a major factor in the outcome of the Ehrlich-Simon bet.

Log (cumulative no. of units produced )

Fig. 3.6 Henderson’s law states that production cost declines by a constant factor for each doubling of cumulative production. This translates into a straight line when plotted on a logarithmic scale.

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Cumulative production, millions of tonnes of TREO

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Fig. 3.7 Dominance of world rare-earth production, as measured by the total amounts produced or “experience” in the terms of Henderson’s law. China surpassed the United States as the leader in total production in the year 2000 and now holds a commanding lead in production experience. Data from the USGS Annual Mineral Commodity Summaries.

The experience curve has other applications relevant to the study of critical materials. It tells us that those who gain experience the fastest will always have an advantage in reducing their cost of production. The cumulative production of rare earths by the United States exceeded the rest of the world in 1974, as depicted in Fig. 3.7, ushering in a period of US dominance sometimes called the “Mountain Pass Era.” Despite a relatively late start, China exceeded the cumulative production of the United States by the year 2000 and continues to be the leading producer overall. Having gained an essential monopoly of experience in the extraction and processing of rare earths, China might be able to maintain a cost advantage if it operated as a single producer with knowledge shared across the nation’s entire rare-earth enterprise. The reality of China’s REE production, however, is that it may be better characterized as a loose cartel that is becoming more consolidated and coordinated. Any nation in the rest of the world would be challenged to produce more REEs than China has and thus gain the cumulative experience advantage, but there are still opportunities at the individual producer level, especially for some of the lower-volume REEs, and investments in research and development can move the experience curve to a steeper trajectory allowing new producers to become competitive in a relatively short period of time.

Population growth and consumption The impact of population growth on demand for raw materials is also nuanced. Homi Kharas, of the Brookings Institution, breaks down global population figures into three categories, corresponding to the wealthy, the middle class, and the poor [29]. In his categorization the poor are people who have essentially no discretionary income: this group therefore contributes to the economy only through the acquisition of necessities

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such as food, fuel, shelter and clothing, and does not create significant demand for other manufactured goods and particularly not for so-called “technology metals” such as the rare earths. We can therefore consider only the wealthy and middle-class populations to be consumers who impact the demand for raw materials. Fig. 3.8 shows the population of the world from 1965, with data projected out to 2030. Although there was an 18% increase in the overall population during the time period covered by the Ehrlich-Simon bet (1980–90), the number of potential consumers only grew by a little less than 9%. The impact of population growth on the demand for raw materials was therefore smaller than might have been expected from a simple populationist viewpoint. The relationship between the number of consumers in the world and the amount of consumption tells an interesting story, as depicted in Fig. 3.9. Between 1965 and 2017 the annual production of copper, per million members of the world’s consuming classes, remained constant within a factor of about two, starting at 3 tonnes/million, rising to 6 and then declining to 5. Over the same time period the production of aluminum per global consumer grew steadily and more than doubled, rising from 9 t/million to about 22. The rate for rare-earth oxide rose from 9 t/thousand consumers to a peak of 73 t/thousand in 2005 and falling back to 46 in 2017. The growth of rare-earth production per consumer was much greater than either copper or aluminum until 2005, presumably as the REEs made their way into more and more high-tech products. The rate of increase was especially high from 1986 when neodymium-based permanent magnets entered the market to 2006. Rare-earth consumption per consumer began to fall rapidly following the first announcement of Chinese export quotas, in 2005, and this may be considered to represent the real onset of the rare-earth crisis. As the ranks of the world’s consumers grow, we may expect to see roughly proportional increases in the demand for industrial commodity metals, but the demand

8

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Fig. 3.9 World production of selected materials per million consumers, where consumers are defined as the members of the middle class and the wealthy, according to the classification used by Kharas. The production of copper per consumer is relatively stable from 1965 to 2017, while the consumption of aluminum has increased. The production of rare earths per global consumer rose rapidly from 1965 but peaked in 2006 and then began to decline shortly after the first announcement of Chinese export restrictions.

for technology metals such as the rare earths is harder to predict. New technologies rapidly drive up the demand for the materials that enable them, and the growth in use of the REEs was an outcome of the digital revolution and the emergence or growth of other technologies. Rapidly evolving technologies also allow for the possibility of reducing the use of certain materials as they are redesigned from generation to generation. Despite the reduced demand per consumer for the REEs since 2005, the increasing number of consumers appears to have caused overall demand to grow, at least through 2010. It may be harder for technological advances to keep up with growing demand in the coming years. Between 2020 and 2030 the world’s population growth is expected to moderate to about 9% for the decade, but the number of consumers will expand by 53% as more and more people join the middle class. These figures compare with 18% and 9%, respectively, over the course of the Ehrlich-Simon bet, from 1980 to 1990: population growth will be halved, but middle-class growth will be higher by a factor of nearly six. The growth of the consuming classes over the next decade will certainly put pressure on the supplies of some materials. The evolution of the consuming classes will not be uniform across the world. Demand growth for consumer products over the coming decades will occur primarily in Eastern Asia as its various economies emerge and enlarge and because the growth of consumption will occur primarily in that region, the growth in manufacturing

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that it demands will also occur primarily there. While the growth of consumption and manufacturing will be dominated by Asia, however, the production of raw materials is a global enterprise: no country is self-sufficient in all of the raw materials that it needs and the supply chains for all materials are sustained by extensive international trade.

Emerging trends Some new technical and societal trends have emerged since the days of the EhrlichSimon bet, and most of these tend to increase criticality, either directly or indirectly.

A broadening palette of materials Increasing numbers of elements are being used in nearly all of our technologies [30]. Today’s devices rely on a wider array of chemical elements than at any time in history, which has the result that there are more opportunities to encounter supplychain challenges. The first commercial cell phone was Motorola’s DynaTAC 8000X, initially produced in 1983: its manufacture required around 35 chemical elements, but a little over 40 years later, a modern smartphone requires somewhere between 65 and 70 chemical elements, as illustrated in Fig. 3.10, and we are reaching a point where all of the devices that we own, with their multitude of functionality and connectivity, could soon require every chemical element in the periodic table except for the ones that are toxic or radioactive. Manufacturers of today’s mobile phones have about twice as many materials in their supply chains as the original builders did and therefore have about twice the exposure to supply-chain failure that Motorola faced when it introduced the DynaTAC cellular telephone phone. The broadening palette of materials contributes to increasing criticality by increasing the number of essential materials. A second effect of the increasing technological palette of materials, combined with progressive device shrinkage, is that the materials are more and more finely intermixed. The size scales of the smart phones and other data-processing devices are shrinking along with all of their components—down to the individual transistors in the central processing units. Some of the materials in these devices are now used in structures that are only a few atoms in thickness, or as low-concentration dopants to convert silicon into an n-type or p-type semiconductor. Separating the individual materials for recycling becomes progressively more difficult as they are mixed together at smaller length scales and lower concentrations, reducing our ability to mitigate supply shortfalls through recycling and driving up the criticality of individual materials.

Middle-class aspirations The growth of the middle class has impacts beyond the increasing demand for devices and the raw materials they contain: it reduces the amount of the world’s geological resources that can be accessed or increases the cost to access them, as a greater fraction

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(B) Fig. 3.10 The growing palette of materials in high-tech devices. (A) The elements known or inferred to be required for the manufacture of a 1983 vintage cellular telephone. (B) The elements required to make a 2018 smart phone. The elements used in the 1983 phone are in blue, the additional elements are in red, and the elements that have been removed are shown in green.

of the population seeks living space that is not compromised by industries like mining. Malaysia saw public protests when Lynas Corporation established its rare-earth processing facilities there [31]. Costa Rica has imposed a ban on open-pit mining [32], and El Salvador has banned all metal mining [33]. Efforts to increase governmental control of the mining sector are under way in several other emerging economies.

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Longer mine development times As described in Chapter 1, the Mountain Pass rare-earth mine first came into production in 1952, just 3 years after the deposit was discovered. Today, it is not uncommon for a mine to take 15–20 years from the beginning of the project to the first production of ore, although there are some notable exceptions. Mountain Pass ceased production in 2002, but it was acquired by Molycorp Minerals, LLC in 2008, and efforts to reopen it began in response to the tightening export restrictions from China. New ore processing facilities were built, with a strong emphasis on protecting the environment against the kinds of spills that had occurred prior to the shutdown, and the mine began operations again in August of 2012, after about 4 years of intensive effort under the title of “Project Phoenix.” This timeframe should be considered atypical because much of the work of developing the mine, notably assessing of the ore body, had been completed during its first cycle of operations, from 1952 to 2002. A significant amount of the mine’s infrastructure was also in place before Project Phoenix began. A new rare-earth deposit was discovered at Mount Weld in Western Australia in the 1980s, and Ashton Rare Earths Pty. Ltd. was incorporated with the intention of mining it and started the process of seeking the necessary approvals in about 1992. With Chinese production ramping up and REE prices falling, however, the project was put on hold in 1993. In about 2001, Lynas Corporation began work to develop a mine at Mount Weld and brought it into production 11 years later, in November of 2012. The company’s processing facilities were located in Kuantan, Malaysia. Northern Minerals’ rare-earth mine at Brown’s Range, Western Australia, began pilot scale production in July 2018, with full-scale production expected in 2020–21. The site was originally acquired for its potential as a uranium mine but, by 2009, exploration of the site was focused on a small area of the property rich in the rare earths, and new rare-earth finds continue to be made there, even today. If we assign a starting date of 2009, however, we can estimate the development time for this rare-earth mine at around 11or 12 years, from discovery to (anticipated) full production. The acquisition of permits to explore, develop, and operate mines is a significantly more stringent process today than it was in the mid-20th century in most parts of the world, and this increases the risk that a mining project might miss the window of opportunity to fill a supply shortfall. Investor enthusiasm rises and falls with the price of a proposed mine’s products, and it is challenging to sustain investor interest through price fluctuations over a decade or more of development time. With the capital costs for opening a rare-earth mine falling in the range of one-half to one and a half billion US dollars at current values, it takes many years and a diverse group of investors to generate this scale of funding as a project moves toward completion. In free-market economies, investors and the mining projects that they support come together in a few stock exchanges that specialize in this area, notably the Toronto Stock Exchange (TSX) and the Australian Stock Exchange (ASX) so there is some degree of expertise in these exchanges, but this does not appear to result in especially rapid rates of investment.

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Lengthening lead times for mine development reduce the responsiveness of supply chains when shortfalls emerge. Longer mine development schedules therefore increase supply-chain fragility and raise the criticality levels for the materials being mined.

Electrification An increasing fraction of the world’s energy is delivered in the form of electricity, and this is especially true in the economies that are responsible for the growth of the middle class [34]. Clean energy sources such as solar, wind, tide, and hydropower all produce electricity rather than fuels, and electrical energy is increasingly replacing other forms in many energy-using technologies, most notably transportation, where the market penetration of hybrid and electric vehicles seems poised for accelerating growth. With increasing electrification comes increasing demand for the materials needed for electrical production, transmission, storage, and conversion. Demand for magnets, in particular, is expected to drive significant growth in the consumption of neodymium over the coming decades. With increasing use of intermittent clean energy sources such as solar and wind, and increasing application in mobile devices from smart phones to vehicles, the world’s need for energy storage is rising rapidly, pushing up the demand for materials for the manufacture of energy storage technologies.

Conflict minerals Concerns about conflict minerals are increasing. Wars have always had impacts on mineral production and have been blamed for supply shortages such as the cobalt crisis of 1978, when the world’s major cobalt production facilities, in Zaire, were threatened by rebel forces. More recently the world’s governments have recognized that mineral resources located in conflict zones can be used to fund the conflict and perpetuate insurrections and wars, while promoting exploitative labor practices. “Blood diamonds” helped to sustain rebel troops in Sierra Leone’s civil war from 1991 to 2002, and tin, tantalum, tungsten, and gold are believed to sustain conflict in the eastern provinces of the Democratic Republic of the Congo, today. Legislation in Europe and in the United States seeks to prevent this by banning the use of materials derived from conflict minerals. While these efforts may have had various levels of success in achieving their goals, they also impact the cost of the affected materials.

Shifting trade policies New approaches to international trade may be expected to ensue when there are changes in the leadership of nations, but the changes in recent years have been unusually abrupt. Since 2017 the United States has departed from or renegotiated many of its trading agreements, in some cases withdrawing from multilateral trading blocs in favor of pursuing bilateral trading agreements, and the United Kingdom has left the European Union, thereby exiting all of its associated trading partnerships. There is a growing focus on the part of some nations on eliminating global or bilateral

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foreign trade deficits, and a reduction of reliance on the negotiation of disputes through the World Trade Organization. Tariffs and countertariffs have proliferated, and there has been something of a resurgence of mercantilism as a guiding principle. Since almost all mineral-based resources are traded internationally, abrupt changes to global trading principles and practices can impact their supply chains. Simple market nervousness concerning such changes prompts consumer behaviors like stockpiling, and there is a great temptation for governments to use access to essential resources as a bargaining chip during trade negotiations: these tend to increase the perception of materials supply-chain fragility. As we saw in the case of the molybdenum market disruptions of 2008, perception quickly becomes reality when there is an absence of actual information. All of the trends identified here combine to support the view that, as indicated by the changes in criticality analysis outcomes over time, there may be a sustained trend toward higher levels of criticality. No countervailing trends that would tend to reduce criticality have been identified.

Regional perspectives on criticality Criticality studies focusing on similar applications in different regions provide an outlook on the impact of geography on criticality. It is particularly instructive to compare the EC studies of materials criticality effects on decarbonization of the European economy with the DOE critical materials strategy that focuses on clean energy technologies from a specifically US viewpoint. Fig. 3.11 summarizes the results.

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EC, both 2011 and 2013

DOE 2011

Fig. 3.11 Comparison of the materials identified as critical in the EC studies of decarbonization and the US DOE’s assessment of materials critical for the deployment of clean energy technologies. Of the six elements identified as critical in both the EU and the United States, five are rare earths.

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The studies identify similar numbers of critical elements: five, for DOE and the 2011 EC report, and eight for the 2013 EC report, probably reflecting similar thresholds for criticality, even though thresholds are set somewhat arbitrarily. Both organizations identified the rare-earth elements yttrium, praseodymium, neodymium, europium, terbium, and dysprosium as critical. The general agreement between these two studies and many others, that at least some of the REEs are critical materials, reflects the worldwide concern about China’s dominance in the supply of these elements— reportedly providing 97% of all of the world’s REEs in 2008, as shown in Fig. 1.4 [35]. There is, however, considerably less consensus between the EC and DOE analyses for materials other than the REEs. A second comparison between the EU and the United States is available if we juxtapose the EC’s economic criticality studies with the USGS critical material list [23], as shown in Fig. 3.12. This reflects a broader-based economic impact and the EC has 31 individual critical elements, and the United States has 48, if we break out groupings such as the rare earths and platinum group metals. There is agreement on the criticality of 30 elements including the REEs, and the United States considers 17 elements critical that the EU does not, while the EU has only two exclusive elements in the list. Notable among the exclusive elements are uranium and aluminum (both critical in the United States only) and silicon (critical in the EU only). The areas of inconsistency largely reflect the geographic sources and uses of the different elements. The most notable point of agreement among all of the different criticality assessments is that rare-earth elements—considered individually in some cases as a single group in some and as two distinct groups (“light” and “heavy”) in others—are almost

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Fig. 3.12 Comparison of the materials identified as critical to the economies of the EU and the United States.

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universally assessed to be critical. This is perhaps not surprising since it was concerns about the rare earths that first precipitated the study of critical materials and rare-earth elements are poster children for critical materials. They are not, however, the only ones. It is historically established that REEs were critical materials in 2009, because they underwent a massive price excursion in 2010–11. With the benefit of hindsight, then, it is safe to conclude that they must have been at risk of a crisis before the crisis occurred, and all of the subsequent analysis confirms that the supply risk and the essentiality of the REEs made them critical materials. It might reasonably be asked, then, if any of the analyses have been influenced in any way by the inevitable conclusion, so the parameters that measure essentiality and supply-chain fragility have been selected and weighted to generate the conclusion that the REEs are critical materials, and whether our present analyses accurately assess the criticality of other materials, rather than assessing how close they are to the situation of the rare earths in 2009. To counter these questions, we note that the NAS study of mineral criticality identified the REEs as critical materials in 2008, more than 2 years before the peak of the rareearth crisis. This study, at least, did not reach a foregone conclusion. As discussed in Chapter 2, there are several materials other than REEs for which supply-chain disruptions have occurred in the past and, as for the REEs, the application of criticality analysis might have identified the risks, if there had been sufficient data available and the analyses were legitimate. No reports have appeared in which the criticality of any affected materials prior to its supply-chain disruptions has been assessed, although many cases have been rationalized ex post facto on the basis of single factors, most commonly the lack of supply diversity.

Indicators of criticality Certain frequently occurring characteristics emerge from the historical cases and the various criticality studies cited here. Some of these arise in analytical surveys because they are explicitly included in the parameters used in the analysis; others emerge in the analyses because they are related to the input parameters or they arise in some of the historical case studies cited in Chapter 2. These characteristics can be taken to be symptoms or indicators of possible criticality that are not conclusive by themselves but call for more complete analysis.

Limited supplier diversity Before the rare-earth price spike, China was the source of
97% of all of the world’s supply of REEs. Whenever a single source dominates the supplies for a single user the user is vulnerable to a wide variety of supply-chain disruptors that might affect or be directed by or at the source. Even as early as 1200 BCE, supply diversity was an issue, as the Mediterranean civilizations had come to rely upon Cyprus as their source of copper. When Cyprus was invaded by outside forces, copper production ended,

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causing a supply crisis for copper that may have been partly responsible for the decline of the various city-states in the area, the collapse of bronze age civilization, and the onset of a dark age that lasted about 200 years [36]. Supply diversity (or lack thereof) is included as a supply-chain risk factor in most criticality analyses, in the form of a modified Herfindahl-Hirschman index (HHI). This statistic is widely used in economics where it was originally developed as a measure of the level of competition in any particular industry. H¼

1n X

s2i

i

where s is the market share of producer i. H takes positive values up to 1, if s is expressed as a fraction, or up to 10,000, if s is a percentage. Larger values of H represent markets that are dominated by a small number of producers. In its original form the “producers” in the HHI were companies, but in criticality analyses the HHI is more frequently applied to entire countries, which possibly conceals some valuable detail. China, for example, had around 350 separate REE production companies in the mid-2000s and is in the process of consolidating these into six large corporations, leaving an unknown amount of production outside of central control. Through all of these changes, the Chinese REE industry is almost always depicted as a single producer, enhancing concerns over the apparent lack of supply diversity but possibly overstating the impact of the monopoly. There is no doubt, however, that however we compute the HHI, China’s REE industry is becoming less, rather than more diverse over time.

Small markets Many of the materials identified as being critical are produced and used in relatively small quantities. This observation emerges from the existing criticality analyses, and it may result from small markets having correspondingly small numbers of producers and therefore limited diversity of supply. Small-market materials are also vulnerable to sudden increases in demand associated with the emergence of new products that use them: these generate much larger relative shifts in the supply/demand ratio in smaller markets rather than larger ones, and it is consequently harder to increase production to meet the increasing demand. Small market size, by itself, however, is a poor predictor of criticality. Fig. 3.13 shows the worldwide production of several elemental minerals for 2017 [37]: 13 materials are produced at rates over 1 million tonnes per year, and six of them are considered critical either by the EC and the United States or both. Notably the United States considers aluminum to be a critical material, largely because of the lack of indigenous primary sources. At the far end of the scale, industrial diamonds and thallium are both produced at levels around 10 t/year and are not considered critical by the EC or the United States, because of the small economic impact of a supply disruption. However, of 30 materials with production levels below 1,000,000 t/year,

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2017 global production(tonnes)

10,000,000,000 1,000,000,000

Critical materials

100,000,000

Noncritical materials

10,000,000 1,000,000 100,000 10,000 1000 100 10

Iron Sulfur Aluminum Chromium Copper Manganese Zinc Boron Silicon Lead Nickel Graphite Magnesium Molybdenum Tin Strontium Titanium Antimony REO Cobalt Tungsten Vanadium Niobium Lithium Arsenic Silver Cadmium Bismuth Yttria Selenium Gold Mercury Tantalum Indium Tellurium Gallium Beryllium Palladium Platinum Germanium Rhenium Diamond Thallium

1

Fig. 3.13 Global annual production of 43 elemental materials, for 2017. Elements shown in red are considered critical for the economies of the EU, the United States, or both. Although criticality is more predominant among low-production materials, market size is not a reliable predictor of criticality.

21 are considered critical—roughly two of every three—a significantly though not overwhelmingly larger fraction than for materials produced at more than 1,000,000 t/year. Materials used in smaller quantities are at greater risk, but larger tonnage materials are by no means immune from criticality.

Coproduction Many critical materials are jointly produced with other materials or products [38]. This varies in form from materials that are produced in comparable quantities, for example, niobium and tantalum from their common ore and coltan [39], to materials that are minor by-products of materials that might be considered to be their hosts (e.g., hafnium is a minor by-product of zirconium mining, and tellurium is a tiny by-product of molybdenum, in the case in which molybdenum, itself, is a by-product of copper). The REEs are a somewhat unique case in that they are generally found together, either in ores like bastnaesite, in which the light REEs dominate, or in lateritic clays, which are richer in the heavy rare earths. Bastnaesite ores are notably rich in the lighter rareearth elements, and the concentrations fall off rapidly as atomic weight increases as shown in Fig. 3.14. Coproduction is somewhat related to market size, too: large-market materials such as iron tend to be obtained from dedicated mines, while small-market materials may not justify the capital expenditure associated with establishing a dedicated facility. Nassar, Graedel, and Harper show that almost all metals are produced in some measure as companion products to 10 primary metals as illustrated in their “wheel of companionality” shown in Fig. 3.15.

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Projected annual production (tons of REO)

10,000

1000

100

10

1 La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Fig. 3.14 Coproduction is typical of the rare earths. This is the mix of rare-earth oxide production, by mass, from a bastnaesite mine (these data represent the projected output from Mountain Pass after its reopening in 2012). In this case the mine predominantly produces light rare earths. Promethium does not occur naturally, and all of the elements heavier than dysprosium are present at concentrations too low to be of economic value.

Coproduction creates supply risk factors that overlay those that emerge from small market size alone. Among these are the following: l

l

The cost of separating coproduced elements. This is always challenging, since coproduced elements are found together because of their chemical affinity for a host mineral or their reactions with each other to form a mineral. In either case the chemical affinity that results in colocation also ensures that the elements will be hard to separate. Bastnaesite ores can require as many as 400 stages in a mixer-settler solvent extraction system to provide industrially useful levels of separation of the REEs that they produce. Production imbalances. The mix of elements in a particular ore body is unlikely to match the market demand for the elements, resulting in some being overproduced and others being underproduced [40]. Underproduced elements are likely to be critical, while materials that are produced in excess may be “anacritical,” being somewhat inverse to critical materials in the sense that they are an economic burden on the production of the underproduced critical materials. They also represent opportunities to improve the economics, as we shall see in Chapter 6.

Although materials that are not coproduced can still be critical, coproduction emerges as a supply-chain risk in several studies, and it is explicitly included as a factor in some criticality assessments, although it is not clear whether it is truly independent from other factors such as market size.

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Fig. 3.15 The wheel of metal companionality. The principal host metals form the inner circle. Companion elements appear in the outer circle at distances proportional to the percentage of their primary production (from 100% to 0%) that originates with the host metal indicated. The companion elements in the white region of the outer circle are elements for which the percentage of their production that originates with the host metal indicated has not been determined. Reproduced with permission of AAAS, from N.T. Nassar, T.E. Graedel, E.M. Harper, Sci. Adv. 1 (2015) e1400180. © The Authors, some rights reserved, exclusive licensee American Association for the Advancement of Science. Distributed under a Creative Commons Attribution NonCommercial Licence 4.0 (CC BY NC) http://creativecommons.org/licenses/bync/4.0/.

Lack of market transparency Many precious metals and some of the major industrial metals are bought and sold through commodity markets such as New York Mercantile Exchange (NYMEX) and London Metal Exchange (LME) where materials are offered for purchasers to bid upon through brokers: the buyers and sellers do not interact with each other directly. These markets are regulated and offer an open environment where all trades are based on physical stocks of materials, and the values of the commodities are

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determined by the prices agreed for individual trades and known to all. They also provide for a variety of financial mechanisms in addition to simple sales and purchases, including futures and options, which effectively provide buyers and sellers with the ability to bet on the price of a commodity at a future date and gain or lose depending on the accuracy of their prediction. This kind of market can only operate for materials where there is a significant amount of trading volume and large numbers of transactions, so there are commodity markets for aluminum, aluminum alloys, cobalt, copper, gold, lead, molybdenum, nickel, palladium, platinum, silver, steel, and tin. In all of these cases, the commodity in question is standardized in terms of its composition, and sometimes its size or shape, and is effectively identical irrespective of the source. Ores of some materials, such as iron, are also traded in commodity markets, but these can vary in value and are “gradeable” rather than being standardized, so they are priced and sold according to the weight percentage of metal that they contain or other measurable characteristics. Commodity markets are open and transparent, but not immune to manipulation. The lack of standardization or gradeability is currently a barrier to commodity exchange pricing for rare earths, which are usually traded in the form of oxides which may contain single REEs or mixtures of them. The International Standards Organization (ISO) has established a Technical Committee with a view to establishing criteria to address this. Some materials are traded in over the counter (or “OTC”) exchanges which provide a mechanism for matching buyers and sellers who then interact directly to negotiate details of volume, price, and delivery date. For many of the minor metals, however, trading is based on bilateral contracts negotiated directly between buyers and sellers. Information about the prices of these metals, including the REEs, is offered as a subscription service by a handful of price reporting organizations (PROs) such as Argus Media, which collect data on recent trades from individual contacts. As in commodity markets, prices reported by PROs are the values of the most recent known trades, but for many commodities, particularly for small-volume materials, a lot of time can elapse between reported trades. When no new information is added, the price can appear to be stable, but that circumstance needs to be evaluated with care: it can arise for several reasons: (a) (b) (c) (d)

No trading occurs because of low levels of demand or large user inventories. No trading occurs because the asking price is too high to attract buyers. No trading occurs because the offering price is too low to attract sellers. Trades have occurred but not reported for reasons of confidentiality related to commercial advantage.

Because the PROs play a powerful role in establishing prices, their work has come under some scrutiny, and concerns have been expressed about the completeness of their information and the ease with which their data can be manipulated by those who report trades to them [41]. Buyers or sellers can mislead the PROs about the details of a trade, or trading partners can engage in “shell trades” in which a batch of metal is bought and then sold back to the seller at a single price. No net amount of material or money actually changes hands, but two trades are reported and a price

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is established, which can then give a buyer or a seller an advantage in negotiating their next actual trade. Similar shenanigans can also occur in open commodity markets, but their impact is much smaller because of the volume of trades that occur, making it unlikely that a single shell trade will have a big impact on the apparent price of a material. In directly traded materials, then, the opportunity for price manipulation or misinterpretation somewhat increases supply risks for purchasers.

Increasingly rigorous materials specifications High technology uses place new requirements on materials. As our devices get smaller, more precise, or more powerful, the materials from which they are made have to be more precise in their composition, sometimes simply meaning more pure, but always meaning more precisely defined and more consistent. They may also need to meet new performance criteria, such as the ability to operate at higher temperatures, under greater loads, or with less maintenance. Materials that might not be critical in general may become critical when they are required at a particular purity or a new performance specification: l

l

l

Silicon is the second most abundant element in the earth’s crust and is highly available, yet high-purity silicon saw a supply shortage and a corresponding price spike from about $30/kg for polycrystalline silicon in 2004, to $475 in 2008, eventually falling back to $17 in 2014. The price increase resulted from restricted production capacity, while demand was driven up by the sudden growth of the solar photovoltaic industry. As new supply came on line, the balance between supply and demand was reset. Carbon is one of the most abundant and available elements, but there are challenges in providing graphite of a quality suitable for use in anodes for lithium-ion batteries. Manganese is widely used in the steel industry and is not high on most criticality lists, but it is showing up as a component of some candidate replacement materials for magnets and phosphors, and these applications demand much higher purity than is available in metallurgical manganese. High-purity manganese has a higher criticality than its metallurgical-grade counterpart.

Misleading indicators Some characteristics of materials or their markets have been used inappropriately as indicators for criticality.

Price Some materials are simply more expensive than others and that, alone, does not make them more critical. For example, the platinum group metals are identified as critical much less frequently than the rare earths, which are considerably cheaper. As noted previously, however, a lack of reliable price information can increase supply risk.

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Price variations Price changes can occur when the market anticipates an imbalance between supply and demand, and when they rise, it is an indication of a collective—and likely expert—opinion that criticality is rising and problems may lie ahead. The most frequently cited symptom of rare-earth criticality is the massive price spike that occurred for some of the rare earths between 2010 and 2011. This, however, is an extreme case that is not so much a symptom of a material that is critical in the sense used here—one that has a supply risk, along with significant consequences of supply failure—it is more an indicator that the rare earths had transitioned from a state of risk to an actual crisis. Radical price instabilities of this type are only indicators that something is already happening or has already happened, and they are therefore not useful predictors upon which to base contingency plans. Price spikes also occur when there is no actual supply shortage, resulting from nervousness that leads to anticipatory buying and stockpiling of materials, raising the price, and reducing availability. There is some evidence that rare-earth buyers and possibly some speculators contributed to the price spike. It is, however, reasonable to ask if there is any link between the level of “noise” in the price of a material and its criticality, so that price instability could be used as a warning sign for increasing criticality. Redlinger and Eggert have studied a related question [42]: whether the prices of by-product materials are more unstable than the prices of “main-product” commodity materials. Since by-products are more likely to be critical, there is some prospect that there could be a correlation between instability and criticality. The study finds that fluctuations of annual average prices are greater for by-product than for main-product materials, but monthly price fluctuations produce a more equivocal outcome. This may relate to small numbers of trades being reported for these materials: in a month when no trades are reported, the PROs simply report the price of the most recent trade, from a prior month, so a lack of trading may give the false appearance of stability in the timeframe over which instability is being assessed. The appearance of month-to-month price stability can therefore be illusory for metals that are not traded in commodity exchanges, which makes it hard to use price instability as an indicator of criticality, even if there is underlying validity to the suggestion that they could be correlated.

Crustal abundance Although frequently cited, the crustal abundance of an element is not closely related to its availability or its criticality. The abundance is the amount of the material in the earth’s crust, and at extremely low abundances, it may have some impact on criticality, but it is not a reliable indicator. Aluminum, for example, is considered critical by the US government, but aluminum is the fifth most abundant atom on earth, as shown in Fig. 1.2. The abundance of the rare-earth elements is lower than most of the transition elements, but not by a very large margin, so it should be recognized that “earthabundant materials” are not necessarily readily available. Conversely the REEs are

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considerably more abundant than the PGMs, but the PGMs are much less frequently cited as critical materials. Availability is more a function of mineable concentrations than of overall global abundance.

Longevity of geological resources Some commentators refer to the number of years of supply that are known to exist as an indicator of criticality. This is measured by taking the total volume of known resources and dividing by the current annual usage rate. To interpret this parameter properly, one must understand the meaning of the terms “resource,” “deposit,” and “reserve”: l

l

l

A resource is the amount of a geologic commodity that exists in known deposits—for practical purposes, an educated guess of what might be accessible within the Earth’s crust. Deposits are, generally speaking, geological finds that have not been completely evaluated for commercial viability. A deposit is an individual natural concentration of minerals in the Earth’s crust, whose size and geologic character is known with a high degree of certainty and might conceivably be developed into a mine at some point in the future. Deposits are identified through mineral exploration, including sampling, drilling, and other activities that locate the deposit and define its basic characteristics. The degree of concentration is called the “grade” of a mineral deposit. An “ore deposit” is a mineral deposit that has high enough grades of metal to suggest that it could be economic to mine. A reserve is the sum of the deposits that have been discovered, have a known size, and can be extracted at a profit—it is a subset of a resource that includes only those deposits that have been mapped out and extraction methods have been evaluated, according to recognized guidelines such as the Canadian NI-43101 [43], Australian JORC [44], or South Africa’s SAMREC [45]. Reserves typically fall under the control of specific corporations or nations.

When the rate of production of a material threatens to use up all of its geological resource or reserves in a small number of years, it is inferred that the material might have a supply risk. Because reserves are a subset of resources, resource life projections are not only always longer than reserve life projections but also much less precise. When the projected life of a reserve is less than the time that it would take to develop a mine, matters may be considered to be serious. The reality, however, is that resource life projections tend to revert toward a steadystate number, typically 30 years or greater, or at least they avoid falling below some critical value. Fig. 3.16 shows the resource life projections over a two-decade period for four metals—two large-market materials and two small-market ones and two critical and two noncritical—based upon the annual USGS Commodity Summaries. Although production rates for most of these metals have grown substantially over the time period, the resource life projections have remained largely constant. Notably the resource life projection for the REEs, despite their acknowledged criticality, is the longest of the group—approaching a thousand years—and cobalt (the other critical material in the group) has the second-longest resource lifetime. These projections tend to maintain certain minimum values because geological exploration in pursuit of new deposits accelerates when the resource life projection sinks to a threshold (which can be different for each mineral) that triggers concern.

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(

)

(A)

(

)

(B)

(C)

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(

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(D) Fig. 3.16 Resource lifetime projections for (A) copper, (B) manganese, (C) cobalt metal, and Fig_cont(D) rare-earth oxide from 1995 to 20,017. The resource lifetimes of these and other products tend to correct upward when they dip to a value that triggers interest in identifying new resources. Cobalt and REO have the longest resource lifetimes in this group, and they are the two that are considered to be critical materials. The higher values for critical materials suggest a greater level of concern, triggering exploration more readily than for noncritical materials. Production and reserve data for these plots are drawn from the USGS’s annual Mineral Commodity Summary.

New resources are being added even as existing reserves are depleted, at a rate that is driven by the depletion rate. Reserves can also grow when new extraction methods are developed, making previously uneconomic resources viable. Anticipated shortfalls of supply often have the effect of galvanizing research on novel methods of extraction, and investments in this area can increase the size of a reserve without any increase in the resource. Recognizing that new resources, or new means of exploiting existing deposits, are sought when concerns about the supply are high, the projected lifetime of a resource or a reserve may be an outcome of criticality rather than a fundamental indicator of it. Based on the examples shown here, long resource lifetimes might reflect a collective concern regarding the security of supply, and the lifetime might be considered as a barometer of expert opinion on this matter with large numbers rather than small ones being associated with criticality.

Import dependence The extent of a nation’s reliance on importation is occasionally used to sound the alarm about the security of its supplies of particular materials, and this gains currency with an increasingly mercantile view of international trade. The annual USGS Mineral Commodity Summaries include a chart showing the minerals for which the United States is highly dependent on imports, and in 2020

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this showed 17 minerals (including all of the rare earths as a single case) for which the United States has a complete reliance on imports and 49 for which the reliance exceeds 50%. International supply chains certainly involve a broader array of risks than domestic ones, but those need to be assessed carefully, case by case. The number of sources is more important than the overall import percentage, so materials that are only imported from one nation are more vulnerable than materials that are imported from multiple sources. Where there is high reliance on a single source, the reliability of the exporting nation also needs to be considered. Most nations have fairly robust trading arrangements with some countries and less dependable relationships with others. Without consideration of other factors, import reliance has the potential to be a misleading, if somewhat emotive, indicator of a material’s criticality.

What does criticality mean? The assessment that a material is critical is a statement that it has a fragile supply chain and that the consequences of a supply failure are significant. The analysis is related to conventional risk analysis, in which risk is assessed as the product of the probability of an event happening and the cost if it does. The value of risk analysis is particularly appreciated in the insurance industry, although the data that are used there are frequently misinterpreted by the public. For insurance purposes, risk is reduced to an assessment of the probability of an event occurring within a particular time period, which is usually the time covered by the insurance premium. A flood of a particular depth may have a probability of 1% in 1 year for a particular location, and it is then referred to as a 100-year flood. The consequence of such an event is assessed in financial terms: if a disaster of this particular magnitude occurs, how much will it cost? Insurance companies then base the price of coverage on the cost of an event multiplied by the probability of its occurrence within the period of coverage, no doubt adding some margin for profit. Criticality assessments typically fall short of risk analyses in terms of the rigor of their quantitation: supply-chain weakness is usually ranked on an arbitrary scale rather than being assessed in terms of the probability that a failure will occur over a particular timeframe and essentiality is not usually quantified in a financial form. A criticality assessment does not, therefore, provide a guide to how much money should be invested in ameliorating a possible supply-chain failure [46]. When we look at a criticality diagram like the one shown in Fig. 3.1, the level of criticality appears to be a sort of vectorial sum of the probability and consequence of a supply-chain failure. In risk analysis the level of risk is the scalar product of probability and consequence. This means that materials plotted along the diagonal of a criticality diagram carry a risk that is proportional to the square of their distance from the origin: that is, the risks associated with highly critical materials are greater than might be inferred from the criticality diagram, and investments in amelioration strategies should be correspondingly greater [47]. The criticality diagram, however, provides some insight into appropriate strategies for mitigating the risks to different materials. In Fig. 3.1, Material C will be affected

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more by efforts to increase its supply diversity than to reduce its essentiality, while Material D is better served by addressing its essentiality rather than its supply diversity. When additional axes are included in the criticality assessment, they can similarly suggest the effectiveness of addressing the matters that contribute to them. If it were possible to conduct materials criticality assessments in the same terms as risk assessments, “essentiality” would be measured by the cost of a particular material’s supply-chain failure, and supply-chain vulnerability would be measured by the probability of that failure occurring in a particular time frame. Multiplying these numbers together yields an assessment of the financial exposure incurred by criticality, which, in turn, suggests how much money should be invested in ameliorating the risk over the assessed time frame. While it may be possible for some manufacturers to be able to assess the essentiality of their materials in terms of cost, the conversion of supply-chain vulnerability to a probability per unit of time has not been addressed. Determining appropriate R&D investments to ameliorate criticality is consequently a matter of managerial discretion for a company, or of political debate for a society. It may be clear that we should invest some effort in ameliorating materials criticality, but it is not yet clear how much. It would, however, be wise to invest disproportionately larger amounts in the materials that appear to be the most critical, because risk increases in proportion to the square of criticality.

Consequences of criticality Criticality, per se, has no immediate consequence but from time to time some critical materials undergo actual supply-chain crises. When this happens, the most visible symptom is usually a spike in price such as the one that occurred for the REEs in 2009–11. Price spikes typically last approximately 2 years, but they may have technological impacts that last considerably longer, and the indication from Fig. 3.9 is that some of those impacts may be felt well in advance of a price spike. When supply-chain crises occur without appropriate preparations in place, the impacts on manufacturing can be severe and immediate, including higher prices for the affected materials, long delivery delays and occasionally production stoppages, any of which can have catastrophic business impacts. With a degree of foresight, additional strategies become available, most of which involve engineering compromises and workarounds. We see some evidence that manufacturers began to put such strategies in place to ameliorate the impact of a rare-earth crisis, as early as 2006. In Chapter 4, we will describe the strategies that were adopted in in the face of rareearth criticality, before, during, and after the price spike.

Tipping points. What takes us from criticality to crisis? Although many materials are considered to be critical, actual supply-chain crises are relatively rare. As the number of critical materials increases, however, the frequency of price spikes or actual supply-chain crises might be expected to rise.

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Price spikes: Symptoms or causes of crises? A price spike, by itself, may not be related to a supply shortage, since prices can fluctuate for a number of different reasons. One of the results of a rapid price increase, however, is that users of the affected materials increase their acquisitions as a means of insuring against further price increases. This kind of anticipatory buying to build stockpiles is a legitimate response to a price increase, but in a small market where the increase in purchasing represents a significant fraction of the apparent demand, it can have two distinct effects: l

l

It gives the impression of the increasing use of the materials, further driving up the prices. This can lead to a runaway feedback cycle in which higher prices generate higher demand and higher demand generates higher prices. The growth of manufacturers’ stockpiles reduces the amount of material available to purchase for immediate use, generating actual shortages for other users.

Price increases—even when they are not related to actual demand for materials—can therefore result in supply shortages.

Supply shocks Critical materials are vulnerable to changes in supply caused by changes in production levels, natural disasters, and man-made disasters. For small markets and especially for those that are only served by small numbers of producers, any loss of production can represent a large fraction of the world’s supply. Mines can be depleted or ore bodies can be completely worked out, but this is actually quite rare and never occurs without warning. When the projected supply lifetime dips to a level that triggers concern, new resources are found, reserves are developed, and new sources are brought on line. There is no evidence that the world is actually running out of any particular material, although some may be getting harder to extract. Supply chains can be affected by natural disasters such including geological and atmospheric events: earthquakes, tsunamis, volcanic eruptions, landslides, blizzards, hurricanes, tornadoes, droughts, floods, etc. Wars can have similar effects, as in the case of the cobalt supply crisis in 1978. Many of these types of disaster occur without warning and can impact the operation of a supply chain at its source (e.g., stopping production at a mine) or elsewhere (by disrupting transport of the material). It is debated whether the incidence of natural disasters is increasing [48]. There has certainly been an increase in the number of disasters that are being reported and their economic impact in recent years, but this could result from increased reporting rather than increased incidence, as the middle class grows and occupies more of the world’s land, disaster detection improves and communication accelerates. Irrespective of the source of the increase in disaster reporting, the impact of this type of disaster is increasing as more and more high-value property is affected. The increasing impact of natural disasters also impacts critical materials as their sources and transport links to end users extend into risk-prone regions or risk-prone regions grow to affect the supply chains.

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An instructive case study of a material not typically considered critical has been outlined by the US Department of Homeland Security (DHS) [49]. The iron used to make steel for the US automobile industry in and around Detroit comes from mines in Minnesota, which produce a relatively unusual mineral called taconite that is a relatively low-grade ore containing 20%–30% of magnetite. Most of the world’s iron mines produce ores that are richer in the iron-bearing components magnetite or hematite. Taconite from Minnesota is transported by ship, through the great lakes, to blast furnaces in Wisconsin, Illinois, Indiana, Michigan, Ohio, Pennsylvania, and Ontario where it is reduced to iron, the primary component of the steel sheet used to make automobile bodies. This is an unusually specialized supply chain essentially linking a single source and a single end-user, relying on a steel-making process that is specialized for the taconite ore. The DHS report points out that this supply chain has a unique vulnerability to a single potential point of failure: all of the taconite ore passes through the Poe Lock in the Soo Canal. One of several parallel locks that accommodate the 23-ft drop in elevation between Lake Superior and Lake Huron and the only one large enough to accommodate the ore ships. The failure of the Poe lock would cut off the steel supply to the US autoindustry within a few months, and it is estimated that repairs to the lock or the development of alternative means of transportation could take years. World markets for finished steel are not sufficiently elastic to meet the demand, and the blast furnaces in this supply chain are not able to process ores richer in hematite or magnetite from other mines. While automotive steel is not typically considered a critical material, this single supply chain results in a criticality for a particular end user because of a single point of failure with the potential to act as a tipping point.

Technology shifts Technologies change over time, generally becoming more sophisticated and incorporating more materials with special properties that provide new capabilities. When technological change is evolutionary, the demand for materials—critical and otherwise—tends to change incrementally and manageably. When more radical technology shifts occur, they can produce sudden changes in the demand for materials that challenge the supply chains, especially in small-market materials. It is difficult to prepare for tipping points caused by this kind of demand shift since they are not easily predictable in terms of their timing and sometimes also in terms of the materials that will be affected. The experience curve can help us to anticipate technological tipping points, which may be the cause of sudden shifts in demand for specific materials and push them from critical to crisis, or reduce their criticality. When an emerging technology challenges an established industry, it must compete against a superior body of manufacturing experience, whether it is in the manufacture of video monitors, lamps, vehicles, electrical power, or anything else. Established manufacturers of cathode ray tube (CRT) monitors, incandescent lamps, internal combustion engines (ICEs), or coal-fueled electric power once had or still have the advantage of vast manufacturing experience relative to the technologies that surpassed or

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Unit production cost

Emerging technology (actual cost)

Entrenched technology

Emerging technology (expected cost)

Anticipated tipping point

Log (cumulative no. of units produced )

Fig. 3.17 New technologies typically command premium prices and are only bought for reasons unrelated to price, or because subsidies reduce the cost-differential. The experience curve suggests how emerging technologies eventually displace existing ones for general use. When new technologies such as flat-panel displays or LED lamps can be produced at costs below existing products, such as CRTs or CFLs, the emerging technology will displace the existing one. Materials needed for the new technology will then experience rapid growth in demand while those required for the old one will see significant drops.

currently challenge them. However, when the emerging technology has a steeper experience curve than the established one, even if it has a higher initial cost, it can eventually gain the cost advantage if enough units can be sold before the pool of early adopters is exhausted or its promoters run out of money, as indicated in Fig. 3.17. If an emerging technology cannot establish a steeper experience curve than the entrenched one, then it can never win in a free market, and it represents a poor investment. When an emerging technology has a steeper experience curve, it has the potential to reduce its costs below that of the established industrial base, and it offers an opportunity for investment or assistance through government incentives, accelerating production and moving more quickly down the experience curve until it can undercut the prices of the existing technology. Such price crossovers have contributed to the replacement of CRTs by flat panel monitors and compact fluorescent lamps (CFLs) by light-emitting diodes (LEDs), each with consequences for the supplies of the materials on which they depend. In the cases of flat panel displays and LED lighting, the effect was to reduce the demand for red phosphors based on europium and green phosphors based on terbium, reducing the criticality of these rare earths. In cases where the emerging technology requires larger amounts of a critical material, the increased demand has the potential to produce a supply crisis, but the likely outcome of such a scenario is that the unit cost of the technology will shift to a shallower experience curve because the value of the material will rise if the technology is adopted and the widespread adoption of the new technology will be delayed. We conclude that demand-driven tipping points occur more readily when they result in reductions of criticality than when they cause it to rise. It is difficult to use the experience curve to predict the date when a technology shift might occur, because the horizontal axis represents the cumulative number of units produced rather than time. Although the production total is clearly related to

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time, the relationship can be complicated and the data needed to establish the correspondence to the date are usually not readily available. Nevertheless, the experience curve is a useful way to rationalize technology shifts and anticipate whether or not they are coming, even if it cannot yet be used to predict the timing with any degree of certainty.

Lessons learned The rare-earth elements are universally agreed to be critical. Other materials may or may not be critical, depending on location, industry sector, and time. Many indicators of materials criticality are interrelated and therefore not independent. Some popular indicators of materials criticality, such as crustal abundance and resource lifetime, are misleading. Some indicators, such as market size, are only moderately correlated with criticality. Some potential indicators, such as price changes or price instability, may not useful if the necessary data are not available. The levels of criticality of individual materials and the numbers of critical materials appear to be growing over time. Criticality is related to, but not the same as, the risk assessment for the threat of materials supply shortfalls. The level of supply-chain risk scales up more rapidly than the level of criticality. Within any group of materials, the supply risks associated with the most critical materials are more acute, relative to the other materials, than their criticality levels would suggest, and differences between assessed criticalities are most significant among the materials with the highest criticalities.

What will we need? The rare-earth crisis raised our awareness of the challenge of critical materials, and history teaches us that supply-chain challenges have consequences both for materials producers and end users. Emerging societal trends include growing numbers of consumers as the world’s middle class grows, and this can be expected to increase the demand for materials, while the expansion of residential areas constrains the locations available for extractive industries. Our technologies are growing more complex, and they rely on the special properties conferred by increasing numbers of elements and compounds. On the present trajectory, our technologies will generate needs for nearly every element in the periodic table. With increasing consumer demand, we will need more of nearly every element, and because of the demands of technology, we will need many of them in special forms or purities.

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On a positive note the world is not running out of any particular element. There is no sign that our mineral resources are in danger of being exhausted, but they are becoming more difficult to obtain as we access lower-grade ores, resort increasingly to coproduction or try to recycle from more and more complex devices. With increasing numbers of critical materials and growing criticality levels for individual materials, we might expect that supply-chain challenges could become more frequent. These trends, however, are offset by improving technologies to help us avoid criticality: the same competition that allows material prices to decline in the face of geometrically increasing demand. Next, we consider how research and innovation can contribute to keeping the world’s supplies of critical materials ahead of its evergrowing appetite for them. Without innovations in the supply of materials, there will certainly be increasingly frequent supply-chain crises. In Chapter 4, we will discuss what happened in the wake of the rare-earth crisis and how supply chains and manufacturing industries recovered from it. In Chapters 5–8, we consider individual strategies for avoiding supply-chain crises and dealing with them if and when they occur.

References [1] T.R. Malthus, An Essay on the Principle of Population, J. Johnson, London, 1798. [2] D. Ricardo, On the Principles of Political Economy, and Taxation, John Murray, London, 1817. [3] W.S. Jevons, The Coal Question; an Inquiry Concerning the Progress of the Nation, and the Probable Exhaustion of Our Coal Mines, Macmillan, London, 1865. [4] President’s Materials Policy Commission, Resources for Freedom: A Report to the President, University of Michigan Library, Ann Arbor, 1952, p. 64. [5] P.R. Ehrlich, The Population Bomb, Sierra Club and Ballantine Books, New York, 1968. [6] D.H. Meadows, D.L. Meadows, J. Randers, W.W. Behrens III, The Limits to Growth; a Report for the Club of Rome’s Project on the Predicament of Mankind, Universe Books, New York, 1972. [7] National Research Council (U.S.). Committee on Critical Mineral Impacts on the U.S. Economy, National Research Council (U.S.). Committee on Earth Resources, National Research Council (U.S.). Board on Earth Sciences and Resources, National Research Council (U.S.). Division on Earth and Life Studies., Ebrary Inc., Minerals, Critical Minerals, and the U.S. Economy, National Academies Press, Washington, DC, 2008 p. xvi, 245 p. ill. (some col.), col. map 23 cm. [8] T.E. Graedel, R. Barr, C. Chandler, T. Chase, J. Choi, L. Christoffersen, E. Friedlander, C. Henly, C. Jun, N.T. Nassar, D. Schechner, S. Warren, M.Y. Yang, C. Zhu, Methodology of metal criticality determination, Environ. Sci. Technol. 46 (2012) 1063–1070. [9] N.T. Nassar, X.Y. Du, T.E. Graedel, Criticality of the rare earth elements, J. Ind. Ecol. 19 (2015) 1044–1054. [10] A.Y. Ku, J. Loudis, S.J. Duclos, The impact of technological innovation on critical materials risk dynamics, Sustain. Mater. Technol. 15 (2018) 19–26. [11] U.S. Department of Energy, Critical Materials Strategy, DOE, Washington, DC, 2010. [12] U.S. Department of Energy, Critical Materials Strategy, DOE, Washington, DC, 2011.

