11). Chromium, which is not extracted Table II.
Spectrophotometric Determination o f Aluminum in Diverse Materials
A1 found, p.p.m.
Sample 2,5
ue.
A1
DlUS
Direct method5
Beryllium oxide, S B L No. 72- 1
72-2 72-3 72-4 72-5 96-1 96-2 96-6
TTOA separationa
Other methods
1
by TIOA under these conditions, is volatilized during evaporation of the HC1-HC104 aqueous phase. Applications. Table I1 shows some applications of the D D B method to the determination of aluminum in beryllium-containing materials. The New Brunswick Laboratories (Nf3L) beryllium oxide samples (0.3 gram) were dissolved in HC1O4 H2F2!and sample aliquots containing about 10 mg. of beryllium used for analysis. Spectrographic intensity ratios for aluminum in these samples were in better agreement with the DDIi, results than with the XBL nominal values.
+
695 400 221 108 92 225 125
703 i 9 391 6 230 f 2 108 i 2 93 i 5
i 12 i9 i3
+
It 3 f4
It 3 i2 27 f 8
... ... ...
792c 414c 252c
l05C 65. 202c 102c 1.F
15d
Each figure is mean and standard deviation of four results using two sample weights. Gravimetric. c Nominal value (New Brunswick Laboratories). d Spectrographic.
ACKNOWLEDGMENT
0
viz., Fe, Cr. Co, C u , Ti, V , IT-, U, and Th-although, with the exception of cobalt and vanadium, the color reactions are far less sensitive t h a n that of aluminum. Advantage may be taken of the inert nature of the aluminum-DDR and E D T A complexes to use EDT.4 as a masking agent for some interfering metals, since the aluminum-dye complex, once formed, is attacked only slowly by E D T A (Figure 3 ) . Some difficulty was experienced in overcoming the interference of iron and cobalt. The brown-colored iron-DDB comp1e.c is destroyed by EDT.4, but even small amounts of iron cause low
aluminum recoveries. Cobalt produces a cherry-red color ( e = 31,000 a t 540 mp) which is unaffected by EDTA. Ferrocyanide proved to be the only masking agent capable of minimizing the iron and cobalt interference, without affecting the aluminum color. Table I is a comprehensive study of interferences in the D D B metkod, using ferrocyanide and E D T A masking agents as described in the Recommended Procedure. Small quantities ot vanadium can be complex with hydrogen peroxide. Many of the interfering elements may be separated from aluminum by a rapid TIO,1 extraction from 8-11 HCI (Table
I t is a pleasure to acknowledge the assistance of Y. J. Farrar and 13. 11. Ryan in obtaining the experimental results. Spectrographic analyses were carried out by L. S. Dale. LITERATURE CITED
(1) Coates, E., Rigg, B., Trans. Farads!! Soc. 5 8 , 2058 (1962).
( 2 ) Florence, T. AI,, AKAL. CHEM.34. 496 (i962j. (3) Florence, T. AI., Izard, D. B., Anal. Chim. Acta 2 5 , 386 (1961). (4) Pakalns, P., Ibid., in press. ( 5 ) Pollock, E. N., Zopatti, L. P., Ibid.,
2 8 , 68 (1963). ( 6 ) Sandell:, E. B., “Colorimetric AIetal Analysis, 3rd ed., Interscience, Yew York, 1959. ( 7 ) Willard, H. H., Dean, J. A4., ANAL. CHEY.2 5 , 249 (1963).
RECEIVED for review December 18, 1964. Accepted February 15, 1965.
Anion Exchange Separations in Hydrobromic Acid-Organic Solvent Media JOHANN KORKISCH and ISIDOR HAZAN Analytical Institute, University of Vienna, IX. Wahringerstrasse 38, Ausfria
b The anion exchange behavior of several metal ions, including gallium, iron, uranium, and cobalt, toward the strongly basic anion exchanger Dowex 1, X 8 has been investigated, in mixtures consisting of 90% organic solvent-1 0% 4.5N hydrobromic acid. Measurements o f the distribution coefficients in these media show that for analytical separations, methanol i s the most suitable organic component of such a mixture. Under this condition gallium, indium, zinc, cadmium, lead, bismuth, and copper are retained b y the resin, whereas all other investigated elements-e.g., iron, alu-
minum, uranium, cobalt, the alkaline earth metals, etc.-pass into the effluent. Subsequent elution with water-1 0% 4.5N hydrobromic acid removes gallium, indium, and zinc, thus separating these metals from cadmium, lead, bismuth, and copper, which are further adsorbed on the resin. To avoid formation of bromine and ensure that all iron i s in the divalent oxidation state, an excess of ascorbic acid i s a d d e d to all solvent-hydrobromic acid mixtures. This separation principle i s applied to the determination of gallium in bauxite samples.
