Arsenite oxidation by a poorly crystalline manganese-oxide. 2. Results from X-ray absorption spectroscopy and X-ray diffraction.

ABSTRACT: Arsenite (As(III)) oxidation by manganese oxides (Mn-oxides) serves to detoxify and, under many conditions, immobilize arsenic (As) by forming arsenate (As(V)). As(III) oxidation by Mn(IV)-oxides can be quite complex, involving many simultaneous forward reactions and subsequent back reactions. During As(III) oxidation by Mn-oxides, a reduction in oxidation rate is often observed, which is attributed to Mn-oxide surface passivation. X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) data show that Mn(II) sorption on a poorly crystalline hexagonal birnessite (?-MnO?) is important in passivation early during reaction with As(III). Also, it appears that Mn(III) in the ?-MnO? structure is formed by conproportionation of sorbed Mn(II) and Mn(IV) in the mineral structure. The content of Mn(III) within the ?-MnO? structure appears to increase as the reaction proceeds. Binding of As(V) to ?-MnO? also changes as Mn(III) becomes more prominent in the ?-MnO ? structure. The data presented indicate that As(III) oxidation and As(V) sorption by poorly crystalline ?-MnO? is greatly affected by Mn oxidation state in the ?-MnO? structure.

SUBMITTER: Lafferty BJ 

PROVIDER: S-EPMC2987725 | biostudies-literature | 2010 Nov

REPOSITORIES: biostudies-literature