Handbook of Natural Zeolites [1 ed.] 9781608052615, 9781608054466

Citation preview

Handbook of Natural Zeolites Editors

Vassilis J. Inglezakis Managing Director of SC European Focus Consulting SRL Bacau Romania

& Antonis A. Zorpas Cyprus Open University, Faculty of Pure and Applied Science Environmental Conservation and Management Institute of Environmental Technology and Sustainable Development Laboratory of Environmental Friendly Technology P.O.Box 34073, 5309 Paralimni Cyprus

eBooks End User License Agreement Please read this license agreement carefully before using this eBook. Your use of this eBook/chapter constitutes your agreement to the terms and conditions set forth in this License Agreement. Bentham Science Publishers agrees to grant the user of this eBook/chapter, a non-exclusive, nontransferable license to download and use this eBook/chapter under the following terms and conditions: 1. This eBook/chapter may be downloaded and used by one user on one computer. The user may make one back-up copy of this publication to avoid losing it. The user may not give copies of this publication to others, or make it available for others to copy or download. For a multi-user license contact [email protected] 2. All rights reserved: All content in this publication is copyrighted and Bentham Science Publishers own the copyright. You may not copy, reproduce, modify, remove, delete, augment, add to, publish, transmit, sell, resell, create derivative works from, or in any way exploit any of this publication’s content, in any form by any means, in whole or in part, without the prior written permission from Bentham Science Publishers. 3. The user may print one or more copies/pages of this eBook/chapter for their personal use. The user may not print pages from this eBook/chapter or the entire printed eBook/chapter for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained from the publisher for such requirements. Requests must be sent to the permissions department at E-mail: [email protected] 4. The unauthorized use or distribution of copyrighted or other proprietary content is illegal and could subject the purchaser to substantial money damages. The purchaser will be liable for any damage resulting from misuse of this publication or any violation of this License Agreement, including any infringement of copyrights or proprietary rights. Warranty Disclaimer: The publisher does not guarantee that the information in this publication is error-free, or warrants that it will meet the users’ requirements or that the operation of the publication will be uninterrupted or error-free. This publication is provided "as is" without warranty of any kind, either express or implied or statutory, including, without limitation, implied warranties of merchantability and fitness for a particular purpose. The entire risk as to the results and performance of this publication is assumed by the user. In no event will the publisher be liable for any damages, including, without limitation, incidental and consequential damages and damages for lost data or profits arising out of the use or inability to use the publication. The entire liability of the publisher shall be limited to the amount actually paid by the user for the eBook or eBook license agreement. Limitation of Liability: Under no circumstances shall Bentham Science Publishers, its staff, editors and authors, be liable for any special or consequential damages that result from the use of, or the inability to use, the materials in this site. eBook Product Disclaimer: No responsibility is assumed by Bentham Science Publishers, its staff or members of the editorial board 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 instruction, advertisements or ideas contained in the publication purchased or read by the user(s). Any dispute will be governed exclusively by the laws of the U.A.E. and will be settled exclusively by the competent Court at the city of Dubai, U.A.E. You (the user) acknowledge that you have read this Agreement, and agree to be bound by its terms and conditions. Permission for Use of Material and Reproduction Photocopying Information for Users Outside the USA: Bentham Science Publishers grants authorization for individuals to photocopy copyright material for private research use, on the sole basis that requests for such use are referred directly to the requestor's local Reproduction Rights Organization (RRO). The copyright fee is US $25.00 per copy per article exclusive of any charge or fee levied. In order to contact your local RRO, please contact the International Federation of Reproduction Rights Organisations (IFRRO), Rue du Prince Royal 87, B-I050 Brussels, Belgium; Tel: +32 2 551 08 99; Fax: +32 2 551 08 95; E-mail: [email protected]; url: www.ifrro.org This authorization does not extend to any other kind of copying by any means, in any form, and for any purpose other than private research use. Photocopying Information for Users in the USA: Authorization to photocopy items for internal or personal use, or the internal or personal use of specific clients, is granted by Bentham Science Publishers for libraries and other users registered with the Copyright Clearance Center (CCC) Transactional Reporting Services, provided that the appropriate fee of US $25.00 per copy per chapter is paid directly to Copyright Clearance Center, 222 Rosewood Drive, Danvers MA 01923, USA. Refer also to www.copyright.com

CONTENTS Foreword

i

Preface

ii

List of Contributors

iv

CHAPTERS Part I: INTRODUCTION 1.

General Introduction

3

Maria D. Loizidou and Vassilis J. Inglezakis 2.

Natural Zeolites Markets and Strategic Considerations

11

Fernando Borsatto and Vassilis J. Inglezakis

Part II: PROPERTIES AND CHEMISTRY 3.

Zeolite Formation and Deposits

28

Ioannis Marantos, George E. Christidis and Mihaela Ulmanu 4.

Mineralogy of Natural Zeolites

52

Mihaela Ulmanu 5.

Physical and Chemical Properties

70

Ulmanu Mihaela and Ildiko Anger 6.

Catalytic Properties of Zeolites

103

Costas N. Costa, Petros G. Savva and Antonis A. Zorpas 7.

Natural Zeolites Structure and Porosity Vassilis J. Inglezakis and Antonis A. Zorpas

133

8.

Sorption Hysteresis in Zeolites

147

Mohsen Hamidpour, Hossein Shariatmadari and Mahmoud Kalbasi 9.

Modified Zeolites (a) Pretreatment of Natural Zeolites by Use of Inorganic Salts

156

Vassilis J. Inglezakis (b) Zeolites Modified with Organic Agents

166

Kathryn A. Mumford, Meenakshi Arora, Jilska M. Perera and Geoffrey W. Stevens (c) Modification of Natural Zeolites for Catalytic Applications

185

Claudia Cobzaru

Part III: RECENT DEVELOPMENTS, CURRENT RESEARCH EDGE AND FIELDS 10.

Environmental Applications of Natural Zeolites

214

Hossein Kazemian 11.

Uses of Natural Zeolites in Operations Involving Organic Gases and Vapors 238 Kyriakos Elaiopoulos

12.

Contribution of Zeolites in Sewage Sludge Composting

288

Antonis A. Zorpas 13.

Natural Zeolites in Medicine

317

Marinos A. Stylianou 14.

Utilization of Natural Zeolites in Catalysis of C-C Bond Formation Processes 335 Claudia Cobzaru

15.

Uses in Solar Energy Production and Heat Pumps Ulmanu Mihaela and Ildiko Anger

369

16.

Natural Zeolites in Space Applications and Occurrence in Extraterrestrial Environments 399 Vassilis J. Inglezakis

17.

Use of Zeolites for Improved Nutrient Recovery from Decentralized Domestic Wastewater 410 Zsófia Ganrot

18.

An Update of Zeolitic and Other Traditional Adsorption and Ion Exchange Materials in Water Cleanup Processes 436 Eva Chmielewská

19.

About Mathematical Modeling and Calculation of Dynamic IonExchange Processes on Natural Zeolites 453 Valentina A. Nikashina

Part IV: COMMERCIAL-SCALE USES AND APPLICATIONS 20.

Environmental Applications of Natural Zeolites

473

Hossein Kazemian, Kadir Gedik and İpek İmamoğlu 21.

Sustainable Use of Natural Zeolites in the Treatment of Waste

509

İpek İmamoğlu and Kadir Gedik 22.

Zeolites in Soil Remediation Processes

519

Maria K. Doula, Victor A. Kavvadias and Kyriakos Elaiopoulos 23.

Utilisation of Natural Zeolite for Air Separation and Pollution Control 569 Shaobin Wang

24.

Zeoponic Systems

588

Mohsen Hamidpour, Hossein Shariatmadari and Mohsen Soleimani 25.

Zeolites in Food Processing Industries Constantina Tzia and Antonis A. Zorpas

601

26.

Applications in Construction Industry

652

Mihaela Ulmanu 27.

Use of Natural Zeolite as Pozzolanic Material in Cement and Concrete Composites 665 Mohammad Shekarchi, Babak Ahmadi and Meysam Najimi

28.

Energy-Saving, High-Efficient Nutrient Recovery from Household Wastewater Using Struvite Precipitation and Zeolite Adsorption Techniques 695 Zsófia Ganrot Index

706

i

FOREWORD Zeolites are formed in nature by a wide range of geochemical processes at countless localities. The pioneering work in the 1930s by Professor Richard Barrer, and that other early workers, studied specimens taken from amygdales and veins arising from hydrothermal activity. These zeolites are of well-formed crystalline habit and many magnificent examples can be seen in all major museum mineral collections. The interest in natural zeolites grew in the 1950s when they were recognised as important rock-forming minerals in a variety of sedimentary rocks where they occur as finely crystalline microscopic crystals. They are amongst the most common silicate minerals in these rocks, and occurrences of this type are vast. They are of great geological significance- as well as being of considerable economic potential. Commercial mining of sedimentary zeolites takes place in at least 17 countries and the products of this activity find a wide range of uses ranging from soil amendment, aquaculture and environmental improvementsespecially in waste water remediation. It is 10 years since the last book on natural zeolites was published so an update is due, but this book is particularly welcome because of its clearly intended function as a teaching tool coupled with a detailed coverage of natural zeolite use in current commercial processes and future market potential. It is an honour to be invited to provide this foreword.

Professor Alan Dyer

University of Salford, UK

ii

PREFACE This book has started back in time, during our PhD study in the National Technical University of Athens, School of Chemical Engineering (Greece) when Vassilis was working in the Chemical Reaction Engineering lab and Antonis in the General Chemistry lab both experimentalists, both on natural zeolites but on different subjects: water/wastewater and sewage sludge treatment, respectively. However, it took more than 14 years to for us to mature as scientists and to come up with the ambition and the determination to write a book on Natural Zeolites. We will never forget our excitement when by accident we have independently discovered a strange behavior of clinoptilolite; the smaller particle size followed slower kinetics towards the ion exchange both in aqueous and solid phase systems, a clear contrast to the basic theory. Our first common article was a reality in 2002: Particle Size Effects on Uptake of Heavy Metals from Sewage Sludge Compost Using Natural Zeolite Clinoptilolite, Journal of Colloid and Interface Science, vol. 250, pp. 1-4. It is a honor for us to have in our book an impressive number of 36 authors coming from 12 different countries, namely Greece, Cyprus, Romania, Slovakia, Russia, Sweden, UK, Turkey, Iran, Canada, Brazil and Australia. The authors are mainly coming from Universities (61%) and public research institutes (28%) with considerable participation of private sector (11%). Thus, we consider that the geographical, cultural, scientific and professional diversity of the authors guarantees the quality of this work. The participation of Professor Alan Dyer in our book as signatory of the Preface is an event that we will never forget and will always be an ultimate honor for us. From this position we have the need to thank by hart all those who have supported us as well as all those who have discourage us throughout our carrier; all experiences are valuable. We have learned that the most important values of life are the ones which are without price; hereby after 14 years we offer you the output of a long-lasting friendship.

iii

For Vassilis and Antonis research is an Art. We hope the readers to appreciate our efforts and to enjoy reading. Please note that no financial contributions or any potential conflict of interest to any of the book chapters exist.

Vassilis J. Inglezakis SC European Focus Consulting SRL Bacau Romania

& Antonis A. Zorpas Cyprus Open University, Faculty of Pure and Applied Science Environmental Conservation and Management Institute of Environmental Technology and Sustainable Development Laboratory of Environmental Friendly Technology P.O.Box 34073, 5309 Paralimni Cyprus

iv

List of Contributors Ahmadi Babak

Research Staff, Construction Materials Institute, Department of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran

Borsatto Fernando

Director, Indústrias Celta Brasil Ltda., Brazil

Chmielewská Eva

Professor, Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia

Christidis George

Professor, Technical University of Crete (TUC), Department of Mineral Resources Engineering, Chania, Greece

Cobzaru Claudia

Lecturer, “Gheorghe Asachi” Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Romania

Costa N. Costas

Associate Professor, Cyprus University of Technology, Department of Environmental Science and Technology, 30 Archbishop Kyprianos, 3036 Lemesos, Cyprus P.O. Box 50329, 3603 Lemesos, Cyprus

Doula Maria

Researcher, Soil Science Institute of Athens, National Agricultural Research Foundation, Likovrisi, Greece

Elaiopoulos Kyriakos

Research Staff, Chemical Processes Engineering Lab., School of Chemical Engineering, National Technical University, Athens, Greece

Ganrot Zsófia

Scientific Staff, Melica Environmental Consulting and Research Staff, Again Nutrient Recovery AB, Göteborg, Sweden

Gedik Kadir

Assistant Professor, Department of Environmental Engineering, Akdeniz University, Antalya, Turkey

v

Hamidpour Mohsen

Assistant Professor, Environmental Soil and Water Chemistry, Soil Science Department, Vali-e-Asr University of Rafsanjan (VRU), Rafsanjan, Iran

Ildiko Anger

Senior researcher, National R&D Institute for Nonferrous and Rare Metals, Eco-technologies and Environment Protection Laboratory, Bucharest, Romania

İmamoğlu İpek

Associate Professor, Department of Environmental Engineering, Middle East Technical University, Ankara, Turkey

Inglezakis J. Vassilis

General Director, SC European Focus Consulting SRL, Bacau, Romania

Kavvadias A. Victor

Associate Researcher, Soil Science Institute of Athens, Hellenic Agricultural Organization “DEMETER”, Likovrisi, Greece

Kazemian Hossein

Department of Chemical and Biochemical Engineering, Faculty of Engineering, Western University, London, Ontario, N6A 5B9, Canada

Loizidou Maria

Professor, Unit of Environmental Science and Technology, School of Chemical Engineering, National Technical University, Athens, Greece

Mahmoud Kalbasi

Department of Soil Science, Islamic Azad University, Khorasgan Branch, Isfahan, Iran

Marantos Ioannis

Scientific Staff, Greek Institute of Geology & Mineral Exploration, Greece

Meenakshi Arora

Lecturer, Department of Civil and Environmental Engineering,, The University of Melbourne, Victoria 3010, Australia

Mumford A. Kathryn

Lecturer, Particulate Fluids Processing Centre, Department of Chemical & Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia

vi a

Najimi Meysam

Department of Civil and Environmental Engineering, University of Nevada-Las Vegas, USA b Concrete Technology Department, Building and Housing Research Center, Tehran, Iran

Nikashina A. Valentina

Head of the research group in the Sorption Methods Laboratory of Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, Russia

Perera M. Jilska

Senior Research Fellow, Particulate Fluids Processing Centre, Department of Chemical & Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia

Savva Petros

Special Teaching Staff, Cyprus University of Technology, Department of Environmental Science and Technology, Cyprus

Shariatmadari Hossein

Professor, Soil Science Department, Isfahan University of Technology (IUT), Isfahan, Iran

Shekarchi Mohammad

Construction Materials Institute (CMI), Department of Civil Engineering, College of Engineering, University of Tehran, Tehran, Iran

Soleimani Mohsen

Assistant Professor, Department of Environmental Science, Faculty of Natural Resources, Isfahan University of Technology, Isfahan, Iran

Stevens W. Geoffrey

Professor, Particulate Fluids Processing Centre, The Department of Chemical & Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia

Stylianou A. Marinos

Research Staff, Unit of Environmental Science and Technology, School of Chemical Engineering, National Technical University, Athens, Greece

Constantina Tzia

Laboratory of Food Chemistry and Technology, School of Chemical Engineering, National Technical University of Athens (NTUA), Greece

Ulmanu Mihaela

Senior Researcher, Environmental Protection and Ecology Department of the Institute for Non Ferrous and Rare Metals

vii

(IMNR), Bucharest, Romania Wang Shaobin

Associate Professor, Department of Chemical Engineering, Curtin University of Technology, Perth, Australia

Zorpas A. Antonis

Cyprus Open University, Faculty of Pure and Applied Sciencem, Environmental Conservation and Management, Director, EnviTech Ltd, Institute of Environmental Technology & Sustainable Development, Paralimni, Cyprus

Part I:

INTRODUCTION

Handbook of Natural Zeolites, 2012, 3-10

3

CHAPTER 1 General Introduction Vassilis J. Inglezakis1,* and Maria D. Loizidou2 SC European Focus Consulting srl, Bacau, Romania and 2National Technical University of Athens, School of Chemical Engineering, Unit of Environmental Science and Technology, Athens, Greece 1

Abstract: The term zeolite coming from the Greek words, which mean stone that boils, was originally coined in the 18th century by a Swedish mineralogist named Cronstedt. A zeolite is a crystalline aluminosilicate with a cage structure. Natural zeolites combine comparative simplicity of mining, relatively low cost, worldwide distribution and in combination with their unique physicochemical properties they became the most important minerals. The zeolite group includes more than 40 naturally occurring species, some of them are rare, all beautiful with diverse complexity and unique crystal habits.

Keywords: Natural zeolites, ion exchange, adsorption, framework, history, stilbite, natrolite, chabazite, analcime, heulandite, philipsite, faujasite, mordenite, clinoptilolite, erionite, ferrierite. INTRODUCTION The discovery of large deposits of sedimentary zeolites together with their comparative simplicity of mining, relatively low cost and worldwide distribution gave easy access to these minerals for large-scale utilization [1]. The unique physicochemical properties of zeolites have made them the most interesting class of minerals for scientists since their first known description. Since the late ‘50s, the interest in natural zeolites has steadily increased. The Greek name of zeolite, “ζέιν”, to boil, and “λίθος”, stone, describes the zeolite behavior under fast heating conditions, when the zeolite seems to boil because of the rapid water loss [2]. The zeolite group belongs to the class of minerals known as tectosilicates, a group that comprises nearly 75% of the Earth crust. Tectosilicates or framework silicates have a three-dimensional framework *Address correspondence to Vassilis J. Inglezakis: EFCon, Str. Banatului nr. 16, Bacau, Romania; Phone/Fax: +40-(0)334415609; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

4 Handbook of Natural Zeolites

Inglezakis and Loizidou

of silicate tetrahedra with SiO2 or a 1:2 ratio and with the exception of the quartz group are aluminosilicates (Fig. 1). The zeolite group includes more than 40 naturally occuring species, the largest group of the minerals among the silicates. Seven of them, namely mordenite, clinoptilolite, ferrierite, chabazite, erionite, philipsite and analcime, occur in sufficient quantity to be considered as viable mineral resources. Clinoptilolite is the most abundant zeolite that occurs in relatively large mineable sedimentary deposits in sufficiently high purity in many parts of the world [3]. Zeolite is an inorganic micro-porous mineral of volcanic origin with highly regular structure of pores and chambers. The crystalline substance with a structure characterized by a framework of linked composed of TO4 tetrahedra (T = Si, Al) with O atoms connecting neighboring tetrahedra. The zeolite composition can be described as having three components as follows [4]: M nm    Si1 n AlnO2   nH 2O m

extraframework cations · framework · sorbed phase

Figure 1: Surface of natural clinoptilolite magnified by 2,500 times (SEM analysis). Some crystals are visible.

General Introduction

Handbook of Natural Zeolites 5

The framework contains open cavities in the form of channels and cages occupied by H2O molecules and extra-framework cations as K+, Na+, Ca2+ and Mg2+ that are commonly exchangeable (Fig. 2 and Table 1). The amount of Al within the framework can vary over a wide range, with Si/Al = 1 to  , the completely siliceous form being polymorphs of SiO2 [4]. In nature most zeolites are of lower Si/Al ratios, but in industry by use of special chemical agents the formation of siliceous zeolites is possible. Zeolites are members of the family of microporous solids known as molecular sieves. This term refers to the ability of certain solids to selectively sort molecules based primarily on their size. This is due to a very regular pore structure of molecular dimensions. In general, zeolites fulfill the following classification rules [2]: a.

Framework cations tetrahedrally coordinated

b.

Channel and cage system in the range of 0.2 Å to 20 Å

c.

Zeolitically bound water

d.

Cation exchange properties

Figure 2: Chemical analysis of natural clinoptilolite (SEM/EDS analysis).

6 Handbook of Natural Zeolites

Inglezakis and Loizidou

Table 1: Chemical analysis of a Greek natural clinoptilolite of 75-85% purity Oxide

%

SiO2

66.462.06

Al2O3

12.783.36

Na2O

1.180.83

K2O

1.420.57

CaO

2.661.29

MgO

1.500.44

FeO

1.150.79

H2O

12.060.55

Rule (c) and (d) is exclusively fulfilled by true zeolites, while rule (a) and (b) is a necessary condition for a structure type to be a zeolite. Zeolite materials known today do have maximum diameters of pore openings of 7.4 Å (alumosilicate-type zeolites) and 12.1 Å (alumophosphate-type zeolites). It is characteristic for true zeolites that the channel and cage systems do have crystalline properties [2]. Naturally occurring zeolites are rarely pure, as they are found along with impurities to varying degrees. Impurities could be other minerals, quartz, other zeolites etc. Then, it is not surprising that frequently natural zeolites are excluded from commercial applications where high degree of uniformity and purity are essential. Although it is true that synthetic zeolites are superior in terms of purity, pore size uniformity and ion-exchange abilities, natural zeolites are more applicable when there are huge demands and fewer quality requirements. Natural zeolites are very often located near the surface and can be easily exploited and used after some simple treatment keeping the cost at low level [5]. A SHORT HISTORY OF NATURAL ZEOLITES For nearly 200 years since their discovery in 1756 geologists considered the zeolite minerals to occur as fairly large crystals in the vugs and cavities of basalts and other rock formations. Then in late 1950s, huge beds of zeolite-rich sediments, formed by the alteration of volcanic ash (glass) in lake and marine waters, were discovered in the western United States and elsewhere in the world. It was the same period when the synthetic zeolite business began to take hold, but

General Introduction

Handbook of Natural Zeolites 7

it was clear that these low-cost natural materials had similar properties and considerable effort has made since that time to develop applications for them [6]. Some well known applications are in soil amendments in agronomy and horticulture, pet litters, ammonia filters etc. In the past they were used in construction during Roman times and they are currently used as hydroponic (zeoponic) substrate for growing plants on space missions [6]. Maybe the fields of agriculture and environmental protection are the most important applications in volume terms. Zeolitic tuff has been used as a sculpturing and as a dimension stone for buildings since approximately 2,800 years ago. Romans utilized zeolites for the production of pozzolanic cement. However, zeolites were identified as mineral group exactly 256 years ago, in 1756 [7, 8]. Since then, 18 naturally occurring zeolites were discovered by 1825, 7 more in the remainder of the 19th centuryand another 25 in the 20th century (Table 2) [9]. Table 2: Discovery timeline of some important natural zeolites [9] Zeolite

Year

Stilbite

1756

Natrolite

1758

Chabazite

1772

Analcime

1784

Heulandite

1801

Philipsite

1824

Faujasite

1842

Mordenite

1864

Clinoptilolite

1890

Erionite

1890

Ferrierite

1918

Axel Fredrik Cronstedt (1722-1765), the famous Swedish mineralogist, was the first scientist who described this class of minerals. Cronstedt examined two samples, one which was said to come from Iceland, the other coming from Svappavaara in northern Sweden near Kiruna where the first zeolite, a stilbite, was collected by Dennis Holmberg, a minerals collector living in the area [10].

8 Handbook of Natural Zeolites

Inglezakis and Loizidou

Stilbite consists of hydrated calcium aluminium silicate, NaCa2Al5Si13O36·14H2O, a mineral of secondary origin, found with other zeolites in basaltic volcanic rocks, sometimes in granite and gneiss and exceptionally in hydrothermal veins (Fig. 3).

Figure 3: Stilbite structure: Cations in color, H2O molecules in blue (International Zeolites Association, IZA Commission of Natural Zeolites, www.iza-online.org/natural/index.htm).

Using the available chemical analyses and crystallographic observations, Haüy (1801) organized information for eight minerals thought to be zeolites. The names he used are harmotome, stilbite, chabasie, analcime, mesotype, prehnite, lapis lazuli (lazurite), and zeolithe efflorescente (laumontite). During the next few decades, improvements in analytical methods and refined observations on crystals caused the number of known zeolite minerals to more than double [11]. In 1858, Eichhorn showed that these materials have ion exchange properties and in 1857 Damour demonstrated their hydration-dehydration properties. Near the end of the 19th century Dana (1899) listed 22 minerals in the zeolite group of which all but two, ptilolite and laubanite, remain valid today. In 1925 Weigel and Steinhof separated gas molecules on the basis of size once the water had been removed from the zeolite's (chabazite) internal structure, a phenomenon termed as molecular sieving by McBain in 1932. Few years later Barrer's monumental work in London (1938) and Samashima's in Tokyo (1929-1935) on zeolite adsorption and molecular sieve phenomena focused on chabazite and other zeolite crystals. In the same decade the first crystal-structure determination of a zeolite was done on analcime by Taylor (1930) and in the same year Hey concluded that zeolites in

General Introduction

Handbook of Natural Zeolites 9

general have aluminosilicate frameworks with loosely bonded alkali or alkaliearth cations, or both [12]. Specific zeolite minerals have been named either from Greek or Latin words or from the names of people or towns connected with the mineral [7]. Analcime from analkis (Greek) = without strength as it has a weak electrical charge when heated or rubbed. Chabazite from chabazios, chalazios or khalazios an ancient Greek name for a stone mentioned in the poem Perilithos, ascribed to Orpheus. Clinoptilolite from the Greek klinein = to bend or slope or from clinic for a wing or down, referring to its lightness, and lithos = stone. Heulandite for J.H. Heuland (1778-1834), an English mineral collector. Erionite from the Greek erion= wool, because of its white, fibrous, wool-like appearance. Ferrierite for W.F. Ferrier (1865-1950), a Canadian geologist and mining engineer. Mordenite for Morden in Nova Scotia, Canada. Natrolite from the Latin natrium or Greek natron = native soda and lithos = stone. Phillipsite for W. Phillips (1775-1829), a British mineralogist and founder of the Geological Society of London. Stilbite from the Greek stilbe = lustre, in allusion to the pearly to vitreous luster [7]. Fred Mumpton, through his paper in 1960 played a pivotal role in the recognition that clinoptilolite is probably the most important zeolite on the surface of the Earth [13]. Although heulandite was first recognized in the 1700s, clinoptilolite was not named until 1932 (Schaller, 1932). Another important zeolite, mordenite, named after its type locality (Morden, Nova Scotia), was discovered by How (1864). ACKNOWLEDGEMENTS We wish to thank the International Zeolites Association (IZA) and in particular the former President (2004-2010) Dr. François Fajula, Director of the Institut Charles Gerhardt Montpellier, Ecole Nationale Supérieure de Chimie, Montpellier-France for the permission to use figures from website of IZA (www.iza.org). CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1]

Tsitsishvili G, Andronikashvili T, Kirov G, Filizova L. Natural Zeolites. Ellis Horwood Limited, England, 1992.

10 Handbook of Natural Zeolites

[2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12]

[13]

Inglezakis and Loizidou

Ghobarkar H, Schiif H, Guth H. Zeolites - from kitchen to space. Prog. Solid St. Chem. 1999; 27: 29-73. Sarıoglu M. Removal of ammonium from municipal wastewater using natural Turkish (Dogantepe) zeolite. Separation and Purification Technology 2005; 41:1-11. Handbook of zeolite science and technology, Scott M. Auerbach, Kathleen A. Carrado, Prabir K. Dutta (Eds), Marcel Dekker Inc, New York-Basel, 2003. Ruren X, Wenqin P, Jihong Y, Qisheng H, Jiesheng C. Chemistry of Zeolites and Related Porous Materials: Synthesis and Structure, Wiley, 2007. Mumpton FA. La roca magica: Uses of natural zeolites in agriculture and industry. Proc. Natl. Acad. Sci. USA 1999; 96: 3463-70. Christie T, Brathwaite B, Thompson B. Mineral Commodity Report 23 - Zeolites. New Zealand Mining 2002; 31: 16-24. Mumpton F. Development of uses for natural zeolites: A critical commentary, In: D. Kallo and H.S.Sherry (Eds.), Occurrence, Properties and Utilization of Natural Zeolites, Akademiai Kiado, Budapest, Hungary, 1988. Barrer RM. Zeolites and Clay Minerals as Sorbents and Molecular Sieves, Academic Press, London, 1978. Colella C, Gualtieri AF. Cronstedt’s zeolite, In: R. S. Bowman and S. E. Delap (Eds.), Zeolite ’06, 7th International Conference on the Occurrence, Properties, and Utilization of Natural Zeolites, Socorro, New Mexico USA, 16-21 July 2006; 3-4. Wise WS. Early discovery of zeolite minerals, In: R. S. Bowman and S. E. Delap (Eds.), Zeolite ’06, 7th International Conference on the Occurrence, Properties, and Utilization of Natural Zeolites, Socorro, New Mexico USA, 16-21 July 2006; 8. Coobs DS, Alberti A, Armbruster T, Artioli G, Colella C, Galli E, Grice GD, Liebau F, Minato H, Nickel EH, Passaglia E, Peacor DR, Peacor S, Rinaldi R, Ross M, Sheppard RA, Tillmanns E, Vezzalini G. Recommended Nomenclature For Zeolite Minerals: Report Of The Subcommittee On Zeolites Of The International Mineralogical Association, Commission On New Minerals And Mineral Names. The Canadian Mineralogist 1997; 35: 1571-606. Mumpton FA. Clinoptilolite redefined. American Mineralogist 1960; 45: 351-69.

Handbook of Natural Zeolites, 2012, 11-27

11

CHAPTER 2 Natural Zeolite Markets and Strategic Considerations Fernando Borsatto1,* and Vassilis J. Inglezakis2 1

Indústrias Celta Brasil Ltda., Brasil and 2SC European Focus Consulting srl, Bacau, Romania Abstract: In the 20th century, in particular from 1930 to 1970, synthetic zeolites were used in most commercial applications. Gradually, due to large deposits being discovered all over the world, low price and good performance in several applications, natural zeolites found their way into the market. The applications of natural zeolites are numerous and enterpreneurs around the globe pay more and more attention to products and technologies based on these extraordinary materials. As a result, there is a worldwide trend to increase production and consumption of natural zeolites and to perform technical studies focused on the development of new products of high added value. This Chapter does not aim to establish rules or to provide robust directions for decisions and actions of entrepreneurs and scientists involved in commercialization projects employing natural zeolites but to raise some issues for brainstorming and to provide some insight in the fascinating world of zeolites business.

Keywords: Zeolite markets, zeolites production, zeolite deposits, zeolite prices.

commercial

applications,

zeolites

INTRODUCTION During most of the 20th century, especially before the discovery of huge deposits of zeolite-containing rocks, most zeolite-based commercial applications involved synthetic zeolites. Zeolites were first synthesized in the 1930s, but the synthetic zeolites market actually kicked off in the 1960s, when the petroleum refining industry started to use them at large scale in catalytic cracking processes [1]. Since then, more than 150 zeolites have been synthesized in an effort to develop more efficient catalysts. In the 1970s, demand peaked again as synthetic zeolites were successfully used to replace phosphate compounds in laundry detergent powders. Gradually, thanks to the occurrence of large zeolite-rich deposits all over the world, low price and good performance in a variety of applications, 

Address corresponding to Fernando Borsatto: Indústrias Celta Brasil Ltda. Cotia/São Paulo-Brasil; Tel: + 55 11 4615 7788; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

12 Handbook of Natural Zeolites

Borsatto and Inglezakis

natural zeolites found their way into the (so far dominated by the synthetic species) zeolite market. The variety of possible uses of natural zeolites derives from their high potential as ion exchangers, adsorbents and molecular sieves. A most well-known application is the removal of heavy metals and other cations, such as lead, nickel, iron and manganese, from contaminated drinking water or from wastewater prior to disposal to receiving water bodies. Natural zeolites have an important role in agriculture, as they are used to improve farmable land, to potentiate chemical and organic fertilizers and as components of substrates for the development of plantation while they are also used in the livestock industry, most commonly as food additive. Therefore, the applications of this natural mineral are quite numerous and greater attention from entrepreneurs around the globe interested in developing products and technologies based on natural zeolites is observed. As a result, there is a worldwide trend to increase production and consumption of natural zeolites and to conduct research work focused on developing products of high added value. More important than simply presenting the history of the production and consumption growth rate of natural zeolites is the need to present to the entrepreneurs and potential investors the real business opportunities that tend to arise in a future which seems to be linked to sustainability and eco-friendly technologies. In such a scenario, natural zeolites are highlighted as products important for the development of new green technologies. GENERAL WORLDWIDE ZEOLITES MARKET SITUATION Aiming to systematically evaluate the global market data about natural zeolites, we face the difficulty of consolidating the information and of drawing parallels with the trends in related applications. There are many reasons to explain these difficulties. Firstly, we face the fact that the various types of zeolites found in nature are often not considered in the production statistics in the country of origin. Another issue is that, in many countries, these natural minerals are used as raw material in the production process of another end product and, in order to evaluate this use, a detailed market-to-market analysis is required. Finally, there are countries, including Brazil as an example, where no reliable data source that could be safely used for statistical evaluation of imports, exports and marketing of natural zeolites exists [1].

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 13

Thus, we are led to present information collected through discussions with business groups around the world combined with reliable statistical data from countries that develop their natural zeolite market at high professionalism standards. A helpful source of information is the work of INZA (International Natural Zeolite Association) and its international conferences organized around the world. These global meetings allow for the interested stakeholders to exchange information on applications of natural zeolites and observe how entrepreneurs put these minerals in value. It is frequently noticed in these conferences that scientists and enterpreneurs have very different views and interests. This is in part explained by the low investments by entrepreneurs in research and development on zeolite natural minerals. The business side justification is that many scientists have no practical project ideas to secure the return of investment to the companies. Although both sides have reasonable and understandable arguments, the point is that both the scientific and the enterprise fields must work together and tuned in to assist, through technical and commercial activities, natural zeolites push their way into an effective scenario of worldwide attention. It is clear that many companies devote their efforts to focusing on some specific fields of application; animal nutrition is an example. There is a concentrated effort by many entrepreneurs to establish natural zeolites and/or modification-based secondary minerals as products with high mycotoxins absorption capacity, and successful commercialization can be found in Europe and the United States. Another field that deserves to be highlighted is the large number of products developed for water treatment, focused on ammonia and heavy metals removal. In this market segment, it is worth underlining the variety of products with high market penetration available for pool water treatment. In this field, the success of – mainly – Australian and European business groups is remarkable. It is also true that some producers tend to make ends meet chasing the best market opportunity in terms of logistics, in other words, they seek to create products and business structure to meet the demands of a segment that is closest to their production or supply area. Cases of successful applications in the production of pozzolanic cements and in agriculture are mainly located at Europe and Asia, where producers can show competitiveness in segments that require natural zeolites at low cost because of the proximity to their market. As a matter of fact, companies

14 Handbook of Natural Zeolites

Borsatto and Inglezakis

tend to organize themselves in accordance with opportunities generated in their operation area resulting in a variety of natural zeolites commercial applications. World resources of natural zeolites have not been well-defined so far but an approximate estimation is that 120 million tons of clinoptilolite, chabazite, erionite, mordenite, and phillipsite are present in near-surface deposits in the basin and range province in the United States while possible resources in the United States could reach up to 10 trillion tons of zeolite-rich deposits. Furthermore, it is estimated that global production lies in the range of 2.5 to 3 Mt per year, based on statistical reports submitted by the main producers as presented in Fig. 1 [1]. In general, markets for natural zeolites are smaller and less associated with construction and manufacturing applications than for most other industrial minerals. Worldwide demand for natural zeolites remained fairly static between 2000-2004, increasing by some 1% per year and remaining in line with production levels. The greatest future market potential, in terms of tonnage, seems to be in zeolitic pozzolans as partial or complete replacement of Portland cement [2]. Generally, Japan has a particularly wide range of zeolite market sectors covering for agricultural, industrial, and consumer uses, in North America the market is directed mainly towards agricultural and pet litter sectors, in China the largest shares are for cement additives and in Europe and Cuba for agricultural purposes, with a growing industrial market sector [3]. 10000000 1000000

Metric Tons

100000 10000 1000 100 10 1

Figure 1: World production of natural zeolites [1]. Metric ton = 1000 kg, short ton ≈ 907 kg.

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 15

As it can be seen in Fig. 1, China is the world's largest producer of natural zeolites. Yet, in terms of technical applications, the Chinese mineral is of low quality in comparison to minerals from other countries and its applications are inevitably focused on economies of scale and on low added value products such as pozzolanic cement [2]. Russia stocks large reserves of this mineral, but zeolite implementation in Russian industry is close to zero. Another country that is renowned for the quality of its mineral is Cuba, which accounts for 0.53% of global zeolite production (16,500 tn). In the 80’s, much research on natural zeolites was carried out thanks to mineralogical investments in Cuba but this evolution was interrupted by the economic crisis in the 90’s after the end of the Soviet Union and the rapid changes in the former socialist countries of Eastern Europe, their main economical and ideological allies. The transport and capital shortage, together with other difficulties brought about by the crisis, considerably brought down the use of zeolite that was on its way to widespread use, mainly for agriculture purposes [4]. The activities resumption and production development of natural zeolites only occurred in the early 2000s, when some foreign countries, like Brazil, Colombia, Canada and Italy, started to get interested in the Cuban mineral leading to an exponential increase in Cuban natural zeolite exports [5]. This burst of Cuban zeolites industry also encouraged natural zeolites application in the domestic market and makes it possible for Cuba to turn into a major natural zeolite producer. Fig. 2 presents information on production and consumption of natural zeolites in the market of the USA [6]. A high level of professionalism characterizes US market and a strong data consolidation of various natural zeolite products is observed. In 2008, natural zeolites were mined by eight companies in the United States with three other companies working with stockpiled material or zeolites purchased from other producers for resale. Mine production was 60,100 metric tons (t), and US consumption was 58,500 tons. The major markets were animal feed, pet litter, water purification and odor control, sorted by tonnage decreasing. Exports and imports of natural zeolites (other than gem quality) were estimated to be less than 200 tones each [1]. In Fig. 2, a significant increase in natural zeolites consumption in the period 2004-2006 is observed. This was due to the fact that several markets, such as animal nutrition, pet litter, water purification and odor control, increased their consumption, nowadays accounting for nearly 80% of the

16 Handbook of Natural Zeolites

Borsatto and Inglezakis

domestic market [1]. It is also worth mentioning the fact that markets such as agriculture and other applications of lower added value lost share in the aforementioned markets because of transportation cost, which is always a limiting factor in marketing, as well as because of the necessity of industries to develop products of higher added value [1]. 70000 60000

Metric Tons

50000 40000 Production 

30000

Consumption 

20000 10000 0 1990

1995

2000

2005

2010

YEAR

Figure 2: The evolution of the US market (1994-2008).

Finally, although no consolidated statistics exist in the countries of South America, some interesting considerations could be presented. The available imports data from Cuba, Brazil and Colombia show a very positive trend of natural zeolites market. Colombia, for example, has placed about 80% of its volume of imports in the animal nutrition market that has been developing for over 7 years [5]. In Brazil, efforts have been concentrated in products of higher added value and applications such as the replacement of phosphates in washing powders and pets odor control [7]. As an example, in 2009, the leading company marketing natural zeolite in Brazil, Indústrias Celta Brasil Ltda, had approximately 38% of its zeolites import volume designated to the pet food market, 38% to the replacement of phosphates in washing powders and almost 15% to the water treatment market, in which a product specially developed to remove iron and manganese from groundwater is highlighted [7]. Despite the emphasis put here on Colombia and Brazil, in the last 2 years some new producers

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 17

of zeolite have gained prominence in the South American area, including Argentina and Ecuador, countries with large reserves of natural zeolites and companies that are nowadays structured so as to operate at national and international level with high competitiveness [8]. The discussion of the data presented here and the experience gained by contacting industry entrepreneurs, leads the authors to the conclusion that, in the future, the zeolite market will tend to behave in two distinct ways. One first step consists in modifying the structure of natural zeolites and working in markets with different characteristics in the economy of scale, a trend that could also reduce consumption in terms of tones, because some companies aim to work with products of higher added value [8]. Later on, production and consumption will tend to increase significantly; at first supported by the entry of new firms and higher professionalization of those who are already in the market and secondly due to the fact that the introduction of high added value products tends to give financial breath for companies that need to be able to meet demands for products of low added value and massively enter into segments of economy of scale. Obviously, the abovementioned periods will vary depending on each country and market special features but the overall trend lies in this direction [8]. At this point, many questions arise. How to gain entry into markets with high added value? How to make the zeolite markets of economy of scale viable? How to direct resources from the business world to research for the development of sustainable natural zeolite products? Which opportunities will emerge for this mineral? These and other issues are discussed in the following paragraphs. STRATEGIC MARKETING CONSIDERATIONS AND THE BRAZILIAN ZEOLITE MARKET AS A CASE STUDY The starting point for identifying an effective marketing action plan is to study the market targeted in order to fully comprehend its needs. Several marketing techniques can be applied, but the key is to study deeply how natural zeolites will behave in the target market and which are the possible reactions of companies already existing in the market and especially if this new product will actually meet a latent need. The authors’ intention is not to create controversy; however, in the commercial world of

18 Handbook of Natural Zeolites

Borsatto and Inglezakis

zeolites, a conflict on the issue of meeting the market needs is observed between the sectors responsible for technical development and sales teams. The first group argues that every product should originate from a thorough scientific study and that it is no use finding the market need if technical viability is not secured. On the other hand, the commercial group advocates that for technical development market need is a prerequisite. The authors have the opinion that both sectors need to work together in constant communication having synergistic goals. Walking side by side certainly is a critical success factor for a company that seeks to do business with zeolites. Taking advantage of the above analysis, this factor is pointed out as essential for any company seeking to engage with the zeolite minerals. A decision will have to be made here as to what should actually be the focus of the company and what its market differentiation will be. Several factors can be discussed here, such as characterization of the product, advertising material, technical support, after-sales service, value added product, economies of scale etc. [9]. Furthermore, there is another conflict concerning the necessity of obtaining high production volume for a mining company to be profitable. Manufacturers are constantly pressed for increases in volumes of tons exploited, as the costs of mineral extraction and transportation are limiting factors. Moreover, markets consuming large quantities of zeolite press industries toward lower costs, often obliging them to explore areas of low zeolitic content and, consequently, lower added value. On the other side, there are companies that direct their activities to the development of products of high added value, typically developed through chemical, thermal or physical modifications of the natural zeolite mineral. Companies with this rationale tend to sell lower volumes of zeolites; however, due to their high added value they manage to achieve good returns and are extremely competitive [8]. Therefore, from this point of view, it is important for a company to find its focus and not waste efforts and investments in contradictory directions. It is true that different objectives should be met at every level of the distribution chain and, in order to succeed, groups with different goals should join their efforts and work synergistically. The efficient management practice is not to avoid the conflicts described here, but rather to take advantage of the different approaches so that, piece-by-piece, all levels of the supply chain be met.

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 19

The authors would like to ask permission of the readers to discuss in more detail the Brazilian zeolites market, analyzing the actions taken to introduce mineralbased technologies. Initially, we must emphasize the fact that, in Brazil, the actions for the investigation of natural zeolite deposits were funded by the Brazilian government and led by the Ministry of Science and Technology [10]. The fruit of this research plan was identified in records of zeolites in sedimentary rocks in some Brazilian regions, especially in the Basin of the Parnaiba River, on the border between the states of Maranhão and Tocantins. However, there is no local production, as more investment in geological and technological knowledge of these minerals is required to be able to establish recommendations for their industrial applications [10]. Therefore, due to the lack of local mineral resources, the Brazilian market is supplied by imports, mostly from Cuba, a country with reserves rich in highquality clinoptilolite. The first purely commercial imports occurred in the late 90’s, but the results were unsatisfactory, because in that case the mineral supplied was neither of an adequate grain size nor properly modified to meet the demands of the application it was designated to and the technical-economical mishit created a considerable commercial barrier at the time [5]. Facing this situation, the business model was revised and a new strategy that included the practical demonstration of the benefits of zeolite to its various target markets was applied, seeking to meet the real needs of the customers. The relevant material is included in the Strategic Business Plan of Industrias Celta Brasil ltda, a company working with zeolite in the Brazilian market [11]. To accomplish this goal, the first step was to create and train a technical team supported by detailed scientific studies conducted by major Brazilian universities. These studies, along with the technical team, were the basis for the realization of two fundamental actions. The first action was to create specific products for real needs. In other words, the company tried to add technology and value to the mineral by translating this development into an appropriate market positioning also counting on a set of product strategies, promotion, distribution and price that matched the expectations of the market. With this approach, the marketed product was not the zeolite mineral itself but products developed from this raw material that were geared to their specific markets. It is also important to point out that at this time the target markets were

20 Handbook of Natural Zeolites

Borsatto and Inglezakis

decided to be water treatment, animal nutrition, agriculture and powder detergents. The second action was to create a Reference Zeolite Center, which was built in the city of São Paulo. The strategic decision to build the first Reference Zeolite Center aimed at developing technologies and disseminating the main applications of the mineral through professional training and demonstration of their uses in practice, with the objective of technical business growth in the Brazilian market. The Reference Center, in addition to gathering a complete technical collection on the zeolite clinoptilolite, relies also on experiment laboratories, coordinated by experts from different scientific areas, which perform tests and demonstrations of the numerous applications of the mineral. In other words, the main goal of this center was to build up a structure that would facilitate the development and dissemination of a culture geared to the use of zeolites as the Brazilian market was unaware of the importance of this mineral and its possibilities, which prompted efforts turned to the technical-commercial knowledge. The success of these two main strategies enabled the gradual commercialization of products based on the zeolite mineral in the Brazilian market and such technical and market actions already performed (together with the positive economic indicators and the expected growth of Brazil in the world scene) aroused the interest of other Latin American producers in introducing their minerals in the Brazilian market. TRENDS FOR THE ZEOLITE MARKETS When market trends are discussed there are various aspects to review. Initially, one can only assess the markets that were responsible for the increase in demand of natural zeolite minerals in recent times, such as pozzolanic cement, animal feed and other segments which have already been described here. One might therefore make a projection of these markets in the long term and consequently trace the dynamics for the exploitation and marketing of zeolites. The big question in this type of analysis is that the market is dynamic and uncontrollable variables or new technologies can often create a diversion in such projections. Moreover, trade dynamics that run positively in some countries sometimes do not reflect the commercial reality of others.

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 21

The authors’ goal here is not to set guidelines or make an accurate projection on the prospects of natural zeolites market but rather to provide topics for reflection so that entrepreneurs and scientists can critically analyze their content and thus adopt commercial practices and techniques that will be more convenient to them. The discussions are centered on a topic that can direct the strategy of several companies and do not focus on the natural zeolites issue alone. However, when this mineral is discussed, this matter becomes more prevalent due to the products and technologies that can be developed through zeolite. The issue of the search for a sustainable development is mentioned. This concept represents a new form of economy, which takes into account the environment. In other words, it is pointed out that the natural mineral zeolite may be increasingly present in the economy due to its great relation and potential to generate development capable of addressing the needs of the present generation without compromising, or at least lessening the impact on the meeting of the needs of future generations [12]. Under this perspective, a few considerations are exposed here about the potential markets for zeolite products based on observations of the strategies of companies in different segments. Natural zeolite is already known by many as the "mineral of a thousand applications". Discussions on market trends could be vastly expanded but the main message that is conveyed here is that the challenges and opportunities are present in the economy and it will be up to the corporate and scientific world to ally objectives and create strategies to make use of the characteristics of the natural zeolite mineral by placing it under the spotlight as an important ally to sustainable development. Water Treatment The main issue discussed in the context of water treatment is to guarantee its availability and access to agricultural production, livestock and industrial use [13]. The biggest uncertainty with regard to water is linked to environmental issues and problems of contamination. Large areas of the planet are facing reduction in the levels of freshwater making this resource scarce for the maintenance of human health and for industries competitiveness [13]. It is a factuality that most of the water on Earth is salty (approximately 97%) and that a proportion of less than

22 Handbook of Natural Zeolites

Borsatto and Inglezakis

0.04% occurs in rivers, lakes or underground; therefore, a subject frequently discussed between companies is water re-use. Water re-use has been discussed as an important source of technology to meet the water demand required in agriculture and in industrial processes. In this field, there are many techniques employing zeolites that can be applied. Nowadays, many applications of zeolitic filters are in operation for the removal of contaminants, for the sustainable disposal of urban and industrial sewage and for other purposes. The specific aim varies and could be the removal of helminthes eggs or simply the final polishing of the water in re-use stations [14]. Considering industrial activity, it is observed that there are three fairly typical situations. The first concerns the scarcity of water as raw or auxiliary commodity for the industrial process. The second refers to possible water contamination during its use in a process. Finally, at the end of the industrial process, the effluent has often turned to an environmental problem for the industry [14]. Therefore, if all the problems of water use in industry are summed up, several opportunities for the application of zeolites in water decontamination and re-use are evident, with a possible extra profit through reduction of operating costs in the primary processes [14]. Some examples are the removal of contaminants such as iron, manganese, ammonia, the removal of heavy metals, color, odor, etc. [15]. It is, then, up to the entrepreneurs and scientists to develop techniques to meet the needs of the market in the scope of water treatment and mainly target the reuse of this mineral resource, exploring the diversity and flexibility of zeolite employment that arises from its unique ion exchange and adsorption properties [4]. Energy Energy is a key issue in global economy. It is energy that drives industrialization and agricultural activities, besides making possible the logistics of all goods and services produced and consumed. Being the pillar for growth and development, energy is synonymous to power in the current global scenario. Currently, oil is the main energy source used worldwide and the countries that exploit and commercialize this fossil fuel are positioned strongly in the world trade relations. However, there are some aspects which are strongly debated today: the world sustainability, the democratization of the energy sources and the physical or economic scarcity of petroleum as energy source. Countries are beginning to

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 23

assess the needs of strategies to establish new diversified energy forms and less polluting matrices to the environment. In this direction, many countries are intensifying partnerships and diversifying knowledge of alternative energy through scientific and technological development and human resources training programs in areas covering Renewable Energy (Aeolic Energy, Solar Energy, Small Hydroelectric Plants, Biomass, other forms). Within this context of the international scenario, some interesting opportunities for the zeolite minerals in this important market segment can arise. Initially, the increasing use of solar energy is pointed out as strongly appealing, because it is a clean and renewable source, it does not rely on fuel and does not pollute the environment. It also has the advantage of easier plants maintenance. On the other hand, the acquisition cost of the equipment is very high. The electrical systems with photovoltaic panels, for example, are, generally, financially viable only in isolated communities without a public power grid. One of the countries that have invested heavily in solar energy is China where some work aiming to evaluate the use of natural zeolites instead of the synthetic zeolite known as 13X in solar energy storage systems has been done [16]. The practical commercial results are not so comprehensive; however, there is a potential for technical development for this application, which can be further explored considering that solar energy tends to gain space in the remodeling of the global energy matrix that will present a tendency to stimulate sustainable and friendly sources to the environment. In this same field of analysis, i.e., sources which are less harmful to the environment, nuclear power, in which many countries are investing aggressively for their development, is pointed out too. For the development of nuclear energy, several actions need to be developed in parallel and one critical point is connected to the technology to be employed for the elimination of the disastrous consequences of a nuclear accident. This is another possible field of opportunities for natural zeolites [15]. Historically, important applications of this mineral were the conditioning of absorbing agent of radioactive compounds as observed at Three Mile Island and Chernobyl as well as the treatment of wastewater and soil containing radionuclides [15]. Finally, a brief comment on ethanol, an important energy source in the Brazilian matrix, with many studies dealing with the possible involvement of natural zeolites in the production process having been undertaken recently, is necessary. The stillage, vinasse, redistill or distillery syrup, a by-product from alcohol production, is

24 Handbook of Natural Zeolites

Borsatto and Inglezakis

characterized by high concentrations in organic matter, potassium, calcium and magnesium. Because of this, it was heavily applied in the cultivation of sugarcane, providing production increase. On the other hand, indiscriminate use has led to contamination both of the soils and of groundwater in several areas. There are two opportunities here for the zeolite mineral and other complementary technologies, which can be best explored by scientists and entrepreneurs: remediation of previously contaminated areas and, preferably, pre-treatment of vinasse to make it more friendly to the environment [17]. The authors had the opportunity to witness the application of zeolite in the treatment of vinasse coming from rum production in Mexico and the preliminary studies in Brazil for the treatment of sugar cane vinasse are quite encouraging. Powder Detergent Phosphates are compounds commonly used in the formulation of powder detergent and Sodium Tri Phosphates (STPP), the most widely used ones, show high capacity for reducing water hardness [18]. On the other hand, there is a large ecological barrier to the use of this kind of materials as a feedstock because excessive quantities of nutrients, mainly phosphorus, gather in water bodies, contributing to the accelerated growth of algae and other forms of aquatic plants causing environmental imbalance known as eutrophyzation. For this reason, many countries have banned the use of these components while several others are working to reduce phosphates employment in powder detergent formulations. Historically, there is wide application of the synthetic zeolites A, P, X and AX as phosphates substitutes, as they provide similar benefits to the detergents without causing the environmental imbalance mentioned above. More than 1,000,000 metric tons/year of synthetic zeolites were used in 2000 in detergents and cleaning products worldwide, of which about 650,000 tons/year in Europe [19]. The technical characteristics of synthetic zeolites helped them gain a significant share of the international market of powder detergents and this technical and commercial success has hindered the natural zeolites intrusion in this market segment. Scientific studies have already confirmed that natural zeolites have the capacity to reduce hardness to even lower levels than their competing products already mentioned above. Moreover, a recent Brazilian scientific development pointed out a business opportunity for the natural raw material in the formulation

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 25

of powder detergents [18]. This study has as a premise the market positioning of the industry of sanitizers in positioning their products in an ecological manner and with the presence of natural raw materials. Thus, it was sought to associate the synthetic material to the natural one to expand the benefits previously derived from phosphates. With the inclusion of natural zeolite in the formulation of powder detergents, production improvements were observed in terms of fluidity of the process in addition to the advantage of its greater affinity to free water that enhances the characteristics of the end product [18]. Briefly, support was sought from the ecological aspect and the use of natural and synthetic zeolite was used in substitution of phosphates. In this market segment, a great opportunity for the technical study of different sources of the natural mineral with the aim of expanding its inclusion in the formulation of powder detergents is manifested. Farming The technological advances in global agriculture and cattle-raising and the concept of sustainability are highlighted in this sector’s discussions. When confronted with the concept of sustainability in this market sector, the need for management plans focused on the rational use of resources and on the use of natural raw materials to help save energy is self-evident. The goal to obtain a positive energy balance, that is, to produce more with lower resources consumption and diminished waste production is the great challenge in this sector and it opens up several business opportunities for natural zeolites [15]. Agriculture can provide low cost solutions for beneficial greenhouse gas (GHG) reduction. Recently, the potential of zeolites to reduce greenhouse gases, especially nitrogen-related compounds, coming from agricultural activities (carbon offset potential) was clearly recognized [20]. As it has been proven, natural zeolites in combination with different types of fertilizers can improve cultivation performance by limiting nutrient loss. On top of this, it is important to mention the natural zeolites capacity to retain water, a property that makes natural zeolites ideal tools for cultivation in areas with limited access to this essential to agriculture resource [15]. Regarding cattle-raising, the use of zeolites as a beneficial nutrition additive is well known, but another feature is their contribution to the treatment of excrements and their disposal in a fully ecological way. Another enormous potential of the mineral is the adsorption of ammonia and other contaminants and the transformation of animal manure to a by-product

26 Handbook of Natural Zeolites

Borsatto and Inglezakis

useful to another market segment, such as agriculture [15]. There are many technical papers that support this type of applications of natural zeolites and such uses are already made quite successfully in several countries. The opportunities are many and they increase day by day; a bit of harnessing might be necessary, since these are strongly pressured financial sectors due to their importance in providing food to an ever-increasing and over-demanding world population [15]. NATURAL ZEOLITES MARKET PRICES Naturally, prices for natural zeolites vary with zeolite content and processing as well as with the country of origin and market development. However, as mining costs are generally low, the price of zeolites is more closely related to the cost of processing required by the buyer [3]. In general, unit values range from $55 to $267 per metric ton while for the bulk of the tonnage sold in the US prices were between $20 and $100 per ton [1, 3]. To compare, one can consider the synthetic zeolite A prices which range from $500 to $600/t for detergent grade and up to US $45/kg for catalyst-grade material (2002 prices) [3]. A short market research for clinoptilolite in 9 countries (excluding USA) conducted by the authors of the present Chapter, showed that prices vary considerably from $70 to $686 per metric ton, with an average value of $242±169 per metric ton (sample size of 36 prices). Another conclusion is that prices for clinoptilolite from China are lower by an average of 40% in comparison to the other countries investigated. However, all these values should be used with great care as the standard deviation of prices is very high. Nevertheless, the trends indicated are useful for a fist approach to the subject. According to US Geological surveys, prices are lower for industrial and agricultural applications, ranging from $30 to $70 per ton for granular products and from $50 to $120 per ton for finer products (-40 to +325-mesh). Smaller volumes of more sophisticated zeolite products are used for pet litter, fish tank media or odor control applications, and prices for such applications ranged from $0.50 to $4.50 per kilogram ($500- $4.500 per ton). Prices vary for different zeolite species and could be quite low, as for example for clinoptilolite granules ($150 per ton), or very high for modified clinoptilolite and extruded and activated chabazite products ($8 per kilogram, equivalent to $8.000 per ton). Quoted prices should be used only as a guideline because actual prices depend on the terms of the contract between seller and buyer [1].

Natural Zeolite Markets and Strategic Considerations

Handbook of Natural Zeolites 27

ACKNOWLEDGEMENTS None declared. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20]

Virta R, Minerals Yearbook, Zeolites [Advance Release], U.S. Department of the Interior, U.S. Geological Survey, 2011. The Economics of Zeolites, Roskill Information Services, Ltd., 2004. Christie T, Brathwaite B, Thompson B. Mineral Commodity Report 23 – Zeolites. New Zealand Mining 2002; 31: 16-24. Avalos AC, Hernández RM. Las Zeolitas naturales cubanas en Brasil. Presentation and report. May 2008. U.S. Geological Survey, Zeolites Statistics and Information, http://minerals.usgs.gov/minerals/pubs/commodity/zeolites/ Indústrias Celta Brasil. Global business report 2009. Borsatto F. Mercados Mundiales de Zeolitas y consideraciones sobre los productos y servicios del futuro. Encuentro Técnico zeolitas Cubanas, La Habana, Marzo 2010. Kotler P, Keller K. Lane Administração de Marketing. 12ed., 2008. Nélio G, Resende M, Bezerra M, Renato P, Zeolitas Naturais, CETEM – Centro de Tecnologia Mineral, Brazilian Federal Institute, 2008. Indústrias Celta Brasil Strategic Business Plan, Internal Report, 2005. Del Campo N. Aplicación de zeolitas en el medio ambiente. Febrero, 2004. CPRM – Serviço Geológico do Brasil, 2010. Zeólita, O mineral dos mil usos. http://www.cprm.gov.br/imprensa/Site/pdf/Clipping/Clipping013-2010.pdf Gobbi SA, I. Hespanhol. Removal helminth eggs of municipal sewage for reuse of treated wastewater in agricultural irrigation and reuse urban non-potable, through rapid filters sand and zeolite. July 2010. Mumpton F. La Roca Mágica: Uses of natural zeolites in Agriculture and Industry. Proc. Natl. Acad. Sci. USA. 1999; March: 96. Baoqi H et al. Utilization of natural zeolites for solar energy storage, China. http://www.fao.org/docrep/t4470e/t4470e0j.htm Barros RP. Estudo dos efeitos da aplicação da vinhaça na qualidade de solos em cultivosde canade-açúcar (saccharum officinarum l.), e o uso de indicadores no sistema de produção. 2007. Gobbi SA, Reduction of environmental pollution caused by phosphate through the use of Natural Zeolite (Clinoptilolite) production of powder detergents. July 2010. Zeolites for Detergents - As nature intended, ZEODET, Association of Detergent Zeolite Producers, CEFIC, the European Chemical Industry Council, January 2000. Brodnax S, Hessenflow Harper S, Van Buggenum L. Carbon Market Potential of Ecotech Zeolite, The Clark Group, LLC, March 2009.

Part II: PROPERTIES AND CHEMISTRY

28

Handbook of Natural Zeolites, 2012, 28-51

CHAPTER 3 Zeolite Formation and Deposits Ioannis Marantos1*, George E. Christidis2 and Mihaela Ulmanu3 1

Institute of Geology and Mineral Exploration, Olympic Village, 136 77 Athens, Greece; 2Department of Mineral Resources Engineering, Technical University of Crete (TUC), 73100 Chania, Greece and 3National R&D Institute for NonFerrous and Rare Metals, IMNR, Bd. Biruintei 102, 77145 Pantelimon, Romania Abstract: Zeolites are the main mineral components in altered volcaniclastic rocks ranging in age and composition. They form by alteration mainly of volcanic glass in various geological environments, under variable geochemical and temperature conditions. Proposed genetic models of zeolite deposits include weathering, diagenesis in open or closed hydrologic systems, low temperature hydrothermal systems, primary magmatic environments and impact craters. The most common zeolite species, which may occur in mineable deposits, are clinoptilolite-heulandite, mordenite, chabazite, analcime, and phillipsite. Mineable zeolite deposits are widespread in many countries worldwide. The world annual production of natural zeolites remains essentially constant over the last 10 years at ca 3 million tons. Although several large high grade zeolite deposits are currently under operation and numerous studies on the suitability of the zeolite materials in various applications have been carried out, most of the annual zeolite production is consumed in massive low value applications like additives in pozzolanic cement and lightweight aggregates.

Keywords: Formation, deposits, geology, volcaniclastic rocks, geothermal gradients, metamorphic processes, hydrothermal zeolites, geoautoclaves, metamorphism, chemical gradients, zonation. INTRODUCTION The term zeolite was first used by Cronsted [1] in 1756 to describe crystals of a mineral from the Svappari copper mine in Sweden, which were “boiling” during heating. Later Murray and Renard [2], recognized zeolite minerals in deep sea sediments and more recently mineralogists and geologists described zeolite minerals in volcanic, volcaniclastic and sedimentary rocks. Today it is generally *

Address correspondence to Ioannis Marantos: Institute of Geology and Mineral Exploration, Olympic Village, 136 77 Athens, Greece; E-mail: [email protected], [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Zeolite Formation and Deposits

Handbook of Natural Zeolites 29

accepted that zeolites are common minerals, which form in a variety of geological environments. The structure of zeolites is characterized by a framework of linked tetrahedra, each containing four O atoms at their apices, surrounding Si or Al. This framework contains open cavities in the form of channels and cages, which are usually filled by H2O molecules and extra-framework cations that are commonly exchangeable, (Fig. 1). The channels are large enough to allow the passage of guest molecules. Dehydration occurs at temperatures mostly below 400o C and is largely reversible. The zeolite framework may be interrupted by (OH,F) groups replacing oxygen atoms; these groups occupy tetrahedron apices that are not shared by adjacent tetrahedra [3]. More than 57 natural zeolite species have been recognized so far [4], but only few species form large mineable mineral deposits. The most common zeolite species which may occur in mineable deposits are clinoptilolite-heulandite, mordenite, chabazite, analcime, phillipsite, erionite and ferrierite. The most common commercial zeolite deposits consist of clinoptilolite, chabazite and mordenite.

Figure 1: Clinoptilolite structure.

ZEOLITE FORMATION Zeolites may form well developed crystals in veins, cavities and vugs of volcanic rocks or may occur as fine grained crystals mainly in volcaniclastic and

30 Handbook of Natural Zeolites

Marantos et al.

sedimentary rocks. In the latter cases, zeolites are homogeneously distributed in the entire mass of the volcaniclastic or sedimentary rocks. Regardless of the formation mechanism, the zeolite deposits are characterized as “sedimentary deposits” [5]. Volcanic glass of silicic, alkali or mafic composition is the most common parent material for the zeolite minerals. Smectite, feldspars, feldspathoiods and biogenic silica may also act as precursors in the formation of zeolite minerals. With increasing temperature certain alkaline zeolites, such as clinoptilolite or mordenite, may become thermodynamically unstable and may act as precursors of more stable zeolite species, such as analcime. Zeolites form by a solution/precipitation mechanism and their genesis is controlled by composition, grain size, porosity and permeability of the host rock, temperature, pore water chemistry (pH, salinity, alkalinity), depth of burial, and age of the geological formation [6, 7]. The role of temperature is a determinative factor in zeolitic alteration, controlling the type of zeolite species which may form, as well as the reaction rate. The mineralogical zoning commonly observed in geothermal areas, around intrusive bodies and during burial diagenesis or/and metamorphism is due to the temperature variation [8-12] among others. The chemistry of the mineralizing fluids including pH, the (Na++K+)/H+ and K+/(Na++Ca2++Mg2+) activity ratios and the H4SiO4, Al(OH)4-, Fe2+, Fe3+, H2O and CO2 activities are additional important factors which may control mineralogical zoning, especially in closed systems [6,13-16] among others. The increase of pressure and temperature by increasing burial in greater depths leads to the formation of a vertical zonal arrangement from more hydrous to less hydrous zeolites, which finally convert to metamorphic mineral assemblages [11, 17]. The composition of the original material, as well as permeability are also important factors during zeolitic alteration because they determine the alteration minerals and the rate of reaction. In the last 60 years, zeolite minerals have been recognized as major constituents of altered volcaniclastic rocks in various geological environments, such as burial metamorphic environments [17-19], saline alkaline lakes [6, 21, 22], marine and fresh water environments [6, 23-24], geothermal environments, etc. The

Zeolite Formation and Deposits

Handbook of Natural Zeolites 31

distribution of the alteration minerals in various zeolite deposits is usually characterized by zonal patterns depending on the environment of formation. Several genetic classification schemes of zeolites based on the type of geological environment and the hydrologic system have been proposed by various workers [25-31]. Following the classification scheme of Iizima [29], the zeolite genetic types can been grouped into four main categories subdivided into various subcategories, which are described below. Zeolite Zonal Patterns at Elevated Temperatures, Resulting Primarily by Geothermal Gradients Magmatic Primary Zeolites In some rare cases it has been suggested that analcime may crystallize at the last stages of crystallization of magmatic rocks [32]. However determination of primary or secondary origin for analcime is rather difficult; therefore the recognition of analcime of magmatic origin still remains controversial [33, 34]. Zeolites Formed By Contact Metamorphic Processes In volcano-sedimentary sequences, concentric alteration zones containing zeolite minerals may be formed around intrusive bodies, as a result of contact metamorphism. A typical case of this type of alteration has been described in the Tanzawa Mountains Japan [8]. In this area zeolitic alteration zones have been developed more or less concentrically around a quartz diorite igneous body. Laumontite occurs in the innermost parts and clinoptilolite and stilbite in the outer alteration zones. Hydrothermal Zeolites Various zeolite species may form by hydrothermal activity associated with different types of igneous rocks. This type of deposits includes mainly alteration in active geothermal fields and alteration associated with ore deposition. Zeolites are common alteration minerals in active and fossil geothermal fields with steep geothermal gradients. Typical examples are: the geothermal field of Yellowstone Park in USA, [10], various geothermal fields in Iceland [9], the geothermal fields at Warakei New Zealand [35] and Onikobe in Japan, etc. The formation and distribution of various zeolite minerals in the geothermal fields is affected mainly

32 Handbook of Natural Zeolites

Marantos et al.

by temperature, which controls the degree of the alteration and the distribution of the different zeolites. Thus, in the geothermal field of Iceland all the zeolites are stable at temperature lower than 230°C, except for analcime and wairakite that are stable at temperatures up to 300°C [9]. Although mineralogical zoning due to temperature gradients is characteristic for hydrothermal zeolites, it may not be well defined in fields with high geothermal gradients. For example zoning in the geothermal field of Iceland is better defined in areas with geothermal gradients lower than 150°C/km compared to areas with gradients higher than 200°C/km [9]. Except for temperature, host rock composition, permeability and geothermal fluid chemistry are also important factors which determine alteration and distribution of zeolites in hydrothermal fields [9, 36]. Zeolite minerals may be formed around ore deposits by mineralizing hydrothermal solutions. A typical example of this environment of formation is the Kuroko-type polymetallic sulfide deposits, which form from hydrothermal activity related to black smokers on the seafloor. In this type of deposits, alteration patterns are rather complex because they are produced by the combined action of submarine hydrothermal alteration and low temperature diagenesis. In the Kuroko-type deposits, which have been developed on acidic tuffs, the analcime and Na-mordenite hydrothermal zones have been superimposed to the burial diagenetic zone of clinoptilolite-mordenite(II) [37, 38]. Zeolites in Geoautoclaves In order to interprete zeolititic alteration of marine ash flow tuffs, in Eastern Rhodope, Bulgaria Aleksiev and Djourova [39] proposed a genetic model that they called “geoautoclave”. According to this model vast quantities of ignimbrites erupted in successive short cycles were deposited in a shallow marine environment. The deposition of the hot pyroclastic flows in shallow water generated large amounts of thermal energy in the alteration system. Due to the insulating properties of pumice and volcanic glass an autoclave-like system was generated, favouring the alteration of volcanic glass to zeolites at relatively elevated temperatures. This model is similar to that proposed by Lenzi and Passaglia [40] for the formation of zeolites in central Italy and considers that the temperature of volcanic glass and the rate of cooling are important factors

Zeolite Formation and Deposits

Handbook of Natural Zeolites 33

controlling the zeolitization of volcanic tuffs. The “geoautoclave” model was accepted by several authors in order to interprete zeolite formation in ignimbrites [41-44]. Nevertheless, the “geoautoclave” environment is rather unlikely to occur in nature [45]. In volcanic terrains, the presence of magmatic bodies at shallow depths, as well as the volcanic rocks themselves may drive the formation of low temperature hydrothermal solutions, favouring the zeolitization of volcaniclastic rocks [46-48]. Burial Diagenesis and Metamorphism In thick sedimentary sequences, volcaniclastic rocks, which are subjected to burial diagenetic or/and metamorphic conditions, often undergo alteration and the volcanic glass is converted to zeolites. Due to progressive burial in greater depths a vertical zonal arrangement of alteration mineral assemblages develops, which is controlled mainly by thermal gradients (Fig. 2). Typical examples of this type of zeolite deposits were first described in Triassic sediments in New Zealand [17]. Moreover, well studied zeolite deposits of burial diagenetic type are widespread in the Green Tuff region in Japan [49-51]. With increasing depth the following alteration zones are observed: zone I which is characterized by partial alteration of glass to smectite and opaline silica and the absence of zeolites; zone II that is dominated by the presence of alkali clinoptilolite and alkali mordenite; zone III characterized by transformation of clinoptilolite – mordenite into analcime and laumontite in its lower parts and zone IV that is characterized by the transformation of analcime to albite. The aforementioned zonal arrangement is controlled mainly by temperature. As is indicated by temperature measurements in boreholes at the Japanese oilfields, the transformation of volcanic glass to alkali-zeolites at the boundary between zones I and II occurs at 41-50°C, the conversion of the alkali zeolites, clinoptilolite and mordenite, to analcime at the boundary between zones II and III, takes place at 84-91°C and the transformation of analcime to laumontite at the boundary between zones III and IV is observed at 120-124°C [50, 11]. Alteration is affected also by pore water chemistry. Pore fluids of high salinity and alkalinity may lower the temperature of the glass-to-alkali zeolite transition to ca 21°C and the clinoptilolite/mordenite transition to ca 37°C [11].

34 Handbook of Natural Zeolites

Marantos et al.

Figure 2: Alteration mineral zoning in burial diagenesis environment, (based on Utada, 1971).

Zeolites At Or Near Surface Conditions, The Zones Being Principally Controlled By Chemical Gradients Percolating Groundwater In this type of alteration, known also as open system tephra alteration [7], meteoric water percolating through a volcaniclastic pile, reacts with volcanic glass, usually of acidic, composition and finally produces alteration mineral assemblages, including various types of zeolites (clinoptilolite/heulandite, phillipsite, analcime etc.), clay minerals (mainly smectite), authigenic K-feldspar, etc. These assemblages display vertical zonal arrangement due to progressive chemical modification of mineralizing fluids migrating downwards. Zeolite deposits of this type hosted in silicic tephra are usually thick and are often formed in depths greater than 200m. Zeolite minerals display usually zonal distribution patterns, (Fig. 3) comparable to those observed in burial diagenesis, with clinoptilolite, phillipsite and chabazite in the upper part and analcime in the lower zone [20] (Fig. 3). Alteration due to percolating groundwater can be distinguished from alteration due to burial diagenesis because a) the glass-to-alkali zeolite zone is significantly thicker in the latter and b) the time span for alteration is much shorter in the former compared to the burial diagenesis [7]. Typical examples of this type of zeolitization are the John Day Formation, in Oregon USA, [23], Yucca Mountain, Nevada, USA, [52], Trans-Pecos, Texas [53], etc. In the John Day Formation zeolite neoformation takes place below the water table; hence pore fluid migration has an important lateral component [23].

Zeolite Formation and Deposits

Handbook of Natural Zeolites 35

Basic volcaniclastics of basaltic composition may be altered to zeolites and clay minerals. However, the contribution of clay minerals is more significant than that of zeolites. Moreover the thickness of the alteration zones is considerably smaller (Fig. 3). Typical examples of this type of deposits occurs in Oahu Island, Hawaii, where tephra of alkali basalt to nephelinite composition has been altered to palagonite and zeolites [54], and in Northeast Jordan where tephra deposits of alkali olivine basalt composition have yielded similar end products [55, 56]. The zeolites formed (faujasite, phillipsite and chabazite) have lower Si-contents than clinoptilolite and mordenite, which are typical alteration products of silicic tephra. In northeast Jordan three diagenetic zones have been developed having sharp contacts, which follow topography and reflect variations in permeability, flow rate and pore-fluid composition [56].

Figure 3: Alteration mineral zoning in open hydrologic systems.

Weathering Various zeolite species have been recognised in soils including clinoptilolite, analcime, chabazite, gismondine, laumontite phillipsite, natrolite and mordenite.

36 Handbook of Natural Zeolites

Marantos et al.

Clinoptilolite is by far the most abundant zeolite found in soils. Although most zeolite occurrences in soils may originate from volcanogenic material such as tuffs, there are soils in which zeolites have neither been inherited into nor formed by the influence of volcanic activity [57]. According to Boettinger and Graham [58], six types of zeolite occurrences have been distinguished in soils: 1) Pedogenic zeolites in saline alkaline soils of non volcanic origin, 2) Pedogenic zeolites in saline alkaline soils of volcanic origin, 3) Lithogenic zeolites inherited from volcanic raw material 4) Lithogenic zeolites inherited from non-volcanic raw material, 5) Lithogenic zeolites from aeolian additions and alluvial deposition and 6) zeolites in other soil environments. Alkaline, Saline Lake Deposits Saline alkaline lakes are hydrologic closed systems, typical of arid or semiarid areas, in which evaporation exceeds inflow [28, 30, 59]. Saline or saline-alkaline brines may develop by evaporation, depending on parent waters composition and chemical evolution [60, 61]. Modern closed basins are classified into two distinct geological environments a) a playa lake complex in which a broad flat valley is surrounded by a high mountain range and b) a rift system, which is a steep walled, flat, narrow valley [61]. In saline, alkaline lake environments, silicic glass is rapidly altered to zeolite minerals, clay minerals, opaline silica and K-feldspar because of the high pH values, often higher than 9. Clinoptilolite, analcime, chabazite, mordenite, phillipsite and erionite are typical zeolite minerals forming in saline alkaline lakes. The deposits exhibit lateral zonal distribution of alteration mineral assemblages, due to zonation of the lake water chemistry from the margins to the centre of the lake. A fresh glass zone develops at the margins of the basin, where fresh water is trapped in the interstitial pore water of the volcaniclastics. The zones bearing zeolite minerals occur in the interiors of the lake, whereas in the innermost parts where higher pH values prevail, a K-feldspar zone is developed (Fig. 4). In such systems the formation of zeolites from reaction of volcanic glass with alkaline solutions takes place in two steps [62]. First a gel forms, with a Si/Al ratio controlled by the Si/Al ratio of the solution followed by nucleation of zeolites from the gel. The Si/Al ratio of the zeolites is then controlled by the composition of the gel.

Zeolite Formation and Deposits

Handbook of Natural Zeolites 37

Figure 4: Alteration mineral zoning in saline, alkaline lake environment (1. fresh glass zone, 2. zeolite zone, 3. K-feldspar zone).

This type of zeolite deposits is relatively common throughout the world. Typical examples among others include the Pleistocene lake Tecopa, the Pliocene Big Sandy Formation and the Miocene Barstow Formation in USA [63], the Pleistocene lake Olduvai Gorge in Tanzania [64], the Pleistocene – Holocene Lake Magadi in Kenya [65], Lake Natron in Tanzania [6], and the Neogene saline alkaline lake of Karlovassi, Samos Ιsland, Greece [66]. Zeolite minerals may also form in saline environments of low alkalinity. In these cases saline minerals indicative of alkaline waters are absent, Ca-rich zeolites form, and the reaction of Ca-zeolites to form K-feldspar suggests mobility of Ca [67]. Zeolites Formed At Low Temperatures, Without Recognized Zonation Marine Environment Zeolite genesis at low temperatures is widespread in deep sea sediments. The most common marine zeolites are clinoptilolite and phillipsite. Analcime is next

38 Handbook of Natural Zeolites

Marantos et al.

in abundance and numerous other zeolite types such as harmotome, heulandite, mordenite, erionite chabazite gmelinite thomsonite and natrolite among others have been identified in various areas [7]. Phillipsite, which is most abundant in sediments younger than the Miocene, usually forms close to the sediment-water interface and disappears at greater depths, possibly because it converts to clinoptilolite. It usually replaces basic volcanic glass in areas characterized by low sedimentation rates such as the South Pacific [51]. Clinoptilolite is common in sediments of Eocene to Cretaceous age and forms within the sediment column, where silica activity is elevated to stabilize it, mainly due to dissolution of opal-A [68]. The source of excess silica is biogenic and occasionally clinoptilolite forms pseudomorphs after radiolarii frustules, even within basic rocks [51, 69]. Analcime has been identified in deep sea sediments, associated with basic rocks. Although it may coexist with phillipsite or clinoptilolite there is not any reported evidence for formation of analcime from replacement of these zeolites [7]. Zeolites Formation In Impact Craters Impact Crater Zeolites and clays may form as secondary minerals by reaction of fluids with shockderived aluminosilicates and impact glasses within meteorite impact craters. The alteration of glass to zeolites follows the same patterns and is controlled by similar parameters as the open systems which are dominated by percolating groundwater. ZEOLITE DEPOSITS AND PRODUCTION Mineable high grade zeolite deposits are widespread in many countries worldwide. Moreover, there are several studies suggesting the suitability of the zeolite materials in many applications [70-76]. Natural zeolites have not confirmed the optimistic predictions made in the beginning of 70’s for widespread use, despite the existence of numerous studies that suggest their applicability in many agricultural and industrial activities [126]. The same trend is valid till today. Mining of zeolites is performed by opencast methods. Processing is rather simple and includes crushing, screening, and classification to various size fractions depending on the application. In certain cases the zeolite ore may be modified further by treatment with acid or salt solutions. The annual production of zeolites remains generally constant over the last 10 years to ca 3 million tons. More

Zeolite Formation and Deposits

Handbook of Natural Zeolites 39

specifically, the total world production in 2008 was 2.5 -3 million metric tons (Mt). Most of this production was consumed by the cement industry for the manufacture of pozzolanic cement. The distribution of the zeolite production among the individual countries is shown in Tables 1 and 2 lists some geological data, zeolite content and physical properties of selected zeolite deposits currently under exploitation in the main production countries. Table 1: World production of zeolites, Virta (2008) [77] COUNTRY

PRODUCTION (thousand tn)

China

1750 to 2250 (including pozzolan applications)

Jordan

400 to 450 (including pozzolan applications)

Republic of Korea

160

Japan

140 to 160 (including pozzolan applications)

Turkey

100

USA

60,1

Slovakia

60

Indonesia

30-50 (including pozzolan application)

Ukraine

20-40

Hungary

20 to 30

New Zealand

17

Cuba

16,5

Bulgaria

15

South Africa

10

Australia

5-10

Spain

5-10

Canada, Greece, Italy, the Philippines, and Russia

3 to 5 each

Mexico

0,7

Argentina, Germany (excluding pozzolan applications), Serbia, and Slovenia

probably less than 1 to 2

40 Handbook of Natural Zeolites

Marantos et al.

