Capric acid-driven three-phase antisolvent precipitation strategy for recycling metal and lixiviant from the leachate of spent sodium-ion batteries cathode

Abstract

Conventional methods for recycling metals from the leachate of spent sodium-ion batteries (SIBs) cathodes encounter several challenges, such as high energy consumption, complicated process and environmental pollution. Herein, a capric acid-driven three-phase antisolvent precipitation (CTAP) strategy is used for the low-energy and sustainable recovery of metal and lixiviant from the leachate associated with SIBs cathode vanadium phosphate sodium (NVP) and low-melting mixture solvents (LoMMSs). The CTAP strategy results in a three-phase precipitation, with the upper layer representing the capric acid phase, the middle layer consisting of the lixiviant phase, and the bottom layer comprising the solid phase. Through the CTAP strategy, capric acid achieves the antisolvent precipitation efficiencies of 86.8% for Na and 50.5% for V when applied to leachate from NVP and LoMMS polyethylene glycol 200:phytic acid; nevertheless, capric acid is ineffective in precipitating metals from leachate derived from LoMMSs that combine polyethylene glycol 200 with citric acid, benzoic acid, urea, or acetamide. Additionally, the LoMMSs using polyethylene glycol 200:phytic acid as the lixiviant achieve maximum leaching efficiencies of 99.1% for Na and 94.4% for V from NVP at a mild temperature of 80 °C over 24 hours, with a liquid-to-solid ratio of 200 after optimizing factors, such as hydrogen bond donors, molar ratios, temperature, time, liquid-to-solid ratio and scalability. This work provides an energy-saving, process-simplified and eco-friendly strategy for the separation of metals from SIBs leachate.