Issue 23, 2022

Origin of the exceptional selectivity of NaA zeolite for the radioactive isotope 90Sr2+

Abstract

In this work, we reported an exceptionally high selectivity of a NaA zeolite (for which the framework type code of LTA was assigned by the Structure Commission of the International Zeolite Association) towards radioactive 90Sr2+ and explained the origin of this high selectivity by combining structural Rietveld refinements and density functional theory (DFT) calculations. Nuclear wastewater with a 90Sr2+ radioactive concentration of 400 Bq L−1 (7.75 × 10−2 ppt) and highly concentrated NaNO3 and NH4NO3 (0.03 M Na+ and 0.4 M NH4+, Na+/90Sr2+ = 3.48 × 1010, and NH4+/90Sr2+ = 4.64 × 1011) was treated with NaA zeolite. The resultant 90Sr2+ radioactive concentration was as low as 0.62 ± 0.12 Bq L−1, close to the upper limit of 90Sr-induced radioactive activity in drinking water, and the distribution coefficient, Kd, was as high as 421.56 ± 13.39 L g−1. The NaA zeolite showed fast adsorption kinetics (ca. 5 min), high capture capacity (294.12 mg g−1), a broad working pH range (4–12), and excellent radiation resistance. The crystallinity and performance of NaA zeolite were not affected by 1000 kGy 60Co γ irradiation. Structural Rietveld refinements revealed that all Sr2+ ions are located at the center of the single 6-membered rings (s6rs) of the NaA zeolite. DFT calculations showed the free energy difference of exchanging different cations with Na+ located in the 8-membered ring (s8r) of the NaA zeolite, and predicted the sequence of Sr2+(−8.17 eV) > Ca2+(−6.17 eV) > K+(−2.13 eV) > Mg2+(−1.94 eV) > NH4+(−0.65 eV) > Cs+(−0.11 eV). The strong tendency of Sr2+ replacing Na+ explains the exceptionally high selectivity of the NaA zeolite for 90Sr2+ in high concentrations of Na+ and NH4+. Along with the ion-exchange process, structural Rietveld refinements revealed that the Sr2+ ions at the s8rs center migrated to the s6rs center.

Graphical abstract: Origin of the exceptional selectivity of NaA zeolite for the radioactive isotope 90Sr2+

Supplementary files

Article information

Article type
Research Article
Submitted
12 sep. 2022
Accepted
01 okt. 2022
First published
03 okt. 2022

Inorg. Chem. Front., 2022,9, 6258-6270

Origin of the exceptional selectivity of NaA zeolite for the radioactive isotope 90Sr2+

W. Hao, N. Yan, M. Xie, X. Yan, X. Guo, P. Bai, P. Guo, T. Cheng and W. Yan, Inorg. Chem. Front., 2022, 9, 6258 DOI: 10.1039/D2QI01958B

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