Influence of phosphorus on current efficiency in aluminum electrolysis at different current densities
Journal article, Peer reviewed
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OriginalversjonJournal of the Electrochemical Society. 2017, 164 (7), E161-E165. 10.1149/2.0941707jes
Many factors may contribute to loss of current efficiency (CE) in aluminum reduction and one of them is a presence of impurities. In this work, the effect of phosphorus on CE is studied in a laboratory cell at different current densities. Due to a growing trend toward higher amperage in retrofitted industrial cells, a study is performed both at a representative industrial current density (0.8 A/cm2) and at a high current density (1.5 A/cm2). More resolution was obtained at phosphorus levels comparable to typical industrial concentration in aluminum reduction cell (0–220 mg/kg). It is shown that the effect of phosphorus on the CE is more significant at high current density. Trend lines for the whole concentration range btw. 0 and 630 mg/kg showed a decrease of 1.1% in CE per 100 mg/kg for the high current density and 0.67% per 100 mg/kg at the low current density. The detrimental effect was more pronounced for relatively low phosphorus contents up to 220 mg/kg. A trend line for that smaller range revealed a reduction of 2.5% per 100 mg/kg of phosphorus at 1.5 A/cm2, while at 0.8 A/cm2 a reduction of 0.92% per 100 mg/kg of phosphorus was obtained. This indicates that increasing amperage in retrofitted cells may amplify the detrimental effect of impurities on the current efficiency.