Lanthanide (Ce, Nd, Eu) environments and leaching behavior in borosilicate glasses.

Area of Science:

• Materials Science
• Nuclear Chemistry
• Geochemistry

Background:

• Borosilicate glasses are crucial for immobilizing high-level radioactive waste for geological disposal.
• Understanding actinide behavior in glass matrices is vital for waste management.
• Lanthanides serve as chemical surrogates for actinides in these studies.

Purpose of the Study:

• To investigate the local structures of cerium (Ce³⁺), neodymium (Nd³⁺), and europium (Eu³⁺) ions in borosilicate glass.
• To determine how lanthanide ions are accommodated within the glass matrix.
• To assess the stability and release behavior of lanthanides in borosilicate glass.

Main Methods:

• Synchrotron radiation-based techniques, including X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS).
• Reverse Monte Carlo (RMC) simulations to analyze atomic parameters and local structures.
• Microscopy and microanalysis for compositional and structural characterization.

Main Results:

• Lanthanide ions (Ce³⁺, Nd³⁺, Eu³⁺) are integrated into the borosilicate glass network, occupying both Si and B sites.
• Atomic parameters derived from XRD and RMC simulations correlate with XAFS data, confirming structural stability.
• Microscopy confirmed the amorphous nature of high-lanthanide-concentration samples.
• Higher release rates were observed for matrix components (Si, B, Na, Ba, Zr) compared to lanthanides (Ce, Nd, Eu).

Conclusions:

• Lanthanide ions are effectively stabilized within the borosilicate glass matrix, indicating their suitability as actinide surrogates.
• The observed lower release tendency of lanthanides over time suggests enhanced long-term stability for radioactive waste immobilization.
• The findings support the use of borosilicate glasses for the safe disposal of high-level radioactive waste containing actinides.