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

Area of Science:

• Materials Science
• Nuclear Chemistry
• Computational Chemistry

Background:

• Radioactive nuclear waste liquid poses significant contamination risks.
• Effective immobilization of radioactive ions is crucial for nuclear waste management.
• Understanding solidification matrices is key to successful radioactive ion immobilization.

Purpose of the Study:

• To investigate the solidification mechanism of Cesium ions (Cs+) in K-struvite crystals.
• To explore the immobilization behavior of Cs+ within an aqueous solution using computational and experimental methods.
• To provide a foundational understanding for designing effective K-struvite cement for nuclide solidification.

Main Methods:

• Utilized ab initio calculations to study the solidification mechanism of Cs+ in K-struvite.
• Conducted experimental analyses using X-ray Fluorescence (XRF), X-ray Photoelectron Spectroscopy (XPS), Atomic Absorption Spectroscopy (AAS), Fourier-transform infrared spectroscopy (FI-IR), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD).
• Developed a calculation method for ΔEaq to analyze ion immobilization tendencies.

Main Results:

• Ab initio calculations and experimental data confirm a remarkable tendency for Cs+ to occupy the K site in K-struvite crystals.
• The immobilization behavior is intrinsically linked to the electronic structures of K-struvite and Cs-struvite.
• The interaction between cations and the aqueous solution significantly influences the energy changes during the solidification process.

Conclusions:

• This research provides fundamental insights into the solidification of nuclides within magnesium phosphate potassium cement.
• The proposed method facilitates the assessment of other nuclide ions' solidification potential in K-struvite.
• The approach is adaptable for studying the chemical immobilization of various ions in different crystalline matrices.