Fly ash-doped biochar fabricated by pyrolysis and hydrothermal strategies: characteristics and potentialities of carbon sequestration

Abstract The oxidation of biochar occurs due to both natural and human influences during the soil carbon sequestration process. Therefore, it is crucial to produce high-stability biochar to achieve carbon neutrality. Fly ash-doped biochar was obtained from fly ash and corn stalks by employing hydrothermal/pyrolysis treatment, along with alkali impregnation at different temperatures. The microstructural characteristics and carbon sequestration potentials were studied as an essential performance parameter that was influenced by mineral doping and treatment temperature. The yield and carbon retention of P500-1:2 improved by 54.15% and 6.81%, respectively, and the carbon loss following H 2 O 2 oxidation was only 9.93% as depicted by the results. In comparison with hydrothermal biochar, pyrolysis biochar is superior in terms of its carbon sequestration potential. SiO 2 , Al 2 O 3 and other components in fly ash continue to dissolve at high temperatures and react with carbon in biochar, promoting the formation of aromatic carbon and generating a physical protective layer to prevent biochar from oxidation, hence improving the chemical and thermal stability of biochar. High temperature and mineral interaction also contribute to high aromatic structure (H:C < 0.4) formation, significantly improving the specific surface area and thermal stability of biochar. Graphical Abstract