Molecular environmental geochemistry

O’Day, Peggy A.

doi:10.1029/1998rg900003

Cited by 65 publications

(35 citation statements)

References 171 publications

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“…The efficiency and reversibility of arsenite adsorption on iron sulfide, iron oxide, iron hydroxide, and phyllosilicate minerals in natural systems depend on many factors, including pH, dissolved arsenic concentration, type of mineral substrate, and presence of competing species, and are thus difficult to predict quantitatively. In general, however, precipitation is a more complete and stable mechanism for removal of solutes from solution than adsorption (49,50).…”

Section: Discussionmentioning

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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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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Section: Discussionmentioning

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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418

306

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“…In the case of chromium, these changes can affect the macroscopic properties of toxicity and mobility in the atmosphere and in the geologic subsurface [1][2][3]. These behavioral attributes have motivated research into surface speciation of Cr-bearing surfaces, with the intent of correlating the explicit chemical form of the metal with transport and toxicity.…”

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confidence: 99%

“…A systematic study of the reactions with H 2 O showed that ions containing undercoordinated metal centers would undergo either addition or radical abstraction reactions [29]. These reactions would proceed in series until a Cr coordination number of 4 was reached, except for CrO 3 Ϫ , which was unreactive. The reactions of the chromium oxyanions with O 2 were also significant, and the present study describes these in detail.…”

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confidence: 99%

Ion-molecule reactions of gas-phase chromium oxyanions: Cr_xO_yH_z⁻ + O₂

Gianotto¹,

Hodges²,

Harrington

et al. 2003

J. Am. Soc. Mass Spectrom.

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“…[3] The environmental implications of mineral surface chemistry are manifold and diverse. They include atmospheric CO 2 drawdown associated with silicate mineral dissolution, [4,5] removal from solution of adsorptive metal and oxyanion contaminants, [6] nutrient retention for plant growth [7] and organic matter stabilisation against microbial biodegradation. [8] Through a combination of macroscopic experiments, molecular spectroscopy studies, and molecular modelling, environmental chemists are developing an improved understanding of the molecular-scale controls over the rates and extents of mineral surface reactions.…”

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confidence: 99%

Foreword to the Research Front on ‘Mineral–Organic Interactions in Aqueous Systems’

Chorover¹

2015

Environ. Chem.

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The mineral-water interface exhibits great diversity in surface functional group composition and associated reactivity towards inorganic and organic solutes that occur in natural soil, sediment and water. [1,2] Chemical processes of environmental significance involving oxidation-reduction, adsorption-desorption, and dissolution-nucleation are promoted by these interfaces because of their propensity for acid-base, ion-or ligandexchange, and redox reactions. Mineral surface hydroxyl groups of iron, aluminium and manganese (oxyhydr)oxides and siloxane groups of layered aluminosilicates, for example, are known to exhibit a range in affinities for reaction with protons, hydroxyl ions, metals, oxyanions, and aqueous organic species and their complexes. [3] The environmental implications of mineral surface chemistry are manifold and diverse. They include atmospheric CO 2 drawdown associated with silicate mineral dissolution, [4,5] removal from solution of adsorptive metal and oxyanion contaminants, [6] nutrient retention for plant growth [7] and organic matter stabilisation against microbial biodegradation. [8] Through a combination of macroscopic experiments, molecular spectroscopy studies, and molecular modelling, environmental chemists are developing an improved understanding of the molecular-scale controls over the rates and extents of mineral surface reactions.This Research Front presents six contributions discussing various aspects of mineral surface reactions and their environmental relevance using experimental, spectroscopic and simulation methods. The Research Front begins with a review by Casey [9] on the mechanisms and kinetics of ligand exchange reactions at mineral surfaces. This paper discusses reactivity trends for ligand and oxygen isotope exchanges in nanometresized molecular clusters and larger mineral structures from the perspective of coordination chemistry. It provides examples of how an understanding of exchange reactions in the molecular clusters can shed light on reaction kinetics of broad environmental relevance, such as those for mineral dissolution and metal-ligand complex formation in aqueous solutions.The second paper, a review by Stack and Kent, [10] discusses how computational modelling, specifically molecular dynamics and quantum chemical simulations, can be used to build insightful kinetic models of mineral surface reactions. Illustrative examples are presented for water ligand exchange, adsorption, crystal growth, dissolution and electron transfer. Interfacial reactions are strongly affected by the speciation of aqueous phase reactants as shown in the third paper, authored by Carbonaro and Stone. [11] This study, which evaluates mineralsurface-mediated rates of Cr III oxidation to Cr VI during surface reaction with hydrous Mn IV oxide, shows that Cr III -chelating ligands alter the pH-dependent kinetics of oxidation. This is important, because most soil systems contain natural organic matter (NOM) that can form stable complexes with polyvalent metals.The fourth paper by Pasakarnis et a...

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Molecular environmental geochemistry

Cited by 65 publications

References 171 publications

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

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

Ion-molecule reactions of gas-phase chromium oxyanions: Cr_xO_yH_z⁻ + O₂

Foreword to the Research Front on ‘Mineral–Organic Interactions in Aqueous Systems’

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Molecular environmental geochemistry

Cited by 65 publications

References 171 publications

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

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

Ion-molecule reactions of gas-phase chromium oxyanions: CrxOyHz− + O2

Foreword to the Research Front on ‘Mineral–Organic Interactions in Aqueous Systems’

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Ion-molecule reactions of gas-phase chromium oxyanions: Cr_xO_yH_z⁻ + O₂