Clay minerals as a scavengers of heavy metals in the soils and sediments and, formation of metal sulphides-experimental study

Abstract

The saturated with the metal ions (Cu, Pb, Cd, Zn, Tl, Ag, Hg) clay minerals were treated by aqueous H 2 S solution under controlled Eh and pH conditions. The heavy metals ions were released and precipitated at 80 o C as sulphides, in most cases appeared to be crystalline. They often form coatings or crystals overgrown on clay minerals or form tight intergroths with clay particles. After 5 days the well crystallised sulphides are formed; covellite-CuS, galena-PbS and sphalerite ZnS were identified by X-ray method. The microscope observations revealed some other Cu-Fe-minerals like chalcopyrite-CuFeS 2 , idaite, bornite. The native copper and pyrite were also observed. Cadmium formed hawleyite-CdS, whereas the crystals of greenockite were rarely found in the reaction products. Mercury react very quickly with S 2-ions and in the heavy fraction of reaction product the metacinnabar-HgS has been determined. The numbers of thallium sulphides were obtained: TlS, Tl 2 S-carlinite, Tl