State Environmental Protection Key Laboratory of Integrated Surface Water-Groundwater Pollution Control, School of Environmental Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, China.
The Key Lab of Pollution Control and Ecosystem Restoration in Industry Clusters, Ministry of Education, South China University of Technology, Guangzhou 510006, China.
J Hazard Mater. 2024 Jul 15;473:134434. doi: 10.1016/j.jhazmat.2024.134434. Epub 2024 May 10.
The behavior of As is closely related to trans(formation) of ferrihydrite, which often coprecipitates with extracellular polymeric substances (EPS), forming EPS-mineral aggregates in natural environments. While the effect of EPS on ferrihydrite properity, mineralogy reductive transformation, and associated As fate in sulfate-reducing bacteria (SRB)-rich environments remains unclear. In this research, ferrihydrite-EPS aggregates were synthesized and batch experiments combined with spectroscopic, microscopic, and geochemical analyses were conducted to address these knowledge gaps. Results indicated that EPS blocked micropores in ferrihydrite, and altered mineral surface area and susceptibility. Although EPS enhanced Fe(III) reduction, it retarded ferrihydrite transformation to magnetite by inhibiting Fe atom exchange in systems with low SO. As a result, 16% of the ferrihydrite was converted into magnetite in the Fh-0.3 treatment, and no ferrihydrite transformation occurred in the Fh-EPS-0.3 treatment. In systems with high SO, however, EPS promoted mackinawite formation and increased As mobilization into the solution. Additionally, the coprecipitated EPS facilitated As(V) reduction to more mobilized As(III) and decreased conversion of As into the residual phase, enhancing the potential risk of As contamination. These findings advance our understanding on biogeochemistry of elements Fe, S, and As and are helpful for accurate prediction of As behavior.
砷的行为与水铁矿的转化密切相关，水铁矿常与细胞外聚合物（EPS）共沉淀，在自然环境中形成 EPS-矿物聚集体。然而，EPS 对富硫酸盐还原菌（SRB）环境中 ferrihydrite 的特性、矿物还原转化以及相关砷命运的影响尚不清楚。在这项研究中，合成了 ferrihydrite-EPS 聚集体，并进行了结合光谱、微观和地球化学分析的批量实验，以解决这些知识空白。结果表明，EPS 堵塞了 ferrihydrite 的微孔，并改变了矿物表面积和磁化率。尽管 EPS 增强了 Fe(III)还原，但通过抑制低 SO 系统中的 Fe 原子交换，它会延迟 ferrihydrite 向磁铁矿的转化。因此，在 Fh-0.3 处理中，有 16%的 ferrihydrite 转化为磁铁矿，而在 Fh-EPS-0.3 处理中没有 ferrihydrite 转化。然而，在高 SO 系统中，EPS 促进了 mackinawite 的形成，并增加了 As 向溶液中的迁移。此外，共沉淀的 EPS 促进了 As(V)还原为更易迁移的 As(III)，并减少了 As 转化为残余相，增加了 As 污染的潜在风险。这些发现提高了我们对元素 Fe、S 和 As 生物地球化学的理解，有助于准确预测 As 的行为。