Table 2: Geological data of selected zeolite deposits Country

Location

Commodity Grade

Clinoptilolite Clinoptilolite and Australia Werris Creek, New South Wales minor mordenite >60%. CEC 1.2 meq/g

Bulgaria

China

Geological Characteristics

Mining Co

Reference

Late Carboniferous, Zeolite Australia [42, 78-80] Escott zeolite P/L formation cosists of massive-laminated lacustrine mudstoneswater-lain, ash fall vitric tuffs, red to green

Quirindi, Castle Mountain, New South Wales

Clinoptilolite Zeosand 85% clinoptilolite CEC 1.47meq/g Zeobrite 54% clinoptilolite CEC 1.19meq/g

Late Carboniferous, Castle Mountain [81, 82] Escott zeolite Enterprises Pty formation cosists of Ltd massive-laminated lacustrine mudstoneswater-lain, ash fall vitric tuffs, red to green

Willows, Queensland

Clinoptilolite 50% zeolite

Drummond basin: Supersorb basal Late Devonian shallow marine sedimentary rocks, overlain by Early Carboniferous fluvial and lacustrine sediments and silicic volcanics.The major zeolite unit is the Ducabrook formation. Water lain, ash fall tuffs.

[78, 83, 84]

Beli Plasti Clinoptilolite Clinoptilolite 52Eastern Rhodopes 95%, HaskovoCEC 1.13-1.51 Kardzhali meqNH4/g

Lower Oligocene zeolitised ash flow (massive tuffs) -

S&B Industrial Minerals S.A.

[46]

Jelezni Vrata, Eastern Rhodopes, Kardzhali

zeolitised pumice flows (massive weakly welded ignimbrites) + zeolitized fall-out tuffs (bedded) – clinoptilolite

Trasingeneering [47, 85, 86] (Bulgarian) – production for cement.

Dushikou Mine, Chi-cheng county, Hebei Province

Clinoptilolite 50-70% zeolite (400Mt)

[87]

Jin-yun county mine, Zhejiang Province

Clinoptilolite >100Mt with minor mordenite

[87]

Hai-ling County Heilongjiang Province

>65% zeolite >100Mt

[87]

Zeolite Formation and Deposits China

Xinyang City

Handbook of Natural Zeolites 41 Table 2: cont…. Broad Xinyang Mining Co

Zeolite powder

Zhejiang Shenshi zeolite

Zhejiang Shenshi Mining Industry Co, Ltd.,

Henan China

Huai zeolite [88] powder Xinyang Industry Co.Ltd Gongyi Zhongdatong Water Material Co, Ltd Changsha Xian Shan Yuan Agriculture & Technology Co, Ltd

Zeolite

Fujian China

Cuba

Esytun Industrial Ltd

Tianjin

Clinoptilolite Clinoptilolite 8085%

Tianjin Bentonite Minchem Co, Ltd

Tsagaantsav, Mongolie

Clinoptilolite Clinoptilolite 8096%

Dorniin Zeolite LLC

Govi-Tamsag, Mongolia

Clinoptilolite 30-70% zeolite

Zeolite beds and stratum occurring in siliceous tuff, tuffaceous sandstone and argillite of the Early Cretaceous Tsagaantsav formation.

[89]

Govi-Tamsag, Mongolia

Clinoptilolite 10-80% zeolite

Early Cretaceous zeolite beds. Can be broken into three productive horizons with a content of 7090% zeolite (clinoptilolite).

[89]

Caimanes, Moa, Holguin

clinoptilolite

Altered Paleogene volcaniclastics

[90]

Bueycito, mordenite Bayamo Granma Prov

Zeolitized Paleocene –middle Eocene Massive volcaniclastics of intermediate composition

[90]

Palenque, Guantanamo

Zeolitized Paleocene –middle Eocene Sabaneta formation

[90]

Cretaceous

[90]

Poijilo, Santa Clara

Clinoptilolite, mordenite

42 Handbook of Natural Zeolites

Marantos et al.

Table 2: cont…. Tasajeroas Santa Clara

Cretaceous

[90]

Chucho Rojas

Cretaceous

[90]

Conductora

Cretaceous

[90]

Joaquina Carolinas, Cienfuegos

Heulandite type zeolites

Cretaceous

[90]

Cretaceous

[90]

Los Congos deposit, Mariel region Germany Kaiserstuhl, SW Germany Hungary

[91]

Zeolites

45%zeolite

Miocene Kaiserstuhl volcanic Comlex

Hans G. Hauri [92] Mineralstoffwerk

Mad-Suba

Clinoptilolitic Clinoptilolite 25-35 Altered sarmatian tuffs %, Montmorillonite rhyolitic tuffs 25-35%, glass 2530%

Geoproduct

[93]

Ratka

Clinoptilolitic Clinoptilolite>40%, Altered sarmatian tuffs average 55%,glass rhyolitic tuffs Rb > K > NH4 > Ba > Sr > Na > Ca > Fe >Al > Mg > Li This preference for lager cations, including NH4+, was exploited for removing NH4 – N from municipal sewage effluent and has been extended to agricultural and aquacultural applications [7]. Clinoptilolite and natural chabazite have also been used to extract Cs and Sr from nuclear wastes and fallout. Cation exchange behavior depends on other factors also, including: the concentration of specific cations in the solution, temperature, the nature of cation species (size, charge) and the structural characteristics of the particular zeolite. Cations may be trapped in structural positions that are relatively inaccessible, thereby reducing the effective ion exchange charge capacity. Cation sieving may also take place when the cation from solution is too large to pass through the entry ports into the central cavities. Table 4 reports the cation selectivity patterns for the main natural zeolites, based on the equilibrium constants, for individual cation pairs [8]. Table 4: Selectivity patterns of natural zeolites for some hazardous cations Natural Zeolite

Selectivity Patterns for Some Cations

Chabazite

Cs > NH4+> Pb > Na > Cd > Sr > Cu > Zn

Clinoptilolite

Cs > Pb > NH4+> Na > Sr > Cd > Cu > Zn

Mordenite

Pb > Cs > NH4+> Na > Cd

Phillipsite

Cs > Pb > NH4+ > Na > Sr > Cd > Zn

Although these series can not be considered absolutely valid, either because values of equilibrium constants depend strongly on the procedure adopted for

Mineralogy of Natural Zeolites

Handbook of Natural Zeolites 59

their computation, or because selectivity is affected by factors above mentioned, these series give strong indications for uses of natural zeolites in the field of environmental interest. Adsorption Properties Crystalline zeolites are unique adsorbent materials. The large central cavities and entry channels of zeolites are filled with water molecules forming hydration spheres around the exchangeable cations. If the water is removed, molecules having cross – sectional diameters small enough for them to pass through the entry channels are readily adsorbed in the dehydrated channels and central cavities. Molecules too large to pass through the entry channels are excluded, giving rise to the molecular sieving property of most zeolites. Dehydration/Rehydration Based on dehydration behavior, zeolites may be classified as: a) those that show no major structural changes during dehydration and exhibit continuous weight loss as a function of temperature and b) those that undergo major structural changes, including collapse, during dehydration and exhibit discontinuities in their weight loss. Typical of the first type are: clinoptilolite, mordenite, erionite and chabazite, which are stable at 700 or 800oC. The dehydration behavior of second type zeolites is such that this exhibit reversible water loss at low temperature, but a major change occurs at elevated temperatures, the material losing its zeolitic character. Physical Properties The physical properties of a zeolite must be discussed in two ways: 

First, as a mineralogical description of the zeolite in terms of its natural properties, including morphology, crystal habit, specific gravity, density, color, grain of crystal size, degree of crystalline, presence of corrosion or etching, presence of contaminants and any other descriptive physical features.



Second, in terms of its physical performance as a product for any specific application, such characteristics as brightness, color,

60 Handbook of Natural Zeolites

Mihaela Ulmanu

Brookfield viscosity, Hercules viscosity, surface area, particle size, hardness, abrasion resistance, wet abrasion durability, thermal expansion and resistance to weathering are interesting. Proper characterization of any zeolite always includes determination of its basic descriptive mineralogical characteristics and assessment of whatever performance characteristics are believed relevant in considering it for specific commercial applications. Generally, a zeolite is a crystalline, hydrated aluminosilicate of alkali and alkaline earth cations having an infinite, open three – dimensional structure. It is further able to lose and gain water reversible and to exchange extra framework cations, both without change of crystal structure. The large structural cavities and the entry channels, leading into them, contain water molecules, which form hydration spheres around exchangeable cations. On removal of water by heating at 350 – 400oC, small molecules can pass through entry channels, but larger molecules are excluded – the so called “molecular sieve” property of crystalline zeolites. The uniform size and shape of the rings of oxygen in zeolites contrasts with the relatively wide range of pore sizes in silica gel, activated alumina and activated carbon, and the Langmuir shape of their adsorption isotherm allows zeolites to remove the last trace of a particular gas from a system. Furthermore, zeolites adsorb polar molecules with high selectivity. Thus, polar CO2 is adsorbed preferentially by certain zeolites, allowing impure methane or natural gas stream to be upgraded. The quadrupole moment of N2 contributes to its selective adsorption by zeolites from air, thereby producing O2 – enriched products. The adsorption selectivity for H2O, however, is greater than for any other molecule, leading to uses in drying and solar heating and cooling [9]. TESTS FOR MINERAL IDENTIFICATION For mineral identification of natural zeolite is necessary to follow some appropriate testing steps. Natural zeolite minerals are identified first by their crystal habit. Chemical analysis alone is not an effective method of identification, as many zeolites have similar chemical composition. Macroscopic zeolites, particularly those occurring in vehicles and fractures in basaltic rocks, may be identified by careful visual examination. Virtually all economic natural zeolite occurrences however are of microscopic grain size. Positive identification and

Mineralogy of Natural Zeolites

Handbook of Natural Zeolites 61

semi – quantitative determination of such fine- grained materials can be done only by laboratory study. The principal methods of identification are by X-ray diffraction and scanning electron microscopy, with lesser use of optical microscopy and different thermal analysis. X-Ray Diffraction (XRD) X-ray diffraction is the most reliable and widely used method for identification of the zeolites and semi-quantitative estimation [10]. This method has a high degree of accuracy and can readily be used to identify individual zeolite minerals in mixtures with zeolite and non-zeolite minerals. It requires only a technician to operate the X-ray diffraction equipment, which may be automated and able to run multiple determinations and to interpret the results. XRD analysis is a nondestructive method and the powder used for the analysis can be further tested in other analytical methods. The method is least reliable in mixtures of minerals; the lower detection limit for an individual zeolite is about 5%. The basic equipment for analysis has moderate cost, but an experienced specialist in X-ray diffraction may be needed to interpret the results. Computerized XRD systems may be programmed to read and interpret semi-quantitative zeolite mineralogy. Scanning Electron Microscopy (SEM) The scanning electron microscopy is effective in identifying zeolite minerals, establishing their size, shape, genesis and mineralogical setting. Representative samples must be used to avoid incorrect results.SEM analysis is relatively slow and costly requiring an expensive electron microscope and an experienced operator to be effective. Optical Microscopy Optical microscopic methods may be used for the identification of zeolite minerals in thin sections or individual crystals. This can determine the size, distribution and relationship of the zeolite and other minerals present. The method is limited by the very fine grain size of the zeolite minerals, their low birefringence and variation of their indices of refraction with changes in chemical composition. This method is slow and requires an experienced mineralogist to be effective.

62 Handbook of Natural Zeolites

Mihaela Ulmanu

Differential Thermal Analysis (DTA) Differential Thermal Analysis (DTA) may be used to identify zeolite minerals, but the method is less effective when several zeolites or certain contaminants are present or for small amounts of mineral. Variations in the exchangeable – cations content may also cause differences in the differential thermal curve. The method is very useful in distinguishing clinoptilolite from the closely related mineral heulandites. Gottardi and Galli [11] have published a comprehensive collection of DTA curves for natural zeolites. Other analytical methods may be used but they are generally complex, very costly and not currently practical for exploration or quality control. Such methods include: infrared absorption spectrography, Moessbauer spectroscopy, electron spin resonance spectroscopy, electron spin echo spectrometry, solid state nuclear magnetic resonance, neutron diffraction etc. Testing for Characterization In characterization of zeolitic materials for commercial uses, it is important to quantify other physical and chemical properties. The following are physical and chemical properties and tests that may typically be required: cation exchange capacity (CEC), specific gravity and bulk density, brightness, whiteness and color, hydration/dehydration testing, gas adsorption, attrition in water, surface area (internal and external). TECHNOLOGY Exploration Techniques Most economic natural zeolite deposits occur in altered ash – fall and ash – flow tuffs or tuffaceous sediments of Tertiary or, to a much lesser extent, Mesozoic age. The predominant natural source for zeolite extraction is bedded zeolites. Prospecting such deposits is difficult because they are finely crystalline, is difficult to identify and usually they appear similar to altered or unaltered tuffaceous rocks, bentonite, diatomite and other fine-grained sediments. Many known zeolite deposits in the world have been not sampled and characterized adequately, so there are many opportunities to develop new zeolite sources. Field exploration for zeolites must rely on careful geologic examination and sampling. Zeolitized tuffs usually appear as obvious altered rocks, but locally may be indistinguishable from unaltered rocks. Zeolitized rocks are commonly white to

Mineralogy of Natural Zeolites

Handbook of Natural Zeolites 63

gray in color, massive and blocky, resistant to weathering and possess identifiable surface textures. Natural zeolites may attract iron oxides or other contaminants and be stained varying shades of red, brown, yellow or green. X-ray diffraction analysis of outcrop and drill samples is the technique most effective in identifying zeolite minerals. Specific zeolite minerals or mixtures of minerals may be identified and semi-quantitative estimates made of their abundance. Ammonia cation exchange capacity (CEC) analysis of samples is also a very effective early screening technique to estimate the ion exchange capacity of zeolitized materials, particularly for clinoptilolite, chabazite, erionite and phillipsite. This also screens out heulandite and analcime, which appear similar. Mordenite samples require X-ray diffraction and gas adsorption or separation tests to gauge their value as they are less responsive to ammonia adsorption. Once a zeolite ore has been identified, mapped and drilled sufficiently to establish its physical parameters and tonnage, it should be thoroughly characterized by bulk sampling and testing to define its suitability to supply raw materials for specific applications. Mining Methods Because of their low unit value, bedded sedimentary zeolites are mined by open pit methods. Excavation is generally done using conventional earth moving equipment; in thicker bodies, it may include mine benching methods. Such mining minimizes costs, as it employs low cost explosives, rubber – tired or tracked earth moving equipment and direct truck loading in the pit for transport to a processing plant. Variations in ore quality may be handled by selective mining and blending during mining or stockpiling. Quality control is commonly done by sampling through drilling, periodic face sampling, visual assessment of the material in place, and systematic sampling of truck loads or the process stream. Zeolites for special high value uses may be recovered by very selective open pit mining. By exemple, chabazite – erionite raw material mineral from a 15 cm- thick bed at Bowie, AZ is used by Union Carbide Corporation to make high value molecular sieve and catalytic products. Mining at the Mud Hills clinoptilolite deposit in southern California recovered ore with strict specifications in 30 cm slices from a 4.6 m-thick deposit to yield a very high value product for ion exchange material used by British Nuclear Fuel Ltd. [4].

64 Handbook of Natural Zeolites

Mihaela Ulmanu

Processing Natural zeolites are sold as crushed and screened, finely ground or micronized to ultra-fine ground products, depending of their utilization. Crushed and screened materials may be used for low grade value, coarser fraction applications, such as soil conditioner one pet litter, that can tolerate a fairly wide range or particle sizes and require low product cost. Many zeolite products are crushed, ground and air classified to a size range of – 60 to + 325 mesh, using Raymond mills and comparable grinding equipment. Micronized products as fine as 5 - 10µm and ultrafine products down to 1µm are prepared for special uses, e.g., paper filler. Natural zeolites may be enhanced in performance by washing them with acid or NaCl solutions to raise the H+ or Na+ content respectively. Clinoptilolite products are particularly enhanced in ion – exchange capacity by washing to replace the slower reacting K+ ions with Na+ ions. Bowie, AZ chabazite products are commonly pelletized and lightly calcined to reduce their overall friability. Specifications Specifications depend on the uses of the zeolite products and vary widely because of the broad range of natural zeolite products serving many markets. The American Society for Testing and Materials (ASTM) Committee No.D-32 has been established to set testing methods and standard specifications for zeolites in the United States. Specifications and standards in Europe and Japan are commonly set by the producing companies in a market – driven setting. Zeolite producers’ deal with specifications in two ways: sell materials on a custom basis to specifications negotiated with the buyer, or sell materials on a product – line basis, where each zeolite product has a name or number designation and specific physical and/or chemical characteristics. In the USA, zeolite products are commonly sold under a trade name rather than as a mineral variety. Markets Zeolites are a relatively new mineral commodity, with little commercial interest shown before the 1960’s except for building stone and pozzolan uses. No formal commodity markets exist and sales for lower value products are confined mostly to the countries with zeolite resources. Higher value products may be sold

Mineralogy of Natural Zeolites

Handbook of Natural Zeolites 65

internationally, but their total value worldwide is still small. Because of their very wide range applications, natural zeolites sell into diverse markets; Japan has a particularly wide range of zeolite markets, for agricultural, industrial and consumer uses. North America sales are principally for agricultural and pet litter applications. Markets in Europe and Cuba are primarily for agricultural products, with a growing industrial market sector. The strongest areas of market growth are expected to be in sewage treatment, deodorants, pet litter, soil treatment and nuclear water treatment and containment. Value and Costs Cost of zeolite products depends mostly on the type and degree of processing that must be done to satisfy specific market specifications. Mining costs are generally fairly low, typically 3 – 6 $/t, unless very selective mining is done. Most natural zeolites are sold onto low value industrial or agricultural markets, commonly selling for 30 – 50 $/t for granular products down to 40 mesh, and 50 – 120 $/t for ground materials in the range of 40 – 325 mesh. Consumer products such as pet litter, fish – tank media or deodorant materials commonly sell for 0.50 – 4.50/kg at the retail level. Products for very special industrial applications, such as radwaste filter media of catalysis in petroleum refining, may show values ranging up to thousands of dollars per ton, although their market demand may be very limited [4]. Transportation Zeolite products are generally transported by highway or rail carriers in bulk, in one – ton super-sacks or in multi – wall paper bags, usually palletized. They present no special problems, subject to proper labeling and handling as a respirable silica – containing material. Natural zeolites, particularly clinoptilolite, that have been dried may adsorb several percent by weight of water en route to their destination. Zeolites prepared as dimension stone are shipped any other stone products, generally palletized and by truck transport. Transportation costs strongly affect the distance a lower value zeolite can travel to profitably reach markets. Agricultural grade clinoptilolite from the western United States can reach markets in the eastern half of the country, but future imports from Cuba, Antigua and other tidewater sources could lower prices to the point where this is impossible. High

66 Handbook of Natural Zeolites

Mihaela Ulmanu

value zeolites can generally be shipped nationwide and even to international points from their processing sources. Alternate Materials When natural zeolites enter the marketplace as new products, they may have to compete with other mineral products that are already well established. There are established alternate materials for most zeolite applications. Market entry of natural zeolites requires demonstration of technical equivalency or superiority and/or some cost advantage in each application in order to gain some of the market. Synthetic zeolites (molecular sieves) are the major alternate materials to natural zeolites. Synthetic zeolites can be tailored in physical and chemical characteristics to serve many applications more closely and they are uniform in quality than their natural equivalents. Natural zeolites hold advantage over synthetic materials in some applications (e.g., cesium and strontium adsorption in radioactive waste cleanup) and are also able to function at lower pH levels. They are also generally much lower in cost than synthetic zeolite products. Activated carbon, silica gel, and similar materials are more effective than zeolites for many ion – exchange applications and are not disproportionately more expensive. Bentonite, attapulgite and other minerals show selective high absorbency and are also available in a competitive price range. Environmental Regulations Environmental regulations vary between states and countries and they can be a source of conflict between government regulators and mine operators. Natural zeolites are relatively innocuous and present no particular environmental problems, with three exceptions: a) Several zeolite minerals (erionite and some mordenite) are fibrous in form and may be classified as asbestiform materials. b) Finely crystalline silica commonly occurs in zeolite deposits and the finely ground products may contain more than 0.1% respirable silica. c) Zeolite mines and dry processing plants tend to generate dust, causing air quality problems.

Mineralogy of Natural Zeolites

Handbook of Natural Zeolites 67

Dust from mining plant facilities may be considered a local environmental pollutant. Most zeolites contain silica in the form of amorphous silica (opal or opal CT) and/or crystalline silica (quartz). Processing plants may therefore be required to use efficient air pollution control systems ranging from standard bag house dust collectors to electrolytic precipitators to minimize worker exposure to fugitive dust at bagging stations or grinding mills to comply with local air quality control requirements. Most zeolite production uses dry processing methods. Zeolite processing will inevitably move into water washing and wet classification methods, requiring proper handling of plant effluent and tailing pond discharges. Zeolite minerals are generally considered to be chemically inert, and most of them are non-fibrous. Erionite is established as a fibrous, acicular mineral and has been labeled a possible carcinogen on the basis of medical studies of high mesothelioma incidence in the Capadoccia District of Turkey. Mordenite is also a fibrous mineral, but is presently not regarded as a potential carcinogen. Safety Regulations Natural zeolites are dusty materials when crushed and ground and air quality standards should be maintained carefully during mining and processing. Because of several natural zeolites are fibrous in nature (erionite and mordenite), appropriate care should be taken in handling these materials. The natural zeolites do not affect any toxic threat to plants or animals, and there are no established procedures for their remedial handling. Future Trends Overall, the zeolites present a healthy, growing industry with continued expansion into new applications and steady demand in industrial markets where they have achieved acceptance. Most of this activity and growth, however, has been in the synthetic zeolite field. Natural zeolites have only a small portion of the markets, commonly those with lower costs or very specific uses, and growth in North America has generally languished. Because the technology has been firmly established, an excellent range of high quality natural zeolite deposits identified and characterized, and a record of successful sales for products with consistent specifications achieved, growth of the natural zeolite field appears likely to continue through the end of the century on a slow and steady base. Natural

68 Handbook of Natural Zeolites

Mihaela Ulmanu

zeolites have established a strong domestic market pattern for several uses: catalysis and petroleum refining, nuclear waste treatment and odor control. These market areas can be expected to continue and expand. Natural zeolite use is particularly tide to (a) pollution control and (b) energy cost and efficiency issues; greater emphasis on these areas would markedly increase the probable adaption of zeolite technology. Higher energy costs and greater environmental demands will spur zeolite production and sales significantly. Japan, the former Soviet Union and a few other countries have evolved strong natural zeolite industries based on the availability, low cost, suitability (agricultural and industrial) and consumer applications of these minerals. Problems The synthetic zeolites are materials with few if any problems, as they are readily made from abundant raw materials and present no toxic or environmental problems. The natural zeolites must penetrate markets where other materials are already used and accepted, and they are also faced with a stigma of being presented as a panacea for too many material supply problems in 1970s. Suppliers of competing materials have capitalized on this past over – selling of zeolites. Several natural zeolites are fibrous minerals and their use or presence even in trace amounts may suppress the use of consideration of zeolites for some new applications. Erionite has been classified as a hazardous material, which precludes its use for some applications, particularly in consumer products. Mordenite is also a fibrous material, but apparently has no record of carcinogenic problems. Natural zeolites commonly contain some crystalline silica, which may require stringent hazardous materials labeling for finished products. The natural zeolites lack any designation of industrial standards on a national or international basis, which inhibits their sale and use, principally in industrial and consumer markets. Creation of standards through ASTM or trade associations would alleviate this problem. ACKNOWLEDGEMENTS None declared.

CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists.

Mineralogy of Natural Zeolites

Handbook of Natural Zeolites 69

REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

Breck DW. Zeolite Molecular Sieves: Structure, Chemistry and Use, John Wiley, New York. 1974; 771pp. Mumpton FA. Natural Zeolites. Mineralogy and Geology of Natural Zeolites. F.A.Mumpton ed. Mineralogical Society of America Short Course Notes, 1977; 4: pp.1-17. Flanningen EM. Crystal Structure and Chemistry of Natural Zeolites. Mineralogy and Geology of Natural Zeolites, F.A.Mumpton ed. Mineralogical Society of America Short Course Notes, 1977; 4; pp.19-52. Holmes DA. Industrial Minerals and Rocks. Cap. Zeolites, 6th Ed., 1994; pp. 1129-1158. Damian Gh, et al., Zeolitic tuffs from Costui zone-Maramures Basin. Carpth.J of Earth and Environment Sciences, 2007; 2 (1): p.59-74. Best MG, Christiansen EH. Origin of broken phenocrystala in ash-flow tuffs. Geological Society of America Bulletin. 1997; 109 (1): p.63-73. Mercer BW.et al., Water Pollut. Control Fed., 1970; 42: R 95-R 107. Colella C. Natural and Microporous Materials in the Environmental Technology. P. Misaelides, F. Macasek, T. Pinnavaia and C. Colella (eds), Kluver A.P., Dordrecht B.V., Olanda, 1999. Mumpton FA., La roca magica : Uses of natural zeolites in agriculture and industry. Proc. Natl. Acad.Sci. USA.1999; 96; pp.3463-3470. Papke KG. Erionite and Other Associated Zeolites in Nevada. Bulletin 79, Nevada Bureau of Mines and Geology, 1972; 32 pp. Gottardi G, Galli E. Natural Zeolites, Spring Verlag, 1985; 409 pp.

70

Handbook of Natural Zeolites, 2012, 70-102

CHAPTER 5 Physical and Chemical Properties Mihaela Ulmanu* and Ildiko Anger National R&D Institute for Non-Ferrous and Rare Metals, IMNR, Bd. Biruintei 102, 77145 Pantelimon, Romania Abstract: A zeolite can be imagined like a house, where the structure (the doors, windows, walls and roof) is really the zeolite while the furniture and people are the water, ammonia and other molecules and ions that can pass in and out of the structure. The chain - like structures can be thought of like towers of high wire pylons. The sheet – like structures can be seen like large office buildings with the sheets analogous to the floors and very few walls between the floors. And the framework structures like houses with equally solid walls and floors. All these structures are still frameworks. These variations make the zeolite group very diverse, crystal habit – wise. Otherwise zeolites are typically soft to moderately hard, light in density, transparent to translucent and have similar origins. There are about 45 natural minerals that are recognized members of the Zeolite Group. In this chapter are presented the main physicochemical properties of zeolites in correlation with their structure. From this point of view there are three large families of zeolites: the natrolite group, the heulandite group and the chabazite group. For each zeolite families the main representing members are presented together with their properties.

Keywords: Natural mineral, zeolites structure, zeolites framework, zeolites physicochemical properties, ion exchange, zeolites families, natrolite group, heulandites group, chabazite group. INTRODUCTION Zeolites are crystalline, porous three dimensional aluminosilicates of the alkali (mainly Na and K) and alkaline- earth (mainly Ca) metals. Their crystal structure is based on a three dimensional framework of (SiAl)O4 tetrahedra with all four oxygen shared by adjacent tetrahedral. As the result, they have a channel structure with molecular dimensions of 3 to 10Å, Fig. 1. Because some of the Si4+are substituted by Al3+, there is a net negative charge which is balanced by extra-framework exchangeable cations mainly Na+, K+, Ca2+ *

Address correspondence to Mihaela Ulmanu: National R&D Institute for Non-Ferrous and Rare Metals, IMNR, Bd. Biruintei 102, 77145 Pantelimon, Romania; E-mail [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Physical and Chemical Properties

Handbook of Natural Zeolites 71

or Mg2+. These cations are loosely held within the central cavities and they are surrounded by water molecules. The water molecules are loosely held in the pores and most zeolites can be reversible dehydrated and their cations readily exchanged. Unlike most other tectosilicates, zeolites have large vacant spaces or cages in their structures that allow space for large cations (above mentioned) and even for relatively large molecules or cation groups such as water, ammonia, carbonat and nitrate ions. In the more useful zeolites, the spaces are interconnected and form long and wide channels with different sizes, depending on the mineral. These channels allow the easy movement of the resident ions and molecules into and out of the structure. The main characteristic of zeolites is the ability to lose and absorb water without damage their crystal structures. The large channels explain the consistent low specific gravity of these minerals. Si

Figure 1: Framework structure of zeolites.

Zeolites have an empirical formula of (M+2, M++)Al2O3.gSiO2.zH2O, where M+ is usually Na or K, Me2+ is Mg, Ca or Fe, and g and z are variable multipliers. Rarely Li, Sr, or Ba may substitute for M+ or M2+. The tetrahedral Si: (Si+Al) ratio is one of the major compositional variables; some zeolites (e.g., mordenite) are the silica – rich and others are more aluminous. Theoretically, the possibilities for different framework structures are infinite; around 45 zeolites are known in nature and more than 150 synthetic zeolites have been prepared [1].

72 Handbook of Natural Zeolites

Ulmanu and Anger

PROPERTIES Because of their unique porous properties zeolites were introduced in 1954 as adsorbents for industrial purifications processes. Worldwide zeolite production was estimated of 2.5 million to 3 million metric tones in 2008 year [2]. The most common natural zeolites are: analcime, chabazite, clinoptilolite, erionite, ferrierite, heulandite, laumontite, mordenite and phillipsite. Generally, zeolites are colourless minerals, white crystals with hardness generally between 3 and 6. Zeolites have a number of characteristic properties that are important for commercial applications, including: -

they have a high degree of hydration and they are easily dehydrated;

-

low density and large void volume when dehydrated;

-

stability of the crystal framework structure when dehydrated;

-

cation exchange properties;

-

uniform molecular – sized channels in the dehydrated crystals;

-

ability to absorb gases and vapours;

-

catalytic properties with H+ exchanged forms;

-

special electrical properties.

Many zeolites are able to lose water fairly continuously over a temperature range of 150 to 400oC without collapse of the framework structure and resorb it from the atmosphere at room temperature. All zeolites are molecular sieves; they can selectively adsorb molecules on the basis of their size, shape or electrical charge. The ion exchange, catalytic and molecular sieves properties of zeolites make them useful in wide range of applications. Ion Exchange Properties Zeolite structure (the presence of large channels and cavities), associated with extra – framework cations, facilitate cation exchange. Natural zeolites have cation exchange capacities between 200 and 400 meq/100g, superior to most other

Physical and Chemical Properties

Handbook of Natural Zeolites 73

inorganic cation exchangers. The cations (e.g., Na or K) in zeolite structure are the role to balance the negative net – charge caused by trivalent aluminum cations which are coordinated tetrahedrically by oxygen anions. By exposing a sodium containing zeolite to a solution containing other cations, the sodium ions can be exchanged by these other cations provided they are not excluded from the pores due to their size (including the water molecules coordinating the respective cations). In general, natural zeolites that are open and silica- rich are highly selective for large univalent cations like Cs+ or NH4+, according the equilibriums [1]: [SiAlO4]- Na+ +NH4+ [SiAlO4]- NH4+ -Na+ [SiAlO4]- Na+ +Cs+ [SiAlO4]- Cs+ -Na+ The Catalytic Properties The catalytic properties of zeolites are due to their large surface areas (both internal and external) and their Si – Al frameworks. The Si →Al + H+ exchange are widely used for catalysis because the Al – tetrahedral can function as proton donors or acceptors. The protons which balance the negative charge of a zeolite framework are not strongly bound to the framework and are able to move within the pores and react with molecules which penetrate into the zeolite pore system. The protonated zeolite can act as a Brontsted acid. Furthermore, Lewis acidity can be produced by cation within the pores. Bronsted acidity: Al – OH – Si, (terminal silanol groups) is associated with water loose at 550oC. Lewis acidity: AlO+, Al(OH)3*x H2O, metal cations is associated with framework dealumination at 500 - 1000oC. Synthetic zeolites are preferred for catalytic industrial applications, although natural zeolites may be important as catalyst in biochemical reactions produced in biological systems [3]. Molecular Sieving Properties The molecular sieving properties vary passing from one zeolite mineral to other according to the pore size of the mineral structure and the sizes of channels and cavities.

74 Handbook of Natural Zeolites

Ulmanu and Anger

Typically, a zeolite is useful as a molecular sieve only after completely dehydration. Examples of natural zeolites in this category are: mordenite, erionite and chabazite. Pore size determines their general usage. Mordenite and the synthetic faujasite are examples of large pore size (maximum free diameter 7.5Å) zeolite minerals. The pore size of zeolites is determined by their structures and may be varied slightly by ion – exchanging the zeolite. By ion - exchange process smaller cations can be positioned in windows making them wider; specific cations may also be positioned on other sites than in the windows, leading to even larger open windows. The window sizes determine the accessibility of the zeolite pore system for other (e.g., organic) molecules. These molecules which can penetrate the pore system are usually strongly adsorbed in the micro pores, due to a significant decrease of the interaction potential (Lennard – Jones) when two surfaces are brought closely together as in microporous materials. The potential of top of the surfaces overlap and lead to a decrease of the interaction potential. In this situation, molecules which may pass through the pore windows of zeolite are “trapped” in these pores, a phenomenon which is advantageous in gas separation processes (e.g., pressure swing process) or in removal of water molecules from organic solvents [4]. Small pore size (maximum free diameter 4.3Å) zeolites such as chabazite, clinoptilolite and zeolite A are used in the radioactive waste, municipal waste treatment and odor control industries. The data about zeolite families presented in this chapter are extracted from Wikipedia Free Encyclopedia and from the data available by the International Association of the European Manufacture of Major, Trace and Specific Feed Mineral Materials. According with these data, zeolites have basically three different structural variations. 1.

There are chains – like structures whose minerals form acicular of needle – like prismatic crystals, i.e., Natrolite.

2.

Sheet – like structures where the crystals are flattened platy or tubular with usually good basal cleavages, i.e., Heulandite.

3.

And framework structures where the crystals are more equant in dimensions, i.e., Chabazite.

Physical and Chemical Properties

Handbook of Natural Zeolites 75

A zeolite can be imagined like a house, where the structure (the doors, windows, walls and roof) is really the zeolite while the furniture and people living inside are the water, ammonia and other molecules and ions that can pass in and out of the structure. The chain - like structures can be imagined like towers of high wire pylons. The sheet – like structures can be seen like large office buildings with the sheets analogous to the floors and very few walls between the floors. And the framework structures like houses with equally solid walls and floors. All these structures are still frameworks. These variations make the zeolite group very diverse, crystal habit – wise. Otherwise zeolites are typically soft to moderately hard, light in density, transparent to translucent and have similar origins. There are about 45 natural minerals that are recognized members of the Zeolite Group. In the following each zeolite family is presented in detail. NATROLITE FAMILY The natrolite group included natrolite, mesolite, scolecite and thomsonite [5]. The earliest names for this group of zeolites was some form of fibrous zeolite, such as Faserzeolithe of Werner and mesotype of Hauy [6]. Referring to its composition, Klaproth [7] proposed the name natrolite, for the mineral from Hohentweil, Hegau, Bade – Wurttemberg, Germany. A tetragonal natrolite, first found at Ilimaussaq, Greenland [8] was later named tetranatrolite by Chen and Chao [9] for similar material from Mont Saint-Hilaire, Quebec, Canada. Gonnardite has a variable composition, both in the framework and in the channels. Both tetranatrolite and gonnardite have the natrolite framework, but it is disordered. In 1998 the International Mineralogical Association, Commission on New Minerals, Nomenclature and Classification approved the abandon of the name tetranatrolite and proposed to use the name of gonnardite for all compositions having the disordered natrolite structure. Paranatrolite was named by Chao [9] for a form of natrolite with the composition [Na2(H2O)3][Al2Si3O10]. It appears to be an overhydrated form of gonnardite, and has been assigned doubtful status [10], based on their Rule 4, which does not recognize states of partial hydration or over-hydration as sufficient grounds for separate zeolite species. Some characteristics of each member of NATROLITE family are presented as follows.

76 Handbook of Natural Zeolites

Ulmanu and Anger

Natrolite General formula: [Na2(H2O)2][Al2Si3O10]. Morphology: orthorhombic single crystals are pseudo – tetragonal prisms terminated by a pyramid, Fig. 2. c c 111

z

58-730

110

a

b

a x

b y

Figure 2: Thin section of natrolite single crystal. Crossed polars, width of view, 5mm.

Sizes range: from a few millimeters to several centimeters, Common forms: {110} and {111}. Physical properties: Cleavage {110} perfect, Hardness: 5.5, Density: 2.2 – 2.26 g/cm3, Luster: vitreous, Streak: white. Optical properties: Color: colorless to gray, bluish, yellowish colorless in thin section, Biaxial (+), α = 1.473 – 1.483, β = 1.476 – 1.486, γ = 1.485 – 1.496, δ = 0.012, 2Vz = 58 – 73o, X = a, Y = b, Z = c, Dispersion: r v, distinct, crossed. α = 1.491 – 1.505, β + 1.493 – 1.503, γ = 1.500 – 1.512, 2V (meas.) = 0o – 55o; 2V (calc.) = 34o, Cell data, Space Group: C2/m. a = 17.72 (2); b= 17.95 (2); c = 7.345 (7), β = 116.46 (5)o Z = 4. Notable occurrence are wide spread : India, Iceland, California, Arizona, Oregon (USA), Canada, Iran, Italy, Brazil, Australia, New Zeeland, Russia, Scotland, Rhone Valley and Switzerland. Uses: as chemical filters and as mineral specimens. Clinoptilolite Clinoptilolite is very closely related to heulandite and is currently considered just be a variety of heulandites. It differs from heulandite significantly only in its rich content in potassium and a little more silica. The name clinoptilolite is widely recognized and used in zeolite industries and by mineralogists. Clinoptilolite means in Greek “oblique feather stone”; he received this name because it was thought to be the monoblinic (or oblique inclined) phase of the mineral ptilotite, as in “oblique ptilotite”. Later, ptilolite was found to be the earlier name of mineral mordenite. Is an important member of heulandites family, a naturally occurring volcanic mineral with an infinite three – dimensional framework of silicon – oxygen (SiO4) tetrahedra. It is a Ca – K – Na – hydrated alumino silicate. Clinoptilolite is not the most well known, but is one of the more useful natural zeolites. We have to mention here the utilization of clinoptilolite as a chemical sieve, a gas absorber, a feed and food additive, an odor control agent and

84 Handbook of Natural Zeolites

Ulmanu and Anger

as a water filter for municipal and residential drinking water and aquariums. Clinoptilolite is appropriate for these applications due to its large amount of pore space, high resistance to extreme temperatures and chemically neutral basic structure. It is able to absorb toxins in the feed that are created by molds and microscopic parasites and enhances food absorption by animals (cows, pigs, horses and chickens). Clinoptilolite can absorb easily ammonia and other toxic gases from air and water; it can be used in filters, for health reasons and for odor removal. The structure of clinoptilolite is the same as heulandites and is like sheet. The sheets are connected to each other by few bonds that are relatively widely separated from each other. Every oxygen ion is connected to either silicon or an aluminum ion. The sheets contain open rings of alternating eight and ten sides; these rings stack together from sheet to sheet to form channels throughout the crystal structure. Typical Chemical Characteristics: SiO2

68.28

Al2O3

12.30

Fe2O3

0.08

CaO

4.34

MgO

1.05

K2O

0.94

Na2O

0.26

Physical properties: Luster: vitreous to pearly on the most prominent pinacoid face and on cleavage surfaces. Transparency: crystals are transparent to translucent. Crystal system is monoclinic; 2/m. Crystal habits: include blocky or tabular crystals with good monoclinic crystal form, more tabular and proportioned than heulandite. Commonly found in acicular crystal sprays. Specific density: 2.16 kg/dm3, Bulk density: 0.85 – 1.1 kg/dm3, Hardness (Mohs scale): 3.5 – 4, may be softer on cleavage surfaces. Alkali stability: 7 – 11 pH domains. Acid stability: 2 – 7 pH. Moisture content: 7%, Streak: white. Fracture is uneven. Cleavage: perfect in one

Physical and Chemical Properties

Handbook of Natural Zeolites 85

direction parallel to the prominent pinacoid face. Colour: colorless, white, pink, yellow, reddish, greenish, ivory. Pore volume: 0.34cm3/cm3. Clinoptilolite forms as a devitrification product (the conversion of glass to crystalline material) of volcanic glass in tuffs (consolidated pyroclastic rocks). This process occurs when the glass comes into contact with saline waters. Clinoptilolite can also be found in the vesicles of volcanic rocks such as basalts, ryolites and andesites. Notable occurrences include: tuffaceous volcanic rocks of Arizona, Hoodoo and Yucca Mountains of Nevada, Altoona Washington, Oregon and several sites in California, British Columbia Canada, in Austria, Bulgaria, Germany, Italy, Japan, New Zeeland, India. Laumontite Laumontite is a handsome mineral; its columnar crystals appear like a monument above a desert plane. Its structure has a typical zeolitic openness permitting the moving of large ions and molecules inside the framework, into and out the crystal structure. Laumontite can act as chemical “sieves”. Laumontite is used like mineral specimen and chemical filter. Formula: [Ca4(H2O)18][Al8Si16O48]. Morphology: Monoclinic, 2/m. Single crystals are pseudo – tetragonal prisms terminated by a flat slanted face of a pinacoid, Fig. 3. Crystal sizes range from a few millimeters to several centimeters. They are commonly grooved or striated. Common forms: {110} and {-201}. Physical properties: Cleavage: {110} perfect, Hardness: 5.5, Density: 2.20 – 2.26 g/cm3, Luster: vitreous to chalky, Streak: white. Optical properties: Color: white to gray, pink, yellowish, brownish, golden brown, colorless in thin section, Biaxial (-), α = 1.510 – 1.514, β = 1.518 – 1.522,

86 Handbook of Natural Zeolites

Ulmanu and Anger

γ = 1.522 – 1.525, δ = 0.010 – 0.012, 2Vx = 23 – 47o, ZΛ c = 8 – 10o (in acute β angle), Y = b, O.A.P. = (010). Dispersion: r< v, distinct, weakly inclined, partially dehydrated laumontite: α =1.502 – 1.507, β = 1.512 – 1.516, γ = 1.514 – 1.518, δ = 0.011 – 0.012, 2Vx = 26 – 44o. c

100

c 110

010

Z

O.A.P

010

X b a

a 201

Figure 3: Single crystal of laumontite.

Crystallography: Unit cell: A = 14.587Å, b = 12.877 Å, c = 7.613Å, β = 111.159o, Z = 1, Space group: C2/m. Partially dehydrated laumontite (leonhardite, [23]), Unit cell: a+ 14.714Å, b = 13.132Å, c = 7.531Å, β = 111.23o [23]. Laumontite was first described by Hauy [6] and named “zeolite efflorescent”. The mineral was considered a distinct species by Werner (Jameson, [25]), who changed the name to “lomonite”, honoring Gillet de Laumont, who collected the material studied by Hauy. In 1809 Hauy [26] changed the spelling to “laumonite”, and finally the name laumontite was suggested by von Leonhard. Leonhardite recently discredited as a species [10], refers to partially dehydrated laumontite with approximately 14 H2O per unit cell.

Physical and Chemical Properties

Handbook of Natural Zeolites 87

Crystal Structure Various structural studies of laumontite with different degrees of hydration (between 10.8 and 18 H2O pfu) show that the framework topology remains unchanged and can be described in C2/m symmetry [27-30]. The framework exhibits two different types of four – membered rings, those where SiO4 and AlO4 alternate and those formed only by SiO4 tetrahedra. Large channels run parallel to the c – axis confined by ten – membered rings (aperture 4.0 x 5.3Å). Ca occupies a four fold site on a mirror within the c- extended channels and is coordinated by three H2O molecules and four oxygens, belonging to AlO4 tetrahedra. Room – temperature unit – cell parameters for fully hydrated launomtite with 18 H2O are: a = 14.863, b = 13.159, c= 7.537 Å, β = 110.18o, Z = 1 [30], whereas the 14 H2O variant has: a = 14.75, b = 13.07, c = 7.60Å, β = 112.7o, Z = 1 [31]. No piezoelectric effect for laumontite and leonhardite was found but a strong pyroelectric effect [32]. Thus, it may be concluded that the structure lacks a center of symmetry and the space group is either C2 or Cm. Stahl and Artioli [29] discussed the possibility of a locally ordered H2O superstructure leading to the lowering of symmetry. The simplest model would lead to doubling of the a – axis with space group P2. The dehydration of laumontite was investigated by [28]. The complicated clustering of H2O and accompanying phase transitions in laumontite with varying degrees of hydration were studied by Gabuda, [33] using NMR 1H and 27Al spectroscopy between 200 and 390 K. Fersman [34] introduced the term “primary leonhardite” for the composition [Na1,24K1.59Ca2.55(H2O)14][Al8.18Fe3+0.03Si15.86O48] later confirmed by Pipping [31]. This “primary leonhardite” with more than five channel cations pfu, neither dehydrates nor rehydrates at room temperature. The excess of channel cations compared with ordinary laumontite indicates that “primary leonhardite” has additional non – framework cation sites [35, 36] occupied by H2O molecules in fully hydrated laumontite. This also explains why “primary leonhardite” cannot be further hydrated and why it shows no indication of weathering as usual for exposed laumontite. The species name “leonhardite”. The species “leonhardite” was recently discredited as a mineral species [10, 25], because “leonhardite” is just a partially dehydrated variety of laumontite.

88 Handbook of Natural Zeolites

Ulmanu and Anger

Chemical Composition Laumontite composition deviates little from the formula [Ca4(H2O)18][Al8Si16O48] both in the Si, Al content of the framework and the cation content of the channels. Most analyses show small amounts of Na and K while Mg and Sr replacement for Ca is minor. Rarely Fe3+ replaces tetrahedral Al, giving crystals an orange color. However, the red color of some laumontite crystals is more likely to be a result of hematite inclusions. Because of the ordered structure TSi (the fraction of Si in tetrahedral sites) varies only slightly from 0.667. The largest compositional variation is in the water content, because laumontite at least partially dehydrates in low humidity air. Typical laumontite analysis yield 14 to 16 weight% H2O, which corresponds to 13 to 17 H2O molecules per unit cell. Fully hydrated laumontite with 18 H2O pfu contains 16.9 weight % H2O. Even through laumontite easily dehydrates with a slight framework collapse, immersion in water permits full rehydration, without any change in the appearance of the crystals. The most alkali – rich laumontite, “primary leonhardite”, contains 1,24 Na and 1,59 K pfu [34]. Laumontite is associated with albite, calcite, chlorite, quartz and clay minerals which occur in many areas of volcanic sediment accumulations. Most laumontite occurs as an alteration product of rocks that had plagioclase and /or basaltic component and have been exposed to temperatures (50 – 250oC) in the presence of water. Mordenite Mordenite was described and named by [36] for material found along the shore of the Bay of Fundy, 3-5 km east of Morden, Nova Scotia, Canada. It is named after the discovery and type locality. Formula: [(Na2, Ca, K2)4(H2O)28][Al8Si40O96]. Morphology: Orthorombic: mmm or mm2. Single crystals are thin fibers, 0.1 to 10 m long, Fig. 4. Common forms: {100}, {010}, {110} and {101}. Physical properties: Cleavage: {100} perfect, {010} distinct, Hardness: 3-4, Density: 2.12 – 2.15 g/cm3, Luster: vitreous to silky, Streak: white.

Physical and Chemical Properties

Handbook of Natural Zeolites 89

c- X O.A.P 101

b- Z a- Y 110

010

100

Figure 4: Single crystal of mordenite.

Optical properties: Color: white, yellowish or pinkish; colorless in this section, Biaxial (+ or -), α = 1.472 – 1.483, β = 1.475 – 1.485, γ = 1.477 – 1.487, δ = 0.004 - 0.005, 2Vz = 76 – 104o, a = Y, b= Z, c= X, O.A.P. = (100) Crystallography: Unit cell: a = 18.052 – 18.168 Å; b = 20.404 – 20.527Å; c = 7.501 – 7.537Å, Z = 1, Space group: The average space group is Cmcm. The true space group is probably Cmc21. Crystal Structure: The crystal structure of mordenite was determined by Meier [38] and refined by Gramlich [39] on Na – exchanged natural crystals from Challis, Idaho, USA. The topology of the framework is characterized by 5 – member tetrahedral rings, which are part of the composite building unit. These building units are linked by edge – sharing into chains along c which are in turn linked together by 4 – rings to form a puckered sheet perforated with 8 – ring holes. These permeable sheets are oriented parallel to (010). Linking these sheets together with 4 – rings, 12 – ring channels are formed parallel to (001). The 8 – ring holes of successive sheets do not align to make channels parallel to (010). Ever since mordenite was synthesized in 1968 [40], it has been known that some synthetic mordenite can accept cations or molecules larger than 4.5Å, while natural mordenite cannot. Explanations for small – port mordenite have remained

90 Handbook of Natural Zeolites

Ulmanu and Anger

controversial. In an effort to solve the problem, Simoncic and Ambruster [41] in 2004 refined a natural and a synthetic large – port mordenite and found that both structures exhibit the same defect features. Domains of the entire Cmcm framework structure are reproduced by a non – crystallographic (001) mirror plane at z = 0 and z = ½. These domain shifts do not influence or obstruct the 12 – membered ring – channels characteristic of this zeolite (and therefore, do not effectively solve the small – port problem). A consequence of refinement with the space group Cmcm is that one oxygen (O8) is located on an inversion center, causing T – 08 – T bond angle to be 180o. Liebau [42] in 1961 showed that such straight angles are energetically unfavorable and are unlikely to occur. Refinement in the space group Cmc2, removes the inversion center and reduces T – O8 – T bond angle from 180 to 155 – 167o [41]. The refinement of the Elba mordenite [43] and another from Jarbridge, Nevada, USA [41] determined the non – framework cation sites and occupancy. Site Ca bonded to oxygen of T3 tetrahedra is 50% occupied by Ca2+, while K+ occurs in the K sites only when the Ca – site is not occupied. Chemical Composition Mordenite is a high – silica zeolite, in which the Si, Al content of the framework and the cation content of the erionite cavities are moderately variable. TSi ranges from 0.08 to 0.86 (38.7 to 40.9 per unit cell). The non – framework cation compositions are mostly Na – dominant. Mordenite samples from cavities in basalt have less than 0.8 K ions per unit cell, whereas those from rhyolitic, tuffaceous rock decidedly more K, in many samples more than one ion per cell. In at least five localities, Yucca Mountain, Nevada, USA; Yeongil, Korea; Polyegos Island, Greece; Island of Samos, Greece [44] and eastern Taiwan [45], analytical results show at least some samples with K as the dominant cation. Judging from several complete analyses, the water content of mordenite is probably 28 H2O molecules per unit cell, which corresponds to about 14.2 weight percent H2O in the analysis. Sedimentary deposits of mordenite are present in several countries, especially in Bulgaria, Hungary, Japan and United States. Quarried material is generally substantial, e.g., a recent estimation of the yearly production in Japan is 150 000 tons. Apart from generic applications in the fields of agriculture and building

Physical and Chemical Properties

Handbook of Natural Zeolites 91

industry (as dimension stone), uses are known as sorbent and molecular sieve [46]. Gas separation processes are reported for the production of high – grade O2 from air by pressure – swing operating generators. Full – scale plants based on mordenite – rich tuffs have been operating in Japan since the end of 1960. With its interconnecting channels of puckered twelve and eight membered – ring openings, mordenite has also been found to be an effective lube dewaxing catalyst with the incorporation of a noble metal hydrogenative function. The catalytic dewaxing process developed by the British Petroleum Company in early seventies [47] is a catalytic cracking process, which employs a bifunctional platinum / H- mordenite catalyst. CHABAZITE FAMILY The chabazite group zeolites – chabazite, herschelite, gmelinite and levyne usually occur as well – formed crystals belonging to the rhombohedral crystal system and can be easily distinguished from the related fibrous minerals erionite and offretite. Within the chabazite group minerals may be visually identified by characteristic habits and in most cases by their optical properties but there is as yet no chemical criterion to distinguish between these minerals [48]. Gmelinite Gmelinite was named as single species in 1825 after Christian Gottlob Gmelin professor of chemistry and mineralogist from Tubingen, Germany, and in 1997 it was raised to the status of a series [49]. The naturally occurring mineral forms striking crystals, shallow, six sided double pyramids, which can be colorless, white, pale yellow, greenish, orange, pink and red. They have been compared to an angular flying saucer. Gmelinite – Na is one of the rarer zeolites but the commonest member of the gmelinite series, gmelinite – Ca, gmelinite – K and gmelinite – Na. It is closely related to the very similar mineral chabazite. Structure: the aluminosilicate framework is composed of tetrahedral linked to form parallel double six – membered rings stacked in two different positions (A and B) in the repeating arrangement AABBAABB. The framework has no Al – Si order [50]. Within the structure there are cavities with a cross – section of up to 4Å, and also wide channels parallel to the c axis with a diameter of 6.4Å [51].

92 Handbook of Natural Zeolites

Ulmanu and Anger

Space group: P63/mmc, Unit cell parameters: a = 13.72Å, c = 9.95Å, Z = 4. Generally occurs in Si – poor volcanic rocks, marine basalts and breccias, associated with other sodium zeolites such as analcime Na(Si2Al)O6.H2O, natrolite Na2(Si3Al2)O10.2H2O and chabazite – Na, Na2Ca(Si8Al4)O24.12H2O. It also occurs in Na – rich pegmatites in alcaline rocks, and as an alteration product in some nepheline syenite intrusions [21]. No sedimentary gmelinite has been found [50]. It is generally assumed that it forms at low temperatures, less than 100oC. It is a widespread as a hydrothermal alteration product of ussingite, Na2AlSi3O8(OH), associated with gobbinsite, Na5(Si11Al5)O32.11H2O, gonnardite, (Na,Ca2)(Si,Al)5O10.3H2O and chabazite – K [21]. Gmelinite – Na occurs extremely rarely at the Francon Quarry, Montreal Canada, in sills of the igneous volcanic rock phonolite which are rich in dawsonite, NaAl(CO3)(OH)2 [52]. It occurs both as pure gmelinite – Na and interlayered with chabazite in water – quenched basalts in Western Tasmania [53]. Associated minerals include other zeolites, especially chabazite, quartz, aragonite and calcite. Chemical formula: Na4(Si8Al4)O24.11H2O. Molar mass: 2,000.77g. Color: colorless, white, yellow, orange, pale green, pink, red, brown and grey. Crystal habit: hexagonal plates, or short prisms showing hexagonal dipyramids, pyramids and basal pinacoid; may also be tabular or rhombohedral. Crystals are striated parallel to (0001). Crystal system: hexagonal 6/m 2/m 2/m, Dihexagonal dipyramidal. Fracture: conchoidal, Tenacity: brittle, Luster: dull to vitreous, Streak: white, Diaphaneity: transparent, translucent or opaque. Specific gravity: 2.04 – 2.17. Optical properties: uniaxial (-). Edingtonite Was described and named by Haidinger (1825) to honor Mr. Edington of Glasgow, in whose collection Haidinger found the first specimen. The type

Physical and Chemical Properties

Handbook of Natural Zeolites 93

material comes from Kilpatrick Hills near Glasgow, Scotland. The composition was not known until Heddie (1855) was able to obtain a complete analysis. Crystal Structure Edingtonite is either orthorhombic, space group P 212121, [12, 54-56] or tetragonal [57] space group P421m. Based on optical observations, Akizuki [58] and Tanaka et al., [59] also discussed triclinic growth sectors in edingtonite. Orthorhombic edingtonite crystals are (Si, Al) ordered, whereas (Si, Al) disorder increases the symmetry to tetragonal. Kvick and Smith [55] used neutron diffraction to locate the H positions. The framework of edingtonite consists of the same Al2Si3O10 chains built as natrolite. However, in contrast with natrolite, the tetrahedral are bonded to neighboring chains with no translation parallel to c. The Ba atoms are located in the center of (001) channels on a two – fold axis and are ten – coordinated to six framework oxygen atoms and four H2O molecules. The coordination polyhedral alternates with vacancies parallel to the c – axis similar to the Ca polyhedral in mesolite, scolecite and thomsonite. In the disordered structures Ba may occupy either of two sites (Ba1 or Ba2). Because these sites are about 0.46Å apart, both cannot be occupied simultaneously. Mazzi et al., [57] found that the Ba1- site has about 95% occupancy, while Ba2 is about 5%. Stahl and Hanson [60] studied the in-situ dehydration process using X – ray synchrotron powder – diffraction data and monitored the breakdown of the structure between 660 and 680K. Chemical Composition Edingtonite shows very little compositional variation, even in the disordered structures. K and Na are commonly present, but do not exceed 0.2 cation per unit cell. However, a possible Ca – dominant edingtonite was found in a sulfide deposit in the Urals, Russia [61]. This edingtonite is so intimately intergrown with albite and quartz and is so fine – grained, that could not be purified for analysis. Formula: [Ba(H2O)4][Al2Si3O10]. Morphology: tetragonal, or orthorhombic. Single crystals are prismatic up to 10 cm. Common forms: {110}, {111}, and {001}.

94 Handbook of Natural Zeolites

Ulmanu and Anger

Physical properties: Cleavage: {110} perfect, Hardness: 4-4.5 D= 2.73 – 2.78 g/cm3, Luster: vitreous, Streak: white. Optical properties: Color: colorless, yellowish to salmon – red; colorless in thin section, Uniaxial (+ or -). Na – rich crystals are length slow, Ca – rich can be length slow or fast. Silky gonnardite prisms on analcime. Width of cluster is 2mm [57]. Crystallography: Unit cell: a = 9.550, b = 9.665, c = 6.523Å Z = 2. Space group: P 212121. Where disordered: a 9.584, c 6.524Å Z = 2. Space group: P421m. Edingtonite occurs in epithermal veins of some ore deposits. There are several examples: Boehlet Manganese Mine Westerfotland Sweden, stare ransko, eastern Bohemia, Czech Rep., New Bruncwick Canada etc. Chabazite There are three variety of chabazite minerals named: chabazite – Na, chabazite Ca and chabazite – K. Recently, was discovered a new natural zeolite of chabazite series, the fourth, chabazite – Mg. Chabazite – Na is the dominant member of the chabazite series. It is synonym to Herschellite. Chemical formula: (Na2, K2, Ca, Mg)[Al2Si4O12].6(H2O). Molecular weight: 1,046.27g. Empirical formula: Na3.11Ca0.19K1.05Mg0.02Sr0.05Al4.53Fe2+0.01Si7.4O24.11.47(H2O). Chemical Composition, %: SiO2

42.50

Al2O3

22.07

FeO

0.07

Na2O

9.21

Physical and Chemical Properties

Handbook of Natural Zeolites 95

K2O

4.73

CaO

1.02

MgO

0.08

SrO

0.50

H2O

19.75

Crystallography: Axial ratios: a:c – 1: 1.08635, Cell dimensions: a = 13.78, c = 14.97, Z = 3; V = 2,461.79 Den (Calc) = 2.12, Crystal system: trigonal – hexagonal scalenohedral H – M Symbol (3 2/m); space group: R 3m. Physical properties: Cleavage: {1011} imperfect, Color: colorless, white, yellowish, pinkish, reddish white. Density: 2.05 – 2.15, average = 2.09. Diaphaneity: translucent to transparent. Fracture: uneven – flat surfaces (not cleavage) fractured in an uneven pattern. Habit: druses – crystal growth in a cavity which results in numerous crystal tipped surfaces. Habit: pseudo cubic – crystals show a cubic outline. Hardness: 4 – Fluorite. Luster: vitreous (glassy). Streak: white. Optical properties: Biaxial (+/-), a = 1.478 – 1.485, b = 1.48 – 1.4895, g = 1.48 – 1.49, bire = 0.0020 – 0.0050, 2V (calc) = 0 – 36, 2V(meas) = 0 – 32. Dispersion: none. Calculated properties: Electron density: bulk density (electron density) = 2.13 g/cm3, Fermion index: 0.0099056302, Boson index: 0.9900943698, Photoelectric: PE = 2.19 barns/electron, U = PE x ρelectron = 4.65 barns/cc. Chabazite – Ca Synonym: acadialite, adipite, chabazite. Chemical formula: (Ca0.5, Na, K)4[Al4Si8O24].12H2o. Molecular weight: 1,039.07g. Empirical formula: Ca 1.86 Na0.03 K0.2 Mg0.02 Sr0.03 Al3.94 Si8.03 O24.13.16(H2O).

96 Handbook of Natural Zeolites

Ulmanu and Anger

Chemical composition, %: SiO2

46.43

Al2O3

19.33

Na2O

0.09

K2O

0.91

CaO

10.04

MgO

0.08

SrO

0.30

H2O

22.82

Name origin: from Greek chabazios, tune or melody, one of twenty stones named in the poem Peri lithos, which extolled the virtues of minerals. The poem is ascribed to Orpheus, legendary founder of the Orphic cult. Crystallography: Axial ratios: a:b:c = 1.001:1:0.9957, Cell dimensions: a = 9.45, b = 9.44, c = 9.4, Z = 1; α = 91.18o, β = 94.08o, γ = 94.07o, V = 834.14 Den(Calc) = 2.07, Crystal system: triclinic – pinacoidal H – M Symbol (1) Group: P1. Physical properties: Cleavage: {1011} imperfect, Color: colorless, green, yellow, white, pink. Density: 2.05 – 2.15, average = 2.09. Diaphaneity: translucent to transparent. Fracture: brittle – uneven – very brittle fracture producing uneven fragments. Habit: druses – crystal growth in a cavity results in numerous crystal tipped surfaces. Habit: pseudo – cubic – crystals show a cubic outline. Hardness: 4 – Fluorite. Luster: vitreous (glassy). Streak: white. Optical properties: Biaxial (+/-), a = 1.478 – 1.485, b = 1.48 – 1.4895, g = 1.48 – 1.49, bire = 0.0020 – 0.0050, 2V (calc) = 0 – 36, 2V (meas) = 0 – 32, Dispersion none. Calculated properties: Electron density: bulk density (electron density) = 2.11 g/cm, Fermion index: 0.01, Boson index: 0.99, Photoelectric: PE = 2.39 barns/electron, U = PE x ρelectron = 5.04 barns/cc.

Physical and Chemical Properties

Handbook of Natural Zeolites 97

Chabazite - K Chemical formula: (K2, Ca, Na2, Mg)[Al2Si4O12].6(H2O). Molecular weight: 504.66g. Empirical formula: K0.6 Ca0.3 Na0.1 Mg0.02 Al2 Si4O12.6(H2O). Chemical Composition, %: SiO2

47.62

Al2O3

20.29

Na2O

0.61

K2O

5.60

CaO

3.33

MgO

0.16

H2O

21.42

The K –chabazite is the dominant member of the chabazite series. Crystallography: Axial ratios: a: c = 1: 1.108635, Cell dimensions: a = 13.78, c = 14.97, Z = 6; V = 2,461.79 Den(calc) = 2.04, Crystal system: trigonal – hexagonal scalenohedral H–M symbol (3 2/m). Space group: R 3m. Physical properties: Cleavage: {1011} imperfect, Color: Colorless, white, yellowish, pinkish, reddish white, Density: 2.05 – 2.15, average = 2.09, Diaphaneity: translucent to transparent, Fracture: uneven – flat surfaces (not cleavage) fractured in an uneven pattern, Habit: druse – crystal growth in a cavity which results in numerous crystal tipped surfaces, Habit: pseudo cubic crystals show a cubic outline, Hardness; 4 Fluorite, Luster: vitreous (glassy), Streak: white. Optical properties: Biaxial (+/-), a = 1.478 – 1.485, b = 1.48 – 1.4895, g = 1.48 – 1.49, bire = 0.0020 – 0.0050, 2V (calc) = 0 – 36, 2V (meas) = 0 – 32, Dispersion: none.

98 Handbook of Natural Zeolites

Ulmanu and Anger

Calculated properties: Electron density: bulk density (electron density) = 2.14 g/cm3, Fermion index: 0.01, Boson index: 0.99, Photoelectric: PE = 1.97 barns/electron, U = PE x ρ electron = 4.22 barns/cc. Chabazite – Mg is a new zeolite mineral of the chabazite series [62]. Chemical formula: (Mg0.6 K0.52 Ca0.48 Na0.08 Sr0.03)Σ1.78[(Al3.16 Si8.89)Σ12.05 O24].9.68H2O, is a new zeolite species of the chabazite series, occurring in basalts from Praga Hill and West Hungary. Crystal system: single colorless rhombohedra up to 0.4mm in size. Luster: strong vitreous, Streak: white, Mohs’ hardness is about 4., Observed density: 1.98 g/cm3 and calculated density is 1.964(7) g/cm3. Chabazite – Mg is anisotropic, uniaxial. In its chemical composition, a predominance or Mg is observed among the extra framework cations. However, K and Ca are also very abundant, while Na and Sr levels are very low. The ratio Si/ (Si + Al) is among the highest found in chabazite of hydrothermal genesis. Crystal system: rhombohedral, space group R3m, a = 9.3433Å. Single crystal structure refinement of chabazite – Mg indicated that the extra framework occupation is distinct from other chabazite – series minerals. CONCLUSIONS There are about 45 natural minerals that are recognized members of the Zeolite Group. They have an empirical formula of (M+2, M++)Al2O3.gSiO2.zH2O, where M+ is usually Na or K, Me2+ is Mg, Ca or Fe, and g and z are variable multipliers. Rarely Li, Sr, or Ba may substitute for M+ of M2+. The tetrahedral Si: (Si+Al) ratio is one of the major compositional variables, with some zeolites (e.g., mordenite) being at the silica – rich and others are being more aluminous. Theoretically, the possibilities for different framework structures are infinite – around 45 are known in nature and more than 150 synthetic zeolites have been manufactured. Zeolites have basically three different structural variations and based in these structures was done the presentation.

Physical and Chemical Properties

Handbook of Natural Zeolites 99

There are chains – like structures whose minerals form acicular of needle – like prismatic crystals (Natrolite family), sheet – like structures where the crystals are flattened platy or tubular with usually good basal cleavages, (Heulandite family), and framework structures where the crystals are more equant in dimensions, (Chabazite family). Natural zeolites are a big family of minerals spread all over the world. They have an impressed variety of structures and chemical compositions. Suit of these varieties of structures and compositions result a lot of properties and utilizations, presented in this book. Unfortunately, natural zeolites are not sufficient known, exploited and used in this moment but, we have to think the future belongs to them. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. ACKNOWLEDGEMENTS None declared. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]

Christie T, Brathwaite B, Thompson B. Mineral Commodity Report 23-Zeolites. New Zeeland Mining, 2002; 31: pp.16-24. Minerals Yearbook: volume I. Metals and Minerals, 2008. Bish DL, Guthrie GD. Mineralogy of clay and zeolite dusts (exclusive of 1:1 layer silicates). Guthrie G.D. ND Moss MN B.T. (eds). Reviews in Mineralogy. 1993; 28: pp.139-184. Gregg SG, Sing KSW. Surface area and porosity. Academic Press.1982. Neuhoff PS, et al. Order/disorder in natrolite group zeolites: A29Si and 27Al MAS NMR studies. Am. Mineral. 2002; 87 :pp. 1307-1320. Hauy RJ. Traite de Mineralogie 3;1801. Chez Louis, Paris, France. Klaproth MH. Chemische Untersuchung des Natroliths. Ges. Naturforschender Freunde zu Berlin, Neue Schriften 1803; 4: pp. 243-248. Krogh Andersen E, Dano M, Petersen OV. A tetragonal natrolite. Meddr om Gronlands 1969; 181: 20pp. Chen TT, Chao GY. Tetranatrolite from Mont St.-Hilaire, Quebec. Can. Mineral. 1980; 18: pp.77-84. Coombs DS. et al. Recommended nomenclature for zeolite minerals. Report of the Subcommittee on Zeolites of the International Mineralogical Association, Commission on New Minerals and Mineral Names. Can. Mineral. 1997; 35: pp. 1571-1606. Pauling L. The structures of sodium and calcium aluminosolicates. Proc. Nat. Acad. Sci. USA, 1930; 16; 453-469.

100 Handbook of Natural Zeolites

[12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34]

Ulmanu and Anger

Taylor WH, Meek CA, Jackson WW. The structures of the fibrous zeolites. Z. Kristallogr. 1933; 84; 373-398. Artioli G, Smith JV, Kvick A. Neutron diffraction study of natrolite, Na2Al2Si3O10.2H2O at 20 K. Acta Crystallogr. 1984; C40: pp. 1658-1662. Pabst A. Natrolite from the Green River formation, Colorado, showing an intergrowth akin to twinning. Am. Mineral. 1971; 56; pp. 676-680. Alberti A, Vezzalini G. A partially disordered natrolite: relationship between cell parameters and Si-Al distribution. Acta Crystallogr. 1981; B37: pp. 781-788. Alberti A, Cruciani G, Dauru I. Order-disorder in natrolite-group minerals. Eur. J. Mineral. 1995; 7; pp. 501-50817. Lee Y. et al. Pressure-induced volume expansion of zeolites in the natrolite family. J. Am. Chem. Soc. 2000; 124; pp. 5466-5475. Hey MH. Studies on the zeolites. Part III. Natrolite and metanatrolite. Miner. Mag. 1932; 23; pp. 243-289. Foster MD. Composition of zeolites of the natrolite group. U.S. Geol. Serv., Prof. Paper 504-D, 1965, pp.7. Ross M, Flohr MJK, Ross D.R. Crystalline solution series and order-disorder within the natrolite mineral group. Am. Miner. 1992; 77; pp. 685-703. Deer A. et al. Rock Forming Minerals. Vol.4B Framework silicates: Silica Minerals, Feldspathoids and the Zeolites. The Geological Society, London, 2004. Gunter ME, Knowles CR, Schalck D.K. Composite natrolite-mesolite crystals from the Columbia River Basalt Group, Clarkston, Washington. Can. Mineral. 31; 1993; pp. 467-470. Anonymous. American Mineralogist. 1999; 84; pp. 1445-1450. Wuest T, Ambruster T. Type locality leonhardite: a chemical and single-crystal X-ray study at 100 K. Colella C, Mumpton FA.Eds. Natural Zeolites for the Third Millenium. De Frede Editore Napoli Italy, 2000; pp. 139-150. Jameson R. System of Mineralogy. II. Bell and Bradfute, Edinburgh, U.K., 1805. Hauy RJ. Tableau Comparatif des Resultats de Cristallographie et de l’Analyse Chimique Relativement a la Classification des Mineraux. Courceir, Paris, France, 1809. Artioli G, Smith JV, Kvick A. Single crystal neutron diffraction study of partially dehydrated laumontite at 15 k. Zeolites. 1989; 9; pp. 377-391. Ambruster T, Kohler T. Re-and dehydration of laumontite: a single crystal X-ray study at 100K. Neues Jahrb. Min., Mh. 1992; pp. 385-397. Artioli G, Stahl K. Fully hydrated laumontite: a structure study by flat-plate and capillary powder diffraction techniques. Zeolites. 1993; 13; pp. 249-255. Stahl K, Artioli G. A neutron powder diffraction study of fully deuterated laumontite. Eur. J. Mineral. 1993; 5; pp. 851-856. Pipping F. The dehydration and chemical composition of laumontite. Mineralogical Soc. India Int. Mineral. Assoc. 1966; pp. 159-166. Coombs DS. Cell size, optical properties and chemical properties of laumontite and leonhardite. Am. Mineral. 1952; 37; pp. 812-830. Gabuda SP, Kozlova S.G. Guest-guest interaction and phase transitions in the natural zeolite laumontite. J. Inclusion Phenom. Mol. Recogn. Chem. 1995; 22 ; pp. 1-13. Fersman AE. Etudes sur les zeolites de la Russie: 1. Leonhardite et laumontite dans les environs de Simferopolis (Crimee). Trav. du Musee Geol. Pierre Le Grand, Acad. Imp. Sci. Petersbourg, Russia. 1909; 2; pp. 103-150.

Physical and Chemical Properties

[35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58]

Handbook of Natural Zeolites 101

Baur WH, et al. Symmetry reaction of the aluminosilicate framework of LAU topology by ordering of exchangeable cations : the crystal structure of primary leonhardite with a primitive Bravais lattice. Eur. J. mineral. 1997; 9; pp. 1173-1182. Stolz J, Ambruster T. X-ray single-crystal structure refinement of Na, K-rich laumontite originally designated “ primary leonhardite”. N. Jahrb. Mineral. Mh. 1997; 131-144. How H. On mordenite, a new mineral from the tap of Nova Scotia. J. Chem.Soc. 1864; 17; pp. 100-104. Meier WM. The crystal structure of mordenite (ptilolite). Z. Kristallogr. 1961; 115; pp. 439450. Gramlich V. Untersuchungen und Verfeinerung pseudosymmetrischer Strukturen. 1971; Diss. No. 4633, ETH Zurich. Sand L.B. Synthesis of large-port and small port mordenite. Molecular Sieves. Society of Chemical Industry, London. 1968; pp. 71-77. Simoncic P, Ambruster T. Peculiarity and defect structure of the natural and synthetic zeolite mordenite: A single-crystal X-ray study. Am. Miner. 2004; 89; pp. 421-431. Liebau F. Untersuchungen uber die Grosse des Si-O-Si Valenzwinkels. Acta Cryst. 1961; 14; pp. 1103-1109. Alberti A, Davoli P, Vezzalini G. The crystal structure refinement of a natural mordente. Z. Kristallogr. 1986; 175; pp. 249-259. Pe-Piper G, Tsolis-Katagas P. K-rich mordenite from late Miocene rhyolitic tuffs, island of Samos, Greece. Clays and Minerals. 1991; 39; pp. 239-247. Lo HJ, Hsieh Y.L. High potassium natural mordenite and the chemical variation of mordenite. Pro. Geol. Soc. China (Taiwan) 1992; 34; pp. 305-312. Colella C. Natural zeolites. Cejka J, H. van Bekkum Eds. Zeolites and Ordered mesoporous Materials: Progress and Prospects, Studies in Surface Science and Catalysis. Elsevier, Amsterdam, 2005;157: pp. 13-40. Bennett RN, Elkens GJ, Wanless GJ. Despite success, S.E. Asia oil hunt started. Oil and Gas J., 1975; 3; pp. 69-72. Rab Nawaz. A chemical classification of the chabazite group zeolites. The Irish Naturalists Journal 1982; 20(10), pp. 435-440. Deer Howie, Zussman. Rock Forming Minerals. 2004; 4B ; pp. 690-696. Gaines et al. Dana ‘s New Mineralogy. Eighth Edition. 1997. Senderov V, Shishakova A. Russian Chemical Bulletin. 1967; 16-1: 151. Tarassoff P, et al. Mineralogical Record. 2006; 37-1: 35. Sutherland FL, Botrill RS. Zeolites of Western Tasmania. Australian Journal of Mineralogy 2004; 10(2); pp.59-72. Galli E. Crystal structure refinement of edingtonite. Acta Crystallogr. 1976; 32; pp. 1623-1627. Kvick A, Smith JV. A neutron diffraction study of the zeolite edingtonite. J. Chem. Phys. 1983; 79; pp. 2356-2362. Belitsky IA. et al. Study of the structure and dynamics of water in the zeolite edingtonite at low temperature by neutron diffraction and NMR-spectroscopy. Neues Jahrb. Miner. Monatsch. 1986: pp. 541-551. Mazzi F, Galli E, Gottardi G. Crystal structure refinement of two edingtonites. Neues Jahrb. Miner. Monatsh. 1984; pp. 373-382. Akizuki M. Al-Si ordering and twinning in edingtonite. Am. Mineral. 1986: 71: pp. 15101514.

102 Handbook of Natural Zeolites

[59] [60] [61] [62]

Ulmanu and Anger

Tanaka T. et al. Origin of low-symmetry growth sectors in edingtonite and yugawarlite, and the crystal structure of the k{011} and v{120} sectors of yugawaralite. Mineral. Mag. 2002; 66; pp. 409-420. Stahl K, Hanson J.C. An in-situ study of the edingtonite dehydration process from X-ray synchrotron powder diffraction. Eur. J. Mineral. 1998; 10; pp. 221-228. Ismagilov MI. Calcium edingtonite from pyrite deposits if the sourthern Urals. Dokl. Acad. Sci. USSR, Earth Science Sect. 1977; 234; pp. 170-172. Montagna G. et al. Chabazite-Mg: a new natural zeolite of the chabazite series. American Mineralogist. 2010; 95(7); pp. 939-945.

Handbook of Natural Zeolites, 2012, 103-132

103

CHAPTER 6 Catalytic Properties of Zeolites Costas N. Costa1,*, Petros G. Savva1 and Antonis A. Zorpas2 1

Associate Professor, Cyprus University of Technology, Department of Environmental Science and Technology, 30 Archbishop Kyprianos, 3036 Lemesos, Cyprus P.O. Box 50329, 3603 Lemesos, Cyprus and 2Institutes of Environmental Technology-Sustainable Development, and Cyprus Open University, Faculty of Pure and Applied Science, Environmental Conservation and Management, Cyprus Abstract: Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. Zeolites also crystallize in post-depositional environments over periods ranging from thousands to millions of years in shallow marine basins. Naturally occurring zeolites are rarely pure and are contaminated to varying degrees by other minerals, metals, quartz, or other zeolites. For this reason, naturally occurring zeolites are excluded from many important commercial applications where uniformity and purity are essential. Zeolites have been shown to be useful catalysts in a large variety of reactions, from acid to base and redox catalysis.

