An Extended Setschenow Model for Pu(IV) Third Phase Formation in 20% Tri‐n‐Butyl Phosphate Based Nuclear Solvent Extraction System

Formation of a third phase during liquid–liquid extraction is observed when solvate concentration in the organic phase exceeds its solubility limit in the diluent. This phenomenon is also observed in certain reaction systems like phase‐transfer catalysis. Although this phenomenon has been known since the early fifties, quantitative models have not been reported in the open literature. Recently, a Setschenow type model for Pu(IV) third phase formation in BESO/diluent system has been proposed. In the present work, the salt‐effect model is extended to cover Pu(IV) third phase formation in 20% TBP/diluent based nuclear solvent extraction system. Since it is an extended form of the Setschenow model for salting, it provides a basic understanding of salting‐in/out during third phase formation and related phenomena.