Stabilization of an elevated heavy metal contaminated site

Heavy metal contamination is a common problem that is encountered at many uncontrolled sites: Immobilization is seen as a promising technology for heavy metal remediation. Here, we report a remediation case study of an elevated and multi-metal contaminated site containing Cd, Cu, Ni, Pb, and Zn. In a laboratory test, when the soil was stabilized with reagent grade stabilizers (CaHPO4 and CaCO3), the toxicity characteristic leaching procedure (TCLP) extractable concentrations of Cd, Cu, Pb, and Zn were reduced by more than 87%. The greatest reduction was shown with Pb (99.8%). In the field, Ca(H2PO4)(2) due to lower cost and higher solubility replaced CaHPO4. The TCLP results of the field treatment showed that the extractable concentrations of Cd, Cu, Pb, and Zn were significantly reduced after 30 days of stabilization. The reduction ratios were 98% (Cd), 97% (Cu), 99% (Pb), and 96% (Zn). Although, the reduction ratio of Ni was only 65%, the average extractable concentration was still less than 4.0 mg/l. The percent reduction can, therefore, be considered reasonable. The significant reduction of extractable metal concentrations showed that the stabilizers, a combination of Ca(H2PO4)(2) and CaCO3, successfully immobilized heavy metals on the site. (C) 2001 Elsevier Science B.V All rights reserved.