Experimental study on the formation of heavy metal sulphides using layer silicates: environmental aspects

摘要

Clay minerals saturated with metal ions (Cu, Pb, Cd, Zn, Tl, Ag, Hg) were treated by aqueous H_2S solutions under controlled Eh and pH conditions. The heavy metal ions were released and precipitated at 80 deg C as sulphides and in most cases appeared to be crystalline. They often formed coatings or crystals overgrown on clay minerals or formed tight intergrowths with clay particles. After 5 days, well crystallised sulphides were formed; covellite (CuS), galena (PbS) and sphalerite (ZnS) were identified by X-ray. The microscopic observations revealded some other Cu-Fe-minerals, like chalcopyrite (CuFeS_2), idaite, and bornite. Native copper and pyrite were also observed. Cadmium formed hawleyite (CdS), whereas the greenockite crystals were rarely found in the reaction products. Mercury reacted very quickly with S~(2-) ions and in the heavy fraction of the reaction products the metacinnabar (HgS) was determined. Several thallium sulphides were obtained: TlS, Tl_2S (carlinite), Tl_2S_5, Tl_4S_3 and TlFeS_2 (raquinite), Cu_3, Tl_2S_5, Cu_2TlS_3, AgTlS, Ag_4Tl_2S_3 and AgTlS_2.