Enhanced Chitosan Material for Water Treatment: Applications of Multi-Functional Chitosan Derivative (Engineering Materials) 3030717216, 9783030717216

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Engineering Materials

Ephraim Igberase Peter Ogbemudia Osifo Tumisang Seodigeng Ikenna Emeji

Enhanced Chitosan Material for Water Treatment Applications of Multi-Functional Chitosan Derivative

Engineering Materials

This series provides topical information on innovative, structural and functional materials and composites with applications in optical, electrical, mechanical, civil, aeronautical, medical, bio- and nano-engineering. The individual volumes are complete, comprehensive monographs covering the structure, properties, manufacturing process and applications of these materials. This multidisciplinary series is devoted to professionals, students and all those interested in the latest developments in the Materials Science field, that look for a carefully selected collection of high quality review articles on their respective field of expertise. Indexed at Compendex (2021)

More information about this series at http://www.springer.com/series/4288

Ephraim Igberase · Peter Ogbemudia Osifo · Tumisang Seodigeng · Ikenna Emeji

Enhanced Chitosan Material for Water Treatment Applications of Multi-Functional Chitosan Derivative

Ephraim Igberase Department of Chemical Engineering Vaal University of Technology Vanderbijlpark, Gauteng, South Africa

Peter Ogbemudia Osifo Department of Chemical Engineering Vaal University of Technology Vanderbijlpark, Gauteng, South Africa

Tumisang Seodigeng Department of Chemical Engineering Vaal University of Technology Vanderbijlpark, Gauteng, South Africa

Ikenna Emeji Department of Chemical Engineering Vaal University of Technology Vanderbijlpark, Gauteng, South Africa

ISSN 1612-1317 ISSN 1868-1212 (electronic) Engineering Materials ISBN 978-3-030-71721-6 ISBN 978-3-030-71722-3 (eBook) https://doi.org/10.1007/978-3-030-71722-3 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Wastewater containing heavy metal ions/adsorbates such as Cu(II), Pb(II), Zn(II), Cd(II), Ni(II) and Cr(VI) from the processing industries ends up in streams of rivers and thereby infecting our water bodies. Since humans and animals directly get water from the rivers and dams, polluted water will damage lives. And so excessive metal ions intake in the human body can cause health hazards. Such metal ions have at present contaminated our water, soil and food due to unregulated disposal of industrial effluent. Eradicating metal ions from wastewater is highly necessary before it contaminates water supplies. Several methods have been applied in the past decades for the elimination of these metal ions of which adsorption technique has proven to be extremely effective. However, the application of chitosan and its derivative has been a major achievement in the past years. This book reports the use chitosan and its derivative as an efficient adsorptive material in eliminating metal ions from wastewater. On this note, seven chapters were introduced. Chapter 1 was authored by E. Igberase and P. O. Osifo, and it explains the comparison of certain adsorbents that have been applied in the past for wastewater treatment; from the investigation, it was observed that chitosan and its derivative have the greater potential due to its high adsorption capacity for metal ion elimination. E. Igberase, I. Emeji and P. O. Osifo authored Chap. 2. In this chapter, a functionalized chitosan derivative obtained from chemical modification of pure chitosan was formulated for the elimination of scavenging metal ions. The enhanced material was characterized using FTIR, SEM, TGA, BET and XRD to determine the chemical functionality of the beads. Adsorbent parameters were examined to determine their physicochemical properties for the maximum removal of metal ions using batch applications. The data acquired from the studies were modelled using isotherm, thermodynamic and kinetic models. The result obtained was reported in this chapter. Chapter 3 was authored by E. Igberase and P. O. Osifo, and it reports the adsorption of heavy metals including Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) and Cd(II) ions using microwave-improved grafting technique of cross-linking composite chitosan beads which were identified to be a highly efficient and of low operational cost for chitosan modification. FTIR, SEM, X-ray, XRD and TGA were used to obtain the chemical properties of the beads. The influence of adsorption variables on the binding of heavy metal ions onto the developed improved beads was examined. Studies based v

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on equilibrium, isotherm and desorption were performed, and the findings were presented in this chapter. Chapter 4 was authored by E. Igberase, P. O. Osifo and T. Seodigeng, and this chapter investigates the grafting of glutaraldehyde cross-linked chitosan beads with polyaniline, a chemical which is highly enriched with amine functional group. The modified adsorbent was used in the removal of lead and cadmium ions in batch mode. The beads were analyzed with XRD and SEM. Batch studies were performed in relation to the parameters of adsorption. Equilibrium data were collected from the adsorption investigation, and the data were compared with the isotherm, thermodynamic and kinetic models. Five consecutive cycles of adsorption/desorption were also performed, and the results of this study are illustrated in this chapter. Chapter 5 was authored by E. Igberase and P. O. Osifo, and in this chapter, a biopolymer chitosan membrane prepared from fishery waste through a step reversal procedure for the removal of zinc ions from aqueous systems by adsorption was carried out. The developed chitosan membrane was cross-linked with glutaraldehyde, and both were characterized by FTIR, XRD, SEM-EDX and TGA prior to adsorption and desorption studies. Chapter 6 was authored by E. Igberase, I. Emeji and P. O. Osifo, and it focuses on the use of packed bed column for the adsorption of Cu (II) ions using modified chitosan beads, since batch procedures are often primarily limited to remedying small quantities of contaminants. The use of packed column systems for large-scale wastewater remediation typically allows large amounts of contaminated water to be handled in a short period of time, and these devices can be scaled up from the laboratory to a pilot plant project where the entire process can be easily monitored. In this chapter, SEM and BET were employed for the characterization of the beads, and Swan model was utilized for the simulation of the adsorption data. Five cycles of adsorption/desorption investigation were also performed, and the results from the study were explained. Chapter 7 was authored by E. Igberase, P. O. Osifo and T. Seodigeng, and this chapter introduces the use of diethylenetriamine grafted onto glyoxal cross-linked chitosan beads for efficient batch system adsorption of adsorbates such as Cu(II), Pb(II), Cd(II), Zn(II), Ni(II) and Cr(VI). The beads were characterized by FTIR, XRD, SEM-EDX and TGA. Chitosan beads (CS) were produced and interlinked with glyoxal solution. The amine concentration which is the most active group in the adsorbent was determined by titration. Equilibrium capacity of the beads was determined using pH equilibrium model, while the kinetic data were simulated and described using batch Swan model. Vanderbijlpark, South Africa

Ephraim Igberase Peter Ogbemudia Osifo Tumisang Seodigeng Ikenna Emeji

Contents

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption: A Review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Adsorption Technique . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Adsorbents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Activated Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.2 Zeolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.3 Peat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.4 Chitin and Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Crucial Factors Affecting Adsorption of Metal Ions onto Adsorbent . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.1 Effect of pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 Effect of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.3 Effect of Adsorbent Dosage . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.4 Effect of Contact Time and Initial Concentration . . . . . . . 1.5 Regeneration/Desorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11 11 14 15 15 16 16 17

2 Thermodynamics, Kinetics and Desorption Studies of Heavy Metal Ions by Grafted Cross-Linked Chitosan Beads Composites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Adsorption Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Isotherm Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Adsorption Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Result and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Classification Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 SEM Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

25 25 28 28 28 29 29 30 30 30 33

1 1 3 4 4 4 7 9

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2.5

Application of Modified Chitosan for Metal Ions Adsorption . . . . 2.5.1 Effect of Solution pH on Metal Ions Adsorption . . . . . . . . 2.5.2 Effect of Contact Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.3 Effect of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 Thermodynamic Parameters of Adsorption . . . . . . . . . . . . . . . . . . . . 2.7 Adsorption Kinetics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Adsorption Equilibrium Isotherm . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

35 35 35 36 37 39 41 42 44

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) and Cd(II) Ions by Microwave-Improved Grafting Technique of Cross-Linking Composite Chitosan Beads. Studies Concerning Equilibrium, Isotherm and Desorption . . . . . . . . . . . . . . . . 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Materials and Equipment’s . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Preparation for Adsorbate . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Chitosan Enhancement from Its Powdered Form . . . . . . . . 3.2.4 Classification of the Beads/Perles . . . . . . . . . . . . . . . . . . . . 3.2.5 Studies in Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Data Assessment Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Outcome of XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 SEM Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.3 Outcome of FTIR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 Outcome of TGA Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.5 pH Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.6 Outcome of Contact Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.7 Effect of Initial Concentration . . . . . . . . . . . . . . . . . . . . . . . 3.3.8 Influence of Adsorbent Dose . . . . . . . . . . . . . . . . . . . . . . . . 3.3.9 Influence of Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Influence of Agitation Speed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Influence of Ionic Strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Isotherm Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.7 Outcome of Thermodynamic Investigation . . . . . . . . . . . . . . . . . . . . 3.8 Outcome of Kinetic Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.9 Regeneration Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.10 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

47 47 50 50 50 50 51 51 52 55 55 55 56 57 59 60 61 61 62 63 63 64 66 66 68 68 69

4 Investigation into the Adsorption of Cadmium and Lead by Polyaniline Grafted Cross-Linked Chitosan Beads from Aqueous Solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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4.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.2 Preparation of Adsorbate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.3 Adsorbent Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Perle/Beads Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Adsorption Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Determination of pHpzc . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Desorption/Regeneration Investigation . . . . . . . . . . . . . . . . . . . . . . . 4.7 Theory of Evaluation of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.1 Adsorption Isotherms Model . . . . . . . . . . . . . . . . . . . . . . . . 4.7.2 Temperature and Thermodynamic Investigation . . . . . . . . 4.7.3 Kinetic Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.4 Error Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7.5 Regeneration/Desorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 Solubility Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.2 Outcome of pH Investigation . . . . . . . . . . . . . . . . . . . . . . . . 4.8.3 Influence of Adsorbent Dose . . . . . . . . . . . . . . . . . . . . . . . . 4.8.4 Influence of Adsorbate Initial Concentration . . . . . . . . . . . 4.8.5 Influence of Contact Time . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9 Outcome of Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.1 X-Ray Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.2 Outcome of SEM Morphology Investigation . . . . . . . . . . . 4.10 Outcome of Adsorption Investigation . . . . . . . . . . . . . . . . . . . . . . . . . 4.10.1 Parameters of Isotherms Model . . . . . . . . . . . . . . . . . . . . . . 4.10.2 Outcome of Temperature and Thermodynamic Investigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10.3 Outcome of Kinetic Investigation . . . . . . . . . . . . . . . . . . . . 4.10.4 Outcome of Desorption/Regeneration Investigation . . . . . 4.11 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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73 73 73 74 74 75 75 76 76 77 78 78 79 79 79 80 81 82 82 83 83 85 86 86 87 88 88 91 91

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste for the Removal of Zinc Ions from Aqueous Systems by Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93 5.2 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.2.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94 5.2.2 Preparation of Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5.2.3 Determining the Chemical Properties of the Membrane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 5.2.4 Adsorption and Permeation Experiments on XCS . . . . . . . 96 5.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 5.3.1 Characterization Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 5.4 Adsorption Capacity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 5.5 Kinetic Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

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Contents

5.6 The Effect of Flux on Adsorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Breakthrough Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8 The Effect of Cations and Anions on Membrane Adsorption . . . . . 5.9 Desorption and Recovery . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10 Reaction Mechanism of Chitosan . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.11 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Modelling of Packed Bed Column for the Adsorption of Cu(II) Ions Using Chemically Enhanced Chitosan Beads . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Theory of Evaluation of Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.1 Shrinking Core Model (SCM) . . . . . . . . . . . . . . . . . . . . . . . 6.3 Application to Column Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3.1 Absorption Column Simulation . . . . . . . . . . . . . . . . . . . . . . 6.3.2 pH Equilibrium Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.5.1 Classification Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6 Equilibrium Parameters from pH Model . . . . . . . . . . . . . . . . . . . . . . 6.7 Breakthrough Curve at Different Bed Height . . . . . . . . . . . . . . . . . . 6.8 Comparison of Adsorption Capacity with Other Adsorbents . . . . . 6.9 Merit and Demerit of Different Models in Light of Shrinking Core Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.10 Regeneration Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.10.1 Metal Ions Regeneration from Its Spent Adsorbent . . . . . . 6.10.2 Adsorbent Regeneration/Reuse . . . . . . . . . . . . . . . . . . . . . . 6.10.3 pH Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.11 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Use of Diethylenetriamine Grafted onto Glyoxal Cross-Linked Chitosan Beads for Efficient Batch System Adsorption . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Evaluation of Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 pH Equilibrium Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Kinetic Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Adsorbent Preparation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.4 Characterization of the Beads . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Adsorption Equilibrium Investigation . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Experimental Kinetics Investigation . . . . . . . . . . . . . . . . . . . . . . . . . .

106 107 109 110 111 111 112 115 115 117 117 119 120 120 122 122 122 125 125 125 126 129 130 131 131 132 132 132 133 135 135 137 137 138 139 139 139 139 140 142 142

Contents

7.6

Outcome of Characterization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.1 XRD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.2 SEM Outcomes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.3 FTIR Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.4 TGA/DTA Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.5 BET Investigation Outcome . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.6 Stability in Acid Solution of the Biological Materials . . . 7.6.7 Concentration of Amines and pKa and Degree of Grafting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.8 Protonation Degree (α) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.9 Influence of the Speed of Motion . . . . . . . . . . . . . . . . . . . . . 7.6.10 Parameters of Equilibrium from pH Model . . . . . . . . . . . . 7.6.11 Kinetic Outcome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.6.12 Desorption/Regeneration . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xi

143 143 143 144 145 147 148 148 149 149 151 152 154 155 156

Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159

About the Authors

Dr. Ephraim Igberase holds a B.Sc. in chemical and polymer engineering from Lagos State University, Lagos, Nigeria and Magister Technologiae in chemical engineering from Vaal University of Technology, South Africa. He obtained his Ph.D. in chemical engineering from Vaal University of Technology and is employed as a lecturer in the chemical engineering department. He has attended conferences where he gave both oral and poster presentations and has published 11 research articles in well-known peer-reviewed journals and in the areas of wastewater treatment. Ephraim is a member of Water Institute of South Africa (WISA, 2017) and a registered candidate of Engineering Council of South Africa (ECSA 2017). Ephraim is also a reviewer for certain journals such as International Journal of Biological Macromolecule and Journal of Environmental Chemical Engineering and Environmental Technology and Innovation. Ephraim has extended his studies to the development of novel polymeric beads for the removal of organic dyes, rare earth elementals and hazardous metals from aqueous solutions due to their hazardous impact on the environment. The primary aim of his research is the chemical modification of chitosan for the preparation of new materials with novel applications. He had the opportunity to supervising research students. Prof. Peter Ogbemudia Osifo currently holds the position of Acting Executive Dean in the Faculty of Engineering and Technology at Vaal University of Technology (VUT), Vanderbijlpark, South Africa. In 1991, he received a bachelor of engineering (B.Eng.) degree in chemical engineering from the University of Benin, Nigeria. In 1992, he joined the Oil Test Services, a petroleum servicing company, in Port-Harcourt, Nigeria. After several years of working, he started research program in the Department of Biotechnology for M.Tech degree at Durban University of Technology in South Africa, where he graduated in 2001 with Master’s in biotechnology. After which he continued with his doctorate programs at the North-West University, South Africa, and where he graduated in 2007 with Ph.D. in chemical engineering. He joined Vaal University of Technology as a lecturer since 2003, and during January 2008 to August 2015, he became the Head of Department of Chemical Engineering. His teaching areas are primarily on reactor technology, process optimization and control and fluid mechanics. His current research focus areas include xiii

xiv

About the Authors

clean technology of wastewater treatment through biodegradation of domestic and industrial wastewater involving membrane filtration, and heavy metals removal from contaminated water using biosorbents. Others include membrane development from bioresource materials for applications in fuel cells. He has published over 21 papers in accredited journals, 8 book chapters and attended several local and international conferences. He has examined more than ten dissertations from various universities in South Africa and graduated Masters’ and Ph.D. students. Dr. Tumisang Seodigeng is a senior lecturer at Vaal University of Technology, where he leads research in the field of Product Design and Process Systems Engineering in the Department of Chemical Engineering. He has more than 15 years’ experience in design, operation, research and development, as well academic research and teaching in the field of chemical engineering. Tumi holds a doctorate from the University of the Witwatersrand (2006), where he also obtained a B.Sc. in chemical engineering (2000). He has been involved with developing numerical models and computational tools for complex chemical engineering processes since his graduate studies. During his Ph.D. studies, he developed the RCC algorithm, a method that can solve virtually any process systems convex optimization problem with reliable robustness and speed. He later joined the University of the Witwatersrand in 2005 as a research officer and lecturer in chemical engineering process synthesis and optimization as well as computational methods for chemical and metallurgical engineers. Tumi later joined Sasol Technology Research and Development, in 2007 where he continued to model and develop innovative computational tools for complex chemical engineering systems for the petrochemical industry. His key responsibility areas included catalyst activity and selectivity modelling, reaction engineering and reactor modelling. He also worked in the design, commissioning, start-up and operation of a number of petrochemical processes at SASOL. In 2012, returned back to academia as a senior lecturer in the Department of Chemical Engineering at University of Johannesburg. In 2015, he joined Vaal University of Technology. Engr. Ikenna Emeji hold a B.Eng. in chemical engineering department of Enugu State University of Science and Technology, Enugu, Nigeria. After his youth service in Kaduna State Water Board, he joined an oil serving company Port-Harcourt, which specializes in providing drilling muds to drill oil wells. He started his research programme in the Department of Civil and Chemical Engineering, University of South Africa (UNISA) where he obtained a Magister Technologiae (M.Tech.) in chemical engineering. He is currently studying for a Ph.D. programme in chemical engineering department at Vaal University of Technology, South Africa, where he is also working as a graduate assistance attached to the Thermochemical Processes and Waste Utilization Research Group (TPWUG) of chemical engineering department. He has attended conferences to give both oral and poster presentations. He has also published journal papers and written book chapters in the areas of wastewater treatment. Ikenna is an active member of the South African Institute of Chemical Engineers (SAIChE) since 2018 and also a member of Water Institute of South Africa (WISA, 2018)

Symbols and Abbreviations

b BET C Ce Co CS CR-CS G/CR-CS D DD DKR Æ F FGCX FTIR GCCS GXXB K Ka Kad Kidm K1 K2 Kf KTh KL KYN L MCA Pe PEO

Heat of adsorption (L/mmol) Brunauer–Emmett–Teller Effluent concentration (mg/L) Final concentration of a solution (mmol/L) Influent concentration (mmol/L) Chitosan Cross-linked chitosan Grafted cross-linked chitosan beads Diameter of column (m) Degree of deacetylation Dubinin–kaganer–Radushkevich Adsorption energy (kJ/mol) Faraday number 4-amino benzoic acid-graft-glutaraldehyde cross-linked chitosan beads Fourier transform infrared Ethyl diamine tetra acetic acid-graft-glutaraldehyde cross-linked chitosan beads Ethylene acrylic acid-graft-glutaraldehyde cross-linked chitosan beads Equilibrium constant Adsorption rate constant (L/mg/min) DKR isotherm constant Intra-particle diffusion rate constant (mmol/gmin1/2 ) Pseudo-first-order rate constant (min) Pseudo-second-order rate constant (g/mg min) Adsorption capacity from Freundlich (mg/g) Thomas rate constant Degree of binding affinity Yoon–Nelson rate constant (min−1 ) Length of packed bed (m) Modified chitosan adsorbent Peclet number Polyethylene oxide xv

xvi

Qm qmax qe qt n R RL χ2 Go Ho So SEM T TGA t tb te Qv Veff mc KYN βL τ ε No Uo μ μ1 α Ka XB Xm XRD XXB Z

Symbols and Abbreviations

Maximum adsorption capacity from Langmuir (mg/g) Maximum adsorption loading (mmol/g) Amount adsorbed at equilibrium (mmol/g) Amount adsorbed at time t (mmol/g) Adsorption intensity (L/mg) Gas constant defined by 8.3145 J/mol K Dimensionless constant Chi-square test Gibbs free energy change (kJ/mol) Enthalpy change (kJ/mol) Enthropy change (kJ/mol K) Scanning electron microscope Temperature (°C) Thermogravimetry analysis Service time of the bed (min) Time for breakthrough (min) Exhaustion time (min) Volumetric flow rate (mL/min) Effluent volume Amount of adsorbent in the column (g) Yoon–Nelson rate constant (min−1 ) External diffusion coefficient Time needed for adsorbate breakthrough (min) Polanyi potential Adsorption capacity for the BDST model (mg/L) Linear flow velocity (L/min/m2 ) Interstitial velocity (m/s) Viscosity of solute solution (pa s) Degree of protonation Adsorption rate constant (L/mg/min) Chitosan beads DKR isotherm constant X-ray diffraction Cross-linked chitosan beads Bed depth of the column (cm)

Chapter 1

A Comprehensive Approach to Heavy Metal Removal by Adsorption: A Review

Abstract In the years, the existence and accumulation of heavy metal in water has become a general problem. Owing to the fact that these heavy metals tend to pose health hazard to human and aquatic live if their concentration exceeds the maximum contaminant level. This study seeks to review the use of chitin- and chitosan-based material in comparison with some other adsorptive materials such as activated carbon, zeolite and peat that have been used in the past for heavy metal ion removal. Their merits and shortcomings in application are also discussed. The maximum adsorption capacities obtained by these adsorbents from Langmuir isotherm model and the conditions such as temperature, equilibrium time, initial concentration range and pH at which these adsorption capacities were obtained are presented. The characteristics of physical and chemical adsorption and factors affecting adsorption of metal ions were presented and discussed. Consequently, the desorption of these ions from metalloaded adsorbent is also highlighted, as they provide important information of the re-use of the adsorbent.

1.1 Introduction Concerns about environmental deterioration have been continuously growing at a significant rate annually initiatives towards environmental damage of all sorts are implemented swiftly. Such interventions vary from basic restrictions to avoid illegal disposal of hazardous substances to aggressive management systems aimed at reducing the amount of waste produced at site [1]. Greatly influenced by contamination, water is among the most critical commodities on Earth today. Water contamination means one or perhaps more chemicals is developed in water to the point that it poses a risk to humans or animals and makes the water unfit for drinking. Popular contaminants that enter water bodies include solid wastes including disposable bags, bottles, tire dust, dissolved combustion gasses and contaminants from numerous sectors such as mining, clothing, dyestuff, iron plating, steel manufacturers and factories use water as a refrigerant [2]. Therefore, by scattering it safely, rivers and other inland waters can actually clean up a considerable level of contamination.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 E. Igberase et al., Enhanced Chitosan Material for Water Treatment, Engineering Materials, https://doi.org/10.1007/978-3-030-71722-3_1

1

2

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

Hence, water contamination is mostly about volume: how much of an environmentally harmful material is released and how high an amount of water is introduced into it by the contaminant. A minimal volume of a harmful contaminants can have a marginal effect if a ship dumps it into the water. But when pumped into a lake or river, where there is less fresh water to spread it, the same volume of the same contaminant may have a much bigger effect. Water can be turned cancerous in different forms, including effluent from the chemical, electroplating, clothing, dyestuff, galvanizing, pigment, dye, mining, pharmaceutical and other processing industries [3–8]. These industries generate substantial amounts of metal ions including Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) and Cd(II) that make their way into aquatic environment and ultimately trigger probable health risks on humans and other living organisms. Heavy metal ions are non-biodegradable and carcinogenic pollutants that are harmful to human beings, wildlife, marine life and the broader ecosystem. In the past, numerous disorders including lung and kidney disease, respiratory inflammation, circulatory collapse, intravascular hemolysis, renal failure, nephritis, fever, vertigo, constipation, epigastric vomiting, nausea, extreme digestive issues, severe multisystem organ damage, comma and even loss of life were documented due to increased intake [9–15]. In this regard, the United States Environmental Protection Agency (USEPA) has laid down stringent rules for the permissible limit for heavy metals in water and wastewater before they are discharged into waterways (Table 1.1). Because of this concrete regulation on hazardous effluents in water systems, it is therefore essential to establish numerous approaches that will help mitigate metal ions from wastewater. A variety of methods for binding metal ions have been established in recent years, but these approaches, including chemical precipitation, membrane filtration, reverse osmosis and electroplating, have shown to be ineffective due to high working cost and low removal of metal ions [16–22]. It is highly necessary to prevent such contaminants from reaching the existing water source for the quality of life of the population; in particular, because significant numbers of people living in rural communities rely on river and stream water usage [23–27]. Table 1.1 Tolerable limit of harmful heavy metal ions

Adsorbate

Tolerable limit by WHO (mg/L)

Tolerable limit by USEPA (mg/L)

Pb(II)

0.01

0.05

Cd(II)

0.003

0.005

Zn(II)

5.0

Hg(II)

0.001

0.002

Cr(VI)

0.05

0.1

As(II)

0.01

0.05

CU(II)

1.3

Ni(II)

1.2 Adsorption Technique

3

1.2 Adsorption Technique Adsorption has been reported to be an inexpensive and efficient method for the elimination of many water contaminants [5]. Adsorption is a mechanism whereby the molecules of a material are attracted and maintained on a solid surface. Adsorption is called mass transfer process, in that, a part from the liquid phase is moved to the solid phase. Adsorption can take place on the material’s external layer and then in the macrospores, mesopores, micropores and submicropores relative to the surface area of the micropores and submicropores; therefore, the surface area of the macro and mesopores is small, and the quantity of substance adsorbed there is generally deemed insignificant. Adsorption can be grouped into two classifications, such as physical adsorption (physisorption) and chemical adsorption (chemisorption), based on the nature of force occurring between adsorbent molecule (metal ion) and adsorbent. Physical adsorption (physisorption) derives from the action of weak forces between molecules, also regarded as adsorption by van der Waals. The energy of contact between the adsorbent and the adsorbent has the same magnitude but is generally higher than the adsorbing condensing energy. Therefore, no activation energy is required. In this instance, adsorption is influenced by the low temperature. Physisorption, consequently, declines with rising temperatures. In physical adsorption, an equilibrium between the adsorbent and the fluid phase is formed, leading to multilayer adsorption. Physical adsorption is unspecific because of low binding forces acting between molecules. The adsorbed molecule on the solid surface is not assigned to a position but is able to move across the layer. By essence physical adsorption is practically reversible. In this circumstance, the adsorbed species are chemically similar with those in the fluid phase, so that adsorption and eventual desorption do not influence the chemical properties of the fluid; therefore, it is not unique in nature [5]. Chemical adsorption (chemisorption) is also dependent at electrostatic force in chemisorption; the interaction forces exiting between adsorbent and adsorbent molecules are probably to be the same as chemical bonds. Thus, the chemisorption energy is regarded as chemical processes. It may be exothermic or endothermic mechanisms, from very small to very large energy magnitudes. The essential stage of chemical adsorption also requires significant energy for activation, which implies that the actual equilibrium can be gradually reached. Similarly, a spontaneous system demands a negative free energy (IFE) value, because when adsorbed, the adsorbate’s translational mobility is reduced [4]. In particular, metal ions’ adsorption to an adsorbent is considered to occur via the following steps. (a) (b) (c)

Movement of metal ions from bulk solution to the adsorbent surface commonly referred to as diffusion. Movement of metal ions through the pores. Engagement of metal ions on the internal surface of pores with accessible sites.

