Extraction of calcium from red gypsum for calcium carbonate production

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, H2SO4 resulted in higher calcium extraction efficiency as compared to HCl and HNO3. 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 H2SO4, HCl and HNO3, respectively.