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 infrared spectroscopy (IRS), X-ray diffraction (XRD) and optical microscopy. Two mixtures at 50 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 (Li2O – 8 wt%, B2O3 – 16 wt%, SiO2 – 76 wt%) or mixture of chemicals (LiOH·H2O, H3BO3, SiO2). 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 the reactions were mostly completed within the temperature range between 1000 and 1100 °C. The glassy materials prepared at 1200 and 1300 °C were composed of vitreous phase and magnetite/trevorite type spinel.