The extractant, N,N,N 0 ,N 0 -tetraoctyl diglycolamide (TODGA) has been evaluated for the separation of actinides(III) and lanthanides(III) from a high active raffinate (HAR). The effect of oxalic acid and HEDTA complexant on the extraction of actinides(III), lanthanides(III), and important fission products (e.g. Mo, Pd, Sr, Zr, Ru etc.) from synthetic HAR has been studied with 0.2 mol/L TODGA in TPH.With an extractant mixture of TODGA and tributyl phosphate (TBP) the amount of oxalic acid can be reduced to less than 0.3 mol/L for the effective complexation of zirconium, whereas the distribution ratios of actinides(III) and lanthanides(III) are still high for the separation from HAR. Furthermore the maximum loading of lanthanides (e.g. Nd) can be significantly increased by adding TBP to the extractant. However, the extraction of oxalic acid and nitric acid also increased by the addition of TBP, which can lead to problems during back extraction of the loaded extractant. Extraction studies after radiolysis and hydrolysis reveal that the TODGA þ TBP mixture is a sufficient stable extraction system suited for further process development studies.

The efficiency of the partitioning of trivalent actinides from a PUREX raffinate is demonstrated with a TODGA þ TBP extractant mixture dissolved in an industrial aliphatic solvent TPH. Based on the results of cold and hot batch extraction studies and with the aid of computer code calculations, a continuous counter-current process is developed and two flowsheets are tested using miniature centrifugal contactors. The feed solution used is a synthetic PUREX raffinate, spiked with 241 Am, 244 Cm, 252 Cf, 152 Eu, and 134 Cs. More than 99.9% of the trivalent actinides and lanthanides are extracted and back-extracted and very high decontamination factors are obtained for most fission products. The co-extraction of zirconium, molybdenum, and palladium is prevented using oxalic acid and HEDTA. However, 10% of ruthenium is extracted and only 3% is back-extracted using diluted nitric acid. The experimental steady-state concentration profiles of important solutes are determined and compared with model calculations and good agreement is generally obtained.

A 30% (w/w)