XPS and AES studies of Hg(II) sorption and desorption reactions on sulphide minerals

The sorption and desorption of aqueous HgCl ₂ on Fe_{1- x}S, FeS ₂, and PbS have been studied using high resolution X-ray photoelectron and Auger electron spectroscopies. Preliminary desorption studies on Fe_{1- x}S, using ligands of differing Hg(II) complexing strengths, indicate that more than one form of sorbed Hg is present. The most weakly sorbed Hg is desorbed by Cl ^- and SO ₃^2-, more strongly bound Hg is removed by S ₂O ₃^2-, and CN ^- removes all sorbed Hg. Detailed studies on PbS indicate that there are at least three Hg(II) species present. The most weakly bound, Hg ₃S ₂Cl ₂ and HgCl_x, are removed by S ₂O ₃^2-. They form on top of a layer of HgS, which is only removed by CN ^-. During adsorption, Pb is leached from the surface. Only weakly bound Hg(II) is deposited on FeS ₂; its composition could not be fully determined.