Determination of free hydroxide ion in synthetic Hanford nuclear waste by capillary zone electrophoresis
ABSTRACT
The U. S. Department of Energy controlled Hanford Site, near Richland, Washington, accumulated over 60 million gallons of nuclear waste stored in 177 large underground tanks between 1944 and 1987. Often referred to as the nation’s number one environmental cleanup problem, the Hanford nuclear waste presents great challenges of maintaining tank safety, waste processing and waste cleanup, and hence, makes routine characterization of the waste indispensable. It is very complex, highly caustic, has many radionuclides, metal ions, organic compounds and many inorganic anions. The determination of free hydroxide and thus estimating free acid in the tanks are paramount and particularly of vital attention because of their relevance to tank corrosion. In addition, pH information is necessary in waste processing, treatment and eventual disposal. The current method for the determination of hydroxide ion at the Hanford Site potentiometric titration, is non-selective, gives false high concentrations in the presence of certain concentrations of aluminate, carbonate, phosphate, and chromate. In addition to being time consuming, it consumes high amounts of acid and generates large volumes of additional mixed waste. Capillary zone electrophoresis methods have been shown to have high promise for anion analysis by indirect detection for non-UV absorbing species.
Chromate ion has been widely used as the absorbing background electrolyte (BGE). This study evaluated the prospective application of capillary zone electrophoretic (CZE) method for the determination of free hydroxide in the synthetic Hanford waste containing high concentrations of aluminate, nitrate, nitrite, and carbonate. CZE method in addition to the simultaneous determination of other inorganic anions such as nitrate, nitrite, and carbonate, offers advantages of high efficiency, rapid analysis, high sample throughput, minimal generation of mixed analysis waste, and overall savings in the cost of analyses.