基于热力学模拟河套平原高砷地下水中硫代砷形态分布特征

Thermodynamic Modeling of Thioarsenic Species Distribution in High As Groundwater in Hetao Plain

硫代砷作为一种最新识别的砷形态越来越受到关注。选取河套平原作为研究区,基于野外调查数据和热力学反应方程,模拟并分析高砷地下水中硫代砷形态的分布特征。结果表明:河套平原高砷地下水中亚砷酸盐是主要的砷形态,其次是硫代砷酸盐和砷酸盐,硫代亚砷酸盐含量最低。其中,硫代砷酸盐以一、三硫代砷酸盐为主,硫代亚砷酸盐以一硫代亚砷酸盐为主。埋深在5～40 m范围内,各种砷形态含量随深度增加变化不明显。40～80 m埋深范围内,亚砷酸盐含量随深度增加而逐渐减小,硫代砷酸盐含量随深度增加逐渐增大;硫化物浓度对砷形态分布存在显著影响,当硫化物浓度小于5μg/L时,随着硫化物浓度的增加各形态无明显变化。当硫化物浓度大于5μg/L时,随着硫化物浓度的增加,亚砷酸盐和砷酸盐的含量呈下降趋势,硫代砷酸盐和硫代亚砷酸盐的含量呈增加趋势,不同硫代亚砷酸盐和硫代砷酸盐形态之间存在相互转化。

Thioarsenic has gained increasing attention as a newly identified arsenic species. This paper selected Hetao Plain as the study area. Based on the field survey data and the thermodynamic reaction equation, the distribution characteristics of thioarsenic speciation in high-arsenic groundwater were simulated and analyzed. The results show that the major of arsenic speciation is arsenite, followed by thioarsenate and arsenate, and thethioarsenite concentrations are extremely low. Among them, monothioarsenate and trithioarsenate are the predominant thioarsnate species, with monothioarsenite being the dominant thioarsenite. In the buried depth of the range of 5~40 m, the content of various arsenic species does not change significantly with increasing depth. In the range of 40~80 m buried depth, the content of arsenite decreases with the increase of depth, and the content of thioarsenite increases with depth. Sulfide concentration has a significant effect on the distribution of arsenic species. When the concentration of sulfide is less than 5 μg/L, the various arsenic species do not change regularly with the increase of sulfide concentration. When the sulfide concentration is more than 5 μg/L, the content of arsenite and arsenate decreases with the increase of sulfide concentration, and the content of thioarsenate and thioarsenite tends to increase, and mutual transformation happens between different thioarsenite and thioarsenate species.