Synergistic Solvent Extraction of Ni, Co, and Mn from Ca/Mg-Containing Sulfate Solutions for Battery Metal Refining

Efficient recovery of nickel, cobalt, and manganese from Ca- and Mg-rich sulfate leachates is essential for battery-grade precursor production. A synergistic solvent extraction (SSX) system combining N,N-bis(4-thiazolylmethyl)octylamine (NNBT) with acidic organophosphorus extractants was developed to achieve coextraction of Ni, Co, and Mn. Among various combinations, the D2EHPA–NNBT system exhibited the highest selectivity and cost efficiency, enabling complete extraction of Ni, Co, and Mn while suppressing Ca and Mg transfer. Multistage countercurrent and scrubbing operations further reduced impurities, producing high-purity Ni–Co–Mn sulfate solutions suitable for battery applications. Thermodynamic and spectroscopic analyses confirmed that synergism originated from selective coordination and cation-exchange interactions. This study demonstrates a practical and scalable route for selective Ni–Co–Mn recovery from impurity-rich sulfate solutions, contributing to the efficient and sustainable hydrometallurgical processing of battery metals.