PHASE FORMATION STUDIES USING X-RAY DIFFRACTION AND INFRARED SPECTROSCOPY IN THE VITRIFICATION OF SAVANNAH RIVER SITE SB4 HLW SLUDGE SURROGATE WITH HIGH IRON AND ALUMINUM CONTENTS AT HIGH WASTE LOADINGS

摘要

Phase formation mechanisms associated with the vitrification of Savannah River Site (SRS) Sludge Batch 4 (SB4) high level waste surrogate with high iron and aluminum contents were studied by X-ray diffraction (XRD) and infrared spectroscopy (IRS). Two mixtures at 60 and 70 wt% SB4 waste loading were prepared as slurries with a water content of ~50 wt% using a waste surrogate and commercially available Frit 503-R4 (Li_3O - 8 wt %, B_2O_3 - 16 wt %, SiO_2 - 76 wt %). The mixtures were air-dried at a temperature of 115 °C and heat-treated at 500, 700, 900, 1000, 1100, 1200, and 1300 °C for 1 hr at each temperature. IR spectra and XRD patterns of the products heat-treated at each temperature were recorded. In both the mixtures phase formation reactions started at low temperatures and yielded intermediate phases (sodalite, pyroxene-type, nepheline), and reactions were mostly completed within the temperature range between 1000 and 1100 °C. The glassy materials prepared at 1200 °C were composed of vitreous phase and magnetite/trevorite type spinel. The materials with 60 wt.% waste loading prepared at 1300 and 1400 °C had the same phase composition whereas at 70 wt.% waste loading, nepheline phase was also detected resulting from crystallization from the melt.