Tuning Crystal Polymorphisms and Structural Investigation of Precipitated Calcium Carbonates for CO₂ Mineralization

Abstract

Mineral carbonation, which involves spontaneous reactions of CO2 with alkaline earth metals such as calcium or magnesium, is considered one of the most attractive options to sequester CO2 because CO2 can be permanently stored in an inert solid forming stable inorganic carbonate. Moreover, the precipitated CaCO3 has various potential applications in industrial areas, including adhesives, sealants, food, pharmaceuticals, paints, coating, paper, cement, construction materials, etc. In particular, it is expected that the total cost of the carbon capture and storage process could be partly offset by producing value-added CaCO3 materials. In order to add value to the precipitated CaCO3 produced in the ex-situ mineral carbonation process, CaCO3’s polymorphs, as well as other properties such as particle size, shape, density, color, and brightness, must be finely tuned. Among CaCO3’s polymorphs, calcite, aragonite, and vaterite, calcite is considered to be the most thermodynamically favorable structure at ambient temperatures. However, kinematic constraints in the crystallization induced by synthetic factors are known to significantly affect the formation of polymorphs as well. Here, we revisited the effects of the synthetic factors such as pH, temperature, feeding order, and concentration and molar ratio of Ca2+ and CO3 2– on the formation of CaCO3’s polymorphs to provide fundamental insight into how to control the polymorphism of CaCO3 with the ultimate goal of creating value-added mineral carbonation products. ATR FT-IR spectroscopy and a powder X-ray diffraction analysis were performed on the precipitated CaCO3 using model chemicals, K2CO3 and CaCl2, and CaCO3’s thermal stability was also investigated.

Increased Sustainability of Carbon Dioxide Mineral Sequestration by a Technology Involving Fly Ash Stabilization

“…Vaterite, the thermodynamically least stable phase among the three polymorphic forms of calcium carbonate, was detected in FA sample, as already found in similar experiments [32]. Vaterite is generally formed at a relatively low temperature condition (also at room temperature) [37].…”

Calcium Carbonate Precipitation for CO2 Storage and Utilization: A Review of the Carbonate Crystallization and Polymorphism

“…A number of mechanistic studies have been conducted thus far to reveal the transformation mechanisms among the CaCO3 polymorphs (Kralj et al, 1997;Spanos and Koutsoukos, 1998;Katsifaras and Spanos, 1999;Wei et al, 2003;Rodriguez-Blanco et al, 2011;Zhang et al, 2012;Kabalah-Amitai et al, 2013;Nielsen et al, 2014). Although it is necessary to heat to temperature exceeding 730 K for irreversible transformation of vaterite to calcite (Chang et al, 2017), the least stable vaterite can be stabilized in an aqueous solution at ambient conditions preventing its transformation into calcite or aragonite (Trushina et al, 2014). Despite ongoing debate (Kamhi, 1963;Wang and Becker, 2009;Kabalah-Amitai et al, 2013), the formation of vaterite and its transformation mechanisms among the polymorphs can be explained in terms of sequential dissolution and (re)crystallization processes (Figure 2) (Kralj et al, 1997;Spanos and Koutsoukos, 1998;Katsifaras and Spanos, 1999;Wei et al, 2003): (i) initially formed ACC particles transform to the least stable vaterite and (ii) the most soluble vaterite undergoes dissolution and crystallization finally forming the most stable calcite.…”

“…The anhydrous crystalline polymorphs of CaCO3 strongly depend on the synthesis variables such as temperature, pressure, pH of the solution, reaction time, degree of supersaturation, ion concentration and ratio, ionic strength, stirring, type and concentration of additives, and feeding order (Tai and Chen, 1998;Jung et al, 2000;García-Carmona et al, 2003a,b;Shen et al, 2006;Meldrum and Cölfen, 2008;Chen and Xiang, 2009;Fuchigami et al, 2009;Ren et al, 2011;Chu et al, 2013;Zhao et al, 2013;Jiang et al, 2014;Ševčík et al, 2015;Chang et al, 2017). Although the formation of CaCO3 can be achieved by a simple precipitation reaction between Ca 2+ and CO 3 2− ions, the controllable formation of a specific polymorph of CaCO3 is still a practical challenge.…”

“…They performed a quantitative analysis by the Rietveld method employing powder X-ray diffraction (PXRD) with the assumption that vaterite exhibits two crystal structures, the well-established hexagonal structure (space group: P63/mmc) (Meyer, 1959) and triclinic structure (space group C1) proposed by Demichelis et al (2013). However, the exact crystal structure of vaterite is still under debate due to the difficulties in obtaining large, pure, single crystals of vaterite (Kamhi, 1963;Mugnaioli Ca ratios using CaCl2 and K2CO3 solutions via ATR FT-IR and PXRD spectroscopies at 25, 50, and 80°C, stirring at 350 rpm (Chang et al, 2017). They confirmed that vaterite is a major component together with calcite at 25°C, and particularly at higher pH (~11) vaterite became the most dominant species.…”

“…It has been reported that the formation behavior of each polymorph is affected by synthesis factors including pH, temperature, concentration, and ratio of carbonate and calcium ions, additives, stirring, reaction time, etc. (Zhao et al, 2013;Chang et al, 2017). In this review, we present a summary of current knowledge and recent investigations involving mechanistic studies on the formation of the precipitated CaCO3 and the influences of the synthesis factors on the polymorphs.…”