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

doi:10.1016/j.gca.2011.06.020

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 journal › Article › peer-review

100 Scopus citations

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 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 language	English (US)
Pages (from-to)	5019-5031
Number of pages	13
Journal	Geochimica et Cosmochimica Acta
Volume	75
Issue number	17
DOIs	https://doi.org/10.1016/j.gca.2011.06.020
State	Published - Sep 1 2011
Externally published	Yes

ASJC Scopus subject areas

Geochemistry and Petrology

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title = "The molecular mechanism of Mo isotope fractionation during adsorption to birnessite",

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 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.",

author = "Wasylenki, {Laura E.} and Weeks, {Colin L.} and Bargar, {John R.} and Spiro, {Thomas G.} and Hein, {James R.} and Anbar, {Ariel D.}",

note = "Funding Information: This work was supported by NSF-OCE 0526618/0526495 to ADA, LEW, and TGS. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University. The authors thank Dr. Gwyneth Gordon at ASU for isotopic analysis of the hydrogenetic Fe–Mn crust sample. In addition, we appreciate constructive comments from three anonymous reviewers. ",

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AU - Wasylenki, Laura E.

AU - Weeks, Colin L.

AU - Bargar, John R.

AU - Spiro, Thomas G.

AU - Hein, James R.

AU - Anbar, Ariel D.

N1 - Funding Information: This work was supported by NSF-OCE 0526618/0526495 to ADA, LEW, and TGS. Portions of this research were carried out at the Stanford Synchrotron Radiation Lightsource, a Directorate of SLAC National Accelerator Laboratory and an Office of Science User Facility operated for the U.S. Department of Energy Office of Science by Stanford University. The authors thank Dr. Gwyneth Gordon at ASU for isotopic analysis of the hydrogenetic Fe–Mn crust sample. In addition, we appreciate constructive comments from three anonymous reviewers.

PY - 2011/9/1

Y1 - 2011/9/1

N2 - 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.

AB - 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.

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The molecular mechanism of Mo isotope fractionation during adsorption to birnessite

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