Uranium is an essential fuel for nuclear-energy production, but its radioactivity and chemical toxicity make the safe management of uranium-contaminated effluents an environmental priority. Adsorption is widely investigated for uranium removal because it is efficient, relatively energy-saving, and operationally straightforward. Sodium alginate, a biodegradable polysaccharide obtained from brown seaweed, is particularly attractive because its hydroxyl and carboxyl groups can bind metal ions. However, conventional calcium-alginate gels often have weak mechanical strength, while copper-alginate materials can aggregate, making it difficult to combine structural stability, adsorption capacity, selectivity, and reusability in a single adsorbent.
A study (DOI: 10.48130/scm-0026-0005) published in Sustainable Carbon Materials on 13 March 2026 by Tao Chen's & Wenkun Zhu's team, Southwest University of Science and Technology, reports that calcium-copper-cross-linked SA-CC microspheres capture uranium(VI) through homogeneous monolayer chemisorption with a capacity of 394.85 milligrams per gram.
The researchers produced three types of approximately two-millimeter sodium-alginate microspheres using a drop-injection process. A sodium-alginate solution was introduced into calcium chloride, copper chloride, or a mixed calcium chloride–copper chloride solution to form SA-Ca, SA-Cu, and SA-CC, respectively. Scanning electron microscopy showed uniformly dispersed spherical particles, while Fourier-transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy confirmed an amorphous, porous structure rich in oxygen-containing functional groups. Calcium and copper were successfully incorporated into SA-CC. The team then compared VI uptake under different contact times, solution pH values, adsorbent doses, initial uranium concentrations, and competing-ion conditions. Adsorption rose rapidly during the first four hours and reached equilibrium within 15 hours. At pH 4.5, SA-CC removed 93.4% of VI; increasing the adsorbent dose raised removal to 99.2%. The material also maintained more than 90% removal at an initial uranium concentration of 100 milligrams per liter. Kinetic data fit the pseudo-second-order model, with a correlation coefficient of 0.98, while equilibrium data best matched the Langmuir model, with a coefficient of 0.99. Together, these results indicated predominantly chemical adsorption onto uniform surface sites in a single layer. SA-CC reached 394.85 milligrams per gram, exceeding the capacities of the sodium-alginate-based adsorbents compared in the study. Most tested ions caused little interference, particularly potassium, sodium, chloride, nitrate, and perchlorate. Calcium, carbonate, and phosphate produced stronger inhibition through competition or complex formation. Reuse experiments showed little decline during the first three adsorption-desorption cycles and 70% capacity retention after five cycles. Spectroscopic analysis indicated that uranium capture involved electrostatic attraction, coordination with hydroxyl and carboxyl groups, and ion exchange at calcium and copper sites.
Overall, the study demonstrates that combining calcium and copper cross-linking can address complementary weaknesses in conventional alginate gels. Calcium helps preserve abundant oxygen-containing binding sites, while copper improves the mechanical stability of the polymer network. This balance gave SA-CC greater uranium uptake than either single-metal formulation while supporting selective adsorption and repeated use. The researchers propose that the microspheres could provide a practical, lower-impact platform for uranium recovery and remediation of uranium-containing effluents. Future work should evaluate their long-term durability, regeneration costs, performance in real wastewater, and scalability for industrial treatment systems.
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References
DOI
10.48130/scm-0026-0005
Original Source URL
https://doi.org/10.48130/scm-0026-0005
Funding information
This work was supported by NSFC (No. U23A20105 and U2267224), Sichuan Natural Science Foundation Innovation Research Group Project (No. 2024NSFTD0012), Sichuan Provincial Natural Science Foundation Project (No. 2025ZNSFSC0949), Innovation Development Fund of China Seawater Uranium Extraction Technology Innovation Alliance (No. CNNC-HSTY-2024-016), and the Research Fund of SWUST for PhD (No. 23zx7110).
About Sustainable Carbon Materials
Sustainable Carbon Materials (e-ISSN 3070-3557) is a multidisciplinary platform for communicating advances in fundamental and applied research on carbon-based materials. It is dedicated to serving as an innovative, efficient and professional platform for researchers in the field of carbon materials around the world to deliver findings from this rapidly expanding field of science. It is a peer-reviewed, open-access journal that publishes review, original research, invited review, rapid report, perspective, commentary and correspondence papers.