Absorption of Neptunium to Muscovite With Different Particle Sizes

Abstract

Neptunium is one of long-life radioelements, whose speciation in different condition of underground water and soil type, including the adsorption characteristics and adsorption mechanism on some soils, is a critical field. The adsorption behavior of Np(Ⅴ) on muscovite minerals was studied by combining theoretical calculations and static adsorption experiments, providing a reference for evaluating the safety of nuclear waste disposal sites in this work. The adsorption behavior of 239Np(Ⅴ) by different particle sizes of muscovite was studied using characterization methods such as X-ray diffraction(XRD), scanning electron microscopy(SEM), material specific surface area(BET), and NaI(Tl) gamma spectroscopy. Explored the effects of factors such as time, pH value, and the presence or absence of \begin{document}${\mathrm{CO}}_3^{2-} $\end{document} on the adsorption of Np(Ⅴ) by muscovite with different particle sizes. Combining density functional based on first principles, B3LYP was selected as the functional and 6-31G* as the basis group, and quantum chemical calculations were carried out to obtain the dissociation constant(pKa) values of the sites, in order to describe the electronic behavior of the skeleton structure. The experimental results show that different particle sizes of muscovite have an impact on the adsorption of Np(Ⅴ), and the presence or absence of \begin{document}${\mathrm{CO}}_3^{2-} $\end{document} in the environment also affect the adsorption distribution coefficient. However, as the particle size of muscovite decreases, more active sites are exposed, and the trend of adsorption distribution coefficient varies. Based on the SEM image and adsorption distribution coefficient curve, it can be seen that as the grinding mesh size of the sample increases, the end face increases, and even layered muscovite is peeled off. In the alkaline region, the adsorption distribution coefficient slightly increases, but the adsorption distribution coefficient is all less than 100. A small amount of Np(Ⅴ) is enriched in fine-grained to extremely fine-grained minerals, related to finer sediment. The adsorption of Np(Ⅴ) by muscovite is weak and not dominant. Np(Ⅴ) mainly migrates with groundwater in muscovite minerals.

Keywords

• muscovite
• np(ⅴ)
• absorption
• groundwater
• migrates