Structural characterization of high-silica zeolites exchanged with REEs elements

In recent years REEs contamination has increased in environmental matrixes, creating problems to humans and ecosystems due to their bioavailability. Despite the vast literature about the research efforts on REE recycling (Meyer & Bras, 2011), less than 1% of the REEs are being recycled. Today there are many conventional methods for the extraction, recovery and separation of Rees, but these methods need a high consumption of reagents and energy also generating waste and secondary pollutants (Tan et al., 2014). Adsorption process is a good ecofriendly and cost effective alternative to the conventional methods due to the possibility of regeneration and reuse of sorption material, for the wide range of applicability and for economic advantages. The properties of sorbent materials like zeolites to capture and concentrate significant quantities of species make them ideal candidates for the development of remediation processes, separation, environmental monitoring and resource recovery processes (Bryce et al., 2012). In this work Na-Y zeolites ion exchanged with rare earth cations from liquid solutions (Nd and Y) were studied by X-ray diffraction in order to locate the rare earth cations in the zeolite framework and the resulting changes in its structural properties. The REEs adsorption capability of zeolites was evaluated by Inductively Coupled Plasma Optical Atomic Emission (ICP-OES). Different adsorption mechanism involves physical and chemical forces such as sorption/desorption, oxidation reduction reaction, surface precipitation or incorporation of the sorbed lanthanides into the solid matrix (Tan et al., 2014). Rietveld refinements revealed that after REEs ion exchange, a systematic decrease in the values of the unit cell parameters a0 is related to the rare earth ionic radius and its coordination to the oxygen framework. Finally, 27Al magic angle spinning NMR measurements indicate a dealumination process strongly depending on the REEs cations adsorbed. Bryce, E., Johnson, P. H., Santschi, C. Y. C., and Shigeyoshi, O.(2012): Collection of Lanthanides and Actinides from Natural Waters with Conventional and Nanoporous Sorbents. Environ. Sci. Technol., 46,11251–11258. Meyer, L., Bras, B. (2011): Rare earth metal recycling. Proceedings of the 2011 IEEE International Symposium on Sustainable Systems and Technology, Chicago, 1-6. Tan, X., Ren, X., Chen, C., Wang, X. (2014): Analytical approaches to the speciation of lanthanides at solid-water interfaces. Trends in Analytical Chemistry, 61, 107–132.