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Red gypsum can be considered as a long term storage of carbon dioxide through mineral carbonation. However, for the efficient carbonation, the calcium ions need to be extracted in the solution phase, followed by the carbonation reaction. Therefore, the extraction step is the key of successful mineral carbonation. In this study, solvent extraction of calcium and iron ions has been carried out using different types of acids and bases. In addition, the kinetic study of the extraction has also been performed. The study showed that the base solution was not capable of extracting significant amounts of calcium and iron, while acid solution was very efficient in extracting the ions. However, H 2 SO 4 resulted in higher calcium extraction efficiency as compared to HCl and HNO 3 . Increasing reaction temperature from 30 to 70 °C and also increasing reaction time from 5 to 120 min were found to be effective in enhancing the degree of extraction for all the three acids used. Kinetic analyses found that the dissolution rate of red gypsum is controlled by the combination of product layer diffusion and chemical reaction control. The calculated activation energy of calcium extraction was 44.02, 37.68, and 42.73 kJ/mol for H 2 SO 4 , HCl and HNO 3 , respectively. [ABSTRACT FROM AUTHOR]

This study focuses on direct mineral carbonation of waste gypsum, a by-product of titanium dioxide production industry and known as red gypsum. The red gypsum is a potential raw material for carbonation with carbon dioxide due to its high content of calcium. Before being used the red gypsum, it was characterized by MASTERSIZER 2000, XRD, and XRF analyses. The carbonation of red gypsum was carried out using a high pressure autoclave reactor. The reaction parameters such as CO2 pressure, reaction temperature and red gypsum particle size were optimized to achieve the maximum yield and purity of calcium carbonate. The purity of calcium carbonate produced and the carbonation efficiency at different temperatures have also been investigated. Both the purity of the product and the efficiency of the reaction were increased when elevated CO2 pressure and reduced particle size were used. They were increased initially with increasing temperature up to 200°C, but dropped with further increase of temperature. The mineral carbonation technology by using red gypsum can potentially contribute to both reduction of CO2 emission and remediation of environmental concern. [ABSTRACT FROM AUTHOR]