PROCEEDINGS
OF THE TOMSK ORDER OF THE RED BANNER OF LABOR POLYTECHNIC
INSTITUTE named after S. M. KIROV

Vol. 174　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　1971

STUDY OF THE SORPTION OF IRON AND THE OPTIMAL CONDITIONS FOR ITS CONCENTRATION BY CERALITE FF

R. D. GLUKHOVSKAYA, Yu. L. LELCHUK, E. D. LUKKER

(Presented by the Department of Analytical Chemistry)

In our previous works [1, 2, 3], results were given of a detailed study of the conditions for chromatographic separation and concentration of traces of iron on the anion exchanger AN-2F. The iron in the eluate was determined by a photocolorimetric method in the form of a red complex with 2,2′-dipyridyl [4]. As a result of the studies, highly sensitive methods were developed for determining traces of iron in Lumifor “L-34” and in various materials used in its production (hydrochloric acid, calcium carbonate, ammonium and calcium hydrophosphates).

The aim of the present work is to study the conditions for separation and concentration of traces of iron on the anion exchanger “Ceralite FF.” The latter is a strongly basic monofunctional anion exchanger based on cross-linked polystyrene and containing quaternary ammonium groups. This anion exchanger has a high exchange capacity, is readily purified of iron impurities, and is convenient in operation.

To determine the optimal conditions for concentrating traces of iron, we studied the sorption and desorption of iron and determined its distribution coefficient.

The sorption capacity of Ceralite FF was determined in solutions containing 1 µg of iron in hydrochloric acid of various concentrations, according to the procedure described by us earlier [1]. From Fig. 1 it is evident that iron is completely sorbed from 8–11 N HCl solutions. With a decrease in acid concentration, the sorption of iron gradually decreases and, beginning with 2 N, ceases completely.

The magnitude of the sorption capacity of an element with respect to a given ion exchanger can be determined in various ways. Many consider that the simplest and most convenient method in practical terms is the determination of the distribution coefficient of the element between the solution and the ion exchanger. We used this method in our work.

Ceralite FF, purified of iron impurities, was converted to the Cl-form and dried to the air-dry state. After determining the moisture content, 0.5 g portions of resin (calculated as dry substance) were placed in flasks with ground-glass stoppers, 50 ml of a standard solution of Fe³⁺ or Fe²⁺ in hydrochloric acid of various concentrations was added, and after 5 days, upon attainment of equilibrium, in the solutions above the resin,

Fig. 7. Dependence of iron sorption by cerarite FF on the concentration of HCl

Fig. 2. Iron elution curve with 0.1 N HCl

iron was determined. From the results of the experiments, the distribution coefficient was calculated by formula [5]:

\[ \varphi=\frac{M_1}{M-M_1}\cdot\frac{V}{m}, \]

where \(M_1\) is the amount of iron sorbed by the resin, mg;
\(M\) is the total iron content in the initial solution, mg;
\(V\) is the volume of the solution above the resin, ml;
\(m\) is the mass of the resin, g.

Table 1 and Fig. 2 give the values of the distribution coefficients of trivalent iron in HCl solutions of various concentrations. For divalent iron we did not obtain stable data. Thus, it was established that the greatest sorption of iron occurs in 8–10 \(N\) hydrochloric acid solutions.

The desorption curve (Fig. 3) shows that the iron is completely washed out by 8–10 ml of 0.1 \(N\) HCl.

The investigations carried out formed the basis of the method we developed for chromatographic concentration and photometric determination of traces of iron in various materials used in phosphor production.

Determination procedure

When determining iron in hydrochloric acid, the latter is diluted to a concentration of 8–10 \(N\) and passed through a previously prepared column filled with cerium FF, purified of iron impurities, with a grain size of 0.1–0.25 mm, in the Cl form. The rate of passage of the solution is 2–3 ml per minute. The sorbed complex is washed three times with especially pure hydrochloric acid of the same concentration, obtained by isothermal distillation followed by chromatographic purification [2]. The iron is eluted with 0.1 \(N\) hydrochloric acid. As the diluted acid passes through, the color of the anion exchanger changes from dark brown for concentrated HCl to light red for a 0.1 \(N\) solution.

When the height of the dark ring decreases to 0.5–1 cm, the stopcock is closed, the lower part of the column is rinsed with water, and 8–10 ml of eluate are collected in a 25 ml volumetric flask.

In the resulting solution the iron is determined by the photometric method with 2,2′-dipyridyl. For this purpose, 2–3 drops of phenolphthalein are added, ammonia to a pink coloration of the solution, hydrochloric acid until decolorization, 5 ml of acetate buffer mixture to maintain the pH within 3.3–4.5, and 1 ml of 10% hydroxylamine hydrochloride.

The solution is mixed, heated to 50–60°C, 0.5 ml of 2% 2,2′-dipyridyl is added, the solution is cooled, diluted with water to the mark, and the optical density is measured on a photocolorimeter–nephelometer with a 50 mm cell thickness and a green light filter with maximum transmission at 508 mµ. Water serves as the reference solution. At the same time the optical density of a blank sample is measured and the corresponding correction is introduced. The calibration graph is constructed in the same way.

Table 2 gives the results of analysis of hydrochloric acid of “chemically pure” grade, of samples of this acid after purification by the well-known method, and of samples of this acid obtained by one-time chromatographic purification. As can be seen from the data presented, especially pure acid, practically completely freed from traces of iron, is obtained by successive purification by isothermal and chroma-

Table 1

Sorption of iron by the anion exchanger of the grade
“Ceralit FF”

Fig. 3. Dependence of the iron distribution coefficient on the HCl concentration.

chromatographic methods, or by passing “chemically pure” grade acid through a chromatographic column two or more times.

Table 2

Determination of traces of iron in hydrochloric acid

When determining traces of iron in calcium carbonate, ammonium and calcium hydrophosphates, and the luminophore “L-34,” the weighed portion of the sample being analyzed is decomposed with \(8\text{–}10\,N\) especially pure hydrochloric acid, and the resulting solution is passed through a column with an anion exchanger according to the procedure described above. The experimental results are given in Table 3.

Table 3

Determination of iron in products of phosphor manufacture

Conclusions

A highly sensitive method has been developed for determining traces of iron in certain materials used in phosphor manufacture, based on chromatographic separation and concentration of iron in the form of its chloride complex on the strongly basic anionite of the “Tseralit FF” grade and its photocolorimetric determination with 2,2′-dipyridyl. The sensitivity of the method is $1\cdot 10^{-6}$—$1\cdot 10^{-7}$. The duration of the analysis is 1.5–2 hours.

Literature

1. R. D. Glukhovskaya, Yu. L. Lel’chuk. III Scientific Conference of the Tomsk Branch of the All-Union Chemical Society named after D. I. Mendeleev. Tomsk, 1966.

2. Yu. L. Lel’chuk, R. D. Glukhovskaya. Izv. TPI, 148, 68, 1966.

3. R. D. Glukhovskaya, Yu. L. Lel’chuk. Abstracts of reports of the conference on analytical chemistry of semiconductor substances. Kishinev, 1965.

4. Yu. L. Lel’chuk, P. V. Kristalev, L. D. Skripova, L. B. Kristaleva. Use of chemical reagents. Information Bulletin of IREA, 4, 109, Moscow, 1964.

5. I. P. Alimarin, T. A. Belyavskaya. Chromatography, Its Theory and Application. 372, Publishing House of the Academy of Sciences of the USSR, Moscow, 1960.