PNNL

Abstract

Radioiodine released during the nuclear-fuel cycle constitutes a persistent radiological hazard. In this study, the IO3– uptake mechanism of CoAl LDH was resolved by combining pH-controlled sorption experiments, synchrotron XAFS, and DFT-based AIMD simulations. At pH close to 6, approximately 90?% of IO3– was removed, and the equilibrium distribution coefficient reached about 1.7 ×?104 mL?g–1. EXAFS analysis indicated an average iodine–oxygen bond length of 1.81?Å and a coordination number near 3, with the fit R-factor equal to 0.002. The simulations faithfully reproduced the experimental spectrum and revealed transient proton hopping events that generated metastable I–O–H species inside the interlayer, thereby confirming nitrate-to-iodate exchange as the controlling capture pathway. Atomic density profiles and radial distribution functions further showed that IO3– adopt an end-on orientation perpendicular to the hydroxide sheets, while water molecules mediate proton migration without disturbing the host lattice. The integrated experimental–computational evidence demonstrates that CoAl LDH can rapidly and selectively sequester IO3– under near-neutral conditions, offering atomic scale guidance for the rational engineering of layered sorbents for advanced radioactive-waste treatment.