Study On The Determination Of Cryolite Ratio And The Recovery Of Li,K In Complex Aluminum Electrolyte System

With the rapid development of electrolytic aluminum industry,a large number of raw alumina containing lithium and potassium were used as electrolytic aluminum raw material in enterprises.This will lead to the enrichment of Li and K in the aluminum electrolytic cell,resulting in the transformation of aluminum electrolyte into a complex system.It can be seen from the actual production situation that the high content of Li and K in aluminum electrolyte has an adverse influence on the electrolytic aluminum production,such as reduction of current efficiency,high energy consumption and uncontrollability of the productive process.Moreover,these impacts are sustained.Therefore,solving the problem brought by the complex aluminum electrolyte has become an important research direction of electrolytic aluminum industry in China.This dissertation focuses on the effect of Li and K on the phase formation of the complex aluminum electrolyte system.The improved mothed of calculating value cryolite ratio by XRD and fluoride ion selective electrode were proposed.The recovery of Li and K in the complex aluminum electrolyte by acid leaching and the kinetics of leaching process were studied.The mechanism of extracting potassium from the potassium-rich aluminum electrolyte by sulfuric acid is investigated by Raman spectroscopy combining with calculating the solution coordination number.Ultimately,the technique extracting of Li and K from aluminum electrolyte by sulfuric acid was invented.The phase of the sample including LiF,KF,AlF3,NaF-3wt%Al2O3-3wt%CaF2 was characterization by XRD,and the effect of Li,K and Ca in the complex aluminum electrolytes was explored by alkalinity ratio.Based on the explored phase composition rule,the aluminum electrolyte cryolite ratio formula measured by XRD was improved,the coefficient of correspondence(N)and the corrected values(?1 and?2)in the cryolite ratio formula by fluoride ion selective electrode method were calculated.The cryolite ratio of complex aluminum electrolyte was determined by using the above two improved methods,and the results show that both methods are suitable for the determination value cryolite ratio of the industrial complex aluminum electrolyte.In addition,the test accuracy is improved and the problem of measuring complex electrolyte error is solved.Extracting Li from the Li-rich aluminum electrolyte using acid was studied.In the concentration of 14 mol/L nitrate solution and the liquid to solid ratio of 12.5,the leaching rate was 93.21%after stirring for 120 min with 300 r/min at 80?.The analysis of dynamics shows that the process of leaching is controlled by unreacted contraction nuclear proliferation,and the apparent reaction activation energy is 18.10 kJ/mol,which indicates that the process is controlled by diffusion.The rate equation of acid leaching is as following 1-3(1-X)2/3+2(1-x)=2.5713 ×e-217(1/T)tLithium element in acid leaching solution was precipitated by adding Na2CO3.Under the situtation that mother liquid at the reaction temperature is 90?,Li+concentration of 15 g/L,the reaction time of 75 min,the dosage of Na2CO3 is1.1 times of the theory,the aging time under the condition of 150 min,Li+ recovery,in the form of Li2CO3 precipitation,can reach up to 92.70%,and the grain size of Li2CO3 increased with the increase of aging time.Extracting K from the K-rich aluminum electrolyte by sulfuric acid was studied.In the concentration of 14 mol/L nitrate solution,the liquid to solid ratio of 10,and the leaching rate was 98.62%after stirring for 150 min with 300 r/min at 80?.K2NaAlF6 can be dissolved in nitric acid,and the acid leaching mechanism of K2NaAlF6 was studied.In addition,NaF is added into K2NaAlF6 nitric acid solution until the molar ratio of NaF and AlF3 in solution is greater than 3.0,and NaF will combine with Al-F complex ions in solution to generate Na3AlF6 and Na5Al3F14 precipitation.The equation of leaching reaction of complex aluminum electrolyte in nitric acid is described as follows4K2NaAlF6+8NaF+12HNO3=Na3AlF6+Na5Al3F14+8KNO3+4NaNO3+12HFThe analysis of dynamics shows that the process of leaching is controlled by unreacted contraction nuclear proliferation,and the apparent reaction activation energy is 19.38 kJ/mol,which shows that the process is controlled by diffusion.The rate equation of acid leaching is as following 1-3(1-x)2/3+2(1-x)=4.0592×e-2331(1/T)tAfter acid leaching and evaporated process of aluminum electrolyte containing K,a mixture of KNO3 and NaNO3 can be obtained.The industrial complex aluminum electrolyte containing Li and K can be leached by acid and thel complex aluminum electrolyte should be based on composition analysis before acid leaching.If Li is in the form of undissolved Na2LiAlF6 phase,it is necessary to convert it to soluble LiF by adding NaF into the aluminum electrolyte.In the concentration of 14 mol/L nitrate solution,and the liquid to solid ratio of 12.5,the leaching rates of Li and K were 91.38%and 92.42%,respectively,after stirring for 120min with 300 r/min at 80?.After the processes of neutralize,evaporation and precipitating by Na2CO3,Li2CO3 can be obtained,and a mixture of KNO3 and NaNO3 can be obtained by evaporating the filtrate after precipitating Li2CO3.