Study of Reaction Mechanisms for Copper-Cobalt-Iron Sulfide Concentrates in the Presence of Lime and Carbon

Abstract

The reaction mechanisms for the carbothermic reduction of complex mineral sulfide concentrates in the presence of lime were studied between 1073 K and 1323 K. The reaction mechanisms were studied by stopping the reduction experiments at different times and analyzing the reaction products by x-ray diffraction and scanning electron microscopy techniques. Magnetite (Fe3O4) and digenite (Cu1.8S) were the initial phases formed during reduction of CuFeS2 and Cu5FeS4 mineral particles, such that metallization of iron occurred before copper above 1173 K and at an equal stoichiometric ratio of CaO and C. The metallization of iron was found to take place via reduction of intermediate oxide phase (Fe3O4/FeO), whereas metallization of copper occurred via diffusion of S2− ions away from the mineral particles or via formation of Cu-O-S liquid phase. Metallic iron and cobalt were embedded in the copper matrix due to a preferential reduction of iron and cobalt from the Cu-Fe-S and Cu-Co-S type of mineral particles. The effects of CaO/C ratio were analyzed and the rate of reactions was increasing with an increase in the CaO/C ratio. The formation of liquid phase has been discussed. The experimental results were found to be in good agreement with the thermodynamic predictions.