In this study anodic oxidation of Cr2(SO4)3 was carried out in an air-sparged divided parallel plate cell. Variables studied were current density, Cr2(SO4)3 concentration, and superficial air velocity. The rate constant of Cr2(SO4)3 oxidation was found to increase with increasing current density and Cr2(SO4)3 concentration. The effect of air sparging was found to depend on Cr2(SO4)3 concentrations, at high Cr2(SO4)3 concentration (> 0.1 M) air sparging does not affect the rate constant of the reaction denoting that the reaction is charge transfer controlled. As Cr2(SO4)3 concentration decreases below 0.1 M the reaction becomes under mixed diffusion and chemical control and the rate constant increases with increasing air superficial velocity, the lower Cr2(SO4)3 concentration the higher the contribution of diffusion to the reaction rate. The current efficiency of the process ranged from 20 to 85% depending on current density and Cr2(SO4)3 concentration. Electrical energy consumption which ranged from 1.8 to 14.4 kW h/kg of Cr6+ was found to increase with increasing current density and decreases with increasing Cr2(SO4)3 concentration. Air sparging was found to decrease electrical energy consumption in the case of dilute solutions << 0.1 M Cr2(SO4)3.
Keywords: Anodic oxidation; Cr2(SO4)3 oxidation; gas sparging; parallel plate reactor; waste solutions.