Ion Exchange Separation of Germanium THOMAS R. CABBELL,' ALLEN A. ORR,Z and JOHN R. HAYES The Pennsylvania State Universify, University Pork, Pa. ,The most widely used method for the separation of germanium from ions which interfere in its determination involves the distillation of the tetrachloride. While reliable, this method is time consuming. Extraction procedures usually result in incomplete recovery of the germanium. A separatory procedure is proposed which utilizes a mixed bed ion exchange column to provide a rapid separation of germanium from most of the ions known to interfere in the photometric determination. The method has been applied to both synthetic and naturally occurring samples. A complete determination may be accomplished in less than 3 hours.
T
HE DETERMIKATION Of gern'lanium by chemical means requires a satisfactory separatory method prior to the determinative step. The most popular method involves a distillation of the volatile tetrachloride (1,6). The procedure is somewhat time consuming, as frequently more than one distillation is required, and it fails to separate germanium from arsenic. Extraction procedures (6) usually result in incomplete recovery of the germanium (4). Cation exchange resins have been employed (3) to separate germanium from cationic interferences. However, if the phenylfluorone photometric method as modified by Luke and Campbell (4) is to be used for the determination, anionic substances are not retained on the resin bed and some of these [vanadium(V), molydenum (VI), and tungsten(V1) ] may interfere in the determination. Because of the limitations of the above methods, it was decided to investigate the applicability of a mixed resin bed containing a weak base resin and a strong acid cation exchange resin to the determination of germanium. APPARATUS AND REAGENTS
A Beckman Model B spectrophotometer with matched 1-cm. cells was used for all photometric measurements. A Beckman Model H-2 p H meter was used in conjunction with glass and Present address, West Virginia State College, Institute, W. Va. * Present address, Hercules Powder Co., Wilmington, Del. 1602
ANALYTICAL CHEMISTRY
saturated calomel electrpdes for all p H measurements. The ion exchange columns were constructed of 14-mm. glass tubing and were about 50 cm. long. They were equipped with a threeway stopcock at the bottom, one outlet being used to collect the effluent while the other was connected by means of Tygon tubing to a reservoir. The resin beds were supported by a 1-cm. glass-wool plug. Columns were filled by adding the mixed resins as a slurry. After draining to about resin bed level, water from the reservoir was admitted in order to backwash the bed, thus settling it and removing any trapped air bubbles. Samples and eluent were added from a separatory funnel fitted to the top of the column by a ground glass connection. Control of the flow rate was accomplished by adjustment of the stopcock a t the base of the column. A mixed resin bed, composed of the strongly acidic cation exchanger Nalcite HCR, 8% cross linkage, 50- to 100mesh, ana the weakly basic anion exchahger Amberlite IR-45 was employed. The resins were obtained from the manufacturers in the fully regenerated form. The Nalcite HCR was washed several times with 6N hydrochloric acid to free it from traces of iron before use. After thorough washing with water, 7 grams of the Kalcite H C R were mixed with 3 grams of Amberlite I R 4 5 and added tg the column. Fresh portions of resin were used for each separation. The reagents used were those described by Luke and Campbell (4). EXPERIMENTAL
The photometric method for the preparation of a standard curve and for the determination of germanium are given by Luke and Campbell (4). Appropriate size samples (ca. 200 to 400 bg. Ge) are dissolved, diluted to about 50 ml., and the pH is adjusted to 2.0. The samples are admitted to the resin bed and the column is washed with water, maintaining a flow rate of about 1 ml. per minute. Three 100-ml. portions of the effluent are collected in volumetric flasks and 10-ml. aliquots are subsequently analyzed by the photometric method. RESULTS A N D DISCUSSION
The efficacy of the ion exchange procedure for separating germanium from various ions known to interfere in the photometric method was tested by analyzing synthetic samples of varying composition. Varying amounts of in-
terfering ions were mixed with known amounts of standard germanium solution containing 300 pg. of Ge, the p H was adjusted, and the solution passed through the ion exchange column. Germanium is not retained on the column and is removed readily by washing with mater. The germanium is recovered in all cases in the first 200 ml. of effluent and usually in the first 100 ml. However, to provide a safety factor, 300 ml. of effluent are collected and tested for germanium. Results are summarized in Table I. Att'empts to separate germanium frpm titanium and from tungsten were unsuccessful. The titanium was incompletely retained on the ion exchange bed and caused interference (high results) in the photometric procedure. A bluish green precipitate formed a t the top of the resin bed in the attempted separation of tungsten and low results for germanium were obtained. I t is believed that the low results are caused by coprecipitation of the germanium. Although no attempt was made to det'ermine the niaximum or minimum concentrations of interferences from IThich germanium could be recovered, the described procedure proved capable of separating germanium from a t least 15 times its \yeight of interfering ion. Segative tests were obtained when reliable spot tests were made on the effluent in an effort to detect the presence of lead, nickel, silver, and arsenic. The absence of color from any source other than the phenylfluorone reagent in the last 100 nil. of effluent indicates the absence of iron, tin, chromium, antimony, and molybdenum since these ions interfere in the photometric analysis. Practical Application. To test the ion exchange procedure further the method was applied to the determination of germanium in coal. Since no coal samples of known germaniur content were available, synthetic samples were prepared. Cluley (2) has applied a pheng-lfluorone method to this analysis, in which the separation of germanium was effected by distillation of germanium tetrachloride after an ashing procedure with 2 grams of sodium carbonate. In the ion exchange method this large quantity of sodium carbonate exhausted the capacity of the resin and a smaller quantity was used. The samples were crushed to 100mesh size and air-dried. Samples of
