Geerite-type structures and the flotation of sphalerite

CIM Bulletin, Vol. 81, No. 911, 1988

RONALD J. GOBLE, University of Nebraska-Lincoln, Lincoln, Nebraska, LOWELL S. WHITESIDE and ALI M. GHAZI*, Georgia Institute of Technology, Atlanta, Georgia

Geerite (CuI6S) is a rhombohedral copper sulphide which occurs naturally in epitactic replacement of sphalerite; cell dimensions closely approximate those of the host sphalerite. Geerite-type structures can be produced by leaching digenite (Cu,sS) in ferric sulphate solutions. X-ray diffraction and electron microprobe studies indicate that eight metastable geerite-type structures can be produced, depending upon the concentration of ferric sulphate solution used and the duration of the leach. Although compositions cluster on or near values observed for natural phases, optical properties indicate that we are dealing with polymorphs of these phases. Leaching of chalcocite (Cu2S) in dilute ferric sulphate solutions produces similar results. In contrast, leaching of chalcocite in more concentrated solutions seems to produce true analogues of natural minerals. During froth flotation, sphalerite is activated with a mono-layer of floatable copper sulphide with the composition, CuS, of the mineral covellite. However, covellite is not significantly more floatable than sphalerite, and has an incompatible structure because of the presence of covalently-bonded atoms of sulphur. Leaching of digenite was used to produce apolymorph of covellite with a geerite-type structure, compatible with that of sphalerite. This polymorph has a flotational behaviour similar to copper-activated sphalerite, suggesting that the monolayer has a geerite-type CuS structure.
Mots Clés: Mineral processing, Flotat ion, Geerite, Sphalerite, Leaching, Sulphu r, Copper.