The formation of thioantimonates in sulfidic waters significantly increases the complexity of antimony (Sb) geochemistry, yet the factors controlling their prevalence in natural systems remain poorly constrained. This study systematically examined the competitive thiolation kinetics among Sb, arsenic (As), and tungsten (W), elements that commonly coexist in sulfidic geothermal waters. Experimental results demonstrate that under sulfide-limited conditions, the kinetics sequence is As > Sb ≈ W, while the kinetic stability of the resulting thio-anions follows thioarsenates > thioantimonates > thiotungstates. This coupled kinetic-stability framework successfully explains the distribution of Sb speciation observed in representative sulfidic hot springs within the Yunnan-Sichuan-Tibet geothermal province (China), where high Sb concentrations (4.32-2128.7 μg/L) originate from rock leaching and magmatic fluids. In sulfide-deficient hot springs, coexisting As and W act as inhibitors of Sb thiolation through competitive exclusion, leading to oxyanion dominance; conversely, in sulfide-sufficient hot springs, they become promoters, enhancing thioantimonates formation (up to 56.6 % of total Sb) potentially through an ionic strength effect. Our findings redefine the competitive thiolation hierarchy among Sb, As, and W and provide a quantitative framework for predicting Sb speciation in sulfidic environments, which is critical for assessing its environmental fate.
Keywords: Antimony; Competitive thiolation; Geochemical kinetics; Hot spring; Thioantimonate.
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