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Chemical Speciation of Inorganic Compounds under Hydrothermal Conditions

Description: This project utilizes the high-intensity x-rays available at the Advance Photon Source (APS) to study the inorganic chemistry associated with tank waste vitrification. Although the chemical conversion of waste under high-temperature conditions is an integral part of these processing technologies, there is virtually no information in the published literature about the chemical speciation of inorganic compounds under actual processing conditions. This is primarily due to the lack of techniques that are capable of making in situ measurements of aqueous systems above 300 C. The ongoing x-ray-based studies are identifying the chemical species, oxidation states and ion pairing of inorganic compounds under extreme solvent conditions. It is imperative to make in situ measurements since we have shown that the chemical speciation is strongly dependent on temperature. Several complimentary techniques are being used in this study including x-ray absorption fine structure (XAFS), diffuse anomalous x-ray scattering (DAS) and vibrational (IR & Raman) spectroscopy. Thus, the results of this work are providing information critical to the calcining and vitrification of tank wastes. The results will also have a direct bearing on specific issues such as volatility of Tc (or Re) compounds and the complex chemistry of chromium compounds.
Date: June 1, 2000
Creator: Stern, Edward A.; Fulton, John L. & Seidler,Gerald
Partner: UNT Libraries Government Documents Department

Chemical Speciation of Inorganic Compounds under Hydrothermal Conditions

Description: By employing XAFS spectroscopy we are seeking a better understanding of the high temperature aqueous chemistry and speciation of those components that are troublesome to the treatment of the Hanford tank wastes: namely Cr, Re (surrogate for Tc), Fe, Ru (surrogate for Pu), and NO3 -/NO2 -. After initial experiments revealed that the high corrosivity of some of these aqueous systems renders the original high-pressure/high-temperature XAFS flow cell unsuitable of these systems, we have quickly implemented a new XAFS flow cell design made from Pt/Ir alloy. Over the last 12 months we have been able to obtain a number of groundbreaking results with this new XAFS cell, which we will briefly highlight.
Date: June 1, 1999
Creator: Stern, Edward A.; Fulton, John L. & Seidler, Gerald
Partner: UNT Libraries Government Documents Department