T
ion exhange behavior of copper, cobalt, zinc, and gallium in aqueous hydrobromic acid solutions has been investigated by Herber and Irvine who showed that anion exchange seliarations in such media offer no advantages over those in hydrochloric acid solutions under comparable experimental conditions. Vsing 0.3 to 0.5S hydrobromic acid as eluent Fritz and Garralda ( 1 ) separated mercury(II), bismuth (111), and cadmium(I1) from most othpr metal ions on the cation exchanger Dowex 50 W X8. I n 0.1 to 0.6.V acid these elements can be separated from each ot’her and from other metal ions. HE
(@j
VOL. 37, NO. 6, M A Y 1965
707
Until now no investigations have, however, been carried out as to the applicability of organic solvents containing hydrobromic acid for separating metal ions by either cation or anion exchange. For this reason the present study was carried out to investigate the anion exchange behavior of several metal ions in hydrobromic acid media containing water and organic solvents such as aliphatic alcohols, acetone, tetrahydrofuran, dioxan, 2-methoxy-lethanol, 2-ethoxy-1-ethanol, and acetic acid. While behavior of the elements in pure aqueous hydrobromic acid media does not deviate appreciably from that observed in hydrochloric acid systems under comparable conditions, their adsorption characteristics in organic solvent-hydrobromic acid mixtures are in some cases different and thus offer separation possibilities which do not exist in hydrochloric acid solutions. Thus in methanol medium it is possible to separate gallium from large amounts of iron and uranium, which is impossible in aqueous hydrochloric acid media of any acidity if these two elements are not previously reduced to their bi- and quadrivalent states, respectively. For this purpose rather strong reducing agents have to be employed to reduce these metal ions in the acidity region (3 to 12.V) in which gallium is preferentially retained by an anion exchange resin ( 9 ) . Also, reoxidation by oxygen-especially of quadrivalent uranium -will occur, so that clean-cut separations cannot easily be performed. I n hydrobromic acid-methanol solution, because the bromide ion is readily oxidized to elemental bromine, ferric ion is reduced instantaneously to ferrous (but not' uranyl to uranous ion) so that after removal of the liberated bromine by an excess of ascorbic acid the separation can be performed without interference caused by a reoxidation to ferric ion. On the basis of these observations, as well as the fact that from methanolhydrobromic acid solution only gallium and a few other elements are adsorbed on the resin, a method for the determination of gallium in bauxite samples was developed. This cannot be carried out using the separat'ion principle earlier described by Korkisch and Hazan (4) employing acetone- and 2-methoxy1-ethanol-hydrochloric acid media for the sequential separation of gallium, indium, and aluminum, because under these conditions the iron behaves exactly like gallium. EXPERIMENTAL
Reagents. The resin used for the separation experiments and measurement of the distribution coefficients was Dowex 1, X8 (100- to 200-mesh; 708 *
ANALYTICAL CHEMISTRY
bromide form). The bromide form of the exchanger was prepared from the chloride form by treatment with a concentrated solution of sodium carbonate until all the chloride ions had been removed. The resin was then washed successively with aqueous hydrobromic acid, water, and finally methanol, followed by drying under reduced pressure. Before being transferred to the ion exchange columns the resin was soaked in 90% met~hanol-lO~c 4 . 5 5 hydrobromic acid. For the determination of the batch distribution coefficients the air-dried form of the resin was used. Standard solutions of uranium, gallium, iron, aluminum, and many other elements were prepared by dissolving the oxides, carbonates, or hydroxides in 9N hydrobromic acid. Mercury was not studied because H g l h is reduced to insoluble Hg213r2and metallic mercury on addition of ascorbic acid. Ailso used were t'he chemically pure solvents : methanol, ethanol (EtOH), 1-propanol (n-P), 2-propanol (i-P), 1-butanol (n-n), 2-methyl-1-propanol (i-I3), acetone (A), tetrahydrofuran (THF), dioxan (D), 2-methoxy-1-ethanol (LIE) (methyl glycol), 2-et'hoxy-1-ethanol (EE) (ethyl glycol) and acetic acid (-kc). The eluting solution was 90 volume % methanol-10 volume % 4.5N hydrobromic acid. For reduction purposes pure ascorbic acid (Wiener Heilmittelwerke) was used. Apparatus. I n the macro experiments the resin bed in the columns had a length of 80 em. and a diameter of 1.0 em. I n the micro experiments (determination of the distribution coefficients in aqueous and methanol-hydrobromic acid solutions) 7.0 X 0.5 em. columns containing 1 gram of the resin were employed. Determination of Distribution Coefficients. The weight distribution coefficients of the investigated elements were determined in media consisting of 90% organic solvent10% 4.5.V hydrobromic acid using the batch equilibrium method (S). In the hydrobromic acid-water-methanol mixtures the distribution coefficient's were determined by the column method, because these media were ultimately used for the separations. For this purpose 500 wg, of the element in question dissolved in 2 ml. of a mixt'ure consisting of 90YG water or methanol10% 4 . 5 5 hydrobromic acid, plus a few crystals of ascorbic acid, was passed through a small column (see above) a t a rate of 0.5 ml. per minute, followed by washing with a mixture of the same composition. I3y determining the metal ion content in small fractions of the effluent the elution curve was constructed, whereby the volume of eluent, V , is ohtained which has passed through the column to elute the masimum of the elution 1)eak. From this value t,he distrihution coefficient, K d , was calculated using the relationship developed by Mayer and Tornpkins (10).