4

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

1.3 Adsorbents Therefore, the utility of an adsorbent in waste disposal relies on the structure, surface form of functional groups, degree of polarity, surface area, and hydrophilicity. Adsorbent is a strong material employed in adsorption studies as the adsorbing phase. Several studies have concentrated on adsorbents which are capable of eradicating adsorbates at reduced cost. Bailey et al. [28] stated that if an adsorbent needs little preparation procedure and is available in large quantities, it could be classified a low-cost material. Hence, cost is therefore a crucial consideration in the choice of an adsorbing material. A number of adsorbents, including activated carbon, zeolite, peat, chitin and chitosan, have been used over the years to remove heavy metal ions from water and wastewater [29]. In this review, these mentioned adsorbents are examined.

1.3.1 Activated Carbon Activated carbon is among the first adsorbents that have been used in various processes such as waste management. Watonabe and Ogawa [30] have proposed the use of activated carbon for the adsorption of heavy metals. A wide surface area (500–2000 m2 /g) is still the main significant physical characteristic that enables gas or vapour to be physically adsorbed. Nevertheless, the significant proportion of pore spaces offers a greater inner layer to the adsorbent which may be the source of its significant adsorption capacity. In addition, activated carbon is an important adsorbent of a variety of contaminant species, such as organic, inorganic, and microbial [31]. Once activated carbon has been depleted owing to metal ion adsorption, and it may be recovered for another use, but the procedure of recovery leads to carbon damage and the recovered material will have a significantly reduced adsorption potential relative to virgin activated carbon and this limits its regenerability property [11, 18, 28, 32]. While activated carbon is a good adsorbent because of its high potential with organic compounds, its massive cost restricts its usage as an adsorbent in developing countries, particularly on a broad scale. Several research studies have successful employed activated carbon in removing heavy metals with different adsorption capacity. Table 1.2 offers the overall recorded adsorption potential of the activated carbon derived from various materials and their operational parameters.

1.3.2 Zeolite Zeolite is an adsorbent and can therefore be utilized to eliminate water and wastewater contaminants. It is a porous aluminosilicate with various structures of the cavities.

0.67

0.67

3

3

3

3

0.83

0.83

8–10

0.83

1

0.5

0.5

1

30 ± 1

30

30

30

30

30 ± 2

30 ± 1

30 ± 1

30

40

60

25

30

25

25–40

40

25–400

25–125

50–200

NM

40–200

40–200

20–50

10–300

10–300

10–300

10–40

40–240

Thespesia populnea bark

Euphorbia rigida

Red mud

Ceiba pentandra hulls

Ceiba pentandra hulls

Sago waste

Waste coconut buttons

Waste coconut buttons

Waste coconut buttons

Coir pith

5

6–6.5

Van apple pulp

Cashew nut shells

4.0 ± 0.3 Cow bone

6.5

5

4

6

6

5

6

7

6

5

6

Ceiba pentandra hulls

Terminalia catappa Linn Shell

7

0.67

60

10–50

Material

Temp. (°C) Equilibrium time (h) Initial concentration pH range (mg/l)

Table 1.2 Adsorption power of activated carbon arising from various materials

Zinc

Lead

Lead

Copper

Lead

Lead

Zinc

Lead

Mercury

Copper

Mercury

Lead

Nickel

Cadmium

Copper

0.1

0.6

0.1

0.025

0.04

0.1

0.3

0.3

0.05

0.1

0.1

0.1

0.02

0.5

0.05

11.72

28.90

47.691

164.176

279.72

64.79

24.1

25.5

55.60

73.6

78.84

92.72

62.5

19.5

38.34

(continued)

[42]

[41]

[40]

[12]

[39]

[38]

[37]

[37]

[36]

[35]

[35]

[35]

[34]

[17]

[33]

Heavy metal Mass of adsorbent (g) Qe (mg/g) References

1.3 Adsorbents 5

1

1

48

3

1

1

0.5

NM

NM

12

12

25

30 ± 1

25

30

18

18

60

20 ± 1

23 ± 1

25

25

Note: NM means not mentioned

2

10–40

1–1000

1–1000

50

10–70

25–250

5–200

5–200

10–400

NM

20–200

50–200

10–100

4.5

4.5

10

5

5

6.7

6.7

6

6

8

6.7

5

Cobalt

Lead

Cadmium

Lead

Bagasse carbon

Bagasse carbon

Coal

Waste parthenium

Dehydrated wheat bran

Hazelnut husks

Hazelnut husks

Zinc

Cadmium

Lead

Nickel

Copper

Lead

Copper

Tannin-immobilized Copper hydrotalcite

Apricot stone

Phaseolus aureus hulls

Pinecone

0.15

0.15

0.5

0.25

0.1

0.3

0.3

0.1

0.1

0.5

0.1

0.5

0.1

31.11

38.03

54.945

54.35

51.50

13.05

6.645

81.47

22.85

15.7

27.53

31.25

192.31

[53]

[53]

[52]

[51]

[50]

[49]

[49]

[48]

[47]

[46]

[45]

[44]

[43]

Heavy metal Mass of adsorbent (g) Qe (mg/g) References

Tunisian date stones Copper

Bagasse pith-based sulphurised

4.5–8.5

4

60

25–1000

Material

Temp. (°C) Equilibrium time (h) Initial concentration pH range (mg/l)

Table 1.2 (continued)

6 1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

1.3 Adsorbents

7

Their structures are composed of three-dimensional SiO4 and AlO4 tetrahedra frameworks, with an oppositely charged lattice and this charge is cations distributed in solutions. Natural zeolites are classified according to the ratio of Al to Si in their structures, and the species and number of cations present within their structures. This adsorbent comprises of a quantity of species; however, the very common of them is clinoptilolite with chemical formula of Na0.1 K8.57 Ba0.04 (Al9.31 Si26.83 O72 ) · 19.56 H2 O [54–56]. Clinoptilolite can be used in its natural also in its chemically modified/pretreated forms to remove adsorbates, pretreatment aims to replace the exchangeable cations present in clinoptilolite with cations that are eager to go through ion exchange phenomenon, thus facilitating metal ion removal [57]. Gunay et al. [58] examined the adsorption of lead from aqueous solution using natural and pretreated clinoptilolite. The optimum adsorption potential was observed to be 80.93 and 122.40 mg/L, respectively. Dirmirkou and Doula [59] conducted an investigation on the adsorption of zinc from drinking water by natural and modified clinoptilolite. The maximum adsorption capacity obtained was found to be 71.3 and 94.8 mg/L, respectively. Zeolite has been examined widely by authors owing to their capability in eradicating small amount of heavy metal ions from aqueous solution by utilizing ion exchange process [60]. Nascimento et al. [61] reported that the adsorption process of zeolite depends largely on many effects including nature and concentration of the adsorbate, the characteristic of the adsorbent and the adsorption variables which comprises of pH, temperature and ratio of solid/liquid. Montolito et al. [62] reported that zeolite contains about 10–25 wt% water in the channels within its structure. This water can be driven out by heating in a vacuum under high temperatures. However, the amount of water removed is therefore a measure of its adsorptive capacity. The adsorption capacity of zeolite for heavy metal ions is shown in Table 1.3. One of the major limitations of using zeolite as an adsorbent is their low permeability; also, the adsorption mechanism of zeolite is complex because of their porous structure and inner and outer charged surfaces [63].

1.3.3 Peat Peat is an adsorbent which is used to treat polluted water. The use of peat as an adsorbent to extract a large variety of pollutants extends back to 1970. In Ireland and Northern Europe, peat is mined and used for fuel and as a soil conditioner in the USA [10]. Brown et al. [76] reported that what makes comparison of peat results difficult are: different locations of origin, degrees decomposition and different experimental conditions. The adsorption mechanism of peat onto heavy metal ions is believed to be that of hydrogen ion exchanger. At pH less than 3, numerous adsorbates can be leached from peat. However, favourable adsorption of metals by peat occurs at pH range of 3–8.5. Moreover, when the pH of the solution is above 8.5, peat adsorbent becomes unstable [77]. Ringqvist and Oborn [78] also reported that when polluted waters are treated with peat, a higher metal removal can be expected at high pH than at low pH. Peat is a permeable adsorbent with a dense

8

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

Table 1.3 Optimum adsorption potential of natural zeolite for metal ions removal Temp. (°C)

Equilibrium Initial pH time (h) concentration range (mg/l)

NM

24

350–7200

4.24 Lead

0.01

66

[64]

21

0.25

0.2–8.0 g/l

8.5

Mercury

NM

121

[65]

23 ± 1 72

10–500

6

Copper

0.1

504.6

[66]

NM

4

10–50

7.5

Copper

NM

6.74

[67]

20

1.33

1–100

10

Copper

0.8

0.21

[68]

30

0.4

10–80

NM

Chromium 0.025

270.27

[69]

30

0.4

10–80

NM

Lead

0.025

204.08

[69]

20

0.75

0.1–100

7

Nickel

1.5

3.28

[70]

20

0.42

1–200

5

Lead

0.1

16.81

[71]

25

5.5

100–400

6–7

Copper

10

141.12

[72]

25

5.5

100–400

6–7

Zinc

10

133.85

[72]

25

5.5

100–400

6–7

Cobalt

10

244.13

[72]

25

2–3

20–100

7

Zinc

25

0.015

[73]

90

1

22 ± 2 0.67

Heavy metal

Mass of Qe (mg/g) References adsorbent (g)

50–500

8

Zinc

0.4

21.2

[74]

20–400

3.5

Copper

15

3.37

[75]

Note: NM means not mentioned

soil substance existing in all phases of organic disintegration and can be classified into four categories: herbaceous peat, woody peat, moose peat and sedimentary peat [79]. This naturally occurring adsorptive material is cheap, readily available and delivers a good adsorption performance [80]. Peat is made up of humic acid, lignin, cellulose and fulvic; these compounds include functional groups that are polar, such as ketones, alcohols, carboxylic acids that may be involved in chemical adsorption; nevertheless, the basic adsorption potential for dispersed solutes including transition metals and polar organic molecules is on the high side, due to the polar nature of peat [79] given the possibility that peat is employed as an adsorbent, there are indeed many deficiencies that restrict its use in processes of adsorption, including high water tolerance, low mechanical strength and tendency to shrink or swell [81]. A significant amount of studies on the adsorption of metal ions were conducted in the past decades utilizing pretreated peat. Yahya and Rosebi [82] stated that when processed with an acceptable percentage of hydrochloric acid, peat can be a suitable copper extraction medium. The authors also stated that peat adsorption on metal ions depends on the characteristics of peat and dried peat is most possible to have additional accessible adsorption surface sites when compared to fresh peat. Table 1.4 gives reported maximum adsorption capacity for peat onto heavy metal ions.

1.3 Adsorbents

9

Table 1.4 Reported maximum adsorption capacity for peat Temp. (o C)

Qt time (h)

Initial conc. range (mg/L)

pH

Material

Heavy metal

Mass of adsorbent (g)

Qe (mg/g)

References

20 ± 0.5

3

40–400

5.5

Romanian peat

Lead

0.125

41.98

[83]

20 ± 0.5

3

40–400

5.5

Romanian peat

Mercury

0.125

77.93

[83]

20 ± 0.5

3

40–400

5.5

Romanian peat

Cadmium

0.125

12.87

[83]

25

4

5–100

4.5

Irish peat moss

Copper

0.4

17.6

[84]

25

4

5–100

4.5

Irish peat moss

Nickel

0.4

14.4

[84]

20 ± 1

24

20–100

2

Sphagnum moss peat

Chromium (VI)

0.4

NM

[85]

25 ± 0.2

50

4–60

4

In natura peat

Chromium (III)

0.1

5.6

[86]

30

NM

NM

6

Peat

Nickel

0.2

11.42

[87]

55

4

40–525

6

Moss peat

Lead

0.125

142.85

[88]

55

4

40–525

6

Moss peat

Mercury

0.125

123.45

[88]

NM

1

NM

4

Sphagnum moss peat

Copper

0.25

16.1

[89]

21

2.5

20–40

5.5

Herbaceous peat

copper

0.5

4.84

[90]

25

15

20–300

5

Sphagnum moss peat

Copper

0.4

16.4

[91]

25

4

10–200

7

Sphagnum moss peat

Nickel

1.0

9.18

[91]

Note: NM means not mentioned

1.3.4 Chitin and Chitosan Chitin is the next more available organic substance following cellulose among numerous adsorbents. It exists in aquatic species, particularly in crustaceans, molluscs and in insects, in which it is a component of the exoskeleton, and in some fungi, in which it is the major fibrillary polymer in the cell wall. β-(1-4) glycosidic bonds bind together the constituent monosaccharide units in chitin (2-acetamido-2deoxy-b-d-glucose). Chitin’s structure comprises of a matrix of structured natural fibres and has stiffness and tolerance to the organisms that possess it [92]. Chitin is strongly hydrophobic and is soluble in organic solvents. It is soluble in hexafluoroisopropanol, hexafluoroacetone, chloroalcohol in combination with mineral acid solutions and 5% lithium chloride dimethylacetamide [93]. Chitin is directly connected with proteins, an inorganic substance that is primarily carbonate calcium (CaCO3 ) pigments, and hydroxide lipids [94]. Chitin was documented to be applied in extraction of copper ions from seawater [95]. Removing the acetyl functional group existing in chitin develops chitosan through a method termed alkaline chitin deacetylation. This acetyl group existing in chitin may impede the mobility of metal ions to the

10

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

adsorption site. Chitosan comprises of 2-amino-2-deoxy-d-glucopyranose that is also connected by glycosidic β-(1-4) bonds. This polymer is correlated mostly with its degree of deacetylation (DD), an estimate of the accessible amine group existing in the chitosan backbone [96]. Chitosan can be used in several application areas, including water treatment, pharmaceutical and health technologies, sustainability of the environment, fabrics, bioengineering, cosmetics, food manufacturing and agricultural development [97]. Sewvandi and Adikary [98] stated that chitosan’s considerable pore size distribution contributes to its unique binding characteristics for metal ions including cadmium, copper, lead, mercury, zinc and chromium. Additionally, chitosan will reduce the concentration of metal ions close to zero [99]. The adsorption mechanism of chitosan onto metal ions is believed to be due to the presence of amine. This group activates a metallic ion coordination bond [98, 100]. The link is established between the nitrogen-free electron pairs in the amine group and the metal’s void orbitals. Whichever is the process and manner (chelation vs. electrostatic attraction), chitosan adsorption of a metal relies on the percentage of deacetylated units (free amine groups), the size of the polymer matrix, crystalline nature, molecular mass, polymer conditioning, chitosan structural attributes, solution pH, nature and amount of the acid utilized for solution, solution concentration, metal ion selectivity and speciation. In addition, very few of the primary amino groups are available for metal binding, as some of these amine sites are engaged in hydrogen bonds [101]. For instance, copper chelation to chitosan with release of hydrogen ions is shown in Fig. 1.1; consequently, flakes are generally produced in the production of chitosan, but this formulation is not reliable in adsorption process owing to its deficient adsorption properties which may lead to reduced adsorption potential. Flakes are modified into chitosan gel beads to counter the said challenge of bad adsorption functionality [102]. Chitosan uniqueness therefore facilitates unlimited modification of the polymer in an effort to alter or improve the adsorption characteristics of chitosan. Chitosan alteration is of two types: physical and chemical. Guibal et al. [103] stated that the alteration of chitosan is a simple means of controlling the polymer selectivity or the adsorption kinetics based on the subject of treatment.

OH H3C OH

O

O

N

CH3

+

CH3

O H3C

Cu

2+

O

+

Cu O

N

NH2 n

Fig. 1.1 Development of chitosan chelates with Cu(II) ions bonding with amine groups [117]

2H+

1.3 Adsorbents

11

Chitosan physically transformed types include powders, nanoparticles, gel beads, sponge, honeycomb and hollow fibres [104–109]. In dilute acid solutions, chitosan can only be soluble in these forms, and this restricts its use. Thus, chemical enhancement approaches including cross-linking and graft copolymerization were designed to transform its solubility attributes in water or acidic solutions and to generate added functional groups, thus further enhancing the metal adsorption performance [110–112]. In a study by Inoue et al. [113], however, the potential for adsorption of metal ions decreases when chitosan polymers are immersed in acid solution owing to cross-linking between the polymer matrix. The researchers further stated that metal ion capacities and binding effectiveness could be strengthened by unique functional group grafting. Graft copolymerization is expected to be highly satisfactory for the application of advanced material and may extend the area of prospective polymer application [114]. Zohuriaan [115] also stated that graft copolymerization is projected to be among the many successful options to a vast wide range of molecular designs, leading to new forms of polymers made from natural polysaccharide and synthetic materials. Over the past decades, extensive research has been performed on chitin, chitosan and chitosan-based adsorbents. Chen et al. [116] stated that chitosan is much more effective in the adsorption cycle than chitin because of the free amino groups on the chitosan network. Table 1.5 presents the published adsorption equilibrium potential of chitosan and modified chitosan as mentioned in literature. Therefore, a large number of different approaches are produced for simple chemical modification. The key benefit of chitin and chitosan is the lack of complexity in transforming them into various designs, including gel beads, nanoparticles, nanofibres, microparticles and scaffolds [118– 121].

1.4 Crucial Factors Affecting Adsorption of Metal Ions onto Adsorbent 1.4.1 Effect of pH The pH of a solution is a significant criterion influencing the process of metal removal efficiency, as it influences the solubility of metal ions, the concentration of ionic species on the adsorbent’s functional groups and the level of ionization of metal ions during reaction. Adsorbent contains reactive groups that can attract metal ions and is therefore considered a complex ion exchanger comparable to a commercial resin. Such bond formation can be supported by proton displacement and is largely related to the extent of protonation predicted by the pH [134]. Kragovic et al. [64] stated that pH performs a vital function in cation adsorption since it influences the chemical evolution of species of the metal in solution and also the ionization of chemically stable sites on the adsorbent surface. Throughout the years, nonetheless, numerous

Qt (h)

3.3–5.0

3.3–5.0

0.5

24

1.33

5.42

5

3.33

4

24

4

3.50

50

24

24

0.4

Temp (°C)

NM

NM

25

20

NM

30

30

30

25

50

NM

NM

30

25 ± 0.5

25 ± 0.5

25

NM

100–1000

100–1000

100–500

100–500

100–500

10–100

0–15

50–200

50–1000

50–1000

100–1000

50–400

50–200

50–1000

50–1000

Initial conc. range (mg/L)

6

4

4

6.3

4

5

5

5

2

5.5

5

6

5

5.3

5.5

4.5

pH

Chitosan

Chitosan-coated ceramic alumina

Chitosan-coated ceramic alumina

Chitosan hydrogel beads

Chitosan-coated PVC beads

Chitosan-coated PVC beads

Cross-linked chitosan

Cross-linked chitosan

Chitosan-coated with poly-methyl thiophene

Cross-linked chitosan-g-polyacrylonitrile

Cross-linked chitosan-g-polyacrylonitrile

Chitosan beads

Chitosan membrane

Chitosan beads

Chitosan graft polyacrylonitrile

Chitosan graft polyacrylonitrile

Adsorbent

Mercury

Arsenic (V)

Arsenic (III)

Cadmium

Copper

Nickel

Copper

Zinc

Chromium

Nickel

Copper

Lead

Copper

Lead

Nickel

Lead

Heavy metal

0.03

1

1

2.28

0.5

0.5

0.1

0.01

0.45

5

6

0.5

0.5

0.02

5

5

Mass of adsorbent (g)

Table 1.5 Optimum adsorption potential of chitosan and chitosan-enhanced material, as stated in literature

1127.1

96.46

56.5

61.31

87.9

120.5

43.47

15.08

127.62

358.54

230.79

72.89

25.64

79.2

239.3

157.6

Qe (mg/g)

References

(continued)

[129]

[128]

[128]

[97]

[127]

[127]

[126]

[116]

[24]

[125]

[125]

[14]

[124]

[123]

[122]

[122]

12 1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

1

5

0.1

20

23

25

30

25

1–1690

2–14

5–25

10–200

Initial conc. range (mg/L)

Note: NM means not mentioned

Qt (h)

Temp (°C)

Table 1.5 (continued)

6.5

7

4

4

pH

Magnetic chitosan beads

Chitosan

Chitosan-coated oil palm shell charcoal

Chitosan-g-polyacrylamide beads

Adsorbent

Cadmium

Zinc

Chromium

Mercury

Heavy metal

NM

0.01

0.15

0.25

Mass of adsorbent (g)

518

1.21

154

322.6

Qe (mg/g)

References

[133]

[132]

[131]

[130]

1.4 Crucial Factors Affecting Adsorption of Metal Ions onto Adsorbent 13

14

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

studies have been under way to establish the impact of pH on environmentally friendly adsorbent adsorption of metal ion. Tumin et al. [14] performed a research on the impact of pH on Cu(II) reduction by activated carbon at a pH range of 2–8. From the investigation, it was confirmed that Cu(II) absorption enhanced significantly from pH 2–6, additional rise in pH led to a reduction in adsorption capacity. This finding was ascribed to the conclusion that the layer of the adsorbent is enclosed by hydrogen ions at lower pH values, thus restricting Cu(II) ions from reaching the adsorbent’s active sites, and as the ph rises moderately to pH 6, more negatively charged surface will become accessible, enabling better elimination of Cu(II) ion. Enhancing the pH value beyond pH 6 led to reduced adsorption power, and it was recorded that this finding was attributed to the presence of Cu(II) ion precipitation. Popuri et al. [126] explored the role of pH on Ni(II) and Cu(II) ion adsorption by chitosan-coated polyvinyl chloride beads, at pH levels of 1–6. The findings suggested that maximal Cu(II) adsorption occurred at pH 4, whereas higher Ni(II) adsorption occurred at pH 5. The authors ascribed this finding to high concentrations of hydrogen ions at reduced pH value, which contend for active site together with Cu(II) and Ni(II) ions. Gyananath and Balhal [131] analysed the role of pH on Pb(II) reduction from aqueous solutions by adsorption on chitosan beads at a pH range of 2–6. The adsorption improved with the solution rising in pH. This finding was attributed to the assumption that the amine groups in the beads are protonated at low pH, resulting in electrostatic repulsion of Pb(II) ion. Consequently, a competition between protons and lead(II) ions for adsorption site exists and hence, the adsorption potential reduced.

1.4.2 Effect of Temperature Temperature has been seen to influence adsorption ability among the design variables which are commonly examined in the literature. The process is called endothermic when the adsorption capacity rises with temperature, and the process is called exothermic when adsorption capacity declines with temperature. The thermodynamic variables focus on providing the basic parameters for consequent engineering assessment of the actual adsorption of the adsorbents and ideally often offer additional perspectives into the process of adsorption required for further process modification and optimization techniques [5, 135]. Han et al. [136] suggested that the growing adsorption potential of the adsorbent with temperature is due to pore enhancement and/or adsorbent surface activation. Kannamba et al. [125] examined the impact temperature has on the adsorption potential of modified chitosan for Cu(II) ion. The researchers concluded a rise in adsorption potential as temperature rises from 20 to 50 °C. This increase was related to the endothermic nature of the binding mechanism. Payne and Abdel-Fattah [52] explored the influence of temperature by activated carbon and zeolite on the adsorption of leads. Activated carbon adsorption efficiency was unchanged by temperature

1.4 Crucial Factors Affecting Adsorption of Metal Ions onto Adsorbent

15

rise, whereas the removal efficiency of lead by zeolite was increased significantly as temperature rises from 296 to 318 K. The influence of temperature on the adsorption capacity of copper ion on activated carbon acquired from palm kernel fibre at a temperature range of 299–399 K was explored by Ho and Ofomaja [137]. Findings from the research demonstrated significant increase in copper ion adsorption capability as the temperature of the reaction is elevated from 299 to 399 K. Workers related the finding to enhanced copper ion mobility as the temperature rises. They also mentioned that the interaction of copper ions and surface functional groups is improved by higher heating rate and that the correlation (rise in adsorption ability with higher temperature) indicates a chemical or activated adsorption process between Cu(II) ions and functional groups on palm kernel fibre.

1.4.3 Effect of Adsorbent Dosage It is crucial to get an appropriate amount of the adsorbent to optimize the interaction between metal ions and adsorption sites of the adsorbent. On this note, several researchers have studied the impacts of the adsorbent dosage on metal ion adsorption. Zhou et al. [138] recorded that adsorption of Cr(VI) in chitosan/attapulgite composite material improved from 77.7 to 95.0% with rising dose from 0.01 to 0.10 g, whereas optimum adsorption efficiency (mg/g) reduced. A rise in the adsorbent dose can enhance the number of adsorption sites accessible, leading to increased efficiency of removal. Consequently, when the adsorbents adsorbed almost all of the heavy metals in the aqueous solutions, the amount of unused effective adsorption sites increased, resulting in a reduction in adsorption potential of the adsorbents. Adsorption of Cu(II), Cd(II) and Pb(II) on magnetic ethyl diamine tetra acetic acidmodified chitosan SiO2 /Fe3O4 adsorbent was examined with rising dose from 0.5 to 0.5 g/L [139]. The researchers found that the efficiency of removal improved dramatically with dose increases from 0.5 to 1.0 g/L and then attained a steady state, but the adsorption potential has no substantial improvements in the range from 0.5 to 1.0 g/L and then reduces noticeably. In a study conducted on the adsorption of Cd(II) and Pb(II) by polyaniline grafted cross-linking chitosan beads, when the dose was varied from 1.5 to 6.5 g/L [140]. They reported that the removal capacity improved markedly from 1.5 to 4.5 g/L and then approached a steady state, which could be due to rising accessible sites.

1.4.4 Effect of Contact Time and Initial Concentration The time required for metal ions to achieve equilibrium in the experimental study is of high significance, since it relies on the process utilized. Therefore, it is crucial to analyze the stability analysis on this device within different design parameters [141].

16

1 A Comprehensive Approach to Heavy Metal Removal by Adsorption …

Arivoli et al. [13] investigated the influence of contact hours on the elimination of Cu(II) ions by activated carbon at different initial concentrations. They stated that percentage removal of Cu(II) ions reduced as the initial concentration of Cu(II) ions raised, but the total amount of Cu(II) ions adsorbed per unit mass of carbon improved as the concentration of metal ions rises, which implies adsorption is largely based on the actual concentration of ions. This finding was attributed to the fact that the ratio of the original concentration of Cu(II) ions to the accessible surface area is small at lesser concentration, and eventually, the fractional adsorption is regardless of the actual concentration. Nevertheless, the accessible site of adsorption is less at greater concentration and thus the percentage of copper ion removal is independent following initial concentration. They further stated that at all concentrations, equilibrium was formed 60 min at the contact hours.

