CURRENT EFFICIENCY IN THE HALL-HEROULT PROCESS FOR ALUMINUM ELECTROLYSIS - EXPERIMENTAL AND MODELING STUDIES

Results are presented from a laboratory study of the influence of elec trolyte composition, temperature, cathodic current density and interpo lar distance on the current efficiency with respect to aluminium (CE). The current efficiency was determined from the weight gain of metal, in a laboratory cell designed to attain good and reproducible convecti ve conditions, and with a flat cathode surface which ensures uniform c athodic current distribution. The cell is believed to more closely rep resent conditions in industrial cells than traditional small-scale cel ls, and is a good basis for an experimental study of the influence of isolated variable parameters on the current efficiency with respect to aluminium. The results show a nonlinear decrease of CE with increasin g electrolyte temperature, a close to linear decrease of CE with incre asing NaF/AlF3 ratio in the electrolyte, a slight increase of CE with increasing electrolyte CaF2 concentration, and no influence of electro lyte Al2O3 concentration on CE. A current efficiency model, based on p revious work and theory of electrochemistry and mass transport, shows good agreement with the obtained results.