An investigation on the kinetics of chromium dissolution from Philippine chromite ore at high oxygen pressure in KOH sub-molten salt solution

• The leaching kinetics of chromite ore at high oxygen pressure was first investigated.
• The oxidization product remained as the “ash” layer and controlled the leaching rate.
• The leaching temperature was greatly decreased by using the pressure leaching method.

The dissolution kinetics of chromite ore at high oxygen pressure in KOH sub-molten salt solution was systematically investigated in this work. The effects of KOH concentration, agitation speed, oxygen pressure, oxygen flow rate, particle size and leaching temperature on the chromium leaching rate were discussed in detail. The results indicate that the leaching rate is independent of agitation when the agitation speed is above 1100 rpm and is not sensitive to the oxygen flow rate. However, the leaching rate increases with the increment of temperature, oxygen partial pressure, as well as the decrease of particle size. The oxidization product remains as an “ash” layer during the leaching process. The kinetics study shows that the dissolution process is controlled by internal diffusion of the reactants. The determined activation energy is 44.31 kJ/mol and the reaction order with respect to the oxygen pressure is 0.68. Finally, a dissolution rate equation is derived to describe the process.