Surface complexation clues to dolomite growth

Brady, Patrick V.; Krumhansl, J. A.; Papenguth, Hans W.

doi:10.1016/0016-7037(95)00436-x

Cited by 102 publications

(57 citation statements)

References 19 publications

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“…The latter possibly points to co-adsorption of Me and S04 at the minerai surface. How this might affect dolomite growth rates has been outlined elsewhere (Brady et al, 1996). Since Ca2+ levels were typically -10-4 M, and the volubility product of gypsum is !0-459, solutions would approach saturation with gypsum only if S00 concentrations exceeded 0.1 M.…”

Section: Effec[s Of Sulfatementioning

confidence: 99%

Metal sorption to dolomite surfaces

Brady

Papenguth

Kelly

1999

Applied Geochemistry

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Potential human intrusion into the Waste Isolation Pilot Plant (WIPP) might release actinides into the Culebra Dolomite where sorption reactions will affect of radiotoxicity from the repository. Using a limited residence time reactor the authors have measured Ca, Mg, Nd adsorption/exchange as a function of ionic strength, Pcoz, and pH at 25°C. By the same approach, but using as input radioactive tracers, adsorption/exchange of Am, Pu, U, and Np on dolomite were measured as a function of ionic strength, Pcoz, and PH at 25"C. Metal adsorption is tYPical@ favored at high pH. Calcium and Mg adsorb in near-stoichiometric proportions except at high pH. Adsorption of Ca and Mg is diminished at high ionic strengths (e.g., 0.5M NaCl) pointing to association of Na + with the dolomite surflce, and the possibility that Ca and Mg sorb as hydrated, outer-sphere complexes. Sulfate amplifies sorption of Ca and Mg, and possibly Nd as well. Exchange of Nd for surface Ca is favored at high pH, and when Ca levels are low. Exchange for Ca appears to control attachment of actinides to dolomite as well, and high levels of Ca2 + in solution will decrease Kds. At the same time, t~the extent that high Pcojs increase Ca2 + levels, &S will decrease with C02 levels as well, but only if sorbing actinide-carbonate complexes are not observed to form (Amcarbonate complexes appear to sorb; Pu-complexes might sorb as well. U-carbonate complexation leads to resorption). This indirect C02 effect is observed primarily at, and above, neutral pH. High NaCl levels do not appear to atTect to actinide Kds

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Section: Effec[s Of Sulfatementioning

confidence: 99%

Metal sorption to dolomite surfaces

Brady

Papenguth

Kelly

1999

Applied Geochemistry

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“…Epitaxial growth, or layer-by-layer growth, at the mineral-water interface has been demonstrated on various systems including homoepitaxial growth of calcite, barite, and celestite under supersaturated solutions (e.g., Higgins et al, 2000;Teng et al, 2000;Risthaus et al, 2001). However, dolomite does not form under similar low-temperature/low-pressure conditions (De Boer, 1977;Deelman, 1981;Hartman, 1982;Reeder, 1982;El-Mofty et al, 1989;Tribble et al, 1995;Brady et al, 1996;Arvidson and Mackenzie, 1997;Pokrovsky, 1998;Titiloye et al, 1998;De Leeuw, 2002) nor has epitaxial growth been observed in recent attempts on dolomite seed crystals . The surface Ca/Mg ratio variability on dolomite surfaces may have implications in the tendency for formation (from supersaturated solution) of non-dolomite phases such as magnesian calcite, aragonite, and various carbonate hydrates (Pokrovsky, 1998).…”

Section: Introductionmentioning

confidence: 99%

X-ray photoelectron spectroscopic studies of dolomite surfaces exposed to undersaturated and supersaturated aqueous solutions

Joshi

Mukhopadhyay

et al. 2006

Geochimica et Cosmochimica Acta

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Cleaved surfaces of dolomite were studied using ex-situ X-ray photoelectron spectroscopy (XPS) following exposure of the surfaces to various experimental conditions. Dolomite samples exposed to air, to a highly undersaturated solution (0.1 M NaCl, pH = 9), and to solution with a supersaturation (ÀDl/kT) of 5.5 (pH = 9) were investigated with semiquantitative methods of analysis to ascertain the degree of non-stoichiometry resulting at the dolomite surface from reactive conditions. It was found that the dolomite cleavage surface in undersaturated solution was not altered significantly from the stoichiometric surface termination. The composition of the cleaved surface after exposure to supersaturated solution, a surface known to have self-limiting growth characteristics under similar conditions, was found to be Ca 2+ rich (Ca x Mg 2 À x (CO 3 ) 2 , 1.7 > x > 1.3). The observations, while underscoring differences in hydration/dehydration kinetics of the two alkaline earth cations, suggest that achievement of equilibrium at dolomite-water interfaces may be subject to significant barriers from both undersaturated and supersaturated solutions.

