Reports of the Academy of Sciences of the USSR
1961. Volume 136, No. 2

Chemistry

Corresponding Member of the Academy of Sciences of the USSR A. V. NIKOLAEV and M. P. MIKHAILOVA

EXTRACTION DIAGRAM OF FERRIC CHLORIDE WITH DIETHYL ETHER

The extraction of ferric chloride with diethyl ether from hydrochloric-acid solutions has been the subject of numerous investigations. However, the available data are insufficient for a more or less complete description of the extraction system \(\mathrm{FeCl_3}—\mathrm{HCl}—\mathrm{H_2O}—(\mathrm{C_2H_5})_2\mathrm{O}\). The present investigation

Fig. 1. Extraction diagram of ferric chloride in the system
\(\mathrm{FeCl_3}—\mathrm{HCl}—\mathrm{H_2O}—(\mathrm{C_2H_5})_2\mathrm{O}\)

was undertaken with the aim of constructing an extraction diagram describing this quaternary system. The method for constructing the diagram was considered earlier (\(^{1}\)). The system was studied at a temperature of \(20 \pm 0.1^\circ\). To establish extraction equilibrium in the system, 3–5 minutes are sufficient. Figure 1 shows an extraction diagram with isolines of the distribution coefficient \(K_p\). The curve \(BB\) is the solubility isotherm of \(\mathrm{FeCl_3}\) in

in hydrochloric acid solutions and limits the region in which liquid phases exist. The equilibrium concentrations of the components in the aqueous phase are expressed in mol/l. The solubility of FeCl₃ in water at 20° found by us (47.5 wt.%) agrees with the value given by Roozeboom and Schreinemakers (48 wt.%)(²).

In the system under consideration, as in other cases studied earlier, the threshold effect described by A. V. Nikolaev (³) is observed. At low FeCl₃ concentrations its distribution coefficient is comparatively small and increases very slowly with concentration. At the threshold FeCl₃ concentration a sharp increase in \(K_p\) is observed; then the rate of increase of \(K_p\) again decreases. As a typical curve, Fig. 2 shows the dependence of \(K_p\) on the equilibrium FeCl₃ concentration at a constant equilibrium HCl concentration equal to \(1.5\,M\) (section along the isoconcentrate \(A—A\), Fig. 1). The threshold FeCl₃ concentration at this acidity is close to \(0.6\,M\). The FeCl₃ concentration required to reach the extraction threshold shifts toward smaller values as the acid concentration increases. At high acid concentrations, beginning with \(2.5\,M\), the extraction threshold disappears completely. The threshold effect is also observed in the absence of HCl; this case corresponds to the maximum threshold FeCl₃ concentration, close to \(2.3\,M\).

Fig. 2. Dependence of \(K_p\) of ferric chloride on the concentration of ferric chloride during its extraction from a solution in \(1.5\,M\) HCl (section \(AA\), Fig. 1)

Institute of Inorganic Chemistry
Siberian Branch of the Academy of Sciences of the USSR

Received
14 IX 1960

CITED LITERATURE

1. A. V. Nikolaev, A. G. Kurnakova, ZhNKh, 3, 1037 (1958).
2. H. W. B. Roozeboom, F. A. H. Schreinemakers, Zs. phys. Chem., 15, 588 (1897).
3. A. V. Nikolaev, DAN, 129, 582 (1959).