Keywords: Zeolite classification, zeolite structure, oxidation processes, zeoliteoxide catalysts, hydrocracking catalysts, hydrothermal treatment. INTRODUCTION Zeolites possess unique physicochemical properties which made them the most interesting class of minerals for scientists and engineers since their first known description [1]. The zeolite behavior under fast heating conditions, when the zeolite minerals seem to boil because of the fast water loss, is very well described by their Greek name, “ζέιν”, to boil, and “λίθος“, stone (the stone that boils). Zeolites were initially classified as framework alumosilicates (older grouping system). Without acting external energy, a pure silicate framework consisting of [SiO2] tetrahedra will be uncharged. In an alumosilicate framework however, [AlO4] tetrahedra are negatively charged with respect to [SiO2] tetrahedra because of the trivalent state of Al. The charge of the whole framework is normally neutralized by mono and/or divalent cations within the framework cavities, while water molecules are also present in the structure cavities. The very first known 

Address correspondence to Costas N. Costa: Associate Professor, Cyprus University of Technology, Department of Environmental Science and Technology, 30 Archbishop Kyprianos, 3036 Lemesos, Cyprus P.O. Box 50329, 3603 Lemesos, Cyprus; http: www.cut.ac.cy; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

104 Handbook of Natural Zeolites

Costa et al.

physicochemical property of zeolites was their capability for exchanging extraframework cations and their reversible water absorption ability [2]. Fig. 1 shows a common zeolitic material commonly used in the kitchen for calcium removal from water by ion exchange during the water purification process (softening).

Figure 1: Zeolite used for household applications – soap-powder zeolite for water softening.

Over 40 years ago, zeolite molecular sieves were initially developed in the lab for use in gas separations. The history of their industrial utilization in the refining of crude oil and fractionated pools of hydrocarbons goes back almost as far as their first laboratory use. High SiOz composition (>95%) zeolites became accessible with the introduction of guest organic molecules (vide infra) into the synthesis gel. It was then when new structures with pores in the range of 5-6 Å and with new properties such as hydrophobicity became available. The breakthrough in the synthesis of zeolites with much higher silica contents (and consequently lower aluminate contents) enabled this class of zeolites to be utilized in the refining industry for the synthesis and separation of petrochemicals [3]. The study of these high-silica zeolite materials has an interesting development in the sense that for some time the momentum for their synthesis, consequent characterization and ultimate use was pioneered in industrial research laboratories. Our perceptive for these materials has unexpectedly accelerated as a consequence of fabulous breakthroughs in the physical chemistry which can be applied to solid materials; and research has swiftly shifted from industrial laboratories to chemical

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 105

engineering and materials science departments in universities. In this review we underline some of these achievements but also cast them as partners, in an aspect of this technology which appears to be very promising in the blooming field of 'nanoscale materials' chemistry [4]. More explicitly, the measurement techniques and the synthesis of novel materials are partners in developing the field of nanoscale materials chemistry, although they have developed mainly independent of each other. The term “nanoscale” refers both to the future applications of these materials and in their design (aiming towards improvement of certain properties), denoting that the action, in terms of the properties of materials, will take place at the nanometer scale. CLASSIFICATION OF ZEOLITES The unusual properties of zeolite materials are caused by their crystal structure (lattice). Consequently, their proper classification starts from the 3-dimensional bonding of the tetrahedrally coordinated framework cations. 800 different zeolites are known up-to-date [5], which can be classified by 119 different zeolite structure types [6]. These structure types are depicted by a three-letter code and analytically listed in the “Atlas of zeolite structure types” (revised version 10/97) [6]. Only about l/4 of them are naturally occurring, while the rest are synthetic. Since the use of the unit cell for the description of a certain zeolite is only specific for the zeolite type, secondary building units (SBU’s) consisting of different tetrahedra arrangements (primary building units) are used [6]. The SBUs are, however, only building elements of the zeolite unit cell. A certain zeolite can be classified by the use of different SBUs. The T-O-T model is used in order to facilitate the zeolite structure description, where the central atoms of framework tetrahedra (T) are drawn as balls, while the binding between two T-atoms, via oxygen (O), are drawn as sticks. However, a SBU graphic interpretation with only sticks is also used as depicted in Fig. 2. Fig. 3 presents the different SBUs used for the classification of zeolite structure types. Zeolites can also be separated from non-zeolite framework structures like tectosilicates by their framework density (FD). The FD of zeolites is defined as the number of T atoms per l000 Å3 and is always lower than the FD for normal

106 Handbook of Natural Zeolites

Costa et al.

Figure 2: Three different presentations of (Si,Al)O.,-tetrahedra forming two 3-dimensional units of NAT-type zeolite chains: a) tetrahedral model, b) ball and spoke model with centers of (Si, Al) as balls and T-O-T bond as stick, c) stick-model.

Figure 3: The different Secondary Building Units (SBUs) of today known zeolite structure types.

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 107

tetrahedral framework structures. This is caused by the zeolite’s channel and cage system [6]. A very characteristic gap between zeolite structure types and nonporous framework structure types exists from under 20 to over 21 T-atoms per 1000 Å3. This single fact can be utilized for the independent control of a structure type to be classified as zeolite; although no actual correlation between framework density and cavity (channel or cage) diameter has been proved so far. The channel and cage systems are the main crystallographic characteristics of zeolites. Zeolite channels are classified according to the number of oxygen/T-atoms forming the window along with the geometrical dimensions of the two dimensional channel opening. For definition the minimum T atoms which are necessary to build up a channel is six [6] but even a four membered ring is actually a gateway to a channel. Up to 20-membered rings exist as channel openings (e.g., the case of the cloverite (-CLO) structure type [6]). However, the cross-section of the opening must not necessarily be ring-shaped, elliptical, drop-shaped or asymmetrically-shaped openings also exist. One-, two- and three- dimensional channel systems are directed to main crystallographic directions of zeolite structures. They are separated by their connectivity. Various kinds of arrangements of 3-dimensional channel systems exist, e.g., tetrahedrally (FAU), octahedrally (PHI), hexahedrally (ANA), trigonal, hexagonal and so on. Even channel systems that are situated in each other do exist. Table 1 reports the dimensions of window openings of alumosilicate based zeolite channels dependenting on the T-atoms forming the opening in different crystallographic directions based on the notation defined in reference [6]. Phosphatebased zeolites are not considered in the last table. In fact the sizes of the channel openings dependent on the water content and/or cation species present in the channel system. In general, the zeolite structures are rather flexible as the unit cell dimensions dependent on the water content of the cavity system. In some cases the change in crystal pattern and structure, caused by the change of water content in the channel system, might be large enough to be observed macroscopically, as in the case of laumontite, where the dehydrated phase is referred as leonhardite. For certain types of zeolites like laumontite dehydration can lead to a collapse of the channel system [6]. Zeolite cages are as important as the channel systems for the determination of zeolite specific properties. A suitable definition of a cage has to consider the fact

108 Handbook of Natural Zeolites

Costa et al.

that the channels themselves are also cages of infinite length. Cages can be defined as gaps bigger in diameter than normal channel systems. They are only accessible through the channel system. The simplest cages are formed by the crossing of two channel systems. Molecules that are bigger than those accessible to the channel system (formed within the cages or remaining from the synthesis process) fit into these cages. In some zeolites, supercages might exist at the crossing of the channel systems, as in the case of FAU. In FAU-type zeolites supercages are formed by the tetrahedral crossing of channel systems. Fig. 4 provides a classification of some well known zeolite cage types. Liebau et al., reported another sub-classification of porous tectosilicates and other related compounds based on geometrical and chemical considerations [7]. They considered porous all the silica phases “zeosils” and “clathrasils” as “porosils”. Based on this definition “clatra” compounds contain cages with guest/foreign species (mainly resulted from the synthesis process) which are too big to go through the linked channel system. Moreover, “zeo” materials are considered as materials with a cavity containing framework topology. Based on the above classification “porolites” contain the group of commonly known zeolites and “clatra-lites” (see definition described above), while all aluminum phases, “poroals”, consist of the groups “clatrals” and “zeoals”, and all are tetrahedrally arranged aluminum oxide phases which do not exist at present. Alumophosphate materials are classified as “poroalpos” which are again composed of “clatralpos” and “zeoalpos”. Table 1: Channel sizes of alumosilicate-based zeolites (in descending order). Data and notation from reference [6] Code

Zeolite Phase

Channel System in 1st Crystallographic Direction

2nd Crystallographic Direction

FAU

Faujasite

(111) 12 7.4 ***

MAZ

Mazzite

(001) 12 7.4*1

LTL

Liude Type L

(001) 12 7.1*

EMT

EMC-2

(001) 12 7.1*↔

┴(001) 12 7.4 x 6.5**

BOG

Boggsite

(100) 12 7.0 x 7.0* ↔

(010) 10 5.2 x 5.8*

GME

Gmelinite

(001) 12 7.0* ↔

┴(001) 8 3.6 x 3.9**

(001) 8 3.4 x 5.6*

3rd Crystallographic Direction

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 109 Table 1: cont….

MEI

ZSM-18

(001) 12 6.9* ↔

┴(001) 7 3.2 x 3.5**

OFF

Offrerite

(001) 12 6.7* ↔

┴(001) 8 3.6 x 4.9**

MOR

Mordenite

(001) 12 6.5 x 7.0* ↔

(010) 8 2.6 x 5.7*

BEA

Beta

(001) 12 5.5 x 5.5*↔

12 7.6 x 6.4**

CON

CIT-1

(001) 12 6.4 x 7.0* ↔

(100) 12 6.8*↔

CAN

Cancrinite

(001) 12 5.9*

VET

VPI-8

(001) 12 5.9*

MTW

ZSM-12

(010) 12 5.5 x 5.9*

MEL

ZSM-11

(100) 10 5.3 x 5.4***

MFI

ZSM-5

(010) 10 5.3 x 5.6 ↔

(100) 10 5.1 x 5.5}***

MFS

ZSM-57

(100) 10 5.1 x 5.4* ↔

(010) 8 3.3 x 4.8*

TER

Terranovaite

(100) 10 5.0 x 5.5* ↔

(001) 10 4.2 x 7.0*

STI

Stilbite

(100) 10 4.9 x 6.1 ↔

(101) 8 2.7 x 5.6*

NES

NU-87

(100) 10 4.7 x 6.0**

MTT

ZSM-23

(001) 10 4.5 X 5.2*

TON

Theta-1

(001) 10 4.4 x 5.5*

FER

Ferrierite

(001) 10 4.2 x 5.4* ↔

RON

Roggianite

(001) 12 4.2*

EUO

EU-1

(100) 10 4.1 x 5.7* with large side pockets

LTA

Linde Type A

(100) 8 4.1***

LAU

Laumontite

(100) 10 4.0 x 5.3*

CHI

Chiavennite

(001) 9 3.9 x 4.3*

KFI

ZK-5

(100) 8 3.9*** │

8 3.9***

RTH

RUB-13

(100) 8 3.8 x 4.1* ↔

(001) 8 2.5 x 5.6*

CHA

Chabazite

┴ (001) 8 3.8 x 3.8***

PAU

Paulignite

(100) 8 3.8*** │

8 3.8***

EPI

Epistilbite

(100) 10 3.4 x 5.6* ↔

(001) 8 3.7 x 5.2*

EAB

TMA-E

┴ (001) 8 3.7 x 5.1**

JBW

NaJ

(100) 8 3.7 x 4.8*

(010) 8 3. x 4.8*

(010) 10 5.1 x 5.1*

110 Handbook of Natural Zeolites

Costa et al.

Table 1: cont….

DAC

Dachiardite

(010) 10 3.4 x 5.3* ↔

RTE

RUB-3

(001) 8 3.7 X 4.4*

VSV

VPI-7

(011) 9 3.3 x 4.5* ↔

ERI

Erionite

┴ (001) 8 3.6 x 5.1***

LEV

Levyne

┴ (001) 8 3.6 x 4.8**

DDR

Deca-Dodecasil 3R

┴ (001) 8 3.6 x 4.4**

LOV

Lovdarite

PHI

(001) 8 3.7 x 4.8* (011) 9 3.3 x 4.5* ↔

(011) 8 3.7 x 3.7*

(010) 9 3.2 x 4.4* ↔

(001) 9 3.2 x 3.7* ↔

(100) 8 3.6 x 3.7*

Phillipsite

(100) 8 3.6* ↔

(010) 8 3.0 x 4.3* ↔

(001) 8 3.2 x 3.3*

RHO

Rho

(100) 8 3.6*** │

8 3.6***

MON

Montesommaite

(100) 8 3.2 x 4.4* ↔

(001) 8 3.6 x 3.6*

PAR

Partheite

(001) 10 3.5 x 6.9*

VNI

VPI-9

┴ (001) { 8 3.5 x 4.0 ↔

(001) 8 3.5 x 3.5}**

MER

Merlinoite

(100) 8 3.1 x 3.5* ↔

(010) 8 2.7 x 3.6* ↔

(001) {8 3.4 x 5.1* + 8 3.3 x 3.3*}

RSN

RUB-17

(100) 9 3.3 x 4.4* ↔

(001) 9 3.1 x 4.3* ↔

(010) 8 3.4 x 4.1*

ABW

Li-A

(001) 8 3.4 x 3.8*

HEU

Heulandite

{(001) 10 3.0 x 7.6* + 8 3.3 x 4.6*} ↔

(100) 8 2.6 x 4.7*

YUG

Yugawaralite

(100) 8 2.8 x 3.6* ↔

(001) 8 3.1 x 5.0*

GIS

Gismondine

{(100) 8 3.1 x 4.5* ↔

(010) 8 2.8 x 4.8}*

BRE

Brewsterite

(100) 8 2.3 x 5.0* ↔

(001) 8 2.8 x 4.1*

GOO

Goosecreekite

(100) 8 2.8 x 4.0* ↔

(010) 8 2.7 x 4.1* ↔

EDI

Edingtonite

(100) 8 2.8 x 3.8** ↔

(001) 8 variable*

BIK

Bikitaite

(001) 8 2.8 x 3.7*

WEN

Wenkite

10 2.6 x 4.9** ↔

(001) 8 2.2 x 2.7*

NAT

Natrolite

8 2.6 x 3.9** ↔

(001) 8 variable*

(001) 8 2.9 x 4.7*

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 111 Table 1: cont….

THO

Thomsonite

(101) 8 2.3 x 3.9* ↔

CAS

Cs Aluminosilicate

(100) 8 2.2 x 4.7*

ANA

Analcime

(110) 8 1.6 x 4.2*** irregular

(010) 8 2.2 x 4.0*

(001) 8 variable

Figure 4: Selected zeolite cages: A = 4-ring (window opening to cage of infinite length); B = 6ring (window opening to cage of infinite length); C = 8-8-cage (s-cage); D = 4-4-cage; E = 8-ring (window opening to cage of infinite length); F = cancrinite cage (&-cage); G = gmelinite cage (‘ycage);H = 6-6-cage; I= sodalite cage (p-cage); J = levyne cage; K =chabazite cage; L = a-cage; M = erionite cage; N =faujasite supercage.

CATALYTIC PROPERTIES OF ZEOLITES Acid Sites in Zeolites It is almost an impossible task to summarize all the relevant work done in this field in a few pages. Nevertheless, this chapter will try to highlight some published work that illustrates the potential of zeolites as acid catalysts. Brønsted acid sites are

112 Handbook of Natural Zeolites

Costa et al.

formed on the surfaces of zeolites when Si4+ is isomorphically replaced by a trivalent metal cation such as, for example, Al3+ [8]. This replacement creates a negative charge in the lattice that can be neutralized by a proton. From the structural point of view, a Brønsted acid site in a zeolite can be seen as a resonance hybrid of structures I and II (Scheme 1), where structure I is a fully bridged oxygen with a weakly bonded proton, and structure II is a silanol group with a weak Lewis acid interaction of the hydroxyl oxygen with an Al atom. In order to explain the interaction between atoms giving and accepting electron pairs [9] and based on Gutmann’s rules, Mortier [10] proposed a general theory that might explain why model I could be more representative of the case of the acid site in a crystalline zeolite structure, while model II would represent the case in an amorphous silica–alumina where no stabilization by long-range symmetry is present [11].

Scheme 1

the presence of those Brønsted acid sites on zeolites upon dehydration has been demonstrated by a large number of physicochemical techniques [12, 13, 24]. Theoretical calculations and modeling studies of zeolites have been done using abinitio calculations that attempted to predict quantitative results of experimental zeolite properties. These modeling studies, embedded model clusters and periodic systems to mimic zeolite structures with growing range of interaction from short to medium and long range. Some illustrative reviews on the subject have been reported [15, 16]. From the point of view of zeolite acid catalyst design, it is clear that the total number of Brønsted sites is, in principle, directly connected to the total number of framework T-III atoms present in the system [17]. In the case of high-aluminumcontent samples however, not all the acid sites have the same acid strength. The strength changes with the number of aluminum atoms in the next nearest neighbor position (NNN) of the aluminum atom which chains the acid site [18]. A completely isolated Al tetrahedronwill will have zero NNN and corresponds to the strongest type of framework Brønsted acid site. Barthomeuf [18] extended the

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 113

latter idea by using topological densities to include the effects of layers one to five surrounding the Al atom. Both the Al NNN and the topological density theory forecast that by changing the Si/Al framework ratio, either by synthesis or by postchemical modification, it is possible to change not only the total number but also the electronic density of the bridging hydroxyl group, and consequently changing the strength of the Brønsted acid site. In consequence, zeolites with lower framework Si/Al ratios will be preferred when reactions demanding low acidities are to be catalyzed. In contrast, zeolites with isolated framework Al (Si/Al ratios ≥ 9–10) will be chosen when strong acidities are required. The strength of the Brønsted acid sites can also be adjusted through isomorphic substitution of Si by trivalent atoms other than Al, either by synthesis or by post treatment methods. For instance, the Ga-substituted zeolites gave stronger acid sites than boron- and weaker than Al-substituted ones. The fine tuning of acid strength in zeolites is a very interesting property in catalysis and of supreme importance for controlling reaction selectivity. The alkylation of benzene and toluene with a bifunctional alkylating agent (cinnamyl alcohol) reactions are provided as an example:

Scheme 2

HY zeolite with weak acidities (low Si/Al ratio and partial Na+→H+ exchange) results in high region-selectivity with respect to the allylic system for the desired intermediate 1, while stronger acidities lead to further condensation and larger amounts of 1,1,3thriphenylpropane (2) that not only lead to the decrease of selectivity but also to the deactivation of the catalyst [34] (Scheme 2). In another example, when high-purity isobutene has to be synthesized for the production of isobutene copolymers, a very selective mildly acidic catalyst is required which can decompose MTBE to isobutene

114 Handbook of Natural Zeolites

Costa et al.

and methanol without promoting side reactions. In the latter case, B-ZSM-5 is used to selectively catalyze the reaction. A zeolite catalyst with weak acid sites such as BZSM-5, containing Ce, is active and selective for the isomerization of 2alkylacroleines into 2-methyl-2-alkenals without promoting skeleton isomerization [20]. Ono has also discussed zeolites as solid catalysts and has shown the influence of the acid strength on the region-specific methylation of 4(5)-methylimidazal to 1,4- and 1,5-dimethyl imidazol (1,4-DMI and 1,5-DMI) [21] (Scheme 3):

’ Scheme 3

Thus, the ratio 1,4-DMI/1,5-DMI can be changed from 0.29 to 2.0 with DMI yields of 100 and 50% by using zeolites HY and H Beta, respectively, both having large pores, but with different acid strengths. Controlling zeolite acidity is of high importance in catalyzing reactions involving strong bases such as ammonia (NH3) or pyridines. In such cases a zeolite catalyst with extra strong acidity can be rapidly poisoned by the adsorption of the basic reactant or product. This is for example the case for the aldol condensation of aldehydes and ketones with ammonia, for the production of pyridine and 3methylpyridine, which are intermediates in the synthesis route of vitamin B3. In the latter case a ZSM-5 zeolite with milder acidity is the active catalyst and is developed by doping with Th, Co, or Pb [22]. Finally, there is the very interesting case where, in contrast to a primary prediction, the use of the very weakly acid internal silanols of ZSM-5 zeolite has lead to a very important commercial application such as the production of ε-caprolactam by the Beckmann rearrangement of cyclohexanone oxime [23]. In the latter process, cyclohexanone oxime is gasified and fed into a fluidized-bed-type reactor with methanol vapor. There, a catalyst, mainly composed of high-silica MFI zeolite, is used to achieve the desired results. MFI containing stronger acid sites with bridging hydroxyl groups gives undesired nitriles and catalyst deactivation precursors. It is

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 115

interesting to note that the less active internal silanols of either ZSM-5 [24] or Beta zeolite are more selective and results in longer catalyst lifetime (Fig. 5). The control of acid strength and the density of acid sites of zeolite catalysts have also led to successful catalysts and processes in the field of petrochemistry and oil refining. For example, in the isomerization of ethylbenzene to xylenes the reaction involves, as the initial step, the partial hydrogenation of the aromatic ring, followed by the ring expansion and contraction to yield xylenes. While the initial step is catalyzed by Pt metal, the ring expansion and contraction is an acidcatalyzed reaction that occurs on mordenite zeolite. However, if the strong Brønsted acid sites of the protonic form of mordenite are present, the cracking of partially hydrogenated ethylbenzene also occurs in a large extent. Consequently, restraining the acid strength by partial exchange of acid sites with alkaline or, even better, with alkaline earth cations results in higher selectivity to xylenes [25]. There is an interesting effect of acid strength in driving the isomerization of xylenes through either a unimolecular or a bimolecular mechanism. It has been proven that zeolites containing strong acid sites lead to mainly unimolecular isomerization, while mesoporous molecular sieves with weaker acid sites catalyze the reactions through a bimolecular intermolecular process [26]. The acid site density is sometimes even more important than acid strength. The site density has an important impact on the adsorption properties of zeolites and therefore can be used to regulate selectivity when a competition between uni- and bimolecular reactions exists. As a consequence, zeolites with a low density of Brønsted sites (low density of framework TIII cations or high TIV/TIII ratios) will favor unimolecular reactions. On the contrary, high density of TIII atoms will favor bimolecular reactions by increasing the adsorption of reactants. The latter parameter is being used together with the control of pore dimensions (size and shape) to control the ratio of xylene isomerization (unimolecular) vs. xylene disproportionation to toluene and trimethylbenzenes (bimolecular). In the case of fluid catalytic cracking (FCC), besides hydrocarbon cracking, hydrogen transfer between olefins and saturated molecules also occurs. The ratio of rates for cracking (uni- and bimolecular) and hydrogen transfer (bimolecular) has an important effect on the final yield of olefins and aromatics, and therefore

116 Handbook of Natural Zeolites

Costa et al.

for gasoline octane number, propylene yield, and coke formation. As a result, when high yields of olefins need to be obtained, higher ratios of cracking to hydrogen transfer should take place and USY zeolites with low framework Al content are chosen.

Figure 5: Catalytic cracking.

Zeolites with Basic Active Sites It is also possible to take advantage of the properties of zeolites in base catalysis by generating basic sites within the pores of zeolites. For zeolites the basic sites are of Lewis type and correspond to framework oxygens. In addition, the basicity of a given oxygen is related to the density of negative charge. Considering this, the basicity will be a function of framework composition, the nature of extraframework cations, and the zeolite structure. The average charge on the oxygens and the changes with framework composition can be identified by calculating the average Sanderson electronegativity (ASE) of the zeolite [27]. In agreement with the above, a good correlation has been found between the average basicities calculated by ASE and catalytic activity for side chain alkylation of toluene with methanol and Knoevenagel condensation of benzaldehyde with various compensating cations and framework compositions [28]. The latter correlation has been also obtained when using probe molecules such as, for example, pyrrole, acetylenes, and chloroform combined with NMR and FTIR spectroscopies [29]. Methoxy groups formed from methyl iodide and

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 117

bounded at framework oxygens of alkali-exchanged zeolites Y and X have also shown (using 13C MAS NMR spectroscopy) a correlation between the isotropic chemical shift of those surface methoxy groups and the ASE [30]. In the case of faujasite the charge changes from oxygen to oxygen when the compensating cations are Na, K, Rb, or Cs as shown by calculation of charges on selected oxygen atoms [31]. This charge was found to increas for oxygens O2 and O3 while it decreases for O1 and O4 when passing from Na to Cs [32]. Additional, analytical information on the basicity of zeolites can be found in some excellent reviews [33]. The basicity of alkaline-exchanged zeolites is relatively weak and thus it is possible to remove protons in organic molecules with pKa of 10.7. However, the basicity of the framework oxygens increases when Si is partially replaced by Ge, and in consequence they can abstract protons from organic molecules with pKa of 11.3. Ono has reported an interesting work on the catalytic activity of alkalineexchanged faujasites [34], where phenylacetonitrile is selectively monomethylated by methanol and dimethylcarbonate. The order of basicity reported was CsX > RbX > NaX > LiX, with CsX > CsY. Alkaline zeolites may also successfully catalyze other reactions such as Knoevenagel, aldol and Claisen– Schmidt condensations that do not require strong basicities [35]. An important and interesting feature of basic zeolites is their ability to catalyze some reactions that require acid–base pairs. In such a case, the Lewis acidity of the cation and the basicity of the oxygen must be balanced. Reactions such as toluene chain methylation and/or selective N-alkylation of N-methylaniline, benefit from the presence of tunable acid– base pairs in alkaline-substituted zeolites [36, 37]. In order to profit from the microporosity of zeolites, while increasing basicity, framework oxygen atoms may be partially substituted by nitrogens. This was first attempted as early as 1968 by treating a Y zeolite with NH3 at high temperature where the authors reported that SiO3(NH2) groups were produced [35]. However, the basicities of the materials were not measured. Stronger basicities have been achieved by generating extra-framework imides within zeolite Y channels by

118 Handbook of Natural Zeolites

Costa et al.

submerging an alkali-exchanged zeolite in a solution of metallic Na, Yb, or Eu in liquid ammonia. Following solvent removal by evacuation and heating in vacuum at ~450 K a basic catalyst was obtained [39]. Moreover, strong basic sites have been reported by forming Na0 clusters in supercages and on the external surface of Y zeolite [40] and by forming alkali or alkaline earth oxide clusters [41]. Zeolites with Redox Active Sites Several oxidation processes that take place in the liquid phase are catalyzed by soluble oxometalic compounds. These oxometallic catalysts present two main limitations. One of these drawbacks is the tendency of some oxometalic species to oligomerize, forming μ-oxocomplexes that are catalytically inactive. Another drawback is the oxidative annihilation of the ligands that lead to the deterioration of the catalysts. Solving these two problems requires the isolation of the catalytically active sites on inorganic matrices through supporting metals, metallic ions, metal complexes, and metal oxides, or the synthesis of molecular sieves where the oxidating atom is integrated into the framework. However, this last type of catalysts also requires many features encountered in oxidation enzymes: isolated and identical stable sites, in an environment sufficient from the point of view of adsorption and geometry. Due to their pores and cavities, zeolites can introduce steric effects, while metal atoms which are incorporated into the framework may, in some cases, be stable towards leaching. If all these characteristics are considered important for a successful heterogeneous solid catalyst working in the liquid phase, what really makes unique the redox molecular sieve catalysts is their adsorption properties, which can be tuned in terms of hydrophobicity/hydrophilicity. The latter could allow these solids to add an extra activity–selectivity property by selecting the proportion of reactants with different polarities which will be adsorbed into the pores. This is especially important when organic compounds have to be oxidized using aqueous hydrogen peroxide (H2O2). Zeolites as Catalysts Out of the large number of zeolites and molecular sieves available today, only a small number have been reported as suitable for hydrocracking while out of these only a few have found commercial use. From the zeolites reported frequently in

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 119

the literature, Y zeolite leads the commercial use for broad range hydrocracking, while ZSM-5 and related materials are usually preferred sources for hydrodewaxing or shape-selective cracking. Zeolites that are used in hydrocracking are usually highly modified materials as compared to the basic synthesized zeolites. They are essentially free of metal cations (in most cases) and are thermally stable at higher temperatures than the parent zeolites. Y zeolites with low sodium content and increased stability were originally synthesized from Y zeolite by a four step process [42]. Sodium Y zeolite was exchange with ammonium ions, calcined at about 540°C, further exchanged to reduce the sodium content below 0.5 wt. %, and finally re-calcined. The resulting material is stable to over 1,000°C, has a quite high surface area, while it maintains a high crystallinity. A new characteristic was the shrinkage in the unit cell parameter from 24.65 to 24.40, approximately. Another method was reported for producing a stabilized zeolite where ammonium Y zeolite, containing about 2 wt.% sodium, was heated to between 550 and 800°C in flowing steam for up to 4 hours. Additional exchange reduces the sodium level to less than 0.2 wt.% [45]. The surface area, unit cell constant, crystallinity and stability of these materials vary with the treatment process. Their properties in hydrocracking vary depending on other treatment histories. In general, increased time of steaming reduces the unit cell dimensions. Although hydrothermal treatments have no effect on the overall silica-alumina ratio of a zeolite, it has recently been shown by magnetic resonance that aluminum atoms are detached from the crystal structure and deposited as an oxidic species in the framework. Consequently, the silica-alumina ratio of the crystal structure is increased above that of the starting solid and this is reflected in the decreased value of the unit cell constant. The latter modified zeolites have both improved hydrothermal and thermal stabilities compared to ammonium Y zeolite and dry air calcined zeolites. The second generation of zeolites suitable for hydrocracking led to catalyst development which yielded substantially enhanced activity. Scherzer has reported a detailed comparison of a series of catalysts of different unit cell sizes prepared by changing the stabilization conditions during zeolite

120 Handbook of Natural Zeolites

Costa et al.

preparation. The reduction of unit cell size reveals changes in the crystal lattice silica-alumina ratio and the possible deposition of alumina in the structure. In addition, the number of acid sites is also reduced [44] together with the formation of larger pores within the zeolite structure, most probably at locations from which alumina is removed. These kinds of treatments enhance the accessibility of the internal parts of the zeolite structure to larger molecules. The allowed increase in feedstock heaviness for usual hydrocrackers was shown earlier reflecting changes in catalysts structure from amorphous to uniform pore zeolites to enlarged pore zeolites. Fig. 6 shows the influence of the unit cell size on kerosene selectivity. As shown in Fig. 6, kerosine selectivity is improved with the decrease in unit cell size for the hydrocracking of a hydrotreated heavy vacuum gas oil. In the same way, the production of light gases initially and as a function of time is also lower for the reduced unit cell catalysts signifying a more stable operation (Fig. 7) [44].

Figure 6: Influence of unit cell size on product selectivity (kerosine).

Figure 7: Comparison of gas composition (%) for different unit cell size zeolite catalysts: (O) high unit cell and (m) low unit cell.

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 121

The performance of different hydrothermally stabilized zeolites has been compared in hydrocracking [45]. Table 2 reports the different zeolites examined. These covered a range of silica-alumina ratios of 5.2 to 11.1, with corresponding unit cell constants from 24.55 to 24.33 and A1/unit cell values were from 33 to 9.9. These solids were converted into hydrocracking catalysts containing 60 wt.% zeolite and 0.5 wt.% palladium. The hydrocracking performance of these catalysts is reported in Table 8. The hydrocracking activity was found to be greater for the catalysts containing the zeolites with the highest A1/unit cell, namely LZ-Y82. However, the latter catalyst gave the highest deactivation rate (TIR) and highest gas yield. Although the CBV 712 sample has ao values comparable to that of LZ-Y20 and CBV 600 (24.33-35), it presented a different behavior. The catalyst exhibited a fair activity and low gas yields on one hand but on the other, high deactivation and coking rates. The CBV 712 and LZ-Y20 catalysts containing 0.25 wt% palladium were examined in more exhaustive recycle testing with a feed containing nitrogen compounds. The overall performance of the latter catalysts is shown in Fig. 8. The CBV 712 catalyst was found to be more active and although initial yields are similar, the CBV 712 catalyst’s yield declines less rapidly with time compared to LZ-Y20. Table 2: Palladium/zeolite catalyst performance in once-through hydrocracking tests Parameter

Catalyst LZ-Y82

LZ-Y20

CBV 600

CBV 712

Alf, Al/unit cell

33

9.9

12

12

Pd, wt.% (anhyd.)

0.50

0.50

0.50

0.50

544

559

554

551

0.087

0.059

0.060

0.085

9.1

7.1

7.1

7.1

280-450 F liquid, LV, % FF

36.0

38.7

37.7

36.1

Coke deposition, mg/h

12.2

7.3

7.1

13.9

Zeolite base

HCR performance Tinit., oF o

TIR, F/h Product yields C4-Gas, wt.% FF o

122 Handbook of Natural Zeolites

Costa et al.

Figure 8: High severity recycle hydrocracking with Pd/zeolite catalysts.

Zeolite modifications have been extended by use of chemical reagents. Whereas hydrothermal treatment removes alumina from the crystal lattice but leaves it in the extraframework structure, chemical treatment can completely remove alumina from the structure. In addition, chemical treatment can result in the introduction of silicon or other elements into the structure in the place of alumina. These variations all result in the preparation of the so called high-silica zeolites. Although most zeolites have well defined uniform pore structures as synthesized, for Y zeolites, the pore aperture is in the order of about 7-9 Å. During hydrothermal or chemical treatment, the zeolite structure is distorted significantly due to migration of alumina species from the crystal lattice into the structure or completely out of the structure. A representative pore distribution of a modified zeolite (by chemical treatment) is shown in Fig. 9 [46]. As seen in Fig. 9, a substantial amount of pore volume is generated between 25 and 500 Å. The ratio

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 123

of the two types of pore volume distribution varies with the extent of treatment. A more severe treatment is expected to give a more broadly modified structure. Because of the enlargement of the pore structure, the modified zeolites are expected to be accessible to larger molecules than that predicted from the structure of the initial solid.

Figure 9: Pore size distribution of modified and unmodified Y zeolites.

Treatment of Y zeolite with a (NH4)2SiF6 solution simultaneously extracts aluminum atoms from the structure and substitutes them with silicon atoms [47]. So, starting with a Y zeolite with a SiO2/A12O3 ratio of approximately 5, the ratio can be increased drastically to about 50. Ratios of between 6 and 15 appear to be the easiest to prepare and are more stable. The above treated Y zeolite solids have been designated LZ-Y210.

124 Handbook of Natural Zeolites

Costa et al.

It was found that during the first stage conditions, increasing the silica-alumina ratio above 9 increases the activity. Table 3 presents data for three catalysts with different ratios containing nickel and tungsten hydrogenation components. There is a progressive enhancement of activity with increasing zeolite silica-alumina ratio [48]. Table 3: Effect of SIO2/A12O3 ratio of LZ210 catalyst on hydrocracking activity Catalyst 1 2 3

SiO2/Al2O3 6.5 9.1 11.7

ΔΤemperature (oF) for 40% conversion of gas oil to 420 oF-8 -18 -23

Treatment of zeolites with acids, such as hydrochloric or nitric, in order to increase the silica-alumina ratio has been reported several times in the past. Ion exchanging a steam stabilized ammonium Y zeolite with an ammonium solution to which adequate nitric acid was added to reduce the pH to less than 4, removed alumina debris from the structures. Table 4 reports the changes which occur after treatment with the lower pH exchange solution. The three reported hydrothermally stabilized Y zeolites contain between 30 and 60% of their aluminum content outside the framework. The extra framework alumina lowers the surface area of the solid and partially fouls the pore structure. A treatment with a low pH ammonium solution removes much of the alumina deposited in the structure and significantly more than that removed with acid alone. In a different procedure, the zeolite was exchanged with rare earth ions before steaming. The results obtained showed that the catalysts were substantially more active than reference in both noble and non-noble metal forms and in both the presence and absence of ammonia. Works on the stabilization of Y zeolites by double calcination have also been reported. Recently, an improved double calcination procedure has been developed [49]. Ammonium zeolite was hydrothermally treated, further ammonium ion exchanged and then again calcined in steam. A quite stable product with a low sodium content of about 0.15 wt.% and a low unit cell of about 24.30-24.35 Å was obtained. The zeolites appeared to be surprisingly hydrophobic (ultra hydrophobic Y). The latter solids have found application for hydrocracking to middle distillate products [49]. Catalysts containing relatively small amounts of

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 125

these materials, although not as active as other zeolites, approach the selectivity of totally amorphous catalysts in middle distillate selectivity. Table 5 from reference [49] compares the above formulations with a commercial middle distillate hydrocracking catalyst. As clearly shown in Table 5, although the catalysts are of almost equal activities, the selectivity of the UHP-Y catalyst to middle distillate is much greater. Table 4: 29Si NMR Analysis

a

Zeolite

Bulka SiO2/Al2O3

Frameworkb SiO2/Al2O3

Extraneous SiO2 (%)

Extraneous Al2O3 (%)

Stabilized Y (Y72)

5.1

7.9

8.3

40.6

Stabilized Y (Y82)

5.4

7.7

6.1

34.2

Stabilized Y (S.Y.2)

5.0

10.7

7.9

57.1

NH4NO3/HNO3 treated

12.1

11.6

12.1

8.1

HNO3 treated

9.8

11.6

10.1

24.0

By chemical analysis, b By NMR.

Table 5: Comparison of hydrocracking with UHP zeolite and stabilized Y zeolite Catalyst

Activity Temp. (oF)

Selectivity (vol.% diesel)

UHP-Y

747

74

Stabilized Y

745

65

These zeolites can be treated with low pH solutions. According to U.S. Patent No. 5047139 [50], the latter zeolites can have characteristics such as SiO2/A12O3 ratio of 4.5 to 35, unit cell dimension of 24.20 to 24.45, and water absorption capacity (at 25°C and at P/Po value of 0.10) of less than 5 wt.%. On treatment with dilute acid (no ammonium salt) the debris of alumina incorporated by the hydrothermal treatment can be removed from the structure. Various formations of catalysts containing about 7 wt% of acid extracted LZ-Y10, 50 wt% silica-alumina, and 15 wt% binder have been reported. The catalyst supports were impregnated with Tungsten and nickel. Table 6 presents results concerning the evaluation of several such catalysts. As shown, the zeolite with a silica-alumina ratio of about 8.5 to 11.5 results in a catalyst which is more active and selective to middle distillates.

126 Handbook of Natural Zeolites

Costa et al.

Table 6: Influence of SiO2/A12O3 ratio on catalyst performance Catalyst

Zeolite SiO2/Al2O3

Activity Temp. (oF)

Diesel Efficiency 300-700 oF (%)

Turbine Efficiency 300-550 oF (%)

1. LZ10

-

758

82.9

76.0

2. Acid extracted LZ10

8.8

751

87.0

81.2

3. Acid extracted LZ10

11.3

748

86.7

80.8

4. Acid extracted LZ10

61.3

>> 780

Various combinations of zeolites in hydrocracking catalysts have been reported. These combinations have been found advantageous in some cases [51]. The results concerning the combination of two stabilized Y zeolites with unit cell constants in the range of 24.20 to 24.85 Å are [resented in Table 7. A superior performance in middle distillate hydrocracking results when utilizing the two zeolites, compared to a similar zeolite with the average of the unit cell. Hydrocracking catalysts which contain mixtures of two zeolites have also been reported. For example, mixtures of beta zeolite with Y zeolites are reported in U.S. Patent No. 4568655 [52]. These mixtures provide improvements in particular environments, especially when adjustments in pour points are desired. Table 7: The influence of amorphous components on catalyst performance Catalyst Description of Support

Activity: Reactor Temp. to Selectivity: Conv. to 300700 oF Product (vol.%) Provide 60% Conv. (oF)

Stability (oF/day)

LZ10 and γ-Al2O3

745

74.8

1.43

LZ10 and SiO2/Al2O3 in γ-Al2O3 matrix (25% SiO2 overall)

743

79.4

0.17

LZ10 and SiO2/Al2O3 in γ-Al2O3 matrix (40% SiO2 overall)

733

79.5

0.88

The hydrothermal treatment of a zeolite after it has been mixed with an amorphous oxide component is another procedure reported [53]. Following the latter procedure it is possible to convert one type of zeolite into a derivative one and also to adjust the zeolite structural parameters such as the unit cell constant. It is also possible to obtain some specific interaction between the two phases. For example, an ammonium exchanged, steamed, ammonium exchanged Y zeolite, such as LZ-Y82, can be mixed with an inorganic metal oxide such as alumina and the composite calcined under steam in order to reduce the unit cell size and in-situ convert the

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 127

zeolite into a solid similar to an ultra hydrophobic zeolite (e.g., LZ-Y10). The latter procedure removes at least one step from the preparation process. The catalysts formed by this method can be used for middle distillate hydrocracking. Mixed Zeolite-Oxide Catalysts Catalysts containing less than the maximum amount of zeolite, after considering the binder, are made up of an amorphous oxide. Typical inorganic oxides are used such as alumina and silica-alumina. Other oxides that are used in some cases include silica-zirconia, silica-titania, alumina-boria, silica-magnesia and a mixture of silicaalumina dispersed on alumina. It was found that the inorganic oxide can significantly influence the activity and selectivity of the catalysts. Table 7 presents a comparison of catalysts with the same type and amount of zeolite incorporated into alumina and a silica-alumina-alumina dispersion. In particular, the table shows comparative data for alumina and silica-alumina-alumina dispersions and also for two concentrations of silica-alumina in alumina [54]. By introducing silica-alumina in the place of alumina, the selectivity to middle distillate is significantly improved while increasing the concentration of silica-alumina in the alumina increases the activity drastically without affecting the selectivity. Comparison of catalysts containing alumina compared to silica-magnesia [55] indicate that for the same zeolite content, the silica-magnesia catalyst is more active (by about 2oF) than the alumina solid catalyst. On the other hand, it is somewhat less selective. The combination of a UHP-Y type zeolite with pillared clay, particularly rare earth treated clay, has been also investigated [56]. Typical results are presented in Table 8. As shown in Table 8, the clay containing solid catalyst is more active and selective than the silica-alumina based catalyst. The use of a layered magnesium silicate, such as sepiolite in conjunction with a pillared clay has also been reported [57]. Table 8: Hydrocracking performance with pillared clay catalyst Catalyst

Temp. for 60% Conv. to Diesel (oF)

Diesel Efficiency (vol.%)

Turbine Efficiency (vol.%)

Reference

758

81.3

74.3

Pillared clay

760

85.7

79.6

The crystal size of the zeolite can be an important parameter in gas oil hydrocracking to distillates [58]. For example it has been known for many years

128 Handbook of Natural Zeolites

Costa et al.

that the crystallite size and morphology of the zeolite are important parameters in shape selective cracking, such as dewaxing. Two Y zeolites, UOP LZ-Y82 and PQ CP300-66 had average crystal sizes of 0.61 and 0.28 μm, respectively. After rare earth exchange, the products were calcined at 1050°F in dry air, following ammonium exchange. Finally they were palladium loaded and extruded into catalysts containing 60 wt.% zeolite. The initial data did not indicate any difference in activity for the two catalysts. Product evaluation however, indicated that the large crystal zeolite produced more low boiling liquids (C5-180°F) but less higher boiling product (280-500°F), although the product qualities were comparable. It was also found that the small crystal solid cracked more readily the higher boiling components of the feedstock, suggesting differences in exterior surfaces of the zeolite crystals.

Figure 10: Temperature (Δ) for 40% conversion of gas oil vs. catalyst percentage zeolite.

The percentage of zeolite and amorphous oxide in hydrocracking catalysts might vary depending on the desired operation and in particular the desired product slate. Catalysts designed primarily for gasoline production usually contain the maximum amount of zeolite. They consist of about 80 wt% zeolite and 20 wt% binder on a hydrogenation metal free basis. Such catalysts are designed usually to give maximum activity for conversion to the desired product. The highest activity obtained by using the maximum amount of zeolite allows low operating

Catalytic Properties of Zeolites

Handbook of Natural Zeolites 129

temperatures which result in lower production of unwanted gaseous products such as C1 to C3 hydrocarbons. A linear relationship was found between catalyst activity and zeolite content in gasoline hydrocracking. This is illustrated in Fig. 10. Catalysts designed for high middle distillate production contain low amounts of zeolite often of the order of 5-15 wt%. For middle distillate production, catalysts are described which consist of supports containing 10 wt% zeolite, 70 wt% alumina, and 20 wt% binder [142]. When a more mixed product slate is required or when it is desired to shift product distribution at different times, an intermediate quantity of zeolite can be used. With the constant hydrogenation component level, Fig. 11 shows that the activity of the catalyst increases by about 25 °F with increasing zeolite content while the selectivity to middle distillate decreases from 80 to 54 vol.%.

Figure 11: Change in activity (O) and efficiency (A) with zeolite content.

CONCLUSIONS Zeolites possess unique physicochemical properties which made them the most interesting class of minerals for scientists and engineers since their first known

130 Handbook of Natural Zeolites

Costa et al.

description. Zeolite chemistry is establishing itself as one of the key areas in the advancement of materials science as a discipline of high importance in both applied and fundamental research. In addition, zeolites have a very luminous future as applications can now be extended based on the additional method of tailored synthesis of highly stable physicochemically active materials of desired properties. Application of zeolites can be performed in respect to known zeolites and with tailored new zeolites with specific new properties. Ion conductivity, semiconductivity, piezoelectricity, as well as special optical properties in combination with already known and new zeolite properties to be developed will widen the existing application fields and open new fields for zeolite application in medicine, technical medicine, pharmacy, biochemistry, etc. ACKNOWLEDGEMENTS None declared. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

Cronstedt AF, Kongl. Vetenskaps, Acad. Handl. Stockh. 1796; 17: 120. Eitel W. Silicate Science Vol. IV Hydrothermal Systems, Academic Press, N.Y., London, 1966. Haag WO: Catalysts by zeolltes - science and technology. In Zeolites and Related Microporous Materials: State of the Art. Edited by Weitkamp J, Karge HG, Pfeifer H, Holderich W. Amsterdam: Elsevier; 1994; 84B:1375-1395. Cheetham AK. Advanced inorganic materials: an open horizon. Science 1994; 264:794-795. W.M. Meier, D.H. Olson and Ch. Baerlocher, Eds., Atlas of Zeolite Structure Types, 4th revised edition, Elsevier, London, Boston, Singapore, Sidney, Toronto, Wellington, 1996. Liebau F, Gies H, Gunawardane RP, Marler B. Classification of tectosilicates and systematic nomenclature of clathrate type tectosilicates: a proposal. Zeolites, 1986; 6: 373 Corma A. State of the art and future challenges of zeolites as catalysts J. Catal. 2003; 216: 298. V. Gutman, The Donor–Acceptor Approach to Molecular Interactions, Plenum, New York, 1978. J. Mortier, structural chemistry of zeolites: the interface between structure and activity, in: Proceedings 6th International Zeolite Conference, 1984, p. 734. G.J. Gajda, J.A. Rabo, in: J. Fraissard, L. Petrakis (Eds.), Acidity and Basicity of Solids, in: NATOASI Series, Vol. 444, Kluwer Academic, London, 1994, p. 127.

Catalytic Properties of Zeolites

[11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

Handbook of Natural Zeolites 131

A. Corma, Inorganic Solid Acids and Their Use in Acid-Catalyzed Hydrocarbon Reactions Chem. Rev. 5 (1995) 559. M. Czjzek, H. Jobic, A.N. Fitch, T. Voght, Direct determination of proton positions in D-Y and H-Y zeolite samples by neutron powder diffraction J. Phys. Chem. 96 (1992) 1535. J. Klinowski, in: J.M. Duer (Ed.), Solid-State NMR Spectroscopy, Blackwell Science, Oxford, 2002, p. 437. (cited: State of the art and future challenges of zeolites as catalysts (2003) Journal of Catalysis, 216 (1-2), pp. 298-312). R.J. Gorke, D. White, Micropor. Mesopor. Mater. 35 (2000) 477. (cited: State of the art and future challenges of zeolites as catalysts (2003) Journal of Catalysis, 216 (1-2), pp. 298-312.) R.A. Van Santen, G.J. Kramer, Reactivity Theory of Zeolitic Brarnsted Acidic Sites Chem. Rev. 95 (1995) 637. W.D. Haag, Catalysis by Zeolites – Science and Technology Stud. Surf. Sci. Catal. 84 (1994) 1375. L.A. Pine, P.J. Maher, W.A.Wachter, Prediction of cracking catalyst behavior by a zeolite unit cell size model J. Catal. 85 (1984) 466. D. Barthomeuf, Zeolite acidity dependence on structure and chemical environment. Correlations with catalysis Mater. Chem. Phys. 17 (1987) 49. R. Fisher, W. Hölderich, W.D. Mrooz, M. Srohmeyer, Eur. Patent 0167021, 1986. D. Feitler, H. Wetstein, US Patent 5,013,843, 1991. Y. Ono, Zeoraito 18 (2001) 2 (cited: State of the art and future challenges of zeolites as catalysts (2003) Journal of Catalysis, 216 (1-2), pp. 298-312). H. Ichihashi, M. Kitamura, in: Presentation at the 4 TOCAT Meeting, Tokyo, July 2002, p. 90. H. Ichihashi, H. Sato, The development of new heterogeneous catalytic processes for the production of ε-caprolactamAppl. Catal. A 221 (2001) 359. N.S. Gnep, M. Guisnet, Bull. Soc. Chim. Fr. 5–6 (1977) 429. (cited: Gun Gas-phase isomerization of ethylbenzene Over pt-heteropoly acid/zeolite catalysts, Dae LEE, Tae Joon HAN, and Ho-ln LEE Korean J. Of Chem. Eng., 3(1) (1986) 53-59). M. Guisnet, N.S. Grup, S. Morin, Micropor. Mesopor. Mater. 35 (2000) 47. (cited: C-14 tracer studies on zeolite catalysis F. Bauer, E. Bilz and A. Freyer). W.J. Mortier, Zeolite electronegativity related to physicochemical properties J. Catal. 55 (1978) 138. A. Corma, V. Fornés, R.M.Martín-Aranda, H. García, J. Primo, Zeolites as base catalysts: Condensation of aldehydes with derivatives of malonic estersAppl. Catal. 59 (1990) 237. H. Knözinger, S. Huber, IR spectroscopy of small and weakly interacting molecular probes for acidic and basic zeolites J. Chem. Soc. Faraday Trans. 94 (1998) 2047. M. Sánchez-Sánchez, T. Blasco, Pyrrole as an NMR probe molecule to characterise zeolite basicity Chemm. Commun. (2000) 491. W.J. Mortier, Electronegativity Equalization and Solid State Chemistry of Zeolites, Stud. Surf. Sci. Catal. 37 (1988) 253. L. Wytterhoeven, D. Dompas, W.J. Mortier, Theoretical Investigations on the Interaction of Benzene with FaujasiteJ. Chem. Soc. Faraday Trans. 88 (1992) 2753. H. Hattori, Heterogeneous Basic Catalysis, Chem. Rev. 95 (1995) 537. J. Weitkamp, M. Hunger, U. Rymsa, Base Catalysis on Microporous and Mesoporous Materials: Recent Progress and Perspectives Micropor. Mesopor. Mater. 48 (2001) 255. Y. Ono, Solid acids and bases catalyze selective alkylations, Cattech 1 (1997) 31. E.J. Rode, P.E. Gee, L.N. Marquez, T. Uemura, M. Bazargami, Aldol condensation of butanal over alkali metal zeolites, Catal. Lett. 9 (1991) 103.

132 Handbook of Natural Zeolites

[36] [37] [38] [39] [40]

[41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58]

Costa et al.

B.L. Su, D. Barthomeuf, Alkylation of aniline with methanol: change in selectivity with acidobasicity of faujasite catalysts Appl. Catal. A 124 (1995) 73. M. Selva, A. Bomben, P. Tanudo, Selective mono-N-methylation of primary aromatic amines by dimethyl carbonate over faujasite X- and Y-type zeolites, J. Chem. Soc. Perkin Trans. I 7 (1997) 1041. G.T. Kerr, G.F. Shipman, Reaction of hydrogen Zeolite Y with ammonia at elevated temperatures, J. Phys. Chem. 72 (1968) 3071. T. Baba, G.J. Kim, Y. Ono, Catalytic properties of low-valent lanthanide species introduced into Y-zeolite, J. Chem. Soc. Faraday Trans. 88 (1992) 891. X.S. Liu, J.K. Thomas, J. Chem. Soc. Faraday Trans. 91 (1995) 759. (cited : Facile Reduction of Zeolite-Encapsulated Viologens with Solvated Electrons and Selective Dispersion of Inter- and Intramolecular Dimers of Propylene-Bridged Bisviologen Radical Cation Langmuir 2000, 16, 4470-4477). F. Yagi, H. Tsuji, IR and TPD (temperature-programmed desorption) studies of carbon dioxide on basic site active for 1-butene isomerization on alkali-added zeolite X, H. Hattori, Micropor. Mater. 9 (1997) 239. Ward, J.W., 1975. Ammonia-stable Y zeolite compositions. U.S. Patent 3,929,672. Bezman, R.D., 1992. Relationship between zeolite framework composition and hydrocracking catalyst performance. Catal. Today, 13: 143-156. Scherzer, J., 1989. Octane-enhancing zeolitic FCC catalysts: Scientific and technical aspects. Catal. Rev. Sci. Eng., 31: 215-354. Scott, J.W. and Bridge, A.G., 1971. The continuing development of hydrocracking. Adv. Chem. Ser., 103:113 129. Skeels, G.W. and Breck, D.W., 1984. Zeolite Chemistry V - Substitution Of Silicon For Aluminum In Zeolites Via Reaction With Aqueous Fluorosilicate., In: D. Olson and A. Bisio (Eds.), Proc. 6th Int. Zeolite Conf. Reno, NV. Butterworth, London, p. 87. Scherzer, J., 1989. Octane-enhancing zeolitic FCC catalysts: Scientific and technical aspects. Catal. Rev. Sci. Eng., 31: 215-354. Best, D.F., Long, G.N., Pellet, R.J., Rabo, J.A. and Wolynic, E.T., 1991. Hydrocracking Process. U.S. Patent 5,019, 240. Gortsema, F.G., Pellet, R.J., Springer, A.R. and Rabo, J.A., 1991. Catalyst for midbarrel hydrocracking and process using same. U.S. Patent 5,047,139. Steigleder, K.Z., 1987. Middle distillate producing hydrocracking process. U.S. Patent 4,661,239. Oleck, S.M. and Wilson, R.C., 1986. Catalyst composition comprising zeolite beta. U.S. Patent 4,568,655. Ward, J.W., 1989. Hydrocarbon conversion process for selectively making middle distillate. U.S. Patent 4,879,019. Ward, J.W., 1983. Hydrocarbon conversion catalyst. U.S. Patent 4,419,271. Ward, J.W., 1974. Hydrocracking with zeolite in a silica-magnesia matrix. U.S. Patent 3,838,040. Gortsema, F.G., McCauley, J.R., Pellet, R.J., Miller, J.A. and Rabo, J.A., 1988. A new and improved midbarrel catalyst. Eur. Patent Publ., PCT Publications, No. W038106614. Occelli, M., 1991. Middle distillate hydrocracking process. U.S. Patent 5,076,907. Dahlberg, A.J. and Bezman, R.D., 1991. The effect of zeolite crystal size on hydrocracking catalyst performance, Adv. in Catal. Syrup., Snowbird, UT (unpublished). NQ. Feng, GF. Peng, Applications of natural zeolite to construction and building materials in China Constr. Build. Mater. 19 (2005) 579.

Handbook of Natural Zeolites, 2012, 133-146

133

’CHAPTER 7 Natural Zeolites Structure and Porosity Vassilis J. Inglezakis1,* and Antonis A. Zorpas2 SC European Focus Consulting srl, Bacau, Romania and 2Open University of Cyprus, Faculty of Pure and Applied Science, Environmental Conservation and Management & Institute of Environmental Technology and Sustainable Development, Cyprus 1

Abstract: Zeolite is micro-porous crystalline mineral having a highly regular structure of pores and chambers usually occupied by H2O molecules and extra-framework cations that are commonly exchangeable. The different zeolites differ in pore diameter and shape and the way these pores are interconnected. In this Chapter the basic principles of the natural zeolites framework and porosity are presented.

Keywords: Natural zeolites, structure, porosity, framework, building units, aluminosilicates. THE FRAMEWORK STRUCTURE The zeolite structure is characterized by a framework composed of TO4 tetrahedra (T = Si, Al) with O atoms connecting neighboring tetrahedral (Fig. 1). Each AlO4 tetrahedron in the framework bears a net negative charge which is balanced by an extra-framework cation. The amount of Al within the framework can vary over a wide range, with Si/Al = 1 to  , the completely siliceous form being polymorphs of SiO2. The zeolite composition can be best described as having three components [1]:

M nm   Si1n AlnO2   nH 2O m

extraframework cations · framework · sorbed phase

Figure 1: Primary building unit of the zeolites framework. *Address correspondence to Vassilis J. Inglezakis: SC European Focus Consulting srl, Banatului 16, Bacau, Romania; Tel: +40-(0)-728063293; Fax: +40(0)-334415609; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

134 Handbook of Natural Zeolites

Inglezakis and Zorpas

The framework contains open cavities in the form of channels and cages, occupied by H2O and extra-framework cations. The water may be removed reversibly by the application of heat and cations may be replaced by others without any structural changes to occur. The topology of zeolite frameworks is given by a code consisting of three capital letters assigned by the Structure Commission of the International Zeolite Association (IZA). The codes are generally derived from the names of the type material, which is the species first used to establish the structure type. Currently, three classification schemes are widely used for zeolite structures. Two of these are based upon specifically defined aspects of crystal structure, whereas the third has a more historical basis, placing zeolites with similar properties into the same group [2, 3]. The first structural classification is based upon the framework topology, with distinct frameworks receiving a three-letter code. The frameworks for zeolites with the same code are identical. A 3-letter framework type code is assigned to zeolites and the priority in the naming of zeolites depends on the first mineral discovered in the group. Gottardi and Galli (1985) proposed another classification scheme, which is similar to the SBU classification of Breck (1974), except that it includes some historical context of how the zeolites were discovered and named [4]. Here, the structural classification is based on a concept termed “secondary building unit” (SBU) as shown in Fig. 2 will be presented in detail. The primary building unit for zeolites is the tetrahedron and the SBUs are the geometric arrangements of tetrahedra [2, 5]. In Fig. 2 only the positions of tetrahedral (T) Si and Al are shown. Oxygen atoms are not shown for simplicity and lie near the connecting solid lines, which are not intended to mean bonds. The classification used by Breck (1974) is based of the framework topology of the zeolites for which the structures are known. Breck classification consists on seven groups (Table 1), within which zeolites have a common sub-unit of structure that is a specific array of TO4 tetrahedra. Due to the large number of ways in which the SBU can be linked to form various polyhedra which when combined create networks of regular channels and cavities there are many possible zeolite structures [8]. Theoretically, the possibilities for different framework structures are infinite; around 40 are known in nature and more than 150 synthetic zeolites have been manufactured [9].

Natural Zeolites Structure and Porosity

Handbook of Natural Zeolites 135

Figure 2: Secondary building units in zeolites [6, 7]. Table 1: Classification of zeolite structures [5] Group 1 2 3 4 5 6 7

Secondary Building Unit (SBU) Single 4-ring, S4R Single 6-ring, S6R Double 4-ring, D4R Double 6-ring, D6R Complex 4-1, T5O10 unit Complex 5-1, T8O16 unit Complex 4-4-1, T10O20 unit

Zeolite pores consist of 6, 8, 10, 12 and 14 membered of oxygen ring systems to form tube-like structure and pores that interconnected to each other. This results in a channel structure with molecular dimensions of 3 to 10 Å. A number of factors, such as the location, size and coordination of the extra-framework cations are also influencing pore size. Thus, the pore opening can be controlled via ion exchange by replacing cations in the framework [1]. In Fig. 3, crystal structure of some important zeolites is given.

136 Handbook of Natural Zeolites

Inglezakis and Zorpas

Each different zeolite topology has a different system of channels and cavities. There are two types of void structures in the framework, an internal pore system comprised of interconected cage like voids and a system of uniform channels which are one- two- or three- dimentional and provide intercrystalline diffusion acess. Another clasification is based on the guest molecules migration [10]: 1.

Intracrystalline channels are parallel and are not inter-connected (1-D diffusion), e.g., laumontite and mordenite.

2.

Channels are inter-connected in two dimensions but not in the third (2-D diffusion), e.g., ferrierite and stilbite.

3.

Channels are inter-connected in three dimensions (3-D diffusion), e.g., chabazite and erionite.

ANALCIME

CHABAZITE

CLINOPTILOLITE

ERIONITE

Natural Zeolites Structure and Porosity

Handbook of Natural Zeolites 137

FERRIERITE

MORDENITE

NATROLITE

PHILIPSITE

STILBITE Figure 3: Crystal structure of some important natural zeolites - H2O molecules in blue and cations in other tan blue colors (International Zeolites Association, IZA Commission of Natural Zeolites, www.iza-online.org/natural/index.htm).

Access to the intracrystalline void of zeolites occurs through rings composed of T and O atoms. For six-membered rings or less, the size of the window is approximatelly 2 Å, movement of species through these rings is restricted and diffusing ions or molecules can be trapped. For zeolites containing larger rings, ions and molecules can

138 Handbook of Natural Zeolites

Inglezakis and Zorpas

enter the intracrystalline space [1]. A great collection of zeolites structures with graphs and detail information on the channels opening and shape and interconnection could be found in the Compendium of zeolite framework types of Henk van Koningsveld [11]. In Fig. 4 the channels of some important natural zeolites is presented and in Table 2 the properties of the most common natural zeolite minerals.

Analcime channels Distorted 8-ring viewed along [110]

Chabazite channels 8-ring viewed normal to [001]

Clinoptilolite channels from left to right: 10-ring viewed along [001] 8-ring, also along [001] and 8-ring viewed along [100]

Erionite channels 8-ring viewed normal to [001]

Ferrierite channels from left to right: 10-ring viewed along [001] and 8-ring viewed along [010]

Phillipsite channels from left to right: 8-ring viewed along [100], 8-ring viewed along [010] and 8-ring viewed along [001]

Mordenite channels from left to right: 12-ring viewed along [001] and limiting 8 ring along [001] between 12-ring channels

Natrolite channels from left to right: 8-ring viewed along and 9-ring viewed along [001]

Stilbite channels from left to right: 10-ring viewed along [100] and 8-ring along [001]

Figure 4: Channels of some important natural zeolites (International Zeolites Association, IZA Structure Commision, www.iza-structure.org/databases/).

Natural Zeolites Structure and Porosity

Handbook of Natural Zeolites 139

Table 2: Properties of the most common natural zeolite minerals [6, 7, 9]

1

Mineral (code)

Formula

SBU

Channels Dimentions (Å)1

Si/Al Channel System

Crystal System

Mordenite (MOR)

(Ca,Na2 ,K2)Al2 Si10O24·7H2 O

5-1

6.5×7 2.6×5.7

5.5

1-D

Orthorhombic

Clinoptilolite (Na,K,Ca)6 (Si,Al)36O72·20H2O (CLI)

4-4-1

3.6×4.6 3.1×7.5 2.8×4.7

6

2-D

Monoclinic

Ferrierite (FER)

(Na, K)2MgAl3 Si15O36(OH)·9H2O

5-1

3.5×4.8 4.2×5.4

5-10

2-D

Orthorhombic

Chabazite (CHA)

CaAl2Si4O12·6H2 O

6-6 or 6 or 4-2 or 4

3.8×3.8

4

3-D

Rhombohedral

Erionite (ERI)

(K2 ,Ca, Na2 )2 Al4Si14O36·35H2 O

6 or 4

3.6×5.1

4

3-D

Hexagonal

Philipsite (PHI)

(K,Na,Ca)1.2 (Si,Al)8 O16·6H2 O

8 or 4

3.8×3.8 3×4.3 3.2×3.3

2

3-D

Monoclinic

Analcime (ANA)

NaAlSi2 O6·H2O

6-2 or 6 or 4-[1,1] or 1-4-1 or 4

1.6×4.2

2

3-D

Cubic

See Fig. 4.

THE NATURAL ZEOLITES POROSITY OUT OF CRYSTALS IDEAL STRUCTURES Porosity is a term used to describe the pore space of a material, defined as the fraction of the bulk volume that is occupied by pore or void space. Beyond the surface area and the pore volume, the distribution of the pore radii of a material has to be known, since the pore radius allows or not a molecule to move through the pores depending on its size. Consequently, a portion of the surface area may not be available to reactants or generally, to diffusing species. The individual pores may vary greatly in both size and shape within a given solid, and between one solid and another. In general, the pores can be classified as [7, 12]: a) macropores, for diameters above 50 nm, b) mesopores (or transitional pores), for diameters in the range of 2-50 nm, and

140 Handbook of Natural Zeolites

Inglezakis and Zorpas

c) micropores, for diameters below 2 nm; they are comparable with molecular radii. 2 1,8

Differential Pore Volume  (mm3/A/g)

1,6 1,4 1,2 1 0,8 0,6 0,4 0,2 0 10,00

100,00

1.000,00

Mean Pore Width (Angstroms)

Figure 5: Pore size distribution of natural clinoptilolite (BET analysis).

Figure 6: Nitrogen sorption-desorption isotherm curves of natural clinoptilolite (BET analysis).

Natural Zeolites Structure and Porosity

Handbook of Natural Zeolites 141

It has to be mentioned that in a solid, a wide and continuous range of pore sizes is to be found, from macropores to micropores. A pore can be also an open pore, seen as a cavity or channel communicating with the surface of the particle, or a closed pore that is not connected to the surface [12]. The pore-size distribution is the distribution of pore volume with respect to pore size (see Fig. 5 and Table 3). It is an important factor controlling the diffusion of reactants and products in the porous solid and thus an essential property for its characterization. An interesting phenomenon about adsorption on solids is swelling caused by exposure to adsorptives. Rigid adsorbents like zeolites do not swell at all or swell by only a few percent, but non-rigid adsorbents, may swell to several times the original size. Table 3: Total pore volume of some natural zeolites, % [7] Mineral

%

Laumontite

32

Natrolite

22

Mesolite

26

Edingtonite

36

Gonnardite

31

Yugawaralite

29

Analcime

20

As presented above, zeolite pores come in regular arrays and have a very uniform size, typically lower than 10Å. However, natural zeolites contain a number of impurities and they are rarely found in pure form of crystals (see Figs. 7 and 8). As a result, natural zeolite pore network consists of micro-, meso- as well as macropores. Primary porosity refers to the cavities and channels, which constitute the zeolite framework, i.e., the specific crystalline structure of the zeolite which in turn depends upon its composition. Secondary porosity refers to the macroporosity and mesoporosity developed between crystals due to matrix (impurities) inserted between zeolite crystals [7, 13]. But even in this case, natural zeolites have a relatively small pore size and in the typical case pore volume is accumulated in the vicinity of 3–20 Å. On the other hand, mesoporous materials like silica gel are typically amorphous with irregularly spaced pores with a broad size distribution while carbons could have homogeneous and heterogeneous structures.

142 Handbook of Natural Zeolites

Inglezakis and Zorpas

Figure 7: XRD graphs of natural clinoptilolite of 70-90% purity. Upper graph: Main peak of each mineralogical phase is marked by the corresponding name. All peaks marked by the same colour belong to the same phase. Lower graph: processed graph peaks without indication of the separate mineralogical phases.

Natural Zeolites Structure and Porosity

Handbook of Natural Zeolites 143

Figure 8: Surface of natural zeolite clinoptilolite taken by scanning electron microscope. Magnification: 5000 (upper), 3500 (middle) and 2000 (lower) picture. In the upper picture the magnification is so high that pure clinoptilolite crystals are visible.

144 Handbook of Natural Zeolites

Inglezakis and Zorpas

Micro- and mesopores are responsible for adsorption; molecules move in macropores towards adsorption sites in the solid [7]. Thus, macropores play the role of the transport routes to where the actual processes of adsorption take place, i.e., the zeolite meso- and microporous area. The latest is the main ground where the ion exchange and molecular sieve action take place. It should be noted that the vast majority of surface area and void volume is created by the microporous and mesoporous part of the material. In total, the surface area could be around 20-200 m2/g and void volume 20-40% of the particle total volume [7]. The meso-porous area is investigated by use of BET analysis (Figs. 5 and 6). Although the mesoporous part of the solid is not playing a critical role in the diffusion process, if blocked could lead to reduced kinetics and other problems as in the case of lead uptake by clinoptilolite, where partial clogging of the pores by dust during the grinding process inhibited the diffusion process in the smaller particles [14]. Another interesting parameter relevant to porosity is the heterogeneity parameter (n) which is characteristic of the adsorbent and it is related to its structure; the more homogeneous the pores the greater its value [15, 16]. This parameter is found in the Dubinin–Astakhov adsorption isotherm:

   n  q  qo  exp        E   where E (J/mol) is the adsorption energy, (n) the heterogeneity parameter and qo (mg/g) is the maximum mass of the adsorbed species per unit mass of sorbent. A number of experiments has shown that (n) varies, increasing as the microporous structure become more homogeneous i.e., the breadth of the micropore distribution about some mean pore size decreases. It can be stated that generally, due to the homogeneity of the zeolites pore structure in comparison to activated carbons values of (n) greater than 3–4 should be expected. A large number of experiments has shown that the average value of the heterogeneity parameter for clinoptilolite is n = 5.84 ± 2.09 (35.8% deviation) with a range of 2.1–10.4 [15]. ACKNOWLEDGEMENTS We wish to thank the International Zeolites Association (IZA) and in particular the former President (2004-2010) Dr. François Fajula, Director of the Institut

Natural Zeolites Structure and Porosity

Handbook of Natural Zeolites 145

Charles Gerhardt Montpellier, Ecole Nationale Supérieure de Chimie, Montpellier-France for the permission to use figures from website of IZA (www.iza.org). CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2]

[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

Handbook of zeolite science and technology, Scott M. Auerbach, Kathleen A. Carrado, Prabir K. Dutta (Eds), Marcel Dekker Inc, New York-Basel, 2003. Armbruster T, Gunter ME. Crystal structure of natural zeolites. Natural Zeolites: Occurrence, Properties, Applications. In: Reviews in Mineralogy and Geochemistry 45, D.L. Bish and D.W. Ming (Eds.), Mineralogical Society of America, Washington, D.C., 167; 2001. Reyes C. Synthesis of zeolites from geological materials and industrial wastes for potential application in environmental problems, PhD Thesis, University of Wolverhampton, School of Applied Sciences, 2008. Gottardi G, Galli E. Natural Zeolites, Springer-Verlag, Berlin, 1985. Breck DW. Zeolite Molecular Sieves: Structure, Chemistry and Use, 1st Ed., John Wiley, New York, 1974. International Zeolites Association, IZA Structure Commision (www.izastructure.org/databases/) Tsitsishvili G, Andronikashvili T, Kirov G, Filizova L. Natural Zeolites. Ellis Horwood Limited, England, 1992. Barrer RM. Zeolites and Clay Minerals as Sorbents and Molecular Sieves, Academic Press, London, 1978. Christie T, Brathwaite B. Thompson B. Mineral Commodity Report 23 – Zeolites. New Zealand Mining 2002; 31: 16-24. Zeolites Science and Technology, F. Ramoa Ribeiro, Alirio E. Rodrigues, L. Deane Rollmann, Claude Naccache (Eds), Martinus Nijhoff Publishers, Hague/Boston/Lancaster, 1984. van Koningsveld H. Compendium of zeolite framework types, Building schemes and type characteristics, Elsevier, 2007. Inglezakis VJ, Poulopoulos SG. Adsorption, Ion Exchange and Catalysis: Design of Operations and Environmental Applications, International Edition, Elsevier, 2006. Roque-Malherbe R. Complementary approach to the volume filling theory of adsorption in zeolites. Microporous and Mesoporous Materials 2000; 41: 227-40. Inglezakis VJ, Diamandis NA, Loizidou MD, Grigoropoulou HP. Effect of pore clogging on kinetics of lead uptake by clinoptilolite. Journal of Colloid and Interface Science 1999; 215: 54-7. Inglezakis VJ. Solubility-Normalized Dubinin-Astanhov adsorption isotherm for ion exchange systems. Microporous and Mesoporous Materials 2007; 103(1-3): 72-81.

146 Handbook of Natural Zeolites

[16]

Inglezakis and Zorpas

Inglezakis VJ, Stylianou M, Loizidou M. Ion exchange and adsorption equilibrium studies on clinoptilolite, bentonite and vermiculite. Journal of Physics and Chemistry of Solids 2010; 71(3): 279-84.

Handbook of Natural Zeolites, 2012, 147-155

147

CHAPTER 8 Sorption Hysteresis in Zeolites Mohsen Hamidpour1,*, Hossein Shariatmadari2 and Mahmoud Kalbasi3 1

Department of Soil Science, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran; Department of Soil Science, Isfahan University of Technology, Isfahan, Iran and 3 Department of Soil Science, Islamic Azad University, Khorasgan Branch, Isfahan, Iran 2

Abstract: To date, a variety of sorbents have been used to immobilize pollutants in contaminated soils and water. Immobilization can be achieved by adding natural and synthetic amendments such as alkaline materials, phosphate minerals, Fe and Mn hydroxides, aluminosilicates and zeolites. Because of unique structure, high cation exchange capacity, low cost and wide spread availability, zeolites are probably the most promising materials interacting with many organic and especially inorganic ions in contaminated soils and water. In the fields of soil and water pollution and remediation, the sorption and desorption play a key role on transport and availability of pollutants. Extensive researches have been focused on contaminant sorption by zeolites. However, desorption behavior of pollutants from zeolite minerals are still poorly understood. For several pollutants, the desorption pathway is different from that of the sorption. This phenomenon is known as hysteresis. Sorption hysteresis of environmental sorbents such as zeolites has important implication for the pollutant transport and bioavailability.

Keywords: Hysteresis, sorption, desorption, heavy metals, contaminant, environment. INTRODUCTION Release of organic and inorganic pollutants into the environment is a potential threat to soil and water quality as well as to plant, animal and human health. Remediation of contaminated soils and water bodies is not only one of the most important issues addressed by environmental politics in industrialized countries, but also is growing in developing countries [1]. In recent years, various natural and low cost sorbents have been used for sorption of organic and inorganic contaminants from polluted sites. The ability of these materials to remove various *Address correspondence to Mohsen Hamidpour: Department of Soil Science, Vali-e-Asr University of Rafsanjan, Rafsanjan, Iran; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

148 Handbook of Natural Zeolites

Hamidpour et al.

pollutants and their potential uses are the subjects of many research programs. Because of high surface area, high cation exchange capacity, low cost and wide spread availability, zeolites are usually the common choice to prevent the release of contaminant, especially heavy metals, into the environment [2, 3]. Control of pollutant bioavailability is the key for remediation technologies [4]. Immobilized contaminants may, however, become again mobile and plantavailable with time [3]. Change in mobilization and bioavailability of pollutants in soils and water treated with natural sorbents such as zeolites is generally controlled by sorption-desorption reactions [3]. Extensive researches have been conducted on contaminant sorption by zeolite, however, desorption behavior of contaminants from zeolite minerals is still poorly described and understood. To predict the fate and transport of heavy metals in the environment, transport and bioavailability models commonly rely on distribution coefficients and maximum sorption levels that are obtained from equilibrium batch sorption experiments [5, 6]. Neglecting the desorption processes in these experiments, however, may cause errors in predicting the potential toxicity of a contaminant [3, 6]. If sorption is irreversible, these models will incorrectly over predict the movement or biological hazard of the metal contaminant. To improve remediation strategies, risk assessments and to make better predictions about contaminants mobility, it is critical to understand the mechanism(s) of sorption-desorption reactions as well as the reversibility or irreversibility of sorbed contaminant on zeolites. DEFINITION Hysteresis, or non-singularity, is a phenomenon in which the sorption and desorption isotherms do not coincide [7]. Several mechanisms have been suggested to explain hysteresis including chemical precipitation, variation of the binding mechanism with time, migration and incorporation of the solute into the sorbents, micropore deformation and trapping [8-10]. Care should be taken to distinguish between real hysteresis and pseudo-hysteresis due to experimental factors such as slow desorption kinetics, non-attainment of equilibrium of the sorption before starting the desorption process [8], mass loss from vessels, colloid aggregation and sorption to non-settling colloids [9]. One possible explanation for slow desorption is that chemisorption reactions usually require a much higher

Sorption Hysteresis in Zeolites

Handbook of Natural Zeolites 149

activation energy in desorption direction than sorption, to break the energetically very favorable bonds of the sorbate with the surface [8, 11]. The pseudohysteresis depends on conditions and can be eliminated, whereas the true hysteresis is reproducible in repeated sorption-desorption cycles [9]. Numerous indices have been presented to quantify sorption hysteresis [9]. These indices may be divided into 6 following groups as indicated in Table 1: (i) the sorbed concentration q (mol kg-1); (ii) the exponent of Freundlich isotherm; N (iii) the distribution coefficient Kd (iv) the area between sorption and desorption isotherms (v) the slope of the desorption isotherm in relation to the sorption one and (vi) the thermodynamic index of irreversibility. Table 1: Hysteresis indices Index Based on

Equation

Nomenclature

Sorbed concentration, q

qsorb and qdesorb: solid-phase solute concentration on sorption and desorption branches of the isotherm, respectively

[12]

Nsorb and Ndesorb Freundlich exponents of sorption and desorption branch, respectively

[13, 14] [15] [12]

Kd (L kg-1): concentration dependent apparent distribution coefficient; m: total number of I desorption step

[16]

(6)

Asorb and Adesorb: areas under the sorption and desorption branch of the isotherm respectively

[17]

(7)

f C first derivatives of the C and f functions describing the sorption and desorption branches of the isotherm respectively

[18]

CS (mol L-1) and CD (mol L-1) are the solute concentrations at the sorption and desorption points and Cγ (mol L-1) is the hypothetical solute concentration corresponding to a reversible point on the sorption branch at the observed sorbed concentration of the desorption point.

[19]

(1)

Freundlich exponent, N

(2) (3) 1 (4)

100 Distribution coefficient

∑

(5)

Area Slope

C

C C

Thermodynamic

References

(8)

SORPTION KINETICS AND DESORPTION HYSTERESIS Due to the unique structure of zeolite, sorption kinetics of some of contaminants on zeolite consist of two distinct phases (biphasic kinetics): an initial rapid and reversible phase followed by a much slower, non-reversible one [20]. According to

Hamidpour et al.

