The Release and Transformation of Sb and As Induced by Microorganisms in Antimony Smelting Soil

Mining and smelting activities have accelerated the release of antimony (Sb) and arsenic (As) into the environment, resulting in high ecological risks. Microorganisms are considered key drivers of Sb and As cycling. However, their effects on Sb/As transformation in antimony smelting soils remain poorly understood. In this study, an indigenous microbial consortium capable of oxidizing both Sb and As was obtained from antimony smelting soil and used to investigate the interactions between microorganisms and Sb-As co-contaminated soils. The results showed that the functional microbial consortium enhanced Sb and As release from the soil by increasing the system pH from 7.41 to 8.89, thereby promoting the dissolution of solid-phase Sb and As. The concentrations of total dissolved Sb and As reached 246.47 and 30.5 µmol L−1 by day 16, respectively, and the released Sb(III) and As(III) were completely oxidized to Sb(V) and As(V). In the abiotic control, the corresponding concentrations of total dissolved Sb and As were 95.89 and 12.08 µmol L−1, respectively, with an As(III) concentration of 3.54 µmol L−1. Sequential extraction results revealed that microbial activity altered the speciation distribution of Sb and As in soils, decreasing the proportions of easily exchangeable and specifically surface-bound fractions while increasing the residual fractions. X-ray photoelectron spectroscopy (XPS) analysis further showed that, compared with the original soil, the functional microbial consortium increased the proportions of Sb(V) and As(V) in the solid phase from 34.79% to 40.54% and from 9.53% to 15.96%, respectively, suggesting that microbial activity might promote the precipitation of Sb(V) and As(V), thereby facilitating the re-immobilization of a fraction of the released Sb and As. Furthermore, the succession of microbial communities during the interaction process was investigated. The release of Sb and As from soil increased the abundance of microorganisms related to Sb/As metabolism. Spearman correlation analysis suggested that Arenimonas, Luteimonas, Arthrobacter, and Brevundimonas were likely involved in Sb(III)/As(III) oxidation, whereas Devosia and Aminobacter contributed to the elevation of system pH. This study provides insights into the microbial-mediated transformation, migration, and oxidation of Sb and As in soils.