X-ray absorption spectroscopic study of Fe reference compounds for the analysis of natural sediments

O’Day, Peggy A.; Rivera, Nelson; Root, Robert; Carroll, Susan A.

doi:10.2138/am-2004-0412

Cited by 229 publications

(220 citation statements)

References 58 publications

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“…The XAS spectra of NiAs-structured pyrrhotite and stoichiometric troilite FeS have been measured, calculated and analyzed in a number of studies; the spectroscopic features are largely similar to those in pyrite, despite different electronic structures, and their detailed description can be found in the literature [43][44][45][46][47][48][49][50][51][52][53][54][55][56]. The main differences observed in the S K-edge XANES (Fig.…”

Section: Xanesmentioning

confidence: 99%

“…A number of XANES studies on iron sulfides have been reported previously [33,[43][44][45][46][47][48][49][50][51][52][53][54][55][56], but the difference between TEY and PFY Kedge spectra of air-oxidized and chemically etched materials has not been analyzed yet. Here, samples of each mineral (i.e., pyrite and pyrrhotite) polished in air were compared with those treated with an acidic ferric chloride solution to probe the effect of exposure to the leaching (etching) medium in hydrometallurgy and natural environments, and in materials science.…”

Section: Introductionmentioning

confidence: 99%

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Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Mikhlin

Tomashevich

Vorobyev

et al. 2016

Applied Surface Science

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a b s t r a c tHard X-ray photoelectron spectroscopy (HAXPES) using an excitation energy range of 2 keV to 6 keV in combination with Fe K-and S K-edge XANES, measured simultaneously in total electron (TEY) and partial fluorescence yield (PFY) modes, have been applied to study near-surface regions of natural polycrystalline pyrite FeS 2 and pyrrhotite Fe 1−x S before and after etching treatments in an acidic ferric chloride solution. It was found that the following near-surface regions are formed owing to the preferential release of iron from oxidized metal sulfide lattices: (i) a thin, no more than 1-4 nm in depth, outer layer containing polysulfide species, (ii) a layer exhibiting less pronounced stoichiometry deviations and low, if any, concentrations of polysulfide, the composition and dimensions of which vary for pyrite and pyrrhotite and depend on the chemical treatment, and (iii) an extended almost stoichiometric underlayer yielding modified TEY XANES spectra, probably, due to a higher content of defects. We suggest that the extended layered structure should heavily affect the near-surface electronic properties, and processes involving the surface and interfacial charge transfer.

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Section: Xanesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Mikhlin

Tomashevich

Vorobyev

et al. 2016

Applied Surface Science

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“…The Fe EXAFS spectrum of smectite (SAZ-1) was obtained from Dr Peggy O'Day at University of California, Merced, CA. [61] Compounds were only included in the fit if the contribution was a fraction greater than 0.05. Fits were approximately within AE5 % of the mole percentages.…”

Section: X-ray Absorption Spectroscopy (Xas)mentioning

confidence: 99%

Effect of biogeochemical redox processes on the fate and transport of As and U at an abandoned uranium mine site: an X-ray absorption spectroscopy study

Troyer

Stone

2014

Environ. Chem.

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Environmental context. Uranium and arsenic, two elements of human health concern, are commonly found at sites of uranium mining, but little is known about processes influencing their environmental behaviour. Here we focus on understanding the chemical and physical processes controlling uranium and arsenic transport at an abandoned uranium mine. We find that the use of sedimentation ponds limits the mobility of uranium; however, pond conditions at our site resulted in arsenic mobilisation. Our findings will help optimise restoration strategies for mine tailings.Abstract. Although As can occur in U ore at concentrations up to 10 wt-%, the fate and transport of both U and As at U mine tailings have not been previously investigated at a watershed scale. The major objective of this study was to determine primary chemical and physical processes contributing to transport of both U and As to a down gradient watershed at an abandoned U mine site in South Dakota. Uranium is primarily transported by erosion at the site, based on decreasing concentrations in sediment with distance from the tailings. Sequential extractions and U X-ray absorption near-edge fine structure (XANES) fitting indicate that U is immobilised in a near-source sedimentation pond both by prevention of sediment transport and by reduction of U VI to U IV . In contrast to U, subsequent release of As to the watershed takes place from the pond partially due to reductive dissolution of Fe oxy(hydr)oxides. However, As is immobilised by adsorption to clays and Fe oxy(hydr)oxides in oxic zones and by formation of As-sulfide mineral phases in anoxic zones down gradient, indicated by sequential extractions and As XANES fitting. This study indicates that As should be considered during restoration of uranium mine sites in order to prevent transport.

