Control of dissolution rates of orthosilicate minerals by divalent metal–oxygen bonds

Casey, William H.; Westrich, Henry R.

doi:10.1038/355157a0

Cited by 160 publications

(96 citation statements)

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“…Our finding of the isotopic mass dependence of k wex implies that any ligand-exchange reaction whose rate constant correlates with k wex [mineral dissolution (28,29), metal binding to organic ligands (26,27), and possibly metal attachment to mineral surfaces (13,18,19,21)] should exhibit significant kinetic isotope fractionation. For such reactions, the overall kinetic isotope fractionation (α kinetic ) has a maximum value in conditions where the forward reaction rate is much larger than the backward rate.…”

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confidence: 97%

“…Likewise, experimental (22,23), theoretical (13,24), and molecular simulation studies (25) suggest that the kinetics of metal attachment at calcite surfaces may be related to the dehydration frequency of the metal near the surface. More broadly, the rate constants of several metal ligandexchange reactions [Mg and Ni binding to a range of organic ligands (26,27), the dissolution of orthosilicate minerals containing a range of divalent metals (28,29)] have been shown to correlate with the water-exchange rates of metals in liquid water, k wex (the inverse of the residence time of water in the first solvation shell of the metal).…”

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confidence: 99%

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Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Hofmann

Bourg

DePaolo

2012

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

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Molecular dynamics simulations show that the desolvation rates of isotopes of Li + , K + , Rb + , Ca 2+ , Sr 2+ , and Ba 2+ may have a relatively strong dependence on the metal cation mass. This inference is based on the observation that the exchange rate constant, k wex , for water molecules in the first hydration shell follows an inverse power-law mass dependence (k wex ∝ m −γ ), where the coefficient γ is 0.05 ± 0.01 on average for all cations studied. Simulated waterexchange rates increase with temperature and decrease with increasing isotopic mass for each element. The magnitude of the water-exchange rate is different for simulations run using different water models [i.e., extended simple point charge (SPC/E) vs. four-site transferrable intermolecular potential (TIP4P)]; however, the value of the mass exponent γ is the same. Reaction rate theory calculations predict mass exponents consistent with those determined via molecular dynamics simulations. The simulation-derived mass dependences imply that solids precipitating from aqueous solution under kinetically controlled conditions should be enriched in the light isotopes of the metal cations relative to the solutions, consistent with measured isotopic signatures in natural materials and laboratory experiments. Desolvation effects are large enough that they may be a primary determinant of the observed isotopic fractionation during precipitation.aqueous geochemistry | kinetic isotope effect | ligand exchange N onequilibrium processes are generally recognized as important influences on isotopic fractionation during mineral precipitation, especially at temperatures below a few hundred degrees Celsius (1, 2). Recent work in "nontraditional" stable isotopes (Li, Mg, Ca, Fe, Cd, Cu, etc.) has confirmed this inference and shown that nonequilibrium fractionation must be accounted for to understand global biogeochemical cycles involving these elements (2-5). A key observation is that light isotopes are preferentially incorporated into precipitating solids (6-8)-the opposite direction of enrichment expected for equilibrium fractionation, which depends on bond energetics (9, 10). The origin of this nonequilibrium light-isotope enrichment is a key unknown in the isotopic geochemistry of mineral growth.Calcite grown from aqueous solutions provides an excellent illustration of light-isotope enrichment during precipitation. Synthetically precipitated and natural samples of calcite and aragonite are fractionated relative to aqueous Ca 2+ such that δ 44/40 Ca in calcite is lower by 0.5-2‰ (7, 11). Equilibrium Ca isotope fractionation between Ca 2+ (aq) and calcite has not been measured in the laboratory, but studies of deep-sea sedimentary pore fluids suggest that the equilibrium fractionation is negligible: ε eq ∼ 0.0 ± 0.1‰ (12). Growth of calcite from seawater-like aqueous solutions is not likely to be diffusion-limited for Ca, so the isotopic effects are inferred to be due to kinetic effects occurring at the solid/fluid interface (11, 13). Diffusion in liquid water can r...

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confidence: 97%

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confidence: 99%

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Hofmann

Bourg

DePaolo

2012

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

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“…Giammar et al, 2005;Oelkers and Schott, 2005;Bearat et al, 2006;Matter et al, 2007;Oelkers et al, 2008;Dufaud et al, 2009;Prigiobbe et al, 2009;Matter and Kelemen, 2009;King et al, 2010;Daval et al, 2011;Guyot et al, 2011;Broecker, 2012;Kohler et al, 2013;Gislason and Oelkers, 2014;Sissmann et al, 2014). This interest has led to a large number of studies aimed at characterizing forsterite dissolution behavior and rates at various fluid compositions and temperatures (Luce et al, 1972;Sanemasa et al, 1972, Grandstaff, 1978, 1986, Murphy and Helgeson, 1987, 1989Blum andLasaga, 1988, Banfield et al, 1990;Walther, 1991, 1992;Casey and Westrich, 1992, Awad et al, 2000, Chen and Brantley, 2000, Rosso and Rimstidt, 2000, Pokrovsky and Schott, 2000a, 2000b, Oelkers, 2001b, Giammar et al, 2005, Hänchen et al, 2006, Olsen and Rimstidt, 2008Davis et al, 2009;Rimstidt et al, 2012;Olsson et al, 2012;Plümper et al, 2012;Wang and Giammar, 2012;Garcia et al, 2013;<...>…”

Section: Introductionmentioning

confidence: 99%

“…Casey and Westrich, 1992;Oelkers, 2001b) or at elevated CO 2 pressures (e.g. Saldi et al, 2013;Wang and Giammar, 2013;Johnson et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

The efficient long-term inhibition of forsterite dissolution by common soil bacteria and fungi at Earth surface conditions

Oelkers

Benning

Lutz

et al. 2015

Geochimica et Cosmochimica Acta

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“…3). Because the mechanism by which a cation leaves a dissolving mineral surface 477 is similar to the mechanisms of water exchange in the hydrated complex, the observed relation is 478 expected to hold for those metals and contamination forms, for which the major chemical bond in 479 the contamination material is that between metal and oxygen (Casey and Westrich, 1992;Casey et 480 al., 1993;Ludwig et al, 1996;Pokrovsky and Schott, 2002). Indeed, the average reactive fraction of 481 anthropogenic or geogenic Fe 3+ and Cr 3+ in soils agrees with predictions of the two reactivity -482 lability relationships if extrapolated outside the six studied metals (Fig.…”

Section: Metal Reactivity In Relation To the Intrinsic Kinetic Labilimentioning

confidence: 99%

Assessing comparative terrestrial ecotoxicity of Cd, Co, Cu, Ni, Pb, and Zn: The influence of aging and emission source

Owsianiak

Holm

Fantke

et al. 2015

Environmental Pollution

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Control of dissolution rates of orthosilicate minerals by divalent metal–oxygen bonds

Cited by 160 publications

References 8 publications

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

Ion desolvation as a mechanism for kinetic isotope fractionation in aqueous systems

The efficient long-term inhibition of forsterite dissolution by common soil bacteria and fungi at Earth surface conditions

Assessing comparative terrestrial ecotoxicity of Cd, Co, Cu, Ni, Pb, and Zn: The influence of aging and emission source

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