A case study of evaluating zeolite, CaCO3, and MnO2 for Cd-contaminated sediment reuse in soil

A simple disposal of metal-contaminated sediment on land can inevitably lead to increased soil concentrations of the elements, which consequently jeopardizes the soil environment for living organisms. In order to make the metal-contaminated sediment recyclable and reusable, one possible option is sediment stabilization using immobilizing amendments, in which the metals can be immobilized and the bioavailable fraction accounting for metal toxicity can be reduced. In the present study, three immobilizing amendments, including zeolite, calcium carbonate (CaCO3), and manganese dioxide (MnO2), were compared for their ability in reducing cadmium (Cd) bioavailability in the soil receiving Cd-contaminated sediment. Soil chemical analysis, calcium chloride (CaCl2)-extractable Cd fraction, plant uptake, and microbial assay were employed to give a relative comprehensive comparison with regard to the amendment efficacy. Results showed that although the total concentrations of Cu, Pb, and Zn were increased with the addition of sediment in soil, they were still under the guideline limit set at an elevated pH condition. Compared with zeolite and MnO2, CaCO3 showed the best mitigating effects on Cd toxicity, evidenced by reduced CaCl2-extractable Cd concentrations, increased dehydrogenase activities, and reduced Cd uptake by sorghum. Incorporation of CaCO3 with contaminated sediment was a new option of dredged sediment treatment for land application in Dongting Lake region, where the sediment was deviated from the waste stream without causing much concern on soil health.