Heavy metal adsorption by sulphide mineral surfaces

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Abstract

The adsorption of aqueous Hg2+, Pb2+, Zn2+ and Cd2+ complexes on a variety of sulphide minerals has been studied as a function of the solution pH and also as a function of the nature of the ligands in solution. Sulphide minerals are excellent scavengers for these heavy metals. The adsorption is strongly pH dependent, i.e. there is a critical pH at which the adsorption increases dramatically. The pH dependence is related to the hydrolysis of the metal ions. Indirect evidence suggests that the hydrolyzed species are adsorbed directly on the sulphide groups, probably as a monolayer. The results also suggest the presence of MCIn2−n species physisorbed on the adsorbed monolayer. A positive identification of the adsorbed species was not possible using ESCA/XPS.

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