Indirect carbonation of titanium gypsum using ammonium citrate: Insights into CO2 mineralization

Indirect mineralization is a promising technology for carbon capture, utilization, and storage that enables CO 2 sequestration while simultaneously producing high-purity CaCO 3 . There remains a research gap in the regulation of the CaCO 3 product in the CO 2 mineralization process. This work innovatively compared CO 2 mineralization in different systems. Ca leaching from titanium gypsum was conducted using ammonium citrate, and then CO 2 mineralization was performed in Ca-rich solution (CRS) and calcium citrate precipitate (CCP) systems. The effects of key parameters including ammonia dosage, CO 2 flow rate, and temperature were studied, and the mineralization conversion rate and mineralization products were investigated. Ammonia dosage significantly influenced the mineralization conversion rate and the crystal form of CaCO 3 , and the conversion rate was 95% at 50 mL/L ammonia for CCP and 85% at 100 mL/L ammonia for CRS. Notably, increasing ammonia dosage promoted the vaterite formation in the CCP system. Temperature exhibited a pronounced impact on the mineralization conversion rate. As the temperature increased, the time required to attain the maximum conversion rate decreased markedly from 20 min to 5 min for CRS and from 60 min to 10 min for CCP. Temperature also influenced particle size and morphology, with both systems producing larger particles at higher temperatures. As to the growth mechanism of CaCO 3 , the CRS exhibited a gas–liquid interface dominated by homogeneous nucleation, while the CCP system proceeded through a gas–liquid–solid mechanism governed by heterogeneous nucleation. The high-quality CaCO 3 product (93.53% purity and 96.40% whiteness for CRS; 95.32% purity and 97.80% whiteness for CCP) meeting the standards of commercial CaCO 3 indicated promising economic benefits.