150 Handbook of Natural Zeolites

Essington [21], for organic compounds, the rapid phase is sorption of the compound on the easily accessible sites located on the surfaces and edges of the mineral layers. This phase of sorption is nonspecific (labile form) and could be easily desorbed. For metals and inorganic ligands, this phase is also characterized as exchangeable form. The slower reaction phase that follows the initial rapid phase generally involves the diffusion and entrapment of inorganic and organic compounds into the zeolite channels. This phase is specific and difficult to desorb. The mechanism of the slow phase may also be the formation of inner-sphere surface complexes and bonds with covalent characters [20]. Fig. 1 shows the sorption kinetics of Pb on zeolite. The figure illustrates two points. First, the time to reach the equilibrium is a function of the initial metal concentration increasing from 0.5 to 12 h when the initial metal concentration increased from 75 to 750 mg L-1.

70 60

Pb sorbed (mg/g)

50 750 mg/l

40 30

75 mg/l

20 10 0 0

5

10

15

20

25

Time (h) Figure 1: Effect of initial metal concentration (75 vs. 750 mg L-1) on kinetics of Pb sorption onto zeolite ( pH=5.5, sorbent dose: 10 g L-1, temperature:23±2 ◦C) [20].

Second, in the first 30 min, the initial rate of sorption is much greater for the higher initial metal concentration. This may be due to the effect of metal concentration gradient on the diffusion of Pb ions onto the surface of sorbents. An

Sorption Hysteresis in Zeolites

Handbook of Natural Zeolites 151

increase of the Pb initial concentration accelerates the diffusion of Pb from the solution into the zeolite channels due to the increase of driving force at the higher metal concentration [20, 22]. Hysteretic behaviour of Pb and Cd [22] and pyrene [24] sorption-desorption on zeolite are illustrated in Figs. 2 and 3. The desorption isotherms of Cd and Pb from the zeolite deviated significantly from the corresponding sorption isotherms (Figs. 2a and b). The amounts of desorbed Cd and Pb are considerably smaller than the amount that would be predicted from the sorption isotherm. According to Essington [21], sorption hysteresis is the apparent increase in the sorption constants (e.g., Kd, KFreundlich, KLangmuir and KP) when equilibrium is approached from the sorption isotherm indicating a hysteresis and suggests that a portion of the sorbed metal ions is tightly bonded to the zeolite sorption sites and is not readily desorbable. As was previously indicated, diffusion and entrapment of the metal ions into the zeolite channels and the strong bonding to the high affinity sites (covalent bonds and inner-sphere complexation) can result in the apparent irreversible retention of Cd and Pb. 2(a)

Pb sorbed / desorbed (mg/g)

80 a) Pb

qd = 49.3C0.04

60 qd = 40.2C0.01 qs= 19.2C0.22

40 qd = 28.5C0.006

20

0 0

50

100

150

Equilibrium Pb concentration in solution (mg/l)

200

Hamidpour et al.

152 Handbook of Natural Zeolites

2(b)

1.6 Cd sorbed / desorbed (mg/g)

b) Cd

1.2

qd = 0.58C0.15

qd = 0.29C0.25

0.8

qs = 0.02C0.9

0.4

qd = 0.14C0.33

0 0

20

40

60

80

Equilibrium Cd concentration in solution (mg/l) Figure 2: Lead and cadmium sorption (●) and desorption isotherms on the zeolite at three initial metal loadings of 50% (□), 75% (∆) and 100% (◊) of the sorption capacity; SCmax. Solid and dashed lines are Freundlich model (q=KF Cen) predictions of sorption and desorption, respectively (pH:5.0, sorption equilibrium time: 24 h, temperature: 23±2 ◦C) [22].

Effects of metal ion loadings on the hysteresis index (

, Equation 2 in

the Table 1) are shown on Table 2. The apparent hysteresis index (HI) is largely dependent on the kind of the metal ion and the initial amount of sorbed metal ions. The lower HI index values indicate increased difficulty of the sorbed metal to desorb from the sorbent. For Pb -zeolite systems, the HI increases with increase of the metal ion loading rates. But, in the case of Cd, the HI decreases with increasing the metal ion loading. At low Cd concentrations, apparently due to a lower concentration gradient, fewer Cd ions can penetrate into the zeolite channels, while, at high metal levels, the higher gradient of concentration may force the sorbed Cd to penetrate deeper into the zeolite channels. When penetrating into the channels, the sorbed Cd is less likely to be diffused from the zeolite channels to equilibrium solution.

Sorption Hysteresis in Zeolites

Handbook of Natural Zeolites 153

Figure 3: Sorption-desorption isotherms of pyrene on the zeolite A [24]. Table 2: Hysteresis index (HI) calculated for quantification of non-singularity of Cd and Pb sorption and desorption isotherms [23]

a

Hysteresis Index

Initial Metal Load (% of the SCmax)a

Pb

Cd

HIb

50

2.77

36.6

HI

75

6.33

27.8

HI

100

20.0

16.2

Legend: SCmax = maximum sorption capacity of the zeolite for Cd or Pb,

b

.

From the environmental implication point of view, irreversible sorption would be advantageous for pollutant immobilization in the remediation of already contaminated soils. A better understanding of sorption-desorption hysteresis of contaminants on the zeolite will provide scientists and engineers with the information to enable them to implement better strategies for dealing with contaminated soils and water. Limited information is available regarding reversibility or irreversibility of desorbed some pollutants from the zeolite and further studies are needed to better understand the causes of the hysteresis in the sorption-desorption of pollutants onto the zeolite using chemical, microscopic and spectroscopic techniques.

154 Handbook of Natural Zeolites

Hamidpour et al.

ACKNOWLEDGEMENTS None declared. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Wingenfelder U, Nowack B, Furrer G, Schulin R. Adsorption of Pb and Cd by aminemodified zeolite. Water Res 2005; 39: 3287-97. Inglezakis VJ, Loizidou MD, Grigoropoulou HP. Ion exchange of Pb2+, Cu2+, Fe3+ and Cr3+ on natural clinoptilolite: selectivity determination and influence of acidity on metal uptake. J Colloid Interface Sci 2003; 261: 49-54. Hamidpour M, Afyuni M, Kalbasi M, Khoshgoftarmanes AH, Inglezakis VJ. Mobility and plant-availability of Cd(II) and Pb(II) adsorbed on zeolite and bentonite. Appl Clay Sci 2010; 48: 342-8. Mench M, Martin E. Mobilization of cadmium and other metals from two soils by root exudates of Zea mays L., Nicotiana tabacum L. and Nicotiana rustica L. Plant Soil 1991; 132: 187-96. Strawn DG, Sparks DL. Effects of soil organic matter on the kinetics and mechanisms of Pb(II) sorption and desorption in soil. Soil Sci Soc Am J 2000; 64: 144-56. Moradi A, Abbaspour KC, Afyuni M. Modelling field-scale cadmium transport below the root zone of a sewage sludge amended soil in an arid region in central Iran. J Contam Hydrol 2005; 79: 187-206. Strawn DG, Sparks DL. Sorption kinetics of trace elements in soils and soil materials. In: Selim HM, Iskandar I, Eds. Fate and transport of heavy metals in the vadose zone. Chelsea, MI: Lewis Publishers, 1999; pp. 1-28. McBride MB. Chemisorption and precipitation reactions. In: Sumner ME, Ed. Handbook of soil science. Boca Raton, FL: CRC Press, 2000; pp. 265-302. Sander M, Lu YF, Pignatello JJ. A thermodynamically based method to quantify true sorption hysteresis. J Environ Qual 2005; 34: 1063-72. Weber WJ, Huang W, Yu H. Hysteresis in the sorption and desorption of hydrophobic organic contaminants by soils and sediments: 2. Effects of soil organic matter heterogeneity. J Contaminant Hydrol 1998; 31: 149-65. Appel C, Ma L. Concentration, pH, and surface charge effects on cadmium and lead sorption in three tropical soils. J Environ Qual 2002; 31: 581-9. Ma L, Southwick LM, Willis GH, Selim HM. Hysteretic characteristics of atrazine adsorption-desorption by a sharkey soil. Weed Sci. 1993; 41: 627-33. O’Connor GA, Wierenga PJ, Cheng HH, Doxtader KG. Movement of 2,4,5-T through large soil columns. Soil Sci 1980; 130: 157-62. Barriuso E, Laird DA, Koskinen WC, Dowdy RH. Atrazine desorption from smectites. Soil Sci Soc Am J 1994; 58: 1632-38.

Sorption Hysteresis in Zeolites

[15] [16] [17] [18] [19] [20] [21] [22] [23] [24]

Handbook of Natural Zeolites 155

Celis R, Cornejo J, Hermosin MC, Koskinen WC. Sorption-desorption of atrazine and simazine by model colloidal particles. Soil Sci Soc Am J 1997; 61: 436-43. Laird DA, Yen PY, Koskinen WC, Steinheimer TR, Dowdy RH. Sorption of atrazine on soil clay components. Environ Sci Technol 1994; 28: 1054-61. Zhu H, Selim HM. Hysteretic behavior of metolachlor adsorption-desorption in soils. Soil Sci 2000; 165: 632-45. Braida, WJ, Pignatello JJ, Lu Y, Ravikovitch PI, Neimark AV, Xing B. Sorption hysteresis of benzene in charcoal particles. Environ Sci Technol 2003; 37: 409-17. Sander M, Lu YF, Pignatello JJ. A thermodynamically based method to quantify true sorption hysteresis. J Environ Qual 2005; 34: 1063-72. Hamidpour M, Kalbasi M, Afyuni M, Shariatmadari H, Furrer G. Sorption of lead on Iranian bentonite and zeolite: kinetics and isotherms. Environ Earth Sci 2011; 62: 559-68. Essington ME. Soil and Water Chemistry: An Integrative Approach. Knoxville: CRC Press, 2004. Hamidpour M. PhD dissertation. Sorption and desorption of Cd and Pb on bentonite and zeolite. Isfahan, Iran: Isfahan University of Technology, 2010. Hamidpour M, Kalbasi M, Afyuni M, Shariatmadari H, Holm PE, Hansen HCB. Sorption hysteresis of Cd(II) and Pb(II) on natural zeolite and bentonite. J Hazard Mater 2010; 181: 686-91. Schlüpen J, Haegel FH, Kuhlmann J, Geisler H, Schwuger MJ. Sorption hysteresis of pyrene on zeolite. Coll Surf A: Physicochem Eng Asp 1999; 156: 335-47.

156

Handbook of Natural Zeolites, 2012, 156-165

CHAPTER 9a Modified Zeolites: Pretreatment of Natural Zeolites by Use of Inorganic Salts Vassilis J. Inglezakis* SC European Focus Consulting srl, Banatului 16, Bacau, Romania Abstract: Pretreatment of natural zeolites covers a wide range of modification techniques leading in several products to a variety of applications. A very common pretreatment type is used for producing modified zeolites for use in ion exchange applications and in particular for the removal of cations from aqueous solutions. In these cases, pretreatment aims to remove certain ions from the structure of the material and locate more easily removable ones, prior to any ion exchange application. Practically, the result of any pretreatment operation is the increase of the content in a single cation, what is called homoionic form. The final homoionic or near homoionic state of the zeolites improves the effective exchange capacity and performance in ion exchange applications.

Keywords: Pretreatment, inorganic salts, modification, ion exchange capacity, homoionic zeolite, chemical treatment, physical treatment, modified zeolites, effective capacity, breakthrough capacity, maximum exchange level. INTRODUCTION In general, pretreatment is a process where the natural ion exchange material is washed with aqueous solutions, containing salt(s), acid or alkali under specific operating conditions as flow rate, solution volume, temperature, etc. The most usual pretreatment agent is the sodium chloride, followed by NaOH, CaCl2 and other salts. The impact of the operational and chemical pretreatment conditions upon the effective capacity of the most commonly used natural zeolite, clinoptilolite has been investigated in a number of studies [1-4]. In the most practical case of fixed bed continuous flow pretreatment operations, an optimal flow rate and a minimum concentration are determined, for a pretreatment that leads to a high effective capacity of the material. In most of the cases, the quality of the modified material is examined by evaluating the effective capacity (EC), which is defined as the amount of the Address correspondence to Vassilis J. Inglezakis: EFCon, Str Banatului nr. 16, Bacau, Romania; Phone/Fax: +40-(0)334415609; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Pretreatment of Natural Zeolites by Use of Inorganic Salts

Handbook of Natural Zeolites 157

cations of the zeolite contained in a specific amount of the material, which are exchangeable under specific experimental conditions. This term is used only for batch-type effective capacity, as the breakthrough capacity (BC) covers the case of column-type effective capacity [5]. EC could be equal to maximum exchange level (MEL) if an infinite contact time and ratio of solution volume to solid mass are utilized. The effective and breakthrough capacity depend not only on the specific ion-exchange system but also on the experimental conditions used for its determination. Experimental conditions are the liquid-volume-to-solid mass ratio, agitation rate, and contact time for batch systems, the volumetric flow rate and breakpoint concentration for fixed bed operations and the temperature and solution normality for both systems. It is true that the most studied natural zeolite is clinoptilolite. Thus, inevitably the most of the data presented in the following paragraphs are coming from the related literature. However, the basic concepts and findings are not expected to vary significantly for other natural zeolites. BASIC TYPES OF PRETREATMENT In Table 1 the most characteristic batch-type methods are presented [4]. In the general case, the natural sample is placed in a vessel containing the pretreatment solution of a specified concentration, under constant temperature and agitation conditions for a Table 1: Characteristic batch-type pretreatment methods for natural clinoptilolite [1, 4] Solution concentration (M)

Agitation

Temperature

Solid to liquid phase ratio

(oC)

(g/100 ml)

1 (NaCl)

No

70

5

10 daysa

2 (NaCl) or 2 (NaOH)

Yes

20-25

10

24 h

3 (NaCl)

Yes

90

10

14 daysb

1 (NaCl)

Yes

90

6.25

2hc

4.3 (NaCl)

Yes

20-25

20

4h

a

renewal of solution every 24h.

b

renewal of solution every 48h.

c

the procedure is repeated twice.

Duration

158 Handbook of Natural Zeolites

Vassilis J. Inglezakis

certain time period. In several cases, the solution is periodically replaced with fresh one. As is evident, the most common salt used is NaCl, as several studies showed that is superior against other inorganic salts (NaCl>CaCl2>KCl> MgCl2) while in the same time is readily available, safe in use and cheap agent. A systematic experimental study for clinoptilolite pretreatment in batch mode is presented by Inglezakis et al., [1]. In the same study batch-type and fixed bed typical methods taken from the related literature are compared. Based on this study as well as in others, the general conclusion is that batch-type pretreatments lead to higher effective capacity than fixed bed treatments, however the later is more practical as higher amounts of product can be achieved in less time and less complicated procedures. It should be noted that in several cases regeneration methods are presented in the literature, which in practice are equivalent to pretreatment methods (see Table 2). Table 2: Operational conditions in fixed beds [4] Q (BV/h) C (M)

V (BV)

pH

Operation

5-55

0.1-3.3 (NaCl)

8.3-50

2.5-10

Pretreatment - downflow

5

1-2 (NaCl)

20-30

-

Pretreatment - downflow

1 (NaCl)

-

-

Pretreatment

5

0.35 (NaCl)

40

11.5

Regeneration - upflow

In Fig. 1 a typical two-column system is presented for continuous pretreatment/regeneration and treatment operation. Volumetric flow rate influences both liquid holdup of the bed and contact time. Generally, ion exchange is operated with low flow rates, i.e., high contact time, in

Pretreatment of Natural Zeolites by Use of Inorganic Salts

Handbook of Natural Zeolites 159

order to give the appropriate time to the system for the exchange. However, by lowering the flow rate, liquid holdup is lowered and liquid maldistribution may have serious negative effects upon the effectiveness of the process [2]. Thus, is not surprising that experimental studies have concluded that both high flow rates (resulting in low contact time) and low flow rates (resulting in lower liquid holdup and partial wetting of the material) are not beneficial for the process [2]. These effects are more intense in downflow mode, while in upflow the effects of non ideal flow are expected to be minimal. A variety of flow rates are used in the related studies for small scale pretreatment of clinoptilolite in fixed beds, with a range of 1 to 55 BV/h [2, 6]. Bed volume (BV) is a unit commonly used in column studies and refers to a volume of liquid equal to the volume of the packed bed. In downflow mode, although total exchange capacity remains unaltered, the sodium content of the pretreated samples is increased by decreasing the volumetric flow rate from 5 to less than 1 BV/h while in up-flow mode, variation of flow rates from 4 to 20 BV/h was shown to have no effect on the process [7]. A comprehensive study on the effect of volumetric flow rate in the range of 5 to 55 BV/h has shown that the intermediate flow rate of 25 BV/h gives the best results [2].

Figure 1: Two-column system. D1/D2: solution(s) tanks, P1/P2: peristaltic pumps, E1: heat exchanger for solution preheating, R1/R2: fixed beds, M1/M2: measurement points (mixing cups), TI1/TI2: temperature recorders, PHR: pH recorder, CR: conductivity recorder.

Experimental results for the pretreatment of clinoltilolite have shown that increasing the concentration above 0.4 mol/l has practically no effect on the

160 Handbook of Natural Zeolites

Vassilis J. Inglezakis

effective capacity of the product [2]. The negative effect of the decreased concentration on the effective capacity is explained by the relative amplitude of the driving force, i.e., concentration difference between solution and solid phase during the ion exchange process. By increasing solution concentration, solid phase is saturated with Na+ ions and further increase has no effect at all. The pretreatment solution concentrations used is varying between 0.2 and 2 mol/l [2, 3, 6-9]. The effect of concentration of the pretreatment solution is examined with controversial results; Semmens and Martin [6] concluded that although total exchange capacity remained unaltered, the sodium content of the pretreated samples was increased with concentration increasing from 1 to 2 mol/l and Guangsheng et al., [10] reported that higher concentrations of sodium chloride, as eluant of Cu2+ ions from clinoptilolite, resulted in better elution of the ions. On the other hand, Koon and Kaufman [7] examined the regeneration of NH+4 exchanged clinoptilolite and concluded that the use of concentrations higher than 0.2 mol/l had no effect on the procedure. Finally, Carland and Aplan [8], studying on elution of Cu2+ from clinoptilolite, concluded that the use of concentrations greater than 0.5 mol/l had no effect on the elution process. The effects of acid and alkali washings are examined by Klieve and Semmens [9], showing no significant differences between the samples. However, a study on clinoptilolite has shown that the best working pH is near 7.5. It is known that low pH, which means high concentration of H+ ions, is leading in simultaneous uptake of hydrogen ions by zeolite, and this could be the explanation for the lower capacity for low values of pH [2]. The lower value of capacity for pH=10, can be explained if OH- ions are entrapped in the structure of clinoptilolite during pretreatment. If this is true, during capacity measurements, possible internal precipitation of lead hydroxide or the formation of complexes may clog the pores. Another explanation is the partial destruction of clinoptilolite structure, which is expected for high values of pH [2]. A wide range of the volume of the pretreatment solution is used in the related literature: 43 and 86BV [9], and 20–30BV [6]. A slight improvement of the capacity is noticed with increasing solution volume in clinoptilolite pretreatment [2]. Less accessible sites in the zeolite structure are supposed to require several pretreatment cycles as mentioned by Carland and Aplan [8], or extensive

Pretreatment of Natural Zeolites by Use of Inorganic Salts

Handbook of Natural Zeolites 161

conditioning with a high concentration of the selected cation to obtain the homoionic form, as mentioned by Semmens and Martin [6]. Increase in solution volume is estimated to be of little use, since a three-fold increase in pretreatment time will end to about 5–10% increase in effective capacity [2]. The effect of temperature has been studied elsewhere, for the range of 25-59oC, in upflow fixed bed operations and clinoptilolite samples [3, 4]. A typical example of the temperature effect on the effective capacity is shown in Fig. 2. The general conclusion for fixed bed as well as for batch-type pretreatment methods is that the increase of temperature leads to considerable increase of effective capacity due to higher uptake kinetics during pretreatment [4]. 1.4

q(meq/g)

1.2 1 0.8 0.6 20

30

40

50 T(oC)

60

70

Figure 2: Temperature effect on the effective capacity (Pb2+) of pretreated clinoptilolite (Q=25 BV/h, C=1.1 M, V=25 BV, Vw=10 BV, pH=7.5).

Washing of pretreated samples is critical because if excess sodium ions are entrapped in the zeolite, they might diffuse out in the solution during capacity measurements, leading to erroneous results. The effect of washing water volume is monitored through the measurement of solution conductivity (mS/cm) at the column outlet vs. bed volumes of passing solution. In Fig. 3 an experimental example of the evolution of conductivity λ (mS/cm) vs. outflow liquid volume V (BV) is presented [4]. A relevant study on clinoptilolite, under the high pretreatment NaCl concentration (3.33 M) has shown that a volume of 10 BV is sufficient for the washing of the material, as washing seems to be completed between 25 and 35 BV [2].

162 Handbook of Natural Zeolites

Vassilis J. Inglezakis

1000

λ (mS/cm)

100 10 1 0.1 0

10

20

30

40

50

60

V(BV)

Figure 3: Effect of washing water volume on the pretreatment of clinoptilolite: Q=25 BV/h, C=3.33 M (λNaCl=220 mS/cm), VNaCl=25 BV, pH=7.5 (tap water λo=1 mS/cm).

Washing is playing a significant role when acids and alkalis are used during pretreatment. Especially in the later case entrapped OH- could affect the ion exchange processes significantly due to internal precipitation of metal hydroxides. In Fig. 4 the pH evolution vs. outflow liquid volume is presented. The washing starts on 25 BV, for two systems with the same pretreatment conditions but different treatment solution pH (2.5 και 10). 10 8

pH

6 4 pH=10 pH=2.5

2 0 0

10

20

30

40

50

V(BV) Figure 4: Effect of washing water volume on the pretreatment of clinoptilolite: Q=25 BV/h, C=1.1 M, VNaCl=25 BV (tap water pHo=7.5).

Pretreatment of Natural Zeolites by Use of Inorganic Salts

Handbook of Natural Zeolites 163

In this example is evident that a volume of washing water of 10 BV is sufficient for the acidic solution of pH=2.5 while for the alkali solution of pH=10 the double volume is needed [4]. This is due to the different behavior of OH- and H+ ions in the zeolite structure, the first being entrapped while the later partly exchanged for cations initially present in the zeolite framework. It can be concluded that in general, a volume of 10 BV is sufficient for neutral to acidic pretreatment solutions while higher volumes are needed for alkali solutions. Finally, the effect of clinoptilolite dust on capacity has been studied by Inglezakis et al., [2]. Surface dust is clogging part of the pore openings in zeolite structure, leading in slower ion exchange kinetics. The results show lower effective capacity for the unwashed material. The slower kinetics during the pretreatment process, due to pore clogging could be lead to the lower uptake of Na+ ions. Furthermore, some effects due to the presence of dust may equally influence the pretreatment process, such as clogging of the packed bed which leads in high pressure loss and consequent overflow and leakage, or difficulties in bed unloading as zeolite fragments are stacked together. EFFECT OF PRETREATMENT ON THE NATURAL MATERIALS Practically, the result of any pretreatment operation is the increase of the content in a single cation, what is called homoionic form [6]. Therefore, pretreatment aims to remove certain ions from the structure of the material and locates more easily removable ones, prior to any ion exchange application of it. For the typical case of sodium chloride as pretreatment solution, investigation on several standard pretreatment methods have shown that composition changes occur for Na (up to 400% increase), K (up to 60% decrease), Ca (up to 90% decrease) and Mg (up to 80% decrease) [4]. The final homoionic or near homoionic state of the zeolites was found to improve their effective exchange capacity and performance in ion exchange applications [6, 9, 11, 12]. Although an extensive change in the chemical composition of the natural material occurs during pretreatment, several studies have shown that mild pre-treatment methods of natural zeolites, i.e., those that do not use highly acidic or alkali solutions are not influencing the structure of the material. In general, the standard methods used for such investigations are BET, XRD, TG/DTA and SEM/EDS. Slight changes in BET surface area measurements are attributed to the removal of surface dust of the raw material.

164 Handbook of Natural Zeolites

Vassilis J. Inglezakis

The net result of pretreatment is the improvement of the ion exchange performance of the modified material and several studies are published on the subject [6-11]. It is true that the most sufficient way to examine these benefits is the continuous flow, fixed bed operation where equilibrium and kinetics are combined in a dynamic mode. Such experiments have shown that the modification of the natural sample is favorable, resulting in 32–100% higher breakpoint values, depending on the specific cation for Pb2+, Cu2+, Fe3+ and Cr3+ [13] while similar results are found elsewhere for the removal of Pb2+, Cd2+ and Cu2+ [6, 8, 11] and ammonia ions from dilute solutions (20–25 mg/L) where the breaking point (C/Co = 10%) was increased by a factor of 1.43–1.73 (43–73%), compared to that of natural sample [9, 14]. Is generally accepted that the improvement in the removal efficiency in ion exchange processes is due to the increase of easy removable Na+ ions in the natural zeolite structure. This modification, in general, has a dual effect; increase of effective capacity (improvement of the equilibrium behavior) and increase of diffusion coefficient (kinetics). The benefits of pretreatment on the material and the equilibrium-kinetics relationship and changes are represented by the exchange site accessibility concept as analyzed by Inglezakis et al., [15]. This discussion is necessary as in several studies in the related literature, different samples of zeolites are compared by examining only equilibrium or kinetic parameters while in actual ion exchange operations both equilibrium and kinetics are influencing the performance of a material. New available sites for exchange, produced by Na+ enrichment of the natural sample, may be in locations which are accessible, and therefore result in higher distribution coefficient and selectivity (equilibrium parameters), but it is possible that cations are moving to some of these new sites with such increased degree of difficulty that the net result is a decreased mean diffusion coefficient (kinetic parameter). In this case, distribution coefficients are expected higher, while diffusion coefficients may be slightly higher, unaltered or even lower. Thus is not always guaranteed that the pre-treatment results in a material which exhibits better equilibrium and kinetic behavior; however, as it has been shown in several studies, the net result of pretreatment is a better overall performance of the final material. ACKNOWLEDGEMENTS None declared.

Pretreatment of Natural Zeolites by Use of Inorganic Salts

Handbook of Natural Zeolites 165

CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

Inglezakis VJ, Papadeas CD, Loizidou MD, Grigoropoulou HP. Effects of pretreatment on physical and ion exchange properties of natural clinoptilolite. Environmental Technology 2001; 22: 75-83. Inglezakis VJ, Hadjiandreou KJ, Loizidou MD, Grigoropoulou HP. Pretreatment of natural clinoptilolite in a laboratory-scale ion exchange packed bed. Water Research 2001; 35: 21612166. Inglezakis VJ, Loizidou MD, Grigoropoulou HP. Studies on the pretreatment of zeolite clinoptilolite in packed beds. Environmental Technology 2004; 25: 133-139. Inglezakis VJ. Design of Ion Exchange Fixed Beds by use of Natural Minerals as Packing Material. PhD Thesis, National Technical University of Athens, School of Chemical Engineering; 2002. Inglezakis VJ. The concept of “capacity” in zeolite ion exchange systems. Journal of Colloid and Interface Science 2005; 281: 68-79. Semmens MJ, Martin WP. The influence of pretreatment on the capacity and selectivity of clinoptilolite for metal ions. Water Research 1988; 22: 537-542. Koon JH, Kaufman WJ. Ammonia removal from municipal wastewater’s by ion exchange. Journal WPCF 1975; 47: 448-465. Carland RM, Aplan FF. Improving the ion exchange capacity and elution of Cu2+ from natural sedimentary zeolites. Mineralogical and Metallurgical Processes 1995; 11: 210-218. Klieve JR, Semmens MJ. An evaluation of pretreated natural zeolites for ammonium removal. Water Research 1980; 14: 161-168. Guangsheng Z, Xingzheng L, Guangju L, Quanchang Z. Removal of copper from electroplating effluents (Potch Water) using clinoptilolite. In: Occurrence, Properties and Utilization of Natural Zeolites, eds D. Kallo, H. S. Sherry, Akademiai Kiado, Budapest, 1988; pp. 529-39. Kesraoui-Ouki S, Cheeseman C, Perry R. Effects of conditioning and treatment of chabazite and clinoptilolite prior to lead and cadmium removal. Environmental Science and Technology 1993; 27: 1108-1116. Chmielewska-Horvathova E, Lesny J. Study of sorption equilibrium in the systems: water solutions of inorganic ions on clinoptilolite. Journal of Radioanalytical and Nuclear Chemistry. 1995; 201: 293-301. Inglezakis VJ, Grigoropoulou HP. Effects of operating conditions on the removal of heavy metals by zeolite in fixed bed reactors. Journal of Hazardous Materials 2004; B 112: 37-43. Hlavay J, Vigh G, Olaszi V, Inczedy J. Investigations on natural Hungarian zeolite for ammonium removal. Water Research 1982; 16: 417-420. Inglezakis VJ, Loizidou MD, Grigoropoulou HP. Ion exchange studies on natural and modified clinoptilolites and the concept of exchange site accessibility. Journal of Colloid and Interface Science 2004; 275: 570-576.

166

Handbook of Natural Zeolites, 2012, 166-184

CHAPTER 9b Modified Zeolites: Zeolites Modified with Organic Agents Kathryn A. Mumford, Meenakshi Arora, Jilska M. Perera and Geoffrey W. Stevens* Particulate Fluids Processing Centre, Department of Chemical & Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia Abstract: In this chapter we address the modification of the surface properties of zeolites. The first method discussed is the attachment of long chain surfactant molecules to enable the sorption of anionic and non-polar species. The second method is known as silation, where the presence of silanol groups on the zeolite surface are exploited to form a hydrophobic material.

Keywords: Surfactant modified zeolite, silane modified zeolite, hydrocarbon uptake, anion uptake, dye uptake, monolayer, bilayer, organosilane. INTRODUCTION Zeolites are crystalline, aluminosilicate minerals comprised of a cage-like framework of SiO4 and AlO4 tetrahedra. These naturally occurring substances are known to have a high surface area and good cationic exchange properties. Their rigid 3D structures offer superior hydraulic properties, are free from shrinking/swelling behaviour and hence have been used as molecular sieves and in applications such as filtration and waste water treatment [1, 2]. The exchange of cations by zeolite minerals has been well documented, examples being the removal of heavy metals and ammonium from water [3-7] and the removal of hazardous cationic radioactive species [1, 8, 9]. However, these materials can be further exploited via surface modification, which can render a material suitable for applications such as hydrocarbon and/or anion adsorption [1, 10, 11]. The aim of this chapter is to summarise the surface modification of natural zeolite and to examine reported applications. The primary chemical methods for *Address correspondence to Geoffrey W. Stevens: Particulate Fluids Processing Centre, Department of Chemical & Biomolecular Engineering, The University of Melbourne, Victoria 3010, Australia; Tel: +61 3 8344 6621; Fax: +61 3 8344 6684; Email: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Zeolites Modified with Organic Agents

Handbook of Natural Zeolites 167

modifying the surface of zeolite materials are by use of cationic surfactants such as high-molecular-weight quaternary amines [10] and by silation with appropriate organosilanes [11]. Other methods such as coating with chitosan [12] have also been reported. SURFACTANT MODIFIED ZEOLITES General The substitution of aluminium for silicon in the structure of zeolites results in the network lattice exhibiting a net negative charge. As a result, natural zeolites usually have little or no affinity for anions and exhibit low adsorption for organics in aqueous solution. One method to modify the zeolite to enable anion and organic uptake is via the use of organic cationic surfactants [1, 10, 11]. Many different surfactants have been trialled for this purpose and include; hexadecyltrimethylammonium (HDTMA) [13-19], tetramethylammonium (TMA) [14], tetraethylammonium bromide (TEA) [20] N-cetylpyridinium bromide (CPB) [16, 21], cis-1aminoctadecen-9 (oleylamine) [22], cetyltrimethylammonium bromide (CTAB) [15, 23], octadecyldimethylbenzyl ammonium (ODMBA) [24, 25], stearyldimethylbenzylammoniumchloride (SDBAC) [26], benzyltetradecyl ammonium chloride (BDTDA) [27], polyhexamethylene-guanidine (PHMG) [28], N, N, N, N’, N’, N’ – hexamethyl-1,9-nonanediammonium dibromide (HMNA) [29], benzyltrimethylammonium (BTMA) [19], dodecyl benzenesulfonate (SDBS) sodium dodecyl sulphate (SDS) [30] and ethylhexadecyldimethyl ammonium (EHDDMA) [31]. Due to viruses and bacteria exhibiting net negative charges at groundwater pH, surfactant modified zeolites have also found use in microbial systems [1, 32, 33]. However, microbial cultivation studies have had mixed results as some surfactants are capable of destroying cell membranes [34]. Structure The mineralogical properties of the zeolite material control the quantity and distribution of surfactant that may be loaded. Due to the relative sizes of the

168 Handbook of Natural Zeolites

Mumford et al.

surfactant molecules to the zeolite pores, surfactant sorption is limited to the external exchange sites only. The largest channels of the zeolite clinoptilolite have dimensions 0.42×0.72 nm. The diameter of the polar head of the surfactant HDTMA is 0.694 nm and the carbohydrate chain has a diameter and length of 0.4 nm and 2.3 nm respectively. Clearly the surfactant would not be able to enter the zeolite channels [17]. Therefore, the area per unit charge on the zeolite external surface relative to the size of the surfactant molecule controls surfactant aggregation on the surface and so the properties of the surfactant modified zeolite. In the case of HDTMA surfactant, it has been found that the amount sorbed by clinoptilolite is a function of the surfactant counter-ion i.e., if HDTMA+Cl-, HDTMA+Br- or HDTMA+ HSO4- has originally been utilized in complex preparation [35]. A number of mechanisms are involved in the binding of surfactants to the zeolite surface. The first layer forms a monolayer or “hemimicelle” at the solid-liquid interface via strong electrostatic interactions between the negatively charged zeolite surface and the positively charged surfactant head-group [10]. This occurs up until the surfactants critical micelle concentration (cmc). If the surfactant concentration in solution exceeds the cmc, then the hydrophobic tails of the surfactant molecules associate to form a bilayer or “admicelle” by hydrophobic bonding (van der Waals forces). The bonding is stabilized by counter-ions in both layers [35-37] due to higher ionic strength increasing the driving force for the formation of admicelles and solution micelles thereby making the bilayer more stable [38, 39]. Different mechanisms are involved for the sorption of hydrocarbons and anions on to surfactant modified zeolites. Therefore different surfactant coverings are appropriate for differing applications. It has been shown that the removal of hydrocarbons from aqueous solutions continues to increase in effectiveness at increasing surfactant concentrations up to the point of full monolayer coverage [40]. Beyond this, as the surfactant bilayer begins to form, there is also a formation of a positively charged surface which no longer provides a hydrophobic coating to promote sorption of the nonpolar organic compounds. Anion adsorption occurs under the bilayer configuration [18, 35, 36, 38, 41]. However, on occasion at very high loadings i.e., very full bilayers, the adsorption capacity may also be

Zeolites Modified with Organic Agents

Handbook of Natural Zeolites 169

reduced. This is due to the release of excess loosely bound surfactant molecules from admicelles into solution which results in competition with the surfactant on the surface of the material [10, 42]. It has also been shown that surface precipitation may also occur [10]. A schematic representation of the attachment of surfactant molecules to the zeolite surface and the partitioning of benzene into the hydrophobic tail groups of the surfactant modified zeolite is presented in Fig. 1. SMZ is reported to have long term chemical and biological stability over a wide range of solution conditions [43]. Although the HDTMA bilayer responsible for SMZ’s sorbent properties is not readily displaced by common aqueous cations and is resistant to biological and chemical degradation it does slowly wash off under continued leaching [44, 45]. Studies have shown that SMZ can be regenerated following contact with anionic or non polar compounds [46], VOCs (from water) [47] and dyes [48, 49]. In columns, some loss of hydraulic conductivity, probably due to particle breakdown has been reported [47].

Figure 1: Schematic representation of the attachment of surfactant molecules to the surface of zeolite particles and the partitioning of benzene into the hydrophobic tail groups of the surfactant modified zeolite. Reprinted from the Journal of Contaminant Hydrology, vol. 108, Simpson JA, Bowman RS, Non-equilibrium sorption and transport of volatile petroleum hydrocarbons in surfactant-modified zeolite, 1-11, 2009, with permission from Elsevier.

170 Handbook of Natural Zeolites

Mumford et al.

Fabrication and Physical Characterisation The fabrication of surfactant modified zeolite generally requires the contacting of the solid material with the surfactant solution, with mechanical shaking for several hours, followed by centrifugation/filtration, removal of the supernatant and finally air drying [10, 16, 23, 30, 50, 51]. The modified material can then be used for direct contact with the solution containing the ion/molecule of interest. Surfactant modified zeolites can be characterised using several methods including thermal analysis such as TG, DTA and DSC [41]; FTIR and DRIFT spectroscopy [23, 41, 52]; XRD [18, 41, 52]; FT-Raman spectroscopy [13]; SEM [18, 41, 52]; zeta potential measurements [18, 53], N2-BET [53] and CEC [18]. X-ray diffraction (XRD) is used to determine the composition of the zeolite material i.e., clinoptilolite, quartz, illite, feldspar etc. It is also often used to ensure that the process of loading surfactant has not altered the structure of the underlying zeolite [19, 25, 27, 39, 54]. Scanning Electron Micrographs (SEM) are used to examine the surface morphology. Zeolites generally show a cubical geometry and there may be some changes in sharp edges and corners with the addition of the surfactant [54]. Fourier transform infrared spectroscopy (FTIR) is used to study the molecular conformation of the surfactant chains in monolayer and bilayer forms as well as to determine the presence of surfactant on the zeolite surface [15, 17, 21, 24]. The determination of the external surface area of clinoptilolite samples is generally based on the BET method [55] with nitrogen adsorption [56]. The zeta potential is used to determine the effects of surfactant on the charge of the material and therefore the point at which a patchy monolayer, monolayer, patchy bi-layer or bilayer are formed. At natural pH in water, zeolites acquire a negative charge. Upon the addition of surfactant the charge will become less negative until it reaches the isoelectric point (a value of zero for electrokinetic potential). At this point the negative surface charges are neutralized and a complete surfactant monolayer is formed. Sorption below this point is likely to be in the form of hemimicelles and above this point admicelles [17, 18]. This has been corroborated in other studies that consider the thermodynamic behaviour of the differing sorption methods [20].

Zeolites Modified with Organic Agents

Handbook of Natural Zeolites 171

The cation exchange capacity (CEC) and the external cation exchange capacity are generally determined or are adapted from a method proposed by Ming and Dixon [57]. In this method the zeolite exchangeable sites are converted to the sodium form. The external exchangeable sodium cations are displaced by washings with a large cation such as tert-butyl ammonium. The internal exchangeable sites are removed with ammonium [57] and the sodium concentrations in solution are measured. The sodium released by washing with tert-butyl ammonium bromide represents the ECEC and those released by washing with ammonium acetate represents the internal exchange sites. The sum of both represents the total. Applications There are many laboratory studies that investigate removal of specific contaminants by a variety of surfactant modified zeolites. Generally work has been restricted to laboratory scale batch and column testing. Such work includes the adsorption of volatile petroleum hydrocarbons [47, 58, 59], ethylene [51], PCE [46, 60], dyes [23, 30, 48, 49, 61], phenols and chlorophenols [27, 50, 62, 63]. A summary of works conducted are presented in Table 1. Surfactant modification has shown to be particularly effective in improving the capacity of zeolites for anionic complexes. For example Yusof et al., [42] utilised zeolite materials modified with HDTMA to capture Cr (VI) and As (V). The base material had a surface area between 485 – 507 m2.g-1, with an external cation exchange capacity of 0.53 – 0.67 meq.g-1. Its capacity for Cr(VI) pre-modification was 0.001-0.0025 mmol.g-1. Post-modification with HDTMA the capacity increased significantly to 0.0314-0.0376 mmol.g-1. Similarly, the material showed a significant increase in capacity for As(V) post-modification, with the capacity increasing from 0.001 mmol.g-1 to 0.0102-0.0179 mmol.g-1. Generally it is envisaged that surfactant modified zeolites are best suited to flow through systems, such as permeable reactive barriers in aquifer systems or for pump and treat systems due to their good hydraulic conductivities [64]. However the actual implementation of these systems has been limited. A pilot scale demonstration was conducted at the Large Experimental Aquifer Program (LEAP) site at the Oregon Graduate Institute of Science and Technology near Portland,

172 Handbook of Natural Zeolites

Mumford et al.

OR. In this study a mixed plume of chromate and perchloroethylene was passed through a reactive barrier containing SMZ in a contained aquifer [1, 65]. Ranck et al., [58] investigated the use of SMZ for treating produced water in pilot scale column experiments at a water treatment facility. Other work on virus removal has been conducted at a submerged flow constructed wetland [32]. Apart from the above examples, this work is generally limited to column studies and to simulate the results using currently available solute transport software so that comparisons can be made among results obtained from batch column and pilot tests [38, 44]. Table 1: Surfactant modified zeolites, target molecule, zeolite and surfactant Target Molecule/Ion

Material/Surfactant

Reference

4-chlorophenol

Clinoptilolite/BDTDA

[27]

4-chlorophenol

Clinoptilolite/HDTMA

[27]

Antimonate

Slovakia zeolite/HDTMA

[39]

As(V)

Clinoptilolite/ HDTMA

[66, 67]

As(V)

Brazil zeolite/EHDDMA/HDTMA

[31]

As(V)

NaY (rice husk ash) / HDTMA

[42]

Benzene

Clinoptilolite/HDTMA

[50, 58]

BPA

ZFA/HDTMA

[63]

Cr(III)

Zeolite 13X/CPB

[21]

Cr(VI)

Zeolite 13X/CPB

[21]

Cr(VI)

Zeolite- A/ HDTMA

[52]

Cr(VI)

Chabazite/ HDTMA

[41]

Cr(VI)

Clinoptilolite/ HDTMA

[10, 13, 16, 36, 41, 45, 53, 68-70]

Cr(VI)

NaY (rice husk ash) / HDTMA

[42]

Cr(VI)

Clinoptilolite/PHMG

[28]

Cr(VI)

Iranian zeolite/HMNA

[29]

DHA

Clinoptilolite/TMA, HDTMA

[14]

Dihydrogen phosphate

Clinoptilolite/Oleylamine

[22]

e. coli ATCC 13706

Clinoptilolite /HDTMA

[32]

Ethylbenzene

Clinoptilolite/HDTMA

[58]

Ethylene

Zeolite NaY/OTAB, HTAB, DDAB

[51]

Hydrogen chromate

Clinoptilolite/Oleylamine

[22]

Nitrate

Clinoptilolite/ HDTMA

[18, 37, 69]

Zeolites Modified with Organic Agents

Handbook of Natural Zeolites 173 Table 1: cont….

Perchlorate

Clinoptilolite/ HDTMA

[38]

Perchloroethylene

Clinoptilolite/HDTMA

[40]

Phosphorous

Zeolite-A/HDTMA

[54]

Phenol

Smectite/HDTMA, BTMA

[19]

Phenol

Clinoptilolite/BDTDA

[27]

Phenol

Clinoptilolite/HDTMA

[27]

Phenol

ZFA/HDTMA

[62]

Selanate

Clinoptilolite/ HDTMA

[10]

Sulphate

Clinoptilolite/ HDTMA

[10, 69]

Sulphate

Clinoptilolite/Oleylamine

[22]

Toluene

Zeolite 13X/CPB

[21]

U(VI)

Heulandite/clinoptilolite/ HDTMA

[71]

Azo dyes

Sepiolite/HTAB

[61]

Fumonisin B1

Clinoptilolite/ODMBA

[24]

DYES

Methylene blue,

ZM-5/SDBS

[30]

Reactive yellow 176

Clinoptilolite/HTAB

[48]

Reactive black 5, reactive red 239

Zeolite/CTAB

[23]

Basic red 46, reactive yellow 176

Zeolite/CTAB

[15]

Zearalenone

Clinoptilolite/ODMBA

[25]

SILANE MODIFIED ZEOLITE General Surface modification of zeolites has been studied quite extensively and has been shown to be effective for the removal of various contaminants from water [13-15, 17-24, 72]. The most significant challenge identified in this work is the need to improve the stability of the coating from long-term leaching effects, as it has been reported that surfactant surface coatings are affected by low ionic strength solutions [1, 35, 40]. An alternative approach is via a process known as silation, where the presence of silanol groups on the zeolite surface are exploited to form a hydrophobic material.

174 Handbook of Natural Zeolites

Mumford et al.

Structure Many comprehensive discussions regarding zeolite structure may be found [73]. However in regards to silation the most important components of zeolite structure are the three types of silanol groups on the surface of the zeolite i.e., single ((SiO)3Si–OH); hydrogen-bonded ((SiO)3Si–OH–OH–Si(SiO)3) and geminal ((SiO)2Si(OH)2). Among these silanol groups, free SiOH groups are the most reactive and may provide the sites for the physical and chemical adsorption of silane coupling agents [74-77]. Organosilanes are reactive chemical compounds possessing up to three nonpolar aliphatic or aromatic moieties which can be grafted covalently to silanol groups on the mineral surface. Various silane coupling agents such as (γ-aminopropyl)triethoxy silane, N-β-(aminoethyl)-γ-aminopropyltrimethoxy silane, (γglycidyloxypropyl)-trimethoxy silane and (3-aminopropyl)-dimethylethoxy silane have been used [78-80]. In this process the modification occurs via chemical reaction whereby aromatic or nonpolar aliphatic silane moieties are covalently bonded to the silanol groups on the zeolite surface, resulting in a material with stable linkages between the bulk material and the organo silane [11]. With appropriate silane coupling agents, one may not only modify surface properties of zeolite from hydrophilic to hydrophobic but also increase zeolite affinity to the varied solvent matrices. A variety of organosilanes [11, 81-84] have been used to generate modified zeolites capable of adsorbing compounds such as o-xylene [11, 85]; naphthalene [11, 85], toluene [11] and paraquat [86]. As an example, a schematic representation of the reaction of surface hydroxyl groups of zeolite Y with TMDS is shown in Fig. 2.

Figure 2: Schematic representation of the reaction of surface hydroxyl groups of zeolite Y with TMDS. Reprinted from Microporous and Mesoporous Materials, vol. 88, Zhang HY, Kim Y, Dutta PK., Controlled release of paraquat from surface-modified zeolite Y, 312-318, 2006, with permission from Elsevier.

Zeolites Modified with Organic Agents

Handbook of Natural Zeolites 175

Fabrication and Physical Characterisation Surface modification by silation is generally carried out by introducing the silating agent into a vessel containing the dry zeolite immersed in an organic solvent. The reaction takes place under controlled temperature and atmosphere with refluxing and stirring for a period of at least 24 hours. Following the surface silation, the modified zeolite is filtered, washed with organic solvent and dried under vacuum or air dried for 24 hours [11, 85]. Variations on this method include various commercial materials and dealuminated zeolites [87-90]. Silane modified zeolite can be characterised using several methods such as NMR [86, 87], IR, FTIR and DRIFT spectroscopy [82, 85, 86, 91]; XRD [84, 85]; STA, DTG, DTA, TGA [11, 85]; SEM [86] and XPS [82]. TGA measurements are done to determine the carbon content of the unamended and modified zeolite which provides the information on extent of modification. FTIR spectra are used to determine the relative functional groups in the modified zeolite. The surface area and pore size distribution is based on BET equation and nitrogen adsorption. XRD spectra are used to determine the composition of modified zeolite and to determine whether the zeolite structure is disrupted following modification. SEM images are used to study the variations in surface morphology and roughness. It has been reported that chlorosilane modified zeolite maintains the sorption behaviour towards aromatics when exposed to extremes in pH and ionic strength [11]. Regeneration at 60ºC with no measurable loss in adsorption ability was also observed. Zeolite modified with octadecyltrichlorosilane (Z-C18) has been reported to show only minor changes in the naphthalene sorption behaviour when exposed to extremes in pH and ionic strength [85]. The sorption of o-xylene is affected by high ionic strength and high pH, with a reduction in performance of up to 34% when exposed to a solution of 1 M CaCO3 and reduced performance of up to 37% at pH 10. Low pH did not affect sorption of either hydrocarbon to any great extent. Regeneration studies suggest that the zeolite could be regenerated and reused at least three times without significant reduction in treatment effectiveness [85]. Applications Various studies have investigated the removal of a range of contaminants by silane modified zeolites. Most of these studies have been restricted to laboratory scale batch and column testing. The research includes the adsorption of volatile

176 Handbook of Natural Zeolites

Mumford et al.

petroleum hydrocarbons [85, 87], ammonia [81], cobalt [91] etc. A summary of these studies is presented in Table 2. Table 2: Silane modified zeolites: target molecule, zeolite and modification Target Molecule/Ion

Material/ Modification

References

Acetaldehyde (degradation)

Clinoptilolite/Triethoxyfluorosilane

[84]

Ammonia

Mordenite/ Disilane

[81]

Argon

Na-Mordenite/ Disilane

[92]

Butane

Na-Mordenite/ Disilane

[92]

Cobalt (cobaltocenium ion)

Zeolite Na-Y /OTS

[91]

Kr

Na-Mordenite/ Disilane

[92]

Methanol

Faujasite, Mordenite, Zeolite NaY/ SiCl4 gas

[87]

MEK

Faujasite, Mordenite, Zeolite NaY/ SiCl4 gas

[87]

n- Pentane

Faujasite, Mordenite, Zeolite NaY/ SiCl4 gas

[87]

Nitrogen

Na-Mordenite/ Disilane

[92]

Naphthalene

Clinoptilolite/ OTS

[85]

Naphthalene

Clinoptilolite/ TMSCl, TBDMSCl, DPDSCl, DMODSCl

[11]

Oxygen

Na-Mordenite/ Disilane

[92]

o-Xylene

Clinoptilolite/ OTS

[85]

o-Xylene

Clinoptilolite/ TMSCl, TBDMSCl, DPDSCl, DMODSCl

[11]

p-Xylene

Faujasite, Mordenite, Zeolite NaY/ SiCl4 gas

[87]

Paraquat

zeolite Y/TMDS

[86]

Toluene

Clinoptilolite/ TMSCl, TBDMSCl, DPDSCl, DMODSCl

[11]

Toluene

Faujasite, Mordenite, Zeolite NaY/ SiCl4 gas

[87]

Xenon

Na-Mordenite/ Disilane

[92]

Silane modification has shown to be particularly effective in improving the capacity of zeolites for a range of contaminants. For example, Meininghaus and Prins [87] utilised zeolite materials modified with steaming and treatment with silicon tetrachloride to capture methanol, methyl ethyl ketone (MEK), toluene, p-xylene and n-pentane. Both the techniques led to dealumination of the zeolite structure and significantly improved the exchange capacity for all the organic solvents tested. CONCLUSIONS Natural zeolites have a large surface area for adsorption of small molecules and a significant cation exchange capacity. This chapter shows how zeolites can be

Zeolites Modified with Organic Agents

Handbook of Natural Zeolites 177

modified by silation to enhance their ability to adsorb hydrophobic materials such as hydrocarbons. The negative charged natural zeolites can also been modified via the addition of layers of materials such as cationic surfactants and chitosan, resulting in a material capable of adsorbing a wide range of substances including chromate, nitrate, perchlorate, phenols and dyes. This material can be used in permeable reactive barrier structures to immobilize ions from contaminated water. This type of modified zeolite not only has ion exchange capacity but is environmentally benign and cheap to deploy. In conclusion, simple and low cost surface modifications to natural zeolites can significantly enhance their utility for a range of applications. ABBREVIATIONS BDTDA

benzyl tetradecyl ammonim (Cl-)

BET

Brunauer-Emmett-Teller

BPA

bis-phenol A

BTEX

benzene, toluene, ethylene, xylenes

BTMA

benzyl trimethyl ammonium

CEC

cation exchange capacity

CMC

critical micelle concentration

CPB

N-cetylpyridinium bromide

CTAB

cetyl trimethylammonium bromide

DDAB

dioctadecyl dimethyl ammonium bromide

DHA

dehydroabietic acid

DMODSCl

dimethyloctadecylchlorosilane

178 Handbook of Natural Zeolites

Mumford et al.

DPDSCl

diphenyldichlorosilane

DRIFT

diffusion-reflectance infrared Fourier transform (spectroscopy)

DTA

differential thermo analysis

DTG

differential thermogravimetric (analysis)

ECEC

external cation exchange capacity

EHDDMA

ethyl hexa decyl dimethyl ammonium

FTIR

Fourier transform infrared

HDTMA

hexadecyl trimethyl ammonium (Cl- or Br-)

HMNA

N, N, N, N’, N’, N’ – hexamethyl-1,9-nonanediammonium dibromide

HTAB

hexadecyl trimethyl ammonium bromide

IR

infrared (spectroscopy)

MEK

methyl ethyl ketone

NMR

nuclear magnetic resonance (spectroscopy)

ODMBA

octa dexyl dimethyl benzyl ammonium

OTAB

octyl trimethyl ammonium

OTS

octadecyltrichlorosilane

SDBAC

stearyl dimethyl benzyl ammonium chloride

SDBS

dodecyl benzenesulfonate

SDS

sodium dodecyl sulphate

Zeolites Modified with Organic Agents

SEM

scanning electron microscopy

TEA

tetra ethyl ammonium

TMA

tetra methyl ammonium

TBDMSCl

tert-butyldimethylchlorosilane

TG

thermogravimetric (analysis)

TMDS

tetramethyldisilazane

TMSCl

trimethylchlorosilane

VOC

volatile organic compound

XPS

X-ray photoelectron spectroscopy

XRD

X-ray diffraction

XRF

X-ray fluorescence (spectroscopy)

ZFA

coal fly ash

Handbook of Natural Zeolites 179

ACKNOWLEDGEMENTS Support from the Australian Research Council, the Particulate Fluids Processing Centre and the Australian Antarctic Division is gratefully acknowledged. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2]

Bowman RS. Applications of surfactant-modified zeolites to environmental remediation. Microporous Mesoporous Mater 2003; 61(1-3): 43-56. Wang SB, Peng YL. Natural zeolites as effective adsorbents in water and wastewater treatment. Chem Eng J 2010; 156(1): 11-24.

180 Handbook of Natural Zeolites

[3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22]

Mumford et al.

Erdem E, Karapinar N, Donat R. The removal of heavy metal cations by natural zeolites. J Colloid Interface Sci 2004; 280(2): 309-14. Chojnacki A, Chojnacka K, Hoffmann J, Gorecki H. The application of natural zeolites for mercury removal: from laboratory tests to industrial scale. Miner Eng 2004; 17(7-8): 933-7. Motsi T, Rowson NA, Simmons MJH. Adsorption of heavy metals from acid mine drainage by natural zeolite. Int J Miner Process 2009; 92(1-2): 42-8. Calvo B, Canoira L, Morante F, et al. Continuous elimination of Pb2+, Cu2+, Zn2+, H+ and NH4+ from acidic waters by ionic exchange on natural zeolites. J Hazard Mater 2009; 166(2-3): 619-27. Teutli-Sequeira A, Solache-Rios M, Olguin MT. Influence of Na+, Ca2+, Mg2+ and NH4+ on the sorption behavior of Cd2+ from aqueous solutions by a Mexican zeolitic material. Hydrometallurgy 2009; 97(1-2): 46-52. Orechovska J, Misaelides P, Godelitsas A, et al. Investigation of HEU-type zeolite crystals after interaction with Sr2+ cations in aqueous solution using nuclear and surface analytical techniques. J Radioanal Nucl Chem 1999; 241(3): 519-27. Abusafa A, Yucel H. Removal of Cs-137 from aqueous solutions using different cationic forms of a natural zeolite: clinoptilolite. Sep Purif Technol 2002; 28(2): 103-16. Haggerty GM, Bowman RS. Sorption of chromate and other inorganic anions by organozeolite. Environ Sci Technol 1994; 28(3): 452-8. Huttenloch P, Roehl KE, Czurda K. Sorption of nonpolar aromatic contaminants by chlorosilane surface modified natural minerals. Environ Sci Technol 2001; 35(21): 4260-4. Arora M, Eddy NK, Mumford KA, et al. Surface modification of natural zeolite by chitosan and its use for nitrate removal in cold regions. Cold Regions Science and Technology 2010; 62(2-3): 92-7. Sullivan EJ, Hunter DB, Bowman RS. Fourier transform Raman spectroscopy of sorbed HDTMA and the mechanism of chromate sorption to surfactant-modified clinoptilolite. Environ Sci Technol 1998; 32(13): 1948-55. Bouffard SC, Duff SJB. Uptake of dehydroabietic acid using organically-tailored zeolites. Water Res 2000; 34(9): 2469-76. Karadag D, Akgul E, Tok S, et al. Basic and reactive dye removal using natural and modified zeolites. J Chem Eng Data 2007; 52(6): 2436-41. Ghiaci M, Kia R, Abbaspur A, Seyedeyn-Azad F. Adsorption of chromate by surfactantmodified zeolites and MCM-41 molecular sieve. Sep Purif Technol 2004; 40(3): 285-95. Rozic M, Sipusic DI, Sekovanic L, et al. Sorption phenomena of modification of clinoptilolite tuffs by surfactant cations. J Colloid Interface Sci 2009; 331(2): 295-301. Schick J, Caullet P, Paillaud JL, Patarin J, Mangold-Callarec C. Batch-wise nitrate removal from water on a surfactant-modified zeolite. Microporous Mesoporous Mater 2010; 132(3): 395-400. Shen YH. Phenol sorption by organoclays having different charge characteristics. Colloids and Surfaces a-Physicochemical and Engineering Aspects 2004; 232(2-3): 143-9. Sullivan EJ, Carey JW, Bowman RS. Thermodynamics of cationic surfactant sorption onto natural clinoptilolite. J Colloid Interface Sci 1998; 206(2): 369-80. Covarrubias C, Garcia R, Yanez J, Arriagada R. Preparation of CPB-modified FAU zeolite for the removal of tannery wastewater contaminants. J Porous Mater 2008; 15(4): 491-8. Vujakovic AD, Tomasevic-Canovic MR, Dakovic AS, Dondur VT. The adsorption of sulphate, hydrogenchromate and dihydrogenphosphate anions on surfactant-modified clinoptilolite. Appl Clay Sci 2000; 17(5-6): 265-77.

Zeolites Modified with Organic Agents

[23] [24] [25] [26] [27] [28] [29] [30] [31] [32]

[33] [34] [35] [36] [37] [38] [39] [40]

Handbook of Natural Zeolites 181

Karadag D, Turan M, Akgul E, Tok S, Faki A. Adsorption equilibrium and kinetics of reactive black 5 and reactive red 239 in aqueous solution onto surfactant-modified zeolite. J Chem Eng Data 2007; 52(5): 1615-20. Dakovic A, Tomasevic-Canovic M, Rottinghaus GE, Matijasevic S, Sekulic Z. Fumonisin B-1 adsorption to octadecyldimethylbenzyl ammonium-modified clinoptilolite-rich zeolitic tuff. Microporous Mesoporous Mater 2007; 105(3): 285-90. Dakovic A, Matijasevic S, Rottinghaus GE, et al. Adsorption of zearalenone by organomodified natural zeolitic tuff. J Colloid Interface Sci 2007; 311(1): 8-13. Lemic J, Tomasevic-Canovic M, Adamovic M, Kovacevic D, Milicevic S. Competitive adsorption of polycyclic aromatic hydrocarbons on organo-zeolites. Microporous Mesoporous Mater 2007; 105(3): 317-23. Kuleyin A. Removal of phenol and 4-chlorophenol by surfactant-modified natural zeolite. J Hazard Mater 2007; 144(1-2): 307-15. Misaelides P, Zamboulis D, Sarridis P, Warchol J, Godelitsas A. Chromium (VI) uptake by polyhexamethylene-guanidine-modified natural zeolitic materials. Microporous Mesoporous Mater 2008; 108(1-3): 162-7. Noroozifar M, Khorasani-Motlagh M, Gorgij MN, Naderpour HR. Adsorption behavior of Cr(VI) on modified natural zeolite by a new bolaform N,N,N,N ',N ',N '-hexamethyl-1,9nonanediammonium dibromide reagent. J Hazard Mater 2008; 155(3): 566-71. Jin XY, Jiang MQ, Shan XQ, Pei ZG, Chen ZL. Adsorption of methylene blue and orange II onto unmodified and surfactant-modified zeolite. J Colloid Interface Sci 2008; 328(2): 243-7. Campos V, Buchler PM. Anionic sorption onto modified natural zeolites using chemical activation. Environmental Geology 2007; 52(6): 1187-92. Schulze-Mokuch D, Bowman RS, Pillai SD, Guan HD. Field evaluation of the effectiveness of surfactant modified zeolite and iron-oxide-coated sand for removing viruses and bacteria from ground water. Ground Water Monitoring and Remediation 2003; 23(4): 68-74. Joshi P, Rayalu S, Bansiwal A, Juwarkar AA. Surface modified zeolite, a novel carrier material for Azotobacter chroococcum. Plant Soil 2007; 296: 151-8. Hrenovic J, Rozic M, Sekovanic L, Anic-Vucinic A. Interaction of surfactant-modified zeolites and phosphate accumulating bacteria. J Hazard Mater 2008; 156: 576-82. Li ZH, Bowman RS. Counterion effects on the sorption of cationic surfactant and chromate on natural clinoptilolite. Environ Sci Technol 1997; 31(8): 2407-12. Li ZH, Jones HR, Bowman RS, Helferich R. Enhanced reduction of chromate and PCE by palletized surfactant-modified zeolite/zerovalent iron. Environ Sci Technol 1999; 33(23): 4326-30. Li Z. Use of surfactant-modified zeolite as fertilizer carriers to control nitrate release. Microporous Mesoporous Mater 2003; 61(1-3): 181-8. Zhang PF, Avudzega DM, Bowman RS. Removal of perchlorate from contaminated waters using surfactant-modified zeolite. J Environ Qual 2007; 36(4): 1069-75. Wingenfelder U, Furrer G, Schulin R. Sorption of antimonate by HDTMA-modified zeolite. Microporous Mesoporous Mater 2006; 95(1-3): 265-71. Li ZH, Bowman RS. Sorption of perchloroethylene by surfactant-modified zeolite as controlled by surfactant loading. Environ Sci Technol 1998; 32(15): 2278-82.

182 Handbook of Natural Zeolites

[41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59]

Mumford et al.

Majdan M, Pikus S, Rzaczynska Z, et al. Characteristics of chabazite modified by hexadecyltrimethylammonium bromide and of its affinity toward chromates. J Mol Struct 2006; 791(1-3): 53-60. Yusof AM, Malek N. Removal of Cr(VI) and As(V) from aqueous solutions by HDTMAmodified zeolite Y. J Hazard Mater 2009; 162(2-3): 1019-24. Li ZH, Roy SJ, Zou YQ, Bowman RS. Long-term chemical and biological stability of surfactant modified zeolite. Environ Sci Technol 1998; 32(17): 2628-32. Li ZH. Chromate transport through surfactant-modified zeolite columns. Ground Water Monitoring and Remediation 2006; 26(3): 117-24. Li ZH, Hong HL. Retardation of chromate through packed columns of surfactant-modified zeolite. J Hazard Mater 2009; 162(2-3): 1487-93. Li ZH, Bowman RS. Regeneration of surfactant-modified zeolite after saturation with chromate and perchloroethylene. Water Res 2001; 35(1): 322-6. Altare CR, Bowman RSB, Katz LE, Kinney KA, Sullivan EJ. Regeneration and long-term stability of surfactant-modified zeolite for removal of volatile organic compounds from produced water. Microporous Mesoporous Mater 2007; 105(3): 305-16. Faki A, Turan M, Ozdemir O, Turan AZ. Analysis of fixed-bed column Adsorption of Reactive Yellow 176 onto surfactant-modified zeolite. Ind Eng Chem Res 2008; 47(18): 6999-7004. Ozdemir O, Turan M, Turan AZ, Faki A, Engin AB. Feasibility analysis of color removal from textile dyeing wastewater in a fixed-bed column system by surfactant-modified zeolite (SMZ). J Hazard Mater 2009; 166(2-3): 647-54. Li ZH, Burt T, Bowman RS. Sorption of ionizable organic solutes by surfactant modified zeolite. Environ Sci Technol 2000; 34(17): 3756-60. Patdhanagul N, Srithanratana T, Rangsriwatananon K, Hengrasmee S. Ethylene adsorption on cationic surfactant modified zeolite NaY. Microporous Mesoporous Mater 2010; 131(13): 97-102. Kumar P, Jadhav PD, Rayalu SS, Devotta S. Surface-modified zeolite-A for sequestration of arsenic and chromium anions. Curr Sci 2007; 92(4): 512-7. Leyva-Ramos R, Jacobo-Azuara A, Diaz-Flores RE, et al. Adsorption of chromium(VI) from an aqueous solution on a surfactant-modified zeolite. Colloids and Surfaces APhysicochemical and Engineering Aspects 2008; 330(1): 35-41. Bansiwal AK, Rayalu SS, Labhasetwar NK, Juwarkar AA, Devotta S. Surfactant-modified zeolite as a slow release fertilizer for phosphorus. J Agric Food Chem 2006; 54: 4773-9. Brunauer S, Emmett PH, Teller E. Adsorption of gases in multimolecular layers. J Am Chem Soc 1938; 60: 309-19. Sprynskyy M, Ligor T, Lebedynets M, Buszewski B. Kinetic and equilibrium studies of phenol adsorption by natural and modified forms of the clinoptilolite. J Hazard Mater 2009; 169(1-3): 847-54. Ming DW, Dixon JB. Quantitative-determination of clinoptilolite in soils by a cationexchange capacity method. Clays Clay Miner 1987; 35(6): 463-8. Ranck JM, Bowman RS, Weeber JL, Katz LE, Sullivan EJ. BTEX removal from produced water using surfactant-modified zeolite. Journal of Environmental Engineering 2005; 131(3): 434-42. Simpson JA, Bowman RS. Nonequilibrium sorption and transport of volatile petroleum hydrocarbons in surfactant-modified zeolite. J Contam Hydrol 2009; 108(1-2): 1-11.

Zeolites Modified with Organic Agents

[60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79]

Handbook of Natural Zeolites 183

Zhang PF, Tao X, Li ZH, Bowman RS. Enhanced perchloroethylene reduction in column systems using surfactant-modified zeolite/zero-valent iron pellets. Environ Sci Technol 2002; 36(16): 3597-603. Armagan B, Ozdemir O, Turan M, Celik MS. Adsorption of negatively charged azo dyes onto surfactant-modified sepiolite. Journal of Environmental Engineering 2003; 129(8): 709-15. Kamble SP, Mangrulkar PA, Ansiwal AKB, Rayalu SS. Adsorption of phenol and ochlorophenol on surface altered fly ash based molecular sieves. Chem Eng J 2008; 138(13): 73-83. Dong Y, Wu DY, Chen XC, Lin Y. Adsorption of bisphenol A from water by surfactantmodified zeolite. J Colloid Interface Sci 2010; 348(2): 585-90. Scherer MM, Richter S, Valentine RL, Alvarez PJJ. Chemistry and microbiology of permeable reactive barriers for in situ groundwater clean up. Crit Rev Microbiol 2000; 26(4): 221-64. Kovalick WW. LEAP Permeable Barrier Demonstration Facility, Portland, OR. Washington, DC: United States Environmental Protection Agency1999. Sullivan EJ, Bowman RS, Legiec IA. Sorption of arsenic from soil-washing leachate by surfactant-modified zeolite. J Environ Qual 2003; 32(6): 2387-91. Li Z, Beachner R, McManama Z, Hanlic H. Sorption of arsenic by surfactant-modified zeolite and kaolinite. Microporous Mesoporous Mater 2007; 105(3): 291-7. Li ZH. Influence of solution pH and ionic strength on chromate uptake by surfactantmodified zeolite. Journal of Environmental Engineering 2004; 130(2): 205-8. Li ZH, Anghel I, Bowman RS. Sorption of oxyanions by surfactant-modified zeolite. J Dispers Sci Technol 1998; 19(6-7): 843-57. Zeng YB, Woo H, Lee G, Park J. Removal of chromate from water using surfactant modified Pohang clinoptilolite and Haruna chabazite. Desalination 2010; 257(1-3): 102-9. Matijasevic S, Dakovic A, Tomasevic-Canovic M, Stojanovic M, Iles D. Uranium(VI) adsorption on surfactant modified heulandite/clinoptilolite rich tuff. J Serb Chem Soc 2006; 71(12): 1323-31. Dakovic A, Tomasevic-Canovic M, Rottinghaus G, Dondur V, Masic Z. Adsorption of ochratoxin A on octadecyldimethyl benzyl ammonium exchanged-clinoptilolite-heulandite tuff. Colloids and Surfaces B-Biointerfaces 2003; 30(1-2): 157-65. Gottardi G, Galli G. Natural zeolites. Berlin; New York: Springer-Verlag 1985. Matsumoto A, Tsutsumi K, Schumacher K, Unger KK. Surface functionalization and stabilization of mesoporous silica spheres by silanization and their adsorption characteristics. Langmuir 2002; 18(10): 4014-9. Plueddemann E. Silane Coupling Agents. 2 ed. New York: Plenum. Pub. Corp. 1991. Flinn DH, Guzonas DA, Yoon RH. Characterization of silica surfaces hydrophobized by octadecyltrichlorosilane. Colloids and Surfaces A-Physicochemical and Engineering Aspects 1994; 87(3): 163-76. Vrancken KC, Possemiers K, Vandervoort P, Vansant EF. Suface modification of silicagels with aminoorganosilanes. Colloids and Surfaces A-Physicochemical and Engineering Aspects 1995; 98(3): 235-41. Mahajan R, Koros WJ. Mixed matrix membrane materials with glassy polymers. Part 1. Polym Eng Sci 2002; 42(7): 1420-31. Duval JM, Kemperman AJB, Folkers B, et al. Preparation of zeolite filled glassy polymer membranes. J Appl Polym Sci 1994; 54(4): 409-18.

184 Handbook of Natural Zeolites

[80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92]

Mumford et al.

Liu YL, Su YH, Lee KR, Lai JY. Crosslinked organic-inorganic hybrid chitosan membranes for pervaporation dehydration of isopropanol-water mixtures with a long-term stability. J Membr Sci 2005; 251(1-2): 233-8. De Hulsters P, Vansant EF. NH4- exchange- A sensitive method for the characterization of structurally modified zeolites. Journal of the Chemical Society-Faraday Transactions 1990; 86(3): 585-9. Huang M, Adnot A, Kaliaguine S. Silylation of H-ZSM-5 - An X-ray photoelectron and Infrared-Spectroscopy study. Journal of the Chemical Society-Faraday Transactions 1993; 89(23): 4231-7. Kawai T, Tsutsumi K. Reactivity of silanol groups on zeolite surfaces. Colloid Polym Sci 1998; 276(11): 992-8. Kuwahara Y, Kamegawa T, Mori K, Matsumura Y, Yamashita H. Fabrication of Hydrophobic Zeolites Using Triethoxyfluorosilane and their Application for Photocatalytic Degradation of Acetaldehyde. Top Catal 2009; 52(6-7): 643-8. Northcott KA, Bacus J, Taya N, et al. Synthesis and characterization of hydrophobic zeolite for the treatment of hydrocarbon contaminated groundwater. J Hazard Mater 2010; 183: 434-40. Zhang HY, Kim Y, Dutta PK. Controlled release of paraquat from surface-modified zeolite Y. Microporous Mesoporous Mater 2006; 88(1-3): 312-8. Meininghaus CKW, Prins R. Sorption of volatile organic compounds on hydrophobic zeolites. Microporous Mesoporous Mater 2000; 35-6: 349-65. Giaya A, Thompson RW, Denkewicz R. Liquid and vapor phase adsorption of chlorinated volatile organic compounds on hydrophobic molecular sieves. Microporous Mesoporous Mater 2000; 40(1-3): 205-18. Tsai WT, Hsu HC, Su TY, Lin KY, Lin CM. Adsorption characteristics of bisphenol-A in aqueous solutions onto hydrophobic zeolite. J Colloid Interface Sci 2006; 299(2): 513-9. Erdem-Senatalar A, Bergendahl JA, Giaya A, Thompson RW. Adsorption of methyl tertiary butyl ether on hydrophobic molecular sieves. Environ Eng Sci 2004; 21(6): 722-9. Singh R, Dutta PK. Use of surface-modified zeolite Y for extraction of metal ions from aqueous to organic phase. Microporous Mesoporous Mater 1999; 32(1-2): 29-35. Yan YG, Vansant EF. Disilane-modified mordenite zeolites. J Phys Chem 1990; 94(6): 2582-6.

Handbook of Natural Zeolites, 2012, 185-213

185

CHAPTER 9c Modified Zeolites: Modification of Natural Zeolites for Catalytic Applications Claudia Cobzaru* Technical University ”Gh. Asachi” Iasi, Faculty of Chemical Engineering and Environmental Protection, D. Mangeron Ave, 71, 70050, Romania Abstract: Zeolites have been recognized for more than 200 years, but only during the middle of the 20th century have attracted the attention of scientists and engineers who demonstrated their technological importance in several fields. Although most of the effort was devoted to synthetic zeolites, in recent years increasing attention has been directed towards natural zeolites, whose status changed from that of museum curiosity to an important mineral commodity. Natural zeolites forming the corresponding group of tectosilicate mineral subclass, due to their specific crystal chemical characteristics providing the unique ion exchange and molecular sieve properties, are known as effective adsorbents and catalysts. The zeolites are highly rigid under dehydration as well as under various aggressive surroundings actions. The molecular sieving and other physico-chemical properties of the zeolites can be managed by the thermal or chemical treatment. Such features provide the effective and wide utilization of these materials in industry, agriculture, medicine, environmental protection and other fields. Synthesized analogues of the natural zeolites are usually applied in different technological processes, and the low output price conditioned by a subsurface location of massive deposits of natural zeolites throughout the world make them significantly more available for a wide utilization. Main fields of industrially important zeolite rocks are presented by clinoptilolite (or mordenite, chabazite, phillipsite, etc.) tuffs and are connected with volcanic formations.

Keywords: Natural zeolites, volcanic tuffs, clinoptilolite (natural) zeolite, ion exchange, dealumination, physical (thermal) activation, thermal activation, chemical treatments, biological treatments, catalytic applications, catalytic processes, adsorption process, heterogeneous catalysis, mineral acids, C-C bonds, acetaldehyde, formaldehyde, aldol condensation, acrolein, crotonaldehyde. INTRODUCTION The present commercial interest to the natural zeolites has no precedent, as proved by the continuously increasing amounts of the minerals mined every year [1]. Their use is quite advantageous since they do not involve laborious synthetic procedures being readily synthesized in the composition of various types of rocks. The rocks fall into three types in function of the main processes leading to the 

Address correspondence to Claudia Cobzaru: Technical University “Gh. Asachi” Iasi, Faculty of Chemical Engineering and Environmental Protection, D. Mangeron Ave, 71, 70050, Romania; Tel: +40 232 278 683/2211; Fax: +40 232 271 311; E-mails: [email protected] and [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

186 Handbook of Natural Zeolites

Claudia Cobzaru

formation of the mineral aggregates, namely magma, sedimentary and metamorphous types. Among them the volcanic tuffs belonging to the magma type are the most valuable deposits of natural zeolites. For this reason in many studies the name of the host sedimentary rock is mentioned namely “volcanic tuffs” or “zeolitic tuffs” [2-16]. The volcanic tuff consists of different minerals such as: clinoptilolite, mordenite, chabazite, phillipsite, quartz, cristobalite, feldspar, montmorillonite and volcanic glass [17]. According to their porous structure these minerals are arranged in several classes, namely micro-, meso- and macroporous of diameters ranging from a few to 75, 000 Å, accessible to large molecules, viruses and even bacteria [18, 19]. Hundreds of thousands tonnes of volcanic tuff are mined in many countries like the United States, Germany, Italy, Japan, Bulgaria, Mexico, etc. but only those containing rather high amounts of zeolites, such as chabazite, clinoptilolite, erionite, ferrierite, phillipsite, mordenite and analcime are taken into account as exploitable natural resources [20]. The potential of these rocks in various activity fields is discussed in several previous papers which demonstrated that the obtained performances are highly dependent on both the chemical and structural properties of zeolite (ion exchange and adsorption capacities, high content of microelements, micro-porosity, acidbasic or redox properties of the surface, etc.) and the conditions of the treatment they are subjected. The agriculture [21-25], purification of the waste waters [2635], medicine [36-41], separation of gases [42-44] and catalysis [45-50] can be cited among the most important application fields. The studies performed on the zeolitic volcanic tuffs destined to the important practical applications have shown that they can be activated [51]. The activation of the zeolitic volcanic tuffs takes in view the procedures of modification, improvement and making evident the physical and chemical properties. For example, for the most applications based on the adsorbing properties of the zeolites, apart from the selection of the proper material type the natural material has to be processed for the necessary granular size and subjected then to the physical (thermal) activation and to the modification of its structure or composition (chemical treatments). In this connection, Vansant [52] has presented

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 187

the beneficial effects of zeolite activation or modification. Although the chemical treatments are usually enough for improving the properties of the zeolites an especial attention is also paid to the biological treatments. PHYSICAL (THERMAL) ACTIVATION The process of physical or thermal activation is performed by heating the grains of zeolitic volcanic tuff at a temperature below its vitrification temperature. Above this limit the zeolite pores close and the adsorption-desorption and ion exchange capacities are canceled. This process is particularly important since by heating the zeolitic water is removed, the pores and cavities are liberated and the zeolites can adsorb water or other molecules. From the chemical point of view the zeolites are known to differ in their content of cations and SiO2/Al2O3 mole ratio. Ions of larger radius, respectively a higher coordination number (Na+, K+, Ca2+, Ba2+), and rarely cations of smaller size, with hexagonal coordination (Mg2+, Zn2+, Fe3+) are placed usually in the vacancies of the crystalline framework. Since the cations in the crystalline framework vacancies occupy only a small part of their space the greatest part of this volume is filled with water molecules. The water content of zeolites is determined by their own volume characteristic of a certain zeolitic structure accessible for water molecules as well as by the number and size of the cations in these vacancies. In the zeolitic structure the water molecules behave as they would be in a viscous solution exchanging the place at a frequency of the 107s-1 order and since they do not occupy all the available positions they can be removed reversibly and gradually with no destruction of the crystalline framework. The zeolitic water content can vary without damaging their crystalline homogeneity, modifying gradually the physical properties namely: transparency degree, refractive index and specific weight [53]. By a gradual heating of the zeolitic material in view of its activation the dehydration was found to show several maxima at different temperatures which affords the conclusion that the process is not linear. Thus, three maximum temperatures of the dehydration process were settled, namely: below 100oC, between 100-350oC and at 410520oC. For example, the tuff dehydrated at temperatures not higher than 100oC has adsorbed only polar molecules of gases, that activated above 100oC has

188 Handbook of Natural Zeolites

Claudia Cobzaru

retained also non-polar molecules, the adsorption being maximum with the sample activated between 350-520oC. The mordenitic tuff dried at 400oC can retain about 11.2% water referring to the dry tuff mass, compared cu 5.1% retained by the same tuff activated at 70oC only [51]. Gottardi et al., [54] noticed that, the dehydration of a clinoptilolite tuff is complete and reversible at 250oC, while Passaglia et al., [55] found that the water is further released attaining an elimination percentage of 80% at 400oC. The fact was also noticed that the calcination of the zeolitic material at 350-500oC caused the physically adsorbed water to be firstly eliminated followed by the zeolitic water, the endothermic effect being maximum at 210oC. On the other hand, the water loss from clinoptilolite was found still to proceed at 700oC with no significant structural modifications, followed by the partial vitrification and alteration of the zeolitic structure at 850oC which resulted in a strong diminution of specific area and volume of the micropores [51]. In this connection, Esenli and Kumbasar [56] have studied the behavior of the natural zeolite in Western Anatolia. The Differential Thermal Analysis (DTA) measurements made evident two peaks at 120oC and 750oC attributable to the water loss and to the destruction of the zeolite framework, respectively. The Thermal Gravimetric Analysis (TGA) measurements have also revealed a total amount of water losses of 14.5% below 800°C. Investigations on the thermal stability of clinoptilolite as its ammonium form at 773 K resulted in making evident the development of the framework dealumination at T≥673 K apart from dehydration and deammoniation [57]. Arcoya et al., [58] applied the X-ray diffraction (XRD) analysis to study the thermal stability of clinoptilolite calcined at 600, 700 and 800°C at a heating rate of 5°C/min. The authors reported that XRD pattern of the natural material shows high crystallinity with characteristic peaks evident at 2θ values of 9.92, 22.43 and 30.50°. Moreover, at 600°C a partial collapse of zeolite structure was noticed. Mimura and Kanno [59] noticed also that the mordenite and clinoptilolite collaps by thermal treatment at 900oC. The fact deserves also mention that, several physical and chemical transformations of zeolite can simultaneously proceed during thermal treatment such as: volatilization of water in the system and the dealumination of zeolite structure, melting of product that has lower melting point and entrapment of gaseous products, etc.

