Fiscal Year 1998

Plans for disposing of the high-level radioactive wastes at the Hanford Site call for retrieving, pretreating, and finally immobilizing the wastes in a glass matrix. Since the cost for vitrifying and disposing of high-level wastes will be very great, pretreatment processes are being developed to reduce their volume. The baseline method for pretreating Hanford tank sludges is caustic leaching. Earlier studies with Hanford tank-sludge simulants and with actual Hanford tank sludges have indicated that treating water-washed and caustic-leached solids with oxidants can significantly increase the removal of Cr. Permanganate and ozone have been shown to be generally the most rapid and effective chemical agents for this purpose. The work described in this report continues to examine the effectiveness of solubilizing additional Cr from Hanford tank wastes by oxidation of the water-insoluble solids from tanks U-108, U-109, and SX-108 under alkaline conditions. The current study confirms that permanganate is highly effective at removing chromium from water solids under alkaline conditions, with Cr removals of up to 99+%. Elemental oxygen can also be highly effective, with removals up to 97+%

The SX Solver: A New Computer Program for Analyzing Solvent-Extraction Equilibria

A new computer program, the SX Solver, has been developed to analyze solvent-extraction equilibria. The program operates out of Microsoft Excel{reg_sign} and uses the built-in ''Solver'' function to minimize the sum of the square of the residuals between measured and calculated distribution coefficients. The extraction of nitric acid by tributylphosphate has been modeled to illustrate the program's use

The chemistry of sludge washing and caustic leaching processes for selected Hanford tank wastes

A broad-based study on washing and caustic leaching of Hanford tank sludges was performed in FY 1995 to gain a better understanding of the basic chemical processes that underlie this process. This approach involved testing of the baseline sludge washing and caustic leaching method on several Hanford tank sludges, and characterization of the solids both before and after testing by electron microscopy, X-ray diffraction, and X-ray absorption spectroscopy. A thermodynamically based model was employed to help understand the factors involved in individual specie distribution in the various stages of the sludge washing and caustic leaching treatment. The behavior of the important chemical and radiochemical components throughout the testing is summarized and reviewed in this report