Synthesis of hierarchical porous silica aerogel for CO2 adsorption using decarbonized coal gasification fine slag

The preparation of hierarchical porous silica aerogels from coal gasification fine slag (CGFS) offers an effective approach to achieving high-value utilization of solid waste and reducing the production cost of solid adsorbent matrix materials. However, the main challenges involve overcoming technical barriers to efficiently and value-added conversion of CGFS into silica aerogels with CO₂ adsorption properties, as well as elucidating the phase transformation mechanisms during the synthesis process. In this study, CGFS was used as the raw material to obtain a silicon-containing precursor through pre-decarbonization (with ash content as high as 99.82 %) and alkali dissolution treatment. A hierarchical porous silica aerogel was then synthesized using an efficient hydrothermal process. The effect of alkali dissolution on silicon extraction and the phase transformation mechanisms were thoroughly discussed, and the leaching mechanism was analyzed through thermodynamic and kinetic models. The results showed that the high leaching rate of silicon was attributed to the presence of a large amount of amorphous SiO₂ in the decarbonized fine slag (DCFS), while the formation of zeolite Na-P1 and hydroxysodalite during the alkali dissolution process affected the efficiency of silicon extraction. Then, the structural formation mechanism and CO₂ adsorption properties of the hierarchical porous silica aerogels were analyzed using N₂ adsorption-desorption and CO₂-TPD. The SiO₂-1-30-0.5 exhibited a high CO₂ adsorption ability of 1.53 mmol g⁻¹, and the CO₂ adsorption capacity maintained 94.78 % of the original value and after 5 adsorption-desorption cycles.