— Pore fluid Sr concentrations tend to increase with depth and time due to calcite dissolution and precipitation (Fig. 1).The increase in pore fluid Sr occurs even if R net = 0, because primary biogenic calcite has Sr concentrations that are much higher than the equilibrium value with respect to seawater (Zhang et al., 2020).When biogenic …
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— The calcite films thus grown within days or weeks varied in thickness but typically were polycrystalline and epitaxial: a variety of morphologies and surface features are recorded. ... In uncoated samples the portlandite crystal dissolves in the aqueous phase and the corresponding rise in calcium concentration is monitored as a function of time ...
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DOI: 10.1016/J.CEJ.2014.04.037 Corpus ID: 93409289; Synthesis and application of magnesium amorphous calcium carbonate for removal of high concentration of phosphate @article{Xu2014SynthesisAA, title={Synthesis and application of magnesium amorphous calcium carbonate for removal of high concentration of phosphate}, author={Nan Xu and …
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— In fact, the deposition of calcite occurring while the film is flowing causes the average concentration of calcium to be progressively reduced from the initial concentrations at the source point. However, the film degassing and the loss of calcium occur on longitudinal scales (greater than 10 cm ) much larger than the crenulation scale [ 7 ].
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— However, the mixture of calcite and vaterite, the mixture of aragonite and calcite, pure calcite cryatals were produced when the concentration of imidazole were 50%, 60%, 70%, respectively; In the ...
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— The non-linearity of Eq. (1) in seawater is consistent with the calcite surface transitioning through three dissolution mechanisms that become active at different critical saturations ("Ω critical s"): retreat of pre-existing steps for Ω = 1 to Ω critical ≈ 0.9, the opening of etch pits at defects for Ω ≈ 0.9 to Ω critical ≈ 0.75, and the opening of etch …
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the film becomes thinner, the flushing efficiency of dissolved elements through the film decreases and the element concentration increases toward equilibrium concentration, leading to a slower dissolution rate in the film. The water film thickness on a single crystal of quartz, glass, calcite, and muscovite has been measured ex-
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— Using recent data on calcite dissolution and precipitation by Plummer et al., the deposition of CaCO 3 from thin films of supersaturated solutions of H 2 O/1bCO 2 /1bCaCO 3 to a CaCO 3 surface is calculated. The results are compared to previous calculations by Dreybrodt, which were based on precipitation kinetics as proposed by …
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— At constant calcium chloride and polymer (polyaspartic acid, sodium salt) concentrations, a pronounced influence of the Mg 2+ /Ca 2+ ratio was observed. Our experiments revealed an increasing inhibitory effect of Mg 2+ on calcite growth with the increase of Mg 2+ /Ca 2+ ratio in the parent solution, but this effect was manifest in …
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— Amorphous calcium carbonate (ACC) is a common precursor to crystalline calcium carbonate, and is of particular importance in biomineralization, where its crystallization in privileged environments ensures a pseudomorphic transformation. While organisms regulate this process using organic molecules and magnesium ions to …
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— We demonstrated the crystallization of calcium carbonate (CaCO 3) on polarized calcite single crystal substrates with three different orientations characterized by the (10.0), (00.1), and (10.4) planes in the presence of polyaspartic acid (PAsp) as an organic additive.The precipitates had a multiple phase structure with thin-film-like and …
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— 4. Kinetic fractionation and evaporation. When calcite precipitates from a thin film of drip water that is supersaturated with respect to calcite Ca 2+ and carbonate are removed from the solution and irreversibly incorporated into the calcite crystal lattice. During this process the concentration of DIC changes with some time dependent function C(t), …
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— Using calcite for high concentration phosphate removal, the results showed that (1) concentrations of phosphate higher than 30 mg.L −1, resulted in a significant phosphate precipitation on calcite surface at both pH7.7 and pH 8.3 within 24 h. The corresponding pH and calcium results confirmed this precipitation occurrence; (2) the ...
