講演情報
[3517]Utilizing Coal Fly Ash for Carbon Storage : Freshwater versus Seawater Carbonation
○テオドラノエリ タンバリア1、菅井 裕一1、江﨑 丈裕1 (1. 九州大学)
司会： 藤井 孝志(産総研)
キーワード：
Coal fly ash、CO2 mineral carbonation、Seawater、Carbon sequestration、Calcium carbonate
Coal fly ash (CFA) is one of the major solid wastes generated by coal-fired power plants and has attracted considerable attention as a feedstock for CO2 mineral carbonation. Although seawater has recently been reported to improve carbonation efficiency compared with freshwater, the influence of fly ash composition on carbonation behavior in different aqueous media remains insufficiently understood. This study investigates the effects of freshwater and seawater on the mineral carbonation of four Indonesian coal fly ash samples with different chemical compositions under ambient conditions. The fly ash samples were classified into high-calcium fly ash (HC-FA) and siliceous fly ash (S-FA) according to ASTM C618. Carbonation experiments were conducted by dispersing 20 g of fly ash in 600 mL of freshwater or artificial seawater at 25°C, followed by CO2 injection at a constant flow rate of 40 mL/min. Changes in inorganic carbon (IC), pH, and dissolved calcium concentration were analyzed in the liquid phase, while X-ray fluorescence (XRF), X-ray diffraction (XRD), and thermogravimetric analysis (TGA) were employed to characterize the solid products and quantify carbonate formation. The results showed that HC-FA exhibited significantly higher carbonation reactivity than S-FA owing to its greater abundance of reactive Ca- and Mg-bearing minerals. Seawater generally produced higher IC concentrations and greater overall CO2 sequestration than freshwater because of its higher buffering capacity and abundant dissolved carbonate species. XRD and TGA analyses confirmed the formation of carbonate minerals after carbonation. Freshwater preferentially promoted calcium carbonate (calcite) formation, whereas seawater enhanced the precipitation of magnesium carbonate phases, including magnesite and hydromagnesite. Although seawater increased dissolved calcium availability, the high Mg2+ concentration inhibited CaCO3 nucleation and crystal growth, reducing calcium carbonate precipitation while favoring magnesium carbonate formation. These findings demonstrate that both fly ash composition and solvent chemistry strongly influence carbonation pathways and CO2 sequestration performance. High-calcium fly ash is the most suitable feedstock for direct mineral carbonation, and seawater provides an effective reaction medium for enhancing overall CO2 uptake despite altering the dominant carbonate products. The results provide useful insights for developing efficient and sustainable CO2 mineralization technologies utilizing coal fly ash.