Selective removal of magnesium from lithium‐rich brine for lithium purification by synergic solvent extraction using β‐diketones and Cyanex 923

In the production of battery‐grade and high‐purity Li 2 CO 3 , it is essential to remove magnesium impurities. The state‐of‐the‐art solvent extraction (SX) process using Versatic Acid 10 and D2EHPA co‐extracts 3.3–5.5% lithium, while removing 86–98% magnesium. Here, we demonstrate that synergic SX systems containing a β‐diketone (HPMBP, HTTA or HDBM) and Cyanex 923 are highly selective for magnesium extraction over lithium (separation factor α > 1,000). The extracted magnesium and lithium complexes have the stoichiometry of [Mg∙A 2 ∙(C923) 2 ] and [Li∙A x ∙(C923) 2 ] ( x = 1, 2), respectively (A represents deprotonated β‐diketone). The three β‐diketone synergic SX systems all considerably outperformed the Versatic Acid 10 system for magnesium removal from a synthetic solution containing 24 g L −1 Li and 0.24 g L −1 Mg. In a three‐stage batch counter‐current extraction, the HPMBP and Cyanex 923 synergic SX system removed 100% magnesium with only 0.6% co‐extraction of lithium. This excellent Mg/Li separation is the best result reported so far.