Cesium immobilization by K-struvite crystal in aqueous solution: Ab initio calculations and experiments

Abstract

The use of immobilization methods to treat radioactive nuclear waste liquid is one of the most effective ways for preventing radioactive contamination. Understanding the solidification matrix for the immobilization behavior of radioactive ions is ​​an important issue. In this work, ab initio calculation was used to study the solidification mechanism of Cs⁺ in K-struvite crystal in the aqueous solution. Corresponding experiments were carried out and analyzed by XRF¹, XPS², AAS³, FI-IR⁴, SEM⁵, EDS⁶ and XRD⁷ . This work proposed a calculation method for the ΔE_aq⁸ . By analyzing ΔE_aq, the tendency of Cs⁺ to occupy the K site in K-struvite crystal is remarkable. Furthermore, in-depth first-principles calculations show that this immobilization behavior is related to the electronic structures of K-struvite and Cs-struvite⁹, and they together with the interaction of cation and aqueous solution determine the energy change of the process. This work provides a basic perspective for the study of magnesium phosphate potassium cement solidified nuclides, which is convenient for judging the solidification of other nuclide ions, thereby designing K-struvite cement for solidified nuclide. This method is also readily extended to other studies of the chemical immobilization of any crystal in the solution to any other ions.

Keywords: Aqueous Solution Substitution Forming Energy; Crystal structure; Electronic structure; Local density of states.