SANS Study of Third Phase Formation in the Extraction of HCl by TBP Isomers in n ‐Octane

Third phase formation in the extraction of HCl by triisobutyl phosphate (T‐iso‐BP) and tri‐sec‐butyl phosphate (T‐sec‐BP) has been investigated and compared with the tri‐n‐butyl phosphate (T‐n‐BP) system. The three TBP isomers exhibit comparable affinities for HCl, but the branched isomers extract much more water than the linear one. For T‐sec‐BP, the LOC (limiting HCl organic concentration) is characterized by much lower HCl concentrations both in the organic and aqueous phase than for the other isomers. SANS data for T‐iso‐BP and T‐sec‐BP organic phases loaded with progressive amounts of HCl have been interpreted using the Baxter model for hard spheres with surface adhesion. The critical values of the stickiness parameter, τ−1, and the interaction potential energy, U(r), are slightly different and characteristic for each of the extractants. Their values are consistent with the expectation derived from the micellar interaction model.