Preparation Technology Of Lithium Hydroxide From Purified Brine By Electrolysis

With the development of science and technology, especially in 21 century, the requirements of lithium increase rapidly in many industries. According to the abundant salt lake lithium resource in our country, the exploration of lithium resource from salt lake brine is of great significance. Lithium hydroxide monohydrate, one of the most important raw lithium products has wide application. However, the impurities in lithium hydroxide monohydrate caused by production technology will limit its application.In this thesis, lithium hydroxide monohydrate has been prepared by membrane electrolysis technology using purified lithium chloride. Research works on the electrolytic process are as following:The researches were investigated systematically using self-made electrolysis equipment and DF988 membrane. The effects of initial concentration of catholyte and anolyte, current density, reaction temperature and circular flow on the operating voltage, cathode current efficiency and power consumption have been studied. The results show that the initial concentrations of cathode solution and current efficiency have major impact on the current efficiency. Reaction temperature on cathode current efficiency and power consumption is large. Anolyte initial concentration and circular flow on the conversion have rare significant effects. The optimum conditions in electrolysis process which obtained from single factor experiments and orthogonal test analysis were as follows:22%~28%(mass fraction)of lithium chloride, 2%~3%(mass fraction)of lithium hydroxide, 1.2~1.6 kA·m-2 of current density, 65 ℃ of the temperature and circular flow was 0.3 L·min-1.In the electrolysis process of lithium chloride by ion-exchange membrane for preparation of lithium hydroxide, the pass of ions through an ion-exchange membrane are accompanied by a solvation shell of water molecules.The chloride ion in the anolyte was migrated to the cathode, increasing the salt content of catholyte thus affects the purity of lithium hydroxide. The chloride ion content in catholyte were determined under different conditions, including anolyte initial concentration, catholyte initial concentration, current density, circulation flow and temperature. The results show that Cl- migration was remarkably affected by the reaction temperature and current density. The speed of Cl- migration in electrolysis increases with the increase of reaction temperature and decreases with the increase of current density. The decrease of anolyte concentration can increase the Clmigration. The initial concentration of the electrolyte has an obvious influence on Clmigration, while the speed of Cl- migration was almost affected by the circular flow.Impacts on current efficiency and power consumption of the impurity ions in the anolyte were studied. Besides the lithium ion, there are sodium, magnesium, calcium ions etc. in the brine. The calcium and magnesium ions through the ion-exchange membrane combined OH- and precipitated surface and inside of the membrane blocking the membrane channel in the electrolysis process. So the current efficiency was reduced and power consumption increased. The effects of sodium, magnesium and calcium ion on the electrolytic efficiency were experimented. And the maximum content of ions was determined for normal electrolysis.The most important is the ion-exchange membrane in electrolysis process. It will influence the current efficient, power consumption and operating voltage. The experiments were done using DuPont N2030 membrane(used) and Dongyue Group DF988 membrane. The results show that the electrolysis property of DuPont membrane was significantly better than the domestic membrane.The content of lithium hydroxide is more than 56.5% with low impurity in lithium hydroxide monohydrate product.