In the quest for safer nuclear waste management, a team of researchers led by A. Varon from the CEA, DES, ISEC, DMRC at Univ. Montpellier has made a significant stride. Their work, published in the journal ‘Cleaner Materials’ (which translates to ‘Cleaner Materials’ in English), focuses on developing high-performance adsorbents for selectively removing strontium ions (Sr2+) from nuclear wastewater. This breakthrough could revolutionize the energy sector by enabling safer long-term storage and disposal of nuclear waste.
Geopolymers, a class of inorganic polymers, have emerged as promising candidates for this task. Their unique structure, characterized by a negative charge on aluminum atoms, acts as a sorption exchange site, promoting ion exchange. “The key to our approach lies in understanding and manipulating the geopolymer’s structure to enhance its sorption properties,” explains Varon.
The researchers found that the Si/Al and H2O/M2O molar ratios during synthesis significantly influence the geopolymer’s structural properties and, consequently, its sorption behavior. By employing techniques like nitrogen adsorption-desorption and Nuclear Magnetic Resonance (NMR) spectroscopy, they probed the material’s structure and aluminum concentration, establishing a clear relationship between the geopolymer’s formulation, microstructure, and sorption properties.
Increasing the Si/Al ratio, for instance, enhances porosity but reduces the concentration of aluminum sites available for sorption. This trade-off highlights the delicate balance between porosity and sorption capacity. “We observed that a Si/Al ratio of 1.52 offered the best selectivity for strontium over calcium,” Varon notes. “This is due to the favorable distance between aluminum sites in the geopolymer’s structure.”
Similarly, the H2O/K2O ratio also plays a crucial role. Increasing this ratio improves sorption properties up to a certain point (H2O/K2O = 12), beyond which the microstructure no longer influences sorption. The researchers developed a 2D surface state model based on the Q4(mAl) silicon centers from the 29Si NMR to correlate the silicon environment with the geopolymer’s sorption properties.
This research not only advances our understanding of geopolymers but also paves the way for developing more efficient and selective adsorbents for nuclear wastewater treatment. As the energy sector grapples with the challenges of nuclear waste management, such innovations could prove invaluable. The insights gained from this study could shape future developments in the field, driving the energy sector towards safer and more sustainable practices.
In the words of Varon, “Our work underscores the importance of tailoring the geopolymer’s structure to achieve desired sorption properties. This could open up new avenues for developing advanced materials for nuclear waste management and other environmental applications.” With this research, the path to cleaner and safer energy solutions seems a little clearer.