1.5 Regeneration/Desorption For correct dumping and for the re-usability of the adsorbent, metal regeneration from packed adsorbent is important. Adsorbent re-use tends to maintain the operation expenses low, and for that intent, it is crucial to regenerate the adsorbent for another period of use. Nonetheless, the adsorption process requires the absorption of metal ions which provide a direction for the design of the desorption strategy [142]. Since pH is such a critical aspect in metal binding, a pH change can enable the metal to desorb, in order to ensure the adsorbent’s unequalled adsorption efficiency, it is essential to use the correct eluant for the desorption process. Shabudeen et al. [139] documented desorption by using (0.25–2) M sodium hydroxide solution of mercury (II) charged activated carbon. With 2 M of NaOH solution, the researchers recorded a maximum recovery of 99%. They further observed increased desorption of Hg(II) as compared to the chloride complexes owing to the establishment of fairly quite stabilized iodide complexes of Hg(II) (Table 1.6).

1.6 Conclusion In this review, a thorough analysis of related literature reveals that of the five adsorbents reviewed in this study, such as activated carbon, zeolite, peat, chitin and chitosan. Chitosan and its derivative have the ability to effectively eliminate heavy metal ions from water and wastewater and to recycle for subsequent use, among many ways to reduce costs. There are several other reports in the literature about the removal of heavy metal ions by other adsorbents; however, it is significant to mention that the overall adsorption ability of different adsorbents varies with the metal ion size, pH, ionic strength, temperature, concentration, contact time, and adsorbent constituents. Nevertheless, in spite of the number of articles which have been reported for heavy metal removal by these adsorbents in recent years, only a

1.6 Conclusion

17

Table 1.6 Percentage desorption of metal ion from their loaded adsorbent and conditions at which they were obtained L Contact Stirring pH of Eluent Metal ion-loaded time speed solution (desorbing adsorbent (h) (rpm) agent)

Percentage References desorption of metal ion

1 24

150

5

EDTA

Copper-loaded chitosan membrane

68.74

[130]

1 24

150

5

EDTA

Nickel-loaded chitosan membrane

45.97

[130]

1 3

120

NM

0.1 M HCl Lead-loaded activated carbon

60

[45]

1 0.58

NM

NM

0.1 M H2 SO4

98

[5]

1 2

200

4

Perchloric Mercury-loaded 96.7 acid chitosan-g-polyacrilamide (70%)

[139]

1 2

200

4

Perchloric Lead-loaded 96.7 acid chitosan-g-polyacrilamide (70%)

[139]

1 0.75

NM

7

0.1 M HCl Nickel-loaded natural zeolite

96

[77]

1 0.75

NM

7

0.1 M NaOH

Nickel-loaded natural zeolite

50

[77]

1 0.75

NM

7

Distilled water

Nickel-loaded natural zeolite

68

[77]

1 NM

NM

NM

0.01 M NaoH

Chromium-loaded-coated 93 chitosan

[25]

1 15

NM

4.7

0.002 M EDTA

Copper-loaded peat

58

[91]

1 15

NM

4.7

0.002 M EDTA

Nickel-loaded peat

28

[91]

Copper-loaded chemically modified chitosan

Note: NM means not mentioned

some has recorded its industrial scale use. Thus, it is useful to design a means of applying these adsorbents a broad scale. In addition, there were no studies on the handling of regenerated metal ions. This area must be given considerable attention in other to avoid repolluting the environment.

References 1. W.H. Cheung, J.C.Y. Ng, G. Mckay, Equilibrium studies of the sorption of Cu(II) ions onto chitosan, J. Colloid Interface Sci. 225, 64–74 (2002)

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Chapter 2

Thermodynamics, Kinetics and Desorption Studies of Heavy Metal Ions by Grafted Cross-Linked Chitosan Beads Composites

Abstract Functionalized grafted cross-linked chitosan bead (G/CR-CS), prepared from pure chitosan for the removal of scavenging metal ions from aqueous solutions, has been studied. The modified material was then characterized using FTIR, SEM, TGA, BET and XRD to assert successful modification. Parameters such as effect of contact time, pH and temperature were investigated to determine their physicochemical properties for the maximum removal of metal ions using batch applications. The results indicated that adsorption performance of the modified chitosan beads can be modelled efficiently using Langmuir isotherm and pseudo-second-order kinetic. Also, calculated thermodynamic parameters (G0 , H 0 and S 0 ) indicated that the adsorption of metal ions onto the grafted cross-linked chitosan is spontaneous and endothermic in nature.

2.1 Introduction Water polluted with heavy metal ions has been reported to be threats to living organism [2]. Impacts from increasing industrial activities, rapid urbanization and natural or geological processes are the resultant source of the pollution. As a result, industries discharge their trace metal containing effluents into the environment without adequate treatments. Such metals include arsenic, lead, cadmium, aluminium, nickel, mercury, chromium, cobalt, zinc and selenium [3–5]. In the environment, most heavy metals do not experience degradation [6], but instead they bioaccumulate for a very long time [7]. So, when heavy metals do not degrade or metabolized by the body and accumulates, they became highly toxic even in trace amount. It has therefore been reported that exposure to heavy metal ion pollutants at considerable level may cause dermatitis, coughing, severe bronchitis, nausea, gastro-intestinal distress, lungs disorder, diarrhoea, circulatory collapse, intravascular hemolysis, renal failure, nephritis, fever, vertigo, vomiting, epigastric pain, acute multisystem organ failure, comma and even death depending on the level of Portions of this chapter have been reproduced from Igberase et al. [1] with kind permission from Elsevier © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 E. Igberase et al., Enhanced Chitosan Material for Water Treatment, Engineering Materials, https://doi.org/10.1007/978-3-030-71722-3_2

25

26

2 Thermodynamics, Kinetics and Desorption Studies …

ingestion [8, 9]. These associated health risks have necessitated adequate legislation and strict regulations on the discharge of toxic metal ions into our water bodies. Consequently, several processes have been developed to adsorb these pollutant water and wastewater [4, 10]. They include chemical precipitation [11], adsorption [12], membrane separation [13], reverse osmosis [14] and electrochemical treatment [15]. Of all the processes, adsorption is considered more reliable due to their convenience, simplicity of design, easy operation and wider applicability in water pollutant removal [10, 16, 17]. On another development, biological-based polymeric materials such as cellulose, lignin, chitosan and starch have been widely reported to play an important role in adsorption processes due to their re-absorbability and biocompatibility capabilities [18]. Hence, chitosan polymetric materials possess higher absorption capacity due to the availability of amine (–NH2 ) and hydroxyl (OH) functional group in their complex structure [19]. These functional groups, however, represent adsorption sites where complexes are formed with different kinds of metal ions. However, solubility of chitosan in acidic (pH ≤ 4) solutions is a limitation. To overcome such limitation and make the material insoluble at lower pH, chitosan beads are modified by cross-linking with epichlorohydrin [18, 20]. This process removes chlorine atom from the epoxide ring and covalently bonds carbon atoms to the hydroxyl group [21], as indicated in Fig. 2.1. It has also been reported that cross-linking reaction reduces the adsorption capacity of chitosan beads [4, 22–24] and this is because some functional groups in the complex structure of chitosan are bound with the crosslinker and therefore cannot interact with the pollutant. Consequently, grafting which OH

HO NH

HO

2

OH

OH

O

HO

O NH

CHITOSAN

O

O

O

OH

HO NH

2

+

CH

O

2

CROSS LINKING NH

2

HO

HO

O CH

O

O NH

NH 2

OH O CH CH

OH

CH

2

HO

O

O NH

2

2

OH 2

O

OH O

HO

HO

2

2

O

2

O O

CH CH

HO

NH

OH

O

HO

O O

HO

CHCH 2 Cl

2

OH NH 2

Fig. 2.1 Projected schematic representation of the cross-linking method of chitosan

2.1 Introduction

27

inserts new functional groups onto the cross-linked chitosan surface becomes very essential. Hence, the cross-linked beads were then grafted with 4-aminobenzoic acid as indicated in Fig. 2.2. The inserted functionality, however, increases the number of adsorption active sites and consequently the adsorption capacity. Hence in this study, three sets of chitosan beads were developed, and they are pure chitosan (CS), cross-linked chitosan (CR-CS), and grafted-cross-linked chitosan (G/CR-CS). This modified chitosan was characterization by FTIR, SEM, XRD, BET and TGA to provide evidence of successful modification process. Applicability of the graftedcross-linked chitosan (G/CR-CS) in determining the effectiveness of the produced G/CR-CS then follows. NH2

HO

O

O

O

HO

O

NH 2

OH

O

HO

O

NH2

CH2 CH

OH

HO

CH 2 CH

OH

O

NH2

HO

O

O

O

NH 2

O

OH O

HO

+

OH

CH 2

CH2

HO

COOH

O

O

OH

HO

NH 2

NH 2 MICROWAVE GRAFTING

NH

NH

COO

n

HO

HO

O

NH 2

OH

O

HO

O

O

O

O

NH 2

CH 2 CH

OH O CH 2 CH

OH

OH

CH 2

CH 2 O

O

OH O

HO

HO

HO

HO

NH 2

O

O

NH

O O

HO

OH NH 2

NH COO

n

Fig. 2.2 Projected structure of the grafting technique of cross-linked chitosan beads

28

2 Thermodynamics, Kinetics and Desorption Studies …

2.2 Materials and Methods 2.2.1 Materials The chemical substances used in this analysis were of analytical degree. Chitosan (85% deacetylation, Mwt 195 kDa) powder, epichlorohydrin and 4-aminobenzoic acid (almost 99.5%), hydrochloric acid (almost 999%), acetic acid (almost 99%) and sodium hydroxide (almost 99%) were acquired from Sigma-Aldrich SA. pH sensors (Hanna HI 8421) were also acquired from Sigma-Aldrich. Distilled water from a pure water distiller (Ultima 888 water distiller) was obtained from the school laboratory. For adsorption equilibrium experiments, a shaker (Labcon Incubator) was utilized. For the comprehensive investigation of ions Pb(II), Cu(II), Ni(II), and Zn(II), the atomic adsorption spectrophotometer (Varian SpectrAA-10) was used.

2.2.2 Methods 2.2.2.1

Adsorbate Preparation

The stock solution used in this research was formulated by selectively disintegrating in distilled water a specified quantity of CuSO4 · 5H2 O, Zn (NO3 )2 · 6H2 O, Pb (NO3 )2 and NiSO4 · 6H2 O. This stock mixture was distilled again with purified water to achieve the initial concentrations of 40–160 mg/L of metal ions available.

2.2.2.2

Preparation of Grafted-Cross-Linked Chitosan Beads

The adsorbent was formulated as follows: first, by disintegrating 30 g of chitosan powder in 1 L of 5.0% (v/v) acetic acid solution. Second, the processed mixture was filtered to eliminate any insoluble solvent molecules, and the filtrate was injected through a glass pipette to a 1 M solution of sodium hydroxide to produce a chitosan gel bead. The gel beads were washed thoroughly multiple times with distilled water to eliminate possible sodium hydroxide traces. Third, in an attempt for cross-linking reaction to occur the beads were treated with 2.5% epichlorohydrin solution with occasional hand shaking for 6 h. The cross-linked gel beads were washed with water to eliminate any residual of epichlorohydrin. Furthermore, approximately 4 g of the cross-linking gel beads was mixed in 0.5 M 4-amino benzoic acid in an open neck flask. The flask was transferred to a microwave oven and subjected to a medium to low-intensity microwave irradiation for 20 min. Once again, the grafted-cross-linked beads were washed with distilled water and available for investigation.

2.2 Materials and Methods

2.2.2.3

29

Characterization Studies of the Prepared Beads

Fourier transform infrared spectroscopy was performed utilizing a Shimadzu FTIR model 8300 Kyoto, Japan; the spectra was collected in the 450–4500 cm−1 range. A Shimadzu XRD model 7000 was applied in exploring the crystalline nature of the beads, and the intensities were reported in the range of 10–90o (2θ ). The mass loss of the beads was analyzed with a Shimadzu TGA 8000 Japan as a measure of temperatures. The SEM study was made by coating the beads with gold, and a JEOL 733 superprobe was used to study the morphology of the coated membranes. Applying a coupled Micromeritics (Australia) Tristar 3000 analyzer, BET surface area, pore length and pore size were measured by nitrogen adsorption at 77 K. The solubility of the different beads formed in acid solution was calculated in solutions with 100 mL of 0.1 M HCl. Briefly, 10.0 g of wet beads were placed into each of the many 250 mL volumetric flask comprising solutions of various concentrations of acids. The flasks were held at 120 rpm for 24 h in a Labcon incubator. The components of each flask were filtered, and the weight of the remaining beads was calculated. The beads are called soluble when the weight loss is >5% and insoluble when the weight loss is 6%.

2.3 Adsorption Experiment 100 mL of a constant amount of G/CR-CS was introduced into each flask in a series of Erlenmeyer flask. The impact of physical and chemical variables was examined based on the following criteria: pH (2–8), contact time (10–80) min, adsorbent dose (2–10) mg, temperature (25–55) °C, mixing rate (50–250) RPM and ionic strength (0.01–0.20) M.

2.3.1 Isotherm Studies Isotherm experiments were performed by passing 8 mg of G/CR-CS, accordingly into a collection of 250 mL Erlenmeyer flasks, and every flask was packed with 100 mL metal solution with initial concentrations of 40–160 mg/L. The initial concentrations were prepared from a stock. The Erlenmeyer flasks were placed in a Labcon incubator for 60 min, and the stirring speed was at 150 rpm in other to reach equilibrium. Thermodynamics was performed at an initial concentration of 40 mg/L.

30

2 Thermodynamics, Kinetics and Desorption Studies …

2.3.2 Adsorption Kinetics This investigation was carried out by introducing 6 mg of G/CR-CS into 100 mL of metal ions solution in a sequence of 250 mL Erlenmeyer flasks having initial concentration of 40 mg/L. The Erlenmeyer flask was put in a Labcon incubator to achieve equilibrium, the solution was shaken at 150 rpm, and the temperature set at 45 °C. The samples were taken at 10–60 min intervals. This process has been conducted for each of the ions. The investigation was conducted in triplicate, and this study provided the mean result. At optimum, 2.1, was used to measure the adsorption power, qe (mg/g), while 2.2 was applied in determining the percentage removal of metal ions from the single component mixture. qe = %R =

(Co − Ce ) × V M

(2.1)

(Co − Ce ) × 100 Co

(2.2)

where qe (mg/g) is the adsorption potential for equilibrium, C o and C e are the initial and equilibrium concentration (mg/L) of heavy metal ion in solution, whereas V (mL) is the volume and M (g) is the mass of G/CR-CS, respectively.

2.4 Result and Discussion 2.4.1 Classification Result The three collection of chitosan beads (pure CS, CR-CS and G/CR-CS) were classified so as to determine most of their physical and chemical properties.

2.4.1.1

FTIR Analysis

The FTIR spectra were presented in Fig. 2.3, and it shows the transformation in the functional groups of the modified beads. A typical FTIR spectrum of pure chitosan (CS) showed characteristic bands at 1029, 1195, 1650, 1734, 2939 and 3324 cm−1 . While the sharp intense peak at 1029 cm−1 was attributed to C–O stretching vibrations [20][1][1][2][2][2][1], the peaks around 1195 cm−1 were assigned to C–N stretching vibrations of amine functional group. Peaks at 1650 and 1734 cm−1 were attributed to C=O stretching vibrations of ketone and amide, respectively. The IR spectra peaks showed at 2939 cm−1 were assigned to asymmetric –CH2 stretching [21, 25]. Finally, the peak at 3324 cm−1 was reported to indicate the presence of exchangeable protons

2.4 Result and Discussion

31

Transmittance (%)

0

1000

100

699

95

771 90

1029

Transmittance (%) Transmittance (%)

102 100

100

2000

3000

4000

2932

3336

1674 1588 1373 1269 1603 1174

CR-CS 779

98

1728

96

1433

94 92

1717

2933 3330

1029

90 110

CS

1195

90

1734 779

80

1650

2939

70 60

5000

G/CR-CS

3324

1029 0

1000

2000

3000

4000

5000

-1 Wavelength (cm )

Fig. 2.3 FTIR pattern of CS, CR-CS and G/CR-CS

from alcohol and amine group [4, 26]. On comparing the FTIR spectrum of pure chitosan (CS) with modified cross-linked chitosan (CR-CS), there was not much difference in their spectrum. The major changes observed include a broadband shift in peaks from (i) 3324–3330 cm−1 , (ii) 2939–2933 cm−1 , (iii) 1734–1728 cm−1 and (iv) 1650–1717 cm−1 . The resultant shifts in peaks were attributed to the chemical bonding of epichlorohydrin to pure chitosan structure. Hence, cross-linking did not affect the structure of the modified chitosan but rather enhances some of its basic functional groups. However, the FTIR of modified grafted cross-linked chitosan (G/CR-CS) was different from pure chitosan as shown in Fig. 2.3. The grafted cross-linked chitosan (G/CR-CS) shows new sharp peaks at wavelengths 1174, 1269, 1373, 1588 and 1674 cm−1 respectively. The peaks at wavelength 1174 cm−1 corresponds to C– O stretching vibrations while the peaks at 1269 and 1373 cm−1 were attributed to strong C–H stretching vibration. Also, while peak at 1674 cm−1 was attributed to vibrations of C=O from carbonyl group, that at 1588 cm−1 represents N–H medium bending vibration. Also increased intensity was observed to be exhibited by (G/CRCS) between wavelengths 1029–1674 cm−1 . The increment in intensity provided evidence of successful modification process. Hence, the presence of carbonyl (C=O)

32

2 Thermodynamics, Kinetics and Desorption Studies …

and amine (N–H) functional groups enables the good binding performances of G/CRCS towards metal ions micropollutants.

2.4.1.2

XRD Analysis

The crystallinity of the three set of beads was generated and plotted as shown in Fig. 2.4. The XRD diffraction pattern of pure chitosan displays an intense characteristic peak at 2 theta = 20° and this corresponds to 110 planes of chitosan. The modified cross-linked chitosan has same diffraction angle with pure chitosan beads but with an increase in intensity. This shows that even after modification, the modified cross-linked chitosan can still retain some of its original properties. The observed increment in intensity suggests increase in crystallinity which may be as a result of the hydroxyl group involvement during the cross-linking process. However, the diffraction pattern of modified grafted cross-linked chitosan depicts a slight shift in the peak to 2θ = 25° with a reduction in intensity. The peak was attributed to copolymer formation which provides evident of successful grafting. A similar trend was observed and reported by Igberase et al. [20]. The drastic reduction in intensity suggests a decrease in the crystallinity of modified grafted cross-linked chitosan. This is in conformity with that observed by Kumar et al. [38] who attributed the decrease in intensity to the elimination of some crystalline structure during the grafting of chitosan process. Fig. 2.4 XRD of CS, CR-CS and G/CR-CS

2500

CR-CS CS G/CR-CS

Inteensity (a.u)

2000

1500

1000

500

0

20

40

60

2 theta (deg)

80

2.4 Result and Discussion

33

2.4.2 SEM Outcome The surface morphology of the three set of chitosan was inspected and presented in Fig. 2.5. The SEM image of pure chitosan demonstrates a rough, uneven and porous structure. After cross-linking pure chitosan with epichlorohydrin the surface of the CR-CS became visible, smooth and non-porous as depicted in Fig. 2.5b. On another hand, the grafting of the cross-linked leads to a homogeneous surface indicating that 4-aminobenzoic acid was chemically bonded onto the surface of the beads. Hence, the surface of chitosan was sufficiently enhanced after grafting the cross-linked chitosan.

2.4.2.1

BET Outcome

The BET analysis demonstrates the surface area, pore volume and pore size values of the various set of beads. As can be seen in Table 2.1, pure chitosan (CS) has a surface area of 190 m2 /g, pore volume of 0.406 cm3 /g and pore size of 41.102 nm. Also observed is that modified G/CR-CS has the greatest surface area of 237 m2 /g and this could provide more available reaction sites for adsorption [1].

Fig. 2.5 SEM of a CS, b CR-CS and c G/CR-CS

34

2 Thermodynamics, Kinetics and Desorption Studies …

Table 2.1 BET surface area, pore volume and pore size values of CS, CR-CS and G/CR-CS

Sample

Surface area (m2 /g)

Pore volume (cm3 /g)

Pore size (nm)

CS

190.0

0.406

41.102

CR-CS

156.2

0.309

34.321

G/CR-CS

237.4

0.503

57.283

The results also show that cross-linking decreases the surface area, pore volume and pore sizes when compared to pure chitosan, and this may be because of the involvement of hydroxyl group in the cross-linking reaction.

2.4.2.2

TGA Outcome

The thermal stability of the three set of beads was investigated with TGA in the air and reported in Fig. 2.6a. As was observed in Fig. 2.6b, pure chitosan (CS) shows three thermal degradation stages. The initial wt loss of 7.5% was observed in the first stage which occurs in the temperature range btw 34 and 148 °C. This wt lost was attributed to the elimination of water from the adsorbent [4]. In the second stage, which was observed in the temperature range of 250–328 °C, the weight loss is up to 35.79%. Omorogie et al. [27] ascribed this weight lost to depolymerization and dehydration of the saccharide rings. In the third and last stage, above 400 °C, complete decomposition of pure chitosan was observed and about 51% of weight lost was recorded. The cross-linked chitosan (CR-CS) also showed three decomposition stages. The first degradation stage is between 34 and 141 °C, and 5% weight loss was recorded. In the second degradation stage, which is between 227 and 330 °C, about 31% weight Fig. 2.6 TGA thermogram of CS, CR-CS and G/CR-CS

120

Weightloss (%)

100 80 60

G/CR-CS CR-CS CS

40 20 0 0

200

400

600

Temperature (oC)

800

1000

2.4 Result and Discussion

35

loss was observed. The last third degradation stage at 500 °C recorded about 10% weight loss. However, this weight loss in different decomposition stages corresponds to the decomposition of new acetylated and deacetylated units, surface water elimination and depolymerization [27, 28]. For grafted cross-linked chitosan (G/CRCS), decomposition started at 51 °C and 10% weight loss occurs as the temperature increases to 150 °C during the first stage of degradation. 24% weight loss was observed in the 2nd stage which started at 280 °C up till 398 °C the third stage which occurs above 500 °C recorded 15% weight loss. Just as previously observed, the loss of weight in the different stages of G/CR-CT degradation corresponds to the decomposition of new acetylated and deacetylated units, surface water elimination and depolymerization [27, 28]. Therefore, the result obtained from TGA analysis indicates increase in thermal stability after grafting or cross-linking the chitosan.

2.5 Application of Modified Chitosan for Metal Ions Adsorption 2.5.1 Effect of Solution pH on Metal Ions Adsorption The solution pH affects adsorption process because it controls the surface charge of the adsorbent, the degree of ionization of the adsorbate in solution and the dissociation of various functional groups on the active sites of the adsorbent (chitosan) [29]. Hence, different concentrations of metal ions bind on chitosan surface at different pH value as shown in Fig. 2.7a. At lower pH value of 1–3, the adsorption capacity was low because various metal ions present in the medium competes with excessive amounts of hydrogen ions for the available adsorption sites, with an apparent preponderance towards H+ ion uptake. However, as the pH value increases, deprotonation of the binding adsorption sites increases as competition between hydrogen ions with metal ions decreases; hence, adsorption of metal ions increases. This increase in adsorption process with decreasing H+ ion concentration (relatively at high pH values) is an indication that ion exchange is an important parameter controlling adsorption processes [30]. Thus, at pH values of 5, 5, 6, 6 and 7, optimal removal efficiency of 91, 95, 93 and 97% was recorded for Cu(II), Pb(II), Zn(II) and Ni(II), respectively. The result obtained is consistent with previous studies such as those by [4, 24, 31], where it was reported that heavy metal ions compete with hydrogen ions in solutions at a low pH value.

2.5.2 Effect of Contact Time Contact time is one of the major parameters used for the evaluation of the kinetics of the adsorption process. The removal of metal ions from aqueous solution depends

2 Thermodynamics, Kinetics and Desorption Studies … 100 90 80 70 60 50 40 30 20

Removal efficeincy (%)

Removal efficiency (%)

36

(a) pb(II) Cu(II) Ni(II) Zn(II) Cd(II) 2

3

4

5

6

7

8

100 90 80 70 60 50 40 30 20

(b)

pb(II) Cu(II) Ni(II) Zn(II) Cd(II) 0

10 20 30 40 50 60 70 80 90

pH Removal efficiency (%)

Contact time (min) 100

(c)

90 80

pb(II) Cu(II) Ni(II) Zn(II) Cd(II)

70 60 50 25

30

35

40

45

50

55

Temperature ( o C)

Fig. 2.7 Plot of physicochemical parameters showing the effect of a pH, b contact time and c temperature (initial concentration; = 40 mg/L, agitation speed of 150 rpm)

on their time of contact with the adsorbent in the medium. The variation of metal ion adsorption onto the G/CR-CS surface with contact time is presented in Fig. 2.7b. As illustrated, the adsorption capacity increased rapidly until equilibrium is reached at an optimal contact time of 45 min for Pb(II) and Cu(II) and 60 min for Ni(II) and Zn(II). The rapid adsorption at the initial stage may be because all active sites on the adsorbent surface were vacant; hence, increasing contact time between the adsorbate and the adsorbent results in the rapid uptake until adsorption equilibrium. However, at equilibrium the adsorption sites are all covered with metal ions which cause repulsion with increase in time.

2.5.3 Effect of Temperature Temperature is one of the most important experimental parameters for heavy metal ion removal from aqueous solution. As a measure of the average kinetic energy of metal ions, temperature decrease or increase, changes the amount of heavy metal ion being removed or retained by the adsorbent. Hence, the temperature effect on metal ions adsorption was studied at a pH of 5, agitation speed of 150 rpm, and equilibrium time of 1 h, adsorbent initial concentration dose of 40 mg/L (modified

2.5 Application of Modified Chitosan for Metal Ions Adsorption

37

chitosan G/CR-CS) and a temperature range of 25–55 °C. It is observed that an increase in temperature leads to a rise in the removal efficiency on all the considered metal ions as shown in Fig. 2.7c. This is because the rise in temperature increases the kinetic energy {KE} of the metal ions making them easier to contact adsorption sites, thus improving their adsorption efficiency [1]. In addition, higher temperature may have caused bond rupture of the absorbent, leading to an increase in adsorption active sites [32]. After optimum, the removal efficiency decreased with increasing temperature. As the temperature exceeds 45 °C, deterioration of the adsorbent begins. Since chitosan material cannot withstand higher temperatures, their adsorption efficiency therefore decreases.

