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Application of enhanced sampling approaches to the early stages of mineralization
Published in Elaine DiMasi, Laurie B. Gower, Biomineralization Sourcebook, 2014
greatly enhanced over traditional mechanisms of crystal growth when crystallization proceeds via an amorphous calcium carbonate (ACC) precursor (Radha et al., 2012; Raz et al., 2003; Wang et al., 2009a; Weiner et al., 2003). Additionally, because the carbonate system also acts as the primary bu er system in natural waters, a robust understanding of the calcium carbonate mineralization pathway is critical not only to aid in the development of novel materials or the interpretation of biomineral-based climate proxy data, but to make informed predictions about the response of the surface ocean to rising atmospheric CO2 levels (Ridgwell and Zeebe, 2005; Ridgwell et al., 2003; Schuster and Watson, 2007) and the extent to which geological formations can act as carbon storage reservoirs (De Silva and Ranjith, 2012). 18.1.2 SPECIATION IN THE CaCO3 SYSTEM For the reasons outlined above, the formation and dissolution of calcium carbonate are among the most important chemical processes occurring in natural and engineered environments. Consequently, much work has been invested over the past century into quantifying the phase equilibria of hydrous and anhydrous calcium carbonates (calcite, aragonite, vaterite, monohydrocalcite, ikaite, ACC) and their interactions with aqueous solutions and nonaqueous solvents over a range of temperature, pressure, and atmospheric conditions. In solution, the solubility of calcium carbonate is equal to the sum over the activities (Ai) of all calcium-bearing species:
A Preliminary Study on the Characteristics of Lime-Based Mortars with Egg White Addition
Published in International Journal of Architectural Heritage, 2021
Kun Zhang, Liqin Wang, Fude Tie, Fuwei Yang, Yan Liu, Yue Zhang
All of these analyses results implied the presence of stable amorphous calcium carbonate (ACC) phases in specimens with egg white addition cured under 50% RH. Stable biogenic ACC phases are hydrated forms that contain a mole of water for every mole of calcium carbonate (CaCO3·H2O), and could be regarded as having short-range orders resembling, to a certain extent, that of monohydrocalcite, with very limited or no long-range order (Addadi, Raz, and Weiner 2003). Some studies on biomineralization (Aizenberg et al. 2002; Becker, Ziegler, and Epple 2005; Cartwright et al. 2012) reported that biogenic ACC in its stable form could function as mechanical stiffener (e.g., in plant cystholiths, calcitic sponge spicules, ascidian spicules), which was confirmed by compressive strength test results in the present study (Figure 8). This is also in accord with the descriptions by some historic recipes that mortars with egg white addition could be very hard after setting (Aikin and Aikin 1807; Chamber and Chamber 1849).
Calcium carbonate precipitation in compacted bentonite using electromigration reaction method and its application to estimate the ion activity coefficient in the porewater
Published in Journal of Nuclear Science and Technology, 2019
Jaka Rachmadetin, Masaya Mizuto, Shingo Tanaka, Tamotsu Kozaki, Naoko Watanabe
The value for Ksp depends on the mineral type and the temperature. There are six CaCO3 polymorphs: calcite, aragonite, vaterite, monohydrocalcite (CaCO3·H2O), ikaite (CaCO3 · 6H2O) and amorphous CaCO3 with the solubility decreasing from the former to the latter [37–41]. Of these CaCO3 polymorphs, the SEM/EDS images and diffraction patterns results strongly suggest that the amorphous CaCO3 is the most likely candidate polymorph. Recent study also reported that precipitation of CaCO3 occurred via amorphous CaCO3 as a pre-nucleation [12]. Moreover, confinement effect could stabilize amorphous CaCO3 [42]. The amorphous phase was also often used as solubility-limiting solid phase in the calculation of radionuclides solubilities and speciation for a conservative estimation [43,44]. The commonly employed Ksp value of amorphous CaCO3 is 10−6.4 [40]. However, recent study reported that the value is 10−7.54 which is about an order of magnitude lower than the previously reported. The author reasoned that the previously higher Ksp value might be due to the polyamorphism of CaCO3 [45]. Therefore, those two Ksp values are used in the mean activity coefficient calculation.
Seawater based bio-cementation for calcareous sand improvement in marine environment
Published in Marine Georesources & Geotechnology, 2022
Figure 4 shows the XRD patterns of the carbonates precipitated by bio-cementation process and seawater based bio-cementation process. During the bio-cementation process, the precipitates are the mixture of calcite and vaterite, corresponding PDF cards are 86-0174 and 72-0506, respectively. The mixture of calcite, monohydrocalcite and calcite magnesium can be found in the seawater based bio-cementation precipitations. Their PDF cards are 86-0174, 83-1922 and 89-1304, as shown in Figure 4.