Preparation of Nano-CaCO3 from Phosphogypsum by Gas–Liquid–Solid Reaction for CO2 Sorption

Nano-CaCO3 was prepared from phosphogypsum (PG) through reactive crystallization in the gas (CO2)–liquid (NH3·H2O)–solid (PG) three-phase system. The effects of temperature, CO2 flow rate, and reaction time on the CaCO3 particle size distribution (PSD) were investigated. The results show that PG-derived nano-CaCO3 with an average particle diameter of 86–104 nm can be obtained under a 251–138 mL/min CO2 flow rate at a corresponding temperature of 30–40 °C. Research indicates that the CaCO3 particle size is subjected to the mutual influences of temperature, CO2 flow rate, and reaction time. A relatively low CO2 flow rate with increasing temperature and a strictly controlled reaction time are advantageous to the formation of nanosized CaCO3 grains. Additionally, PG-derived nano-CaO maintains a CO2 sorption capacity of 0.27 g of CO2/g of CaO after 10 calcination–carbonation cycles, which is the same as for commercial nano-CaO.