The Behavior of Additives LiF, MgF2 and KF on Current Efficiency in Aluminium Electrolysis

Abstract

The effects of LiF, MgF2 and KF additions to the electrolyte on current efficiency were investigated during aluminium electrolysis using base NaF−AlF3−Al2O3 system with a cryolite ratio of 2.5, 4% Al2O3 and 5% CaF2 at 980°C in laboratory scale. The duration of each electrolysis experiment was 4 h with a graphite anode and a cathodic current density of 0.85 Acm−2. The influences of various additives on the current efficiency of the aluminium electrolysis are compared. Additions of LiF up to 5 wt % were found to improve the current efficiency of aluminium deposition. Additions of MgF2 had a positive effect on current efficiency and KF addition was harmful for the current efficiency. Current efficiencies for aluminium deposition were obtained when the additions of LiF mixed together with the additions of KF and MgF2. The concentration of the alkali metals including K, Na and Li in deposited aluminium were analyzed as a function of the additives. Results are presented from a study of the influence of the additions on the cathode process. Correlations between the sodium content in aluminium with different additions and the current efficiency are discussed.