Salt roasting of an off-grade copper concentrate

Abstract

Laboratory investigations have been conducted to explore the feasibility of a salt roast-water leach route as a means of recovering copper and zinc simultaneously from an off-grade chalcopyrite concentrate (from Sikkim) with a significant amount of associated sphalerite. Detailed studies indicate the possibility of recovering over 95% Cu and 97% Zn into leach liquor (with negligible Fe and Pb) by treatment of the concentrate at 350°C for 3 h, employing 20 wt% NaCl, 6 mm bed depth and an air flow rate of 1 l/min. Mineral phase identification in the salt-roasted calcines by X-ray diffraction, analyses of the off-gases and reactor condensates, and determination of the chloride to sulphate ratios of leach liquors indicate that the chemistry of salt roasting of the sulphide concentrate is a truly complex process.