Research On The Extraction Of Metallic Aluminum From Primary Aluminum-silicon Alloy Produced By Electrothermal Method

In recent years,with the rapid development of the aluminum industry,the contradiction between the shortage of bauxite and the supply of alumina has become increasingly prominent,and the development of the aluminum industry is facing huge challenges.Actively exploring non-traditional aluminum-containing minerals to produce metal aluminum and research and development of new aluminum smelting methods can not only alleviate the problem of insufficient aluminum resources in my country,but also promote the sustainable development of the aluminum industry.Using low-grade aluminum-containing resources or aluminum-containing solid wastes as raw materials to produce primary aluminum-silicon alloy by carbon electrothermal reduction,and then using primary aluminum-silicon alloy as raw materials to extract metal aluminum by electrolysis is a new energy-saving and environmentally-friendly aluminum smelting process.Not only can it alleviate the dual pressure of our country’s resources and the environment,but it can also open up a new path for aluminum production technology.The main research content of this subject is the extraction of aluminum from aluminum-silicon alloys by electrolysis.The mechanism of electrolytic aluminum extraction in NaCl-KCl-Na3AlF6 and AlCl3-NaCl-KCl molten salt systems and the effect of different process parameters on the electrolysis of aluminum-silicon alloys are discussed.The step cooling curve method and the CVCC method were used to measure the primary crystal temperature and conductivity of the NaCl-KCl-Na3AlF6 system.The test results show that when the msaa ratio of NaCl-KCl-Na3AlF6 is 1:1.28:0.3,the minimum primary crystal temperature is 632℃,the higher conductivity is 2.55κ/S·cm-1,The experiment of electrolytic aluminum extraction with the molten salt system of this ratio shows that when the electrolysis temperature is 690℃,the cathode current density is 0.2A·cm-2,and the electrolysis time is 1.5h,the current efficiency can reach up to 78%.The purity of the product obtained by electrolysis in this system is about 94%,and the main impurities in the electrolysis product are silicon and iron.Different electrolysis process parameters were set,and the AlCl3-NaCl-KCl(66:20:14 wt%)ternary molten salt system was used to conduct an experimental study of aluminum-silicon alloy electrolytic extraction.The experimental results show that when the electrolysis temperature is 170℃,the cathode current density is 30mA·cm-2,and the electrolysis time is 1.5h,the current efficiency can reach more than 94%,and the aluminum purity of the electrolysis product can reach 99.3%.During electrolysis under this experimental condition,the impurities in the anode do not participate in the reaction,and the process of Al deposition is the reduction process of Al2Cl7-and AlCl4-.Using Princeton PARSTAT 2273 electrochemical workstation,linear sweep voltammetry and potentiostat chronoamperometry were used to investigate the behavior of anode impurities in the electrolysis process.The research results show that the magnesium and calcium in the anode will dissolve into the molten salt before the aluminum,but because of their higher decomposition voltage,they will not affect the purity of the electrolysis product.The discharge sequence of the ions in the electrolyte is:Fe>Si>Al>Mg>Ca.The potentiostatic electrolysis test shows that when the electrolysis potential is 0.3 V,the purity of the cathode aluminum can reach 99.9%.With the increase of the electrolysis potential,the impurity silicon and iron will also undergo electrochemical dissolution,resulting in the deterioration of the quality of the cathode product.