Molecular mechanisms and environmental implications of thallium complexation with butyl xanthate

Mining activities promote the release of thallium associated with sulfide ores into the near-surface environment, posing serious threats to both environmental quality and human health. Meanwhile, large quantities of organic flotation reagents are widely present in mining-impacted environments and may interact with thallium to form complex contamination systems, thereby altering its environmental mobility and ecological toxicity. In this study, solution chemistry experiments combined with advanced spectroscopic analyses and density functional theory (DFT) calculations were employed to systematically elucidate the complexation mechanisms between butyl xanthate (BX) and Tl(I), as well as their environmental implications. The results demonstrated that the BX-Tl(I) interaction was governed by the stoichiometric ratio (n_Tl/n_BX) and the initial concentrations, with the reaction tending toward a 1:1 equilibrium. Sparingly soluble white flocculent complexes were formed when both concentrations exceeded 250 μmol/L. Tl(I) preferentially coordinated with sulfur atoms in the CS or C-S moieties of BX, forming stable monodentate or four-membered bidentate chelate configurations. Such complexation markedly retarded Tl(I) migration and significantly reduced its phytotoxicity to lettuce, mung bean and rapeseed seedlings compared to free Tl(I). These findings revealed the critical role of flotation reagents in regulating Tl mobility and bioavailability, and provided new molecular-level insights into the environmental geochemical behavior of Tl under mining-related complex contamination conditions.