Effect of Al and Fe sources on conversion of high-level nuclear waste feed to glass

Highlights: • Glass batch (melter feed) components affect melting rate through enthalpy and foaming. • Alumina sources affect silica dissolution, glass melt formation, and foam generation. • Gibbsite particle size controls glass production rate through affecting melt foaming. • Chemically bound water in Al and Fe sources affects the glass production rate. Pilot-scale melter testing has shown that Al and Fe sources in high-level nuclear waste feeds influence the glass production rate. To examine melting behaviors of these feeds, we employed X-ray diffraction, differential scanning calorimetry, thermo-gravimetric analysis, particle size analysis, and the feed expansion experiments. Both the chemical form and the particle size of the Al and Fe sources affect the rate of melting through their effects on the conversion enthalpy and the primary foam formation that control the energy demand for melting and the heat accepted by the cold cap. The particle size of gibbsite controls the rate of alumina incorporation in the initial glass-forming melt that in turn, through its effect on viscosity, affects the rate of dissolution of silica particles, thus governing the glass melt fraction, open pore closure, and primary foam formation. Since the temperature of primary foam collapse limits the heat flow to the cold cap, the gibbsite (and generally Al source) particle size ultimately influences the glass production rate that increases as the particle size increases. Variation in the Fe source affects the glass production rate mainly through their content of chemically bound water.