Effect of phosphate on ferrihydrite transformation and the associated arsenic behavior mediated by sulfate-reducing bacterium

Authors：Gao, Kun; Zhu, Huiyan; Zhou, Wenjing; Hu, Shiwen; Zhang, Bowei; Dang, Zhi; Liu, Chongxuan^*

Source：Journal of Hazardous Materials, 2023, 448: 130863.

DOI：10.1016/j.jhazmat.2023.130863

• Arsenic
• Iron (oxyhydr)oxide
• PO43-loadings
• Sulfate-reducing bacteria
• Biogeochemistry

Although PO43-is commonly found in association with iron (oxyhydr)oxide, the effect of PO43-on ferrihydrite reduction, mineralogical transformation, and associated As behavior in sulfate-reducing bacteria (SRB)-rich environments remains unclear. In this study, batch experiments, together with geochemical, mineralogical, and biological analyses, were conducted to elucidate these processes. The results showed that SRB can reduce fer-rihydrite via direct and indirect processes, and PO43-promoted ferrihydrite reduction by supporting SRB growth at low and medium PO43-loadings. However, at high loadings, PO43-stabilized the ferrihydrite. PO43-shifted the transformation of ferrihydrite from magnetite and mackinawite to vivianite, which scavenges As effectively by incorporating As into its particle. In systems with 0.5 mM SO42-, PO43-exerted a weak effect on As mobilization. However, in systems with 10 mM SO42-, substantial amounts of As were released into the solution, and PO4 3 -impacted As behavior strongly. Low PO43-loadings increased the mobilization of As because of the competitive adsorption of PO43-on mackinawite. Medium and high PO43-loadings were beneficial for As immobilization because of the substitution of mackinawite by vivianite. These findings have important implications for un-derstanding the biogeochemistry of iron (oxyhydr)oxide and As behavior in SRB-containing sediments.