EFFECT OF CURRENT DENSITY AND PHOSPHORUS IMPURITIES ON THE CURRENT EFFICIENCY FOR ALUMINUM DEPOSITION IN CRYOLITE-ALUMINA MELTS IN A LABORATORY CELL

摘要

The current efficiency in industrial Hall-Heroult cells foraluminum production may be up to 96%. [1]. The back reactionbetween the dissolved metals (aluminum and sodium) and theanode product play the major part in the loss in currentefficiency. Also impurities, such as phosphorous, whichparticipate in cyclic red/ox reactions at the electrodes contributesignificantly to reduced current efficiency. Phosphorous andother impurities are recycled with secondary alumina. Furtherpotline amperage increase in industrial cells may require highercurrent densities. Thus the current efficiency dependence oncurrent density and phosphorous content was studied at currentdensity ranging from 0.85 - 1.5 A/cm~2 in a laboratory cell.Current efficiencies from 90 - 97% were obtained and increasedslightly by increasing cathodic current density. The currentefficiency decreased by about 3.8% per 100 ppm of phosphorusin the electrolyte.