A Separation of Beryllium from Aluminum, Trivalent iron, Yttrium, Cerium, and the Rare Earths by Cation Exchange Chromatography F. W. E. STRELOW National Chemical Research laboratory, South African Council for Scientific and Industrial Research, Pretoria, South Africa
b A systematic study of the adsorbabilities of cations with A G 50W-X8 resin in hydrochloric and nitric acids indicated that the difference in the equilibrium distribution coefficients among beryllium and a number of other cations i s large enough to warrant a good separation. This fact was used to develop a cation exchange chromatographic procedure for the separation of Be from AI(III), Fe(lll), Y(III), and Ce(lll). Other elements that are completely separated include Sr(ll), Ba(ll), Ga(lll), La(lll), and the rare earths, Zr(lV) and Th(lV). A number of elements, such as Cd(ll), Sn(lV), Se(lV), Hg(ll), V(VL W V ) , Au(lll1, As(lll), and Sb(lll), can be eluted from the column with 0.5N HCI before the separation of beryllium from the more strongly absorbed elements i s started. The method of separation i s applied to the determination of beryllium in a gadolinite ore.
D
a previous study (6) of equilibrium distribution coefficients of cations in hydrochloric acid and AG 50 resins, a considerable difference between the distribution coefficients of beryllium and many other cations precipitable by ammonium hydroxide was noticed. Thus, Kd values of 13.3, 35.5, 60.8, 144.6, and URIKQ
Table I.
264.8 were reported (6), respectively, for beryllium, trivalent iron, aluminum, vttrium, and trivalent cerium in 1N hydrochloric acid and AG 50V-X8 resin in the hydrogen form. Based on these Kd value differences, an attractive ion exchange chromatographic separation of beryllium was developed. The method is particularly useful for the separation of aluminum, which resembles beryllium in analytical properties and accompanies it in many nonion exchange separations. A number of ion exchange separations of beryllium from other elements have already been published. The most iinportant procedures are summarized in Table I. S o noteworthy anion exchange procedures seem t o have been developed, although i t is reported that the sulfosalicylic acid complex of beryllium is strongly absorbed by anion exchange resins at p H values above G
(4). Of the methods mentioned above for the separation of beryllium, those involving the use of (ethylenedinitril0)tetraacetic acid (EDTA) are probably the most important. They seem to furnish an excellent and fairly selective separation. They have, however, the disadvantage that the EDTA, which is used to elute the other elements, may constitute a serious obstacle if further separations of these elements are con-
Cation Exchange Separations of Beryllium
Type of Exchange Material Polystyrene resin (8mberlite IR-112)
Elements Separated from Al, Cu, Zn, Cd, Pb, Co, Xi, Th
Polystyrene resin (Dowex 50)
Cu, U, and Ca
Diallyl phosphate polymer Polystyrene resin Polystyrene resin
Ca, Sr, Cu, Zn, Al, Fe, Cd, Bi, Hg, Po, and lant hanides A1 A1 and Fe
Alginic acid
.41
Eluent O.5Y0EDTA at pH 3.7 for
other elements, dil. HCl for Be ( 8 ) 0.02 to 0.10M sulfosalicylic acid at pH 3.5 to 4.5 for Be ( 4)
542
ANALYTICAL CHEMISTRY
EDTA solns. for other cations, 0.5M XH4F or 1 . O M HNOI for Be ( 2 ) 0.01J.1 CaClz for Be ( 1 ) Oxalate of pH 4.4for A1 and Fe, dil. HC1 for Be ( 3 ) Be with dil. HNO,, A1 with more coned. acid ( 7 )
templated. The E D T A forms very stable complexes with almost all the commonly occurring cations, with the exception of the alkalies. and will thus interfere with subsequent separations and determinations of these cations. For this reason, a chromatographic separation using only hydrochloric acid as eluent, which can be readily removed and which does not interfere in many analyses, will very often have distinct advantages. EXPERIMENTAL
Tables of equilibrium distribution coefficients published previously (6) were used to evaluate approximately the most favorable hydrochloric acid concentration for the separation of beryllium from aluminum, trivalent iron, yttrium, trivalent cerium, and the rare earths. Single element elution curves Kere prepared for beryllium, aluminum, trivalent iron, yttrium, and trivalent cerium for some favorable hydrochloric acid concentrations. From these curves it was concluded that l.OLV hydrochloric acid is the most effective concentration for the separation of beryllium from aluminum, yttrium, trivalent cerium, and the rare earths. The exchange columns were prepared and the elution curves obtained by the procedure outlined previously (6),using columns of AG 50W-X8 resin, 100- to 200-mesh, 19 to 20 cm. in length, and 1.9 to 2.0 em. in diameter. Each column contained 20 & 0.1 grams of resin (oven dry weight) in the hydrogen form, and the flow rate was 3.5 + 0.5 ml. per minute. Subsequently, composite elution curves n-ere prepared for cation pairs using the same columns and procedures. Aliquots, 25-ml., of the eluate were collected using an automatic fraction collector and the amounts of the elements in the aliquots were determined by an appropriate analytical procedure. The composite elution curve for beryllium-trivalent iron for about 5 meq. of each of the cations is shown in Figure 1A. The iron peak with 2.5 meq. of iron is given on the same graph to show the effect of the amount of iron present. Aluminum, yttrium, trivalent cerium, zirconium, and thorium did not appear in the first 800 ml. of eluate when
Figure 1. A. B.
