A biochar-based material offers a promising route for uranium recovery from seawater

Researchers have developed a new biochar-based composite that can capture uranium from water while also converting part of it into a less toxic chemical form, offering a potential strategy for recovering uranium from seawater and supporting future nuclear energy resources.

Uranium is a key fuel for nuclear power, but land-based uranium reserves are unevenly distributed and limited. Seawater contains an enormous amount of dissolved uranium, estimated to be roughly 1,000 times greater than the reserves found in terrestrial ores. However, extracting uranium from seawater remains difficult because uranium occurs at very low concentrations and must be selectively separated from many competing ions.

In a new study published in Biochar, researchers report the design of a novel material called BN-PDA@Fe3S4. The material combines biochar nanospheres, a polydopamine coating, and iron sulfide Fe3S4. Together, these components create a hybrid adsorbent that can bind uranium efficiently and promote its chemical reduction.

“Seawater uranium extraction is a long-standing challenge because the material must be efficient, selective, stable, and practical for recovery,” said corresponding author Si Luo. “Our study shows that a biochar nanosphere platform decorated with Fe3S4 can not only adsorb U(VI), but also help convert part of it into less toxic U(IV), which is important for both resource recovery and environmental safety.”

The team synthesized the composite through a two-step method. First, biochar nanospheres were functionalized with polydopamine, a mussel-inspired material rich in active groups that can interact with metal ions. Then, Fe3S4 was grown on the surface to introduce iron and sulfur sites with strong affinity for uranium.

Laboratory tests showed that the composite achieved a maximum U(VI) adsorption capacity of 203.4 mg g⁻¹ at pH 5 and 298 K. The adsorption process followed the Langmuir isotherm model and pseudo-second-order kinetic model, indicating a monolayer chemisorption process. Thermodynamic analysis further showed that the adsorption was spontaneous and endothermic.

The material also performed well in more complex conditions. Tests with coexisting ions suggested that BN-PDA@Fe3S4 maintained strong uranium removal ability in the presence of several common ions, although carbonate and sulfate reduced performance by forming stable uranium complexes in solution. In natural seawater experiments, the composite reached a uranium extraction capacity of 4.5 mg g⁻¹ after 15 days.

A key finding of the study is the dual adsorption and reduction mechanism. Spectroscopic analyses showed that uranium was successfully immobilized on the composite surface. X-ray photoelectron spectroscopy revealed that part of the captured U(VI) was converted to U(IV). The researchers attributed this reduction to Fe(II) and S(-II) species in Fe3S4, while amino groups from the polydopamine layer also contributed to uranium binding. Density functional theory calculations supported the strong interaction between uranium species and the Fe3S4 surface.

The composite also showed magnetic separability, which could simplify recovery after use, and antibacterial activity against S. aureus and E. coli, suggesting potential resistance to biofouling in marine environments.

Although further optimization is needed to improve long-term cycling stability, the study presents a promising biochar-based platform for uranium recovery from seawater. By combining adsorption, reduction, magnetic recovery, and biofouling resistance, BN-PDA@Fe3S4 may provide a useful direction for future materials designed for sustainable nuclear fuel recovery and radionuclide pollution control.

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Journal Reference: Zhang, S., Liu, SS., Liu, D. et al. Synergistic adsorptive reduction for enhanced U(VI) recovery from seawater via Fe₃S₄-decorated biochar nanosphere hybrids. Biochar 8, 99 (2026).   

https://doi.org/10.1007/s42773-026-00605-z

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About Biochar

Biochar (e-ISSN: 2524-7867) is the first journal dedicated exclusively to biochar research, spanning agronomy, environmental science, and materials science. It publishes original studies on biochar production, processing, and applications—such as bioenergy, environmental remediation, soil enhancement, climate mitigation, water treatment, and sustainability analysis. The journal serves as an innovative and professional platform for global researchers to share advances in this rapidly expanding field. 

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