CARBOTHERMIC REDUCTION OF COMPLEX SULFIDES CONTAINING ARSENIC AND ANTIMONY .3. CARBOTHERMIC REDUCTION OF COPPER-ANTIMONY SULFIDES

Famatinite (Cu3SbS4) and tetrahedrite (Cu12Sb4S13) were synthesized fr om their elemental components and their reduction by carbon (graphite or coal) in the presence of lime was investigated in the temperature r ange 700-1000-degrees-C. In addition, the exchange reactions between f amatinite and tetrahedrite and lime were investigated in the temperatu re range 800-1000-degrees-C. Thermogravimetry was used to determine re action kinetics. X-ray diffraction and optical and scanning-electron m icroscopy of the reaction products were employed to elucidate reaction mechanisms. A study was also made of exchange reactions with lime and carbothermic reductions in the presence of lime for a famatinite-tenn antite (Cu12As4S13)-based concentrate that contained PbS, ZnS and SiO2 as minor constituents. The exchange reactions proceed by oxidation of the antimonial component with only partial oxidation of the copper su lphide. Carbothermic reduction in the presence of lime procceds by the formation of calcium antimonate intermediates and subsequent reductio n to copper antimonides, thus reducing antimony losses by volatilizati on. In treatment of the complex concentrates the exchange reaction of the antimonial component with lime is more favourable than that of the arsenic component. During carbothermic reductions the arsenic tends t o associate with iron, whereas antimony combines with copper. The zinc sulphide that is present in the concentrate is easily reduced, formin g zinc vapour, and the lead content of the concentrate reports as meta llic lead in the reduction products.