Research On Chemical Stabilization Of Heavy Metal Contaminated Soils

Heavy metal pollution has become a global problem which increasingly draw attention of people. Among of various methods to remove heavy metal, the chemical stabilization process is most widely used because of its advantages such as low cost and good flexibility. Especially, the phosphate-based and CaO-based chemical stabilization has been intensely studied to treat heavy metal.The city of Daye is rich of mineral resources with various types and huge amount, and its industrial development is based on a metallurgical, building materials-based industry. For a long time, the metallurgical plant created rich material wealth for the country and regions, but it led to the discharged waste and consequently caused serious pollutions to the surrounding environment. It has been found excessive heavy metals in soil.In this paper, phosphate and Calcium hydroxide were used as the stabilizing agents to eliminate heavy metals. Various reaction conditions were optimized to get the favorable removal efficiency. Moreover, such chemical stabilization processed were applied to treat the Daye actual contaminated soil. The major contents are describes as follows:(1) The extraction of available heavy metals from soil was studied. It was confirmed MgCl₂ and HAc were the most highly efficient extraction agent and the optimal conditions were listed in detailed: the concentrations of MgCl₂ and HAc were 0.50 mol L^-1 and 0.25 mol L^-1, respectively, the ratio of extractive to soil was 20:1(v/v), and the extraction time was 18 h.(2) It studied that phosphate and Calcium hydroxide were used as stabilization agents to remove heavy metals. It was found the use of single stabilization agent either phosphate or Calcium hydroxide could not stabilize heavy metal in soil. When both 10 % KH₂PO₄ and 5 % Ca(OH)₂ were added, almost all the Pb, Zn could be removed completely, while 29 % of Cd and 75% of Cu were removed. The available phosphorous content was 388 mg kg^-1 in soil with pH 9.21.(3) Phosphate and Calcium hydroxide were applied to stabilize heavy metals in situ with the Daye contaminated soil as the treated sample. When 0.33 % KH₂PO₄ and 0.33 % Ca(OH)₂ were used, the removal of Pb and Cu were 48.4 % and 13.3 % respectively, while the available phosphorous content was 16.1 mg kg^-1 in soil with pH 9.21. It has little effect on the production of Peanut, in which the heavy metal content decreased slightly.