Synergistic leaching of valuable metals from spent Li-ion batteries using sulfuric acid- L-ascorbic acid system

With increase in the number of scrapped portable electronics and new energy powered vehicles, the production of spent Li-ion batteries (LIBs) has increased progressively each year. Harmful substances in spent LIBs can pollute the environment and threaten human health. A sustainable technology should be developed to recycle the spent LIBs. Accordingly, a new environmentally friendly hydro-metallurgical process was proposed for leaching Li, Co, Ni, and Mn from spent LIBs using sulfuric acid with L-ascorbic acid as a reductant. Over the leaching process, several parameters, including sulfuric acid and L-ascorbic acid concentrations, solid to liquid ratio, temperature and time were systematically investigated. The maximum recovery efficiencies of Li, Co, Ni, and Mn were as high as 99.69%, 99.56%, 99.60%, and 99.87% under the optimized conditions (C(H2SO4 concentration) = 1.5 mol/L, C(C6H8O6 concentration) = 0.25 mol/L, the agitation speed was 300 r/min, the liquid-solid ratio was 15 mL/g, and the temperature was 333 K for 60 min), respectively. The synergistic mechanism was analyzed by X-ray diffraction, scanning electron microscopy, and Fourier-transform infrared spectroscopy of the structure of cathode materials, residues, and leachate. The analysis results indicate that the dissolution rate of Ni, Mn, and Co was significantly improved under the condition of adding L-ascorbic acid as a reducing agent. Finally, 98.96 of Ni, 99.57% of Mn, 99.76% of Co, and 89.81% of Li were recovered in the form of C8H14N4NiO4, MnCO3, CoC2O4, and Li2CO3 through precipitation-solvent extraction methods.