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• Red gypsum is an industrial waste rich in calcium favored for CO 2 sequestration. • Mono-ethanolamine absorbed more CO 2 in the aqueous solution rich in calcium ions. • Proposed accelerated carbonation consumed lower energy while forming calcite. This study provides a novel approach to sequester carbon dioxide (CO 2) using industrial waste red gypsum (RG) in an accelerated mineral carbonation process. In this study, RG samples and products were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), field emission scanning electron microscopy (FESEM), and transmission electron microscope (TEM). The XRD analysis of RG revealed that two main constitutions of RG are gypsum (CaSO 4.2H 2 O) and hematite (Fe 2 O 3). From XRF analysis, RG samples consisted of calcium oxide (CaO), sulfur trioxide (SO 3), and ferric oxide (Fe 2 O 3) as major components and titanium dioxide (TiO 2), manganese oxide (MnO), and europium oxide (Eu 2 O 3) as minor components. The accelerated mineral carbonation of RG was first performed using different concentrations of sulfuric acid (H 2 SO 4) from 0.5 M to 2 M to extract the calcium ions from the RG. Then, the mineral carbonation process was performed within an Autoclave mini reactor by preparing an aqueous solution containing RG, CO 2 , and 5 wt% 0.1 M to 1.4 M mono-ethanolamine (MEA). The results showed that using 1.4 M MEA could absorb the highest amount of CO 2 to precipitate the calcite. The significant advantages of using MEA were related to the further absorption of CO 2 than 2 M H 2 SO 4 in the slurry and the lower consumption of energy to precipitate the calcite. The findings presented in this study shed new light on precipitating carbonate minerals like calcite from industrial wastes rich in calcium as well as ones rich in iron, barium, and magnesium. [ABSTRACT FROM AUTHOR]

Highlights • Red gypsum is an iron and calcium rich source favored for mineral carbonation. • The morphology of red gypsum samples was changed during the carbonation process. • Mineral carbonation of red gypsum shows a distinct separation of reaction progress. Abstract In this research, the characterization of red gypsum (RG) and its reaction progress during the indirect mineral carbonation process were studied. X-ray diffraction results showed that the calcium sulfate and hematite are the dominant components in the RG samples. Three main phases of calcium in the RG were recognized: Ca (OH) 2 , Ca-S-O, and Ca-Fe-O. Element analysis by ICP-OES also revealed that the RG consists of three major constitutions: CaO (32.2%), SO 3 (31.6%), and Fe 2 O 3 (28.99%). To understand the reaction progress of RG in the carbonation process, the reaction model code PHREEQC-2.18 was found to be a very useful tool since it allows the exposure of all dissolved species of RG and presents its mineral phases at each time step. Furthermore, the mineral carbonation of RG delivered the reaction progress changes with Ca phases and, therefore, dissolved calcium (hydr)oxide starts to control the pH and the CO 2 uptake. In short, the findings of this study could be useful in resolving problem of greenhouse gases with less environmental issues. [ABSTRACT FROM AUTHOR]

In this research, the feasibility of CO 2 mineral carbonation by the use of by-product red gypsum (RG obtained from Huntsman Tioxide, Terengganu, Malaysia) to form iron carbonate (FeCO 3 ) was evaluated. Toward this aim, the wide-range conditions of key procedure variables such as reaction temperature, reaction time, and CO 2 pressure on the rate of mineral carbonation were studied. In addition, preliminary analyses on red gypsum were carried out to determine its physical and chemical characteristics. The feasibility of direct carbonation of RG to form FeCO 3 was assessed at different CO 2 pressures of 1 to 70 bar and different reaction temperatures of 25 to 200 °C to discover the effects of the key functions on overall direct carbonation. In general, increasing CO 2 pressure to 10 bar was found to increase the overall FeCO 3 purity and carbonation efficiency to 97% and 98%, respectively. Moreover, the reaction temperature affected the conversion rate at two different functions. First, FeCO 3 purity and its carbonation efficiency increased to the maximum values when the reaction temperature increased to 150 °C, and then they were slightly decreased to 91% and 92%, respectively, with increase of temperature to 200 °C. The results also showed that the maximum product purity is achieved at optimum reaction time of 150 min. [ABSTRACT FROM AUTHOR]