Selective extraction of Li and Mn from spent lithium-ion battery smelting slag: insights from isomorphous replacement in minerals

Recycling the high content of valuable metal elements contained in spent lithium-ion batteries (SLIBs) has attracted significant interest. By leveraging the concept of substitution of isomorphous replacement in earth minerals, this study proposes a novel approach for the selective extraction of Li and Mn from the artificial spodumene-type lithium-rich slag comprising LiAlSi2O6 and Mn2SiO4 through two-step selective roasting process with Na2SO4 and CaCl2, respectively. The thermodynamic calculations confirmed the feasibility of selective Li extraction by Na2SO4 roasting, with the experimental results showing that over 99% Li was preferentially extracted as LiNaSO4. In the subsequent CaCl2 roasting step for Mn recovery, the Mn2SiO4 was effectively transformed into soluble Na2MnCl4, achieving a maximum Mn extraction efficiency of 86.5%. The leaching kinetics of the Na2SO4 roasting products were investigated, revealing that the leaching of Li was governed by diffusion and chemical reactions in line with the shrinking core model. Characterization methods such as XRD, SEM, XPS, and TG-DSC were employed to reveal the phase transformation mechanisms of Li and Mn during Na2SO4 and CaCl2 roasting, respectively. The proposed process introduces a novel paradigm for its remarkable selective recovery of Li and Mn from SLIBs smelting slag.