Unlocking Battery-Grade MnSO₄ via Synergistic Chelator Regulation: Molecular Insights into Inhibiting Ca/Mg...

The selective removal of divalent cations like Ca²⁺ and Mg²⁺ from a matrix containing a predominant divalent ion (Mn²⁺) is the fundamental challenge in inorganic synthesis, critically impeding the production of battery-grade MnSO₄. Current purification methods are plagued by high energy consumption due to the similar physicochemical properties of these ions. Herein, we report a breakthrough strategy that addresses this selectivity issue via the synergistic use of multidentate chelators. Using MnSO₄ feedstock containing 756.87 mg·kg^-1 Ca²⁺ and 2126.67 mg·kg^-1 Mg²⁺, we integrated diethylenetriaminepentaacetic acid (DTPA) and citric acid (CA) into a conventional crystallization process. This approach selectively sequesters Ca²⁺ and Mg²⁺, effectively inhibiting their cocrystallization without complicating manganese recovery. As a result, the removal efficiencies for Ca²⁺ and Mg²⁺ are markedly enhanced, reaching 94.6% and 95.1%, respectively. This molecular-level design reduces the required number of crystallization cycles to just two, significantly lowering the energy footprint. The product unambiguously qualifies as battery-grade. Beyond the practical achievement, we provide a profound mechanistic understanding through DFT calculations, which quantify the relative binding affinities and coordination mechanism of the chelator cocktail, rationalizing the observed synergy. This study represents a fundamental advance in the application of coordination chemistry to control crystallization processes, offering a powerful and general platform for the purification of advanced inorganic materials.