Facilitated arsenic immobilization by biogenic ferrihydrite-goethite biphasic Fe(III) minerals (Fh-Gt Bio-bi-minerals).

Biogenic iron(III) minerals (BIM) widely occur in aquatic systems. However, characteristics and mechanisms of As sequestration by biogenic biphasic Fe(III) minerals (Bio-bi-minerals) are not clearly understood. We investigated characteristics of Bio-bi-minerals induced by Pseudogulbenkiania sp. strain 2002 and explored their As sequestration mechanisms by monitoring particle morphology, mineralogical composition, and As binding properties. Results showed that Fe(II) oxidation (about 3 mM) by Pseudogulbenkiania sp. strain 2002 under growth condition produced biogenic ferrihydrite-goethite biphasic Fe(III) minerals (Fh-Gt Bio-bi-minerals), which showed better performance in As immobilization compared to corresponding biogenic monophasic Fe(III) minerals (Bio-mono-minerals). Decreased particle size, increased abundance of ferrihydrite and occurrence of bidentate mononuclear edge-sharing (2E) and monodentate mononuclear edge-sharing As complexes (1V) contributed to enhanced As immobilization by Fh-Gt Bio-bi-minerals. We suggest that the Bio-bi-minerals have the potential to illuminate As biogeochemical cycles in aquatic systems and to remediate As and nitrate co-contaminated groundwater.