Mechanism and technological method of leaching metals from waste lithium-ion batteries by synergistic action of natural organic reductants and mechanochemical method

In this study, litchi peel powder (LPP) was selected as a natural organic reductant to study the mechanism of green leaching of valuable metals from spent lithium-ion batteries (LIBs) by ball milling. LPP and cathode material were co-ball-milled(CBM) with water and then leached, LPP-assisted ball milling reduces the agglomeration tendency of the particles and increases the dispersion. Premixing by CBM makes the LPP and the cathode material fully contracted and tightly fused, and the mechanical force provides the activation energy of the reaction to accelerate the leaching. The leaching rates of Li, Co, Mn and Ni were 99.21 wt%, 96.52 wt%, 98.21 wt% and 94.79 wt% when LPP was added at 0.15 g and only 0.2 mol/L H3Cit was used. Compared with direct leaching, the amount of organic acids was reduced by 86.67 %. The proanthocyanidins contained in the LPP are the key to act as a reducing agent, and proanthocyanidins are the products of the combination of anthocyanins and glycosides. The natural phenolic and ester components in LPP are hydrolyzed into phenolic acids (protocatechulic acid, salicylic acid) and flavonoids (catechins) under the action of H3Cit, which accelerates the dissolution of metal oxides. The mechanism of natural organic reductant in auxiliary ball milling and organic acid leaching was clarified, which provided a new idea for the selection of ball milling auxiliary materials and proposed a economic and environmental protection method to leach valuable metals from spent LIBs.