Surface speciation of calcite observed in situ by high-resolution X-ray reflectivity

Fenter, Paul; Geissbühler, P.; DiMasi, Elaine; Srajer, G.; Sorensen, L. B.; Sturchio, Neil C.

doi:10.1016/s0016-7037(99)00403-2

Cited by 247 publications

(232 citation statements)

References 37 publications

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“…This suggests that the adsorbed water molecules saturate the broken bonds of the surface Ba ions, in analogy to that observed previously for Ca ions at the calcite-water interface. 12 Including additional adsorbed water to saturate the single broken Ba-O bond associated with the inner Ba ion did not improve the fit (as expected since the quality of fit was ∼1). Such models also resulted in a high degree of covariance between the parameters associated with the adsorbed water structure, further implying that these data cannot uniquely determine any further detail of the adsorbed water structure.…”

Section: The Barite (001) Surfacementioning

confidence: 58%

“…Despite the higher structural heterogeneity of barite surfaces, we find that the location and number of adsorbed water molecules for both barite and calcite surfaces are consistent with the saturation of broken metal-oxygen bonds. 12 In each of these cases, the lateral two-dimensional densities of the adsorbed water layers [0.05 H 2 O/Å 2 for calcite, 12 0.056 H 2 O/Å 2 for barite (001), and 0.06 H 2 O/Å 2 for barite (210)] were found to be substantially smaller than that of a closed-packed water layer (F 2d ∼ F 3d 2/3 ∼ 0.10 H 2 O molecule/Å 2 ). This suggests the relatively simple picture that water acts to saturate broken bonds at ionic mineral surfaces.…”

Section: Discussionmentioning

confidence: 99%

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Structure of Barite (001)− and (210)−Water Interfaces

et al. 2001

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The structures of the barite (001) and (210) cleavage surfaces were measured in contact with deionized water at 25°C. High resolution (∼1 Å) specular X-ray reflectivity and atomic force microscopy were used to probe the step structures of the cleaved surfaces and the atomic structures of the barite-water interfaces including the structures of water near the barite-water interfaces. The barite (001) and (210) cleavage surfaces are characterized by large (>2500 Å) domains separated by unit-cell steps (7.15 and 3.44 Å steps for the (001) and (210) surfaces, respectively). This observation was unanticipated for the (001) surface in which adjacent BaSO 4 layers are displaced vertically by c/2 and symmetry related through a 2 1 screw axis along (001). The atomic structures of the two cleavage surfaces derived by X-ray reflectivity reveal that near-surface sulfate groups exhibit significant (∼0.4 Å) structural displacements, while Ba surface ion displacements are significantly smaller (∼0.07 Å). Water adsorbs to the barite surfaces in a manner consistent, in both number and height, with the saturation of broken Ba-O bonds; no evidence was found for additional structuring of the fluid water near the surface.

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Section: The Barite (001) Surfacementioning

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Structure of Barite (001)− and (210)−Water Interfaces

et al. 2001

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“…Polycarboxylic acids are known to strongly complex Ca 2+ and to lesser extent Na + ions [48][49], which could result in a reduction of the capacity of the additive to bind to the surface. The second reason may be the highly layered structure of water found above a calcite surface with regions of alternating low and high water density [40,50]. As the additive backbones are hydrophobic, the molecules will have a tendency to stay in low density water regions, which are known from both experiment [50] and simulations [40] to be located roughly at 2.8 Å and 3.9 Å from the surface.…”

Section: Resultsmentioning

confidence: 99%

Growth modification of seeded calcite using carboxylic acids: Atomistic simulations

Aschauer

Spagnoli

Bowen

et al. 2010

Journal of Colloid and Interface Science

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a b s t r a c tMolecular dynamics simulations were used to investigate possible explanations for experimentally observed differences in the growth modification of calcite particles by two organic additives, polyacrylic acid (PAA) and polyaspartic acid (p-ASP). The more rigid backbone of p-ASP was found to inhibit the formation of stable complexes with counter-ions in solution, resulting in a higher availability of p-ASP compared to PAA for surface adsorption. Furthermore the presence of nitrogen on the p-ASP backbone yields favorable electrostatic interactions with the surface, resulting in negative adsorption energies, in an upright (brush conformation). This leads to a more rapid binding and longer residence times at calcite surfaces compared to PAA, which adsorbed in a flat (pancake) configuration with positive adsorption energies. The PAA adsorption occurring despite this positive energy difference can be attributed to the disruption of the ordered water layer seen in the simulations and hence a significant entropic contribution to the adsorption free energy. These findings help explain the stronger inhibiting effect on calcite growth observed by p-ASP compared to PAA and can be used as guidelines in the design of additives leading to even more marked growth modifying effects.

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“…[42][43][44] There are numerous experimental studies investigating various aspects of the calcite(1014)/water interface as well. 18,[45][46][47][48][49][50][51][52][53] In our work we aimed for an improved theoretical understanding of the incorporation mechanism of selenium into calcite surface layers similar as carried out in an earlier experimental work by Heberling et al 18 Hence we studied the incorporation of selenium into bulk calcite, similarly as had been done by Aurelio et al 21 But we extended this study by investigation how selenium is incorporated into the surface and subsurface layers of the calcite (1014) surface. For this we used different models for the dry and hydrated calcite surface allowing an additional view on the influence of surface water.…”

Section: Introductionmentioning

confidence: 99%

Quantum Chemical Investigation of the Selenite Incorporation into the Calcite (101̅4) Surface

et al. 2017

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Selenium is a common pollutant in soils and aquifers. The radioisotope 79 Se, an abundant fission product of 235 U, is of particular concern in the context of nuclear waste disposal safety due to its long half-life and its expected high mobility in the multi-barrier system around potential nuclear waste disposal sites. Oxidized selenium species are relatively soluble and show only weak adsorption at common mineral surfaces. However, a possible sorption mechanism for selenium in the geosphere is the structural incorporation of selenium(IV) (selenite, SeO 2− 3 ) into calcite (CaCO 3 ).We carried out a detailed quantum chemical study of the incorporation of SeO 2− 3 into the calcite surface and the subsurface layers.As the main result we present the structural changes upon incorporation of selenite (SeO −2 3 ) into the dry and hydrated calcite (1014) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 coefficient D for SeO −2 3 incorporation into the surface and subsurface layers. The results corroborate the recently proposed entrapment model for selenium(IV) coprecipitation with calcite and show that equilibrium incorporation of selenite into calcite may occur in the surface layer, but is practically impossible in subsurface layers or the bulk.2

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Surface speciation of calcite observed in situ by high-resolution X-ray reflectivity

Cited by 247 publications

References 37 publications

Structure of Barite (001)− and (210)−Water Interfaces

Structure of Barite (001)− and (210)−Water Interfaces

Growth modification of seeded calcite using carboxylic acids: Atomistic simulations

Quantum Chemical Investigation of the Selenite Incorporation into the Calcite (101̅4) Surface

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