The Role of Key Impurity Elements on the Performance of Aluminium Electrolysis -Current Efficiency and Metal Quality

Abstract

The behaviour of phosphorus and silicon in industrial aluminium cells was measured in QATALUM cells by analysis of bath and metal after addition of AlPO4, Na3PO4 and SiO2 to the bath. Phosphorus showed a much longer retention time in the bath than silicon. Start-up and anode effects influence the phosphorus and silicon level in the cells. Data trends showed that the amount of phosphorus decreases with increasing temperature. The effect of phosphorus on current efficiency was determined by measuring the metal inventory by copper dilution. The results were compared with current efficiencies estimated from measuring sodium concentration in the produced aluminium. The mass transfer coefficient for silicon was determined to be 3.1 x 10-5 m/s. Mass balance for phosphorus was carried out. It was found that massive amounts of phosphorus entering the cells were transported with the off-gases to the dry scrubbers. 2016 by The Minerals, Metals & Materials Society.