The accumulation of heavy metals in soil under landfill is a serious environmental problem. It is well known that heavy metals have an affinity for different compartments of soil. The risk associated with the presence of metals in soil is the ability of their transfer in water or plants. The total heavy metals (Cd, Cu, Pb and Zn) in soil is determined by the sequential extraction method. Chemical properties such as pH, CEC, organic carbon and buffer capacity of concerned soils are also analyzed. Results of these analysis showed that Cd is mainly associated with the residual fraction (45.58%). Nearly 28.39% of total Cd is associated to carbonates and only 20.22% and 5.81% of total Cd are associated respectively to metallic (oxy) hydroxides and organic matter. Cd is therefore mainly associated to the mobile fraction and the risk of its transfer is high. Zn is mainly bound to the metallic (oxy) hydroxides and carbonates, while Cu and Pb are mostly bound to organic matter and metallic (oxy) hydroxides in the proportions of 54.26% (Cu) and 26.43% (Pb). The study of the potential mobilisation shows that metals are retained by co-precipitation or incorporation into crystalline particles. So, aggressive conditions could release them. The soil treatment with hydrochloric acid at pH 0.5 allow the extraction up to 69% of total Cd, eliminating more than 34% of the portion bound to silica, 23.84% (Cu), 65.52% (Zn) and 31.62% (Pb).
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