HYDROTHERMAL EXTRACTION OF LITHIUM COMPOUNDS FROM PETALITE Li[AlSi4O10]

Based on studies of the decomposition of pe­ta­lite ore, the hydrothermal method for the extraction of lithium and aluminum compounds from lithium aluminosilicate Li[AlSi4O10] (petalite) has been developed. The studied sample of ore contains, wt. %: Li2O – 0.75 and Al2O3 – 14.65. For unenriched petalite ore with low lithium content, it is proposed to use the hydrochemical method of aluminosilicate processing – Ponomarev – Sazhin method. According to this method, the decomposition of ore is carried out directly in autoclaves by chemical interaction of ore components with NaOH solution in the presence of calcium oxide. The conditions (high temperature and pressure) for the destruction of petalite and the transition of lithium into the liquid phase are created exactly in the hydrothermal process. In this case, lithium and aluminum compounds pass into the solution, and calcium and silicon form a partially soluble compound in the solid phase – sodium-calcium hydrosilicateNa2O·2CaO·2SiO2·2H2O. The degree of extraction of lithium reaches 89–94 %, aluminum reaches 77–95 % within 1 hour at a tempe­rature of 240–280 °C, given caustic modulus 14–18, the concentration of the initial solution of 400–450 g/dm3 of Na2O and the ratio of CaO : SiO2 = 1 : 1 in the reaction mixture. Aluminate or lithium carbonate and other compounds can be obtained from an aluminate solution containing 1.5–2.5 g/dm3 of Li2O and 32–44 g/dm3 of Al2O3. The solid phase formed as a result of decomposition, with a high degree of extraction of lithium from the ore contains a small amount of Li2O in its composition and therefore can be used in the cement industry. Depending on the quality of the decomposed raw material, the course of the hydrothermal process is influenced by a set of factors. With a small content of lithium and aluminum in the ore, the caustic modulus of aluminate solutions (αк = 1,645*Na2O/Al2O3) formed after decomposition is important. Its calculation is required in order to determine the amount of alkaline solution of the required concentration to ensure almost complete decomposition of the ore. This value should be higher the lower the decomposition temperature and the concentration of the initial solution to achieve the same degree of recovery of useful components in the liquid phase. With the same caustic modulus, the efficiency of ore decomposition increases significantly with increasing process temperature and increasing the concentration of the initial solution. This can be seen in the values of the degree of extraction of aluminum, which increases by 12 % with increasing temperature from 240 to 280 °C, while the extraction of lithium remains practically unchanged.