Distribution of U(VI) and Pu(IV) by N,N-di(2-ethylhexyl)Butanamide in Continuous Counter-Current Extraction with Mixer-Settler Extractor

Abstract

The extraction properties of 1.5 mol/dm3 (M) N,N-di(2-ethylhexyl)butanamide (DEHBA) with n-dodecane toward U(VI) and Pu(IV) were studied using a single stage batch method with different concentrations of nitric acid (0.1 – 4.9 M), U(VI) (38 μM – 0.38 M), and Pu(IV) (3.9 μM – 0.29 mM). The distribution ratios toward U(VI), D U, and Pu(IV), D Pu, were expressed by the following equations: and . These equations, and , respectively, indicate concentrations of nitrate ion and free DEHBA which can make complexes with U(VI) or Pu(IV). A continuous counter-current experiment with 1.5 M DEHBA as an extractant was performed using mixer-settler type extractors consisting of 5 steps: U-Pu extraction, scrub, U recovery, Pu back-extraction, and U back-extraction. The feed solution employed for the continuous counter-current experiment was 3 M nitric acid containing U(VI), Pu(IV), and simulated fission products. The ratios of U(VI) and Pu(IV) extracted by 1.5 M DEHBA in the U-Pu extraction step were more than 99.9%. The extracted Pu(IV) was scrubbed from the organic phase using 0.67 M nitric acid, and more than 97% of Pu(IV) in the feed was recovered in the Pu fraction. The present results indicated that DEHBA works as an extractant for mutual separation of U(VI) and Pu(IV) by adjusting the nitric acid concentration without using Pu(IV) reductants.