Microbial reduction of As(V)-loaded Schwertmannite by Desulfosporosinus meridiei

Arsenic-rich schwertmannite may cause arsenic (As) release during phase transition. In this study, microbial sulfidogenesis on As(V)-loaded schwertmannite (As-Sch) and associated As mobility at different SO₄^2- concentrations were investigated under anaerobic conditions by Desulfosporosinus meridiei (D. meridiei). For biotic treatments, the more SO₄^2- was added, the more Fe³⁺ was reduced to Fe²⁺, and the more As(V) was released during the reductive dissolution of As-Sch. The reduction of As(V) to As(III) by D. meridiei resulted in a higher concentration, toxicity, solubility and mobility of As than the corresponding abiotic treatments. However, compared with the abiotic treatments, a variety of new minerals (such as mackinawite, vivianite, sulfur, As₂S₃, and parasymplesite) were generated in the biotic treatments, and the As concentration in aqueous solution was less than 1 μM at the end of the incubation period regardless of the presence of SO₄^2-. The results of continuous extraction of different species of As from secondary minerals showed that the effect of microorganisms decreased As content of amorphous iron oxide-bound phase, while increasing that bound on the surface of iron oxide surface-bound phase, thus increasing As fluidity. Our findings indicated that under anaerobic conditions, D. meridiei sulfidogenesis can trigger significant As mobilization in the early stage and remove As from the aqueous solutions when new minerals are formed at a later stage.