MANGANESE(II) OXIDATION AT MINERAL SURFACES - A MICROSCOPIC AND SPECTROSCOPIC STUDY

被引:273
作者
JUNTA, J [1 ]
HOCHELLA, MF [1 ]
机构
[1] STANFORD UNIV,DEPT GEOL & ENVIRONM SCI,STANFORD,CA 94305
关键词
D O I
10.1016/0016-7037(94)90226-7
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
The products of the heterogeneous oxidation of Mn(II)aq at hematite, geothite, 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 beta-MnOOH.
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页码:4985 / 4999
页数:15
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