The molecular mechanism of Mo isotope fractionation during adsorption to birnessite

Laura E. Wasylenki, Colin L. Weeks, John R. Bargar, Thomas G. Spiro, James R. Hein, Ariel D. Anbar

Research output: Contribution to journalArticlepeer-review

97 Scopus citations


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 δ97/95Modissolved-δ97/95Moadsorbed=1.8‰ 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 MoO42- 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.

Original languageEnglish (US)
Pages (from-to)5019-5031
Number of pages13
JournalGeochimica et Cosmochimica Acta
Issue number17
StatePublished - Sep 1 2011
Externally publishedYes

ASJC Scopus subject areas

  • Geochemistry and Petrology


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