2.6 Thermodynamic Parameters of Adsorption Thermodynamic parameters which existed as a result of the effect of temperature changes on the adsorption capacity of metal ions onto modified chitosan surface were entropy, S, enthalpy, H and the Gibbs free energy, G. The value of these parameters determines if an adsorption process is spontaneous or not. However, the Gibbs free energy change, Go , is the fundamental criterion of spontaneity, and reactions occur spontaneous at a given temperature if the Go is a negative quantity [32]. Relevant equations for the calculation of thermodynamic parameters are thus: Gibbs free energy 2.3, Van ’t Hoff 2.4, equilibrium constant 2.5 and Van ’t Hoff plot of ln K C versus 1/T as expressed in 2.6. G o = H o −T S o

(2.3)

G o = −RT ln K

(2.4)

K C = qe /Ce

(2.5)

ln K C = −H o /RT + S o /R

(2.6)

where Go , H o and S o are the standard free energy, enthalpy and entropy of adsorption, respectively, R is the universal gas constant (∼8.314 J K−1 mol−1 ), T is the temperature and K C is the equilibrium constant, while qe and C e are the adsorption capacity at equilibrium and equilibrium concentration, respectively. The values of G° and S° were determined from the slope and intercept of the plot of ln K C against 1/T, and thermodynamic parameter values were recorded and presented in Table 2.2. As observed, the negative values of Go rise as the temperature increases and this is an indication that the adsorption reaction of heavy metal ions onto the adsorbent is a spontaneous process. The positive value of H o confirms that the adsorption

42.441

50.454

53.622

Zn(II)

Cd(II)

Cu(II)

Ni(II)

55.572

45.653

Pb(II)

S o (kJ/mol/k)

Metal ions

0.413

0.432

0.603

0.644

0.761

H o (kJ/mol)

−1.963 −3.132 −3.994

−3.542

−3.181

−2.232 −2.323

−3.231

−1.232 −1.631

T = 303 K

T = 298 K

Go (kJ/mol)

−5.451

−4.642

−2.433

−3.452

−3.990

T = 318 K

−7.763

−6.692

−3.563

−4.122

−4.783

T = 328 K

0.989

0.999

0.998

0.994

0.998

R2

2.45 × 103

3.182

2.403

2.454 4.32 × 108

3.13 ×

3.873 104

3.322

E ad (KJ/mol) 1.54 × 107

2.12 ×

109

K c (mg/g min)

Rate constant

Table 2.2 Thermodynamic parameters for the adsorption of metal ions onto the absorbent at an initial concentration of 40 mg/L

38 2 Thermodynamics, Kinetics and Desorption Studies …

2.6 Thermodynamic Parameters of Adsorption

39

process is endothermic in nature. Also, the positive value of (S°) indicates increased degree of randomness at solid–solution interface during the adsorption process of heavy metal ions onto the adsorbent. This result therefore demonstrates that the adsorption of metal ions onto the adsorbent increases with increase in temperature (Table 2.3).

2.7 Adsorption Kinetics To comprehend the kinetic behaviour of the binding process of metal ions onto the modified G/CR-CS, linear forms of pseudo-first-order and pseudo-second-order models as given in 2.7 and 2.8 were used. ln(qe − qt ) = ln qe − K 1 t   t 1 1 t = + qt K 2 qe2 qe  

2   n  1  q q e(exp)− e(pred) MPSD = 100 N − P i=1 qe(exp)

(2.7) (2.8)

(2.9)

where qe and qt signify the quantity of metal ions absorbed on the adsorbent (mmol/g) at equilibrium and at time, t respectively. K 1 and K 2 (min−1 ) are the first- and the second-rate constants. N is the number of measurements, P is for number of parameters in the model, qe(exp) and qe(pred) are experimental and predicted uptake rates, respectively [33]. In order to validate the most suitable kinetics and isotherm models to represent the obtained adsorption data, error analysis is carried out, taking into consideration the experimental adsorption capacities (qe exp) for the metal ions adsorbed by G/CR-CS and the values predicted/calculated (qe cal) from the linear isotherm equations. In this study, a nonlinear regression Marquardt’s percent standard deviation (MPSD) test of statistical analysis is used as shown by 2.9. Hence, the smaller the error values for each model, the better is the fit for the obtained adsorption data except for R2 which indicates goodness of fit if its value is closer to unity. The slope and intercept of the linear plot of t/qt versus t give the values of qe and K 2 respectively. It was observed in Table 2.4 that the qe values for the experimental and the predicted for the pseudo-second-order kinetics are very close, indicating good agreement. For the pseudo-first-order kinetics, the qe values were observed to be not in agreement with one another. Also, for both first- and second-order kinetics, their adsorption capacity (qe ) was found to increase with increase in metal ion concentration. The smaller MPSD values observed (0.53–1.99) for the pseudo-second-order kinetic model indicates unique agreement and goodness of fit. Likewise, the high

Zn(II)

Ni(II)

Cu(II)

Pb(II)

38.4 ± 3.99

40.5 ± 3.5

48.4 ± 1.2

31.7 ± 3.1

33.6 ± 3.4

29 ± 2.8

42.9 ± 3.8

36.8 ± 1.2

20.2 ± 1.2

22.3 ± 2.1

28 ± 2.2

31.4 ± 3.1

160 mg/L

40 mg/L

80 mg/L

120 mg/L

160 mg/L

32.2 ± 3.14

23.3 ± 3.87

40 mg/L

26.2 ± 4.65

60.4 ± 1.2

43.8 ± 2.6

160 mg/L

30.3 ± 2.1

55.5 ± 1.2

39.3 ± 2.1

120 mg/L

120 mg/L

49.5 ± 1.3

35.3 ± 3.4

80 mg/L

80 mg/L

61.4 ± 3.2

160 mg/L

43.5 ± 1.3

56.5 ± 2.2

45.3 ± 3.1

120 mg/L

49.4 ± 2.1

54.1 ± 2.4

43.6 ± 3.2

80 mg/L

30.3 ± 2.2

50.5 ± 1.8

40.3 ± 1.3

40 mg/L

40 mg/L

qe(pred)

qe(exp)

12.4 ± 2.3

10.2 ± 3.3

10.6 ± 3.2

12.4 ± 2.5

13.9 ± 1.2

12.2 ± 3.4

10.8 ± 3.45

11.7 ± 2.99

15.2 ± 1.2

15.1 ± 1.2

13.1 ± 1.3

16.1 ± 1.3

14.2 ± 4.4

12.2 ± 4.2

16.5 ± 2.3

17.1 ± 0.8

MPSD

Pseudo-first-order kinetic model

0.476 ± 0.01

0.493 ± 0.02

0.511 ± 0.02

0.544 ± 0.02

0.409 ± 0.23

0.417 ± 0.15

0.406 ± 0.11

0.509 ± 001

0.564 ± 0.03

0.549 ± 0.02

0.547 ± 0.01

0.498 ± 0.02

0.696 ± 0.01

0.687 ± 0.02

0.587 ± 0.01

0.403 ± 0.01

K1

0.77

0.814

0.765

0.765

0.877

0.807

0.816

0.816

0.814

0.814

0.785

0.874

0.783

0.832

0.765

0.874

R2

31.4 ± 3.1

28.2 ± 2.2

22.2 ± 2.1

20.1 ± 1.2

36.8 ± 1.2

30.3 ± 2.1

26.2 ± 4.6

23.3 ± 3.7

43.8 ± 2.6

39.3 ± 2.6

35.3 ± 3.4

30.2 ± 2.2

49.4 ± 2.8

45.3 ± 3.1

43.5 ± 3.2

40.3 ± 1.2

qe(exp)

33.5 ± 2.8

29.8 ± 2.2

24.2 ± 2.4

21.7 ± 1.1

37.4 ± 2.8

32.5 ± 2.4

27.7 ± 2.9

22.1 ± 1.5

44.2 ± 2.4

38.7 ± 3.9

35.3 ± 2.8

30.2 ± 2.2

48.4 ± 3.3

46.5 ± 2.2

44.1 ± 2.4

40.4 ± 1.9

qe(pred)

3.2 ± 2.6

1.2 ± 0.3

0.9 ± 0.0

1.5 ± 0.0

0.9 ± 0.0

0.8 ± 0.0

1.4 ± 0.5

1.9 ± 0.9

1.4 ± 0.1

1.5 ± 0.9

0.3 ± 0.2

0.7 ± 0.01

1.7 ± 0.2

1.1 ± 0.1

0.8 ± 0.1

1.2 ± 0.9

MPSD

Pseudo-second-order kinetic model

Table 2.3 Kinetic parameters at various concentrations for the binding of metal ions on G/CR-CS

18.2 ± 2.5

16.8 ± 2.2

14.9 ± 2.6

14.8 ± 1.2

19.2 ± 2.9

18.4 ± 3.5

17.5 ± 3.1

16.4 ± 2.4

20.4 ± 2.8

18.9 ± 2.8

17.9 ± 2.2

17.2 ± 2.2

21.9 ± 3.5

21.5 ± 2.4

19.8 ± 2.4

19.5 ± 2.2

K2

0.986

0.999

0.987

0.987

0.996

0.999

0.987

0.996

0.999

0.984

0.987

0.999

0.997

0.997

0.986

0.997

R2

40 2 Thermodynamics, Kinetics and Desorption Studies …

2.7 Adsorption Kinetics

41

MPSD values (9.87–17.21) recorded for the pseudo-first-order model reveal unsatisfactory agreement between experimental and predicted (qe ) data. The obtained R2 values for the pseudo-second-order model are higher and closer to one from (0.984– 0.999) as compared to the smaller values obtained for pseudo-first-order model which is from (0.765–0.877). These results therefore suggested that the sorption kinetics can be approximated by pseudo-second-order kinetic model for the adsorption of selected metal ions onto grafted cross-linked chitosan.

2.8 Adsorption Equilibrium Isotherm Adsorption isotherms indicate different models used to establish the amounts of adsorbate molecules absorbed onto the adsorbent at constant temperature [1]. Isotherms such as Langmuir and Freundlich model were used herein to predict the adsorption capacity of the adsorbent. The Langmuir model which is defined by 2.10 assumes that sorption of a molecule takes place at a specific binding site within the adsorbent and that maximum adsorption occurs when molecules adsorbed on the adsorbent surface form a saturation layer [32]. 1 1 Ce = Ce + qe Qm Qm K L RL =

1 1 + K L CO

log qe = log K F +

1 log Ce n

(2.10) (2.11) (2.12)

where C e is the adsorbate concentration at equilibrium (mg/g), qe is the observed adsorption capacity at equilibrium, Qm is the maximum adsorption capacity, K L is the adsorption equilibrium constant, K F and n are constant representing the adsorption capacity and adsorption intensity, respectively. The slope and intercept of the plot C e /qe versus C e in 2.10 define the parameters of Langmuir isotherm for the adsorption of metal ions onto modified G/CR-CS. Expressing Langmuir model as a dimensionless constant called the separation factor (2.11), and an adsorption system can be suggested to be favourable or not. Hence, when RL > 1, RL = 1, RL = 0 and RL value is between 0 and 1, then adsorption indicates unfavourable, linear, irreversible and favourable [34]. For a single adsorption system, C 0 is usually the highest concentration of the liquid phase encountered [35]. On another hand, Freundlich adsorption model which is stipulated by 2.12 is most often valid for heterogeneous surfaces and assumes that sorption active sites are distributed exponentially with respect to their heat of adsorption and multilayer adsorption [32]. With the plot of log qe against log C e , the parameters of Freundlich model were determined.

42

2 Thermodynamics, Kinetics and Desorption Studies …

However, data generated using Langmuir and Freundlich isotherm were presented in Table 2.4. As can be seen from the table, in the Langmuir model, the maximum capacity of adsorption for the adsorbent, Qm (mg/g) for metal ions is high and was observed to increase as temperature increases from 25 to 45 °C. This is an indication that adsorption process is endothermic, and that molecular interaction is non-covalent. Pb(II) has the highest maximum adsorption capacity of 147.3 mg/g, followed by Cu(II); hence, adsorption process was found to follow the sequence Pb(II) > Cu(II) > Ni(II) > Zn(II). This observation showed that Pb(II) ions were the most effective ion on the surface of the absorbent having the strongest affinity towards multifunctional group. The K L values of Langmuir model were found to follow the same trend as Qm values; hence, RL values calculated using 2.11 give 0.28, 0.2, 0.16 and 0.22 for Cu(II), Pb(II), Ni(II) and Zn(II), respectively. These values indicate favourable Langmuir adsorption processes. Also, obtained R2 values of Langmuir model are greater than 0.98, which is very close to unit, indicating stronger mathematic data fit. On the other hand, the data generated from Freundlich adsorption model gives high values of K F which indicates high adsorption intensity [36]. Obtained n values were greater than 1, and this is an indication for convenient and favourable adsorption for all considered heavy metal ions. With R2 values greater or equal to 0.763, which is far from unity is an indication that Freundlich model was not efficient in describing the experimental data on the adsorption of metal ions onto the modified chitosan surface. Similar result was obtained by Doˇgan et al. [37] who depicted that Langmuir adsorption isotherm was reasonably correlated with experimental data in metal ions adsorption. Therefore, in this study, the Langmuir model best fits the obtained experimental data, suggesting that metal ions’ adsorption onto the modified chitosan bead surface is dominated by homogenous distribution onto the adsorption active sites.

2.9 Conclusion In this work, an environmentally friendly, low-cost and high removal efficient adsorbent was synthesized and applied in adsorption studies. The synthesized modified grafted cross-linked chitosan (G/CR-CS) adsorbent was characterized by FTIR, XRD and SEM. The characterization revealed the presence of carbonyl (C=O), hydroxyl (O–H) and amine (N–H) functional groups that enable good binding performances towards metal ion micropollutants. The metal ion removal from aqueous solution was found to increase with increase in contact time, temperature and pH until an adsorption equilibrium is reached. The metal ion adsorption kinetics onto the modified G/CR-CS surface were best fitted with the pseudo-second-order kinetic study showing that chemical adsorption is the rate limiting step. The values for the thermodynamics parameters of Go , H o and S o indicate spontaneous and endothermic adsorption process. Modified G/CR-CS was efficiently fitted by the Langmuir adsorption isotherm which indicates surface monolayer adsorption coverage.

298 K

0.006 ± 0.02

0.005 ± 0.01

0.004 ± 0.02

137.53 ± 1.52

130.12 ± 1.82

Ni(II)

Zn(II)

2.32 ± 0.02

2.65 ± 0.02

1.76 ± 0.01

1.98 ± 0.02

29.32 ± 0.05

28.43 ± 0.05

25.43 ± 0.06

24.49 ± 0.04

Pb(II)

Cu(II)

Ni(II)

Zn(II)

Freundlich

0.006 ± 0.02

147.30 ± 2.30

140.52 ± 3.12

K L (l/mg)

Cu(II)

Qm (mg/g)

Pb(II)

Langmuir

Ions

0.865

0.812

0.763

0.763

0.988

0.985

0.999

0.989

R2

27.23 ± 0.03

27.65 ± 0.01

30.67 ± 0.02

33.31 ± 0.02

137.83 ± 3.51

142.14 ± 2.61

149.93 ± 3.32

153.20 ± 3.70

Qm (mg/g)

1.74 ± 0.02

1.65 ± 0.02

1.76 ± 0.03

1.65 ± 0.02

0.007 ± 0.02

0.008 ± 0.02

0.008 ± 0.03

0.009 ± 0.02

K L (l/mg)

308 K

Table 2.4 Adsorption isotherm parameters for the selected metal ions adsorption onto G/CR-CS

0.763

0.754

0.821

0.842

0.984

0.999

0.997

0.989

R2

30.17 ± 0.03

30.60 ± 0.01

34.24 ± 0.04

36.98 ± 0.02

150.81 ± 1.74

155.12 ± 2.21

157.22 ± 2.82

162.14 ± 3.20

Qm (mg/g)

1.67 ± 0.01

2.97 ± 0.02

1.56 ± 0.01

2.54 ± 0.02

0.008 ± 0.02

0.008 ± 0.03

0.009 ± 0.02

0.010 ± 0.02

K L (l/mg)

318 K

0.798

0.843

0.821

0.843

0.992

0.995

0.999

0.991

R2

2.9 Conclusion 43

44

2 Thermodynamics, Kinetics and Desorption Studies …

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Chapter 3

Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) and Cd(II) Ions by Microwave-Improved Grafting Technique of Cross-Linking Composite Chitosan Beads. Studies Concerning Equilibrium, Isotherm and Desorption Abstract Due to the flexibility of chitosan, chemical improvement of chitosan has become progressively important, allowing the material to be easily changed in a way that enhances its characteristics in binding processes. Chitosan solution was crosslinked with glutaraldehyde in this study, and the cross-linked solution was used in the manufacture of the beads and then grafted with ethylene acrylic acid afterwards. Fourier transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were used to obtain the chemical properties of the beads. Binding of Pb(II), Cu(II), Ni(II), Zn(II), Cr(II) and Cd(II) ions from aqueous solution by grafted cross-linking chitosan beads (GXXB) was examined in relation to pH, temperature, initial concentration, contact time, agitation speed and ionic strength. The results found from binding investigation were applied in isotherm, thermodynamic and kinetic report. The model such as Langmuir, Temkin and Dubinin–kaganer–Radushkevich (DKR) was effective in explaining the isotherm data for the binding of adsorbate onto adsorbent, while the model Freundlich was not productive in explaining the experimental data. Pseudo-second-order and intraparticle model were accurate in explaining kinetic data. Thermodynamic parameters including Gibb free energy shift (Go ), enthalpy change (H o ) and entropy change (S o ) were measured and the marks reported a spontaneous and endothermic binding of Pb(II), Cu(II), Ni(II), Zn(II), Cr(II) and Cd(II) ions on GXXB. For the adsorbate examined, the regeneration of the spent GXXB was successful.

3.1 Introduction Large amounts of adsorbates including Pb(II), Cu(II), Ni(II), Zn(II), Cr(II) and Cd(II) ions and others reach our food chain each year via wastewater discharges into water supplies, especially in developing countries [1]. The main basis of these adsorbates is the ever-rising chemical, electroplating, leather, tannery, galvanizing, mining, pharmaceutical, pigment and colouring industries [2–4]. That results in the application of these metal ions globally. Heavy metal ions are unbiodegradable and poisonous pollutants that are harmful to human, animal, aquatic and general environment. In the past, © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 E. Igberase et al., Enhanced Chitosan Material for Water Treatment, Engineering Materials, https://doi.org/10.1007/978-3-030-71722-3_3

47

48

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

numerous diseases such as lung and kidney problems, pulmonary fibrosis, circulatory collapse, intravascular hemolysis, renal failure, nephritis, fever, vertigo, diarrhea, epigastric vomiting, nausea, extreme gastrointestinal discomfort, acute multisystem organ failure, comma and even death were documented owning to extreme intake [3, 5]. In this point, before their release into water supplies, the United States Environmental Protection Agency (USEPA) issued specific rules for the permissible level for heavy metals in water and wastewater. Because of this firm guideline on the emission of toxic contaminants in waterways, it becomes relevant to acquire different techniques that reduce or remove metal ions from water. Numerous practices for binding metal ions have been developed in the past decades but such techniques including chemical precipitation, membrane separation, ion exchange and electrolysis have proved unproductive due to rising running costs and low metal ion removal [6]. The quest for effective, low cost, ready-to-use, sludge-free service, profitable and effortless service has led to the application of adsorption method [7, 8]. Chitosan has become very convincing in development as a binding material with market availability, wide surface area, high adsorption efficiency, easy processing, non-toxicity, environmentally friendly and post-adsorption regeneration capability [9]. Chitosan is an N-deacetylation derivative of chitin, and chitin is a naturally occurring polysaccharide found in crustaceans. The presence of the functional group amine (–NH2 ) and hydroxyl gives the biopolymer its unusual binding characteristics. Chitosan, however, has its weakness that limits its use, and therefore, researchers have concentrated on physical and chemical alteration. Physical modification involves changing chitosan powder or flakes into gel beads for easier handling and better diffusion to binding sites, while chemical modification involves cross-linking and grafting. Enhancement of chitosan by cross-linking (Fig. 3.1) makes the beads insoluble in acid media, and thus improving their mechanical and chemical stabilities, this approach has presented OH

HO

HO

NH 2

CHITOSAN

OH

OH

O

HO

O

O

O

O

OH

HO NH 2

NH 2

HO

HO

N

OH

OH

O

HO

NH

CH

O

O

O

O

HO

2

OH N CH

(CH 2 ) 3

(CH 2 ) 3

CH

CH N

OH

O

HO HO OH

HO

N O

O NH 2

c

O (CH 2 ) 3

GLUTARALDEHYDE

CROSSLINKING REACTION OH

o H

O

HO

O OH

OH

Fig. 3.1 Schematic depiction of chitosan cross-linking mechanism

C

H

3.1 Introduction

49

a reduced adsorption potential because the amine group of chitosan is involved in the cross-linking process, making it necessary to graft other chemical functionalities onto the backbone of the cross-linking chitosan beads (Fig. 3.2). In this analysis, chitosan solution (XB) was cross-linked to glutaraldehyde and then the mixture was used to create cross-linked beads of chitosan. The cross-linked beads (XXB) were then grafted with ethylene acrylic acid. FTIR, TGA, XRD and SEM were used in characterizing the three sets of beads. The impact of adsorption variables on binding metal ions to GXXB was also investigated upon. OH

OH

OH O

HO

O

HO

N

OH

HO

H

C

C OH

N

NH 2

CH

C

O

O

O

HO

O

H

H

ETHYLENE ACRYLIC ACID

CH

(CH 2 ) 3

(CH 2 ) 3

CH

CH N

OH O

HO HO

N O

O

O

O

HO

OH

NH

OH

HO

OH

2

GRAFTING

O

CH 3 CH 2 COO

O

O

O

HO

OH

OH

n

O

HO

O

HO

N CH

OH

HO N

NH 2

CH

(CH 2 ) 3

(CH 2 ) 3

CH

CH N

OH O

HO

O

HO OH

N O

O O

HO NH 2

HO

OH OH

Fig. 3.2 Structure suggested for glutaraldehyde cross-linking chitosan beads grafted with acrylic acid ethylene

50

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

3.2 Experimental 3.2.1 Materials and Equipment’s The chemicals applied in this analysis have been of analytical quality and have been used without any further treatment. Chitosan powder was acquired from China with a degree of 74% deacetylation. Sigma-Aldrich purchased glutaraldehyde and ethylene acrylic acid (almost 99.5%). Domestic oven was introduced when the crosslinked beads were grafted. Hydrochloric acid (about 99%), acetic acid (about 99%), sodium hydroxide (about 99%) have all been purchased from Sigma-Aldrich. The solution’s pH was measured with a pH metre (Hanna HI 8421) from Sigma-Aldrich and bought from. Ultima 888 water distillery was used in school laboratory production of distilled water. In the adsorption experiment, a Shaker (Labcon incubator) was used. For determining the sum of adsorbed metal ions, the atomic adsorption spectrophotometer (Varian SpectrAA-10) was applied.

3.2.2 Preparation for Adsorbate The stock solution that was used in this analysis was formulated by separately dissolving a specific amount of CuSO4 · 5H2 O, CdCl2 · H2 O, Zn(NO3 )2 · 6H2 O, Pb(NO3 )2 , NiSO4 · 6H2 O and K2 CrO7 in purified water the produced stock solution was diluted with distilled water once again to acquire the necessary initial concentrations of 0.5 to 2.5 mmol/L.

3.2.3 Chitosan Enhancement from Its Powdered Form GXXB preparation requires four steps; first, 30 g of chitosan powder has been dissolved in a solution of 5.0% (v/v) acetic acid in 1 L. Second, the dissolved solution was mixed with a 2.5% glutaraldehyde solution (chemical cross-linking) and stirred for a cross-linking reaction with a magnetic stirrer for 2 h. Third, the cross-linked solution was then transferred to a 1 M solution of sodium hydroxide through a glass pipette assisted by a peristaltic pump, this procedure leads to the production of glutaraldehyde cross-linked chitosan gel beads. The gel beads were rinsed numerous times with distilled water to detach any sodium hydroxide residues. Fourthly, microwave technique was used in the grafting the interlinked beads. It was made achievable by combining 4 g of the cross-linked beads in an open neck flask with 0.1 g/L of ethylene acrylic acid. This flask was then put in a microwave oven for 20 min, with a medium–low capacity. Once more, the grafted cross-linked beads were rinsed with distilled water and ready for study use. The percentage of the water content (WC) present in the GXXB was calculated using 3.1.

3.2 Experimental

51

WC =

W1 − W2 W2

(3.1)

where W 1 and W 2 denote the wet GXXB and dry GXXB weights, respectively.

3.2.4 Classification of the Beads/Perles Approximately 1.0 g XB, XXB and GXXB were weighed separately and then oven dried at 60 °C. The dried beads were blended to their powdered form, and infrared measurement was done with a Shimadzu FTIR model 8300 Kyoto, Japan; the spectra were acquired within 500–4000 cm−1 limit. The crystallinity of the beads was studied with a Shimadzu XRD 7000 model, and the intensities were reported at 10–90° (2 θ ) range. The weight loss of the beads was studied with a Shimadzu TGA 8000 Japan at various temperatures. The SEM analysis was performed by bisecting XB, XXB and GXXB separately in order to gain a well-defined view of the inner fibres. The bisected perles are wrapped in gold, and the morphology of the coated beads was examined with Jeol 733 superprobe.

3.2.5 Studies in Adsorption Investigation on batch adsorption was actualized in a shaker controlled by temperature. A provided mass of GXXB was placed in a series of Erlenmeyer flasks, and samples of 100 mL with a known concentration were then measured in each flask. The sample pH was 0.1 M HCl, or 0.1 M NaOH, controlled. The influence of the adsorption variables was analysed based on the following conditions: pH (2–8), contact time (10–80) min, initial concentration (0.5–2.5) mmol/L, adsorbent dose (2–10) g/L, temperature (25–55) °C and ionic strength (0.01–0.2) M. The research was performed in parallel, and this analysis reported the average outcome. Experiment on isotherms, thermodynamics, kinetics were also performed. The sum of metal ions adsorbed to the adsorbent can be estimated from the mass balance equation as shown in 3.2 for any system under equilibrium conditions. qe =

(Co − Ce ) × V M

(3.2)

where qe (mmol/g) is the adsorption potential for equilibrium, C o and C e are the initial and equilibrium concentration (mmol/L) of heavy metal ion in solution, respectively, while V (mL) is the volume and M (g) is the adsorbent weight. Equation 3.3 is used in calculating the efficiency of removal of metal ions from a single component mixture. %R =

(Co − Ce ) × 100 Co

(3.3)

52

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

3.2.6 Data Assessment Theory 3.2.6.1

Isotherm

Adsorption isotherms are essential in achieving the binding process mechanism. Basically, an adsorbent’s binding capability can be derived from isotherms such as the model Langmuir, Freundlich, Temkin and DKR. Model constants are measurements of adsorbent binding power for the metal ions being studied. The Langmuir model assumes binding occurs at common homogeneous binding sites of the adsorbent and monolayer binding, and maximal adsorption occurs when adsorbed molecules form a saturation layer on the adsorbent surface [10]. The linear form of this model is defined in 3.4. Ce 1 Ce = + qe Qm Qm K L

(Linear form)

(3.4)

The Langmuir constant Qm (mmol/g) represents the maximum capacity to adsorb, and K L (L/mmol) refers to the adsorption bonding strength. The K L represents the degree of binding affinity that the metal ions have to the adsorbent. Higher K L values suggest much stronger metal ion binding affinities [11]. The Langmuir model parameters can be found from the slope and intercepts of C e /qe versus C e. The essential characteristics of the Langmuir model can be seen in respect to a dimensionless constant known as the separation factor (RL ) that is applied in verifying if an adsorption process is favourable [12], as seen in 3.5. The RL command, RL = 1 and RL command between 0 and 1, respectively, means unfavourable, linear and favourable. RL =

1 1 + K L Co

(3.5)

The Freundlich isotherm is focused on the relation of balance between heterogeneous surfaces. This isotherm is based on the postulation that the adsorption sites are spread-out exponentially with regard to adsorption heat, it also implies that the stronger adsorption sites are first saturated and the adsorption strength decreases with increased occupation of the site [11]. This model is explained in the linear form in 3.6. log qe = log K F +

1 log Ce (Linear form) n

(3.6)

K F and n are constant representing the respective adsorption capability and adsorption strength. The higher the K L values, the higher the possibility of more reactive definition of the adsorbent [13]. This model’s parameters can be estimated from the slope and intercepts log qe against log C e plot. Under normal binding conditions, n values should be within the limit of 1–10 [14].

