Oxidation of cobaltite

Abstract

The control of arsenic in the oxidation of cobaltite is important in oxidative roasting/leaching processes. The process mineralogy of the oxidation of cobaltite was evaluated based on the performances of X-ray diffraction, reflected light microscopic and scanning electron microscopic analyses on the roasted cobaltite concentrates. Oxidative roasting below 550°C did not show any crystal structural change in cobaltite but heating to 650°C, yielded Co-As-oxide whose composition varied. Direct oxidation of cobaltite to cobalt oxides with traces of arsenic was observed by roasting at 750°C or above. The arsenic concentration within the particles decreased with the increase of temperature. The arsenic removal from the lattice of cobaltite was found to be temperature dependent in the oxidation process. Differential Thermal Analysis on pure cobaltite showed that three exothermic reaction peaks existed in the oxidation process. The overall kinetics of oxidation of cobaltite have been studied for temperatures up to 900°C, based on experiments in P-E TGS-2 TGA system. Up to temperatures of 640°C, pore-blocking kinetics gave a satisfactory fit of the data, whereas above 670°C, the shrinking core kinetics model was applicable. The activation energy was 479 KJ/mol below 565°C and 265.5 KJ/mol above 670°C.