Fly ash-enhanced biochar provides new opportunity for soil carbon sequestration
image: Fly ash-doped biochar fabricated by pyrolysis and hydrothermal strategies: characteristics and potentialities of carbon sequestration
Credit: Gang Li, Rongchuan Ye, Shumin Wu, Xianghui Liu, Meijing Huang, Jianda Guo, Yan Gao, Wei Chen & Yan Ma
Researchers in China have unveiled a promising method to boost the carbon capture potential of biochar by integrating fly ash into the production process. The new study, published in Carbon Research, explores how the combination of agricultural and industrial byproducts can help tackle climate change by efficiently stabilizing carbon in soils.
Biochar, a carbon-rich substance formed when plant biomass is converted at high temperatures in low-oxygen environments, is attracting global attention for its role in soil improvement and carbon storage. Its ability to lock carbon away from the atmosphere offers a low-cost, negative-emissions technology that could help countries achieve carbon neutrality goals.
However, not all biochars are equal. Their stability, carbon retention, and long-term effectiveness depend on how they are produced and what additives are used. The research team, led by Gang Li and colleagues, set out to determine how doping biochar with fly ash, a byproduct from coal-fired power plants, affects its structure and carbon sequestration potential. The group compared two main production approaches: pyrolysis and hydrothermal treatment, examining the effects of different temperatures and fly ash ratios.
The findings were striking. Adding fly ash during pyrolysis significantly improved the yield, thermal stability, and resistance to chemical oxidation of the resulting biochar. Special mineral components in fly ash, such as silica and alumina, react with the biomass to promote the formation of resilient aromatic carbon structures. These minerals also help form a protective coating that shields the biochar from oxidation, making it less likely to decompose and release stored carbon back into the atmosphere.
At higher production temperatures, the team observed that the biochar developed more aromatic carbon, a desirable trait because it enhances persistence in soil. While increasing the pyrolysis temperature gradually reduced the overall carbon retention, the addition of fly ash more than offset this effect. Compared to biochar without fly ash, the fly ash-doped samples showed higher carbon content and a greater protective effect.
The research also revealed that while fly ash improved both microstructure and carbon retention in pyrolysis biochar, hydrothermal biochar did not benefit to the same extent. The team used advanced techniques, including electron microscopy and spectroscopy, to confirm the structural and chemical changes brought about by fly ash.
“Our results demonstrate that fly ash-doped pyrolysis biochar exhibits excellent stability and carbon sequestration capacity,” the authors state. “This points toward a scalable pathway to produce cost-effective, high-performance biochar using widely available agricultural and industrial residues.”
The new process not only provides an environmentally friendly use for fly ash that would otherwise be discarded, but also maximizes the climate benefits of biochar application in agriculture. The research suggests that optimizing production conditions and mineral additives can significantly enhance the role of biochar in long-term carbon management strategies.
Looking ahead, the study’s authors recommend further research on the energy consumption and full carbon balance of the whole process, from feedstock preparation to soil application. As climate targets become more urgent, innovations like fly ash-modified biochar could play a vital role in negative-emissions technologies for a greener future.
===
Journal reference: Li, G., Ye, R., Wu, S. et al. Fly ash-doped biochar fabricated by pyrolysis and hydrothermal strategies: characteristics and potentialities of carbon sequestration. Carbon Res. 4, 23 (2025). https://link.springer.com/article/10.1007/s44246-024-00185-2
===
About Carbon Research
The journal Carbon Research is an international multidisciplinary platform for communicating advances in fundamental and applied research on natural and engineered carbonaceous materials that are associated with ecological and environmental functions, energy generation, and global change. It is a fully Open Access (OA) journal and the Article Publishing Charges (APC) are waived until Dec 31, 2025. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon functions around the world to deliver findings from this rapidly expanding field of science. The journal is currently indexed by Scopus and Ei Compendex, and as of June 2025, the dynamic CiteScore value is 15.4.