I' =
Kd X (mass of dry resin in the column)
Determination of Metal Ions. The various metal ions in the corresponding eluate fractions and filtrates (after batch equilibrations) were determined spectrophotometrically or titrimetrically with 0.01M or 0.001M solutions of EI)TAI (disodium salt) in the presence of suitable indicators. Procedure for Separation of Gallium from Iron, Aluminum, Uranium, and Other Elements. PRETREATMENT OF RESINBED. For this purpose 100 ml. of the eluting solution were passed through the column (80 x 1.0 em.). SORPTIONSTEP. Two milliliters of 4.51V hydrobromic acid containing known amounts of gallium and thz metal ions from which gallium was to be separated was diluted with methanol to 20 nil. and excess of bromine which is present especially if the solution contained iron is reduced by addition of some solid ascorbic acid (about 100 to 200 mg. per 20 ml. of sorption solution are usually sufficient or until the color due to bromine is discharged). This solution (over-all acidity = 0 . 4 5 s hydrobromic acid) was then passed through the resin column a t a flow rate of about 0.4 ml. per minute. If for solubility reasons (large amounts of aluminum and iron) the volume of this sorption solution has to be increased to bring all the salt,s into solution, this can be done without aftecting the separation. Thus even from 100 nil. of above hydrobroniic acid-methanol misture, adsorption and separation of gallium from the other elements were complete. During this sorption step gallium together with indium, bismuth, lead, zinc, cadmium, and copper was strongly adsorbed on the resin, whereas all other investigated elements passed into the effluent and 5-nil. fractions were collected and analyzed for the metal ion in question. WASHING.Alfter the sorption solution had passed, the resin was washed portionwise with the eluting solution containing some ascorbic acid until the element to be separated from gallium was eluted completely. Each 5-ml. fraction of this eluate was separately analyzed for its metal ion content. ELVTION. The gallium was then eluted by passing 100 nil. of aqueous 0.45.V hydrobromic acid through the resin bed. During this process only indium and zinc accompanied the gallium into the eluate, whereas lead, bismuth, copper, and cadmium remained furt'her adsorbed on the resin. Determination of Gallium in Eluate. W t h o u t preliminary evaporation gallium in the eluate vias determined by E D T A titration. Analysis of Bauxite Samples. One to 2 grams of the finely ground sample was treated with about 50 ml. of a 1 to 1 mixture of 48% hydrobromic acid and concentrated hydrofluoric acid (polyethylene beaker). The mixture was evaporated to drynez\ q on a water bath, the residue was taken up in about 10 ml. of concentrated hydrofluoric acid, and subsequently the solution was taken to dryness. T o the residue, 20 t o 30 nil. of 487c hydro-
bromic acid solution and enough boric acid were added to mask fluoride ions. After evaporation to dryness excess of boric acid was removed by addition of methanol, which was subsequently boiled off. The solution was then evalwrated t o dryness, the residue was dissolved in a suitable volume of the eluting solution, and the solution (after addition of some solid ascorbic acid) was passed through the pretreated resin bed as described above. If aluminum bromide precipitates on addition of the methanol-hydrobromic acid mixture, it is either filtered off and the preciliitate is washed with 10 to 20 ml. of the eluting solution or the solution is diluted with more of the eluting solution. The insoluble excess of aluminum bromide thus removed never contained any detectable gallium.
