Heavy metal speciation trends in the slime dams at a typical gold mine in Zimbabwe were studied using a six-step sequential extraction technique to give six fractions, namely, the exchangeable, acid soluble, easily reducible, moderately reducible, oxidizable and residual fractions. The elements studied include Cd, Co, Ni, Cu, Zn, Cr, Fe and Mn. Cadmium was found mainly in the acid soluble fraction, and to a lesser extent in the exchangeable and easily reducible fractions. For the other elements, speciation trends within the slime dams appear to depend, in the main, on the stability of metal cyano complexes formed during the cyanide extraction process, and the ease with which the metals co-precipitate with Mn oxides and/or CaCO3. For Fe speciation trends depend mainly on the pH within the slime dam.
Key words: Heavy metal speciation, heavy metal mobility, slime dam, mine tailings, sequential extraction.
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