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[13] Ad Hoc Working Group on Defining Critical Raw Materials, Report on Critical Raw Materials for the EU, European Commission, Brussels, 2010. [14] Ad Hoc Working Group on Defining Critical Raw Materials, Study on the Review of the List of Critical Raw Materials, European Commission, Brussels, 2014. [15] Deloitte Sustainability, British Geological Survey, Bureau De Recherches G
eOlogiques Et Minie`Res, Netherlands Organisation for Applied Scientific Research, Study on the Review of the List of Critical Raw Materials, European Commission, Brussels, 2017. [16] R. Moss, E. Tzimas, H. Kara, P. Willis, K. Jaakko, Critical Metals in Strategic Energy Technologies—Assessing Rare Metals as Supply-Chain Bottlenecks in Low-Carbon Energy Technologies, Joint Research Centre, Luxembourg, 2011. [17] R. Moss, E. Tzimas, P. Willis, J. Arendorf, P. Thompson, A. Chapman, N. Morley, E. Sims, R. Bryson, J. Pearson, E.L. Tercero, F. Marscheider-Weidemann, M. Soulier, A. L€ullmann, C. Sartorius, K. Ostertag, Critical Metals in the Path Towards the Decarbonisation of the EU Energy Sector, European Union, Luxembourg, 2013. [18] Aps Panel on Public Affairs and the Materials Research Society, Energy Critical Elements: Securing Materials for Emerging Technologies, American Physical Society, Washington, DC, 2011. [19] Minerals UK Center for Sustainable Mineral Development, Risk List 2011, https://investingnews.com/files/2011/11/British-Geological-Survey-RiskList2011.pdf, 2011 (Accessed 12 July 2018). [20] Minerals UK Center for Sustainable Mineral Development, Risk List 2012, https://www.goo gle.com/url?sa¼t&rct¼j&q¼&esrc¼s&source¼web&cd¼3&ved¼0ahUKEwjSx6nYpprc AhVFxYMKHfqMBgMQFgg7MAI&url¼https%3A%2F%2Fwww.bgs.ac.uk%2Fdownloads %2Fstart.cfm%3Fid%3D2643&usg¼AOvVaw0QxYhyDKnlx3rNdw69QBwk, 2012 (Accessed 12 July 2018). [21] Minerals UK Center for Sustainable Mineral Development, Risk List 2015, http://www.bgs.ac.uk/mineralsuk/statistics/risklist.html, 2015 (Accessed 23 June 2016). [22] National Science and Technology Council Subcommittee on Critical and Strategic Mineral Supply Chains, Assessment of Critical Minerals: Screening Methodology and Initial Application, Office of the President of the United States, Washington, DC, 2016. [23] S.M. Fortier, N.T. Nassar, G.W. Lederer, J. Brainard, J. Gambogi, E.A. Mccullough, Draft Critical Mineral List—Summary of Methodology and Background Information—U.S. Geological Survey Technical Input Document in Response to Secretarial Order No. 3359, U.S. Geological Survey, Reston, VA, 2018. [24] National Science and Technology Council Subcommittee on Critical and Strategic Mineral Supply Chains, Assessment of Critical Minerals: Updated Application of Screening Methodology, Office of the President of the United States, Washington, DC, 2018. [25] G.M. Mudd, An analysis of historic production trends in Australian base metal mining, Ore Geol. Rev. 32 (2007) 227–261. [26] G.M. Mudd, The Sustainability of Mining in Australia: Key Production Trends and Their Environmental Implications for the Future, Monash University, Melbourne, Australia, 2007. [27] T.P. Wright, Factors affecting the cost of airplanes, J. Aeronaut. Sci. 3 (1936) 122–128. [28] Boston Consulting Group, Perspectives on Experience, Boston Consulting Group, Boston, 1972, 109. [29] H. Kharas, The emerging middle class in developing countries, in: The Emerging Middle Class in Developing Countries, Organization for Economic Cooperation and Development, Paris, 2010.

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[30] A. Greenfield, T.E. Graedel, The omnivorous diet of modern technology, Resour. Conserv. Recycl. 74 (2013) 1–7. [31] Reuters Staff, Thousands of Malaysians Rally Against Lynas Rare Earths Plant, Reuters, London, 2012. [32] Reuters Staff, Costa Rica Lawmakers Vote to Ban Open-Pit Mining, Reuters, London, 2010. [33] N. Lakhani, El Salvador makes history as first nation to impose blanket ban on metal mining, The Guardian (2017). [34] J. Edmonds, T. Wilson, M. Wise, J. Weyant, Electrification of the economy and CO2 emissions mitigation, Environ. Econ. Policy Stud. 7 (2006) 175–203. [35] U.S. Geological Survey, Mineral Commodity Summaries, http://minerals.usgs.gov/min erals/pubs/mcs/2008/mcs2008.pdf, 2009 (Accessed 23 June 2016). [36] E.H. Cline, 1177 B.C. The year civilization collapsed, in: Turning Points in Ancient History, Princeton University Press, Princeton, 2014, p. 1 online resource (260 p.). [37] U.S. Geological Survey, Mineral Commodity Summaries, http://minerals.usgs.gov/min erals/pubs/mcs/2018/mcs2018.pdf, 2018 (Accessed 23 June 2018). [38] N.T. Nassar, T.E. Graedel, E.M. Harper, By-product metals are technologically essential but have problematic supply, Sci. Adv. 1 (2015) e1400180. [39] G.M. Mudd, Z. Weng, S.M. Jowitt, I.D. Turnbull, T.E. Graedel, Quantifying the recoverable resources of by-product metals: the case of cobalt, Ore Geol. Rev. 55 (2013) 87–98. [40] K. Binnemans, P.T. Jones, Rare earths and the balance problem, J. Sustain. Metall. 1 (2015) 29–38. [41] Economist Staff, Fixing the fix, The Economist (2014). [42] M. Redlinger, R. Eggert, Volatility of by-product metal and mineral prices, Res. Policy 47 (2016) 69–77. [43] Canadian Institute of Mining Metallurgy and Petroleum, National Instrument 43–101: Standards of Disclosure for Mineral Projects, http://web.cim.org/standards/MenuPage. cfm?sections¼177,181&menu¼229, 2011 (Accessed 16 June 2016). [44] Joint Ore Reserves Committee, The Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves, http://www.jorc.org/index.asp, 2012 (Accessed 16 June 2016). [45] Samcodes Standards Committee, The South African Code for the Reporting of Exploration Results, Mineral Resources and Mineral Reserves, http://www.samcode.co.za (Accessed 16 June 2016). [46] M. Frenzel, J. Kullik, M.A. Reuter, J. Gutzmer, Raw material ’criticality’-sense or nonsense? J. Phys. D. Appl. Phys. 50 (2017) 123002. [47] S. Gloeser, L.T. Espinoza, C. Gandenberger, M. Faulstich, Raw material criticality in the context of classical risk assessment, Res. Policy 44 (2015) 35–46. [48] J. Leaning, D. Guha-Sapir, Natural disasters, armed conflict, and public health, N. Engl. J. Med. 369 (2013) 1836–1842. [49] National Protection and Programs Directorate, Unanticipated Closure of the Poe Lock, U.S. Department of Homeland Security, Washington, DC, 2015.

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Impacts of the rare earth crisis The rare earth crisis had several impacts that appear to have begun as early as 2006, soon after China’s export quotas were first announced. In Fig. 3.9, we saw that perconsumer demand for rare earths grew rapidly between 1965 and 1985 (assuming that production is roughly indicative of demand). With the commercialization of Nd2Fe14B permanent magnets in 1986, a two-decade phase of even more rapid growth in per-consumer demand began as the new magnets found their way into motors, generators and nearly all technological devices, including personal computers and entertainment systems. After 2006, with growing concerns about China’s export quotas, the per-consumer demand for rare-earth materials declined as manufacturers began to shift away from using them wherever possible. This trend was been somewhat masked in total rare-earth production figures, however, because of the rapid growth in the number of consumers, as shown in Fig. 3.8. The total demand for rare-earth materials continued to grow between 2006 and 2010, while individual consumption declined, because of the rapid growth of the middle class with its voracious appetite for mobile electronics. The price shock of 2010 had a bigger impact than the first announcement of the quotas. The total production of rare earths declined significantly in 2011, and it only returned to the 2010 level in 2017, and the production increase in 2017 probably reflects a trend of increasing numbers of consumers, even though the per-capita consumption of REEs was still below its 2006 level. Fig. 4.1 shows the global production of REO for 1950–2019 based on data from the USGS’ annual Mineral Commodity Summaries, with a superimposed trendline. The overall growth in rare-earth production is unmistakable, as is the drop below the longterm trendline, possibly starting in 2007, but clearly established immediately after the price spike of 2010. In 2018 and 2019, however, production exceeded the long-term trendline. It is not clear if this represents a real increase in consumption, a rebuilding of manufacturers’ inventories, or an overcorrection of the production level as the crisis recedes and production levels resume the long-term trend. Fig. 4.2 shows the changing contributions of major producing nations through 2019, and the salient features are the increasing output from Australia, starting in 2011, and the renewal of US production in 2018 along with the growth of production elsewhere in the world. China’s share of the mine production is shown in Fig. 4.3, and it has declined from a peak of around 97% to about 62% in 2019. While China’s near monopoly of rare-earth production has abated in the wake of the rare earth crisis, it still holds significant advantages that are not necessarily reflected in criticality analyses that rely on the Herfindahl-Hirschman index to Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00004-9 © 2021 Elsevier Inc. All rights reserved.

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Fig. 4.1 Global production of rare-earth oxides from 1950 to 2019. The trendline is fitted to the data through 2010 and extrapolated beyond that point. The drop of production below the trendline within the green band indicates the demand destruction that was caused by the rare earth crisis. Production data are taken from the USGS Mineral Commodity Summaries for the relevant years.

Fig. 4.2 Principal national contributions to global rare-earth oxide production from 1950 to 2019.

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Fig. 4.3 China’s share of global rare-earth oxide mining from 1985 to 2019.

characterize source diversity. The US contributions now consist only of ore concentrate from the Mountain Pass mine, all of which is exported to Asia for processing: several vital links of the supply chain still lie in China, even though total production and the diversity of primary sources now exceed precrisis levels. In this chapter, we explore what has evolved in the aftermath of the concerns that began with the introduction of China’s export quotas.

Conflicts and conflict resolution Disagreements between nations are a fact of life. These are often minor issues that are handled discretely through diplomatic processes, but occasionally, they escalate into other arenas. Military displays of force between rival nations are rarer, but still daily occurrences around the globe, and occasionally international bodies, are called upon to adjudicate conflicts. A common form of international posturing involves establishing a presence in disputed territory, defying responses from rival claimants. While these events are common in a variety of forms, they rarely escalate into actual conflict. The China-Japan fishing boat incident near Diaoyu/Senkaku is unusual in that physical contact occurred, but it was not unprecedented: the Japanese Coast Guard (JCG) had rammed and sunk a Taiwanese sport-fishing boat in the same area in 2008, and there have been several other incidents between Japan and Taiwan or the Peoples’ Republic of China since about 1972. The collisions between the Chinese trawler and two JCG vessels on September 7, 2010 represented a breakdown of protocol, resulting in the Chinese captain and 14 crew members being taken into Japanese custody. Six days after the collisions, after several official protests from China, the trawler and the crew members were released, but the captain was detained and charged with interfering with a Japanese public servant in the execution of his duties. Seven days later, China detained four Japanese citizens on charges of photographing military establishments.

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On September 24, Japan released the trawler captain, and on October 9, China released the four Japanese citizens with all charges dropped on both sides. The month-long incident became very public with government statements being made on both sides, along with public protests of moderate intensity occurring in both countries for several more weeks. It is unlikely that there was a considered decision at a high government level on either side, to cause a collision to promote a strategy regarding the rare earths: territorial disputes and trade disputes have traditionally been kept separate in the diplomatic arena. Nevertheless, on September 22—two days before the release of the Chinese skipper—the New York Times and other sources reported that the Chinese government had blocked rare-earth shipments to Japan. This would have been a violation of World Trade Organization (WTO) regulations, and it was formally denied by China, which had worked hard to win membership in the WTO in 2001. Some kind of administrative halt to the loading of rare earths on ships bound for Japan certainly appears to have gone into effect, but it is not clear where that decision was made. The reports of an export ban increased concerns about rare-earth supplies, driving a price surge that undoubtedly exacerbated the supply-chain problems by stimulating anticipatory buying as a hedge against further increases. The threat to halt Japan’s rare-earth supply may or may not have won the trawler captain’s release, but the impact on the rare-earth market was immediate, and the sense of an international crisis became firmly attached to the issue. Two years later, after two additional rounds of rare earth export quota reductions, the United States filed a complaint with the WTO’s Dispute Settlement Body, claiming that China’s export restrictions on rare earths, along with tungsten and molybdenum, violated the WTO’s governing treaty. Japan and the EU quickly joined with the United States in the complaint. The WTO treaty establishes that export quotas and duties are disallowed except for certain specifically listed commodities, which did not include the materials under dispute. China contended that the WTO treaty allows its members to restrict exports for reasons of conservation, environmental protection or safety, but the Dispute Settlement Body ruled against China in 2014, resulting in an appeal, which was rejected, and China dropped its export quotas early in 2015. By then, rare-earth production was still well below its 2010 volume, and prices were close to their prespike levels. The extent of the Chinese government’s control of its domestic rare-earth industry is somewhat in question. Before, during, and after the export quotas, a significant portion of the rare-earth production in the country was “illegal,” occurring in unlicensed mines with their products supposedly smuggled out of the country. According to some estimates, as much as half of China’s rare-earth production was illegal at the time of the price peak, but that is hard to verify. China’s exports, however, are estimated based on the known acquisitions of rare-earth oxide by importing countries, which counts both legal and illegal products: the total amounts imported by the rest of the world closely match China’s export quotas, so there is some question whether illegal mining products somehow enter the official export stream. Illegal mining was particularly prevalent in lateritic clay leaching operations in the south, which are the major source of heavy rare earths. Among the various kinds of

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rare-earth mine, these are the most prone to causing environmental damage, and much was heard from official quarters about bringing the illegal mines under control in the interest of environmental protection. China’s government has promoted the consolidation of its rare-earth production industry through mergers and acquisitions, and this may help to shift some of the unlicensed mining into the official realm where it can be better regulated. Formal rare-earth exchanges have been established in Bautou and Ganzhou, operating in the OTC mode. The Shanghai Futures Exchange is planning to introduce trading in rare-earth futures [1], and these new exchanges may help to improve the transparency of the market for Chinese-sourced rare earths. China is also taking the lead in the ISO effort to establish international standards for rare-earth products, that might provide for gradeability of rare-earth ores or partially processed intermediate products, eventually allowing them to be traded more like commodities.

The supply side Stimulation of new mining projects The rare-earth mine at Mountain Pass had been out of operation for 6 years when a newly formed company, Molycorp Minerals LLC, acquired it from Chevron Corporation in 2008, 2 years after the onset of the Chinese export quotas. As rare-earth prices rose in 2009 and 2010, investor enthusiasm for new mine development grew and as many as 400 mining projects were under development when the prices reached their peak, although Mountain Pass had a lead, having started earlier and having all of the geological survey data in hand and much of the infrastructure in place. The developers benefited from excellent timing as the rising prices for rare earths attracted investment in the project. Molycorp set out to build a sophisticated and highly integrated processing facility to replace the existing separations plant, with a goal of achieving an environmental footprint as close as possible to zero. The plant was intended to operate in a nearly “closed loop” mode with respect to water and many of its process chemicals. Rare-earth production began in the summer of 2012, by which time rare-earth prices were in rapid decline, having peaked in 2010. The new processing facilities faced a number of difficulties as they started up and the costs of beneficiation and separation at Mountain Pass could not be brought down below the market value of the rare-earth oxides produced by the mine, before the company’s capital resources were exhausted. Molycorp declared bankruptcy in 2015, and operations at the mine were reduced to care and maintenance. Following reorganization, the mine was acquired by MP Materials, a company formed by a conglomerate of investment fund advisors. In 2018 the production of ore concentrate recommenced. This product is essentially bastnaesite, separated from the other minerals or “gangue” in the ore body by crushing, grinding, and beneficiation but without any subsequent chemical processing. All of the concentrate from the mine now goes to China for processing.

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In 2009 Lynas Corporation obtained funding to mine the Mount Weld rare-earth deposit, and it began production in 2011. The mine is located in a desert region, and since rare-earth extraction and separation are water intensive, the company located most of its processing remotely, opting for Kuantan, in Malaysia. With a phosphate and aluminophosphate ore body, the mine is richer in heavy rare earths than either Mountain Pass or Bautou, but facing challenges from declining rare-earth prices, Lynas reduced its operating expenses by halting the production of heavy rare earths, and it obtained significant financial backing from Japan in return for a guaranteed portion of the mine’s output. The company also moved its headquarters from Australia to Malaysia. It remains in production and is currently the largest single producer of rare-earth metal outside of China. Another new rare-earth deposit was identified in association with a uranium deposit at Brown’s Range, also in Western Australia, in 2010—close to the height of the rare-earth price spike. The rare-earth elements in this deposit are contained in the mineral xenotime, and the deposit is richer in heavy rare earths than Mount Weld. With the promise of high-value output, initial funding for the mine was obtained quickly, and pilot-scale production of dysprosium began in 2018. Rising prices galvanize interest in the development of new mines and several workable deposits of rare earths were identified around the world, including the United States, Australia, Canada, Greenland, Africa, and on the Pacific Ocean floor. Starting with a very small handful of endeavors in 2005—probably less than 10—230 rare earth mine projects were in active development in 22 countries by September of 2010, supported by a total of 145 companies. At the peak of the price spike in mid-2012, the count had risen to 441 projects in 37 countries, involving 269 companies [2]. Nearly all of these were initiated in response to the increasing rare earth prices during 2009 and 2010, reflecting the developers’ expectations that elevated prices would persist until their projects came to fruition. As prices fell back to around their precrisis levels between 2011 and 2013, investor interest waned, and most of the projects were put on hold or abandoned completely. Despite the weakening investment climate, many of the projects had progressed through several of the stages toward commissioning, and these are now well placed to move ahead quickly, in the event that a new rare earth crisis should emerge—or, better, if prices rise in an orderly fashion. The financial, scientific, and technical challenges of opening new mines will be described in more detail in Chapter 6.

Recycling efforts Japan’s industrial base has a particularly high reliance on rare earths, which go into products such as conventional and hybrid automobiles, electronics (notably hard disk drives and loudspeakers), along with some household appliances. China’s export restrictions were therefore a particularly significant concern in Japan, and in 2010 the New Energy and Industrial Technology Development Organization (NEDO) announced a major investment in “Urban Mining” to provide rare earths through the recycling of discarded electronics and vehicles.

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Several institutions contributed to the Urban Mining project, but it was strongly focused on the National Institute of Advanced Industrial Science and Technology (AIST) in Tsukuba near Tokyo and Tohoku University in Sendai. On April 7, 2011, Sendai and the Tohoku region were struck by a major earthquake and tsunami, and the Urban Mining efforts at Tohoku University subsequently became a focus of the Japanese government’s economic recovery efforts. The European Union also emphasized recycling in its efforts to assure REE supply chains, and out of the 81 recycling projects funded under the Horizon 2020 Research and Innovation Programme that began in 2014, at least five focused on the recovery of rare earths from end-of-life products. Several European nations also funded recycling research independently, but the European approach, overall, was a patchwork of individual projects and rather less coordinated than Japan’s Urban Mining efforts. One recycling success story concerns cerium oxide (ceria), which is widely used as an abrasive for polishing silicon wafers and glass, because it combines a mild chemical attack of the silicon with mechanical abrasion, resulting in excellent surface finish provided by “chemical mechanical polishing.” Although technologies had been developed for recycling ceria polishing powders in the early 2000s [3] and polishing slurries are much less impacted by separation challenges than rare-earth materials recovered from devices, the recovery methods were not widely applied before the rare earth crisis, as ceria was a low-cost material and capital investments in recycling systems could not be justified. However, Chinese export quotas were initially applied to rare earths across the board, so if any single importing nation could reduce its demand for ceria, it would allow for a corresponding increase in access to other REOs. As a result the recycling of ceria polishing powder quickly became widespread, and up to 80% reductions of demand were achieved in short order. This represents a destruction of demand that is arguably a negative result for the rare-earth mining industry, since cerium production already exceeded demand and the excess only grew as a result of the recycling efforts. Recycling typically faces several economic and technical challenges, and these are described in more detail in Chapter 7.

The demand side Technology responses Technology continued to move forward while the rare earth crisis unfolded, and rapid changes were particularly evident in several clean-energy industries. Conventional vehicles with internal combustion engines (ICEs) were being made lighter and more fuel efficient. Hybrid vehicles were becoming well established. All-electric vehicles were growing from a niche product to gain increasing market acceptance. Compact fluorescent lamps (CFLs) were rapidly gaining market share at the expense of incandescent light bulbs, and light-emitting diodes (LEDs) were beginning to emerge in niche markets. Wind power was experiencing accelerating growth, worldwide. All of these rely to some degree on rare-earth elements, usually in combination with other materials that confer essential capabilities.

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As concerns grew about the availability of REEs, the development paths of many of these technologies were affected, as a result of their reliance on rare earths for magnets or light emitters.

A permanent magnet primer At the time of the rare earth crisis, permanent magnets were the largest single use of REEs, at least if measured by value, and technologies that rely upon permanent magnets were among most significantly impacted by the rare earth crisis. The most powerful magnets available at industrial scale are based on the Nd2Fe14B formulation, and these contain about 27% of neodymium by weight. These magnet materials are available in a variety of different grades, made with a variety of different processes, and it is important to understand the differences between them. Permanent magnets are made from hard magnetic materials, which can be magnetized and retain their magnetization: these are used in electric motors, generators, and actuators. Soft magnetic materials can also be magnetized, but they easily lose their magnetization, a property that is put to use in transformers. Magnetization is achieved by applying a strong external magnetic field to the material to align the magnetic moments of the individual atoms, which can be regarded as being equivalent to individual bar magnets. The strongest magnetization levels are produced when all of the atoms have their magnetic moments aligned in the same direction. Although perfect alignment is never achieved in practice, materials scientists use a combination of approaches to maximize it, and we will examine these, later. When the external magnetizing field is removed, the atoms in a permanent magnet made from a hard magnetic material remain largely aligned unless the external field is reversed or the temperature is raised above the Curie point, at which entropy takes over and the alignments of all of the atomic spins are randomized, resulting in zero net magnetization. The essential properties of a magnet are best illustrated in a magnetization curve, which shows how the internal magnetization is affected by externally applied magnetic fields. A magnetic field is characterized by the direction and the density of its magnetic flux lines, in the vector quantity B. The magnetic flux’s magnitude is given in the SI units of teslas (T), which are equivalent to kg/A/s2 or kg1/2/m1/2/s, although the older cgs gauss units (G), equivalent to g1/2/cm1/2/s, are also frequently used: one tesla is 104 gauss. The magnetization of a material is the strength of the magnetic field within it. This is the sum of the field that the material generates itself, through the magnetic fields of its individual atoms, and the effects of any external fields: B ¼ μ 0 ðH + M Þ where μ0 is the material’s magnetic susceptibility, H is the applied magnetic field, and M is the magnetization of the material.

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B BR

–HC

HC

H

–BR

Fig. 4.4 Magnetic hysteresis curve for a ferromagnetic material. The externally applied magnetic field is H, and the internal field, B, is the sum of the external and internal fields within the magnet. BR is the remanant magnetic field in the material, after it has been magnetized to the saturation level and then the external field is removed. Hc is the coercivity, which is the strength of the reversed applied magnetic field that is required to bring the internal field to zero. Materials with large coercivities are “hard” magnets, and materials with small coercivities are “soft” magnets.

Fig. 4.4 is a schematic magnetization curve showing how the internal field in a magnet, M, varies with changes in the applied field, H, that is used to magnetize it or reversed to demagnetize it. From a practical perspective, we usually start with unmagnetized material and apply an increasingly powerful external magnetic field. As the applied field strength grows, the material’s internal magnetic field strength increases until it reaches a maximum value called the saturation magnetization. This represent the point at which the magnetic alignment of the individual atoms reaches its maximum. If the applied field is reduced back to zero, the alignment of the individual atoms is partially retained, and the material holds a residual or remanent magnetization, usually known simply as the remanence, Br. Reversing the sign of the magnetizing field, we drive the internal magnetization to zero at a field strength that is called the coercive force, or coercivity, and is denoted by Hc. Materials with large values of Br are capable of providing strong magnetic fields. High remanence values are achieved in materials where the individual atoms have large magnetic moments and it is possible to align a large fraction of them in the same direction. This is related to the types of atoms and the structure of the material, which impose intrinsic limits on the value that can be achieved. Materials with large values of Hc are able to withstand demagnetization when they interact with external magnetic fields. Large coercivities are achieved when it is difficult to randomize the orientations of the magnetic moments of the atoms in the material: this is related to the motion of magnetic domain walls and their interactions with other microstructural features. The coercivity is affected by the microstructure of the material, which can be controlled by the way in which it is processed. Permanent magnets are made from ferromagnetic materials, which are defined by coupling between the magnetic moments of adjacent atoms that tends to make them align in the same direction. In antiferromagnets adjacent, atoms tend to align in opposite directions, canceling out the magnetic field in the material.

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The alignment of magnetic moments is also affected by the crystal structure, whose symmetry may provide for easier magnetization in some directions than others, through an effect called magnetocrystalline anisotropy. The magnetization can be aligned either north-south or south-north with equal ease along an easy magnetization direction. In body-centered cubic iron, the easy magnetization directions are of the h100i type, and there are three equivalent easy directions in any single crystal and therefore six possible magnetic field orientations. In face-centered cubic nickel, the easy directions are h111i, of which there are four per crystal, giving eight magnetic field orientations. In hexagonal close-packed cobalt, the easy direction is h0001i, and there is just one per grain, providing only two magnetic field orientations. In a typical polycrystalline material with a moderate grain size, each grain will contain multiple regions, called magnetic domains, within which the atomic magnetic moments are coaligned, as shown in Fig. 4.5. In the unmagnetized state the distribution of the domains is random and their magnetic fields cancel out. As the material is magnetized, the domains that are aligned with the magnetizing field grow at the expense of their less favorably aligned neighbors, and the predominant magnetization direction approaches that of the magnetizing field through the process of domain wall migration. The saturation magnetization is determined by the strength of the magnetic moment per atom and the degree to which it can be aligned to the magnetizing field. Iron is widely available, and it has a large magnetic moment so it is a common ingredient in permanent magnet materials. The symmetry of the cubic crystal structure of pure iron, however, provides domain orientation options that do not necessarily align with the direction of the magnetizing field, so the achievable magnetization is reduced (Fig. 4.6). A higher saturation magnetization can be achieved if the orientations of individual crystals can be organized such that a crystallographic easy magnetization direction in each grain lies parallel to the desired magnetization direction for the magnet (Fig. 4.7) and a significant amount of effort goes toward processing the material to achieve this sort of crystalline polycrystalline alignment, which is described by the technical term “texture” in materials science and engineering.

Fig. 4.5 Magnetic domains within individual grains in an unmagnetized ferromagnet. The magnetic dipoles within each domain are aligned parallel to each other, but the domains are magnetized in random orientations, so the net magnetization is zero.

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H

Fig. 4.6 When an external magnetic field is applied, domains that are aligned parallel to the imposed field tend to grow at the expense of those that have the antiparallel alignment and the material develops a net magnetization parallel to the direction of the applied field.

H

Fig. 4.7 Materials that have a crystal structure with only a single easy magnetization direction can be magnetized strongly, if the easy magnetization direction is aligned with the applied magnetic field.

The remanence is always smaller than the saturation magnetization, since magnetic domain walls can rearrange as the magnetizing field is reduced. The amount of this reduction and also the magnitude of the coercivity both depend on the ease with which domain walls move. This depends to some extent on the magnetocrystalline anisotropy, since it is easier to move a 90° domain wall than a 180° one, so crystal structures that have only a single easy magnetization direction generally have higher values of Br/Bs and Hc. Domain wall migration can also be impeded by structural defects such as impurities, precipitates, and grain boundaries. Hexagonal and tetragonal crystals have symmetry elements that can favor the existence of single easy magnetization directions, but not all do. In a hexagonal crystal, it is possible for the easy axis to lie parallel to the c-direction, h0001i, or to lie in the basal plane. If it lies in the c-direction, then the magnetization direction changes by 180° at all domain walls. If the easy axis lies in the basal plane, however, the symmetry of the crystal makes all directions within the plane equivalent, and there can be walls that separate domains that have very small differences of magnetic orientation: these are easily moved and generally result in small values of Br/Bs and Hc. Permanent magnets with large values of both Br and Hc are highly valued, and this leads to the use of the energy product, BHmax, as a figure of merit for permanent magnet materials. This is defined as shown in Fig. 4.8. BHmax has units that are equivalent to energy per unit volume, although it does not relate to the amount of energy that is stored in a magnet, or the amount of energy that it can be used to produce. The energy

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Critical Materials

B BR BHmax –HC

H

Fig. 4.8 The maximum energy product, BHmax, is a widely used indicator of the strength of a permanent magnet material. It is the area of the largest rectangle that can be inscribed in the second quadrant of the magnetic hysteresis curve. While this is a useful guide to magnet strength, it is not always the best indicator of performance in a particular application.

Fig. 4.9 General features of the thermal performance of rareearth magnets. All magnets lose strength with increasing temperature, but this effect is much more significant for neodymium-iron-boron than for samarium-cobalt magnets.

product is better understood as a magnetic figure of merit than a thermodynamic quantity: materials with greater values of BHmax simply make stronger magnets than those with smaller values. Depending on the application, either Br or Hc may be a more important design criterion than BHmax. The energy product is most commonly quoted in units of megagauss-oersteds (MGOe) reflecting its magnetic roots. Where SI units are preferred, it can be measured in kilojoules per cubic meter, and 1 MGOe ¼ 7.9577 kJ/m3. The SI units are considered by some to be more “fundamental” and clearly reflect the dimensionality of energy per unit volume, but it must be recognized that this does not reflect the energy that can be extracted from a magnet. Temperature has an important effect on magnetic materials, as illustrated in Fig. 4.9. In all ferromagnetic materials, the magnetization declines with increasing temperature as the interactions between the atoms weaken and the magnetic moments of the individual atoms become more randomly oriented. If the temperature is reduced before the magnetization is completely lost, then it will be partially recovered spontaneously and can be fully recovered by remagnetizing. Magnetization is lost completely when the temperature reaches the Curie point, Tc, and there is no spontaneous recovery when cooling from this temperature or above.

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Neodymium iron boride, Nd2Fe14B, has several attributes that make it an excellent permanent magnet: l

l

l

l

It is predominantly made of iron atoms, making large magnetic moments available. Neodymium has strong ferromagnetic coupling with iron, and it improves the alignment of the iron atoms’ magnetic moments. The crystal structure, shown in Fig. 4.10, is tetragonal, and it has large magnetocrystalline anisotropy with its easy magnetization direction parallel to the c-axis, h001i. It therefore supports domain walls that are predominantly 180° magnetic field inversions, and relatively resistant to migration. Crystals of Nd2Fe14B are amenable to alignment by a number of methods, often allowing the magnetic field of the material to be aligned according to the needs of specific applications.

Although Nd2Fe14B provides very large energy products, remanences, and coercivities, it suffers from significant declines as temperature increases and is not regarded as suitable for applications where the temperature is elevated, as illustrated in Fig. 4.9. The high-temperature properties of the material can be improved, however, by replacing some of the neodymium with terbium or dysprosium, which increase the coercivity and the Curie temperature of the material. Terbium is more effective than dysprosium in this regard, but it is more expensive because it has lower natural abundance, and it is also used for lighting where dysprosium is not an option. Dysprosium, then, is the additive of choice for improving the performance of Nd2Fe14B. It has a slightly negative effect on the magnetization because it couples antiferromagnetically with neodymium, but it significantly increases the coercivity; overall, it increases the energy product, as seen in Fig. 4.11. Although less costly than terbium, dysprosium is Fig. 4.10 The crystallographic unit cell of Nd2Fe14B. The neodymium atoms are shown in green, iron in red, and boron in pink. The unit cell is tetragonal, and the magnetic moments of the neodymium and iron atoms are most easily aligned along the c-axis, which is the vertical direction, here. The high strength of the magnetic moment of iron, the strong alignment of the individual magnetic moments, and the single preferred alignment direction all help to make this an exceptionally strong magnet.

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Critical Materials

Fig. 4.11 The effect of replacing some of the neodymium with dysprosium, in Nd-Fe-B magnets. The dysprosium magnetic moments align opposite to those of iron and neodymium, and this reduces the remanence, but the coercivity is increased very considerably so the overall effect is an increase in the energy product. This also improves the performance of the magnets at elevated temperatures. Courtesy of Cajetan Ikenna Nlebedim and Wei Tang, of the Ames Laboratory’s Critical Materials Institute. This figure was created, in whole or in part, under Contract No. DE-AC0207CH11358 with the US Department of Energy.

a heavy rare-earth element that is much scarcer and more expensive than neodymium. It is mostly obtained from lateritic clay deposits in southern China, and in most analyses, it is found to be significantly more critical than neodymium. The dysprosium contents of “neodymium” magnet materials depend upon their applications, and it is generally higher for magnets that require larger coercivity or need to operate at higher temperatures. Neodymium magnet materials are marketed in different grades, designated by their energy products and operating temperatures, so “N40H,” for example, refers to a neodymium magnet material with an energy product of 40 MGOe that is rated for “high temperature” use, which translates to 150°C. A list of temperature rating codes is given in Table 4.1. Higher grades typically contain more dysprosium and are more expensive, but neodymium magnet materials are unique in that they are sold according to their performance rather than their composition. Almost all other material standards are specified by composition so any specific grade of aluminum, copper, or steel will contain other elements within narrowly defined compositional limits but two magnets that meet a particular specification, such as N40H, may have quite different compositions. Neodymium-based magnet materials are formed into magnets in two different ways. They can be sintered or bonded, but the starting point for both methods is a nearly phase-pure metal powder of an appropriate grade and particle size, that can be produced in a variety of different ways. The individual powder particles are ideally single crystals of the Nd2Fe14B phase.

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Table 4.1 Temperature-rating codes for neodymium magnets. Temperature code

Nominal Curie temp. (°C)

Maximum operating temp. (°C)

(No code) M H SH UH EH AH

590 644 644 644 662 662 662

176 212 248 302 356 392 428

Data from https://www.kjmagnetics.com/specs.asp.

Sintered magnets are essentially pure magnet material and provide effective energy products in the range of 25–54 MGOe. They are made by loading powder into a compression die, aligning the particles’ crystallographic c-axes with an applied magnetic field, and then compressing and heating the powder to sinter it to full density. Small amounts of sintering aids such as copper may be added to allow full density to be achieved at lower temperatures or shorter sintering times. Magnets can be made directly by this process at the dimensions required for a particular application, but they must first be protected from oxidation by adding a coating of metal (such as nickel or zinc), polymer, or paint. Die compression has a number of challenges. It is not possible to make very large magnets this way, because of the size of the equipment that would be required to generate the aligning magnetic field and the pressure for sintering. The largest sintered magnets available today are around 1 kg. It is also not practical to make very small magnets this way because of the unevenness of the pressure distribution within a compression die, as illustrated in Fig. 4.12. Friction between the powder particles and the walls of the die tends to result in nonuniform pressure and may also restrict particle rotation during the alignment process, so there is a layer on the surface of any diecompressed magnet that is not as well formed as it might be, and in very small magnets this layer of inconsistent material can extend throughout the entire body. Careful design of the compression dies and process parameters can minimize this effect, but small magnets are usually made by trepanning, slicing, or dicing them from large sintered blocks prior to coating. Cutting operations of this kind result in material losses that grow larger as the final product size decreases, and the swarf produced by sawing is typically recovered and remelted so it repeats the entire powder production process, in some cases many times over. The surfaces of sliced or diced magnets also sustain damage during the cutting process, and this reduces the magnetic flux emitted by the magnet: when the magnet volume is very small, the surface-damaged layers can represent a large fraction of the magnet’s mass, causing a significant reduction from the material’s nominal performance.

110

(A)

Critical Materials

(B)

(C)

Fig. 4.12 Schematic illustration of the effects of die-compression sintering. Nd-Fe-B powder is loaded into a die as shown in (A), and it is usually exposed to a magnetic field to align the easy magnetization directions of the individual particles. The material is then heated and compressed to sinter it into a solid block of material, ideally maintaining the crystal orientations of the particles, as shown in (B). In reality, friction with the die surfaces restricts the particles that they touch, so the orientations are distorted as indicated in (C). Surface layers, adjacent to the dies, are the most strongly affected. The surface distortions are minimized with lubrication, and surface-to-volume ratio to reduce the amount of material that is affected.

In bonded magnets, magnetic metal powder is embedded in a polymer medium and formed into the desired shape. With a lower magnetic material content, they provide significantly poorer performance than their sintered counterparts. If the powder particles are not magnetically aligned, the material is isotropic, with the magnetic moments of the particles distributed in all orientations, and the effective energy product falls in the range of 6–10 MGOe. Anisotropic bonded magnets are produced by using single-domain particles and aligning them with an applied magnetic field before the polymer bonding medium hardens, and this can improve the energy product to around 24 MGOe, but the additional processing steps and processing constraints make these magnets very expensive. In 2006, researchers from Japan’s Shin Etsu Chemical company reported a new method for adding HREEs to sintered neodymium magnets using grain boundary diffusion (GBD) [4]. In the GBD process, magnets are formed without dysprosium and, if necessary, cut to their final dimensions, before a source of dysprosium or terbium is coated onto their surfaces. Annealing at a moderate temperature allows the HREE to diffuse into the magnet along its grain boundaries, leaving them enriched in dysprosium or terbium up to a certain distance from the surface, depending on the annealing time, as shown schematically in Fig. 4.13. The grain centers remain essentially free of the HREE. This approach avoids the loss of remanence that occurs when the HREE is

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Fig. 4.13 The principle of the grain boundary diffusion method for dysprosium addition. In traditional processing, dysprosium is substituted for neodymium before the alloy is melted, and after solidification, it is uniformly distributed through the material. For the grain-boundary diffusion method the dysprosium is added after the magnet is formed, by coating the surface with a dysprosium source and then annealing at a low temperature. The dysprosium diffuses into the magnet via the grain boundaries, which operate as fast-diffusion paths. The resulting dysprosium distribution is as shown on the right. This results in lower usage of dysprosium and smaller impact on the remanence.

distributed throughout the material. It provides large increases in coercivity for two reasons: 1. The major impact of dysprosium on the coercivity results from its pinning effect on the motion of magnetic domain walls where they intersect with grain boundaries. The grain boundary diffusion method effectively concentrates the HREE elements in locations where they can positively impact the coercivity without negatively impacting the remanence. 2. In most applications, demagnetization is most likely to occur at the surfaces of a magnet, and especially at its edges and vertices. The GBD process produces a distribution of HREE concentration, which is richest at the surface and declines with depth into the magnet, and the HREE is thus concentrated where its impact is most needed in real applications.

The combination of these effects allows for enhanced magnet performance to be achieved with significantly smaller quantities of HREEs than when they are added throughout the material. Because the prices for HREEs rose by larger factors than those of the LREEs during the rare earth price spike, there were correspondingly greater concerns about dysprosium than neodymium, and the HREE-efficient GBD neodymium magnets grew rapidly in popularity starting in 2009. This was a solution to dysprosium supply challenges that had been developed just in time to make an impact when the rare earth crisis arose but it is not clear whether it was developed in response to early indicators of the looming adversity, or it was blessed by fortuitous timing.

112

Critical Materials

Vehicles Conventional ICE-driven vehicles contain several electric motors and actuators to drive their starters, pumps, windshield wipers, air conditioners, fans, windows and mirror adjustments, along with other amenities such as power steering, seat adjusters, and door and trunk openers, depending on the vehicle’s level of luxury. A modern passenger car can contain more than 30 electric motors and a dozen loudspeakers. There is a large array of electric motor types and designs, but permanent-magnet, direct current motors dominate the vehicle market and starting in the 1980s rare-earth magnets gradually increased their market share of vehicle-born motors. General Motors had developed the initial neodymium magnet composition based on Nd2Fe14B in 1982, as a response to the impact of the 1978 cobalt crisis on samarium/cobalt-based magnets and neodymium magnet production began in 1986, through a spin-off company called Magnequench. The same composition was simultaneously invented and commercialized by Sumitomo Metals Corporation in Japan in partnership with Hitachi. Neodymium-based magnets are the strongest permanent magnets available in the world, and they can be used in smaller volumes than other materials to produce the necessary magnetic fields for electric motors. Rare-earth permanent magnet (REPM) motors are generally smaller, lighter, and more efficient than motors based on other kinds of permanent magnet. A 2012 study indicated that a single ICE vehicle might contain up to 1.3 kg of magnets, containing about 350 g of REEs, in its various electric motors and loudspeakers [5]. A more recent tear down of light vehicles manufactured after the rare earth crisis showed that the use of these magnets had become restricted to door-mounted loudspeakers where they still provide a distinct size advantage, and the amount of REE per vehicle was then only about 40 g [6]. The avoidance of REEs in vehicle components is a clear example of demand destruction in the wake of a price spike. It causes the components to be larger, heavier, and less efficient than they would have been if they used REE permanent magnets, but the overall impact on vehicle performance is small. The commercial recycling of rare earths from scrapped vehicles has never been viable to date, and the reduction of rare-earth content that followed the price spike makes that prospect even less likely. Even at the precrisis rates of use, the value of the REEs a car or a light truck was only a tiny fraction of the total cost of the vehicle so the REE price increases would have had only a small impact on the purchase price or the profit margin of the vehicle. The impact of the price increase was greater for the component manufacturers, which are generally independent suppliers to automobile manufacturers. A considerable fraction the bill of materials for an individual electric motor or loudspeaker can depend on the price of the REEs, if they are used for its permanent magnets. Before the REE price spike, car makers had encouraged the vendors of these components to adopt smaller, lighter, and more efficient designs resulting in the widespread use of rare-earth permanent magnets. Auto makers would negotiate fixed-price contracts for motors and loudspeaker sets to install in their vehicles, typically a year or so before production began for a new model.

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113

Small motor and loudspeaker manufacturers, in particular, are very sensitive to the cost of their magnet materials, with loudspeaker manufacturers being more sensitive than motor makers because of the higher fractional value of permanent magnet materials in their products. As the REE prices started to rise, loudspeaker manufacturers found themselves in a very difficult position: they were contracted to provide sets of speakers at prices set a year or two earlier, and in some cases the cost of the magnets alone rose above the contracted prices of the entire systems, resulting in operating losses on the sales of some of their largest market-volume products. The profits for electric motor manufacturers also dipped or went negative during the price spike. Component manufacturers took two approaches to overcome this problem: l

l

They changed the designs of their products to incorporate lower-cost ferrite magnets in place of REPMs and persuaded the automakers to adopt these as they updated the designs of their vehicles. They changed the structure of their contracts with the automakers, moving away from simple fixed-price contracts and adding options for price adjustments to be triggered by increases in the cost of materials.

These adjustments were slow to have an impact and the price of the rare earths abated before they really took effect, but the price spike did have a lasting impact: it changed the design of motors and loudspeakers in light vehicles, and it had impacted the viability of some of their manufacturers who then became targets for mergers and acquisitions. Large electric motors required different strategies. The main tractor motor in a hybrid or all-electric vehicle is significantly bigger and more powerful than any of the electric motors in an ICE vehicle. The options for the design of this motor differ from those for small auxiliary-device motors, but manufacturers have made choices and adopted development strategies that are still driven, at least in part, by materials availability concerns. First introduced in 1997, well before the rare earth crisis, successive generations of motors for the Toyota Prius line of hybrid vehicles have used REPM motors with smaller and smaller rare-earth magnets, providing the necessary performance levels by refining the motor designs and increasing their rotational speed. Higher rotation rates allow for more efficient operation, but they require more complex transmissions with higher gearing ratios. Tesla’s line of all-electric vehicles first came to market in 2008, a few years after the announcement of China’s export restrictions. It initially used induction motors that are free from permanent magnets, but this choice was probably driven by more than just the concern about magnet material availability. Targeting wealthy purchasers who could afford the inevitably high price of an entirely new product, the company stressed the performance of its vehicles when they first came to market, and it is possible to generate greater torque from an induction motor than from a permanent magnet motor—although there are some other impacts. The induction motors in Tesla’s vehicles were larger than permanent magnet motors would have been, and they were also less efficient and they became the leading cause of system failures in some of the early vehicle models. With the introduction of the Model 3 in 2017, Tesla’s focus has

114

Critical Materials

shifted to lower vehicle cost, targeting the mass market, and greater efficiency that was required to address concerns about the car’s range on a single charge of the battery. Some years after the rare earth crisis, then, with REE prices apparently stable, Tesla has embraced the use of Nd2Fe14B-based permanent magnet motors in the Model 3. Most other major vehicle manufacturers are producing some quantities of hybrid or all-electric vehicles and have made investments in reducing their dependence on rare earths, especially the HREEs. Ford, for example, has redesigned the tractor motors of its electric vehicles to reduce their operating temperatures, allowing the company to use magnet grades that contain less dysprosium. In February 2018, Toyota announced the development of a new magnet material that can reduce the critical rare-earth content by 50%, avoid the use of heavy rare earths completely, and allow operation at high temperatures. It adapts the Nd2Fe14B formulation by substituting some of the neodymium with optimized concentrations of lanthanum and cerium and has a fine grain size with neodymium concentrated preferentially in the grain boundaries. This material is likely to be used in forthcoming generations of Toyota electric vehicles. Honda has taken a related approach to reducing its dependence on heavy rare earths. In August 2018, it announced that it had found a way to use deformation processing of Nd2Fe14B to provide coercivities and temperature resistance comparable to conventional materials containing dysprosium or other heavy rare earths. Honda’s approach creates a fine grain size, like Toyota’s, and in this case, it has been combined with processing to make magnets that are optimally aligned for use in the electric motors. The company announced that this material was to be used in some of its vehicles within the 2018 calendar year.

Wind Wind energy was beginning to emerge as a significant contributor to energy portfolios around the world just as the rare earth crisis began to emerge in the mid-2000s. Fig. 4.14 shows the installed wind capacity of the United States from 1999 to 2018, and a pronounced acceleration is seen between 2004 and 2007. The installation rate in the United States averaged 7.2 GW/year between 2007 and 2018, and most of that capacity has been land based. The rated capacities of individual “utility-scale” turbines have grown from roughly 750 kW in the earliest installations, to about 3.5 MW for the largest land-based units of today, and these have hub heights of 82 m and blade lengths of 58 m. Wind turbines can use a number of designs with different advantages and disadvantages, which are summarized in Table 4.2. Direct-drive generators avoid the use of gearboxes, but the low rotational speeds of their generators require high magnetic fields that can only be provided by rare-earth permanent magnets with high coercivities and high-temperature performance that require additions of the heavy REE dysprosium. With supplies of both Nd and Dy under threat, wind turbine manufacturers opted for gearbox-enabled designs such as the induction generator system, which uses no permanent magnets, and hybrid systems that use gearboxes and smaller

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115

100,000 90,000

US installed wind capacity (MW)

80,000 70,000 60,000 50,000 40,000 30,000 20,000 10,000

19 99 20 00 20 01 20 02 20 03 20 04 20 05 20 06 20 07 20 08 20 09 20 10 20 11 20 12 20 13 20 14 20 15 20 16 20 17 20 18

0

Fig. 4.14 US installed wind capacity from 1999 to 2018. Data from the American Wind Energy Association.

Table 4.2 Principal generator types used in utility-scale wind turbines.

Generator RPM Gearbox Rated power REPM requirementa REE requirementa

Induction

PM hybrid drive

PM direct drive

1800 Yes 0–5 MW None None

400–1200 Yes 2.5–7.5 MW 160 kg/MW 50 kg/MW

12 No 3–10 MW 650 kg/MW 210 kg/MW

a The motors that control the turbine’s tilt, yaw, and blade-pitch are not included in these figures. Data from D.D. Imholte, R.T. Nguyen, A. Vedantam, M. Brown, A. Iyer, B.J. Smith, J.W. Collins, C.G. Anderson, B. O’Kelley, An assessment of U.S. rare earth availability for supporting U.S. wind energy growth targets, Energy Policy 113 (2018) 294–305.

permanent magnets. Induction generators are less efficient than direct drive generators, have more complex power electronics and are noisier, and their largest single cause of downtime is gearbox failure [7]. All of these performance challenges have been accepted in the face of the criticality of the REEs, and less than 1% of all land-based, utility-scale wind turbines in Europe and the United States are direct drive systems. Considerable developmental effort has been expended on reducing the gearbox failure rates of induction generators, part of which results from the need to run at a constant speed. If the wind speed rises, then the generator produces a braking force, changing the sign of the torque on the gearbox and the frequent stress reversals cause fatigue fractures. The impacts of torque reversals are reduced by using double-fed induction generators (DFIGs), which effectively operate as two generators one of which runs at a fixed speed, while the other can change its rotation rate in response

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Critical Materials

to changes in the speed of the wind. DFIGs are more complicated than permanent magnet generators and they introduce new points of potential failure in their electronic components and control systems. The effects of land-based wind turbine reliability levels are quite readily observable. At any given time, any substantial wind farm will typically have one or more turbines that do not rotate while all of the rest do. These turbines have typically suffered a failure of their gearbox or their electrical system—failures that could have been eliminated or drastically reduced by using direct drive generators. Wind energy development entered a new phase in the late 2010s, with offshore installations becoming increasingly common. Offshore wind energy production has several advantages over land-based installations including more reliable wind flow and the opportunity to build much larger units, which are more efficient. Offshore installations up to 10 MW per tower are currently in development, with blade lengths of 94 m: a blade of this length could not be delivered to a land-based location by road or rail because of the restricted turn radius that it could accommodate but can be delivered offshore on a barge. Reliability is a major concern for offshore wind farms where inhospitable environments and tall towers make maintenance and repair operations much more challenging than on land. Accordingly, most offshore wind farms are expected to use direct-drive generators and require large quantities of REEs [8]. While the worst of the rare earth crisis may seem to be over, the REEs are still prominent as critical materials, but their prices are currently stable and their advantages in this particular application appear to outweigh the concerns about their availability. It is anticipated that advances in generator design will reduce the per-kilowatt REE requirement over time, and particular attention has already been paid to reducing the need for dysprosium, which is added to allow the magnets to resist the temperatures reached in operation. Siemens Gamesa is a major manufacturer of wind turbines that has announced “dramatically reduced” need for heavy rare earths in its 7 MW offshore generators and none in its forthcoming 10 MW systems. This is apparently being achieved by advanced system design and the provision of cooling to minimize the operating temperature of the magnets in the generators.

Wishful thinking in the magnet world Following the rare earth crisis, papers and presentations about magnets would often include a diagram like the one shown in Fig. 4.15 [9]. It was common to observe that major advances in magnet performance had occurred with the invention of new materials roughly once a decade from the 1920s to the 1980s and recall that the current stateof-the-art materials, based on Nd2Fe14B, had been invented in the wake of the 1978 cobalt crisis [10, 11]. With no transformative magnetic material discovery since 1984, roughly 30 years previously, there was a sense in many parts that a breakthrough was overdue and a higher-performance material might be just around the corner. Despite many efforts to bring forth the next major advance, no major discoveries have yet emerged. The timely discovery of Nd2Fe14B had helped to solve the cobalt problem, but such good fortune should not be relied upon to solve future supply-chain issues.

What changed after the rare earth crisis?

117

60

Anisotropic bonded Nd-Fe-B

40

Isotropic bonded Nd-Fe-B Sm-Co

30

Sintered ferrite Alnico-9

20

Alnico-7

20 10

00 20

90 19

80 19

70 19

19 60

50 19

40

Alnico-5

19

30 19

10

20 19

19

00

10

Pt-Co M-K steel K-S steel

19

Energy product (MGOe)

Sintered Nd-Fe-B Anisotropic bonded Sm-Fe-N

50

Fig. 4.15 Magnet performance improvements from 1900 to 2010. Based on M.J. Kramer, R.W. McCallum, I.A. Anderson, S. Constantinides, Prospects for nonrare earth permanent magnets for traction motors and generators, JOM 64 (2012) 752–763.

