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

Abstract

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⁻¹) and purified slag (0.42 μg L⁻¹) significantly exceeded groundwater safety thresholds (0.1 μg L⁻¹). 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⁻¹). The DIFS model analyzed the adsorption-desorption dynamics of Tl at the soil water-solid micro-interface. The derived response time (T_c) and desorption rate constant (K_-1) indicated that purified slag enriched the labile Tl reservoir in the soil (K_d: 143 cm³ g⁻¹). Tl was rapidly resupplied from the soil solid phase to the water phase (K_-1: 1.23 × 10⁻² s⁻¹), maintaining Tl levels in the pore water phase over a short period (T_c: 0.128 s). Our study systematically evaluated the migration and distribution characteristics of soil Tl contamination, providing a scientific basis for the environmental management.