Selective separation of lithium, magnesium and calcium using 4-phosphoryl pyrazolones as pH-regulated receptors

Ensuring continuous and sustainable lithium supply requires the development of highly efficient separation processes such as LLE (liquid-liquid extraction) for both primary sources and certain waste streams. In this work, 4-phosphoryl pyrazolones are used in an efficient pH-controlled stepwise separation of Li${}^{+}$ from Ca${}^{2+}$, Mg${}^{2+}$, Na${}^{+}$ and K${}^{+}$. The factors affecting LLE process, such as the substitution pattern of the extractant, diluent/water distribution, co-ligand, pH, and speciation of the metal complexes involved, were systematically investigated. The maximum extraction efficiency of Li${}^{+}$ at pH 6.0 was 94 % when Mg${}^{2+}$ and Ca${}^{2+}$ were previously separated at pH<5.0, proving that the separation of these ions is possible by simply modulating the pH of the aqueous phase. Our study points a way to separation of lithium from acid brine or from spent lithium ion battery leaching solutions, which supports the future supply of lithium in a more environmentally friendly and sustainable manner. (© 2023 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH)