Vitrification of sulphate bearing high level wastes in borosilicate matrix

The paper deals with the development and characterization of vitreous matrices for the containment of sulphate bearing high level wastes. Studies were conducted in the sodium borosilicate system with the introduction of CaO, BaO, MgO, etc., and also in the lead borosilicate system. The results reveal that the lead borosilicate system is compatible with sulphate bearing high level wastes. Detailed product evaluation involving melting behavior, homogeneity, chemical durability, thermal stability, viscosity, etc. were carried out on selected formulations of the lead borosilicate system. A composition having 25% waste oxides, 25% PbO, 10% B2O3, 10% Fe2O3 and 30% SiO2 by weight is found to be promising for incorporation of sulphate bearing high level wastes. This formulation shows high sulphate retention of >85%, reasonable pouring temperature of 950°C and a low leach rate of 6.8×10−2 g m−1d−1.