Effectively reducing the bioavailability and leachability of heavy metals in sediment and improving sediment...

Heavy metal-contaminated sediment is a common environmental problem. In situ stabilization is an effective and low-cost method to remediate heavy metal-contaminated sediment. In this study, a red mud-based low-cost composite (RMM) was used to stabilize heavy metal-contaminated sediment. RMM was mixed with heavy metal-contaminated sediment at the doses of 0%, 1%, 3% and 5%. The CaCl₂-extractable, DTPA-extractable, leachability (TCLP) and heavy metal fractions were analysed to evaluate the stabilization efficiency of RMM for heavy metals. The selected properties and microbial activities of the sediment were analysed to verify the safety of RMM to sediment. The results showed that RMM reduced the DTPA-, CaCl₂- and TCLP-extractable heavy metals in sediment. At an RMM dose of 5%, DTPA-, CaCl₂- and TCLP- extractable heavy metals were reduced by 7.60%, 72.34% and 69.24% for Pb; 18.20%, 76.7% and 23.57% for Cd; 32.7%, 96.50% and 49.64% for Zn; and 35.0%, 61.20% and 55.27% for Ni, respectively. TCLP- and DTPA-extractable Cu was reduced by 71.15% and 12.90%, respectively. In contrast, CaCl₂-extractable Cu increased obviously after the application of RMM. RMM reduced the acid-soluble fraction of Zn by 6.99% and increased the residual fraction of Ni by 4.28%. However, the influence of RMM on the fractions of Pb, Cd and Cu was nonsignificant. In addition, the application of RMM increased the pH values of the sediment, and the microbial activity in the sediment was also obviously enhanced. These results indicated that RMM has great potential in the remediation of heavy metal-contaminated sediment.