The Research On The Solubility Of Aluminum In Cryolite-based Electrolyte

Current efficiency is an important production index in aluminum electrolysis industry.However,aluminum dissolves into the electrolyte by the means of physical dissolution or chemical reaction,and is oxidized by anode gas,which is one of the most significant reasons for the loss of current efficiency.Therefore,the dissolution of aluminum has captured much attention for a long time.The solubility of aluminum is generally used to describe the capacity of aluminum dissolving in the electrolyte.The studies on solubility of aluminum in cryolite-based electrolyte have been reported seldom,and a consistent conclusion has not yet formed.In this article,we measured the solubility of aluminum in the electrolyte by volumetric method,exploring the influence factors of aluminum solubility and the form of aluminum dissolution.The influence of cryolite ratio,the content of KF,the mass ratio of electrolyte and aluminum on the solubility of aluminum has been explored by a race gas measurement device.The results show that aluminum solubility vary from 0.013%to 0.02%in CR=2.2?3.0 NaF-AlF3-5wt%CaF2-3wt%Al2O3 melts system with the addition of 0?5wt%KF at 980?.The content of KF has no obvious effect on the solubility of aluminum in the same cryolite ratio melts.The solubility of aluminum increases with the increase of cryolite ratio,from 0.014wt%in CR=2.2 to 0.026 wt%in CR=4.0.The content of sodium both in quenched samples and in aluminum increases with increasing molar ratio of NaF/AlF3,which may be partly attributed to the chemical reaction of Al+4NaF=NaAlF4+3Na.Higher mass ratio of bath/aluminum gave lower value of solubility before aluminum dissolved saturation.The system with a ratio of 2 is selected to achieve more accurate aluminum solubility.0?7wt%Al2O3,MgF2,CaF2 and LiF has been respectively added into CR=2.4 NaF-AlF3 electrolyte to explore the influence of alumina and additions on aluminum solubility.The results show that alumina may promote aluminum to dissolve into melts in the form of a colloidal dispersion of aluminum,which give poor-reproducibility data that fluctuates apparently between 0.0152%and 0.0326%.The solubility of aluminum decreases with the decrease of MgF2 and CaF2 content.Considering the chemical reaction of MgF2+2/3Al=Mg(in Al)+2/3AlF3,magnesium content in aluminum increases with increasing of MgF2.There is no notable effect on aluminum solubility adding LiF,which concentrates around 0.025%.The content of sodium and lithium are almost stable.