Separation of Copper and Iron Using Ion Exchangers
Abstract Generated abstract
This paper describes a chromatographic ion exchange procedure for separating and concentrating trace copper and iron from hydrochloric acid solutions. The method exploits the much stronger sorption of iron than copper on ceralite FF in 9 N hydrochloric acid, while copper is subsequently retained on an AN-2F anion exchanger, followed by elution with 0.1 N hydrochloric acid and photometric determination using 2,2′-dipyridyl for iron and sodium diethyldithiocarbamate for copper. The procedure was applied to calcium carbonate and calcium and ammonium hydrophosphates used in phosphor production, giving trace determinations of both elements and improving the sensitivity of the authors’ earlier sorption photometric approach.
Full Text
Separation of Copper and Iron Using Ion Exchangers
R. D. Glukhovskaya, Yu. L. Lel’chuk, E. D. Lukker
(Presented by the scientific seminar of the Department of Analytical Chemistry)
Earlier [1–4] we studied the sorption and desorption of iron and copper by the anion exchangers AN-2F and tseralit FF in hydrochloric acid solutions of various concentrations. It was established that both copper and iron are sorbed by these anion exchangers from hydrochloric acid solutions of 8–9 N concentration.
As a result, a method was developed for determining copper and iron from a single weighed sample, based on the simultaneous concentration of their chloride complexes by an anion exchanger, elution of the latter with 0.1 N hydrochloric acid, and photometric determination in aliquot portions of the eluate: iron with 2,2′-dipyridyl, and copper with sodium diethyldithiocarbamate [5].
In order to further increase the sensitivity of the method, we studied the conditions for chromatographic separation of these elements using ion exchangers.
Many investigators have dealt with the chromatographic separation of copper and iron. Thus, the literature describes methods based on the separation of these elements in the form of their pyrophosphate complexes using the cation exchanger SBS [6] and wofatit P [7]. Many authors [8, 9] propose for this purpose anion exchange based on the sorption of the chloride complexes of these elements from concentrated hydrochloric acid solutions and their subsequent washing out with 2.5–0.5 N HCl.
We used the different ratios of the chloride complexes of iron and copper toward such anion exchangers as AN-2F and tseralit FF. In studying the exchange capacity of these anion exchangers with respect to copper and iron in hydrochloric acid solutions of various concentrations, we encountered the fact that both copper and iron have rather similar distribution coefficients with respect to the AN-2F resin. As for tseralit FF, here a large difference is observed in the sorbability of these elements. Thus, the distribution coefficient for iron in 9 N HCl solution is 703.2 [3], while that of copper under the same conditions is only 17 [5]. Thus, the ratio of the distribution coefficients of iron and copper in 9 N HCl is 41.1. This was used by us to develop a chromatographic method for separating these elements.
Experimental Part
For sorption and separation of iron, a small column was used, filled with tseralit FF to a bed height of 2 cm. When checking the sorption of iron and copper on this column, we once again confirmed that iron is com-
is sorbed by the resin and is not washed out of the column when 50–60 ml or more of 9 N HCl is passed through it. Copper, under these conditions, is not retained by the anion exchanger. For the sorption and concentration of copper, a column packed with AN-2F anion exchanger with a bed height of 22 cm was used. Preparation of the column for operation has been described earlier [1, 2].
The conditions developed for the chromatographic separation and concentration of copper and iron were used by us to increase the sensitivity of the sorption–photometric determination of traces of these elements in calcium carbonate and calcium and ammonium hydrophosphates used in the production of phosphor L-34.
Procedure. The sample to be analyzed is dissolved in 10–15 ml of 9 N HCl. The two columns are fixed successively on one stand so that the eluate flowing out of the small column enters the column with AN-2F. The flow rate from both columns should be 2–3 ml per minute.
10–15 ml of 9 N HCl is passed through the columns to convert the anion exchangers to the Cl-form. Then the hydrochloric-acid solution of the substance being analyzed is passed through, and both columns are washed with 20–30 ml of HCl of the same concentration. The stopcocks are closed, the small column with ceralite FF is fixed on another stand, and the column with AN-2F is washed with another 10 ml of 9 N HCl.
The iron sorbed by ceralite FF is washed out with 10 ml of 0.1 N HCl into a 25-ml volumetric flask and determined photometrically with 2,2′-dipyridyl [1–3].
The copper sorbed by the AN-2F anion exchanger is eluted with 20 ml of 0.1 N HCl into a separatory funnel and determined photometrically with sodium diethyldithiocarbamate [4, 5].
The results of the analysis of samples of certain materials used in phosphor production are given in the table.
Table
Results of parallel determinations of copper and iron
in certain materials used in phosphor production
| Substance analyzed | Number of determinations | Found, % copper | Found, % iron | Maximum deviation from the mean value, % copper | Maximum deviation from the mean value, % iron |
|---|---|---|---|---|---|
| $(\mathrm{NH}_4)_2\mathrm{HPO}_4$, chemically pure | 3 | $4.5\cdot10^{-5}$ | $5.9\cdot10^{-4}$ | $\pm 22.2$ | $\pm 10.1$ |
| $(\mathrm{NH}_4)_2\mathrm{HPO}_4$ | 3 | $2.9\cdot10^{-4}$ | $1.17\cdot10^{-2}$ | $\pm 20.6$ | $\pm 2.5$ |
| $\mathrm{CaCO}_3$, pure | 3 | $3.7\cdot10^{-5}$ | $5.7\cdot10^{-4}$ | $\pm 27.0$ | $\pm 8.9$ |
| $\mathrm{CaHPO}_4$, pure | 4 | $5.38\cdot10^{-4}$ | $2.16\cdot10^{-4}$ | $\pm 2.04$ | $\pm 4.6$ |
Conclusions
Conditions have been developed for the chromatographic separation and concentration of traces of iron and copper using the anion exchangers AN-2F and ceralite FF. The developed procedure was used to increase the sensitivity of the sorption–photometric determination of traces of these elements in calcium carbonate and calcium and ammonium hydrophosphates used in the production of phosphor L-34.
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