Research On Solubility Of Aluminum In Na₃AlF₆-Al₂O₃-AlF₃-KF-LiF Melts

There are some impurities contained in domestic alumina, especially a certain amount of K2O and Li2O in alumina which would lead to enrich the high concentrations of LiF and KF in electrolytic cell during aluminum produced. Meanwhile the enrichment of LiF and KF in electrolytic cell can affect the solubility of aluminum, as well as current efficiency. In order to provide theoretical basis for reducing aluminum dissolution loss and to achieve a high efficient and energy-saving aluminum production process, it is necessary to explore the solubility of aluminum in Na3AlF6-Al2O3-AlF3-KF-LiF melts.This paper has studied the effect of different cryolite ratio of the electrolyte, KF and LiF added on the solubility of aluminum. Furthermore, this paper also analyzed the effect of different additives on cathodic overvoltage and cathodic secondary reactions. The main conclusions in this thesis have been summarized as follows.(1) Without the external power supply, solubility of aluminum could saturated wihtin 3h. In this case, the saturated solubility of aluminum increases with increasing cryolite ratio of electrolyte, and it decreases with the amount of LiF increasing. However, the saturated solubility of aluminum is nothing to do with the amount of KF.(2) In the condition of the electrolysis, the aluminum dissolution increases with increasing cryolite ratio of electrolyte, and it decreases with increasing both content of KF and LiF, and it decreases with the amount of LiF increasing. However, the aluminum dissolution is nothing to do with the amount of KF; Electrochemical dissolution of aluminum exists in the dissolution process, and it can be suppressed by a suitable external polarization current.(3) Adding KF and LiF can make the cathodic overvoltage increased. There are some relationships between aluminum dissolution and cathodic overvoltage, neither proportional nor inversely proportional.(4) The content of sodium dissolved in Al increases with increasing cryolite ratio of electrolyte, and it decreases with the amount of LiF increasing. However, the content of sodium in Al is nothing to do with the amount of KF. Moreover, the content of lithium in Al increases with the increasing of LiF.Experimental studies have shown that the content of LiF should be appropriate to increase and try to reduce or not use KF even. By these means, it can have a positive effect on reducing the aluminum dissolution and improving the current efficiency. It can also improve the efficiency of aluminum production.