Investigation of chrome(VI) oxide production from chromite concentrate by alkali fusion

The possibility of producing chrome(VI) oxide from domestic chromite concentrates was investigated by carrying out laboratory-scale alkali fusion and water leaching experiments. The effects of temperature, the amount of NaOH added and the flow rate of air on chromium extraction efficiency in an alkali fusion step were investigated. Fusion product was leached with water to produce a clean Na₂CrO₄ solution. The parameters of the water leaching experiments were the temperature and the solid/liquid ratio. The effect of purity of the monochromate solutions was tested by producing dichromate both from impurities-containing and purified Na₂CrO₄ solutions. The purity of chrome(VI) oxides, prepared both from monochromate with an impurity content and monochromate purified with CO₂ were also examined. Kinetic investigations revealed that the fusion process can be described most adequately by a shrinking core model for surface chemical reaction with an apparent activation energy of 43.5 kj mol^-1. The results from leaching experiments, however, suggested that the reaction rate is limited by the product layer mass-transfer control. This analysis is supported by an apparent activation energy of 10.5 kJ mol.