Demonstration of the Use of Formohydroxamic Acid in the UREX Process

Abstract

The Uranium Extraction (UREX) process was developed to separate U and Tc from the transuranic elements and the remaining fission products. To prevent the extraction of Np and Pu, a dilute nitric acid scrub stream containing acetohydroxamic acid (AHA) is used in the process. When the AHA contacts nitric acid, the complexant begins to decompose producing acetic acid and hydroxylamine nitrate (HAN). The HAN decomposes to gaseous products and water; however, the acetic acid is relatively stable and will contaminate nitric acid recovered from waste streams. To address this issue, formohydroxamic acid (FHA) was evaluated as a replacement for AHA. Formohydroxamic acid prevents the extraction of Np and Pu and its decomposition products (formic acid and HAN) readily decompose. Neptunium and Pu distribution coefficient measurements demonstrated that FHA was an acceptable replacement for AHA. Additional extraction experiments performed with the addition of uranyl nitrate to the aqueous phase showed that its presence had little effect on the distribution coefficients. A steady increase in distribution coefficients with increasing nitrate concentrations was consistent with a salting-out effect. When the actinides were back-extracted into the aqueous phase, the Np and Pu distribution coefficients were larger than the distribution coefficients measured in an extraction mode potentially due to kinetic limitations. These data imply that a greater number of scrub stages would be required in the first bank of the UREX process contactors than would be calculated based on the Pu and Np distribution data generated in the extraction experiments.