The impacts of CO2 mineralization reaction on the physicochemical characteristics of fly ash: A study under different reaction conditions of the water-to-solid ratio and the pressure of CO2

Utilizing fly ash (FA) directly to mineralize CO2 and injecting carbon sequestration products into goafs of coal mines is a novel and promising technology. The impact mechanisms of CO2 direct mineralization reactions on the characteristics of key groups, physical phases, surface micromorphology, particle size and pore structure of FA are discussed systematically in detail. The focus is imposed on the impacts of different reaction conditions (water-to-solid ratios and pressures of CO2). Based on the FT-IR, XRD and ESEM-EDS analysis, CO2 is transformed into carbonates of five vibrational models after mineralization and largely sequestered as calcite by portlandite, which forms a passivated layer on the FA surface. The particle size of carbonated FA particles gets smaller and less uniform, and the variation laws of the particle size at full scale are analyzed by particle size intervals. The variation process of the pore can be divided into the dissolution of FA for pore expansion, the low degree of CO2 mineralization reaction for further expanding the pore and the high reaction degree for pore shrinkage. This paper provides theoretical bases for improving the direct CO2 sequestration capacity and research directions for the subsequent application properties of carbon sequestration products.