Third phase formation caused by iron in DIDPA extraction system

In a four-group partitioning process, which has been developed, transuranium elements are extracted with diisodecylphosphoric acid (DIDPA) from a high-level radioactive liquid waste (HLW). Fe(III) is contained in HLW as a corrosion product, and the distribution ratio of Fe for DIDPA is very large. A third phase which prevents the separation is formed when the concentration of Fe in the organic phase increases. The behavior of Fe in the extraction with DIDPA was studied, as a function of the concentration of TBP, which was added to DIDPA in order to improve the separation of the phases. It was proven that the extraction rate of Fe decreased and the limit of the Fe concentration against the third phase formation remarkably decreased with the increase of the TBP concentration. A consideration of the influence of TBP showed that the water extracted with TBP contributed to the third phase formation. (author)