A clean and efficient leaching process for chromite ore

In order to improve the chromate salts cleaner production technology, a pressure leaching process for chromite ore in 50 wt% KOH solution was studied for the first time and the results were presented in this manuscript. It was found out that the chromium extraction rate increased significantly with the increase of temperature and oxygen partial pressure, and the kinetics study confirmed that the leaching process was controlled by the surface chemical reaction. The iron in chromite ore was oxidized to form crystalline Fe2O3 particles with compact surface which was different from the conventional amorphous residue. The effect of the KOH solution concentration on the leach residue was investigated, and the characteristics of the leach residues were determined and compared. When the concentration of KOH solution was 60 wt% or less, the leach residues mainly consisted of crystalline particles, and the residual chromium (VI) contents met the disposal standard for chromium-containing waste. The reaction conditions of the pressure leaching process were investigated, and the preferred reaction parameters in 50 wt% KOH solution were determined. In summary, this leaching process exhibited significant advantages over the traditional roasting and other hydrometallurgical methods with respect to both environmental protection and process economy, providing an attractive alternative to upgrade the current chromate salts production processes.