Recent progress in radionuclides adsorption by bentonite-based materials as ideal adsorbents and buffer/backfill materials

The extensive use of nuclear energy and the rapid development of the nuclear industry have produced a large amount of harmful radionuclide-containing wastewater, and bentonite-based materials with high specific surface area and high adsorption affinity for radionuclides are ideal adsorbents in the treatment of radioactive wastewater. Furthermore, bentonite is also a suitable buffer/backfill material for a deep underground repository to dispose of stored nuclear waste, and adsorption processes between bentonite and radionuclides are of significant importance for the migration or retention of radionuclides from the repository. Therefore, the adsorption behaviour of bentonite-based materials for radionuclides has been extensively studied in recent years. This review presents the current status (about 25 years) of bentonite-based materials for adsorption radionuclides. The adsorption behaviours and mechanisms of radionuclides by bentonite-based materials investigated by various conventional and advanced techniques have been summarized. The main adsorption mechanisms of bentonite-based materials for radionuclides include ion exchange, electrostatic attraction, surface complexation, and hydrogen bonding. We introduce the adsorption of bentonite-based materials for common radionuclides such as U(VI), Cs(I), Sr(II), Eu(III), Am(III), Yb(III), La(III), Tc(VII), Th(IV), Pu(V)/(VI), Ra(II), and Co(II). Finally, we present the current challenges of using bentonite for treating radionuclide-containing effluents and as a buffer/backfill material for the geological repository. We believe that this review will provide a vital reference and guidance for future research and applications related to the radioactive wastewater treatment and the repository of nuclear waste disposal using bentonite-based materials.