Molecular-scale mechanisms of distribution and isotopic fractionation of molybdenum between seawater and ferromanganese oxides

Kashiwabara, Teruhiko; Takahashi, Yoshio; Tanimizu, Masaharu; Usui, Akira

doi:10.1016/j.gca.2011.07.022

Cited by 130 publications

(117 citation statements)

References 114 publications

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“…This could be described accurately with a model that contained tetrahedral molybdate having 4 Mo-O interatomic distances of ~1.76 Å (Table 5). This is in excellent agreement with results published earlier for similar systems (Arai, 2010;Kashiwabara et al 2011). In the organic samples the first shell was dominated by two contributions that were identified as 2…”

Section: Exafs Spectroscopysupporting

confidence: 93%

“…In addition, he observed octahedrally coordinated MoO 6 polymers at low pH. In another Mo K-edge EXAFS study, molybdate adsorption on ferrihydrite was found to involve mostly outer-sphere complex formation, as there was only a minor contribution from second-shell Fe (Kashiwabara et al 2011); however, it should be noted that the pH value was high (8), which may be important when interpreting these results.…”

Section: Introductionmentioning

confidence: 95%

“…For a long time it has been known that molybdate is bound to a variety of different iron(III) and aluminium(III) (hydr)oxides (Jones, 1957;Reisenauer et al 1962). Examples include ferrihydrite (Gustafsson, 2003;Kashiwabara et al 2011), goethite (Bibak and Borggaard, 1994;Arai, 2010), hematite , gibbsite (Manning and Goldberg, 1996;Miedaner et al 2011) and alumina (Spanos et al 1990). In addition, molybdate is bound also to titanium oxides such as titania (Bourikas et al 2001).…”

Section: Introductionmentioning

confidence: 99%

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Molybdenum binding to soil constituents in acid soils: An XAS and modelling study

Gustafsson

Tiberg

2015

Chemical Geology

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Highlights:-Molybdenum(VI) is bound to ferrihydrite and aluminium hydroxide predominantly as tetrahedral, edge-sharing inner-sphere and outer-sphere complexes.-On natural organic matter, molybdenum(VI) is bound at low pH as an octahedrally coordinated monomeric complex.-Results for a spodic B horizon show an Al(OH) 3 -type phase to be an important sorbent for molybdenum(VI).-The results were used to suggest new complexation constants for the CD-MUSIC and Stockholm Humic models. 2 AbstractDespite its importance as a trace element, the binding mechanisms of molybdenum in soils are not well known. In this study, we studied the binding of molybdenum onto selected soil samples, and we used X-ray absorption spectroscopy (XAS) to characterise the coordination of molybdenum on three important environmental sorbents: ferrihydrite (Fh), amorphous aluminium hydroxide (Al(OH) 3 ) and fulvic acid. The X-ray near-edge structure (XANES) data showed that the added molybdenum(VI) was not reduced, although for the organic samples the coordination shifted from tetrahedral to octahedral. The EXAFS (extended X-ray absorption fine structure) analysis showed that molybdenum(VI) on Fh and Al(OH

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Section: Exafs Spectroscopysupporting

confidence: 93%

Section: Introductionmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

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Molybdenum binding to soil constituents in acid soils: An XAS and modelling study

Gustafsson

Tiberg

2015

Chemical Geology

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“…1C). Bostick et al (2003) Kashiwabara et al (2011) attribute the magnitude of fractionation observed during Mo adsorption to Mnoxides to formation of distorted inner-sphere complexes. It may be that when adsorption of aqueous Mo involves significant Mo restructuring and the formation of innersphere complexes, whether under oxic or anoxic conditions, the magnitude of the associated fractionation is the same.…”

Section: Discussionmentioning

confidence: 99%

“…1B and C). The process responsible for this particular fractionation appears to be related to a change in coordination from tetrahedral to octahedral (e.g., Wasylenki et al, 2011;Kashiwabara et al, 2011).…”

mentioning

confidence: 99%

Molybdenum isotope fractionations observed under anoxic experimental conditions

2012

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Experiments were carried out to determine molybdenum isotope fractionation associated with adsorption to pyrite. Results show that the Mo isotope composition of the aqueous solution becomes progressively heavier as Mo is adsorbed, with a Mo isotope fractionation as large as 2.9‰. This fractionation is larger than observed for typical anoxic continental margin marine sediments (e.g., ~0.7‰), suggesting that Mo adsorption to pyrite is not the dominant process operating in these environments. However, our adsorption results do suggest the possibility that anoxic fractionation processes could impart an isotope signature within the geologic record similar to the isotope fractionation observed under oxygenated conditions. Additional experiments were conducted at high (~100 µM) dissolved Mo concentrations, but at varying pH and ∑H 2 S concentrations, and in each case these experiments promoted Mo-sulfide precipitation. Even though the experiments were conducted under differing conditions and produced different amounts of precipitate, the results suggest a constant fractionation of ~0.9‰ associated with this Mo removal process. This fractionation is more consistent with that inferred for anoxic continental margin marine sediments, suggesting that a process similar to Mo-sulfide precipitation, rather than an adsorption process, may be responsible for the Mo isotope compositions observed in these environments. The findings of this study suggest that, regardless of the geochemical mechanism employed, sediment Mo sequestration under anoxic conditions may impart a significant isotopic fractionation relative to parent seawater.

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Establishing the Basis for Using Stable Isotope Ratios of Metals as Paleoredox Proxies

Wasylenki

2012

Isotopic Analysis

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Molecular-scale mechanisms of distribution and isotopic fractionation of molybdenum between seawater and ferromanganese oxides

Cited by 130 publications

References 114 publications

Molybdenum binding to soil constituents in acid soils: An XAS and modelling study

Molybdenum binding to soil constituents in acid soils: An XAS and modelling study

Molybdenum isotope fractionations observed under anoxic experimental conditions

Establishing the Basis for Using Stable Isotope Ratios of Metals as Paleoredox Proxies

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