INVESTIGATION OF CHROME(VI) OXIDE PRODUCTION FROM CHROMITE CONCENTRATE BY ALKALI FUSION

The possibility of producing chrome(VI) oxide from domestic chromite c oncentrates was investigated by carrying out laboratory-scale alkali f usion and water leaching experiments. The effects of temperature, the amount of NaOH added and the flow rate of air on chromium extraction e fficiency in an alkali fusion step were investigated, Fusion product w as leached with water to produce a clean Na2CrO4 solution. The paramet ers of the water leaching experiments were the temperature and the sol id/liquid ratio. The effect of purity of the monochromate solutions wa s tested by producing dichromate both from impurities-containing and p urified Na2CrO4 solutions. The purity of chrome(VI) oxides, prepared b oth from monochromate with an impurity content and monochromate purifi ed with CO2 were also examined. Kinetic investigations revealed that t he fusion process can be described most adequately by a shrinking core model for surface chemical reaction with an apparent activation energ y 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(-1).