Effect of silica particle size on rheological properties of low-activity waste melter feed

Abstract

Glass-forming chemicals (GFCs) are added to Hanford low-activity waste to form melter feeds for vitrification with the quantities of GFCs designed to produce a suitable final glass for long-term immobilization of radionuclides. In designing melter feeds, material properties should be considered such that feeds can be easily mixed, transported, and reagitated. Silica is the largest contributor to the GFCs and significantly influences the physical properties of the melter feed. This study evaluated the impact of changing silica particle size, using sources with a d ₉₅ ranging from ∼8 to 118 μm, on the physical and rheological properties of a low-activity waste melter feed simulant. We discovered a non-linear relationship between silica particle size and yield stress in melter feeds. A small d ₉₅ and a large d ₉₅ both produce a high yield stress, and there is a local minimum yield stress between ∼36 and 89 μm. A relationship is derived to cover the range of particle sizes measured using an adaptation of the Kreiger and Dougherty model for yield stress. This relationship may be able to predict the yield stress of melter feeds given the particle size of silica, and further work should be done to expand this modeling effort.