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 189

In function of their chemical nature the natural zeolites can contain different Si/Al ratios even they are coming from the same deposit. In Table 1 the Si/Al ratios corresponding to the most important natural zeolites along with some significant structural characteristics are given [42]. Table 1: Structural characteristics of the most important natural zeolites Natural Zeolite

Si/Al

Major Cations

Kinetic Pore Diameter, nm

Max.H2O Total Pore Capacity, Kg/Kg Volume, %

Chabazite

1.5-4.0

Na, Ca, K

0.43

0.28

48

Clinoptilolite

4.0-5.2

Na, Ca, K

0.35

0.14

34

Erionite

3.0-4.0

Na, K, Ca

0.43

0.20

36

Ferrierite

4.3-6.2

K, Mg, Na

0.39

0.12

24

Mordenite

4.4-5.5

Ca, Na

0.39

0.15

26

Phillipsite

1.3-3.4

K, Ca, Na

0.26

0.22

30

According to literature data the natural zeolites in Table 1 show a higher thermal stability and a better resistance to the acid treatment than many common synthetic adsorbents [60-62]. The thermal stability of zeolites containing cations of alkaline elements and high Si/Al ratios shows an increasing tendency of their thermal stability. For instance, the phillipsite as its Na+ and K+ forms and a high silicium content is stable at 725 K while the Ca2+ form with a low silicium content is degraded at temperatures lower than 575K [63, 64]. These observations lead to the conclusion that the behavior differences of the natural zeolites under thermal treatment are caused by their chemical composition, the Si/Al ratio in the framework and the types of cations in the channels [65-69]. Catalytic Processes with Natural Zeolites Thermally Activated Due to its high thermal stability given by the framework high silicium content and the presence of the univalent cations (Na+, K+) in the channels (Table 1) the natural clinoptilolite is constantly used in catalytic processes, the nitrogen separation from the methane among them [58]. In this process the dehydrated clinoptilolite shows high selectivities and the efficiency is correlated with its activation temperature. Another significant process is the α-pinene isomerization where Akpolat et al., [70] have tested the catalytic properties of the clinoptilolite calcined at various temperatures: 300, 450 and 600oC. The catalytic activity of the

190 Handbook of Natural Zeolites

Claudia Cobzaru

clinoptilolite thermally treated was noticed to decrease with increasing calcination temperature. The natural zeolites can also be activated prior to the ion exchange process or acid treatment. This is the case with the natural clinoptilolite used for reducing the toxic components in noxious gases evolved by the combustion engines. Firstly, it is thermally activated at 270oC and then subjected to chemical modification [71]. On the other hand, the natural zeolites may be firstly chemically modified and then thermally activated. In this connection, for catalytic dehydrogenation of propane Katranas et al., [72] have prepared a proton form of clinoptilolite beginning with its ion exchange with an ammonium salt solution followed by calcination, washing and a final thermal treatment at 500oC under helium atmosphere. Sejidov et al., [73] have performed the process of phthalic anhydride esterification with 2-ethylhexanol by means of a natural clinoptilolite treated firstly with a 60% H2SO4 solution and calcined subsequently at 450-500oC. Lee et al., [74] used a natural zeolite exchanged with ammonium ions, dried at 110oC and calcined finally at 400oC for achieving the catalytic degradation of polystyrene. Many other such examples are to be found in scientific literature. Modification of Structure or Composition of Natural Zeolites (Chemical Treatments) The structure or composition of natural zeolites can be modified by a great deal of procedures applied in accordance with their application domains. Among the applied procedures the dealumination, ion exchange, adsorption, introduction of amines, introduction of surfactant cations, modification by isomorphous substitution deserve mention. Dealumination The catalytical properties of zeolites are strongly dependent on the Si/Al ratio in their composition. As a rule every aluminium atom is a potential Brønsted or Lewis acid site. The decrease in the aluminium content of a zeolite composition results in the obtaining of a zeolitic material of significantly improved properties compared to the starting material [75]. Zeolites of different Si/Al ratios can be obtained either directly by synthesis (synthetic zeolites) or by post-synthesis processing as in case of the natural zeolites. Dealumination of natural zeolites has

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 191

been achieved by chemical, hydrothermal (steaming), thermal and combined (hydro) thermal and chemical methods [76]. The Chemical Method or Treating with Mineral Acids This method results in the elimination of the cations and impurities from the zeolite channels and their replacement by the hydrogen proton of a smaller diameter. Besides, the volume of the vacancies in channels and cavities increase and so does the adsorption capacity. The most zeolites are destroied by acid treatment excepting for those of high SiO2 content, such as mordenite and clinoptilolite. Barrer and Makki [77] were the first who made evident that the dealumination of the natural zeolite framework can be performed with no structure damage and the clinoptilolite can be dealuminated by hydrogen chloride treatment. The concentration of the acid solution, temperature and the process duration of the zeolitic material treating are the factors affecting the dealumination process. The ion exchange capacity shows a decreasing tendency while the SiO2/Al2O3 increases with increasing acid concentration and treatment duration. Apart from this, the specific area increases with increasing temperature of the treating mixture and with increasing duration of the zeolite treating at the normal temperature [51]. The dealumination of natural zeolites by their treating with mineral acids is studied in many publications in scientific literature [78-84]. These studies reveal that during the treatment applied to cationic zeolites the decationization (ion exchange between zeolite cations and H3O+ ions in the acid solution) also takes place simultaneously with dealumination. Besides, a high acid concentration (≥1 M) is required for removing 30% of the aluminium total amount in the clinoptilolite framework which could result in a significant crystallinity reduction. During the dealumination process the aluminium atoms extracted from the zeolite framework are converted into some extra-framework species that cause the blocking of the zeolite pores [85, 86]. These species can generally be removed by zeolite treating with a leaching acid. Moreno and Poncelet [87] pointed out the dealumination process applied to zeolites to be more efficient when it consists of two calcination treatments followed by an acid leaching one. The acidul leaching

192 Handbook of Natural Zeolites

Claudia Cobzaru

treatment followed by the calcination stage results in the dissolution of the extraframework aluminium species. Garcia-Basabe et al., [88] have advanced a new strategy on the dealumination of zeolites leading to amounts of extracted aluminium significantly higher than described in previous papers [79, 80, 89-92]. Moreover, the effect on the zeolite crystallinity and the amount of extra-framework aluminium species retained in the pores are negligible. The acid treatment of small-pore zeolites affords the removal of impurities blocking the pores, the gradual elimination of cations and finally their structure dealumination [61, 93, 94]. The dealumination process is influenced by its duration. Thus, the specific area and porous volume of clinoptilolite increases proportionally to the duration of the acid treatment [62, 75]. Instead, the alkaline treatment on the same natural zeolite causes a modification of both pore size and volume while the treatment with neutral compounds was suggested for reducing irreversibly the adsorption [42, 95]. Dapaah et al., [96] mentioned that the treatment with an ammonium salt solution (NH4Cl and [NH4]2SO4) determines a higher catalytic activity due to the increased concentration of the strong Brønsted acid sites. Furthermore, they have advanced a possible mechanism for generating the Brønsted and Lewis active sites on the surface of a zeolite exchanged with an ammonium salt and then calcined (Fig. 1). O

O Si

Na+ -

O

O

O

Si

Si

Al

Na+ -

O

O Si

Al

O O O O O O O O O O O O ion exchange +NH4+ O

O Si

NH4+ NH4+ O O - O O O Si Si Al Si Al

H+ ion exchange

O O O O O O O O O O O O calcination - NH3 O

O Si

H+ -

Al

O

O

O Si

Si

H+ -

Al

O

O Si

O O O O O O O O O O O O Brønsted

- H2O calcination

O

O Si

Al

+

Si

O

+

Si

O

-

Al

O

O Si

O O O O O O O O O O O O Lewis

Figure 1: A possible mechanism for the formation of Brønsted and Lewis acid sites on the surface of a zeolite exchanged with an ammonium salt and then calcined.

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 193

The authors started from the idea that the ammonium ion is released by calcinations from the surface of the protonated zeolites and for this reason the Brønsted acid sites are generated in/on the pore surface. According to literature data, the deammoniation of clinoptilolite as its ammonium form is achieved at 400oC when a protonated zeolite is formed and the dehydroxylation made at the same temperature affords the formation of Lewis active sites, when two Brønsted active sites are canceled per every occurred Lewis active site [96, 97]. Sonnemans et al., [98] have also confirmed that both the dehydroxylation and dealumination of mordenite cause losses of Brønsted active sites as well as a structure degradation simultaneously with occurence of Lewis acid sites. Treating with Water Vapour at High Temperatures The natural zeolites can also be subjected to the water vapor (steam) treatment at high temperatures. The studies made in this sense showed that the water vapor treatment on mordenite at 500oC for about 2 hours can cause probably its dealumination [99]. In this connection, Haag et al., [100] proved that the dealumination of zeolite structure can be achieved with a quite low vapor concentration (0.66%) for 2.5 hours at 538oC. Hong et al., [101] have confirmed that the mordenite can significantly be dealuminated in very short time when treated with a vapor concentration of 2.6% at 500oC. As regards the dealumination mechanism, Chen and Smith [102] and Haas et al., [103] have assumed the vapor to determine the migration of extra-framework aluminium species within the zeolite microporous framework. Miller et al., [104] have found the same proving that the crystallinity differences are simply connected with the great mobility of the Al species. In the presence of steam and heat these species can be located within the zeolite pores. But, Kuhl [105] advances the following mechanism of the dealumination process (Fig. 2). According to this mechanism a silicium cation carrying a positive charge occurs by dehydroxylation of two hydroxy groups at high temperatures. At the same time an extra-framework aluminium complex is formed. The zeolite framework is recovered by the formation of a new -Si-O-Si- bond. The catalytic performances of natural zeolites modified by hydrothermal treatment are dependent on certain factors such as temperature, solution concentration, etc. Thus, Kang et al., [106,

194 Handbook of Natural Zeolites

Claudia Cobzaru

107] have observed that the clinoptilolite modification by hydrothermal treatment with 2M NaOH for 16 hours at 103oC is dependent on the reaction conditions. Watanabe et al., [108] have also applied the hydrothermal treatment to clinoptilolite and mordenite by 0.1, 0.3, 1.0, 3.0 M NaOH solutions at temperatures between 25-150oC for 7 days. These authors have also noticed that the modifications induced in these zeolites depend on the reaction conditions, namely: temperature of the hydrothermal process, the NaOH solution concentration and the material composition. The hydrothermal treatment of the natural zeolites was proved to be an efficient method for obtaining materials utilizable for retaining metallic ions. Thus, by a hydrothermal treatment with NaOH at 100-105oC an increase in the ion exchange capacity of clinoptilolite for the Zn2+ and Cr3+ ions was obtained [51]. Also, Komarneni and Roy [109, 110] have examined the thermal and hydrothermal treatment of zeolitic tuffs for fixation of ion-exchanged 137Cs and Sr2+. They found that after the applied treatments the phillipsite was the best natural zeolite for the exchange and fixation of 137Cs due to its high selectivity and exchange capacity for this ion. H

H Si

Si

Al Si

Si

Al

Si

-H2O

+ Si

Si

Al Si

Si

Si

Al

Si

Si

Si

Al

Si

Si

AlO + Si

Si

Si

Figure 2: Dealumination mechanism advanced by Kuhl.

Thermal Method The Lewis active sites can also occur by the transformation of the Brønsted active sites by thermal treatment. The fact is known that the calcination of zeolites as their ammonium form at temperatures lower than 300oC results in generation of Brønsted acid sites. At temperatures exceeding 500oC a dehydroxylation process

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 195

develops and two Brønsted sites generate one acid site and one basic site of the Lewis type (Fig. 3). NH4 O

O

O Si

Al O

H

+

O O

O

O 2NH3 + 2 Al O

O

O Si

O O

-H2O

O

O O

- O Al

O Si

O O Lewis acid

O Al

+ O

O

+ Si

O O Lewis base

O O

Figure 3: Conversion of acid sites by calcination [111].

If the structure is reorganized and the aluminium ion leaves the framework the negative charge is counter-balanced by the adjacent aluminium ion (AlO+). Regarding the thermal treatment, Komarneni [112] suggests that the 137Cs ion in the tuff of high phillipsite content can easily be immobilized by the formation of crystalline cesium aluminosilicates by heating in air or under hydrothermal conditions. The experimental results were indicative of phillipsite as an ideal material for cesium immobilization when treated thermally at low temperature subsequently to its use as an adsorbent for water purification. Jeethendra Kumar et al., [113] have studied the behavior of heulandite from Pashan (India) toward the thermal treatment. The authors noticed that the structure is firstly transformed into some intermediary metastable phases at temperatures between 250-400°C begining then to degrade at 500oC. Altamirano et al., [114] have also noticed that chabazite and mordenite are less structurally affected than heulandite, stilbite, phillipsite and clinoptilolite by thermal treatment. Chemical and Thermal Combined Method In practice, in most cases the chemical and thermal methods are combined in order to obtain a zeolitic material with properties suitable for the desired purpose. Numerous examples can be mentioned. Mimura şi Kanno [59] have studied the ion exchange capacity of mordenite and clinoptilolite for 137Cs by treating the native tuffs firstly with an ammonia solution followed by a thermal treatment at 350-500oC. In this way they obtained the acid form of the zeolitic materials. Horváthová [115] has shown that the ion exchange capacity of clinoptilolite increases by 15% after the ion exchange with Na+ ions and by 30% after an acid treatment followed by heating treatments.

196 Handbook of Natural Zeolites

Claudia Cobzaru

Elimination of aluminum molecules by thermal and chemical treatment could change the pore size distribution and the hydrophilic or hydrophobic affinity and the zeolite can acquire special adsorption characteristics. A clinoptilolitic tuff treated previously with ammonia, calcined and then treated with acid was turned into an active adsorbent of nitrogen oxides [51]. The combined chemical and thermal treatments did not result in a visible modification of the adsorption isothermal curve shape at 400oC. On the contrary, at the temperature of 900oC the partial destruction of the micropore framework and the development of mesopores have happened. Furhermore, by the chemical and thermal treatment the specific area of the tuff increased about 2.5 times and the SiO2/Al2O3 was modified. The alkaline treatments followed by drying and thermal treatments were found to modify the tuff ion exchange capacity affecting insignificantly the chemical composition [51]. Thus, Boveri et al., [116] have studied the influence of the acid and hydrothermal treatment on the mordenite structure and its acidic properties as well as the behavior in the synthesis process of linear alkylbenzenes. A comparison of the material subjected to the combined treatment with the parent material or with that subjected to acid treatment made evident significant changes in the zeolite microporous surface accompanied by a dramatic increase in the intrinsic activity and significant decrease in the deactivating rate. Catalytic Processes with Dealuminated Natural Zeolites The natural zeolites dealuminated by one of the above mentioned methods can be used in chemical processes as revealed by numerous sudies on the subject. Thus, the mordenitic tuff was proved to separate efficiently CH4 from CO after being treated chemically with a 1N HCl solution followed by heating at 273oC [51]. Aritsuka and Iwanaga [117] have advanced a method for eliminating nitrogen oxide, nitrogen dioxide and dinitrogen difluoride from nitrogen trifluoride by making use of some natural zeolites treated thermally at temperatures between 250-700oC, namely: analcime, clinoptilolite, mordenite, ferrierite, phillipsite, chabazite, erionite and laumotite. Hernández et al., [118] have applied a gascromatography technique to measure the adsorption isotherms of the chloroorganic compounds on clinoptilolite dealuminated by an acid treatment and Aliyev et al., [119] have studied the activity of dealuminated clinoptilolite and its

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 197

H form in the esterification process of acetic acid with ethylic alcohol. Yeniova et al., [120] have studied the isomerization, disproportionation and hydrocracking of a 1,2,3, trimethylbenzene/n-decan mixture by means of dealuminated clinoptilolite and another one exchanged as its ammonium form. They noticed the highest conversion (40%) and selectivity of isomerization with the dealuminated clinoptilolite. Kim et al., [121] have tested the catalytic activity of dealuminated clinoptilolite with the process of polypropilene degradation and noticed that the dealumination causes an increase in the medium acid sites and microporous diameter which influenced the catalytic process. Ünveren et al., [122] have investigated the α-pinene isomerization with clinoptilolite treated with hydrogen chloride of various concentrations for 3-24 hours. They noticed the acid treatment to result in increased catalyst selectivity to camphene formation along with decrease selectivity to limonene. Apart from this the number and distribution of the Lewis and Brønsted sites affect the formation of the monocyclic and dicyclic compounds. Lee et al., [123] have investigated the catalytic performances of the clinoptilolite dealuminated by a boric acid treatment in the process of isomerization of n-butene to isobutene. They found the main effect of the acid treatment to consist in the increasing in the acid sites of medium strength with no collapse of the zeolite structure. These sites of a medium strength are regarded as selective and stable sites for isomerization of n-butene to isobutene. Hutchings et al., [124] have studied the catalytic properties of the clinoptilolite dealuminated by treating with hydrogen chloride in the methanol conversion to hydrocarbons. The catalyst life time was found to be rather short, of about 2-3 hours, due to the high rate of the coke formation. The volcanic tuff dealuminated by acid treatment can also be used as a catalyst in the aldol condensation of acetaldehyde with formaldehyde at low temperatures (250oC). In this case the amount of resulting acrolein is higher with a catalyst dealuminated for a longer time (10 h) than with the crude catalyst [45]. Ion Exchange The Lewis acid sites on zeolites can also be generated by ion exchange with polyvalent cations which can act as such sites, due to their capacity of accepting

198 Handbook of Natural Zeolites

Claudia Cobzaru

the electronic pair. This is true under the conditions of a zeolite complete dehydration (T>500oC), although the case is a rather seldom encountered since some zeolites are not stable at higher temperatures (Fig. 4) [111]. [M2+(2Zeol-)(H2O)n]hidrat.

[(2 Zeol-)M2+]complete dehidrat.

Figure 4: Complete dehydration of a zeolite.

Three aspects are important with ion exchange applications [125]:  Kinetics of ion exchange consisting in the making evident the evolution in time of the migration of the exchange ion to the site or the replacement of the initial cations in the structure. The migration of the exchange ion proceeds in the stationary film around the particle whose thickness decreases while stirring. The cation diffuses through this film, through pores and channels to the places of the internal cations where the exchange happens and the replaced cation folows the reverse line [126]. The ion exchange rate is influenced by the zeolite grain size and temperature. Thus, the small particles assure a higher diffusion rate through pores (on the shorter line along the channels) than the large particles. Since the placement of cations inside zeolites is not rigid the ion exchange may develop into one or several stages.  Ion exchange capacity is expressed by the number of cation milliequivalents (meq) per zeolite gram. This is a function of the Si/Al mole ratio, structure type and cationic form of zeolites [127]. The ion exchange capacity of zeolites is dependent on the substitution degree of the Si atom by Al in zeolite structure. The higher substitution degree the higher framework charge is and the number of cations required for compensation increases. The ion exchange capacity can be affected by the following factors: pH number; temperature; nature and concentration of cations; solvent nature and presence of complexon ions [128].  Selectivity for certain cations. The selectivity is an essential factor since it influences upon the potential technical applications in various

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 199

activity fields (agriculture, industry, medicine, etc.). The selectivity to certain cations means the preference order of zeolites to cations based on the cationic radius and hydration energies. The selectivity is dependent on the following factors: geometry of the zeolite framework; charge density in the zeolite framework; number and shape of the involved cations and valency and concentration of cation in aqueous phase [129]. In Table 2 the series of ionic selectivity for various natural zeolites are presented. Table 2: Series of ionic selectivity for some natural zeolites [125] Zeolite

Si/Al

Cations of Exchange

Sites of Exchange

Selectivity Order

clinoptilolite

2.7-5.3

Na+, Ca2+, K+

channels

NH4>Cs+>K+>Sr2+>Ba2+>Ca2+>Na+ Pb2+>Ag+>Cd2+ >Zn2+>Cu2+>Na+

chabazite

1.4-2.8

K+, Ca2+

cavities

Ti4+>Cs+>K+>Ag+>Rb+>NH+4>Pb2+ Na+= Ba2+>Sr2+>Ca2+>Li+

phillipsite

1.3-2.9

Na+, Ca2+, K+

channels

Ba2+>Rb+>Cs+>K+ >Na+ >Li+

channels

Cs+>K+>NH+4>Na+>Ba2+>Li+ NH+4>Na+>Mn2+>Cu2+>Zn2+>Ni2+

mordenite

4.4-5.5

+

Na , Ca

2+

The cations at the beginning of the series can substitute the following ones till attaining the equilibrium between the two phases. A crucial problem with the selectivity of zeolites arises usually when several cations are to be changed. Studies made on phillipsite regarding the retaining of the pair of Cs+- Sr2+ ions from the waste water made evident that this natural zeolite is not selective for the cation pair. This was due to the selectivity for the exchanging ion dependent on the strength of the anionic field in zeolites. Thus, due to the low strength of the field the silicious zeolites are selective for the large cations such as Cs+ of a low charge density while the aluminious zeolites are much more selective for the cations of a high charge density such as Sr2+ [130, 131]. Cataytic Processes with Natural Zeolites Modified by Ion Exchange The most ion exchange applications of natural zeolites are destined to purification of drinking water and waste water. Several other chemical processes are also catalyzed by zeolites modified by ion exchange.

200 Handbook of Natural Zeolites

Claudia Cobzaru

The hydrocracking is one of the processes performed with natural zeolites. In this process the C5-C9 paraffins are adsorbed selectively suffering then hydrocracking at the temperature of 525-700 K and pressure of 1.36-13.6 MPa. The natural zeolites used as catalysts were the erionite as its Ni2+ form obtained by ion exchange or impregnation, an erionite-clinoptilolite mixture and mordenite as its Pt4+ form [132]. Moreno-Tost et al., [133] have studied the catalytic reduction of NO by means of natural zeolites (mordenite and clinoptilolite) obtained as Zn2+ and Ag+ forms by ion exchange process. The authors found that the two transitional metals slightly improved the catalytic performances of the material taken in this process. The zeolites as their Zn2+ form show satisfactory catalytic activity attaining NO conversions of 58% and a high selectivity to N2 at high temperatures. MorenoTost et al., [134] have also performed another study on the catalytic reduction of NO by using mordenite and clinoptilolite exchanged in the Cu2+ form. The authors have noticed that the zeolites exchanged in the Cu2+ form are very active affording NO conversions of 95%, a high selectivity to N2 and showing a good tolerance to water. Choo et al., [135] have tested the catalytic activity and selectivity of clinoptilolite exchanged as the Ni2+ form in the ethylene dimerization process. The performances of the natural catalyst were found to depend on the reaction temperature, the type of the formed cocations and the amount of the Ni2+ ions incorporated within the extra-framework sites. For example, a higher amount of the Ni2+ ions incorporated into such sites of clinoptilolite determines an increase in the n-butene amount formed. Lee et al., [136] have investigated the isomerization of 1-butene to isobutene on the clinoptilolite exchanged in the Co2+ and Ba2+ forms. They proved that the natural zeolite as the Co2+ form shows a higher selectivity to isobutene compared to that attained with the native material while with the Ba2+ form the activity is high and selectivity to isobutene very low. Onyestyák and Kalló [137] have obtained a clinoptilolite as the Cd2+ form both by an ion exchange process in liquid phase and by the contact of a cadmium solid salt with the zeolite in the ammonium form at about 300oC. These catalysts were tested in the reaction of acetylene hydration and the natural zeolite prepared by

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 201

ion exchange in liquid phase was noticed to be much more active. The authors found that the activity of the natural zeolite prepared by ion exchange in liquid phase was significantly lower than that of the zeolite prepared by the contact with the solid cadmium salt. Aykaç and Yilmaz [138] have studied the hydrogenation of citral in liquid phase on monometallic nickel and bimetallic Ni-Sn catalysts on mordenite as Na+ form and clinoptilolite as supports. They noticed the type of zeolitic support to affect the catalyst activity and selectivity. Yilmaz et al., [139] have investigated the process of citral hydogenation in liquid phase with paladium on clinoptilolite as a support under various reaction conditions. The zeolite support was found not to affect the properties of the active metal, the catalytic activity being influenced by the reaction temperature. Moreover, the selectivity to citronelal increased from 78% to 90% with increasing catalyst amount. Natural Zeolites Used in the Adsorption Process The natural zeolites can also be used as adsorbents in various domains. According to literature data these materials can act as proper adsorbents for various polar and non-polar molecules such as: CO2, SO2, NO2, NO, H2S, NH3, H2O, aliphatic and aromatic hydrocarbons, alcohols, ketons and other similar molecules [140-142]. The first studies on zeolites used as adsorbents in certain processes were reported as far back as 1938 when Barrer published some information on the properties and characteristics of zeolites [127]. In order to make better evident the adsorption capacity of natural zeolites they were modified by various methods. Thus several researchers reported in their studies the significance of using modified zeolites for removing the undesirable ions from the waste water by adsorption process [143-145]. The adsorption technique was applied at the industrial level to purification of the waste water containing noxious organics [146]. The adsorption process was also applied to removing of dyes from the waste water in the textile industry [147-149]. Asilian et al., [150] have studied the process of ammonia elimination from air by using the clinoptilolite. The authors concluded that this natural material can be an efficient adsorbent for the ammonia in air. Mačala and Pandová [71] have noticed that the clinoptilolite modified thermally and by ion exchange can be used for reducing by adsorption the

202 Handbook of Natural Zeolites

Claudia Cobzaru

nitrogen monoxide in noxious gases released by the combustion engines. Moreover, the adsorption capacity increases very much by chemical treatment, the clinoptilolite exchanged with ammonium chloride and cobalt chloride showing a high ability for reducing the nitrogen monoxide content in noxious gases. Faghihian and Pirouzi [151] have investigated the catalytic properties of the native and modified (as Na+, K+, Ca2+ and Mg2+ forms) clinoptilolite in the adsorption process of cis-trans-2 butenes. The authors noticed these catalysts to have a good potential for the separation of the two hydrocarbons. Zeolites Modified by Amine Introduction in Zeolite Structure The natural zeolites may also be modified by the introduction of functional group in their structure [152]. A type of treatment applied to natural zeolites for adsorbing chlorinated hydrocarbons (trichloro-ethylene, dichloro-ethane, dichloro-ethylene, chloroform, etc.) consists in introducing the methylamine chloride in cationic positions of the structure [153]. By this treatment the adsorption capacity of the zeolitic material increases by 35-40% which would indicate the organic cations to be able to be linked by electrostatic actions. As regards the uses of zeolites modified with amines in various chemical processes Gebremedhin-Haile et al., [154] have studied the adsorption capacity of the natural zeolites modified with cysteamine toward metallic ions, mercury among them. They noticed that the introduction of cysteamine in the clinoptilolite structure results in the increase in the adsorption capacity toward the mercury ion. Wingenfelder et al., [155] have investigated the adsorption of Cd2+ and Pb2+ on the clinoptilolite modified with cysteamine or propylamine. They found that the higher amount of the retained amine the lower amounts of adsorbed Cd2+ and Pb2+ are. The Zeolites Modified by the Introduction of Cationic Surfactants The natural zeolites may also be modified by introducing cationic surfactants in their structure. Due to their large specific area and negative structural charge the zeolites can be modified by introducing cationic surfactants in their structure such as: hexadecyl-trimethylammonium (HDTMA) [156], octadecyl-trimethylammonium [157], cetyl-pyridinium [158] and 4-methylpyridinium [159]. The amount of the cationic surfactants retained by zeolites is controlled by both exchanged cation and

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 203

hydrophobic interactions [160]. The ion exchange process between the cationic surfactants and cations such as Na+, K+, Ca2+, Mg2+ on the external surface of zeolite can balance its negative charge [156]. The zeolites modified with cationic surfactants were used for removing the phosphate ions from the waste water [158, 161]. In this case the zeolite modified with cetylpyridinium chloride was noticed to be able to remove the phosphate ion as much as 90% and the process is influenced by several factors: surfactant and phosphate ion concentrations, contact time and the initial pH value. Apart from this, the unmodified zeolites and those modified with HDTMA were studied for removing the Sr2+ ion from the waste water [161]. The obtained results made evident the amount of retained Sr2+ of 75meq/kg on the unmodified zeolite and 15meq/kg on the modified one. For the sake of comparison with the Sr2+ ions the amounts of Pb2+ retained on the unmodified zeolite and on that modified with HDTMA were about the same. Moreover, Matijašević et al., [162] pointed out that both clinoptilolite and heulandite modified by the introduction of surfactants in their structures could be used for removing the uranium ion from the soil and waste water. Nikashina and Myasoedov [163] have investigated the potential of the modified clinoptilolite for Escherichia Coli retaining from the drinking water. The natural zeolite was modified with polyhexamethylene guanidine chloride followed by combination with epichlorhydrin resulting finally an organo-zeolite named clinotsid. The authors concluded that Escherichia Coli can be taken out 100% from the drinking water by this modified zeolite. Bowman [164] has also studied the Escherichia Coli removing from water by means of clinoptilolite modified with hexadecyl-trimethylammonium (HDTMA). The obtained results indicated that Escherichia Coli can completely be extracted by the modified zeolite. Regarding the catalytic processes, Faghihian and Mousazadeh [165] have investigated the catalytic properties of the clinoptilolite exchanged with hexadecyl-trimethylammonium for removing the polycyclic aromatic hydrocarbons from n-paraffins. They found that this natural material modified with the surfactant can remove as much as 50% of the polycyclic aromatic hydrocarbons from paraffins.

204 Handbook of Natural Zeolites

Claudia Cobzaru

The Zeolites Modified by the Isomorphous Substitution The natural zeolites can also be modified by the isomorphous substitution method. Thus, Cerjan Stefanovic et al., [166] have modified a group of zeolites by substituting phosphorous ions for the aluminium in their structure regarding this modification as suitable for using the modified natural materials for adsorbing the anions from the waste water. Hossein and Mohammad Hadi [167] have also studied the properties of the clinoptilolite modified by isomorphous substitution with P5+ ions and noticed that the zeolite framework is thus affected the negative charge being turned into positive charge. The exchange capacity of the natural material toward this ion was noticed to be high which makes it proper for removing the NO3-, NO2- and F- ions from waste water. Biological Treatments (Activation) The volcanic tuffs can be “impregnated” with nutritive media and “inoculated” with bacterial population or fungus mycelia, then used in various purposes particularly the purification of waste water. The inoculation with nitrifying bacteria accelerates the transformation process of the organic material accumulated into the bio-filters containing zeolitic materials in comparison with the natural process developing with more difficulty. Keeping the granular volcanic tuff in the pre-treated waste water (especially in the compartments of tertiary biological purification) results in the loading of the zeolitic filtering mass with residual organics and minerals as well as with the newly formed biogenic material. This material can periodically be collected, dried in the sunshine and ground. The resulting flower contains both the characteristic mineral components as well as nutrients which makes it proper for being used as a fodder additive. In this case the zeolitic material is twofold used, namely for purification and as fodder material the first achieving also an activation for the second [51]. In this connection, Hrenovič et al., [168] have studied the adsorption capacity of clinoptilolite modified by biological treatment toward the phosphorous ion in waste water and have pointed out that the material resulting after adsorption could be a good fertilizer.

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 205

ACKNOWLEDGEMENTS None declared. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

Scott PW, Bristow CM. Industrial Minerals and Extractive Industry Geology. London: Published by Geological Society 2002; pp 17-41. Flint LE, Selker JS. Use of porosity to estimate hydraulic properties of volcanic tuffs. Advances in Water Res 2003; 26 (5): 561-571. Capasso S, Salvestrini S, Coppola E, et al. Sorption of humic acid on zeolitic tuff: a preliminary investigation. Appl Clay Sci 2005; 28(1-4): 159-165. Gutiérrez-Segura E, Solache-Ríos M, Colín-Cruz A. Sorption of indigo carmine by a Fezeolitic tuff and carbonaceous material from pyrolyzed sewage sludge. J Hazard Mater 2009; 170(2-3): 1227-1235. Díaz-Nava C, Olguín MT, Solache-Ríos M, et al. Phenol sorption on surfactant-modified Mexican zeolitic-rich tuff in batch and continuous systems. J Hazard Mater 2009; 167(1-3): 1063-1069. Mustafa F, Al-Ghouti MA, Khalili FI, et al. Characteristics of organosulphur compounds adsorption onto Jordanian zeolitic tuff from diesel fuel. J Hazard Mater 2010; 182 (1-3): 97-107. Capasso S, Coppola E, Iovino P, et al. Sorption of humic acids on zeolitic tuffs. Microp Mesop Mater 2007; 105(3): 324-328. Daković A, Kragović M, Rottinghaus GE, et al. Influence of natural zeolitic tuff and organozeolites surface charge on sorption of ionizable fumonisin B1. Colloid Surf Biointerf 2010; 76(1): 272-278. Krestou A, Xenidis A, Panias D. Mechanism of aqueous uranium (VI) uptake by natural zeolitic tuff. Miner Eng 2003; 16(12):1363-1370. Trgo M, Perić J. Interaction of the zeolitic tuff with Zn-containing simulated pollutant solutions. J. Colloid Interf Sci 2003; 260 (1): 166-175. Dávila-Jiménez MM, Elizalde-González MP, Mattusch J, et al. In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions. J Colloid Interf Sci 2008; 322(2): 527-536. Can Ö, Balköse D, Ülkü S. Batch and column studies on heavy metal removal using a local zeolitic tuff. Desalination 2010; 259(1-3): 17-21. Trgo M, Perić J, Vukojević Medvidović N. Investigations of different kinetic models for zinc ions uptake by a natural zeolitic tuff. J Environ Management 2006; 79(3): 298-304. Rajic N, Stojakovic D, Jevtic S, et al. Removal of aqueous manganese using the natural zeolitic tuff from the Vranjska Banja deposit in Serbia. J Hazard Mater 2009; 172(2-3): 1450-1457.

206 Handbook of Natural Zeolites

[15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

Claudia Cobzaru

García-Mendieta A, Solache-Ríos M, Olguín MT. Evaluation of the sorption properties of a Mexican clinoptilolite-rich tuff for iron, manganese and iron–manganese systems. Microp Mesop Mater 2009; 118(1-3): 489-495. Marañón E, Ulmanu M, Fernández Y, et al. Removal of ammonium from aqueous solutions with volcanic tuff. J Hazard Mater 2006; 137(3): 1402-1409. Gottardi G, Galli E. Natural Zeolites. Berlin: Springer 1985; pp 409-415. Kalló D. Natürliche Zeolithe-Herkunft und Wirkungsmechanismen. Abwassertechnik 1992; 43(2): 40-43. Papp J. Einsatzmöglichkeiten von Zeolith in der Abwassertechnik. Abwassertechnik 1992; 43(2):44-47. Kesraououki S, Cheeseman C, Perry R. Effects of conditioning and treatment of chabazite and clinoptilolite prior to lead and cadmium removal. Environ Sci Technol 1993; (27): 1108-1116. Spedding CRW. Zeo-agriculture: Use of natural zeolites in agriculture and aquaculture: In: Wilson GP, Mumpton FA, Eds. The role of natural zeolites in agriculture and aquaculture. Colorado: Westview Press 1984; pp.285-290. Colella C. Natural zeolites in environmentally friendly processes and applications. Stud Surf Sci Catal 1999; (125): 641-655. Li Z. Use of surfactant-modified zeolite as fertilizer carriers to control nitrate release. Microp Mesop Mat 2003; 61(1-3): 181-188. Rehákova M, Čuvanová S, Dzivák M. et al. Agricultural and agrochemical uses of natural zeolites of the clinoptilolite type. Current Opinion Solid State Mater Sci 2004; 8(6): 397404. Colella C. Natural Zeolites. Stud Surf Sci. Catal 2005; (157): 13-40. Sarioglu M. Removal of ammonium from municipal wastewater using natural Turkish (Dogantepe) zeolite. Sep Purif Techn 2005; 41(1): 1-11. Panayotova MI. Kinetics and thermodynamics of copper ions removal from wastewater by use of zeolite. Waste Manag 2001; 21(7): 671-676. Wang S, Peng Y. Natural zeolites as effective adsorbents in water and wastewater treatment. J Chem Eng 2010; 156(1): 11-24. Ozdemir O, Turan M, Zahid Turan A, et al. Feasibility analysis of color removal from textile dyeing wastewater in a fixed-bed column system by surfactant-modified zeolite (SMZ). J Hazard Mater 2009; 166(2-3): 647-654. Meteš A, Kovačevič D, Vujevič D, et al. The role of zeolites in wastewater treatment of printing inks. Water Res 2004; 38(14-15): 3373-3381. Wang S, Zhu Z.H. Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution. J Hazard Mater 2006; 136(3): 946-952 Rosa-Gómez I, Olguín MT, Alcántara D. Antibacterial behavior of silver-modified clinoptilolite–heulandite rich tuff on coliform microorganisms from wastewater in a column system. J Environ Manag 2008; 88(4): 853-863. Widiastuti N, Wu H, Ang M, et al. The potential application of natural zeolite for greywater treatment Desalination 2008; 218(1-3): 271-280. Englert AH, Rubio J. Characterization and environmental application of a Chilean natural zeolite. Intern. J Min Proc 2005; 75(1-2): 21-29. Al-Anber M, Al-Anber ZA. Utilization of natural zeolite as ion-exchange and sorbent material in the removal of iron. Desalination 2008; 225(1-3): 70-81.

Modification of Natural Zeolites for Catalytic Applications

[36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55]

Handbook of Natural Zeolites 207

Cerri G, De'Gennaro M, Bonferoni MC, et al. Zeolites in biomedical application: Znexchanged clinoptilolite-rich rock as active carrier for antibiotics in anti-acne topical therapy. Appl Clay Sci 2004; 27(3-4): 141-150. Bonferoni MC, Cerri G, De'Gennaro M, et al. Zn2+-exchanged clinoptilolite-rich rock as active carrier for antibiotics in anti-acne topical therapy: In vitro characterization and preliminary formulation studies. Appl Clay Sci 2007; 36(1-3): 95-102. Colarte I. Antacid drug based on purified natural clinoptilolite. Microp Mesopor Mater 2006; 94(1-3): 200-207. Grce M, Pavelić K. Antiviral properties of clinoptilolite. Microp Mesopor Mater 2005; 79(1-3): 165-169. Izmirova N, Aleksiev B, Djourova E, et al. Clinoptilolite and the possibilities for its application in medicine. In: Galarneau A, Di Renzo F, Fajula F, et al. Eds. Studies in Surface Science and Catalysis vol. 135. Amsterdam: Elsevier 2001; pp. 8-15. Poljak Blazi M, Katic M, Kralj M, et al. In vitro and in vivo effect of natural clinoptilolite on malignant tumors. In: Galarneau A, Di Renzo F, Fajula F, et al. Eds. Studies in Surface Science and Catalysis vol. 135. Amsterdam: Elsevier 2001; pp. 374-380. Ackley MW, Rege SU, Saxena H. Application of natural zeolites in the purification and separation of gases. Microp Mesop Mater 2003; 61(1-3): 25-42. Ackley MW, Giese RF, Yang RT. Clinoptilolite: Untapped potential for kinetics gas separations. Zeolites 1992; 12(7): 780-788. Jayaraman A, Hernandez-Maldonado AJ, Yang RT, et al. Clinoptilolites for nitrogen/methane separation. Chem Eng Sci 2004; 59(12): 2407-2417. Cobzaru C, Oprea S, Dumitriu E, et al. Gas phase aldol condensation of lower aldehydes over clinoptilolite rich natural zeolites. Appl Catal Gen 2008; 351(2): 253-258. Stöcker M. Gas phase catalysis by zeolites. Microp Mesop Mater 2005; 82(3): 257-292. Mishima H, Hashmoto K, Ono T, et al. Selective catalytic reduction of NO with NH3 over natural zeolites and its application to stationary diesel engine exhaust. Appl Catal Environ 1998; 19(2): 119-126. Moreno-Tost R, Santamaría-González J, Rodríguez-Castellón E, et al. Selective catalytic reduction of nitric oxide by ammonia over Cu-exchanged Cuban natural zeolites. Appl Catal Environ 2004; 50(4): 279-288. Yilmaz S, Ucar S, Artok L, et al. The kinetics of citral hydrogenation over Pd supported on clinoptilolite rich natural zeolite. Appl Catal Gen 2005; 287(2): 261-266. Onyestyák Gy, Pál-Borbély G, Kalló D. Acetylene hydration on different Cd-zeolites. Stud Surf Sci. Catal 2004; 154(3): 2831-2838. Barbat A, Marton A. The zeolitic volcanic tuffs. Cluj Napoca: Dacia Publishing House 1989; pp. 67-80. Vansant EF. Pore Size Engineering in Zeolite. New York: J. Wiley & Sons Chichester 1990; pp. 15-45 Cruceanu M, Popovici E, Bilba N, et al. Zeolite Molecular Sieves. Bucharest: Ştiintif Enciclop Publishing House 1986; pp. 41-80. Gottardi G. Mineralogy and crystal chemistry of zeolites. In: Sand LB, Mumpton FA, Eds. Natural zeolites. New York: Pergamon 1978; pp.31-44. Passaglia E, Galli E, Leonardo L, et al. The crystal chemistry of stilbites and stellerites. Bullet Minér 1978; (101): 368-375.

208 Handbook of Natural Zeolites

[56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77]

Claudia Cobzaru

Esenli F, Kumbasar I, Thermal Behavior of Heulandites and Clinoptilolites of Western Anatolia. Zeolit Relat Microp Mater 1994; (84): 645-651. Tomazović B, Ćeranić T, Sijarić G. The properties of the NH4-clinoptilolite Part 2. Zeolites 1996; (16): 309-312. Arcoya A, Gonzalez JA, Label G, Seona XL, et al. Role of the counterions on the molecular sieve properties of a clinoptilolite. Microp Mater 1996; (7): 1-13. Mimura H, Kanno T. Processing of radioactive waste solution with zeolites (I). Thermaltransformations of Na, Cs and Sr forms of zeolites. Sci Rept Res Inst 1980; (29): 102-111. Zarchy AS, Correia R, Chao CC. Process for the adsorption of hydrogen sulfide with clinoptilolite molecular sieves. US Patent 5164076, 1992. Vaughan DEW. Properties of natural zeolites. In: Sand LB, Mumpton FA, Eds. Natural Zeolites: Occurrence, Properties, Use Oxford: Pergamon Press 1978; pp. 353-371. Ogawa H, Ito Y, Nakano M, et al. Method for adsorbing and removing ethylene and method for purifying an exhaust gas. US Patent 6309616, 2001. Tsitsishvili GV, Andronikashvili TG, Kirov GN, et al. Natural Zeolites, New York: Ellis Horwood 1992; pp. 40-47. Mumson RA. Properties of Natural Zeolites. Report of Investigations No.: 7744, Washington: US Bur Mines 1973. Alietti A. Polymorphism and crystal-chemistry of heulandites and clinoptilolites. Amer Mineral 1972; (57): 1448-1462. Boles JR. Compositions, optical properties, cell dimensions and thermal stability of some heulandite group zeolites. Amer Mineral 1972; (57): 1463-1493. Mason B, Sand LB. Clinoptilolite from Patagonia. The relationship between clinoptilolite and heulandite. Amer Miner 1960; (45): 341-350. Mumpton FA. Clinoptilolite redefined. Amer Miner 1960; (45):351-369. Alietti A, Brigatti MF, Poppi L. Natural Ca-rich clinoptilolites (heulandites of group 3): New data and review. N Jb Miner Mh 1977; (11): 493-501. Akpolat O, Gündüz G, Ozkan F, et al. Isomerization of α-pinene over calcined natural zeolites, Appl Catal Gen 2004; (265): 11-22. Mačala J, Pandová I. Natural zeolite-clinoptilolite-raw material serviceable in the reduction of toxical components at combustion engines noxious gases. Gospodarka Surow Miner 2007; 23(4): 19-26. Katranas TK, Vlessidis AG, Tsiatouras VA, et al. Dehydrogenation of propane over natural clinoptilolite zeolites. Microp Mesop Mater 2003; (61): 189-198. Sejidov FT, Mansoori Z, Goodarzi N. Esterification reaction using solid heterogeneous acid catalysts under solvent-less condition. J Molec Catal Chem 2005; (240): 186-190. Lee SY, Yoon JH, Kim JR, et al. Catalytic degradation of polystyrene over natural clinoptilolite zeolite. Polym Degrad Stab 2001; (74): 297-305. Dumitriu E, Cobzaru C, Hulea V, et al. Dealuminated Natural Zeolites for Aplications in Catalytic Processes with Formation of C-C Bonds. 1. Modification of the Natural Clinoptilolite by Dealumination. Rev Chim Buc 2009; 60(3): 297-300. Chen NY, Degnan TF. Industrial catalytic applications of zeolites. Chem Eng Prog 1988; (84): 32-41. Barrer RM, Makki MB. Molecular Sieve Sorbents from Clinoptilolite. Canadian J Chem 1964; (42): 1481-1487.

Modification of Natural Zeolites for Catalytic Applications

[78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95]

Handbook of Natural Zeolites 209

Christidis GE, Moraetis D, Keheyan E, et al. Chemical and thermal modification of natural HEU-type zeolitic materials from Armenia, Georgia and Greece. Appl Clay Sci 2003; (24): 79-91. Radosavljević-Mihajlović A, Dondur VT, Daković A, et al. Physicochemical and structural characteristics of HEU-type zeolitic tuff treated by hydrochloric acid. J Serb Chem Soc 2004; (69): 273-282. Cakicioglu-Ozkan F, Ulku S. The effect of HCl treatment on water vapor adsorption characteristics of clinoptilolite rich natural zeolite. Micropor Mesopor Mater 2005; (77): 47-53. Misaelides P, Godelitsas A, Link F, et al. Application of the 27Al (p,y)28Si nuclear reaction to the characterization of the near-surface layers of acid-treated HEU-type zeolite crystals. Micropor Mater 1996; 6(1): 37-42. Arcoya A, González JG, Travieso N, et al. Physicochemical and catalytic properties of a modified natural clinoptilolite. Clay Miner 1994; 29 (1): 123-131. Rožić M, Cerjan-Stefanović Š, Kurajica S, et al. Decationization and dealumination of clinoptilolite tuff and ammonium exchange on acid-modified tuff. J Colloid Interf Sci 2005; (284): 48-56. Jiao J. Quantitative Characterization of Aluminum in Non-hydrated Zeolite Catalysts by Multi-nuclear Solid-state NMR Spectroscopy. Ph D Thesis. Institut für Technische Chemie Der Universität Stuttgart 2006. Sawa M, Niwa M, Murakami Y. Change of Pore-opening Structure of Mordenite upon Dealumination by Hydrochloric Acid. Zeolites 1992; (12): 175-179. Hong Y, Fripiat JJ. Microporous Characteristics of H-Y, H-ZSM-5 and H-mordenite dealuminated by calcinations. Microp Mater 1995; (4): 323-334. Moreno S, Poncelet G. Dealumination of small-and large-port mordenites: a comparative study. Microp Mater 1997; (12): 197-222. Garcia-Basabe Y, Iznaga IR, De Menorval LC, et al. Step-wise dealumination of natural clinoptilolite: Structural and physicochemical characterization. Micropor Mesop Mater 2010; 135 (1-3): 187-196. Hernández MA, Rojas F, Lara VH. Nitrogen-Sorption Characterization of the Microporous Structure of Clinoptilolite-Type Zeolites. J Porous Mater 2000; 7(4): 443-454. Elizalde-González MP, Pérez-Cruz MA. Interaction between organic vapors and clinoptilolite–mordenite rich tuffs in parent, decationized, and lead exchanged forms. J Colloid Interf Sci 2007; 312 (2): 317-325. Kouvelos E, Kesore K, Steriotis T, et al. High pressure N2/CH4 adsorption measurements in clinoptilolites. Microp Mesopor Mater 2007; 99 (1-2): 106-111. Vasylechko VO, Gryshchouk GV, Kuzma YB, et al. Adsorption of cadmium on acidmodified Transcarpathian clinoptilolite. Micropor Mesopor.Mater 2003; 60 (1-3): 183-196. Mihaila G, Barbu HC, Lutic D, et al. Adsorption of sulphur dioxide on clinoptilolite volcanic tuff. In: Kirov G, Filizova L, Petrov O, Eds. Natural Zeolites: Proceedings of the Sofia Zeolite Meeting’95. Sofia-Moskow: Pensoft 1997; pp.146-153. Tsitsishvili GV. Adsorption and catalytic properties of Borne soviet natural zeolites. In: Sand LB, Mumpton FA, Eds. Natural Zeolites: Occurrence, Properties, Use, Oxford: Pergamon Press 1978; pp. 397-401. Peterson DL, Helfferich F, Blytas GC. Sorption and ion exchange in sedimentary zeolites. J Phys Chem Solid 1965; 26(5): 835-848.

210 Handbook of Natural Zeolites

[96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116]

Claudia Cobzaru

Dapaah JKA, Andalaluna L, Kobayashi T, et al. Enhancement of Catalytic Activity of Natural Zeolites by Surface Modification for 1-Butene Izomerization. Mem Muroran Inst Tech 1997; (47): 89-95. Detrekoy EJ, Jacobs PA, Kallo D, et al. The nature of catalytic activity of hydroxyl groups in clinoptilolite. J Catal 1974; (32): 442-451. Sonnemans MHW, Den Heijer C, Crocker M. Studies on the Acidity of Mordenite and ZSM-5. 2. Loss of Bronsted Acidity by Dehydroxylation and Dealumination. J Phys Chem 1993; (97): 440-447. Hutchings GJ, Burrows A, Rhodes C, et al. Dealumination of mordenite catalysts using a low concentration of steam. J Chem Soc Faraday Trans 1997; 93(19): 3593-3598. Haag WO, Lago RM. Enhancement of zeolite catalytic activity. US Patent 4326994, 1982. Hong Y, Gruver V, Fripiat JJ. Role of Lewis acidity in the isomerization of n-pentane and o-xylene on dealuminated H-mordenites. J Catal 1994; (150): 421-429. Chen NY, Smith FA. Preparation of Dealuminized Mordenite. Inorg Chem 1976; 15(2): 295-297. Haas J, Fetting F, Plog C, et al. Influence of the hydrothermal treatment on the catalytic behavior of mordenite and on the aluminum distribution in the crystallite. Appl Catal 1987; 35(2): 311-320. Miller JT, Hopkins PD, Meyers BL, et al. The Effect of Non-Framework Aluminum on Acidity in Dealuminated Mordenites. J Catal 1992; 138(1): 115-28. Kuhl GH. The coordination of aluminum and silicon zeolites as studied by x-ray spectrometry. J. Phys. Chem. Solid 1977; (38): 1259-1263. Kang SJ, Egashira K. Modification of different grades of Korean natural zeolites for increasing cation exchange capacity. Appl Clay Sci 1997; (12): 131-144. Kang SJ, Egashira K, Yoshida A. Transformation of a low-grade Korean natural zeolite to high cation exchanger by hydrothermal reaction with or without fusion with sodium hydroxide. Appl Clay Sci 1998; (13): 117-135. Watanabe Y, Yamada H, Tanaka J, et al. Hydrothermal modification of natural zeolites to improve uptake of ammonium ions. J Chem Techn Biotech 2005; (80): 376-380. Komarneni S, Roy R. Zeolites for fixation of cesium and strontium from radwastes by thermal and hydrothermal treatments. Nucl Chem Waste Management 1981; (2): 259-264. Komarneni S, Roy R. Alternative radwaste solidification route for Three Mile Island wastes. J Amer Ceram Soc Communic 1982; (65): 190-198. Barrer RM, Kerr IS. Intracrystalline channels in levynite and some related zeolites. Trans Faraday Soc 1959; (55): 1915-1923. Komarneni S. Phillipsite in Cs Decontamination and Immobilization Clays. Clay Miner 1985; 33(2): 145-151. Jeethendra Kumar PK, Mohan Rao P, Setty DLR. Thermal behaviour of natural heulandite crystals. Cryst. Res. Techn 1989; 24(10): 1027-1033. Altamirano M, Johnson K, Karlsson HR, et al. A study of Natural Zeolite outgassing by simultaneous thermal analysis/quadrupole mass spectrometry. Geolog Soc Amer 2007; 39 (3): 60-68. Horváthová E. Ionselektiver Austausch an slowakischem Klinoptilolith-Tuffit. Acta Hydrochim Hydrobiol 1986; 14(6): 495-502. Boveri M, Márquez-Álvarez C, Laborde MÁ, et al. Steam and acid dealumination of Mordenite. Characterization and influence on the catalytic performance in linear alkybenzene synthesis. Catal Today 2006; (114): 217-225.

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 211

[117] Aritsuka M, Iwanaga N. Method for purifying nitrogen trifluoride gas. US Patent 4933158, 1990. [118] Hernández MA, Gonzalez AI, Rojas F, et al. Adsorption of chlorinated compounds (chlorobenzene, chloroform, and carbon tetrachloride) on microporous SiO2, Ag-doped SiO2 and natural and dealuminated clinoptilolites. Ind Eng Chem Res 2007; 46 (10): 33733381. [119] Aliyev AM, Sarijanov EE, Tunç Savaşçi Ö, et al. Selection of an active zeolite catalyst and kinetics of vapor phase esterification of acetic acid with ethyl alcohol, Stud Surf Sci Catal 2002; (142): 787-794. [120] Yeniova H, Karaduman A, Alibeyli R. Isomerization, disproportionation and hydrocracking of 1,3,5-trimethylbenzene and n-decane mixture over natural clinoptilolite zeolites. Petrol Sci Techn 2007; 25 (3): 387-398. [121] Kim JR, Kim YA, Yoon JH, et al. Catalytic degradation of polypropylene: Effect of dealumination of clinoptilolite catalyst. Polym Degrad Stab 2002; 75 (2): 287-294. [122] Ünveren E, Günüz G, Cakicioǧlu-Özkan F. Isomerization of alpha-pinene over acid treated natural zeolite. Chem Eng Commun 2005; 192 (1-3): 386-404. [123] Lee HC, Woo HC, Ryoo R, et al. Skeletal isomerization of n-butenes to isobutene over acid-treated natural clinoptilolite zeolites, Appl Catal Gen 2000; 196 (1): 135-142. [124] Hutchings GJ, Themistocleous T, Copperthwaite RG. Methanol conversion to hydrocarbons using modified clinoptilolite catalysts: Investigation of catalyst lifetime and reactivation. Appl Catal 1988; 43 (1): 133-140. [125] Post MFM. Diffusion in Zeolite Molecular Sieves. In: Van Bekkum H, Flanigen EM, Jansen CJ, Eds. Studies in Surface Science and Catalysis. Amsterdam: Elsevier 1991; pp. 388:391. [126] Szostak R. Molecular Sieves-Priciples of synthesis and identification. NewYork: Van Nostrand Reinhold 1989; pp. 51-59. [127] Barrer RM. Zeolites and Clay Minerals as Sorbents and Molecular Sieves. London: Academic Press 1978; pp. 141-148. [128] Barrer RM, Galabova IM. Advances in Chemistry. American Chem Soc 1973; (121): 356361. [129] Kesraoui-ouki S, Cheeseman CR, Perry R. Natural zeolite utilisation in pollution control: A review of applications to metals' effluents. J Chem Tech Biotech 1994; (59): 121-126. [130] Post MFM. Introduction to Zeolite Science and Practice. Amsterdam: Elsevier 1991; pp. 392-401. [131] Ruthven DM. Principles of Adsorption & Adsorption Processes. New York: John Wiley 1984; pp. 498-505. [132] Oudejans JC. Zeolite Catalysts in some organic reactions, PhD dissertation. Delft University of Technology 1984. [133] Moreno-Tost R, Santamaría-González J, Rodríguez-Castellón E, et al. Selective catalytic reduction of nitric oxide by ammonia over Ag and Zn-exchanged Cuban natural zeolites, Zeitsch Anorg Allgem Chem 2005; 631 (11): 2253-2257. [134] Moreno-Tost R, Santamaría-González J, Rodríguez-Castellón E, et al. Selective catalytic reduction of nitric oxide by ammonia over Cu-exchanged Cuban natural zeolites. Appl Catal Environ 2004; 50 (4): 279-288. [135] Choo H, Kevan L. Catalytic Study of Ethylene Dimerization on Ni (II)-Exchanged Clinoptilolite. J Phys Chem 2001; 105 (27): 6353-6360.

212 Handbook of Natural Zeolites

Claudia Cobzaru

[136] Lee HC, Woo HC, Chung SH, et al. Effects of metal cation on the skeletal isomerization of 1-butene over clinoptilolite. J Catal 2002; 211 (1): 216-225. [137] Onyestyák G, Kalló D. Catalytic behavior of Cd-clinoptilolite prepared by introduction of cadmium metal onto cationic sites, Stud Surf Sci Catal 2002; (142): 1047-1054. [138] Aykaç H, Yilmaz S. Hydrogenation of citral over Ni and Ni-Sn catalysts, Turk J Chem 2008; 32 (5): 623-633. [139] Yilmaz S, Ucar S, Artok L, et al. The kinetics of citral hydrogenation over Pd supported on clinoptilolite rich natural zeolite, Appl Catal Gen 2005; 287(2): 261-266. [140] Malherbe R, Fernandes L, Colado L. Phsico-chemical properties of natural zeolites used for adsorption of water. Int Comm Nat Zeolit 1995: 199-207. [141] Malherbe R, Fernandez L, Lopez L, et al. Natural zeolites. In 93 conference volume international committee on natural zeolite, NewYork: Brockport 1995; pp. 299-308. [142] Malherbe R. Complementary approach to the volume filling theory of adsorption in zeolites, Microp Mesop Mater 2000; 41(1): 227-240. [143] Englert HA, Rubio J. Characterization and environmental application of a Chilean natural zeolite. Inter J Miner Proces 2005; 75(1-2): 21-29. [144] Oliveira CR, Rubio J. Adsorption of ions onto treated natural zeolite. Mater Res 2007; 10(4): 407-412. [145] Oliveira CR. Rubio J. New basis for adsorption of ionic pollutants onto modified zeolites. Mater Eng 2007; 20(6): 552-558. [146] McKay G. Use of adsorbents for the removal of polutants from wastewaters. Boca Raton: CRC Press 1996; pp. 2-3. [147] Chang WS, Hong SW, Park J. Effect of zeolite media for the treatment of textile wastewater in a biological aerated filter. Proc Bioch 2002; (27): 693-698. [148] Armağan B, Turan M, Çelik MS. Equilibrium studies on the adsorption of reactive azo dyes into zeolite. Desalination 2004; (170): 33-39. [149] Benkli YE, Can MF, Turan M, et al. Modification of organo-zeolite surface for the removal of reactive azo dyes in fixed-bed reactors. Water Res 2005; (39): 487-493. [150] Asilian H, Mortazavi SB, Kazemian H, et al. Removal of Ammonia from Air using Three Iranian Natural Zeolites, Iran. JPubl Health 2004; 33(1): 45-51. [151] Faghihian H, Pirouzi M. Cis/trans-but-2-ene adsorption on natural and modified clinoptilolite, Clay Minerals 2009; 44(3): 405-409. [152] Luna JF. Modificação de zeólitas para uso em catálise. Revi Quim Nova 2001; 24(6): 885892. [153] Rustamov SM, Bashirova YY, Nasiri FM, et al. Use of zeolites for purification wastewaters from toxic organic chlorine compounds. In: Kalló D, Sherry HS, Eds. Occurrence, Properties and Utilisation of Natural Zeolites, Budapest: Press 1988; pp. 521-528. [154] Gebremedhin-Haile T, Olguín MT, Solache-Ríos M. Removal of mercury ions from mixed aqueous metal solution by natural and modified zeolitic materials. Water Air Soil Pollut 2003; (148): 179-200. [155] Wingenfelder U, Nowack B, Furrer G, et al. Adsorption of Pb and Cd by amine-modified zeolite. Water Res 2005; (39): 3287-3297. [156] Haggerty GM, Bowman RS. Sorption of inorganic anions by organo-zeolites. Environ Sci Technol 1994; 28(3): 452-458.

Modification of Natural Zeolites for Catalytic Applications

Handbook of Natural Zeolites 213

[157] Schulze-Makuch D, Pillai SD, Guan H, et al. Surfactant modified zeolite can protect drinking water wells from viruses and bacteria. EOS, Trans Amer Geoph Union 2002; 83(18): 193-201. [158] Nunez YR. Removal of Phosphates from Water using Tailored Zeolites. PhD Thesis. University of Puerto Rico, 1998. [159] Bowman RS, Haggerty GM, Huddleston RG, et al. Sorption of nonpolar organics, inorganic cations, and inorganic anions by surfactant-modified zeolites. In: Sabatini DA, Knox RC, Harwell JH. Eds. Surfactant-enhanced remediation of subsurface contamination. ACS Symposium Series 594. Washington, DC: American Chemical Society 1995; pp.5464. [160] Li Z. Use of surfactant-modified zeolite as fertilizer carriers to control nitrate release. Microp Mesop Mater 2003; 61(1-3): 181-188. [161] Bowman RS, Sullivan EJ, Li G. Uptake of cations, anions and nonpolar organic molecules by surfactant-modified clinoptilolite-rich tuff. In: Colella C, Mumpton FA, Eds. Natural Zeolites for the Third Millennium. Napoli. Italy: De Frede Editore 2000; pp. 341-347. [162] Matijašević S, Daković A, Tomašević-Čanovič M, et al. Uranium (VI) adsorption on surfactant modified heulandite/clinoptilolite rich tuff. J Serb Chem Soc 2006; 71(2): 13231331. [163] Nikashina VA, Myaosedov BF. Environmental applications of modified natural zeolites. In: Misaelides P, Ed. Natural Microporous Materials in Environmental Technology, Netherlands: Kluwer Academic Publisher 1999; pp. 335-343. [164] Bowman RS. Applications of surfactant-modified zeolites to environmental remediation. Micropor Mesopor Mater 2003; 61(1-3): 43-56. [165] Faghihian H, Mousazadeh MH. Removal of PAHs from n-Paraffin by Modified Clinoptilolite. Iran J Chem Eng 2007; 26(3): 121-127. [166] Cerjan Stefanovic S, Kastelan Macam M, Filipan T. Ion Exchange Characterization of Modified Zeolite. Watt Sci Tech 1992; 26(9): 22-69. [167] Hossein F, Mohammad Hadi M. Isomorphous Substitution of P(V) in Natural Clinoptilolite: Evalution of the Product for Removal of NO3-, NO2- and F- from Aqueous Solutions. Iran J Chem Eng 2008; 27(4): 115-118. [168] Hrenović J, Büyükgüngör H, Orhan Y. Use of Zeolite to Upgrade Activated Sludge, Food Technol. Biotechnol 2003; 41(2): 157-165.

Part III: RECENT DEVELOPMENTS, CURRENT RESEARCH EDGE AND FIELDS

214

Handbook of Natural Zeolites, 2012, 214-237

CHAPTER 10 Environmental Application of Natural Zeolites Hossein Kazemian* Senior Researcher, Department of Chemical and Biochemical Engineering, Faculty of Engineering, Western University, London, Ontario, Canada N6A 5B9 Abstract: Currently, there is a rapidly emerging crisis involving the access of clean drinking water due to the increasing release of various pollutants by industries to the environment. Industrial wastewater streams contain a wide range of pollutants from toxic cationic and anionic species, to extremely poisonous organic compounds, which are very harmful to humans and the environment. Therefore, the development of novel, efficient, and inexpensive technologies for the decontamination of polluted waters, soils, and the air is essential. Amongst the variety of techniques that have been developed to treat contaminated areas in the environment; adsorption-based processes are believed to be the most simple and effective techniques which largely depend on the development of efficient adsorbents. Generally, adsorbents based on zeolitic materials are known to be safe for the health of humans and the well-being of the environment. To date, many zeolite-based products have been developed to degrade heavy metals and organic toxins within the environment, and even in the human body. In this paper, some of the recent achievements of the potential applications of natural zeolites; particularly their surface modified forms for the removal of anions, cations, and organic pollutants from contaminated waters and soils will be discussed.

Keywords: Natural zeolite, surfactant modified zeolite (SMZ), VOC removal, environmental pollution, wastewater treatment, ion exchange, adsorption, heavy metal, ammonium, radioactive waste. INTRODUCTION Undoubtedly, the emergence of technology was intended to enhance our lives in many ways. However, the increase of technology in our society became the cause of sudden environmental concerns, thereby increasing the need for other technologies to address them. Increasing release of various pollutants to the environment is considered to be one of the main causes of the crises being faced today such as clean water shortage. Furthermore, large industrialization processes 

Address correspondence to Hossein Kazemian: Senior Researcher, Department of Chemical and Biochemical Engineering, Faculty of Engineering, Western University, London, Ontario, Canada N6A 5B9; Tel: 519-661-2111 ext. 81295; Fax: 519-661-3498; E-mails: [email protected]; [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 215

have been discharging remarkable quantities of diverse classes of pollutants into the environment. Since these problems have been recognized, researchers have been seeking novel, environmentally friendly technologies to eliminate pollutants caused by previously developed technologies—industries, transportation, etc. Amongst different techniques, adsorption-based processes have drawn much interest in the past decade not only for their relatively simple approach for the adsorption of pollutants, but also because there are many types of efficient adsorbents. Due to the excellent selectivity of natural zeolites to different adsorbates, and the abundance of these precious minerals all around the globe, the utilization of natural zeolitic materials for environmental remediation is one of the largest interests in many scientific disciplines. Most of the reported applications of natural zeolitic materials in the past decade have been focused on the removal of ammonium and heavy metal due to their high selectivity for cations, and cation exchange. [1-3]. However, many industrial activities, particularly in petroleum industries, introduce poisonous organic molecules such as volatile organic compounds (VOC) and toxic anions such as chromate, nitrate, and arsenate into water bodies and wastewater streams. Currently, VOC’s and anionic species have become one of the major concerns for water treatment facilities. Therefore, recent research on natural zeolites has focused on the removal of anions and VOC’s from water systems using modified forms of natural zeolites. SURFACE MODIFIED NATURAL ZEOLITES Zeolitic aluminosilicate frameworks possess negative charges, and thus are considered excellent for selective cation exchange. Cation exchange can be used for the removal of cationic species from contaminated wastewater streams. Natural zeolites modified with surfactants generally serve as excellent multipurpose adsorbents. Surfactant modified zeolites (SMZ) are capable of adsorbing major water contaminants, including poisonous organic molecules, toxic anions, heavy metal cations, and pathogens. Furthermore, SMZ’s are capable of eliminating bacterial odors, formaldehyde, and sulfur dioxide from contaminated air, and water streams. The ability of SMZ’s to adsorb a wide variety of contaminants makes them exceptional adsorbents for treating a vast range of pollutants. Enhancement of the

216 Handbook of Natural Zeolites

Hossein Kazemian

decontamination of polluted waters can be achieved by using SMZ’s in combination with processes such as chemical reduction by zero valent iron (ZVI), and/or biological degradation. In the modification of natural zeolites with organic surfactants, charge-balancing cations present on the surface sites of very fine-grained natural zeolite (e.g., clinoptilolite) can be replaced by high-molecular-weight quaternary amines such as hexadecyltrimethylammonium (HDTMA) as organic cations, while the internal cationic sites of the zeolite remains accessible for small cations. In this process, a stable HDTMA bilayer will be formed on the external surface of the natural zeolite, which can absorb anionic species [4]. Fig. 1 below demonstrates the formation of a monolayer, and bilayer tail to tail on the surface of a natural zeolite using HDTMA as the surfactant.

Figure 1: Schematic illustration of SMZ showing the partitioning of typical mono-aromatic molecules and anionic species on the modified surface.

The cationic surfactants that are used to modify natural zeolites usually consist of long alkyl chains with a quaternary amine [5]. The sorption of a cationic surfactant on the external surface of a natural zeolite is governed primarily by cationic exchange and hydrophobic interaction [6]. At low concentrations of a given cationic surfactant, the surfactant ions are exchanged with the exchangeable cations at the surface sites of the natural zeolite until a monolayer of surfactant is

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 217

formed on the external surface. At concentrations higher than the critical micelle concentration (CMC) of a surfactant, a bilayer of surfactant molecules (admicelle) will be attached to the external surface of the zeolite, where the outer layer of surfactant molecules is bound by hydrophobic interactions [7]. Non-polar organics are adsorbed by the organic layer, while anionic species such as chromate and arsenate are retained on the outer surface pointing towards positively charged head groups of the surfactant bilayer. In addition, cations bind to the internal cationic sites present in the zeolite. Various types of commercial and reagent grade surfactants have been used to modify natural zeolites in order to develop suitable adsorbents for compounds resulting from petrochemical spills such as methyl tert-butyl ether (MTBE), phenol, pyridine, naphthalene, BTEX chemicals (benzene, toluene, ethyl benzene and xylenes) [8, 9]. Technologies for the preparation of low-cost surfactant-modified zeolites (SMZ) have been developed in multi-ton quantities for use as subsurface permeable barriers in order to control the migration of ground-water contaminants [4]. Modification of natural zeolites with particular organic materials (e.g., cationic surfactants) in parallel with other contaminant treatment technologies, such as precipitation, allows treatment of a much broader range of pollutants. Thus, surfactant modified zeolites are capable of treating polluted groundwater streams, storm water runoff, and solvent vapors from paint-related operations [8-12]. The kinetics of the degradation of organic contaminants by modified zeolites has been investigated in laboratory and pilot-scale setups. Based on these experiments, new industrial technologies for the treatment of wastewater using SMZ’s have been developed [13]. The precipitation of MnO2 on the surface of clinoptilolite was successfully applied for the removal of Mn3+ from surface waters and in the treatment of effluents discharged from paint-shops [14-16]. Generally, the high physico-chemical stability (e.g., attrition resistance) and high reactivity demonstrated by natural zeolites promote their applications in wastewater treatment processes. However, for the successful application of SMZ in environmental remediation processes, a few challenges must be addressed.

218 Handbook of Natural Zeolites

Hossein Kazemian

Firstly, it is necessary to improve the long-term chemical and physical stability of the SMZ. Research has shown that layers of HDTMA surfactant on the surface of modified zeolites slowly wash off under continued leaching—although it is not readily displaced by aqueous cations and is resistant to biological and chemical degradation. The enhancement of the physico-chemical durability of SMZ’s may be achieved by using other surfactants, a different type of zeolite, and by heat treatment of unmodified and modified zeolites. Utilization of natural zeolites, particularly clinoptilolite-rich tuffs modified with cationic surfactants was widely investigated to remove multiple types of contaminants from water [17-19]. Some of these investigations revealed that zeolites obtained from different regions exhibit different ion-exchange capacities and selectivities [20]. This allows for the use of zeolites for a wider range of applications. Secondly, treatment of effluents discharged by wastewater treatment plants may require the addition of several units thereby expanding a given plant potentially past its capacity. This problem is solved through the application of natural zeolites in the aeration basin of wastewater treatment plants. This improves the efficiency of the treatment process without increasing the size of the plant. Zeolite particles are known to be good carriers of bacteria, in which bacteria adsorbs on the zeolite surface resulting in increased activity of sludge required for the process. However, one of the significant drawbacks for the application of zeolitic additives involving bacteria is the slow kinetics associated with the formation of bacterial layers on the zeolite surface. Nevertheless, novel zeolite modification methods can accelerate the interaction between zeolites and activated sludge, which further enhances the sludge activity. INORGANIC ANIONS POLLUTANTS Inorganic anions including acid ions (NO3−, SO4 2−, PO4 3−, F−, ClO4−, CN−), metalloids (selenates, arsenic species), and metal anions (e.g., chromates) are largely present in industrial wastewater streams. Some heavy metal anions are extremely toxic and exposure to these metals presents a serious hazard to biological systems. Among these heavy metals, chromium in the form of chromate is one of the most toxic pollutants in wastewater that requires considerable attention. Removal of anions can be done via ion-exchange or by use

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 219

of surfactant-modified natural zeolites. Surface modified natural clinoptilolite with a cationic surfactant has shown an effective adsorption capacity for the cleanup of chromate (Cr (VI)) in contaminated water [21]. For example, surface modified natural mordenite modified with ethyl-hemadecyldi-methyl ammonium (EHDDN), and (HDTMA) has shown impressive adsorption capacities for the removal of Cr(VI) [22]. Removal of acid anions such as F− and CN− using modified natural zeolites has also been studied. Several modified homo-cationic forms of Iranian natural clinoptilolite-rich tuffs were evaluated for the potential removal of cyanide anions from aqueous solutions [23]. While the cyanide uptake on un-modified natural zeolite was 0.070 meq/g, the cobalt modified zeolite showed a higher uptake of 1.95 meq/g-zeolite. In addition, Mexican natural heulandite–clinoptilolite and its sodium, calcium, lanthanum, and europium modified forms were evaluated for the removal of fluoride anions [24]. It was found that fluoride uptake and retention of the untreated zeolite was similar to the modified cationic forms. It was concluded that occlusion and adsorption of the anions on the zeolite surface was responsible for the fluoride removal. Based on these studies, Al3+, La3+, and ZrO2+ forms of natural clinoptilolite were applied for the uptake of fluoride anions present in contaminated water. Before loading the cationic modifiers, three zeolite samples were pre-conditioned with nitric acid, sodium nitrate, and de-ionized water. The adsorption isotherms were well fitted to the Langmuir and Freundlich models. Fluoride uptake using an aqueous solution containing a fluoride concentration of 2.5mg/L on the acidtreated metal loaded zeolite with an adsorbent concentration of 6.00 g/L was 94%. The adsorption capacity of the modified zeolites showed the highest results with the ZrO2+ form, followed by La3+, then Al3+[25, 26]. In aqueous systems, chromium is mainly found as Cr(III) and or Cr(VI), with the former being relatively insoluble and immobile and the latter being soluble and having great mobility in groundwater. Cr(VI) generally occurs in the form of chromate under oxidized conditions. However, Cr(VI) is much more toxic than Cr(III) for environmental and biological systems [27]. While Cr(III) plays an essential role in the metabolism of plants and animals, Cr(VI) shows negative effects on biological functions and is extremely carcinogenic [28, 29]. The most common techniques

220 Handbook of Natural Zeolites

Hossein Kazemian

applied to remove Cr(VI) from aqueous effluents are adsorption, the reduction of Cr(VI) to Cr(III) and chemical precipitation, ion exchange on a polymeric resin, reverse osmosis, and electrodialysis extraction. Many of these methods involve high capital costs, and are only suitable for small-scale applications [30]. Adsorption processes are generally known to be one of the most effective techniques for the removal of environmentally hazardous metallic species. As it is easy to separate the adsorbent from aqueous media after treatment, adsorption based techniques are generally considered to be one of the simplest methods for chromate removal from contaminated water [4, 31]. Since earlier studies have been conducted on the utilization of cationic surfactants to modify surface charges of zeolitic materials in order to develop suitable adsorbents for anions and organic molecules, extensive research has been carried out in this area globally [32]. More specifically, the performance of both natural and synthetic zeolites modified with HDTMA, cetylpyridinium chloride (CPC), and modified mesoporous MCM-41 have been studied for the removal of chromate from aqueous solutions [33]. The results revealed that natural clinoptilolite modified with CPC, and HDTMA exhibited higher adsorption characteristics than modified ZSM-5 (synthetic zeolite), but less than that of modified mesoporous MCM-41. Depending on the surfactant loading, the maximum chromate adsorption on HDTMA, and CPC modified clinoptilolite was in the range of 4.4–16.6 mmol/kg and 3.9–21.4 mmol/kg, respectively. The higher adsorption capacity of the natural zeolite can be attributed to the lower Si/Al ratio of the natural zeolite compared to the ratio present in ZSM-5. The natural zeolite has a larger number of cationic sites and therefore presents a higher adsorption capacity for the deposition of surfactant molecules on its surface. Thus, the higher surfactant deposition generally means better adsorption of contaminants. Moreover, the high adsorption capacity of the modified mesoporous MCM-41 can be attributed to its larger pore size compared with that of clinoptilolite and ZSM5. This allows for a larger adsorption surface area and therefore a higher adsorption capacity. In alternative studies, natural mordenite modified with HDTMA and ethylhexadecyldimethylammonium (EHDDMA) have been studied as adsorbents for the removal of Cr (VI) from aqueous streams [34]. The results showed that the

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 221

zeolite modified with HDTMA coupled with hydrogen sulfide (HSO4) exhibited a higher affinity for Cr(VI) comparing to EHDDMA modified mordenite. A combination of coulombic forces as well as hydrophobic effects, are responsible for the sorption of chromate on the surface of the HDTMA modified zeolite. Cordoves et al., [35] also studied a surfactant-modified clinoptilolite for sorption of Cr(VI) and Cr(III). Cation and anion exchange capacities of the zeolite were calculated based on the experiments conducted. It was demonstrated that the affinity distribution analysis combined with the Freundlich binding model allows for the characterization of the SMZ binding properties for Cr (VI) thereby providing a method for the separation of Cr(VI) from Cr(III). In addition to chromate, inorganic arsenic has also been identified as a highly toxic element to mammals and aquatic species. The US EPA has classified arsenic as a human carcinogen and is considering lowering the maximum allowable level for drinking water down to 10 ppb or less. Arsenic (As) sorption onto clinoptilolite-heulandite rich tuffs modified with lanthanum, HDTMA, or iron has been reported [36]. The sorption capacities of As(V) for zeolites modified with lanthanum, HDTMA, and iron were found to be 75.4µgAs/g at pH 3, 3.9µgAs/g at pH 5, and 53.6µgAs/g at pH 6, respectively. This revealed that the retention of arsenic on the zeolite surface depends on the type of zeolitic material used, the chemistry of arsenic species being adsorbed, pH, as well as the characteristics of the additives applied to modify the zeolites. The adsorption of As (III) and As (V) on modified clinoptilolite-rich tuff by different organic and inorganic iron salts was also studied [37], by introducing of iron corresponded to four coordinated species with a tetrahedral geometry. The iron modified zeolite exhibited an adsorption of 12µg/g with arsenite, which is equal to 99% removal of As(III) in a solution of 360µgAs(III)/L. In addition, the zeolite showed an adsorption of 6µg/g with arsenate from a 230µgAs(V)/L solution. In the series of exchanged zeolitic tuffs, arsenite and arsenate adsorption reached a plateau at a Fe/Si ratio of 0.1. Using speciation analyses, it was revealed that arsenite oxidizes to become arsenate in contact with iron modified samples. The retention of As(III) and As(V) on three natural clinoptilolite-rich tuffs and their iron (II & III) modified forms were also studied [38, 39]. In this study, the

222 Handbook of Natural Zeolites

Hossein Kazemian

effects of particle size, pH, temperature, concentration of arsenic, and zeolite dose were investigated. Since the arsenic species did not leach off the zeolitic surface during experimentation, it was concluded that the saturated adsorbents can be disposed as nonhazardous solid wastes. Also, the adsorption of As(III) and As(V) on clinoptilolite samples from Mexico and Hungary without modification were investigated [40]. Both clinoptilolites were able to decrease the initial arsenic concentration of a 200µg/L in contaminated de-ionized water, drinking water, ground water, and surface water by more than 75%. In the case of the Mexican zeolite, it was found that both arsenite and arsenate concentrations can be lowered from 200µg/L to 10µg/L. Furthermore, the presence of other cations and anions in the waters did not reduce the efficiency of the selected zeolites. The mechanism of adsorption regarding the unmodified zeolites was not mentioned in the study, however it is speculated that the iron present in the chemical composition of the zeolites were the main active components responsible for adsorption. Based on the promising results obtained from the studies conducted with iron modified zeolites, three untreated inorganic adsorbents—metakaoline, clinoptilolite-rich tuff, and synthetic zeolite—as well as their Fe2+ modified forms were studied for their sorption capabilities of arsenate in aqueous solutions [41]. It was found that the sorption capacity of the sorbents modified with Fe(II) increased significantly from 0.5 to 20.0 mg/g showing more than 95% removal of the total arsenic present. The uptake of As (III & V) was studied with three different adsorbents including natural clinoptilolite, manganese greensand, and cationic exchange resin modified with Fe3+ ions [42]. Results revealed that Fe3+ saturated zeolites are effective adsorbents for arsenic removal, having a capacity of 55.3µg/g for As(III), and 36.4µg/g for As(V). The sorption of antimonite (Sb) anions using HDTMA modified zeolites were also investigated [43]. Antimonate binding was more efficient on the zeolites loaded with HDTMA. An HDTMA modified zeolite concentration of 50 g/L could adsorb up to 42% of antimonite anions from solutions containing 0.09 to 2.15 mmol Sb/L. Antimonate sorption on modified zeolite was best fitted with the Langmuir isotherms. ORGANIC CONTAMINATNTS Apart from natural organic compounds that mostly come from humic substances (approximately 80% of organic matter in dark soils are a result of plant decay;

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 223

designated as either humic acid, fulvic acid or humin), organic dyes and contamination generated by various industrial processes has added to the naturally occurring organic matter raising serious concerns worldwide. The presence of humic compounds in water produces toxic chemicals during disinfection processes and should therefore be removed. .

