Separation Science and Technology, Vol.31, No.15, 2045-2063, 1996
Recovery of Neptunium from Highly Radioactive-Waste Solutions of Purex Origin Using Tributyl-Phosphate
The present work deals with the extraction of neptunium into the TBP/dodecane phase under conditions relevant to highly radioactive waste solutions, along with uranium and plutonium, by oxidizing it to the hexavalent state using 0.01 M K2Cr2O7 and subsequently recovering it by selective stripping. Three types of simulated HLW solutions, namely sulfate-bearing (SB, in similar to 0.3 M HNO3) and nonsulfate wastes originating from the reprocessing of fuels from pressurised heavy water reactors (PHWR) and fast breeder reactors (FBR) (both in 3.0 M HNO3), have been employed in this study. Very high extraction of U(VI), Np(VI), and Pu(VI) was obtained from PHWR and FBR-HLW solutions, whereas extraction was less but reasonably high from the SB-HLW solution. The uptake of cerium at tracer level concentrations in the millimolar range (encountered in HLW solutions) and from the simulated HLW solutions containing 0.01 M K2Cr2O7 by 30% TBP has shown that its extraction takes place only at tracer level concentrations and not at millimolar levels. The stripping of the metal ions from the loaded organic phase was done with a mixture of 0.01 M ascorbic acid and 0.1 M H2O2 in 2.0 M HNO3 at organic to aqueous phase ratios of 1:1, 2:1, and 4:1. Quantitative recovery of neptunium and plutonium was achieved. Based on these results, a scheme was formulated for the recovery of neptunium, and it was tested using the actual high level waste solution originating from the reprocessing of research reactor fuels.