spectrographically. Methods similar to that described for the analysis of thorium (8, 9) could be applied readily for determination of impurities in the parts per million range. I n the samples previously cited, at least one other rare earth was found to be present as a trace impurity in the commercial starting material. In preliminary experiments, the rare earths were adsorbed by an anion exchange resin from mixtures of nitric acid and a number of miscible organic solvents. Distribution coefficients increased when the added solvent was a higher alcohol, acetone, cellosolve (2ethoxyethanol) , dioxane, tetrahydrofuran, or an alcohol-ester mixture. Methanol was chosen primarily because the solubility of rare earth nitrates was extremely good. Nitric acid solutions of up to 175 mg. per ml. of rare earth oxides did not precipitate when methanol of any proportion was added. Only one of the other solvents tested, Cellosolve, was satisfactory in this regard.
ACKNOWLEDGMENT
The authors appreciate the counsel and encouragement given by several members of the laboratory. We are
indebted to John Hines for radiochemical analyses of the rare earth activities and for isolation of the promethium and to Morris Wahlgren for neutron activation analyses of the neodymium. LITERATURE CITED
(1) Buchanan, R. F., Faris, J. P., Conf.
on Use of Radioisoto es in Ph . Sci. and Industry, Rept. dCC/173, 6openhagen, Denmark, 1960. (2) Bunney, L. R., Ballou, N. E., Pascual, J., Foti, S., ANAL.CHEM.31,324 (1959). (3) Choppin, G. R., Silva, R. J., J.
Inorg. Nucl. Chem. 3, 153 (1956). (4) Danon, J., Ibid., 7, 422 (1958). (5) Edge, R. A., J. Chromatog. 5, 539 (1961). (6) Ibid., p. 526. (7) Ibid., 6, 452 (1961). (8) Faris, J. P., .4ppl. Specfr. 12, 157 (1958).
(9) Faris, J. P., Buchanan, R. F., Nucl. Reactor Tech. TID-7606, p. 185, 4th
Conference, Gatlinburg, Tenn., October 1960, Oak Ridge National Laboratory. (10) Fred, M., Nachtrieb, N. H., Tomkins, F. s., J . Opt. SOC.Am. 37, 279 I 1 947). \ - - - . I .
(11) Fritz, J. S., Pietrzyk, D. J., Talanta 8 , 143 (1961). (12) Higgins, C. E., Baldwin, W. H., U. S. Atomic Energy Comm., Oak Ridge Nat. Lab. Rept. ORNL 894 (19.51
\ - - - - I .
).
(13) Huffman, E. H., Oswalt, R. L., J. Am. Chem. SOC.72, 3323 (1950). (14) Hulet, E. K., Gutmacher, R. G.,
Coops, M. S., J . Inorg. Nucl. Chem. 17, 350 (1961). (15) Ichikawa, F., Bull. Chem. SOC.Japan 34, 183 (1961). (16) James, D. B., Powell, J. E., Spedding, F. H., J. Inorg. Nucl. Chem. 19, 133 (1961). (17) Korkisch, J., Tera, F., ANAL. CHEW 33, 1265 (1961). (18) Kraus, K. A., Nehon, F., Am. SOC. Testzng Mater., Spec. Tech. Publ. No. 195, p. 27, 1958. (19) Marcua, Y., Abrahamer, I., Israel Atomic Energy Comm. Rept. IA-608 (1961). (20) Marcus, Y., Nelson, F., J . Phys. Chem. 63, 77 (1959). (21) Minczewski, J., Dybcsynski, R., J . Chromatog. 7, 98 (1962). (22) Powell, J. E., “The Rare Earths,” p. 55, F. H. S edding and A. H. Daane, eds., Wiley, ew York, 1961. (23) “Rare Earth Elements,” English transl., p. 97, OTS 60-21172, originally Dublished bv Acad. of Sci.. U.S.S.R.. 1959. (24) Stevenson, P. C., Nervik, W. E., “The Radiochemistry of the Rare Earths, Scandium, Yttrium, and Actinium,” Natl. Acad. Sci.-Natl. Research Council, Nuclear Science Series NAS-NS-3020 (1961). (25) Suds, J. P., Jr., Choppin, G. R., J . Inorg. Nucl. Chem. 4, 62 (1957). (26) Tera, F., Xorkisch, J., Anal. Chim. Acta 25, 222 (1961). (27) Wilkins, D. H., Smith, G. E., Talanta 8, 138 (1961).
k
RECEIVEDfor review March 7, 1962. Accepted May 31, 1962. Based on work performed under the auspices of the U. S. Atomic Energy Commission.