Among different hydrocarbons present in petroleum, monoaromatic hydrocarbons, including benzene, toluene, ethylbenzene, and xylene isomers (BTEX), are a very important class of contaminants. These volatile compounds are very hazardous due to their fast migration into soil and water bodies and their acute and chronic toxicities when inhaled or ingested. Benzene is a known carcinogenic molecule [44]. With recent progress in health sciences and detection techniques, strict concentration limits are proposed for these compounds in water. According to the drinking water standards set by the World Health Organization (WHO), the allowable concentration for benzene in drinking water is 10 ppb (10 μg/L) [45]. The main sources of BTEX compounds in water bodies and groundwater are effluents being discharged from petrochemical industries, petroleum refineries, and related industries or adhesive factories. In addition, continuous fuel leakage from underground gasoline storage tanks in urban areas with unmaintained storage tanks is another source [46-48]. Porous zeolitic materials are common adsorbents for the removal of organic materials; however, removal of organics using zeolites usually requires their modification with surfactants or other promoters. Adsorption of perchloroethylene (PCE) as a nonpolar organic on natural zeolites modified with HDTMA was reported [49]. The results obtained showed that the PCE sorption coefficient on the SMZ was proportional to the fractional organic carbon content of the monolayer of the surfactant on the surface of the zeolite. However, increasing the fractional organic carbon content on the monolayer coverage resulted in a minimal increase in the PCE sorption coefficient. Adsorption of benzene, phenol, and aniline on SMZ were also studied, and the results showed that sorption was highly influenced by the pH of the solution [50]. Researchers have investigated the effects of surfactant modifier molecules on BTEX adsorption [8]. Modification of clinoptilolite-rich tuffs with hexadecyltrimethyl ammonium chloride (HDTMA-Cl), and N-cetylpyridinium

224 Handbook of Natural Zeolites

Hossein Kazemian

bromide (CPB) was conducted, and the resulting SMZ’s were tested for BTEX uptake from contaminated solutions. The results of the adsorption tests revealed that the adsorption capacity of the modified zeolites improved by increasing the surfactant loading to a higher concentration than the critical micelle concentration (CMC), which caused an increase in the sorption capacity from 60% to 70% for HDTMA-modified zeolites, and from 47% to 99% for CPB-modified zeolites. Kinetic tests for the adsorption process ensured that the optimum contact time was 48 h with an average BTEX removal of 90, and 93% for HDTMA, and CPB modified zeolites, respectively. They also showed that by increasing the pH from 3 to 11, the sorption capacity of the adsorbent decreased remarkably from 97 to 75%. Analyzing the influence of temperature on BTEX sorption showed that the adsorption efficiency of adsorbents for benzene reduced from 93% at 20°C to 10% at 48°C. However, the influence of temperature on other compounds was not remarkable. In brief, it was concluded that CPB modified zeolites exhibited higher selectivity towards BTEX compounds at optimum experimental conditions. Although their experimental results revealed that commercial powder activated carbon (PAC) shows a higher capacity for all BTEX compounds and faster adsorption kinetics, the adsorption capacity of the CPB modified zeolites at optimal conditions was still quite competitive with PAC results. Various types of dyes including basic, acidic, reactive, and dispersive dyes are widely used by textile, printing, food, and leather industries. There are more than 100,000 commercial dyes with an estimated production of 7x105–1x106 tons per year [51, 52]. It is believed that up to10–15% of the used dyes are discharged to the environment in different forms of waste [53]. While some dyes are toxic and carcinogenic, their presence in waters also influences the environment by inhibiting the penetration of sunlight, which causes the reduction of photosynthetic reactions [54]. Therefore, these dyes must be removed before the wastewater can be discharged safely [55-57]. Wastewater containing organic dyes is very difficult to treat because the organic dye molecules are resistant to aerobic digestion and most of them are stable in the presence of light, heat, and oxidizing agents [58]. The adsorption of two basic dyes, MG-300 and MG-400 on natural clinoptilolite and granular activated carbon has been reported [59]. The effects of the initial dye concentration, adsorbent concentration, and agitation time were

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 225

studied using a batch wise system. The adsorption capacities MG-300 and MG400 on natural clinoptilolite were reported to be 55.9 mg/g and 14.9 mg/g, respectively. In the past few years, a composite made of zeolites and PVC was tested for dye adsorption from aqueous solutions [60]. The possibility of the application of natural zeolites and their surface modified forms for the removal of methylene blue, rhodamine B [61], Malachite green [62], reactive black 5, reactive red 239 [63], reactive yellow 176 [64], reactive red 46 [65], and toluidine blue-O [66] has been extensively studied. Extensive research on natural clinoptilolite for the possible adsorption of three reactive azo dyes (reactive black 5, reactive red 239, and reactive yellow 176) have been conducted and compared with sepiolite clay sample [67-70]. The study revealed that both natural clay samples and the zeolites have limited adsorption capacities toward the reactive dyes. However, it has been demonstrated that surface modification of minerals by quaternary amines of hexadecyl-trimethylammonium bromide (HTAB), significantly improved the adsorption capabilities observed. An electrostatic adsorption mechanism, which involves the formation of a bilayer of amine molecules on the clinoptilolite surface, was suggested as a possible reason for the adsorption of anionic dye molecules. The adsorption capacities of organo-modified zeolites for reactive red, yellow, and black were 111 mg/g, 89 mg/g, and 61 mg/g, respectively. Some studies have been conducted on the possibility of using modified natural zeolites for the adsorption of humic substance [71-73]. Natural clinoptilolite modified with HDTMA was applied for the adsorption of fulvic acids (FA) [74]. The influence of surfactant loading, FA concentration and flow rate in a fixed bed reactor were studied. It was discovered that FA adsorption on SMZ surfaces is largely due to hydrophobic interactions and hydrogen bonding. The SMZ bed with an HDTMA loading of 120% of its external CEC, at a flow rate of 5 BV/h has shown the best performance. Complete regeneration of the saturated SMZ with 23 BV of 30 vol% ethanol solution at the feed flow rate of 5 BV/h was successfully performed. Furthermore, the adsorption of aniline and nitrobenzene on natural, and HDTMA modified zeolite has been studied [75]. It was found that while the adsorption of aniline and nitrobenzene on un-treated natural zeolite was negligible, the

226 Handbook of Natural Zeolites

Hossein Kazemian

adsorption of the modified zeolite was quite significant. The breakthrough capacity was determined to be 2.36 mg/g and 3.25 mg/g for aniline and nitrobenzene, respectively. HDTMA modified zeolite was evaluated in a permeable reactive barrier for the removal of organic and anionic contaminants from sub-surface water [4]. A 15 week pilot test of the manufactured barrier showed that the retardation factors of chromate and PCE were 44 and 39, respectively. SOIL REMEDIATION In addition to the concerns surrounding the availability of drinking water, the pollution of soils with hazardous heavy metal, inorganic anions, and organic species has attracted much attention in the past few decades. Intensive use of water for irrigation, increasing utilization of pesticides and herbicides, vehicle exhausts, mining, and smelting as a result of rapid industrialization have resulted in large accumulations of heavy metals and other chemical contaminants in the soil [76-80]. Naturally, soils have a capacity to control the bioavailability and the movement of some contaminants such as cations and anions by means of different mechanisms including adsorption, precipitation, and redox reactions. However, when the concentration of pollutants exceeds the soil’s carrying capacity, contaminants can be mobilized, resulting in serious damages to the environment. Thus, it is an urgent necessity to take appropriate action treating polluted soils. Soil remediation has been extensively studied using different remediation techniques [79, 81-83]. Generally, unlike organic contaminants, heavy metals are generally non-biodegradable, and thus require precise attention and treatment [84]. It has been proven that in situ immobilization of heavy metals in contaminated soils can be considered a sustainable technique to improve soil quality. Natural and synthetic zeolites have been considered as potentially useful additives to bind heavy metals of the contaminated soils. Immobilization of the pollutants is the main mechanism in the remediation of contaminated soils using zeolitic porous materials. Additives made of the natural zeolites clinoptilolite and phillipsite were used to reduce the leaching rate of Pb2+, Cd2+, and Ni2+ from contaminated soil [85]. The used additives, which contained approximately 35% active zeolite enhanced the

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 227

sorption capacity of soil and reduced the leaching rate. Lead leaching was reduced by greater than 97% using a minimum of 25% zeolite additives at the lowest contamination level (500 mg/kg of each metal), and 40% additive at the highest contamination level (5000 mg/kg of each metal). However, the use of zeolite additives poorly reduced Cd2+ and Ni2+ concentrations. The results from the repeated leaching column experiments confirmed the selectivity of the additive and a satisfactory leaching reduction was achieved for Pb2+ and Cd2+. In another experiment, six synthetic zeolites and one natural zeolite (clinoptilolite) were tested to evaluate their effectiveness in the binding of cadmium and zinc cations in contaminated soils [86]. The results showed that the free ion concentrations of Cd2+ and Zn2+ strongly decreased with the addition of zeolites. To stabilize Cd2+ in a variety of a soil textures, natural clinoptilolite was examined at different pH values [87]. The addition of 15% natural clinoptilolite remarkably reduced the leaching rate of Cd2+ within the deeper soil horizons. Therefore, groundwater and soil in underlying ground layers can be treated from Cd2+ pollution. These results assured the efficiency of natural zeolites for the remediation of contaminated soils. In many countries, based on health and environmental regulations, all hazardous waste disposal facilities must be lined with suitable impermeable barriers [88], which normally consist of multiple barriers and drainage layers. Various types of engineered barriers made of natural clay minerals have been developed in recent decades in order to act against the migration of contaminated leachate into the environment [89]. Geosynthetic clay liners (GCL), compacted clay liners (CCL, particularly bentonite), geo-membrane (GM), or a combination of these barriers are traditionally used to prevent subsurface contamination. However, compacted clays may display shrinkage and/or cracking problems. Studies have shown that compacted clays undergo large changes in their physicochemical properties when exposed to shrink–swell and/or freeze–thaw cycling [90]. Having three dimensional rigid structures of natural zeolites can be considered a promising substitute to the natural clays in order to address the problems mentioned above. In a research study the application of natural zeolites as a liner for the retention of Cu(II) was reported [91]. The natural zeolite used exhibited excellent adsorptive characteristics for the removal of copper (II) from leachate, thereby making it a very good liner material [92].

228 Handbook of Natural Zeolites

Hossein Kazemian

RADIOACTIVE WASTE TREATMENT Utilization of nuclear energy is one of the predominant candidates to substitute fossil fuels, which means more industrial hazardous waste containing radionuclide will be produced. Radioactive waste streams need very particular treatment technologies. Natural zeolites (particularly clinoptilolite-rich tuffs) are well known adsorbents for the selective capturing of heat-generating fission products such as Cs-137 and Sr-90. Despite the extensive research and development that are done on the development of new processes for immobilizing fission products by means of natural zeolites, the use of solidification (e.g., vitrification) of radionuclide loaded zeolites, and the removal of other radionuclides using natural zeolites have gained remarkable interest in the field of nuclear waste treatment technologies. Natural clinoptilolite-rich tuffs were examined for their ability to remove 137Cs and 90Sr/90Y in the presence of competing cations such as Na+, K+, Cs+, Ca2+, Mg2+, and Sr2+. It was concluded that the presence of the interfering cations, which are potentially present in aqueous nuclear wastes, showed negative effects on the utilization of clinoptilolite for treating radioactive wastes containing 137Cs and 90Sr/90Y [93]. Solidification of radioactive material in ceramics, glass, and other matrices has been considered as a safe long-term conditioning technology for high level radioactive wastes (HLW). A suitable glass host is used to dissolve the HLW in order to form a glassy (vitreous) homogenous product that can be casted into suitable compact shapes. Borosilicate glass has become the optimum choice for the immobilization of nuclear wastes. The main advantages of vitrification technologies are the ability to process glass at relatively low temperatures, the tolerance of glass to variations in waste compositions, and its reasonable chemical durability. Studies have shown that the “radionuclidesaturated” zeolites can be transformed into glass, ceramics, and concrete, and can be stored indefinitely [94]. Various natural and synthetic zeolites were studied for the solidification of 137Cs and 90Sr in liquid waste. Studies on solidification of loaded zeolites at higher temperatures demonstrated very favorable results. Natural zeolites have shown superior selectivity for several radionuclides (90Sr, 137 Cs 60Co, 45Ca, and 51Cr) compared with organic resins. They are relatively cheaper, and much more resistant to nuclear radiation degradation. Many papers

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 229

have published results on the capabilities of many natural zeolites for capturing different radionuclides [95, 96]. For the treatment of contaminated waters at Three Mile Island, USA a mixture of synthetic zeolite A and natural chabazite were used to adsorb 137Cs and 90Sr, respectively [97]. At Sellafield nuclear facility in the UK, natural clinoptilolite was used for over 20 years in order to remove 137Cs and 90Sr before the release of low-level effluents from nuclear power plants into the Irish Sea [98]. At West Valley, NY, USA, clinoptilolite was used to capture the radioisotopes from leaking repository containers [99]. The possibility of stabilizing natural zeolites loaded with 137Cs and/or 90Sr radionuclides into a matrix made with ordinary Portland cement (OPC) was investigated. In this study, the mechanical strength, and leaching behavior of the radionuclides which affect the characteristics of the final solidified waste product have been studied. The results showed that the presence of zeolites in the final cemented waste has improved the mechanical characteristics of the solidified cement matrix. Furthermore, the radionuclides leach rates have been considerably reduced [100]. Special attention has been paid to the selective removal of Cs+ and Sr2+ cations from radioactive waste solutions that contained higher concentrations of Na+. Separation of 137Cs and 90Sr radionuclides in the presence of high concentrations of sodium ions have been studied using different inorganic adsorbents. Potassium nickel hexacyanoferrate (KNiFC) is known as an inorganic adsorbent which shows very high selectivity for Cs+ even in the presence of small amounts of sodium ions. On the other hand, zeolites like clinoptilolite and synthetic zeolite P—which can be synthesized by using clinoptilolite as a starting material—exhibited very strong physico-chemical stability and high affinity towards Sr2+ and Cs+ in the absence of competing sodium cations. While KNiFC can be obtained readily through the precipitation of Ni(NO3)2 with K4Fe(CN)6, the product is composed of aggregates of very fine crystallites (30 nm diameter) with low mechanical stability. KNiFC becomes colloidal in aqueous solutions which is not suitable for practical applications at larger scales (e.g., for column operations). In order to improve the mechanical properties of KNiFC it must be prepared via precipitation on solid supports such as zeolites and silica gels. Knowing that the particle size of natural zeolites can be controlled using appropriate milling and sieving procedures, they can be considered as an

230 Handbook of Natural Zeolites

Hossein Kazemian

appropriate support for KNiFC precipitation to make a composite with potential applications in larger scale processes. Natural clinoptilolite can be used as a carrier of microcrystalline ferrocyanides. This zeolite is a selective ion-exchanger for Cs+ and has a relatively large distribution coefficient (KdCs) of about 104 cm3/g, however its affinity tends to decrease remarkably in the presence of higher concentrations of Na+ ions. A multifunctional composite adsorbent can be produce by means of precipitation of KNiFC on natural zeolites in order to use it as a mixed granular adsorbent. It is intended to be a suitable adsorbent for Cs+ and Sr2+ in saline radioactive waste solutions [101]. Moreover, zeolites can be considered as alternative materials for the removal of multivalent and heavier radioisotopes like actinides and lanthanides. Lanthanides such as cerium (Ce) are commonly found in the waste streams of nuclear power plants and research centers. On the other hand, thorium-232 appears as an impurity in the production of nuclear fuels. The conventional processes for the removal of this radionuclide are solvent extraction, and organic ion exchange resins. Natural clinoptilolite, and synthetic zeolite P made from the natural clinoptilolite were examined for their ability to adsorb cerium and thorium form nuclear wastewater [102]. HDTMA modified clinoptilolite exhibits enhanced sorption of U6+ ions [103, 104]. Some research results on the removal of other radionuclide such as americium, yttrium, zirconium, hafnium, niobium, and thorium from water using natural zeolites have been reported in literature [105-107]. For the treatment of radioactive wastewater at Oak Ridge National Laboratory (Tennessee, USA), several natural and synthetic zeolitic cation exchangers were tested in a bench-scale setup achieving promising results [108, 109]. Natural chabazite was found to be effective for removing cesium and strontium in ppb concentration from polluted waters that contain high concentrations of nonradioactive salts (e.g., 10 -3 M). In Japan, decontamination of waters polluted by radioactive cesium and strontium using zeolites was thoroughly investigated [110114]. The results have shown that zeolitic molecular sieves should be considered as alternative materials for radioactive waste treatment and management. CONCLUSIONS Although research has commonly been done on natural zeolites, it was not until recent years that research has focused on the cation exchange properties of natural

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 231

zeolites and its applications in wastewater treatment processes. Today, current research is primarily focused on the potential application of modified zeolites as adsorbents of organic molecules and anionic species. In this regard, environmental applications of natural zeolites (specifically clinoptilolite-rich tuffs) and the possibility of the utilization of surface modified zeolites for the adsorption of organic and anionic species from contaminated media gained more attention. The large surface area available for surface modification, high selectivity, environmentally friendly nature, and appropriate phisico-chemical stabilities of zeolitic adsorbents can be considered as some of the main factors which gained researchers’ interest toward zeolitic materials. However, recent studies have shown that although the nano-sized surface modified natural zeolites exhibit promising adsorption capacities towards organic pollutants [113, 114], the loss of crystallinity of the mechanically prepared natural zeolites, still remain a concern towards the production of nano-sized natural zeolitic adsorbents [115]. ACKNOWLEDGEMENTS None declared. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6]

Hedstrom A. Ion exchange of ammonium in zeolites: a literature review. Journal of Environmental Engineering: ASCE 2001; 127: 673-681. Kesraouiouki S, Cheeseman CR, Perry R. Natural zeolite utilization in pollution-control—a review of applications to metals effluents. Journal of Chemical Technology and Biotechnology 1994; 59: 121-126. Caputo D, Pepe F. Experiments and data processing of ion exchange equilibria involving Italian natural zeolites: a review, Microporous and Mesoporous Materials 2007; 105: 222-231. Bowman RS. Application of surfactant-modified zeolites to environmental remediation. Microporous and Mesoporous Material 2003; 61: 43-56. Li Z, Bowman RS. Regeneration of Surfactant-Modified Zeolite after saturation with chromate and perchloroethylene. Wat Res. 2001; 35: 322-326. Mier MV, Raymundo LC, Gehr R, Cisneros Blanca EJ, Alvarez Pedero JJ. Heavy metal removal with Mexican clinoptilolite: Multi-component in ionic exchange. Wat. Res 2001;35: 373-378.

232 Handbook of Natural Zeolites

[7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24]

Hossein Kazemian

Oliveira CR, Rubio J. New basis for adsorption of ionic pollutants on to modified zeolites. Minerals Engineering 2007; 20: 552-558. Torabian A, Kazemian H, Seifi L, Bidhendi GN, Azimi AA, Ghadiri SK. Removal of Petroleum Aromatic Hydrocarbons by Surfactant-Modified Natural Zeolite. CLEAN 2010; 38(1): 77-83. Cadena F, Cazares E. in: Ming DW. Mumpton FA. (eds.), Natural Zeolites’93: Occurrence, Properties and Use, Int. Comm. Natural Zeolites, Brockport, N.Y., 1995, p. 309. Nikashina VA, Gembitskii PA, Kats EM, Boksha LF, in: Kirov G, Filizova L, Petrov O, (eds.), Natural Zeolites-Sofia’95, Pensoft, Sofia, 1997, p. 55. Popovici E, Vatajanu A, Anastasiu A, in: Kirov G, Filizova L, Petrov O, (eds.), Natural Zeolites-Sofia’95, Pensoft, Sofia, 1997, p. 61. Saponaro S. et al. Groundwater remediation by an in situ biobarrier: A bench scale feasibility test for methyl tert-butyl ether and other gasoline compounds, Journal of Hazardous Materials 2009; 167: 545-552. Princz P, Olah J, Smith SE, Hatfield K, Litrico ME, Wastewater Treatment Using Modified Natural Zeolites: in Nato Science Series: IV: Earth and Environmental Sciences, Volume 52, pp. 267-282, Springer Netherlands, 2005. Pólyak K, Hlavay J, Maixner J, in: Ming DW, Mumpton FA, (eds.), Natural Zeolites ’93: Occurrence, Properties and Use, Int. Comm. Natural Zeolites, Brockport, N.Y., 1995; p. 385. Tarasevich, Yu.I., Polyakov, V.E., Ivanova, Z.G., Krysenko, D.A. Obtaining and properties of clinoptilolite modified by manganese dioxide Journal of Water Chemistry and Technology 2008; 30 (2): 85-91 Papp J, Heinzel K, Adams S. in: Ming DW, Mumpton FA, (eds.), Natural Zeolites ‘93, Occurrence, Properties and Use, Int. Comm. Natural Zeolites, Brockport, N.Y., 1995; 415. Li Z, Jones HK, Bowman RS. Helferich R, Enhanced reduction of chromate and PCE by pelletized surfactant-modified zeolite/zero valent iron, Environ, Sci. Technol 1999; 33: 4326-4330. Li Z, Willms AC, Kniola K. Removal of anionic contaminants using surfactant-modified palygorskite and sepiolite Clays. Clay Miner 2003; 5: 445-451. Bowman RS, Sullivan EJ, Li. Z, Uptake of cations, anions, and nonpolar organic molecules by surfactant-modified clinoptilolite-rich tuff. In Colella C, Mumpton FA (Eds). Natural Zeolite for Third Millennium. De Frede Editore, Napoli, Italy, 2000; 287-297. Gevorkyan RG, Sargsyan HH, Karamyan GG, et al. Study of Absorption Properties of Modified Zeolites. Chem. Erde. 2002; 62: 237-242. Cordoves PA, Granda M, Ferna´ndez CJ, et al. Characterization of the binding site affinity distributionof a surfactant-modified clinoptilolite. Microporous and Mesoporous Materials 2008; 109: 38-48. Campos V, Morais LC, Buchler PM, Removal of chromate from agues solution using treated natural zeolite, Environ. Geol 2007; 52: 1521-1525. Faghihian H. Removal of cyanide from liquid wastes by modified clinoptilolite, International Journal of Environment and Pollution 2004; 22: 732-739. Diaz-Nava C, Olguin MT, Solache-Rios M. Water defluoridation by Mexican heulanditeclinoptilolite, Separation Science and Technology 2002; 37: 3109-3128.

Environmental Application of Natural Zeolites

[25] [26] [27] [28] [29] [30] [31] [32]

[33] [34] [35] [36] [37] [38] [39] [40]

Handbook of Natural Zeolites 233

Samatya S, Yuksel U, Yuksel M, Kabay M. Removal of fluoride from water bymetal ions (Al3+, La3+ and ZrO2+) loaded natural zeolite. Separation Science and Technology 2007; 42: 2033-2047. Vikrant S, Pant KK. Removal of chromium from industrial waste by using eucalyptus bark. J. Hazard. Mater 2006; 97: 15-20. Toxicological Review of Hexavalent Chromium, U.S. Environmental Protection Agency, National Center for Environmental Assessment, Office of Research and Development, Washington, DC, 1998. Mohan D, Pitman Jr. Activated carbons and low cost adsorbents for remediation of tri and hexavalent chromium from water. J Hazazard Mater 2006; 137: 762-811. Toxicological Profile for Chromium, Agency for Toxic Substances and Disease Registry (ATSDR), U.S. Public Health Service, U.S.Department of Health and Human Services, Atlanta, GA, 1998. Geselbarcht J. Micro filtration, Reverse osmosis pilot Trials for Livermore, California, Advances water Reclamation, in: 1996 water Reuse conference Proceedings, AWWA; 1996: P. 187. Haggerty GM, Bowman RS. Sorption of chromate and other inorganic anions by organozeolite, Environ. Sci. Technol 1994; 28: 452-458. Leyva-Ramos R, Jacobo-Azuara A, Diaz-Flores PE, Guerrero-Coronado RM, MendozaBarron J, Berber-Mendoza MS. Adsorption of chromium(VI) from an aqueous solution on a surfactant-modified zeolite. Colloids and Surfaces A: Physicochemical and Engineering Aspects 2008; 330 (1): 35-41. Ghiaci M, Kia R, Abbaspur A, Seyedeyn-Azad F. Adsorption of chromate bysurfactantmodified zeolites and MCM-41 molecular sieve. Separation andPurification Technology 2004; 40: 285-295. Campos V, Morais LC, Buchler PM. Removal of chromate from aqueous solution using treated natural zeolite, Environmental Geology 2007; 52: 1521-1525. Cordoves AIP, Valdes MG, Fernandez JCT, Luis GP, Garcia-Calzon JA, Garcia MED. Characterization of the binding site affinity distribution of asurfactant-modified clinoptilolite, Microporous and Mesoporous Materials 2008; 109: 38-48. Macedo-Miranda MG, Olguin MT. Arsenic sorption by modified clinoptilolite-heulandite rich tuffs. Journal of Inclusion Phenomena and Macrocyclic Chemistry 2007; 59: 131-142. Davila-Jimenez MM, Elizalde-Gonzalez MP, Mattusch J, et al. In situ and ex situ study of the enhanced modification with iron of clinoptilolite-rich zeolitic tuff for arsenic sorption from aqueous solutions, Journal of Colloid and Interface Science 2008; 322: 527-536. Menhaje-Bena R, Kazemian H, Ghazi-Khonsari M, Hosseini M, Shahtaheri SJ. Evaluation of some Iranian natural zeolites and their relevant synthetic zeolites as sorbents for removal of arsenate from drinking water. Iranian Journal of Public Health 2004; 33(1):36-44. Shahtaheri SJ, Kazemian H, Menhaje-Bena R. Removal of arsenic species from drinking water by Iranian natural and synthetic zeolites. In: Studies in Surface Science and Catalysis, 2004; 154 B: 1892-1899. Elizalde-Gonzalez MP, Mattusch J, Wennrich R. Application of natural zeolites for preconcentration of arsenic species in water samples, Journal of Environmental Monitoring 2001; 3: 22-26.

234 Handbook of Natural Zeolites

[41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60]

Hossein Kazemian

Dousova B, Grygar T, Martaus A, Fuitova L, Kolousek D, Machovic V. Sorption of As (V) on alumino silicates treated with Fe-II nanoparticles, Journal of Colloid and Interface Science 2006; 302: 424-431. Habuda-Stanic M, Kules M, Kalajdzic B, Romic Z. Quality of groundwater in eastern Croatia:The problem of arsenic pollution, Desalination 2007; 210: 157-162. Ingenfelder U, Furrer G, Schulin R. Sorption of antimonate by HDTMA modified zeolite. Microporous and Mesoporous Materials 2006; 95: 265-271. Farhad N, et al. Detection and Remediation of Soil and Aquifer SystemsContaminated with Petroleum Products: An Overview. J Petrochem Sci Eng 2000; 26: 169-178. Guidelines for Drinking-water Quality, 3rd Ed., Vol. 1 (Recommendations), World Health Organization, Geneva 2008. Tiburtius E R L, Peralta-Zamora P, Emmel A. Treatment of Gasoline-contaminated Waters by Advanced Oxidation Process. J Hazard Mater 2005; 126:86-90. Smith J A, Bartelt-Hunt S L, Burns S E. Sorption and Permeabilityof Gasoline Hydrocarbons in Organobentonite Porous Media, J Hazard Mater 2003; 96: 91-97. Daifullah AAM, Girgis BS. Impact of Surface Characteristics of Activated Carbon on Adsorption of BTEX, Colloids Surf-A 2003;214:181-193. Li ZH, Bowman RS. Sorption of perchloroethylene by surfactant-modified zeolite as controlled by surfactant loading, Environmental Science & Technology 1998; 32: 22782282. Li ZH, Burt T, Bowman RS. Sorption of ionizable organic solutes by surfactant modified zeolite. Environmental Science & Technology 2000; 34: 3756-3760. Christie RM. Environmental Aspects of Textile Dyeing. Woodhead, Boca Raton, Cambridge; 2007. Husain Q. Potential applications of the oxidoreductive enzymes in the decolorization and detoxification of textile and other synthetic dyes from polluted water: a review. Crit Rev Biotechnol 2006; 26:201-221. Hai FI, Yamamoto K, Fukushi K. Hybrid treatment systems for dye wastewater. Crit. Rev. Env. Sci. Technol. 2007; 37: 315-377. Wang SB, Boyjoo Y, Choueib A, Zhu ZH. Removal of dyes from aqueoussolution using fly ash and red mud. Water Research 2005; 39: 129-138. Crini G, Non-conventional low-cost adsorbents for dye removal: A review. Bioresource Technol 2006; 97: 1061-1085. Banat IM, Nigam P, Singh D, Marchant R. Microbial decolorization of textile-dyecontaining effluents: a review. Bioresource Technol 1996; 58: 217-227. Robinson T, McMullan G, Marchant R, Nigam P. Remediation of dyes in textile effluent: a critical review on current treatment technologies with a proposed alternative. Bioresource Technol 2001; 77: 247-255. Sun Q,. Yang L. The adsorption of basic dyes from aqueous solution on modified peat-resin particle. Water Resource 2003; 37: 1535-1544. Meshko V, Markovska L, Mincheva M, Rodrigues AE. Adsorption of basic dyes on granular acivated carbon and natural zeolite. Water Research 2001; 35: 3357-3366. Balkose D, Ulutan S, Ozkan F, Ulku S, Kokturk U, Flexible poly(vinyl chloride)-zeolite composites for dye adsorption from aqueous solutions. Separ Sci Technol 1996; 31: 12791289.

Environmental Application of Natural Zeolites

[61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78]

Handbook of Natural Zeolites 235

Wang SB, Zhu ZH. Characterisation and environmental application of an Australian natural zeolite for basic dye removal from aqueous solution, Journal of Hazardous Materials 2006; 136: 946-952. Wang S, Ariyanto E. Competitive adsorption of malachite green and Pb ions on natural zeolite. Journal of Colloid and Interface Science 2007; 314: 25-31. Karadag D, Turan M, Akgul E, Tok S, Faki A. Adsorption equilibrium and kinetics of reactive black 5 and reactive red 239 in aqueous solution onto surfactant-modified zeolite. Journal of Chemical and Engineering Data 2007; 52: 1615-1620. Armagan B, Ozdemir O, Turan M, Celik MS. The removal of reactive azo dyes by natural and modified zeolites. Journal of Chemical Technology and Biotechnology 2003; 78: 725-732. Karadag D, Akgul E, Tok S, Erturk F, Kaya MA, Turan M. Basic and reactive dye removal using natural and modified zeolites. Journal of Chemical and Engineering Data 2007; 52: 2436-2441. Alpat SK, Ozbayrak O, Alpat S, Akcay H. The adsorption kinetics and removal of cationic dye, Toluidine Blue O, from aqueous solution with Turkish zeolite. Journal of Hazardous Materials 2008; 151:213-220. Armagan B. Factors affecting the performances of sepiolite and zeolite for the treatment of textile wastewater. Journal of Environmental Science and Health Part A: Toxic/Hazardous Substances & Environmental Engineering 2003; 38: 883-896. Armagan B, Turan M, Celik MS. Equilibrium studies on the adsorption of reactive azo dyes into zeolite. Desalination 2004; 170: 33-39. Armagan B, Turan M, Ozdemir O, Celik MS. Color removal of reactive dyes from water by clinoptilolite. Journal of Environmental Science and Health Part A: Toxic/Hazardous Substances & Environmental Engineering 2004; 39: 1251-1261. Armagan B. Factors affecting the performances of sepiolite and zeolite for the treatment of textile wastewater. Journal of Environmental Science and Health Part A: Toxic/Hazardous Substances & Environmental Engineering 2003; 38: 883-896. Capasso S, Salvestrini S, Coppola E, Buondonno A, Colella C. Sorption of humic acid on zeolitic tuff: a preliminary investigation, Applied Clay Science 2005; 28: 159-165. Capasso S, Coppola E, Iovino P, Salvestrini S, Colella C. Sorption of humic acids on zeolitic tuffs. Microporous and Mesoporous Materials 2007; 105: 324-328. Wang S, Terdkiatburana T, Tadé MO. Adsorption of Cu(II), Pb(II) and humic acid on natural zeolite tuff in single and binary systems. Separation and Purification Technology 2008; 62: 64-70. Wang SG, Gong WX, Liu XW, Gao BY, Yue QY. Removal of fulvic acids using the surfactant modified zeolite in a fixed-bed reactor. Separation and Purification Technology 2006; 51: 367-373. Ersoy B, Celik MS. Uptake of aniline and nitrobenzene from aqueous solution by organozeolite. Environmental Technology 200425 () 341-348. Kumpiene J, Lagerkvist A, Maurice C. Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments:a review. Waste Manage 2008; 28 : 215-225. Sunarso J, Ismadji S. Decontamination of hazardous substances from solid matrices and liquids using supercritical fluids extraction: a review. J Hazard Mater 2009; 161: 1-20. Li PJ, Wang X, Allinson G, et al. Risk assessment of heavy metals in soil previously irrigated with industrial wastewater in Shenyang, China. J Hazard Mater 2009; 161: 516521.

236 Handbook of Natural Zeolites

[79]

Hossein Kazemian

Peng JF, Song YH, Yuan P, et al. The remediation of heavymetals contaminated sediment. J Hazard Mater 2009; 161: 633-640. [80] Silva E, Roldan PS. Simultaneous flow injection preconcentration of lead and cadmium using cloud point extraction and determination by atomic absorption spectrometry. J Hazard Mater 2009: 161: 142-147. [81] Chen HM, Zheng CR, Tu C, Shen ZG. Chemical methods and phytoremediationof soil contaminated with heavy metals. Chemosphere 2000; 41: 229-234. [82] Fawzy EM, Soil remediation using in situ immobilisation techniques. Chem Ecol 2008; 24: 147-156. [83] Andres NF, Francisco MS. Effects of sewage sludge application on heavy metal leaching from mine tailings impoundments, Biores. Technol 2008; 99: 7521-7530. [84] Lu XW, Wang LJ, Lei K, et al. Contamination assessment of copper, lead, zinc, manganese and nickel in street dust of Baoji, NW China. J Hazard Mater 2009; 161:1058-1062. [85] Shanbleh A, Kharabsheh A. Stabilization of Cd, Ni and Pb in soil using natural zeolite. Journal of Hazardous Material 1996; 45 (11): 207-217. [86] Oste LA, Lexmond TM, Van Riemsdijk WH. Metal immobilization in soils using synthetic zeolites. Journal of Environmental Quality 2002; 31: 813-821. [87] Ansari Mahabadi A, Hajabbasi MA, Khademi H, Kazemian H. Soil cadmium stabilization using an Iranian natural zeolite. Geoderma 2007; 137: 388-393. [88] Cokca E, Yilmaz Z. Use of rubber and bentonite added fly ash as a liner material. Waste Manag 2004; 24: 153-164. [89] Bergado DT, Ramana GV, Sia HI. Evaluation of interface shear strength of composite liner system and stability analysis for a landfill lining system in Thailand, Geotext. Geomembranes 2006; 24: 371-393. [90] Kaya A, Durukan S. Utilization of bentonite-embedded zeolite as clay liner. Appl. Clay Sci 2004; 25: 83-91. [91] Turan NG, Ergun ON. Removal of Cu(II) from leachate using natural zeolite as a landfill liner material. Journal of Hazardous Materials 2009; 167: 696-700. [92] Shia W, Shaoa H, Li H, Shao M, Du S. Progress in the remediation of hazardous heavy metal-polluted soils by natural zeolite-Review. Journal of Hazardous Materials 2009; 170: 1-6. [93] Dyer A, Chimedtsogzol A, Campbell, L, William C. Micropor Mesopor Mater2006; 95(13): 172-175. [94] Kazemian H, Darybi P, Mallah MH, Khani MR. Vitrification of Cs and Sr loaded Iranian Natural and synthetic Zeolites. J Radioanal Nucl Chem 2006;267(1): 219-223. [95] RobinsonS M, Kent T E, Arnold W D, in: Natural Zeolites ’93: Occurrence, Properties, Use, eds. Ming D W, Mumpton, FA. Int. Comm. Nat. Zeolites, Brockport, NY, 1995; 579-586. [96] Kazemian H, Rajec P, Macasek F, Orechovska Kufcakova J. Investigation of lead removal from wastewater by Iranian natural zeolites using radioanalytical methods. Studies in Surface Science and Catalysis 2001; 135:369-74. [97] Hofstetter J K. Hite GHSep Sci Technol 1983; 18: 1747-1764. [98] British Nuclear Technology, British Nuclear Technology (Risley, Warrington, U.K.) 1987; Paper 9. [99] Grant DC, Skirba M C, Saha A K. Environ Prog 1987; 6(2): 104-109.

Environmental Application of Natural Zeolites

Handbook of Natural Zeolites 237

[100] El-Kamash AM, El-Naggar MR. El-Dessouky MI, Immobilization of cesium and strontium radionuclides in zeolite-cement blends. Journal of Hazardous Materials 2006; 136(2): 310316. [101] Kazemian H, Zakeri H, Rabbani MS. Cs and Sr removal from solution using potassium nickel hexacyanoferrate impregnated zeolites. J Radioanal Nucl Chem2006; 268(2): 231236. [102] Kazemian H, Modarres H, Ghasemi mobtaker H. Evaluating the performance of an Iranian natural clinoptilolite and its synthetic zeolite P for removal of Cerium and Thorium from nuclear wastewaters. J Radioanal Nucl Chem 2003; 258(3): 551-556. [103] Prikryl JD, Pabalan RT. Mater. Res. Soc. Symp. Proc., 556: Scientific Basis for Nuclear Waste Management XXII, 1999; 1035. [104] Prikryl JD, Bertetti FP, Pabalan RT. Mater Res Soc Symp Proc 608: Scientific Basis for Nuclear Waste Management XXIII, 2000; 281. [105] Mimura H, Ishihara Y, Akiba K. Adsorption behavior of americium on zeolites. J Nucl Sci Technol 1991; 28: 144-151. [106] Dyer A, Kadhim FH. Inorganic ion exchangers for the removal of zirconium, hafnium and niobium radioisotopes from aqueous solutions. J Radioanal Nucl Chem1989; 131(1): 161169. [107] Dyer A, Jozefowicz LC. The removal of thorium from aqueous solutions using zeolites. J Radioanal Nucl Chem 1992; 159(1): 47-62. [108] Robinson SM, Begovich JM, Brown Jr. CH Campbell DO, Collins ED. Treatment of radioactive wastewaters by chemical precipitation and ion exchange. AIChE Symp Ser 1987; 83(259): 52-58. [109] Robinson SM, Kent TE, Arnold WD. Treatment of contaminated wastewater at Oak Ridge national laboratory by zeolites and other ion exchangers. In: Ming DW, Mumpton FA, (eds.), Int. Comm. Nat. Zeol, Brockport, New York 14420, 1995; pp. 579-586. [110] Mimura H, Kanno T. Distribution and fixation of cesium and strontium in zeolite a and chabazite. J Nucl Sci Technol 1985; 22: 284-291. [111] Mimura H, Akiba K, lgarashi H. Removal of heat-generating nuclides from high-level liquid wastes through mixed zeolite columns. J NuclSci Technol 1993; 30: 239-247. [112] Mimura H, Kobayashi T, Akiba K. Chromatographic separation of strontium and cesium with mixed zeolite column. J Nucl Sci Technol 1995; 32: 60-67. [113] Seifi L, Torabian A, Kazemian H, Nabi Bidhendi Gh, Azimi A A, Charkhi A. Adsorption of Petroleum Monoaromatics from Aqueous Solutions Using Granulated Surface Modified Natural Nanozeolites: Systematic Study of Equilibrium Isotherms, Water, Air, & Soil Pollution, 2011l; 217(1-4):611-625. [114] Seifi L, Torabian A, Kazemian H, Bidhendi G.N, Azimi AA, Farhadi F, Nazmara S. Kinetic Study of BTEX Removal Using Granulated Surfactant-Modified Natural Zeolites Nanoparticles. Water, Air and Soil Pollution, 2111; 219 (1-4): 443-457. [115] Charkhi A, Kazemian H, Kazemeini M. Experimental design optimized ball milling of natural clinoptilolite zeolite for production of nano powders, Powder Technology 2010; 203: 389-396

238

Handbook of Natural Zeolites, 2012, 238-287

CHAPTER 11 Uses of Natural Zeolites in Operations Involving Organic Gases and Vapors Kyriakos Elaiopoulos* Chemical Process Engineering Laboratory, School of Chemical Engineering, National Technical University of Athens (NTUA), Athens, Greece Abstract: The scope of this chapter is to present a review of relatively recent research work on operations and processes that involve the interaction of natural zeolites with organic vapors or gases, in a simple and comprehensive way. The time horizon for the bibliographic search was set at 20 years back. Modified natural zeolites have also been included, since a modification step (most usually by ion-exchange) of the naturally occurring materials is usually considered essential prior to any use.

Keywords: Natural zeolite, organic vapor, organic gas, adsorption, adsorption heat, isotherm, separation, purification, selectivity, diffusion, accessibility, gas chromatography, catalysis, zeolite modification, binary adsorption, pore engineering, dealumination, henry, langmuir, microporous, mesoporous. INTRODUCTION In order to help the readers focus on the topics they are specifically interested in, the operations and processes that involve the interaction of natural zeolites with organic vapors and/or gases have been divided in 5 groups: 

Adsorption: referring to the removal of traces – or relatively low amounts – of organic vapors or gases from an inert gas, usually air (mostly applied for environmental and/or health protection purposes).



Selective adsorption: referring to the separation of organic vapors or gases from each other or from a carrier stream of inorganic gas. In general, selective adsorption is applied for the purification/enrichment of commercial & industrial gas streams. The term «bulk separation» is typically used for such processes, as concentrations of all substances of interest usually exceed 5%.



Address correspondence to Kyriakos Elaiopoulos: Chemical Process Engineering Laboratory, School of Chemical Engineering, National Technical University of Athens (NTUA), Athens, Greece; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 239



Modification by organic vapors: referring to the effect of organic vapors on the texture properties of natural zeolites through chemical reactions and mass transfer phenomena.



Catalysis of reactions involving organic vapors or gases as reactants.



Gas chromatography (GC).

This classification has only been made for the readers’ convenience. In practice, all operations mentioned in this chapter imply the adsorption of organic molecules on the zeolite surface and/or within the micropores, at least as a first step. Selective adsorption processes are based on the fact that some species are considerably faster or much more strongly adsorbed than others; chemical reactions on the inner surface of zeolites, either with (modification) or without (catalysis) the participation of the solid phase, are feasible only after the organic reactants have been adsorbed; GC is essentially an adsorption-desorption application. Thus, adsorption plays a dominant role in all processes involving zeolites and organic vapors or gases. Zeolite-based separation membranes are not discussed here. These are, usually, made of synthetic zeolites: thin layers of zeolitic material crystallized on a suitable substrate. Alternatively, zeolite membranes can be fabricated on porous supports by dip-coating natural zeolite powder, but the processes involved in the membrane preparation affect the zeolite properties strongly enough to be considered as totally different from those of the starting material. Moreover, the catalytic properties and relevant applications of natural zeolites are thoroughly discussed in the corresponding chapters. In this chapter, some catalytic reactions involving organic species are listed, just to provide a starting point of literature research for readers interested in such topics. Characterization techniques, such as temperature programmed desorption (TPD) and porosimetry measurements using organic compounds are not discussed in this chapter. The text is addressed to anyone that may be interested in potential applications (and the relevant operation principles) of natural zeolites. A minimum of special background knowledge is necessary for the understanding of the text:

240 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

undergraduate chemists, geologists and engineers should find it relatively easy to see through the whole chapter. Besides, the basic concepts of adsorption theory, processes and unit operations are briefly presented. A large portion of general information and data is appropriately summarized in tables and figures for readers who are interested in a resume of potential applications. ORGANIC GASES AND VAPORS Gases are all constituents of a gaseous phase that cannot be isothermally liquefied whatever the pressure applied, as the temperature is higher than a feature property called critical temperature Tc. Substances like nitrogen, argon and methane, with a Tc fairly lower than ambient temperature, are usually referred to as permanent gases. If the pressure applied exceeds the characteristic critical pressure Pc, permanent gases switch over to the supercritical fluid state. Vapors, on the other hand, are the constituents of a gaseous phase that will condensate establishing liquid-vapor (or solid-vapor or solid-liquid-vapor) equilibrium if their partial pressure p gets equal to their vapor pressure (usually symbolized as p0 or ps) which is a temperature dependent parameter. Processes involving the interaction of zeolites with organic substances can be carried out under a wide range of temperature and pressure conditions. In processes involving adsorption from a gaseous phase, the distinction between gases and vapors can be substantial, as these two phases behave differently. Generally, vapors should be expected to exhibit higher adsorptive capacity and slower kinetics than gases. In practice, the term «gases» is often used in a more relaxed way, having in mind ambient conditions as a reference state. Thus, substances with a normal boiling point lower than ambient temperature, like propane and ethylene, are sometimes referred to as organic gases. Most frequently, organic gases are used as raw materials in industry or fuels (i.e., natural gas). Purification, bulk separations and recovery of organic gases are issues of great interest upon which natural zeolites, with their unique properties, can offer viable technical solutions. Volatile organic compounds (VOCs) constitute a special group of organic substances of great technical and environmental interest. VOCs are defined as the chemical substances with a vapor pressure equal to or higher than 0.02 psia at STP (standard temperature and pressure conditions) [1]. VOCs can be used as

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 241

fuels or raw materials (petrochemicals, chemical industry). Chemical and petrochemical industries, automobiles, dye industries, sewage treatment facilities, municipal waste incinerators and biological processes units are sources that emmit large quantities of VOC vapors. Many VOCs are toxic or carcinogenic and their uncontrolled emission in the atmosphere largely contributes to the greenhouse effect due to their high photoreactivity. Natural zeolites have the potential to perform superbly as substrates in processes designed to efficiently remove (filtration) or destruct VOCs. ADSORPTION Adsorption Mechanisms and Equilibrium Data In discussing the fundamentals of adsorption, it is useful to distinguish between physical adsorption, involving only relatively weak intermolecular forces, and chemisorption, which involves the formation of a bond of chemical nature between the sorbate molecule and the adsorbent. This distinction is useful to start with, but there are many intermediate situations and it is not always possible to characterize a given system unequivocally. The heat of adsorption (ΔH) provides a direct measure of the strength of the bonding between sorbate and sorbent. Physical adsorption from the gas phase is exothermic: ΔH values are negative and adsorption is favored by lowering temperature. 30

a

b

c

d

25 20

q 15 [gasml/g] 10 5 0 0

10

20

30

40

p [KPa]

50

60

70

Figure 1: Experimental isotherms of methane adsorption on gmelinite at a) 50 b) 30 c) 0 and d) 23 oC, after Yamazaki et al., [2].

242 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

The general features of physical adsorption are: 

Low heat of adsorption (typically, -ΔH < 50 KJ/mol)



Non specific



Monolayer or multilayer



No dissociation of adsorbed species



Only significant at relatively low temperatures



Rapid, non-activated and reversible



No electron transfer (although polarization of sorbate may occur)

The forces involved in physical adsorption include both van der Waals forces and electrostatic interactions. The latter are pronounced in systems consisting of zeolites and small dipolar molecules. Capillary condensation occurs in mesopores and macropores at high sorbate loading, when multilayer adsorption is driven to such an extent that the thickness of the adsorbed phase becomes equal to the pore radius. Then, the pore is literally filled with liquefied sorbate (from a thermodynamics point of view, the condensate in the macropores has virtually the same properties as the liquid phase under the same pressure and temperature conditions). In physical adsorption, there is no change in molecular state (i.e., no association or dissociation). Thus, for adsorption on a uniform surface at sufficiently low concentrations (concentrations low enough to let us consider that there is no interaction between sorbate molecules), the equilibrium relationship between fluid phase and adsorbed phase concentrations will be linear, following Henry’s Law: or

(1)

where q and c are adsorbate concentrations in the adsorbed and fluid phase respectively, p is partial pressure of the adsorbate in the gaseous phase and K or K΄ is the Henry constant. From the ideal gas low it follows that

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 243

(2) Usually, a dimensionless Henry constant k is preferable for comparison purposes. The dimensionless Henry constant can be calculated if the zeolite crystal density ρc is known by equation: (3) 18 16

chromatography gravimetry

14 12

-lnk

10 8 6 4 0.0014

0.0016

0.0018

0.002

0.0022

0.0024

0.0026

0.0028

1/T [1/K]

Figure 2: Vant Hoff plot for toluene on Na-FAU(Y) derived from chromatographic and gravimetric data, after Canet et al., [3].

The temperature dependence of the Henry constant is formulated using the vant Hoff equation which, neglecting differences in heat capacity between the two phases, is integrated to yield an Arrhenius-type relation: ,

(4)

ΔU0 and ΔH0 are the adsorption energy and isosteric heat of adsorption respectively. In accordance with equation (4), plots of lnK vs. 1/T (referred to as vant Hoff plots) are often found to be linear over a wide range of temperatures, allowing for estimation of –ΔH0 or –ΔU0 from experimental K or K΄ values. Denayer & Baron [4] studied the adsorption of paraffins in faujasite (Y) zeolites. They found that the Henry constants of branched paraffins are somewhat higher than those of the linear isomers, which is evidence that chain branching has little effect on the adsorption parameters in a 3-dimensional system with large

Kyriakos Elaiopoulos

244 Handbook of Natural Zeolites

supercages. Furthermore, the Henry constants and the heats of adsorption of paraffins increased exponentially and linearly, respectively, with molecule size. The following general correlation was extracted for Na-faujasite: .

.

.

. ,

 

(5)

where CN stands for the number of carbon groups. The adsorption of paraffins in H-, dealuminated and PtNa-faujasite exhibited similar behavior.

Figure 3: Temperature dependence of Henry’s law constants of n-alkanes over 100% crystalline Na-faujasite. Experimental data are from Hampson & Rees [5].

For an adsorbent-adsorbate system being at equilibrium, the adsorbent concentration (load) of adsorbate plotted vs. fluid concentration (or partial pressure p, or relative pressure p/ps) at a certain temperature is called an adsorption isotherm. Brunauer et al., have divided the isotherms for physical adsorption into five classes. Adsorption capacity of porous solids results from their surface and structural heterogeneity. In zeolitic materials with a regular structure, heterogeneity may be due to defects in the framework and/or on the inner (micropore) or external (crystal) surfaces.

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 245

1

I II III IV V

relative load

0 0

1

relative pressure

Figure 4: The Brunauer classification of isotherms.

Figure 5: Temperature dependence of Henry constants for benzene, n-heptane and toluene over a natural HEU/MOR-rich specimen (previously unpublished data from author’s work).

Figure 6: Experimental isotherms of n-butane adsorption on 100% crystalline Na-faujasite zeolite, after Hampson & Rees [5].

Kyriakos Elaiopoulos

246 Handbook of Natural Zeolites 40 30

q 20 [gasml/g] 10 0 0

200

400

600

p [mmHg]

Figure 7: Isotherms of ethylene (full symbols) and propene (open symbols) adsorption on Nastilbite at 25 oC, after Li et al., [6].

The isotherms of truly microporous adsorbents, in which pore size is comparable to the sorbate’s molecule diameter, are normally of type I of the Brunauer classification. This is because in such systems there is a definite saturation limit corresponding to complete filling of the micropores [7]. The adsorption of small molecules on highly activated finely powdered natural zeolite specimens may exhibit such behavior, since access to micropores is feasible and, at the same time, mesopore volume is eliminated. It should be denoted that the packing density in micropores can differ significantly from the corresponding liquid density; it can be slightly higher (the adsorbate molecules might jam in favor of higher uptake) or as much as 4 times lower, due to geometry restrictions [8]. When intermolecular attraction effects are large, an isotherm of type V is observed. An isotherm of type IV suggests the formation of two fairly discernible surface layers either on a plane surface or on the walls of pores much wider than the molecular diameter of the adsorbate. Isotherms of types II and III are generally observed only with adsorbents in which there is a wide range of pore sizes, like naturally occurring zeolites. In such systems there is a continuous progression, with increased loading, from monolayer to multilayer adsorption and then to capillary condensation. A major increase in adsorption capacity at high relative pressures is due to capillary condensation taking place in pores of increasing diameter as the pressure is raised. In general, the adsorption process on the external surface (mesopores or larger) differs from that in cages and cavities by a low adsorption energy and a high adsorption rate (looser bonding and easier diffusion, respectively). With adsorbate molecules small enough to enter the zeolite micropore system (after proper activation), isotherms of type II

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 247

are more likely to occur. Activation is a significant step for the micropore nature of natural zeolites to be revealed [9, 10]. Instead, if the adsorbate molecules are too large and/or access to the micropores is somehow hindered, adsorption virtually takes place only in extracrystalline pores, with surface adsorption and capillary condensation being the main adsorption mechanisms, and isotherms of type III are to be expected. An illustration of steric hindrance due to the presence of water is presented in Fig. 8. In this example, benzene adsorption on clinoptilolite samples exhibits type II isotherm behavior after activation by oven-drying at 105 oC, but equilibrium capacity is significantly lower and the isotherm shape turns to almost linear (an upwards shift might be expected at higher p/p0 values) when the zeolite samples are water-saturated. (b)

(a) 6

90

q [mg/g]

60

q [mg/g]

4

2

30

0

0 0

1

p/p0

0

1

p/p0

Figure 8: Isotherms of benzene adsorption at 25 oC on clinoptilolite clay material (circles) and 75% pure clinoptilolite from New Mexico, USA (triangles) after dehydration at 105 oC (a, open symbols) and saturation with water vapors (b, full symbols). Data are from Breus et al., [9].

The simplest theoretical model for monolayer adsorption is due to Langmuir. The basic assumptions of the Langmuir model are: 1.

Molecules are adsorbed at a fixed number of well-defined localized sites.

2.

Each site can hold one adsorbate molecule.

3.

All sites are energetically equivalent.

4.

There is no interaction between molecules adsorbed on neighboring sites.

Kyriakos Elaiopoulos

248 Handbook of Natural Zeolites (a)

(b)

1.5

1.5

1

1

q [mol/Kg ]

Clin

0.5

KClin CaClin

0.5

0

0 0

10

20

30

40

p [KPa]

0

10

20

30

40

p [KPa]

Figure 9: Adorption isotherms of ethylene at 4 oC on unmodified, K-, Ca- and Na-exchanged clinoptilolite-rich tuff specimens from Gordes (a) and Bigadic (b), Turkey. Data are from Erdogan et al., [11].

The Langmuir model is formulated as follows: (6) where b is referred to as the adsorption equilibrium constant and qs represents a fixed number of surface sites (correspondingly, maximum adsorption capacity). At low sorbate concentrations Henry’s law is approached: (7) The temperature dependence of the equilibrium constant follows a vant Hoff equation: (8) The Langmuir model is of the correct qualitative form to represent a type I isotherm, so it may provide a good fit for many data sets. However, unless the experimental data extend over the entire concentration (or partial pressure) range, from the Henry’s law region to nearly saturation, the constants derived by matching the experimental data to the model may lack physical meaning [12].

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 249

In principle, the assumption that sorption takes place at a set of distinct localized sites would be more appropriate to chemisorption than to physical adsorption, since a physically adsorbed layer can be highly mobile resembling more closely a two-dimensional gas. However, the Langmuir equation can derive from the Gibbs adsorption isotherm as an approximation for mobile physical adsorption at relatively low coverage and the application of this model to physical adsorption is therefore not without theoretical justification [12]. Moreover, there are zeolite/adsorbent systems for which the basic assumptions of Langmuir’s model can be fulfilled as each cage can only host one sole adsorbate molecule. Physical adsorption generally involves multilayer adsorption, unless the p/ps value is particularly low. In certain pores, a secondary, then a tertiary and subsequent molecular layers may start building up at pressures below the pressure required for completion of the monolayer, so it is not directly obvious how to extract the monolayer capacity (and thus calculate the specific surface area) from an experimental isotherm. Brunauer, Emmett and Teller (BET) have developed a simple model isotherm to account for multilayer adsorption. The equation for the BET isotherm is: (9) in which qm represents the saturation limit of the monolayer. The BET equation is suitable for isotherms of type II and, despite the fact that it is based on quite a number of serious idealizations, it has been found to provide a good representation of experimental isotherms in the range 0.05 < p/ps < 0.35. Capillary condensation occurs because the saturation vapor pressure in a small pore is reduced by the effect of surface tension. Assuming cylindrical pore geometry, capillary condensation will occur in all pores with a radius smaller than the critical radius r at a given pressure p according to the Kelvin equation: (10) where σ is the liquid surface tension, Vm is molecular volume, T is temperature and θ is the contact angle of the condensate meniscus to the pore wall.

Kyriakos Elaiopoulos

250 Handbook of Natural Zeolites

The onset of capillary condensation generally coincides with an upward turn of the equilibrium isotherm. However, the capillary effect is significant only in relatively small pores or quite high partial pressures. Taking benzene at 20 oC as an example and assuming θ = 0, it can be calculated that in cylindrical pores with a diameter of 50 Å capillary condensation will occur at a relative pressure p/ps ≈ 0.67 [12]. Yet, pores of large dimensions are intrinsic in natural zeolites due to the – more or less – random arrangement of crystals and other structural defects. With large grain sizes, macropores with diameters even in the order of 500 Å can be present. 5.E‐04 4.E‐04 3.E‐04

q [mol/g] 2.E‐04 1.E‐04 0.E+00 0

10

20

30

40

50

p [mmHg]

Figure 10: Type-II isotherms (4, 11 and 26 oC) of n-heptane adsorption in a 0.80-1.18 mm granular fraction of a heulandite/mordenite-rich tuff covering the whole p/p0 range [13].

The different mechanisms of adsorption that may be prevalent depending on adsorbate properties (such as molecule size and polarity, volatility, etc.) and natural zeolites unique structural characteristics along with a variety of optional activation states and pore engineering techniques can lead to a vast variety of potential applications. With dealumination, hydrophilicity of natural zeolites can be reduced yielding better adsorption properties for organics in humid fluids. Moreover, dealumination by acids often results in improved accessibility and diffusion rates as a secondary mesoporous structure is created due to the leaching of amorphous substances. On the other hand, with higher Si/Al ratios the active sites in the cavities may decrease and, unless surface adsorption prevails, the overall uptake at low pressures will be decreased [14].

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 251

Natural clinoptilolite has a considerable potential for the removal of ethylene vapors from air and could be used as an effective adsorbent in storage facilities prolonging storage life of fruit and vegetables [11]. Yoda et al., found that ethene and propene adsorb selectively on the acidic –OH groups in the small pores of ferrierite while butenes adsorb on the silanol groups of the external surface as well [15]. Dealuminated faujasite seems to be a very effective adsorbent for the chlorinated C2-VOCs dichloroethane, trichloroethane and tetrachloroethane with potential use in air cleaning processes [16]. In contrast, chlorofluorocarbons are weakly adsorbed in the internal channels of zeolites [17]. Large polar molecules that cannot enter the zeolites cavities on the basis of the molecular sieving effect, can still be protonated by the terminal hydroxyl groups of the external silanol sites and adsorb strongly there [18]. In the case of mordenite-alkane systems, it has been shown that for methane and ethane possible sorption sites exist in the side pockets of the cavities whereas longer n-alkanes essentially reside in the main 12ring channel [19]. Molecular simulation studies by Wender et al., [20] showed that alkanes adsorbed in Na-faujasite fill the supercages only. Also, the interaction between organic molecules and acidic zeolites does not depend only on the Brønsted group centers but also on the lattice framework surrounding the adsorption site [21]. Amines can be adsorbed by H-mordenite: The amine molecule is protonated (forming RNH+) by the H-MOR framework and stabilized by hydrogen bonding between the negatively charged zeolite framework and the N-H bonds [22]. The adsorption of acetophenone on dealuminated mordenite is the result of the formation of relatively weak hydrogen bonds between the external silanol groups and the OH- group [23] while with non-dealuminated mordenite the acetophenone molecule can be much more strongly adsorbed through the formation of a complex where silanol groups are perturbed by benzene rings and the acetophenone oxygen is bonded directly to lattice Al3+ (see Fig. 11). Moreover, Grillo & Ramirez de Agudelo [24] studied the effect of counter-balancing ions on adsorption mechanisms and reported that at high Pt loadings, the effective pore blocking by Pt particles leads to the adsorption of nbutanes in small side pockets of Pt-mordenite, where high coordination with lattice oxygen ions offers the best stabilization through optimization of adsorbatezeolite dispersion forces.

252 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

Figure 11: Conformation of acetophenone molecule on non-dealuminated mordenite surface.

Porosimetric properties and structural/chemical characteristics do not always provide all the information necessary to evaluate a natural zeolite’s potential for adsorption applications. Erdogan et al., [11] found that the uptake of ethylene by ion-exchanged clinoptilolite increased in the sequence Na-CLIN < Ca-CLIN < KCLIN < Natural CLIN, although specific surface area followed the trend Ca- < Na- ≈ Natural < K-CLIN. On the other hand, adsorption of organic compounds can be used in porosimetry measurements, either providing feedback data or by using the organic molecules as probe molecules. Guil et al., [8] used differences in the uptake of organic molecules of different geometry (n-hexane, toluene, nxylene and 1,3,5-trimethylbenzene) by dealuminated mordenite in combination with microcalorimetry measurements to determine the micropore diameter and confirmed the existence of micropore sets of different diameter. Moreover, postadsorption experiments after pre-adsorption of different adsorbates gave information on the connectivities or crossings between sets of zeolite channels. Basic Concepts of Adsorption Operations In most adsorption processes the adsorbent is contacted by the fluid phase in a packed column. Particle size and shape, fluid velocity and bed dimensions are the factors that primarily determine the pressure drop having an important impact on the economics of the process, since they determine the pumping cost as well as the extent of axial mixing and the heat transfer properties. Additional problems like dispersion, channeling and large length of unused bed (LUB) potentially caused by loose packing (in fixed beds), extreme bulk flow velocity or unsuitable particle dimensions must be considered when designing such process systems [25]. The basic concepts encountered when dealing with adsorption operation systems are:

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 253



Cyclic batch or semibatch systems: The adsorbent bed is alternatively saturated (or nearly saturated) and regenerated in a cyclic manner. With the use of a few beds functioning in parallel at different time phase, the overall operation can meet the demands of continuous feed treatment.



Continuous flow systems: Continuous countercurrent contact between adsorbate feed stream and adsorbent particles. The adsorbent is recirculated from adsorption bed to regeneration vessel.



Adsorption capacity: The amount of adsorbed molecules being at equilibrium with the fluid phase at any given set of temperature and pressure conditions.



Regeneration: The adsorbent is forced to desorb the adsorbed molecules under controlled conditions (depending on the nature of the application the desorbed gases or vapors are retrieved or destroyed) in order to be reused. Ideally, the adsorbent returns to its starting (activated) condition after regeneration. Regeneration can be achieved using elevated temperature (thermal swing adsorption – TSA, usually with hot gas), lowered pressure (a pressure swing adsorption – PSA system, in its basic form, consists of two beds which are alternately pressurized and depressurized according to a preprogrammed sequence), purge gas stripping, displacement (as in displacement chromatography) or a combination of the above. Regeneration by microwave heating has also been proposed [26].



Fixed bed: A column is packed with the adsorbent particles and feed velocity is kept at low levels so that no particle movement occurs.



Bed voidage or bed void fraction or bed porosity: The portion of the bed volume actually unoccupied by the solid phase and thus available for the bulk flow of the gaseous phase. Bed voidage is primarily affected by particle shape and size. The normally expected bed voidage values of tightly packed granular solids are between 0.35 –

254 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

0.55. Catalyst-shaped particles may result in significantly higher void fractions [27]. 

Packing: Packing refers to the proper arrangement and settlement of the adsorbent particles so that bed voidage is kept to a minimum. Tight packing is necessary not only in order to augment the storage capacity of the column but also to eliminate non ideal flow phenomena such as channeling and axial dispersion.



Non ideal flow: The feed flux is supposed to move through the bed length with a steady front offering the same contact time for all feed molecules. Non ideal flow phenomena may emerge because of loose packing, irregular particle shape and/or extremely low or high feed velocity, especially in columns with a low height to width ratio. In the presence of non ideal flow regimes, the real residence time distribution is widely spread reducing the process efficiency since the length of unused bed is increased.



Breakthrough: A breakthrough curve is a plot of the concentration of the adsorbate in the outlet of a bed operating in cyclic mode vs. time. Adsorption kinetics are, in general, quick enough to make sure that the outlet concentration of a plausibly long bed will be literally zero for a prolonged time period but also slow enough to provide a time period during which the outlet concentration rises little by little before reaching the same level as inlet concentration. In other words, there is a time period during which a portion of the adsorbate escapes the bed boundaries while the packing material is not totally saturated. Since it is normally desired to stop operation and regenerate the material at the breakthrough point (or breakthrough time) tb, namely at the time when the outlet concentration exceeds a threshold value imposed by the process special demands, the adsorptive capacity of the solid is not fully exploited.



Stoichiometric time: The stoichiometric time ts is a theoretical value that can be estimated by mass balance calculations. It represents the

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 255

time necessary to saturate the whole packing material of the bed supposing that adsorption was spontaneous. 

Length of unused bed (LUB): It is a measure of the extent to which the capacity of the adsorbent is not exploited. %

(11)



Competitiveness: Competitiveness refers to the fact that physical adsorption is a non-selective process. Thus, molecules of substances with similar properties (i.e., polarity, dimensions, volatility) have to compete for the adsorption sites. In bulk separation (selective adsorption) processes, the term selectivity is more usual. By saying that there is high selectivity for one component of the gaseous phase we mean that, for some reason (i.e., much lower volatility, chemical character of sorption, etc.), this component is sorbed preferably enough to permit complete removal from the fluid with very little adsorption of other components.



Fluidized bed: As the feed velocity increases, there is a limit above which the adsorbent particles are drifted into short-range vortexes by the bulk flow and the bed active length increases (swelling). The next step, with even higher velocities, is fluidization, a state in which the adsorbent particles are fully suspended and the suspension behaves like a dense fluid. Fluidization, which is easier to achieve in upflow mode, is sometimes preferable to eliminate external mass transfer effects. The fluidized solids can be drained from the bed and circulated through pipes and valves just like a liquid. This option offers better handling of solids, especially in continuous flow systems [28].



Pore engineering: A general term given to methods such as calcination (implying rather high temperatures), steaming, ion-exchange, acid leaching etc. applied for the modification of zeolites in an attempt to manipulate kinetic separation properties (although adsorption capacities are certainly affected as well) by altering pore geometry and surface texture.

256 Handbook of Natural Zeolites

Kyriakos Elaiopoulos



Activation: Most adsorbents must be activated before usage in adsorption processes so as to remove impurities and humidity that may hinder access to pores and adsorption sites. Thorough washing, drying and mild calcination at atmospheric or vacuum pressure is a typical activation procedure. Heavier treatments that can modify the crystal structure, like acid leaching or high-temperature calcination, are rather considered as modification or pore engineering techniques.



Equilibrium separation: A separation process based on the differences in adsorption capacity of two molecules or groups of molecules.



Kinetic separation: A separation process based on the differences in diffusion rates.



Steric separation (molecular sieving): A separation process based upon the exclusion of one or more of the gases in the mixture by the zeolite pores.



Selectivity: Selectivity is a measure of the tendency of any adsorbent to preferentially adsorb one species rather than one other under a well defined set of experimental conditions. Sometimes, a discrimination between equilibrium selectivity and kinetic selectivity is necessary. The former is based on differences in adsorption capacity; the latter refers to differences in uptake rates that can lead to efficient separation (usually by PSA application).

Accessibility The sorptive and catalytic properties of zeolites depend on their ability to host molecules selectively on the basis of their size, geometry and interaction strength. As a principle, only molecules with cross-sections small enough to pass through the windows and channels of the zeolite structure can reach the sorptive sites within the zeolite cages; larger molecules can only adsorb on external surfaces. Access to acidic –OH groups or to large proportion of pore surface of zeolites can be hindered by a variety of factors such as pore size and geometry, adsorbate molecule dimensions and polarity, humidity and zeolitic water, charge-balancing cations nature,

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 257

concentration and distribution, presence of impurities and degree of crystallinity. Highly restrained accessibility is associated to molecular sieving phenomena. Accessibility can be extensively modified by proper activation and pore engineering techniques, although excessive acid leaching and/or calcination may have an opposite effect if lattice collapse and crystallinity loss should take place. Cations entrapped in the channels of the crystals can restrict effective pore volume and surface area either by cloaking or by hindering access to sites otherwise available for adsorption.

Gas phase molecular ratio

Severe kinetic restrictions may turn pores and adsorption sites that should normally be considered accessible, on the basis of equilibrium conditions, to practically inaccessible, at least under the consideration of a specific application needs and working conditions (in other words, an undesired kinetic selectivity issue might come up). 0.4% 0.3% 0.2% 0.1% 0.0% 0

10

20

30

40

50

60

Time [min]

Figure 12: An explanatory scheme of a breakthrough curve. In this example, the inlet molecular ratio is equal to 0.315% (dotted line). The outlet molecular ratio is increased with time producing a typical S-shaped breakthrough curve. An early rise – like the one at ~8 min in this example – implying channeling or other flow problems may occur. Outlet and inlet concentrations converge only after ~135 min, as slow kinetics cause an asymptotic behavior at the right wing of the breakthrough curve. With the maximum value of outlet molecular ratio acceptable set at 0.010% or 0.025% or 0.100%, the breakthrough time will be equal to 18 or 27 or 29 min, respectively. At any rate, the stoichiometric rate is equal to 31.5 min.

Adsorption Heat Adsorption heat is a common simplified term for the isosteric heat of adsorption. At any given temperature, the isosteric heat of adsorption –ΔH0 is higher than the respective condensation heat. The variation of adsorption heat with uptake may

258 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

provide information on the surface chemistry allowing one to determine whether there is adsorption specificity or not [8]. At low coverage, especially with small polar molecules, the isosteric heat of adsorption can be relatively high, since the presence of strong electrostatic fields may result in partially chemical bonding. As coverage turns higher and capillary condensation becomes the main sorption mechanism, adsorption heat values converge to a minimum value which is approximately equal to the value of condensation heat. With well activated microporous adsorbents having relatively insignificant mesoporous volume, -ΔH0 values can be expected to be nearly constant in a wide coverage range, from the end limit of the Henry region up to quite high coverage [29]. Adsorption heats can be calculated using either experimental or computational (molecular simulation) techniques. The values calculated by molecular simulations are very close to experimental ones provided that the same activation level of the adsorbent is taken into account. Adsorption heat is only slightly affected by temperature, so it can be considered constant for small and medium temperature ranges. It is correlated to adsorption energy, a temperature independent property, by equation: (12) Dealumination results in a decrease in adsorption energy due to a reduction in polarization energy. An increase in adsorption energy after dealumination, especially with acid leaching, might be associated to differences in accessibility: the micropores and cages of a dealuminated zeolite specimen are expected to be less occupied by counter-balancing cations and extraframework materials than the parent material [30]. Arcoya et al., [31] studied the adsorption of methane over clinoptilolite loaded with a variety of cations. They calculated very similarly low –ΔH0 values for H-, Na-, K-, Cs- and Mg-exchanged clinoptilolite, indicating that adsorption is controlled by diffusion rate rather than by electrostatic interactions. In H-zeolites, as the cation content in the framework is decreased, the perturbations of OH bonds in methanol adsorbed are weakened and adsorption heats are decreased. But the protonic acid sites of decationated mordenite can

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 259

form strong hydrogen bonds with adsorbed CH3OH molecules, or even protonate them, thus compensating for the decrease of the ion-dipole interaction contribution. As a result, adsorption heat values of CH3OH for Na- and Hmordenite are almost equal at low coverage [32]. Ruthven & Kaul [33] reported that the adsorption heat of aromatics on Nafaujasite (X) is not dependent on molecule shape but increases linearly with carbon number. Similar observations for n-paraffins and branched isomers adsorbed on Na-, H-, PtNa- and dealuminated FAU(Y) were made by Denayer & Baron [4]. A linear correlation between isosteric heat of adsorption and carbon number for the adsorption of linear alkanes in zeolites is also supported by studies based on molecular simulation [34]. Table 1: Adsorption heats calculated for various adsorbent-adsorbate systems. The prefix D stands for «dealuminated» and the prefix St for «steamed». Abbreviations: m sim: molecular simulation, exp: experimental, mpuc: molecules per unit cell, θ: relative coverage (amount adsorbed divided by maximum adsorption capacity) Organic Adsorbate

Zeolite

Loading

-ΔH [Kcal/mol]

methane

3.3 / 3.7

ethane

5.0 / 4.8

propane

7.2 / 6.6

n-butane n-pentane

FAU

n-hexane

at infinite dilution

8.4 / 8.8 11.0 / 10.7 12.9 / 13.1

cyclohexane

11.2 / 11.2

ethylene

60.0 / -

benzene

18.9 / 19.0

pyridine

13.4 / -

p-xylene

20.5 / -

o-xylene

21.0 / 21.7

n-xylene

21.2 / 20.2

methane

DFAU

10-30 mpuc

ethane propane n-butane

~3.3-3.6

Method Used

Ref #

m sim / exp

[19]

exp & m sim

[35]

m sim

[36]

4.7-6.4 DFAU

1-32 mpuc

6.1-7.9 9.3-12.5

Kyriakos Elaiopoulos

260 Handbook of Natural Zeolites Table 1: cont….

19-20.5

exp

19-21

m sim

θ1% (Fig. 18). Daems et al., [60] reported that the benzene/n-hexane separation factor at 260 oC was 19.7 for Na-FAU(X) but only 8.4 for Na-FAU(Y). Also, The adsorption of benzene, toluene, n-hexane and tetrachluoromethane on CLIN/MOR-rich tuffs from Mexico and Hungary was studied by Elizalde-Gonzalez & Perez-Cruz [45] and the selectivity order was C6H6 > C7H8 > C6H14 > CCl4 for all three unmodified, dealuminated and Pb-exchanged samples at 100 oC and p/ps < 2×10-3.

