The Effect of a Molasses Reductant on Acetic Acid Leaching of Black Mass from Mechanically Treated Spent Lithium-Ion Cylindrical Batteries

Abstract

Recovery of valuable metals from end-of-life cylindrical lithium-ion batteries (LiBs) by leaching using acetic acid in the presence of an organic reductant is a promising combination to overcome environmental concerns that arise from employing inorganic reagents. This study investigated the effect of using molasses as a reductant in acetic acid leaching of a mixture of cathode and anode materials (black mass) prepared using mechanical treatments from spent LiBs. The effects of temperature, solid/liquid ratio, stirring speed, and acid concentration on the leaching of target metals (Co, Ni, Mn, and Li), current collector metal foil elements (Al and Cu), and Fe from the battery casing, with and without reductant, were investigated to obtain the optimum leaching conditions. The effect of adding the molasses at the start of leaching and after 1 h of leaching was tested. Acid leaching without molasses extracted the target metals Li, Ni, Co, and Mn with an efficiency <35% for all leaching parameters. However, the Al and Fe extractions increased as the acid molarity increased. Molasses addition at the start of leaching increased the extraction of the target metals to >96% at temperatures >50 °C. This is likely due to oxidation of the reducing sugars in the molasses that reduced the insoluble Co(III), Ni(III), and Mn(IV) components to soluble Co(II), Ni(II), and Mn(II) species, respectively. The kinetics of Co extraction in the presence of molasses were analysed, which has indicated that the rate-determining step in the Co leaching process is the reduction of Co(III) on the surface of particles in the black mass. Excess molasses can precipitate out target metals, especially Co, due to the presence of oxalic acid in the molasses. The reducing effect precipitated Cu(II) to Cu2O, and could further reduce Co to metal, which suggests that leaching with the optimum dosage of acetic acid and molasses may selectively precipitate copper.