Table l.
Elution Characteristics of Metal Ions in 90% Water or Methanol-l 0% 4.5N Hydrobromic Acid Mixtures (0.5-mg. load on 7 . 0 X 0 . 5 cm. resin column)
Water, ml. Breakthrough Elution Iid vol. vol. 1 2 5 2 1 2 5 2 1 2 5 2 Precipitation on resin 3 8 >400 > 1000 1 4 5 2 1 ~
h!etal ion 1lnlII) CJII) Sr(I1) Cu(I1) Zn(I1) Cd(I1)
Kd 2 2
2
5 5
>600 2
1(IJ,1
Zr(I\ I
2 1
1 5
3 8
2
3 2.3
1
4 5
2 1
6 5
3 9
Methanol, ml. BreakElution through vol. vol. 0 75 3 0 75 3 0 75 3
0 75
3 75
0 75 1 25
2 75 4 5
RESULTS A N D DISCUSSION
Methanol - Water - Hydrobromic Acid System. Determinations of the distribution coefficients of the various metal ions using the column method gave the elution characteristics recorded in Table I . The adsorption of the elements from pure aqueous 0 . 4 5 5 hydrobromic acid follows the pattern previously observed in hydrochloric acid solutions of comparable acidity (8). Exceptional behavior in the hydrobromic acid medium is, hovvever, shown by lead, which has a stronger adsorption by about one order of magnitude than in hydrochloric acid solution. This effect could be used to selmrate lead from all other elements listed in Table I escept cadmium and bismuth. In the methanol--hydrobromic acid mixture remarkable diffrrences between the adsorption behavior of some elements with respect to their adsorption from hydrochloric acid solutions exist. Thus uranium, which has a Kd value of about 1000 in niet,hanol-hydrochloric acid medium ( 6 ) , is practically nonadsorbable from the hydrobromic acid medium; a similar behavior is shown by cobalt, which has a distribution coefficient of about 50 in methanolhydrochloric acid solution. Further excaeptional behavior is shown by gallium and indium, which have lower Kd values in hydrobromic acid than in hydrochloric acid media ( 5 ) . 'Table I s h o w that zinc, vadmium, gallium, indium, lead, copper, and bismuth as a group can be separated completely from all other elements listed. Subsequent elution of zinc, gallium, and indium using 0.45S aqueous hydrobromic acid separates these elements from cadmium, lead, copper, and bismuth, which are further retained by the w i n . .\ddition of ascorbic acid causes c o l q w to be reduced, which is then retained by the resin and cannot be removed by clution with 0.45.V hydrobromic acid. 'The adsorption be-
Fe(I1) C O ( I1j Si(I1 j
2.3
1.5 1
6.5
4 3.5
havior of thorium from methanol medium as well as from the other hydrobromic acid-organic solvent mixtures (see below) was not investigated because of the very low solubility of its bromide in this medium. Molybdenum is partly retained as a molybdenum blue compound and part passes into the effluent, as do the other practically nonadsorbable elements. Investigations as to the variation of the Kd values of the various elements with changing concentration of hydrobromic acid showed that as in hydrochloric acid media the Kd values increased with an increase in acid concentration, without, however, appreciably changing the separation factors of the metal ions. Likewise a decrease or increase of the methanol concentration a t the constant over-all acidity of 0.45N hydrobromic acid caused the Kd values to change correspondingly, as in the case of hydrochloric acid solutions-Le., the adsorption increases with increasing methanol content of the mixtures when the adsorption of the stronger adsorbed ele-
Table II.
Sample so.
1 2
ments is concerned, whereas in the case of the practically nonadsorbable elrments no change of the Kd values, proceding from pure aqueous t o 90% methanol solutions, was observed (see Table I). The effect of concentration of metal ions on their Kd values was similar to that observed in hydrochloric acid media-decreasing adsorption with increase in metal ion concentration. The same behavior with respect to the influence of acidity, organic solvent concentration, and concentration of metal ions on the adsorption was observed in all the other media investigated. On the basis of all these results a series of column operations was carried out to determine wbether gallium can he separated quantit tively from other elements, especial1 from iron, uranium, and aluminum. This separation is difficult, if not completely iml)ossible, in other media, particularly if these elements are present in great excess. From the results of experiments using the working procedure described above, it is evident (see Table 11) that
4
Determination of Gallium in Bauxite Samples
Composition of sample, 7G SiOz (3.6), Fe203 (15j, CaO (
