Remediation of metal-contaminated leachate using chitosan flakes

The objective of this study was to study, under various physicochemical con ditions, the ability of chitosan to trap heavy metals leached during remedi al. washing of contaminated soils with organic extractants. The contaminate d soil was washed with 0.1 M citric acid, pH 5.5, for 24 h, producing a met al-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 result ed in about 50% reduction in metal ion contents of the leachate. However, t he adsorption of metal ions by the chitosan was found to depend on the rela tive concentrations of metal ions present in the leachate. The mass of chit osan required for achieving adsorption equilibrium was consequently depende nt on the initial concentrations of metal ions. Reduction in metal ion cont ents of the leachate by chitosan flakes did not appear to be significantly improved by agitation. In addition, heavy metal removal by chitosan was fou nd to be highest at pH 6.0. Results from the experiments involving replacem ent of metal-laden chitosan with fresh chitosan suggested that at least fou r replacements of chitosan would be required for absolute remediation of th e leachate.