A novel approach to mineral carbonation using deep eutectic solvents for the synthesis of nano-sized amorphous CaCO3

Abstract

This paper proposes a novel synthesis method for nanosized amorphous CaCO3 based on advanced mineral carbonation using the macromolecular properties of deep eutectic solvents (DESs). DESs are generally synthesized by mixing hydrogen bond acceptors (HBAs) and hydrogen bond donors (HBDs), and their properties vary depending on the HBDs and HBAs used for the synthesis. To synthesize DESs with CO2-philic properties, monoethanolamine (MEA) was selected as the HBD because it possesses a CO2-active site. However, alkanolamine-based DESs are difficult to use in practical applications because of their high viscosity following CO2 absorption. To mitigate the onset of high viscosity, H2O was added to the synthesized DESs, with the molar ratio HBA:HBD:H2O as 1:5:10 and 1:5:15. In the proposed process, CO2 was captured by the DESs-H2O system and converted into particle-size- and morphology-controlled CaCO3. Nanosized amorphous CaCO3 (ACC) with average particle sizes of 38.1 and 48.0 nm was formed by DESs based on the molar ratio of 1:5:10. The results demonstrated the need for an adequate ratio of H2O to DES to form nanosized ACC, implying that the strength of hydrogen bonding in DES-H2O systems is the primary factor affecting the performance of the solvent. The DES-H2O systems with inter- and intramolecular hydrogen bonding inhibited the crystallization of CaCO3. The findings of this study are applicable to CO2 utilization processes designed for the production of nanosized ACC.