e ic.e
E- e
U O B
Experimental elution curves for beryllium-trivalent iron when 5 meq. of each are present
1.ON HCI as eluent; for comparison, elution p e a k of Fe(lll) when 2.5 meq. of Fez03 are present i s also shown 1.2N " 0 3 as eluent
about 5 meq. of these elements n-ere present. I t is obvious from Figure 1A that the separation of beryllium froin triralent iron is not satisfactory when larger amounts of iron are present. Increasing the size of the volumn to, say, 30 grams of resin would improve the separation, but this would require larger amounts of eluting agent and longer elution times. A better solution of the problem is suggested when one compares the equilibrium distribution coefficients of the cations of interest in hydrochloric and nitric acids. Some of the coefficients are shon-n in Table 11. These Kd values indicate that nitric acid compared to hydrochloric acid is a more promising eluting agent n hen Be is to be separated from larger amounts of Fe(II1). The separation factors for Be and the other elements are only very slightly lowered in nitric acid, so that their separations are not affected adversely. When an oxidimetric determination of the iron is planned, the nitric acid can be washed out of the columii with 100 ml. of distilled water and the iron then eluted with 2 X hydrochloric acid. From single element elution curves i t was established that 1.2N nitric acid was the most effective concentration for the elution and separation of beryllium from the cations of Table 11. Composite elution curves were prepared for beryllium-trivalent iron, beryllium-aluminum, beryllium-yttrium, and beryllium-trivalent cerium, using 1.2N nitric acid as eluent and the same chromatographic procedurw as described for the elution with 1.O.l' hydrochloric acid. The beryllium-trivalent iron curve is shown in Figure 1,B. Five milliequivalents of aluminum appeared in the eluate after 750 ml. of 1.2AVnitric acid had been passed through the column, while no yttrium or trivalent
Kd Values for Cations of Interest in Hydrochloric and Nitric Acids Be Fe A1 Y Ce Th Zr 13 3 35 5 60 8 144 6 264 8 2049 7250 14 8 73 7 79 3 174 4 245 6 1860 6500 1 2 5 HNO3 12 7 52 0 56 0 115 1 159 1 1500 3030 Table II.
Medium 1 S HC1 1'V HX08
Table 111. Analytical Procedures Used to Determine Amounts of Cation in Eluates
Element Be(I1) A l ( 111)
Fe(II1)
I-(111) and Ce(II1)
Procedure Gravimetrically as R e 0 after pptn. with ?;HIOH Gravimetrically as 8quinolinol complex i-olumetrically by dichromate titn. after reduction nith Ag reductor Gravimrtiically as 172;03 and CeO, after pptn. as oxalates
HC1 to elute yttrium, and 700 nil. to elute cerium. When nitric acid was used to elute the beryllium, the residual nitric acid was washed from thc column with 100 ml. of distilled water. This wash solution was discarded and the iron was subsequently eluted with 2 S hydrochloric acid. The extra step -cas not necessary in the case of the other cations. The analytical procedures used to determine the amounts of cation in the eluates are indicated in Tablc 111. The results of the senarations of the synthetic solutioiis ate presented in T Pble IT'. DISCUSSION ,
cerium could be detected in the first 1000 ml. of eluate when the same amounts of these elements were present. ANALYSIS O F SYNTHETIC MIXTURES
As a result of the work described above, a method for the separation of beryllium was developed and applied to synthetic solutions, prepared by memuring out and mixing amounts of standardized solutions of the different cations. These were absorbed on a resin column (same as described previously) from a solution not more than 0.3N in cations (hydrogen cation included). Beryllium was eluted either by passing 375 ml. of 1 . O N hydrochloric acid or 425 ml. of 1.2N nitric acid through the column at a flow rate of 3.5 k 0.5 ml. per minute. Then 300 ml. of 2147 HC1 mere used to elute trivalent iron, 500 ml. to elute aluminum, 500 ml. of 3N
The described methods provide a simple means for separating beryllium quantitatively from aluminum, trivalent iron, yttrium, and trivalent cerium. It takes about 2 hours to elute the beryllium from a column of the described size. Kot more than about 60 mg. of trivalent iron (90 mg. of Fez03) should be present when the column is of the described size and 1 . O N HCl is used as eluent for beryllium. I n a triplicate separation of 5 meq. of beryllium from the same amount of trivalent iron by using 375 ml. of 1 . O S HC1, one of the final B e 0 precipitates contained 0.4 mg. of Fez03, while the other two were free from iron (
