Development of partitioning method

Solvent extraction process with DIDPA (diisodecyl phosphoric acid) and stripping process with oxalic acid have been studied for the purpose of separating Np(V) from high-level liquid waste. The present paper describes studies on continuous counter-current extraction and stripping using a miniature mixer-settler to examine the industrial applicability of these two processes. It was found that more than 99.96% of Np(V) could be extracted with DIDPA from simulated high-level liquid waste with addition of hydrogen peroxide. Hydrogen peroxide decomposed in the mixer-settler under the influence of some elements such as Pd, and then the acceleration of Np extraction by hydrogen peroxide was reduced. However, it was found possible to increase the Np extraction rate again by resupply of hydrogen peroxide. In the experiment on stripping, it was found that more than 99.94% of Np(IV) could be stripped with 0.8M oxalic acid from DIDPA. The stripping behavior of Np was well explained by the distribution ratios obtained through batchwise experiments. (author)