Influence of Monoisodecyl Phosphoric Acid on Extraction of Neptunium with Diisodecyl Phosphoric Acid

Abstract

The influence of monoisodecyl phosphoric acid (MIDPA) on the separation of Np with diisodecyl phosphoric acid (DIDPA) was studied from the aspects of the extraction rate and the back-extraction with H₂C₂O₄ solution. This study is important for the development of the partitioning method for high-level waste because MIDPA is one of the radiolysis products of DIDPA
The increase in the MIDPA concentration was found to accelerate the extraction of Np initially in the pentavalent oxidation state. When the MIDPA concentration was 0.1 _M, the extraction rate was ten times faster in the absence of H₂O₂ and twice faster in the presence of 0.5 _M H₂O₂. It was also found that the extraction mechanism in the aspect of Np redox reactions did not change even in the presence of MIDPA
On the other hand, Np became less back-extracted with increasing MIDPA concentration. However, the tolerable concentration of MIDPA, determined by the required distribution ratio for the Np back-extraction, is higher than the estimated concentration of MIDPA produced radiolytically in the partitioning process.