Study on the mechanism of direct wet mineralization of fly ash for CO2 storage and optimization of key influencing factors

WANG Shengtao; TANG Jiaxu; YANG Ning; WANG Qingxiang; WANG Shilin; CAO Xuqiang; ZHANG Xinquan; SONG Xiaolin; MA Chicheng

doi:10.13347/j.cnki.mkaq.20241797

Abstract：In order to enhance the CO2 sequestration efficiency of fly ash and promote its resource utilization in CO2 mineralization sequestration and fire prevention and extinguishing projects,an optimization study was conducted on the reaction conditions and ad-ditive ratios of the fly ash mineralization process.A direct wet mineralization technique was employed to establish a gas-liquid-solid three-phase reaction system.The effects of water-to-ash ratio,reaction time,and gas flow rate on mineralization efficiency were sys-tematically examined through an orthogonal experimental design.Range analysis and variance analysis were used to determine the primary and secondary influencing factors as well as the optimal parameter combination,thereby evaluating the impact of different conditions on mineralization performance.Additives including Na2CO3,NaCl,NaOH,and NaHCO3(at a concentration of 0.5 mol/L)were introduced,and a single-factor experiment was conducted to screen for the optimal formulation.The mineralization products were characterized by X-ray diffraction(XRD)and scanning electron microscopy(SEM),while thermo gravimetric analysis(TGA)was used to quantitatively assess the CO2 sequestration capacity.Fire suppression performance was evaluated through simulated coal pile spontaneous combustion experiments by monitoring temperature and CO volume fraction variations to verify the practical fire extinguishing effect.The results indicate that:in terms of mineralization condition optimization,a water-to-ash ratio of 4∶1,reac-tion time of 45 minutes,and gas flow rate of 150 mL/min yielded a CO2 sequestration capacity of 57.75 kg/t,significantly surpassing other parameter combinations;among the additive selection experiments,0.5 mol/L Na2CO3 exhibited the best performance by in-creasing theCO32-concentration in the liquid phase and maintaining an alkaline environment to promote CaCO3 formation.Con-versely,NaCl reduced mineralization efficiency by enhancing CaCO3 solubility,while NaOH,due to its strong alkalinity,decreased calcite grain size,thereby inhibiting precipitation;XRD and SEM characterization confirmed the disappearance of portlandite(Ca(OH)2)and quicklime(CaO)diffraction peaks in mineralized fly ash,with a significant enhancement of calcite(CaCO3)peaks.The microstructural analysis revealed the transformation of the originally porous surface into a dense layer of spherical CaCO3 particles,verifying the feasibility of the CO2 mineralization pathway;in fire extinguishing experiments,the fly ash-based material ef-fectively reduced coal pile temperatures below 120℃within 600 seconds through oxygen barrier coverage,heat absorption via moisture evaporation,and penetration cooling mechanisms.The CO volume fraction stabilized below 30×10-6 after 180 seconds.