PNNL

Abstract

Experiments were conducted to determine sulfur solubility in Hanford low-activity waste (LAW) glass melts by a sulfur saturation method. Sulfur-incorporated glass melts were prepared by salt saturation and bubbling methods. The salt saturation method was performed by mixing crushed pre-melted baseline glasses with an excess amount of Na2SO4 prior to melting the mixture at 1150°C for one hour. The bubbling method involved bubbling the glass melt at 1150°C in a Pt crucible with an SO2/O2/N2 gas mix to equilibrate the melt at a known pressure of SO3. Preliminary results suggested that performing one cycle of mixing and melting was not sufficient to saturate the glass. The bubbling method successfully incorporated sulfur into the glass but caused significant losses of sodium from the melt. In order to saturate the glass melt with sulfate without causing noticeable sodium loss, a modified crucible salt saturation method was developed by repeating the mixing and melting of the glass and salt mixture. For all three representative LAW glasses tested in this study, it was found that after three mixing and melting cycles, the sulfur concentration reaches a plateau, indicating reasonable sulfur saturation.