Lighting Thomas Edison’s first incandescent electric light bulbs came to market in 1882 with filaments made from graphitized bamboo. Tungsten filaments emerged in 1904, producing more light, longer life and somewhat improved efficiency. They remained the mainstay of electric lighting for five decades, despite a rather woeful output of heat relative to light. The 1950s saw the first widespread use of fluorescent lamps, which are much more efficient. These pass an electric current through low-pressure mercury vapor, inducing the emission of ultraviolet light from the mercury atoms. High-energy ultraviolet photons are absorbed by phosphors in the white coatings inside the lamp envelopes, which then emit lower-energy photons in the visible range of the spectrum, as shown schematically in Fig. 4.16. Early fluorescent lamps produced light that was distinctly green or blue, but in the 1990s it became possible to tune the color of a fluorescent tube by adjusting its output in the red, green, and blue wavelengths individually. This was achieved through the use of a “triband” phosphor that produced red light from europium-doped yttria, Eu3+:Y2O3, green light from lanthanum phosphate doped with terbium in its 3+ oxidation state, Tb3+:LaPO4, and blue light from Ce3+:LaPO4. The color balance is tuned to consumer preferences simply by adjusting the amounts of the different phosphors, allowing for “daylight,” “warm white,” and “cool white” fluorescent tubes to be produced and allowing the lamps to gain greater acceptance in office and residential markets. Fluorescent tube design developed steadily over the years, improving the output colors, increasing efficiency, reducing noise emission, and increasing the lifespan. Early tubes were 1.5 in. in diameter and are designated as T12, where the number 12 refers to the diameter in eighths of an inch. T8 lamps, 1 in. in diameter, became

118

Critical Materials

Hg eUltraviolet light

Eu3+ Phosphor coating

Tb3+

Ce3+

Glass envelope

Red light Green light

Blue light

Fig. 4.16 The operating principle of a fluorescent lamp. Mercury atoms in the vapor contained in the lamp are excited through collisions with electrons, inducing the release of ultraviolet light. Ultraviolet photons are subsequently absorbed by rare-earth dopants in the phosphor layer coating the inside of the glass envelope, and the Eu3+ ions emit lower-energy red light, Tb3+ ions emit green light, and Ce3+ ions emit blue light.

the dominant format in the 1980s; compact fluorescent lamps (CFLs) came onto the market as direct replacements for incandescent bulbs in the mid-1990s; and T5 longtube lamps were on the verge of penetrating the market in the early 2010s, promising nearly double the efficiency of their T8 forebears. In April 2011, DOE proposed a change to the US energy conservation standards that would have set higher efficiency standards for fluorescent lamps, effectively pushing a transition from T8 to T5. The lighting industry responded with concerns about the availability of terbium and europium needed for the lamp phosphors and the rule change was first delayed for 18 months, and then abandoned in 2014. Coming very soon after rare-earth prices had peaked and needing two of the most highly impacted rare-earth elements, the proposed rule was a direct victim of the rare earth crisis. Despite the delay in implementing the new rule on fluorescent lamp efficiency, DOE projected in 2012 that fluorescent lamps would quickly take over from incandescent bulbs and would then slowly yield market share to LEDs [12]. Fluorescents were expected to retain about 50% of the market (as measured by lumen-hours) into 2030. Just 2 years later, DOE projected that fluorescents would only retain about 5% of the market by 2030 [13]. Fig. 4.17 shows the projections made in 2012 and 2014.

What changed after the rare earth crisis?

119

50,000

Installed base (Tlm h)

45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 2013

2020 Fluorescent Halogen

HID Other

2030 CFL LED Lamp

Incandescent LED luminaire

(B) Fig. 4.17 Changing predictions of the future of lighting (A) represents the projected market shares of different lighting technologies from the DOE’s report on the Energy Savings Potential of Solid-State Lighting in General Illumination Applications published in 2012, while (B) represents the projection produced in 2014. The later report anticipates a much more rapid growth of LED and decline of fluorescent lighting.

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Critical Materials

Silicone lens Front surface wire bond

Ce-YAG phosphor InGaN blue LED chip

Substrate

Cathode

Anode

Fig. 4.18 The principal components of a white LED lamp. The InGaN chip emits blue light, which passes through a Ce-YAG phosphor. This phosphor absorbs some of the blue light and emits a broad range of lower frequencies that mix together to form white light. This technology is much less dependent on heavy rare earths than fluorescent lamps.

White LED lamps made rapid inroads into the market starting in 2013, with a design shown schematically in Fig. 4.18. The essential features are a blue LED made from indium gallium nitride and a broad-spectrum phosphor based on ceria-doped yttria-alumina garnet. Blue light from the LED passes through the phosphor, and some of it is absorbed and reemitted at longer wavelengths producing an approximation of natural white light. Although they use cerium and yttrium, these lamps do not require any of the REEs that were affected by the price spike. LED prices fell below those of equivalent fluorescent lamps and very quickly displaced them from the market. The switch from fluorescent lamps to LEDs was inevitable in the long term, but it was certainly accelerated by concerns about the need for heavy REEs in the fluorescents: it was possible for LEDs, requiring much smaller amounts of lower-valued REEs, to be sold at lower cost and accelerate the displacement of CFLs from the marketplace. The prices of the rare earths were also affected by the loss of one of their major uses. Europium, in particular, dropped to about one-fourth of its precrisis level, after 2013. Terbium has uses other than lighting, and its price did not drop in parallel with that of europium. The criticality of europium and terbium certainly played a role in accelerating the adoption of new technology in the area of efficient lighting.

Postcrisis rare earth prices and utilization The price peak of 2011 had clear impacts on REE utilization. It helped to drive early wind energy technology toward gearbox-reliant designs, and it led to the avoidance of REPMs in many small motors and actuators. It helped to accelerate the switch from fluorescent to LED lighting. This destruction of demand helps to drive prices down from the peak levels seen in Fig. 1.6, but the effects are not uniform across all of the REEs. Europium, in particular, suffered from a 75% price drop in 2015, as LED lamps displaced fluorescent tubes and

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their need for triband phosphors: europium produces the red light component of a fluorescent tube, but is not required for an LED. Terbium produces green light in fluorescent tubes, but the drop in demand resulting from the LED revolution has not caused a corresponding drop in price, probably because terbium can now be mixed with or to completely replace dysprosium to improve the performance Nd2Fe14B magnets. We will see, in Chapter 6, that the use of Tb-Dy mixtures allows for improvements in the efficiency of REO processing.

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Technologies are not static. They evolve, and the impacts of materials criticality are the greatest for technologies that are on the verge of change. The use of a critical material in an emerging technology can halt or delay its adoption or force the use of suboptimal components and subsystems. The use of a critical material in a legacy technology can accelerate its replacement by emerging solutions. The most immediate response to a materials supply crisis is the replacement of the technology that uses the material, rather than addressing the materials required for the technology itself. Performance compromises are often made to avoid the use of critical materials, but, with time, performance requirements and materials evolve so that demand for the materials may recover. Investor enthusiasm for mine development reacts to price variations over much shorter periods than the time required to commission a new mine. The most critical materials attract the most attention: HREEs have had more impact on technology, have suffered from larger price shocks, and have had more R&D efforts devoted to them than LREEs. Primary sources do not provide a complete picture of production diversity. While new rareearth mines have reduced China’s monopoly on REE ore production they have not had a corresponding impact on its monopoly of REE separations and metal production. The component of the supply chain with the least diversity is its weakest link, so the link with the highest HHI should always be used in measuring criticality, rather than focusing only on the diversity of mining.

References [1] T. Daly, China’s Ganzhou Launches Rare Earths Exchange, Reuters, London, 2020. [2] G. Hatch, Personal Communication, (2019). [3] C.R. Borra, T.J.H. Vlugt, Y.X. Yang, S.E. Offerman, Recovery of cerium from glass polishing waste: a critical review, Metals 8 (2018) 16. [4] K. Hirota, H. Nakamura, T. Minowa, M. Honshima, Coercivity enhancement by the grain boundary diffusion process to Nd-Fe-B sintered magnets, IEEE Trans. Magn. 42 (2006) 2909–2911. [5] E. Alonso, T. Wallington, A. Sherman, M. Everson, F. Field, R. Roth, R. Kirchain, An assessment of the rare earth element content of conventional and electric vehicles, SAE Int. J. Mater. Manf. 5 (2012) 473–477.

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[6] R.T. Nguyen, D.D. Imholte, A.C. Matthews, D.W. Swank, NdFeB content in ancillary motors of U.S. conventional passenger cars and light trucks: results from the field, Waste Manag. 83 (2019) 209–217. [7] S. Faulstich, B. Hahn, P.J. Tavner, Wind turbine downtime and its importance for offshore deployment, Wind Energy 14 (2011) 327–337. [8] T. Fishman, T.E. Graedel, Impact of the establishment of US offshore wind power on neodymium flows, Nat. Sustain. 2 (2019) 332–338. [9] M.J. Kramer, R.W. McCallum, I.A. Anderson, S. Constantinides, Prospects for non-rare earth permanent magnets for traction motors and generators, JOM 64 (2012) 752–763. [10] J.J. Croat, J.F. Herbst, R.W. Lee, F.E. Pinkerton, Pr-Fe and Nd-Fe-based materials—a new class of high-performance permanent-magnets, J. Appl. Phys. 55 (1984) 2078–2082. [11] H. Onodera, Y. Yamaguchi, H. Yamamoto, M. Sagawa, Y. Matsuura, H. Yamamoto, Magnetic-properties of a new permanent-magnet based on a Nd-Fe-B compound (Neomax) .1. M€ossbauer study, J. Magn. Magn. Mater. 46 (1984) 151–156. [12] Navigant Consulting Inc., Energy Savings Potential of Solid-State Lighting in General Illumination Applications, U.S. Department of Energy, Washington, DC, 2012. [13] Navigant Consulting Inc., Energy Savings Potential of Solid-State Lighting in General Illumination Applications, US Department of Energy, Washington, DC, 2014.

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One of the three pillars of DOEs Critical Materials Strategy is the development of alternative materials to substitute for those with supply-chain challenges. Much has been learned in the course of applying this approach to rare earth materials following the rare earth crisis of 2012, and there have been some limited successes. The most important discoveries, however, concern the identification of the biggest challenges to materials discovery “on demand” and a clearer understanding of the cases that are (or are not) amenable to materials substitution and the characteristics by which we may identify them.

The challenge of inventing materials on demand As we have seen in Chapters 1 and 2, the timescale of a modern materials supply-chain failure is short—a matter of a year or two if we only look at the duration of a price spike, or maybe as long as a decade if we start the clock when warning signs first appear and also include the time period over which technology adjustments continue to be made. Unfortunately the time span of materials discovery and deployment is rather longer: it is typically asserted that 20 years or more elapse between the invention of a new material and its eventual adoption. A substantial amount of time is also spent in research before an invention is announced, so the total time required to bring a new material to market is likely to exceed 20 years, quite considerably. The “20-year rule” was first introduced by Tom Eagar, in a paper in MIT’s Technology Review [1]. He cites nine examples of 20-year gaps between discovery and commercialization, over a time period from the mid-19th to the late-20th century. Others have added to the list, and a summary is presented in Table 5.1. It would be easy to conclude that 20 years is the norm, but the reality is more complicated. The examples selected by Eagar and others clearly identify an opportunity for improvement, but if it were possible to conduct a study of all of the materials that have been discovered or developed in the lab, we would certainly find many examples of materials that have taken longer than 20 years to achieve commercial success, many that have been invented more than 20 years ago and still not been commercialized, and a handful that have taken significantly less time to reach the marketplace, including some that were described in Chapter 2. There are, however, only a few that have taken less than the time span of a typical materials supply-chain crisis, so it is clearly unwise to rely generally on a strategy of inventing one’s way out of a crisis once the need is identified, unless the timescales Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00005-0 © 2021 Elsevier Inc. All rights reserved.

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Table 5.1 Time from discovery to commercialization for selected materials innovations. Material

Invention

Commercialization

Time lag

Vulcanized rubber Low-cost aluminum Titanium Velcro Polycarbonate Gallium arsenide Diamond-like films Amorphous magnetic materials Fuel cell electrocatalysts Li-ion batteries Carbon fiber composites

1839 1886 Mid-1940s Early 1950s Early 1950s Mid-1960s Early 1970s Early 1970s Early 1990s Mid-1970s Mid-1960s

Late 1850s Early 1900s Mid-1960s Early 1970s About 1970 Mid-1980s Early 1990s Early 1990s Mid-2010s Mid-1990s Mid-2010s

30 years 20 years 20 years 20 years 20 years 20 years 20 years 20 years 20 years 20 years 50 years

can be significantly shifted or specific circumstances favor exceptionally rapid invention and industrial adoption. In this chapter, we will look broadly at ways to reduce the lag between criticality and substitution and also explore some materials that have been commercialized more rapidly to identify the circumstances that favor rapid commercialization, so substitution strategies can be applied to cases where they may be particularly effective. The mismatch between the timescales of materials criticality and new material deployment can be mitigated in at least three ways: 1. Improve the identification of prospectively critical materials to provide greater time for response. 2. Replace critical materials with existing materials rather than inventing new ones. 3. Where new materials are the only option, improve the speed at which they are invented, qualified, and deployed.

Improving the forecast As we saw in Chapter 3, criticality assessment is still emerging as a tool for identifying materials that may be at risk of supply-chain failure. While the general principles are broadly agreed, they are implemented in different ways by different practitioners, with widely different values being assigned to the measures that go into the quantification of essentiality and supply risk. To have a real chance of responding to emerging crises through materials substitution, we would need to extend forward-looking criticality assessments to a length of time that exceeds what is required for materials discovery, or identification and subsequent deployment. This will not provide accurate forecasts of materials crises: Those tend to be precipitated by singular events or accumulations of events that are themselves unpredictable, as in the case of the LED revolution, but the criticality analyses can provide a sense of the susceptibility of particular materials to such events.

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If it were possible to establish that a particular material will become increasingly susceptible to a supply-chain crisis over the coming 10 or 20 years, then it would make sense to invest, today, in research aimed at finding alternatives, allowing sufficient time for the newly discovered materials to be commercialized. This is something of a pipe dream for now, for several reasons: l

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As with all predictive models, criticality analysis is most reliable when the circumstances are the most specifically described and when the model is not asked to look too far into the future. They are somewhat like weather forecasts in this regard: the further into the future and the less specific the level of detail of the model, the less reliable is the output. We might imagine that a criticality analysis could be projected into the future, something like the track of hurricane, with increasing levels of uncertainty over the projection period as illustrated schematically in Fig. 5.1. If all possible materials are considered, however, and their uncertainty haloes all grow over the time of the projection, then the information becomes less and less useful in discerning which materials should be prioritized for research efforts in pursuit of alternatives. It would be impractical to apply this approach if the number of materials targeted for replacement becomes too large, and we saw in Chapter 3 that the number of critical materials and their individual levels of criticality have been increasing, even for analyses that are not forward looking.

Analyses performed in the context of a particular manufacturing sector, producer, or production facility are likely to be more useful to that specific entity than analyses performed over broader contexts, possibly exhibiting lower initial uncertainty that may also grow more slowly over the time period of the projection. Criticality assessments are not standardized, even within specific sectors, and it is not clear that there would be any particular advantage if they were. Weather forecasting has challenges akin to those of forward-looking criticality analyses, with uncertainty increasing as the period of projection extends further into the future, and different approaches and assumptions being applied in different models. In that arena, consensus results from multiple models are commonly adopted, and these provide

Increasing essentiality

Fig. 5.1 A schematic forward-looking criticality analysis for a single material. The uncertainty of the analysis increases as it is projected further into the future, and there can be differing variations of uncertainty relative to the two axes of the diagram.

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demonstrably more accurate results in most cases. It is possible that a similar approach might be effective in improving the effectiveness and utility of criticality analysis. There is also some knowledge to be gained by looking at how the results from different criticality analyses vary over time and possibly also by “backtracking” some analyses by applying their methods and assumptions to the data that were available at specific times in the past to see how accurately their projections have evolved [2]. There would appear to be opportunities for the application of artificial intelligence (AI) to finding trends in the complex, time-varying datasets that inform our criticality analyses, and this, as yet, is an unexplored area of research.

Using existing materials The need to invent new materials and the part of the time lag associated with that process can be eliminated if substitutable materials already exist. These may be identified through the usual materials selection processes, but there are still some challenges: l

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A replacement material must still be qualified for use in a particular manufacturing application. Manufacturers cannot simply switch from one material to another without rigorously qualifying the new material to ensure that it is compatible with the existing product. The replacement material will almost certainly differ from the original material in some of its properties—weight, strength, melting point, etc. These differences will call for adjustments to the manufacturing process and may also require changes in the design of the product itself. It is likely that the critical material in current use was selected over its potential replacement (if the replacement existed at the time of selection) because the chosen material was superior in some way.

True “plug-in” substitutes are rare, and even in the cases that come closest to complete interchangeability, the qualification of a new material can take months or years. Where manufacturing process changes or product design changes are required, the adoption of a new material can take around 5 years, depending to some degree on the life cycle of the product itself: for products that are updated and redesigned on a shorter timeframe, the adoption time can be reduced. Automobiles and light trucks typically undergo minor design updates on an annual basis and major redesigns on a longer timescale that may be 5–10 years. These product updates present opportunities to introduce new materials, either in response to criticality or for other reasons.

Improvements in materials selection The first step toward substituting a critical material is finding if a suitable replacement exists, and selecting the best one if there are several options. Selecting materials for particular applications was, at one time, a fairly simple process that depended more upon availability than optimization. Before, and for some time after the industrial revolution, buildings, tools, weapons, containers, and various forms of transportation were made from the most readily available local resources, be they wood, stone, clay, animal products, or metal. With industrialization and the development of mass production, materials were called upon to withstand

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increasingly challenging operating requirements, starting with the ability to operate at the temperatures and pressures required by steam power, so materials began to be chosen with an eye toward optimization of performance or cost, and then materials began to evolve along with the technologies that applied them. Lawrence J. Henderson (1878–1942) observed that “Science owes more to the steam engine that the steam engine owes to science,” and thermodynamics, in particular, underwent a series of revolutions as steam power emerged. Among these was the recognition that higher operating temperatures and pressures lead to greater efficiency, but they also call for better materials. Initially driven by simple rules of thumb or attention to single properties like strength, melting point, electrical conductivity, or magnetism, the selection of materials slowly become a science in its own right, in which the choice of a material for a particular application is based upon a multidimensional search for optimal properties. For railroads the primary driver for materials selection was originally strength per unit of cost, possibly moderated by weight because of its influence on the process of laying track; in aviation the primary driver is strength per unit weight, possibly moderated by cost. These considerations led to the selection of steel and the need for a steel industry to support railroads in the late 19th century and aluminum for military aviation, starting between the World Wars I and II in the 20th century. With the development of these and other materials industries various branches of materials science emerged, focusing on inventing materials with ever-improving properties: lower cost per unit strength, or greater strength per unit weight, or any of a myriad of other properties, and huge ranges of alloys and other materials began to be developed. The first standardized formulation for a steel alloy was issued by the American Society for Testing and Materials (ASTM) in 1898, in an effort to address proliferating failures in steel rails. Today, about 3500 different grades of steel are available, and they are classified using different numbering systems in different parts of the world. Simply identifying the best choice for a particular application from all of the available steels is a challenge, and when all of the other competing materials are considered, too, it becomes a time-consuming process with potentially high stakes. When we extrapolate to all of the materials used in manufacturing, it is not a trivial matter to quickly identify substitutes when a particular material or one of its component elements becomes critical. In reality, most critical materials are rather more specialized than steel and are used for specific properties such as magnetism or light emission, as in the case of the rare earths. They are also available in smaller numbers of variants than steel. Nevertheless, identifying a material for a specific application is a nontrivial challenge, and identifying a substitute in the event of a supply-chain failure may be even harder: The “best choice” for the application is presumably the material currently in use—which must now be replaced—and other choices are likely to have shortcomings. The process of identifying and selecting materials has been revolutionized by the database-driven methods pioneered by Ashby, starting at the end of the 1980s [3]. These methods and the databases that enable them are now available commercially, in the form of the Cambridge Engineering Selector (CES) available from ANSYS Granta. With appropriate input, this system is able to identify suitable materials

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choices for specific applications according to criteria set by the user. In a recent update the system has been enhanced with the addition of a criticality database, allowing users to consider supply-chain risks during the materials selection process. Criticality can fluctuate over time, much as prices do. Even the instantaneous price of a material may be uncertain to some degree, but the assignment of a criticality measure is much more challenging because of the variability among different analyses. The CES system allows users to assign their own criticality measures, reflecting their particular needs and concerns, and this must be done with some care, but this facility may allow manufacturers to reduce their supply-chain risks into the future. In the event of an unanticipated supply-chain failure, CES provides a valuable tool that can help to reduce the response time for finding and selecting a substitute material. Even if a substitute material can be identified, however, there are considerable challenges involved in adopting it.

Case study: Replacing steel with aluminum in the Ford F-150 pickup truck Some of the key steps required to make a materials substitution are illustrated in a case study from the automotive industry [4]. In pursuit of improved fuel efficiency, the Ford Motor Company reduced the weight of its F-150 pickup trucks by about 320 kg through the extensive use of aluminum alloy body panels in place of steel starting in the 2015 model year, which went into production in October of 2014. The introduction of the new version of the truck followed a process that began with a 2009 decision to make the switch to aluminum—a decision that had probably already taken some time to make. Two rounds of prototype trucks were built in 2009 before development work on the new model started in earnest, in October 2010. Extensive efforts were expended on design, assessing the manufacturability, salability, and repairability of the new trucks and lining up suppliers for the new materials. More than 100 preproduction units were built to validate the production process and test the new version of the vehicle for durability and reliability. Finally, each of the company’s existing F-150 production lines had to be shut down for a month to make the switch from electrically welded steel to aluminum construction relying on laser welding, glue bonding, and riveting. Substituting an in-use material with an already existing replacement material took around 5 years after selecting and deciding to adopt the alternative material. This is shorter than the time usually required to invent and deploy a new material, because the time required for invention is eliminated, but it is still rather longer than the timescale over which most materials supply-chain crises emerge. From this case, we see that the biggest challenges in the use of existing materials to substitute critical ones are reducing the times required for (1) product redesign, (2) qualification of the new materials in the product, and (3) modification to the manufacturing process. Among these the qualification step creates the greatest delay and is the area where improvements offer the greatest payoff.

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Case study: Catalytic converters Although they are rare, a few true plug-in alternative materials do exist, and these present attractive scenarios for materials substitution, since they can be used without substantial retooling. Automotive catalytic converters are built according to several similar though not interchangeable designs. Differing regulatory standards call for different converter designs in North America, Europe, and Japan, but within each of those regions, there is some flexibility. The basic design of a catalytic converter is a “honeycomb” multitube ceramic support that bears tiny particles of metal catalysts on its surfaces. The honeycomb structure is commonly made from cordierite, and it supports nanoparticles of ceria or ceria-zirconia, which provide oxygen storage, and catalysts made from a variety of transition metals. Vehicle exhaust gases pass through the fine tubes of the honeycomb support, where they encounter the catalyst particles, which convert noxious gases to less hazardous products at operating temperatures above 425°C. Specifically the converter: l

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Reduces nitrogen oxides to nitrogen, releasing oxygen. Utilizes the oxygen to oxidize carbon monoxide to carbon dioxide. Oxidizes unburnt hydrocarbons to form water and carbon dioxide.

Platinum is used to catalyze both the oxidation and reduction reactions, but palladium also catalyzes the oxidation reactions, and rhodium can promote the reduction reaction. Other metals can be used, too, but nickel is banned in Europe, and copper is banned in Japan. Cerium, iron, and manganese can be used everywhere, but they are not as effective as the PGMs. Palladium-rhodium mixtures can be used interchangeably with platinum in some catalytic converters, and these materials are effective plug-in substitutes for each other. Palladium was less expensive and more available than platinum for several years, leading to palladium-rhodium becoming the predominant catalytic converter material. However, the price of palladium has risen steadily since 2016, and in mid-2019, its price stood at more 50% higher than that of platinum, allowing manufacturers to consider switching from palladium to platinum. If a supply crisis were to emerge suddenly for either platinum or palladium, there is a ready substitute at least for use in catalytic converters, but the availability of such prequalified, direct plug-in substitutes for specialized materials in any other applications is truly rare.

Increasing the speed of new material discovery and deployment Reducing the delay between materials discovery and deployment to a level significantly below the current benchmark of around 20 years is a grand challenge. If we can shrink this time to something more comparable with the timescale over which materials supply-chain challenges emerge, then materials invention can become a viable approach to coping with critical materials, but this will probably require a response

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time on the order of 2 years unless criticality predictions can be made reliable over significantly longer timescales. Some gains in the speed of materials deployment have been made over the span of human civilization. The gap between the end of the Bronze Age in the Eastern Mediterranean and the onset of the Iron Age was about 200 years, representing the time that it took to develop and deploy ferrous metallurgy to replace bronze. Three thousand years ago, then, the materials deployment delay was about one order of magnitude longer than today’s 20 years. Assuming that some form of Henderson’s law might apply and extrapolating extravagantly from just two data points, we might anticipate that the benchmark could be reduced by another order of magnitude lower, to reach the target of 2 years, after another three millennia or so. We cannot afford to wait to see if that happens, and a number of efforts are underway to accelerate the process.

Materials genome initiative If substitute materials cannot be found from existing sources, it becomes necessary to invent new options. The invention or discovery of new materials has long followed a process based on the methods used by Edison to find the right material for his light bulb filaments, and these are notoriously slow. They involve testing candidate substances in the laboratory and eliminating them one by one until a suitable material emerges. Edison famously commented at one point during his search for a workable lamp filament “I have not failed. I’ve just found 10,000 ways that won’t work.” A new approach is being pioneered through an effort known as the materials genome initiative (MGI) that seeks to take advantage of the burgeoning computational and experimental capabilities available to researchers, just as the Human Genome Initiative had previously leveraged computational tools and databases to accelerate the achievement of goals in the life sciences. MGI is organized as a “multiagency initiative designed to create a new era of policy, resources, and infrastructure that support US institutions in the effort to discover, manufacture, and deploy advanced materials twice as fast, at a fraction of the cost” [5]. Researchers from around the world also contribute to the effort. NIST has suggested a standardized method for measuring the time between discovery and commercialization to provide a basis for measuring success that would seem to be called for in the phrase “twice as fast” in the description of MGI [6]. The process of inventing a new material for a specific purpose has several successive steps as illustrated in Fig. 5.2. It is still essentially a process of eliminating everything that will not work: 1. Candidate materials or materials classes are identified based on theoretical considerations and/or databases of known materials properties. Artisanal knowledge occasionally plays a role, and sometimes (as in Edison’s search for the perfect light bulb filament) the list of candidate materials appears to be unbounded. 2. Candidate materials are then synthesized. Although some materials can be created in theory, they may not be realizable in practice for several reasons, and they are eliminated at this stage.

0 Specifications for a replacement material

1 Identification of a candidate material

2 Lab-scale synthesis of candidate material

3 Property testing of synthesized material

4 Development of process to manufacture the tested material

5 Incorporation and testing of new material in prototype product

6 Qualification for use in manufactured product

Fig. 5.2 Steps in the invention of a new material. The requirements for the material are set in step 0, and candidate materials that might meet the requirements are identified on the basis of theory, computation, or experience in step 1. The remaining steps successively eliminate candidate materials, sending the process back to earlier steps, until one candidate survives.

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3. Materials that can be synthesized are tested to determine whether they have the desired properties, and materials that do not pass this test are eliminated or variations of composition, and the method of synthesis might be tried. 4. When a material with the necessary properties can be synthesized, the next step is to find methods by which it can be manufactured at a scale consistent with the likely demand, in a form that is amenable to manufacturing, while maintaining the properties obtained in lab-scale synthesis. 5. A material that can be manufactured must then be incorporated into a product, which will require product redesign in most cases, and manufacturing process changes in nearly every case. 6. The performance of the material in its target product must be assessed, in the process known as “qualification.”

A replacement material may fail at any one of these stages. It is common to conduct the early stages of the invention cycle on several materials in parallel, but downselection results in fewer and fewer candidates in the later stages, with typically only one entering the final stages of development. As we saw in the case of Ford’s F-150 pickup truck, using existing materials allows us to bypass steps 1–4, but steps 5 and 6 of the process, alone, can take 5 years. MGI seeks to accelerate nearly all of the steps of the materials invention cycle. Its principal activities include facilitating access to materials data and integrating experimentation, computation, and theory for materials design. It also has a significant and vital goal to build a qualified workforce that is ready to use the tools that it develops. Through these goals, MGI may accelerate the identification of existing materials by enhancing access to online data, which is an area of great opportunity particularly when it is recognized that most “failed” experiments have not traditionally resulted in published data even though they contain potentially useful information. Capturing and making available information from “the 10,000 ways that won’t work” can have great benefits, but it is not a common practice in scientific research where there is a strong premium on publishing successes rather than “failures.”

Computational tools MGI aims to accelerate the discovery of new materials by moving a larger part of the development process from the laboratory to the computer, using state-of-the-art theoretical concepts. The discovery process still involves testing the potential of particular materials composition to meet specific needs, and the process involves testing large numbers of candidate materials just as in the Edisonian method, but computation is much faster than experimentation, and it allows the process of eliminating unsuitable materials to proceed much more quickly. The increased use of computational tools in the materials development process will therefore help to reduce the number of materials that must be made and tested in the laboratory, and MGI also strives to accelerate laboratory testing through a variety of accelerated testing methods. Inventing new materials is an immensely complex task. It is usually directed, at least initially, toward finding a material with a single property: strength, magnetism,

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light emission, or others, but the mechanisms by which materials attain these behaviors cover a wide range of phenomena and length scales, so no universal system exists to accomplish the task. At the smallest scale, some properties of materials relate to the behaviors of electrons. Magnetism results from quantum-mechanical spin interactions, while light absorption and emission relate to electron energy levels, which can be affected by size effects in the nanoscale. Strength is affected by interatomic bond types, and for metals, it is also determined by atomic-scale defects and larger length scales such as phase distribution and grain sizes. These and many other materials properties all call for different types of theoretical understanding and different computational tools to apply it. Even with reliable theories and outstanding computational tools, the challenge of finding materials with specific properties is daunting. The periodic table gives us a palette of about 100 chemical elements from which we might construct materials. If we restrict a search to materials that contain only two elements, then we have about 5000 binary combinations to consider. And for each combination of two elements, say “A” and “B,” we must survey the range of compositions from pure A to pure B at some level of resolution: If we choose to survey binary compositions in steps of 5%, then we need around 20 compositions for every combination of two elements, and our candidate pool grows to 100,000 materials. If we extend the search to three elements and survey in composition steps of 5%, then the candidate pool grows to 167,000 combinations of elements and over 200 compositions per combination or about 33 million possible combinations. For materials comprising four elements, we would have over a billion combinations to evaluate. Even with the fastest computers available today, we cannot search blindly for combinations of chemical that would give us the desired properties, so surveys are always restricted by other considerations including the intuition of the researcher, who might choose to focus on particular types of chemical bond, metallic, ionic or covalent, or on materials that include elements with large magnetic moments—but the size of the search domain still remains very large. It is impractical to try to make and test all of the candidate materials in the lab, so computational tools are increasingly employed, and MGI promotes their development and application in the search for new materials. Different computational tools are required for the development of different properties. Some properties of materials derive from the atoms that make them up, while others derive from the ways that atoms interact with each other and/or the behavior of imperfections in the atomic structure that might be defined at length scales equivalent to single-atom diameters on up to hundreds of micrometers or more. Researchers have developed an extensive array of tools to meet needs in different domains. Density functional theory (DFT) is useful tool for predicting properties that depend primarily on the quantum mechanics of electrons in a material, and it has been growing steadily in its ability to make accurate predictions ever since it first emerged in the 1970s. It can be used to predict the stable structures of materials based on the bonding between atoms, along with some aspects of magnetism. Robust DFT codes are available and can be applied to surveying combinations of atoms in pursuit of particular properties if sufficient computational power is available. At this time, DFT codes still have some challenges in dealing with f-electron materials (i.e., lanthanides and

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actinides), but even here, they can be used, with appropriate modification and interpretative caution, to identify compositional regimes that might be worth further study using other techniques. Molecular dynamics (MD) is used to study the interactions between atoms in large ensembles and is useful for studying how they respond to stimuli such as stress. This technique is particularly useful for studying interactions between atomic-scale defects in crystalline material, which are important in materials properties such as strength and diffusional transport. With increasing computational power, MD simulations have grown in the length scales and timescales that can be addressed, but the limits in both regimes remain somewhat restrictive compared with the experimentally observable phenomena that they address. The reliability of MD simulations depends very significantly on the choice of interatomic interaction potentials and other computational details. For some applications that rely on understanding the mechanical properties of materials, the limitations of MD simulations are addressed by using computational dislocation dynamics, which ignores the interactions between individual atoms and focuses on the interactions between dislocation segments in an elastic continuum. This allows the study of increasingly large ensembles of dislocations and is helpful in the investigation of mechanical properties of crystalline materials in regimes that are more closely aligned with experimental observations and practical applications. The field of integrated computational materials engineering (ICME) is advancing rapidly, with new capabilities emerging at a fast rate, but the validation of the computational methods by experimental testing lags by at least a few years. Nevertheless, the simulation of materials in the computer often helps us to identify trends in properties that result, for example, from crystal structure or atomic size, and these are often more valuable than specific property predictions for individual materials, because they allow the search for a new material to focus on compositions with greater promise. As ICME develops and computational capacity improves, we expect to see increasingly reliable property predictions, but even before we reach that point, computational methods help to reduce the amount of Edisonian experimentation that goes into discovering a new material. Predicting that a desired property can be obtained from particular combination of atoms in a specific geometric arrangement is an important goal that we are beginning to achieve in some areas. It is, however, not sufficient. DFT and other tools can tell us if a material with a given composition and structure is stable within certain bounds and assumptions, but they do not always predict its stability relative to other materials and thus the likelihood that it can actually be fabricated and used reliably. Of course, it is possible simply to try to mix the ingredients together and apply a suitable temperature or pressure to see if the desired structure forms, but this quickly turns into another exercise in trial and error. Happily, some increasingly powerful computational tools are available to guide the processing of materials, under the general title of calculation of phase diagrams, or CalPhaD. Phase diagrams are powerful guides to the production of particular materials and microstructures, and accurate phase diagrams are available for many different combinations of elements, but when a new combination is considered, the appropriate

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phase diagram may not yet exist. The experimental determination of phase diagrams is traditionally a slow process involving hundreds or thousands of samples across the full range of composition and temperature. The CalPhaD approach was developed to provide an alternative to the tedious work of experimentally constructing a phase diagram for a material of a new composition. It collects available experimental information on phase equilibria in a system and thermodynamic information obtained from thermochemical and thermophysical studies. The thermodynamic properties of each phase are then described with a mathematical model containing adjustable parameters that are evaluated by optimizing the fit of the model to the information, including information about coexisting phases. The phase diagram and the thermodynamic properties of all the phases are then recalculated with the goal of obtaining a consistent description of the phase diagram and the thermodynamic properties of all of the phases. This enables prediction of stable phases and their thermodynamic properties in regions of compositional space where experimental information is unavailable and also for metastable states that can form during phase transformations. CalPhaD relies upon databases of thermodynamic information for the elements included in the calculation and their interactions, and although this information may be unavailable, unreliable, or insufficient in some cases, the method has been developed into a powerful tool, and it has made significant contributions in many situations.

Accelerated experimental methods When CalPhaD is challenged by the lack of input data or where its results need to be validated experimentally, it may be necessary to determine a phase diagram experimentally. Traditional methods require the production of samples at all compositions of interest, annealing to ensure that they come to equilibrium and then analyzing their phase content using X-ray diffraction. Performing this work on multiple samples is tedious and time consuming: in the late 20th century, it was not uncommon for the determination of a single-phase diagram, or even a part of one, to take several years and form the substance of an entire doctoral dissertation. Combinatorial methods have significantly accelerated this process [7]. These began to emerge in the first decade of the 21st century and were based on technologies that had been pioneered in the microelectronics industry, where thin films of materials are routinely deposited on silicon wafers in the process of building integrated circuits. When physical vapor deposition methods are used with offset sputter targets or other kinds of material sources, they result in varying quantities of material being deposited, as shown schematically in Fig. 5.3A. Using multiple off-axis material sources, each loaded with a different element or alloy, the result is a substrate covered with a thin film of varying composition as shown in Fig. 5.3B. This effectively makes a library of different compositions that can be probed point by point for its composition, structure, phase content, and, in some cases, physical properties. A great deal of experimental effort is saved by the ability to make a library containing a full range of compositions in one simple process.

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Fig. 5.3 Combinatorial methods accelerate the refinement of materials compositions. A combinatorial library is an array of materials with varying composition, which allows the bestperforming composition to be identified. (A) In thin-film processes the amount of material deposited on the substrate can be varied by using an offset evaporation source, among other methods. (B) Using multiple sources simultaneously a range of compositions can be formed.

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The impact of the combinatorial approach increases with the addition of robotic measurement of the chemical composition, phase structure, and other properties at each point in the library. This allows for isothermal sections of a phase diagram to be determined in days, rather than years. If we also provide for the library to be studied at different temperatures, we can quickly determine further isothermal sections and build up entire phase diagrams for complex mixtures of elements. Facilities for performing high-throughput analysis of combinatorial libraries have been built in a number of labs, including facilities open to general users such as the Stanford Synchrotron Research Lab (SSRL) [8]. Computational tools such as DFT can rapidly identify materials that might meet a specific need. CalPhaD can help to determine whether those materials can be synthesized, and combinatorial methods allow for rapid synthesis, allowing for the DFT and CalPhaD calculations to be validated and for optimal compositions to be found. The combination of these tools and techniques promises to accelerate materials discovery and design, but all cases are different, and there is no universal recipe for achieving the desired outcome.

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The use of thin-film combinatorial libraries can be misleading in cases where materials properties are affected by the morphology. The structures and behaviors of thin films are dominated by their large surface-to-volume ratios that can affect the preferred crystal orientation (or texture) or even the crystal structure itself. Magnetism is particularly impacted by morphological and structural variations, with the result that thin-film combinatorial libraries may be less helpful in searching for new magnetic materials. For this reason, there is still a need for combinatorial libraries of materials in more bulk-like forms. One approach to meeting this need uses an adaptation of a 3D additive manufacturing system that provides for compositional control. The laserengineered net shaping (LENS) system uses a laser to create a melt pool into which feedstock powder particles are added. With multiple powder feeders operating under computer control, along with 3D motion of the workpiece, it is possible to build up samples of varying shape, size, and composition. The Critical Materials Institute (CMI) has developed and used a system of this type to create combinatorial libraries of materials for various applications, avoiding the constraints of traditional thin-film libraries, as illustrated in Fig. 5.4.

Database management With growing use of ICME and combinatorial synthesis, materials data are being generated at unprecedented rates, and all of this information presents new challenges. One of the goals of MGI is to bring some order to the management of materials databases, allowing researchers to find and use information relevant to their particular needs.

Fig. 5.4 Thin-film specimens are not appropriate when the properties in question are affected by reduced dimensionality as, for example, in the case of magnetism. The Critical Materials Institute builds combinatorial libraries consisting of pillars of individual composition using a modified laser-engineered net shaping (LENS) 3D printer. Each column in this array is about 1 cm tall, formed in a controlled atmosphere in 1–2 min, and is built from powders of up to four different compositions. Courtesy of Emrah Simsek and Ryan Ott of the Ames Laboratory’s Critical Materials Institute. This image was created, in whole or in part, under Contract No. DE-AC02-07CH11358 with the US Department of Energy.

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Essential to this process is the development of database standards that allow different types of materials information to be collected in a consistent searchable form. A particular challenge in this regard is persuading researchers to submit their data to a centralized repository. An even greater challenge is to encourage the research community to adopt a practice of submitting information about “failed” materials that can be extremely useful, as we will see later. Early results from MGI are encouraging. The process of identifying suitable materials for specific applications is being accelerated in some cases. However, the goal of deploying new materials twice as fast as the prevailing norm—that is, going from around 20 years to 10—is still not sufficient to allow new materials discovery to be an effective tool for responding to materials criticality unless it is combined with improved criticality analysis to extend our foresight out to 10 years, which seems unlikely in the near term. MGI’s current efforts focus primarily on accelerating the essential processes of identifying new materials, corresponding to steps 1, 2, and 3 in Fig. 5.2. While necessary, this may not be sufficient, since a large part of the delay in materials deployment occurs in the process of adopting the new substance and adapting product design to use it. MGI will help us to sprint to the start line of the adoption process, but that process can be a marathon, especially for completely new materials.

Accelerated insertion of materials Recognizing that the process of materials adoption does not end with the selection of a substance from which to make a particular object, in 1999 the US’s Defense Advanced Research Projects Agency (DARPA) began a program on accelerated insertion of materials (AIM) that initially focused on materials for aerospace applications. AIM addresses stages five and six of the materials invention process. The utilization of a material depends on the development of a suitable means of making it and forming it into the object for which it is intended. While chemistry and physics may be applied to finding materials with particular properties, materials science recognizes that those properties may be affected by the way in which the material is processed. The insertion of a material in a particular device such as an airplane, therefore, requires the performance of the material to be proven in the form in which it will eventually be used. The AIM program addressed the process by which a material and its processing are integrated into the manufacturing process. Like MGI, it made extensive use of computational tools, applying them specifically to the development of property-structure relationships and structure-processing relationships, particularly in the pursuit of improved mechanical properties. A significant contribution from the AIM program was the integration of statistical variability into the methodology. The strength of a material can be measured in several ways, of which one or more may be important in a specific application: The yield stress, the ultimate tensile strength, the creep rate, and the fatigue limit may all be considered in selecting a material, and it is relatively easy to find database values

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Fig. 5.5 A simple illustration of the importance of property variability on materials performance. A material will break when we apply a load equivalent to the ultimate tensile strength (UTS), but if we measure the UTS in repeated experiments, we obtain variable results that depend on variations in the microstructure that are always present. In this illustration a material with a higher UTS (Material A) has greater variability than a material with a lower UTS (Material B). Although it may be considered to be stronger, Material A has a higher probability of failure at stresses below the line marked with an asterisk.

for all of those parameters. In a real material, however, the values will all vary with the processing of the material, and the values will always exhibit some variability, as illustrated in Fig. 5.5. The component fails when the stress on the material exceeds its ability to resist it, and this depends on the weakest point in the material rather than the average. Mechanical design has traditionally determined the acceptable loading of a component based on the material’s average strength, with some added “safety factor” to account for the fact that not all parts of the material are as strong as the average value would suggest. Much of the process of materials testing for use in specific products is taken up by the process of probing the limits of the safety factors in the performance of the materials, and because this necessarily involves low-probability events, the required amount of testing becomes large. As we see in Fig. 5.5, it is possible for a material with a greater average or nominal strength to have a larger strength variability than a weaker one, so the “weaker” material can be used with a smaller safety factor. In the case illustrated in Fig. 5.5, the “stronger” material is more prone to failure than the “weaker” material at stresses below the level marked by an asterisk. The variability of a material’s performance can be more important than its absolute value, and much effort goes into assessing critical property variability to qualify a material for use in a particular product. The AIM process seeks to incorporate statistical property variations into to the design of materials processes, as a means of reducing the amount of testing required to confirm the performance of a part made from a particular material. This is achieved both experimentally and computationally by incorporating models of structureproperty relationships and assessments of structural variability.

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A second and extremely important contribution from the AIM program was its impact on the way in which materials engineers and product designers interact, through the use of designer knowledge bases (DKBs) that manage materials data and link processing, microstructure, properties, and producibility while calculating confidence bounds for system predictions. Some of the applications of the AIM process indicate that the materials insertion timescale can be reduced by a factor of two [9]. This is a significant achievement, but it still does not bring the speed of materials adoption into line with the rate at which materials criticality can impact supply chains.

Is anything missing? The MGI and AIM programs have made and continue to produce improvements in the speed at which new material are deployed. MGI addresses phases 1–3 of the materials discovery process, and AIM addresses stages 5 and 6, but there has been no corresponding effort to address stage 4—the development of manufacturing processes to meet the engineering needs for new materials. This is often described as the “scaleup challenge.” Scaling up usually involves proving out a method to make the new material at successively larger scales until the necessary throughput is achieved. In some cases it simply involves making the original lab-scale synthesis method work in larger volumes, but in many, it requires entirely new approaches to making the material. Most materials processes change as they scale up, as heat and mass have to be transported over larger distances to penetrate larger batches of the material. Quenching rates that can be easily achieved in the lab may be inaccessible at production scales, for example, so the challenges can be large. The required volumes may be small for some materials, and this may reduce the challenges associated with scaling production up to industrial levels. As we saw in Chapter 3, some critical materials are used in relatively small volumes, but in most cases those volumes are still not so small that their replacements would avoid all of the scale-up challenges. Scientists-turned entrepreneurs frequently find that scaling up their production method is the biggest stumbling block in the process of commercializing a new material, and this is an area in which a consistently applied and well-constructed program would make significant improvements.

Some hints of success Despite consensus that it takes 20 years and the gaps in existing R&D efforts to speed it up, there are a few cases of materials that have gone from the lab to the production line considerably faster. It is worthwhile to study these “fast track” cases to find approaches that can be applied more generally. The cases described later have all occurred in relatively recent years, but it is not clear if this represents a sustainable trend toward shorter commercialization times. In at least a few cases, the new materials have emerged as a direct result of materials criticality.

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Nylon Two years from discovery to commercialization DuPont invented nylon in 1937. At first the material was a product in search of a use, but the company began selling nylon stockings in 1939, and by the end of the World War II, the polymer was one of the world’s most essential materials. The rapid initial transition to commercial use can be attributed to the company’s shrewd choice of a target application: Relatively small volumes of material are required to make stockings, so it was not as challenging as it might have been to ramp up to full production. Stockings were also something of a luxury item, and women were used to paying high prices for silken hosiery, so DuPont received large revenues from its small production volumes. Finally the use of the material in hosiery required much less testing and qualification than would have been the case if its initial use had been for parachutes or towropes, but the subsequent adoption of the material for those more demanding applications was facilitated by the experience gained from making it into stockings.

Lead-free solder Twelve years from discovery to commercialization Soldering has been an important method of joining glass or metal components to each other for about 2500 years. It relies upon alloys that melt significantly below the melting points of the pieces being joined, so the solder forms a liquid that envelops the solid parts at an elevated temperature, solidifying into a metallic “glue” upon cooling. For centuries, solders have been developed and optimized through a process of trial and error, and the most common ones were alloys of lead and tin with around 40–45 wt % of lead, close to the eutectic point of 38% Pb. Soldering has been used in making stained glass windows, plumbing, and electronics. For electrical and electronic applications, soldering has the advantage of creating electrically conductive joints. As the impacts of lead on human health became known, regulations were adopted around the world in an effort to keep it out of the environment. The United States banned the manufacture of lead-based paint in 1978. Lead pipes were banned from plumbing systems in 1986. Tetraethyl lead was completely eliminated from gasoline in 1995 after several years in which cars that required it were no longer made. Lead became, in a sense, the opposite of a critical material—an anacritical material, which is a substance that is plentiful but needs to be removed, as opposed to a critical material that is in short supply and must be replaced. In the 1990s regulators in the United States, Europe, and Japan began to develop proposals to ban either the manufacture or disposal of electronic devices containing lead-based solder. A substitute material was needed, and the research community produced several candidate materials during the 1990s [10]. Recognizing the challenges of adopting a material to replace tin-lead solder in electronics, the National Electronics Manufacturing Initiative (NEMI)—later known as the International Electronics Manufacturing Initiative (iNEMI)—undertook a project to (1) choose a single leadfree solder that could be recommended as an industry standard, (2) provide a set of manufacturing processes and tools that would enable a participating company to

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quickly implement lead-free soldering if it decided to do so, and (3) provide sufficient data to demonstrate manufacturability and reliability of the alloy and processes that were chosen [11]. The project began in 1999 with a team that included manufacturers of electronics, components, solder, and manufacturing machinery along with academia and government laboratories. It finished its work in 2003 with the recommendation of a common alloy composition for electronics manufacturing, along with several manufacturing protocols. The solder material recommended by iNEMI was an alloy of tin, silver, and copper that had been invented in 1994, through a research collaboration between DOE’s Sandia and Ames national labs [12]. This material melts about 5°C hotter than the traditional tin-lead solder that it was to replace, so its use required some changes to the manufacturing process, but those were relatively minor and easy to work into the cycle of product updates for this rapidly advancing industry. With every appearance that a viable alternative was available, the removal of lead was mandated by regulations introduced in both the EU and in Japan in 1997—the year that the iNEMI-selected alloy was patented. The new solder quickly became the worldwide standard. The rapid adoption of the Sn-Ag-Cu solder alloy was facilitated by at least three factors: l

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Governmental regulations effectively required its use, but the ability of governments to impose those regulations also depended upon the existence of a suitable alternative material. The material was selected, developed, and qualified for use by a consortium of industrial interests that spanned the supply chain, supported by cutting-edge research capabilities in academic and government labs. There was broad commitment to the goals of the project in the electronics manufacturing industry, and companies that ordinarily compete with each other collaborated to achieve success. The combination of effort significantly shortened the time required to qualify the new material.

Quench and partition steel Twelve years from discovery to commercial deployment The quench and partition (QP) processing method was developed in 2003 [13]: it produces very high-strength steel by forming the hard martensite phase through quenching and then toughens the retained austenite phase by annealing to allow carbon to diffuse from the martensite into the austenite. The high-strength levels resulted in materials processed this way being designated as “third-generation advanced highstrength steel.” Initially invented through a collaboration between the Colorado School of Mines, Ghent University, and General Motors, the material was developed for industrial scale use in small vehicles by a partnership of GM R&D’s China Branch, GM’s US R&D Center, GM’s Chinese product team (also known as the Pan Asia Automotive Tech Center), Baosteel Corporation, and Tongji University. A QP steel with a strength of 980 MPa was introduced into model-year 2016 vehicles made by GM China beginning in 2015.

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This material contributes to reducing the weight of the vehicles’ body panels by as much as 20% compared with the previous steel used in the same application, producing significant gains in fuel efficiency. A notable feature of this transition is the strength and breadth of the research and development teams. There was close collaboration between academia and industry in the earliest stages of the research, and the contributions from academia continued up to and including the adoption in an industrial application. The industrial participants in the development team included both a materials producer and the end user.

YInMn blue Ten years from invention to commercialization Blue pigments are the rarest of all color-imparting materials and have historically been the most expensive of all. The great master painters of the Renaissance horded their supplies of lapis lazuli or Prussian blue and used the color in their compositions only sparingly because of the cost. Other blue pigments had a propensity to fade over time, and many were also toxic. Most of today’s commercially available blue pigments are based on cobalt blue, CoAl2O4, which was originally discovered in 1802; the supply chain for these materials suffers from cobalt’s price volatility, growing competition from lithium-ion batteries, and concerns about ethical sourcing. In a search for new multiferroic materials, scientists at the University of Colorado synthesized YIn1
xMnxO3 in 2009, and it proved to be a failure as a multiferroic but had a piercing blue color [14]. The intensity of the blue color is controllable through the In:Mn ratio, and the material is very stable. The researchers recognized the potential of their accidental discovery and applied for a US patent for the pigment, which they received in 2012. A development license was signed with the Shepherd Color Company in Australia, a pigment producer supplying a variety of industries, that is actively marketing the new blue pigment. A few artists are now using paints containing YInMn blue, and it will also be used in the housings of graphics processors made by AMD. This accidental material benefited from the awareness of its discoverers regarding needs in a realm outside of their research area and its superior performance in one area of application. It has not yet been adopted at a large scale, but the emergence of commercial uses is encouraging.

