Multi-isotopes (18O, 34S, 15N, and 13C) reveal the enrichment mechanism of antimony in high-antimony groundwater

Abstract

Multi-isotopes can be effectively utilized to offer new insights into heavy-metal oxidation dynamics and variations in redox conditions. Therefore, hydrochemical data and isotopic characteristics (δ¹⁸O_H2O, δD, δ³⁴S_SO4, δ¹⁸O_SO4, δ¹⁵N_NO3, δ¹⁸O_NO3, δ¹³C_DOC and δ¹³C_DIC) were determined the oxidation mechanism of Sb(III) to Sb(V) in D₃x⁴ groundwater. The results showed the concentration of Sb in D₃x⁴ groundwater ranges from 0.005 to 20.700 mg/L, with an average of 2.300 mg/L, and Sb(V) represented the dominant form present within D₃x⁴ groundwater. The δ³⁴S、δ¹⁵N values in D₃x⁴ groundwater ranges from -4.20‰ to 6.30‰, 1.20‰ to 22.70‰, respectively. the δ¹³C_DOC and δ¹³C_DIC content in D₃x⁴ groundwater vary in the ranges of -26.97‰ to -16.70‰ and -17.84‰ to -2.30‰, respectively. Stibnite oxidation significantly influenced the enrichment of Sb(V) and SO₄²⁻, while microbial nitrification notably contributed to elevated NO₃⁻ levels in high-Sb groundwater by converting Sb(III) to Sb(V). The presence of redox-active moieties in DOM facilitated electron transfer for promoting Sb(III) oxidation rate during the stibnite oxidation process. Additionally, microbial oxidative degradation of DOM can promote Sb(V) enrichment, with carbon serving as an energy source for nitrification, facilitated this process and enhances the oxidation rate of Sb(III) to Sb(V). These findings contribute to a more comprehensive understanding of the geochemical behavior of antimony in groundwater and enhance our knowledge regarding Sb(III) oxidation mechanism in oxygenated groundwater.