CaCl2–O2 Roasting of stibnite and a complex copper concentrate at 500–650 °C

Abstract

Complex copper sulfide concentrates normally contain As, Sb, Bi, Zn, Pb, as the main impurities. Because of the high levels of these impurities, conventional smelting due to the high risk of environmental pollution cannot treat these concentrates. Oxidizing roasting has been used to remove the unwanted impurities through the gas phase, a process where arsenic is removed effectively but antimony and bismuth removal is very deficient. Because of the poor removal of antimony in oxidizing roasting, an alternative chloridizing roasting of pure stibnite and complex MH copper concentrate (Ministro Hales mine, CODELCO, Chile) has been studied. In roasting in the range of 500–650 °C, temperature and oxygen concentration affected significantly the Sb volatilization in the case of solely Sb2S3–CaCl2 sample. At 600 °C and 10% oxygen, antimony volatilization was 60% in 30 min. The volatilization proceeded through intermediate oxides and formation of nonvolatile antimony oxide Sb6O13 as confirmed by XRD spectroscopy. In roasting the MH concentrate at 600 °C and 5% oxygen, arsenic from enargite can be eliminated in less than 20 min most likely as a mixture of arsenic trichloride and trioxide. Oxygen concentration in the gas phase affects not only the rate of weight loss due to volatilization of arsenic, but also the rate of formation of non-volatile compounds.