Selective lithium leaching from industrial mixed lithium-ion battery waste in an HCl–H2O2 system: Factor interactions, model development, and process optimization

The rapid growth of end-of-life lithium-ion batteries (LIBs) has intensified the need for critical metal recovery and resource recycling. However, industrial mixed LIB waste has complex compositions and diverse phases, and the distinct reactions of its active materials in acidic media often induce Fe co-leaching, excessive acid consumption, and complex pH evolution, hindering stable and selective lithium recovery. To address these challenges, an HCl–H 2 O 2 leaching system was developed for industrial mixed LIB waste to achieve highly selective lithium extraction while suppressing Fe dissolution and clarifying the coupled effects of process parameters and the associated phase and valence evolution. At room temperature, the effects of HCl concentration, H 2 O 2 concentration, and liquid-to-solid ratio (L/S) on Li-selective leaching were systematically investigated, and a two-factor interaction (2FI) regression model was established to quantify parameter coupling and pH after leaching evolution. The 2FI models for Li and Fe leaching efficiency, and pH after leaching were all statistically significant ( p < 0.0001), with R 2 of 0.872, 0.893, and 0.916, respectively, indicating good explanatory power and predictive accuracy. Analysis of variance demonstrated that HCl concentration and L/S were identified as the dominant factors governing Li leaching, Fe suppression, and pH after leaching, whereas H 2 O 2 mainly acted through interactions with other variables. Under the optimal conditions predicted by the model (0.75 mol/L HCl, 4% H 2 O 2 , and an L/S of 8 mL/g), triplicate scale-up validation experiments yielded Li and Fe leaching efficiencies of 99.16% and only 0.10%, respectively, in close agreement with the predicted values. XRD, Raman, XPS, and SEM–EDS analyses showed that LiFePO 4 was delithiated into FePO 4 , accompanied by Fe(II) oxidation to Fe(III), while the Fe–P–O framework was largely retained in the residue. This study provides a predictable process window and mechanistic basis for highly selective lithium extraction and Fe suppression from complex mixed LIB waste.