Radioactive uranium waste needs to be safely contained. Adsorption is an easy and cost-effective way of removing ions such as UO₂²⁺ from aqueous solutions. Several materials, e.g. polymers and activated carbon, can be used for this purpose, however, removing the adsorbents from the solution can be time-consuming. Magnetic adsorbent materials such as Fe₃O₄ (magnetite) can solve this removal problem, but often have smaller adsorption capacities than other sorbents.

Lichao Tan, Harbin University of Science and Technology and Harbin Engineering University, China, and colleagues have developed high-capacity sulfur-doped hollow magnetite spheres for the removal of UO₂²⁺. The team synthesized Fe₃O₄ hollow spheres by preparing a solution of FeCl₃, sodium citrate, polyethylene glycol (PEG) 2000, and sodium acetate in ethylene glycol and heating the mixture to 200 °C for 8 hours. The resulting magnetite hollow spheres were dispersed in a solution of L-cystine and subjected to hydrothermal treatment to introduce the desired sulfur doping.

The adsorbent material was used in uranium adsorption from aqueous solutions and the team found significantly improved adsorption capacities compared with other magnetic materials (up to 450 mg uranium/g). The researchers attribute this improvement to changed adsorption characteristics caused by the sulfur doping and to the large surface area of the hollow spheres. The results indicate that the material could be a promising candidate for the adsorption of uranium(VI).

• Facile preparation of S-doped magnetite hollow spheres for highly efficient sorption of uranium(vi),
  X. M. Song, L. C. Tan, H. Y. Ma, Y. Guo, L. Zhu, X. Q. Yi, J. Y. Gao, R. J. Yang, Q. Dong,
  Dalton Trans. 2017.
  DOI: 10.1039/c7dt00209b