Structural Origins of High MoO₃ Solubility in Peraluminous Borosilicate Glasses

Area of Science:

• Materials Science
• Nuclear Engineering
• Geochemistry

Background:

• Molybdenum (Mo) incorporation in nuclear waste glasses is limited by phase separation and crystallization of alkali molybdates.
• Conventional borosilicate glasses struggle with high Mo loading due to the formation of tetrahedral molybdate species.

Purpose of the Study:

• To investigate molybdenum trioxide (MoO3) solubility in peraluminous sodium aluminoborosilicate glasses.
• To understand the structural mechanisms behind enhanced Mo solubility.

Main Methods:

• Raman spectroscopy
• Multinuclear and dipolar-correlation magic angle spinning nuclear magnetic resonance (MAS NMR)
• Electron paramagnetic resonance (EPR)
• Scanning transmission electron microscopy (STEM)-energy dispersive spectroscopy (EDS)

Main Results:

• Achieved unprecedented 13.96 wt % MoO3 solubility in peraluminous glasses, a ~15x increase over peralkaline counterparts.
• Identified stabilization of octahedral MoO6 units under Na-deficient, low optical basicity conditions.
• Observed polymerization into molybdite-like Mo-O clusters, suppressing Na2MoO4 precipitation and promoting Na2Mo2O7 formation.

Conclusions:

• Peraluminous glass composition enables significantly higher Mo incorporation by altering Mo coordination and promoting specific cluster formation.
• Structural insights provide guidelines for designing advanced aluminoborosilicate waste forms for efficient Mo-rich waste immobilization.