In-situ stabilization of Pb, Zn, Cu, Cd and Ni in the multi-contaminated sediments with ferrihydrite and apatite composite additives

Three additives were evaluated for their effectiveness in the attenuation of Pb(2+), Zn(2+), Cu(2+), Cd(2+), Ni(2+) in contaminated sediments. Apatite, ferrihydrite and their composite were applied to the sediments. For the remediation, BCR, SEM/AVS and TCLP were adopted as the evaluating method and comparison of their results were used for the first time to test in-situ stabilization effect. The results showed that after 5 months composite treatment, more than 70% Pb(2+), 40% Zn(2+), 90% Cu(2+), 50% Cd(2+) and 80% Ni(2+) was immobilized in oxidizable and residual phases, respectively. Compared to untreated sediment, Pb2+, Zn2+, Cu(2+), Cd(2+) in residual fraction increased 20%, 10%, 10%, 10% with composite treatment after 5 months, respectively. Sigma SEM/AVS ratio declined from 12.6 to 9.3, in addition, composite treatments reduced the leaching of Pb(2+) and Zn(2+) from 10.6 mg L(-1) and 42.5 mg L(-1) to 5.4 mg L(-1) and 24.1 mg L(-1) in the sediment by TCLP evaluation. Meanwhile, apatite and ferrihydrite composite additives lowered the bioavailability and toxicity of sediments as well. Ferrihydrite had a positive effect in controlling the bioavailability, and toxicity of heavy metals because it effectively retarded the oxidation of AVS in sediment. (C) 2009 Elsevier B.V. All rights reserved.