亚硫酸盐对三价砷在土壤中氧化固定作用机制研究

土壤中硫的氧化还原过程对砷的释放与固定具有重要的影响，但有关硫形态对三价砷(As(Ⅲ))的氧化过程的机制与贡献并不清楚。基于此，本研究以土壤中普遍存在的硫转化中间产物亚硫酸盐为研究对象，研究其对土壤中As(Ⅲ)的氧化固定机制。结果表明，亚硫酸盐显著促进了土壤中As(Ⅲ)的氧化，与对照组相比，10 h内土壤悬液中As(Ⅲ)的氧化效率提高了近30%，而土壤固相提取态As(Ⅲ)氧化更加明显，吸附态As(Ⅲ)浓度从73.53μg/L降低至35.27μg/L；与此同时亚硫酸盐的加入显著降低了溶液中总砷含量，促进了砷在土壤中的固定。通过电子顺磁共振技术分析发现亚硫酸根自由基(SO·₃~–)是As(Ⅲ)氧化的主要动力，而铁离子与亚硫酸根耦合是形成自由基的主要机制。综上，亚硫酸盐显著促进土壤中As(Ⅲ)的氧化及固定。

Mechanism of Effects of Sulfite on Oxidation and Immobilization of As(III) in Soil

The redox process of sulfur in soil plays an important role in the release and immobilization of arsenic(As),but the mechanism and contribution of sulfur species to the oxidation process of trivalent As are not clear.In this study,sulfite(SO₃^{2^-}which is a ubiquitous intermediate of sulfur transformation was selected to examine its oxidation and immobilization mechanism for As(III)in soil.The results showed that sulfite significantly promoted the oxidation of As(III)in soil.Compared with CK,the oxidation efficiency of As(III)in soil suspension increased by nearly 30%within 10 h,while the oxidation of As(III)in soil solid phase extraction was more significantly,and the concentration of As(III)in adsorbed state decreased from 73.53μg/L to 35.27μg/L.At the same time,the addition of sulfite significantly reduced the total As content in the solution and promoted the fixation of As in soil.Electron paramagnetic resonance(EPR)analysis showed that sulfite radical(SO₃·^–)was the main driving force of As(III)oxidation,and the coupling of iron ions and sulfite was the main mechanism of the formation of free radicals.In conclusion,sulfite significantly promoted the oxidation and fixation of As(III)in soil.