ELEMENTAL SULFUR FORMATION DURING THE FERRIC-CHLORIDE LEACHING OF CHALCOPYRITE

The formation of elemental sulphur during the FeCl3 leaching of chalcopyrite has been elucidated. More than 95% S° formation, and less than 5% SO4 generation, is observed regardless of the leaching time (0-90 h), the FeCl3 concentration (0-2 M), the HCl concentration (0-3 M) and the chalcopyrite particle size. Furthermore, the relative amounts of S° and SO4 do not vary systematically with any of the above variables. Surprising is the observation that the presence of air or O2 in the leach reactor has no significant effect on the relative amounts of S° and SO4, 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 FeCl3 or HCl. © 1990.