Oxidative leaching of a Vietnamese chromite ore in highly concentrated potassium hydroxide aqueous solution at 300 °C and atmospheric pressure

Hydrometallurgical processing of a Vietnamese chromite ore was attained through oxidative leaching in highly concentrated KOH aqueous solution in the presence of compressed air at 300 °C under atmospheric pressure. Followed by diluting with fresh water or dilute KOH aqueous solution, the leaching process achieved the salting-out of hexavalent chromium in the form of K2CrO4 crystal due to the relatively low solubility of hexavalent chromium in concentrated KOH aqueous solution. The difference in particle size and bulk density enabled the effective separation of the obtained K2CrO4 crystal and the chromite ore leaching residue through gravity sedimentation. During the leaching process, other accompanying elements such as aluminum and silicon were extracted out from the chromite ore as well. However, their leaching products easily formed a compound of potassium aluminosilicate and therefore precipitated into the leaching residue. Additionally, thermodynamic and kinetic investigations of the leaching process were preliminarily carried out and briefly discussed.