Binding of heavy metal contaminants onto chitosans - An evaluation for remediation of metal contaminated soil and water

The binding efficiency of chitosan samples for Ag+, Cd2+, Cu2+, Pb2+ and Zn2+ has been evaluated in order to consider their application to remediate metal contaminated soil and water. The sorption behaviour of metal ions was assessed using a batch technique at different contact time and initial metal concentration with different background electrolytes. The kinetics followed a pseudo-second-order model, while the equilibrium data correlated well with the Freundlich and Langmuir isotherm models. For example, the maximum sorption capacity (Q) for chitosan was estimated as 1.93 mmol/g for Ag+, 1.61 mmol/g for Cu2+, 0.94 mmol/g for Zn2+, 0.72 mmol/g for Cd2+ and 0.64 mmol/g for Pb2+. Covalent interaction between metal ions and functional groups (amino and hydroxyl) of the chitosans was the main binding mechanism. Ion exchange is not an important process. Chitosan and cross-linked chitosans were able to bind metal ions in the presence of K+, Cl- and NO3+. The nature of Cl+ and NO3- ions did not affect Zn2+ binding by the chitosans. Even at 11x dilution, the chitosans were able to retain metal ions on their surfaces. (C) 2011 Elsevier Ltd. All rights reserved.