Investigations of the use of 4-(5-nonyl)pyridine as a liquid anion exchanger for tetrachloroferrate ions in aqueous chloride media

In an attempt to gain an understanding of factors affecting the extraction of iron(III) by 4-(5-nonyl) pyridine, the equilibria between hydrogen chloride and benzene solutions of 4-(5-nonyl) pyridine have been studied. From acid distribution data and visible absorption spectra of the organic phases, it was concluded that FeCL4- ion with a tetrahedral sp3 configuration is the principal iron containing species. The pyridine extraction of macro and trace amounts of the metal has indicated the formation of 1 : 1 and 2 : 1 complexes, respectively. The 2 : 1 complexes are assumed to result from association of a 1 : 1 complex with a molecule of the pyridine hydrochloride. The salting-out effect increases in the order LiCl<NaCl<MgCl2<AlCl3 and these differences in the effect have been attributed to the different degrees of hydration of cations of the salts present and to the ionic radii. The effect of various anions including the reducing agents has been described. Separation factors of several metal ions relative to ferric iron, in 6M HCl, are also reported. (T.G.)