Study on the cathodic process of co-existing LiF and KF in Na3AlF6–Al2O3 molten salt with various cryolite ratios

Abstract

Selective and efficient electrochemical analytical methods for examining the deposition of metallic aluminum are significant and necessary. Herein, the electrochemical behaviour of aluminium was studied at an inert tungsten electrode in an Na₃AlF₆–Al₂O₃–LiF–KF eutectic melt at 1253 K by means of transient electrochemical techniques. Electrochemical measurements are based on the potentiodynamic steady-state polarization curve plotting, continuous potential pulse method, constant potential method, constant current method and open-circuit chronopotentiometry. The cathodic overpotential for the deposition of metallic aluminum first decreased and then increased, while the activity of aluminum gradually decreased, as the cryolite ratio increased. Na⁺ ions discharged and precipitated when the cryolite ratio exceeded 3.0. KF played a decisive role in modifying electrode reactions, whereas the effect of LiF was not significant in the Na₃AlF₆–Al₂O₃–LiF–KF melt. The addition of KF not only influenced the current efficiency, but also affected the purity of the metallic aluminum, and the simultaneous addition of KF and LiF increased the dissolution loss of aluminum.