Aqueous ammonia capture integrated with ex-situ mineralisation using recyclable salts for industrial CCS

Carbon dioxide capture and storage by mineralization (CCSM), also known as ex-situ mineralization, is an important technology for industrial CCS. The feedstocks for CCSM can not only be Mg/Ca-silicate minerals, but can also include waste materials from industries, such as steel slags and waste cement. Aqueous ammonia capture is preferred for industrial CCS, since industrial emissions present high CO₂ concentrations (around 25 vol.%) and more impurities (SO2/NOx) than that from power plants. Aqueous ammonia CO₂ capture integrated with ex-situ mineralisation avoids stripping CO₂ as pure gas from absorbents and compression of CO₂, and therefore reduces the high energy consumption of capture. In this study, optimization experiments were conducted on this process. The dissolution efficiency of Mg from serpentine using 2.8 M NH₄HSO₄ at 100 g/l solid to liquid ratio for 1 h was around 80 %. The decrease in dissolution efficiencies is because of the Si passive layer on the surface of serpentine particles. The molar ratio of Mg: NH⁴⁺ salts: NH₃ is the key factor controlling carbonation efficiency, and when using the molar ratio of Mg: NH⁴⁺ salts: NH₃ is 1:1.5:2, the carbonation efficiency was 96 %.