Elemental sulphur formation during the ferric chloride leaching of chalcopyrite

Abstract

The formation of elemental sulphur during the FeCl 3 leaching of chalcopyrite has been elucidated. More than 95% S° formation, and less than 5% SO 4 generation, is observed regardless of the leaching time (0–90 h), the FeCl 3 concentration (0–2 M), the HCl concentration (0–3 M) and the chalcopyrite particle size. Furthermore, the relative amounts of S° and SO 4 do not vary systematically with any of the above variables. Surprising is the observation that the presence of air or O 2 in the leach reactor has no significant effect on the relative amounts of S° and SO 4, and this observation was confirmed in separate leaching tests with pure sulphur. The morphology of the elemental sulphur reaction product also was ascertained. Although discrete globules of S° form on large chalcopyrite particles, smaller chalcopyrite grains (<20 μm) become completely enveloped in a continuous layer of sulphur within the first 15 min of leaching. The morphology of the sulphur does not change with the concentration of either FeCl 3 or HCl.