Giant magnetoresistance Nine years from discovery to commercialization Hard disk drives (HDDs) were first introduced as a medium for computer random access memory (RAM) by the IBM Corporation in 1954. They became the dominant data storage format in mainframe computers in the 1960s and quickly took over personal computers after they were first introduced into this sector by IBM, in 1983. The data density of HDDs has increased steadily over time, through the adoption of a variety of new technologies: The first hard disk in a PC had a capacity of 10 MB in a 5¼ in. format, and today’s units offer multiple terabytes in drives as small as

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2½ in. The ability to detect magnetic field changes on a tiny scale has been a major contributor to this improvement in data density: Small magnetic domains can be packed closely together on the surface of the hard disk, but the magnetic flux associated with each binary digit of data also depends on the domain size. Tiny data bits produce correspondingly minute amounts of magnetic flux, and they can only be detected by highly sensitive detectors. Early read/write systems for HDDs—along with other magnetic recording devices—relied upon the current induced in a coil of wire as it moved through the changing magnetic field produced by the recorded data. This system is limited at small sizes because the induced current in the field coil depends on the amount of the magnetic flux and the number of turns in the coil. As the data bits shrank, the flux declined, and the number of turns in the field coils also had to be reduced to make them smaller, and the readable current in the read head threatened to shrink below the detection limit. An alternative technology for reading data from a magnetic storage unit is the use of magnetoresistance; an effect first discovered by Lord Kelvin in 1856. The electrical resistance of some materials can change when they are placed in a magnetic field, depending on the alignment of the current with the field direction. The resistance of a small conductor is also easier to measure, using an externally applied voltage, than is the current induced in a very small electromagnetic generator. The resistance detection method gains the advantage over current detection when the devices are scaled down to very small sizes. IBM began developing HDD systems based on anisotropic magnetoresistance (AMR) in 1969 and brought its first one into production 14 years later, in 1983. This is a moderately rapid material-dependent technology adoption, but it is also fair to note that it was based on a discovery made 127 years earlier, and the materials involved and the basics of sensor design were already well known before IBM began its development efforts. The development time reflects the complexity of bringing new technologies to market in the high-technology sector, and the fact that the MR drives were, in reality, radically different devices than the induction current HDDs that they replaced. A revolution in the science of magnetoresistance occurred in 1988 when giant magnetoresistance (GMR) was discovered independently by teams working in France and Germany [15, 16], a discovery for which Albert Fert and Peter Gr€unberg shared the 2007 Nobel prize in physics. GMR occurs in conductive thin-film superlattices of iron and chromium with individual layers about 10 atomic layers thick, and it produces much larger changes of resistance than AMR, leading to greater sensitivity and the ability to scale magnetic memory to much smaller sizes. GMR was commercialized in IBM’s HDDs in 1997, 9 years after it was first discovered, and it quickly became the industry standard for these pervasive memory devices. IBM’s rapid adoption of GMR technology doubtless benefited from its previous work on adapting AMR to work in HDDs, but the replacement of AMR by GMR still required a significant R&D effort. The speed with which the new material systems involved in both AMR and GMR drives were adopted owes a great deal to a large economic driving force, with very strong competition among the HDD manufacturers of the time. IBM also benefitted

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from close links to between its manufacturing divisions and its own world-class basic research capacity (a program that was demonstrably capable of producing its own Nobel Prize winners).

Questek’s ferrium steels Eight years from invention to commercialization for Ferrium S53 QuesTek is a company that specializes in materials by design. Founded as a spin-off from Northwestern University in 1996, it utilizes the full range of ICME tools across the range of activities included in the MGI and AIM programs, to develop and commercialize new materials that meet specific and typically envelope pushing needs. Among its first inventions, Ferrium C61 is a high-strength and high fracture toughness carburizable steel that also has high-temperature resistance and hardenability, and Ferrium C64 has similar properties combined with superior fatigue strength. Both were patented in 1998. Ferrium S53 is a corrosion resistant, ultrahigh-strength steel for structural aerospace and other applications where it provides greater resistance to general corrosion and stress corrosion cracking, excellent resistance to fatigue and corrosion fatigue, and high hardenability relative to the incumbent materials. Its resistance to general corrosion is similar to that of stainless steel, but it has much greater fracture toughness than any applicable stainless steel alloy. It is claimed that Ferrium S53 was developed using only five prototypes over a 2-year period, and the material was patented in 2001. It was licensed for production by Carpenter Technology Corporation 6 years later, in 2007, suggesting a total invention-to-commercialization time of 8 years. QuesTek adopts several key approaches to achieve such rapid results: l

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The company remains very closely connected to cutting-edge advances in materials science and engineering, through its connection with Northwestern University. It utilizes all of the tools of ICME to reduce the amount of physical experimental work that is required. It uses processes based in traditional steelmaking practices for its ferrium alloys, largely eliminating the need to scale up new manufacturing methods. It focuses on the specific needs of end users rather than general improvements in materials properties. It partners closely both with end users and materials producers in the development of its materials.

Neodymium permanent magnet materials Six years to discover and two more years from discovery to commercialization In 1978 the world’s strongest permanent magnets were made from alloys based on samarium and cobalt, and they were on the verge of being adopted in mass-market products. General Motors, in particular, was ready to introduce a samarium-cobalt permanent magnet starter motor in some of its trucks. Those plans were shelved, however, as a result of the cobalt price spike and supply-chain concerns that were caused by antigovernment rebellions in Zaire, which was then the world’s dominant

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cobalt producer. Cobalt had become a critical material, and the search was on for a replacement. As noted in Chapter 2, one of the outcomes of the cobalt crisis was the emergence of nickel-based superalloys to replace the dominant cobalt-based ones. Magnet researchers began studying combinations of rare earth and transition metal elements mirroring the makeup of Sm-Co, and in 1984 a ferromagnetic phase with a composition typified by Nd2Fe14B was discovered simultaneously by researchers at GM, in the United States, and the Sumitomo Special Metals Corporation in Japan [17, 18]. In 1986 GM established a subsidiary company, Magnequench, to produce the new material in Anderson, Indiana, and Sumitomo also went into commercial production. The two companies have had complicated relationships and histories since then, but those are not the subjects of this chapter. In many regards, Nd2Fe14B was a better material than the samarium-cobalt formulations that it was developed to replace, but it also had a few shortcomings: l

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Nd2Fe14B has a significantly larger energy product at room temperature. Nd2Fe14B is more robust than the samarium-cobalt formulations that are subject to large production losses caused by brittle fractures during motor assembly. Nd2Fe14B avoided the supply-chain concerns associated with cobalt, although these were later replaced by concerns with the rare earths. Sm-Co magnets can sometimes be magnetized after assembly into a motor or generator, while Nd2Fe14B magnets must be magnetized before assembly. In situ magnetization has some advantages, making the Sm-Co magnets the preferred choice in some cases. The magnetic properties of Nd2Fe14B decline more rapidly as temperature increases, effectively limiting their use to about 200°C. For higher operating temperatures, Sm-Co magnets are preferred.

The rapid discovery of Nd2Fe14B can be attributed, in part, to the narrowing of the search to combinations of rare earths and transition metals, allowing much faster progress than would have been the case if a wider range of elements had been considered. The rapid adoption of Nd2Fe14B was probably facilitated by its development in industrial, rather than academic or government research laboratories: the researchers who invented it, both in Japan and the United States, had direct access to information from the end users that would have helped them to avoid a variety of blind alleys.

Aluminum-cerium alloys Three years from discovery to commercialization In 2013 the Critical Materials Institute (CMI) began working on ways to develop new uses for cerium, which is an anacritical material produced in excess of demand at bastnaesite mines such as Baotou and Mountain Pass. The underlying goal was to improve the economics of mining for rare earth elements and thereby encourage new mine development. A series of aluminum alloys based on the Al-Ce eutectic was conceived in 2014 [19], and it was quickly found to have excellent castability, flowing well into complex casting molds. This material also has good intrinsic mechanical properties, but unlike most other high-strength aluminum alloys, it derives its strength from the as-cast eutectic structure rather than heat treatments designed to create precipitates.

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The microstructure consists of an α-aluminum matrix surrounding fine dendritic Al11Ce3 intermetallic particles. The intermetallic phase is very strong, and in isolation, it has a melting point above 1100°C: Cerium is effectively insoluble in the solid phase α-aluminum matrix, and the high melting point of the intermetallic phase makes it essentially immune from coarsening up to the eutectic melting temperature. The alloy therefore retains most of its strength at elevated temperatures. The material can be enhanced with the addition of traditional precipitate-forming elements such as magnesium, silicon, copper, and/or iron that dissolve in the α-aluminum matrix and allow its strength to be enhanced by traditional solution treatment and aging. Development of the Al-Ce-X series of alloys proceeded through the efforts of a team that included a highly engaged industrial partner and three DOE national laboratories. The industry partner, Eck Industries, is an aluminum foundry that was able to obtain information from its customer base regarding their specific needs and conduct tests to demonstrate the alloy’s ability to perform as required. Lawrence Livermore National Laboratory conducted computational alloy design work, the Ames Laboratory performed combinatorial prototyping of the compositional ranges suggested by Livermore, and Oak Ridge National Laboratory provided advanced characterization of the material under stress at elevated temperatures, using neutron diffraction. The team was able to demonstrate and optimize the alloy’s ability to provide the following: l

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Superior castability in both sand and metal molds. High strength at room temperature and excellent strength retention at elevated temperatures. Excellent corrosion resistance. The ability to use castings without subsequent heat treatment, avoiding the distortion that typically accompanies it.

The first sale of an Al-Ce-X alloy for use in a commercial product occurred in 2017, in a case where avoidance of heat treatment was the key attribute. It was used to make hydrofoil blades with shapes that are highly optimized to maximize their efficiency for use in low-speed water turbines. The long, thin hydrofoils were cast to final shape avoiding subsequent machining and heat treatment, and they are used in the modular, scalable, dam-free hydropower systems made by Emrgy Inc. Further applications of this new class of alloys are in development. The development and rapid deployment of this alloy were made possible through close collaborations among of state-of-the-art computational and experimental researchers and materials production capabilities, directly connected to end users’ needs. End-user input was essential at the early stages, and advanced research capabilities from the national labs were vital at the later stages.

High-stiffness aluminum alloy One year from discovery to commercialization? In 2014 Apple introduced the iPhone 6 with an aluminum alloy body that could be bent with bare hands. In 2015 it introduced the iPhone 6S with a newly developed and patented 7000-series alloy that was much stiffer. We do not know when the development

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of the new alloy began, but we can assume a development-to-commercialization time on the order of 1 year. Apple’s stiffer aluminum alloy was invented to meet a specific commercial need. The company had been criticized for the bendability of the iPhone 6 and was probably concerned about the sales impact of releasing another similarly deformable device. On the other hand a lengthy qualification process like that of the Ford F-150 was not necessary, because of the short life spans of a smartphone and the smaller levels of product liability risk associated with case failures. The rapid transition of this material from the lab to the production line was probably enabled mostly by computationally accelerated materials design and the lack of need for a lengthy qualification process. All of the materials described in these examples had different attributes and paths to commercial success, but they illustrate some key features and distinctions that separate them from the 20-year cases cited by Eagar. Most importantly, they were developed to meet specific needs, rather than being developed because their properties or performance were expected to find revolutionary applications. All of the materials considered by Eagar provided attractive new capabilities, but there were no products that immediately needed them: their use depended on the development and commercialization of new products and devices that eventually took advantage of the new materials’ properties. Some of these fast-track materials are only used in the application for which they were initially developed, but some, notably the Nd2Fe14B magnet composition, have achieved much broader success as their new properties have come to be appreciated, modifications have been developed, and new uses have emerged: Early adoption in a single application certainly helps in this process, and this is one of the keys to fasttrack commercialization of a new material. The lessons learned from these cases have guided R&D efforts directed toward finding substitutes for rare earth elements, in the wake of the 2011 price spike.

New phosphors for fluorescent lamps In the early 2010s the primary options for energy-efficient lighting were fluorescent lamps, in the form of long tubes, formed tubes, and compact fluorescent lamps (CFLs), which were rapidly replacing incandescent light bulbs. In 2012 the US DOE projected that fluorescent lamps would be the dominant source of lighting until around 2030 (Fig. 4.17A), when light-emitting diodes (LEDs) were expected to reach a market share of 50%. With decades of market dominance anticipated, manufacturers invested in the continued development of fluorescent lamp technology. The CFL was introduced as a direct replacement for traditional incandescent lightbulbs in 1980, and the helical units that had been invented but shelved by GE in 1976 first became available from China’s Shanghai Xiangshan in 1995. Long-tube lamps grew more efficient over time, and in the early 2010s high-output T5 tubes (5/8ths of an inch in diameter) produced almost twice as many lumens per watt as the 1 in.-diameter T8 tubes that they were intended to replace. In 2011 DOE proposed to introduce rules that would have required the use of T5 lamps in commercial buildings in the United States.

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Lamp manufacturers responded to DOE’s proposed rule with concerns about their ability to meet the demand that would be created for the new lamps. They had serious reservations about the supplies of europium and terbium that were used to produce red and green light in the phosphors that coat the inside of the lamps’ glass tubes. As described in Chapter 4, fluorescent lamps work by producing ultraviolet light by ionizing atoms in the mercury vapor contained in the lamp. The ultraviolet photons are absorbed by the phosphors, where their energy promotes electrons out of their ground states to higher energy levels. The vacant ground states are then filled by electrons from higher-energy orbitals, resulting in the emission of photons of specific energy or, equivalently, wavelength. Phosphors need to be efficient absorbers of the ultraviolet photons emitted by mercury, and they need to have electron orbitals separated by energies that correspond to wavelengths in the visible range. The triband phosphors used in modern fluorescent lamps produce three distinct wavelengths of visible light: l

l

l

Red light comes from Eu3+, which is used as a dopant in Y2O3: Eu3+. Green light comes from Tb3+, typically in LaPO4: Tb3+. Blue light comes from Eu2+, either in BaMg2Al16O27: Eu2+ or (Sr,Ca,Ba,Mg)5(PO4)3 Cl: Eu2+; or from Ce3+ in LaPO4: Ce3+.

These phosphors can be mixed in different proportions to provide different color balances according to customers’ desires. They all rely on europium or terbium; supplies of which were questionable in 2011 and among the most severely affected rare earths when the price spike occurred in 2012. Among other approaches, lamp manufacturers sought alternatives to the established rare earth-based phosphors, and various efforts began to apply the design methodology shown in Fig. 5.2. With significant scientific expertise and computational facilities at its disposal, the Critical Materials Institute very quickly completed a computational survey corresponding to step 1 of the process and identified 12 materials that could act as a red phosphor without the need for europium and a similar number of alternatives for green phosphors. Barely 3 months after starting work, the team held a meeting to discuss the next steps, which were expected to involve synthesizing the 12 candidate materials to determine if the theoretical predictions of red light emission were correct. Sitting in on the meeting, a representative from GE ranked the candidate materials from the company’s perspective, rejecting 9 of the 12 for a variety of reasons including “we have tried that and it doesn’t work,” “that one is not stable in mercury vapor,” “we will not use that because of toxicity issues,” and “this one is not compatible with our process chemicals.” The rapid elimination of three quarters of the candidate materials significantly accelerated progress toward the goal of creating a new red phosphor. The reasons for which they were eliminated also provide some important lessons: l

l

We have tried that and it doesn’t work. Negative results are not always available, but they have great value. It is vitally important for them to be included in databases to avoid future generations of researchers rediscovering square wheels. That one is not stable in mercury vapor. A material that may work in many respects, such as absorbing and emitting light efficiently in the relevant wavelengths, may be incompatible with a specific device. This phosphor may work in other applications, but not in fluorescent tubes.

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Materials that are critical in multiple applications may not be replaceable by a single material in all of them. We will not use that because of toxicity issues. A material that appears to have all of the desired properties may not be salable for other reasons. This one is not compatible with our process chemicals. This reflects a preference for plug-in replacement materials over alternatives that require manufacturing process changes. In this particular case, it had become clear in mid-2013 that LED lamps would displace the fluorescents more quickly than had been anticipated. This change in the market was also reflected in DOE’s 2014 lighting market projections (Fig. 4.17B). With a declining market for fluorescent lamps, the fading prospect for recovering investments in process updates made it extremely unattractive to adopt new materials that would require any change to the manufacturing process.

The rapid elimination of candidate materials in this case shows that the materials design process can be regarded as the application of a set of filters to the pool of candidate materials, as illustrated in Fig. 5.6. This is not incompatible with the design process illustrated in Fig. 5.2, where each step in the process can be considered to be equivalent to a filter—except that the example cited here illustrates that the filters do not have to be applied in a fixed order, as might be inferred from Fig. 5.2. If a filter can eliminate a candidate material earlier in the process, then the intervening steps do not need to take place for that material, and the entire process is accelerated because the available research resources can be applied to materials that may still be viable. In general, all available filters should be applied as early as possible in the process. Most importantly, this experience teaches us that separating “applied” development from “fundamental” or “basic” research is counterproductive. In basic research, we taught to believe that all knowledge is useful and that even negative results teach us something—even if we usually don’t publish them. When we perform basic research in pursuit of a specific goal, however, it pays dividends to avoid pursuing options that will never be adopted to concentrate resources on options that might succeed both in

Materials that have the right properties

Materials that can be made

Materials worth developing

Materials that OEMs might adopt

Fig. 5.6 The materials invention process can be viewed as the application of different filters to pools of candidates. The process illustrated in Fig. 5.2 envisages these filters being applied in a fixed order, but it is better to apply all filters as early in the process as possible. Early input from the OEM avoids a great deal of experimental effort to synthesize materials that they would be unlikely to adopt.

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the lab and on the production line. The input of the end user is vital, even at the earliest stage of the progression from basic research to applied product or process development. Lacking that input, good science may get done, but it will not necessarily help to solve the problem at hand. When CMI proceeded in close collaboration with its industrial partner, with just three candidate materials, it was able to move ahead quickly and develop a new red phosphor that could be used as a process-compatible plug-in substitute for Eu3+ in fluorescent tubes, entering qualification testing with the manufacturer in less than 3 years [20].

Challenges and successes in rare earth magnets Neodymium magnets were first developed to replace samarium-cobalt magnets following the cobalt crisis of 1978, so they represent a successful application of the strategy of materials substitution. Indeed the strategy exceeded its goal in some ways, because Nd2Fe14B magnets continued the trend of ever-improving permanent magnet performance, with energy products that considerably exceeded those of the Sm-Co magnets that they replaced, as illustrated in Fig. 4.15. When the rare earth crisis arose in 2010, there were hopes that a similar breakthrough would occur, and a new, even stronger magnet would emerge. Among the candidates were bulk materials such as iron nitride (Fe16N2) or L10-ordered iron-nickel (tetrataenite) and nanostructurally controlled exchange-coupled spring magnets that depend on finely ordered mixtures of high-coercivity/low-magnetization and low-coercivity/high-magnetization phases. All of these have the theoretical potential to produce higher energy products than Nd2Fe14B. While significant efforts have been expended on each of these materials, none of them has yet proven manufacturable in sufficient volume to make an impact, so they remain as wished for rather than achieved materials, sometimes referred to as “unobtainium.” It is also unclear what might be required for such strong magnets to be handled safely in a manufacturing context, raising additional development challenges that can be expected to lengthen the time required for industrial adoption. Most of the efforts to improve on Nd2Fe14B so far have related to making the current materials more effective. One of the successes in this regard has been the reduction of the need for heavy rare earths such as dysprosium in the higher magnet grades, through the use of the grain boundary diffusion method, described in Chapter 4. Chemical analysis of magnets extracted from end-of-life HDDs and electric motors also reveals a broader manufacturing strategy of substituting rare earths for each other. Neodymium can be replaced with praseodymium in this material, and dysprosium can be replaced with terbium and/or holmium: in each case the substitute elements are adjacent in the periodic table to the nominal constituents with the result that their physical properties are similar enough for them to work interchangeably, to some extent. The composition of the magnetic phase found in a real device is more accurately expressed as 

 ð Pr, NdÞx ðTb, Dy, HoÞ1
x 2 Fe14 B

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and there are considerable variations in the ratios of Pr:Nd and Tb:Dy:Ho. Within limits, these are plug-in substitutes within the current magnet materials: Up to 25% of the neodymium is commonly replaced with praseodymium, and 100% of the dysprosium can be replaced with terbium, while holmium is typically a relatively minor substitute. The substitution of rare earth elements for each other provides for some flexibility in the manufacture of rare earth magnets, in response to short-term supply variations. It is made possible because these magnets, unlike almost all other man-made materials, are sold according to performance-based rather than composition-based specifications. If a magnet has the specified energy product, coercivity, and Curie temperature, it is salable irrespective of its composition. This type of substitutability has some interesting consequences, and it results in distinct cost savings, at least for the magnet manufacturers. As we shall see in Chapter 6, a significant part of the cost of rare earths is incurred in the process of chemically separating them from each other. REEs that are adjacent to each other in the periodic table can be especially challenging to separate, with praseodymium and neodymium being the most difficult of all. If they are left unseparated, then the cost of production is considerably reduced, especially if they can be used at their naturally occurring ratio of Pr:Nd  1:3 to 1:4 in a typical bastnaesite ore body. The chemical and physical similarity of praseodymium and neodymium allows them to be used together in many applications, where mixtures of them are sometimes referred to as “didymium.” The main reason to separate praseodymium from neodymium is to provide sources for their exclusive uses. Praseodymium must be separated for alloying with magnesium to make a high-strength lightweight structural material and for compounds that work as yellow pigments in enamels, glasses, and glazes for ceramicware. Neodymium must also be separated for use in pigments for decorative glassware, lasers, and UV-transparent glass, along with catalysts for polymerization reactions. In most other applications, Pr is broadly substitutable for Nd and is used simply by eschewing the separation of the two elements during the processing of their bastnaesite ores, resulting in significant cost and energy savings. Similar considerations apply to the HREEs, Tb, Dy, and Ho. With declining demand for Tb for green phosphors in fluorescent lamps, this element is being used increasingly in magnets, where it is probably used without ever being separated from Dy. The widespread use of performance-based specifications for magnet materials allows for magnets that fail to meet their performance targets to be magnetized to a lower level and sold as a lower grade of material, effectively using a higher grade as a substitute for a lower-grade material. This presumably occurs for magnets cut from regions of sintered magnet blocks that are less than optimally processed because of the variation in compression at the die’s edges and corners, leading to weaker texture or other effects that reduce the magnetic performance. The displacement of other uses of rare earths like praseodymium and terbium allows them to be used in magnets as plug-in substitutes for neodymium and dysprosium, respectively, even though the substitute materials are not particularly characterized by an abundance of supply. Supplanting the use of a material or an element in one

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area allows it to be used as a substitute in other applications, in an indirect form of materials substitution. While hope springs eternal that a new magnet material will emerge with higher performance than the current choices, an alternative target for indirect substitution can be identified in the ranges of energy products that are provided by the current permanent magnet materials, as illustrated in Fig. 5.7. There is a gap between the energy products of the highest-performing sintered Alnico and bonded Nd-Fe-B magnets and the lowest-performing sintered samarium and neodymium magnets. This “performance gap” extends from about 11 to 15 MGOe, and wherever a magnet with this level of performance is required, a higher-grade rare earth magnet is used instead. If “gap magnets” can be produced at low enough cost, they can reduce the demand for samarium and neodymium magnets, making more available for the highperformance applications where they are really needed. An encouraging step in this direction has been the development of printable magnet materials that are a new form of bonded magnet in which Nd2Fe14B or Sm-Co powder is embedded in a thermoplastic medium that is tailored to support a large volume fraction of the magnet powder and become formable at an elevated temperature. This allows the material to be used in additive manufacturing systems to create magnets in the sizes and shapes required for any application. A team at the Vienna University of Technology has focused on 3D printing of small magnets, thus avoiding the losses involved in cutting magnets from sintered blocks [21], and in the United States, CMI has focused on printing large magnets [22], avoiding the need to assemble industrial motors and generators using rectangular magnetic “bricks” produced by slicing sintered blocks [23] Fig. 5.8.

BH Fig. 5.7 The performance ranges of the currently available families of permanent magnet materials. Much effort has been expended on realizing materials that have higher energy products than today’s strongest magnets, but there are also opportunities in the BHmax range between 11 and 15 MGOe, which is sometimes called the “performance gap.” No existing magnets have strengths in this part of the magnet “spectrum,” and where these performance levels are needed, they are met with NdFeB or Sm-Co magnets. A material with a performance in the gap range and a reasonable cost could be an effective substitute material for the rare earth magnets.

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Fig. 5.8 An electric motor designer can exploit the characteristics of a gap magnet. On the right, we show a motor design using N28AH sintered neodymium magnets in the form of rectangular bricks that would typically be sliced from large sintered blocks. The design on the left produces equivalent motor performance using 25% less magnet material in the form of a polymer-bonded powder composite. The composite magnet material is 3D printed, allowing for a more nearly ideal shape for the motor design, requiring no cutting, so it produces less waste than the sintered magnet version. Courtesy of Cajetan Ikenna Nlebedim, Abhishek Sakar and Ajay Singh, of the Ames Laboratory’s Critical Materials Institute. This figure was created, in whole or in part, under Contract No. DE-AC02-07CH11358 with the US Department of Energy.

Although these printable gap magnets still use the same critical materials as conventionally manufactured sintered magnets, they are able to produce comparable performance with smaller quantities of them. The powder content of these materials ranges up to about 75% by volume, and their energy products are reduced from those of the pure powder materials by the square of the powder volume fraction. This loss of magnetic performance can be offset in two ways. First, the process allows magnets to be formed in ideal shapes for their applications, reducing performance losses that result from using shapes that can be cut from or built up with sintered magnet blocks. Second, the powder particles can be aligned during processing, with the application of a small magnetic field; this allows the optimum alignment of the magnetic moments with the desired magnetic field orientation [24]. Using these two effects, printed magnets have been shown to be able to replace sintered magnets in existing electric motor designs and produce increased power output for the same magnet volume or match the existing output with a smaller magnet volume—using less critical materials, in either case [25]. The system also allows for different magnetic materials to be used to optimize the properties and processability of the composite material. For example, samariumcobalt powders might be used in printed magnets in applications where sintered samarium-cobalt magnets are not used because their brittleness causes unacceptable manufacturing losses. Other new magnet powder formulations can be readily adapted to the printing method without the need to develop sintering processes [26].

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Success factors for materials substitution The adoption of a new material in any specific application depends on several factors. It helps considerably if the material can be used directly in the existing manufacturing process—if it is a “plug-in substitute” for an existing material. Truly processcompatible substitutes are rare, however, and the smaller the number of process changes that are required, the more easily a new material is adopted. The level of interchangeability between platinum and palladium in catalytic converters is an exception and not the rule. The red phosphor developed by Cherepy et al. is also exceptional in that it is process compatible with one kind of fluorescent lamp, as a result of close collaboration with the manufacturer throughout the development process. The leadfree solder invented by Miller, Anderson, and Smith melts a few degrees hotter than the lead-tin solder that it replaced, and the higher reflow temperatures called for other adjustments in the production of integrated circuits, but those were within reach and could be adopted in the designs of next-generation devices, so the new solder was quickly adopted. Tolerance of the need for process adjustments ultimately depends on the manufacturer’s ability to invest in adopting a new material. Adoption is easier in growing markets with frequent product redesigns where new processes are always under development; it is harder in stable or shrinking markets with unchanging products. The flexibility of dynamic markets adds another challenge, however: if a material is being developed to target a product with a short redesign cycle like a smartphone, then that material will have to meet some tough deadlines. Adoption of new materials is faster in applications where the qualification process is less demanding, and this is typically related to the degree of liability that a manufacturer might incur if the new material causes failures. Weaknesses in the body of a pickup truck or an airplane generate greater risk for the user than weaknesses in the body of a smartphone, so the qualification process for a new material in the pickup truck and the airplane is correspondingly more rigorous and takes more time. Qualification demands are also reduced if the product in question has a shorter life span: a product expected to last 3–5 years, like a smartphone, requires less testing than a product with a life expectancy of a decade or longer, like a pickup truck or a plane.

Target selection In seeking to reduce the demand for a critical material, it is necessary to pick specific target products rather than seeking general substitutes. This is effective because as the material is replaced in one of its applications, more of its supply becomes available for use in others. The success of a substitute material in one application can also lead to its deployment in others, but it does not guarantee its success as a general substitute. All substitutes should be regarded as being application specific and often manufacturer specific, too. Applications that are good targets for substitution of critical materials will ideally have the following characteristics: l

They consume nontrivial fractions of the available supply of the targeted critical material, so there is significant impact.

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They are growing markets, so the impact continues into the future. They have short product cycles, with new models appearing regularly, providing redesign opportunities to accommodate the new material. Short product lifetimes also tend to reduce the demands of qualification testing. The use of the new material creates relatively low levels of potential product liability, also reducing the qualification needs. The new material is as close as possible to a true plug-in substitute in the existing manufacturing process, reducing the cost of adoption.

Most target products will not meet all of these requirements, but there can be some trade-offs among them. In the case of the fluorescent lamp phosphor, the substitute material did represent a significant fraction of the current use of europium, but it was also targeted to a shrinking market with a stable product having essentially no redesign cycle. The new material, however, is very close to a true plug-in substitute for the existing REE-based red phosphor.

Effective R&D approaches Research and development efforts aimed at developing new materials are streamlined when they are focused on a single end use, especially if a manufacturer is involved from the beginning of the process. Developing a new material is, at least at the outset, a process of elimination, and the input from the manufacturer and the materials suppliers can eliminate candidate substances very quickly, curtailing the need to synthesize and test a large palette of contenders. This is illustrated as a Venn diagram in Fig. 5.6, which summarizes the experience of CMI in developing phosphors for efficient lighting: without input from an industrial partner, synthesis and testing of 12 material systems would have been undertaken. A short review by the manufacturer cut this to just three, with the other nine being eliminated for a range of technical and business reasons, reducing the projected experimental work by 75% and accelerating the R&D effort by a factor of four. Among the nine phosphors rejected at this stage, there may be some that are suitable for other applications. The commercialization of a new material is a process of downselection—the systematic rejection of unacceptable solutions—which is achieved by applying filters to the pool of candidates. Each step of the materials design process in Fig. 5.2 is a filter, but they do not need to be applied in a strict sequence as implied by this flowchart. The sooner we make a No-Go decision, the more the resources that can be applied to the remaining candidates and the early application of available filters accelerates the process. No-Go decisions are great accelerators in the materials design and deployment process, and they should be used aggressively, especially at the outset of the work.

Effective commercialization approaches In the prevailing view of commercialization, materials are first developed in the lab and then offered to the commercial sector. Progress along the path is characterized by the technology readiness level (TRL), a scheme originally developed by NASA during

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the Apollo program of the 1960s, that has been adapted by many other technology developing agencies and corporations, around the world. TRL values from one to nine are assigned to R&D projects, depending on their current stage of development. Low TRL values are associated with basic research, which is often considered the domain of research centers, increasingly in universities and national labs. Higher TRL values are associated with increasingly mature technologies, which are increasingly considered to be the domain of the commercial sector. The definitions of the nine levels in the TRL scale are given in Table 5.2. In some cases there is a general trend toward higher TRLs as we progress through the design steps shown in Fig. 5.9, but it should not be assumed that there is a one-to-one correspondence between TRLs and design steps: the design process is often cyclic rather than linear, since it returns to earlier steps as materials fail to pass the various selection filters. Table 5.2 Definitions of the technology readiness levels (TRLs). TRL

Description

Exit criteria

1

Basic principles observed and reported

2

Technology concept and/or application formulated

3

Critical function proof of concept

4

Validation in laboratory environment

5

Validation in relevant environment

6

Prototype demonstration in an operational environment

7

System prototype demonstration in an operational environment

8

Actual system completed and qualified through test and demonstration Actual system proven through successful mission operations

Peer-reviewed publication of research underlying the proposed concept/ application Documented description of the application/concept that addresses feasibility and benefit Documented analytical/experimental results validating predictions of key parameters Documented test performance demonstrating agreement with analytical predictions. Documented definition of relevant environment Documented test performance demonstrating agreement with analytical predictions. Documented definition of scaling requirements Documented test performance demonstrating agreement with analytical predictions Documented test performance demonstrating agreement with analytical predictions Documented test performance verifying analytical predictions

9

Documented operational results

Based on https://www.nasa.gov/pdf/458490main_TRL_Definitions.pdf (Accessed 3 March 2020). The “exit criteria” are the requirements for a technology to be promoted to the next TRL.

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Fig. 5.9 The involvement of research institutes and industry in the process of developing new materials. Top: the conventional view, in which there is a more or less sharp transition between work done in the research institute and the commercial entity. Bottom: the profile more often seen in cases where materials are adopted on a fast track, where there is considerable input from industry at the earliest part of the process and involvement of the research institute in the development of pilot and full-scale manufacturing processes.

The prevailing view of the transition from the lab to the factory is illustrated schematically in the upper part of Fig. 5.9, but materials that have made the transition on the fast track have more frequently taken a path more like the lower part, in which there is early involvement from industry, setting the goals and limiting the scope of the low-TRL efforts. At the “back end” of the process, there is also substantial input from the research lab, overcoming barriers to success on the production line, based on detailed understanding of the relationships between structure, properties, and processing of the material. Materials that are commercialized quickly are usually observed to benefit from interactions between researchers, materials producers, and product manufacturers at low TRLs, and extensive researcher input up to the highest TRLs, and with frequent interactions at all points in the process. Separating “research” from “development” is counterproductive when rapid solutions are needed. For several decades, materials research in national labs and universities has focused on inventing new materials with exciting properties and potential for enabling new technologies, and this has led to novel materials like high-temperature superconductors, fullerenes, quasicrystals, and conducting polymers, all of which have resulted in Nobel Prizes, along with many others that have not won quite such lofty distinctions. These discoveries have great potential in the long term and are a vital role of materials science, but it takes a long time to invent and commercialize the applications, devices, and products in which they will have make an impact. Many of the 20-year cases cited by Eagar are inventions of this type: new materials with new properties but no existing applications. Searching for a generic substitute for a critical material has more in common with the traditional discovery process than seeking an immediate substitute for a specific application in close collaboration with an engaged and motivated manufacturer. Inventing a new material, metaphorically throwing it over the lab wall in the form of a publication or a patent and expecting investors and manufacturers to find it, is not effective. The far side of that wall is where the valley of death begins.

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Lessons learned l

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Only under ideal circumstances can substitute materials be developed and adopted in a timeframe that is comparable with the timescale of materials supply-chain crises. New materials that are developed for specific applications are more likely to be adopted than materials that are developed to meet a general need. Collaborations with materials manufacturers and end users are vitally important. New materials are more readily accepted if they are process compatible with the materials they replace. A new material may not replace an old one in all of its applications, but still have impact on the overall balance of supply and demand. There can be value in new materials that do not perform as well in some regard as the ones they replace, if they offer advantages in other areas, for example, “gap” magnets. Substitution can be applied to uses of a material other than the one for which it is most critically needed, if the supplies can be diverted to the critical need. The replacement of a critical material should typically be considered to be a permanent choice that will not be reversed if or when the supply-chain crisis abates.

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[14] A.E. Smith, H. Mizoguchi, K. Delaney, N.A. Spaldin, A.W. Sleight, M.A. Subramanian, Mn3+ in trigonal bipyramidal coordination: a new blue chromophore, J. Am. Chem. Soc. 131 (2009) 17084. [15] M.N. Baibich, J.M. Broto, A. Fert, F.N. Vandau, F. Petroff, P. Eitenne, G. Creuzet, A. Friederich, J. Chazelas, Giant magnetoresistance of (001)Fe/(001) Cr magnetic superlattices, Phys. Rev. Lett. 61 (1988) 2472–2475. [16] G. Binasch, P. Grunberg, F. Saurenbach, W. Zinn, Enhanced magnetoresistance in layered magnetic-structures with antiferromagnetic interlayer exchange, Phys. Rev. B 39 (1989) 4828–4830. [17] J.J. Croat, J.F. Herbst, R.W. Lee, F.E. Pinkerton, Pr-Fe and Nd-Fe-based materials—a new class of high-performance permanent-magnets, J. Appl. Phys. 55 (1984) 2078–2082. [18] H. Onodera, Y. Yamaguchi, H. Yamamoto, M. Sagawa, Y. Matsuura, H. Yamamoto, Magnetic-properties of a new permanent-magnet based on a Nd-Fe-B compound (Neomax). 1. M€ossbauer study, J. Magn. Magn. Mater. 46 (1984) 151–156. [19] Z.C. Sims, O.R. Rios, D. Weiss, P.E.A. Turchi, A. Perron, J.R.I. Lee, T.T. Li, J.A. Hammons, M. Bagge-Hansen, T.M. Willey, K. An, Y. Chen, A.H. King, S. K. Mccall, High performance aluminum-cerium alloys for high-temperature applications, Mater. Horiz. 4 (2017) 1070–1078. [20] N.J. Cherepy, S.A. Payne, N.M. Harvey, D. Aberg, Z.M. Seeley, K.S. Holliday, I.C. Tran, F. Zhou, H.P. Martinez, J.M. Demeyer, A.D. Drobshoff, A.M. Srivastava, S.J. Camardello, H.A. Comanzo, D.L. Schlagel, T.A. Lograsso, Red-emitting manganese-doped aluminum nitride phosphor, Opt. Mater. 54 (2016) 14–21. [21] C. Huber, C. Abert, F. Bruckner, M. Groenefeld, O. Muthsam, S. Schuschnigg, K. Sirak, R. Thanhoffer, I. Teliban, C. Vogler, R. Windl, D. Suess, 3D print of polymer bonded rareearth magnets, and 3D magnetic field scanning with an end-user 3D printer, Appl. Phys. Lett. 109 (2016) 4. [22] L. Li, A. Tirado, I.C. Nlebedim, O. Rios, B. Post, V. Kunc, R.R. Lowden, E. Lara-Curzio, R. Fredette, J. Ormerod, T.A. Lograsso, M.P. Paranthaman, Big area additive manufacturing of high performance bonded NdFeB magnets, Sci. Rep. 6 (2016), 36212. [23] B.G. Compton, J.W. Kemp, T.V. Novikov, R.C. Pack, C.I. Nlebedim, C.E. Duty, O. Rios, M.P. Paranthaman, Direct-write 3d printing of NdFeB bonded magnets, Mater. Manuf. Process. 33 (2018) 109–113. [24] I.C. Nlebedim, H. Ucar, C.B. Hatter, R.W. McCallum, S.K. McCall, M.J. Kramer, M.P. Paranthaman, Studies on in situ magnetic alignment of bonded anisotropic Nd-Fe-B alloy powders, J. Magn. Magn. Mater. 422 (2017) 168–173. [25] H.A. Khazdozian, L. Li, M.P. Paranthaman, S.K. McCall, M.J. Kramer, I.C. Nlebedim, Low-field alignment of anisotropic bonded magnets for additive manufacturing of permanent magnet motors, JOM 71 (2019) 626–632. [26] K. Gandha, L. Li, I.C. Nlebedim, B.K. Post, V. Kunc, B.C. Sales, J. Bell, M.P. Paranthaman, Additive manufacturing of anisotropic hybrid NdFeB-SmFeN nylon composite bonded magnets, J. Magn. Magn. Mater. 467 (2018) 8–13.

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A material that is only available from a small number of sources inevitably suffers from supply-chain fragility, especially in the extreme case where it has only one source. In these circumstances, supplies of the material may be restricted or cut off from some or all of its end users in several different ways: l

l

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l

l

l

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Production of the material may cease because the source is depleted. Production capacity may be unable to rise in response to increasing demand. A fall in demand for a major use of the material may make production unprofitable and put the source out of business, affecting all of the material’s users. Production may be halted by natural disasters. Production may be suspended by plant failures, maintenance, environmental concerns, or workforce disputes. Production could be affected by wars or insurrections in some cases. Deliveries could be affected by trade disputes between supplier and consumer nations. The route of delivery between the source and the users of a material could be affected by conflicts, industrial action, trade disputes, or natural disasters. And, of course, producers with monopolies may exert their power to control the price of the material.

The broad scope of these risks makes increasing source diversity an important factor in reducing the criticality of a material. Almost all criticality analyses place a large emphasis on this issue, and almost all strategies for mitigating criticality include efforts to increase source diversity. There is a difference, however, between mitigating criticality and dealing with an immediate supply crisis. As with efforts to invent alternative materials, new sources for critical materials usually cannot be established on the timescale over which materials supply crises occur as it typically takes between 10 and 20 years for a mine to achieve first commercial production after work begins on a new ore body. There is no direct impact on a supply crisis from a response that relies on the development of new mines, and this is unlikely to change unless the prediction of supply crises can be extended out to a decade or two, or the development of new mines can be accelerated. Altering these timescales is a worthwhile long-term goal, but it remains unlikely that they will converge sufficiently to allow completely new sources to be established as workable responses to supply crises. Even if new mining projects do not contribute to solving immediate crises, there are indirect short-term benefits from signaling to commodity markets that solutions to the supply shortfall are being developed, and there is value in reducing the underlying materials criticality in the long term. Mine development efforts are usually much more visible than materials development efforts so they provide a clearer perception that

Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00006-2 © 2021 Elsevier Inc. All rights reserved.

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something is being done to solve a crisis, even if neither type of effort is likely to produce actual results in a timeframe corresponding to a supply crisis. The near monopoly of rare earth production by China was a major concern during the rare earth crisis and if the rare earth crisis stimulated the development of additional sources, then the criticality of the rare earths may decline and future crises will become less likely. The prices of the rare earths may also be expected to decline, for three reasons: 1. Supply increases with new mines coming into production, so the balance between supply and demand is reset. Increasing the supply/demand ratio generally results in lower prices. 2. New mines allow for new and more efficient extractive technologies to be adopted, reducing the cost of production. 3. With increasing competition between different suppliers, prices experience negative pressure.

How are mines developed? Most of the inorganic materials used in manufacturing are obtained from geological ores. Geological exploration and systematic mapping of the earth’s surface is typically the domain of national governments through their various geological survey offices such as the USGS and BGS. Surface mapping often allows exploratory geologists to infer what lies beneath the surface, but actual subsurface mapping involves the use of core drilling, ground-penetrating radar, active or passive seismic surveying, and gravimetric surveying or magnetometric surveying, and it is more complicated and costly; so information about subsurface strata is less complete in most areas, and it quickly becomes even less complete with increasing depth. Detailed mapping, including the subsurface, provides vital information on where to dig for needed resources, and this is the information that is hard to obtain on short notice, given the vast areas that may need to be surveyed. Many governments increased the funding of their geological surveys following the rare earth crisis, but the groundwork that this funding enables does not impact any immediate supply crises and only sets the stage for mine development that might be needed in the future. As we saw in Chapter 3, the known reserves of rare earths already amount to a 700-year global supply at current rates of use—one of the largest supply lifetimes projected for any material—so the purpose of further exploration for rare earth resources would appear to relate more to establishing local control than meeting global needs. The identification of a geological formation that contains materials of interest does not guarantee that they can be extracted. The establishment of an economically viable mine requires several further steps. Geological formations that contain potentially valuable minerals are called “deposits,” which may become classified as “inferred resources,” “indicated resources,” “measured resources,” or “reserves,” depending on the extent of data concerning the size, content and content distribution, and the development of plans for extracting the target mineral. An inferred resource is that part of a deposit for which the quantity of material and the grade or quality, estimated on the basis of limited geological evidence and sampling, indicate the possibility of developing a viable mine. Information about an

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inferred resource has a lower level of confidence than for an indicated resource or a measured resource. For an indicated resource the quantity, grade or quality, density, shape, and physical characteristics of the deposit have been estimated with sufficient confidence to allow for mine planning and evaluation of the economic viability of the deposit. To be considered a measured resource, the characteristics of the deposit must be known with sufficient confidence to support detailed mine planning and projection of its economic viability. A reserve is an ore deposit that has known size and can be extracted at a profit. Increasing amounts of geological data are required to establish the higher resource levels, and they require successively greater amounts of sampling and analysis, which is usually gathered by means of drilling core samples through the deposit. The standards required for resources to be considered as “indicated” or “measured” are established by regional or national organizations such as Australia’s JORC [1], Canada’s NI-43101 [2], and South Africa’s SAMREC [3]. These standards are also used outside their nominal jurisdictions by mine developers seeking investors for their projects. Trading in the stock of mining companies tend to focus on a few markets such as the Toronto Stock Exchange (TSX) and mining projects located outside Canada will typically report their resource assessments according to NI-43101 if they seek to raise capital by selling stock on the TSX. Once a deposit is established as a measured resource, it can become a proven reserve if it can be shown that the means also exist to extract minerals from it, taking into consideration all relevant mining, processing, metallurgical, infrastructure, economic, marketing, legal, environmental, social, and governmental factors. This usually requires a series of successively more detailed planning studies, including the following: l

l

l

Scoping study. This is an order-of-magnitude technical and economic study of the potential viability of the resource that includes appropriate assessments of realistically assumed factors and relevant operational issues that are necessary to demonstrate that investment in a prefeasibility study can be justified. Prefeasibility study (PFS). A PFS is a comprehensive study of technical and economic options for a mine that has reached a stage where a preferred underground mining method or open pit configuration is established and an effective method of mineral processing is determined. It includes a financial analysis that is sufficiently detailed to determine if all or part of the resource could be converted to a reserve. Feasibility study. A detailed feasibility study (DFS) is a more comprehensive technical and economic study of the selected development option for a mine, including appropriately detailed assessments of all known factors and operational issues and a detailed financial analysis to demonstrate that extraction is reasonably justified. The results of this study may serve as the basis for decisions by investors to finance the development of the project. This study is more detailed and provides a higher confidence level than that of a PFS.

Depending on the nature of the deposit, it may be more or less costly to conduct all of the surveying and analysis that is necessary to raise its status from an indicated to a measured reserve. Where cost can be saved, it is possible to perform a scoping study, PFS, and DFS on an indicated resource rather than a measured resource, and if these are all successful, the resource is designated as a probable reserve rather than a proven reserve. As shown in Fig. 6.1, promotion to a proven reserve will still require the

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Fig. 6.1 Summary of the stages in the development of a mine that follow the discovery of an ore deposit.

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Geological discovery

Ore deposit Geological assessment

Inferred resource Geological assessment

Indicated resource Geological assessment

Measured resource Scoping study

PFS

Feasibility study

Proven reserve Permits and approvals

Pilot plant construction Process testing

Process established

Permits and approvals

Full plant construction Commissioning

Permits and approvals

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Scoping study

PFS

Feasibility study

Probabe reserve

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surveying and analysis necessary to establish it as a measured reserve. Pursuing this route can avoid the cost of the additional surveying in the event that the deposit is not found to be viable, so it reduces the overall cost of reaching a negative decision. If the scoping and feasibility studies are encouraging, the additional surveying and analysis necessary to establish a measured resource must still be conducted, and the work done in the scoping study, PFS, and DFS based on the indicated resource can contribute to the final determination of the reserve status based on the measured resource. Fig. 6.1 shows the major hurdles that must be passed to establish a proven reserve and the subsequent steps to establish a working mine. Every step in this process involves considerable expenditures that are typically funded by investors who anticipate a return on their investment (ROI) when the mine comes into operation. The process is the accepted “stage gate” method of moving a mining project forward, and the standards applied to each of its steps are designed to ensure that funds are committed only when there is a clear justification to move on to the next stage. There is broad agreement among miners that fundraising is a significant ratelimiting factor in establishing a new extraction facility: recent rare earth mining projects have reportedly required investments on the order of a billion US dollars before they were able to begin production. Research and development efforts assist in establishing new sources of critical materials only if they encourage investor interest, by demonstrating a realistic opportunity to accelerate ROI. If we wish to promote the diversification of critical material production by mining new resources, we need to systematically identify and overcome the major challenges, delivering solutions in time to impact the key funding decisions. Each mine development project faces unique challenges, and the R&D efforts needed to overcome them can often be quite narrowly defined. While there are large differences between the processes of extracting different metals from their ores, resulting in different R&D needs, there are also differences between different ores for the same material and, to a significant extent, differences among different instances of the same ore: bastnaesite from Inner Mongolia differs from other bastnaesite sources in the amounts of the individual rare earth elements and the companion products that they contain, for example. The location of a deposit also introduces unique ecological and logistical challenges resulting, for example, in the decision by Lynas Corp. to transport rare earth ore from its Mount Weld mine to Malaysia for processing. The impact of R&D on establishing new mines is limited, unless it addresses the actual technical needs and investor concerns for a specific project, and delivers solutions in time to be incorporated in the design of the mine or its processing facilities.

Conventional mines The output of a conventional mine is rock, part of which is the ore which contains the intended target material, and the remainder is gangue, or waste. Although the extraction processes vary widely depending on the target material and the characteristics of the ore, several generic steps are typically involved in extracting marketable material, and these are illustrated in Fig. 6.2. In hydrometallurgical processes the ore is

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Rock

Mining Benefication Ore -sorting

Communication

Froth flotation

Hydro metallurgy

Pyrometallurgy

Digestion Roasting

Reduction

Acid dissolution Separation

Separation

Reduction

Metal

Metal

Fig. 6.2 Generic processing stages for the extraction of a metal from its ore.

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dissolved to form an aqueous solution suitable for chemical processing, while pyrometallurgical processes such as those used for iron extraction treat the ore in a blast furnace or similar facility, to produce metal directly at elevated temperatures. In the case of steelmaking, chemical separation of carbon from the iron occurs after the reduction process. Not all of the steps are included in all ore treatment processes, and hybrid hydropyrometallurgical processes are used in some cases, where the compounds precipitated from solution are reduced to metal via pyrometallurgy. The extraction of metal from ore has been part of humankind’s technological toolkit since the beginning of the Bronze Age about 5500 years ago, and all of the steps in the process have been optimized through extensive trial and error. This does not mean, however, that there is no room for further improvement, and any reduction in the cost of building or operating mines increases the likelihood that new mines will open and thus helps to diversify the sources of materials and reduce their criticality. The range of opportunities to improve the economics of mining and metal extraction, however, varies widely from metal to metal, and it is necessary to focus on the details of specific metals and mining projects of interest.

Rare earth elements REEs can be extracted from several different types of ore, including bastnaesite, monazite, xenotime, and ion-adsorption clays. Each of these presents different challenges and opportunities, but they share two important features: 1. Different REEs coexist in most ores, and they are most likely to be found together with REEs that are close to each other in the periodic table. Some ores, like bastnaesite, favor the lighter REEs while others, like ionic adsorption clays, are richer in the heavies. The colocation of REEs results from geological deposit formation processes that do not distinguish between the similar chemical characteristics of the different elements, and the similarity between the elements that promotes colocation also makes them difficult to separate by chemical means. 2. REEs bind very strongly with oxygen. They are therefore difficult to reduce to metal, and metallic REEs oxidize rapidly, or even pyrophorically, if they are not protected from the atmosphere. For this reason, most rare earths are traded and shipped in the form of their oxides.

Most of the world’s REE production now comes from bastnaesite, which is usually found as one of several components in a carbonatite matrix, and in some cases the carbonatite contains other ores, including monazite, and several forms of gangue. Carbonatite seams may also be intermixed with other minerals that contain no REE ore.

Ore sorting Where large individual rocks can be discriminated from each other, it can be advantageous to sort the ore-bearing carbonatite rocks from those that only contain gangue as the first step in the extraction process. This avoids burdening the downstream processes with handling unnecessarily large quantities of gangue and the economic value of ore sorting is enhanced if the process can be made more efficient. Automated

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processes are necessary to handle the quantities of rock produced in a typical mine, and these typically rely on sensors that can observe and discriminate between rocks as they pass by on a conveyor system. Rocks that contain ore continue in the processing stream, while rocks that are poor in ore are diverted to waste. Ore sorting can be performed on the basis of chemical analysis, using X-ray fluorescence (XRF) or laser induced breakdown spectrometry (LIBS). It can also be conducted by discriminating certain physical properties such as density, color, reflectivity, or magnetism. Selecting the best detector, optimizing its performance for the output at a specific mine and integrating it into the ore-handling system may require expert capabilities across a range of basic scientific disciplines and applied technologies. Among the many available tools, LIBS is a relatively new technique [4] that shows some promise for being able to operate at a high sampling rate and produce reliable quantitative measures of chemical composition of materials containing REEs [5]. Opportunities may exist to implement new sorting technologies, to meet the needs of specific ore bodies, to reduce the operating costs of mining them.

Comminution Comminution is the process of reducing rocks to a suitable size for further processing. It is one of the most energy-intensive steps in the extractive process, typically utilizing crushers and grinders to break up large rocks, and ball mills to reduce the fragments to powder. Because these processes are energy intensive, it is important to understand the particle size requirements for the downstream processes and reduce the minerals to the necessary size but no further [6]. The particle-size requirements are determined by two considerations: 1. Liberation of the ore from the associated gangue. Fig. 6.3 shows how different minerals are bonded together in the Bear Lodge, Wyoming, rare earth ore deposit. In this case the rare

(A)

µ

(B)

µ

Fig. 6.3 The intermixed nature of an ore deposit. This ore, from Bear Lodge, WY, includes ancylite, strontianite, and calcite, but the rare earth elements are contained principally in the ancylite. The goal of the comminution process is to separate the ancylite particles from the other minerals, which are classified as gangue. From H. Cui, C.G. Anderson, Alternative flowsheet for rare earth beneficiation of bear lodge ore, Miner. Eng. 110 (2017) 166–178.

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earth elements are contained in ancylite, which is mixed with strontianite and calcite. Ideally the crushing process will release the ancylite particles from the other materials, so the target particle size is partly determined by the size of the ancylite particles in the ore body. The sizes of these particles always fall in a distribution, so there will be some particles smaller than the average that may not be released by crushing or grinding. The goal of crushing is to release 80% of the targeted mineral. 2. Requirements of the downstream processes. The powdered material will be subjected to processes such as froth flotation and acid digestion, whose performance depends on the sizes of the powder particles.

