Physics
Scientific paper
Nov 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.4985j&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 22, pp.4985-4999
Physics
8
Scientific paper
The products of the heterogeneous oxidation of Mn(II) aq at hematite, goethite, and albite surfaces were studied, using Scanning Force Microscopy (SFM), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), Scanning Auger Microscopy (SAM), and X-ray Diffraction (XRD). Oxidation experiments were conducted at room temperature in aerated solutions containing 4.0-26.7 ppm Mn(II) aq at pHs ranging from 7.8 to 8.7. Exposure times ranged from a few minutes up to six months. Through this study, it was found that steps are the most reactive sites for initiating the adsorption-oxidation reaction, independent of the mineral surface used. After the initial oxidation of Mn(II) at or near these sites, the continued adsorption-oxidation process is mineral surface dependent resulting in two types of growth paths, substrate and precipitate controlled growth. Substrate controlled growth (hematite and goethite) is characterized by the formation of a thin coating of protocrystallites that grows across the mineral surface away from the initial adsorption-oxidation site. In contrast, precipitate controlled growth (albite) is characterized by the development of precipitate ridges along a step edge. These two surface-controlled growth processes influence the distribution of the precipitates found with SEM and in hand-samples. However, independent of the mineral surface used in the experiments, the resulting precipitates consisted of Mn(III) bearing oxyhydroxides, predominately -MnOOH.
Hochella Michael F. Jr.
Junta Jodi L.
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