Perrhenate sodalite growth from alkali silicate melts by noble metal catalysis

Perrhenate sodalite (Na₈Al₆Si₆Re₂O₃₂) which contains the perrhenate anion (ReO₄⁻) has been synthesised in equilibrium with Na–Fe-rich aluminosilicate melt and Re metal at 1100 °C and 500 MPa. Quenched glasses contain a homogeneous distribution of nepheline and magnetite, whereas sodalite only forms a crust on noble metal surfaces (Pt, Pt–Rh, Ag–Pd, and Re) in contact with the glass. The sodalite have been characterised by wavelength-dispersive X-ray spectroscopy and Raman spectroscopy. The experimental products contain both Re(0) and Re(VII), but other oxidation states of Re were not detected, suggesting the role of Na as a higher oxidation state stabiliser. Sodalite has potential uses for immobilising volatile Re and Tc during nuclear waste vitrification. Our study demonstrates the thermodynamic stability of perrhenate sodalite at Na-rich aluminosilicate melts at high temperature and pressure conditions.