0.3000 gram of the airdried coal were weighed into platinum crucibles and thoroughly mixed with 0.15 gram of sodium carbonate. The samples were then ashed a t 450" C. with occasional stirring. A final heating a t about 1000° C. completed the ashing process. After cooling, the fusion was dissolved in excess 6M hydrochloric acid. To the resulting solution, standard germanium solution equivalent to 0.300 mg. of germanium was added. After filtration the pH was adjusted to 2.0 by addition of sodium hydroxide solution. The sample was then admitted to the ion exchange column and the column rinsed with water. The collected effluent was analyzed for germanium by the procedure described above. Typical results are shown in Table 11. Qualitative spectrographic analysis of the coal samplcs revealed the presence of lead, silicon, magnesium, iron, aluminum, copper calcium, titanium, chromium, and sodium, but gave no evidence of the ,presence of germanium. Blank determinAions gave further evidence of the absence of germanium in the original coal samples. The efficiency of the separation was dependent on the acidity of the sample solutions and upon the quantity of sodium carbonate used. At pH values below 1.0 the column failed to retain the interfering ions completely. A t pH values much above 2.0 precipita-
Effect of Various Ions on Determination of Germanium (Each sample contained 0.300 mg. of Ge) Relative No. Error, Mg. Std.Dev., Mg. Interfering Ions Added Detns. Average Maximum % 0.~ .2 +0.002 5 +o .001 Sb(II1) 0.5 -0.006 As(II1) 9 -0.003 1.1 +0.013 5 each +O. 008 Mo(VI), Ca, Mg 6 each +O ,004 +0.009 0.6 1.4 +O. 004 rt0.018 Nil Bi plus 6 each 5 each Sn(IV), Zn, Fe(II1) Table
I.
E!&,
Table II. Analysis of Coal (All samdes contained 0.10% Ge) . I "
Sample Weight, Gram
Ash Content, yo
0,3000 0.3000
17.29 4.80
No. Detns. 5
Relative Std. Dev.,
Absolute Error, yo Average Maximum -0.001 -0.001
3
%
0.03 0.001
-0.004 -0.001
LITERATURE CITED
tion of hydroxides begins to occur and low results are obtained, probably because of coprecipitation of germanium. A p H of 2.0 was found to be satisfactory for the separation. Care must be exercised in the use of sodium carbonate to ensure that the capacity of the resin will not be exhausted. For the samples used here and the amount of resin employed, 0.15 gram of sodium carbonate was found to be satisfactory.
(1) Cluley, H. J., Analyst 76, 523 (1951). (2) Ibid., p. 535. (3) Klement, R., Sandmann, H., 2. anal. chem. 145. ~~- 325 . - 11955). ,- --, (4) Luke, C'. L., Campbell, M. E., A N A L . CHEM.28, 1273 (1956). (5) Payne, S. T., Analyst 77,278 (1952). (6) Schneider, W. A., Sandell, E. B., Miktochim. Acta 1954, 263.
RECEIVEDMay August 22, 1960.
16,
1960. Accepted
Radiochemical Precipitation Studies of Ra re-Ea rth Oxa Iates KENNETH G. BROADHEAD and HOWARD H. HEADY Reno Metallurgy Research Center, Bureau o f Mines,
b Radiochemical techniques are used to determine quantitatively the effect of temperature, digestion time, pH, rare-earth concentration, oxalic acid concentration, stirring, and the presence of other rare-earth ions on the oxalate precipitation of lanthanum, samarium, and yttrium. A Latin Square experi.mental design is used to evaluate some of the variables statistically. Precipitation losses range from near zero to about 7%, and mineral acid and rare-earth concentrations are the predominant factors affecting completeness of precipitation. Optimum conditions are given for precipitating rare-earth oxalates.
D
the past 20 years research aimed at developing more efficient separation and purification techniques applicable to the rare-earth URING
U. S.
Department o f the Inferior, Reno, Nev.
elements and yttrium has been extensive. Common to most of these procedures has been the use of oxalic acid to precipitate this group of elements selectively. However, this particular use of oxalic acid has a much earlier origin; its application in precipitating yttrium was first reported by Mosander (8) in 1843. Despite long and popular employment of this technique, only limited and somewhat conflicting data are available regarding the many factors affecting the degree of rare-earth oxalate precipitations. In comprehensive studies of the rareearth elements, Spencer (12) and Vickery (13) emphasized the advantages of using oxalic acid. Vickery also pointed out the depressant effect of excess oxalic acid upon the solubility of rare-earth oxalates in mineral acids. Sarver and Brinton (10) made a careful study of rare-earth oxalate solubilities
and observed that excess mineral acid is to be avoided, as the oxalate solubility is increased. In their discussion of separation methods, Quill and Rodden (9) suggest that rare-earth solutions should be precipitated with saturated oxalic acid and digested at 90' C., then digested several hours a t room temperature. The somewhat different procedure described by Schoeller and Powell (11) recommends that the oxalates are best precipitated from a cold solution; after an hour the solution is stirred vigorously while being heated to boiling, then cooled overnight. According to Boyd and, Hume ( I ) , Myers applied tracer techniques in attempting to determine the most suitable conditions for precipitating rareearth oxalates. Loss was minimum when the precipitation was performed a t room temperature. However, it was VOL. 32, NO. 12, NOVEMBER 1960
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