Recovery of copper and zinc from an off-grade/complex sulphide concentrate

Laboratory investigations have been carried out on the recovery of copper and zinc from off-grade and complex sulphide-chalcopyrite concentrate of the Sikkim Mining Corporation employing the slat roasting-solvent extraction route. Utilizing the conditions (optimised earlier in our laboratory) the concentrate has been subjected to salt roasting at 350 C for 3 hrs using 10wt% NaCl in a multi-bed roaster. The leach liquors, obtained from the calcines by their dissolution in hot water, have been sub-liquors, obtained from the calcines by their dissolution in hot water, have been subjected to solvent extraction studies using using the organic solvent LIX-64N with kerosene as the diluent. Investigations have been conducted on the effects of phase ratio (organic aqueous), concentration of organic solvent and addition of H2SO4, some salting agents (Na2SO4 and NaCl) and pH. Results indicate that the best extraction of copper and zinc are achieved by employing 10 vol.% LIX-64N (in kerosene), phase ratio of unity at 1.0 pH with appropriate additives (1M each of H2SO4 and Na2SO4). Under these conditions, it has been possible to achieve not only high distribution co-efficient values for copper but also excellent separation factors both Cu/Fe and Cu/Fe. A four-stage extraction and appropriate scrubbing and stripping procedure enabled preparation of aqueous copper solution suitable for electrowinning.