Removal of Acetic Acid from a UREX+ Raffinate Stream

In the UREX+ process, acetohydroxamic acid is added to the UREX step to suppress plutonium extraction. Hydrolysis of acetohydroxamic acid (AHA) produces acetic acid and hydroxyl ammonium nitrate (HAN). The capability to remove acetic acid from aqueous process solutions is desirable as UREX+ flowsheets continue to evolve. Reasons for acetic acid removal include enabling recycle of the nitric acid solution and prevention of problems in downstream process steps. After a literature review, solvent extraction was determined to be the most promising approach for removal of acetic acid at the low concentrations involved. The goal was to identify a solvent that is both insoluble in the aqueous phase and will selectively remove acetic acid. Solutions of tributylphosphate (TBP) have been shown to selectively extract acetic acid over nitric acid with sufficiently high distribution coefficients. Extractant solutions tested in this study include TBP in dodecane and TBP in phenyltrifluoromethyl sulfone (FS-13). The two solvents are both compatible with the UREX+ process flowsheets, so selection of the solvent will be based on the placement of the removal step. The location of the removal step within the process is dependent on many factors including avoiding raffinate stream solutions containing quantities of actinides that TBP would extract, interference of acetic acid with the process steps, and the ratio of nitric to acetic acids in each step so the distribution coefficient can be maximized.