Cation Exchange Separation of Vanadium from Metal Ions JAMES S. FRITZ and JANET E. ABBINK Institute of Atomic Research and Department of Chemistry, Iowa State University, Arnes, Iowa
b Vanadium(1V) or (V) can be separated from other metal ions by elution from a cation exchange column with dilute acid containing 1% or less hydrogen peroxide. Vanadium is quantitatively removed as a vanadium(V)hydrogen peroxide complex; the other metal ions are eluted later with stronger acids. Separations of vanadium(lV) or (V) from 25 metal ions are reported. Varying ratios of vanadium(V) to iron(ll1) up to 1 : 100 are separated.
A
T THE outset, an attempt was made
to separate vanadium(V) from various metal cations, using a cation exchange column in the hydrogen form. Vanadium(V) exists either as anionic VOs- or as a cationic form such w, V02+, which can be eluted readily from a cation column with dilute acid. Experiments showed that while the
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ANALYTICAL CHEMISTRY
bulk of vanadium(V) is eluted readily from a cation exchange column, some vanadium is apparently reduced by the column to VO+s, which is not eluted. Vanadium, in the form of its hydrogen peroxide complex (4), passes readily through a hydrogen-form cation exchange column. Furthermore, any vanadium(1V) is oxidized by hydrogen peroxide to the vanadium(V)-hydrogen peroxide complex and is also eluted from the column. Alimarin and Medvedeva (1) developed an ion exchange method in which molybdenum is eluted from a cation exchange column by a dilute solution of hydrogen peroxide. They noted that vanadium and tungsten are eluted along with molybdenum. Ryabchikov and Bukhtiarov (S) found that titanium and tungsten form complexes with hydrogen peroxide at p H 5; a cation exchange column retains the titanium complex but the tungsten
complex passes quantitatively through the column. The purpose of the present work is to study the ion exchange separation of vanadium from other metal ions by elution of the vanadium from a cation exchange column with an acidic solution of hydrogen peroxide. Although molybdenum and tungsten interfere in this separation, vanadium can be separated from titanium, iron, and many other metal ions. EXPERIMENTAL
Ion Exchange Resin. Dowex 50WX8, 100- to aOO-mesh, is used in the hydrogen form. One pound of resin is purified by placing it in a large column and backwaahing with distilled water to remove the fine particles. Then it is washed with 3 liters of 10% ammonium citrate followed by 3 liters of 3M HCl. It is washed with water until the eluent gives a negative chloride test with AgNOs.
