Kinetic model for quartz and spinel dissolution during melting of high-level-waste glass batch
The dissolution of quartz particles and the growth and dissolution of crystalline phases during the conversion of batch to glass potentially affects both the glass melting process and product quality. Crystals of spinel exiting the cold cap to molten glass below can be troublesome during the vitrification of iron-containing high-level wastes. To estimate the distribution of quartz and spinel fractions within the cold cap, we used kinetic models that relate fractions of these phases to temperature and heating rate. Fitting the model equations to data showed that the heating rate, apart from affecting quartz and spinel behavior directly, also affects them indirectly via concurrent processes, such as the formation and motion of bubbles. Because of these indirect effects, it was necessary to allow one kinetic parameter (the pre-exponential factor) to vary with the heating rate. The resulting kinetic equations are sufficiently simple for the detailed modeling of batch-to-glass conversion as it occurs in glass melters. The estimated fractions and sizes of quartz and spinel particles as they leave the cold cap, determined in this study, will provide the source terms needed for modeling the behavior of these solid particles within the flow of molten glass in the melter.
The effect of composition on spinel crystals equilibrium in low-silica high-level waste glasses
The liquidus temperature (TL) and the equilibrium mass fraction of spinel were measured in the regions of low-silica (less than 42 mass% SiO2) high-level waste borosilicate glasses within the spinel primary phase field as functions of glass composition. The components that varied, one at a time, were Al2O3, B2O3, Cr2O3, Fe2O3, Li2O, MnO, Na2O, NiO, SiO2, and ZrO2. The effects of Al2O3, B2O3, Fe2O3, NiO, SiO2, and ZrO2 on the TL in this region and in glasses with 42 to 56 mass% SiO2 were similar. However, in the low-silica region, Cr2O3 increased the TL substantially less, and Li2O and Na2O decreased the TL significantly less than in the region with 42 to 56 mass% SiO2. The effect of MnO on the TL of the higher SiO2 glasses is not yet understood with sufficient accuracy. The temperature at which the equilibrium mass fraction of spinel was 1 mass% was 25C to 64C below the TL.
Influence of Batch Moisture on Melting Behavior of Glass
Melting behavior in the system sand-potash-dolomite was found to depend strongly on the amount of H2O added to the batch, which was varied from 0.5 to 9.0 wt%. This dependence holds primarily for the formation and dissolution of K2Ca(CO3)2, but other compounds are also influenced, e.g., α-K2MgSi3O8, CaMgSiO4, Ca2MgSi2O7, andCaSiO3.