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 275

150 125 100

q [μl/g] 75 50 25 0 0

0.5

1

1.5

%Sn

Figure 18: Influence of tributyltin concentration on the adsorption capacity of (C3H9)3Sn-MOR for n-C6 (circles) and i-C8 (squares). Experimental data are from [80].

The Neapolitan yellow tuff, a phillipsite/chabazite containing volcaniclastic rock, rich in phillipsite, was proposed by Colella et al., [81] for an inexpensive dehydration process of ethanol vapors based on fixed bed columns [81]. In a relevant work, a phillipsite/chabazite specimen from Campania, Italy, is reported to show high selectivity for water vapors offering water/ethanol separation factors in the order of 6-7 for the azeotropic mixture [46]. Triebe et al., [41] reported that experimental values of separation factors for the ethylene/methane binary system over H-mordenite started from ~40 at 0 oC and progressively dropped to ~20 at 200 oC. Separation of unsaturated hydrocarbons from alkanes can be achieved by Ca-mordenite, since Ca2+ ions seem to interact strongly with C=C bonds leading to high alkene/alkane separation factors. It has been experimentally observed that separation of halocarbons from air is possible using Na-Y zeolites. Halocarbons are substances of major global environmental concern. Chatterjee et al., [82] made first-principle calculations and showed that for the separation of hydrogenated halocarbons cation migration is the key which further enhances the Na-F interaction resulting in better separation of hydrogenated fluorocarbons. The interaction of fluoride with Na+ was found to be dependent on the fluorine concentration. Thus, depending on the concentration of chlorine / fluorine and with an appropriate faujasite matrix, halocarbons can be efficiently separated.

276 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

It has been proposed that changes in adsorption selectivity can be achieved by microwave emission onto zeolites loaded with (pre-adsorbed) polar molecules, based on the principle that adsorbed polar molecules readily adsorb microwave energy and are heated selectively, locally producing heat at adsorption site [26]. Separation by selective adsorption is feasible using fixed beds filled with an adsorbent showing higher affinity for the substance which is more abundant in the gaseous phase. In Fig. 19, an example of ethylene-water containing gas feed treated with a Na-mordenite fixed bed is presented. Ethylene shows up early in the outlet stream, as the water molecules are preferentially adsorbed by Na-mordenite [26]. The outlet ethylene concentration progressively increases, but it reaches values higher than that of the inlet concentration. This is due to ethylene desorption, caused by the zeolite’s higher selectivity for water: ethylene molecules are displaced by water molecules. When equilibrium is approximated, water shows up at the outlet and, at the same time, ethylene concentration is decreased. At equilibrium, most of the ethylene molecules will have been desorbed and the adsorbed phase will contain almost exclusively the favored water molecules. Thus, the hydrophilicity of the adsorbent, which would be considered a drawback if ethylene uptake was the issue, turns out to be beneficial for the separation of ethylene form humid gas streams. Apparently, the separation of ethylene from water is based on the time period from the breakthrough point of ethylene till the breakthrough point of water, when the outlet gas stream contains only ethylene vapors. CATALYSIS The possible use of zeolites in catalytic reactions has been largely studied in the last two decades. Emphasis has been given to mordenite, faujasite, clinoptilolite, ferrierite and chabazite. Most researchers tend to use synthetic zeolites in experimental work; this is, probably, due to convenience: basic properties and specifications are provided by the suppliers and experimental data are free of any extra obscurities possibly deriving from the complexity of natural specimens. Yet, the principal conclusions coming from such experimental works can – normally – be extrapolated to the natural zeolite analogues, at least on the basis of reaction mechanisms and kinetics.

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 277

water ethylene 1

Cout / Cin

0

t

Figure 19: Paradigmatic binary breakthrough curve of a water-ethanol vapor containing gaseous phase passing through a fixed bed filled with Na-mordenite.

The variety of zeolite types offers many options for potential catalytic applications. Faujasite, in example, is a very versatile catalyst well suited for catalytic cracking and hydrocracking of hydrocarbons. Moreover, its large pore size allows for the reforming of linear paraffins with a low octane number to branched high octane paraffins [4]. In recent literature, numerous examples of natural zeolites showing extraordinary catalytic behavior in specialized applications of great technical/economical interest can be found. With transition metals impregnation and pore engineering techniques the range of possible applications is infinite. The subject of natural zeolites used as catalysts is thoroughly dealt with in other chapters of this book. Here, a brief survey of recent literature about natural zeolites used as catalysts in reactions involving organic gases or vapors is presented. The list in Table 4 should only be considered as a denotation of the versatility and possible advantages of natural zeolites in catalysis or as a hint for further bibliographic search. Table 4 is not representative of the interest shown on each zeolite or catalytic application, as in the majority of published papers it is not clear, especially for faujasite, whether the final catalyst product is based on a natural starting material or not.

Kyriakos Elaiopoulos

278 Handbook of Natural Zeolites

Table 4: Survey of recent literature concerning the use of natural zeolites in catalytic reactions involving organic vapors and gases Reaction

Catalyst

Comments

Ref #

Toluene combustion

Fe-CLIN, Co-CLIN, MnCLIN

Up to 93% conversion at 350oC

[83]

H-CLIN

High selectivity

[84]

FER

Steamed/acid-washed FER free of amorphous phases exhibitted excellent selectivity and stability

[85]

H-ERI

NaK-ERI is catalytically inactive

[76]

H-CLIN treated with boric acid

Very good performance

[86]

Ethylene hydrogenation

Ni-CHA, Mo-CHA, NiMoCHA

NiMo-CHA showed unique selectivity and resistance to sulfur poisoning

[87]

n-hexane isomerization

Pd-MOR/CLIN

High efficiency

[88]

n-hexane cracking

H-MOR

Steaming enhances the rate of reaction due to the formation of Lewis acid sites with enhanced adsorption heat

[42]

Propane dehydrogenation

CLIN, H-CLIN

H-CLIN showed higher conversion but lower propylene selectivity

[89]

n-heptane cracking

H-FAU

Skeletal isomerization of nbutene to isobutene

Co-FER, Co-MOR NOx reduction by CH4

Co-FER, Mn-FER, Ni-FER

NOx reduction by octane & isooctane

Pt-CHA, Ag-CHA, PtAgCHA

Methanol to dimethylether dehydration

NH4-CLIN

[90] Promissing catalysts

[91] o

More active than Co-ZSM5 at T>500 C, more selective in the use of CH4

[92] [93]

Low activation energy

Cu-MOR

[94] [95]

Cu-MOR, DealMOR

Better resistance to hydrothermal aging than the synthetic analogue / up to 80% conversion at 400oC

[96]

Preparation of methylamines from methanol and from dimethylether

CHA

Low trimethylamine selectivity can be achieved at high conversion

[97]

Photodecomposition of organic contaminants

CLIN/TiO2 photocatalytic paper

Enhanced ability in the presence of CLIN

[98]

n-hexane hydroisomerization

PtH-MOR, DealPtHMOR

Dealumination resulted in higher uptake and reaction rate / increased primary reduction products observed

[14]

NOx reduction by C3H6

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 279 Table 4: cont….

a-pinene isomerization

CLIN, NH4-CLIN, PbCLIN, Ba-CLIN

[99]

Preparation of acrolein from lower aldehydes

CLIN, Ca-CLIN, HCLIN, DealH-CLIN

[100]

n-alkanes hydrocracking

Sulfided NiH-ERI

Absence of branched products / selectivity towards C3H8 formation

[101]

1-butene hydration

H-CLIN

Kinetic inhibition may arise by inactive alcoxonium ions

[102]

Conversion of methanol into light alkenes

MOR, DealMOR

MOR is rapidly deactivated by coke deposition / DMOR shows higher selectivity to light alkenes / with lower pressure and water added to the feed the production of aromatics is constrained

[103]

Chlorofluorocarbons decomposition

MOR, FAU

[17]

Skeletal isomerization of 1-butene

Co-, Ba-, Ni-, Zn-, Mg-, Ca-, Sr-, Mn- and CuCLIN

[104]

MODIFICATION OF NATURAL ZEOLITES BY ORGANIC GASES AND VAPORS The application of organic reactants in order to modify zeolites is not very common in recent literature. In addition, most applications of such nature are carried out with the organics involved being in the liquid phase. Thus, only two examples are presented here. Kucherov et al., [105] presented a new method for the introduction of multicharged cations into the zeolite cages. They used active gas-phase species formed in situ upon thermal treatment of a (H-zeolite + modifier oxide) mixture with an air flow containing CCl4 vapors. The formation of reactive and mobile oxychloride fragments provided effective dissipation of the oxide phase and migration of active species into the zeolite channels at temperatures 150-300 oC. Silanation of the external surface of zeolite crystals can be achieved by Si(OCH3)4 vapors [106]. The reaction mechanisms are: ≡SiOH + Si(OCH3)4 → ≡SiO−Si(−OCH3)3 + CH3OH and

280 Handbook of Natural Zeolites

Kyriakos Elaiopoulos

2≡SiOH + Si(OCH3)4 → (≡SiO−)2Si(−OCH3)2 + 2CH3OH resulting in the production of shape selective catalysts without adversely affecting the inherent activity of the zeolite. GAS CHROMATOGRAPHY In theory, due to their molecular sieve properties, natural zeolites could be used as packing materials in gas chromatography (GC) columns. Data from experiments (originally carried out for other purposes) indicate that natural zeolites could easily separate gaseous hydrocarbons from each other and from a variety of inorganic gases, such as N2, O2, CO and H2S. Yet, little research has been carried out in this field in the last two decades. Tezel & Apolonatos [107] determined adsorption equilibrium constants and selectivities of CO, CH4 and N2 on natural chabazite and synthetic zeolites, in the Henry law region. Their results indicated that, on the basis of adsorption equilibrium selectivities, CO-CH4 separations are easy with all the materials tested, but chabazite offered the least promising results for the gases studied. Also, An & Joye [108] achieved N2/CH4/Ar/O2 separation in a GC column of 2m length packed with Ca-exchanged natural chabazite (40/60 mesh size), obtaining high resolution data at relatively low column temperatures, with small sample quantities and short analysis time. In practice, the materials that are typically used in commercial GC columns are porous C- or Si- polymers, carbon molecular sieves and other carbonaceous materials. Synthetic zeolites, mainly 5A and 13X, are also used [109]. Natural zeolite specimens of the same type can vary significantly in terms of impurities and counter-balancing cations content. This can affect very strongly various parameters which are critical in gas separation operations, such as specific surface area, diffusivities of gaseous species, micropore blockage/accessibility, selectivities, etc. These parameters have not been satisfactorily correlated in a cause-effect basis. Consequently, one cannot safely use experimental data concerning – for example – one mordenite specimen to estimate the exact behavior of any other mordenite specimen. Sometimes, natural zeolite deposits can be heterogeneous enough to generate unpredictable behavior of specimens coming from the same location. On the other hand, GC column manufacturers

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 281

need to guarantee for optimum and reproducible results of their products. So, it is natural that synthetic zeolites, with a well defined and easily reproducible structure, provide a more tempting solution.

Figure 20: Chromatogram showing the separation of argon, oxygen, nitrogen and methane from a temperature-programmed gas analysis using a column packed with Ca-chabazite. Retention times are 2΄50΄΄, 3΄18΄΄, 8΄24΄΄ & 11΄35΄΄, respectively, with a non-linear temperature raise from 303 to 438K. Data are from [108].

ACKNOWLEDGEMENTS None declared. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6] [7]

Stander L, Theodore L, Eds. Environmental regulatory calculations Handbook. New Jersey: John Wiley & Sons Inc 2008. Yamazaki T, Nishimura H, Ozawa S. Adsorption behavior of some gas molecules in Ωzeolite pores. Micropor Mesopor Mater 2000; 38: 187-96. Canet X, Nokerman J, Frere M. Determination of the Henry constant for zeolite-VOC systems using massic and chromatographic adsorption data. Adsorption 2005; 11: 213-16. Denayer J, Baron GV. Adsorption of normal and branched paraffins in faujasite zeolites NaY, HY, Pt/NaY and USY. Adsorption 1997; 3: 251-65. Hampson JA, Rees LVC. Adsorption of ethane and propane in silicalite-1 and zeolite NaY: determination of single components, mixture and partial adsorption data using isosteric system. J Chem Soc, Faraday Trans 1993; 89: 3169-76. Li J, Qiu J, Sun Y, Long Y. Studies on natural STI zeolite: modification, structure, adsorption and catalysis. Micropor Mesopor Mater 2000; 37: 365-78. Roque-Malherbe R. Complementary approach to the volume filling theory of adsorption in zeolites. Micropor Mesopor Mater 2000; 41: 227-40.

282 Handbook of Natural Zeolites

[8] [9] [10] [11] [12] [13]

[14] [15] [16]

[17] [18] [19] [20] [21] [22] [23]

Kyriakos Elaiopoulos

Guil JM, Guil-Lopez R, Perdigon-Melon JA, Corma A. Determining the topology of zeolites by adsorption microcalorimetry of organic molecules. Micropor Mesopor Mater 1998; 22: 269-79. Breus I, Denisova A, Nekljudov S, Breus V. Adsorption of volatile hydrocarbons on natural zeolite-clay material. Adsorption 2008; 14: 509-23. Elaiopoulos K, Perraki Th, Grigoropoulou E. Mineralogical study and porosimetry measurements of zeolites from Scaloma area, Thrace, Greece. Micropor Mesopor Mater 2008; 112: 441-49. Erdogan B, Sakizci M, Yorukogullari E. Characterization and ethylene adsorption of natural and modified clinoptilolites. Appl Surf Sci 2008; 254: 2450-57. Ruthven DM, Ed. Principles of adsorption and adsorption processes. New York: John Wiley & Sons 1984. Elaiopoulos K, Grigoropoulou E, Salmas K. Prediction of adsorption isotherms of volatile organic compounds vapors on mesoporous materials through the CPSModel. Proceedings of the 19th International Congress of Chemical and Process Engineering; 2010 Aug 28 – Sept 1; Prague, Czech Republic. Prague: The Organizing Committee 2010. Van Donk S, Broersma A, Gijzeman OLJ, van Bokhoven JA, Bitter JH, de Jong KP. Combined diffusion, adsorption and reaction studies of n-hexane hydroisomerization over Pt/H-Mordenite in an oscillating microbalance. J Catal 2001; 204: 272-80. Yoda E, Kondo JN, Wakabayashi F, Domen K. Shape selective adsorption of olefins on Bronsted acidic OH (OD) groups on ferrierite studied by FT-IR. Appl Catal, A 2000; 194195: 275-83. Clausse B, Garrot B, Cornier C, Paulin C, Simonot-Grange MH, Boutros F. Adsorption of chlorinated volatile organic compounds on hydrophobic faujasite: correlation between the thermodynamic and kinetic properties and the prediction of air cleaning. Micropor Mesopor Mater 1998; 25: 169-77. Hannus I. Adsorption and transformation of halogenated hydrocarbons over zeolites. Appl Catal, A 1999; 189: 263-76. Armaroli T, Bevilacqua M, Trombetta M, Gutierrez Alejandre A, Ramirez J, Busca G. An FT-IR study of the adsorption of aromatic hydrocarbons and of 2,6-lutidine on H-FER and H-ZSM-5 zeolites. Appl Catal, A 2001; 220: 181-90. Mentzen BF. Energetics and siting of sorbed molecules in zeolite by computer simulations. Comparison with calorimetric and structural results. I – aliphatics and aromatics in faujasite and mordenite. Mater Res Bull 1995; 30: 1193-200. Wender A, Barreau A, Lefebvre C et al., Adsorption of n-alkanes in faujasite zeolites: molecular simulation studies and experimental measurements. Adsorption 2007; 13: 43951. Kasuriya S, Namuangruk S, Treesukol P, Tirtowidjojo M, Limtrakul J. Adsorption of ethylene, benzene and ethylbenzene over faujasite zeolites investigated by the ONIOM method. J Catal 2003; 219: 320-28. Jiang N, Yuan S, Wang Z, Jiao H, Qin Z, Li Y-W. A theoretical study of amines adsorption in HMOR by using ONIOM2 method. J Mol Catal A: Chem 2004; 220: 221-28. Ahmad I, Anderson JA, Dines TJ, Rochester CH. Infrared study of acetophenone adsorption on mordenite and dealuminated mordenite. J Colloid Interface Sci 1998; 207: 371-78.

Operations Involving Organic Gases and Vapors

[24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42]

Handbook of Natural Zeolites 283

Grillo ME, Ramirez de Agudelo MM. Structure and initial interaction of butane and butane isomers in a Pt/H-mordenite catalyst. J Mol Catal A: Chemical 1997; 119: 105-12. McCabe WL, Smith JC, Harriott P, Eds. Unit operations of chemical engineering. New York: McGraw-Hill Int 1993. Kim SI, Aida T, Niiyama H. Binary adsorption of very low concentration ethylene and water vapor on mordenites and desorption by microwave heating. Sep Purif Technol 2005; 45: 174-82. Tilton JN. Fluid and particle dynamics. In: Perry RH, Green DW, Eds. Perry’s chemical engineers’ handbook. 7th ed. New York: McGraw-Hill 1997. Pell M, Dunson JB. Gas-solid operations and equipment. In: Perry RH, Green DW, Eds. Perry’s chemical engineers’ handbook. 7th ed. New York: McGraw-Hill 1997. Nokerman J, Canet X, De Weireld G, Frere M. A new method for the determination of low coverage adsorption heats for zeolite-VOC systems. Adsorption 2005; 11: 121-25. Elaiopoulos K, Perraki Th, Grigoropoulou. Monitoring the effect of hydrothermal treatments on the structure of a natural zeolite through a combined XRD, FTIR, XRF, SEM and N2-porosimetry analysis. Micropor Mesopor Mater 2010; 134: 29-43. Arcoya A, Gonzalez JA, Llabre G, Seoane XL, Travieso N. Role of the countercations on the molecular sieve properties of a clinoptilolite. Microporous Mater 1996; 7: 1-13. Izmailova SG, Karetina IV, Khvoshchev SS, Shubaeva MA. Calorimetric and IRspectroscopic study of methanol adsorption on zeolites. J Colloid Interface Sci 1994; 165: 318-24. Ruthven DM, Kaul BK. Adsorption of aromatic hydrocarbons in NaX zeolite, 1: Equilibrium. Ind Eng Chem Res 1993; 32(9): 2047-52. Pascual P, Kirsch H, Boutin A. Adsorption of various hydrocarbons in siliceous zeolites: A molecular simulation study. Adsorption 2005; 11: 379-82. Maurin G, Bell R, Kuchta B, Poyet T, Llewellyn P. Adsorption of non polar and quadrupolar gases in siliceous faujasite: molecular simulations and experiments. Adsorption 2005; 11: 331-36. Wongthong P, Rungsirisakun R, Probst M, Limtrakul J. Adsorption and diffusion of light alkanes on nanoporous faujasite catalysts investigated by molecular dynamics simulations. Micropor Mesopor Mater 2007; 100: 160-66. Mentzen BF. Structural investigations on zeolitic faujasite/benzene host/guest systems (Si/Al =2.43 and ≈200) by using combined powder diffraction, adsorption calorimetry and molecular mechanics simulation. C R Chim 2005; 8: 353-68. Papaioannou C, Petroutsos G, Gunber W. Examination of the adsorption of hydrocarbons at low coverage on faujasite zeolites. Solid State Ionics 1997; 101-103: 799-805. George AR, Catlow CRA, Thomas JM. A computational investigation of the sorption of methane into zeolitic structures. Microporous Mater 1997; 11: 97-105. Delgado JA, Uguina MA, Gomez JM, Ortega L. Adsorption equilibrium of carbon dioxide, methane and nitrogen onto Na- and H-mordenite at high pressures. Sep Purif Technol 2006; 48: 223-28. Triebe RW, Tezel FH, Khulbe KC. Adsorption of methane, ethane and ethylene on molecular sieve zeolites. Gas Sep Purif 1996; 10: 81-84. Van Bokhoven JA, Williams BA, Ji W, Koningsberger DC, Kung HH, Miller JT. Observation of a compensation relation for monomolecular alkane cracking by zeolites: the dominant role of reactant sorption. J Catal 2004; 224: 50-59.

284 Handbook of Natural Zeolites

[43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62]

Kyriakos Elaiopoulos

Haase F, Sauer J. Ab initio molecular dynamics simulation of methanol interacting with acidic zeolites of different framework structure. Micropor Mesopor Mater 2000; 35-36: 379-85. Grey TJ, Travis KP, Gale JD, Nicholson D. A comparative simulation study of the adsorption of nitrogen and methane in siliceous heulandite and chabazite. Micropor Mesopor Mater 2001; 48: 203-09. Elizalde-Gonzalez MP, Perez-Cruz MA. Interaction between organic vapors and clinoptilolite-mordenite rich tuffs in parent, decationized and lead exchanged forms. J Colloid Interface Sci 2007; 312: 317-25. Caputo D, Iucolano F, Pepe F, Colella C. Modeling of water and ethanol adsorption data on a commercial zeolite-rich tuff and prediction of the relevant binary isotherms. Micropor Mesopor Mater 2007; 105: 260-67. Kortunov P, Chmelik C, Karger J et al., Sorption kinetics and intracrystalline diffusion of methanol in ferrierite: An example of disguised kinetics. Adsorption 2005; 11: 235-44. Hashimoto S. Zeolite photochemistry: impact of zeolites on photochemistry and feedback from photochemistry to zeolite science. J Photochem Photobiol, C 2003; 4: 19-49. Granato MA, Jorge M, Vlugt TJH, Rodrigues AE. Diffusion of propane, propylene and isobutane in 13X zeolite by molecular dynamics. Chem Eng Sci 2010; 65: 2656-63. Fujikata Y, Masuda T, Ikeda H, Hashimoto K. Measurement of the diffusivities within MFI- and Y-type zeolite catalysts in adsorption and desorption processes. Micropor Mesopor Mater 1998; 21: 679-86. Sanborn MJ, Snurr RQ. Diffusion of binary mixtures of CF4 and n-alkanes in faujasite. Sep Purif Technol 2000; 20: 1-13. Krishna R. Predicting transport diffusivities of binary mixtures in zeolites. Chem Phys Lett 2002; 355: 483-89. Szczygiel J, Szyja B. Computer simulated diffusion of C7 hydrocarbons in microporous materials. Micropor Mesopor Mater 2005; 83: 85-93. Qi S, Hay KJ, Cal MP. Predicting humidity effect on adsorption capacity of activated carbon for water-immiscible organic vapors. Adv Environ Res 2000; 4: 357-62. Tsitsishvili GV, Andronikashvili TG, Kirov GN, Filizova LD, Eds. Natural zeolites. New York: Ellis Horwood Ltd 1992. Ackley MW, Rege SU, Saxena H. Application of natural zeolites in the purification and separation of gases. Micropor Mesopor Mater 2003; 61: 25-42. Karger J. Measurement of diffusion in zeolites – A never ending challenge? Adsorption 2003; 9: 29-35. Zhen S, Seff K. Structures of organic sorption complexes of zeolites. Micropor Mesopor Mater 2000; 39: 1-18. Kornatowski J. Expressiveness of adsorption measurements for characterization of zeolitic materials – A review. Adsorption 2005; 11: 275-93. Daems I, Leflaive P, Methivier A, Baron GV, Denayer JFM. Influence of Si:Al-ratio of faujasites on the adsorption of alkanes, alkenes and aromatics. Micropor Mesopor Mater 2006; 96: 149-56. Deeg FW, Ehrl M, Brauchle C, Hoppe R, Schulz-Ekloff G, Wohrle D. Dynamics of adsorbed molecules in zeolites. J Lumin 1992; 53: 219-22. Chao CC. Process for purification of hydrocarbons. US Patent 5019667, 1991.

Operations Involving Organic Gases and Vapors

[63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79]

[80] [81]

Handbook of Natural Zeolites 285

Ogawa H, Ito Y, Nakano M, Itabashi K. Method for adsorbing and removing ethylene and method for purifying an exhaust gas. US Patent 6309616, 2001. Seery MW. Bulk separation of carbon dioxide from methane using natural clinoptilolite. US Patent 5938819, 1999. Chao CC, Rastelli H. Process for purification of hydrocarbons using metal exchanged clinoptilolite to remove carbon dioxide. US Patent 4935580, 1990. Chao CC, Rastelli H. Process for modifying clinoptilolite adsorbent. US Patent 5116793, 1992. Herden H, Mayer-Schwinning G, Boening G. Purification of incinerator flue gases by adsorption. Ger Patent 666098, 1994. Meier WM, Wild J, Scanian F. Smoker’s Article. Eur Patent 0740907B1, 1996. Zarchy AS, Correia R, Chao CC. Process for the adsorption of hydrogen sulfide with clinoptilolite molecular sieves. US Patent 5164076, 1992. Zeng Y, Ju S. Adsorption of triophene and benzene in sodium-exchanged MFI- and MORtype zeolites: A molecular simulation study. Sep Purif Technol 2009; 67: 71-78. Ackley MW, Giese RF, Yang RT. Clinoptilolite: untapped potential for kinetic gas separations. Zeolites 1992; 12: 780-88. Kouvelos E, Kesore K, Steriotis T et al., High pressure N2/CH4 adsorption measurements in clinoptilolites. Micropor Mesopor Mater 2007; 99: 106-11. Melo DMA, de Souza JR, Melo MAF, Martinelli AE, Cachima GHB, Cunha JD. Evaluation of the zinox and zeolite materials as adsorbents to remove H2S from natural gas. Colloids Surf, A 2006; 272: 32-36. Hernandez-Huesca R, Diaz L, Aguilar-Armenta G. Adsorption equilibria and kinetics of CO2, CH4 and N2 in natural zeolites. Sep Purif Technol 1999; 15: 163-73. Garcia-Perez E, Parra JB, Ania CO et al., A computational study of CO2, N2 and CH4 adsorption in zeolites. Adsorption 2007; 13: 469-76. Richter M, Ehrhardt K, Roost U, Kosslick H, Parlitz B. Molecular sieving of n-butenes by zeolite erionite and by isostructural silicoaluminophosphate SAPO-17. Stud Surf Sci Catal 1994; 84: 1285-92. Kraikul N, Rangsunvigit P, Kulprathinpanja S. Study on the adsorption of 1,5-, 1,6- and 2,6-dimethylnapthalene on a series of alkaline and alkaline earth ion-exchanged faujasite zeolites. Adsorption 2006; 12: 317-27. Krishna R, van Baten JM. Separating n-alkane mixtures by exploiting differences in the adsorption capacity within cages of CHA, AFX and ERI zeolites. Sep Purif Technol 2008; 60: 315-20. Ghoufi A, Gaberova L, Rouquerol J, Vincent D, Llewellyn PL, Maurin G. Adsorption of CO2, CH4 and their binary mixture in faujasite NaY: A combination of molecular simulations with gravimetry-manometry and microcalorimetry measurements. Micropor Mesopor Mater 2009; 119: 117-28. Nedez C, Theolier A, Lefebvre F et al., Chemical grafting of tin alkyl complexes on the external surface of mordenite: a method for controlling the size of the pore entrances of zeolites. Microporous Mater 1994; 2: 251-59. Colella C, Pansini M, Alfani F, Cantarella M, Gallifuoco A. Selective water adsorption from aqueous ethanol-containing vapours by phillipsite-rich volcanic tuffs. Microporous Mater 1994; 3: 219-26.

286 Handbook of Natural Zeolites

[82]

Kyriakos Elaiopoulos

Chatterjee A, Ebina T, Iwasaki T, Mizukami F. Chlorofluorocarbons adsorption structures and energetic over faujasite type zeolites – a first principle study. J Mol Struct THEOCHEM 2003; 630: 233-42. [83] Ozcelik Z, Pozan Soylu GS, Boz I. Catalytic combustion of toluene over Mn, Fe and Coexchanged clinoptilolite support. Chem Eng J 2009; 155: 94-100. [84] Woo HC, Lee KH, Lee JS. Catalytic skeletal isomerization of n-butenes to isobutene over natural clinoptilolite zeolite. Appl Catal, A 1996; 134: 147-58. [85] Pellet RJ, Casey DG, Huang HM et al., Isomerization of n-butene to isobutene by ferrierite and modified ferrierite catalysts. J Catal 1995; 157: 423-35. [86] Lee HC, Woo HC, Ryoo R, Lee KH, Lee JS. Skeletal isomerization of n-butenes to isobutenes over acid-treated natural clinoptilolite zeolites. Appl Catal, A 2000; 196: 13542. [87] Greenhalgh BR, Kuznicki SM, Nelson AE. Chabazite supported NiMo catalysts: Activity and sulfur poisoning. App Catal, A 2007; 327: 189-96. [88] Patrylak KI, Bobonych FM, Voloshyna YG et al., Ukrainian mordenite-clinoptilolite rocks as a base for linear hexane isomerization catalyst. App Catal, A 1998; 174: 187-98. [89] Katranas T, Vlessidis A, Tsiatouras V, Triantafyllidis K, Evmiridis N. Dehydrogenation of propane over natural clinoptilolite zeolites. Micropor Mesopor Mater 2003; 61: 189-98. [90] Komatsu T, Ishihara H, Fukui Y, Yashima T. Selective formation of alkenes through the cracking of n-heptane on Ca2+-exchanged ferrierite. Appl Catal, A 2001; 214: 103-09. [91] Armor JN. Catalytic reduction of nitrogen oxides with methane in the presence of excess oxygen; A review. Catal Today 1995; 26: 147-58. [92] Li Y, Armor JN. Metal exchanged ferrierites as catalysts for the selective reduction of NOx with methane. Appl Catal, B 1993; 3: L1-11. [93] Martens JA, Cauvel A, Jayat F, Vergne S, Jobson E. Molecule sieving catalysts for NO reduction with hydrocarbons in exhaust of lean burn gasoline and diesel engines. Appl Catal, B 2001; 29: 299-306. [94] Royaee SJ, Falamaki C, Sohrabi M, Talesh SSA. A new Langmuir-Hinshelwood mechanism for the methanol to dimethylether dehydration reaction over clinoptilolitezeolite catalyst. Appl Catal, A 2008; 338: 114-20. [95] Kim MH, Hwang U-C, Nam I-S, Kim YG. The characteristics of a copper-exchanged natural zeolite for NO reduction by NH3 and C3H6. Catal Today 1998; 44: 57-65. [96] Chung SY, Oh S-H, Kim MH, Nam I-S, Kim YG. Hydrothermal stability of dealuminated mordenite type zeolite catalysts for the reduction of NO by C3H6 under lean-burn condition. Catal Today 1999; 54: 521-29. [97] Wilhelm FC, Gaffney TR, Parris GE et al., Chabazite catalysts for the preparation of methylamines from ammonia and methanol or dimethyl ether. Can Patent 2126834, 1995. [98] Ko S, Pekarovic J, Fleming PD, Ari-Gur P. High performance nano-titania photocatalytic composite. Part I: Experimental design study for TiO2 composite sheet using a natural zeolite microparticle system and its photocatalytic property. Mater Sci Eng, B 2010; 166: 127-31. [99] Ozkan F, Gunduz G, Akpolat O, Besun N, Murzin DY. Isomerization of a-pinene over ionexchanged natural zeolites. Chem Eng J 2003; 91: 257-69. [100] Cobzaru C, Oprea S, Dumitriu E, Hulea V. Gas phase aldol condensation of lower aldehydes over clinoptilolite rich natural zeolites. Appl Catal, A 2008; 351: 253-58.

Operations Involving Organic Gases and Vapors

Handbook of Natural Zeolites 287

[101] Heck RH, Chen NY. Hydrocracking of n-butane and n-heptane over a sulfided nickel erionite catalyst. Appl Catal, A 1992; 86: 83-99. [102] Kallo D, Magdolna Mihalyi R. Mechanism of 1-butene hydration over acidic zeolite and ion-exchange resin catalysts. Appl Catal, A 1995; 121: 45-56. [103] Marchi AJ, Froment GF. Catalytic conversion of methanol into light alkenes on mordenitelike catalysts. Appl Catal, A 1993; 94: 91-106. [104] Lee HC, Woo HC, Chung SH, Kim HJ, Lee KH, Lee JS. Effects of metal cation on the skeletal isomerization of 1-butene over clinoptilolite. J Catal 2002; 211: 216-25. [105] Kucherov AV, Kucherova TN, Slinkin AA. Modification of zeolites by multi-charged cations by the use of in-situ formed «active gas-phase species». Micropor Mesopor Mater 1998; 26: 1-10. [106] Impens NREN, van der Voort P, Vansant F. Silylation of micro-, meso- and non-porous oxides: a review. Micropor Mesopor Mater 1999; 28: 217-32. [107] Tezel F, Apolonatos G. Chromatographic study of adsorption for N2, CO and CH4 in molecular sieve zeolites. Gas Sep Purif 1993; 7: 11-17. [108] An S, Joye SB. An improved chromatographic method to measure nitrogen, oxygen, argon and methane in gas or liquid samples. Mar Chem 1997; 59: 63-70. [109] Barry EF. Columns: Packed and capillary; Column selection in gas chromatography. In: Grob RL, Barry EF, Eds. Modern Practice of Gas Chromatography. New Jersey: John Wiley & Sons Inc 2004; pp. 79-88.

288

Handbook of Natural Zeolites, 2012, 288-316

CHAPTER 12 Contribution of Zeolites in Sewage Sludge Composting Antonis A. Zorpas* Cyprus Open University, Faculty of Pure and Applied Science, Environmental Conservation and Management, Institute of Environmental Technology and Sustainable Development, Laboratory of Environmental Friendly Technology, P.O.Box 34073, 5309, Paralimni Cyprus Abstract: There are three kinds of sludge: sewage sludge from municipal treatment works, septage pumped from septic tanks, and industrial sludge. All three are a growing management problem in this state, and throughout the world. Problems associated with sewage sludge disposal and treatment remains a challenge for the waste industry and for many researches around the world. Sludge is presented with significant issues like heavy metals, nitrogen, phosphorous, pathogens, organics etc. Some them when added to soil is necessary to control the consecration due to potential toxicity and especially the heavy metals like Cr, Cd, Cu, Pb, Zn, Cd, Hg, Co, Ni etc. Natural zeolites are a popular group of minerals for collectors and an important group of minerals for industrial and other purposes. Zeolite utilization has become popular in the last decade, due to its cation exchange and molecular sieving properties. Zeolites have many useful purposes. They can perform ion exchange, filtering, odor removal, and chemical sieve and gas absorption tasks. Many researchers investigated the use of natural zeolites in several applications of sewage sludge and they found out the final products presented with excellent characteristics. This chapter presents the use of zeolites in sewage sludge and other treatment.

Keywords: Sludge composting, land application, metals removal, metals partitioning, compost evaluation, metals leachability, compost evaluation. INTRODUCTION Sludge is the solid material removed during the treatment of wastewaters. There are three kinds of sludge: sewage sludge from municipal treatment works, septage pumped from septic tanks, and industrial sludge. All three are a growing management problem in this state, and throughout the world. *

Address correspondence to Antonis A. Zorpas: Cyprus Open University, Faculty of Pure and Applied Science, Environmental Conservation and Management, Institute of Environmental Technology and Sustainable Development. Laboratory of Environmental Friendly Technology, P.O.Box 34073, 5309, Paralimni Cyprus; Tel: +35723743440; Fax: +35723743441; http: www.ouc.ac.cy, www.envitech.org, [email protected], [email protected], [email protected], [email protected]

Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Contribution of Zeolites in Sewage Sludge Composting

Handbook of Natural Zeolites 289

Sludge is a generic term for solids separated from suspension in a liquid. This 'soupy' material usually contains significant quantities of 'interstitial' water (between the solid particles). Commonly sludge refers to the residual, semi-solid material left from industrial wastewater, or sewage treatment processes. It can also refer to the settled suspension obtained from conventional drinking water treatment, and numerous other industrial processes. When fresh sewage or wastewater is added to a settling tank, approximately 50% of the suspended solid matter will settle out in an hour and a half. This collection of solids is known as raw sludge or primary solids and is said to be "fresh" before anaerobic processes become active. The sludge will become putrescent in a short time once anaerobic bacteria take over, and must be removed from the sedimentation tank before this happens. This is accomplished in one of two ways. In an Imhoff tank, fresh sludge is passed through a slot to the lower story or digestion chamber where it is decomposed by anaerobic bacteria, resulting in liquefaction and reduced volume of the sludge. After digesting for an extended period, the result is called "digested" sludge and may be disposed of by drying and then landfilling. More commonly with domestic sewage, the fresh sludge is continuously extracted from the tank mechanically and passed to separate sludge digestion tanks that operate at higher temperatures than the lower story of the Imhoff tank and, as a result, digest much more rapidly and efficiently. Excess solids from biological processes such as activated sludge may still be referred to as sludge, but the term biosolids, is more commonly used to refer to the material, particularly after further processing such as aerobic composting. Industrial wastewater solids are also referred to as sludge, whether generated from biological or physical-chemical processes. Surface water plants also generate sludge made up of solids removed from the raw water. Biosolids, the treated form of sewage sludge, have been in use in UK and European agriculture for more than 80 years, though there is increasing pressure to stop the practice of land application. In the 1990s there was pressure in some European countries to ban the use of sewage sludge as a fertilizer. Switzerland, Sweden, Austria, and others introduced a ban. Since the 1960s there has been cooperative activity with industry to reduce the inputs of persistent substances from factories. This has been very successful and, for example, the content of cadmium in sewage sludge in major European cities is now only 1% of what it was in 1970. European legislation on dangerous substances has eliminated the

290 Handbook of Natural Zeolites

Antonis A. Zorpas

production and marketing of some substances that have been of historic concern such as persistent organic micropollutants. The European Commission has said repeatedly that the "Directive on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture" (86/278/EEC) [1] has been very successful in that there have been no cases of adverse effect where it has been applied. The EC encourages the use of sewage sludge in agriculture because it conserves organic matter and completes nutrient cycles. Recycling of phosphate is regarded as especially important because the phosphate industry predicts that at the current rate of extraction the economic reserves will be exhausted in 100 or at most 250 years. Characteristics of Sewage Sludge Increasing urbanization and industrialization has culminated in a dramatic growth in the volume of municipal wastewater produced worldwide. This wastewater contains all the substances that enter human metabolism, such as food, beverages, pharmaceuticals, a great variety of household chemicals and the substances discharged from trade and industry to the sewer system. Moreover, rain water and its contact materials also contribute to this composition. As a result, the constituents of the municipal wastewater discharged into the sewer system are a mirror of our civilization and of human and urban metabolism. Sewage sludge is the concentrated bioactive residue of mostly organic clay-sized particles derived from wastewater treatment processes. The consolidation and hydraulic characteristics of the dewatered sludge material are of major importance with regard to its long-term behavior in landfills (sludge mono-fills, municipal landfills or sludge lagoons), currently the principal means of disposal in the European Community. In many countries, there is almost complete reliance on landfilling since the spreading of sewage sludge material on land is banned and incineration may not be an option. The sludge landfill and its engineered capping system are subject to considerable settlement that must be assessed at the design stage. In practice, sewage sludge shows unpredictable consolidation behavior that can be attributed to a number of causes. Sewage sludge several substances which are consider to be toxic like pathogenic bacteria, viruses and protozoa along with other parasitic helminthes. Those parameters can have negative impact to human health, animals and plants. Apart

Contribution of Zeolites in Sewage Sludge Composting

Handbook of Natural Zeolites 291

from those components of concern, sewage sludge also contains useful concentrations of nitrogen, phosphorus and organic matter. The availability of the phosphorus content in the year of application is about 50% and is independent of any prior sludge treatment. Nitrogen availability is more dependent on sludge treatment, untreated liquid sludge and dewatered treated sludge releasing nitrogen slowly with the benefits to crops being realised over a relatively long period. Organic matter in sludge can improve the water holding (retaining) capacity, the porosity and the erection of some soils. The application of sewage sludge to land in member countries of the European Economic Commission (EEC) is governed by Council Directive No. 86/278/EEC (Council of the European Communities 1986). This Directive [1] prohibits the sludge from sewage treatment plants from being used in agriculture unless specified requirements are fulfilled, including the testing of the sludge and the soil. The directive includes several parameters which must take into consideration before the disposal of sludge like: Dry matter (%), Organic matter, Metals like Cu, Ni, Zn, Cd, Pb, Hg, Cr (mg/kg dry solids), pH, TN, NH3, TP. All those parameters must referred in % dry solids. The department of Environment in UK (1989) has added also some other parameters like Mo, Se, As, and fluoride in the recent 'Code of Practice for Agricultural Use of Sewage Sludge'. Sludge must be analyzed for the Directive parameters at least twice per year. Sludge Treatment Sewage sludge, also referred as biosolids, is a byproduct of sewage treatment processes. Land application of sewage sludge is one of the important disposal alternatives [3-5]. Characteristics of sewage sludge depend on the quality of sewage and type of treatment processes followed. Being rich in organic and inorganic plant nutrients, sewage sludge may substitute fertilizer, but availability of potential toxic metals often restricts its uses. Sludge amendment to the soil modifies its physico-chemical and biological properties. Sewage sludge is a wastewater industrial sub-product with high organic matter and nutritional contents traditionally used as an agricultural soil fertilizer and to promote biomass production [6]. Sludge resulting from wastewater treatment constitutes a valuable source of essential nutrients for agricultural cultivation [7]. In addition, organic

292 Handbook of Natural Zeolites

Antonis A. Zorpas

matter from sludges improves some physical and chemical properties of soil, leading to better plant growth. Along with this, sludge application to soils is considered a useful method for their final disposition [7]. However, sludge may contain high amounts of potentially toxic trace elements, which may exceed soil natural concentration by two or more order of magnitude [7]. Land application of sewage sludge (biosolids) has been a worldwide agricultural practice for many years [8]. Land application of sewage sludge has been extensively used as an effective dispersive method throughout Canada, the United States and Europe for more than 40 years. Many studies have demonstrated the positive effect of land application of sewage sludge or sludge compost on corn and forage yields and soils [9-12]. It effectively disposes of a ‘waste’ product while recycling valuable nutrients into the soil-plant ecosystem; however, too often the dispersal has created environmental problems that force government agencies to restrict the amount and type of sewage sludge which can be land applied. A number of vegetation sludge treatment methods have been recently employed, and these can be divided into physico-chemical, biological methods and physical methods. The use of sewage sludge in agriculture is not new, since it is an inexpensive source of organic matter and its use contributes to solving a serious environmental problem [5, 6, 13, 14]. However, there are certain risks involved in its use, some of which, such as those derived from the instability of the organic matter or from the mineralizable organic nitrogen content, are only of transitory nature. Such problems are easily eliminated by composting, a process which stabilizes the organic matter content. Various processes are employed to reduce any potential negative effects of sewage sludge applications; composting wastes to stabilize the components is one process used now more frequently. The mineralization of biogenic substances is a part of the natural recycling process, which occurs at any place where organic material is synthesized by plants and degraded by animals and by microflora. This mechanism keeps the global balance upright. Environmental problems associated with sewage sludge disposal have prompted strict legislative actions over the last years. At the same time, the upgrading and expansion of wastewater treatment plants have greatly increased the

Contribution of Zeolites in Sewage Sludge Composting

Handbook of Natural Zeolites 293

volume of produced sludge. The sludge is classified as solid waste that requires special methods of disposal, because of its noxious properties. However, much of the sludge originating from urban wastewater treatment is contaminated with heavy metals [15-20]. The management of the sewage sludge is becoming increasingly difficult due to the presence of heavy metals. Natural zeolite is capable of removing quantities of cations from aqueous solution and from solid phase by utilizing the phenomenon of ion-exchange, [21, 22]. Clinoptilolite, for example, has received extensive attention due to its attractive selectivity’s for certain heavy metal ions such as Pb2+, Zn2+, Cd2+, Ni2+, Fe2+ and Mn2+ [22]. The most common treatment methods of sludge are landfill, the composting, the incineration, the agricultural use. All those methods present to have some potential environmental impacts. Landfill present to have emissions of CH4, CO2, odours and also is produced leaching of salts, heavy metals and persistent organics to ground water. Also landfill and the uncontrolled used of sludge in agricultural of sludge accumulate the hazardous substances in soil and the toxic substances in food chain. Incineration is a very promises treatment method due to that fact that the volume of the raw material is limited however presented with environmental impact if the incineration is not controlled like emission of SO2, NOx, COx, dioxins, heavy metals etc. Table 1 presents several sewage sludge treatment and handling processes which have been used in the UK. Table 1: Examples of effective sludge treatment processes Procedure

Explanation

Sludge Pasteurization

At least 30 min. at 70°C or less of 4 h at 55° C (or appropriate intermediate conditions), followed in all cases by primary mesophilic anaerobic digestion.

Mesophilic Anaerobic Digestion

Mean retention period of at least 12 d primary digestion in temperature range of 35°C ± 3°C or of at least 20 days primary digestion in temperature range 25°C ± 3°C followed in each case by a secondary stage which provides a mean retention period of at least 14 d.

Thermophilic Aerobic Digestion

At least 7 d digestion. All sludge to be subject to 55°C (at least) for not less than 4h.

Composting (Windrows or Aerated Piles)

The compost must be maintained at 40°C for at least 5 d and for 4 h during this period at a temperature of 55°C (at least) within the body of the pile followed by acceptable period of maturation to guarantee that the compost reaction is substantially broad.

294 Handbook of Natural Zeolites

Antonis A. Zorpas

Table 1: cont….

Lime Stabilization of Liquid Sludge

Addition of lime to rise pH more than 12.0 and satisfactory to confirm that the pH is not less than 12 for a minimum period of 2 h. The sludge can then be straight used.

Liquid Storage

Untreated liquid sludge must be storage for at least 3 months

Dewatering and Storage

If sludge has been subject to primary mesophilic anaerobic digestion, storage to be for a minimum period of 14 d. Conditioning of untreated sludge with lime or other coagulants followed by dewatering and storage for 3 months at least

Source: Department of the Environment (1989) [23].

COMPOSTING Composting of organic wastes is a microbiologically mediated process with which the readily degradable organic matter in organic wastes is degraded and stabilized. During the process, part of organic C is released as CO2, part incorporated into microbial cells and part humified. The organic nitrogen primarily as protein prior to composting is mineralized to inorganic N (NH4-N and NO3-N), which is then re-synthesized into other forms of organic N in microbial biomass and humic substances during the composting process. Degradation of organic C during composting is carried out by bacteria, fungi, and actinomycetes, depending on the stage of degradation, the characteristics of materials, and temperature [5, 24, 25]. Actinomycetes prefer moist but aerobic conditions with neutral or slightly alkaline pH. There are many thermophilic actinomycetes, which can tolerate composting temperatures in the 50 oC and low 60 oC. Actinomycetes tend to be common in the later stages of composting and can exhibit extensive growth. Bacteria are by far the most important decomposers during the most active stages of composting due to rapid growing ability on soluble substrates and tolerant of high temperatures. Thermophilic bacteria are dominant species at temperatures above 55 oC, which kill pathogens [6, 26]. Fungi have a limited role in composting. Most fungi are eliminated above 50 oC, and their optimal temperatures are much lower [6, 27]. Both bacteria and actinomycetes have a protoplasmic C:N of about 5:1, whereas fungi have approximately a 10:1 ratio [5, 6, 28]. These micro organisms assimilate C and N in a different way. Differing nutrients available during composting will preferentially favour diverse microbial populations. Bacteria can utilize materials with narrow C:N of 10 - 20:1, while fungi can use materials with

Contribution of Zeolites in Sewage Sludge Composting

Handbook of Natural Zeolites 295

wide C:N of 150 - 200:1 [5, 6, 29]. Although microbes are the real agents responsible for composting, their type and population size rarely are a limiting factor [6, 30]. Stabilization of organic wastes is often done with composting, which is a microbiologically mediated process. Composting provides a simple and a cost effective alternative treatment method for sewage sludge by decomposing organic matter, producing a stabilized residue and disinfecting pathogens [5, 6, 31, 32]. The composted product can also be used as a fertilizer or soil conditioner because of its large content of stabilized organic matter [66]. Compost contains many essential nutrients and improves soil physical and chemical properties. It without a doubt is a valuable product as compost improves soil organic matter content, nutrient availability soil aeration, and water holding capacity, and reduces soil bulk density. Compost, if properly prepared, is beneficial to the productivity of field and container crops. Soil incorporation of composted materials (like municipal solid waste, sludge) usually results in a positive effect on the growth and yield of a wide variety of crops and the restoration of ecologic and economic functions of land. Agricultural uses of compost have given a promise for a variety of field crops (e.g., maize, sorghum, forage grasses) and vegetables for human consumption (e.g., lettuce, cabbage, beans, potatoes, cucumbers). Responses by plant systems have ranged from none to over a twofold increase in yield. Specific responses are crop and site dependent. In most cases, yields were higher when composts were applied with fertilizer management programs. In some cases, elevated trace metal uptake was noted with lead and boron of greatest concern. Where long-term monitoring has been possible, benefits persist and actually accrue when sound soil/crop management practices are followed. Levels of toxic elements in plants for human consumption are either not well known or thresholds were not reached, as little mention was made in the literature. One of the most serious problems for the application of sewage sludge in agriculture is the presence of the heavy metals. Some of these are extremely toxic and when added to the soil along with the organic amendment, negatively affect plant development and even enter the food chain. Composting of sewage sludge with natural zeolite (clinoptilolite) can enhance its quality and suitability for agricultural use. Zeolites have been used worldwide for the last decades, either for

296 Handbook of Natural Zeolites

Antonis A. Zorpas

their cation exchange or molecular sieving properties. Natural zeolites nowadays are mostly used in catalysis, in air enrichment, as filers in paper and rubber industry, in soil benefication, as animal feed supplements, and in water and wastewater treatment for the ammonia and heavy metal removal. At present the zeolite group includes more than 40 naturally occurring species, and is the largest group of minerals among the silicates. Before 1960s, zeolite minerals were thought to be mainly distributed in hydrothermal veins and geodes in basalts, andesites and other volcanic rocks, [33, 34]. Zeolite in such settings forms large, well-shaped crystals and druses. Due to the usual small size of veins and because of poly-minerality, these deposits have no practical importance, but samples of vein origin have been used to establish the properties of the mineral and the possibility of their utilization in industry [34]. According to the bibliography [34], in the 1980s more than 300000 t of natural zeolites were used in world market (150000 t in Europe and 90000 in Japan) and the most common zeolites were: clinoptilolite, mordenite, phillipsite, chapazite. Zeolite minerals are known to distribute rather unevenly in Nature. Clinoptilolite, mordenite, phillipsite, chapazite, stilbite, analcime and laumontine are very common whereas offretite, paulingite, barrerite and mazzite, for example, are much rarer, and sometimes limited to single occurrences [34]. According to Zorpas 1999 [6] and Tsitsishvili (1992) zeolites [34] can be used as structurally materials, in paper industry, to improve soil properties, in the animal feeds industry, in wastewater treatment plants, for the cleaning and improve the properties of the drinking water, for metal removal, etc. Zorpas [3-6, 21] the last years referred to the applications of zeolite in the composting process of sewage sludge as an alternative sustainable solution for the removal or uptake the heavy metals. The final results indicate that the application of 25% (w/w) zeolite (2.5-2.7 mm) to the sewage sludge has the ability to take up a significant (p 9). Zeolite-Struvite-Mix (ZSM) as Fertilizer Recycling and reuse of ammonium loaded zeolites as slow-release fertilizers have been studied previously, and the technique is well documented since many decades in the field of agricultural research, so called “zeo-agriculture” (reviewed in [44, 66]). However, a combination of struvite and ammonium-zeolites as a product from urine nutrient recovery and its value as a fertilizer was not investigated before.

Figure 7: Two experimental setups, one with drip-irrigation (left) and one with manual irrigation (right) for testing of struvite and ZSM in climate chamber on common wheat (Photo: Ganrot).

A first step for evaluation of the struvite alone and the zeolite-struvite-mix (ZSM) as fertilizers was made in our projects. A series of short-term (3 - 4 weeks long) plant testing experiments were performed under rigorously controlled climate chamber conditions. Common wheat and barley were tested in different substrates (soils). The main focus was on the bioavailability of P. A mix of struvite and nutrient loaded zeolite was compared to two well-known commercial fertilizers with similar P nutrient composition as struvite, and to a liquid fertilizer containing optimal concentrations of all nutrients. Biomasses, as well as the mineral nutrient

426 Handbook of Natural Zeolites

Zsófia Ganrot

composition of the cultivated plants, were used as assessment parameters. Detailed descriptions and results were published in [21, 68, 69].

Figure 8: Wheat plants harvested after 33 days growth. The soil was a mixture of peat, dolomite and sand and the nutrients used were (from left to right): a liquid fertilizer containing optimal concentrations of all nutrients; DAP (di-ammonium-phosphate), our ZSM (zeolite-struvite-mix); CaP (mono-calcium-phosphate) and the right one is the treatment using a balanced liquid fertilizer for all nutrients except P (Photo: Ganrot).

Fig. 7 illustrates two of the experimental designs frequently used for testing of struvite or ZSM as fertilizers and Fig. 8 clearly shows that the plant using ZSM was fully comparable with the controls using those 3 balanced nutrient sources which are commercially available and most used in agriculture. Biomasses, as well as the mineral nutrient composition of the cultivated plants could confirm this. The overall conclusion made from these studies can be highlighted as follows: Nutrients recovered from urine as zeolite-struvite-mix (ZSM) used in proper amounts acts as a good P source, fully comparable with DAP (di-ammoniumphosphate) and CaP (mono-calcium-phosphate) slow release commercial Pfertilizers. These fertilizers were also similar as P sources to the liquid fertilizer used in the short-term climate chamber experiments. CONCLUSIONS AND FUTURE OUTLOOK After a decade of applied research, hundreds of tests made on natural zeolites rich in clinoptilolite with or without struvite precipitation as a complementary step for maximal nutrient recovery from human urine, and finally, after testing the

Nutrient Recovery from Domestic Wastewater

Handbook of Natural Zeolites 427

fertilizer value of the zeolite-struvite-mix in climate chamber conditions, some general conclusions can be drown: 

Natural zeolites (especially clinoptilolite) ion-exchanged ammonium from NH4Cl-solutions rapidly (< 1 minute). The quality of zeolite, the grain size and the ionic strength of the solution affect the process.



Mineral adsorption in combination with struvite precipitation (MgO addition to urine) could recover 64 - 80% of the N and 100% of the P in laboratory tests. The N recovery from fresh and stored human urine is a complex process affected by the amounts of MgO and zeolite added. MgO contributed to struvite formation with c:a 10% uptake of the ammonium-N in urine and the added zeolite ion-exchanged the rest.



To some extent the P recovery through MgO addition was affected also by the zeolite adsorbing small amounts of P probably on its structural sites (hydrous oxides).



Optimal combined recovery of N and P occurred at added concentrations of 0.1 g of MgO and 15 - 30 g of zeolite per liter stored and diluted urine and is dependent on the initial N and P concentrations of the urine.



The changes in pH and the acute toxicity to Daphnia magna of the remaining supernatant solutions indicated some ampholitic behaviour of the zeolite in contact with neutral to strongly basic solutions.



The zeolite itself was non-toxic for Daphnia magna. The supernatant toxicity was related to the increased pH followed by increased ammonia toxicity. In stored and diluted human urine high concentrations of added MgO increased the acute toxicity of the supernatants to Daphnia magna, but addition of zeolite reduced it.



Short-term climate chamber experiments on wheat and barley showed that the nutrients recovered from urine as zeolite-struvite mineral mix

428 Handbook of Natural Zeolites

Zsófia Ganrot

(ZSM) and used in proper amounts acts as a good nutrient source, fully comparable with DAP (di-ammonium-phosphate) and CaP (mono-calcium-phosphate) slow release commercial fertilizers. These fertilizers were also similar to the liquid fertilizer containing optimal concentrations of nutrients used as control in the experiments. Nutrient recovery as solids by struvite precipitation with adsorption and ionexchange on zeolites is probably the most efficient way to radically improve the shortcomings of the urine handling system and to solve some problems related to urine handling. C:a 100% of P, 60 - 80% of N, 30% of K, 3% of Ca, and some S can be recovered as c:a 60 g of solids (zeolite-struvite mix) from 1 liter (ca 1 kg) undiluted urine. A factor 17 can be achieved in weight reduction and a huge volume reduction with radical impact on storage and transport. Hygienic aspects are greatly facilitated when handling a solid product, instead of liquid urine. The solids are wellknown slow release fertilizers (non-burning for plants, not threatening groundwater or surrounding water bodies with leaching, not loosing N to atmosphere) in class with MAP industrial fertilizers. These are probably more easily accepted (economically, socio-culturally) by users worldwide than urine. Struvite production and mineral use is a very simple, robust method, not demanding special equipments or working conditions. The storage tanks used today for urine collection can be used for this purpose with some modifications, to be able to make a simple stirring and emptying of the struvite and minerals after treatment. The added materials are in small amounts. MgO is made of dolomite (found worldwide, not being a scarce resource). The N adsorbent type is a choice to be made according to the local possibilities for each situation. Zeolites are present almost everywhere on earth in soils (Scandinavia is one of the few exceptions!), and are also worldwide mined for their special properties and areas of application. Their beneficial effect in agriculture is well known in the field of “zeo-agriculture”. Zeolite prices are very low today on the global market (75-95 USD/tone; source: www.findstone.com/1202.htm, 201007-07). In Scandinavia, other minerals like wollastonite or some clay minerals like bentonite can be used, if zeolite is not an option. Every fertile soil type in every region or part of the world contains inorganic adsorbent components originating from the bedrock weathering. Finding and using them in the first place, is the best choice for the environment and sustainable resource management.

Nutrient Recovery from Domestic Wastewater

Handbook of Natural Zeolites 429

The energy costs for stirring and drying needed for struvite production and mineral adsorption are considered to be negligible in the total budget of energy costs for running different nutrient recycling sanitation systems [72]. Dewatering or drying is dependent on the local possibilities (from simple air-drying to centrifugation, slight heating, etc.). Nutrient concentration or nutrient recovery as solids from urine also means that a rest solution (called here supernatant) most be taken care of in the sanitation systems. In the ECOSAN approach, when the ambition is to close all the nutrient loops, this rest solution from urine processing (containing very small amounts of nutrients or having a pH over 9) can be connected to other loops in the whole sanitation system. The supernatants can be utilized in many ways, depending on the system applied and the local conditions, such as irrigation, dilution for an aquaculture system or simply mixing it with the other household wastewater streams and treatments (infiltration, re-sorption beds, wetlands, or sent to a centralized sewage system). These studies on urine processing by struvite precipitation and zeolite use revealed many new questions and research topics. Some of them are summarized here: Testing different forms of activation of zeolites to increase the adsorption or CEC is an important research issue. It is known that zeolites can be pre-treated (activated) in different ways for this purpose. Moreover, zeolites can be regenerated and reused several times to reduce the amounts necessary in a process. Testing and evaluation of these methods could be important for selection of the most cost-efficient and sustainable ways to apply. To be able to evaluate the real costs and find possible upcoming problems it is necessary to conduct tests on pilot equipments and pilot plants placed in different environments (from one family houses to more centralized urine collecting systems). One such example is presented later (in Chapter 4), but much more are needed. It is of outmost importance to test and evaluate the struvite + zeolite process as part of different ECOSAN system solutions. Only in this way it is possible to draw conclusions, make recommendations about how, when or if the struvite precipitation and zeolite usage is a desirable nutrient recovery method or not.

430 Handbook of Natural Zeolites

Zsófia Ganrot

Further research is needed to evaluate the fertilizer value and behaviour of struvite alone and zeolite-struvite-mix compared with urine spreading and other commercial fertilizers or animal manure in long-term field studies. Closing the nutrient loops can be reached only by a high level of acceptance and everyday use of urine or the nutrients recovered from urine. For this reasons research and financing should be oriented not just for behaviour studies on liquid urine acceptance and attitudes to spreading. These studies must include and evaluate also the attitude toward struvite or other fertilizers made by urine processing. One of the major concerns is the spreading of heavy metals, pharmaceutical residues and hormone mimicking substances on arable land when urine or faeces is used as fertilizers. A large part of these substances are eliminated via urine and can be spread via urine irrigation on arable land. This is an emerging, new field of research and some studies and evaluations have already been made on wastewater, sludge and toilet waste sorting systems. It is important that even products from urine processing (struvite, ZSM) are included in these tests. It would be very interesting to test zeolites and especially the nutrient-loaded zeolites (the fertilizer itself) for these pollutants. ACKNOWLEDGEMENTS During a decade many people contributed with valuable work to the research studies and I am grateful to all! Special thanks to prof. Bo Lind and prof. Göran Dave for their much appreciated supervising on precipitation chemistry, zeolite analysis, and toxicity tests. Thanks to Göteborg University for the research financing and to ODAL (Swedish Agricultural Organisation) for financial contributions. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1]

Werner C, Fall PA, Schlick J, Mang H-P. Reasons for and principles of ecological sanitation. In: Werner C, et al. Eds. Ecosan - closing the loop. Proceedings of the 2nd

Nutrient Recovery from Domestic Wastewater

[2] [3] [4] [5]

[6] [7] [8] [9] [10] [11] [12] [13] [14]

[15] [16] [17] [18]

Handbook of Natural Zeolites 431

International Symposium 7-11 April 2003; Lübeck, Germany. GTZ Eschborn 2004; pp. 2330. Otterpohl R. New technological development in ecological sanitation. In: Werner C, et al. Eds. Ecosan - closing the loop. Proceedings of the 2nd International Symposium 7-11 April 2003; Lübeck, Germany. GTZ Eschborn 2004; pp. 455-462. Jönsson H. The role of ecosan in achieving sustainable nutrient cycles. In: Werner C, et al. Eds. Ecosan - closing the loop. Proceedings of the 2nd International Symposium 7-11 April 2003; Lübeck, Germany. GTZ Eschborn 2004; pp. 35-40. Wolgast M. Rena vatten. Om tankar i kretslopp. (In Swedish), Creamon HB Uppsala, 1993; pp.1-186. Palmquist H, Jönsson H. Urine, faeces, greywater and biodegradable solid waste as potencial fertilizers. In: Werner C, et al. Eds. Ecosan - closing the loop. Proceedings of the 2nd International Symposium 7-11 April 2003; Lübeck, Germany. GTZ Eschborn 2004; pp. 587-594. Palm O, Malmén L, Jönsson H. Robusta, uthålliga små avloppsystem - en kunskapsammanställning (Robust, sustainable small sewage systems - a knowledge survey). Report 5224, Swedish Environmental Protection Agency, 2002; pp 1-118. Maurer M, Schwegler P, Larsen TA. Nutrients in urine: energetic aspects of removal and recovery. Water Sci Technol 2003; 48(1): 37-46. Hellström D, Kärrman E. Exergy analysis and nutrient flow of various sewerage systems. Water Sci Technol 1997; 35(9): 135-144. Hellström D, Johansson E. Swedish experiences with urine-separating systems. Wasser & Boden 1999; 51(11): 26-29. Hellström D. Nutrient management in sewerage systems: Investigations of components and exergy analysis. PhD dissertation. Luleå University of Technology, Department of Environmental Engineering, Division of Sanitary Engineering, Luleå, Sweden, 1998. Jensen PD. Ecological engineering for wastewater treatment: fundamentals and examples. Environ Res Forum 1996; 5-6: 15-24. Larsen TA, Gujer W. Separate management of anthropogenic nutrient solutions (human urine). Water Sci Technol 1996; 34(3-4): 87-94. Kärrman E. Environmental system analysis of wastewater management. PhD dissertation, Chalmers Technical University, Göteborg, Sweden 2000. Adamsson M, Ban Zs, Dave G. Sustainable utilization of human urine in urban areas – practical experiences. In: Werner C, et al. Eds. Ecosan - closing the loop. Proceedings of the 2nd International Symposium 7-11 April 2003; Lübeck, Germany. GTZ Eschborn 2004; pp. 643-650. Misselbrook TH, Smith KA, Jackson DR, Gilhespy SL. Ammonia emissions from irrigation of dilute pig slurries. Biosystems Engineering 2004; 89(4): 473-484. Parkinson R, Gibbs P, Burchett S, Misselbrook T. Effect of turning regime and seasonal weather conditions on nitrogen and phosphorus losses during aerobic composting of cattle manure. Bioresource Tehnol 2004; 91: 171-178. Kirchmann H. Phosphorus flows in Swedish society. KSLA Tidskrifter 1998; 137(7): 145156. Boistelle R, Abbona F, Lundager Madsen HE. On the transformation of struvite into newberylite in aqueous systems. Phys Chem Miner 1983; 9: 216-222.

432 Handbook of Natural Zeolites

[19] [20]

[21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35]

[36]

Zsófia Ganrot

Lind B-B, Bán Z, Bydén S. Nutrient recovery from human urine by struvite crystallization with ammonia adsorption on zeolite and wollastonite. Bioresource Technol 2000; 73: 169174. Ronteltap M, Biebow M, Maurer M., Gujer W. Thermodynamics of struvite precipitation in source separated urine. In: Werner C, et al. Eds. Ecosan - closing the loop. Proceedings of the 2nd International Symposium 7-11 April 2003; Lübeck, Germany. GTZ Eschborn 2004; pp. 463-470. Ganrot Zs. Urine processing for efficient nutrient recovery and reuse in agriculture. PhD dissertation, ISBN 91 88376 29X, Göteborg University, Sweden 2005; pp 1-164. Bridger GL, Salutsky ML, Starostka RW. Metal ammonium phosphates as fertilizers. Agr Food Chem 1962; 10: 181-188. Ghosh GK, Mohan KS, Sarkar AK. Characterisation of soil-fertilizer P reaction products and their evaluation as sources for gram (Cicer arietinum L.). Nutr Cycl Agroecosys 1996; 46: 71-79. Schuiling RD, Andrade A. Recovery of struvite from calf manure. Environ Technol 1999; 20(7): 765-768. Momberg GA, Oellermann RA. The Removal of Phosphate by Hydroapatite ans Struvite Crystallisation in South Africa. Water Sci Technol 1992; 26(5-6): 987-996. Shin HS, Lee SM. Removal of nutrients in wastewater by using magnesium salts. Environ Technol 1997; 19: 283-290. Booker NA, Priestley AJ, Fraser IH. Struvite formation in wastewater treatment plants: Opportunities for nutrient recovery. Environ Technol 1999; 20(7): 777-782. Battistoni P, de Angelis A, Pavan P, Prisciandaro M, Cecchi F. Phosphorus removal from real anaerobic supernatant by struvite crystallisation. Water Res 2001; 35(9): 2167-2178. Celen I, Turke M. Recovery of ammonia as struvite from anaerobic digester effluents. Environ Technol 2001; 22: 1263-1272. Liberti L, Petruzzelli D, de Florio L. REM NUT ion exchange plus struvite precipitation process. Environ Technol 2001; 22: 1313-1324. Münch VE, Barr K. Controlled struvite crystallisation for removing phosphorus from anaerobic digester sidestreams. Water Res 2001; 35(1): 151-159. Ueno Y, Fujii M. Three years experience of operating and selling recovered struvite from full-scale plant. Environ Technol 2001; 22: 1373-1381. Doyle JD, Parsons SA. Struvite formation, control and recovery, Water Res 2002; 36: 3925-3940. Prasad R, Britton A, Balzer B, Shafran G. Nutrient Recovery by Struvite Crystallization Process: Virginia Experience. Proceedings of thee WEFTEC`07, San Diego, USA. Water Environment Federation (WEF) Publication 2007; pp. 344-358 Burns, R.T., Moody, L.B., Phosphorus recovery from animal manures using optimised struvite precipitation. Proceedings of Coagulants and Flocculants: Global Market and Technical Opportunities for Water Treatment Chemicals; 2002 May 22-24; Chicago, Illinois, USA. 2002; pp 1-7. Suzuki K, Tanaka Y, Osada T, Waki M. Removal of phosphate, magnesium and calcium from swine wastewater through crystallization enhanced by aeration. Water Res 2002; 36: 2991-2998.

Nutrient Recovery from Domestic Wastewater

[37] [38] [39] [40] [41] [42] [43] [44]

[45] [46] [47] [48] [49] [50] [51] [52] [53] [54]

Handbook of Natural Zeolites 433

Kim BU, Lee WH, Lee HJ, Rim JM. Ammonium nitrogen removal from slurry-type swine wastewater by pre-treatment using struvite crystallization for nitrogen control of anaerobic digestion. Water Sci Technol 2004; 49(5-6): 215-222. Jorgensen SE, Libor O, Graber KL, Barkacs K. Ammonia removal by use of clinoptilolite. Water Res 1976; 10: 213-224. Beler-Baykal B, Oldenburg M, Sekoulov I. The use of ion exchange in ammonia removal under constant and variable loads. Environ Technol 1996; 17: 717-727. Beler-Baykal B, Guven DA. Performance of clinoptilolite alone and in combination with sand filters for removal of ammonia peaks from domestic wastewater. Water Sci Technol 1997; 35(7): 47-54. Beler-Baykal B. Clinoptilolite and multipurpose filters for upgrading effluent ammonia quality under peak loads. Water Sci Technol 1998; 37(9): 235-242. Kithome M, Paul JW, Lavkulich LM, Bomke AA. Kinetics of ammonium adsorption and desorption by the natural zeolite clinoptilolite. Soil Sci Soc Am J 1998; 62: 622-629. Rozic M, Cerjan-Stefanovic S, Kurajica S, Vancina V, Hodzic E. Ammoniacal nitrogen removal from water by treatment with clays and zeolites. Water Res 2000; 34(14): 36753681. Ming DW, Allen ER. Use of natural zeolites in agronomy, horticulture and environmental soil remediation. In: Bish BL, Ming DW, Eds. Natural zeolites: occurrence, properties, applications. Mineralogical Soc. Of America. Reviews in Mineralogy and Geochemistry 2001; 45: 619-654. Jorgensen TC, Weaterley LR. Ammonia removal from wastewater by ion exchange in the presence of organic contaminants. Water Res 2003; 37: 1723-1728. Liberti L, Limoni N, Lopez A, Passino A, Boari, G. The 10 m³h-1 RIM-NUT demonstration plant at West Bari for removing and recovering N and P from wastewater. Water Res 1986; 20(6): 735-739. Blouin GM. Use of ammonia in agricultural and chemical industries. In: Slack AV, Ed. Ammonia - part IV, Fertilizer Science and Technology series –vol. 2. Marcel Dekker, ISBN 0- 8247-6189-8, 1979. Haneaus Å, Hellström D, Johansson E. Conversion of urea during storage of human urine. Vatten, 1996; 52: 263-270. Rodhe L, Richert Stintzing A, Steineck S. Ammonia emissions after application of human urine to clay soil for barley growth. Nutr Cycl Agroecosys 2004; 68: 191-198. Jönsson H, Richert Stinzing A, Vinnerås B, Salomon E. Guidelines on the use of urine and faeces in crop production. EcoSanRes Publications, Report 2004-2, 2004; pp 1-43. Höglund C. Evaluation of microbial health risks associated with the reuse of sourceseparated human urine, PhD dissertation, Royal Inst. of Technology, Dept. of Biotechnology, Stockholm, Sweden, 2001. Weast RC, Astle MJ. CRC Handbook of Chemistry and Physics. 60th edition. CRC Press, Boca Raton, Florida, 1981. Mohajit K, Bhattarai K, Taiganides EP, Yap BC. Struvite deposits in pipes and aerators. Biol Waste 1989; 30: 133-147. Mumpton FA. Natural zeolites. In: Pond WG, Mumpton FA, Eds. Zeo-agriculture –use of natural zeolites in agriculture and aquaculture. Westview Press, Brockport, NewYork 1984; pp. 33-43.

434 Handbook of Natural Zeolites

[55]

Zsófia Ganrot

Semmens MJ. Cation-exchange properties of natural zeolites. In: Pond WG, Mumpton FA, Eds. Zeo-agriculture –use of natural zeolites in agriculture and aquaculture. Westview Press, Brockport, NewYork 1984; pp. 45-54. [56] Wild D, Kisliakova A, Siegrist H. P-fixation by Mg, Ca and zeolite-A during stabilization of excess sludge from enhanced biological P-removal. Water Sci Technol 1996; 34(1-2): 391-398. [57] Sakadevan K, Bavor HJ. Phosphate adsorption characteristics of soils, slags and zeolite to be used as substances in constructed wetland systems. Water Res 1998; 32(2), 393-399. [58] Ban Zs, Dave G. Laboratory studies on recovery of N and P from human urine through struvite crystallization and zeolite adsorption. Environ Technol 2004; 25: 111-121. [59] Dyer A, White KJ. Cation diffusion in the natural zeolite clinoptilolite. Thermochim Acta 1999; 41: 341-348. [60] Rivera A, Rodríguez-Fuentes G, Altshuler E. Time evolution of natural clinoptilolite in aqueous medium: conductivity and pH experiments. Micropor Mesopor Mat 2000; 40: 173179. [61] Wakatsuki T, Esumi H, Omura S. High performance and N & P-removable on-site domestic wastewater treatment system by multi-soil-layering method. Water Sci Technol 1993; 27(1): 31-40. [62] Kalló D. Wastewater purification in Hungary using natural zeolites. In: Ming,D.W. and Mumpton, F.A. (eds): Natural Zeolites ’93. Int. Comm. Natural Zeolites, Brockpost, New York, 1995; pp. 341-350. [63] Oldenburg M, Sekoulov I. Multipurpose filters with ion exchanger for the equalization of ammonia peaks. Water Sci Technol 1995; 32(7): 199-206. [64] Lahav O, Green M. Ammonium removal using ion exchange and biological regeneration. Water Res 1998; 32(7): 2019-2028. [65] Jung JY, Chung YC, Shin HS, Son DH. Enhanced ammonia nitrogen removal using consistent biological regeneration and ammonium exchange of zeolite in modified SBR process. Water Res 2004; 38: 347-354. [66] Pond WG, Mumpton F.A. Zeo-agriculture –use of natural zeolites in agriculture and aquaculture. Westview Press, Brockport, New York, 1984. [67a] Griffith DP, Musher DM, Itin C. Urease, the primary cause of infection-induced urinary stones. Invest Urol 1976; 13(5), 346-350. [67b] Griffith DP, Bragin S, Musher DM. Dissolution of struvite urinary stones –experimental studies in vitro. Invest Urol 1976; 13(5): 351-353. [68] Ganrot Zs, Dave G, Nilsson E. Recovery of N and P from human urine by freezing, struvite precipitation and adsorption to zeolite and active carbon. Bioresource Technol 2007; 98: 3112-3121. [69] Ganrot Zs, Slivka A, Dave G. Nutrient recovery from human urine using pretreated zeolites and struvite precipitation in combination with freezing-thawing and plant availability tests on common wheat. CLEAN-Soil Air Water 2008; 36(1): 45-52. [70] Vaughan DEW. Properties of natural zeolites. In : Sand, LB, Mumpton FA, Eds. Natural zeolites. Occurrence, properties, use. Pergamon Press, Elmsford, New York, 1978; pp. 353371. [71] Filippidis A, Kantiranis N.Experimental neutralization of lake stream waters from N. Greece using HEU-type rich natural zeolitic material. Desalination 2007; 213(1-3): 47-55.

Nutrient Recovery from Domestic Wastewater

[72]

Handbook of Natural Zeolites 435

Åsblad A. Recovering N and P from urine – energetical and technical aspects. (In Swedish). CIT Industriell Energianalys AB, Chalmers Technical University, Göteborg, Sweden. CIT Raport 1998; pp. 1-11.

436

Handbook of Natural Zeolites, 2012, 436-452

CHAPTER 18 An Update of Zeolitic and Other Traditional Adsorption and Ion Exchange Materials in Water Cleanup Processes Eva Chmielewská* Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia Abstract: This review article highlights the characteristic features of adsorption and ion exchange materials for environmental cleanup processes, especially for water purification, with an emphasis on the recent developments in this field, particularly in synthesis and manufacturing of the advanced cost-effective organic-inorganic (hybridized) zeolite-based adsorbents. An organic-inorganic composite adsorbent termed as a hybrid material too, may be defined hereto as a combination of a polymerous substance immobilized onto surface of the inorganic e.g., zeolite carrier to avail advantages of both zeolitic and polymerous constituents as well. Accordingly, hybridization can be used to modify organic or inorganic materials and hybrids should therefore be considered as the new generation of composites that may encompass a wide variety of applications. The conversion of inorganic ion exchange materials into hybrid fibrous or nanoscale ion exchangers is considered to be the latest development of this discipline. These nanomaterials are drawing a great attention as they exhibit a high efficiency and rate of sorption with short diffusion path towards environmental pollutants. Advances in nanoscale science and engineering are providing unprecedented opportunities to develop more cost effective and environmentally acceptable water purification processes, respectively. For the water purification, besides the metalcontaining nanoparticles, carbonaceous materials and dendrimers, also the zeolites are being evaluated as the most progressive functional and nanosized materials of the millennium. A progress in marketing natural zeolites is encouraging, given that natural zeolites are being considered to be a commodity of great potential since the industry´s beginning in the late 1960s. Zeolite unique market position is progressing by continued development of their ion exchange and adsorption properties and especially through their surface treatment. The zeolite crystal structure is unique, in contrast to silica gel or traditional activated carbon adsorbents, in uniform pores distribution. This distribution limits the filling of zeolite micropores volume on the basis of the relative sizes of adsorbates and their states of solvation inside and outside the zeolite. Mesoporous organosilica (MOS) by which the structural characteristics arise from the used surfactant micelles and the final framework is usually amorphous, have attracted lately a great interest in analytical and preparative chromatography and organic pollutants removal, too. In spite of many progressive characteristics of recent MOS, regarding to zeolite, this potential adsorbent does not pose a shape selectivity, such as that found in the molecular sieving effect of crystalline zeolite, is hydrothermal instable, fragile and 

Address correspondence to Eva Chmielewská: Faculty of Natural Sciences, Comenius University, Bratislava, Slovakia; Tel: 00421 260296410; Fax: 00421 226549064; E-mail: [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

Water Cleanup Processes

Handbook of Natural Zeolites 437

currently for massive technical applications still too expensive. A laboratory set-up was used also to examine the uptake of mono- and polyatomic single or mostly double charged anions like chromate, arsenate, nitrate, sulfate, phosphate, halogenides and some organic substances like azodyes (acid red, indigo carmine) and phenol from aqueous model solutions by the octadecylammonium (hereafter ODA) modified, carbonized or alginate pelletized clinoptilolites. The adsorption isotherms of the systems studied are usually expressed and mathematically fitted according to the adsorption isotherm models of Freundlich, Langmuir, Brunauer-Emmet-Teller. Removal efficiencies of the surface functionalized clinoptilolites towards above water pollutants are compared and evaluated with the other low-cost natural or commercial adsorbents, like activated charcoal, pyrolysis char, lignite and expanded perlite, respectively.

