Enhancing CO2 adsorption capacity through Fe2O3/CaO ratio engineering in simulated fly ash-derived zeolite synthesis through gradient oxide modulation.

Zeolite synthesis from fly ash offers recycling and environmental benefits for carbon dioxide capture, but varying fly ash composition from different sources has different compositions, leading to inconsistent adsorption results. To achieve high CO2 adsorption performance and stability in zeolite synthesis from fly ash systems, this study established an element-controlled simulated fly ash system with Ca/Fe gradient differences. Hydrothermal synthesis yielded zeolites with optimized oxide ratios for CO2 adsorption. Solid wastes such as red mud were then added to adjust the composition of natural fly ash, resulting in improved adsorption performance and synthesis process stability. Analysis of the simulated fly ash system showed that when CaO content was 4-6 % and Fe2O3 content was 12-16 %, the synthesized zeolite achieved the best CO2 adsorption effect, reaching 34.58 cm3/g and outperforming standard industrial zeolites. Adjusting the oxide ratio of natural fly ash to the optimal performance range with red mud increased the adsorption capacity of natural fly ash-based zeolites by more than three times at 50 °C, while maintaining stable adsorption performance over 20 industrial cyclic adsorption tests. Economic analysis confirmed greater benefits from this waste-enhanced approach, offering promising strategy for industrial CO2 capture.