Aluminosilicate host phases govern hazardous trace element mobility in lithium slag: Speciation quantification and mineralogical detoxification

The surging demand for lithium has generated massive lithium slag (LS) stockpiles containing elevated beryllium (Be) and thallium (Tl). However, the quantitative partitioning of Be and Tl among host phases, along with its regulation by additive composition during lithium smelting, has not been established. To address this gap, we (i) identified probable Be and Tl hosts in three LS samples with contrasting Na/Ca ratios by pH-dependent leaching, quantitative mineral dissolution, and density functional theory calculations; (ii) developed a mineralogy-tailored six-step sequential extraction procedure to quantify host-phase partitioning; and (iii) assessed waste-glass-powder-assisted sintering for mineralogical stabilization and ultra-lightweight aggregate (ULWA) production. Results showed that Tl release closely tracked leucite dissolution, and Tl substitution at K sites was energetically favored. Be was mainly distributed among newly formed aluminosilicates, with the dominant associated fractions varying with slag mineralogy. Operational fractionation showed that 80.11–86.73% of Tl occurred in acid-resistant Al-poor aluminosilicate-associated fractions, whereas 90.98% of Be in Na-rich LS was associated with acid-sensitive Al-rich phases. Standard single-step leaching tests captured scenario-specific short-term release but did not fully represent cumulative Be mobilization under sustained acidic weathering. Sintering reconstructed the acid-sensitive assemblage into stable plagioclase while meeting ULWA requirements. Under simulated strong acid rain exposure test, the cumulative Be and Tl releases were reduced by 99.5% and 93.6%, respectively. This work uncovers the mineralogical roots of potential long-term ecological risk in lithium extraction residues and offers a feasible strategy for safely valorizing solid wastes containing trace toxic metals.