Impact of alkali activation on the structure and mineralization performance of fly ash

QIN Lei; LIN Siheng; LIN Haifei; LI Shugang; LI Jiawei; ZHANG Feilong; XIONG Meiling

doi:10.13247/j.cnki.jcumt.20240359

Abstract：The structural properties of alkali-activated fly ash critically influence its CO2 miner-alization capacity.Understanding the CO2 mineralization performance of alkali-activated fly ash is key to improving the efficiency of carbon sequestration in coal-based solid waste.Lignite fly ash from a coal-fired power plant in Shijiazhuang,China,was investigated.Structural charac-teristics of fly ash subjected to varying concentrations of alkali activation were analyzed using laser particle size analysis,scanning electron microscopy-energy dispersive spectroscopy(SEM-EDS),and infrared spectroscopy.The CO2 mineralization performance of alkali-activated fly ash was assessed using high-temperature and high-pressure stirred reactor experiments and thermogravimetric analysis.Experimental results reveal that alkali activation causes fragmen-tation and decomposition of fly ash particles,reducing the particle size distribution.At the mi-croscopic level,fly ash particles exhibit regular spherical morphologies,with alkali activation producing finer particles that expose more reactive calcium elements,enhancing carbon seques-tration.Alkali activation disrupts the alumina-silicate tetrahedral network structures in fly ash,with the surface of the fly ash particles covered by calcium silicate hydrate(C-S-H)gel,which has a high degree of Si—O polymerization.At an optimal alkali concentration of 15％,lignite fly ash achieves the highest carbon sequestration performance,with a CO2 absorption of 8.9 g/kg and a calcium conversion rate of 27.8％.These values represent a 71.2％increase in CO2 absorption and a 70.6％increase in calcium conversion compared to untreated fly ash.