Sustainable and efficient recovery of lithium from sodium sulfate by-product of lithium hydroxide production process using solvent extraction

Abstract

Currently, with the increasingly stringent requirements of carbon emissions and the rapid development of the new energy industry, the strategic position of lithium has been elevated unprecedentedly. Improving the lithium yield in the ore lithium extraction process is very important for the sustainable development of the lithium production industry. In this study, the by-product mirabilite from the lithium hydroxide production was treated as the material to deeply recover lithium. The effect factor of equilibrium extraction, the separation mechanism, and the removal of residual organic matter was discussed. The results showed that the optimized organic phase composed of 0.5 M 1-benzoyl-2-nonanone(HBNA) and 0.5 M trialkyl phosphine oxide(TRPO) could effectively extract lithium from mirabilite dissolved solution, and 99% of lithium could be recovered through 3-stage countercurrent extraction under the condition of O/A = 1/1, mixing time = 5 min, and temperature = 20 °C. The 95% of co-extracted sodium in the loaded organic could be easily eluted by 0.5 M HCl at an O/A = 10/1, and afterward, the lithium in the organic phase could be concentrated to 25 g/L through stripping by HCl or H2SO4. The dissolved organic matter in the extraction raffinate was deeply removed by the resin adsorption method under the condition of pH = 2.0, adsorption time = 4 h, and solid to liquid ratio = 1/5. The DFT study demonstrated that the complexes have the lowest energy and the most stable structure when the stoichiometric ratio of Li, HBNA, and TRPO is 1:1:1 and a dimer is formed. This process provided a novel approach to improving the lithium recovery of lithium hydroxide production.