Ion Exchange Columns. Conventional ion exchange columns 1.2 cm. in diameter are used unless otherwise stated. A slurry of resin is added until a resin bed of 6 cm. is reached. Eluent is added dropwise from a 125-ml. cylindrical separatory funnel which is attached to the top of the ion exchange column through a one-holed rubber stopper. Metal Ion Solutions. Except for the ones listed, all metal ion solutions used are 0.05M solutions of the nitrate or perchlorate salt. Vanadium(1V) is a 0.05M VOS04 solution. Vanadium(V) solution is made by dissolving 0.2274 gram of VZOSin water and one pellet of NaOH. Heating is sometimes needed to effect solution. Sufficient acid is added to make the solution 0.1M in H2S04 or HClOa. The volume is adjusted to 50 ml. This solution is stable for onlv 1 or 2 days. Chromium(II1) is a 0.05M solution of CrC13. TitaniumUV) is a 0.05M solution made by 'dissolving TiClr in concentrated H2S04 and evaporating to fumes of H.2804. The solution is diluted to volume with the total concentration of H2S04being 1%. Zirconium(1V) is a 0.05M solution of ZrOC12 in 10% HC1. The Zr+4 salt is dissolved in the concentrated HC1 and then diluted t o volume. Procedure for Separation. Place on the column 10 ml. of a mixture of 0.25 mmole of vanadium(V) and 0.25 mmole of a second metal ion. The sample should be approximately 0.1M in acid. Elute the vanadium first with 50 ml. of 0.01M H&04 or HCIOI containing 1% hydrogen peroxide. Collect the effluent; before analysis remove the hydrogen peroxide by boiling for about 15 minutes or until the disappearance of the yellowish-brown color of the vanadium(V)-hydrogen peroxide complex. Add sufficient ascorbic acid to reduce to vanadium(1V). Titrate the vanadium with EDTA as outlined in Table I. Strip the other metal ion with the amount of eluent indicated in Table 11. Evaporate the samples almost to dryness and dilute to approximately 100 ml. for titration. With the exception of H g f 2 Crf4, Ag+, and U02+2,analyze with EDTA according to conditions given in Table I. Determine Ag+ by the Volhard method, Cr +6 by oxidation-reduction titration with ferrous iron, and U02+2 by standard oxidation-reduction method of titrating' with (NH4)2Ce(S04)4 after passing the U02+2 through a lead reductor. Titrate Hg+2 with 0.05M thioglycerol using Thio Michler's ketone as an indicator after adjusting the pH to 5 with pyridine. With mixtures where the other metal ion present forms an insoluble sulfate salt' use HC104 instead of H2S04 in the eluent and also to acidify the vanadium solution. HC1O4 is used with Ag +,P b +2, U02+2, and Zr +4. If titanium(1V) is present, dilute the sample with water before adding it to the column so that the pH is 1.2 or above (free sulfuric acid concentration not greater than 0.02M). This is
Table 1.
Metal ions Co+Z Znf2 Dy +;, Y +3, La+3, Pb +2
Conditions for EDTA Titrations
Titration method EDTA-(D) EDTA-( D)
Indicator NAS NAS
pH 6 6
sc +3
NAS EDTA-( D ) EDTA-( D) NAS EDTA-(D) XOr Mg+Z, Mn+2, Ca+2 Erio T EDTA-( D) Zr + 4 EDTA-( B)Bi XOr V+', Nif2, Ga+3 EDTA-( B)Zn NAS Fe +3 EDTA-( B)Zn NAS Cd f2, I n +a EDTA-( B)Cu NAS Al+3 EDTA-( B)CU NAS Ti+' (3 drops of HzOZ) EDTA-( B)CU NAS NAS = Naphthyl Azoxine S (g); XOr = Xylenol Orange; ( D ) direct titration (B) back titration cu+:' Bi
to reduce the H2S04 concentration, because too high a HzS04 concentration causes part of the titanium(1V) to be washed through with the V+5. RESULTS
The initial study revealed that either vanadium(1V) or vanadium(V) can be quantitatively eluted from a 6- or 16-cm. cation ion exchange column, by dilute acidic hydrogen peroxide. The eluent used contained '/a to 1% hydrogen peroxide in approximately 0.01M sulfuric or perchloric acid. A 6-cm. column was satisfactory for the separation of vanadium from approximately an equal molar quantity of another metal ion. Vanadium is quantitatively eluted from either a 6- or 16-cm. column by 50 ml. of eluent. I n the separation method used, vanadium is added to the column either as vanadium(1V) or vanadium(V). Much of the vanadium(V) passes directly through the column but a part is reduced by the ion exchange resin to vanadium(1V). However, the valence state of vanadium is immaterial because hydrogen peroxide converts either form to the hydrogen peroxide complex, which is then eluted from the column. Neither the dilute acid nor the hydrogen peroxide of the eluent has any effect on the other metal cations which are retained on the cation exchange column. Individual synthetic mixtures of vanadium(V) and another metal ion were separated by this procedure and the vanadium was titrated with EDTA (see Table I). I n each case 50 ml. of 1% hydrogen peroxide-0.01M sulfuric or perchloric acid was used to elute the vanadium. Then the other metal ion was eluted from the column as outlined in Table I1 and determined quantitatively (see Table I). Vanadium was successfully separated from each of the following metal ions: Ag+, Al+3, Bi+3, Cd+2, C O + ~Cr+3, , CufZ, Dy+3, Fe+3, Ga+3, Hg+2, In+s, La+3, Mg+2,
4
5
1 to 3 10 2
Table 11.
