Influence of Additives on Alumina Dissolution in Superheated Cryolite Melts

Alumina dissolution is of first concern in modern electrolysis cells. The rate of dissolution strongly depends on the physical and chemical conditions in the cryolitic melts. In this work, the alumina dissolution rate has been measured with the gravimetric methods in NaF-AlF3-CaF2-Al2O3 systems. To evaluate the influence of the additives and the superheat, a parametric study has been conducted. A wide range of additive content has been studied to meet industrial conditions. Thus, bath compositions with different liquidus temperatures, in the range from 924 to 970 degrees C, were used to dissolve alumina at fixed superheat. Results show consistency with physico-chemical expectations so that the additive content decreases the alumina dissolution rate and the superheat increases this rate. The experimentally obtained correlations can help to adjust the parameters taking into account their effect on the dissolution.