Facilitated desorption and stabilization of sediment-bound Pb and Cd in the presence of birnessite and apatite

Desorption of lead (Pb) and cadmium (Cd) from contaminated sediments was investigated to clarify the effect of stabilizing agents on Cd and Pb desorption kinetics. The desorbed aqueous Cd and Pb concentrations and the residual amounts of Cd on the sediments in the desorption tests were best fitted to a pseudo-second-order kinetics with the highest R(2) values among the models used in the kinetic studies. The average residual Cd on sediments were 24% and 19% less in the presence of apatite and birnessite, respectively, than in the absence of them. However, the Pb desorption was not affected by the stabilizing agents. The negligible aqueous concentrations of desorbed Cd and Pb in the presence of apatite and birnessite suggest the stabilization of desorbed Cd that was facilitated by apatite and birnessite and Pb. The kinetics study with Cd shows that the rate constants are not affected, but the desorption extents are affected in the presence of apatite and birnessite. The Tessier sequential extraction method and toxicity characteristic leaching procedure indicate that Pb is more strongly bound on the stabilizing agents than Cd. Overall, birnessite and apatite can be successfully applied in remediation of Cd and Pb contaminated sediment.