Hausmannite is the 5th most common Mn oxide, and is abundant in soil and sediments. Natural hausmannite often contains minor and trace metal impurities (e.g., nickel (Ni)), yet the presence of Ni in the structure or on the surface and its impact on the reactivity of hausmannite is not well understood. In this study, we therefore attempted to fill this knowledge gap by comparing the oxidation rate of arsenite (As(III)) to arsenate (As(V)) on pure, Ni-substituted, and Ni-adsorbed hausmannite. We synthesized hausmannite with 1, 5, and 10 weight % Ni-substitution and made Ni-adsorbed samples by varying concentrations of added nickel chloride (NiCl2) solution. All the mineral samples were characterized for crystal structure, size, morphology and total Ni content using X-ray diffraction, transmission electron microscopy, and inductively coupled plasma-optical emission spectroscopy. Batch oxidation reactions were performed using a total of 1 g/L mineral loading with 470 μM sodium arsenite (NaAsO2) in solution (pH 5) and stirred for 8 hours. Eight aliquots were collected during the experiment and analyzed for As(V), with ion chromatography. A decrease of almost 58.6% in As(V) release was measured in the 10% Ni-substituted and 100 ppm Ni-adsorbed hausmannite compared with pure hausmannite, indicating that the mobility and toxicity of arsenic could be strongly dependent on the presence of Ni in the hausmannite lattice or on the surface. We further analyzed the surface reaction of arsenic on minerals using attenuated total reflectance Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. This work aims to provide a fundamental understanding of the role of metal impurities in the surface reactivity including redox mechanism and surface complexation of arsenic on Mn oxide and thus better predict the fate and cycle of arsenic in the environment.

Impact of metal impurities on redox reactivity of hausmannite (MnIIMnIII2O4)

255th National Meeting (2018)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.