While crushing and ball milling remain the mainstays of the mining industry, comminution by high voltage electrical pulse discharges is an emerging technology that may offer significant energy savings, although there are several challenges yet to be overcome [7].

Beneficiation The powdered material that emerges from a ball-mill is, ideally, a mixture of discrete ore and gangue particles, and the next step is to separate them from each other. Although several different techniques may be applied, the most common is froth flotation, which exploits the differing densities and surface properties of the minerals in the mixture. The method first emerged in the 19th century, when it was discovered that heavier-than-water particles could be captured by rising bubbles and suspended in the froth on top of an aerated water tank as illustrated schematically in Fig. 6.4. The process can selectively capture ore particles if appropriate frothing agents are available, and these have traditionally been found through trial and error. Most froth flotation processes currently use some kind of mineral oil as a flotation agent. Froth flotation is never a perfectly efficient process. It always collects some of the gangue with the ore and also leaves some of the ore uncollected. In many cases, powder particles are mixtures of ore and gangue that may be collected or rejected in the froth flotation process, leading to dilution of the ore concentrate if they are collected, or loss of collection efficiency if they are rejected. At a typical mine, 35% of the ore may be left in the slurry that goes to the tailings heap, and improvements in the ore capture efficiency have the potential to generate significant economic benefits. Air Ore-bearing froth

Concentrate launder

Slurry feed

Stirrer Gangue

Tailings

Fig. 6.4 Schematic illustration of the froth flotation process. A slurry of ground rock and water is fed into the bath, and bubbles collect the ore particles in the floating froth, leaving the gangue to fall to the bottom.

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The capture efficiency is affected by the details of the frothing process itself: the shape of the frothing tank, the air-flow rate, the powder particle size and size distribution, and the pH of the fluid all have an impact, and there has been renewed interest in research on these areas [8–10]. The selection of an optimal frothing agent depends on the details of the ore body being treated, and the cost of acquiring, using and recycling or disposing of the reagent. Recent research efforts have focused on the design of binder molecules that attach themselves to the ore surfaces and bind them to air bubbles. This requires detailed understanding of the mineral surfaces [11] and the use of computational molecular design techniques to accelerate the search for ligands that will bind to them [12] both of which require state-of-the-art fundamental science to be applied to the individual geological phases and compositions found at a particular mine. With this approach, it is possible to design “bespoke” binding agents for froth flotation systems, to replace the mostly generic options that are used today. Although this can produce triumphs of research and identify novel, highly optimized binding agents, the manufacture and sale of bespoke chemical reagents is challenging to chemical producers: it is always more expensive to produce small-batch chemicals, and these products tend to compete with the sales of the manufacturer’s mainstream product lines. It is important for researchers to collaborate closely with both mine developers and chemical producers to identify solutions that work well and can be produced economically. If they are to have any impact, the development of new steps in the beneficiation process must reach the demonstration or pilot stage before the overall design of the mine’s ore processing facilities is settled.

Digestion Mixed-element rare earth ores are processed hydrometallurgically. Bastnaesite or other ores are dissolved in strong acids to form a liquor that is subjected to further chemical processing. Sulfuric or hydrochloric acids are typically used to digest the ore, with the choice depending mostly on cost, the nature of the ore body, and the design of the chemical separation system. Large amounts of acid are involved in this stage of ore processing, and there is limited scope for minimizing it. In some applications, ore is roasted prior to acid digestion, and this can result in a reduction of the amount of acid that is required, albeit with a considerable energy input. Efforts to recycle acids inevitably face a hard thermodynamic reality: if the dissolution of ore in acid is driven by the reduction of Gibbs free energy, then recovering it requires energy as an input. The efficiency of such a closedloop process is determined by a Carnot cycle, and there is limited scope for reducing the energy losses after the recycling plant design is implemented.

Leaching In some cases, notably for the extraction of REEs from ionic adsorption clays, acid can be applied directly to an ore body to form a liquor, without the need for most of the steps that precede the digestion stage in Fig. 6.2. Leaching may be applied to the ore in

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the ground, it may be applied to open heaps of ore, or it may be conducted in tanks where the ore is immersed in the acid. The ability to leach directly from the ground depends on several factors including the geomorphology and porosity of the deposit that must allow the acid to flow through it and pool where it can be collected, the ability of the acid to attack and dissolve the ore minerals at ambient temperature, and the need for appropriate environmental controls. Heap leaching and tank leaching offer successively greater control of the process and reduction of its ecological risks, along with increasing operating costs. The possibility of using living organisms to leach target elements from ores has been studied for several decades [13], and it has begun to make inroads in commercial extraction facilities [14]. Bioleaching can rely on the lifecycle processes of bacteria or fungi that produce acids, to promote the release of elements from ores into aqueous solutions, and it has advantages over mineral acid leaching, including its lower impact on the environment, but it is relatively slow and may be hard to control when deployed in the field where bioleaching agents may either reproduce or die out depending on climate, season, weather, and other aspects of the local environment. Recent research has identified bacteria that are able to leach REEs and these may be able to operate economically on sources such as bastnaesite [15] and monazite [16]. Bioleaching may prove to be particularly advantageous for REE extraction if it rejects radioactive elements such as uranium and thorium that are found in some ores.

Separation The product of the digestion or leaching process is an acidic solution containing a mixture of rare earth ions along with other cations. Separating the individual elements from this liquor is one of the most challenging and energy-consuming processes in REE extraction: it is expensive in chemicals, time, and energy, in addition to requiring large capital investments. All rare earth producers currently use some form of solvent extraction (SX) process, which operates on the principle illustrated in Fig. 6.5. The solubility of a metal depends on the solvent. A particular element, or its ions, will have different affinities for different liquids and more of it may dissolve more in some solvents and less in others. If two solvents do not mix with each other so they separate, like oil and water, dissolved atoms can migrate from one solution to the other

Organic solvent

Mix

Settle

Aqueous solvent

Fig. 6.5 Basic operation of a mixer-settler solvent extraction separation unit. An aqueous solution of mixed elements is mixed with an organic solvent and then allowed to settle. One element migrates preferentially into the organic solvent, but the separation is not perfect.

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when the solvents contact each other, in response to the difference in their solubilities. Solvent extraction uses the enrichment of the target ions in one solution to extract that material from the other. For rare earth extraction the immiscible solvents are an acidic aqueous phase derived from the ore digestion process and an organic phase. In practical operation, these are introduced into mixer-settler cells where they are mechanically mixed to accelerate the exchange of solutes and then allowed to separate leaving a higher concentration of the target ion in one phase than the other. After some time the migration of atoms between the solutions results in an equilibrated state in which the concentrations in the two solutions are in a fixed ratio: KD ¼

Xorg Xaq

where KD is called the distribution coefficient, Xorg is the concentration of the target ion in the organic solvent, and Xaq is its concentration in the aqueous solvent. This ratio is a constant and is determined by the thermodynamic properties of the solutions. The concentration ratio is maintained if the volumes of the two solvents are changed, and the extraction factor takes this into account: EF ¼

Xorg Vorg Vorg ¼ KD Xaq Vaq Vaq

where Vorg and Vaq are the volumes of the organic and aqueous phases, respectively. EF is the amount of the target ion that will move from the aqueous phase to the organic phase in a single stage of the process if the organic phase starts without any of the target ions in solution. If the extraction factor is low, only a small fraction of a target element may be transferred to the organic phase in a single step, and the mixer-settler process will need to be repeated several times to achieve acceptable levels of separation. In the simplest case the aqueous phase is successively exposed to fresh batches of the organic solvent. A mass balance shows that the concentration in the aqueous phase after one exposure will be ð1Þ ð0Þ Xaq ¼ Xaq =ð 1 + E F Þ

where the superscripts indicate the concentrations after zero exposures and one exposure. After n cycles with successively lower aqueous phase concentrations ðnÞ Xaq

ð0Þ ¼ Xaq =

  EF n 1+ n

and the concentration in the aqueous phase asymptotically approaches zero as more and more stages are added and more and more of the target element is transferred to the organic phase.

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The distribution coefficients vary for different elements, and this is used to separate them from each other in the SX process. The ratio of the distribution coefficients for any pair of elements is their separation factor: if it is close to one, then the elements are not well separated in a single stage of the process and their concentrations only diverge significantly after a large number of exposures. The distribution coefficients for REEs adjacent to each other in the periodic table are very similar, especially for praseodymium and neodymium, so it takes several mixer-settler cycles to achieve reasonable levels of separation between them and large numbers of extraction stages must be used. A more common approach than applying fresh extractant in every stage of the process is the counterflow arrangement illustrated schematically in Fig. 6.6. This reduces the demand for extractant, but multiple mixer-settler stages are still needed to separate any single pair of REEs that lie adjacent to each other in the periodic table. The design of individual separation stages provides some scope for improvements: the process is optimized by adjusting the pH values of the solutions and the relative volumes of each solvent in every stage of the mixer-settler array along with other parameters. Individual control of the process parameters for each stage allows for each stage of the separation to be optimized, but any change to a single stage impacts all of the other stages in the chain so there is no simple way to ensure that the entire process is optimized. Designing a separation chain requires careful simulation and testing of a number of scenarios, and new computational process-simulation tools are beginning to assist in this process, with very encouraging results [17]. This level of optimization, however, still only addresses single points of separation along the lanthanide series of the periodic table: we are effectively addressing the use of SX to separate all of the elements below a certain atomic number from all of those above it. The separation of all of the economically recoverable rare earths from a bastnaesite mine requires successive separations at individual points in the lanthanide series. It can involve as many as 400 individual mixer-settler units to produce 6–10 individual elements at industrially useful purity. This has many consequences: l

The cost of building a separation facility depends on the number of mixer-settler units that it contains and, with the large numbers involved, it is one of the largest single capital expenditures for a rare earth producer.

Fresh organic solvent

Mixed aqueous feed solution

Fig. 6.6 Schematic counterflow system linking multiple mixer-settler units to achieve more complete separation. The separation of praseodymium from neodymium may require up to 60 units linked in this manner.

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Large amounts of water, acids and volatile organic compounds are in use, with associated costs, health and safety risks, and environmental challenges. The mixers consume large amounts of energy. The settling process can require significant amounts of time. The process works in a steady state in which the input and output concentrations are fixed, but a large volume of REEs always remains in the system. This material represents a significant financial resource locked up in an inaccessible inventory.

These factors all make the separation of rare earth elements an important target for improvement. There are several opportunities for research and development to reduce the capital expenditures (capex) and operating expenditures (opex) associated with the process, but these may also be expensive to implement. These opportunities include the following: l

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Improving separation factors by developing new solvent chemicals. Reducing the number of mixer-settler stages and the volume of material that they contain, by improved process design. Reducing the volume of material in the process by developing alternatives to mixer-settler systems.

The implementation of any of these approaches in an existing facility requires modifications to the infrastructure that will be expensive and can place a functioning, if not fully optimized, operation at risk. The process adjustments may involve the loss of the existing in-process REEs when the modifications are made, and there will be losses of production while the plant is recommissioned, debugged, and returned to steady-state operation. It is therefore less likely that existing facilities will be improved than that new and better facilities will be built to replace them. The abandonment of existing capital facilities and establishment of new ones raises the level of capex involved in such a process transformation, presenting investment challenges. Solvents with improved extraction factors may be the easiest modification to apply in existing solvent extraction facilities, allowing reuse of the mixer settlers although they will still require a redesign of the mixer-settler array configuration. Computational chemistry approaches are being developed and applied to speed the search for new extractants, with several encouraging results being reported [18]. The invention of new chemicals, however, only succeeds in diversifying the sources of a material if a chemical manufacturer will produce the material and a mine or separations plant operator will use it to expand production. Following the discovery of new extractants in the computer, their development will depend upon close collaboration with producers and end users, and this collaborative work should start even before any new materials are tested at laboratory scale: discussion with producers and consumers of the materials can avoid conducting research efforts that are not usable, even if they produce scientifically novel results. While the operation of existing mixer-settler units can be improved by the development of new solvents, the design of multiunit arrays can also produce significant improvements. These can be implemented at the level of individual element separations and also in the context of multielement separation strategies.

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The separation of individual elements is tied to the overall multielement strategy, and the approach taken early in the use of solvent extraction for the REEs was to separate the elements successively from the lights to the heavies, as illustrated in Fig. 6.7A. The separation process is tuned to separate adjacent pairs of elements by adjusting the pH of the aqueous solution. Any single separation, however, may still require several mixer-settler stages in the counterflow arrangement shown in Fig. 6.6: in some cases, as many as 60. Successive separation of the REEs in order, across the lanthanide series, is a robust and simple approach, but it has the result that all of the low-value REEs must be separated before any of the high-value HREEs can be accessed, and all of the HREEs pass through the entire array. With their higher prices, it is unattractive to keep large captive volumes of the HREEs in the SX array so alternative strategies have been introduced in which the LREEs are first separated from the HREEs and the two sets are subsequently separated in the usual successive sequences. The cascade strategy 57

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(B) Fig. 6.7 Different strategies for separating all of the rare earth elements. Each “cut” requires a multistage counterflow process as illustrated in Fig. 6.6. (A) a sequential separation sequence and (B) a cascade separation sequence, which can reduce the amounts of heavier rare earths trapped in the process.

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illustrated in Fig. 6.7B, for example, avoids having large volumes of HREE-laden solvent passing through a multistage array that separates two LREEs, reducing the amount of in-process inventory that has to be maintained. In some cases there may also be advantages to leaving groups of REEs unseparated. For example, praseodymium and neodymium are the most difficult elements of the lanthanide series to separate, requiring the largest number of mixer-settler stages of any pair of rare earths, but they can be used together in some magnets so that savings can be achieved by simply not separating them. Similar considerations apply to holmium, dysprosium, and terbium, at least in magnet applications. The design of the separation sequence either in the form of a simple sequential approach or a cascade, as illustrated in Fig. 6.7, offers some scope for optimizing the process, reducing the total number of SX stages, and reducing the amount of REEs trapped in the separation system. This requires a significant amount of computational process modeling, beyond that which is needed to optimize a counterflow mixersettler array for a single separation. While there is still scope to optimize mixer-settler SX systems, greater improvements may be achievable by developing entirely new approaches to solvent extraction. Among these a columnar continuous-flow system called RapidSX, under development by the Innovation Metals Corporation, shows some promise for increasing the rate of extraction and reducing the mass of rare earth elements trapped in the system. A membrane-based approach developed in a collaboration between Idaho National Lab and Oak Ridge National Lab has some specific advantages for applications in recycling [19] and has been licensed to Momentum Technologies, Inc. Bioseparation of LREEs from HREEs has been demonstrated using roseobacter, which adsorbs all of the REEs at pH 6.0 but releases LREEs as the pH is reduced [20]. This may provide a method for directly extracting the higher-valued HREEs, or it might be incorporated as the first stage of separation in an SX sequence such as the one illustrated in Fig. 6.7B. The challenges of SX systems applied to REEs all derive from the low selectivity of all of the separations between adjacent lanthanide elements, which calls for large numbers of mixer-settler units in the counterflow arrays used to make every single “cut” of the series. A different approach to the extraction of these and other elements from aqueous solutions is the development of ligands that bind to the target atoms with extremely high selectivity, so the separation can be achieved in a single stage. This approach has been pioneered by IBC Advanced Technologies, Inc., in a process called Molecular Recognition Technology (MRT). According to IBC, this is a highly selective, nonion exchange process, using specially designed organic chelating agents or ligands. The MRT process utilizes supramolecular, “lock and key” or “host guest,” chemistry as a basis for its high selectivity. A single ligand is developed for each target element, and it is attached to a substrate in a flow-through column. Pregnant liquor passes successively through individual MRT columns containing ligands for the target elements, and it is claimed that the system extracts a high percentage of the elements in a single pass. When the MRT ligands in a column are fully loaded, the extracted elements are recovered by flowing a stripping solution through it.

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MRT has been successfully deployed for the extraction of platinum group metals (PGMs) among others, and it is being developed for application to the rare earths in joint ventures between mining companies and IBC. MRT promises much greater simplicity and flexibility than SX in handling different feedstocks and turning “on” and “off” the production of different elements, but the crown ether compounds at the heart of the process are highly specialized and must be produced with great precision and purity in small quantities. They will inevitably be expensive, and the cost/benefit ratio of the technology and its scalability in REE extraction remain to be determined.

Separation as a stand-alone business Separation units at rare earth mines are large and complex. They are usually the mine’s largest single capital investment, one of the greatest operating costs, and embody some of the greatest risks to the production chain. The Mountain Pass mine had its own separation plant in its first incarnation, from 1952 to 2002. Molycorp built an entirely new state-of-the-art SX facility when it reopened the mine in 2012, and then struggled to get it fully operational until the company went bankrupt in 2015. Starting in 2018 the mine has been producing ore concentrate and shipping it to China for separation. There are important technical, business, and strategic issues to consider in deciding whether a mine should operate its own dedicated separation facility, operate its separation plant on a “tolling” basis, accept material for processing from other sources including mines and recycling centers, or subscribe to an outside tolling separation operation. The primary case for operating a dedicated facility rests on the ability to optimize the separation process for the ore produced by the mine, based upon a relatively consistent feedstock. Performing the separations at the mine may also avoid some of the cost of transporting ore, ore concentrate, or pregnant liquor to a stand-alone facility: if the product is separated at the mine, then little or none of the waste material from the process has to be transported, but process chemicals still have to be delivered to the mine. Transportation issues are site-specific and while Molycorp elected to separate locally at Mountain Pass, Lynas established its dedicated processing facility in Kuantan, Malaysia, 3000 miles away from the Mount Weld mine by land and sea, partly because of the poor supply of water at Mount Weld. The availability of sufficient power to run the separations facility can also be a concern and Molycorp built an electrical generating station at Mountain Pass to meet its anticipated needs. Mines in remote areas must ensure the delivery of fuel for their generators, creating further logistical challenges. The investment needs to open a new mine would be significantly reduced by the existence of a suitable tolling facility with sufficient processing capacity or the ability to expand as needed. Both the capital investment in a new plant and the debugging issues associated with it are avoided by using an existing facility. This could considerably reduce the investment barrier to new mine development within the catchment area of a processing facility.

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The use of a tolling facility, however, has a few disadvantages for the miner. The miner has no choice of processing methodology. The separation plant will be designed to use only one type of aqueous solvent, which is typically either hydrochloric acid or sulfuric acid, but certain ore bodies can produce greater or lesser value depending on the choice of the acid, either because the ore may need to be roasted in one case but not the other or because the acid may dissolve undesirable elements from the ore, or leave some potentially high-valued elements undigested. Chemically leached feedstocks and bioleached feedstocks may require some kind of pretreatment to be made compatible with the input requirements for the separation plant. A tolling facility also presents some challenges to its operator. A tolling plant is unlikely to be optimized for all of the feedstocks that it processes, unless it serves only one mine. SX arrays, in particular, can be optimized for the concentration profile of a particular feedstock, but cannot easily be reconfigured to optimize for different feedstocks and some kind of “average” configuration has to be adopted rather than a fully optimized one. The large quantity of REEs contained in the mixer settlers of a solvent extraction plant presents some operating challenges when a plant deals with different feedstock suppliers, and this may impact the business model of a tolling facility. In one business concept a tolling plant charges a fee to process a batch of feedstock, and the separated output is returned to the supplier. When the feedstock is switched over to a new source, however, the output from the SX plant continues to be from the old source until that material is flushed through the system. For an SX plant with a large volume of fully charged solvent in its system, the time lag from input to output may be large so, for example, the switch from a LREE-dominated source to a HREE-dominated source does not result in an immediate change from relatively lower-value LREE to higher-value HREE output. An alternative approach might be based on the acceptance of feedstock with assayed REE content and the delivery of an agreed mix of separated REEs or REOs back to the originator. The material delivered to the miner might not actually have come from his or her mine, but the quantities can be adjusted to reflect the input material. This approach requires the processor to operate sophisticated assay capabilities and maintain a “buffer” inventory of different REEs to adjust the amounts delivered to the provider of the source material. Yet another way to operate a multisource separation facility is for it simply to buy its source material from the mines and sell its output onward into the supply chain. This is less of a “tolling” facility and more of a traditional value-adding business. Finally, it is important to recognize that the operation of any kind of a centralized separation facility may have the effect of shifting rather than solving the problem of low source diversity. Removing the burden of building a separation plant from every new mine is likely to encourage the establishment of a greater diversity of mines, since it directly reduces the amount of investment required and the lowers risk associated with commissioning new processes. However, if a monopoly on mining is replaced by a monopoly in the REE separation process, the supply chain as a whole still has a lack of diversity, with a single point of potential failure, and the supply-risk for the rare earths is not substantially reduced.

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Unconventional sources While most inorganic materials are won from “hard rock” mines, a few, notably including lithium, are obtained from other sources including aqueous brines, mine waste heaps, and the ocean floor, and there have been suggestions of mining celestial objects such as the moon, asteroids, and other planets. Each comes with its own challenges and opportunities.

Brines Brines are aqueous liquid resources that contain dissolved minerals. They may be obtained from lakes or oceans, from groundwater (including geothermal fluids) or from process water in the waste streams of a variety of industrial processes. A large fraction of the world’s supply of lithium is obtained, today, as a companion product of potassium that is extracted from natural brines in the Atacama Desert, in the high Andean regions of Argentina and Chile, and also in China’s Tibetan Himalayas. In South America, briny groundwater is pumped up to the desert surface, while much of China’s extraction comes from Lake Zabuye, a landlocked salt lake at an elevation of 4400 m. Extraction from these sources accesses the output of millennia of natural in situ leaching by low levels of moisture percolating through mineral-bearing rocks: it by-passes nearly all of the infrastructure and energy demands associated with creating hydrometallurgical mineral liquors at traditional mines. The extraction of lithium or other critical materials from these natural brines involves two challenges: l

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The brines are dilute compared with the concentrations of minerals found in hard rock ores, so large amounts of liquid must be processed to obtain economically significant quantities. The brines contain multiple elements, so chemical separation is required. In South America the primary product of brine mining is potassium, and lithium coproduction began in the late 1990s responding to demand from aircraft manufacturers, whose use of lightweight aluminum-lithium alloys was growing, and the newly emerging rechargeable lithium ion battery industry.

Lithium producers have some natural advantages in the Andean region. The land is essentially empty, and it is a high-altitude desert with plentiful sunshine that has less of its ultraviolet radiation filtered out by the atmosphere than at lower elevations. When the brine is pumped to the surface, it is captured in large shallow ponds called salars, where the water is allowed to evaporate into some of the world’s driest air, with no energy input other than natural solar radiation. The concentration of minerals in the brine increases as the water evaporates, and after about 18 months, it is high enough for efficient extraction processing. The long evaporation time makes this batch-processing system very slow, and there is a corresponding time lag involved in increasing production rates in response to growth in demand. The salars are also vulnerable to an unusual kind of “natural disaster.” Although they are located in one of the driest regions in the world, there is still a risk of rain, and this may be exacerbated by climate change. Floods of varying

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magnitude have occurred in the Atacama Desert in 2015, 2017, and 2019, and although their impact on the production of lithium is not completely clear, it is likely that they caused setbacks in the evaporation process for at least some salars. The prices of lithium on the open market have responded accordingly. The criticality of lithium increases if rainfall affects the desert that has grown into one of the world’s principal sources. The extraction of minerals from brines relies on relatively simple chemistry. As water evaporates from the brine in a salar and the mineral concentration increases, sodium chloride is the first compound to precipitate out as a solid. The brine is then pumped into another salar where potassium chloride is precipitated and the remaining elements become more highly concentrated in the solution. After sodium and potassium are removed as chlorides, calcium hydroxide (lime) is added to remove magnesium in the form of Mg(OH)2 and sulfur in the form of CaSO4. The dissolved lithium is then reacted with sodium carbonate to produce technical-grade lithium carbonate, Li2CO3, which can be purified to meet the requirements of lithium-ion batteries by redissolving it and purifying via ion exchange. Mineral production from brines generates several products with different uses: sodium chloride, potassium chloride, and lithium carbonate; all have commercial value, but the demand for them may not correspond to the output from a brine facility. The production of an excess of one material to meet the demand for another is called the “balance problem,” and it impacts almost all materials that are brought to market through some form of companion production. Producers can obtain some flexibility in responding to this challenge by extracting some of the lithium as a phosphate, which precipitates more quickly from the brine than lithium carbonate. The phosphate is then converted to battery-grade material by electrolysis. The use of lithium has continued to grow rapidly since the development of lithiumion batteries in the 1970s and their commercialization in the 1990s. These have become a mainstay of rechargeable electric power in applications from personal electronics, to electric vehicles and static storage from home to grid-scale units. This rapid growth has resulted in lithium being designated as a critical material in several studies, even though lithium is abundant in the earth’s crust and there are many known deposits. Among the various deposits, brines are particularly attractive because of the reduction in the amount of processing that is required, compared with hard rock mines. Brines have been exploited in Chile and Argentina, but their neighbor in the Andean region, Bolivia, may have a larger resource than either of them. California’s Imperial Valley has a concentration of geothermal facilities that produce electricity from superheated groundwater below the Salton Sea, and this water, like the geologically similar Andean brines, is rich in lithium. Several research efforts have focused on the efficient extraction of lithium from brines, to reduce the processing time compared with solar evaporation, and to mitigate the balance problem.

Adsorbents An attractive option for the extraction of cations from solution is the use of adsorption systems in which the ions are selectively bound to ligands, allowing their direct removal from the brine, independently from the extraction of other solutes.

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This approach calls for a system that includes the following: l

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A ligand tailored to the target element in question. This is simpler for lithium than for the REEs, which are much more similar to each other in terms of their chemistry than lithium is to the other anions found in brine, but it is still not trivial to find suitable reagents. A substrate to support the ligand. This needs to be stable in the brine and resistant to fouling by other contaminants; it should provide a large surface area relative to its weight and volume; and it must be resilient to the mechanical rigors of interacting with fluids and being handled. A means of stripping (or “eluting”) the target material from the adsorption system without damaging the ligand or the substrate, so they can be reused.

These underlying needs can be described in thermodynamic terms. Adsorption depends on the reduction of Gibbs free energy when a lithium ion shifts changes from a solute to an adsorbate. Elution depends on the reduction of free energy when the ion goes from an adsorbate to a solute in a stripping medium. The challenge is to find an adsorbate that binds with lithium strongly enough to extract it efficiently from the brine, but not so strongly that it resists desorption in the stripping step. Finding a suitable substrate and binding the adsorbent ligand to it may be regarded as secondary challenges, but they are also nontrivial. Progress is being made in the development of systems that meet these needs for the case of cerium extraction [21], and these efforts are most likely to be effective when they are tailored to specific resources. For example, a lithium extraction facility built to access the brine from a geothermal energy plant must be able to adsorb efficiently at the temperature of the brine, which is likely to be above the ambient temperature and should be selective against all of the other elements contained in the brine. The operating temperature can have a strong effect on the chemical affinity of the adsorbent for the adsorbate, and the composition of the brine determines what other elements need to be avoided. The adsorbent system also should not interfere with the operation of the facility in which it is hosted, so the development and design of the recovery system requires close collaboration between researchers and plant operators, from the very beginning. It is not possible for researchers to invent economically effective systems without close collaboration of this kind. Adsorbents for the extraction of REEs from solution are an active topic of investigation with various ligands and substrates under investigation, although in many cases these efforts seem to be more focused on research than the development of systems to meet the needs of specific targets [22–31]. In some cases, living organisms can serve as selective adsorbents for specific cations. Just as bacteria can be used to promote the leaching of metal cations into solution, they can also be used to adsorb cations from brines. Several different bacteria have been shown to adsorb REEs on their surfaces, with varying levels of selectivity [32]. Key challenges include identifying bacteria that are able to survive in the occasionally harsh environment of the brine and also survive the elution process so they can be reused. Unlike conventional substrate-ligand adsorbents, bacteria also need to be fed with suitable nutrients. The US DOE has developed several of the necessary technologies to use the caulobacter bacillus for REE adsorption and has genetically

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engineered the bacterium to increase the number of lanthanide binding sites on its surface, thus increasing its adsorption capacity [33–37].

The ocean floor The possibility of obtaining minerals from the ocean floor came to the world’s attention when discussion about manganese nodules gained currency in the 1960s and 1970s. These had first been discovered in the Arctic Ocean in 1868 and subsequently found in most deep oceans and shallow seas, along with some lakes. They are rocks ranging from a few millimeters to 20 cm in diameter, lying on or just below the sedimentary surface, and they are made up of concentric layers of iron and manganese hydroxides along with other minerals. The composition of manganese nodules varies, but they typically comprise 27%–30% Mn, 6% Fe, 5% Si, 3% Al, 1.2%–1.5% Ni, 1%–1.4% Cu, and 0.2%–0.25% Co, and smaller quantities of various other elements. They can occur in high densities covering as much as 70% of the ocean floor in some locations and may be gathered quite simply since they are not physically attached to each other or the ocean floor. These nodules are now described as polymetallic nodules, rather than manganese nodules, reflecting the higher value, if lower content, of some of the other metals in them. In the 1960s and 1970s, a variety of government and private organizations explored the possibility of harvesting manganese nodules from the ocean floor. In 1974, exploratory work on manganese nodules provided the cover story for a CIA covert operation, in which a large vessel equipped for deep-sea exploration was deployed in an attempt to recover a soviet submarine and the secrets that it contained that lay sunken in the Pacific Ocean. The public story was that the Hughes Glomar Explorer was funded by the American industrial magnate Howard Hughes, one of whose companies built and operated the ship. With all of the contemporary interest in manganese nodules, the cover story was apparently convincing, and the actual objective and the role of the CIA only became public much later. Real projects that targeted the nodules proceeded, too, going so far as testing recovery methods in some cases, but interest in this source faded away by the end of the 1970s when the costs and complications of recovering the nodules from deep ocean floors became clear. Many technologies were developed for working at depths as great as 5000 m, and these contribute in other areas today, but the availability of land-based resources that could be accessed at lower cost eventually settled the case against harvesting these minerals from the ocean floor. Ocean-floor mining is not, however, a dead issue. Diamonds are collected from sea-bottom mud off the coast of Namibia, and sand is dredged from ocean, lake, and river bottoms around the world to meet rapidly growing demands for concrete production. The greatest depth that has yet been accessed for any commercial solid resource recovery, however, is the 200 m achieved in the offshore diamond mining efforts pursued jointly by the diamond conglomerate de Beers and the Government of Namibia: in this case the cost of operating at depth is justified by the high value of the product. Interest in new ocean-floor projects is growing, with revived interest in polymetallic nodules being driven by increases in the price of metals such as cobalt,

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and declining costs deriving from technological advances including the availability of satellite-based global positioning systems (GPS) for precise navigation, autonomous underwater robots, and many other enabling tools. Rare earth deposits have been located in some parts of the Pacific Ocean floor including waters that lie within the exclusive economic zone (EEZ) of Japan near the island of Minamitorishima, more than 1000 miles southeast of Tokyo. This deposit is in the form of ocean-floor mud, or silt, and it was first announced in 2011 [38]. More complete surveying of the resource shows that it is made up of phosphate particles containing rare earths at concentrations up to 700 parts per million (ppm). Although the total REO concentration is low compared with most landbased deposits, the mineralization is particularly rich in the most valuable REEs, the heavies, and the resource is large enough to contain amounts of some elements that would be sufficient to meet demand, at current consumption rates, for several hundred years [39]. The resource lies at a depth of about 5000 m below the ocean surface, however, considerably deeper than the current state-of-the-art for ocean floor mining. The source of the REE-bearing minerals on the ocean floor appears to be similar to those found in phosphate rocks, which were formed from the teeth and skeletons of fish and other marine creatures in ancient oceans. The phosphate resources on land were raised from the ocean floor by tectonic activity after they were formed. It is likely that material that was formed on the ocean floor and is now on land will be less expensive to obtain than material that is still at depth, although considerations other than the technology of collecting the minerals may have impacts. Notable among these are governmental concerns for national sovereignty over the resources and public concerns about the environmental and quality-of-life issues associated with mining in or near populated lands. We will discuss land-based phosphate resources later in this chapter. Seabed mining raises environmental concerns, even if it is conducted out of sight of large human populations, and these are different from the concerns that affect landbased mines. They are also regulated differently. Following the initial surge of interest in manganese nodules, the international community recognized that legal frameworks did not exist for licensing and managing mining operations in international waters. Even with the demise of immediate interest in exploiting polymetallic nodules, the International Seabed Authority (ISA) was created in 1994 under the auspices of the United Nations Convention on the Law of the Sea. It regulates deep seabed mining and is charged with ensuring the marine environment is protected from any harmful effects, which may arise from mining activities. The ecological impacts of seabed mining have been studied with increasing intensity in recent years, but large knowledge gaps still exist and the prospect of disturbing the ocean floor raises concern in the oceanographic community [40]. The site of one of the nodule-harvesting tests from the 1970s has been reinspected, and the tracks made by the dragline buckets remain visible more than 40 years later, suggesting that the ecosystem does not have a rapid mechanism to efface this kind of disturbance, although the actual impacts on marine flora and fauna have not been determined [41].

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With growing concerns about the impacts, ocean-floor mining projects will face some risk from emerging regulations that may impact their cost in ways that are not yet predictable.

Extraterrestrial mining If the ocean floor is a largely unexplored resource with many physical, technical, and regulatory challenges, space is appropriately described in the popular-culture phrase “the final frontier.” Despite the many challenges, proposals have been made, and early investments have followed, in efforts to obtain industrial minerals from asteroids, the moon, and other planets. The status of these efforts appears to be less advanced in the late 2010s than oceanfloor mining was during the first wave of interest in manganese nodules in the 1970s: there is no demonstration that any specific resource exists, and there is no conceptual technology to recover it if it does. Both of those were in place for ocean-floor mining in the 1960s and 1970s, and deep-seabed resources have not yet been realized: any utilization of extraterrestrial mineral resources is many decades away and beyond the time-horizon for effective solutions to any currently or prospectively critical materials.

Coproduction From the cases described previously, we see that a major opportunity for improving the economics of mineral extraction is often found in the separations process. This is a necessary evil, because ores are often mixed. Most of our minerals are obtained at least in some measure as coproducts or by-products from 10 primary metals [42], and others such as niobium and tantalum are mixed with each other in some of their major sources. Coproduction of different materials from a single resource provides some environmental and economic benefits. We do not need individual mines for every element in the periodic table: nobody has ever dug a mine for hafnium, because it is obtained as a by-product of zirconium, and both are obtained from titanium mines. The rare earth elements are all found together in single ores. Rhenium is a by-product of a by-product, obtained exclusively as an adjunct of molybdenum production, but only in the cases where the molybdenum is obtained as a by-product of copper. Coproduction is essentially the only economically viable means of producing small-volume materials for which the demand would not justify the capital expenditure of building a dedicated mine, even if a workable deposit could be found. The world consumed just 9 tonnes of thallium in 2017, for example, and the market for rhenium was 52 tonnes, and these quantities are too small to amortize the cost of building a mine over a reasonable timescale. For comparison, about 200 t of platinum and over 3000 t of gold were produced in the same year: the larger quantities and higher prices of these metals produce sufficient revenue to sustain dedicated mines, but a

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considerable fraction of the world supply of platinum and gold still comes from coproduction facilities that generate additional revenue from other metals. The production of different elements from the same ore body can be classified according to its economic significance to the operation of a mine: l

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Coproducts are materials extracted in comparable quantities from a single mine, as in the production of niobium and tantalum from their joint ore, coltan. By-products are materials produced in small quantities relative to a dominant host material. Rhenium is a by-product of copper (via molybdenum), and tellurium is a by-product of copper and/or gold. Companion products encompass both types of multielement extraction. The rare earth elements span a range from the light REEs that can be considered to be coproducts, to the heavies that are more akin to by-products. The term Multiple Elements from Single Sources produces an acronym that is redolent of the challenges associated with this kind of production.

All of a mine’s products contribute meaningfully to the generation of revenue, but a by-product—no matter how valuable it might be per pound or tonne—makes a negligible contribution to the profitability. By-products do not conform to the usual economic logic of supply and demand: if demand for a by-product rises, it is not necessarily advantageous for a mine operator to increase production, even if the price of the material increases very significantly. It may be possible to increase the rate of recovery of the by-product relative to the host product, but this will involve process modifications that can impact the production of the host product. When the rates of recovery of the host and companion product are not independently controllable, the only way to double the production of the by-product is to double the production of the host product, which is not viable unless the market can absorb the increased production without impacting the price. We should not expect that rhenium production will grow in response to higher demand and increasing prices, if that requires multiplying copper production by the same factor. The practical result of obtaining a material as a by-product is that the “invisible hand of the free market” does not operate as might be hoped for that material. Technological solutions to these economic challenges may be effective if they (a) reduce the risk of plant disruptions caused modifications associated with increasing the recovery of a by-product, or (b) they enable the plant to operate such that the recovery of the host product and the by-product can be controlled independently. To find ways to meet these needs, we start by classifying companion products according to the chemical phenomena that result in their colocation in the same deposit: l

l

Elements that are chemically similar may coexist as substitutional cations in the host mineral. These are sometimes considered to be impurities. For example, the most common form of bastnaesite is known as bastnaesite-(Ce), with the chemical formula (Ce,La)CO3F. The predominant cation in this mineral is cerium, but cerium ions can be replaced by lanthanum or almost any of the other REEs, with concentrations tending to decline as their atomic weight increases, as shown in Fig. 3.14. Elements that are chemically dissimilar may react with each other, along with other elements in most cases, to form a mineral. In many cases, one of the companion products is a cation

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l

Critical Materials

while the other forms an anionic complex with oxygen, as in the case of phosphates and titanates. Less common are cases in which the companion elements are bonded together without oxygen, and in the most common cases, one of them is a semimetal, as in calaverite (AuTe2), petzite (Ag3AuTe2), and sylvanite (AgAuTe4), which are found in some gold mines. Elements may form different ore minerals that are codeposited. Coltan, for example, is often described as an ore that contains both niobium and tantalum, but it is actually a mixture of two separate minerals, columbite, and tantalite that are intimately mixed together. In some cases, coal seams are comingled with fine distributions of REE-bearing minerals or lie over clay layers that contain moderate concentrations of REEs [43].

Different strategies are required for extracting each of these classes of companion products. Substitutional cations generally require extensive chemical separation processing, which is typically achieved via solvent extraction. The level of chemical similarity that allows the substitution of one element by another in the structure of a mineral also ensures that the atoms are hard to separate by chemical means, so it is likely that the solvent extraction process will require many stages to achieve marketable levels of purity. Elements that react with each other are chemically different, while those that substitute for each other are chemically similar. For this reason, compound-forming companion products may be easier to separate from each other in a single chemical process than cations that substitute for each other in a mineral compound such as bastnaesite or phosphate rock. Substitutional companion products are more common than compound-forming companion products or codeposited ores. Codeposited but distinct minerals can sometimes be sorted before comminution, they may be separated by froth flotation, or they can be extracted either by treating the mixture as a single ore and applying chemical separation methods after digestion. Coproduction is most challenging in cases where the concentration of a target material is low. Consider, for example, that the total concentration of all rare earth oxide (TREO) in the Mountain Pass bastnaesite ore is between 8% and 12%, that is, 80,000–120,000 ppm. This far exceeds the TREO concentration of phosphate rock (around 500–700 ppm) or most coal-related sources (with a maximum of around 400 ppm). It would normally be considered questionable to invest in a 400 ppm source if a 500 ppm source were available, and clearly unwise if there were a 100,000 ppm alternative. A simple calculation of the amount of source material required to produce 1 tonne of TREO reveals the scale of the challenge for low-concentration sources. Assuming that the source material has to be delivered to a processing facility using highway trucks of 20 t capacity, we can calculate the required arrival rate for those trucks for any desired production rate. In Table 6.1, we show the figures for the production of 1 tonne of TREO, assuming that the process captures 100% of the REEs in the source. If an annual production of 10,000 t is needed for the source to be economically viable, a 500 ppm resource requires a facility that can receive and process one million truckloads of material per year, which is about 2740 a day if it operates for 365 days, or 4000 every workday if it operates on a 5-day work week. Operating on a 24-h basis, every day of the year, the plant would need to receive and process an average of one truckload of raw material every 32 s.

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Table 6.1 The impact of ore grade on the quantities of source material that must be processed to produce 1 tonne of rare earth oxide. Source concentration

Tonnes of source material required to produce 1 t of TREO Truckloads (of 20 t each) required to produce 1 t of TREO

500 ppm

1000 ppm

100,000 ppm

2000

1000

10

100

50

0.5

The logistics of dilute sources are daunting, even when we only consider the needs under ideal circumstances. In real processing operations the needs are increased by a number of factors: 1. The numbers computed here assume that 100% of the mineral content is recoverable, but this is never achieved in real processes. A very good recovery rate in a real facility might be around 80%, and the drop from 100% increases the necessary rate of delivery, proportionately. 2. The numbers quoted here assume that consistent ore grades can be maintained. It is not unusual for resource owners to quote the maximum grade rather than the average grade of their ore, so some allowance must be made to account for variable, and often lower actual concentrations. 3. When trucks are loaded at high rates, the amount of incidental material included in each load tends to increase, further reducing the effective ore grade and increasing the rate at which trucks of ore must be received. The trucks may also be filled below capacity. 4. Operational downtime must be considered. Work stoppages occur for several predictable and unpredictable reasons including holidays, plant maintenance, and accidents. All of these increase the rate at which the plant must operate during the time that it is in production mode. 5. The examples shown in Table 6.1 assume a “24/7/365” work schedule. The reality is likely to be a lower utilization rate, taking account of labor contracts and regulations that may restrict work at nights and weekends. In the extreme case a plant that operates for only 8 h a day, 5 days a week excluding holidays operates for about 23% of the hours available in a “fulltime” plant, so it must work at more than four times the rate to achieve the same output. 6. Other process chemicals such as acid for digestion must also arrive, and waste material from the process must be removed and disposed of at a rate comparable to the delivery of raw material.

Taking the first five of these into account, the required delivery rate can increase significantly from the minimum of one truckload every 32 s. The sixth item adds other loading and unloading needs with similar challenges. Loading and unloading trucks at such rates requires a large amount of infrastructure that is subject to unusual levels of wear and tear relative to the value that it produces. Managing the arrival and departure of the trucks calls for sophisticated traffic management within the plant and on the roads and highways that feed it. Most of the material moving in and out of a low-concentration recovery plant has no commercial value: for this kind of resource, the logistics of moving large quantities of low-value rock are often the largest operating expense, the most likely showstopper,

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and the greatest opportunity for innovation. Without a robust solution to the logistical challenge, R&D on downstream processes such as beneficiation, digestion, and separation, represents an expense that may never be amortized. In some cases, these challenges can be ameliorated if the need to carry large amounts of material to a processing facility is avoided, or if the cost can be shared among several companion products. The delivery challenge is reduced if the resource is in a single location, and even further reduced if it can be processed there. If the resource contains multiple potential value streams, then the cost of transportation can be allocated across all of them.

Coal Coal-related resources include REE-bearing ore particles embedded in geological coal seams, REE deposits in strata adjacent to coal seams, REEs dissolved in acid mine waste, and REEs in coal combustion products such as fly ash. In all of these cases, the resource may contain valuable elements such as precious metals in addition to the REEs. They may also bear other impurities that can degrade the performance of the REEs in some of their applications, and toxic elements and compounds that must be handled in accordance with established, rules, regulations and laws. In the United States and Europe, the coal industry is under considerable economic pressure as coal-fired power plants are being displaced by lower-cost sources of electricity including natural gas and, to a growing extent, wind and solar where the costs are declining quite rapidly. Coal’s share of US electrical generation dropped from 52.8% in 1997 to 27.4% in 2018, and the number of coal-fired power plants dropped from 1024 in 2000 to 359 in 2017. The shift away from coal in the mix of energy sources has had a devastating impact on the coal industry, with several major producers entering bankruptcy in 2018 and 2019. There has been some hope that the extraction of by-products might generate revenues that can help to keep some mines in operation, but it will be difficult to attract investment in projects that are built as adjuncts to declining resources.

Coal codeposits Some coal deposits are associated with clay seams that have been found to contain hundreds of ppm of REO. These seams are usually not accessed in underground mines, but they are exposed when coal is extracted from open-pit mines. Extraction of REEs from coal-related clay has been demonstrated at lab-scale, using froth flotation to beneficiate the ore [44]. Two major challenges arise when we consider how such a process might be deployed at industrial scale. First, it will be necessary to separate the clay seams from the coal that typically overlies them and the bedrock that underlies them would be a relatively simple case: in most cases the seams are actually found in striated layers. While the clay seams are easy to recognize, they range from a few to several inches in thickness, making it difficult to collect them separately using conventional digging equipment, and especially difficult if we need to load trucks at a rate of the order of 20 t/min. If the material transported for processing contains a significant amount of gangue, then the average

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REO content is reduced and the number of truckloads required to meet a particular production target increases proportionately. As trucks are loaded ever faster, the average clay content can be expected to decline even further, and the downstream processing is burdened with ever-increasing volumes of gangue. Second, even with perfect selection of the clay layers, the low REO content of the clay requires that large volumes of material must be subjected to froth flotation to generate any significant quantity of saleable REO. This means that large capital investments in froth flotation units will be required, and the operating costs will be large because of the volume of flotation agents that will be needed. The major barrier, then, is the difficulty of handling the necessary volume of material at a rate sufficient to achieve economic viability. There is no practical application for research successes in digestion and separation methods, if the source handling problem is not solved first.

Acid mine drainage Acid mine drainage (AMD) is a result of natural processes but is often exacerbated when geological structures are disturbed by human activity. The percolation of water through certain minerals—particularly sulfides—can result in their oxidation and the formation of acids, with or without the action of acidophilic bacteria. Underground mines typically extend well below the water table so they are kept dry by constant pumping as acidified water seeps into them from above. This water is discharged into streams or holding ponds, and when a mine is abandoned, AMD accumulates in its various chambers and cavities. Since the drainage fluid can have pH values as low as 3, it is an effective leachant for the rocks through which is passes, and it may contain valuable elements such as REEs [45]. AMD is treated in several ways to neutralize the acid and remove harmful contaminants. Where it is collected in holding ponds, solid matter is allowed to settle out, the water is removed, and the remaining sludge is allowed to dry. This sludge can contain 500–1000 ppm of combined REEs, making it an attractive target for their extraction, at least insofar as it is compared with other coal by-products. The largest challenge in realizing this goal, however, is the same as for most of the other coal by-products: the raw material has to be collected from a large number of distributed sites and brought to a processing facility. Even at a relatively rich concentration of 1000 ppm of REE, massive amounts of raw material have to be delivered to make an economically viable venture, and designing a system that can load, deliver, and unload the necessary quantities of dried sludge is a profound and unsolved challenge. As with other cases the economics of extracting REEs from this source can be improved if it is possible to extract other valuable products. In this case, it may also be possible to derive some value from cleaning up an environmental problem.

Fly ash Fly ash is the solid material that escapes with the gaseous products of combustion. Industrial facilities usually capture most of their fly ash before their combustion products are released to the atmosphere and 130 Mt of fly ash were produced by coal-fired

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Critical Materials

power plants in the United States in 2014. Fly ash production is declining rapidly as other means of electrical generation displace coal, but the existing stockpile of fly ash is a resource that might last for several years if all of the processing challenges can be solved. Revenues generated from this resource may help the power producers, but they will not directly benefit coal mining companies. Fly ash contains potentially significant amounts of REO, along with precious metals and other elements of value that might be recovered for sale [46] although these compete with other sources for the same materials, and the entire process competes with other, simpler, uses for the fly ash in products such as cement, concrete, soil stabilizers, and geopolymers. The most REE-rich fly ash in the United States comes from power plants that burn certain types of Appalachian coal and it contains a concentration of around 590 ppm of TREO [47], so for the sake of a simple estimate, let’s assume that the average for all of the United States is around 300 ppm. If all of the fly ash produced in 2014 averaged 300 ppm of TREO, and it were processed with 100% efficiency, then it could generate 39,000 t of TREO, which would satisfy a significant fraction of world demand and it would represent almost twice the output of the Mountain Pass rare earth mine. Unfortunately, this resource is distributed across thousands of miles, at hundreds of sites in dry landfills and aqueous slurry ponds, or it has been released in waterways or used in construction materials. Only the material in the landfills and slurry ponds is accessible, and this can only be used if the logistical problem of delivering it to a processing facility can be solved, or if the ash can be treated at the power plants where it is produced, or the material in all of the landfills and slurry ponds can be processed in situ. While these approaches might reduce the volume of source material that must be transported, they still require process chemicals, power, equipment, and personnel to be delivered to the individual processing sites, so the logistical challenge of the dilute source cannot be easily solved. Fly ash is chemically challenging, because the fine ash particles are glassy or are covered in a glassy layer that resists many acids. Although some progress has been made in developing digestion processes for this material [48], these are unlikely to have any impact without a solution to the logistical challenges of collecting the raw material and disposing of the postprocessing residue. The production of fly-ash declines as the number of coal-fired power plants dwindles, and it is questionable whether it is worthwhile to invest in developing this source to produce rare earths or any other material.

Phosphate rock A possible target for coproduction is the phosphate industry, which produces large amounts of mined material, mostly for use in the production of fertilizers. Two hundred seventy million tonnes of phosphate rock were extracted, worldwide, in 2018, and although that rock only contains moderate concentrations of other materials, the large quantities involved, and the fact that it is already being mined and transported to processing facilities can make it an attractive resource if suitable methods of extraction can be developed. Phosphate rock originated from the teeth and skeletons of

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Mesozoic Era marine creatures in the world’s ancient oceans, such as the Tethys Sea, and it is mined around the world with the largest producing nations being China, Morocco, and the United States. The phosphate rock mined worldwide every year is estimated to contain enough REO to meet all of the world’s current annual demand. Fig. 6.8 depicts the major steps in the production of phosphoric acid from phosphate rock, for eventual use in making fertilizer. The input materials, products, and waste-streams from each step in the process are illustrated along with the percentage of the total rare earth content that is contained in each stream. No step in the process provides access to all of the REO contained in the ore. Uranium was produced as a by-product of Florida’s phosphate fertilizer industry from the late 1970s to 1998. At one point, Florida provided as much as 20% of the US supply from this source, and it is estimated that the phosphate rock in the Bone Valley still contains as much as a million tonnes of U3O8. Uranium oxide was recovered by solvent extraction from the phosphoric acid liquor that is created in the fertilizer process, and this method of production was economically viable in the 1980s, but uranium prices fell after the cold war came to an end, eventually leading to the cessation of production from this source. With uranium prices recovering again, the potential for reviving production from phosphate rock has been reassessed assuming the use of solvent extraction or ion exchange to separate uranium from the fertilizer-process phosphoric acid [49]. The authors conclude that sustained higher prices and/or technological advances that lead to lower production costs would be necessary to revive this activity. Coproduction of uranium and REEs from the phosphoric acid liquor could be economically viable where the production of either, alone, may not.

Mining Phosphate rock

Beneficiation

Sand tailing

s ~10%

Waste clay

~40%

Phosphate ore Sulfuric acid

Dissolution Sludge

Filtration

Phosphogypsum ~3 8%

Phosphoric ~ 12% acid

Fertilizer production

Fig. 6.8 Principal stages in the production of phosphoric acid from phosphate rock, showing the fractions of the total REO content that are contained in the various streams of material.

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Critical Materials

The recovery of uranium as a by-product of phosphate fertilizer production was a rare example of commercial material recovery from a dilute source. Several facets of the process contributed to its success: l

l

l

l

l

l

Uranium was a true “in-process” by-product rather than being collected from a waste stream, so logistical challenges were not a barrier. The target material was delivered to the processing facilities as a component of the main phosphate feedstock, and its extraction did not result in any additional waste material for disposal. The uranium offtake method accessed existing process fluids and did not substantially impact the production of the primary product, phosphate fertilizer. Phosphoric acid containing dissolved uranium was diverted through a solvent extraction system and then returned to the main phosphate process at the same point. The source was capable of meeting a significant fraction (around 20%) of the national demand. The producers had fixed-price offtake agreements with end-users of the uranium, essentially guaranteeing the uranium revenue-stream. The market price of uranium was high during the time the process was in place so the process was profitable to the producer and economical to the end user, even if it was not the lowestcost option. Domestic sources of this material were strategically and politically desirable during the cold war era.

