Effect Of Alkali Metals On The Properties Of Electrolytes And Cathodes In Aluminum Electrolysis

There are some impurities contained in domestic alumina,especially a certain amount of Li in alumina which would lead to the enrichment of the high-concentrations lithium salts in electrolytic cell during aluminum produced and the content of lithium is up to about 8%.The constant change of composition affects the physicochemical property of the electrolyte in electrolytic cell,especially the lithium-rich electrolyte greatly reduces the solubility of Al₂O₃ and the precipitation is easy to form at the bottom of the electrolytic cell.The intercalation compound formed by alkali metals penetration further reduces the service of the electrolytic cell.Potassium fluoride can improve the solubility of alumina,but the radius of potassium ion is much larger than that of sodium in the same main group,so the intercalation compound formed by its infiltration into the cathode it is more harmful to the damage of the cathode.KAlF₄ is a tetragonal crystal system with a small dissociation and good stability under high stability.Even if the temperature exceeds the melting point,it can still behaves as KAlF₄ and molecular groups in the entire liquid phase,compared with the traditional additive KF.So it can replace KF additives.This paper aims at the problems in the electrolytic process of lithium-rich electrolyte.By adding KAlF₄ to the electrolyte,the relationship between its content and the initial temperature of electrolyte and the solubility of alumina was discussed.At the same time,in order to further understand the influence of the alkali metal precipitated during the electrolytic process on the performance of aluminum electrolytic cathodes,the effect of intercalation compounds on the properties of carbon cathode materials was studied from the atomic scale.In order to study the influence of KAlF₄ on the physicochemical properties of lithium-rich electrolyte,the liquidus temperatures and the solubilities of Al₂O₃ were tested for lithium-rich electrolyte with different content of KAlF₄ by cooling curve and the mass loss of rotating sintered corundum disc,respectively.The components and microstructure of the lithium-rich electrolyte were studied by X-ray diffraction(XRD)and scanning electron microscopy(SEM).The results show that the solubilities of Al₂O₃ in melts could be decreased by Li Na₂Al F₆ generated easily through the reaction between Li⁺and Al F₅^2-.It could result in decreasing the liquidus temperatures and improving the solubilities of Al₂O₃ adding proper amount of KAlF₄ to lithium-rich electrolyte,for low-temperature aluminum electrolysis purposes.This work has important theory guidance significance for the production of lithium-rich electrolyte during low-temperature aluminum electrolysis.The electronic structure and mechanical properties of the carbon cathode for aluminum electrolysis by potassium were investigated by using the first principle calculations based on density functional theory.The expansion of cathode carbon materials was studied at atomic scale by a modified Rapoport equipment.The results show that the interaction between C-K increases with the intercalation of potassium atoms.The number of C₃₂K at the Fermi level increases in the process of K insert into graphite,indicating the improvement of electrical conductivity.The structural stability deteriorates in the process of K insert into graphite.The theoretical results of carbon cathode materials by potassium are consistent with methods from experiment.