3.2 Experimental

53

The Temkin model states that the heat of adsorption is decreased linearly due to contact with the adsorption distribution, and unlike the Langmuir and Freundlich model, the Temkin model considers the impact of certain indirect metal ions/adsorbent contact on binding processes [14] and is defined through 3.7. qe =

RT (ln A + ln Ce ) b RT =B b

(3.7) (3.8)

where R (8.314 Jmol/K) is the universal gas constant, T (K) is the temperature, C e (mmol/L) is the metal ion equilibrium. A (L/mmol) and B (J/mol) are the Temkin isotherm constant correlated with the adsorption constant and adsorption rate of the equilibrium (3.8). A linear plot of the quantity adsorbed, qe , versus ln C e gives the constant values A and b from the slope and intercept of the graph. The DKR model is a realistic model that was produced following a pore filling mechanism for the adsorption of less important vapours to solid microspores, based on the premise that the adsorption curve characteristic is related to the porosity of the binding material [15]. The equation to the model is shown in 3.9. ln qe = ln X m − K ad ε2

(3.9)

where K ad (mol2 /KJ2 ) and X m (mmol/g) are the isotherm DKR constant and the Polanyi potential defined by 3.10.   1 ε = RT ln 1 + Ce

(3.10)

The plot of ln qe versus slope and intercept gives the values of K ad and X m, respectively. Nevertheless, the adsorption energy (E) is the free energy of transfer from infinity (in solution) to the adsorbent surface of a single mole of solute. The extent of E is used for binding mechanism type study. If the value of E is about 8 kJ/mol, the phase of adsorption is physical in nature, but if it is between 8 and 16 kJ/mol, it can be clarified by the mechanism of ion exchange [16]. You can measure the value of E using the relation in 3.11. 1 E=√ −2K ad 3.2.6.2

(3.11)

Thermodynamic Adsorption Specifications

Thermodynamic adsorption specifications are necessary to determine whether an adsorption system is random or not. The change in entropy and enthalpy, related to the phase, can be determined from 3.12.

54

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

ln K = −

H o S o + RT R

(3.12)

The free energy shift of the Gibbs is the basic spontaneity criterion. At a given temperature, reactions occur spontaneously if it is a negative quantity [17]. Considering the adsorption equilibrium constant, K, the free energy of the adsorption reaction is given by 3.13. G o = −RT ln K

(3.13)

The mathematically expressed equilibrium constant ‘K’ is given in 3.14 K =

qe Ce

(3.14)

S o is the change of entropy while H o is the change of enthalpy. S o and H o estimated from the slope and intercept of a plot of ln K as a function of 1/T.

3.2.6.3

Kinetic Adsorption

The kinetics of a process affects the time of residence of the metal ions. It is regulated by the adsorbent’s physical and chemical characteristics which also influence the binding mechanism [17] Many researchers apply Lagargren’s pseudo-first-order kinetics, [18], pseudo-second-order kinetic model that Ho and McKay [19] and the intraparticle diffusion model as described in 3.15–3.17 developed to examine kinetics of a process. These models are applied in examining the operating mechanism of adsorption process. log(qe − qt ) = log(qe ) − t

k1 2.303

(3.15)

where qe and qt , respectively, represent the amount of metal ions absorbed by the adsorbent (mmol/g) at equilibrium and time t. K 1 (min−1 ) is the pseudo-first-order kinetic constant. The adsorption rate constant value, k 1, can be calculated from the plot of the straight line versus t. t 1 1 = + t qt K 2 qe2 qe

(3.16)

where k 2 (g/mmol min) is the rate constant for a pseudo-second-order model and the definitions of qe and qt remain the same. The slope and intercept of the straight-line plot of t/qt versus t provide the values of qe and K 2 correspondingly.

3.2 Experimental

55

The model of intraparticle diffusion is very important as it is the rate determining step in any liquid adsorption system [3]. This model describes three stages of adsorbate binding process by adsorbent. In step one, binding takes place on the adsorbent external surface until the external surface is saturated with metal ions. In step two, the metal ions at the adsorbent surface enter the pores making intense opposition to dispersion due to crowding. The third step is very slow owning to decreased metal ions concentration in the solution, and at this stage, equilibrium is reached between the ions in solution and the adsorbed ions [3]. Intraparticle diffusion model varies directly with the rate constant and also the square root of time. √ qt = kidm t

(3.17)

t is the time (min), k idm (mmol/gmin1/2 ) is the intraparticle diffusion rate constant. The slope of the straight-line plot of qt against t 1/2 provides the value of k idm .

3.3 Result 3.3.1 Outcome of XRD An X-ray diffraction analyser was used to test the crystallinity of the formed GXXB relative to XB and XXB. Chitosan is said to be crystalline in nature in its original state and this crystalline characteristic of native chitosan interferes with the effective adsorption of metal ions. Figure 3.3a–c displays XB, XXB and GXXB diffraction patterns, correspondingly [3]. A specific feature of 2θ = 20◦ was noticed in Fig. 3.3a, b, which agrees to 110 planes of chitosan, since it is feasible to change chitosan and preserve some of its qualities. However, due to copolymer formation, which proves indication of positive grafting, there was a small change in the peak in Fig. 3.3c [2]. In Fig. 3.3c, however, there was a note of a decrease in intensity in that several crystalline chains have been eliminated during grafting procedure.

3.3.2 SEM Outcome Following cross-linking and grafting, SEM was used to examine the morphology and changes of chitosan. SEM images of various set of beads are shown in Fig. 3.4a–c. Since of the reaction between chitosan and glutaraldehyde, the XXB surface tends to be more noticeable and smoother relative to XB, and as such glutaraldehyde has been chemically bonded with chitosan. The grafting of ethylene acrylic acid onto XXB’s backbone contributes to surface evenness.

56

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

Fig. 3.3 a, b and c XRD of XB, XXB and GXXB correspondingly

3.3.3 Outcome of FTIR FTIR spectrum was used to determine the major functional groups of the adsorbent produced for metal ion binding and to develop a significant change between the collection of beads. The plot is elucidated Fig. 3.5a–c. The big band of XB, XXB and GXXB at 3396, 3463 and 3339 cm−1 reveals the presence of exchangeable protons from alcohol and amine groups. In the modification process, the small shift in band can be due to exchangeable protons. At 2918, 2926 and 2890 cm−1 wavelength, the C–H stretch agrees with XB, XXB and GXXB correspondingly [20]. The three sets of beads had a similar wavelength of 1000 cm−1 which shows C–O stretching vibration, since some of its qualities can be retained after enhancement by an adsorbent [3]. The sharp peaks in XXB at wavelength of 1217 and 1508 cm−1 signifies C–N stretching vibration and N=O stretching vibration. The XXB IR spectra demonstrates a rise in intensity between 1217 and 1653 cm−1 wavelength in comparison with XB, the carboxylic function signifies C=O stretching vibration at wavelength of 1664 cm−1 for GXXB. The GXXB also demonstrated changes in intensity between the 1390 and 1659 cm−1 wavelengths. This ligand’s high binding potential is attributed to the existence of the groups such as COOH, OH and NH2 . These groups have the ability for metal ion complex formation.

3.3 Result

57

Fig. 3.4 a, b and c XB, XXB and GXXB SEM analysis, respectively

3.3.4 Outcome of TGA Analysis TGA was applied testing the heat characteristics of the collection of beads when heat was introduced. For testing the heat firmness of the collection of beads, a plot of weight per cent versus temperature was produced. Figure 3.6 illustrates the stages involved in the heat breakdown of bead sets. XB decomposition took place in three stages in the first stage with a weight loss of 6% between 34 and 148 °C [21]. The second stage commenced with a weight loss of 36% at 250 °C up to 320 °C. This weight loss is attributed to saccharide ring dehydration, depolymerization and decomposition of the adsorbent acetylated and deacetylated units [22]. In the third stage, weight loss of 51% was noticed above 400 °C which is due to the disintegration of non-cross-linked chitosan at this point. During the first stage, the XXB showed a weight loss of 5% at temperatures between 34 and 141 °C. The second stage started at 227 °C and proceeded with a

58

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

Fig. 3.5 a, b and c XB, XXB and GXXB FTIR, respectively

Fig. 3.6 a, b and c TGA of XB, XXB and GXXB, respectively

3.3 Result

59

weight loss of 31% up to 330 °C. There was a 10% weight loss over 500 °C in the third stage This weight loss in the first, second and third stages leads to the absorption of surface water, the depolymerization and the decomposition of the acetylated and deacetylated adsorbent units and the decomposition of the cross-linked chitosan, respectively [10, 23]. In the first stage of deterioration, the GXXB shows a 13% weight loss at temperatures between 46 and 200 °C. The second stage began at 252 °C and proceeded with a weight loss of 28% up to 311 °C. There was a 17% weight loss over 470 °C in the third stage. This weight loss in the 1st, 2nd and 3rd stages leads to the absorption of surface water, depolymerization and decomposition of the adsorbent and deacetylated units of GXXB correspondingly [10, 23].

3.3.5 pH Effect The pH associated with the adsorbent and functional binding site groups plays an significant role in the adsorption of metal ions in that it influences the degree of ionization, speciation and surface characteristics of an adsorbent [24, 25]. Figure 3.7a shows the influence of pH on the metal ions in question, at a pH value of 2–8. It was found that the removal efficiency for all the metal ions tested was greater than 50% at low pH of 2. This group was electrostatically bound to the adsorbent according to 3.18 which may be due to the grafting of carboxylic feature onto the backbone of the cross-linked chitosan beads. − R-NH2 + CH3 COOH → R-NH+ 3 COO

(3.18)

For Cu(II), Cr(VI), Cd(II), Pb(II), Zn(II) and Ni(II), respectively, higher removal efficiency of 97, 96, 97, 98, 97% was recorded at pH values of 5, 5, 6, 5, 6 and

Fig. 3.7 a and b Influence of pH on percentage GXXB removal of heavy metal ions (conditions: 7 g/L GXXB; contact time: 70 min; temperature: 25 °C; initial concentration: 0.80 mmol/L, agitation speed: 120 rpm), b zero GXXB charge point

60

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

7. Higher absorption at these pH values may be due to the presence of free lone pair of electrons on nitrogen atoms, ideal to combine with metal ions to give the corresponding metal ions/adsorbent complex [21]. Due to the formation of metal hydroxides and insoluble precipitation of metal ions, the decrease in the removal efficiency of metal ions above the optimum pH value. The pH effect can also unfold in terms of the adsorbent zero-charge point (pHPZC ) (Fig. 3.7b). PHPZC is the point where the acidic surface or the basic functional group no longer imparts to the solution pH [3]. Nevertheless, the adsorbent surface is charged negatively at pH > pHPZC , positively charged at pH < pHPZC and neutral at pH = pHPZC . Adsorbent pHPZC was 4.3 which favoured adsorption because surface charging is negative.

3.3.6 Outcome of Contact Time Increasing the time of contact accelerates the interface existing between the active sites in the adsorbent and the metal ions in solution which ultimately increases the uptake of metal ions [26]. Figure 3.8 explains the influence of contact time on the adsorption of adsorbents from a single component solution and the 10–80min time limit. It was noticed that 40 min was adequate for all the metal ions to achieve equilibrium. Quick adsorption was initially observed due to the accessible and well-arranged binding site of the considered metal ions, but became slower until equilibrium was formed as the binding sites were filled with metal ions, causing repulsion with increased time [4, 27]. This finding is important since repeated contact will take up large quantities of energy and therefore raise treatment costs. 100

Removal efficiency ( %)

Fig. 3.8 Contact time influence on the percentage removal by GXXB of heavy metal ions (conditions: 7 g/L GXXB; pH: Pb(II) = 5, Cu(II) = 5, Ni(II) = 7, Zn(II) = 6, Cd(II) = 6, Cr(VI) = 6; temperature: 25 °C, initial concentration: 0.80 mmol/L, agitation speed: 120 rpm)

90 80 70 60 50 40

0

20

40

60

80

100

Contact time (min) pb

Cu

Ni

Zn

Cd

Cr(VI)

3.3 Result 120

Removal efficiency (%)

Fig. 3.9 Initial concentration influence on the percentage removal of heavy metal ions by GXXB (conditions: 6 g/L GXXB; pH: Pb(II) = 5.0, Cu(II) = 5.0, Ni(II) = 7.0, Zn(II) = 6.0, Cd(II) = 6.0, Cr(VI) = 6.0; contact time: 40 min, agitation speed: 120 rpm, temperature: 45 °C)

61

100 80 60 40 20 0

0

1

2

3

Initial concentration mmol/L Pb

Cu

Ni

Zn

Cd

Cr(VI)

3.3.7 Effect of Initial Concentration The influence on removal of heavy metal ions from the initial concentration was studied at different concentrations of 0.5–2.5 mmol/L, and Fig. 3.9 sheds light on the plot. It was found that the removal efficiency for each of the metal ions considered was very high at a lower initial concentration of 0.5 mmol/L (Pb(II) = 99.1, Cu(II) = 99.2, Ni = 98.0, Zn(II) = 98.0, Cd(II) = 97.3, Cr(VI) = 98.2%), but with a higher initial concentration of 2.5 mmol/l, the removal efficiency was reduced. However, the removal efficiency decreases at higher concentrations of considered metal ions due to saturation of the adsorbent surface/competition for a limited number of vacant sites resulting in blockage of binding site. The vacant site is available at lower concentrations and is active for metal binding [28, 29].

3.3.8 Influence of Adsorbent Dose It is necessary to obtain a maximum dosage of the adsorbent to increase the interaction between adsorbent and adsorbate [25]. Figure 3.10 illustrates the impact adsorbent dose has on metal ion removal efficiency. There was a significant improvement in the removal efficiency of each metal ion in the 2–4 g/L GXXB dose range, and no further improvement in the GXXB dose was recorded beyond 4 g/L. This remark at the onset is due to the accessibility of adequate binding sites for the complexation of adsorbates and the increase in the dose beyond 4 g/L which resulted in a balance between the metal ions bound to GXXB and those remaining unabsorbed in the solution [30, 31].

62

100

Removal efficiency (%)

Fig. 3.10 Influence of adsorbent dose on percentage removal of heavy metal ions (conditions: pH: Pb(II) = 5.0, Cu(II) = 5.0, Ni(II) = 7.0, Zn(II) = 6.0, Cd(II) = 6.0, Cr(VI) = 6.0; contact time: 40 min, initial concentration: 0.50 mmol/L, agitation speed: 120 rpm, temperature: 45 °C)

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

80

60

0

2

4

6

8

10

Cd

Cr(VI)

Adsorbent dose (mmol/g) Pb

Ni

Cu

Zn

3.3.9 Influence of Temperature It is observed that temperature is a significant variable in adsorbent binding of metal ions. This is because the temperature of a solution will affect the solid/liquid interface, the movement of metal ions and the adsorbents’ swelling properties [25]. Figure 3.11 illuminates the influence of temperature on adsorbent removal of metal ions even at a temperature range of 25–65 °C. The increase in temperature has been seen to accelerate binding of metal ions until an maximum of 45 °C is established. This result is attributable to the fact that the diffusivity of metal ions in solution is increased at higher temperatures which then decreases the time taken to achieve equilibrium [32, 33]. In addition, the higher removal efficiency of Pb(II) = 98.2, Cu(II) = 97.1, Ni(II) = 94.4, Zn(II) = 88.3, Cd(II) = 98.2, Cr(VI) = 99.3% observed at 45 °C is due to swelling of the adsorbent’s internal pores to trap more metal ions on the surface [33]. Nevertheless, there is a degeneration of the adsorbent beyond the maximum temperature which results in a reduced removal of metal ions. This is a good outcome regardless of the costs. 100

Removal efficiency (%)

Fig. 3.11 Influence of temperature on percentage removal of heavy metal ions by GXXB (conditions: 4 g/L GXXB; pH: Pb(II) = 5.0, Cu(II) = 5.0, Ni(II) = 7.0, Zn(II) = 6.0, Cd(II) = 6, Cr(VI) = 6.0; contact time: 40 min, initial concentration: 0.50 mmol/L, agitation speed: 120 rpm)

90 80 70 60 20

30

40

50

60

Temperature (oC) Pb

Cu

Ni

Zn

Cd

Cr(VI)

3.4 Influence of Agitation Speed 100

Removal efficiency (%)

Fig. 3.12 Influence of stirring velocity on percentage removal of heavy metal ions by GXXB (conditions: 4 g/L GXXB; pH: Pb(II) = 5.0, Cu(II) = 5.0, Ni(II) = 7.0, Zn(II) = 6.0, Cd(II) = 6.0, Cr(VI) = 6; contact time: 40 min, initial concentration 0.50 mmol/L; temperature: 45 °C)

63

90

80

70

0

50

100

150

200

250

Agitation speed (RPM) Pb

Cu

Ni

Zn

Cd

Cr(VI)

3.4 Influence of Agitation Speed Figure 3.12 depicts the influence of stirring velocity on the removal efficiency of GXXB metal ions at a 50–250 rpm stirring range. The agitation level has been found to have a positive effect on the removal of metal ions by GXXB. However, the removal of metal ions up to 150 rpm was quickly increased, and thereafter, it was continuous. This is because the boundary layer becomes thinner at high stirring velocity which ultimately influences the velocity at which metal ions are distributed through the boundary layers [34]. Nevertheless, a further increase above 150 rpm will result in the adsorption site being saturated (Fig. 3.12).

3.5 Influence of Ionic Strength Figure 3.13 describes the influence of ionic strength on metal ion bonding to GXXB. In this graph, the efficiency of removal with an increase in NaNO3 concentration was decreased. This result can be interpreted on the basis of two points: first, the movement of ions to the adsorbent surface is limited because of the adverse influence of ionic strength on metal ion activity coefficient. Furthermore, based on the theory of surface chemistry when two substances, such as industrial waste and metal ions, are in contact with an aqueous mixture, they are surrounded by an electrical double layer due to electrostatic interface causing a reduction in adsorption [33].

64

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

3.6 Isotherm Outcome The power of the models used was calculated by coefficient of correlation (R2 ). The more R2 is to one better the model fits [27]. The parameters for the respective metal ions in the isotherm models are presented in Table 3.1. The values of R2 (almost 0.98) suggest that the adsorption isotherm data for the investigated metal ions are very well represented by the model Langmuir, Temkin and DKR as opposed to the Freundlich model’s R2 (almost 0.78). The Langmuir model supports single-layer adsorption from aqueous solution to the GXXB surface of the considered metal ions. Qm values derived from the Langmuir equation decreased in the order of Cu(II)(4.43), Pb(II)(4.22), Ni(II)(3.87), Cd(II)(3.80), Cr(VI)(2.93), Cr(VI)(2.57) (mmol/g), whereas K L values followed a decreasing trend of Cu(II)(3.98), Pb(II)(3.46), Ni(II)(2.93), Cd(II)(2.63), Cr(VI)(1.98) (L/mmol). The higher value obtained for Cu(II) ions indicates greater affinity for GXXB’s multifunctional group. The higher KL values also suggest heavy electrostatic interface between the multifunctional GXXB group and the metal ions studied. The RL values for the ions Cu(II), Pb(II), Ni(II), Cd(II), Cr(VI) and Zn(II) were correspondingly 0.33, 0.37, 0.39, 0.41, 0.43 and 0.50, and these values are favourable. The Freundlich model had failed to explain the experimental results the values of n suggested desirable adsorption for the metal ions considered. The Temkin model represented the adsorption data very well owing to the fact that the filling of the more energetic binding sites is taken into consideration at first. Can et al. (2016) tabled a similar paper. The adsorption energy values from the DKR model indicates that ion exchange mechanism may also define the process. 100

Removal efficiency (%)

Fig. 3.13 Influence of ionic strength on percentage removal of heavy metal ions by GXXB (conditions: 4 g/L GXXB; pH: Pb(II) = 5.0, Cu(II) = 5.0, Ni(II) = 7.0, Zn(II) = 6.0, Cd(II) = 6.0, Cr(VI) = 6; contact time: 40 min, initial concentration 0.5.0 mmol/L; temperature: 45 °C, agitation speed: 150 RPM)

90 80 70 60 50

0

0.05

0.1

0.15

0.2

0.25

Na+ concentration (Mol) Pb

Cu

Ni

Zn

Cd

Cr(VI)

4.430

4.220

3.872

3.800

2.932

1.761

Pb(II)

Ni(II)

Cd(II)

Cr(VI)

Zn(II)

Qm (mmol/g)

1.983

2.631

2.932

3.113

3.462

3.981

K Lc (L/mmol)

Langmuir parameters

Cu(II)

Ions

0.991

0.992

0.993

0.980

0.990

0.990

R2

1.493

2.602

2.681

3.112

3.410

3.581

n

1.901

1.622

1.464

1.973

1.792

1.703

K f (mmol/g)

Freundlich parameters

0.83

0.85

0.86

0.79

0.82

0.78

R2

1.143

1.491

1.873

2.434

2.972

3.412

A (L/mmol)

7.132

8.542

5.454

7.763

8.342

6.124

B (J/mol)

Temkin parameters

Table 3.1 Langmuir, Freundlich, Temkin and DKR isotherm criteria for binding ions on GXXB at 45 °C

0.992

0.992

0.983

0.994

0.981

0.992

R2

2.323

3.124

3.252

3.562

4.123

4.183

X m (mmol/g)

9.651

9.152

10.244

11.962

13.113

13.512

E (kJ/mol)

DKR parameters

0.993

0.982

0.983

0.984

0.991

0.992

R2

3.6 Isotherm Outcome 65

66

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

Fig. 3.14 ln K thermodynamic plot versus 1/T for binding of metal ions to GXXB

3

lnqe/Ce

2.5 2 1.5 1 0.5 0 0.003

0.0031

0.0032

0.0033

0.0034

1/T (K) Pb

Cu

Cd

Zn

Ni

Cr(VI)

Table 3.2 Thermodynamic parameters for heavy metal ions adsorption onto GXXB at an initial concentration of 0.50 mmol/L Metal ions

S o (kJ/mol/k)

Pb(II)

66.871

H o (kJ/mol)

0.533

Go (kJ/mol)

R2

T= 298 K

T= 303 K

T= 318 K

T= 328 K

−2.322

−2.481

−3.794

−4.122

0.994

Cu(II)

73.223

0.482

−2.892

−2.983

−3.993

−4.564

0.994

Ni(II)

55.763

0.384

−2.312

−3.672

−5.894

−7.563

0.983 0.963

Cr(VI)

61.342

0.443

−2.124

−2.153

−2.962

−4.652

Zn(II)

56.664

0.392

−1.873

−3.781

−5.342

−7.671

0.992

Cd(II)

58.321

0.352

−2.231

−3.872

−5.641

−8.421

0.974

3.7 Outcome of Thermodynamic Investigation Figure 3.14 shows the plot of ln K versus 1/T for adsorption of ions Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) and Cd(II) onto GXXB. Parameters for thermodynamic studies are given in Table 3.2. The free energy change acquired during the absorption process at temperatures of 25, 35, 45 and 55 °C was more negative as the temperature rose, indicating that the binding of heavy metals onto GXXB is spontaneous and favourable. The positive value of when adsorbing heavy metal ions to GXXB suggests increased randomness at the solid–solution interface [3]. This result indicates the degree of stability of the respective metal ions on the surface of the GXXB.

3.8 Outcome of Kinetic Experiment The values of the parameters are given in Table 3.3 for every case. From the table, it is verified that in comparison with the pseudo-first-order model, the R2 value for the

0.011

0.021

0.022

0.044

0.012

0.032

Cu(II)

Ni(II)

Cr(VI)

Zn(II)

Cd(II)

k1

(min−1 )

2.141

1.752

2.104

1.953

1.981

1.930

qe (mmol/g)

Pseudo-first-order parameters

Pb(II)

Metal ions

0.792

0.883

0.791

0.822

0.794

0.842

R2

Table 3.3 Kinetic criteria for binding the metal ions to GXXB

4.321

4.592

5.942

6.163

8.224

7.782

k 2 (g/mmol.min)

2.543

3.112

3.222

3.352

4.784

4.383

qe (mmol/g)

Pseudo-second-order parameters

0.982

0.993

0.992

0.993

0.994

0.992

R2

4.982

5.323

6.182

7.133

7.592

7.103

k idm (mmol/gmin1/2 )

0.983

0.973

0.992

0.963

0.974

0.993

R2

Intraparticle diffusion parameters

3.8 Outcome of Kinetic Experiment 67

68

3 Adsorption of Pb(II), Cu(II), Ni(II), Zn(II), Cr(VI) …

pseudo-second-order and intraparticle model is higher and closer to one. The order for the constant rate to decrease (k 2 ) is as follows: Cu(II)(8.22) > Pb(II)(6.78) > Ni(II)(6.16) > Cr(VI)(5.94) > Zn(II)(4.59) > Cd(II)(4.32) in g/mmol min. K 2 values indicate that the adsorption process occurred in the sequence from fast to slow, and that copper has great affinity for the multifunctional group. This means that the binding of metal ions to GXXB is a pseudo-second-order reaction model, and the model postulates that the rate limiting stage may be chemical adsorption or chemisorption involving valence forces by exchange of electrons between metal ions and GXXB delivers best agreement of data [3].

