Faculty Publications

The Molecular Mechanism of Mo Isotope Fractionation During Adsorption to Birnessite

Document Type

Article

Journal/Book/Conference Title

Geochimica et Cosmochimica Acta

Volume

75

Issue

17

First Page

5019

Last Page

5031

Abstract

Fractionation of Mo isotopes during adsorption to manganese oxides is a primary control on the global ocean Mo isotope budget. Previous attempts to explain what drives the surprisingly large isotope effect have not successfully resolved the fractionation mechanism. New evidence from extended X-ray absorption fine structure analysis and density functional theory suggests that Mo forms a polymolybdate complex on the surfaces of experimental and natural samples. Mo in this polynuclear structure is in distorted octahedral coordination, while Mo remaining in solution is predominantly in tetrahedral coordination as MoO2-4. Our results indicate that the difference in coordination environment between dissolved Mo and adsorbed Mo is the cause of isotope fractionation. The molecular mechanism of metal isotope fractionation in this system should enable us to explain and possibly predict metal isotope effects in other systems where transition metals adsorb to mineral surfaces.

Department

Department of Chemistry and Biochemistry

Original Publication Date

9-1-2011

DOI of published version

10.1016/j.gca.2011.06.020

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