Closed-loop recovery of waste lithium iron phosphate by safe and environmentally friendly nitric acid selective leaching with bipolar membrane

Abstract

While nitric acid is efficient for recycling spent LiFePO₄ cathodes, its inherent explosion risk poses major safety and storage challenges. This work presents a safe and environmentally friendly closed-loop process that integrates HNO₃/H₂O₂ selective leaching with bipolar membrane electrodialysis (BMED) to eliminate these hazards. The optimized leaching step achieves exceptional selectivity, extracting 99.6% of lithium while suppressing iron dissolution to 2.7%, through the synergistic oxidation provided by HNO₃ and H₂O₂. The core innovation lies in using a custom BMED stack to treat the resultant lithium-rich waste solution, in situ regenerating both HNO₃ (>85% purity) and NaOH (>95% purity) with over 90% recovery. Crucially, these regenerated reagents are directly recycled into the leaching and purification steps, creating a true closed-loop that obviates external nitric acid procurement and storage. The entire system recovers ∼99% of valuable metals with a BMED energy consumption of 17.26 kW h kg⁻¹ and a high current efficiency of up to 88%. This study demonstrates a sustainable and hazard-free recycling route for LiFePO₄ batteries, transforming the problematic nitric acid into a safely circulating reagent within a closed-loop.