Some of these features may also apply to REE extraction from phosphate rock, suggesting that they might also be a successful by-product from fertilizer production. Phosphate rock containing REO is probably a better economic prospect if it is already being delivered to established processing facilities than if it must be collected from remote locations and delivered to a new, dedicated processing plant, as in the case of the Japanese resources on the ocean floor near the Pacific island of Minamitorishima. An additional consideration in favor of this source is that phosphate production is growing robustly, in comparison with the shrinking coal industry in the United States and Europe. There are, however, some challenges in developing REE coproduction from phosphate processing plants. First the rare earths are distributed among different process streams, as indicated in Fig. 6.8, so although the resource may contain 500 ppm or more of REO, at least four different streams must be processed to access the full amount. Some of these streams are unprocessed waste as far as the phosphate process is concerned, which means that they have no value to producers of fertilizer and accessing them presents no risk to production of their primary revenue stream; this waste material is also available in large stockpiles from past mining and processing operations. However, the waste material, whether it is sand, clay, or gypsum, has to be brought to a processing facility or processed in situ, requiring a certain amount of logistical and processing infrastructure. A second challenge with phosphate rock is that it contains radioactive elements, particularly uranium and thorium, whose handling and disposal is regulated. In most phosphate processing facilities in the United States, this material is considered to be

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naturally occurring, and its disposal in process waste is allowed. If the radioactive element concentrations are enhanced during the extraction of REEs, however, they may be classified as hazardous waste that would add considerable disposal costs along with compliance expenses, regulatory overheads, and potential legal liabilities. The phosphogypsum that is removed in the filtration step of the process, for example, not only contains a significant fraction of the rare earth from the ore but also contains thorium which is radioactive. Unprocessed phosphogypsum is considered to be naturally occurring radioactive material (NORM): it produces radioactive α- and β-particles that do not penetrate skin and are only slightly elevated from background levels. This material is disposed of in large waste piles or “stacks.” Extracting the rare earths from this stream would change its classification from NORM to low-level radioactive waste that is more highly regulated, and this affects the economics of REE extraction from this stream. Selecting a strategy for extracting REEs as a by-product of phosphate fertilizer is not simple, but the principal “pros” and “cons” of each material source can be summarized as shown in Table 6.2. A full-scope regulatory and technoeconomic analysis of the different process streams, considering all of their pros and cons, is required to determine whether any of them are viable. CMI researchers and partners in Florida’s phosphate industry have embarked on efforts to downselect to one of these extraction sources and develop a processing Table 6.2 Summary of the advantages and disadvantages of extracting rare earth elements from various components of the phosphate rock process stream. Extraction target

Advantages

Disadvantages

Sand tailings (gangue)

Large stockpiles available

Waste clay (gangue)

Contains 40% of the phosphate-related REEs Large stockpiles available

Gypsum (process waste)

Contains 38% of the phosphate-related REEs Large stockpiles available

Phosphoric acid

Readily accessible as an in-process fluid Extraction of uranium in the 1970s suggests feasibility Possible coproduction of U along with REEs

Contains only 10% of the phosphate-related REEs Must be transported or processed in situ with chemicals transported to the site May contain radionuclides Must be transported or processed in situ with chemicals transported to the site May contain radionuclides Must be transported or processed in situ with chemicals transported to the site Contains radionuclides Contains only 12% of the phosphate-related REEs Only current production is accessible Part of the existing process: risk to primary product Contains radionuclides

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Critical Materials

strategy for the selected source. Although it has one of the lower REE concentrations, the phosphoric acid stream appears to be the most likely to be successful and detailed studies of extractive technologies are under way, to assess their economic viability either with or without uranium coproduction. While uranium was originally extracted from this source using solvent extraction, there have been advances in adsorbent technologies that might make this approach more attractive [50–55].

The balance problem Coproduction is an attractive approach to providing industry with many of the smallmarket specialty materials that it uses. It avoids the creation of new mines, particularly where they might be needed for low-demand products which would have small annual sales requiring long times to achieve a return on investment. A pervasive challenge with coproduction, however, is the “balance problem.” The balance of concentrations of the different elements in a geological resource is moreor-less fixed—it may vary with location within an ore body, but this variation has only been exploited in a few cases, such as the extraction of old lead from the Polaris zinc mine. If the concentrations of different elements in the ore are fixed, then the ratios of the quantities of separated elements are also fixed for any particular extraction method, although the production balance may not exactly match the concentration balance because of differences in the extraction efficiency for different elements. Zirconium and hafnium, for example, are found together in zircon (ZrSiO4) in a ratio of about 50:1, so the production of 1 tonne of hafnium is accompanied by the production (or disposal) of 50 tonnes of zirconium. Zircon, itself, is by-product of titanium extraction from ilmenite (FeTiO3) or rutile (TiO2), or tin extraction from cassiterite (SnO2), so the balance of production with titanium and tin must also be considered. While the production ratios of different elements in a resource are more-or-less fixed, the ratios of their market demand are variable. A major use for hafnium, for example, is for neutron absorbers in nuclear reactors, which also use zirconium (purified to remove the hafnium) in fuel cladding materials, which must be both corrosion resistant and neutron transparent. The demand for the two materials rises and falls in parallel, along with the fortunes of the nuclear industry. A new use for hafnium emerged in 2008 when the length scales of individual devices in integrated circuits shrank below 45 nm. The design of these circuits called for a new gate oxide material with a higher dielectric constant than the existing industry standard, SiO2, and a variety of hafnia and hafnia-silica mixtures emerged to meet the need, generating new demand for hafnium and shifting balance of demand toward hafnium. Soon after the electronics industry adopted hafnium in its products, the nuclear industry was impacted by public reaction to the Fukushima power plant disaster of 2011. Many nations moved sharply away from relying on atomic energy, and this resulted in a slump in demand for zirconium, which impacted the production of hafnium because the balance of production could not change to accommodate the shifting balance of demand. The price of hafnium doubled between 2014 and 2015.

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Minority co-products, or by-products, suffer from supply risks associated with events that impact their majority, or host coproducts. The production of rare earth elements from bastnaesite mines creates another balance problem. The relative production levels of different rare earths at the Mountain Pass mine are shown in Fig. 1.3. There is a general trend toward lower concentration as the atomic weight increases, but the most notable feature of the distribution is that about half of all of the REE in the mine is cerium. While this element has several uses, these do not generate enough demand to sustain the cerium production levels that could be achieved at Mountain Pass or Bayan Obo. The World mines an excess of cerium, to meet its needs for neodymium and other heavier, rare earths. We regard cerium as an “anacritical” material—something that is produced in excess of demand. Several strategies may be considered as means to cope with the balance problem. These include the following: 1. Develop single-product mines for at-risk by-products. This is impractical in most cases because of (a) lack of single-product deposits, and (b) if such deposits existed, they would be unattractive to investors because of the long times required to achieve ROI on lowvolume products. 2. Manage the product balance among groups of mines that have different elemental concentrations, adjusting the offtake from each mine so the overall product mix matches market demand. This is unattractive because it inevitably requires the operation of some mines at less than full capacity, impacting the ROI or the profitability for the affected facilities. 3. Implement extractive technologies that are capable of adjusting the relative production rates of different elements. This results in potentially valuable elements being sent to tailings where they may or may not be recoverable if demand shifts in their favor: such a situation requires both the physical and economic management of the tailings as a potential stockpile. This approach also requires that some of a mine’s extraction facilities may operate below their full capacity most of the time, resulting in ROI challenges for the capex invested in the individual element production lines. High-selectivity separation approaches such as Molecular Recognition Technology and other adsorption-based methods may have the capability to tailor the production rates of different companion elements independently, in some cases. 4. Leave some elements unseparated for applications in which impurities do not impact performance (e.g., in zirconium with hafnium impurities used for metallurgical applications or zirconia used for abrasives). Separate the elements only where the application demands it (e.g., zirconium for reactor fuel cladding, hafnium for neutron moderators, or high-κ dielectrics). The use of unseparated mixtures is only helpful where the minority element is anacritical: it does not help if the majority element is anacritical. 5. Separate all of the elements and maintain stockpiles of those that are anacritical. This potentially builds up significant inventories of low-value material creating large storage and management costs. 6. Find new uses for the anacritical companion products.

Some of these strategies have been applied—with varying levels of success—to solve the balance problem for rare earth mining. The most successful strategy appears to relate to adjusting the amounts of different elements that are separated in solvent extraction facilities, and there are two specific groups of REEs where this seems to be applied: these may be described as the praseodymium-neodymium nexus and the terbium-dysprosium-holmium nexus.

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Praseodymium-neodymium Pr and Nd lie adjacent to each other in the periodic table, with the atomic numbers 59 and 60, respectively. These two elements are chemically very similar, and, like all adjacent rare earths, their separation requires multiple SX stages and involves large amounts of REE residing in the process solutions, representing capital value that is inaccessibly locked up in the process capital. The SX separation factors for Pr and Nd are the lowest of any pair of adjacent REEs using current SX technology and extractants, so the number of SX stages is the largest, and the amount of inventory locked up in it is also the largest for any stage of the REE separation process. There are obvious economic advantages to avoiding the separation of Pr and Nd, and mixtures (sometimes referred to as “didymium”) can be used in some applications. While both elements have multiple individual uses, the largest single application of neodymium is in Nd2Fe14B permanent magnets, and the substitution of Pr for Nd up to a certain level does not significantly impact the performance of the magnets made from this material. In bastnaesite ores, the ratio of Pr to Nd is about 1:4, and analyses of scrapped magnets show that their Pr content varies from zero up to this level, although it is quite variable within that range. It may be inferred that rare earth producers extract praseodymium when they have a client for it as an individual element, but they provide the remainder in variable compositions of didymium to magnet manufacturers after the required Pr has been removed. This is acceptable because of the unique way in which magnet specifications are defined: while most standard materials have grade-specific compositions defined by standard-setting organizations such as ASTM, magnet grades are defined by their performance rather than their composition. If a magnet reaches a performance corresponding to N45, say, then its composition is not questioned. It is not clear at this stage, whether a reproducible variation of any aspect of magnet performance occurs with changes of Pr-content. If any performance measure exhibits a maximum in the available composition range, it might result a preferred value for the Pr-Nd ratio, but that would tend to reduce producers’ flexibility in dealing with their Pr-Nd balance problem.

Terbium-dysprosium-holmium Terbium, dysprosium, and holmium are three adjacent HREEs, with atomic numbers 65, 66, and 67, respectively. Dysprosium has traditionally been substituted at levels up to a few percent for some of the neodymium in Nd2Fe14B and although this reduces the remanant magnetization, it increases the coercivity and the energy product, and it reduces the loss of performance with increasing temperature. Terbium has similar effects on magnet strength to those of dysprosium, and holmium is slightly less desirable since it has a larger impact on the remanant magnetization, but it still has a positive impact on elevated-temperature performance. As with all adjacent rare earths, separating Tb, Dy, and Ho is difficult and requires multiple SX stages, with large amounts of material held captive in the system. Although the separation factors may be more favorable than for the Pr-Nd nexus, dysprosium is typically at least on order of magnitude more expensive than neodymium

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so the value of the process capital is very large for this group of HREEs. Supplies of separated Tb have long been required for the production phosphors that produce green light, particularly for fluorescent lamps, but this use is in decline with the growth of LEDs’ share of the lighting market. The impact of the shift in the lighting market is observed clearly for europium, which is used to produce red light: after LEDs displaced many former applications of fluorescent lamps in 2013, the price of europium dropped to about a quarter of its precrisis level. Europium has few uses other than lighting, but terbium’s loss of its green light applications was balanced by its increasing use in rare earth magnets, and its price was less impacted by the LED revolution. With lower demand for Tb in phosphors, smaller amounts of it are being separated, and larger amounts are being found alongside Dy and Ho when scrapped magnets are chemically analyzed. We infer that REE producers are opting to reduce their production balance challenges using some version of strategy #4 from the previous list. Some research efforts have attempted to apply strategy #6, specifically for the case of cerium overproduction at bastnaesite mines. When Molycorp reopened the mine at Mountain Pass, California, in 2012, it had a new separations facility that was designed to prepare all of the mine’s rare earths for sale in oxide form, and the largest-volume product was ceria. With high production volumes but low sales, the company sought to create new uses for the material, and it developed an industrial-scale water purification process called SorbX that used ceria as a consumable sorbent to remove phosphorus, heavy metals, and other contaminants from industrial waste water. Although the SorbX system was licensed to a major chemical distributor, it did not achieve significant market penetration and failed to generate any significant revenue for the mine. Also seeking to create new markets for cerium, novel, and highly effective ceriabased catalysts have been developed for at least two organic synthesis processes [56, 57], but these have not yet found any uses, partly because of a lack of investment in new plant for the materials in question. Even if the new processes had been adopted, the potential for impact on the cerium market is questionable because of the small amounts of catalyst that would be required. Compound semiconductors based on cerium sulfide have a number of promising capabilities [58, 59], but so far, there has been little or no commercial interest in developing new products that use this family of materials, and no new products have yet emerged. A somewhat more promising case has been the development of a series of alloys based on Al-Ce [60]. This material offers a number of advantages over conventional aluminum alloys, including superior strength at elevated temperature and superior corrosion resistance. It is hardened by the formation of a two-phase eutectic structure that includes α-aluminum and a high-melting intermetallic, Al11Ce3, that is resistant to coarsening. This alloy can be utilized as cast without further heat treatment, or, with the addition certain elements, it can be further strengthened like conventional agehardenable aluminum alloys. Using the material as-cast avoids the distortion that usually accompanies annealing, so that complex shapes can be maintained, and there is no need for machining to the final shape. As described in Chapter 5, this material achieved its first commercial sales very quickly, and it appears to have strong potential

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in a number of different markets. If successful in a few of these, it could eventually create a demand for tens of thousands of tonnes of cerium, per annum, which would have a significant positive impact on mines that produce excess cerium alongside the more critical rare earth elements.

Progress since the rare earth crisis As the rare earth crisis unfolded and prices peaked in 2012, as much as 98% of the world’s supply of these essential elements came from China. Three significant mines are now in production outside the Peoples’ Republic: l

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Lynas Corporation’s Mount Weld mine in Australia began production in 2011, with significant financial backing from Japan. Ore from the mine is shipped to Malaysia for processing. During the postcrisis price collapse, Lynas suspended the separation of HREEs as it restructured to remain profitable. The Mountain Pass mine in California reopened in 2012, closed in 2015, and restarted again in 2018. It produces ore concentrate that is now shipped to China for processing. Northern Minerals began pilot production at its Brown’s Range mine in Western Australia in 2018, with separation facilities located on site, producing rare earth carbonates. This mine produces heavy rare earths such as dysprosium, from the phosphate mineral xenotime.

By 2019, China’s share of the world’s REE mine production had fallen to around 62%, but it controls a larger portion of the REE separation capacity, including the processing of all of the output from Mountain Pass. Several other mine development projects have moved forward, if somewhat haltingly, and have achieved different stages of development. These will have some advantages when the investment climate for rare earth production improves and will be positioned to go into production somewhat more quickly. Efforts to develop new rare earth separation facilities are under way in various locations, some in conjunction with mines, others as stand-alone facilities. Notably in this regard, Ucore corporation collaborated with IBC to develop an MRT-based REE separations facility for its proposed mine at Bokan Mountain in Alaska, although this collaboration has ended. IBC is now working with Materion, Inc., with a view to offering an MRT-based tolling service. The state of the art in beneficiation and separation has advanced as a result of R&D efforts that were stimulated by the rare earth crisis. Ways to improve existing technologies have been developed, and entirely new methods have also been tested, but these are most likely to be implemented in new facilities since replacing or retrofitting them into existing plant is challenging. Although exceptions exist, the surge of innovation in this area is quite poorly linked to implementation, as compared with the effectiveness of technology substitution and material substitution. This is mostly a result of the long timescale for development of a new mine or processing facility: design decisions may be made as long as 20 years before these operations come on line, and research discoveries that occur in the intervening time typically cannot be incorporated without making changes that may require revisions to the project’s feasibility plan. Change adds risk and delays the progress of a mining or separations project, with the result

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that most of these projects eventually come on line with processing facilities that lag the state of the art to some degree. There is always a mismatch between the timescales of industrial change and scientific research. In most cases industry moves at a pace that outstrips the ability of science to respond; in the production of primary materials, however, R&D moves ahead faster than industrial projects, and this generates different challenges in building collaborations between research labs and industrial partners.

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Financing is a major rate-limiting step for starting a new mine. Reducing the capex requirements for a mine reduces the investment need. – Process improvements can have a big impact. For the rare earths, separations technologies are an important target. – Process technology improvement accelerates after a price spike. – Every new mine that comes on line operates with obsolete technology. Reducing opex accelerates return on investment. – This attracts investors and accelerates financing. Research and development only encourage the establishment of new sources if they impact the cost of building and operating an actual mine. Process improvements have to be incorporated in the design of the mine, and they make no impact if they are provided after the design is implemented. Research and development are often out of phase for innovations in extractive technologies. Dilute sources are challenging because of the large volumes of feedstock that must be transported and processed to produce small volumes of saleable product. Access to many materials is enabled only through coproduction with other materials. Despite the pervasiveness of coproduction, the economic and technological systems and their interactions are poorly understood and generally not managed very systematically. – Flexibility may be as valuable as efficiency of extraction in coproduction situations, but the trade-off is not quantified. – Early revenue streams are essential during the start-up of all new mines: new coproduction facilities need to focus on their highest revenue-generating products upon start-up. – It is important to find uses for all of a mine’s products and/or manage its production and inventory levels according to market needs and opportunities. The demand for materials can shift on a timescale that is shorter than the development of a new mine. The prices of materials can decline when new sources become available, and this may affect the viability of the supply chain. Improving the diversity of primary sources for a material may have little impact on its criticality if a lack of diversity remains in any other aspect of its supply chain.

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[2] Canadian Institute of Mining Metallurgy and Petroleum, National Instrument 43-101: Standards of Disclosure for Mineral Projects, http://web.cim.org/standards/MenuPage. cfm?sections¼177,181&menu¼229. (Accessed 16 June 2016). [3] Samcodes Standards Committee, The South African Code for the Reporting of Exploration Results, Mineral Resources and Mineral Reserves, 2016, http://www.samcode.co.za (Accessed 16 June 2016). [4] R.E. Russo, A.W. Miziolek, Laser-induced breakdown spectroscopy (LIBS) fundamentals and applications preface, in: W. Miziolek, V. Palleschi, I. Schechter (Eds.), Laser-Induced Breakdown Spectroscopy, Cambridge University Press, Cambridge, UK, 2006, pp. XV–XVII. [5] M.Z. Martin, R.V. Fox, A.W. Miziolek, F.C. Delucia, N. Andre, Spectral analysis of rare earth elements using laser-induced breakdown spectroscopy, in: M.A. Druy, R. A. Crocombe, D.P. Bannon (Eds.), Next-Generation Spectroscopic Technologies VIII, SPIE, Bellingham, WA, 2015. [6] H. Cui, C.G. Anderson, Alternative flowsheet for rare earth beneficiation of bear lodge ore, Miner. Eng. 110 (2017) 166–178. [7] F.N. Shi, E. Manlapig, W.R. Zuo, Progress and challenges in electrical comminution by high-voltage pulses, Chem. Eng. Technol. 37 (2014) 765–769. [8] R.Q. Honaker, J. Groppo, R.H. Yoon, G.H. Luttrell, A. Noble, J. Herbst, Process evaluation and flowsheet development for the recovery of rare earth elements from coal and associated byproducts, Miner. Metall. Process. 34 (2017) 107–115. [9] C.L. Owens, G.R. Nash, K. Hadler, R.S. Fitzpatrick, C.G. Anderson, F. Wall, Zeta potentials of the rare earth element fluorcarbonate minerals focusing on bastnasite and parisite, Adv. Colloid Interf. Sci. 256 (2018) 152–162. [10] W. Zhang, R. Honaker, J. Groppo, Concentration of rare earth minerals from coal by froth flotation, Miner. Metall. Process. 34 (2017) 132–137. [11] S.G. Srinivasan, R. Shivaramaiah, P.R.C. Kent, A.G. Stack, A. Navrotsky, R. Riman, A. Anderko, V.S. Bryantsev, Crystal structures, surface stability, and water adsorption energies of La-bastnasite via density functional theory and experimental studies, J. Phys. Chem. C 120 (2016) 16767–16781. [12] F. Zahariev, N. De Silva, M.S. Gordon, T.L. Windus, M. Dick-Perez, Parfit: a pythonbased object-oriented program for fitting molecular mechanics parameters to ab initio data, J. Chem. Inf. Model. 57 (2017) 391–396. [13] T. Rohwerder, T. Gehrke, K. Kinzler, W. Sand, Bioleaching review part a: progress in bioleaching: fundamentals and mechanisms of bacterial metal sulfide oxidation, Appl. Microbiol. Biotechnol. 63 (2003) 239–248. [14] G.J. Olson, J.A. Brierley, C.L. Brierley, Bioleaching review part B: progress in bioleaching: applications of microbial processes by the minerals industries, Appl. Microbiol. Biotechnol. 63 (2003) 249–257. [15] L.M. Zhang, H.L. Dong, Y. Liu, L. Bian, X. Wang, Z.Q. Zhou, Y. Huang, Bioleaching of rare earth elements from bastnaesite-bearing rock by actinobacteria, Chem. Geol. 483 (2018) 544–557. [16] H. Fathollahzadeh, J.J. Eksteen, A.H. Kaksonen, E.L.J. Watkin, Role of microorganisms in bioleaching of rare earth elements from primary and secondary resources, Appl. Microbiol. Biotechnol. 103 (2019) 1043–1057. [17] K.L. Lyon, V.P. Utgikar, M.R. Greenhalgh, Dynamic modeling for the separation of rare earth elements using solvent extraction: predicting separation performance using laboratory equilibrium data, Ind. Eng. Chem. Res. 56 (2017) 1048–1056.

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[18] B.W. Mccann, N. De Silva, T.L. Windus, M.S. Gordon, B.A. Moyer, V.S. Bryantsev, B. P. Hay, Computer-aided molecular design of bis-phosphine oxide lanthanide extractants, Inorg. Chem. 55 (2016) 5787–5803. [19] D. Kim, L. Powell, L.H. Delmau, E.S. Peterson, J. Herchenroeder, R.R. Bhave, A supported liquid membrane system for the selective recovery of rare earth elements from neodymium-based permanent magnets, Sep. Sci. Technol. 51 (2016) 1716–1726. [20] W.D. Bonificio, D.R. Clarke, Rare-earth separation using bacteria, Environ. Sci. Technol. Lett. 3 (2016) 180–184. [21] M.P. Paranthaman, L. Li, J.Q. Luo, T. Hoke, H. Ucar, B.A. Moyer, S. Harrison, Recovery of lithium from geothermal brine with lithium-aluminum layered double hydroxide chloride sorbents, Environ. Sci. Technol. 51 (2017) 13481–13486. [22] G.S. Lee, M. Uchikoshi, K. Mimura, M. Isshiki, Distribution coefficients of La, Ce, Pr, Nd, and Sm on Cyanex 923-, D2ehpa-, and Pc88a-impregnated resins, Sep. Purif. Technol. 67 (2009) 79–85. [23] S.R. Dave, H. Kaur, S.K. Menon, Selective solid-phase extraction of rare earth elements by the chemically modified amberlite Xad-4 resin with azacrown ether, React. Funct. Polym. 70 (2010) 692–698. [24] S.S. Tong, S.J. Zhao, W.H. Zhou, R.G. Li, Q. Jia, Modification of multi-walled carbon nanotubes with tannic acid for the adsorption of La, Tb and Lu ions, Microchim. Acta 174 (2011) 257–264. [25] A.R. Turker, Separation, preconcentration and speciation of metal ions by solid phase extraction, Sep. Purif. Rev. 41 (2012) 169–206. [26] J. Roosen, K. Binnemans, Adsorption and chromatographic separation of rare earths with EDTA- and DTPA-functionalized chitosan biopolymers, J. Mater. Chem. A 2 (2014) 1530–1540. [27] T. Ogata, H. Narita, M. Tanaka, Adsorption behavior of rare earth elements on silica gel modified with diglycol amic acid, Hydrometallurgy 152 (2015) 178–182. [28] I. Anastopoulos, A. Bhatnagar, E.C. Lima, Adsorption of rare earth metals: a review of recent literature, J. Mol. Liq. 221 (2016) 954–962. [29] W.A.W. Ibrahim, H.R. Nodeh, M.M. Sanagi, Graphene-based materials as solid phase extraction sorbent for trace metal ions, organic compounds, and biological sample preparation, Crit. Rev. Anal. Chem. 46 (2016) 267–283. [30] S. Iftekhar, V. Srivastava, M. Sillanpaa, Synthesis and application of LDH intercalated cellulose nanocomposite for separation of rare earth elements (REES), Chem. Eng. J. 309 (2017) 130–139. [31] F.P. Zhao, E. Repo, Y. Song, D.L. Yin, S. Ben Hammouda, L. Chen, S. Kalliola, J.T. Tang, K.C. Tam, M. Sillanpaa, Polyethylenimine-cross-linked cellulose nanocrystals for highly efficient recovery of rare earth elements from water and a mechanism study, Green Chem. 19 (2017) 4816–4828. [32] N. Das, D. Das, Recovery of rare earth metals through biosorption: an overview, J. Rare Earths 31 (2013) 933–943. [33] Y. Fujita, J. Barnes, A. Eslamimanesh, M.M. Lencka, A. Anderko, R.E. Riman, A. Navrotsky, Effects of simulated rare earth recycling wastewaters on biological nitrification, Environ. Sci. Technol. 49 (2015) 9460–9468. [34] D.M. Park, D.W. Reed, M.C. Yung, A. Eslamimanesh, M.M. Lencka, A. Anderko, Y. Fujita, R.E. Riman, A. Navrotsky, Y.Q. Jiao, Bioadsorption of rare earth elements through cell surface display of lanthanide binding tags, Environ. Sci. Technol. 50 (2016) 2735–2742.

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[35] D.W. Reed, Y. Fujita, A.L. Daubaras, Y. Jiao, V.S. Thompson, Bioleaching of rare earth elements from waste phosphors and cracking catalysts, Hydrometallurgy 166 (2016) 34–40. [36] V.S. Thompson, M. Gupta, H.Y. Jin, E. Vahidi, M. Yim, M.A. Jindra, V. Nguyen, Y. Fujita, J.W. Sutherland, Y.Q. Jiao, D.W. Reed, Techno-economic and life cycle analysis for bioleaching rare-earth elements from waste materials, ACS Sustain. Chem. Eng. 6 (2018) 1602–1609. [37] P.J. Antonick, Z.C. Hu, Y. Fujita, D.W. Reed, G. Das, L.L. Wu, R. Shivaramaiah, P. Kim, A. Eslamimanesh, M.M. Lencka, Y.Q. Jiao, A. Anderko, A. Navrotsky, R.E. Riman, Bioand mineral acid leaching of rare earth elements from synthetic phosphogypsum, J. Chem. Thermodyn. 132 (2019) 491–496. [38] Y. Kato, K. Fujinaga, K. Nakamura, Y. Takaya, K. Kitamura, J. Ohta, R. Toda, T. Nakashima, H. Iwamori, Deep-sea mud in the pacific ocean as a potential resource for rare-earth elements, Nat. Geosci. 4 (2011) 535–539. [39] Y. Takaya, K. Yasukawa, T. Kawasaki, K. Fujinaga, J. Ohta, Y. Usui, K. Nakamura, J. I. Kimura, Q. Chang, M. Hamada, G. Dodbiba, T. Nozaki, K. Iijima, T. Morisawa, T. Kuwahara, Y. Ishida, T. Ichimura, M. Kitazume, T. Fujita, Y. Kato, The tremendous potential of deep-sea mud as a source of rare-earth elements, Sci. Rep. 8 (2018) 5763. [40] K.A. Miller, K.F. Thompson, P. Johnston, D. Santillo, An overview of seabed mining including the current state of development, environmental impacts, and knowledge gaps, Front. Mar. Sci. 4 (2018) 418. [41] D.O.B. Jones, S. Kaiser, A.K. Sweetman, C.R. Smith, L. Menot, A. Vink, D. Trueblood, J. Greinert, D.S.M. Billett, P.M. Arbizu, T. Radziejewska, R. Singh, B. Ingole, T. Stratmann, E. Simon-Lledo, J.M. Durden, M.R. Clark, Biological responses to disturbance from simulated deep-sea polymetallic nodule mining, PLoS One 12 (2017) e0171750. [42] N.T. Nassar, T.E. Graedel, E.M. Harper, By-product metals are technologically essential but have problematic supply, Sci. Adv. 1 (2015) e1400180. [43] S.F. Dai, I.T. Graham, C.R. Ward, A review of anomalous rare earth elements and yttrium in coal, Int. J. Coal Geol. 159 (2016) 82–95. [44] W.C. Zhang, X.B. Yang, R.Q. Honaker, Association characteristic study and preliminary recovery investigation of rare earth elements from fire clay seam coal middlings, Fuel 215 (2018) 551–560. [45] G. Naidu, S. Ryu, R. Thiruvenkatachari, Y. Choi, S. Jeong, S. Vigneswaran, A critical review on remediation, reuse, and resource recovery from acid mine drainage, Environ. Pollut. 247 (2019) 1110–1124. [46] S.F. Dai, X.Y. Yan, C.R. Ward, J.C. Hower, L. Zhao, X.B. Wang, L.X. Zhao, D.Y. Ren, R. B. Finkelman, Valuable elements in Chinese coals: a review, Int. Geol. Rev. 60 (2018) 590–620. [47] R.K. Taggart, J.C. Hower, G.S. Dwyer, H. Hsu-Kim, Trends in the rare earth element content of US-based coal combustion fly ashes, Environ. Sci. Technol. 50 (2016) 5919–5926. [48] J.F. King, R.K. Taggart, R.C. Smith, J.C. Hower, H. Hsu-Kim, Aqueous acid and alkaline extraction of rare earth elements from coal combustion ash, Int. J. Coal Geol. 195 (2018) 75–83. [49] H. Kim, R.G. Eggert, B.W. Carlsen, B.W. Dixon, Potential uranium supply from phosphoric acid: a US analysis comparing solvent extraction and ion exchange recovery, Res. Policy 49 (2016) 222–231.

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Mitigating criticality, part III: Improving the stewardship of existing supplies

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Reuse and recycling are potential means of diversifying our sources for materials and thus reducing their criticality. Along with the avoidance of waste, these potentially offer attractive options from the perspective of sustainability, but our main focus here is their impact on criticality. If we do not engage in reuse and recycling, the life cycle of a material will always start in a mine and end in a landfill where its concentration is likely to be smaller than it was in the mine from which it originally came, so the use of landfills as mines has all of the dilute source challenges that were discussed in Chapter 6. The target material will also be embedded in a much more complex and chemically diverse matrix, so it has all of the coproduction challenges, too, probably at a greater level of complexity. Environmental controls may make critical materials in landfills harder to access than those in geological resources, because of their proximity to population centers and the ecological risks that can result from disturbing landfills. It is therefore desirable to divert objects that contain critical materials from waste streams before they reach landfills and return them to use through processes that have been described collectively as “the circular economy.” When the rare earth crisis erupted, one of the first responses was Japan’s announcement of a national effort to meet its needs for critical materials through a recycling program called “Urban Mining.” Around the world, proponents of green economic principles continue to promote reuse and recycling as a solution to material shortages, and manufacturers have turned to recycling to mitigate some of their supply-chain shortfalls while promoting their efforts to an increasingly ecologically conscious public. Recycling can be considered to be an unconventional source for critical materials, so this topic has much in common with Chapter 6 but there are additional features and challenges that we address here. In this chapter, we consider the extent to which reuse, recycling, and other supply stewardship efforts are able to reduce the criticality of materials, what barriers impede such efforts, and where research and development can make a positive impact.

Urban mines versus conventional mines The basis of a conventional mine is a mineral resource that is typically contiguous, located within a bounded geographical area, is rich in the target material and consistent in composition. An urban mine relies on resources such as end-of-life products Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00007-4 © 2021 Elsevier Inc. All rights reserved.

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that may be geographically discontinuous, widely dispersed, variable in form, poorer in the target material, and inconsistent in composition. They may also be inconsistent in their availability over time. Although conventional mines frequently have scope for coproduction, particularly to access critical materials, urban mines almost always contain more than a single material of value, even when they only provide noncritical materials. If urban mining is analogous to conventional mining, it is like a mine where the ore is contained in discrete rocks of different minerals, distributed widely across the landscape—often far apart from each other—that must be identified and collected individually. Urban mining has the advantage that the target materials are on the surface of the earth, rather than below it, but they are not necessarily easy to collect, and large amounts of energy may be expended in the collection process compared with the extraction of ore from a mine. Geological mines can have processing facilities colocated with the mineral source, or they will have a single logistical link to a processing facility, based on bulk transport. The feedstock sources for urban mines are always distributed, and they rely on complex logistical networks for delivery to processing facilities. In a conventional mining operation, the extraction process is consistent because the feedstock is always the same, so the extractive technologies can be optimized and improved steadily over time. In urban mining the feedstock is usually more variable, which leads to challenges in optimizing the extraction process, although there are certainly some cases of highly consistent recyclable devices such as fluorescent lamps and hard disk drives that contain critical materials and might appear to make attractive recycling targets. The recovery of manufacturing scrap is in some respects more akin to conventional mining than is end-of-life urban mining: The target material may be obtained in a single location, and it is consistent in its composition. It is a better source than a conventional mine because the material has already had its value increased through several costly and energy-intensive processing steps. Most factories strive to reduce the amount of scrap that they produce, and many recycle the scrap that cannot be avoided. Figures for the amount of scrap that is recycled during the manufacturing process are not easily obtained, and in some cases manufacturers’ scrap management strategies are confidential, presumably because they impact profit margins.

Regulatory versus economic drivers Proponents of recycling often focus on the role of regulation in promoting the circular economy. This strategy is more effective in some parts of the world than others, depending on the will of governments to legislate and the will of populations participate. Even in places with strong regulatory requirements, effective consumer incentives, and socially conscious populations, however, recycling rates can be disappointingly low. Seven years after the rare earth crisis, there is still only a negligible contribution to the rare earth material flow from end-of-life recycled material.

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The importance of economics in the promotion of recycling is emphasized in a paper by Dahmus and Gutowski [1] who identify an apparent limit to recycling that depends on the complexity of the object to be recycled and the value of the material to be recovered, as illustrated in Fig. 7.1. Lower-complexity objects and higher-value materials are more likely to be recycled than higher-complexity objects and lowervalue materials. The balance between the cost of separating materials from complex objects and the revenue that can be generated from them certainly has an influence on what gets recycled. Higher recycling rates are generally achieved when the recycling process generates revenues that exceed its costs, so there is no need for governmental regulation or incentive programs. Economic drivers are more effective than regulatory ones, irrespective of location. Price spikes often stimulate the development of recycling efforts, just as they stimulate interest in mine development projects, and recycling has an apparent advantage over mining because it can appear to be less expensive and it takes less time to set up a recycling process than to commission a new mine. These advantages are usually offset

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by other considerations, however, and these challenges represent opportunities to make a positive impact through well-focused R&D efforts.

Reducing manufacturing waste All manufacturing processes waste some of their input materials. In some cases the amount of scrap can exceed the amount of material that goes into salable products, and in a few the waste can be extreme. The aerospace industry refers to the “buyto-fly” ratio for materials used in the manufacture of aircraft, and for some titanium alloys, this can reach 10 or higher: i.e., more than 90% of the material goes into the waste stream. Although manufacturing scrap is an attractive target for recycling, preventing its creation has greater potential economic benefit than recycling it. Reported recycling rates for critical materials can seem disappointingly small, but the quoted numbers often fail to include waste avoided by in-factory recycling, and this may represent a significant, if undocumented contribution to the supply chain. Manufacturing feedstock material may be scrapped for several reasons: l

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Machining is commonly used to reduce parts to their final shape, and this produces swarf, which is scrap in the form of chips of removed material, that are typically coated with machining fluid and mixed with abrasives or particles from the machine tools. A manufacturing process may require the use of excess material. In casting, for example, metal flows into the mold through channels called runners, and solidification shrinkage is controlled by overfilling the mold into reservoirs, called risers, that feed liquid into the mold during the solidification process. After the mold cools, the solidified runners and risers are sawn off and scrapped. Wrought products almost always require excess material to be scrapped. Examples of this include the ends of rolled sheets and drawn wires, and the flash formed where forging dies meet. Some materials are used in the form of thin films or coatings, which are applied by vapor deposition or spraying. In this case a significant fraction of the material may fail to reach or adhere to its intended substrate, so it accumulates in the coating chamber and may be removed periodically. In photolithography the applied material is deposited all over the intended substrate and subsequently removed from the areas on the part where it is not needed. A manufactured part may fail to meet its performance specifications after processing, leading to the rejection, and complex materials with sensitive processing-structure-property relationships are especially prone to this sort of failure. There is evidence that this affects some fraction of sintered rare earth magnets, as described in Chapter 4, and some of the “failed” magnets are sold at lower specification levels than targeted. Parts may be broken during the manufacturing process and assigned to waste.

Each of these forms of waste can be controlled and hopefully reduced, but the approaches will be different for each case. Machining operations are one of the most significant targets for avoiding inprocess waste. They are also significant consumers of energy and have high tooling costs, so the potential for economic benefit extends beyond the specific material

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supply chain, and there has been growing interest in “net-shape manufacturing” in recent years. With respect to currently critical materials, almost all Nd2Fe14B magnets undergo some machining, and as they are made in smaller sizes, there is a corresponding growth in the fraction of the material that is made into swarf. Recycling this swarf requires the extraneous material to be separated because the carbon that is contained in the cutting fluid and tungsten-carbide or diamond from the cutting tool has a deleterious effect on the performance of the magnet material. A potential alternative to cutting magnets to size is the use of 3D printing methods whose development was described in Chapter 5. This technique enables the formation of more complicated shapes, which can have advantages over the simple parallelepipeds, disks, and rings that are typically produced. The magnet powders used in 3D printing can also be produced from recycled materials, avoiding much of the processing required to convert recycled magnet material into sintered magnets. Samarium-cobalt permanent magnets command a smaller fraction of the market, partly because of the superior properties of Nd2Fe14B, but the differences decline at elevated temperatures, and Sm-Co can outperform Nd2Fe14B above 100°C. Neodymium magnets retain their performance edge with the addition of dysprosium or other heavy rare earths, which are expensive and suffer from high criticality. The choice to continue using neodymium-based materials is complicated, because samarium and cobalt are both potentially critical materials, but one of the major factors is that Sm-Co materials suffer from high scrap rates during manufacturing. The magnets used in motors and generators are machined to their final shape and then fitted into cavities of the same dimensions in the armatures of a motor or generator. Close tolerances apply to the magnet and the cavity to avoid motion of the magnet during operation, and the magnet is often tapped into the close-fitting armature cavity with a mallet. Unfortunately, sintered Sm-Co magnet materials are very brittle, and the breakage rate during machine assembly can be as high as 50%. Broken Sm-Co magnets are recycled, but it would be better to avoid the breakage than to recycle its results. Efforts to reduce the breakage rates of Sm-Co magnets focus on improving assembly processes to place less stress on them or making the Sm-Co tougher so that it can better withstand impacts or sustained stresses. Recent work conducted by CMI has demonstrated substantial toughness improvements for these materials through grain size control, without any loss of magnetic performance. If these improvements reduce the magnet breakage rate during the manufacture of electric machines without substantially increasing the cost of making the magnets, there will be a net improvement in the process economics. This can translate into a positive impact on the samarium and cobalt supply chains by reducing the amount of in-factory recycling, illustrating a case in which reducing the recycling rate results in net economic and ecological improvements along with potential reductions in criticality. The apparent success of this effort also increases the likelihood of using Sm-Co to substitute for Nd-FeB in some cases. This is a case where the avoidance of recycling, rather than its promotion, has benefits for the supply chain.

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In-process recycling When China’s rare earth export quotas were reduced in 2010, many industries sought ways to reduce their reliance on materials that were subject to the quotas, and there were some notable successes in reducing process waste.

Ceria abrasives Cerium oxide (ceria) is widely used as an abrasive for polishing silicon wafers and glass, because it combines a mild chemical attack of the silicon with mechanical abrasion, resulting in excellent surface finish provided by “chemical-mechanical polishing.” Although technologies had been developed for recycling ceria polishing powders in the early 2000s [2] and polishing slurries are much less impacted by separation challenges than rare earth materials recovered from devices, the recovery methods were not widely applied before the rare earth crisis, because ceria was a low-cost material and capital investments in recycling systems could not be justified. However, Chinese export quotas were initially applied to rare earths across the board, so if any single importer could reduce their demand for ceria, it would allow for a corresponding increase in access to other REOs such as neodymium. As a result the recycling of ceria polishing powder quickly became widespread, and up to 80% reductions in consumption were achieved. This represents a destruction of demand that was arguably a negative result for the rare earth mining industry, since cerium production already exceeded demand and the excess only grew as a result of the recycling efforts.

Yttria-stabilized zirconia Yttria-stabilized zirconia (YSZ) is a hard, tough structural ceramic suitable for use in high-temperature environments such as jet engines. Pure zirconia cannot be used in these applications because as the temperature rises, it undergoes phase transformations from a monoclinic structure to tetragonal (at 1173°C) and from tetragonal to cubic (at 2370°C). These transformations are accompanied by volume changes that would generate stresses and lead to cracking when the engine cycles between ambient temperature at rest and elevated temperature in operation. The addition of yttria can stabilize the cubic phase all the way down to room temperature and thus avoids the impact of the phase transformations during operational cycling. In jet engines and gas turbines, YSZ is used as a thermal barrier coating (TBC) to protect metal turbine blades from the high temperatures in the combustion zone of the engine, allowing the surface of the metal to remain below its melting temperature despite the higher temperature of the burning jet fuel. The YSZ coatings are layers between 100 μm and 2 mm in thickness, applied to the surface of the turbine blades by plasma spraying. These coatings would quickly crack and spall away from the underlying metal if they underwent the volume changes associated with phase transformations, with potentially catastrophic results.

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YSZ compositions include 8%–9% of yttria in current applications, but this results in less than complete stabilization of the material, which can still degrade at elevated temperature. Thicker coatings with higher yttria contents may be necessary in future jet engines, enabling them to provide greater efficiency by running at higher temperatures than current designs. The plasma spraying process used to coat turbine blades with YSZ is akin to spraying paint. YSZ powder particles are injected into a high-temperature plasma flame that melts them and accelerates them toward the workpiece, which they strike at high velocity. Even in well-optimized processes, as much as 80% of the material fails to adhere, either because it is overspray that misses the intended target or it hits the target but bounces off. This material accumulates in the spray booth and has traditionally been assigned to scrap. With the threat of reduced supplies of yttrium and the possibility of needing larger concentrations in YSZ for future generations of jet engines, GE and CMI have investigated processes to enable the reversion and reuse of the in-process waste. The waste powder collected from a spray booth is contaminated with other materials including metals ablated from the plasma gun and the workpiece, and to reuse the TBC waste, the YSZ powder must be separated from other materials, and the particle size distribution must be adjusted because the waste does not have the same size distribution as the virgin feedstock. Processes for achieving these requirements have been developed, and the use of reverted powder has been tested successfully. GE is now implementing the recovery and reversion of YSZ powder in its jet engine manufacturing lines, with a significant reduction of its dependence on yttrium sourced from China. The processes for recycling of ceria and YSZ powders have succeeded for several reasons, including the following: l

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They are in-factory processes, removing the need for collection and transportation of the material. They meet the Dahmus and Gutowski criteria by having low-complexity feedstock and highvalue output materials. The materials need minimal reprocessing and are returned to the manufacturing process essentially in their original form. They generate quantifiable value for their owners.

As in the case of ceria recovery, however, the overall impact of successfully recycling YSZ may be to increase the criticality of other rare earth elements. Cerium is a coproduct of light and medium REEs from bastnaesite. It is the largest product of this type of mine, and it is extracted in excess of demand: reducing the demand for cerium impacts a revenue source for bastnaesite mines and therefore increases the cost of producing lanthanum, praseodymium, and neodymium. Yttrium is a coproduct of heavy REE production from lateritic clays and phosphate rocks and is usually the largest-volume REE produced from these sources. Reducing the demand for yttrium exacerbates the balance problem and increases the criticality of the heavy REEs. In both of these cases, reducing the need for one material can have a positive impact on its users but may have a negative impact on the criticality of other materials to which it is linked through coproduction.

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End-of-life recycling Discarded consumer products are the most challenging targets for recycling, for at least two reasons: 1. The cost of collecting and delivering them to a processing center can exceed the value of the materials that can be recovered. The carbon footprint of the collection process is large and remains hidden when it depends on volunteer efforts or consumers bringing objects to collection centers. 2. For many high-tech products, materials are becoming more finely intermixed with a broadening palette of materials and shrinking device sizes, so successive generations of electronic products move inexorably further to the right in the Dahmus and Gutowski plot, as demonstrated in Fig. 3.10, and thus they become more difficult to recycle.

Success stories: Even the simplest cases are complicated Despite all of the challenges, the recycling of materials from some products is remarkably successful: in 2018 the United States obtained as much as 67% of the aluminum that it used in manufacturing from factory waste or end-of-life scrap [3]—and the rate has been even higher in a few prior years, as illustrated in Fig. 7.2. While aluminum is regarded as a simple case, even the humble and famously recyclable beer can has some degree of complexity: aluminum scrap always takes the form of alloys whose compositions usually have to be adjusted depending on their next use. The material used for the body of a beverage can is usually Aluminum Alloy 3104 (in the designation scheme of the Aluminum Association), and it requires a minimum of 0.05% and up to 0.25% of copper, but the Alloy 5052 endcap must not contain more than 0.1% of copper, and the Alloy 5182 pop-tab is limited to 0.15%. Melting the whole container

Fig. 7.2 The fraction of total US annual aluminum demand that has been met by recycled material, from 1995 to 2018. “New scrap” refers to factory waste, and “old scrap” is postconsumer material. Based on data from the relevant annual USGS Material Commodity Summaries.

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results in a composition that can exceed the allowable copper content for making poptabs or endcaps. This might be prevented, in theory, by reducing the copper content of beverage can bodies into the range from 0.05% to 0.1%, so the copper content of the scrap is consistent with the specifications for all three alloys used to make the cans. However, narrowing the composition range for copper in the bodies of the cans has impacts in terms of process control, and although it is possible to find a copper concentration that lies within the specifications of all three components of a beverage can, it is not possible to do so for other alloying elements, including magnesium, manganese, or chromium. In short, you cannot simply melt beer cans to make more beer cans. One approach to producing suitable alloy compositions from scrap is to fully separate all of the elements in the feedstock by chemical means and then recombine them in the appropriate proportions, but this is expensive, and it consumes large amounts of energy. It would also be possible to separate the bodies, endcaps, and pop-tabs and recycle them separately, but this is also a costly process because the cans typically arrive at the recycling plant in a crushed and compacted form, making it difficult to separate the different components. In practice, most recyclers adjust compositions by melting whole cans and then adding lower-copper or higher-copper scrap or primary copper metal to adjust the copper content, and they adjust the content of the other alloying elements in similar ways. The need to include these elements in some aluminum alloys while excluding them from others adds complexity for the recycling of aluminum scrap [4]. The hidden complexity of relatively simple consumer items like beverage containers is part of the reason why “new scrap” or in-process-recycled material contributes more to the supply chain that “old scrap” or postconsumer recycled material. The material scrapped from sheet stock for can bodies, caps, or tabs can be remelted directly for the same uses, avoiding a large part of the processing that is applied to ore or old scrap. As additional elements are added to aluminum alloys designed for new products, recycling becomes progressively more challenging, ultimately because of the energy that it costs to reduce the entropy of the mixture of materials in the recycling stream.

Complexity adds to the problem Civilizations are enabled, defined, and sometimes limited by the technologies that allow them to exist. In this regard the mobile telephone is one of the defining technologies of the day for much of the world’s population. In advanced countries, there are more active cell phones than members of the population, and economically emerging countries are rapidly approaching one phone per capita. In the world’s poorest regions, the first use of newly available disposable income (after food and shelter needs are met) is often a mobile telephone that provides access to online banking. The cellular telephone has evolved rapidly. The first commercial mobile phone was Motorola’s DynaTAC 8000X, initially produced in 1983, and it required around 35 chemical elements to manufacture (Fig. 3.10A). Less than four decades later, the

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requirements have grown to somewhere between 65 and 70 elements for a 2019 model smart phone (Fig. 3.10B) [5]. A modern mobile phone weighing 200 g, containing 70 different chemical elements in a volume of about 100 cm3, is effectively a high-entropy object, even if it contains no high-entropy alloys. Separating those materials is an exercise in reducing entropy, and the second law of thermodynamics tells us that this can only be achieved through the expenditure of energy. As the entropy increases, so does the energy requirement for recycling. As we see in Fig. 3.10B, the smart phone contains many critical elements, so it would appear to be a good target for recycling in support of supply diversification for those materials. There are, however, some major challenges to achieving this. The collection of used phones is not as systematic or comprehensive as it would need to be to make a significant impact on the supply of any critical material. Most used phones appear to stay in the possession of their owners for various reasons, and owners who decide to recycle them often face barriers such as finding collection points and delivering the phones to them. This is being ameliorated to some extent by a shift in the ownership model that is being promoted by cellular service providers or phone makers: Options for phone leasing are gradually supplanting phone ownership, and these promote the exchange of old phones for new ones. Unfortunately, they also promote updating and disposal of older phones on a shorter timescale than is typical when the end user owns the phone, so it is not yet clear if this has a positive impact on the supply of all of the materials that outweighs the negative impact on their demand. The phones are monolithic objects that are intentionally made difficult to disassemble. Prior to the introduction of smart phones, starting with Apple’s first iPhone in 2007, almost all mobile phones had removable batteries, but today almost none feature even that level of disassemblability, which is a key step in reducing the complexity of the recycling process. A lithium-ion battery can be processed much more simply to extract the electrolyte and the electrode materials for reuse, if it is separated from all of the other materials in the phone. Similar simplifications can be achieved by recycling other components separately from each other, to allow for rare earth magnet materials to be recovered from microphones, loudspeakers, and haptic feedback motors, for example, but progress toward simplifying the disassembly process has been slow. A variety of modular phones have been developed, allowing individual components to be upgraded and recycled separately, but these have yet to gain a significant share of the market. Apple, among other manufacturers, have developed robotic tools that are able to disassemble their own products, but these are model specific, and it is not clear how much impact they have made on most of the materials used in the phones. The phones contain materials of varying value, some of which may be economically recyclable, while others are not. The precious metals used in connectors on circuit boards are attractive targets because of their value. Bodies made from aluminum or other metals may be recovered because their relatively large mass makes them valuable. Other materials in the phone may or may not be recovered, and those that are not recycled must be disposed in traditional landfills or downcycled to other uses. Of

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particular concern, here, is the specialized glass screen, which is not acceptable for recycling like other glass objects. The screens are highly engineered and unusually complex in their composition, to make them tough enough to withstand scratches and impacts. The composition of the glass is altered close to its surface to create compressive stresses that help it to withstand cracking, and if it were remelted, the toughening elements would be redistributed uniformly, so they would not provide the same effect. And, finally, the screens have thin layers of other materials on their surfaces to provide functionality such as light emission and touch sensitivity. While these layers contain valuable materials including europium, terbium, indium, and tin, the quantities are so small, and they are so well attached to the glass that it has not yet proven economical to recover them. One of the biggest economic challenges to recycling smart phones and tablet-style devices in general is the cost of disposing of the glass screen, which can exceed the value of the recyclable materials in the device. Recycling all of the materials in a device as complex as a smart phone is a challenge that is unlikely to be achieved through economic drivers alone. A more promising approach than developing more and more complex recycling schemes is to focus on reducing the complexity of the device itself [5], and there has been some progress in this regard: when Apple introduced its iPhone 6 model in 2014, the company boasted about several materials that were not in the device—it had a mercury-free backlit LED display and arsenic-free glass, and it was free of brominated flame retardant (BFR), poly-vinyl chloride (PVC), and beryllium. It also used lead-free solder, as have essentially all consumer electronic devices since 2006. The exclusion of these materials was in response to toxicological concerns, and it has a potentially positive impact on the recyclability of the remaining materials in the phone.