Keywords: Water treatment, adsorption, ion exchange, indigo carmin, acid red, clinoptilolite, carbonized clinoptilolite, shungite, TEM analysis, SEM analysis, Langmuir, Freundlich, BET isotherm, phenol, phosphate, nitrate, halogenide, sulphate, Fe alginate/zeolite, hydrophobized ODA - zeolite, Slovakite, active charcoal, lignite, perlite. INTRODUCTION Advancement in nanoscale science and engineering are providing unprecedented opportunities to develop more cost effective and environmentally acceptable water purification processes. For water purification, beside the metal-containing nanoparticles, carbonaceous materials and dendrimers, the zeolites are being evaluated as the most progressive functional and nanosized materials in the last few decades. Since that time, zeolite´s unique market position has been carried out by continual development of their ion exchange and adsorption properties and especially through their surface treatment. Currently, a development of new hybrid organic and inorganic materials is one of the principal directions of modern material sciences. Usually, the inorganic component of such hybrids provide mechanical, thermal or structural stability of the new product (adsorbent) and the organic component functionalizes the adsorbent´s surface [1-3]. Surface induced removal of specific pollutants on powdered natural zeolites, montmorillonite, active coke or simple addition of polymerous substances, like starch, polyacrylamide, cellulose, etc. into flocculation process, has been applied in water treatment processes for many years. Both ways improve or intensify specific pollutant removal from surface or industrial waste waters during this treatment stage. Supramolecular assemblies with characteristic length scales of 10-9- 10-7m incl. clusters, macromolecules, nanoparticles and colloids like metal oxides, biotic

438 Handbook of Natural Zeolites

Eva Chmielewská

extracellular polymeric and macrocyclic ligands, fulvic and humic acids and the other water constituents have a significant impact on water quality in natural ecosystem. In water purification, such nanomaterials are getting significant attention as they exhibit a high efficiency and rate of sorption with short diffusion path, towards pollutants [4]. Increase of human population, industrialization and agricultural innovations result in the production of enormous quantity of wastes and untreated disposal. Synthetic colouring substances are extensively used in industries like textile, pulp and paper, tanneries, photoprinting. According to estimations, more than 10, 000 different dyes are in use across the world and about 700,000 tones of dyes are manufactured annually, in which azodyes occupy the major portion of them. It has been observed that almost 10-15% of pigments and dyes applied are discharged in the effluents. Occurrence of the synthetic pigments in the effluents usually interferes with the ongoing water purification process. From this point of view, decolourization of the effluents prior to their treatment is most essential step. Currently, many physico-chemical techniques like chemical oxidation, membrane processes, filtration and coagulation are available, however they suffer from many disadvantages like high cost, salt content in the effluent, disposal necessities, etc. [5, 6]. Based on these facts, the objective of our study was to testify an alternative process of decolourization, using the native, easily accessible in the local market, surface functionalized zeoadsorbent. Two model synthetic colours acid red 1 and acid blue 74 (indigo carmin), commonly used in food industry, have been selected for experimental work. Sources of phenolic waste waters are herbicide, phenolic resin, plastics and fiberglass manufacturers, petroleum refineries, stocking factories. The conventional treatment methods for phenolic waste waters are similar as already mentioned ones, however, mostly adsorption, solvent extraction, biological or chemical oxidation are currently used at the water treatment facilities [7, 8]. In the current study, aquatic pollutants like phenol and azodyes (acid red 1, acid blue 74) have been examined for removal, using the model solutions of these pollutants. Adsorption performance of surface functionalized clinoptilolite for the targeted water pollutants was compared to the other natural or commercial adsorbents, e.g., activated charcoal, pyrolysis char, lignite and expanded perlite (volcanic glass). Surface architecture of such zeolite hybrid material has been visualized by SEM and HR TEM. Simultaneously, S(BET) characterization of individual adsorbents has been done.

Water Cleanup Processes

Handbook of Natural Zeolites 439

EXPERIMENTAL METHODS The principal rock constituent of the volcanic-sedimentary zeolite deposit in Eastern Slovakia at Nižný Hrabovec is clinoptilolite. This sample was used for all experiments accomplished in this study. Detailed mineralogical and chemical analyses of zeolitic rock and the procedures of hydrophobization with octadecylammonium (ODA) surfactant as well as pyrolytic carbonization were published elsewhere [9]. Sample carbonization was accomplished in a pilot scale plasmachemical reactor (pyrolytic chamber) installed at the laboratory, using the waste vegetable together with some twigs of garden or park bushes. A combustion oven directed the produced carbonization gases to the flue gas cleaning system, based on the electrical discharge and nonthermal plasma regime. The carbonization chamber was heated directly using the exhaust produced in a natural gas oven (10 m3/h). The carbonization zone with a total volume of 24 L was placed 10 cm above the burners to manage the combustion process in an oxygen free atmosphere and to produce the final carbon char instead of ash. At lower temperatures (till about 350° C) the main cracking process produced condensable liquid tar compounds and then at temperatures between 500° and max. 650°C, smaller hydrocarbons with radicals including hydrogen were analytically recorded [10]. Surface functionalization of the native zeolite was done due to its cation exchange behaviour, which is usually not or only negligible adsorbing aqueous anions or organic substances. Ammonium and some heavy metal´s selectivity of clinoptilolite species is generally known, however for the current study purpose, it has been lowered [11, 12]. The domestic natural clinoptilolite was chosen as the interface carrier on the base of its low-price availability in the local market, cost effectivness and due to its sufficiently large surface area, the highest one among the other natural products (Table 2), rigidity and surface functionality. The common physical characteristics of this clinoptilolite-rich tuff are following: bulk density 2.39 g/cm3, shipping weight 0.84 g/cm3, total porosity of about 35%. Surface functionality of the natural clinoptilolite towards the actual octadecylammonium surfactant, responsible for anions adsorption is illustrated in Fig. 1. For material characterization and structural investigation of these synthesized zeolite-based hybrids, the external surface area and porosity of composed zeolite including competetive samples were determined at liquid nitrogen temperature (76 K) on a Micromeritics ASAP 2400 Apparatus, using the

440 Handbook of Natural Zeolites

Eva Chmielewská

static volumetric technique and t-plot methods with BHJ pore diameter computation. Surface topography of carbonized zeolite has been visualized through a high resolution transmission microscopy (HR TEM) on ATEM 2000FX equipped with EDS spectrometer and scanning electron microscopy (SEM) on JEOL-JXA 840A integrated with energy dispersive multichannel X-ray (EDX) microanalyser KEVEX equipped with Si(Li) detector.

Figure 1: A proposed architecture of ODA-surfactant bilayer incorporated on the clinoptilolite surface (ODA admicelle on clinoptilolite surface – Z5).

Aqueous model solutions of phenol and colour substances (Fig. 2) were analysed by means of Diode Array Spectrometer Hewlett Packard 8452A. Phenol was determined in the UV spectral region at 286 nm, the dyes i.e., acid red in VIS spectral region at 506 nm and acid blue 74 (indigo carmin) at 610 nm against the calibration curves by distilled water pH values. All the solutions used were prepared from the chemicals of the analytical grade (Aldrich). Commercial adsorbent purchased under the trade mark Vapex, was expanded and hydrophobized volcanic perlite from Eastern Slovakian quarries with S(BET) equalled to 2.11 m2/g. Perlite is actually a hydrated volcanic glass, i.e., aluminosilicate of characteristic light weight, porosity, gray-white coloured, which was thermally (by about 950 °C) and chemically (with silicone oil) treated at a local Company (Kerkotherm Košice). The product is used for petroleum

Water Cleanup Processes

Handbook of Natural Zeolites 441

hydrocarbons removal as sanitary agent; in construction industry for heat insulating purposes and in the agriculture for soil conditioning. Granular activated charcoal, trade marked as HYS-N, was produced also at local chemical factory in size-granulation of 0.3 – 1.5 mm and with S(BET) surface area of 850 m2/g. It was manufactured from black coal as main component and some lignocellulose substance, using the activation with water steam. The product is accepted for drinking water purification fulfilling the European Norm EN 12 915. The shipping weight of this product was 0.480 g/cm3, the bulk density 2.19 g/cm3 and total porosity of about 62%. Carbonized char originated from the same pyrolysis matter as the carbonized clinoptilolite enriched surface, however without any addition of support. Carbonaceous fossils like lignite was of domestic origin and the shungite from the North-western site of Russia (St. Petersburg vicinity). Above fossil materials in general possess some specific properties due to rich humic components, low toxic metal content, suitable physical structure, sorption properties and sensorial features, which support their usage as a fertiliser, soil conditioner, bio- and humidity regulator and other agrochemical agents. These fossils used to be considered as first product of coalification processes on the globe and potential intermediates between peat and bitumenous coal. Their colour is brown to black, formed probably from peat under a moderate pressure. Both natural products contain about 60 – 80% organic carbon, however they are characterized with low heating values (about max. 20 MJ/kg). Their mineral matter, like quartz, montmorillonite, kaolinite, gypsum, calcite or pyrite, is largely organically bound and inseparable by standard washing techniques [13]. To provide the comparable kinetic measurements, all the used materials were grainsized into the compatible size-granulation of 0.3 – 1.0 mm. A brief description of the all applied adsorbents examined in this study is summarized in Table 1. a)

b)

Figure 2: Structural formula of indigo carmin (a) and acid red (b) (http://upload.wikimedia.org).

442 Handbook of Natural Zeolites

Eva Chmielewská

RESULTS AND DISCUSSION Generally, a suitable adsorbent for adsorption processes of pollutants should meet several requirements: (i) efficient in removal of a wide variety of target (hydrophobic) pollutants, (ii) high capacity and rate of adsorption, (iii) important selectivity for different concentrations, (iv) granular type with good surface area, (v) high physical strength, (vi) able to be regenerated if required, (vii) tolerant for a wide range of wastewater parameters, (viii) and low cost. The cost effective repositories of zeolitic or mostly siliceous minerals like volcanic perlite have forced Slovakia to the forefront of EU countries, which stresses to focus on further research, prospective activities and fabrication of new, innovative and sustainable zeolitic or other siliceous products. The volume of mining, processing and export of such commodities abroad is supposed to increase. Natural clinoptilolite, opposite to a conventional activated charcoal or synthetic ion exchange resins, posess a solid skeleton based on Al and Si polyoxides, sufficient large hydrophillic, polar, microporous, temperature and radiation resistant surface, a lower mechanical attrition and better hydraulic properties than activated charcoal. Based on these reasons, the main objective of this study was to develop such zeolite composed (hybridized) adsorbents, which potentially improve or broaden their adsorption performance towards the selected, even hydrophobic or anionic pollutants like phenol and azo-dyes. As proven so far, surface charging or templating with carbonaceous substances including application of sol-gel methods had the major influence for broadening of zeolite adsorption properties [9]. In Fig. 3, N2 – adsorption/desorption isotherms is given and Table 1 refers to the mostly mesoporous nature of the all used competetive adsorption materials among which the native clinoptilolite dominates as the adsorbent with the highest specific surface area. Adsorption isotherms of natural zeolite – clinoptilolite and its carbonized form have very similar shape and differ mainly in total adsorbed volume of nitrogen (Fig. 3). After carbonization, the total pore volume decreased from 0.106 to 0.050 cm3/g. The zeolitic micropore volumes in parent clinoptilolite (0.005 cm3/g) after carbonization little decreased (0.003 cm3/g), but both values were negligible in comparison with total pore volume. The specific surface area of

Water Cleanup Processes

Handbook of Natural Zeolites 443

carbonized clinoptilolite (23.7 m2/g) was about 25% lower than those of clinoptilolite (31.7 m2/g), as a result of mesopore volume decrease. The specific surface of shungite was even 5 m2/g smaller than those of carbonized clinoptilolite. 90 80

V0 (cm3/g STP)

70

Clinoptilolite

Carbonized clinptilolite

60

Shungite

50 40 30 20 10 0 0

0.2

0.4

0.6

0.8

1

P/P0

Figure 3: N2 – adsorption/ desorption isotherms of clinoptilolite, carbonized clinoptilolite and shungite.

Shungite did not confirm any micropores. While the pore size distribution of both clinoptilolite samples was quite wide (10-70 nm), with maximum at about 30 nm for clinoptilolite and about 15 nm for its carbonized form, the pore size distribution of shungite was narrow, recorded as ink-bottle pores with 3.5 nm entrance diameter. Surface of carbonized clinoptilolite and some other adsorbents examined were investigated by detailed microscopic SEM and HR TEM analyses under which individual carbon nanotubes (hereafter denoted as CNT), as a new allotropic carbon modification besides an amorphous carbon occurrence on the used zeolite carrier was explored (Figs. 4-7). As it can be seen according to Fig. 4, graphene sheets of the individual carbon nanotubes are paralel to the tube axis, however often defective and twisted. The carbonized clinoptilolite covered with CNT has

444 Handbook of Natural Zeolites

Eva Chmielewská

been synthesized under a typical pyrolysis, in laboratory conditions. Fe-metal and reduced Fe-metal oxides nanoparticles, present in the native zeolite, fulfilled probably the nucleation role for a potencial CNT growth. Typical tubular morphology of the surface of carbonized clinoptilolite has been confirmed using the SEM technique (Fig. 6). Based upon the EDS measurements, the individual carbon nanotubes were of about 0.35 – 0.4 nm thickness and consisted of over 100 graphene layers. The inside diameter of those carbon nanotubes reached the values of 4 up to 40 nm. The length of tubes was estimated for about 1 μm. While the examined pure CNT product adsorbed the selected azodye pollutants thoroughly, such a combined zeolite based adsorbent removed this industrial dye from water with a considerably lower capacity so far. The reason may be found in the total CNT content of both carbonized clinoptilolite and industrial CNT product (of Belgian provenience). The second one was quite 100% CNT fabricated material, what finaly caused the giant removal efficiency (graphically not shown). Table 1: Specific surface areas and porosity values of some materials studied. S(BET): active surface area determined by nitrogen adsorption and BET isotherm, S(t): surface area of mesopores plus external surface area determined by t-plot method, V(micro): volume of micropores determined by tplot method and BJH: average pores diameter according to Barrett, Joyner and Halenda. Sample

SBET (m2/g)

St (m2/g)

Vmicro (cm3/g)

BJH (Ǻ)

Slovakian clinoptilolite-rich tuff (Nižný Hrabovec)

31,7

21,4

0,0045

145

US Death-Valley clinoptilolite-rich tuff

14,3

14,5

0

92

Synthetic clinoptilolite (University of Wolverhampton, GB)

99,7

65,5

0,015

14

Carbonized Slovakian clinoptilolite-rich tuff

23,7

17,6

0,0026

8,39

ODA-hydrophobized Slovakian clinoptilolite-rich tuff

10,8

-

-

Alginite (Pinciná, Slovakia)

-

27

27

0

111

Shungite rock silicate (St. Peterburg, Russia)

18,3

17,8

ODA-zeolite (Acid Blue 74, iodide) > active charcoal (Acid Red 1) > geocomposed slovakite, natural zeolite (phosphate). Slovakite decodes an adsorbent, manufactured from domestic dolomite, bentonite, diatomic clays, alginite and zeolite, justified only with clinker and final pressurizing. Flexible component i.e., alginate biopolymer with a rigid component (pulverized) zeolite were crosslinked using Fe(III) and Ca(II) chlorides to promote the native zeolite adsorption performance and thus to prepare more efficient amphoteric tailor-made product for specific environmental targets (Fig. 13). The detailed procedure for biosorbent synthesis is published elsewhere [14]. ACKNOWLEDGEMENTS This project was funded by the Slovak Scientific Council VEGA (Project # 1/0185/12) and Slovak-Chinesse Cooperation grant SK-CN-0002-09 for which the authors express thank.

452 Handbook of Natural Zeolites

Eva Chmielewská

CONFLICT OF INTEREST No financial contributions and any other conflict of interest to this eBook chapter exists. REFERENCES [1] [2] [3] [4] [5] [6]

[7] [8] [9] [10] [11] [12] [13] [14]

Kalfat R, Ben Ali M, Mlika R, Fekih-Romdhane F, Jaffrezic-Renault N. Polysiloxane-gel matrices for ion sensitive membrane. International Journal Inorganic Materials 2000; 2: 225-31. Wu C, Tseng L. Preparation of highly porous carbon from fir wood by KOH etching and CO2 gasification for adsorption of dyes and phenols from water. Journal of Colloid and Interface Science 2005;294: 21-30. Zhao X, Lu Q, Millar J. Advances in Mesoporous molecular Sieve MCM-41. Ind. Eng. Chem. Res. 1996;35: 2075-90. Jurate V, Mika S. Distribution and Removal of Radionuclides from contaminated Medium: A Review. Research Journal of Chemistry and Environment 2007; 11: 86–103. Huddleston G, Willauer D, Boaz R, Rogers D. Separation and recovery of food coloring dyes using aqueous biphasic extraction chromatographic resins. Journal of Chromatography 1998;B 711: 237-44. Subhaschandra M, Shankara S, Keshava G, Channappa S. Continuos Decolourisation of Mixed Textile Dye Effluent by an Immobilized Packed Bed bacterial Consortium. In: Gargh SL, Ed. Book of Proceedings  Abstracts ICCE; 2005 Decem 24-26; Naiduma Printery Indore, India: 2005; pp. 434-38. Manahan E. Environmental Chemistry. Lewis Publ. Boca Raton. Ann Arbor. London. Tokyo: 1994; pp. 1-811. Saleem M, Pirzada T, Qadeer R. Sorption of some azo-dyes on wool fiber from aqueous solutions, Colloids and Surfaces A: Physicochem. Eng. Aspects 2005; 260: 183-8. Chmielewská E, Pilchowski K. Surface modifications of natural clinoptilolite dominated zeolite for phenolic pollutant mitigation. Chemical Papers 2006;60: 98-101. Morvová M, Morva I, Janda M, Hanic F, Lukáč P. Combustion and Carbonisation exhaust utilisation in electric discharge and its relation to prebiotic chemistry, Int. Journal Mass Spectrometry 2003; 223–224: 613-25. Hudec P, Smiešková A, Židek Z, Schneider P, Šolcová O. Determination of Microporous Structure of Zeolites by t-plot Method - State of the Art. Surface Science and Catalysis 2002;142: 1584-94. Pansini M. Natural zeolites as cation exchanger for environmental protection. Mineralia Deposita 1996;31: 563-75. Parker P. Encyclopedia of Science and Technology. 7th Edition. McGraw-Hill. New York, 1992. Chmielewská E, Sabová L, Sitek J, Gáplovská K, Morvová M. Removal of nitrates, sulphate and Zn(II) ions from aqueous solutions by using biopolymeric alginate/clinoptilolite rich tuff pellets. Fresenius Environmental Bulletin 2010;19: 884-91.

Handbook of Natural Zeolites, 2012, 453-472

453

CHAPTER 19 About Mathematical Modeling and Calculation of Dynamic IonExchange Processes on Natural Zeolites Valentina A. Nikashina* Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, 119991 Moscow, Kosygin str. 19, Russia Abstract: Сlinoptilolite-containing tuffs as ion-exchangers play an important role in water decontamination. The shortest scientifically grounded way to determine the optimal conditions or to forecast the results of ion-exchange processes lies in the mathematical modeling of both sorption and regeneration stages. The theory of the ion-exchange dynamics has been developed and used for modeling and calculation of technological tasks on ion-exchange resins. A bank of solutions for the dynamic ion-exchange tasks was created in the Laboratory of Sorption Methods of the Vernadsky Institute. The ion exchange on natural zeolites – clinoptilolites is characterized by a number of specific features, particularly, two-stage particle diffusion kinetics. The possibilities for using available solutions of sorption dynamics for modeling and calculation of the ion-exchange processes on natural zeolites were estimated. It was shown that the use of available solutions is possible if the sorption of target components is described by linear or nearly linear isotherms. The actual examples of application of known theoretical solutions of the sorption dynamics for modeling and calculating of ion exchange processes on natural clinoptilolites are presented in this article. The breakthrough times of some technological filters loaded with clinoptilolite are also calculated.

Keywords: Сlinoptilolite-containing tuffs, waters decontamination, ion-exchange, the dynamic ion-exchange tasks, mathematical modeling and calculation, bank of solutions, examples of application, technological filters, forecast of the ion-exchange process results, breakthrough times estimation, optimal conditions. INTRODUCTION Among other methods, the ion exchange plays an important role in water decontamination. The well-grounded choice of optimized conditions and modes under which to carry out the ion-exchange process has essential practical importance and value. The shortest scientific way to determine the optimal conditions or to forecast the ion-exchange process results lies in the mathematical 

Address correspondence to Valentina A. Nikashina: Vernadsky Institute of Geochemistry and Analytical Chemistry of Russian Academy of Sciences, 119991 Moscow, Kosygin str. 19, Russia; Tel: 8(495)-939-7085; Fax: 8(495)-938-20-54; Email: [email protected]; [email protected] Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

454 Handbook of Natural Zeolites

Valentina A. Nikashina

modeling of every stage (sorption and regeneration). Mathematical modeling allows to calculate the modes of dynamic ion-exchange processes based on the minimal number of experimental data depending on quite different parameters (depth of a sorbent bed, solution flow rate, sorbent grain sizes, etc.). For this reason, modeling becomes the important investigation phase for the solution of actual practical tasks using natural clinoptilolites. The theory of ion-exchange dynamics was being developed for many years in the Sorption Methods Laboratory of Vernadsky Institute of Geochemistry and Analytical Chemistry of the Russian Academy of Sciences [1-4] on the basis of more earlier works in this area [5]. At present a lot of different studies connected with mathematical modeling of ion-exchange processes on clinoptilolites number published [6-9]. But many of them have specific constraints. The objective of this article is to demonstrate the possibilities of simulation of some dynamic ionexchange processes on clinoptilolite-containing tuffs using the results of Sorption Methods Laboratory investigations. Initial data for Choice of Model and Mathematical Modeling The dynamics of ion-exchange process can be described by a set of the differential equations, which in the general form is as follows:



сi c a   i  i  0 the balance equation x t t

(1)

a  f (ci , ci , ai , d , v, D part , D film ) the kinetics equation t

(2)

ai  i (ci ) the equilibrium equation

(3)

The numerical solutions of this set of equations, in dimensionless variables for unicomponent and multicomponent tasks and for corresponding initial and boundary conditions, were obtained for various types of isotherm and kinetic mechanisms [1-3]. These solutions present graphically a set of the breakthrough curves in dimensionless variables U= f (T), V=f (T) for different values of X, where U = c/co is the relative concentration of studied ion in solution, V = a/ao is

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 455

the relative concentration of studied ion in ion exchanger, X is dimensionless length (sorbent bed depth), T is dimensionless time. The constraint of the dimension and dimensionless parameters are as follows: X film 

T film 

 L

(4)

v

  co ao

(5)

t

for film diffusion mechanism,  part =

Tpart =

L  G  D part

(6)

  r2 Dpart  t

(7)

r2

for particle diffusion mechanism, H=

  r2

(8)

Dpart  G X film = H  X part ;

Tfilm = H  Tpart

for mixed diffusion mechanism

where Xfilm and Xpart is dimensionless sorbent bed depth for the case of film- and particle- diffusion kinetics, accordingly; Tfilm and Tpart - dimensionless time for same cases; - film-diffusion coefficient, s-1;. Dpart – particle diffusion coefficient, cm2s-1; Dfilm –film diffusion coefficient, cm2s-1; G is the dimensionless distribution coefficient,; t- time, s; r - grain radius of sorbent, cm; v - solution flow rate, cm.s-1; L- the bed depth of sorbent in column, cm; co - initial concentration of a studied ion in solution, meq.ml-1; ao - equilibrium capacity of sorbent, meq.g-1; H is the parameter, characterizing the relative contribution of the film- and particle- diffusion in the ion exchange process (see Eq. (8)). If H > 100, the particle diffusion kinetics is the limiting stage of ion-exchange process; if H< 1, the film diffusion kinetics determines the rate of ion-exchange process; and if 1 < H < 100, the mixed diffusion

456 Handbook of Natural Zeolites

Valentina A. Nikashina

kinetics takes place and the mixed diffusion dynamic model must be selected. As an illustration, the solution results of ion exchange dynamic problems in the form of dimensionless set of breakthrough curves are presented in Fig. 1. The Laboratory of Sorption Methods has created a bank of solutions for the ionexchange (sorption) dynamic problems for the unicomponent systems described by film-, particle-, and mixed-diffusion kinetics, and by various types of isotherms, as well as for the multicomponent systems (see Table 1). These solutions are available as computer programs or as graphic diagrams (sets of the dimensionless breakthrough curves). This solutions bank allows to simulate a broad spectrum of practically important problems. In many cases, the multicomponent systems can be reduced to simple unicomponent ones. For example, the problem of deep decontamination of solutions can be considered. In this case, the dynamic ion exchange process is calculated as the unicomponent system on the least sorbed ion. This approach is possible, because one of the established laws of ion exchange dynamics says that the breakthrough curve of the least sorbed ion depends only on total concentration of ions in a solution [10]. Another example is the sorption of target components from the complex composition solutions. Unicomponent model can be used in this case if the target components sorption is described by a linear isotherm. In this connection, the methodology of modeling of any dynamic ion exchange process is based on the estimation of the following parameters [1-3]: 

theoretical and real number components determined by the isotherm type of sorbed ions.



the equilibrium characteristics (the ion exchange equilibrium coefficients - Кij or the distribution coefficient - G ij).



the kinetic characteristics of ion-exchange process–film-diffusion kinetic coefficient (β) and particle diffusion coefficient (Dpart) of the studied ions.



relative contributions of film- and particle-diffusion in dynamic processes depending on flow rate, particle size of sorbent, and so on (estimation of criterion Н by means of Eq. (8)).

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 457

Table 1: Content of the solutions bank for the ion-exchange (sorption) dynamics problems System components Unicomponent (2)

Unicomponent (2)

Multicomponent (2+n)

Isotherm

Kinetic

linear

film-diffusion

linear

particle - diffusion

linear

mixed- diffusion

non-linear (Langmuir, rectangular, etc.)

film-diffusion

non-linear (Langmuir, rectangular, etc.)

particle - diffusion

non-linear (Langmuir, rectangular, etc.)

mixed- diffusion

non-linear

film-diffusion particle - diffusion mixed- diffusion

Figure 1: Dimensionless breakthrough curves for dynamic model described by linear isotherm (K=1) and mixed diffusion kinetics (H=50).

Equilibrium and kinetic characteristics (the mathematical model coefficients) can be obtained by using two methods: (1) to use the basic experimental data. The equilibrium characteristics (ionexchange constants or distribution coefficients) can be obtained from the ion-

Valentina A. Nikashina

458 Handbook of Natural Zeolites

exchange isotherm data. Kinetic characteristics of the exchanging ions (particle diffusion coefficients) can be experimentally obtained by "a thin layer method" [11]. The film diffusion coefficient  can be calculated for the diluted solutions using the formula [1]: 1,53

 1     4,86 10      4



1  z1 z2      1 2 

2

 3

 0,47

(9)

d 1,53

where  – solution flow rate, сm.s-1;  –sorbent porosity; d – sorbent grain size, сm; z – charge value of exchanged ions;  – equivalent electroconductivity of ions, ohm-1сm2.

1,0

0,8

a/a0

0,6

0,4

0,2

0,0 0,0

0,2

0,4

0,6

0,8

1,0

c/c0

Figure 2: Ion-exchange isotherms of Cu2+ (■-■, ●-●), Sr2+ (▼-▼), Zn2+ ( ▲-▲), Ni2+ (♦-♦) on Na-form of clinoptilolite. The initial concentration of solutions is 0.1 N, pH = 5. ■-■ - Cu2+, contact time 3 weeks; ●-●- Cu2+, contact time 6 months.

(2) to use the method of the solution of "reverse problems" for processing of the experimental breakthrough curves [12]. In this case, both kinetic coefficients, D and β, and equilibrium coefficients, Gij and Kij, can be received. More correct processing of the experimental breakthrough curves is the computer simulation for "reverse problems", less correct – by fitting of a set of theoretical and experimental breakthrough curves [2]. The obtained equilibrium and kinetic coefficients are named as effective ones.

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 459

The above-mentioned parameters are necessary and sufficient to represent the physicochemical model of the dynamic ion-exchange process, and, on this basis, to choose the corresponding mathematical model and to carry out the simulation for the wide range of conditions [1, 2]. Ion exchange on the zeolites is characterized by a number of specific features. One of the major physicochemical features of zeolites is the two-stage particle diffusion kinetics – fast and slow ones [13-15]. Features of an Ion Exchange on Natural Zeolites Ion Exchange Equilibrium The ion-exchange isotherms on the clinoptilolite-rich tuffs can be of various types depending on concentration and the nature of exchanging ions. The ion-exchange isotherm of two-charge ions, in particular, copper-ions on the Na-clinoptilolite is considered as S-shaped one (contact time is 21 days) [16]. However as shown in Fig. 2, the type of an ion-exchange isotherm of copper has been changed through 6 contact months of the solution and the sorbent. The noticed effect can be explained by the kinetic factor, for example, the intracrystal diffusion of copper [14, 15]. This effect is observed also at Sr2+ sorption, but to a lesser degree and practically is not swept up at the sorption of ammonium ions under equal conditions (see Fig. 3).

1,0

0,8

a/a0

0,6

0,4

0,2

0,0 0,0

0,2

0,4

0,6

0,8

1,0

c/c0

Figure 3: Ion-exchange isotherms of NH4+ on Na-form of Tedzami deposit clinoptilolite from solutions of the different concentration. ▲-▲  NH4+ + Na+ = 0.1 N ; ao = 2.01 meq/g; ♦-♦ -  NH4+ + Na+ = 0.04N ; ao = 1.40 meq/g.

Valentina A. Nikashina

460 Handbook of Natural Zeolites

Ion Exchange Kinetics on Clinoptilolite-Containing Tuffs The two-stage kinetics of ion exchange on natural clinoptilolites is the distinctive property of this sorbent and is proved experimentally by different authors [13-15]. This feature of the natural clinoptilolites is directly connected with structure and chemical properties of the clinoptilolites and appears in a various degree depending on the nature of exchanged ions and their concentration in solution. The kinetics of Sr2+ sorption on clinoptilolites from various composition solutions is shown in Fig. 4. Strontium sorption is slowed in the area a/ao =0.2- 0.3 depending on the concentration of exchanging ions. As shown in Fig. 5, the sorption equilibrium of ammonium ions is reached on Na-clinoptilolite Теdzami (Georgia) for 60-80 minutes from 0,1N solution NH4С1. Ammonium sorption on the same clinoptilolite from 0.01 N solution is characterized by the delay of process. It can be supposed that the first kinetic stage is finished in area a/ao = 0.50.6. There are various explanations of this fact in literature [14-16].

a/ao

1

0,1

100

1000

10000

100000

Time, s

Figure 4: Ion-exchange kinetics of Sr2+ on Na- and natural forms of clinoptilolites depending on the solution composition and the grain size of sorbent. a) 0.01 N Sr(NO3), d=-0.07+0.04 cm ; ■-■ Na-form; -- natural form; b) 10 mg/l Sr2+ +0.7 N NaCl ; d =-0.07+0.04 cm; ▲-▲-Na-form; ▼▼- natural form; ♦-- natural form, d= 0.2 cm.

The two-stage particle diffusion kinetics is characteristic for an ion exchange on clinoptilolites, and it is necessary to create corresponding mathematical models

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 461

for more correct description of their behavior. The attempts to create this model were undertaken and described in the literature [17, 18]. One of these solutions of sorption dynamics problem for biporous sorbents is presented [18], but its use in practice is difficult enough. At present a computer program is developed for the ion exchange dynamic model considering two-stage particle diffusion kinetics and available interruption of the ion-exchange process [19]. Earlier we have estimated the possibilities for the use of available solutions of sorption dynamics for modeling and calculation of the ion-exchange processes on natural zeolites in technological regimes [20, 21]. This estimation shows the possibility of application of existing mathematical models of sorption dynamics for simulation of the ion-exchange processes on natural clinoptilolites in the case if the sorption of the target components is described by a linear or nearly linear isotherm. The analysis of variety of decontaminating problems showed, that the problems of removal of the radioactive impurities or heavy metal ions from the natural and waste waters can be reduced to single-component problem, because, as a rule, the sorption isotherms of ions-pollutants are linear or close to linear for natural clinoptilolites. This substantially facilitates the problem of mathematical modeling of the decontamination ion-exchange processes on clinoptilolites and allows to use the above mentioned solutions and approaches. Below, the actual examples of the use of known theoretical solutions for sorption dynamics for simulation of ionexchange processes on clinoptilolites will be presented.

1 0,9 0,8 0,7 0,6

a/a0

0,5 0,4 0,3

0,2

100

1000

10000

Time, s

Figure 5: Sorption of NH4+-ions depending on time on clinoptilolite of various grinding and from solutions of various composition. -■-■-0.1 N NH4Cl, d =0.03-0.04 cm; -●-● - 0.1 N NH4Cl, d =0.05-0.07 cm; -▲-▲ -200 mg/l NH4+ + 1.6 g/l NaCl.

462 Handbook of Natural Zeolites

Valentina A. Nikashina

Modeling and Calculation of Ion-Exchange Processes on ClinoptiloliteContaining Tuffs For modeling and calculation of dynamic ion exchange processes, we used equilibrium and kinetic characteristics received both by the manner 1 (from basic experiences), and from breakthrough curves (the manner 2). Task 1. Simulation of the decontamination process of the surface drinking water from radioactive Sr and Cs by clinoptilolite-containing tuff of Tedzamy deposit (Georgia). The cationic composition of the initial surface drinking water was as following, meq/liter: Na +-0.28; K +-0.10; Mg2 +-0.82; Ca2 +-2.10-3; Cl--0.13; SO42--0.60; HCO3 1--2.57; Sr2+-5.10-3; Cs+-1.10-3; The sorption isotherms for Sr2+ and Cs+ from water of mentioned composition has been obtained. As can be seen in Figs. 6 and 7, these isotherms are linear in studied concentration area.

Figure 6: Ion-exchange isotherms for Sr-ions on natural and Na- form of Tedzamy deposit clinoptilolite from simulated solution of surface drinking water. ●-● - natural form; ▲-▲ - Naform [22].

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 463

A, meq/g

0,1

0,01

1E-7

1E-6

C, meq/ml

Figure 7: Ion-exchange isotherm for Cs+ on clinoptilolite of Tedzami deposit from the simulated surface drinking water.

1

a/a0

0,1

0,01

100

1000

10000

100000

Time, s

Figure 8: Sr2+ sorption depending on the time on Na-form of various deposits clinoptilolites from simulated solution of surface drinking water. ■-■ - Beli Plast deposit (Bulgaria); ▼-▼- Tedzami deposit (Geogia);▲-▲- Sokirnitsa deposit (Ukraine); ♦ -♦ - Ai-Dag deposit (Azerbaidjan);-Yagodninskoye deposit (Russia); -- Dzegvi deposit (Georgia); -- Nevada deposit (USA) [23, 24].

Valentina A. Nikashina

464 Handbook of Natural Zeolites

The Sr2+ and Cs+ diffusion coefficients were obtained by "a method of a thin layer" (the method 1) [11] and by “a method of solution of reverse problems” (the method 2) [12]. As an example, sorption of Sr2+ depending on the time on Naform of different clinoptilolites is presented in Fig. 8 ("a method of a thin layer"). The values of the particle diffusion coefficients D and the film-diffusion coefficients β were calculated. For example, the obtained ion-exchange characteristics of the clinoptilolite of Tedzamy deposit are presented in Table 2. Table 2: Equilibrium (G) and kinetic coefficients of Sr2+ and Cs+ sorption by clinoptilolite from surface drinking water*) Element

G [ml/g]

D [sm2/s]

[s-1] calculated

Sr2+

2.8x103

1.5x10-10

0.12

0.16

+

4

2x10-9

0.57

0.51

Cs

5.5x10

[s-1]exper

*) solution flow rate =0.17cm/s, grain size of sorbent =0.05 cm.

As it is shown in Table 2, the distribution coefficient for Sr2+ is smaller than that one for Cs+. It means that Sr2+ is the least sorbed ion, and the breakthrough time of sorbent bed for water decontamination depends on Sr2+ breakthrough only. Owing to it, all the following calculations were realized for Sr2+. The obtained equilibrium and kinetic coefficients allow to calculate the values of criterion H (see Eq. (8)). These calculated values for different experimental conditions of Sr2+ sorption on clinoptilolite are presented in Table 3. Table 3: H values for Sr2+ sorption on clinoptilolite depending on the solution flow rate (V, cm/s) and the sorbent grain sizes (d, cm) V, cm/s

d, cm

0.030

0.065

0.095

0.05

-

57

-

0.085

52

75

-

0.15

69

105

-

0.37

108

150

184

The values H (from 50 to 180) indicate on the mixed diffusion kinetic mechanism of Sr2+ sorption for given experimental conditions. Using suitable mixeddiffusion model of sorption dynamics for linear isotherm, we have calculated a breakthrough curve of strontium from the investigated solution. As it is shown in

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 465

Fig. 9, the calculated and experimental breakthrough curves of strontium coincided closely.

Figure 9: Calculated (■-■) and experimental (○-○) breakthrough curves of Sr2+ on clinoptilolite (2g) from modeling solution of surface drinking water of composition, meq/L: Sr2+ -7.10-3; Ca2+ 3.0; the solution flow rate v= 0.4 ml/min; the sorbent grain size d=-0.5+0.36 mm.

Task 2. Modeling and calculation of stable strontium sorption by clinoptilolite from the underground drinking water [21]. The cationic composition of initial underground water was, mg /liter: Na + + K + 0.65-101.2; Mg2 +-6.6 – 40.0; Ca2 + - 26.0 -107.2; Sr2 + 0.3-35.0; Fe2+-1.0 –50.0. The Sr2+ concentration in underground water is high enough (up to 20 mg/l) and ionexchange isotherm for Sr -ions on clinoptilolite of Tedzami deposit (Georgia) is non linear [21]. The calculated Sr2+ breakthrough curves using the distribution coefficient and kinetic characteristics of ion-exchange process obtained by the manner 1, did not give the satisfactory correlation with the experimental breakthrough curves. Therefore we used second way of modeling: the effective equilibrium and kinetic characteristics were obtained from the dynamic experiments (from the breakthrough curves). The constancy of the calculated Def and Gef values obtained from the various experimental breakthrough curves is the criterion of the adequacy of the ion exchange process to the chosen model. The breakthrough curves of strontium from the underground drinking water depending on the solution flow rates and sorbent

Valentina A. Nikashina

466 Handbook of Natural Zeolites

grain sizes were obtained. A comparison of experimental breakthrough curves with a set of theoretical curves for various models of ion -exchange dynamics showed that they coincided most closely if the model of sorption dynamics for linear isotherm and particle diffusion kinetics were used. Gef and Def calculated values are presented in Table 4. Table 4: Effective distribution coefficients and diffusion coefficients of Sr2+ depending on bed depth (L), sorbent grain size (d), solution flow rate (V) for clinoptilolite-containing tuff of deposits Tedzami (Georgia) from underground drinking water Sorbent volume, ml

L, cm

d, mm

V, cm/s

Gef

Def, cm2/s

5.0

7.0

0.25-0.50

0.14

470

1.40x10-8

5.0

7.0

0.25-0.50

0.22

450

1.45x10-8

3.0

4.0

0.50 - 1.0

0.06

600

1.50x10-8

3.0

4.0

0.50 - 1.0

0.13

600

1.52x10-8

3.0

4.0

0.50 - 1.0

0.22

550

1.60x10-8

5.0

7.0

1.0 - 3.0

0.14

500

1.55x10-8

10.0

14.0

1.0 - 3.0

0.14

520

1.70x10-8

As shown in Table 4, the values of effective distribution coefficients and particle diffusion coefficients are relatively constant in the investigated interval of solution flow rates (V=0,05 – 0,2 cm /s) and sorbent grain sizes (0,25 – 3,0 mm): (Gef = 500 – 600; Def=1,5.10-8 cm2 /s), therefore, these values can be used for the calculation of breakthrough times for another bed depth of clinoptilolite. Special experiments were carried out on the pilot plant to confirm the conclusions on an opportunity to forecast the breakthrough curves on the basis of mathematical modeling. The calculated and experimental breakthrough curves of Sr2+ from the drinking underground water (t=8о С) on the pilot plant in real conditions are presented in Fig. 10. As the obtained data show, quite satisfactory coincidence of calculated and experimental breakthrough curves takes place. On the basis of the obtained data, it can be concluded that the use of dynamic models for approached description of ion-exchange processes expands the opportunities of modeling and allows to carry out the proved comparative estimation of technological properties of clinoptilolites of various deposits, and also to calculate operating modes of the

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 467

industrial filters. For example, the equilibrium and kinetic characteristics of Cs+ and Sr2+ sorption on clinoptilolite of Tedzami have been used to calculate the values of breakthrough times of the clinoptilolite trenches constructed for natural and waste water deactivation after Chernobyl accident. Some of obtained results are presented in Table 5.

Figure 10: Calculated (●-●) and experimental (■-■) breakthrough curves of Sr2+ from real underground drinking water on Na-forms of clinoptilolite (Tedzami, Georgia). Experimental conditions: sorbent bed depth L=113 cm, section column S=113 cm2, solution flow rate V = 2 liter/min, sorbent grain size d =3-5 mm, t=8o C. Table 5: Breakthrough times of clinoptilolite bed of Tedzami deposit for natural water decontamination from radioactive Sr2+ and Cs+ depending on the solution flow rate Bed depth, cm d, cm

С/Со -3

10 200

0.05

V=1 m/days

V=2 m/days

V=5 m/days

V=10 m/days

days

years

days

years

days

years

days

years

4167

11.4

2025

5.5

555

1.5

289

0.8

-2

4398

12.1

2037

5.6

613

1.7

393

1.1

5x10-2

4513

12.4

2060

5.7

729

1.9

463

1.3

10

Task 3. Simulation and calculation of the underground potable water decontamination process from NH4+ by clinoptilolite of Chuguevskoye deposits (Russia). Composition of initial water, mg /liter: Na +-60.0; Mg2 +-10.0; Ca2 +-11.0; Cl-25.4; NH4+-3,0; SO42--40.0; HCO3- -159.0; pH = 6.5-7.0. A series of the

Valentina A. Nikashina

468 Handbook of Natural Zeolites

experiments has been carried out to obtain all necessary initial data for modeling and calculating. It was obtained isotherm of NH4+ sorption. The breakthrough curves of ammonium on clinoptilolite of Chuguevskoye deposits (Russia) have been obtained depending on the sorbent bed depth, the solution flow rate, sorbent grain size. The total ion- exchange capacity of this clinoptilolite is 1,6 meq/g. The value β was determined from values of equivalent electroconductivity of exchanging ions, taking into account the hydrodynamics principles [1]. The basic equilibrium and kinetic characteristics of an ammonium sorption on clinoptilolite obtained as a result of processing of breakthrough curves and sorption isotherms, are presented in Table 6. Table 6: The carried out experiments and results of their processing NN Experiments Experimental conditions

1

2

3

5

6

7

8

V, sm/s

0.015

0.026

0.03

0.017

0.067

0.017

0.067

Volume of sorbent, ml

6.0

5.6

4.2

3.2

44

3.2

44

Вed height, sm

8.2

7.3

5.5

4.2

16

4.2

16

Section, sm

0.73

0.78

0.76

0.76

2.74

0.76

2.74

Grain size, mm

1-2

0.5-3.0

0.5-3.0

0.5-1.0

0.5-3.0

0.5-1.0

0.5-3.0

G, ml/ml (from isotherm)

900-1000

-

-

-

-

-

-

1000

800

1000

1000

0.016

0.030

0.024

0.014

0.031

0.023

5.0

11

1.5

2

Gef, ml/ml (from dynamic) β, s-1 (experiment)

0.02

-1

0.017

β, s (calculation) 2

Def, cm /s Н = r2/DG)

1,1.10-8

2.10-8 7.2

As shown the represented data, equilibrium and kinetic coefficients obtained by different methods practically coincide. Thus, the basic data necessary for calculation of breakthrough curves of ammonium on clinoptilolite from the drinking artesian water are received. These are the following data: Gef =1000 ml/ml; Def = 1.5.10-8 cm/s. Based on received equilibrium and kinetic data the values H was calculated, the mathematical model was chosen and calculation of a

Dynamic Ion Exchange Processes on Natural Zeolites

Handbook of Natural Zeolites 469

breakthrough curve of an ammonium ion for 44 ml clinoptilolite was realized for the solution flow rate 11 ml/min = 0,067 cm/s. Experimental check of calculation is carried out. Results are presented on Fig. 11.

C/Co

1

0,1

0,01 1 000

Time, s

Figure 11: Experimental (■ - ■ -) breakthrough curve of ammonium ion on clinoptilolite of Chuguevskoye deposits.Vsorbent = 44 ml, solution flow rate 0,067cm /s. d=0.12-0.17 cm. The calculated breakthrough curves of an ion of ammonium for the following conditions. ▲ sorbent grain size d = 0.17cm; ▼ grain size d=0.12сm. Table 7: Breakthrough times (hours) vs. column operating for removal of ammonium ions from artesian drinking water by clinoptilolite. Sorption conditions: the bed depth 1 m ; V= 7 m / hour = 0,2 cm /s; СoNH4 = 3 mg /l; the sorbent grain size of 0,17 cm and 0,12 cm, distribution coefficient -1000 С/Сo

d =0.17cm

d= 0.12cm

0.02

58

68

0.05

73

78.6

0.1

86

90.8

As shown Fig. 11, calculated and experimental data well coincide among themselves if the average sorbent grain size was accepted equal 0,12 cm and distribution coefficient 1000. These results have allow to forecast the breakthrough time of clinoptilolite column by bed depth 1 m for solution flow rate

470 Handbook of Natural Zeolites

Valentina A. Nikashina

7 m/hour=0,02 cm/s depending on decontamination degree (C/Co) and sorbent grain size. Results are resulted in Table 7. CONCLUSIONS The opportunity and expediency of the mathematical modeling and calculation of ion- exchange processes on natural cliniptilolites is shown on actual examples for the cases described by a linear isotherm or close to linear isotherm using the theoretical solutions of ion exchange dynamics developed for more ordinary one-stage particle diffusion kinetics.The breakthrough times of a clinoptilolite of any bed depth and any sorbent grain size can be calculated for practical problems on the basis of the obtained equilibrium and kinetic characteristics of ion exchange processes and the corresponding solutions of the sorption dynamics depending on the column operating conditions in each considered case. The use of dynamic models for the approached calculation of ion- exchange processes on the natural clinoptilolites expands the opportunities of modeling and allows to carry out the proved comparative estimation of technological properties of different clinoptilolite deposits, and also to calculate the operating modes of the certain industrial filters. ACKNOWLEDGEMENTS This work is largely a review. It presents the studies results of sorption methods Laboratory of Vernadsky Institute RAS for mathematical modeling of the ionexchange processes on natural zeolites for a certain period of time, also some new results, and it is dedicated to the memory of Professor Senyavin M.M. –the organizer of these studies.The author is grateful to the collaborators of the Laboratory who participated in these studies. CONFLICT OF INTEREST Please note that no financial contributions or any potential conflict of interest to this eBook chapter exists. REFERENCES [1]

Senyavin MM, Rubinstein RN, Venitsianov EV, Komarova IV, Galkina NK, Nikashina VA. Osnovy rascheta i optimizatsii ionoobmennykh processov.[Fundamentals of Calculation and Optimization of Ion-Exchange Processes]. Nauka, Moscow 1972; 172 p. Russian.

Dynamic Ion Exchange Processes on Natural Zeolites

[2] [3] [4]

[5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]

[16] [17] [18]

Handbook of Natural Zeolites 471

Nikashina VA, Galkina NK, Senyavin MM. Raschet sorbtsii metallov ionoobmennymi filtrami [Calculating of the sorption of metals by ion-exchange filters], Russian Institute of Scientific and Technical Information, Moscow, Article No.3668, 1977; 44 p. Russian. Venitsianov EV, Rubinstein RN. Dynamika sorbtsii iz zhidkikh sred. [Dynamics of Sorption from Liquids]. Nauka, Moscow, 1983; 240 p. Russian. Nikashina VA, Galkina NK, Komarova IV, Anfilov BG, Argin MA. Evaluation of clinoptilolite-rich tuffs as ion-exchangers. In: Ming DW, Mumpton FA, eds. Natural Zeolites ‘93: Occurrence, Properties, Use. Int. Comm. Natural Zeolites, Brockport, New York 1995; 289–97. Zsuchovitsky AA, Zabezsinsky YaL, Tichonov AN. Adsorbtsiya gasa iz potoka vozdukha sloem zernennogo materiala. [Gas adsorption from air streamflow by bed of grain material.] Zshurnal Fisicheskoy khimii. [J Phys.Chem] 1945; 19: 253-261. Russian. Inglezakis VJ, Grigoropoulou HP. Modeling of ion exchange of Pb2+ in fixed beds of clinoptilolite. Micropor Mesopor Mater 2003; 61: 273-282. Markovska LT, Meshko VD, Marinkovski MS. Modeling of the adsorption kinetics of zinc onto granular activated carbon and natural zeolite. J Serb Chem Soc. 2006; 71: 957-967. Warchol J, Petrus R. Modeling of heavy metal removal dynamics in clinoptilolite packed beds. Micropor Mesopor Mater. 2006; 93 (1-3): 29-39. Rabideau AJ, Van Benschoten J, Patel A, Bandilla K. Performance assess of zeolite treatment wall for removing Sr-90 from groundwater. J Сontaminant Hydrology 2005; 79(1-2): 1-24. Galkina NK, Senyavin MM. O nekotoriykh zakonomernostyakh dinamiki ionnogo obmena smeseyi ionov [ About some regular dependences of ion-exchange dynamics of ions compounds]. Zshurnal Fisicheskoy khimii. [J Phys Chem.] 1969; 43(7):1783-9. Russian. Boyd GE, Adamson AW, Meyers LS. The exchange adsorption of ions from aqueous solutions by zeolites. J Amer Chem Soc 1947; 69: 2836–2848. Tikhonov AN, Arsenin VJ. Methody Resheniya Necorrektniykh Zadach, [Methods of solving “reverse” problems], Moscow, Nauka, 1979; 288 p. Russian. Brown LM, Sherry HS, Krambek FJ. Mechanism and kinetics of isotopic exchange in zeolites. J Phys Chem 1971; 75: 3846–3855. Thompson PW, Tassopoulos MA. Phenomenological interpretation of two-step uptake behaviour by zeolites. Zeolites 1986; 6: 9–12. Tolmachev AM, Nikashina VA, Chelischev NF. Ionoobmenniye svoiystva i primenenie synteticheskikh i prirodnikh zeolitov.[Ion exchange properties and application of synthetic and natural zeolites]. In: Senyavin MM Ed., Ion Exchange, Nauka, Moscow, 1981; 4563.Russian. Nikashina VA, Tyurina VA, Mironova LI. Sorption of copper (II) ions on the sodium and the calcium forms of zeolites. J Chromat 1980; 201: 107-12. Venitsianov EV.Metod limitiruuyschei stadii v dinamicheskikh sorptsionnikh processach [ Method of limiting stage in dynamic sorption processes]. Izvestiya RAN, Chem. Series 1980; 9:1981-5. Russian. Khamizov RKh. Physiko-khimicheskie osnovi kompleksnogo osvoeniya mineralnikh resursov okeana. [Physico-chemical basis of integrated development of ocean mineral resources]. Doctoral thesis, Vernadsky Institute of RAS, Moscow, Russia, 1998; 332 p. Russian.

472 Handbook of Natural Zeolites

[19]

[20]

[21]

[22]

[23]

[24]

Valentina A. Nikashina

Токmachev МG, Tikhonov NА, Nikashina VA, Bannich LN.Process sorbtsii tokcichnikh zagryazneniy prirodnim zeolitom kak geokhimicheskim baryerom. [Sorption process of toxic pollutions by natural zeolite as geochemical barrier]. Matematicheskoe modelirovanie [Mathematical modeling] 2010; 5: 97-103. Russian. Nikashina VA, Senyavin MM, Mironova LI, Tyurina VA. Modeling and Calculating IonExchange Processes of Metal Sorption by Natural Clinoptilolite. In:.Murakami Y, Iijima A, Ward JW, Eds. "New Developments in Zeolite Science Technology", Proceeding of the 7th Inter. Zeolite Conference, Tokyo, Japan, 1986; 283-8. Nikashina VA, Zaitseva EV. Modeling and calculation of the ion-exchange processes of excess strontium removal by Tedzami clinoptilolite from underground drinking water. Program and Abstracts, Zeolites`91, 3rd Inter. Conf. on the Occurance, Properties and Utilization of Natural Zeolites, Havana, Cuba, 1991;169-70. Nikashina VA, Tyurina VA, Senyavin MM, Stefanov GI, Gradev GD, Stefanova IG, Avramova AI. Comparative characteristics of the ion-exchange properties of natural clinoptilolites from Bulgaria and the USSR for the purpose of purification of liquid wastes from nuclear power plants. Part 1. Study of the equilibrium sorption of Cs and Sr ions from solutions of different composition. J Radioanal Nucl Chem., Lett., 1986; 105: 175-184. Senyavin MM, Nikashina VA, Novikova VA, Gradev GD, Stefanova IG, Avramova AI. Comparative study of the ion-exchange properties in natural clinoptilolites of the USSR and Bulgaria with the aim of purifying liquid sewages from atomic power station. Part 2. Kinetics of strontium sorption by clinoptilolites of different cationic forms. J Radioanal Nucl Chem., Lett. 1989; 130: 293-8. Berkovich SE, Nikashina VA. Osobennosti ionnogo obmena Sr na razlichnikh kationnikh formakh prirodnikh klinoptilolitov. [Features of Sr ion exchange on different cation forms of natural clinoptilolites]. Neorganicheskie materiali [Inorganic materials] 1990; 26: 10357. Russian.

Part IV: COMMERCIAL-SCALE USES AND APPLICATIONS

Handbook of Natural Zeolites, 2012, 473-508

473

CHAPTER 20 Environmental Applications of Natural Zeolites Hossein Kazemian1,*, Kadir Gedik2 and İpek İmamoğlu3 1

Department of Chemical and Biochemical Engineering, Faculty of Engineering, The University of Western Ontario, London, Ontario, N6A 5B9, Canada; 2 Assistant Proffessor Department of Environmental Engineering, Akdeniz University, Antalya, Turkey; and 3Department of Environmental Engineering, Middle East Technical University, 06531, Ankara, Turkey Abstract: Environmental pollution particularly at very low concentrations is very difficult to remove from contaminated media. Adsorption by means of relatively inexpensive natural adsorbents such as zeolites can be considered as a cost effective alternative treatment of such contaminated streams. The unique chemical and structural characteristics of natural zeolites made them potential materials for a multitude of environmental applications where materials are needed for effective binding, adsorbing, and filtering. In this chapter, some of the commercially available environmental treatment technologies based on utilization of natural zeolitic materials will be discussed.

Keywords: Natural zeolite, environmental pollution, wastewater treatment, ion exchange, adsorption, heavy metal, ammonium, radioactive waste. INTRODUCTION Rapid growth in human population and subsequent industrialization has introduced numerous hazardous materials into the environment resulting in serious environmental degradation. Rapid industrialization during the past century has led to the dissemination of a wide variety of pollutants, including toxic elements into the environment. Many industries such as mining, refining, plating, and metals processing are challenged with managing the integrity of process materials and process waste. Over the recent decades, there has been increasing global concern over the public health impacts attributed to environmental *Address correspondence to Hossein Kazemian: Zeolitic and Nano Materials Lab. (ZNML), Department of Chemical and Biochemical Engineering, Faculty of Engineering, The University of Western Ontario, London, Ontario, N6A 5B9, Canada; Tel: (519) 661 -2111 Ext: 81295, E-mail: [email protected], [email protected]; Homepage: http://www.eng.uwo.ca/zeolite/kazemian.htm, http://www.eng.uwo.ca/zeolite/ Vassilis J. Inglezakis and Antonis A. Zorpas (Eds) All rights reserved-© 2012 Bentham Science Publishers

474 Handbook of Natural Zeolites

Kazemian et al.

pollution particularly for the global burden of disease. The World Health Organization (WHO) estimates that about 25% of the diseases humankind suffers occur due to prolonged exposure to environmental pollution due to contaminated air, water and soil. Removal of these pollutants requires relatively cheap, cost effective and economically viable technologies. Nowadays, adsorption is believed to be a simple and effective technique for water and wastewater treatment and the success of the technique largely depends on the development of efficient and cheap adsorbents. Activated carbon [1], clay minerals [2, 3], biomass [4], natural zeolites [5, 6], and even some industrial solid wastes [7, 8] have been widely used as adsorbents for removal of ions and organics in wastewater treatment plants. Chemical contaminants at low concentrations are typically difficult to remove from water. Treatment processes for contaminated waste streams include chemical precipitation, membrane filtration, ion exchange and adsorption. Cost effective alternative sorbents for treatment of contaminated waste streams are needed. Although there is increasingly strict legislation regarding permissible effluents, due to economic pressure, companies are unable to spend vast sums of money on environmental clean-up operations. As a result, inexpensive solutions are sought. Natural materials that are available in large quantities, or certain waste products from industrial and agricultural operations, may have potential for use as inexpensive sorbents. The unique chemical and structural characteristics of natural zeolites made them as potential materials for a multitude of environmental applications where effective, low cost materials are needed to bind, absorb, adsorb, fill, and filter. Molecular sieve and ion exchange properties, as well as availability and cost are the major factors that make natural zeolites commercially attractive for environmental remediation and industrial applications [9, 10]. In this context, the discovery of zeolite deposits with relatively high purity in the United States and some other countries in the 1950s marked the beginning of the natural zeolite era of commerce [11]. After that time, chabazite, erionite, and mordenite were introduced into the commercial area as “acid” natural gas drying adsorbents in the 1960s [12]. Since then, the potential outlook for natural zeolites changed dramatically due to increasing demand for cost-effective, simple-to-operate, so called “low technology treatment strategies” in the field of pollution control.

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 475

Natural zeolites for the commercial market, on the other hand, are generally prejudiced as limited compatibility due to variations in mineral purity, availability, heterogeneity in crystal size, etc. in the sedimentary deposits. Out of the 40 known natural zeolite types, the most common ones, namely, chabazite, clinoptilolite, erionite, ferrierite, phillipsite, mordenite and analcime; and even further, only chabazite and clinoptilolite are considered to be exploitable natural resources with sufficient quantity and purity [13, 14]. Data presenting some physicochemical properties which enable them to be utilized in various specific technological fields on commercially available types of natural zeolites are given in Table 1. Table 1: Some properties of sedimentary zeolites [13] Type

TSi

CEC (meq/g) Cations

Window size (A) Void Volume

Analcime

0.60-0.74

3.6-5.3

Na

1.6*4.2

0.18

Chabazite

0.58-0.80

2.5-4.7

Ca,Na,K

3.8

0.48

Clinoptilolite

0.80-0.85

2.0-2.6

Na,K,Ca

3.1*7.5

0.34

Erionite

0.72-0.79

2.7-3.4

K,Na,Ca

3.6*5.1

0.36

Ferrierite

0.83-0.85

2.1-2.3

Ca

4.2*5.4

0.24

Mordenite

0.80-0.85

2.1-2.4

Na,Ca

6.5*7.0

0.26

Phillipsite 0.52-0.77 2.9-5.6 K,Na,Ca 3.8 0.30 TSi : Fraction of tetrahedral positions occupied by Si; CEC : Cation exchange capacity in the idealized Naform formulas; Window size refer to the largest channel; Void volume expresses ml of liquid water/ml of crystal.

An examination of Table 1 reveals that while the medium to high silica zeolites (chabazite, phillipsite, clinoptilolite, mordenite) are suitable for ion exchange applications, zeolites having medium to large pore sizes (chabazite, clinoptilolite, mordenite) are potentially useful for adsorption and catalysis applications [13]. Therefore, this table can also assist an engineer to identify the type of zeolite suitable for an application of environmental concern. Unlike naturally occurring zeolites, synthetic zeolites are manufactured in energyintensive chemical processes and are significantly more expensive than natural ones. Due to their negatively charged framework, natural zeolites exhibit high selectivity and performance in adsorption of cations such as ammonium and heavy metals. It is noteworthy to mention that natural zeolites show different

476 Handbook of Natural Zeolites

Kazemian et al.

cation selectivity and competitive adsorption in a multi-component system. Furthermore, unmodified natural zeolites are not suitable as effective adsorbents for the removal of anionic species or organic molecules; however, surface modification using particular organic molecules such as cationic surfactants can change the surface charge of natural zeolites, making them suitable for removal of such species [15, 16]. Modification of natural zeolites by some metals (e.g., Ag+) can also render them useful medium for inorganic anion (e.g., Cl-) adsorption by means of surface precipitation mechanism [17]. Some of the major commercial usage of natural zeolites can be summarized under the following topics: 

drinking water treatment



wastewater treatment



swimming pool water purification



management of radioactive wastes



gas separation and treatment of gaseous emissions



miscellaneous applications

DRINKING WATER TREATMENT Filtration and purification characteristics of natural zeolites can be applied for removing impurities existing in water in the form of insoluble, colloidal and dissolved physical states, which are of mineral, organic or biological origin [18]. Taking into account the selective, effective and relatively high exchange capacity of natural zeolites for ammonia and other metallic cations (i.e., the most abundant pollutants found in drinking water), natural zeolites are considered as one of the effective replacements for sand/anthracite and multimedia beds in surface and ground water filtration. Furthermore, the standards of drinking water enforced worldwide for microorganisms, pathogens, and turbidity can be most easily met using a natural and relatively low-cost natural zeolite product rather than traditional sand filters. In the 1970s, a water-reuse process stream in Denver, Co,

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 477

USA, was designed and constructed based on using several natural clinoptilolite cation-exchange columns (≈ 9 m long, 3 m in diameter, ≈ 0.3-0.85 mm particle size) for producing one million gallons of drinking water per day while the ammonium ion content of sewage effluent was reduced down to potable water standards [19]. A clinoptilolite filtration process for drinking water was designed and evaluated for the city of Logan, UT, USA. Adding a layer of zeolite powder tripled the filtration rate without any deleterious effects [20]. Ammonia is a common contaminant together with a variety of impurities found in natural waters. Its presence in waters can cause serious environmental problems like toxicity to aquatic life and has a role in eutrophication depending on temperature and pH. Most of the natural zeolites have high selectivity for ammonium ion. In this context, zeolites were often used to reduce the levels of ammonium and some other impurities in water treatment plants from Budapest (Hungary), Colorado (USA), Tbilisi (Georgia) and Ukraine [21, 22]. In these pilot or full-scale applications, the ion exchange and filtering properties of clinoptilolite-rich tuffs were utilized with subsequent treatment systems. In water treatment process in Hungary, by using a clinoptilolite filtration system, the ammonia content of drinking water was reduced from 15–22 ppm to less than 2ppm [23]. Use of natural clinoptilolite beds to upgrade river water to potable standards at Russia and Ukraine were also reported [24, 25]. Practical applications of phillipsite-rich tuff from Tenerife, Canary Islands, were also shown to favorably remove indicator bacteria and dissolved organic matter from water in a packed percolator reactor [21]. Recently, Harleman et al., [26] reported a patented micro-filtration system, namely, Jossab Aqualite, by the integration of clinoptilolite into an appropriate technical set-up for purifying drinking water in emergencies where the requirement of safe drinking water has been critical for the public health. The technique is able to filter out particles down to the size of 1–2 μm without any chemical additives. The subsequent UV filter ensures complete removal of bacteria and parasites. For emergency situations, the mobile units have a capacity ranging between 7-15 m3/h which corresponds to fresh water to 5000–12000 persons for 8–10 h/day or up to 20 000–25 000 persons for 20 h/day in compliance with the WHO’s standards. Mobile water purification units such as the one shown in Fig. 1 were utilized

478 Handbook of Natural Zeolites

Kazemian et al.

between 1999-2006 in Rosersberg, Sweden; Grozny, Chechenya; Belgrade, Kosovo for rapid transportation to the point-of-need, and for immediate performance at the emergency site. This system is further proposed for the elimination of radioactive fallout and for the removal of arsenic or geogenic pollutants from groundwater [26].

Figure 1: A mobile water purification unit based on natural zeolite, capacity: 4–7 m3/h, weight: 1800 kg [26].

The selectivity of several natural zeolites for Pb2+ suggests an inexpensive means of removing lead from drinking water. Recently a filter based on natural zeolite for filtering raw water into potable water is registered as a patent [27]. The Filter contains a series of different material layers in the following order: 1) sand to gravel or coarse silica; 2) zeolite; 3) activated carbon; 4) a second layer of sand to gravel or coarse silica; and 5) a second layer of zeolite, which is claimed as a water filter and a water filter system for raw water filtration and methods of filtering raw water into potable water. Optionally, this filter further has a ceramic media layer. This filter setup may have a reactive coating such as calcium hypochloride. Further options include ferruginous latertic clay spheres (FLCS) or iron oxide brick particles, at least one grid, which may be charged, and/or at least one sand arch. The media layers are contained within a vessel [27]. WASTEWATER TREATMENT Our world is faced with increasing demands for treatment of municipal, agricultural, and industrial wastewaters for high-quality effluent. The fate of

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 479

heavy metal cations, anions, organic molecules and other trace elements in industrial and natural waters is a rapidly growing concern to the world population. Natural zeolites are used as an effective material for improving waste water treatment operations, effluent discharge quality and in producing a higher value added sludge product for agricultural applications. In this concern, natural zeolites may improve settling, clarification, ammonia and heavy metal adsorption, etc. Plenty of research projects have been conducted on water and wastewater treatment using a wide variety of sorbents with special attention to the natural zeolites in the low-cost adsorbents category [28]. According to the evidences, the first attempts on water purification using natural zeolites were carried out in the nineteenth century [29]. This appears to be the first commercial application of zeolites and reveals that zeolite cation exchange properties have been known for over 100 years [30]. Despite this early discovery, the cation exchange properties of zeolites were not used for treatment for a long time, and were considered with a relatively minor interest for industrial application. In fact the higher cation exchange capacities, faster reaction kinetic; and in some extent, higher chemical stabilities of organic resins seemed to make their use far more convenient in water/wastewater treatment than natural zeolite materials. Historically, commercial utilization of natural zeolites in cation-exchange processes were first reported in 1960s [31], where the effective performance of clinoptilolite for removal of NH4+ from municipal and agricultural waste streams were demonstrated. Clinoptilolite is one of the well known zeolites amongst natural zeolite minerals and synthetic zeolites [32], which is abundant worldwide in huge zeolite-rich tuffs deposits, readily available and inexpensive. From an industrial applications viewpoint, natural zeolites are usually less effective in comparison to organic resins or other synthetic zeolites, mostly due to their slow kinetics, phase impurities, relatively lower cation exchange and adsorption capacities and their inability to be completely regenerated. However, the lower cost and environmental friendly nature of natural zeolites are attractive for use due to logical reasons when compared to their alternatives. Nevertheless, fundamental studies on the cation exchange properties of zeolites from the 1950s onward [33] overturned the previous judgments, at least in some

480 Handbook of Natural Zeolites

Kazemian et al.

practical applications concerning environmental protection. Unlike organic resins that have partially amorphous structures, zeolite is characterized by a three dimensional, rigid and crystalline anion framework which generates a particular electric field. Various cations interact differently with various zeolite frameworks and the electrical fields. This consideration explains why zeolites display different affinities for cations and forms the theoretical basis of their cation selectivity trends [30]. Taking into account the cation selectivity sequences of zeolitic minerals, they can be used as effective materials in the selective removal of cationic pollutants from water streams that are particularly effective in the presence of interfering cations. Natural zeolites have excellent capability to remove (or reduce) cationic contaminants, bio-particle (algae), dirt (turbidity), silt, and in some extent some of organic compounds from contaminated water streams. It enhances clarification performance and decreases filter bed solids loading. Saturated spent zeolitic material can be landfilled or in some case they can be used as soil conditioners, whereas spent organic resins (as a solid waste generated) must be taken to a licensed landfill. Some of the natural zeolites are well known as ideal physical adsorbents of pathogens such as Giardia, cryptosporidium, and other bacteria and their spores. Most of these organisms and their spores are in the size range of 0.5-10 microns, therefore the zeolite powder can adsorb a high percentage of these microorganisms while the water passes through the zeolite [34]. Furthermore, the use of naturally occurring zeolites for this purpose is viable in economic point of view, because of their wide availability in many countries and relatively low cost. However, the main applications of natural zeolitic materials in wastewater treatment processes can be summarized as: 1.

Removal of ammonium ion/nutrients from water and wastewater.

2.

Removal of heavy metal cations from water and wastewater.

These are discussed, in terms of their commercial applications, in corresponding subsections.

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 481

Ammonium Ion/Nutrient Removal One of the most common cation in waters and wastewater that is a potentially hazardous species affecting human and animal health is ammonium. It can be removed by a very simple ion-exchange reaction with biologically safe and acceptable cations such as K+, Mg2+, Ca2+ and Na+ existing on the exchange sites of natural zeolites. Most of the natural zeolite exhibits high selectivity for ammonia in solution [30] and even in the gas streams [35], in which depending on flow rates, temperature, pH, particle size of the zeolitic adsorbent, volumes and loading, remarkably reduce the ammonia content of wastewater streams. Thereby reducing the release of excess levels of ammonium and inhibiting the growth of algae and the depletion of oxygen in aqua-system. In the last 20 years, the possible removal of ammonia from water containing alkaline earth and alkali cations by using clinoptilolite has been the objective of plenty of research projects [36]. It has also been applied commercially in municipal wastewater treatment processes. The early work of Ames [37] demonstrated that clinoptilolite had high selectivity towards ammonium ions and so could be used to treat sewage and agricultural effluents. Clinoptilolite is highly selective to ammonium-ion because of the size and charge of the hydrated cation and specific crystal structure and distribution of the exchange sites in the zeolite framework. In the 1950s, the cation selectivity series for a typical natural clinoptilolite was determined to be as following [22]: Cs+ > Rb+ > K+ > NH4+ > Ba+ > Sr2+ > Na+ > Ca2+ > Fe3+ > Al3+ > Mg2+ > Li+ Those cations that are more amenable to adsorb by clinoptilolite (i.e., Cs, Rb, and K) are not commonly found in sewage streams, except for potassium. Unusual selectivity of many zeolites toward NH4+ ions is caused by structurally related ion sieve properties found in various extents in many zeolites. The selective absorption of ammonium in the presence of bivalent cations determines by steric reasons due to a molecular sieve effect because of different ionic radii (known as kinetic radii) [38]. It is reported that ammonium exchange capacity can be

482 Handbook of Natural Zeolites

Kazemian et al.

estimated from the cationic strength of the wastewater. It was observed a sharp decreasing in capacity by increasing of cationic concentration [39]. They have also shown that the extent of ion sieving depends on: a) The size of pore openings into the ion cages contained in the 3-D lattice structure; and b) The strength of bonding energy between water molecules and zeolite framework. It was found that ammonium exchange capacity in bi-solute system with sodium ions or potassium ions was reduced due to the competition with coexisting ions. Obviously, potassium ion reduces the exchange capacity more than sodium [40, 41]. The natural zeolite clinoptilolite, which was used in a sewage treatment process at the Tahoe–Truckee (Truckee, CA, USA) effectively removes >97% of the NH4+ from tertiary effluent [42]. Pilot scale studies of NH4+ removal from municipal wastewater by using clinoptilolite-rich tuff were reported from various countries. After exchange and subsequent regeneration of the zeolite with NaCl/KCl solutions ammonia was stripped from the solution and an ammonium phosphate fertilizer was produced [43, 44]. Between 1978 and 1993, the Tahoe-Truckee Sanitation Agency (CA, USA), treated some 8.107 m3 wastewater applying a clinoptilolite tuff for ammonia exchange. The system was designed to accommodate a flow rate of 26,100 m3/day of wastewater and to extract 19.5 mg NH4/liter (507 kg) from a feed water containing ca 25 mg/liter [42]. Adding of natural zeolites (e.g., powdered clinoptilolite) to sewage before aeration could increase oxygen consumption and sedimentation yield, resulting in a sludge, which can be more easily dewatered and used as a fertilizer [43]. Utilization of natural clinoptilolite accelerates nitrification of sludge. Clinoptilolite selectively uptakes NH4+ from wastewater and provides an ideal growth environment for nitrifying bacteria, which oxidizes NH4+ to nitrate [44-46]. Several tons of clinoptilolite-rich tuff were also used for the same purposes especially in the United States, e.g., in Upper Occoquan, Virginia (57000 m3/day); in Alexandria, Virginia (245 000 m3/day); in Denver,

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 483

Colorado (3800 m3/day); in Rosemont, Minnesota (2250 m3/day) and some other small plants in Toba, Japan [13, 21, 30, 47,]. In a pilot scale study, clinoptilolite-rich tuffs from Tokaj Hills, Hungary have been used in two stages of the process of municipal wastewater treatment [43]. The addition of 30-100 g of powdered tuff of 40-160 μm grain size to 1 m3 of raw sewage before the aeration tank was found to (1) increase the oxygen consumption rate ( i.e., the biological activity of the living sludge by a minimum of 25%), (2) cause an increase in sedimentation rate because the content of suspended solids in the effluent after the secondary settling tank decreased (e.g., from 35 to 18 mg/liter or from 10 to 4 mg/liter), and (3) decrease the mole ratio of added Fe3+ or Al3+ salts to phosphate from 2.0-2.5 to 1.2-1.8 (i.e., similar amounts of phosphate were removed using less of an excess of these salts). The resulting sludge was more easily dewatered and could be used as a fertilizer. Its anaerobic digestion required 20-24 days instead of 30—35 days. Heavy metals bound to the clinoptilolite in the sludge were more slowly released by orders of magnitude than from normal sludge. Ammonium from treated effluent was removed in an ion-exchanger bed filled with 0.5-2 mm granules of the zeolitic tuff. By using alkaline regenerating solutions of KCI/NaCl, ammonia was removed by stripping and absorbed in phosphoric acid. Ammonium hydrophosphate was thus produced and used as a fertilizer. They concluded that in addition to the natural zeolite favorable ion exchange properties, the texture of the rock played an important role in this technology by providing a broad distribution of pore spaces, which allowed easy access to the embedded zeolite crystals thereby permitting sorption of large particles, such as bacteria, and by serving as a reservoir for salt solutions. Main features of the suggested technology were patented as “zeoflocc” process. Scheme of a typical process used for municipal wastewater treatment is illustrated in Fig. 2. Cation active polyelectrolytes (acrylic acid-amide containing Praestol 444K or Cytec C573), on the other hand, were applied for the modification of clinoptilolite-rich tuff to increase the formation of a bacterial layer on the zeolite surface. This new process is named as “zeorap” and implemented in Szob treatment plant, Hungary [48]. Zeograp process represented a significant increase in the decomposition of organic compounds, in nitrification activity, in the degradation of nitrogen compounds. As another example, Ca-saturated

484 Handbook of Natural Zeolites

Kazemian et al.

clinoptilolite from Wyoming was successfully used to remove ammonium from the National Space Administration (NASA) regenerative life-support wastewater system [13].

Figure 2: Typical schematic process for municipal treatment with natural zeolite.

RIM-NUT Process Over the last two decades, resurgent interest has been observed in the industrial recovery and recycling of phosphorus containing compounds from contaminated water streams. Italian scientists at Italy’s National Research Council developed an advanced physico-chemical nutrient-removal process based on selective ion exchange and chemical precipitation, called RIM-NUT (i.e., Removal of Nutrients) that uses the selective exchange by clinoptilolite and an organic resin to remove N2 and P from sewage effluent [49, 50]. A three months demonstration of RIM-NUT confirmed the possibility to prevent eutrophication by removing ammonium and phosphate ions from municipal secondary effluents and to recover quantitatively magnesium ammonium phosphate, a slow-release premium quality fertilizer, in a simple and technically

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 485

affordable manner. Economic projections for a 5.3 MGD (20,000 m3/d) plant indicate that RIM-NUT is cost effective. The overall costs are almost completely covered by the value of the fertilizer recovered and the non-eutrophic potential of the wastewaters discharged [51]. RIM-NUT process allows for P, NH4 and K removal from dilute streams by a selective ion exchange followed by struvite precipitation under optimized conditions. The process is suitable for different applications, thus overcoming limitations of biological processes, and may be integrated with (rather than substituted for) other P-recovery technologies, particularly as a mainstream (tertiary) treatment in small-medium size waste water treatment plant where bio-P might not be easy to operate [52]. In fact, this technology developed in the mid 1980s for removal and recovery of phosphate, ammonium and potassium ions from wastewater in the form of a high quality slow-release fertilizer (i.e., ammonium and potassium struvite MgNH4PO4, and MgKPO4 in its basic configuration). Schematic flowchart of conceptual basics of a RIM-NUT process is shown in Fig. 3. The RIM-NUT process consists of two main unit operations: 

selective ion exchange for removal of nutrients (NH4+, K+, HPO4=) from wastewater and subsequent concentration by regenerating the saturated ion exchangers.



chemical precipitation of nutrients from this concentrated liquid in the form of struvite after addition of Mg2+ at controlled pH, while the supernatant solution is recycled.

The main features of the RIM-NUT technology can be summarized as following: 

two ion exchange units, cationic and anionic, based on a natural zeolite (Clinoptilolite, Phillipsite or Chabazite) and a “scavenger” strong base resin respectively, are used for selective removal (>90%) of nutrients from wastewater to the discharge limits imposed by current legislation according to the following equations:

486 Handbook of Natural Zeolites

Kazemian et al.

Z-Na + NH4+ (K+) === Z-NH4 (K+) + Na+ 2R-Cl + HPO4= === R2-HPO4 + 2Cl(Z = zeolite, R = anion exchanger) 

regeneration of both ion exchangers is carried-out with neutral 0.6M NaCl brine (i.e., seawater wherever possible) with cyclic regeneration make-up as low as 2BV (ion exchanger Bed Volume) through a “zero discharge” closed loop technique [50].



cation and anion exchangers’ regeneration eluates are properly mixed, pH is raised to 9.5 (where incidental presence of heavy metals retained by the zeolite is precipitated) and a soluble Mg salt (e.g., MgCl2) is added to yield a virtually non-toxic sterile struvite-rich precipitate (Table 2) according to: Mg2++NH4+(K+)+HPO4====MgNH4(K+)PO4 (s)+H+

Figure 3: Conceptual schematic diagram of the RIM-NUT process.

Environmental Applications of Natural Zeolites

Handbook of Natural Zeolites 487

Table 2: Typical analysis of struvite-rich precipitate recovered from municipal sewage with RIMNUT process [50] Struvite content : >93% w Organic matter: