Direct recovery of high-purity Li3PO4 from ternary brines via solubility-driven separation in redox flow desalination

초록

The escalating demand for high-purity lithium to support the global transition to electric vehicles necessitates the development of efficient technologies for extracting lithium from complex aqueous sources such as continental brines and battery leachates. However, effective lithium fractionation is often hindered by the presence of chemically similar monovalent sodium and divalent magnesium. Here, we present an integrated single-cell redox-flow desalination (RFD) system capable of direct lithium recovery as high-purity Li3PO4. The system utilizes a solubility-driven Li/Na phase-separation mechanism, complemented by an ethylenediaminetetraacetic acid-assisted chelation strategy to exclude Mg2+ interference. Optimization of the electrochemical parameters revealed that a low current (15 mA) is critical for maximizing precipitation kinetics while keeping the cell-level specific energy consumption at 0.4 kWh/mol of Li (57.6 kWh/kg Li). Li3PO4 formation was consistently achieved, even at a disadvantageous Li:Na ratio of 1:10. The addition of 3% H3PO4 to the FePO4 cathode further enhanced performance, achieving a peak precipitation efficiency of 56.1% by reducing internal cell resistance. The resulting Li3PO4 product exhibited high purity (98.6%). The proposed RFD configuration provides a single-cell pathway for the direct production of high-purity Li3PO4 from multi-ion feedstocks, significantly reducing the process complexity and chemical intensity associated with conventional hydrometallurgical methods. © 2026 Elsevier B.V.

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