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“…2; see Table 3, which is published as supporting information on the PNAS web site, and ref. 41 for detailed analysis). The spectral signal for iron in sediments is dominated by iron substitution in detrital phyllosilicate minerals (probably mica).…”

Section: Xasmentioning

confidence: 99%

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions

O’Day

Vlassopoulos

Root

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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422

306

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The chemical speciation of arsenic in sediments and porewaters of aquifers is the critical factor that determines whether dissolved arsenic accumulates to potentially toxic levels. Sequestration of arsenic in solid phases, which may occur by adsorption or precipitation processes, controls dissolved concentrations. We present synchrotron x-ray absorption spectra of arsenic in shallow aquifer sediments that indicate the local structure of realgar (AsS) as the primary arsenic-bearing phase in sulfate-reducing conditions at concentrations of 1-3 mmol⅐kg ؊1 , which has not previously been verified in sediments at low temperature. Spectroscopic evidence shows that arsenic does not substitute for iron or sulfur in iron sulfide minerals at the molecular scale. A general geochemical model derived from our field and spectroscopic observations show that the ratio of reactive iron to sulfur in the system controls the distribution of solid phases capable of removing arsenic from solution when conditions change from oxidized to reduced, the rate of which is influenced by microbial processes. Because of the difference in solubility of iron versus arsenic sulfides, precipitation of iron sulfide may remove sulfide from solution but not arsenic if precipitation rates are fast. The lack of incorporation of arsenic into iron sulfides may result in the accumulation of dissolved As(III) if adsorption is weak or inhibited. Aquifers particularly at risk for such geochemical conditions are those in which oxidized and reduced waters mix, and where the amount of sulfate available for microbial reduction is limited. Despite intensive study in recent years, quantitative biogeochemical models that explain and predict conditions controlling the uptake or release of dissolved arsenic in groundwaters remain incomplete, due partly to a lack of knowledge of arsenic speciation in subsurface sediments. Worldwide, elevated concentrations of arsenic (Ͼ10 g⅐liter Ϫ1 , the World Health Organization and new U.S. Environmental Protection Agency drinking-water standard) in groundwater have the potential to have an adverse impact on Ϸ90 million people (1, 2), including 13 million in the United States (3, 4). Arsenic is a known carcinogen and mutagen that can lead to both acute and chronic adverse health effects (5, 6). Arsenic in ground-and surface waters results from both natural and anthropogenic sources, but its mobility and attenuation, and thus impact on humans and other organisms, is directly tied to its chemical speciation (3,7,8).Recent studies using direct spectroscopic characterizations have begun to verify differing chemical states of arsenic in natural samples and their influence on arsenic mobility (9-12). Under oxic conditions, it is widely accepted that arsenic in sediments is removed from solution by adsorption to or coprecipitation with ferric oxyhydroxide and possibly by adsorption to manganese oxide and phyllosilicate minerals (7, 13). As subsurface conditions change from oxidized to progressively more reduced, As(V) is reduced to As(III...

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X-ray absorption spectroscopic study of Fe reference compounds for the analysis of natural sediments

Cited by 229 publications

References 58 publications

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Hard X-ray photoelectron and X-ray absorption spectroscopy characterization of oxidized surfaces of iron sulfides

Effect of biogeochemical redox processes on the fate and transport of As and U at an abandoned uranium mine site: an X-ray absorption spectroscopy study

The influence of sulfur and iron on dissolved arsenic concentrations in the shallow subsurface under changing redox conditions

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