Basic Study on Lithium Recovery from Lithium Containing Solution

Abstract

Abstract Basic study of Li recovery using high purity sodium aluminate solution as coprecipitating agent has been made. Al concentration, pH and temperature greatly affect the Li recovery, and in this study the temperature was maintained constant (25 °C). For reference lithium solution, the optimum (initial) pH obtained increased with an increase in Al concentration. Optimum pH=11.0–12.5 for [Al]=50–1000 mg dm−3. The optimum pH values obtained were lower than those in the previous work by about one pH unit. The following relationship was found between the Al concentration CAl (mg dm−3) and the optimum pH; Opt. pHexp=8.23+1.5log CAl. Furthermore, these experimental pH values were in fair agreement with the pH values calculated from the solubility product of aluminium hydroxide, Ksp (HAlO2)=[H+][AlO2−]=10−13.2, i.e., pHcalcd=9.5+log CAl. Effects of coexistent ions on Li recovery were examined. Sodium and potassium ions did not interfere, while calcium, magnesium, and monosilicate ions did. However, the interference from Ba2+ ions was small. Especially, interference by calcium and monosilicate ions were significant. Bubbling of CO2 gas into the Li solution with proper Al concentration made a remarkable improvement on Li recovery. Accordingly, the influence of water soluble carbonates on Li recovery was investigated. The carbonates (Na2CO3, K2CO3, (NH4)2CO3) used were found to be very effective for Li recovery. The addition of sodium aluminate solution (500 mg dm−3) to untreated geothermal water showed around 70% of Li recovery at the best. This incomplete recovery of lithium is due to the matrix effect of geothermal water. For reference Li solution with Al concentration of 500 mg dm−3, optimum pH was 12.5, while for Ca, SiO2-free geothermal water the same pH gave very low Li recovery. However, when a pH value of 11.5 is chosen, a remarkable increase in Li recovery was obtained (98–99%). The silica component in geothermal water interfered with the Li recovery, but the influence was relatively small. The silica in the geothermal water in this case, was polymerized and showed some buffering action, such as prevention of interference from calcium ions. This is the significant difference between poly and monosilicate ions which do not show any buffering action. The addition of sodium carbonate to the Ca,SiO2-free geothermal water caused a remarkable acceleration of the Li recovery, similar to that for the reference Li solution.