A High-Pressure Gas–Solid Carbonation Route to Produce Vaterite

Abstract

A novel synthetic strategy based on a high pressure gas–solid reaction using urea as an additive to produce value-added CaCO3 material is reported. Results showed that at about 150 °C and 12 MPa the reaction attained complete carbonation with predominant spherical vaterite crystals via a self-sustained reaction. The influences of working conditions including pressure, temperature, Ca­(OH)2/urea mass ratio, and reaction time on the mineralization process were studied. The as-prepared CaCO3 powder exhibited vaterite content as high as 94.2% and a surface area up to 32.9 m2/g. The mechanism study showed that the high-pressure CO2 acted as an inhibitor for urea decomposition at high temperature besides as a reactant; the urea entrapped Ca­(OH)2 via its melt to stabilize vaterite formation by an amine functional group and initiated the carbonation process via tiny water triggered by its slight decomposition. The separation to obtain the fine product was simple and allowed high urea recovery (for example, 93.6%). The method has merits for both the high CO2 utilization and production of value-added CaCO3 without discharging inorganic salts; thus, it would be an environmentally friendly and potential route for industrial application.

Vaterite Microdisc Mesocrystals Exposing the (001) Facet Formed via Transformation from Proto-Vaterite Amorphous Calcium Carbonate

“…17 Indeed, vaterite crystals were successfully synthesized by using additives containing charged groups such as amines, 18−26 carboxyl groups, 22,27−32 sulfonic groups, 33,34 amino acids, 31,35 peptides, 36 polyols, 37,38 and proteins. 26,39 Vaterite crystals have been synthesized in aqueous solutions, 18−25,28,30,31,36,40−44 alcohol−water mixed solvents, 17,22,34,45 DMF−water mixed solvents, 18,46 and non-aqueous solvents. 29,47,48 Wetting and hydration of ions in alcohol−water solvents are very different from those found in aqueous solutions, which may affect the formation of nucleation and crystal growth centers.…”

The Crystallization Process of Vaterite Microdisc Mesocrystals via Proto-Vaterite Amorphous Calcium Carbonate Characterized by Cryo-X-ray Absorption Spectroscopy

“…Vaterite crystals have been synthesized in aqueous solutions [13][14][15], alcohol-water mixed solvents [16,17], dimethyl formamide-water mixed 2 of 12 solvents [13,18], and non-aqueous solvents [19,20]. Vaterite crystals were successfully synthesized in the presence of additives such as proteins [21], peptides [22], amino acids [23], and polyalcohols [24].…”

Solvent-free preparation of uniform styrene/maleimide copolymer microspheres from solid poly(styrene-alt-maleic anhydride) microspheres

“…32,33 Compared to solution or liquid-solid reactions, the gassolid reaction is considered a very simple and convenient method because it avoids the use of solvents and the products are easily isolated. 34 Moore et al reported a solvent-free way of preparing SMI by the gas-solid reaction. They used gaseous ammonia to react with ground SMA (about 60 mesh), and then converted the formed maleamic acid copolymer to SMI by heating.…”