The journal Biochar published a comprehensive review by lead author Xinni Xiong and a team of researchers exploring the role of biochar-based materials in remediating uranium contamination. Uranium is a heavy metal that poses severe risks to human health and ecosystems due to both its chemical toxicity and radiological hazards. While traditional methods like soil washing or reverse osmosis exist, they are often expensive and can cause secondary pollution. Biochar offers a sustainable alternative that aligns with global waste recycling and carbon sequestration goals.

The effectiveness of biochar in trapping uranium depends heavily on how it is made and modified. Raw biochar often has limited surface sites to interact with contaminants. To overcome this, researchers use various “tuning” methods, such as ball-milling to create nano-sized particles with massive surface areas or chemical doping with iron and phosphorus to create specific “docking” sites for uranium ions. For example, biochar treated with sodium hydroxide has reached adsorption capacities nearly eighteen times higher than those treated with acid. Some innovative techniques even involve biological modification, where microorganisms are grown on biochar to create “green trapping agents” that precipitate uranium directly onto the surface.

Understanding the science of how biochar “captures” uranium is critical for designing better materials. The process typically involves several stages, starting with a rapid phase where uranium ions move quickly to the biochar’s outer surface, followed by a slower phase where they diffuse into deep internal pores. Chemically, uranium binds to active groups on the biochar surface—such as hydroxyl and carboxyl groups—through a process called complexation. In some cases, biochar can donate electrons to chemically reduce highly mobile uranium (VI) into stable, insoluble uranium (IV), effectively “locking” it in place so it cannot leach back into the environment.

The environment surrounding the contamination significantly influences how well biochar works. Solution pH is the most critical factor; at low pH, hydrogen ions compete with uranium for space on the biochar, while at very high pH, the biochar surface and uranium both become negatively charged, causing them to repel each other. Most studies find that a slightly acidic environment provides the perfect balance for maximum capture. Additionally, the presence of other substances in the soil, such as natural organic matter or phosphates, can either help by forming stable complexes or hinder by competing for the same active sites on the biochar.

One of the most promising aspects of biochar is its potential for resource recovery and long-term sustainability. Because many biochar materials are durable and can be separated easily—especially those modified to be magnetic—they can be reused over multiple cycles with minimal loss in performance. Furthermore, captured uranium can be removed from the biochar and potentially processed back into nuclear fuel. While most research is currently limited to laboratory simulations, the field is moving toward large-scale applications and using advanced tools like machine learning and artificial intelligence to predict the best biochar designs for specific contaminated sites.

Source: Xiong, X., Liu, J., Xiao, T., Lin, K., Huang, Y., Deng, P., Hu, H., & Wang, J. (2025). Remediation of uranium-contaminated water and soil by biochar-based materials: a review. Biochar, 7, 41.