Recovery of lithium from waste liquid of rock salt brine using aluminum hydroxide precipitation method

An integrated process consisting of Li+ precipitation by Al(OH)3, roasting, water leaching, evaporation, and Li2CO3 precipitation was used to recycle Li+ from the waste liquid of rock salt brine (0.099 g/L Li+). Waste liquid from roc salt brine was discharged wastewater after NaCl crystallization and the removal of impurities in the salt manufacturing plant of the good rock salt mine. The influences of Al3+/Li+ mole ratio, Na+/Al3+ mole ratio, precipitation temperature, and time on the recovery of Li+ were investigated during Li+ precipitation by Al(OH)3 stage. The results showed that the optimal condition was Al3+/Li+ mole ratio = 2.5, Na+/Al3+ mole ratio = 2.2, precipitation temperature of 60℃ (333.15 K) for more than 20 min, whose recovery of Li+ reached 97.25%. The thermodynamic analyses of the simulated Li+–Al+–Mg2+–Cl––H2O system were conducted to construct the potential-pH (φ-pH) diagrams. The results showed that the pH value should be located in the LiCl · 2Al(OH)3 · 2H2O salt region with no formation of Mg(OH)2, which started at pH = ~6.5 and ended at pH from 10.09 to 8.55 as the temperature changed. Subsequently, the Li+precipitate was roasting for the transformation of insoluble LiCl · 2Al(OH)3 · xH2O salt to soluble LiCl, followed by the water leaching to obtain the enriched Li+ solution (1.951 g/L Li+) with Li+ recovery of 85.52%. To meet the requirement of Li2CO3 precipitation, the enriched Li+ solution was evaporated, and Na2CO3 was added to precipitate the Li2CO3 product after SO4 2–, Ca2+, and Mg2+ removal. The total recovery of Li+ was 66.69% after the experimental process, and the purity of Li2CO3 product was 99.3%, which can be regarded as industrial-grade Li2CO3. In conclusion, the success in lithium recovery using the aluminum hydroxide precipitation method provided a new perspective for preparing Li2CO3 from the waste liquid of rock salt brine, which could be considered as a newly developing lithium resource to meet the dramatically increasing demand for lithium in new energy vehicle industry.