| Abstract
| - The reductive dissolution of MnO2 by Fe(II) under conditionssimulating acid mine drainage (pH 3, 100 mM SO42-)was investigated by utilizing a flow-through reaction celland synchrotron X-ray absorption spectroscopy. Thisconfiguration allows collection of in situ, real-time X-rayabsorption near-edge structure (XANES) spectra and bulksolution samples. Analysis of the solution chemistrysuggests that the reaction mechanism changed (decreasedreaction rate) as MnO2 was reduced and Fe(III) precipitated,primarily as ferrihydrite. Simultaneously, we observedan additional phase, with the local structure of jacobsite(MnFe2O4), in the Mn XANES spectra of reactants andproducts. The X-ray absorbance of this intermediate phaseincreased during the experiment, implying an increase inconcentration. The presence of this phase, which probablyformed as a surface coating, helps to explain the reducedrate of dissolution of manganese(IV) oxide. In naturalenvironments affected by acid mine drainage, the formationof complex intermediate solid phases on mineral surfacesundergoing reductive dissolution may likewise influencethe rate of release of metals to solution.
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