Kinetics and mechanisms of the carbothermic reduction of chromite in the presence of nickel

Abstract

Carbothermic reduction of chromite in the presence of nickel as the alloying element was investigated in a wide temperature range up to 1500 °C using thermogravimetric analysis coupled with continuous off-gas analysis (TG-DSC-MS). Both isothermal and non-isothermal linear heating tests were performed for the kinetic study with the calculation of activation energies. In order to further elucidate the reduction mechanism, the reduced products were characterized by SEM–EDS and XRD. It was concluded that the reduction sequence followed a multi-stage mechanism, reflected partly by the dependency of the activation energy on the extent of reduction. With the progress of reduction, refractory oxide layers gradually formed on/close to the surface of each chromite particle, causing the shift of the rate-limiting factor from chemical control to diffusion control. The promoting effect from the addition of Ni was evident at temperatures higher than 1300 °C due to the formation of alloys of lower melting point.