3.9 Regeneration Studies Adsorbent regeneration provides (i) metal ions recovery for effective disposal to prevent secondary pollution (ii) adsorbent reusability (iii) process cost reduction (iv) recognition of the adsorption mechanism. The spent adsorbent for the metal ions was washed separately with distilled water after adsorption trial and treated for 180 min with 0.5 M HCl. Capacity in desorption was calculated by 3.19. %Desorption =

Ce × 100 Co

(3.19)

The recovered percentage of Cu(II), Pb(II), Ni(II), Cr(VI), Zn(II) and Cd(II) is 99.3%, 99.1%, 98.5%, 99%, 97.6% and 98.3%, correspondingly. With the metal ions, the reusability of the regenerated GXXB was observed, and the Qm obtained from the Langmuir model was not affected.

3.10 Conclusion It explored the possibility of using GXXB as a binding agent for extracting heavy metal ions from wastewater. The multifunctional groups present in GXXB have been beneficial in the binding of metal ions even at low pH values, and the binding of metal ions has been observed as a complex process consisting mainly of chelation, chemisorption, electrostatic attraction and ion pair formation. GXXB’s water content was found to be 76.70%, which helps to move metal ions to binding sites. GXXB could be a good candidate for binding heavy metal ions at industrial level.

References

69

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20. A. Itodo, F. Abdulrahman, L. Hassan, S. a. Maigandi, H. Itodo, Intraparticle diffusion and intraparticulate diffusivities of herbicide on derived activated carbon. Researcher 2(2) (2010), pp. 74–86 21. M.M. Rao, G.P.C. Rao, K. Seshaiah, N.V. Choudary, M.C. Wang, Activated carbon from Ceiba pentandra hulls, an agricultural waste, as an adsorbent in the removal of lead and zinc from aqueous solutions. Waste Manag. 28(5), 849–858 (2008) 22. S. Hao, A. Verlotta, P. Aprea, F. Pepe, D. Caputo, W. Zhu, Optimal synthesis of aminofunctionalized mesoporous silicas for the adsorption of heavy metal ions. Microporous Mesoporous Mater. 236, 250–259 (2016) 23. K.J. Adarsh, D.G. Madhu, A comparative study on metal adsorption properties of different forms of chitosan. Int. J. Innov. Res. Sci. Eng. Technol. 3(2), 9609–9617 (2014) 24. X. Luo, Z. Zhang, P. Zhou, Y. Liu, G. Ma, Z. Lei, Synergic adsorption of acid blue 80 and heavy metal ions (Cu2+ /Ni2+ ) onto activated carbon and its mechanisms. J. Ind. Eng. Chem. 27, 164–174 (2015) 25. B. Li, M. Li, J. Zhang, Y. Pan, Z. Huang, H. Xiao, Adsorption of Hg (II) ions from aqueous solution by diethylenetriaminepentaacetic acid-modified cellulose. Int. J. Biol. Macromol. 122, 149–156 (2019) 26. A. Selvakumar, S. Rangabhashiyam, Biosorption of rhodamine B onto novel biosorbents from Kappaphycus alvarezii, Gracilaria salicornia and Gracilaria edulis*. Environ. Pollut. 255, (2019) 27. E. Igberase, P. Osifo, A. Ofomaja, Adsorption of metal ions by microwave assisted grafting of cross-linked chitosan beads. Equilibrium, isotherm, thermodynamic and desorption studies. Appl. Organomet. Chem. (2017) 28. M. Doˇgan, Y. Turhan, M. Alkan, H. Namli, P. Turan, Ö.¨ Demirba¸s Functionalized sepiolite for heavy metal ions adsorption. Desalination 230(1–3) (2008), pp. 248–268 29. L. Nouri, I. Ghodbane, O. Hamdaoui, M. Chiha, Batch sorption dynamics and equilibrium for the removal of cadmium ions from aqueous phase using wheat bran. J. Hazard. Mater. 149(1), 115–125 (2007) 30. C. Dong, F. Zhang, Z. Pang, G. Yang, Efficient and selective adsorption of multi-metal ions using sulfonated cellulose as adsorbent. Carbohydr. Polym. 151, 230–236 (2016) 31. J.B. Neris, F.H.M. Luzardo, E.G.P. da Silva, F.G. Velasco, Evaluation of adsorption processes of metal ions in multi-element aqueous systems by lignocellulosic adsorbents applying different isotherms: a critical review. Chem. Eng. J. 357 (2019), pp. 404–420 32. J. Shen, Z. Duvnjak, Adsorption kinetics of cupric and cadmium ions on corncob particles. Process Biochem. 40(11), 3446–3454 (2005) 33. A.A. Taha, M.A. Shreadah, A.M. Ahmed, H. Fathy, Multi-component adsorption of Pb (II), Cd (II), and Ni (II) onto Egyptian Na-activated bentonite; equilibrium, kinetics, thermodynamics, and application for seawater desalination. Biochem. Pharmacol. 4(1), 1166–1180 (2016) 34. W.S.W. Ngah, S. Ab Ghani, A. Kamari, Adsorption behaviour of Fe(II) and Fe(III) ions in aqueous solution on chitosan and cross-linked chitosan beads. Bioresour. Technol. 96(4) (2005), pp. 443–450

Chapter 4

Investigation into the Adsorption of Cadmium and Lead by Polyaniline Grafted Cross-Linked Chitosan Beads from Aqueous Solution

Abstract This research explored the enhancement of chitosan beads by crosslinking and grafting to use the grafted beads to extract cadmium and lead from polluted water. XRD and SEM characterized the beads to bear evidence of positive cross-linking and grafting. Batch investigation was conducted with regards to the parameters of adsorption such as pH, initial concentration, contact time and adsorbent dose. Equilibrium data were collected from the adsorption investigation, and the data were compared with the isotherm models including Langmuir and Freundlich. The maximum adsorption potential for cadmium and lead ions was found to be, respectively, 145 mg/g and 114 mg/g at a temperature of 45 °C from the Langmuir model. Thermodynamic parameters such as Gibbs free energy change (Go ), enthalpy change (H o ) and entropy shift (S o ) were subsequently determined and the findings illustrate that polyaniline adsorption of cadmium and lead ions on the produced adsorbent (GXCS) is spontaneous and endothermic in nature. The firstorder pseudo- and second-order pseudo-models have been used for the study of kinetic data for both metal ions. The data match well with the second-order pseudomodel. Over five consecutive cycles of adsorption/desorption, the GXCS filled with cadmium and lead ions was measured. Nevertheless, 0.5 M HCl was successfully used among the eluents examined in desorbing the adsorbent expended and among the eluents that was investigated 0.5 M HCl was successfully used in desorbing the spent adsorbent and a percentage desorption of 98.94 and 97.50% was acquired for cadmium and lead ions correspondingly, at a desorption time of 180 min.

4.1 Introduction The pollution of surface by heavy metal ions has been a problem harming the environment in the last decades. The main causes of these heavy metals are the alreadyrising factories that generate different forms of physicochemical contaminants that enter the water [1, 2]. Rising levels of these metals in water pose severe hazard to health because they are not environmentally friendly [3, 4]. For example, cadmium causing the preceding potential health risks, renal damage, tai-tai, hypertension, emphysema and testicular atrophy is manufactured by economic sectors including © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 E. Igberase et al., Enhanced Chitosan Material for Water Treatment, Engineering Materials, https://doi.org/10.1007/978-3-030-71722-3_4

71

72

4 Investigation into the Adsorption of Cadmium and Lead …

the mining, smelting, metal plating, battery and phosphorus companies [5, 6]. Lead on the other hand poses health risks like iron deficiency, brain trauma, kidney and liver dysfunction, pregnancy complications [7–9] is manufactured in industrial sectors including coatings, battery packs, combustion, pesticides and herbicides, plastic materials, water systems, food, beverages, sweetener and flavouring balms and curative mixtures. The current maximum limit given by the US environmental protection agency (USEPA) for cadmium and lead is 0.005 and 0.05 mg/L correspondingly. Because of the stringent regulations on the release in water sources of such toxic metals, it then becomes necessary to promote new methods which would reduce or eliminate such contaminants to their acceptable levels. In the past, technologies including chemical coagulation, layer separation, reverse osmosis and electrodialysis have been used to remove ions from materials. Consequently, previous findings have suggested that adsorption is perhaps the most optimistic method of removing toxic metals due to its effectiveness, ease of handling, simple design, could remove various kinds of pollution, and it can be regenerated by certain process of desorption [3, 10]. Ali et al. [11] reported that the procedure of adsorption can eliminate up to 99.9% of contaminants found in wastewater. Chitosan has proved to be an important adsorbent among the numerous adsorbent’s materials, possessing particular attributes including antibacterial properties, processability, non-toxicity and relatively cheap [11]. Chitosan is a product of Ndeacetylation of chitin, a polymer which occurs naturally in sea creatures, i.e. snails and crabs, and fungal biomass [12]. The availability of amine and hydroxyl group in the backbone of chitosan provides the polymer its excellent adsorption ability. Chitosan can eliminate concentration levels of metallic ions to extremely low concentration [13]. The distinctiveness of chitosan allows for better improvements of the polymer in an attempt to modify or boost the adsorption properties of chitosan. Polymer chains transformation of chitosan appears to make the polymer impermeable in acidic environment, thus boosting the chemical and mechanical steadiness. Many researches have found these procedure to have a detrimental impact on adsorption potential owing to the fact that the amine group of chitosan is participating in the cross-linking mechanism [14], and thus, it becomes necessary to graft the crosslinked beads to boost the metal adsorption characteristics of the target group [10]. This report presents the use of crosslinked chitosan beads with polyaniline graft to extract cadmium and lead from aqueous solution. Because there is an amine group in polyaniline which is effective in absorbing metallic ions, it is, however, important to create an adsorbent that will adsorb metallic ions significantly faster than any other chitosan composite materials. Chitosan beads were cross-linked with hydrochloric acid and then grafted with polyaniline. Characterization of the beads was based on scanning electron microscope (SEM) and X-ray diffraction (XRD). It examined the effect of pH, adsorbent dosage, initial concentration, contact time, and cadmium and lead adsorption. The models of Langmuir and Freundlich have been used to interpret isotherms of equilibrium for cadmium adsorption and lead to cross-linked and grafted beads. The adsorption thermodynamics of both metallic ions on grafted crosslinked beads were represented by quantities including standard Gibbs free energy change

4.1 Introduction

73

(Go ), standard enthalpy change (H o ) and standard entropy change (S o ), while the first-order and pseudo-second-order kinetic models were used to explain kinetic data for the grafted cross-linked beads. Desorption experiments were performed to obtain the cost effectiveness of grafted cross-linked beads.

4.2 Experimental 4.2.1 Materials The chitosan particles were acquired from LabChem with a relative molecular mass of 400 kDa and a degree of deacetylation of 74%. Aniline was procured from AEC AMERSHAM (PTY) LTD (99.5%, extra pure). Ammonium persulfate (>98%), ethanol (>99%), hydrochloric acid (99%), 1-Methyl-2-pyrrolidinone (>99%), sodium hydroxide (>99%), acetic acid (>99%), glutaraldehyde and ethylenediamine tetra-acetic acid (EDTA) were acquired from Sigma-Aldrich. Deionized water was generated by means of a purified water dispenser (Ultima 888 water distiller) and as used in all solutions formulation. The solution’s pH was calculated by means of a pH metre (Hanna HI 8421), procured from Sigma-Aldrich. For adsorption experiments, a shaker (Labcon incubator) was used, and a stirring velocity of 120 rpm was sustained. Spectrophotometer for atomic adsorption (Variant SpectrAA-10) was applied to verify the quantity of cadmium and lead ions adsorbed.

4.2.2 Preparation of Adsorbate The standard solution of Cd(II) and Pb(II) in distilled water was processed by sequentially breaking down the amount needed of cadmium chloride and Pb(NO3 )2 . The standard solution to preferred initial concentrations of 40, 80, 120, 180 and 220 mg/L was then dissolved in distilled water.

4.2.3 Adsorbent Preparation 4.2.3.1

Chitosan Beads Production

In 1 L of 3.0% (v/v) acetic acid solution, 75.3 g of chitosan granules were broken down. The chitosan prepared solution for the removal of toxic substance was sieved via a polystyrene membrane filter with mesh 100 µm. Development of chitosan gel beads arose when 1 M of sodium hydroxide solution interacted with the filtrate.

74

4 Investigation into the Adsorption of Cadmium and Lead …

The soaked chitosan beads were washed with deionized water numerous times and drained to eliminate all excess sodium hydroxide.

4.2.3.2

Preparation of Interlinked Chitosan Beads

Chitosan covalently linked with glutaraldehyde was determined by adding chitosan beads prepared in a glutaraldehyde solution of 0.5%. The dispersions were shattered properly, and the repeated manual shaking was made to balance for 24 h.

4.2.3.3

Grafting of the Interconnected Beads

The beads were grafted in the manner suggested by Igberase et al. [12]. In brief, 0.45 g/L of cross-linked chitosan beads and 0.1 g/L of aniline were moved into a round-bottom flask containing 200 mL of 0.4 g/L HCl and a magnetic stirrer was used to shake the content vigorously. After 30 min, 0.35 g of ammonium persulfate was added to the activated medium and this was taken as time zero. At 35 °C, grafting was permitted to occur for an hour. To extract every unused or passive polyaniline, the grafted cross-linked beads were cleaned off with N-methyl pyrrolidone (NMP). The grafted polymer was consequently cleaned with distilled water, and fully prepared for use.

4.3 Perle/Beads Classification Nearly 0.45 g of chitosan beads, cross-linked chitosan beads, and graft-crosslinked chitosan beads were measured concurrently, oven dried in an oven at 60 °C, and grinded to a crushed form. A Shimadzu FTIR, model 8300 (Kyoto, Japan) and Shimadzu XRD, version 7000 has been used to measure the grinded beads. The SEM study was performed by intersecting and covering the same collection of beads with gold. The covered beads were then analysed with a Jeol 733, superprobe.

4.4 Adsorption Investigation The adsorption investigation was done in 100 ml Erlenmeyer flasks at different solution pH, adsorbent dose, contact time, initial concentration and temperature. The impact of pH of the solution on Cd(II) and Pb(II) adsorption on CS, XCS and GXCS was explored by combining 0.45 g of the adsorbents in a 100 mL sample with an initial 40 mg/L concentration. The pH of the measurements was altered by 0.1 M HCl and 0.1 M NaOH to different pH values in the pH 2–8 range. The temperature and stirring velocity were simultaneously fixed at 25 °C and 120 rpm,

4.4 Adsorption Investigation

75

whereas the contents of the flask were rattled for 150 min. The influence of adsorbent dosage on metal ion adsorption was made possible through active stirring of the adsorbent in the range of 1.5–6.0 mg/L, in 100 mL sample, with an initial 40 mg/L concentration. Contact time influence was examined over a time range of 30–180 min while initial concentration influence was investigated upon at a concentration range of 40–220 mg/L. The adsorption isotherms were performed at 25–45 °C temperatures. Adsorption kinetics was conducted at a concentration range of 40–220 mg/L, with a time range of 30–150 min. The adsorption power of the equilibrium was determined from the equation of mass balance, as seen in (4.1). qe =

(Co − Ce ) ×V M

(4.1)

where qe (mg/g) is the adsorption capacity for the equilibrium, C o and C e are the initial and equilibrium concentration (mg/L) of metal ion in solution correspondingly, V (mL) is the volume and M (g) is the mass of the different adsorbent.

4.5 Determination of pHpzc GXCS ‘zero-charge point (pHpzc) was performed according to the technique illustrated by Ofomaja and Ho [15]’. 45 mL of identified concentration KNO3 mixture was transferred into a flask array. The solution’s initial pH (pHi ) values were modified by adding ether 0.1 M HCl or NaOH, from pH 2 to 8. For each flask, the maximum volume of solution was produced up to 50 mL by adding the same concentration of the KNO3 solution. The solution’s pHi was observed, and each flask was introduced with 0.45 g of GXCS. The suspensions were continuously shaking and were required to stabilize with occasional manual shaking for 48 h. The pH values were measured for the supernatant liquids. The variation was plotted against the pHi between the initial and final pH values (pH = pHf − pHi ). The equilibrium point of the resultant curve at which pH = 0 gave the pHpzc.

4.6 Desorption/Regeneration Investigation The grafted beads filled with Cd(II) and Pb(II) ions were rinsed with deionized water after adsorption, before being treated at a pH of 4 with 50 mL of 0.01–1.0 M HCl, EDTA and HNO3 eluent. The quantity of desorbed metal ions was estimated using an atomic adsorption spectrometer. The desorption percentage was calculated by (4.2). %Desorption =

Ce × 100 Co

(4.2)

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4 Investigation into the Adsorption of Cadmium and Lead …

where C e represents the final concentration of metal ions and C o is the initial concentration of metal ions in the mg/L. The GXCS was washed with deionized water after desorption and was recycled for the next adsorption cycle. The procedure conducted three phases of adsorption/desorption.

4.7 Theory of Evaluation of Data Adsorption isotherms are the necessary component for the development of an adsorption process; in order to maximize the layout of an adsorption system, it is necessary to create a connection suitable for the adsorption curve of equilibria; for the evaluation of adsorption parameters, a precise mathematical description of the equilibrium adsorption capacity is needed in any particular system.

4.7.1 Adsorption Isotherms Model The Langmuir and Freundlich models were used to assess the adsorption data of metallic ions onto adsorbent. The formula of Langmuir and Freundlich models is defined in 4.3 and 4.4, in their standard form. The Langmuir model is built on the assumption that each adsorption site is similar and intensely comparable and suggests that the adsorption takes place on the adsorbent at different uniform sites and is applied effectively in single-layer adsorption systems [16]. Ce 1 Ce = + qe Qm Qm b

(4.3)

where qe is the equilibrium metal adsorption amounts on the beads (mg/g), C e is the equilibrium concentration of solute in the bulk solution. Qm and b represent single-layer adsorption capacity and a constant related to the adsorption equilibrium constant. The parameters of Langmuir model can be calculated from the slope and intercept of the straight-line plot of C e /qe against C e . The empirical isotherm Freundlich is related to the relationship of equilibrium between heterogeneous surfaces. log qe = log K f +

1 log Ce n

(4.4)

in this formula, K f and n depict the adsorption potential and adsorption intensity accordingly and are dimensionless constant. Within standard adsorption conditions, n values will vary between 1 and 10 [17]. The variables of the Freundlich model can determine from the slope and intercept of the Log qe versus Log C e linear plot.

4.7 Theory of Evaluation of Data

77

4.7.2 Temperature and Thermodynamic Investigation Temperature is seen to influence adsorption efficiency among the process variables commonly researched in the literature. The procedure is termed endothermic when the adsorption potential increases with temperature, and the procedure is termed exothermic when adsorption reduces with temperature. The thermodynamic parameters reveal the important parameters for future engineering assessment of the overall adsorption of the adsorbates and hopefully also provide perspectives into the adsorption process used for more capacity expansions and enhancement [18]. The change in entropy and enthalpy, related to the phase, can be determined from 4.5. ln K = −

H o S o + RT R

(4.5)

The free energy change of the Gibbs, Go , is the essential predictability factor. Interactions happen quickly at a specific temperature if it is a negative quantity [15]. The free energy of the adsorption reaction is described by 4.6, assuming the adsorption equilibrium constant, K. G o = −RT ln K

(4.6)

Taking into account the relation between free energy change and constant equilibrium (K). In 4.7, the temperature change in K can be computed in the differential equation. d ln K =

H o RT 2

(4.7)

The integrated 4.7 form is seen in 4.8 upon integration. ln K = −

H o +Y RT

(4.8)

where Y remains unchanged. Equation 4.9 is derived through readjustment of 4.8 −RT ln k = H o − T RY

(4.9)

S o = RY

(4.10)

supposing,

The replacement of 4.6 and 4.10 by 4.9 G o = H o − T S o

(4.11)

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4 Investigation into the Adsorption of Cadmium and Lead …

the equilibrium constant ‘K’ as numerically described by Liu et al. [6] is provided in 4.12. where qe is the sum of copper ions adsorbed into the adsorbent in mg/g, and C e is the concentration at equilibrium in mg/L. The gas constant R is 8.3145 J/mol as described. T is the temperature of the solution in Kelvin. S o is the change in entropy while H o is the increase in enthalpy. The slope and intercept can be determined from the plot of the ln K as a function of 1/T. K =

qe Ce

(4.12)

4.7.3 Kinetic Models The kinetic model was used to examine the time course of adsorption of metal ion to the adsorbent. It is quite essential to ascertain how a descriptive assessment demonstrates the behaviour of metal ion absorption. The metal ion adsorption data on GXCS was defined in relation to Lagargren’s pseudo-first-order kinetic model [19] and the pseudo-second-order model that was presented by Ho and McKay [20]. The models are shown in 4.13 and 4.14. log(qe − qt ) = log(qe ) − t

K1 2.303

(4.13)

where qe and qt signify the proportion of copper ions absorbed at equilibrium and time t on the adsorbent (mg/g), correspondingly. The K 1 is the pseudo-first-order kinetics rate constant. The adsorption reaction rate value of K 1 can be assessed from the graph of the linear plot of log(qe − qt ) against t. where K 2 is the rate constant for a pseudo-second-order model and the definitions of qe and qt remain the same. t 1 1 = + t 2 qt K 2 qe qe

(4.14)

The slope and intercept of the straight-line plot t/qt versus t give the qe and K 2 values correspondingly.

4.7.4 Error Analysis Aside from the linear determination coefficient (R2 ), the chi-square test is a nonlinear way of explaining scientific data. The chi-square statistic is the sum of squares of the

4.7 Theory of Evaluation of Data

79

variations between the observational data and the data derived by evaluating models, separated by the equivalent data obtained by measuring from the models [15]. That is demonstrated in scientific equations in 4.15. χ2 =

 (qe(Exp) − qe(Cal) )2 qe(Cal)

(4.15)

while qe(Exp) (experimental qe ) is the quantity adsorbed in mg/g at equilibrium, and qe(Cal) (derived qe ) is the quantity determined from the kinetic model. When the model data are identical to the experimental data, it will be a smaller number and will be a larger number if they are inconsistent. Then the data collection for the nonlinear chi-square test must be examined to authenticate the best-fit kinetic model for adsorption process.

4.7.5 Regeneration/Desorption Metal retrieval from the adsorbent used is essential for complete recycling as well as for the adsorbent reusability. One of several key benefits of using chitosan as an adsorbent is the simplicity of retrieval of bound metal ions. The continuous use of the adsorbent helps in holding operation costs down, and for this purpose, the adsorbed metal ions must be desorbed, and the adsorbent regenerated for flexible and easier application. Nevertheless, it may not necessitate nonstop reuse due to the degradation qualities of chitosan [21]. The adsorption process requires the diffusion of metal ions which can give a direction for the layout of the desorption approach [22]. Because pH is a major determinant in metal absorption, a change in pH may ensure desorbing of the metal, it is essential to use the correct eluent for the desorption procedure to maintain the undiminished adsorption efficiency of the regenerated chitosan beads.

4.8 Results and Discussion 4.8.1 Solubility Test The solubility of chitosan and cross-linked chitosan was analysed in water after crosslinking in separate acid and base concentrations ranging from 0.1 to 10 M. It was been noticed that the cross-linked beads stayed insoluble, whereas the native chitosan was permeable in these solutions. This finding may be attributed to the reason that chitosan’s increased hydrophilic nature with the main amino group makes hydrogel production soluble in dilute acid solutions. The cross-linking interaction, however, improves its efficiency in an acidic media.

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4 Investigation into the Adsorption of Cadmium and Lead …

4.8.2 Outcome of pH Investigation It can be seen from Fig. 4.1, that the percentage of metal ion loss rises with increment in pH to a limit of pH 6 for Cd(II) and pH 5 for Pb(II) and subsequently decreases with more pH increase. At lower pH levels, hydrogen ions will penetrate the GXCS surface allowing decreased adsorption sites with metal ions to deal with. Raising the pH of the solutions contributes to a reduction in the rivalry of hydrogen ions with metal ions for adsorption sites, thereby allowing the elimination of higher proportion

Fig. 4.1 a Influence of pH on cadmium and lead elimination (conditions: 2.5 g/L GXCS; contact time: 120 min; temperature: 25 °C), b influence of point of zero charge

4.8 Results and Discussion

81

of heavy metals. At pH value beyond 6, insoluble cadmium hydroxide and lead hydroxide begin to precipitate from the solution, inducing a decline in the percentage reduction of metal ions. The influence of pH can also be described in terms of the pHPzc of adsorbent. The zero-charge point is the point at which the acidic or basic functional surface groups no longer participate to the solution’s pH value. The pHPzc was observed to be about 4.5. Under pH 4.5, the outer layer is charged positively, and metal ion linkage appears to be weak because of the electrostatic repulsion. Raising the pH beyond pHP zc, the GXCS layer becomes negatively charged, thus increasing the adsorption of metal ions.

4.8.3 Influence of Adsorbent Dose The observational study revealed that the level of extraction is significantly affected by a change in the number of adsorbents. Additionally, a significant rise in the percentage removal was confirmed for both metal ions, by increasing the dose from 1.5 to 4.5 g/L. This reported phenomenon could be based on the fact that adequate adsorption sites were able to facilitate cadmium and lead ion complexation. Raising the adsorbent dose above 4.5 g/L did not produce such a relevant changes in the removal efficiency, and this improvement could be attributed to the attachment of nearly all metal ions to GXCS and the balance between the adsorbent ions and those kept unadsorbed in the solution [23] (Fig. 4.2). 100

Removal, %

90 80 70 60

cadmium 50

lead

40 1

2

3

4

5

6

7

Adsorbent dossage (g/l) Fig. 4.2 Influence of adsorbent dosage on per cent removal of cadmium and lead by GXCS (conditions: initial ion conc: 40 mg/L; contact time: 120 min; solution pH: cadmium = 6.0, lead = 5.0; temperature: 25 °C)

82

4 Investigation into the Adsorption of Cadmium and Lead …

100

Removal, %

80

60

cadmium

40

lead 20 0

40

80

120

160

200

240

Initial concentration (mg/l) Fig. 4.3 Influence of initial concentration on percentage removal of cadmium and lead by GXCS (conditions: contact time: 120 min; solution pH: cadmium = 6.0, lead = 5.0; temperature: 25 °C; adsorbent dosage: 4.5 g/L)

4.8.4 Influence of Adsorbate Initial Concentration Figure 4.3 shows the impact of initial cadmium concentration and leads on percentage elimination. The percentage of the removal for cadmium reduces from 99.6 to 30% whereas that of lead dropped from 99.3 to 25% as the concentration rose from 40 to 220 mg/L. This pattern is popular and has been documented in previous research via a series of adsorption studies [24–26]. Subsequently, ample functional groups for cadmium and lead are accessible at decreased concentration level of metal ions. The fractional adsorption thus is independent of the actual concentration of ions. Comparison with the available adsorption sites, the quantity of cadmium and lead ions is really higher at an elevated concentration. The percentage of heavy metal ions taken away thus primarily depends on the initial ions concentration and reduces with a rise in initial ions concentration [13].

