Study On The Dissolution And Electrolytic Performance Of Na₂O·xAl₂O₃ In Low Temperature Electrolyt

Carbon free aluminum electrolysis technology based on inert anode eliminates greenhouse gas emission in the process of aluminum electrolysis.However,the corrosion rate of inert anode in high temperature molten salt is fast,which hinders the industrial application of this technology.Low temperature aluminum electrolysis technology can greatly reduce the corrosion of inert anode,prolong the service life of inert electrode,inert electrode aluminum electrolysis technology is only combined with low temperature aluminum electrolysis technology is easier to achieve success..The main problem of low temperature aluminum electrolysis is the slow dissolution rate of alumina,so improving the dissolution rate of alumina in low temperature electrolyte will become the key to industrialization of low temperature aluminum electrolysis technology.In this project,it is innovatively proposed to use Na₂O·x Al₂O₃（x is 50-90）as raw material for aluminum electrolysis to improve the dissolution rate of alumina in low-temperature electrolyte.In this paper,the effects of different roasting temperatures,different components of Na₂O·x Al₂O₃（x is the molar ratio of Al₂O₃to Na₂O）raw materials,electrolyte components,temperature and other factors on the solubility of alumina were investigated,and analyzed from the perspective of kinetic characteristics,and finally electrolytic experiment was carried out.The main conclusions are as follows:（1）At the same molten salt temperature,the solubility of alumina in electrolyte increases with the increase of cryolite ratio（CR）.When CR is the same,the solubility of alumina in electrolyte increases with the increase of molten salt temperature,and the effect of molten salt temperature on the solubility of alumina is enhanced with the increase of CR.At the same temperature of CR and molten salt,the alumina solubility in the electrolyte decreased with the increase of the addition of Li F and Ca F₂,and the effect of Li F on the alumina solubility was significantly greater than that of Ca F₂.（2）After adding Na₂O to alumina,the dissolution rate of alumina in the low temperature electrolyte is accelerated.The higher the content of Na₂O in alumina,the faster the dissolution rate.Na₂O·70Al₂O₃in the NaF-KF-AlF₃-Ca F₂-Li F system,the larger the electrolyte CR,the faster the alumina dissolution rate in molten salt.When the temperature of CR and molten salt remains unchanged,the average dissolution rate of alumina decreases by 6%when the content of NaF increases from 30%to 40%.When Ca F₂and Li F were added to the electrolyte,the average dissolution rate of alumina was reduced by 10%.In the molten salt temperature range of 750-850℃,the average dissolution rate of Na₂O·x Al₂O₃under molten salt is 1.5-3 times that of blank Al₂O₃.（3）When the dissolution time of alumina in molten salt is 0-5 minutes,the dissolution of alumina follows the zero-order reaction,and the dissolution rate is faster;When the time is 5-240 min,the dissolution of alumina follows the first order reaction and the dissolution rate slows down.The zero-order reaction rate constant is greater than the first-order reaction rate constant,indicating that the dissolution rate of alumina is the fastest in 0-5 minutes.Diffusion control is dominant in alumina dissolution reaction.With the increase of CR and the influence of temperature,the dissolution reaction in molten salt is easier to proceed,which is reflected in that k（reaction rate）increases with the increase of CR.（4）In the constant current electrolysis of NaF-KF-AlF₃system,under the premise of a certain feeding amount,the electrolytic cell adding blank alumina has a higher voltage and is prone to anode effect,indicating that the dissolution rate of blank alumina is lower than that of Na₂O·70Al₂O₃raw material.The increase of molten salt temperature can promote the dissolution rate of alumina in the electrolyte and reduce the voltage of electrolytic cell,while the addition of Ca F₂-Li F can inhibit the dissolution rate of alumina in the electrolyte,which is easy to appear anode effect.