The immobilization performances of Diatomite, Ca(H2PO4)2, CaCO3, Hydroxyapatite (HAP) and Nano-HAP (n-HAP) for Zn, Mn, Pb, and Cd contaminated sediments were investigated by immobilization experiments and evaluated by the European Community Bureau of Reference (BCR) extraction test, toxicity characteristic leaching procedure (TCLP). The result of BCR indicated that HAP and Nano-HAP (n-HAP) had a better immobilization effect on metal contaminated sediments, and the residual fractions of Zn, Mn, Pb, and Cd increased from 30.4, 31.9, 55.49 and 54.27% to 36, 39, 72, and 57%, respectively. The order for immobilized effects of additive was: n-HAP > HAP > CaCO3 > Ca(H2PO4)2 > diatomite. However, the cost-effectiveness of HAP was slightly higher than that of n-HAP, so HAP was more suitable for immobilization of heavy metals in sediment. The TCLP test showed that with HAP as immobilization the leaching amount was reduced by approximately 76, 28, 78, and 85% for Zn, Mn, Pb, and Cd, respectively, compared to the blank group. The results also proved that HAP would be an effective and economical agent for immobilizing heavy metals in sediment, with the optimum mass dosage of 10% (the mass ratios of HAP/sediment (dry weight)) of the sediment.

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