to the formation of hydrogen bond between the dioxonium ion and the phosphoryl group P=O. It indicates that di-2-ethylhexylphosphoric acid extracts vanadium(V) with the formation of ionic associates. For the evaluation of the number of extractant molecules solvating the dioxonium ion the method of molar ratios was used. It follows from the extraction isotherm that one molecule of di-2-ethylhexylphosphoric acid corresponds to 10 vanadium ions. Considering our previous data on the ionic state of vanadium(V) in the range under study this means that one molecule of extractant corresponds to one decavanadate anion [8]. Hence, the method of saturation of organic phase permits not only to establish the number of solvating molecules of extractant in the composition of complex, but also to make the preliminary conclusion that vanadium(V) enters the composition of extracted complex as decavanadate anion. It is confirmed by the results of studies of the IR spectra of extracts of vanadium(V) with di-2-ethylhexylphosphoric acid. At high concentrations of vanadium(V) a broadening of absorption band at 1030 cm –1 is observed at the side of low frequencies and two shoulders at ~970 cm –1 and ~920 cm –1 appear. The comparative analysis of IR spectra of the extract of vanadium(V) with di-2ethylhexylphosphoric acid and the reported data on the IR spectra of vanadium(V) dioxocation and decavanadate anions [8] permits to attribute the low intensity bands at ~960 cm –1 and ~920 cm –1 to two types of binding of vanadium with terminal oxygen atoms of f- and g-type of decavanadate anion. Hence, the method of saturation and the results of IR studies of the extracts of vanadium(V) with di-2DOI: 10.1134/S1070363213060261 Di-2-ethylhexylphosphoric acid is known as the cation-exchanging extractant. It is widely used for the extraction of vanadium(IV) [1-5]. The extraction of vanadium(V) in a form of dioxocation with this substance proceeds with the very low distribution coefficient, and due to that it is not utilized [6]. We have worked up the conditions under which the change in the extraction mechanism from the cationexchanging to the solvate one takes place in the course of extraction what permits to extract vanadium(V) with di-2-ethylhexylphosphoric acid with high distribution coefficient. In this work we present the results of study of extraction of vanadium(V) with di-2-ethylhexylphosphoric acid. The investigation of extraction of vanadium(V) with di-2-ethylhexylphosphoric acid was carried out by means of IR and electronic spectroscopy. For the evaluation of the composition of extracted complex IR spectra of pure di-2-ethylhexylphosphoric acid and the vanadium(V) extract were recorded. In the IR spectra of the extract together with the absorption bands of di2-ethylhexylphosphoric acid the bands at 1650, 1750, 2140, and 3390 cm –1 are present which are characteristic of dioxonium ion [7]. The bands at 1170, 1370, and 2900 cm –1 which are also characteristic of H5O2 + ion are partially overlapped with more intense bands of di-2-ethylhexylphosphoric acid. The absorption band of P=O bond (νP=O) in the vanadium(V) extract has the frequency 1210 cm –1 . In the IR spectrum of pure di-2ethylhexylphosphoric acid the band of P=O bond (νP=O) has a maximum at 1225 cm –1 . As it was shown above, in the vanadium(V) extracts the dioxonium ion is presented. Due to that the shift of the band of P=O bond to the side of low frequencies may be attributed as