Investigation of the iodate sorption mechanism by CoAl LDH through experiments and ab initio molecular dynamics...

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.