Remediation of metal-contaminated leachate using chitosan flakes

The objective of this study was to study, under various physicochemical conditions, the ability of chitosan to trap heavy metals leached during remedial. washing of contaminated soils with organic extractants. The contaminated soil was washed with 0.1 M citric acid, pH 5.5, for 24 h, producing a metal-rich leachate containing 0.06, 0.02, 0.003, and 5.87 mu moles ml(-1) of Zn, Cu, Cd, and Pb, respectively. Equilibrium and kinetic sorption studies revealed that chitosan significantly reduced the levels of these metal ions in the leachate. A 12 h mixing of the leachate with chitosan flakes resulted in about 50% reduction in metal ion contents of the leachate. However, the adsorption of metal ions by the chitosan was found to depend on the relative concentrations of metal ions present in the leachate. The mass of chitosan required for achieving adsorption equilibrium was consequently dependent on the initial concentrations of metal ions. Reduction in metal ion contents of the leachate by chitosan flakes did not appear to be significantly improved by agitation. In addition, heavy metal removal by chitosan was found to be highest at pH 6.0. Results from the experiments involving replacement of metal-laden chitosan with fresh chitosan suggested that at least four replacements of chitosan would be required for absolute remediation of the leachate.