Radioactive iodine released from nuclear power plants has been recognized to pose significant risks and environmental hazards. In response to these challenges, extensive investigations into iodine sorbents have been conducted with a particular focus on the utilization of layered double hydroxides (LDH) as a promising candidate. Herein, we have focused on the investigation of LDH materials featuring diverse transition metals for their synthesis, with specific emphasis on CoAl LDH for its proficiency in removing iodine species, particularly IO3 –. Nevertheless, a comprehensive understanding of the removal mechanisms employed by these LDH materials remained elusive. Hence, the primary aim of this study is to elucidate the intricacies of the removal mechanisms through sorption tests, spectroscopic techniques, and theoretical chemistry analyses, subsequently contrasting the experimental outcomes with computational results. For the experimental facet, the synthesis of CoAl LDH was conducted utilizing 0.15 mol L−1 of Co(NO3)2⋅6H2O and 0.06 mol L−1 of Al(NO3)3⋅9H2O to attain a molar ratio (M2+:M3+) of 2.5:1. Subsequently, pH-dependent IO3 – sorption tests were carried out, coupled with X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy, facilitating the elucidation and discourse of the removal mechanism. The theoretical chemistry in this research harnessed ab initio molecular dynamics (AIMD) simulations for structural modeling, atomic density profiles, radial distribution function, analysis of oxide species, and MD-EXAFS spectrum analysis. In summary, this study aims to elucidate iodine removal mechanisms using diverse experimental results, culminating in the revelation that ion-exchange with NO3 – present in the interlayer predominates as the principal mechanism for IO3 – removal. Notably, a distinct spectral feature at approximately 33,190 eV emerged, defying identification through XANES and EXAFS analyses conducted under experimental conditions. In the AIMD simulations, meticulous scrutiny of individual iodine atoms uncovered the prevalence of I−O and I−O−H molecular species, marked by interactions between O and H atoms, with a coordination number of I−O = ~3. This transformation was primarily instigated by proton hopping. As a result, the comparative investigation reveals the dominance of IO3 – intercalation in the CoAl LDH material with the potential to undergo a transformation to the I−O−H molecule upon interaction with protons.

99Tc is a long-lived radioactive fission product whose mobility in the subsurface is largely governed by its oxidation state. Migration of Tc from a waste repository may be prevented by immobilizing Tc(IV) in durable glass forms. Thus, efficient incorporation and high retention of Tc by glasses is very important for radioactive waste management and environmental remediation. Tc(IV) oxidation to higly volatile Tc(VII) (TcO4 −) at glass vitrification temperatures results in poor Tc retention in the final waste glass. Retention of Tc in the glass is generally improved by reducing conditions since Tc(IV) is not volatile. However, experiments with Tc-magnetite under high temperature and oxic conditions showed re-oxidation of Tc(IV) to volatile pertechnetate. To understand this phenomenon, we employed ab initio molecular dynamics simulations to study structural and electronic properties of Tc-incorporation in magnetite. The study provides the ramification of high temperature on Tc mobilization and changes of Tc retention in magnetite. Theory predictions also indicated enhanced Tc retention in the presence of 1st row transition metal dopants in Tc-incorporated magnetite that was confirmed by experiments. Furthermore, the overwhelming concentration of Cr(VI) co-mingled with Tc(VII) within the secondary waste form where Cr(VI) is more readily reduced than Tc(VII) by reduction potential metrics. Experiments with Tc-magnetite under high temperature and oxic conditions showed re-oxidation of Tc(IV) to volatile pertechnetate. Experiments also showed that magnetite transforms to maghematite resulting in disproportionation and re-oxidation of Tc. This transformation can be suppressed through incorporation of trace elements such as Co, Ni, Zn into magnetite forming spinel. In this talk, I will present results from ab initio molecular dynamics simulations and experiments on the structural and electronic properties of Tc and/or Cr incorporation in magnetite. I will also discuss the temperature effect on Tc/Cr mobilization and changes of Tc/Cr retention in magnetite. In addition, I will discuss the effect of Tc/Cr concentration and 1st row transition metal dopants on their incorporation in magnetite.