Precipitation of calcium carbonate during direct aqueous carbonation of flue gas desulfurization gypsum

CO2 sequestration by indirect carbonation of artificial gypsum generated in the manufacture of titanium dioxide pigments

“…When the carbonation was complete, the pH approached a constant value of approximately 7.0, being the most apparent indication of the completion of the carbonation reaction (Eq. (2.4)) [25,26].…”

“…Using the same methodology as previously published work, the experimental procedure begins by dissolving the sample (50 g), earlier dried at 50°C, in either alkaline solution (NaOH) [24] or NH 4 OH [25], where the following simplified reactions occur: In the first experiment, approximately 20 g of NaOH was added to 1 L of water (Eq. (1.1)) and, in the second experiment, the same amount of sample was added to 1 L of ammonia solution 3.8% (v/v) (Eq.…”

“…(1.2)). By considering that the content of calcium sulphate (CaSO 4 Á2H 2 O) in RG is around 70-80% [18,22], an amount of ammonia that was equal to a slight excess (120%) of the stoichiometric ratio was used, because previous studies [25,26] suggest that excess ammonia (110-120%) would be desirable for the stability of the reaction and for obtaining CaCO 3 with higher purity. Both mixtures were kept at room temperature for 3 h under constant stirring.…”

Polymorphs of pure calcium carbonate prepared by the mineral carbonation of flue gas desulfurization gypsum

“…FGD gypsum was supplied by Yeongheung Thermal Power Plants, Incheon, Korea and was the same material as was used in our previous work [6,7]. It was used without performing a pulverizing or grinding process, because the particle size fraction of the sample was in the 1-100 lm range, which corresponds to the fraction generally employed in mineral carbonation [12].…”

“…Mineral carbonation of FGD gypsum is one of the methods that have been investigated for CO 2 sequestration [5]. Previously [6], we demonstrated the feasibility of producing high-purity CaCO 3 through the direct carbonation of FGD gypsum under ambient conditions, which can be described by the following reaction:…”