Substitutional Disorder of SeO32–/IO3– in the Crystalline Solid Matrix: Insights into the Fate of Radionuclides 79Se and 129I in the Environment

As the crucial soluble species of long-lived radionuclides 129I and 79Se, iodate and selenite anions commonly share similar geometry of the trigonal pyramid XO3 (X = I, Se) but in different valence states. Although large amounts of investigations have been performed aiming at understanding the environmental behavior of these two anions individually, studies on cases when they coexist are extremely scarce. Structurally well-characterized natural/synthetic crystalline solids simultaneously incorporating these two anions as potential solubility-limiting products at the nuclear waste geological depository remain elusive. We report here a crystalline solid Th(IO3)2(SeO3) representing the first example of aliovalent substitution between IO3– and SeO32– sharing the same structural site, as demonstrated by single crystal X-ray diffraction, laser-ablation inductively coupled plasma mass spectrometry analysis, and spectroscopic techniques including infrared, Raman, and X-ray absorption spectroscopies. Sequentially,...