| Nuclear and hazardous wastes are continually generated in the industrialized world. Safe and inexpensive disposal of those materials has been the subject of extensive research in recent years. Vitrification is one of the options under investigation. The basis for vitrification of nuclear and hazardous wastes is the immobilization of radioactive and hazardous elements within a stable glass matrix. The processibility of a waste melt, which includes the melt viscosity, conductivity and liquidus temperature, and the chemical durability of the resulting glass are important factors in vitrification studies. Unlike commercial glasses, which have a limited number of components and small compositional variations, nuclear and hazardous wastes have many more components and very large compositional variations. Thus, their vitrification presents a more difficult problem, requiring a sound understanding of multi-component glass systems.;Glasses containing major components CaO, Na;A eutectic point in liquidus temperature was found by the variation of calcium to sodium ratio in a multi-component glass system made with incinerator ashes and some additives. The minimum in liquidus temperature enables a lower processing temperature for ashes without affecting the waste loading. It has been found that the viscosity of the glass melt is well correlated to the non-bridging oxygen numbers per tetrahedra and that the conductivity of the glass melt can be explained by the structural roles of alkali elements in glass matrix. An empirical model has been developed to correlate the glass melt conductivity with its chemical composition. A general thermodynamic model has been developed for the liquidus temperature of a glass melt by using the regular solution model as the first approximation to the glass melt. The validity of the model is well supported by our experimental data in several special cases of the model. The effects of Fe-Ni spinel formation on the leachability of mixed waste glasses have been systematically studied. It has been determined that the formation of Fe-Ni spinels can decrease the leaching rate of nickel by up to an order of magnitude without affecting the leaching rate of other hazardous and radioactive elements. |
