CO2 sequestration by direct mineral carbonation of municipal solid waste incinerator fly ash in ammonium salt solution: Performance evaluation and reaction kinetics

In this study, we investigated CO2 mineral sequestration by municipal solid waste incineration fly ash (MSWI-FA) in both pure water and ammonium salt solutions [NH4Cl, (NH4)2SO4 and CH3COONH4]. The introduction of NH4+ significantly promoted the solid–liquid mass transfer of the active calcium on the MSWI-FA particles and the generation of free ammonia in the solution, which enhanced the carbonation kinetics and crystallization of the calcium carbonate product. Changes to the mineralogy, morphology, and surface properties of the MSWI-FA particles before and after carbonation confirmed the reaction mechanism. A novel kinetic model based on the two-film theory was developed to evaluate the mass transfer and chemical reaction of heterogeneous carbonation in both pure water and ammonium salt solutions. To optimize the carbonation rate and efficiency, the complex effects of various operating parameters on the CO2 sequestration characteristics were systematically investigated. Maximum carbonation kinetics was achieved at 60 °C, an ammonium salt concentration of 1.0 mol/L, and a gas flow rate of 1.0 L/min, resulting in a carbonation efficiency and CO2 sequestration capacity of 78.49 % and 0.236 g CO2/g MSWI-FA, respectively. A comparison of the present results with those of other studies suggests that direct aqueous carbonation in ammonium salt solutions is feasible owing to its higher carbonation kinetics and CO2 sequestration capacity.