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.