Abstract
This study reports the development of low-cost CO2 adsorbents derived from solid residues using simple washing and steam or chemical treatments as a sustainable approach to mitigate rising CO2 emissions. Fly ash (FA) and unburned carbon (UC) obtained from biomass combustion were converted into adsorbents with improved textural and CO2 adsorption properties. Among the prepared materials, AUC-C exhibited the highest CO2 adsorption capacity of 2.03 mmol/g at 1 bar and 25 °C and maintained stable performance over five adsorption–desorption cycles, indicating good reusability. Adsorption behavior for all samples was well described by the Langmuir model, with R2 values exceeding 0.96. Steam treatment enhanced the CO2 adsorption capacity of FA-based adsorbents from 0.11 to 0.24 mmol/g, corresponding to an improvement of approximately 118 %. Cost analysis showed that washed UC was the most cost-effective adsorbent, with a capture cost of 2.25 USD per mole of CO2, while steam-activated materials also exhibited low costs (2.41 USD per mole of CO2). Overall, all prepared adsorbents were substantially less expensive than commercial alternatives.