Recovery of lithium from oxalic acid leachate produced from black mass of spent electric vehicle Li-ion batteries

Abstract

Lithium (Li) demand is surging due to the adaptation of Lithium-ion batteries (LIBs) in electric vehicles (EV). To ease the supply from virgin sources and meet new legislative recycling targets it's imperative to secure supply from secondary sources. Recently oxalic acid leaching has been reported for early-stage recovery of Li from black mass (BM) of spent EV LIBs. Such processes often face challenges in electrodes separation, thermal treatment of cathode material, and leachate up-concentration. Herein, the synergistic application of benzoyltrifluoroacetone (HBTA) and trioctylphosphine oxide (TOPO) to extract Li from oxalate streams of an industrial BM has been demonstrated for the first time. Under optimum conditions, ∼92 % Li was extracted from the leachate in 6mins, aqueous/organic (A/O) phase ratio 1, and pH 11. McCabe Thiele diagram indicated two counter-current stages for the complete extraction of Li at A/O 1. The slope analysis method indicated equal moles of HBTA required to extract Li and FT-IR spectroscopy confirmed the synergism of the extractants. The organic phase was scrubbed with Li salt and stripped with hydrochloric acid (HCl) resulting in a concentrated (Li ∼4 mol/L) solution precipitated as lithium carbonate (>99 % pure). The transition metals during oxalic acid leaching were reduced and precipitated as respective oxalates due to low solubility. They were successfully recovered using a second leaching step with HCl. The excess acid was recovered as oxalic acid by cooling crystallization, not reported earlier for BM recycling streams, facilitating a closed-loop process. The developed flowsheet significantly advances the early-stage Li recovery processes from BM.