Tungsten speciation in sulfidic waters: Determination of thiotungstate formation constants and modeling their distribution in natural waters

Mohajerin, T. Jade; Helz, George R.; White, Christopher D.; Johannesson, Karen H.

doi:10.1016/j.gca.2014.08.037

Cited by 63 publications

(31 citation statements)

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“…For many thiometalates (e.g., Mo, Re, W), information on speciation has been limited to thermodynamic predictions based on laboratory experiments (Erickson and Helz, 2000;Helz and Dolor, 2012;Mohajerin et al, 2014). The thiometalates of As (Planer-Friedrich et al, 2007;Härtig et al, 2012) and Sb (Planer-Friedrich et al, 2011) (TBA + ) cations are attracted to the hydrophobic stationary phase while simultaneously forming ion pairs with the thiomolybdates.…”

Section: Discussionmentioning

confidence: 99%

“…The chemical transformations for Mo linked to transitions from oxic to sulfidic waters have been well characterized in the laboratory (Helz et al, 1996;Erickson and Helz, 2000;Vorlicek et al, 2002Vorlicek et al, , 2004Helz et al, 2014). As sulfide accumulates in the water column or sediments, sulfur substitutes progressively for oxygen in geochemically inert Mo VI O 4 2− , leading to reactive tetrathiomolybdate (Mo VI S 4 2− ) by way of transient thiomolybdate intermediates (Mo VI O x S 4-x 2− ) (Helz et al, 1996;Erickson and Helz, 2000 (Tossell et al, 2005).…”

Section: Accepted Manuscriptmentioning

confidence: 99%

“…Although UV-vis spectroscopy is commonly employed to quantify thiometalate (Mo, Re, W) speciation in the laboratory (Erickson and Helz, 2000;Vorlicek et al, 2002Vorlicek et al, , 2004Helz and Dolor, 2012;Mohajerin et al, 2014), optical methods are not suitable for characterizing the anions in nature because they have high detection limits and are prone to interferences.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

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A new analytical approach to determining Mo and Re speciation in sulfidic waters

et al. 2015

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confidence: 99%

Section: Accepted Manuscriptmentioning

confidence: 99%

Section: Accepted Manuscriptmentioning

confidence: 99%

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A new analytical approach to determining Mo and Re speciation in sulfidic waters

et al. 2015

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“…Both oxyanions are conservative components in the ocean (Sohrin et al 1987;, although WO 2has a mean residence time appreciably shorter than MoO 4 2-(14,000 vs. 740,000 y according to Firdaus et al 2008). In sulfidic waters, both MoO 4 2and WO 4 2become thiolated, forming a series of thioanions, MO x S 4-x 2-(M = Mo or W and x =0-4; Erickson and Helz, 2000;Mohajerin et al 2014a); however considerably higher sulfide concentrations are needed for this transition in the case of W. Both Mo and W have nearly matching ionic radii, and therefore compositionally comparable Mo and W minerals are usually isomorphs. Protonation near pH 4 converts both tetrahedral anions to octahedral species, possibly Mo(OH) 6 0 and W(OH) 6 0 .…”

Section: Introductionmentioning

confidence: 99%

“…Sulfide produced by sulfate reduction is believed to play a key role in fixing Mo in these environments (Adelson et al 2001;Helz and Adelson, 2013). As yet, little is known of the corresponding behavior in these sediments of W, which is less sulfide-reactive than Mo (Mohajerin et al 2014a).…”

Section: Introductionmentioning

confidence: 99%

Tungsten–molybdenum fractionation in estuarine environments

Mohajerin

Helz

Johannesson

2016

Geochimica et Cosmochimica Acta

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Dissolved tungsten (W) and molybdenum (Mo) concentrations were measured in surface waters and sediment pore waters of Terrebonne Bay, a shallow estuary in the Mississippi River delta, to investigate the biogeochemical processes that fractionate these Group 6 elements relative to one another during transit from weathering to sedimentary environments. Although many of the chemical properties of W and Mo are similar, the two elements behave autonomously, and the fractionation mechanisms are only partly understood. In sulfidic pore waters, dissolved Mo is depleted relative to river water-seawater mixtures, whereas dissolved W is >10-fold enriched. Reductive dissolution of poorly crystalline phases like ferrihydrite, which is a preferential host of W relative to Mo in grain coatings on river-borne particles, can explain the dissolved W enrichment. Dissolved W becomes increasingly enriched as H 2 S(aq) rises above about 60 μM due to transformation of WO 4 2to thiotungstates as well as to additional reductive dissolution of phases that host W. In contrast, as rising sulfide transforms MoO 4 2to thiomolybdates in pore waters, dissolved Mo is suppressed, probably owing to equilibration with an Fe-Mo-S phase. This putative phase appears to control the aqueous ion product, Q = [Fe 2+ ][MoS 4 2-] 0.6 [H 2 S 0 ] 0.4 /[H + ] 0.8 , at a value of 10-7.78. Concentrations of dissolved W and Mo in pore waters bear no relation to concentrations in surface waters of the same salinity. In surface waters, dissolved Mo is nearly conserved in the estuarine mixing zone. Dissolved W appears also to be conserved except for several cases where W may have been enhanced by exchange with underlying, W-rich pore waters. With increasing salinity, the molar Mo/W ratio rises from about 10 to about 1000 in surface waters whereas it is mostly <10 in underlying pore waters and in highly sulfidic pore waters is mostly near 1. Differences in two chemical properties may account for this fractionation of Mo with respect to W; Mo VI is more susceptible to reduction than W VI , but the latter is more prone to adopting octahedral coordination. We propose that the first difference facilitates Mo but not W precipitation in sulfidic sediments, whereas the second explains tungsten's proportionately greater sequestration on river-borne particles and its subsequent release to sulfidic pore waters after the particles are deposited in the delta and become subject to reductive dissolution during diagenesis. Electronic Annex Click here to download Electronic Annex: Revised Electronic Annex_KHJ.docx *Revised Manuscript (marked MS Word) Click here to download Source or Other Companion File: Revised_GRH_KHJ.docx

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Tungsten

Helz¹

2017

Encyclopedia of Earth Sciences Series

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Tungsten speciation in sulfidic waters: Determination of thiotungstate formation constants and modeling their distribution in natural waters

Cited by 63 publications

References 65 publications

A new analytical approach to determining Mo and Re speciation in sulfidic waters

A new analytical approach to determining Mo and Re speciation in sulfidic waters

Tungsten–molybdenum fractionation in estuarine environments

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