4.8.5 Influence of Contact Time The time it needs to accomplish stability by metal ions and adsorbent is of major significance in the experimental investigation as it focuses on the type of the method used. The impact of interaction duration by GXCS for cadmium and lead adsorption is shown in Fig. 4.4. The findings show that the quantity of cadmium and lead adsorbed on GXCS improves rapidly with contact time up to 60 min after which no additional

4.8 Results and Discussion

83

100

Removal, %

80

60

cadmium lead

40 0

30

60

90

120

150

180

Contact Ɵme (min) Fig. 4.4 Influence of contact time on percentage removal of cadmium and lead by GXCS (conditions: initial concentration: 40 mg/L; solution pH: cadmium = 6.0, lead = 5.0; temperature: 25 °C; adsorbent dosage: 4.5 g/L)

meaningful adsorption is noticed. Through this observation, it is clear that the time taken to achieve stability is a result of the initial ion concentration. Quantitatively it was determined that the interaction time to achieve stability was around 60 min. This finding is significant as compared to most adsorption studies published in the literature, and it required GXCS absorbent shorter duration to attain stability.

4.9 Outcome of Characterization 4.9.1 X-Ray Diffraction X-ray diffraction method was used to investigate the crystallinity of chitosan, crosslinked chitosan and polyaniline grafted cross-linked chitosan beads. Chitosan is a moderately crystallographic polysaccharide, but this crystallographic form of chitosan is mainly attributable to the aggregation of repeating units in the polymer matrix [27]. Consequently, this crystalline structure renders the intended heavy metals unavailable to some group [28]. In Fig. 4.5a–c, the strong 2θ = 20° reflection correlates to 110 chitosan planes. In this illustration, the strength of chitosan and cross-connected chitosan at approximately 2θ = 20° is 1100 and 1700 Angstrom units and, as predicted, polyaniline grafting on cross-lined at 2θ = 20° corresponds to 110 planes of chitosan [10]. On grafting polyaniline onto cross-linked chitosan, the intensity ratio decreased to about 580 Angstrom units, indicating a reduction

84

4 Investigation into the Adsorption of Cadmium and Lead …

Fig. 4.5 a, b and c X-ray diffraction outcome

4.9 Outcome of Characterization

85

in the crystallinity of GXCS. This observation is due to the fact that some of the crystalline chains have been eliminated in the process of grafting.

4.9.2 Outcome of SEM Morphology Investigation Scanning electron microscope (SEM) was utilized to analyse the surface morphology of the generated adsorbents. The SEM micrograph of chitosan beads, cross-linked chitosan beads and grafted cross-linked chitosan beads are shown in Fig. 4.6a–c. Because of the glutaraldehyde deposition, the layer of the cross-linked beads seemed smooth and without pores. The grafting of the interconnected beads changed the layers of the beads, the accumulation of polyaniline on the layer of the interconnected

Fig. 4.6 a, b and c SEM morphology investigation

86

4 Investigation into the Adsorption of Cadmium and Lead …

beads contributed in the layer unevenness, suggesting that polyaniline was chemically attached to the layers of the beads.

4.10 Outcome of Adsorption Investigation 4.10.1 Parameters of Isotherms Model To evaluate the correct isotherm for cadmium and lead to GXCS, the Langmuir and Freundlich model is utilized. From the slope and intercepts of C e /qe versus C e and log qe versus log C e plots, the constants of the two models were measured at various temperatures, and the values are presented in Table 4.1. The nearer R2 is to one the better the model fits. The Langmuir model was best represented by Langmuir model. Nevertheless, this model recognizes the presence of single-layer coverage on the GXCS adsorption site. Consequently, as the temperature rose from 25 to 45 °C, the overall adsorption potential (Qm ) of cadmium and lead onto GXCS seemed to rise. However, this model supports the presence of monolayer coverage on the adsorption site. This improvement in adsorption efficiency with temperature rise implies that the adsorption mechanism is of an endothermic type. The development certainly implies chemisorption which is the adsorption mechanism. Table 4.1 Langmuir and Freundlich isotherm requirements for Cd(II) and Pb(II) at varying temperatures into GXCS Mental ions

Isotherm model

Parameters

Cd(II)

Langmuir

Freundlich

Pb(II)

Langmuir

Freundlich

25 °C

35 °C

45 °C

Qm (mg/g)

98.40

115

145

b (L/mg)

0.022

0.05

0.07

R2

0.995

0.987

0.999

N

2.00

3.2

3.40

K F (mg/g)

2.30

3.88

4.56

R2

0.85

0.966

0.911

Qm (mg/g)

92.90

103.5

114

b (L/mg)

0.02

0.08

0.15

R2

0.999

0.986

0.993

N

1.00

1.74

2.32

K F (mg/g)

5.41

12.82

15.21

R2

0.885

0.926

0.942

4.10 Outcome of Adsorption Investigation

87

4.10.2 Outcome of Temperature and Thermodynamic Investigation Figure 4.8 displays the significant impact of temperature on the maximum adsorption capacity (Qm ) of Cd(II) and Pb(II) IONS on GXCS, and it was noted that a temperature rise from 25 to 45 °C enhanced the adsorption capacity from 98.4 to 145 mg/g for Cd(II) ions and from 92.9 to 114 mg/g for Pb(II) ions correspondingly. This increase in adsorption capacity with increase in temperature indicates the adsorption process is endothermic in nature. This trend strongly suggests that the adsorption process is chemisorption. ln K’s plot for Cd(II) and Pb(II) ions onto GXCS against 1/T is shown in Fig. 4.7. The parameter values for thermodynamic analyses are given in Table 4.2. The free energy change recorded at different temperatures during the adsorption process for 4

y = -7731.1x + 27.61 R² = 0.988

3.5

Cadmium

y = -6733.5x + 23.992 R² = 0.9998

3

Lead

Ln K

2.5 2 1.5 1 0.5 0 0.00305

0.00315

0.00325

0.00335

0.00345

1/T (K) Fig. 4.7 Thermodynamic plot of Ln K versus 1/T of Cd(II) and Pb(II) onto GXCS

Table 4.2 Thermodynamic parameters for the adsorption of Cd(II) and Pb(II) ions onto GXCS at an initial concentration of 40 mg/L Metal ion

Temperature (K)

Go (kJ/mol)

Cd(II)

298

−1.86

308

−5.53

Pb(II)

318

−6.90

298

−2.73

308

−6.22

318

−8.27

H o (kJ/mol)

S o (kJ/mol/K)

R2

+64.28

+0.28

0.998

+55.99

+0.20

0.999

88

4 Investigation into the Adsorption of Cadmium and Lead …

both metal ions was all negative and this means that the reaction is random and satisfactory. The positive value of H o suggests the adsorption system’s is endothermic in nature. The positive values of H o while adsorbing these metal ions GXCS confirm the elevated randomness at the solid–solution interface. This result coincides with the outcome provided by Liu et al. [29].

4.10.3 Outcome of Kinetic Investigation The results collected from the investigation performed were used to study the adsorption of cadmium kinetics and lead ion on GXCS. The kinetic data were designed using the pseudo-first-order and pseudo-second-order model. Previous studies have proven that the pseudo-second-order kinetic model makes the adsorption data better suited [2]. Table 4.3 displays the parameter values for the pseudo-first and second-order kinetic models, and it was found that the coefficient of correlation for the linear plot of t/qt against t from the pseudo-second-order rate law provided the best support for both metal ions in comparison with the coefficient of correlation of the pseudofirst-order kinetic model derived from the linear plot of log (qe − qt ) against t. The chi-square test (λ2 ) of data collection was introduced to further analyse the kinetic results. The values of 2 for the pseudo-first-order kinetic model and pseudo-secondorder kinetic model were indicated in Table 4.3 as being comparable. Consequently, the qe measured value by evaluating from the pseudo-first-order kinetic model and experimental values were significantly different. In the case of the second-order pseudo-model, the qe(Cal) values are very much in line with the experimental results. This implies that the adsorption of cadmium and lead ions to GXCS is a pseudosecond-order mechanism model, and this model is assumed that the rate limiting step could be chemical adsorption or chemisorption requiring valence forces via the exchange of electrons between adsorbents (metal ions) and adsorbents (GXCS) [12].

4.10.4 Outcome of Desorption/Regeneration Investigation Figure 4.8 depicts the influence of utilizing specific eluents such as HCl, HNO3 and EDTA to desorb used GXCS at a concentration range of 0.01–1.0 M and 3 h of desorption time. Optimum desorption of 98.94% of HCl, 95.32% of EDTA and 76.56% of HNO3 was achieved at a concentration of 0.5 M for cadmium ion packed GXCS and a total desorption of 97.5% of HCl, 92.4% of EDTA and 65% of HNO3 was recorded at the same concentration. This finding is important as it can assist to uncover the correct eluent and the concentration to be introduced to the used adsorbent in the desorption medium. Efforts were made to assess the reuse and regeneration of metal ions from its used adsorbent. Five phases of adsorption/desorption experiments were conducted, and it was noticed that the adsorption potential of GXCS for cadmium and lead ions

Pb(II)

Cd(II)

Metal ion

0.04

0.03

0.04

120

180

220

0.03

220

0.04

0.03

180

80

0.04

120

0.03

0.03

80

40

0.03

K 1 (min)

40

mg/L

First-order kinetic model

87.6

52.4

36.3

22.1

11.3

94.5

55.4

39.8

25.2

13.5

qe(Cal) (mg/g)

0.09

0.14

0.15

0.49

0.35

0.15

0.02

0.04

0.01

0.01

χ2

0.94

0.93

0.92

0.84

0.96

0.83

0.99

0.98

0.99

0.99

R2

90.45

55.12

38.70

25.42

83.22

98.45

60.33

42.76

28.26

15.54

qe(Exp) (mg/g) 18.30 31.10 45.77 64.56

3.23 × 10−2 2.84 × 10−2 1.75 × 10−2 10−4

15.67 28.45 42.10 60.64 95.11

3.8 × 10−2 3.2 × 10−2 3.3 × 10−2 1.5 × 10−2 10−3 9.0 ×

102

6.98 × 10−4

9.76 ×

qe(Cal) (mg/g)

K 2 (g/mg min)

Second-order kinetic model

Table 4.3 Kinetic variables for the binding of Cd(II) and Pb(II) ions onto GXCS at pH 5

0.99

0.99

0.99

1.00

0.99

0.99

0.99

0.99

0.99

0.99

R2

0.23

0.50

0.27

0.32

0.36

0.12

0.28

0.20

0.26

0.40

χ2

4.10 Outcome of Adsorption Investigation 89

90

4 Investigation into the Adsorption of Cadmium and Lead …

a

100

DesorpƟon %

80

60

40

Cd-HCl

20

Cd-EDTA Cd-HNO3

0 0

0.2

0.4

0.6

0.8

1

1.2

1

1.2

ConcentraƟon (M)

b

100

DesorpƟon %

80

60

40

Pb-HCl 20

Pb-EDTA Pb-HNO3

0 0

0.2

0.4

0.6

0.8

ConcentraƟon (M) Fig. 4.8 a Influence of eluent concentration on cadmium desorption, b influence of eluent concentration on cadmium desorption

appeared mostly consistent up to the fourth phase, with a 3% drop in bead mass in the fifth phase. This improvement could be attributed to the beads ‘cross-linking process with glutaraldehyde, which strengthens the beads’ mechanical and chemical performance in acid solution.

4.11 Conclusion

91

4.11 Conclusion The current investigation demonstrated that polyaniline grafted cross-linked chitosan bead is capable of removing cadmium and lead from polluted water and must be taken into consideration as a low-cost adsorbent. Consequently, the adsorption findings indicate that metal ion binding is a function of variables including pH, adsorbent dose, contact time, initial concentration and zero-charge point. The Langmuir model, as such, has proved to accurately interpret the adsorption isotherms for both metal ions. The Langmuir model, Qe , was noted to be 145 mg/g for cadmium ions and 114 mg/g for lead ions at 45 °C temperature and an optimum pH of 5. The assessment of thermodynamics confirms the random and endothermic nature of cadmium and lead onto GXCS. Kinetics of metal ions adsorption to GXCS was accurately explained by pseudo-second-order kinetic model. Research on desorption revealed that 0.5 M HCl can desorbed GXCS filled with cadmium and lead ions safely and correctly Five cycles of adsorption/desorption investigation were performed, and in the fourth cycle, the overall adsorption efficiency was hardly impaired. This development could contribute to minimizing the cost of the operation.

References 1. E. Igberase, A. Ofomaja, P.O. Osifo, Enhanced heavy metal ions adsorption by 4-aminobenzoic acid grafted on chitosan/epichlorohydrin composite: Kinetics, isotherms, thermodynamics and desorption studies. Int. J. Biol. Macromol. 123, 664–676 (2019) 2. E. Igberase, P. Osifo, A. Ofomaja, Adsorption of metal ions by microwave assisted grafting of cross-linked chitosan beads. Equilibrium, isotherm, thermodynamic and desorption studies. Appl. Organomet. Chem. (2017) 3. E. Igberase, P.O. Osifo, A comparison study of the adsorption of metal ions by chitosan derivatives in aqueous solution (2020) 4. E. Igberase, P. Osifo, A. Ofomaja, Mathematical modelling of Pb2+ , Cu2+ , Ni2+ , Zn2+ , Cr6+ and Cd2+ ions adsorption from a synthetic acid mine drainage onto chitosan derivative in a packed bed column. Environ. Technol. (United Kingdom) (2017) 5. M. Madhava Rao, A. Ramesh, G. Purna Chandra Rao, K. Seshaiah, Removal of copper and cadmium from the aqueous solutions by activated carbon derived from Ceiba pentandra hulls. J. Hazard. Mater. 129(1–3) (2006), pp. 123–129 6. J. Liu, Y. Chen, T. Han, M. Cheng, W. Zhang, J. Long, X. Fu, A biomimetic SiO2 @chitosan composite as highly-efficient adsorbent for removing heavy metal ions in drinking water. Chemosphere 214, 738–742 (2019) 7. M.O. Omorogie, J.O. Babalola, E.I. Unuabonah, W. Song, J.R. Gong, Efficient chromium abstraction from aqueous solution using a low-cost biosorbent: Nauclea diderrichii seed biomass waste. J. Saudi Chem. Soc. 20(1), 49–57 (2016) 8. E. Igberase, P.O. Osifo, Application of diethylenetriamine grafted on glyoxal cross-linked chitosan composite for the effective removal of metal ions in batch system. Int. J. Biol. Macromol. 134, 1145–1155 (2019) 9. E. Igberase, P.O. Osifo, Mathematical modelling and simulation of packed bed column for the efficient adsorption of Cu(II) ions using modified bio-polymeric material. J. Environ. Chem. Eng. Ii (2019), p. 103129 10. L. Li, J. Iqbal, Y. Zhu, P. Zhang, W. Chen, A. Bhatnagar, Y. Du, Ag-hydroxyapatite nanocomposite beads as a potential adsorbent for the efficient removal of toxic aquatic pollutants. Int. J. Biol. Macromol. 120, 1752–1759 (2018)

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4 Investigation into the Adsorption of Cadmium and Lead …

11. I. Ali, M. Asim, T.A. Khan, Low cost adsorbents for the removal of organic pollutants from wastewater. J. Environ. Manage. 113, 170–183 (2012) 12. E. Igberase, P. Osifo, A. Ofomaja, The adsorption of copper (II) ions by polyaniline graft chitosan beads from aqueous solution: Equilibrium, kinetic and desorption studies. J. Environ. Chem. Eng. 2(1), 362–369 (2014) 13. Y. Lu, J. He, G. Luo, An improved synthesis of chitosan bead for Pb(II) adsorption. Chem. Eng. J. 226, 271–278 (2013) 14. P.O. Osifo, A. Webster, H. van der Merwe, H.W.J.P. Neomagus, M.A. van der Gun, D.M. Grant, The influence of the degree of cross-linking on the adsorption properties of chitosan beads. Bioresour. Technol. 99(15), 7377–7382 (2008) 15. Y.S. Ho, A.E. Ofomaja, Kinetics and thermodynamics of lead ion sorption on palm kernel fibre from aqueous solution. Process Biochem. 40(11), 3455–3461 (2005) 16. E.S. Dragan, M.V. Dinu, Advances in porous chitosan-based composite hydrogels : synthesis and applications. React. Funct. Polym. 146 (2020), p. 104372 17. X. Luo, Z. Zhang, P. Zhou, Y. Liu, G. Ma, Z. Lei, Synergic adsorption of acid blue 80 and heavy metal ions (Cu2+ /Ni2+ ) onto activated carbon and its mechanisms. J. Ind. Eng. Chem. 27, 164–174 (2015) 18. C.M. Futalan, C.C. Kan, M.L. Dalida, K.J. Hsien, C. Pascua, M.W. Wan, Comparative and competitive adsorption of copper, lead, and nickel using chitosan immobilized on bentonite. Carbohydr. Polym. 83(2), 528–536 (2011) 19. L. Zhang, Y. Zeng, Z. Cheng, Removal of heavy metal ions using chitosan and modified chitosan: a review. J. Mol. Liq. 214, 175–191 (2016) 20. Y.S. Ho, G. McKay, Application of kinetic models to the sorption of copper(II) on to peat. Adsorpt. Sci. Technol. 20(8), 797–815 (2002) 21. P.O. Osifo, The use of chitosan beads for the adsorption and regeneration of heavy metals (2007), p. 156 22. E. Igberase, P. Osifo, A. Ofomaja, Mathematical modelling of Pb2+ , Cu2+ , Ni2+ , Zn2+ , Cr6+ and Cd2+ ions adsorption from a synthetic acid mine drainage onto chitosan derivative in a packed bed column. Environ. Technol. (United Kingdom) 39(24), 3203–3220 (2018) 23. M. Doˇgan, Y. Turhan, M. Alkan, H. Namli, P. Turan, Ö.¨ Demirba¸s Functionalized sepiolite for heavy metal ions adsorption. Desalination 230(1–3) (2008), pp. 248–268 24. E. Igberase, A. Ofomaja, P.O. Osifo, Enhanced heavy metal ions adsorption by 4-aminobenzoic acid grafted on chitosan/epichlorohydrin composite: Kinetics, isotherms, thermodynamics and desorption studies. Int. J. Biol. Macromol. 123(November), 664–676 (2019) 25. R. Bassi, S.O. Prasher, B.K. Simpson, Removal of selected metal ions from aqueous solutions using chitosan flakes. Sep. Sci. Technol. 35(4), 547–560 (2000) 26. K. Kurita, H. Akao, J. Yang, M. Shimojoh, Nonnatural branched polysaccharides: synthesis and properties of chitin and chitosan having disaccharide maltose branches. Biomacromol 4(5), 1264–1268 (2003) 27. Y. Cheng Lin, H. peng Wang, F. Gohar, M.H. Ullah, X. Zhang, D. fang Xie, H. Fang, J. Huang, J. xing Yang, Preparation and copper ions adsorption properties of thiosemicarbazide chitosan from squid pens. Int. J. Biol. Macromol. 95 (2017), pp. 476–483 28. S.A. Xaba, E. Igberase, J. Osayi, T. Seodigeng, P.O. Osifo, Optimization of primary sewage sludge and coal lignite by microwave-assisted pyrolysis for the production of bio-oil. Environ. Technol. 0 (2020), pp. 1–15 29. C. Ling, F. Liu, C. Long, T. Chen, Q. Wu, A. Li, Synergic removal and sequential recovery of acid black 1 and copper (II) with hyper-crosslinked resin and inside mechanisms. Chem. Eng. J. 236, 323–331 (2014)

Chapter 5

Biopolymer Chitosan Membranes Prepared from Fishery Waste for the Removal of Zinc Ions from Aqueous Systems by Adsorption

Abstract Chitosan was derived from the Cape rock crab outer shell, as seen in the areas of Cape Town, South Africa, and was exploited in the manufacture chitosan particles employed in the development of porous polymer chitosan membranes through a step reversal procedure. The chitosan membrane was crosslinked with 2.5% glutaraldehyde; chitosan membrane (CS) and cross-linked chitosan membrane (XCS) were characterize by FTIR, XRD, SEM-EDX and TGA. Equilibrium findings showed that the Langmuir equilibrium model can be appropriately applied in explaining zinc adsorption on XCS and the maximum adsorption potential for temperatures between 303 and 313 K was 2.64 mmol g−1 . The adsorption operation was discovered to be endothermic, with 20 kJ mol−1 adsorption enthalpy. Flux via XCS is a mechanical mechanism with a decline in the adsorption rate (1.91– 1.30 mmol g−1 ) as the flux rises (2–55 L m−2 hr−1 ). XCS adsorption of metal ions has also been noticed to be impacted by co-ions, where the influence of nitrates has been considered to restrict adsorption, whereas sulphates have been proven to raise adsorption. The regeneration of the adsorbed zinc ions was accomplished employing sulphuric acid and hydrochloric acid solutions as eluants. The former was considered to be a more powerful eluant. As a result, a sulphuric acid solution with a pH of 2 can retrieve up to 90% of the adsorbed zinc. Consequently, upon recovery, the adsorption capacity was observed to be lowered. Upon regeneration, this decline in adsorption efficiency may be due to membrane mass loss of approximately 11%. The functional stability of the membrane was compromised following two regeneration periods, and the membranes were no longer functional.

5.1 Introduction Separated from aquatic life, polymeric composite materials are relatively economical and ecologically convenient solid adsorbents that show significant affinity against metal ions. Numerous authors have documented findings in which chitosan biopolymers bind with metal ions to produce chitosan–metal complexes, usually to extract heavy metals from polluted waters [1–3]. Polysaccharide biopolymers, derived from aquatic organisms, are potentially inexpensive and environmentally sustainable © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 E. Igberase et al., Enhanced Chitosan Material for Water Treatment, Engineering Materials, https://doi.org/10.1007/978-3-030-71722-3_5

93

94

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

stable adsorbents that reveal a wide explicitly, chitosan has shown a good compatibility for aluminium metal ions [4], cadmium [1], chromium [5], copper [6], iron [7], mercury [8]. The next quite common, readily available polymer besides cellulose, is chitosan extracted from chitin. Chitin comprises of amino glucose with a normal dispersion of acetyl groups and is found in arthropods, crustaceans and insect exoskeletons. While chitin can be obtained from mushrooms and algae, it is only produced commercially from crustaceans, i.e. crabs, lobsters, prawns and shrimp shell waste. The processing of chitin at such a heated level of high basic solution such as sodium hydroxide and potassium hydroxide is used to manufacture chitosan by the process known as chitin deacetylation. The utility of chitosan polymers resides in its potential to turn into particles or gel form which could be transformed onto various shapes to be used in a wide range of end-user applications. Chitosan gel beads have been extensively documented for use in water purification [8–10], though gel-type materials may not be researched regularly, probably, owing to insufficient data concerning its design and use. The performance of the chitosan membranes in terms of flux and adsorption capability relies on the production process in the areas of water processing [3]. In past findings, the surface characteristics of chitosan membranes in relation to metal ion removal from aqueous solution were investigated [3]. The adsorption properties of crosslinked chitosan membranes were explored in this research, while further focusing on adsorption to Zn(II). To offer additional perspective through their use of chitosan geltype biopolymer membranes to water management processes, both the adsorption stability and the kinetics of adsorption and desorption were studied.

5.2 Materials and Methods 5.2.1 Materials Chitosan particles are extracted from seashell shrimp which were acquired in Cape Town, South Africa’s natural environment. The extent of deacetylation was estimated to be 80 mol per cent, and molecular weight was determined to be 144 kg/mol using size exclusion chromatography (SEC). The formulation and corresponding evaluation of chitosan particles were carried out as originally proposed by Osifo et al. [11]. Glutaraldehyde was obtained from Sigma-Aldrich (about 99.5%). Hydrochloric acid (about 99%), acetic acid (about 99%), sodium hydroxide (about 99%) have all been procured via Sigma-Aldrich. The solution’s pH was regulated with a pH metre (Hanna HI 8421) and was acquired from Sigma-Aldrich. Ultima 888 water distiller was applied in the school laboratory for the production of pure water. A shaker (Labcon incubator) was employed for the sample adsorption investigation.

5.2 Materials and Methods

95

5.2.2 Preparation of Membrane The membranes were developed utilizing a phase separation approach as Osifo et al. [3]. Most experts [10, 12, 13] also used this method to make chitosan beads. Chitosan formulations were made with a concentration of 7 wt% by breaking down the chitosan particles in an acetic acid solution (4 wt% in distilled water). The formulation of the gelatinous chitosan was placed into a mould on a smooth plane (glass plate). The mould and chitosan formulation were properly poured in a 5 wt% minimum aqueous sodium hydroxide solution (97% high purity, supplied by Saarchem Ltd.) at a constant temperature of 25 °C for 15 min. The produced membranes were rinsed after production using running distilled water ( 6 at such concentration levels of Zn(II). Therefore, this drop in the concentration of Zn(II) above a pH of 6 may be attributed to zinc(II) hydroxide precipitation from solution. Consequently, it was established that the adsorption investigations had to be conducted at a pH of 6 or lower for high concentrations of Zn(II), instead the reduction in concentration of Zn(II)-ion would be a consequence of adsorption by the chitosan membranes and precipitation The pH of the Zn(II) input mixture was however regulated in this investigation at a pH of 5–6 utilizing dilute sulphuric acid (98% purity provided by Saarchem Ltd.) and dilute sodium hydroxide (97% purity provided by Saarchem Ltd.) and a Jenway 3310 pH metre.

98

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

5.3 Results and Discussion 5.3.1 Characterization Result 5.3.1.1

Outcome of FTIR Analysis

FTIR spectroscopy was used to classify the important control groups and to determine if glutaraldehyde was properly attached to the chitosan membrane. Figure 5.1 illustrates the diagram; in this graph the wavelength absorption band 3357 and 3322 cm−1 for CS and XCS suggests the existence of alcohol and amine exchangeable protons [1]. However, during molecular cross-linking cycle, the small shift in the band may be attributed to replaceable protons. For CS and XCS, the alkenyl C–H stretch at a wavelength of 2921 and 2922 cm−1 implies the displacements of CH2 and CH3 , accordingly [17]. The sharp peaks for CS and XCS at 1561 and 1602 cm−1 define that of aromatic C=C bending vibrations, accordingly. The peak for CS at 1427 cm−1 and for XCS at 1375 cm−1 reflects bending vibrations of CH2 and CH3 , correspondingly. In CS and XCS, a sharp peak of 1000 cm−1 was recorded which demonstrates stretching vibration of C–O. C–H bending vibration was observed at 879 cm−1 for CS, and 774 cm−1 for XCS. New peaks at wavelength of 1211 cm−1 support glutaraldehyde cross-linking onto CS. The peak for CS at 1427 cm−1 and for XCS at 1375 cm−1

XCS CS 1211

% Transmittance / a.u

774

1375 1272 1000

2922

3322

1602

879

2921 3357

1561 1000 1427

500

1000

1500

2000

2500

3000

3500 -1

Wavelength (cm ) Fig. 5.1 FTIR of CS and XCS, respectively

4000

4500

5.3 Results and Discussion

99

Intensity (a.u)

(a) 2000

XCS CS

1500 1000 500 0 0

20

40

60

80

100

800

1000

2 Theta (deg) Weight (a.u)

(b)

120 100

XCS CS

80 60 40 0

200

400

600 0

Temperature( C) Fig. 5.2 a and b. a XRD of CS and XCS, b TGA of CS and XCS

reflects bending vibrations of CH2 and CH3 , correspondingly. In CS and XCS, a strong peak of 1000 cm−1 was detected which signifies asymmetric stretching of C–O. C–H bending vibration can be observed at 879 cm−1 for CS and 774 cm−1 for XCS. New peaks at wavelength of 1211 cm−1 support glutaraldehyde cross-linking onto CS.

