LIQUID-LIQUID-EXTRACTION OF ALKALINE-EARTH METAL-IONS WITH A NONIONIC SURFACTANT HAVING A POLY(OXYETHYLENE) CHAIN (TRITON X-100)

The ion-pair extraction of poly(oxyethylene) alkylphenyl ether (Triton X-100, S) complexes of alkaline earth metal ions (M2+) with picrate ion (Pic-) into 1,2-dichloroethane (1,2-DCE) was studied. The extraction equilibria are interpreted by the extraction of the ion pair, [SM2+.(PiC-)2], and the dissociation of the ion pair into [SM2+.(Pic-)] and Pic- in 1,2-DCE. Thermodynamic constants of the extraction and the dissociation of the ion pairs were evaluated. The extraction constant increases in the order Ca2+ < Sr2+ < Ba2+. This order is explained by the magnitudes of the formation constants of the alkaline earth metal ion complexes with Triton X-100 in the aqueous phase. The dissociation constant of the ion pair in 1,2-DCE is almost constant for the alkaline earth metal ions.