Efficient and Sustainable Removal of Magnesium from Brines for Lithium/Magnesium Separation Using Binary Extractants

Abstract Lithium is becoming increasingly important due to its essential role in lithium-ion batteries. Over 70% of the global lithium resources are found in salt lake brines, but lithium is always accompanied by magnesium. It is a challenge to efficiently separate lithium from magnesium in brines. The state-of-the-art processes for lithium/magnesium separation either consume large quantities of chemicals and generate large amounts of waste or are energy-intensive. In this study, we develop a sustainable solvent extraction process based on binary extractants to efficiently separate lithium and magnesium. A binary extractant composed of Aliquat 336 and Versatic Acid 10, [A336][V10], was prepared and investigated for removal of magnesium from both a (synthetic) concentrated brine (106 g L–1 Mg and 10 g L–1 Li) and an (synthetic) original brine (15 g L–1 Mg, 80 g L–1 Na and 0.2 g L–1 Li). Through batch counter-current experiments and mixer–settler experiments, it was found that [A336][V10] is able to quantitatively remove magnesium from the original brine in three continuous counter-current extraction stages with as little as about 10% coextraction of lithium. The loaded organic phase can be stripped and regenerated by water. The whole process (extraction and stripping) does not consume any acid or base but makes use of the differences in the chloride concentration during extraction and stripping. This process is an environmentally friendly alternative to the state-of-the-art processes and represents a step forward in the sustainable production of Li2CO3 from brines.