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 Pb2+, Zn2+, Cu2+, Cd2+, Ni2+ 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% Pb2+, 40% Zn2+, 90% Cu2+, 50% Cd2+ and 80% Ni2+ was immobilized in oxidizable and residual phases, respectively. Compared to untreated sediment, Pb2+, Zn2+, Cu2+, Cd2+ in residual fraction increased 20%, 10%, 10%, 10% with composite treatment after 5 months, respectively. ΣSEM/AVS ratio declined from 12.6 to 9.3, in addition, composite treatments reduced the leaching of Pb2+ and Zn2+ from 10.6 mg L−1and 42.5 mg L−1to 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.