Migration and distribution of thallium related with lead-zinc smelting enterprises from raw materials to soil: In-situ insight using diffusive gradients in thin-films.

Thallium-related industrial materials (TIMs) from the mining and smelting of lead-zinc ores may lead to thallium (Tl) contamination in the soil. Building upon the soil column experiments, this study employed the diffusive gradients in thin-films (DGT) technique and the DGT-induced fluxes in soils (DIFS) model to understand the migration and distribution characteristics of Tl from lead-zinc industrial raw materials to soil, as well as its adsorption-desorption kinetics in soil. The results indicated that Tl concentrations in the leachate from fly ash (0.3 μg L) and purified slag (0.42 μg L) significantly exceeded groundwater safety thresholds (0.1 μg L). This significantly increased the content of acid-exchangeable and reducible Tl in the soil, particularly in the purified slag-soil system, where the proportions of acid-exchangeable and reducible Tl in the topsoil increased by 20% and 37%, respectively, compared to the control. Further, the in-situ distribution of labile Tl was observed with a precision of 1 cm through the DGT, and the labile Tl in soils contaminated by purified slag was the highest (up to 635 μg L). The DIFS model analyzed the adsorption-desorption dynamics of Tl at the soil water-solid micro-interface. The derived response time (T) and desorption rate constant (K) indicated that purified slag enriched the labile Tl reservoir in the soil (K: 143 cm g). Tl was rapidly resupplied from the soil solid phase to the water phase (K: 1.23 × 10 s), maintaining Tl levels in the pore water phase over a short period (T: 0.128 s). Our study systematically evaluated the migration and distribution characteristics of soil Tl contamination, providing a scientific basis for the environmental management.