Current efficiency studies in a laboratory aluminium cell using the oxygen balance method

There have been many studies investigating the effects of various parameters on the current efficiency in aluminium smelting cells. One of the most important and most widely debated of these parameters is alumina concentration, because of its implications in feed strategies and cell management. This paper presents the results from a study investigating the effects of alumina concentration, bath chemistry, current density and anode-cathode spacing on current efficiency. Gas emissions from a laboratory scale cell were measured by on-line mass spectrometry, current efficiency was determined by an oxygen balance method. Electrolysis was performed from various starting alumina concentrations of 6 - 8 wt% until anode effect was reached. After initial start-up periods there was no variation in current efficiency as the alumina was depleted and anode effect approached. Increasing the cryolite molar ratio, in agreement with other reports, has a strong negative effect on current efficiency. Results also show a strong increase in current efficiency with increasing current density. No effect of electrode spacing was detected.