Herein is reported a novel green process involving natural l-tartaric acid leaching, developed for the sustainable recovery of Mn, Li, Co, and Ni from spent lithium-ion batteries (LIBs). Operating conditions affecting the leaching efficiencies of Mn, Li, Co, and Ni, including the concentrations of l-tartaric acid (C4H6O6) and hydrogen peroxide (H2O2), pulp density, temperature, and leaching time, were investigated. The leaching efficiencies were 99.31% for Mn, 99.07% for Li, 98.64% for Co, and 99.31% for Ni under the optimized conditions (4 vol% H2O2, 2 M l-tartaric acid, 17 g/L pulp density, 70 °C, and 30 min). The leaching mechanism was studied preliminarily based on the structure of l-tartaric acid. The kinetics data for the leaching of Mn, Li, Co, and Ni fit best to the shrinking-core model of chemical control. For the first stage, the activation energies (E as) for the leaching of Mn, Li, Co, and Ni were 66.00, 54.03, 58.18, and 73.28 kJ/mol, respectively. For the second stage, the E as for the leaching of Mn, Li, Co, and Ni were 55.68, 53.86, 58.94, and 47.78 kJ/mol, respectively. The proposed hydrometallurgical process was found to be simple, efficient, and environmentally friendly.

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The effects of metal ions such as Na + , K + , Mg 2+ , Cu 2+ , Al 3+ , and Fe 3+ on the crystal morphology and size of calcium sulfate whiskers in aqueous HCl solutions were investigated. The average diameter, aspect ratio, length, crystal water content, phase composition, and elemental composition of the products were determined and compared. When the concentration of monovalent Na + or K + ions was low, with the increase in the ion concentration, the average diameter increased and the aspect ratio decreased. However, with further increase in the ion concentration, the average diameter decreased. The presence of divalent Mg 2+ or Cu 2+ ions increased the crystal diameter and length. All the products were calcium sulfate hemihydrate in the presence of Na + , K + , Mg 2+ , or Cu 2+ ions within the studied concentration range. The presence of trivalent Al 3+ or Fe 3+ ions at low concentrations resulted in bigger and shorter crystals; furthermore, at higher ion concentrations, partial phase transformation from calcium sulfate hemihydrate to calcium sulfate dihydrate was induced. Among the metal ions investigated, only Na + ions were found be incorporated into the crystals.

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