Leaching strategies for Si and Al impurity manag 2026 Journal of Environment

Understanding impurity behavior during hydrometallurgical recycling of lithium-ion batteries is essential for producing high-purity battery-grade products and enabling graphite purification. This study investigates the leaching behavior of silicon (Si) and aluminum (Al) during black mass processing in sulfuric (H2SO4) and hydrochloric (HCl) acid systems, considering the influence of acidity, temperature, reaction time, and H2O2 addition. The results show that increasing acid concentration from 2 M to 4 M enhances Si dissolution by ~20%-units in both leaching systems at 60°C. The role of H2O2 strongly depends on the acid medium. In H2SO4 systems, H2O2 increases Si extraction from ~43% to ~54%, indicating a significant oxidant-enhanced dissolution effect. In contrast, in HCl systems, H2O2 decreases Si extraction from ~37% to ~17%, suggesting the formation of surface-stabilized or passivating conditions under chloride-rich environments. Lowering the temperature to 20°C significantly suppresses Si leaching to below 15%, highlighting strong temperature dependence. Al dissolution shows weaker sensitivity to acid concentration and type, indicating limited reactivity and possible surface stabilization effects; however, H2O2 increases Al extraction by ~10%-units. These findings provide quantitative insights into oxidant- and acid-dependent impurity control and support process design for recycling Si- and Al-rich battery waste.