Atomic-Scale Study of Calcite Nucleation in Calcium Oxide

Abstract

In spite of its wide use, the properties of the CaO/CaCO3 system are still far from being understood, especially the mechanisms underlying the transition between both phases. To investigate this issue, important in practice for storage devices, we employ first-principles atomic-scale simulations of the solid–gas interactions between CO2 and CaO, by considering insertion of CO2 within the subsurface, in configurations characteristic of calcite surface nucleation. Comparing the (001) and (111) surfaces demonstrates that nucleation should be strongly surface-selective, with a sharp preference for (111), and an important role of the CO2 arrangement in the surface layer. To interpret these results, especially the important structural instabilities detected, we investigate the elastic properties of coherent CaO/CaCO3 layered systems. This reveals the special role played by the (111) interface orientation and confirms the behavior detected at the atomic scale. From our study, we propose a mechanism for calcite nucleation as well as a plausible explanation for the degradation of performances crippling the CaO-based devices used for CO2 storage.

New kinetic model for the rapid step of calcium oxide carbonation by carbon dioxide

“…The presence of large induction periods indicates that the nucleation process can be sluggish depending on experimental conditions. This observation can be correlated with an ab initio study of the calcite nucleation at the CaO surface [14] which has shown that nucleation can be a tricky process on some surfaces due to strong structural instabilities related with CO 2 insertion. Indeed the (100) surface of the CaO crystal appears unfavorable for nucleation whereas the (111) surface emerges as much more stable for CO 3 incorporation.…”

“…Figure 8 shows the good agreement between Eq. (14) and the experimental values for temperatures in the range 450-650°C and for CO 2 partial pressure in the range 2-30 kPa.…”

The Calcium-Looping technology for CO2 capture: On the important roles of energy integration and sorbent behavior

“…33,89,90,103 It has been proposed that a progressive growth of the regenerated crystal structure along preferential surfaces, which are more stable but less favorable for CaCO 3 nucleation, could play a role on the loss of multicyclic CaO conversion. [104][105][106] On the other hand, empirical results seem to indicate that decarbonation in CO 2 is a complex process involving a two-stage reaction mechanism, which consists of the endothermic chemical decomposition of Thermograms corresponding to the different experiments above reviewed are shown in Figure 8. The higher conversion of the CaO precalcined in air in the first cycle, as observed in Figure 7, is due to its high reactivity in the fast carbonation phase, and its drastic drop in conversion can be associated to the high susceptibility of the soft CaO skeleton resulting from precalcination in air to sintering.…”

Diffusion in CaCO3 Calcite Investigated by Atomic-Scale Simulations

“…Although an apparently well-known textbook case, the CaO + CO 2 ↔ CaCO 3 (de)carbonation process still offers many unknown aspects, in particular as regards the factors controlling its reaction rate; however, this issue has become of high importance in the current context of wide-scale CO 2 handling. While much knowledge on the mechanisms underlying the above reaction has remained essentially empirical for long, currently available experimental as well as theoretical methods of investigations now provide remarkable opportunities to clarify these mechanisms, and special efforts in this direction have been carried out in the last few years.…”

“…These studies therefore provide a rather good insight into several possible mechanisms underlying diffusion in CaCO 3 . In a work 5 published in 2004, Labotka et al performed detailed investigations, by means of the secondary-ion mass spectrometry (SIMS) technique, of C and O diffusion in calcite, between 600 and 800°C in a pressure range from 0.1 to 200 MPa of pure CO 2 . They concluded that the oxygen diffusion coefficient remains almost constant over the whole pressure range, whereas increasing the pressure entails a decrease of C diffusion by approximately 2 orders of magnitude.…”