Removal of fluoride from the mixed Ni-Co-Mn sulfate leach solution of spent lithium ion batteries using polyaluminum sulfate

Abstract

The mechanism and application of defluorination in a simulated leaching solution of spent lithium-ion batteries (LIBs) using poly‑aluminum sulfate (PAS) were studied. The experimental results indicated that reaction parameters such as the molar ratio of Al to F, pH of the solution, reaction temperature, initial concentration of fluorine, and concentration of lithium and nickel, significantly affected the reaction efficiency. Under the optimum reaction conditions, the percentage of defluorination was 95.5 (wt%). During the defluorination reaction, Al3+, Al(OH)3 reacted with F−, HF to generate AlF3 and AlF(OH)2. The crystallinity of AlF3, AlF(OH)2, and Al(OH)3 and the chemical stability of the precipitates improved with the increase in temperature and pH. The Li+ concentration in the solution increased the defluorination efficiency by forming LiAlF4. At the same time, high concentrations of NiSO4 inhibited the defluorination effect and were lost in association with the solids, NiSO4·6H2O and Ni(OH)2. According to the study of reaction kinetics, the rate equation of the aluminum‑fluorine reaction was -d[F]/dt = 0.0384exp(−8.59/RT) [F0]1.11[Al]0.31. The activation energy of the precipitation reaction was 8.59 kJ/mol, and the reaction rate was relatively high. In the actual defluorination process of the acid-leaching solution of waste battery powder with Ni-Mn-Co chemistry, the F− concentration reduced from 1205 mg/L to 48 mg/L and the loss of valuable metals was <6%, and the Ni, Co, and Mn in the precipitates were predominantly sulfates and hydroxides.