Influence of Additives on Alumina Dissolution in Superheated Cryolite Melts

In collaboration with UQAC: Alumina dissolution is of first concern in modern electrolysis cells. The rate of dissolution strongly depends on the physical and chemical conditions in which the cryolitic melts. In this work, the alumina dissolution rate has been monitored with the gravimetric methods in NaF-AlF3-CaF2-Al2O3 systems. To evaluate the main influences of the additives and the superheat, a parametric study has been conducted. A wide range of additive content has been studied to fit industrial conditions. Thus, bath compositions with different liquidus temperatures, in the range from 924 °C to 970 °C, were used to dissolve alumina at fixed superheat. Results show consistency with physicochemical expectations so that the additives content decreases the alumina dissolution rate and the superheat increases this rate. Then the experimentally obtained correlations can help to adjust the parameters to obtain the desired rate of dissolution.