Identification of Solid Phases in Saltcake from Hanford Site Waste Tanks

Abstract

One of the primary tasks in the clean up of the Hanford Reservation is the retrieval of waste from single-shell and double-shell storage tanks. The waste will be used as feedstock for the vitrification plant under construction in the Hanford 200 East area. To accomplish this tank waste retrieval, the River Protection Project requires physical and chemical data on the nature of the wastes. For several years, laboratory tests have been conducted at the 222-S Laboratory on the dissolution characteristics of Hanford saltcake waste from single shell tanks (Herting 1998, 1999, 2000,2001). The bulk physical and chemical data determined during these studies has provided valuable input for evaluating the Environmental Simulation Program produced by OLI Systems, Inc. of Moms Plains, New Jersey. This computer program is used by the River Protection Project to predict chemical solubility during dilution and retrieval of tank wastes. The characterization of solid phases found in saltcake undergoing dissolution and evaporative concentration is an important adjunct to the bulk physical and chemical properties of the saltcake waste. The phase analysis of Tank BY-109' saltcake, described in this report, was conducted using polarized light microscopy (PLM), X-Ray diffraction (XRD) and scanning electron microscopy (SEM). The phases Na{sub more » 7}F(PO{sub 4}){sub 2} {center_dot} 19H{sub 2}O, Na{sub 3}FSO{sub 4}, Na{sub 2}C{sub 2}O{sub 4} and NaF were identified in BY-IO9 saltcake by all three instruments, while Na{sub 3}AlF{sub 6} was observed in XRD and SEM analyses. In addition, the SEM found significant amounts of a fine-grained aluminum-rich phase, frequently associated with lesser amounts of chromium and sodium. PLM noted the presence of a fine-grained agglomerated phase that was probably this aluminum-rich phase, and XRD confirmed the presence of an aluminum hydroxide, bayerite, in one sample. Finally, the SEM located a number of discrete particles of an aluminosilicate phase and a uranium-rich phase, as well as occasional particles of exotic composition, such as chromium-rich, calcium/strontium-rich and bismuth/palladium-rich. These phases were too rare, or too poorly crystalline, to be identified by PLM or XRD analysis. While the emphasis of this report is on phase analysis of Tank BY-IO9 saltcake, examples of phases identified in other tanks are included where appropriate. The hope of the authors is that this document will serve as a visual reference for future phase analysis efforts, both at the 222-S Laboratory and at other Department of Energy sites where similar tank waste samples are characterized. At the same time, the reader is cautioned that this is a work in progress, that is, the methods employed here are still being developed and refined. « less