Optimisation of operation conditions and thermal analysis kinetics of roasting nickel-chromium mixed oxidised ore by ammonium sulphate

The operation conditions of roasting nickel-chromium mixed oxidised ore using (NH4)(2)SO4 were optimised by an orthogonal test. The optimised conditions were concluded as a molar ratio of (NH4)(2)SO4 to mixed oxidised ore of 1.7:1, the roasting temperature of 475 degrees C and the roasting time of 2 h at an ore particle size of 74 mu m. The molar ratio was the most significant factor affecting the nickel, magnesium and iron extraction, followed by roasting time and temperature. Under optimal operation conditions, the extraction ratios of nickel, magnesium and iron are 94.3%, 84.9% and 88.7%, respectively. The reaction process, during roasting, was analysed based on the XRD study of specimens roasted at different temperatures and the TG-DTA curves obtained at varied heating rates. Each TG-DTA curve has five endothermic peaks. The first and third endothermic peaks are important and selected for thermal analysis kinetics using Doyle-Ozawa and Kissinger methods. The kinetic parameters, including the apparent activation energy, reaction order and frequency factor, are calculated corresponding to the two peaks before drawing the kinetic equations. Finally, the kinetic equations are obtained.