Recycling as a response to criticality: Successes and failures Supply-chain problems have stimulated efforts to reuse and recycle critical materials, including Japan’s Urban Mining project, for example. Success in bolstering the supply chain has been mixed, and it is instructive to study the reasons why some efforts have succeeded, while others have failed. These case studies can help us to identify suitable targets and approaches to supply-chain stewardship as new critical materials emerge.

Rhenium Gas turbine manufacturers use highly specialized and optimized materials in their engines, especially for the turbine blades that operate under large stresses at temperatures near their melting points. These materials must be able to withstand the corrosive environment of the engine and resist creep deformation. Individual manufacturers develop proprietary alloys to meet these needs, and GE utilizes rhenium in some of its superalloy turbine blades. This is an extremely scarce element and a by-product of a by-product: it is obtained during the production of molybdenum from the anode sludge that forms during the electrolytic reduction of copper.

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Faced with potential rhenium supply shortfalls, the company engaged a multifaceted effort that included redesigning its turbine blade alloys to require smaller amounts of the critical element and recycling old turbine blades to help boost the supply [6]. The ability to recycle old turbine blades was enhanced when the company shifted the emphasis of its business model from selling to leasing its jet engines, which ensured that end-of-life engines were returned to the manufacturer, so they were available for refurbishment and reuse or eventually recycling. With reduced rhenium content in the newer turbine blades, the higher rhenium content in the older blades allowed recycling to be an effective supply solution, at least during the transition from the older, high-Re composition to the newer, low-Re material. As we shall see it is vital to ensure the ability of a recycling stream to contribute significantly to meeting current needs.

Tantalum Concerns about the supply of tantalum have emerged repeatedly, and a variety of R&D efforts have focused on recycling the material from capacitors, which have traditionally been one of its major applications [7, 8]. Supplies of tantalum are dominated by the DRC, and low supply diversity makes it a critical material. When the issues of political instability and exploitative labor practices are also considered among the supply risks, concerns about this material are further elevated. Japanese researchers focused their efforts on the automated identification and extraction of the capacitors from devices such as cell phones and developed robotic tools that were able to harvest the components at a high rate, from a wide range of traditional (i.e., not “smart”) phones. When the system was built and testing began, it was found that circuit boards from many of the phones did not contain the expected numbers of capacitors, and this was particularly true for the most recent models. Tantalum capacitors had been replaced to a large extent by ceramic-based units. This outcome illustrates a pervasive challenge for recycling efforts: whenever a component or a material reaches a level of cost or concern over the security of its supply that justifies recycling, those concerns also motivate its replacement. If a substitute material is adopted before recycling gets under way, the manufacturer’s need for the material declines, and the recycler’s source also dwindles. If recycling is to succeed as a response to criticality, then it needs to be established more quickly than any alternative solution.

Europium and terbium As the rare earth crisis unfolded in the late 2000s, the leading consumer of europium and terbium was fluorescent lamps. Eu and Tb are heavier rare earth elements that are produced in very small quantities from mining: the heavy rare earths, as a group, were assessed to have the highest levels of criticality in most studies. This immediately attracted attention to fluorescent lamps as targets for recycling, for several reasons:

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A collection infrastructure was already in place. Long-tube and compact fluorescent lamps are banned from disposal as trash in most of the world’s advanced nations, because of the need to protect against contaminating the environment with the mercury that they contain. Retailers are required to accept postconsumer end-of-life units which are then collected by recyclers who extract the mercury from the lamps, recycle the aluminum endcaps, and dispose of the glass, which is nonrecyclable. The mercury is handled as hazardous waste rather than being reused, and the cost of the process is met through fees levied on the manufacturers and/or distributors of the lamps. Europium and terbium are heavy rare earth elements and are among the most critical of them REEs, so there is a large impetus to improve the diversity of their supplies. Europium and terbium command high prices, providing a financial incentive to recycle them. The lamp phosphor contains no rare earth elements other than yttrium, europium, and terbium, which are not adjacent to each other in the periodic table. It should therefore be relatively easy to separate them using methods like solvent extraction that are poorer at discriminating between adjacent rare earths. The concentrations of europium and terbium in lamp phosphors can be significantly higher than in the ores of primary sources.

With all of these advantages, lamp recyclers were eager to try to add a new revenue stream to their businesses, from the sale of recycled europium and terbium. In France, one of the leading chemical processing companies, Solvay, set up a solvent extraction line dedicated to separating europium and terbium from used lamp phosphor, which it obtained from recyclers in Europe and North America. In the United States the Global Tungsten & Powders Corporation (GTP) reportedly invested as much as $600 M in building its own processing plant. Solvay’s plant operated for a few years before shutting down, and the GTP project was abandoned before it was commissioned. The reasons for these failures are only partly available to the public, and they are certainly complex. At GTP, there may have been technical challenges in reducing the mercury content in the feedstock to a concentration that is considered safe. Both efforts were impacted when LED lamps began to gain market share at the expense of fluorescents, after 2013: This quickly reduced the demand for the two rare earth elements involved, and it also started a decline in the numbers of lamps in the recycling stream. Despite the challenges, Solvay is believed to have been able to produce europium and terbium at costs below the market price of the materials, so by all appearances the company should have been able to sell its product at a profit. One interpretation of Solvay’s decision to shut down its phosphor recycling line relates to the relatively small quantities that it was able to produce, in view of low recycling rates and shrinking feedstock volumes. Unable to meet a significant fraction of the needs of any major lamp manufacturer, the company was unable to break into a market. This failure may have resulted from one or both of two causes: l

New sources of material require qualification by each manufacturer for adoption in their production process. While this may not be as extensive as the qualification process of an entirely new material, it is still an expensive and time-consuming process, and its costs may not be justified for a small fraction of total need.

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Monopolistic providers of a material can exert pressure on its users, if they reduce the quantities that they buy.

If this is correct or even if it is only part of the reason for Solvay exiting the Eu-Tb recycling business, it demonstrates that it is vital to be able to produce sufficient quantities of recycled material to meet the majority of some users’ needs with good reliability over a long period of time, to overcome the reluctance to qualify a new material and avoid retaliatory actions from a majority or monopolistic provider. In this regard the recycling rate presents a challenge: Despite the legal requirement to recycle mercury-containing fluorescent lamps, recycling only captures around 30% of the lamps that are produced in the United States, and this has an impact on the amount of Eu and Tb that can be produced from the recycling stream.

What fraction of current need can be met by recycling? The need to produce sufficient amounts of material from recycled end-of-life objects to meet a significant fraction of the needs for a particular material prompts the question of how much material can actually be produced this way. A simple model suggested by Karen Hanghøj indicates some of the answers [9]. We assume that the demand for a material grows at a constant fractional rate of G per year. If the material all goes into objects that have a fixed lifetime of L years and we ignore additions and withdrawals from stockpiles, then the amount of material that becomes newly available for recycling in Year n is equal to the amount produced in Year n
(L + 1), as illustrated in Fig. 7.3. If Pn is the amount produced in year n, the amount produced in year n
(L + 1) was Pn
L ¼ Pn =ð1 + GÞL + 1 The maximum fraction of the demand in Year n that could be met by recycling material produced in Year n
(L + 1) is then ¼ Pn
L =Pn ¼ 1=ð1 + GÞL + 1 Fmax R To achieve this fraction, it would be necessary to collect all of the end-of-life products and extract the target material with perfect efficiency, neither of which can be achieved in practice, so this fraction can be regarded as a “utopian” baseline. Rare earth production has grown at a rate of approximately 14% per year over the last half century, and most REE materials go into devices like industrial motors with a lifetime of more than 10 years or electronics with a lifetime of around 5 years. Using G ¼ 0.14 and L ¼ 5, we see that utopian recycling of electronics can meet about 46% of the needs for electronics, and with L ¼ 10 recycling of motors can meet less than 24% of the REE demand for motors.

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Material demand

Volume of demand for year n

Volume in use during year n (for lifetime L = 7 years)

Volume available to recycle during year n

n–16 n–15 n–14 n–13 n–12 n–11 n–10

n–9

n–8

n–7

n–6

n–5

n–4

n–3

n–2

n–1

n

Year

Fig. 7.3 A simplified model to estimate the fraction of current demand for a material that can be met by recycling. Demand grows by a constant fraction per year, and all of the material is assumed to be used in products that have a lifetime of L years, so that L years-worth of production are tied up in current use. Material produced L + 1 years ago is available to recycle.

We can add to our analysis the impact of less-than-perfect collection efficiency, Ec, and extraction efficiency, Ee, to provide a better estimate of the fraction of current demand that can be met by recycling: FR ¼ Ec E e = ð 1 + G Þ L + 1 For most devices the collection efficiency is less than 30%, but the extraction process may reach an efficiency of 90% or better. With these efficiency levels the fraction of demand that can be met by recycling is only likely to reach 27% of the utopian values, so we may expect that as little as 6% of the rare earth demand for industrial electric motors will be met by recycling and even less if the average service life is longer than 10 years. With such small fractions of their needs available from recycling, manufacturers must continue to rely on newly mined material for the majority of their needs. An alternative source for 6% of a supply chain makes only a small impact on the criticality of a material from the perspective of a manufacturer and may not justify the cost of qualifying the source or complicating their negotiations with a primary supplier. Recognizing that recycling is only likely to meet a small fraction of the total demand for many materials, a more successful business model for recyclers might be to channel all of their recycled material into a single product or manufacturer, rather than trying to sell it into the market more broadly. The single recipient may then be able to rely solely or very significantly on recycled material, while all others benefit from the reduced demand for newly mined material. In this scenario, however, all of

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the users of the material still have low diversity of supply, whether they rely on mining or recycling for the majority of their needs. In the extreme case where one user relies exclusively on the recycling stream and no others receive any material from this source, then none of the users see an increase in their diversity of supply and criticality is not reduced. We conclude that for any material that exhibits a positive demand growth, it is not possible to provide sufficient material for current needs entirely through recycling. Larger positive growth rates result in smaller contributions from recycling and thus greater reliance on primary production, and critical materials are often associated with rapid growth in demand. If demand is neither growing nor shrinking, the contribution from recycling depends on the collection rate and the recovery rate from the collected scrap. Most material extraction processes are already highly optimized and produce high recovery rates, so the greatest opportunity for increasing the contribution from recycling lies in improving the efficiency and effectiveness of collecting products for recycling. When the demand for a material shrinks, the value of G is negative, and it may be possible to obtain larger fractions of current needs through recycling, but this will probably be a transient condition. This is apparently the case for europium and terbium in fluorescent lamps, but the fraction of need that can be provided from recycling is still not yet sufficient to make an impact, because of the low collection efficiency. Extending the useful life of products that contain critical materials is an effective way to conserve the materials and reduce demand, but this approach to supply-chain stewardship impacts the viability of recycling programs. Extending the product life, L, reduces the potential contribution from recycling, but it may also reduce the rate of demand growth, G, which has the opposite effect. The net impact of life extension on the economics of recycling will need to be assessed on a case-by-case basis. The simple model presented here is a steady-state analysis, in which material recycled only from the production of Year n
(L + 1) contributes to meeting the demand for Year n. For most critical materials, there has been little or no impact from recycling up to the emergence of a crisis, and if a recycling program were to be started, it could use older discarded products, provided that they are still accessible. In this case it might be possible to increase the contribution of recycled material to the supply for Year n by accessing discarded objects from earlier years, but this clearly cannot be sustained: In Year n + 1, we would have to reach deeper into landfills and scrap heaps to make up the contribution, and this “stockpile” would quickly become depleted of all of the accessible material that it contains. Recycling would be a transient solution in this case, but supply-chain crises are usually transient problems: the questions are whether a “pop-up” solution can generate enough material to relieve the temporary shortfall; and its prospects for economically viability. Supply-chain failures are usually short-term events embodying rapid increases followed by rapid decreases in demand, driven at least in part by anticipatory buying by supply-chain managers and/or commodity speculators. It is unlikely that recycling can be used to ameliorate the effects of these demand excursions without an underlying business model that generates profit in a steadily progressing market. It does not appear to be practical to start up an end-of-life recycling program as an immediate response to a supply crisis. The

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cases of ceria abrasives, yttria-stabilized zirconia, and rhenium-containing superalloys show, however, that in-house recycling can be effective: In each of these, recycling produces a significant fraction of the manufacturer’s needs, and we conclude that the fraction of the supply chain that can be replaced through recycling is an important consideration, but there is no clearly defined threshold value.

Emerging targets for recycling Although it is challenging to set up a recycling program as a response to an emergent supply-chain crisis, there is still value in considering this approach as a means of avoiding anticipated crises. When a material is found to be critical, though not yet in crisis, recycling options should be considered, while there is still time to develop them. It is essential, however, to pick targets that are likely to produce a real impact. When recycling is viewed from the critical material perspective, we may be tempted to think in terms of recycling a particular target material. Recycling businesses, however, think in terms of reusing or recycling an object that may contain several materials, all of which are either potential sources of revenue or cost for disposal. Recycling is economically sustainable only when the revenues exceed the costs, integrated over all of the materials in the object being recycled.

Rare earth magnets As we look for sources of critical materials, we need to identify targets that contain significant amounts of the materials that we seek and are also viable as recycling businesses. The largest volume of rare earth magnet materials, accounting for about 40% of the market, goes into industrial electric motors and generators, which also contain large quantities of copper and ferrous alloys, with a relatively small amount on nonrecyclable material. These devices, however, typically have long service lives and are retired infrequently. Their collection and delivery to recycling centers involve transport over long distances, and the devices are of variable size and form, making their disassembly difficult to automate. The second largest single component of the market for rare earth magnets is in hard disk drives, accounting for around 16% of the market in 2014. The needs of this industry can change quite rapidly as HDDs are supplanted by other technologies and the form factors of the HDDs shrink with their ever-increasing memory density. The replacement of HDDs by solid-state memory predominantly affects consumer and business computers, while HDDs remain the technology of choice in large data centers because they are robust over large numbers of read/write operations: The life of solid-state memory is limited to a fixed number of such operations, and data centers store and transfer information at rates that would burn out solid-state RAM very quickly. Data centers proliferate with the growth of cloud computing services and Internet-based social and business applications, so they represent good targets for urban mining: They contain large amounts of rare-earth magnet material in a small geographical footprint, and a typical data center can retire hundreds of thousands

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of nearly identical hard disk drives each year. These HDDs contain significant amounts of precious metals along with aluminum and ferrous alloys, so they have potential as a recycling business venture. There are two sets of rare earth permanent magnets in a typical hard disk drive. One of these is in the spindle motor, which turns the disk assembly, and the other makes up the voice coil motor, which positions the read/write head (Fig. 7.4). In a 3½ in. HDD, the magnets in the voice-coil motor total between 10 and 20 g of sintered neodymium magnet material with little or no dysprosium added; for a 2½ in. drive the voice-coil magnets total around 2.5 g [10]. Spindle motors contain smaller quantities of resinbonded neodymium magnet material that is usually not considered economical to recover. Early efforts to recover magnets from HDDs were based on manual disassembly. A typical HDD is opened by removing about 10 screws from its lid, and then several more must be removed to extract the voice-coil and spindle motors. The spindle motor is more complicated to extract, and because it contains a smaller magnet than the voice-coil motor, it is usually ignored in manual processes. An experienced disassembler with an electric screwdriver may be able to extract the voice-coil magnet assembly from an HDD in less than 10 min. For a 3½ in. HDD at the high end of the magnet size range, this assembly would contain approximately $0.45 worth of REEs at 2018 prices, so extracting REEs from around 10 HDDs per hour does not pay the hourly wage of a low-skilled worker in a developed country, and disassembly is only the first step in recovering the value of the rare earth. After extracting the voice-coil

Fig. 7.4 The internal components of a hard disk drive, showing the locations of the rare earth magnets. Reproduced with permission from A. Walton et al., The use of hydrogen to separate and recycle neodymium-iron-boron-type magnets from electronic waste, J. Clean. Prod. 104 (2015) 236–241. Copyright 2015, Elsevier.

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magnet assembly, several further steps are required to recover the magnet materials, including separating the magnets from their μ-metal backing, demagnetizing, stripping the coating, and preparing the material for reuse through some process such as grinding or hydrogen decrepitation [11]. Smaller-format HDDs take about the same amount of time to disassemble as larger ones, but they contain significantly less magnet material, so the economics of manual recycling grow progressively worse as HDD technology advances. Coproduction of other recyclable parts and materials, including precious metals, aluminum, and ferrous alloys, helps the economics, but the amounts of these also decline as the drive sizes shrink. Alternatives to manual disassembly have been developed to reduce the cost of extracting rare earth permanent magnets from HDDs. A Hitachi-developed system tumbles HDDs in a drum to loosen and/or remove the screws, and this is reported to increase the disassembly rate into the range of hundreds of units per hour. An automated system developed at Oak Ridge National Lab in collaboration with the Critical Materials Institute identifies the location of the voice-coil assembly and slices off the corner of the drive that contains it [12]: a single machine system can extract voice-coil magnets at rates of thousands of units per hour, with minimal labor costs, although a larger capital investment is required for this type of machinery. An alternative approach is to shred entire HDDs without separating their components and then extract the various materials through chemical methods. While this approach has lower costs at the front end of the process, it may involve more complex chemical separations further downstream. It also suffers from the challenge that shredded magnets accumulate into “hairballs” along with shards of other magnetizable materials and entrapped nonmagnetic ones, and they stick to the ferrous metal components in the shredding machines. There are several technological choices for recycling HDDs, each with its own advantages and disadvantages. The development of a successful commercial system will depend on optimizing overall value recovery including all of the recoverable materials and disposal of the materials whose value does not justify recovery. The International Electronics Manufacturing Initiative (iNEMI) has convened a project team made up of HDD manufacturers, data center operators, and recyclers, along with government and university researchers, to identify a system that achieves this goal and then build a pilot version of it [13, 14]. While this is a work in progress, it has several features that lean in favor of its eventual success: l

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It is a pragmatic approach that focuses on total value recovery from a single class of device, rather than simply recycling critical materials. The team includes major contributors across the entire life cycle of the device and the materials that it contains, and it has access to leading-edge labs and researchers. With increasing data density and decreasing HDD sizes, the overall materials demand for HDDs is not growing as rapidly as in other sectors, so recycling older, larger-format HDDs may be able to provide a significant fraction of the industry’s needs for newer, smaller ones. The fraction of the material for new HDDs that can be provided from recycling old ones could be relatively large, and it may, indeed, be possible to make new HDDs out of old ones because of their shrinking size.

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The HDD market has some unique features that must be considered in designing a value-recovery system, and these can impact the use of specific technologies. The options for value recovery from failed HDD units are shown schematically in Fig. 7.5. The greatest value that can be obtained from a retired disk is achieved by repairing it and/or reusing it rather than recycling it. Hard disks are retired when they lose access to a predetermined fraction of their capacity, and this can occur because of software Identification of failed HDD

Correct software errors

Reformat to avoid bad sectors Qualify disk at lower capacity

Return HDD to service

Use or sell refurbished HDD

Extract and reuse magnet assembly

Manufacture new HDDs

Extract and reuse magnets

Manufacture new magnet assemblies

Shred HDD unit

Separate and recycle magnet material

Manufacture new REE magnets

Separate elements from magnet material

Manufacture new REE materials

Declining value recovery

Recycle

Assign to scrap

Fig. 7.5 The principal value-recovery options for failed HDDs. Recycling is only an option after all of the options above it are exhausted, so the higher-value options reduce the volume that is available for recycling.

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errors that can be corrected, allowing the unit to be returned to service, or it can occur because of hardware errors that are more difficult to remediate. A disk that has significant unrecoverable capacity can be reformatted as a lower-capacity unit that still has usable life. There is a thriving market in recovering and selling retired HDDs for reuse, which provides greater value recovery than any recycling process: it also significantly reduces the volume of HDDs that are available for recycling at any time, which can reduce the fraction of the supply chain that can be met through recycling. When an HDD is retired from service, it contains a large amount of data that must be protected against unauthorized access. This may be achieved by erasing the data if the disk is to be reused, and this is part of the process of preparing a disk for secondary markets, but the data on disks removed from recycled units can still be accessed, and the assurance of data destruction is an important consideration. This impacts decisions about how and where HDD recycling is done: it generates a preference for systems that physically destroy the disks from the HDDs and for processes that are conducted at the site where the disks are retired, under the supervision of their owner. There are clearly several technological options to be considered with regard to recycling HDDs, and the iNEMI project will examine them in detail. With regard to the most prominent critical material in an HDD, the neodymium magnet, the range of options runs from recovering the individual elements in the magnets, to recovering the magnet material, to recovering and reusing the magnets themselves, and eventually to recovering and reusing the magnet assemblies. Each of these calls for successively less processing before the material is reused, and the last three, in particular, are attractive if the recovered materials, magnets, or magnet assemblies are used for making new HDDs: this avoids the need to adjust the composition that is likely to be required if the magnets or materials go into other applications. The most attractive option is perhaps the reuse of magnet assemblies, but this requires stability of the HDD design from generation to generation, and it restricts the process to the supply chain of an individual manufacturer unless industry-wide magnet assembly designs can be adopted. Some level of magnet assembly reuse may be possible for voice-coil motor components, but it is rather less likely that magnet assemblies from spindle motors can be successfully harvested, so the economic viability of recycling the different types of magnets in a HDD is likely to be different, and the voice-coil motor is certainly the more attractive target.

Li-ion batteries As electric vehicles move from a niche to a toehold to a mainstream component of the mobility market, there has been growing concern about the materials needed to build them. Permanent magnets are required for smaller, lighter, and more efficient motors, and this leads to concerns about the rare earth elements that go into REPMs as demand for EVs grows. There are similar concerns about the materials used in the rechargeable batteries used in EVs, especially about lithium and cobalt used in the electrolyte and graphite, which is used in the anode. An all-electric car has a battery pack weighing up to 200 kg, representing a significant fraction of the mass of the vehicle.

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The demand for battery materials grows as more EVs come into service, and this results in a large value of G in our model for the contribution from recycling, suggesting that recycling will contribute very little to overall needs during the growth of this market sector. As the market matures, however, the number of EVs on the road will stabilize, and the value of G will approach the value of the overall vehicle market, which has been around 2.8% for the last decade. The approach toward stable growth in the EV market will occur on a timescale that is related to that of the vehicle lifetime, so it will occur at around the same time as large-scale recycling of these vehicles ramps up. If the market growth for EVs settles out at 2.8% and their service life is the same as today’s average vehicles at 8 years, then recycling could eventually supply 81% of the need for battery materials, assuming perfect recovery and recycling. If we assume that EVs have longer lives, given their lower maintenance needs relative to IC-driven cars and the green sensibilities of their owners, then the contribution from recycling falls, but for a 10-year life, it can still produce 77% of the annual need, and for a 15-year life, it still has the potential to contribute 68%. On this basis, recycling of battery materials appears to have the potential to grow into a viable proposition, and it makes sense to invest in the necessary research and development to build effective recycling systems. Even with a strong potential for supply-chain impact, however, recycling of battery materials faces some challenges. The prospect of a growing market for lithium and cobalt generated considerable optimism in the mining sector, and investment in new mining capacity has been outstripping the growth in demand. In the summer of 2019, market prices for lithium and cobalt both fell as the balance between supply and demand shifted, and both metals suffered from oversupply. It was announced that the world’s largest cobalt mine, at Mutanda in the DRC, would be placed in care and maintenance mode by the end of 2019. The shifting markets for lithium and cobalt illustrate how quickly material criticality can change, and the particular circumstances of these materials are also instructive. Although it is listed as a critical material in many reports, there is no real shortage of lithium. Large deposits exist, and there are proven technologies for extracting it. The only challenge is the speed at which production can be increased, and it appears that growth of the world’s mining capacity has, for now, outstripped the growth in demand. Over time, normal economic processes will correct the imbalance. The cobalt price has been impacted by another process. Cobalt has suffered from large price swings ever since its first price spike in 1978, and manufacturers share an aversion to the material because of this unpredictability. The emergence of cobalt as a conflict mineral has added to the concerns. Alternatives and workarounds are popular, and as lithium ion battery technology has matured, there has been a concerted effort to reduce its dependence on cobalt. The electrolyte in the earliest “lithium” batteries was actually lithium cobalt oxide (LCO). When lithium ions move between the electrolyte and the anode of the battery, the changing charge in the electrolyte is accommodated by changes in the oxidation state of the cobalt, without a crystallographic phase change. Early generations of lithium-ion batteries used LCO with a cobalt content of 55%, by weight. Later generations have used lithium nickel manganese cobalt oxide (NMC) containing 15% of cobalt and lithium nickel cobalt aluminum oxide (NCA) with 10% of cobalt or less. Industry reports suggest that the batteries in Tesla

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electric vehicles use NCA electrolytes with 3% of cobalt and that efforts are under way to reduce it to zero. The progressive reduction of cobalt content in lithium ion batteries is a successful application of the material substitution approach to ameliorating criticality. The success of this approach, however, comes at the possible expense of source diversity because it has resulted in the closure of a major mine. It also impacts the prospects for recycling by reducing the value of the materials in a battery pack, and the changing composition of the electrolyte will present challenges for developing recycling processes.

Recycling and the competition to provide supply chain solutions The cases of lithium and cobalt teach us that supply-chain issues can be solved in many ways. If our concern is criticality, we should focus on the strategy that provides the greatest relief in the shortest time at the lowest cost, and this has proven to be source expansion for lithium and material substitution in the case of cobalt for battery electrolytes. If our concern is sustainability, then we might have a stronger preference for recycling, and we would need to find ways to make it the most effective choice. The cases described in this chapter have shown that recycling faces barriers that vary from case to case, including some or all of the following: l

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Inability to meet a large enough fraction of need to overcome the barriers to market penetration. The cost of collection and separation of end-of-life objects. The cost of disposal of low-value co-products from recycled objects. Competition with other means of cost recovery such as re-use, that reduce the volume of material available for recycling.

Recycling also has advantages in some cases: l

Recycled materials are in a value-added form compared with their corresponding first-use materials, so it may be possible to insert them into the supply chain further downstream and thus avoid some processing steps. Recycled factory waste has particular advantages in this regard. For certain cases such as aluminum, the avoidance of energy-intensive primary metal processing can be very valuable.

R&D efforts aimed at promoting recycling need to focus directly on overcoming the biggest barriers and those that have the greatest impact on the process economics. In a recent technoeconomic comparison between two recycling methods for postconsumer electronic scrap, Diaz and Lister showed that an electrochemically mediated hydrometallurgical process has the potential to generate approximately 3% more cash flow over a 20-year period than a comparable pyrometallurgical process [15]. Their data also show that the largest single cost for both processes is the acquisition of feedstock, which amounts to more than 85% of the operational costs for the electrochemical method and more than 60% for the pyrometallurgical route. Although it is important to select the best processing method, there is clearly more scope for improving the economic viability of recycling in this case, by addressing the cost of feedstock acquisition than by selecting one or other processing method. Most of the revenue from

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either process comes from the recovery of gold, silver, copper, and steel, with only a small fraction coming from rare earth elements, and it is not clear that the amounts of the REEs that can be produced this way are sufficient to overcome the barriers to market acceptance. The mining of geological resources has a cost advantage over urban mining primarily in the area of collection and separation of the feedstock. For a geological mine the feedstock is uniform and geographically confined, while for an urban mine, it is nonuniform and widely distributed. Once the feedstock enters a separation process, however, many of the processing steps are very similar, and one approach to extracting materials from recycling streams is to add the urban mine’s feedstock to that of a geological mine. If we consider the competition between urban and geological mining through the lens of a learning curve, as illustrated in Fig. 3.17, we recognize that geological mining is a much more mature industry, so its costs have been reduced by the large cumulative volume of material that it has produced. If the costs of urban mining are currently higher, there is still the possibility that they can be reduced, and if the rate of cost reduction is large enough, the urban mining line may cross the geological mining line at some point in the future. There are several challenges to reaching this point: l

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As long as the costs of urban mining remain higher than those of geological mining, the recycling rate remains low, so its cost reductions proceed relatively slowly. Experiencebased cost reductions will accelerate only when the cost of recycling falls below that of traditional mining. While material production from recycling remains low and only produces a small fraction of current demand, it is hard for material produced this way to achieve significant market penetration. This creates an economic barrier to accelerating the production rate to accelerate cost reductions. Many efforts to reduce the cost of urban mining produce new knowledge that also benefits geological mining. For example, improvements in separation technology that are aimed at recycling may also be applied to traditional mining, so they tend to make the experience curves decline in parallel rather than leading to their intersection.

The promotion of recycling over mining is part of the sustainability agenda rather than being necessary to the criticality agenda, but it can still help us to reduce criticality. If we seek to advance recycling, it is necessary to make improvements in the cost areas that are particular to recycling or capitalize on its advantages. The process might be accelerated with incentives for recycling, if they are designed to bring forward the crossover of the lines in Fig. 3.17.

Potentially viable recycling technologies If recycling is to be made into a viable means of reducing criticality, it has to compete with all of the other approaches. It is necessary to reduce its costs and capitalize on its advantages wherever possible.

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Maximizing the recycling contribution to the supply chain Recycling is most likely to succeed when it can provide a significant fraction of the demand in a specific supply chain. This occurs for products that have a short product life, low growth in demand, high end-of-life retrieval rates, and high recovery process efficiency. Among these the recovery process is often already highly optimized with efficiencies above 90% being quite common.

Reducing the costs of collection and separation The largest single costs for most recycling programs are the collection of end-of-life products and disassembling them to access subassemblies that are richer in specific target materials. These operations distinguish urban mining from conventional mining and account for much of the cost differential between the two. Recycling widely distributed end-of-life devices through curbside collection programs is particularly costly. Requiring items to be brought to recycling collection points merely shifts the costs to the consumer and may have an even larger carbon footprint than curbside collection. The most attractive solution is to focus efforts on large concentrations of recyclable products where there is high turnover, such as HDDs in computer server farms, or on products that are already recycled in high volumes, such as automobiles. Where large volumes of recyclable material can be accumulated with minimal cost, the challenge shifts toward the extraction of components that contain the desired materials. This remains an artisanal operation in many cases; the manual disassembly of household appliances is common, for example. Standardized device formats assist in speeding the disassembly process, but these are relatively rare: HDDs and EV batteries are attractive targets in this regard. “Design for Disassembly” or DfD is an approach that is sometimes promoted as a system that could contribute to reducing the front-end cost of recycling by reducing the number of steps required to disassemble a device and/or allow it to be disassembled robotically. However, the financial incentives for using this approach do not fall where they can have the greatest impact. DfD primarily creates advantages for recyclers, but the cost of adoption is born by the device manufacturers. If manufacturers do not recycle their own products, the costs and rewards of DfD are separated, and there is little incentive for the approach to be used. In most cases we continue to optimize the manufacturing process and the recycling process separately, rather than optimizing over the entire lifecycle of a device or a material: this is a business-model challenge more than a technology challenge.

Process improvements A viable supply of devices to be recycled will enable the production of quantities of recycled materials that are sufficient to make an impact on the market. It will also generate economies of scale for the recycling process and provide options for automation. When the recycling target is a single device like a hard disk drive or a battery,

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the mix of materials may provide extraction options that have lower cost than those used for virgin ore. For example, rare earth magnets contain fewer rare earth elements than bastnaesite ores, so the separation challenges can be reduced. Recovered magnets can be dissolved in acid and added to the separation feedstock serving a mine, but that repeats some or all of the separation processes that were applied to them when they entered the supply chain the first time, as virgin material. Alternatively, they could be separated in a smaller plant that takes advantage of the processing that they have already received. The choice between these two paths is a trade-off between increased operating expense in the first case and increased capital expense in the second. New approaches to chemical separations may be particularly appropriate for recycling if they offer advantages such as small capital equipment needs or low environmental risk.

Membrane solvent extraction Membrane solvent extraction (MSX) is an adaptation of the conventional mixersettler approach that significantly reduces the amount of the target material that resides in the process solutions. In one approach [16], solutes are extracted from the feedstock liquid phase to the extracting liquid, through a thin liquid layer supported by porous membranes, as illustrated in Fig. 7.6. In mixer-settler solvent extraction processes, separation is limited by thermodynamic equilibrium and requires sufficient contact time for equilibrium to be

Fig. 7.6 Schematic illustration of the membrane solvent extraction process. This uses the preferential transport of REEs into the organic liquid membrane to separate them from other ions, and the separated ions are then collected in the stripping solution. The membrane acts as a filter that allows REEs to pass through but retains other elements in the feedstock solution.

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reached by solute transfer between two immiscible phases. The conventional process requires stripping of the extracted solute from the organic solvent as a separate step, while MSX combines extraction and stripping into a single process. In the MSX system, three liquid phases work together. The organic solvent serves the same role as in conventional SX systems, but it takes the form of a thin liquid film supported by a fine mesh, and it is formed into hollow cylinders making up an array of fine capillary tubes. The aqueous feedstock flows continuously through these capillaries, and the interface between the aqueous and organic phases allow the selective transfer of target ions, as in the case of the conventional system. Flowing around the outside of the capillaries, a stripping solution extracts the target material from the organic solvent. The membranes of liquid organic solvent may be understood as a filter that allows the passage of the target ions from a feedstock to a collector solution, while preventing the passage of other materials. Compared with conventional solvent extraction, MSX eliminates the need for large amounts of solute loading and avoids other challenges including the risks of flooding, third-phase formation, and extractant loss. The MSX process is accelerated by operating under nonequilibrium conditions because circulating the feed and strip solutions maintains high driving forces compared with the asymptotic loss of driving force across the stages in traditional solvent extraction counterflow array. The hollow fiber membrane system enables dispersion-free operation and large surface area per unit extractor volume, resulting in low-energy operation and high extraction rates. This process is being developed by CMI, in collaboration with Momentum Technologies, Inc., as a means of extracting rare earth elements from neodymium magnets. In this process the feedstock is made by dissolving magnets in acid, and it includes neodymium (and possibly other rare earths) along with iron and boron, along with sintering aids such as copper and coating materials such as zinc or aluminum. The system separates the rare earths from the other elements, which can also be recovered.

Acid-free dissolution While MSX offers significant advantages over conventional solvent extraction, it still relies on the same underlying chemistry, including the use of strong acids to dissolve the feedstock. An alternative magnet recycling process developed by researchers at the Critical Materials Institute dissolves magnets in an acid-free aqueous solution and recovers high-purity rare earth elements and other valuable metals [17]. The solvent is highly selective to the rare earths and specific transition metals, so the process does not require separation, presorting, or demagnetization of the feedstock, and it is appropriate for shredded wastes that contain rare earth magnets. This method recovers rare earth oxides of high purity, without the release of atmospheric pollutants or the use of hazardous mineral acids. The process has been adapted for the recovery of rare earth elements from both Nd-Fe-B and Sm-Co magnets. Other valuable coproducts of ewaste can be recovered, including copper, chromium, and nickel.

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Direct reuse of value-added materials Recycling processes such MSX and acid-free dissolution produce separated chemical elements or compounds, much like primary extraction from ores. While these separated materials may be inserted into the supply chain somewhat further downstream from primary feedstocks, there are even greater opportunities to reduce the number of processing steps if production materials are recovered and reused directly. The production of magnet alloys from elemental or master-alloy feedstocks can be avoided, for example, if the material in magnets can be simply reused. This is not necessarily a simple proposition. It requires magnets to be extracted from the retired devices in which they are contained, which is not necessary for the MSX or acid-free processes. Rare earth magnets are always coated with a metal or paint layer to protect them from oxidation, and the magnet material must also be separated from the coating. Magnet materials come in a variety of grades and compositions and if they are mixed together, the result is likely to be some kind of a “least common denominator” grade, which may or may not meet manufacturers’ needs for their products. Finally, when the recovered material embodies engineered composition distributions such as the grain boundary diffused dysprosium now found in most higher-grade Nd-Fe-B magnets, it is important to avoid distributing the dysprosium throughout the material. Some of these challenges can be addressed by maintaining a consistent feedstock stream that includes only a single product, presumably with a single grade of magnet. As we have seen, however, even single grades of magnet can have significant variations of composition, and focusing only on a single product potentially reduces the volume of the input and thus also the output of the process. All of these challenges notwithstanding, significant efforts have been focused on recovering and reusing the value-added material from magnets in retired devices. Two processes that are used in preparing Nd-Fe-B alloys for sintering during primary production have been applied to making powdered material from recovered magnets. The hydrogen decrepitation (HD) process attacks Nd-Fe-B grain boundaries and can be used to turn solid sintered Nd-Fe-B magnets into demagnetized powder for further processing [18]. The resulting powder has an average particle size in the range of 250–300 μm. This process has also been used to separate Nd-Fe-B magnets from hard disk drives. The powder particle size can be reduced to 10–15 μm using the higher-temperature hydrogenation, disproportionation, desorption, and recombination (HDDR) process, which promotes intragranular fracture. Nd-Fe-B powder derived directly from retired magnets can be used to make new sintered magnets, or it could be mixed with a thermosetting polymer and used as feedstock for making printed magnets.

Direct reuse of components Even greater value can be retained by avoiding all of the reprocessing of recycled materials and reusing them in the form in which they are extracted from retired devices. Magnets recovered from motors or disk drives might be used in making new devices, but this requires some development before it can be realized.

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It is often difficult to extract magnets from electrical machines without damaging them, and successful reuse will depend on recovery methods that produce little or no loss due to breakage or surface flaws. Damaged magnets can be reprocessed to reclaim their materials, but this would require the recycler to operate two processes: one to recover reusable magnets and another to recover reusable magnet materials. This adds capital and operating costs, and the two processes would also be mutually parasitic, effectively consuming each other’s feedstock. The reuse of successfully recovered magnets requires a product or products that use exactly the same dimensions and magnetic properties as the recovered units. A magnet that is optimized for one purpose, such as an HDD, is unlikely to be well suited to a different purpose such as an electric motor, and in cases where a magnet has a second life in a different product than its original use, the device is unlikely to produce cutting-edge performance. The best use of a recovered magnet, or any other component of a device, is in making a new version of the same device. For this to occur the design of the device needs to remain constant, at least with respect to the component being reused. In the case of an HDD, then, retaining a stable voice-coil assembly design would allow for reuse of the large Nd-Fe-B magnets that it uses, but improvements in the read-write head and/or the data storage media could still provide performance improvements over time. Manufacturers who plan to reuse parts from old devices in new production need to adopt a strategy that includes several components: l

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They need a process to assure the recovery of a large fraction of their products when they are retired from service. They need to commit to stability in their product design. They need to design their products to facilitate extraction of the components that are to be reused.

The last of these makes the connection between the costs and benefits of a DfD strategy as the manufacturer also benefits directly from the recycling process.

Lessons learned l

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You don’t recycle a material; you recycle an object or a device. – This is often a pathological case of material coproduction. – Design for disassembly is a hard sell unless there is a clear benefit to the manufacturer. – The most likely user of the material recycled from a device is the device’s manufacturer. Recycling costs can easily exceed the value that can be recovered. – Collection and disassembly are usually the largest costs for recycling processes. – Nonrecyclable materials are a significant economic burden on a recycling process. – Device complexity increases the cost of recycling. Recycling competes with other strategies for assuring supply chains, including device substitution, material substitution, and the expansion of primary sources. – The successful strategy is usually the one that produces the fastest results. – R&D that accelerates the experience curve for recycling often accelerates cost reduction for geological mining. Critical mass is important. – Economies of scale are essential to reducing recycling costs.

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Production volumes must provide a significant fraction of current demand in order for recycled materials to be adopted. Economic drivers are more effective than regulatory requirements in promoting recycling, irrespective of location. R&D efforts in support of supply-chain stewardship need to focus on the areas of greatest potential impact for each material, supply chain, device, and manufacturer.

References [1] J.B. Dahmus, T.G. Gutowski, What gets recycled: an information theory based model for product recycling, Environ. Sci. Technol. 41 (2007) 7543–7550. [2] C.R. Borra, T.J.H. Vlugt, Y.X. Yang, S.E. Offerman, Recovery of cerium from glass polishing waste: a critical review, Metals 8 (2018) 16. [3] U.S. Geological Survey, Mineral Commodity Summaries, http://minerals.usgs.gov/min erals/pubs/mcs/2019/mcs2019.pdf, 2019 (Accessed 4 March 2019). [4] A.V. Iyer, H. Lim, O. Rios, Z. Sims, D. Weiss, An economic model and experiments to understand aluminum-cerium alloy recycling, JOM 70 (2018) 547–552. [5] A.H. King, Our elemental footprint, Nat. Mater. 18 (2019) 408–409. [6] D. Konitzer, S. Duclos, T. Rockstroh, Materials for sustainable turbine engine development, MRS Bull. 37 (2012) 383–387. [7] T. Fujita, H. Ono, G. Dodbiba, K. Yamaguchi, Evaluation of a recycling process for printed circuit board by physical separation and heat treatment, Waste Manag. 34 (2014) 1264–1273. [8] M. Ueberschaar, D.D. Jalalpoor, N. Korf, V.S. Rotter, Potentials and barriers for tantalum recovery from waste electric and electronic equipment, J. Ind. Ecol. 21 (2017) 700–714. [9] K. Hanghøj, Personal Communication, (2019). [10] B. Sprecher, Y. Xiao, A. Walton, J. Speight, R. Harris, R. Kleijn, G. Visser, G.J. Kramer, Life cycle inventory of the production of rare earths and the subsequent production of NdFeB rare earth permanent magnets, Environ. Sci. Technol. 48 (2014) 3951–3958. [11] M. Zakotnik, I.R. Harris, A.J. Williams, Possible methods of recycling NdFeB-type sintered magnets using the HD/degassing process, J. Alloys Compd. 450 (2008) 525–531. [12] R.J. Daniels, T. Mcintyre, R. Kisner, S. Killough, R. Lenarduzzi, IEEE, design and implementation of a hall effect sensor array applied to recycling hard drive magnets, in: IEEE Southeastcon 2015, IEEE, New York, 2015. [13] C. Handwerker, W. Olson, W. Rifer, Value Recovery From Used Electronics, International Electronics Manufacturing Initiative, 2017, p. 90 Morrisville, NC. [14] C. Handwerker, W. Olson, Value Recovery Project, Phase 2, International Electronics Manufacturing Initiative, Morrisville, NC, 2019, p. 80. [15] L.A. Diaz, T.E. Lister, Economic evaluation of an electrochemical process for the recovery of metals from electronic waste, Waste Manag. 74 (2018) 384–392. [16] D. Kim, L. Powell, L.H. Delmau, E.S. Peterson, J. Herchenroeder, R.R. Bhave, A supported liquid membrane system for the selective recovery of rare earth elements from neodymium-based permanent magnets, Sep. Sci. Technol. 51 (2016) 1716–1726. [17] D. Prodius, K. Gandha, A.V. Mudring, I.C. Nlebedim, Sustainable urban mining of critical elements from magnet and electronic wastes, ACS Sustain. Chem. Eng. 8 (2020) 1455–1463. [18] M. Zakotnik, I.R. Harris, A.J. Williams, Multiple recycling of NdFeB-type sintered magnets, J. Alloys Compd. 469 (2009) 314–321.

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What have we learned? Nearly a decade has passed since the rare earth crisis peaked. Efforts to assure supplies of the lanthanides and other critical materials have been undertaken in industry, government, and academia, and these include technology replacement to avoid the need for critical materials, stockpiling, new approaches to purchase agreements, diplomacy, trade disputes (within or without the World Trade Organization), and R&D projects directed toward sustaining supplies or providing replacements for critical materials. The threat of supply-chain failures has fluctuated, but it has not been removed, and it may have increased. The criticalities of individual materials have varied, but the majority have increased, and those that increased have changed by larger margins than the ones that have declined. The number of materials that are considered to be critical has also grown, and as many as 35 elements are now listed as critical by at least one national organization or entity, somewhere in the world. These represent two distinct trends toward higher levels of criticality, suggesting a growing likelihood of materials supply-chain crises and a need for effective responses if they should occur. In this chapter, we reflect on the responses to the rare earth crisis and suggest some refinements to the strategies that were developed for that case, to enable more effective approaches in the future. Unsurprisingly, nearly all of the responses to the events of 2010–12 addressed issues specific to the rare earths, and with the perspective of nearly a decade, it is now possible to recognize that some of the approaches had a short-term or tactical focus, while others are more likely to produce results on a longer time frame, and these might be considered to be more strategic in nature. Some of the longer-term strategies can be applied to reduce the risks associated with any critical material, while tactical responses have tended to be more specific, focusing on challenges related to the materials immediately under threat. The R&D approaches that have been applied to reduce criticality have been essentially unchanged since the first policy statements were issued [1, 2] despite the accumulation of considerable information about the impact—or lack of it—that has been achieved. It is time to consider our successes and failures in dealing with the rare earths so that we can focus our efforts where they are most likely to succeed and identify the strategies that are most likely to be effective in dealing with other materials. We may not yet have solutions to all of the problems, but we may have gained some clarity about the questions that we need to ask.

Critical Materials. https://doi.org/10.1016/B978-0-12-818789-0.00008-6 © 2021 Elsevier Inc. All rights reserved.

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Time is the biggest challenge If we measure them by the duration of commodity price spikes, materials supply crises typically last around 18 months. There are usually signs of impending trouble before prices begin to spike, however, and the rare earth crisis of 2010 was presaged by nearly a decade of increasing tension and concern, with an early-warning signal showing up in the per-consumer consumption, illustrated in Fig. 3.9. Price spikes are also followed by several years of technology disruption, that might include the acceleration or deceleration of technological innovation, as we saw in the accelerated adoption of LED lamps and the delayed adoption of direct drive wind turbine technology in the mid-2010s, and both of these contributed to reducing demand for the rare earths. Small motors and loudspeakers also moved away from using rare earth magnets in the same timeframe. These outcomes echo the shift away from using cobalt in magnets and superalloys that occurred after it underwent a price spike in 1978. This phenomenon is sufficiently widespread and common that economists have a name for it: it is called “demand destruction.” Demand destruction is a natural economic reaction to a price spike, but in the case of critical materials, it does not occur through general reductions of demand affecting all uses to a similar extent. It is rather expressed in specific technological shifts or adaptations that affect some technologies more than others. These shifts may be catastrophic to those who rely on the affected technologies, but they can also be a means of promoting technological progress. They might be considered a necessary part of the technological ecosystem in the same way that forest fires are now understood to be a vital part of the natural ecosystem [3]. As with forest fires, we need to consider whether we will do more harm than good by trying to prevent the occurrence of materials price spikes. While occasional forest fires are considered broadly beneficial to the ecosystem, they impact individual flora and fauna to varying degrees and may destroy economic assets and infrastructural resources. Materials price spikes can likewise move technology forward, globally, while they can have positive or negative impacts on individual technologies and can seriously impact the assets of a specific company or nation. When it is necessary to fight fires to protect local resources, an effective defensive strategy is required, and a fast response is essential, and if we choose not to fight the natural process, we still need a recovery plan to deal with the aftermath. The same is true for critical materials: we may or may not choose to develop a fast response to abate a threat, but we always need a plan for dealing with the aftermath of a price spike, either as a nation, an economic sector, or a manufacturing corporation. In the case of the threats to rare earth supplies, many governments made efforts to avert the crisis, but no national plans were developed to deal with aftereffects from the rare earth price spike. In contrast, some manufacturers were quite inventive in their approaches to recovery. For example, wind turbine manufacturers in the United States and Europe built onshore units based on fast-rotating generators with gearboxes in their power trains to avoid the use of rare earth magnets, but as time went by and the technology moved toward larger offshore units, they have moved to direct-drive

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systems with slower-rotating generators that require rare earth magnets. Forests grow back after fires, often with different mixes of flora and fauna. Materials return from the demand destruction caused by price spikes, but with a different spectrum of uses. Rare earth demand recovered its precrisis growth trajectory within 5 years of the price spike, although the uses for rare earth elements have changed: rare earth magnets are used to a reduced extent in midsize motors and actuators but in greater quantities in large wind turbines. Use has shifted from applications where the properties of rare earth magnets are merely desirable to those where they are essential, and we should expect similar shifts to occur after any material suffers from a price spike. The shift of usage has tended to increase the essentiality for some of the rare earths, and this increases their criticality within the affected applications. In this regard, neodymium and praseodymium are now more essential than ever for wind turbines, but the manufacturers have been also successful in reducing the need for heavy rare earths such as dysprosium and terbium. These shifts in the usage of individual critical materials impact the value of R&D if it is directed toward the precrisis uses rather than those that are more important in the aftermath. The timescale of R&D almost always results in impacts that occur during the aftermath of a supply-chain crisis rather than helping to avert it, but most of the national R&D strategies for rare earths seemed designed to forestall rather than recover from the crisis.

Tactical responses Government-driven critical materials R&D strategies fell broadly into two categories: l

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Increasing the supply by developing new sources. Reducing the demand by developing alternative materials.

These approaches have historically been slow to bear fruit. New supplies of materials can come from primary sources such as mining or secondary sources such as recycling, and the timescale of mine development is around a decade, and recycling infrastructures can take at least as long to ramp up to industrially significant levels of production. The time between the invention of a new material and its adoption in manufacturing is of the order of 20 years [4]. Calling for these solutions to deal with an emerging materials crisis is something like calling for the construction of a water pipeline to quench an outbreaking forest fire. By the time the pipeline is in place, there will be no fire to fight, and although it might help with the next fire or the one after that, it is just as likely that it will be in the wrong place when another fire breaks out. If mines are built or new materials are invented in response to materials crises, there is no guarantee that there will be sufficient demand for them by the time they go into production. If these solutions are to be truly effective for emerging crises, they must be able to deliver solutions on the timescale over which a crisis emerges, but that is not the only imperative. We need to decide which materials supply “fires” should be fought and which ones should be allowed to burn themselves out by responding to normal market forces. Where we must respond, we need to seek ways to make the strategies work on a

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time frame that matches the challenge of a materials supply crisis. We also need to better understand and deal with the aftermaths of crises.

Choosing which fires to fight Some critiques of government interventions assert that the free market should always be relied upon to produce the best outcome, the most efficiently. Supply will respond to the “invisible hand of the free market economy” with its interplay of production, consumption, and price, as described by Adam Smith [5], and whatever technical innovations are needed will be stimulated by the opportunity to profit from them. This perspective is analogous to the view that all forest fires should be allowed to burn themselves out because the forest’s ecosystem will grow back stronger. However, there are clearly some circumstances where a forest fire must be fought, and there are similarly circumstances in which a materials supply challenge must be addressed. As with the risk of forest fires, materials criticality is either proliferating in real terms, or perhaps it is being more widely recognized. More and more substances appear in lists of critical materials with each passing year, and it is becoming harder to discern which are the most important ones to address in a crowded criticality plot. Much attention has been given to refining the definition of a critical material with a view to making the measurement of criticality more precise and presumably therefore more able to discriminate among different materials, but the reality is that all definitions depend on arbitrary assessments of the importance of different parameters, and greater precision in their measurement does not necessarily result in better prediction of materials supply crises. Governmental intervention comes in many forms, among which the creation of R&D programs and the establishment of strategic stockpiles tend to feature prominently. The current viewpoints on such interventions range a spectrum from “never intervene, always allow market forces to do their work” to “pick your fights carefully based on ever more data.” Not even the most extreme free market adherent would suggest that no case deserves intervention, no more would the most extreme interventionist would suggest that we need all-out efforts on all of the materials that appear on critical lists, and a well-designed strategy should consider all available options. It will also be helpful to apply an additional consideration. We can identify materials that appear to be critical but are likely to respond effectively to free market forces, and intervention might be more restrained for these. There are, however, materials for which the relationship between supply, price, and demand is less straightforward, and market forces should not be relied upon to provide efficient solutions. These are likely to progress from criticality to crisis quite suddenly, and there is value in developing strategies to avoid that eventuality and/or deal with it if it occurs. Finally, there are materials that are needed for strategic uses, and these need to be available irrespective of market conditions, so they require intervention irrespective of their response to market forces. We can illustrate the variable market responses that might be expected with three specific cases.