5.3.1.2

Outcome of XRD

Figure 5.2a illustrates the CS and XCS diffraction behaviours. A specific trait of 2θ = 20° corresponding to 110 chitosan planes was identified for both membranes since chitosan can be changed and some of its characteristics can still be preserved [18]. In the case of XCS, nevertheless, the intensity was elevated owing to a chemical cross-linking reaction which gave indications that glutaraldehyde was chemically attached to CS.

5.3.1.3

TGA Analysis

With TGA, the heat characteristics of CS and XCS were assessed after heat is added. To research the heat stability of the membranes, a plot of mass against temperature was made. Figure 5.2b displays the essential steps in CS and XCS thermal decomposition. The degradation of CS proceeded in three steps, whereas in the first step there was a loss of weight of 10% around 40–157 °C temperatures which correlates to

100

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

water loss [19]. The second step began with a weight loss of 38% at 200 up to 350 °C. This weight loss is due to the degradation of the saccharide chains, depolymerisation and decomposition of the adsorbent acetylated and deacetylated units [20]. In the third step, weight loss above 400 °C was 54%. The disintegration of non-cross-linked chitosan membrane is observed in this step. When glutaraldehyde was cross-linked with chitosan membrane, a weight loss of 5% was noted at the first step of breakdown and at temperatures around 34–141 °C. The second step began at 227 °C and proceeded with a weight loss of 31% up to 330 °C. There was a weight loss of 15% over 500 °C in the third step. This weight loss in the first, second and third steps relates to the removal of surface water, the depolymerisation and the decomposition of the acetylated and deacetylated adsorbent groups and the decomposing of the cross-linked chitosan membrane [21, 22].

5.3.1.4

Outcome of SEM Analysis

CS and XCS morphology were examined employing electron microscope (SEM) scanning. Sem scans with 50× magnification following EDX findings are shown in Fig. 5.3a, b; glutaraldehyde cross-linking on the layer of the chitosan membrane contributes to a smoothness of the layer suggesting that glutaraldehyde is strongly attached to the layer of the membrane. The EDX finding indicated several important elements in the membranes, and the elements found in CS (N, C, H and O) were also available in XCS only that the percentage mass of N was decreased following cross-linking, and this may well be predicted because some of the chitosan amine group is used in the cross-linking interaction. Consequently, owing to glutaraldehyde cross-linking to chitosan, XCS has been confirmed to generate enough of C, O and H. The graphical illustration of the method of cross-linking is shown in Fig. 5.4, In this illustration, glutaraldehyde binds selectively to nitrogen and allows covalent links across chains.

5.3.1.5

The Influence of pHPZC

The influence of pH can be explained in view of the adsorbent pHPZC . CS ‘pHpzc was noted to be 4.62, whereas XCS’s was determined to be 4.93, accordingly. The rise in pHpzc from 4.62 for CS to 4.93 for XCS can be attributed to a reduction in acidic groups owing to glutaraldehyde interaction and amide-forming acid groups that lower total acidity. PHPZC is the pH solution where the maximum adsorbent surface charge measured is zero [16]. If an adsorbent is put in a solution with pH < pHpzc of the adsorbent, certain functional groups are protonated and the adsorbent behaves as a positive charged poly-matrix [23]. The negatively charged ions available in the solution are attracted by this. Metal ions, nevertheless, are generally charged positively except the oxyanions of other metals such as arsenate and chromate, which are charged negative. At this point, those negative ions are attracted by the adsorbent.

5.3 Results and Discussion

101

50 45

Sum of H

40 Sum of C

Weight (%)

35

Sum of N

30 25

Sum of O

20 15 10 5 0

Elements

60

Weight (%)

50

Sum of H

40

Sum of C

30

Sum of N Sum of O

20 10 0

Elements

Fig. 5.3 a and b SEM/EDX of CS and XCS, respectively OH

HO

HO

NH2

CHITOSAN

OH

OH

O

HO

O

O

O

O

OH

HO NH2

NH2

HO

HO

N

OH

OH

O

HO

O

O

O

O

HO

NH2

CH

OH N CH

(CH 2 ) 3

(CH 2 ) 3

CH

CH N

OH

O

HO HO OH

HO

N O

O NH2

c

O (CH 2 ) 3

GLUTARALDEHYDE

CROSSLINKING REACTION OH

o H

O

HO

O OH

OH

Fig. 5.4 Schematic depiction of the chitosan cross-linking process

C

H

102

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

A rise in pH beyond this level will deprotonate the functional groups on the adsorbent and act as negative. Consequently, the adsorbent surface is charged negatively at pH > pHPZC , positively charged at pH < pHPZC and neutrally at pH = pHPZC . The CS and XCS pHPZC was lower than the solution pH which supported adsorption as the surface is charged negatively.

5.4 Adsorption Capacity Figure 5.5a displays the effects of chitosan membrane and zinc ion equilibrium adsorption investigations at a pH of 5 and changing temperatures (between 293 K and 313 K, with 5 K intervals). The pH of the permeate was observed to be moderately larger than the input solution (a mean rise of 0.2 was noted). The shape of the

(b)

(a) 2.0

6 5

Ce/q (g/L)

qe(mmol/g)

1.6 1.2 0.8

293K 298K 303K 308K 313K

0.4 0.0 0

2

4

6

3 293K 298K 303K 308K 313K

2 1 0

8

Ce (mmol/L)

(c) 0.4

4

0

1

2

3

4 5 Ce (mmol/L)

6

7

8

(d) -3.9

0.2 -4.0

-1

ΔΗ= 20kJ.mol

-4.1

-0.2 -0.4

293K 298K 303K 308K 313K

-0.6 -0.8 -1.0

ln (b)

log (qe)

0.0

-4.2 -4.3 -4.4 -4.5

-1.0

-0.5

0.0

log(Ce)

0.5

1.0

0.0032

0.0033 -1

0.0034 -1

T (K )

Fig. 5.5 a, b, c, and d: a quantitatively determined Zn(II) equilibrium adsorption isotherms on chitosan membranes at various temperatures and at a pH of 5, the set of data is the mean triplicate experimental value. b Simple fits by linear forms of Langmuir isotherm adsorption model (5.3). c The Freundlich isotherm model of adsorption (5.5). d Van’t Hoff Zn plot of Zn(II) adsorption onto chitosan gel polymer membranes at a pH = 5 and at different temperature

5.4 Adsorption Capacity

103

adsorption isotherms (Fig. 5.5a) indicates a fast initial rise in adsorption potential, owing to chitosan’s great selectivity for the Zn(II)-cations. The isotherm adsorption models, Langmuir and Freundlich, were utilized to design Zn(II) adsorption onto the chitosan membranes. The Langmuir model is the model that is widely utilized explaining the adsorption of metal ions on chitosan [2, 16, 24]. The Langmuir model suggests equal adsorption energies on the layer and no sorbent transmigration on the top layer level. This model is true for single-layer sorption on a layer consisting a limited number of sites [2] and is defined by the linearization form: Ce 1 Ce = + qe Qm Qm b

(5.3)

In (5.3), qe and Qm are the equilibrium and maximum monolayer adsorption potential accordingly, and C e is the equilibrium concentration of metal ion in mmol L−1 , b is the criterion of affinity in L mmol−1 . The regression plot of C e /qe versus concentration at equilibrium, C e , could be used to evaluate criterion b of affinity and optimum adsorbent power, Qm . The essential features of the Langmuir model can be interpreted in terms of a non-dimensional factor identified as the separation factor (RL ) applied only to assess whether or not an adsorption mechanism is desirable [2], as indicated in 5.4. The conditions of RL > 1, RL = 1 and RL between 0 and 1 signify unfavourable, linear and favourable correspondingly [19]. RL =

1 1 + bCo

(5.4)

The Freundlich model is the next most commonly utilized isotherm model and reflects a semi-analytical correlation between the concentration of adsorbents and the concentration of adsorbents [7]. The Freundlich model’s linearized form is calculated by using (5.5), for the determination of adsorption efficiency and adsorption rate. The value of parameter n is in the range of 1–10 under standard adsorption requirements [19]. log qe = log K F +

1 log Ce n

(5.5)

where K F and n (non-dimensional coefficients) separately indicate the adsorption power and the adsorption strength [19]. The tests of the Langmuir and Freundlich models linearized plots using (5.3) and (5.5) are shown in Fig. 5.5b, c accordingly, and the criteria for the model are presented in Table 5.1. From the R2 -values of 0.966–0.985 for predictable fitting to the Langmuir model (Fig. 5.2a), and the R2 -values of 0.774–0.911 for predictable fitting to the Freundlich model (Fig. 5.2b), it was established that the Langmuir model offered the more precise explanation of performance.

104

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

Table 5.1 Langmuir and Freundlich model constants for Zn(II) adsorption onto chitosan gel polymer membranes at a pH = 5 and at varying temperature Temperature (K)

Langmuir

Freundlich

Qm (mmol Zn g−1 chitosan)

b (L mmol−1 )

R2

KF

N

R2

293

1.171

1.344

0.98

0.704

2.352

0.91

298

1.793

1.163

0.97

0.789

1.941

0.77

303

2.552

1.343

0.93

0.897

2.013

0.89

308

2.561

1.452

0.98

0.963

2.363

0.92

313

2.642

1.354

0.99

0.962

2.064

0.90

The Langmuir equilibrium parameters assessed as shown in Table 5.1 from Fig. 5.5b indicated that the maximum adsorption capacity (Qm ) rises with temperature to a value of 2.55 mmol g−1 . This temperature rise probably be attributed to the detail that chitosan membranes are gel form membranes where the amount of free water plays an important role [25]. A rise in temperature results in membrane swelling and hence a rise in the amount of free water [25], which may make the adsorption sites more available and contribute to a higher adsorption capacity. But this impact is only apparent at temperatures under 303 K, while the adsorption power stays fairly stable at temperatures beyond 303 K. The values for RL calculated from (5.4) were 0.09, 0.10, 0.09, 0.09, 0.09, 0.09, 0.09 and 0.09, respectively, for zinc adsorption on XCS at a concentration of 7.65 mmol/L and at a temperature of 293, 298, 303, 308 and 313 K, and those values suggest desirable isotherms. The adsorption potential as calculated in this report is greater than that recorded for chitosan beads by Becker et al. [26], and for chitosan flakes by Bassi et al. [27]. For related system requirements, adsorption capacities of less than 1.53 mmol g−1 have been documented in each of the above-listed research. Ho and McKay [28] recorded a chitosan powder adsorption potential of 2.5 mmol g−1 , with a Langmuir affinity parameter of 0.46–0.85 L mmol−1 , even though solution pH had not been documented. Osifo et al. [29] calculated a maximum adsorption potential of 1065 mmol g−1 , at a pH of 5, utilizing chitosan beads produced from the same raw material as that employed in this research. A distinction between the chitosan beads and the membranes indicates that the adsorption ability of membranes may be beneficial over beads. Forced interaction between water and chitosan in the membrane (due to natural convection flow of water via the membrane) not just improves the distribution level but may also enhances interaction between the metal ion and the functional groups of chitosan, leading to a rise in adsorption potential. The influence of temperature in the Langmuir model on the affinity parameter b can be defined by employing the Van’t Hoff equation as shown in 5.6:   Hads b = bo · exp − R·T

(5.6)

5.4 Adsorption Capacity

105

where bo and b are the parameters of affinity at temperature T 0 and T accordingly, R is the standard gas constant (83,144 J/mol K), T is the temperature in K and H ads is the J mol−1 adsorption enthalpy. And the linear type of the Van’t Hoff equation (5.7) was considered to evaluate the adsorption enthalpy: ln(b) = ln(bo ) −

Hads R·T

(5.7)

Consequently, referring to the regression analysis predictions as shown in Fig. 5.3, the enthalpy of Zn(II) adsorption on the cross-lined chitosan membranes was observed to be 20 kJ mol−1 . The adsorption enthalpy measured indicates endothermic adsorption, i.e. a rise in temperature supports Zn(II) adsorption, as confirmed by the results shown in Table 5.1. Lima and Airoldi [30] and Ho and McKay [28] reported negative values (−27.7 kJ mol−1 in beads and −17.7 kJ mol−1 in powder) for chitosan adsorption enthalpy in Zn(II). Many adsorption operations are exothermic [1, 28], although for the adsorption copper and mercury, Ho and McKay [28] reported positive adsorption enthalpies for chitosan powder. This phenomenon may also probably be due to the effect of temperature on the chitosan’s free volume of water, as stated with the rise in adsorption capability with temperature rise. The essence of adsorption may also be interpreted as physical adsorption from the adsorption enthalpy value (20 kJ mol−1 ) of Zn(II) onto the chitosan membrane. If a solute, like metal ions, is adsorbed into an adsorbent material like chitosan, the adsorption process may rely on the forms of contact (reaction) that exist between the solute and the adsorbent; for most cases, the degree of energy that exists is needed to identify the form of adsorption wherein the process of adsorption can be either chemical (i.e. covalent bond is the relationship between the solute and adsorbent) or physical (van der Waals forces are the relationship) in essence; the quantity of energy used in the adsorption has been recorded for both cases. In the case of physical adsorption (those concerning Van der Waals), the enthalpy range was 20–100 kJ mol−1 and the enthalpy range for chemical adsorption (those concerning covalent bonding) is 200–500 kJ mol−1 and is mainly an exothermic reaction [29]. One of the most important considerations for the adsorption operation is the quality of the bond between the adsorbate and the adsorbent [28]. A tight bond between adsorbent and adsorbent improves adsorption efficiency which causes the adsorbent to be quite challenging to desorb. Chitosan membrane performance is validated with other chitosan materials and also with other adsorbents in Table 5.2 (only the optimum value presented in the literature are given). From this relation (Table 5.2), cross-linked chitosan membranes have a high capacity for adsorption relative to several other forms of chitosan and other adsorbents.

106

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

Table 5.2 Chitosan membrane adsorption compared to the highest adsorption capacities on other adsorbent materials for zinc

Material

Adsorption capacity (mmol g−1 )

References

Cross-linked chitosan membranes

2.64

This study

Chitosan powder

2.51

[28]

Chitosan flakes

1.27

[27]

Chitosan beads

1.06

[38]

Chitin

0.27

[39]

Activated sludge

0.38

[31]

Lignin

1.45

[32]

Activated carbon (GAC-C)

0.28

[32]

Peat moss

0.20

[32]

Bentonite

0.81

[32]

5.5 Kinetic Studies Predicting the rate of binding for a specified process is one of the most essential aspects in the configuration of the adsorption process with residence time for metal ions and the reactor and reactor regulated by the kinetics of the process [1, 14]. Accordingly, the adsorption rate was explored using transient curves. A Zn(II) solution was required to percolate via the membrane, and the waste water concentration of Zn(II) was evaluated as function of time. Breakthrough investigations with specific zinc concentrations, membrane sizes and trans-membrane pressures were performed.

5.6 The Effect of Flux on Adsorption These investigations were performed under unsteady environmental conditions, with the solution circulating only once through the membrane. It was conducted to evaluate the impacts of increased flux ratios on adsorption efficiency. Consequently, the impact of flux on chitosan membrane adsorption of Zn (II) is seen in Fig. 5.4. Since the flux relies on the trans-membrane pressure, this was varied until the particular flux was obtained, and the adsorption was then calculated at this particular flux. It is apparent from Fig. 5.4 that the mass of Zn(II) reduces with a flux rise. This is triggered by the decrease in adsorption time. So, the system is kinetic; hence the higher the flux, the lower the adsorption. So, it can be stated that internal distribution tends to play a function in adsorption kinetics. A linear correlation between the adsorbed Zn(II) and the trans-membrane flux was observed to occur from ranges of fluxes reported, as shown in Fig. 5.4. Also, it is important to note that when one extrapolates to 0 flux, therefore, the capacity is

5.6 The Effect of Flux on Adsorption

107

Table 5.3 Equivalent membrane volumes at which breakthrough occurs (pH = 5 and temperature = 298 K) and the permeate concentration Metal concentration (mmol L−1 )

Breakthrough equivalent membrane volumes

C t (mmol L−1 )

0.762

43

0.081

1.533

22

0.142

7.651

5

0.152

1.82 mmol g−1 , which correlates to the significance in Table 5.3, but the regression interaction also does not seem to hold when the flux reaches 0, which means that at that point one could attain the empirical maximum capacity of adsorption.

5.7 Breakthrough Studies Figure 5.5a shows the observational breakthrough curves for Zn(II) feed solutions which contain 0.76, 1.53 and 7.65 mmol L−1 Zn(II) at an applied trans-membrane pressure change of 100 kPa and a pH of 5. The dimensionless concentration (C t /C in ) is indicated in this figure as a result of the amount of comparable membrane volumes required to percolate via the membrane. C in and C t is the feed and permeate concentration of Zn(II), respectively (Fig. 5.6). 2.5

q(mmol.g-1)

2

1.5

y = -0.0114x + 1.8196 R² = 0.959

1

0.5

0

0

10

20

30

40

50

60

Jv (L.m-2.hr-1) Fig. 5.6 Relationship between Zn(II) adsorption and membrane flux [non-equilibrium, pH = 6, temperature = 298 K, and 0.75 mmol L−1 Zn(II)]

108

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste … 1.0 0.9 0.8 0.7

Ct/Cin

0.6 0.5 0.4

7.65 mmol/L Zn

0.3

0.79 mmol/L Cu

0.2

1.53 mmol/L Zn

0.1

0.76 mmol/L Zn

0.0

0

10

20

30

40

50

60

70

80

90

100 110 120 130 140 150

Equivalent membrane volume

Fig. 5.7 Breakthrough profile of Zn(II) solutions (pH = 5, and temperature at 298 K)

If the breakthrough is established at a concentration of 10% of the inlet concentration (C t /C in = 0.1); i.e. the point when the concentration of Zn(II) in the permeate exceeds 10% of the concentration of Zn(II) in the intake, the number of comparable membrane volumes can be calculated as the breakthrough of Fig. 5.7 as shown in Table 5.3. The moderate corresponding membrane volume value for the 7.65 mmol L−1 Zn(II) feed stream indicates that chitosan membranes are not well suitable for applications with high concentration of metal ions. It was estimated from a following equation that the breakthrough took place at 2% membrane capacity, independent of the concentration of the solute. In Fig. 5.7, it is also possible to correlate the breakthrough profile of the 0.762 mmol L−1 Zn(II) feed solution and chitosan membrane with the breakthrough profile of a 0.79 mmol L−1 Cu(II) solution produced utilizing chitosan beads (3.8 mm), formulated from the same raw material as employed in this research. The bed volume in which the breakthrough took place for Cu(II) utilizing chitosan beads is obviously lesser than those of Zn(II) utilizing a chitosan membrane, although the adsorption efficiency of chitosan to Cu(II) is greater relative to that of Zn(II). It can therefore be suggested that a greater amount of the membrane equivalent can be handled with chitosan membranes as opposed to beads. Due to convective transport via the membrane, this phenomenon can be attributed to the improved interaction between water and adsorbent.

5.8 The Effect of Cations and Anions on Membrane Adsorption

109

5.8 The Effect of Cations and Anions on Membrane Adsorption A control sample of 7.65 mmol L−1 zinc (ZnSO4 · 7H2 O) was considered to analyse the influence of several other pollutants on the chitosan adsorption. The control sample was separated into nine samples, and these samples were subsequently separated into three sample sets. They compared all pollutants to the controlled sample. The first collection of samples was designed to evaluate the impact of nitrates and chlorides on the adsorption capacity; the second collection was chosen to measure the impact of calcium, sodium, potassium and magnesium, and the third collection was utilized to measure the impact of sulphates by raising the sulphate concentration. The solutions were controlled with a 0.8 mm membrane within 100 kPa of transmembrane pressure and 298 K It can be inferred from Table 5.4 that nitrates, and to a smaller degree chlorides, have a negative impact on the adsorption ability as defined by Becker et al. [26]. In the presence of nitrates, efficient adsorption may take place as nitrates are recorded to adsorb chitosan at a pH range of 3–5 and to a lower pH range of 6 [31]. Kurita et al. [32] also recorded a decrease in adsorption potential due to chlorides and was clarified by the development of multiple zinc-chloro compounds. Standard wash water has low nitrate concentration but large chloride concentration which can has a detrimental impact on chitosan membrane adsorption. The impact of sodium, potassium, magnesium and calcium on the adsorption ability of chlorides does not contribute to considerable differences in the adsorption capacity and does not prevent the adsorption of zinc metal ions when collectively available. EL-Hefnawy et al. [33] also reported this and stated that the existence of calcium and magnesium ions did not affect adsorption. Nevertheless, a small improvement in the adsorption potential was observed with an improvement in the concentration of sulphates. This phenomenon can be described Table 5.4 effect of cations and anions on membrane adsorption Set

Contaminant

Concentration (mmol L−1 )

q qref

Zn

SO4

NO3

Cl

K

Mg

Na

Ca

Ref.

ZnSO4 · 7H2 O

7.65

7.65

–

–

–

–

–

–

100

1

ZnSO4 · 7H2 O

0.76

0.76

–

–

–

–

–

–

103

Zn(NO3 )2 · 6H2 O

0.76

–

1.53

–

–

–

–

–

84

2

3

ZnCl2

0.76

–

–

1.48

–

–

–

–

91

KCl

–

–

–

1.35

1.41

–

–

–

97

MgCl2 · 2H2 O

–

–

–

1.37

–

0.71

–

–

92

NaCl

–

–

–

1.37

–

–

1.39

–

94

CaCl2 · 2H2 O

–

–

–

1.37

–

–

–

0.70

91

CaCl2 · 2H2 O

–

–

–

2.41

–

–

–

1.28

85

CaSO4 · 2H2 O

–

1.25

–

–

–

–

–

1.28

95

(%)

110

5 Biopolymer Chitosan Membranes Prepared from Fishery Waste …

in conjunction with sulphate-induced design improvements in chitosan, and such increased capacity for transition metal ion adsorption in sulphate media has also been documented by Mitani et al. [34].

5.9 Desorption and Recovery The membranes that were designed for desorption experiments were initially adsorbed. Each membrane has been controlled at a pH of 6 with a 7.65 mmol L−1 Zn(II) solution during the adsorption procedure. The concentration of the solution Zn(II) was measured before and after the procedure to evaluate the adsorption potential at equilibrium. Desorption, i.e. regeneration, was achieved by processing the membranes in different samples with distilled water and hydrochloric acid solutions (pH = 2 and 4) and sulphuric acid (pH = 2 and 4). The membranes were soaked in an acid solution for 6 h. A volume of 200 mL of distilled water and acid was used per treatment, respectively. Table 5.5 summarizes the percentage of Zn(II) that was desorbed (estimated on the amount adsorbed) and the percentage of membrane mass loss (estimated on the original mass) during the treatment for recovery. No large numbers of Zn(II)-ions have been identified to have been desorbed by water. Nevertheless, it was observed that the percentage regeneration provided by sulphuric acid (90%) was more than that provided by hydrochloric acid (85%). With the use of hydrochloric acid, the membrane decrease involved with the treatment process (up to 5%) was greater than when employing sulphuric acid (up to 3%). Thus, it is suggested that sulphuric acid is a stronger agent for recovery than hydrochloric acid. Milot et al. [35] also demonstrated that chitosan is much less soluble in sulphuric acid than in hydrochloric and nitric or organic acids. Therefore, sulphuric acid was needed to examine the number of periods a membrane can withstand until degradation and deterioration of the membrane’s functional control. Multiple period investigations with the most effective desorption agent (H2 SO4 , pH = 2) were performed. Following the second period, the adsorption capacity was decreased to 75% of the initial adsorption capacity (following the original membrane mass) with a 70% recovery rate (based on the new adsorption power) and an 11% Table 5.5 Adsorption and desorption

Desorption medium

pH

Desorption (% of adsorption)

Mass loss (% of the original)

Water

7.4

2.20

0.00

HCl

2.0

85.10

5.10

HCl

4.0

70.32

2.20

H2 SO4

2.0

90.12

3.12

H2 SO4

4.0

81.22

1.41

5.9 Desorption and Recovery

111

mass loss (following the original membrane mass). At best, it was found that the membrane can be recovered twice, before the membrane loses its mechanical strength to a considerable extent.

5.10 Reaction Mechanism of Chitosan Zinc adsorption on chitosan can arise from various effects including chelation, electrostatic, hydrophobic, donor electrons and polarity [36]. The existence of hydrophilic groups including amine (–NH2 ) and hydroxyl (–OH) on the chitosan backbone will make chitosan and zinc polar, since these reactive groups interact with metal ions based on various factors including metal type, pH, deacetylated unit fraction (free amine groups), polymer chain length, crystallinity, molecular weight, polymer conditioning, chitosan physical structure, solution pH, acid type and concentration used for solution, solution composition, metal ion selectivity and speciation [6]. The polarized structure of chitosan and zinc metal nevertheless causes them to be engulfed by molecules of water. The water molecules adsorbed on the adsorbent and adsorbent surfaces (via inter- or intramolecular attachment of the hydrogen) must be separated and the adsorbent molecules substitute the water molecules on the adsorbent surface [37]. This method is called replacement of solvents. The amine group establishes a coordinate attachment with the metal ions, the connection is developed between the nitrogen free electron pairs in the amine group and the metal’s void orbitals. The free electron doublet of nitrogen in amine groups is indeed accountable for the adsorption of metal cations at pH close to neutrality and at a decreased pH value, in which amine group protonation occurs; the polymer reaches cationic groups that can adsorb anions through electrostatic interactions [6].

5.11 Conclusions Studies of equilibrium isotherm showed that the adsorption of Zn(II) by thick chitosan membranes can be represented by a Langmuir equation with a maximum adsorption capacity of 2.64 mmol g−1 of chitosan at temperatures around 3.03–313 K. The adsorption process was also reported to be endothermic with an adsorption enthalpy of 20 kJ mol−1 . The Zn(II) breakthrough was influenced by the initial concentration of Zn(II) in the solution, but chitosan membranes were designed to work better than some other chitosan types such as beads. This is mainly attributable to the higher adsorption capacity of the thick chitosan membranes, especially in comparison with beads, that is correlated to much more appropriate interaction between the adsorbate and the chitosan adsorbent while selected as a thick adsorption layer, i.e. membrane. While operating at low initial concentrations (