The anodic oxidation of Cr(III) to Cr(VI) in a laboratory-scale chromium electrowinning cell

The factors affecting the anodic processes in the electrowinning of chromium were investigated by carrying out electrolysis experiments with a chromium ammonium sulfate solution in a laboratory-scale cell of approximately 90 ml equipped with a diaphragm. The current density (838-1077 A m^-2), temperature (50-70°C), and rate of electrolyte flow (5-18 ml/h) from catholyte to anolyte were varied to determine their effects on the anodic oxidation of Cr(III) to Cr(VI). There was no attempt to optimize the cathodic deposition process. The behavior of the traditional lead - silver anode with an effective surface area of 10 cm² was compared with that of two commercially available dimensionally stable anodes. The current efficiency for the anodic oxidation of the chromic ion varied from about 75 to 100% with the lead - silver anode while it was only about 10 to 20% with the dimensionally stable anodes. The other variables had a much less significant effect.