Little is known about the reaction mechanism of actinyl complexes on mineral surfaces, i.e. the role of the redox potential, the nature of the reductant, the importance of minerals in terms of providing catalytic surfaces, the role of anions in solution that polarize a mineral surface to promote or inhibit electron transfer, and the activated states that may slow down the kinetics of the redox process. In order to resolve these, an electrochemical studies using a micropowder electrode technique were performed in combination with a quantum-mechanical approach. The electrochemical approach allows us to determine the specific redox potential of actinide reduction on a given mineral surface.  For example, uranyl reduction takes place at -0.22 V on hematite, -0.17 V on magnetite, and at -0.14 V on pyrite.  The calculations show that the energy gain of the co-adsorption of hydroquinone (as an analogue for microbial reduction) and uranyl is on the order of 0.5 eV (�50 kJ/mol) as compared to the separate adsorption of uranyl and hydroquione. Similar co-adsorption on FeS (mackinawite) reveals that Fe(II) cations in the mineral surface become high spin (Fe(II) in bulk mackinawite is low spin), thereby increasing its potential for electron transfer.

Combined computational and electrochemical approach to determine the redox reaction mechanism of actinide oxides on sulfide surfaces

243rd National Meeting (2012)

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