6
5.5 5 6.4
Ga+3,In+3, UOZ + I Pb +2 Ag+l
Hg + 2 Cr +a
Ti +( Zr +'
NHaOH Pyridine Acetate Acetate
Pyridine HAC-NaAc, XaOH 4to5 Erio T = Eriochrome Black T
Eluent Metal ions Co+*,Fe+3, Ni+2 D Y + ~Y, +3 La+3,Al+3,Znf2, Bi +* Mg+2, Mn+2 Ca+Z, Cd;2 Sc +3
c u +z
Buffer Pyridine Pyridine, Cu +? added Acetate Acetate
Used for Metal Ions
Eluent 100 ml. of 2M HCI 200 ml. of 3M HN03 150 ml. of 3M HYOs
200 ml. of lllf HC1 200 ml. of 1M HCl 200 ml. of 2M HC1 100 ml. of 2M "0, 200 ml. of 2M HC1
300 ml. of 2M HCl 100 ml. of 3M HN03 50 ml. of 0.1M HBr 150 ml. of 3M H2SOI 100 ml. of 1.OM HClOi 4- 1% HzOz 500 ml. of 4M HC1
Mn+2, Pb+2, S C + ~T, h + 4 , 'l'i+4, UOz+2, Y+3, Zn+2, and Zr+4. The average recovery of vanadium and other metals for 122 individual analyses was 100.0% with a standard deviation of S0.013 ml. I n most cases 5 or 6 ml. of titrant was required. Although titanium(1V) also forms a complex with hydrogen peroxide, it remains in a rather tight band near the top of the column so long as the acidity is low. Thus titanium can be quantitatively separated from vanadium. By increasing the acid strength of the eluent to 0.5M or 1M in the presence of peroxide, titanium is quantitatively eluted from the column. A threecomponent separation of vanadium(\') titanium(IV), and iron(II1) v,as effected. First vanadium(V) was removed with 50 ml. of 0.01111 HC104 with 1% Hz02 and then the titanium (IV) was eluted with 100 ml. of 1.OM HClO4 with 1% H202. Finally, iron (111) was eluted with 100 ml. of 261 VOL. 34, NO. 9, AUGUST 1962
1081
Table 111.
Quantitative Separations of Vanadium from Higher Ratios of Other Metal Ions on Cation Exchange Columns
Metal ione V*: Fe+a V +I: Fe +* V* :Fe +* V*: Fe +I V+I:Fe+’ V *:Fe +* V*:CU+’ V+I:Cu+’
Ratio V*:M+” 1:lO 1:25 1:50 1:50 1:loo 1:loo 1:loo 1:loo
Co!umn
M1.EDTA to titrate V+L
me,
em. 1.2 X 1.2 X 2.2 X 2.2 X 2.2 X 2.2 X 1.2 X 1.2X
HCl. Although i t was not attempted, it appears that titanium(1V) can be separated from other tri- or quadrivalent metal ions. Separation of titanium(1V) from divalent ions appears doubtful because divalent ions are a t least partly eluted by 0.5 to 1M acid. In Table 111 the results of separations are reported in which a high ratio
6 16 6 6 6 6 16 16
Theory
Actual
1.02 0.98 2.00 2.00 2.00 2.00 0.78 0.78
1.02 0.99 1.99 2.00 1.99 1.99 0.78 0.77
Difference f0.00 $0.01 -0.01 10.00 -0.01 -0.01
column. This difficulty waa overcome by using wider diameter columns. Following the separation of vanadium, iron(II1) or copper(I1) was eluted with 100 to 200 ml. of 3M nitric acid or 2M hydrochloric acid. Although the results are not reported in Table 111, the recovery of iron(II1) or copper(I1) was quantitative. LITERATURE CITED
f0.00 -0.01
of the other metal ion to vanadium is used. Iron(II1) was selected as a typical trivalent metal ion and copper (11) as a typical divalent metal ion. The separation of vanadium from large amounts of copper went very smoothly. With large amounts of iron, some difficulty was originally encountered, caused by bubbling of the
(1) Alimarin, I. P., Medvedeva, A. M., Zavdsk. Lab. 21, 1416 (1955).