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“…Synthesis of low-temperature dolomite is hindered by slow reaction kinetics (2). Kinetic inhibition is attributed to lack of solution supersaturation (3), sulfate inhibition (1), cation desolvation (4), and lack of nucleation sites (5). Laboratory precipitation at low temperature has only been successful in producing disordered dolomite: from solutions with high salinity (6); through intermittent (7) or complete dehydration (8); by using organic or inorganic compounds that effectively dewater Mg 2+ ions (9-11); or in the presence of microorganisms, their exudates, or surfaces (12,13).…”

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confidence: 99%

Surface chemistry allows for abiotic precipitation of dolomite at low temperature

Roberts¹,

Kenward²,

Fowle³

et al. 2013

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

207

150

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Although the mineral dolomite is abundant in ancient lowtemperature sedimentary systems, it is scarce in modern systems below 50°C. Chemical mechanism(s) enhancing its formation remain an enigma because abiotic dolomite has been challenging to synthesize at low temperature in laboratory settings. Microbial enhancement of dolomite precipitation at low temperature has been reported; however, it is still unclear exactly how microorganisms influence reaction kinetics. Here we document the abiotic synthesis of low-temperature dolomite in laboratory experiments and constrain possible mechanisms for dolomite formation. Ancient and modern seawater solution compositions, with identical pH and pCO 2 , were used to precipitate an ordered, stoichiometric dolomite phase at 30°C in as few as 20 d. Mg-rich phases nucleate exclusively on carboxylated polystyrene spheres along with calcite, whereas aragonite forms in solution via homogeneous nucleation. We infer that Mg ions are complexed and dewatered by surface-bound carboxyl groups, thus decreasing the energy required for carbonation. These results indicate that natural surfaces, including organic matter and microbial biomass, possessing a high density of carboxyl groups may be a mechanism by which ordered dolomite nuclei form. Although environments rich in organic matter may be of interest, our data suggest that sharp biogeochemical interfaces that promote microbial death, as well as those with high salinity may, in part, control carboxyl-group density on organic carbon surfaces, consistent with origin of dolomites from microbial biofilms, as well as hypersaline and mixing zone environments.biomineralization | carbonates A lthough synthesis of dolomite in laboratory settings at high temperature (80-250°C) has yielded valuable information regarding dolomite formation (1, 2), the validity of extrapolating kinetic data at 250°C down to 25°C is questionable. Synthesis of low-temperature dolomite is hindered by slow reaction kinetics (2). Kinetic inhibition is attributed to lack of solution supersaturation (3), sulfate inhibition (1), cation desolvation (4), and lack of nucleation sites (5). Laboratory precipitation at low temperature has only been successful in producing disordered dolomite: from solutions with high salinity (6); through intermittent (7) or complete dehydration (8); by using organic or inorganic compounds that effectively dewater Mg 2+ ions (9-11); or in the presence of microorganisms, their exudates, or surfaces (12, 13).Microbial dolomite has been produced in the presence of several different metabolic pathways including sulfate reduction, methanogenesis, methanotrophy, sulfide oxidation, and aerobic respiration (12-16), which may drive precipitation through the supersaturation of solutions with respect to dolomite. Recent work, however, has focused on the role of microbial cells and exopolymeric substances (EPS) as surfaces for dolomite nucleation (17). Whereas these studies clearly demonstrate that these surfaces are involved in dolomite formation, specific ...

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Surface complexation clues to dolomite growth

Cited by 102 publications

References 19 publications

Metal sorption to dolomite surfaces

Metal sorption to dolomite surfaces

X-ray photoelectron spectroscopic studies of dolomite surfaces exposed to undersaturated and supersaturated aqueous solutions

Surface chemistry allows for abiotic precipitation of dolomite at low temperature

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