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Conventionally responsive materials: The case of lithium Lithium is considered to be a critical material primarily because it is essential in one particular technology, Li-ion batteries, and it has relatively few sources. It scores highly in assessments of its essentiality and its supply vulnerability. However, there are many undeveloped lithium resources that are easily accessible, and it is easy to process. Although it is only extracted in a few places today, there is no major challenge to expanding its production, and it might be expected that lithium extraction will grow in response to progressive increases in demand or shrink in response to decreases. The only major challenge to this scenario is the possibility that the booming demand for lithium could outstrip the development of new supplies, but growth in extraction has more than kept pace with the growth in demand, so far. Lithium might rank moderately highly as a critical material, but there is not a correspondingly high risk of a supply disruption, because it is responsive to free market forces. Many other materials are similarly responsive, but there are a few that do not obey the laws of supply and demand so straightforwardly. There are many materials for which the economic response to increasing demand or shrinking supply is suppressed, and there is at least one case in which the response seems to be exaggerated and the resulting hyperresponsivity possibly contributes to price instability, with the result that supply and demand rise and fall out of phase with each other.

Unresponsive materials: The case of tellurium Almost any material that is a by-product of another suffers from some distortion of its market responses. Tellurium, for example, is a by-product of copper extraction and sometimes also a by-product of gold mines. The world market for tellurium is around 450 tonnes/year, while for copper, it is around 20,000,000 t/year: The global production of tellurium is about only 0.002% of the production of copper, by mass, but not all copper extraction produces tellurium. Tellurium is refined from electrolytic copper anode sludge, and it takes about a million tonnes of copper ore to produce 1 t of tellurium this way. The same million tonnes of ore will typically produce around 8000 t of copper. If the demand for tellurium increases by 1 t, the production of copper would have to rise by about 8000 t to meet the new demand. If demand for tellurium doubles, copper production would need to rise by 3.6 Mt., or 18%. In 2016 the revenue generated by a million tonnes of ore would have amounted to $31,000 from Te and $36,000,000 from Cu. The imbalance between the values of copper and tellurium ensures that the demand for copper controls the production of tellurium, and it is hard to imagine any scenario in which the demand for tellurium can impact its supply through normal market processes. No mine can afford to produce excess copper to meet the demand for tellurium, and tellurium’s unresponsiveness to market forces is illustrated by its price varying by a factor of more than 10, from $350/kg in 2011 to $31/kg in 2016, while its production was almost constant. Changing demand created a change in price, but it had no corresponding effect on production: it is a case where free market dynamics do not create effective supply-chain solutions.

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In the event of an even more severe shortage resulting in even higher prices, it is conceivable that tellurium production could be decoupled from that of copper by recovering the material from copper-mine tailings or other process wastes that are still accessible. This approach involves the development of new processes and new processing capacity, so it requires process development and capital investments, which demand significant amounts of lead time. R&D efforts directed toward this outcome have very high value: If started in a timely manner, they can produce results that are ready if or when they are needed, and they would then have the longer-term benefit of unlinking tellurium production from that of copper so that free market forces are more likely to operate efficiently. All coproduced materials are similarly impacted, to an extent that depends on the ratios of production quantities and prices of the companion materials contained in an ore. Tellurium, rhenium, and gallium are all cases where miniscule outputs accompany the mass production of major host materials. The rare earths are a particularly complex case in which most of the 16 naturally occurring lanthanides are coproduced, and the production ratios do not match the industrial demands. All instances of coproduction represent cases in which conventional market forces may be challenged in their ability to produce the most efficient solution in the shortest time. The extent to which this is problematic or amenable to effective R&D solutions must be determined case by case.

Hyperresponsive materials: The case of cobalt While coproduced material supplies can be unresponsive to market forces to varying degrees, other materials can be hyperresponsive. The history of global cobalt production and price can be seen in Fig. 2.3, where we find periods when production and price rose and fell in parallel and other times when they moved in opposite directions. The global market for cobalt is about 140,000 t/year, and at this size the market is roughly comparable with titanium, antimony, tungsten, vanadium, and niobium, or all of the rare earths combined. In recent years, more than 60% of the world’s cobalt has come from the DRC, where it is coproduced with either copper or nickel in a ratio of roughly one-to-one by mass and two-to-one by value (but with a value ratio that varies considerably over time). With the value of cobalt being greater than its coproducts, we might expect market forces to generate shifts in cobalt supply with changing demand, and indeed, this does happen. However, the demand and the supply for cobalt have historically been quite “lumpy” with large shifts in both directions happening on both sides of the equation from time to time, rather than small changes occurring continuously over time. When change is continuous, the usual laws of economics are followed, but when it is discontinuous, there can be challenges. On the demand side, the consumption of cobalt has undergone significant shifts as new technologies have emerged over the last century or so. In the 1920s the emergence of cobalt-cemented tungsten-carbide cutting tools significantly increased demand. AlNiCo magnets emerged and drove up demand, again, starting in around 1940. Later in the 1940s the invention of Inconel superalloys caused another surge. In 1978 samarium-cobalt magnets threatened to drive up demand at the same time that

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DRC cobalt mines were threatened by insurrections, and the resulting price spike stalled the introduction of the new supermagnets and drove demand down again as the cobalt-based Inconel alloys began to be displaced by nickel-based alloys. Li-ion batteries with their reliance on lithium cobalt oxide have driven up cobalt demand at ever increasing rates since their invention in 2002, although efforts to reduce the ratio of cobalt to lithium have produced striking results, considerably abating the rate of growth in demand per kilogram of battery. Each of these shifts has caused significant percentage changes in global demand for cobalt, sometimes upward and, slightly less frequently, downward. The supply of cobalt has seen similarly impressive variations. In the 1970s the DRC commanded a larger fraction of the world’s cobalt production, and when the country’s principle mining areas were threatened by guerilla incursions, as much as 85% of the global production capacity was at risk. Although global cobalt production was actually increasing in 1978, prices for the metal underwent a spike in response to the threats from insurrections in the DRC, stimulating demand destruction, even while the supply was growing. In 2019, with cobalt prices falling because of softening market growth as a result of successful efforts to reduce the cobalt requirements for lithium ion batteries, the multinational mining company Glencore announced that it would suspend operations at its cobalt mine at Mutanda in the DRC. Although the DRC’s fraction of world production has shrunk since the 1970s, Mutanda was still the biggest single cobalt mine in the world, providing about 20% of the global production capacity. The closure of the Mutanda mine represents a significant stepfunction decline in production. With its history of sudden, large changes in usage and production, cobalt supply has frequently been out of phase with demand: it has often been in high supply when demand was low and in low supply when demand was high. This makes the price fluctuate significantly, and cobalt has earned a reputation for price instability that makes manufacturers think very hard before incorporating it into their products. If price instability is a hallmark of a critical material [6], then cobalt is a poster child, and this is a result of the large fractional changes that can occur in either or both of its global supply and demand. In cases like tellurium or cobalt, where the market feedback cycle connecting price and production is either suppressed or exaggerated, we may not be able to rely on free market forces to resolve imbalances between supply and demand; these are circumstances that call most urgently for intervention. The monopolization of production is a major factor that distorts the operation of free markets, and it is included in many criticality analyses, through the inclusion of modified Herfindahl-Hirschman indices: it is not however the only factor that has this effect on market response. A more comprehensive approach would be supplement current approaches to criticality analysis with a triage based on the likelihood of recovery through normal market responses. For materials that might not respond straightforwardly to the market, R&D efforts should be directed toward overcoming the factors that distort the normal market dynamics rather than simply increasing supply or decreasing demand. For materials that are likely to undergo repeated price excursions, well-conceived R&D efforts can help us to break out of cycles of repeated supply failures, eventually allowing market

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forces to exert their “invisible hand” more effectively. These tend to be cases in which the timescale of R&D is well matched to the timescale of the problem, so technological solutions can be effective.

A 10-year strategy for materials with unusual supply-demand responses A distinct and important goal is to reduce the threat of supply crises that are caused by unusual relationships between supply and demand. The materials affected by this problem suffer from repeated price surges and drops with a frequency of 10 years or more. This timescale is reasonably well matched to the timescale of research and development today, and efforts in this direction would appear to be wise investments. Specific needs include the following: l

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l

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Identifying materials for which the economic relationships between supply and demand are complicated. Measuring or at least estimating the extent of the economic complications and projecting their trajectories. Identifying and addressing the technological issues that contribute to or may ameliorate nonstandard supply-demand responses. So far, we are aware that coproduction carries this risk to varying degrees, but other factors may contribute. For the case of coproduction, we need to develop technologies that allow production rates of by-products to be adjusted independently from those of their host materials. For hyperresponsive commodities, we should seek to develop capabilities that allow extraction rates to be ramped up and/or reduced in volume and on a timescale that better matches the demand shifts occur to deal with the problems of lumpy supply and demand. Estimating the economic value of building production flexibility and comparing it with the associated cost. Building flexibility and resilience into coproduction facilities comes at a price, and it is important to establish that it has a corresponding value.

Alleviating challenges to supply-chain evolution that derive from nonstandard supplydemand responses will reduce, but will not eliminate all materials supply crises. Efforts along these lines represent a long-term approach somewhat akin to fire suppression. When a crisis does occur, it is necessary to respond on an appropriate timescale, just as we engage in fighting forest fires when we must, and matching the timescale of the response to the timescale of the problem is the biggest challenge.

A 5-year plan for improving tactical R&D responses to materials supply crises Despite our best efforts to deal with supply chains that are economically complicated, the affected materials will still undergo supply crises from time to time, as will more normally responsive materials. These crises can be caused by extraneous events that impact materials supply, coupled with a slow market response caused by long lead times for implementing solutions.

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If research and development does not produce solutions quickly enough in the face of a looming supply crisis, other outcomes will occur. These may include the temporary unavailability of some materials and technologies, or their permanent replacement, as we have seen in the case of the rare earths. Such outcomes may have consequences that are deemed unacceptable, including the inability to access systems that are vital to the interests of a nation, an industry sector, or a company. If responses based on R&D are to be considered as possible solutions to these materials supply crises, then they must be delivered significantly more quickly than has been achieved to date. Deploying an innovative technical solution as a bulwark against a looming supply crisis requires an order of magnitude reduction of the current timescale for materials innovations, and there are fundamentally only two ways to deliver a technological solution on a faster schedule: start the work earlier and do the work faster.

Starting sooner Governments around the world recognized the threats and began to consider their responses to the rare earth crisis between 18 months and 2 years before lanthanide prices peaked. In some cases they were able to establish programs to develop responses a few months before the peak occurred, but the majority of governmentfunded projects only started after the prices had begun to decline. It is clearly necessary to begin to build solutions much more quickly. Several actions can help with this: l

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Build a stronger capacity to foresee supply-chain crises and direct R&D resources where they are most needed. It is important to resist the urge to classify all materials as critical, and it is equally important to build more reliable predictive tools. This calls for greater investment in the accumulation of materials flow data, technology scenario predictions, economic analysis, and the application of artificial intelligence to finding patterns in all of the data. Build a prioritization scheme that considers the differing levels of materials criticality, the differing responsiveness to market conditions, and the differing potential for R&D impact on different materials to focus innovation efforts where they are most needed and most likely to succeed. Remove the delays associated with governmental funding approval cycles by maintaining significant longer-term research activities under leadership that has the authority to move resources as needed for emerging shorter-term needs.

The combination of these actions should allow R&D efforts to start progressively earlier, as our ability to foresee crises improves, allowing innovators a greater opportunity to impact emerging supply-chain crises.

Working faster Research efforts that are intended to produce specific deliverables are sometimes compared with the Manhattan Project or the race to put a man on the moon in the 1960s. The Manhattan Project took less than 7 years to go from concept to completion, and NASA’s Project Apollo succeeded in its primary goal in about 8 years. Efforts of

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this kind differ from “blue skies” research where the primary goal is the generation of new knowledge. All new knowledge has great value, although it may take years or decades for that value to be realized. Mission-driven research also produces new knowledge—frequently of a very fundamental nature—but it is pursued intentionally for its immediate value in achieving the overall project goal. Historians have observed that a significant difference between the Allied and German efforts to create nuclear weapons during WWII was that the Manhattan Project took a unified, mission-driven approach, while the German efforts operated in a more traditional research mode with different teams pursuing their own goals more independently, sometimes competitively, and with a primary focus on new knowledge. Committing to a comprehensive mission-driven approach gave the edge to the American-led effort, and it is necessary to adopt a similar approach if we are to deliver timely technological solutions, based on fundamental research, to materials supply crises [7]. The first challenge is to establish a path to the solution and identify the research questions that need to be answered to enable it. We need to understand the likelihood of success from different paths such as materials substitution, source diversification, and recycling, and in the early stages, it may be necessary to pursue several of these in parallel, to find their individual barriers to success. Where barriers are found, resources need to be applied to overcoming them, and if they are not overcome quickly enough, then the affected path should be abandoned, no matter how interesting the work or how much long-term promise it may have. The Manhattan Project, for example, dropped its efforts to develop gas centrifuges for uranium enrichment because of the mechanical challenges involved. It met its goals through a combination of other methods, even though centrifuges would eventually become the dominant method for enhancing the fissile content of nuclear fuel. This anecdote defines a hallmark of mission-driven R&D: immediate needs are more important than optimal solutions. When time is of the essence, a workable solution today is more desirable than a better solution tomorrow. In research, however, it is the normal practice always to pursue the “best” method, and project leaders needs to steer R&D in the direction of the fastest workable solution despite the predilections of individual researchers. Allowing research to take its usual path is effective in promoting serendipitous discoveries but is not the most productive approach when solutions are needed in a short time frame. Nevertheless, as demonstrated by the Manhattan Project, research directed with the utmost urgency toward time-sensitive outcomes can still lead to notable basic science discoveries. The Manhattan Project demonstrated the value of focusing available resources on overcoming the principle barriers to success, rather than allowing researchers to pursue the topics of greatest interest to themselves. One important aspect of this is maintaining a rigorous process for eliminating R&D efforts that show no prospect of reaching their goals and redirecting their resources in more promising directions. Go/No-Go reviews—and specifically the ones that result in No-Go decisions—are great accelerators for directed research. The effort’s leadership must seize every opportunity to obtain input on the viability of a particular effort, starting from the commissioning a project, and act on that input as quickly as possible.

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The staples of critical materials amelioration are R&D efforts directed toward building new or strengthening existing supply chains. Materials supply chains are systems of processes in which the output of one stage is the input for the next and research is usually conducted in project units that address one particular process, or link, in the chain. Although supply chains are built from individual links, each link must be properly connected to its neighbors all the way from end to end, and there is no use in developing a process or a new material for which there is no upstream source or downstream use. Each effort to improve any part of a materials supply chain must start with input from the immediately adjacent and distantly coupled links in the chain: before we set out to invent a new material, we first need to be sure that there are reliable sources for its ingredients and potential users of its output. And we need to recognize that both the availability of the input and the demand for the output can be impacted by other R&D efforts that address the needs of other links in the chain. A project that is highly successful by any of the usual measures applied to research can be rendered valueless by developments elsewhere in the supply chain. When that happens, the project should be terminated or find other sources of support as a blue-sky effort, rather than continuing to absorb resources that can support the overall mission goals of the program. If we try to increase supply by developing a new material, we have to understand all of the factors that go into a corporate decision to adopt it. Materials developers have commonly started from generalized specifications such as “the world needs a new material that emits red light, to replace europium.” University and government research centers are very capable of inventing materials in response to such a perceived need but, once they succeed, the researchers are often disappointed to find that there is no interest in their inventions. While the new material does, indeed, have the desired property, there are always other requirements, some of which may be specific to particular users. As described in Chapter 5, when the Critical Materials Institute set out to develop a europium-free red phosphor for efficient lighting, the work began in the traditional manner, with fundamental theoretical and computational studies that identified 12 distinct materials systems that could meet the need. Plans were conceived to synthesize, test, and optimize each of these, to identify the best possible choice. However, in a 10min review, an engineer from an industrial lamp manufacturer cut the candidate pool to just three, with the other nine materials being eliminated for a range of technical and business reasons, and this reduced the projected experimental work by 75%, accelerating the R&D effort by a factor of four. A new material, meeting all of the manufacturer’s needs, was developed after only 3 more years of work, but this was only possible because of the early avoidance of work on materials that would not be acceptable [8]. Despite all efforts to rationalize it, the commercialization of a new material is still an Edisonian process of downselection—the systematic rejection of unacceptable solutions—which is achieved by applying filters to the pool of candidates, as illustrated in Fig. 5.6. The order in which the filters are applied is not important: All filters should be used as soon as they are available, because the sooner we make a No-Go decision, the more the resources that can be applied to the remaining candidates, and the early application of available filters accelerates the process.

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Policies that draw distinctions between the domains of government-funded and industry-funded research efforts may be appropriate to “blue-sky” research, but they are inimical to fast-turnaround responses to emerging technological crises. Developments that affect any link in a supply chain have to be compatible with all other links in the chain, so input from all components is essential at every stage, as illustrated in Fig. 5.9.

Characteristics of effective research teams The ability to conduct rapid-turnaround research is not innate, and it is not typically part of the training provided to young researchers. The research apprenticeships provided in most doctoral degree programs emphasize individual achievements, while the kind of research and development described here is always highly collaborative. In the universities, students’ theses are written after working on a single subject for several years, while responsive R&D programs rely on the ability to switch quickly between different efforts as Go/No-Go decisions are made. Doctoral dissertations in science disciplines focus on discoveries or the testing of theories, while those in engineering focus on optimal solutions to problems. Neither of them focuses on the rapid delivery of workable solutions. The best training for team-based research is conducting team-based research. It relies on skills and attitudes that are not typically addressed in graduate programs but which, nonetheless, can be trained and honed through practice. Even if teams are constantly being reassigned, researchers and developers who are used to teamwork can readily adjust and adapt to a new assignment. When a research team is formed to complete a particular task, its members must have a clear understanding of what the task is and what constitutes its completion. It must have the expectation that the effort will end in a finite period of time—either in success or in a decision that other paths are better, even if the work is producing excellent scientific results. The team must also have the full range of competencies and infrastructure required to carry out its mission, and those competencies include a clear vision of research goals and how they connect to the upstream and downstream links in the supply chain. Ideally the research team should include or at least consult frequently with people who bring expertise with the adjacent links and the ends of the supply chain. With short time frames, it is not feasible to bring teams together and build the infrastructure they need in a single location or institution. Hiring and relocating people and acquiring the infrastructure and equipment they need consume valuable time. The preferred mode of operation is to form collaborations among researchers who stay in their home institutions and use equipment and expertise that is already in place: this calls for particular attention to communication among the team members, with the connecting links in the supply chain and with the overseeing authorities. This level of communication commands a much larger portion of the team members’ effort than is typical in a conventional research project. It is simpler to form, manage, and dissolve team efforts of this kind if the team members are familiar with each other and with the overall approach to collaboration

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and its management. This is facilitated by using a pool of researchers that is large enough to encompass all of the skills and disciplines that might be needed and small enough to meet together from time to time—somewhat along the lines of the staff of Bell Laboratories during its heyday [9]. The Critical Materials Institute has drawn on the efforts of about 350 researchers at any one time, and they have been employees of a dozen institutions with industrial collaborations that span the entire supply chains of the materials that it addresses. This has proven to be an effective organizational construct, but it is certainly not the only path forward: significantly smaller organizations have also demonstrated the ability to impact materials supply chains in a very short period of time, by focusing on single aspects such as the invention of alternative materials.

Special needs of recycling efforts The need to move quickly in response to a materials supply crisis is especially intense for solutions based on recycling, but demand destruction creates special opportunities for this approach. As we saw in Chapter 7, recycling is perennially challenged in its ability to make an impact on the supply versus demand balance for materials that exhibit market growth, especially if they are used in devices that have long service lives. Conversely, however, shrinking markets allow for recycling to provide a larger fraction of need, albeit over a relatively short period of time since markets cannot shrink forever. Shrinking markets thus represent singular but short-lived opportunities to establish recycling programs that can be optimized under favorable business conditions and then sustained if demand eventually stabilizes. The short durations of shrinking markets mean there is only a short time in which to establish a recycling program while the market for its output remains favorable. These efforts should be considered to be either “pop-up” businesses that make a quick payoff and then vanish or (preferably) businesses that use the transient market opportunity to get started then refine their process to remain profitable as the market conditions grow less advantageous. In either case, it is essential to move with the greatest urgency to develop and implement recycling programs before they lose their ability to operate at a profit.

A 5-year strategy for dealing with the aftermath of supply-chain crises A sudden increase in price is one symptom of a supply-chain crisis, although not all crises result in price excursions and not all price spikes result from actual supply-chain crises. Nevertheless, price spikes do result in demand destruction for the affected commodities, as does the expectation of supply shortages, and this can profoundly affect the development of technologies that depend on materials with particular properties. These effects are captured in the economics of commodities, and we have seen in the case of the rare earths that, following a crisis, the affected material tends to be reserved for its most essential uses and replaced in applications where it is less crucial.

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This moves the material upward on the scale of essentiality, which therefore increases its criticality rather than decreasing it. There is considerable room for refinement of this picture and a need for case studies focusing on some specific questions that can help us to predict and respond to the supply-chain shifts that occur in the wake of a price spike.

Nascent technologies Emerging technologies are particularly susceptible to the effects of supply-chain failure. The first samarium-cobalt magnet alloy was discovered in 1967 [10], and by 1978 Sm-Co magnets were on the verge of mass production for starter motors in GM trucks, despite some concerns about the availability of samarium. The introduction of the new starter motor was put on hold, however, when the cobalt crisis erupted. Sm-Co magnets only began to appear in small-volume products, such as audiophile-quality headphones, a few years later in the mid-1980s.

Aging technologies The demise of some technologies can be accelerated in the wake of a price spike. In 2012 DOE projected that the share of the lighting market commanded by fluorescent lamps would decline slowly over several decades, as they were expected to be replaced by new technologies including light-emitting diodes [11]. In this projection, fluorescents would decline from 55% of the market in 2010 to 35% in 2030. When the report was updated 2 years later, the projected decline was much faster and expected to shrink to 14% by 2030 [12]. Built around triband phosphors that rely on yttrium, europium, and terbium, fluorescents were seriously impacted by the rare earth price spike. In 2013 the retail prices of LED lamps fell below those of fluorescent lamps with equivalent output, and the fluorescent lamp industry went into accelerated decline. Compact fluorescents disappeared from the marketplace in 2016, while long-tube fluorescents persist mainly as replacement units for the large installed base. Although the early demise of fluorescent lamps can be blamed on the price of rare earths, their disappearance from the market also impacted the price of europium, which saw its value diminish by about 75% when its primary use—in fluorescent lamps—fell away in 2013. The price of terbium was not affected in the same way because, in addition to fluorescent lamp phosphors, it can be used to replace dysprosium in Nd-Fe-B magnets. The price histories of europium and terbium illustrate the impact of demand destruction and the complications of coproduction and substitution.

Knock-on criticality The destruction of demand for cobalt that occurred in the wake of its 1978 supply scare included a shift away from cobalt-based superalloys toward nickel-based materials. Because nickel aluminide required significant alloying additions of niobium to ameliorate its propensity for hot cracking, there was an ensuing period of concern about niobium supplies, which also came from the DRC, but these concerns were quite short

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lived and rather more muted that the concerns about cobalt: this was a muffled echo of the cobalt crisis, with the apparent criticality of one material helping to create a knockon effect on another. We need a deeper and more detailed understanding of this effect as a general phenomenon and the phenomena that cause it, either to dispel unfounded market concerns or to help to focus attention, as appropriate. When prices rise for critical materials, there is a need for immediate supply-chain analyses of the potential substitutes, to determine if any of them are also vulnerable to supply-chain disruptions caused by sudden increases in demand.

Constraining complexity: A 20-year strategy for criticality reduction Many phenomena contribute to the criticality of materials, and one that has received relatively little attention is the ever-increasing complexity of our devices, with a corresponding growth in the numbers of materials that they contain. With around 100 stable elements at our disposal, today’s technologies rely upon an increasingly complex palette of materials, and individual materials are made from increasingly complex mixtures of chemical elements [13]. Even relatively simple devices are growing more complex. Beer cans, originally made of a single type of steel, now use three distinct aluminum alloys and a total of at least five chemical elements, providing materials optimized individually for the can’s body, top, and pop-tab. And beverage containers are relatively simple: when aluminum beverage cans first appeared, in 1959, it was rare for a structural alloy to include more than three or four elements; today, it is common to have eight or more as we continue to set new records for key material properties. As we saw in Fig. 3.10, the first commercial mobile telephone was produced in 1983, and it required around 35 chemical elements to manufacture. Less than four decades later, the requirements have grown to somewhere between 65 and 70 elements for a modern smartphone. All of those elements are combined into materials with specific properties that deliver specific functions, and as the individual materials are growing ever more complex and specialized, more and more complex mixtures of elements and materials are being used. In many cases the compositions of materials are tailored at fine length scales to create nanoscale devices or deliver specific surface and interface properties. The trend toward materials of greater complexity not only enables technological advances that improve the lives of billions but also creates three distinct challenges: l

l

l

All of the elements that we need have to be mined somewhere. Supply-chain risks are multiplied as the number of different supply chains increases. Disposal risks increase, but recycling becomes more difficult and costly.

The mining challenge is perhaps not as great as it might appear. We do not need new mines for every new element that we use, because increasing numbers of them are coproduced, although this increases risks by complicating the feedback loop linking supply, demand, and price. Almost all of our chemical elements are obtained today, at

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least in some measure, as by-products of just 10 primary metals [14]. As long as we mine bauxite for aluminum, we will have a source of gallium, although the supply of gallium will be determined by the demand for aluminum rather than its own, unless we develop technologies that unlink the production of these two elements. An increasing fraction of the elements in the periodic table is critical in at least one application [15], posing supply risks for increasing numbers of manufacturers. The mushrooming complexity of our technology contributes to the risk: a mobile phone that requires as many as 70 elements clearly has a greater exposure to supply disruptions than a device that requires only 35. Materials are becoming more finely intermixed because of the broadening palette of materials and shrinking device sizes, and the rising level of “material mixing” creates barriers for recycling [16]. A mobile phone weighing 200 g, made up of 70 elements in a volume of about 100 cm3, is effectively a high-entropy object, even if it contains no high-entropy alloys. Separating those materials is an exercise in reducing entropy, and the second law of thermodynamics tells us that this can only be achieved through the expenditure of energy. As the entropy increases, so does the energy requirement for recycling. The value of simplicity has been recognized and promoted as a design criterion in a wide range of areas both closely and distantly related to materials science. The standardization of parts, starting with screws, was a major enabler of the industrial revolution, reducing the catalog of manufacturing components and allowing for the interchangeability of common parts. Simplification persists as a major theme in manufacturing, and today, industrial engineers universally strive to reduce their “part counts” to control manufacturing costs. Additive manufacturing is one of the methods that can be used to reduce the number of parts in a device, although it can also add structural and compositional complexity within an individual part [17, 18]. The development of Reduced Instruction Set Computer (RISC) began in the early1960s as a means of simplifying chip design. It was adopted in Cray’s highperformance processors by the mid-1960s and was widely used in personal computers by the 1980s. Its underlying principles of reducing the number of distinct circuitdesign building blocks have evolved, but they still continue to influence chip architectures today. A narrower array of computational unit processes produces greater aggregate computational power. Less is more. Simpler is better. One ongoing “design project,” however, is older than all others. Life on this planet was once generally believed to be made from a palette of only 27 chemical elements, from which DNA constructs an endless variety of proteins and other biomolecules to form the simplest to the most complex organisms [19]. The list of life essential elements grows occasionally as functions are discovered for additional trace chemicals including boron [20] and bromine [21], but life itself is not adding elements. The palette of elements required to sustain life is shown in Fig. 8.1, and comparing it with the equivalent information for a mobile telephone, shown in Fig. 3.10, is instructive. The materials supply chain for life includes the production of amino acids and their assembly into proteins. Most of the life-forms on this planet are built using of just 20 amino acids out of more than a hundred that exist in nature. Evolution seems to be able to add functional complexity without adding significant elemental complexity, and it

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H Li

He Be

B

C

N

O

F

Na Mg

Al

Si

P

S

Cl Ar

K

Ca Sc

Rb Sr

Y

Ti

V

Ne

Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr

Zr Nb Mo Tc Ru Rh Pd Ag Cd In

Sn Sb Te

Pt Au Hg Tl Pb

I

Xe

Cs Ba

Hf Ta W Re Os Ir

Bi Po At Rn

Fr Ra

Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Ac Th Pa

U Np Pu Am Cm Bk Cf Es Fm Md No Lr

Fig. 8.1 All of the chemical elements that are necessary to the majority of the life-forms on planet earth. Based on W. Mertz, The essential trace-elements, Science 213 (1981) 1332–1338.

minimizes molecular complexity along the supply chain, too. Using only a few building blocks, the biosphere is a triumph of diversity and complexity far beyond anything created by any human engineer. Materials scientists are fascinated with the ability of life to create materials that embody different functions such as strength, sensing, energy conversion and storage, self-healing, communication, and data processing. You would write almost the same list of functions for the components of a smartphone, but nature does it all with fewer than 30 elements, and it is fully recyclable. Where we optimize the mechanical properties of the individual components of a beer can by adding materials with different chemistry, nature optimizes the mechanical properties of bones by changing the arrangement of a fixed set of materials [22]. The ever-increasing complexity of materials in man-made devices is problematic. As we continue to add more elements and more specialized materials into our devices, we increase supply-chain vulnerability and the cost of managing it, we reduce our ability to recycle materials, and we multiply the risks to the environment. The conditioned reflex of materials scientists, based on their training and the tools available to them, is to create the best possible material irrespective of its complexity. It is time to think about options for reducing the element counts in our technologies, just as industrial engineers have been reducing their part counts for several decades. Great achievements have been made in materials science by mimicking biological materials designs at the nanoscale [23], the microscale [24], and the mesoscale [22]. We need to mimic biology at the system level, too, and work toward reducing the elemental complexity of our devices even while we add functionality. Apple’s removal of mercury, BFR, PVC, and beryllium from its products is a small step in the right direction, even though the palette continues to grow, overall.

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The removal of these materials appears to have been driven by concerns about environmental contamination rather than supply-chain protection, but the environmental agenda and the supply-chain agenda sometimes converge [25]. The adoption of lead-free solder in the electronics industry illustrates how the environmental and complexity agendas can also diverge: solders made of lead and tin have been replaced by alloys of tin, copper, and silver, increasing the number of elements and including one precious metal, but the increase in the overall criticality of the solder is small, compared with the benefit to the environment. Encouragingly, electric vehicles are significantly less mechanically complex than those that rely on internal combustion engines. This means that they have smaller maintenance requirements, with no scheduled fluid changes, and it also means that they can be built from a smaller palette of materials, which reduces their supply-chain complexity and potentially increases their recyclability, both of which tend to reduce their exposure to supply-chain risks and their impact on the environment. Materials science should never abandon the search for the best possible materials with the least possible environmental impact, but materials engineers also need to consider whether the “best possible material” might be the one that embodies the least complexity, if all other requirements are met. This can be addressed through the numbers of materials in our devices and also through the numbers of elements in each of our materials, and we do not need an abrupt change of paradigm to make some progress on reducing our elemental footprint. We can reduce the material count in a device by adopting a systems strategy. Where multiple components require similar or interchangeable materials, standardize on a single option. We can reduce the element counts in our materials through careful materials selection or advanced materials design. Where more than one candidate material meets the requirements for a device or a component, we should lean toward the one that contains the smallest number of elements. When designing new materials, we should place some value on constraining the number of chemical elements. Our technologies may never duplicate the biosphere’s modest footprint on the periodic table, but small steps in that direction will pay dividends and help to reduce the frequency of materials criticality events.

Summary Critical materials have been a focus of attention for a little more than a decade, although the phenomenon of materials criticality has impacted technologies and societies for hundreds if not thousands of years. Criticality evolves as technology grows more complex. We need to adapt our approaches to deal with it in the light of shortening timescales and the lessons learned both from historic and more recent events. The approaches that were developed in response to the rare earth crisis have been tested over a decade of concerted effort, and we can now revisit them with the prospect of improving their effectiveness.

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The ability of a material’s supply to respond to changes in its demand should be a focal consideration in developing a strategy for dealing with its criticality. There are many outcomes from materials supply-chain disruptions, and they occur in different timescales. It is essential to match the time frames of solutions to materials criticality to the timescales of the challenges that it creates. A mix of long- and shortterm strategies is needed with different emphases for different materials. The impacts of price spikes on the postcrisis uses of materials are complex. Organizations that understand and prepare for these effects will have significant advantages over their competitors.

Epilog: Criticality in the time of coronavirus As the manuscript of this book is being completed, in March of 2020, the world is dealing with the pandemic disease COVID-19, caused by the novel coronavirus that first emerged in late-2019. This highly communicable illness has created imbalances between the supply of and demand for medical supplies. It has forced the widespread adoption of quarantine and social distancing regimes that have had a negative effect on economic activity, worldwide. Natural disasters have created supply-chain challenges in the past, but the impacts of this one on critical materials are yet to emerge. Reductions in availability may occur where the workforces of production facilities and logistical systems are impacted by the virus, and reductions in demand will result from the downturn in the economy, so the net effect on materials supplies is still unclear, both as a general issue and for specific materials. We can expect and need to prepare for the following: l

l

l

l

l

New technologies will emerge, and some established ones will fade away. The criticalities of nearly all materials will be affected. The impact on materials supply chains will be the greatest for the most critical materials, and some of these will undergo supply-chain crises. Materials that are essential for medical technologies may become particularly critical. Current patterns of industrial materials usage will be changed in the aftermath of the pandemic.

References [1] European Commission, The Raw Materials Initiative—Meeting Our Critical Needs for Growth and Jobs in Europe, European Commission, Brussels, 2008. [2] U.S. Department of Energy, Department of Energy (Ed.), Critical Materials Strategy, DOE, Washington, DC, 2010. [3] D. Bowman, J.K. Balch, P. Artaxo, W.J. Bond, J.M. Carlson, M.A. Cochrane, C.M. D’Antonio, R.S. Defries, J.C. Doyle, S.P. Harrison, F.H. Johnston, J.E. Keeley, M.A. Krawchuk, C.A. Kull, J.B. Marston, M.A. Moritz, I.C. Prentice, C.I. Roos, A.C. Scott, T.W. Swetnam, G.R. Van Der Werf, S.J. Pyne, Fire in the earth system, Science 324 (2009) 481–484. [4] T.W. Eagar, The real challenge in materials engineering, Technol. Rev. 90 (1987) 24–34.

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[5] A. Smith, An Inquiry Into the Nature and Causes of the Wealth of Nations, William Strahan, Edinburgh, 1776. [6] M. Redlinger, R. Eggert, Volatility of by-product metal and mineral prices, Res. Policy 47 (2016) 69–77. [7] R. Rhodes, The Making of the Atomic Bomb, Simon & Schuster, New York, 1986. [8] N.J. Cherepy, S.A. Payne, N.M. Harvey, D. Aberg, Z.M. Seeley, K.S. Holliday, I.C. Tran, F. Zhou, H.P. Martinez, J.M. Demeyer, A.D. Drobshoff, A.M. Srivastava, S.J. Camardello, H.A. Comanzo, D.L. Schlagel, T.A. Lograsso, Red-emitting manganese-doped aluminum nitride phosphor, Opt. Mater. 54 (2016) 14–21. [9] J. Gertner, The Idea Factory: Bell Labs and the Great Age of American Innovation, Penguin, London, 2012. [10] K. Strnat, G. Hoffer, J. Olson, W. Ostertag, J.J. Becker, A family of new cobalt-base permanent magnet materials, J. Appl. Phys. 38 (1967) 1001. [11] Navigant Consulting Inc., Energy Savings Potential of Solid-State Lighting in General Illumination Applications, U.S. Department of Energy, Washington, DC, 2012. [12] Navigant Consulting Inc., Energy Savings Potential of Solid-State Lighting in General Illumination Applications, U.S. Department of Energy, Washington, DC, 2014. [13] A. Greenfield, T.E. Graedel, The omnivorous diet of modern technology, Resour. Conserv. Recycl. 74 (2013) 1–7. [14] N.T. Nassar, T.E. Graedel, E.M. Harper, By-product metals are technologically essential but have problematic supply, Sci. Adv. 1 (2015) e1400180. [15] T.E. Graedel, E.M. Harper, N.T. Nassar, B.K. Reck, On the materials basis of modern society, Proc. Natl. Acad. Sci. USA 112 (2015) 6295–6300. [16] J.B. Dahmus, T.G. Gutowski, What gets recycled: an information theory based model for product recycling, Environ. Sci. Technol. 41 (2007) 7543–7550. [17] Y.M. Wang, T. Voisin, J.T. McKeown, J.C. Ye, N.P. Calta, Z. Li, Z. Zeng, Y. Zhang, W. Chen, T.T. Roehling, R.T. Ott, M.K. Santala, P.J. Depond, M.J. Matthews, A.V. Hamza, T. Zhu, Additively manufactured hierarchical stainless steels with high strength and ductility, Nat. Mater. 17 (2018) 63. [18] X.Y. Zheng, W. Smith, J. Jackson, B. Moran, H.C. Cui, D. Chen, J.C. Ye, N. Fang, N. Rodriguez, T. Weisgraber, C.M. Spadaccini, Multiscale metallic metamaterials, Nat. Mater. 15 (2016) 1100. [19] W. Mertz, The essential trace-elements, Science 213 (1981) 1332–1338. [20] M. Redondo-Nieto, L. Pulido, M. Reguera, I. Bonilla, L. Bolanos, Developmentally regulated membrane glycoproteins sharing antigenicity with rhamnogalacturonan II are not detected in nodulated boron deficient Pisum sativum, Plant Cell Environ. 30 (2007) 1436–1443. [21] A.S. McCall, C.F. Cummings, G. Bhave, R. Vanacore, A. Page-McCaw, B.G. Hudson, Bromine is an essential trace element for assembly of collagen IV scaffolds in tissue development and architecture, Cell 157 (2014) 1380–1392. [22] U.G.K. Wegst, H. Bai, E. Saiz, A.P. Tomsia, R.O. Ritchie, Bioinspired structural materials, Nat. Mater. 14 (2015) 23–36. [23] R.R. Naik, S.J. Stringer, G. Agarwal, S.E. Jones, M.O. Stone, Biomimetic synthesis and patterning of silver nanoparticles, Nat. Mater. 1 (2002) 169–172. [24] F.T. Moutos, L.E. Freed, F. Guilak, A biomimetic three-dimensional woven composite scaffold for functional tissue engineering of cartilage, Nat. Mater. 6 (2007) 162–167. [25] A.H. King, When agendas align: critical materials and green electronics, in: 2016 Electronics Goes Green 2016 + (EGG), IEEE, Berlin, 2016.

Index Note: Page numbers followed by f indicate figures and t indicate tables. A Anacritical material, 78, 141, 146, 195 Accelerated experimental methods, 135–137 Accelerated insertion of materials (AIM), 138–140 Acid-free dissolution, 231 Acid mine drainage (AMD), 189 Adsorbents, 180–182 Allies of World War II, 33–38 Aluminum alloy, 147–148 cerium alloys, 146–147 World War II (1939-45), 28–29 American Society for Testing and Materials (ASTM), 127 Ames Project, 33–34 Association of Chinese Rare Earth Industries (ACREI), 11 Atomic weapons, 29–38, 31f Australian Stock Exchange (ASX), 71 B Balance problem, 194–198 Bastnaesite, 8 Beneficiation, 169–170, 169f Boer War of 1899–1902, 23 Brine mining, 179–182 British Geological Survey (BGS), 57 Bronze Age, 19–21 By-products, 185 C CalPhaD, 135–136 Cambridge Engineering Selector (CES), 127–128 “Care and maintenance”, 43 Catalytic converters, 129 Cathode ray tube (CRT), 89–90, 90f Cerium, 3–4 Cerium oxide, 5, 210

Chalcolithic era, 20 Chemical-mechanical polishing, 210 Chicago Pile-1, 34 China conflicts and conflict resolution, 97–99 rare earths (2005–15), 9–13, 10f Chromium, 27–28 Coal acid mine drainage, 189 codeposits, 188–189 fly ash, 189–190 Cobalt, 40–41, 240–242 Combinatorial methods, 135 Comminution, 168–169 Commodity price, critical materials, 62–66, 62–66f Compact fluorescent lamps (CFLs), 89–90, 101, 117–118, 148 Companion products, 185 Compounded annual growth rate (CAGR), 13 Conflict minerals, 72 Congo Free State, 40 Conventional mines beneficiation, 169–170, 169f comminution, 168–169 digestion, 170 leaching, 170–171 ore sorting, 167–168 processing stages, 165–167, 166f separation, 171–177, 171f, 173f, 175f stand-alone business, 177–178 vs. urban mining, 205–206 Copper Bronze Age, 19–21 World War II (1939-45), 28 Copper Age, 20 Coproduction, 184–198 acid mine drainage, 189 balance problem, 194–198 coal codeposits, 188–189 fly ash, 189–190

256

Coproduction (Continued) phosphate rock, 190–194 praseodymium-neodymium, 196 terbium-dysprosium-holmium, 196–198 Coproducts, 185 Cordite, 23–24 Cristallo, 21–22 Critical materials, 19 assessments of, 54–57 biggest challenge, 236–252 Bronze Age (1200 ΒΧΕ), 19–21 classification of, 54f cobalt, 40–41, 240–242 commodity prices, 62–66, 62–66f consequences of, 87 consistency and contrast, 57–60, 58t constraining complexity, 249–252 cordite, 23–24 crisis price spikes, 88 supply shocks, 88–89 technology shifts, 89–91 defining, 53 emerging trends broadening palette, 69 conflict minerals, 72 electrification, 72 longer mine development times, 71–72 middle-class aspirations, 69–70 shifting trade policies, 72–73 experience curve, 65 global trends, 60–62 indicators of coproduction, 77–78 increasingly rigorous materials specifications, 81 limited supplier diversity, 75–76 market transparency, 79–81 misleading indicators, 81–86 small markets, 76–77 lessons learned, 47–50, 91 lithium, 239 mean, 86–87 molybdenum (1980 and 2004), 42–43 national lists, 57 niobium (1979), 41–42 old lead (1978), 38–39 photovoltaic silicon (mid-2000s), 44–46

Index

population growth and consumption, 66–69, 67–68f R&D responses, 242–247 regional perspectives, 73–75 rhenium (2006–08), 47 silk and nylon (1930s and 1940s), 24 supply-chain crises, 247–252 supply-chain failures, 19 supply-demand responses, 242 tactical responses, 237–238 tantalum (1997, 2000, and 2008), 43–44 tellurium, 239–240 Venetian monopoly, 21–22 World War I (1914–18), 23–24 World War II (see World War II (1939-45)) Critical mineral, 54 Cyprus, 20 D Demand destruction, 236 Demand side, rare earth lighting, 117–120 magnet world, 116 permanent magnet primer, 102–111 technology responses, 101–120 vehicles, 112–114 wind, 114–116 Density functional theory (DFT), 133–134 Design for Disassembly (DfD), 229 Detailed feasibility study (DFS), 163 Double-fed induction generators (DFIGs), 114–116 Dynamic random-access memory (DRAM), 38–39 Dysprosium, 9, 196–198 E Eastern Mediterranean, 19–21 Electrification, 72 Electromagnetic separation, 35–36 Emerging trends, critical materials broadening palette, 69 conflict minerals, 72 electrification, 72 longer mine development times, 71–72 middle-class aspirations, 69–70 shifting trade policies, 72–73

Index

European Commission (EC), 11–12, 73–75 Europium, recycling, 216–218 Extraterrestrial mining, 184 F Feasibility study, 163 “Fizzle”, 30–31 Fluid cracking catalysts (FCCs), 5, 13 Fluorescent lamps, 148–151 Fly ash, 189–190 Ford F-150, 128 Free-market economies, 71 Froth flotation, 169–170 G Gadolinium, 3 Gadolinium gallium garnet, 5 Gadolin, Johan, 3 Gaseous diffusion, 36–37 Geological resources, 83–85 Germany World War I (1914–18), 23–24 World War II (1939-45), 32–33 Giant magnetoresistance (GMR), 143–145 Glass production, Venice, 21–22 Government Rubber-Styrene (GRS), 26 Grain boundary diffusion (GBD), 110–111 H Hard disk drives (HDDs), 143–144, 221–225, 222f, 224f Heavy rare earth element (HREE), 110–111 Heavy water molecule, 32–33 Herfindahl-Hirschman index (HHI), 76 High-strength low-alloy (HSLA), 41 Holmium, 196–198 I Indicated mineral resources, 163 Inferred mineral resources, 162–163 Integrated circuit (IC), 43 Integrated computational materials engineering (ICME), 134 Internal combustion engines (ICEs), 101 International Electronics Manufacturing Initiative (iNEMI), 141–142

257

J Japan rare earths, 11 World War II (1939-45), 25 Japanese Coast Guard (JCG), 97–98 L Lanthanum, 3–4 Laser-engineered net shaping (LENS), 137, 137f Laser induced breakdown spectrometry (LIBS), 168 Leaching, 170–171 Lead, 38–39 Lead-free solder, 141–142 Light-emitting diodes (LEDs), 120, 120f Lithium critical material, 239 ion batteries, 225–227 Lithium cobalt oxide (LCO), 226–227 London Metal Exchange (LME), 79–80 M Magnequench, 112 Magnetic moments, 104 Magnet world, 116 “Make do and mend”, 26 Manhattan Project, 33–38, 244 Manufacturing waste, 208–209 Materials genome initiative (MGI), 130–138 Material substitution aluminum-cerium alloys, 146–147 effective commercialization approaches, 156–158 effective R&D approaches, 156 existing materials catalytic converters, 129 Ford F-150, 128 materials selection improvements, 126–128 fluorescent lamps, 148–151 forecast, 124–126 giant magnetoresistance, 143–145 high-stiffness aluminum alloy, 147–148 inventing materials on demand, 123–124 lead-free solder, 141–142 neodymium permanent magnet materials, 145–146

258

Material substitution (Continued) new material deployment accelerated experimental methods, 135–137 accelerated insertion of materials, 138–140 computational tools, 132–135 database management, 137–138 materials genome initiative, 130–138 nylon, 141 quench and partition steel, 142–143 Questek’s ferrium steels, 145 rare earth magnets successes, 151–154 success factors, 155 target selection, 155–156 YInMn blue, 143 Measured mineral resources, 163 Megagauss-oersteds (MGOe), 105–106 Membrane solvent extraction (MSX), 230–231, 230f Mineral resources, 162–163 Mining brine, 179–182 conventional (see Conventional mines) development, 162–165, 164f extraterrestrial, 184 ocean-floor, 182–184 projects, 99–100 Mischmetal, 4 Molecular dynamics (MD), 134 Molecular Recognition Technology (MRT), 176–177 Molybdenum, 27, 42–43 Monazite, 7–8 Mountain Pass, 8, 99 N Natural uranium, 31 Neodymium magnet materials, 108 Neodymium permanent magnet materials, 145–146 New York Mercantile Exchange (NYMEX), 79–80 Nickel, 27 Nickel cobalt aluminum oxide (NCA), 226–227 Nickel manganese cobalt oxide (NMC), 226–227

Index

Niobium (1979), 41–42 Nuclear weapons, 29–38, 31f Nylon, 24, 141 O Ocean-floor mining, 182–184 Oil, 26 Old lead (1978), 38–39 “Optician’s rouge”, 5 Ore sorting, 167–168 Over the counter (OTC), 80 P Permanent magnet magnetic domains, 104–105f magnetic field, 102 magnetization curve, 103, 103f Nd2Fe14B, 107, 107f Phosphate rock, 190–194, 191f Photovoltaic silicon (mid-2000s), 44–46 Placer deposits, 7–8 Platinum group metals (PGMs), 177 Plutonium bombs, 30–31 Polyethylene, 29 Polysilicon, 44–45 Praseodymium-neodymium, 196 Prefeasibility study (PFS), 163 Price reporting organizations (PROs), 80 Proven reserve, 163 Q Quench and partition (QP), 142–143 R Rare earth crisis conflicts and conflict resolution, 97–99 demand side lighting, 117–120 magnet world, 116 permanent magnet primer, 102–111 technology responses, 101–120 vehicles, 112–114 wind, 114–116 impacts of, 95–97, 96–97f lessons learned, 121 prices and utilization, 120–121

Index

supply side mining projects, 99–100 recycling efforts, 100–101 Rare earth elements (REEs), 1 China (2005–15), 9–13, 10f crisis, 15–17, 15–16t critical material, 12 current uses of, 6t essentiality of, 2–7, 4f lanthanide series, 2f monopoly, 11 potential and emerging uses, 7t price spike, 13–14, 13f sources, 7–9, 8–9f Rare earth magnets, 221–225, 222f, 224f Rare earth mines, 2–3 Rare earth oxide (REO), 13f Rare-earth permanent magnet (REPM), 112–113 “Rare earths plus yttrium”, 2–3 Recycling efforts, 100–101 emerging targets for Li-ion batteries, 225–227 rare earth magnets, 221–225, 222f, 224f supply chain, 227–228 end-of-life recycling, 212–215, 212f fraction, current need, 218–221 in-process recycling, 210–211 potentially viable technologies acid-free dissolution, 231 components, 232–233 membrane solvent extraction, 230–231 single costs, 229 supply chain, 229 value-added materials, 232 reducing manufacturing waste, 208–209 regulation vs. economic drivers, 206–208, 207f successes and failures europium, 216–218 rhenium, 215–216 tantalum, 216 terbium, 216–218 urban mines vs. conventional mines, 205–206 Regional perspectives, criticality, 73–75 Reserve mineral resources, 163 Rest of the world (ROW), 10

259

Return on investment (ROI), 165 Rhenium, 47, 215–216 Rubber, 26 S Scoping study, 163 Seabed mining, 183 Silk, 24 “Soft errors”, 38–39 Solvent extraction (SX), 171, 176, 196 Source diversification conventional mines beneficiation, 169–170 comminution, 168–169 digestion, 170 leaching, 170–171 ore sorting, 167–168 separation, 171–177 stand-alone business, 177–178 coproduction, 184–198 acid mine drainage, 189 balance problem, 194–198 coal codeposits, 188–189 fly ash, 189–190 phosphate rock, 190–194 praseodymium-neodymium, 196 terbium-dysprosium-holmium, 196–198 mines development, 162–165, 164f rare earth crisis, 198–199 unconventional sources adsorbents, 180–182 brines, 179–182 extraterrestrial mining, 184 ocean floor, 182–184 Stage gate method, 165 Steel quench and partition, 142–143 World War II (1939-45), 26 Stone Age, 19 Supply chain, recycling, 227–229 Supply side rare earth mining projects, 99–100 recycling efforts, 100–101 T Tantalum, 43–44, 216 Technology readiness level (TRL), 156–157, 157t

260

Tellurium, 239–240 Terbium, 196–198, 216–218 Toronto Stock Exchange (TSX), 71, 163 Tungsten, 28 U Ultimate tensile strength (UTS), 139f Unconventional sources adsorbents, 180–182 brines, 179–182 extraterrestrial mining, 184 ocean floor, 182–184 Uranium bombs, 30 Uranium enrichment, 31–32 “Urban Mining”, 100 vs. conventional mines, 205–206 recycling, 205 V Vehicles, 112–114 Venice, 21–22 W Wind energy, 114–116 World Trade Organization (WTO), 12, 98

Index

World War I (1914–18), 23–24 World War II (1939–45) Allied efforts, 33–38 aluminum, 28–29 atomic weapons, 29–38, 31f chromium, 27–28 copper, 28 German efforts, 32–33 Japan, 25 molybdenum, 27 nickel, 27 oil, 26 polyethylene, 29 rubber, 26 steel, 26 tungsten, 28 X X-ray fluorescence (XRF), 168 Y YInMn blue, 143 Yttria-stabilized zirconia (YSZ), 5, 210–211 Yttrium oxide, 5