(2) Fritz, J. S., Abbink, J. E., Payne, M. A., ANAL. CHEM.33, 1381 (1961). (3) Ryabchikov, D. I., Bukhtiarov V. E., Zh. Analit. Khim. 15, 242 (1960).
(4) Sidqwick, N. V.,
“The Chyfniod Elements and Their Compounds, Vol. I, p. 812, Oxford Univ. Press, London, 1950.
RECEIVEDfor review February 19, 1962. Accepted June 4, 1962. Work performed in the Am- Laboratory of the U. S. Atomic Energy Commission.
A Highly Specific Method of Separating Cesium by Ion Exchange on Thallous Phosphotungstate HENRI
L.
CARON
Woods Hole Oceanographic Institution, Woods Hole, Mass.
T. T. SUGIHARA leppson Chemistry laboratory, Clark University, Worcester, Mass. ,Thallous phosphotungstate (TPT) is a highly specific cation exchanger for cesium. The heteropoly salt is converted into a form suitable for column use by mixing with paper pulp. The affinity of several monovalent ions for the exchanger is in the order Cs Ag Rb K. A simple method for obtaining essentially quantitatively a cesium fraction of high purity from virtually any starting solution is based on absorption on TPT, washing with 0.005M thallous nitrate which removes contaminants, and eluting cesium with 0.15M thallous nitrate. A maior advantage over other methods using synthetic ,inorganic exchangers is that the final cesium fraction is obtained free of ammonium ion, a frequently used eluent which is troublesome to remove. The column retention capacity of TPT is 0.5, 0.3, and 0.1 meq. per gram for cesium, rubidium! and potassium, respectively.
>
I
>>
>
ion exchangers have received increased attention recently (1, 8, 1.2) because of their high resistance to radiation and their very efNORGANIC
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ANALYTICAL CHEMISTRY
ficient separation of alkali metal ions. Naturally occurring exchangers such as the zeolites have been known for a very long time, but the recent work has been with synthetic exchangers ( I , 4, 6, 8-1 3). A very large separation factor, K F / K Z b (where the K J s are equilibrium distribution constants between exchanger and solution), can be obtained ( l a ) with the ammonium salts of heteropoly acids, notably ammonium Qualphosphomolybdate (APM) . itatively similar results were obtained for thallous phosphomolybdate (TPM) by Hara (6). Under appropriaE conditions, exchangers of this type should be very specific for cesium in the presence of high concentrations of rubidium and other alkali metal ions. In fact, Hara was able to recover tracer Csla7 nearly quantitatively from 2 liters of sea water-that is, from a 0.5M sodium chloride solution. I n Hara’s work no attempt waa made to remove the cesium that had been adsorbed on TPM. I n other work (1, 4, 8-13) the synthetic inorganic ion exchangers have been used in column form and alkali metals have
been adsorbed and subsequently eluted, the usual eluent being ammonium salt of rather high concentration (>3M in general). Nitric acid is sometimes used. Large amounts of ammonium ion in the effluent cause dficulty in a radiochemical analysis. Ammonium ion interferes in essentially all gravimetric determinations of cesium (5). With exchangers of the APM type the presence of ammonium ion in the cesium fraction is inevitable, even though the eluent is some other reagent such as concentrated acid. The ammonium ion can be removed, but the necessary operations are time-consuming and unpleasant. The use of T P M or thallous salt of another heteropoly acid in column form and elution with a monovalent ion such as silver or thallium(1) appeared much more desirable. These ions are easily removed from a cesium fraction. A thallous salt of a heteropoly acid was also expected to be more specific for cesium than APM. The order of decreasing adsorbability on APM (1.2) is Cs = T 1 > R b > Ag > K = NH, > Na. Thus, if the same order is pre-