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— Recently, it has been found that trace concentrations of NaNO 3 severely affect calcite's (104) surface and its reactivity. Here we combine molecular dynamics …
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— We reconcile the offset between lab and in-situ rates by dissolving calcite in the presence of elevated orthophosphate (20 μm) and dissolved organic carbon (DOC) …
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Addition of Mg 2+ to the PAH ([PAH] = 20 μg mL –1)/ CaCl 2 ·2H 2 O reaction solution at a concentration of [Ca 2+] = [Mg 2+] = 10 mM led to the formation of ≈300 nm thick polycrystalline calcite films (Figure 7) that …
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— Particles of calcite start to dissolve in environments where the ambient seawater carbonate ion concentration falls beneath the equilibrium carbonate ion concentration (which is elevated towards the …
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of the annealed films can be controlled according to the mag-nesium content of the ACC precursor, and pure aragonite films comprising single crystal domains are formed at very low mag-nesium concentrations. With the ability to characterize the thin films using transmission electron microscopy (TEM), these
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Experimental Methods of Calcite Dissolution 107 by Nernst (1904). It assumes that mass transport by molecular diffusion is essentially across a Nernst layer of thickness B, which has to be defined for each special case. For a first-order heterogeneous reaction at the surface, the flux Fe from the
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— The main challenges are as follows: (i) calcite has a soluble mineral surface involved in dissolution and precipitation processes in solutions; (ii) Ca 2+ and CO 3 2− are released by calcite dissolution and Ca 2+ ions combine with PO 4 3− to form calcium phosphate precipitates, while CO 3 2−, as a base, has a strong impact on the ...
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At low concentration (o24 mM), Mg2+ modifies the habit to form calcite with a prismatic shape; while at higher concentrations, approaching that of seawater (51 mM), the calcite is mostly inhibited, thus enabling the …
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— There is new development in nanostructured calcite research offering high potential sensitive application due to its non-toxic inorganic metal properties. Previous research revolves around calcium carbonate in powder form and mainly used as fillers in industry. However, nanostructured calcite thin film synthesis is lacking reports despite its …
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— At low water-film thickness this reaction becomes rate limiting. The time dependent diffusion–reaction equations are solved for free drift dissolution by a finite-difference scheme, to obtain the dissolution rate of calcite as a function of the average calcium concentration in the water film. Dissolution rates are obtained for high ...
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— A) Bright‐field TEM image and B) corresponding SAED pattern of a single crystal domain in dolomite film generated from ACC films prepared at [Ca²⁺] = 10 × 10⁻³ m and [Mg²⁺] = 100 × 10 ...
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— This work aimed to study the detachment mechanism of organic molecules by scCO 2 from a water invasion calcite surface. The model consisted of four layers: the calcite layer, the organic molecule layer, the water layer and the scCO 2 layer, as shown in Fig. 1.The calcite layer was built by cleaving the calcite (104) surface with a size of 40.97 Å × …
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— Nevertheless, our calcite films remained intact and continuous throughout the SFA experiments, ... (SI) with respect to calcite and Ca 2+ concentration were calculated in the PhreeqC software, ...
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— About 50% of total dissolution of marine calcium carbonate occurs in the water column below 300 m depth while sinking to the seafloor, according to a reconstruction of settling fluxes of calcium...
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— Changes in calcification of marine organisms must be considered to explain the deepening of carbonate accumulation during ocean recovery from acidification …
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— In this work, the removal of phosphate with or without added sulfate at various concentrations was studied at 48 h and at pH 4.5 or 13.0 (Fig. 3)pared to the results without the addition of sulfate at pH 4.5, low SO 4 2− /PO 4 3− ratios of 1.5 and 3.0 enhanced the removal of phosphate. Because sulfate increased dissolution of calcite …
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— As the water reacts with calcite, CO2 concentration decreases while HCO 3 ... mass transfer of the Ca 2+, HCO 3 − and CO 2 molecules through the diffuse film layer around the calcite particles [14, 15]; the models from these two papers are hereafter referred to as Yamauchi model [15] and Letterman model [14] respectively. When one of …
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