Dissolution of aluminum-, titanium-, and zirconium-based crystalline waste form components under hydrothermal conditions

Solubility effects were measured on ceramic and single crystal alumina, titania, SrTiO3 (perovskite structure), and ceramic zirconia at 300 and 4000C for times of 7 and 18 days. Selected fluids were deionized water, a high-bicarbonate, high-sulfate simulated connate water (about 1% total dissolved solids), saturated NaCl brine, and a high-magnesium, high-calcium bittern brine. There is measurable dissolution of Al3+ in the connate water and in the bittern brine only. In both cases this can be related to the low pH conditions expected in these fluids at high temperature and to the increase in aluminum solubility with decreasing pH. The SrTiO3 breaks down to some extent in all fluids in the order bittern brine > NaCl > bicarbonate water > deionized water. Dissolution attack on both titanium and zirconium oxides is very small, indicating that the oxides are stable in the pressure-temperature-fluid composition regime. Breakdown of the perovskite phase appears to be by incongruent dissolution with concurrent precipitation of the titanium oxide