Composition of the Organic Phase Species in the Synergistic Extraction of Sr2+ by Mixtures of Di(2‐Ethylhexyl) Alkylenediphosphonic Acids and Dicyclohexano‐18‐crown‐6

Abstract The extraction of Sr2+, Ba2+ and Ra2+ from aqueous nitric acid solutions by P,P′‐di(2‐ethylhexyl) ethylene‐ (H2DEH[EDP]) and butylene‐ (H2DEH[BuDP]) diphosphonic acids in o‐xylene is synergized by the cis‐syn‐cis and cis‐anti‐cis stereoisomers of dicyclohexano‐18‐crown‐6 (DCH18C6). However, no information is available on the composition of the synergistic complexes. In this work a detailed investigation of the composition of the organic phase species formed in these systems has been performed using Sr2+ as a probe, with a variety of techniques such as infrared spectroscopy, vapor pressure osmometry, and distribution methods. The latter methods have been employed under conditions ranging from trace metal concentration to organic phase saturation. The results from these experiments indicate that for the H2DEH[BuDP] system, the synergistic complex contains one Sr2+ ion, one crown ether molecule, and two diphosphonic acid trimers. For the H2DEH[EDP] system, the predominant synergistic complex has the 1:1:1 metal ion:crown ether:diphosphonic acid hexamer stoichiometry. Some of the results, however, indicate that a complex containing two H2DEH[EDP] hexamers can also be formed. †Work performed under the auspices of the Office of Basic Energy Sciences, Division of Chemical Sciences, U.S. Department of Energy, under contract W‐31‐109‐ENG‐38. The submitted manuscript has been created by the University of Chicago as Operator of Argonne National Laboratory (“Argonne”) under Contract No. W‐31‐109‐ENG‐38 with the U.S. Department of Energy. The U.S. Government retains for itself, and others acting on its behalf, a paid‐up, nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.