Chemical substitution reaction between Cu(II) and Hg(II) and hydrous CdS(s)

The chemical reaction between hydrous CdS(s) and Cu(II) and Hg(II) were studied by electrophoretic mobility measurements and adsorption experiments. The results show that cation exchange, following readsorption of the released Cd(II) ions onto the freshly-formed CuS(s) and cadmium hydroxide precipitation reactions occur when CdS particles come into contact with these metal ions which have sulfide precipitates less soluble than CdS(s). The effect of organic ligands on the ion exchange reaction, exemplified by EDTA (a strong complexing ligand) and phthalic acid (a weak complexing ligand), was also investigated. Both organic compounds have little effect on the lattice ion exchange reaction unless a large amount of strong complexing agent is present in the system. The dissolution of CdS(s), however, is slightly hindered in the presence of weak complex former such as phthalic acid and greatly enhanced in the presence of strong complex former such EDTA.