Occurrence, environmental risks and recovery potential of beryllium and thallium in lepidolite smelting slag: Mineralogical insights into leaching behavior

Lepidolite smelting slag (LSS), as an energy metal lithium extraction residue, is enriched in toxic beryllium (Be) and thallium (Tl), posing huge challenges for safe management and disposal. Although phenomenological studies on the leaching behavior, recovery potential, and environmental risks of Be and Tl have been reported, mechanistic insights into mineralogical controls governing their release remain limited. To address this knowledge gap, we integrated mineralogical analysis, spatially resolved elemental mapping, and controlled leaching experiments. Our results reveal that Be and Tl are predominantly hosted in anorthite and leucite, respectively. Under simulated environmental conditions, the stability of anorthite and leucite directly dictates Be and Tl release. Column experiments demonstrated delayed but persistent Be release, in contrast to transient, rapidly attenuated Tl release, indicating that differential dissolution of host minerals leads to contrasting environmental toxicological risks. Using sulfuric acid leaching, high recovery efficiencies of 81.68% for Be and 84.31% for Tl were achieved. Toxicity leaching concentrations of the post-treatment residues were 5.66 μg/L for Be and 2.95 μg/L for Tl, within regulatory limits for solid waste (Be: 20 μg/L, Tl: 5 μg/L). DFT calculations showed that the Ca-O bond is substantially more stable than the K-O bond, suggesting that leucite dissolves more readily than anorthite during H2SO4 leaching, consistent with the experimental leaching trends. This study elucidates the mineralogically controlled occurrence, leaching behavior, and recovery of Be and Tl in LSS, providing a mineralogy-informed reference for the integrated management and valorization of this industrial residue.