Selective lithium recovery from LFP-Type black Mass: Comparative evaluation of inorganic and organic acid systems under Constant-pH leaching conditions

A systematic comparison of inorganic and organic acids under constant-pH conditions identifies acetic acid as a green, selective, and low-temperature leaching system for lithium recovery from LiFePO 4 black mass. • Constant-pH leaching enables precise control of Li extraction and selectivity. • Acetic acid achieves 96% Li recovery with < 0.1% Fe dissolution at 25 °C. • Systematic comparison reveals acid–oxidant chemistry governs LiFePO 4 leaching. • FePO 4 residues produced are suitable for direct relithiation and cathode reuse. • Acetic and HCl systems combine high efficiency, selectivity, and sustainability. The rapid growth of lithium iron phosphate (LiFePO 4 , LFP) batteries in electric vehicles has intensified the need for efficient and sustainable recycling. This study systematically compares five acid–oxidant systems, H 2 SO 4 , HCl, HNO 3 , H 2 C 2 O 4 , and CH 3 COOH, for selective lithium recovery from spent LFP black mass under constant-pH leaching conditions. The effects of pH, temperature, and H 2 O 2 concentration were evaluated using a statistically designed framework. Characterization by SEM–EDX, Raman spectroscopy, XRD, and ToF-SIMS confirmed that the feed consisted of crystalline LiFePO 4 and graphitic carbon phases with Li- and F-enriched surfaces. All systems achieved high Li extraction (>95%) under optimized conditions, but selectivity depended on acid chemistry and oxidation potential. Sulfuric and hydrochloric acids enabled near-complete Li recovery, with HCl showing superior selectivity (Li:Fe > 100) at 38 °C. Nitric acid alone exhibited limited oxidative strength, but addition of H 2 O 2 significantly improved efficiency. Oxalic acid dissolved Li completely but lacked selectivity due to ferrioxalate complexation. Acetic acid delivered the best overall performance, achieving 96% Li recovery with negligible Fe (<0.1%) and minimal P (3%) dissolution at pH 4.3 and 25 °C. Cost analysis showed that while sulfuric acid is least expensive, acetic and hydrochloric acids offer the best balance of selectivity, efficiency, and safety. This study provides a unified framework for evaluating leaching systems and demonstrates that selective lithium recovery from LFP can be achieved under mild, low-acid conditions with minimal environmental impact.