er
olumetric
niu
GEORGE J. ABEL, Jr. Central Research Laboratories, American Smelting and Refining Co., South Plainfield,
b The method for the iodimetric titration of germanium is described. By simple distillation from a hydrochloric acid solution, macro amounts of germanium are separated from interfering elements. The germanium distillate is reduced by hypophosphite to divalent germanium and titrated iodimetrically. The method is simple and the resulfs are precise and accurate. has achiered prominence in recent years because of iss extensive application in the field of electronics. To meet the growing demand, germanium concentrates are being produced from various byproducts and ores. The difficulty in determining germanium in these concentrates by available methods led to development of a procedure which can be used to determine germanium accurately and rapidly as a major constituent. The results of the investigation are reported below. Several volumetric methods have been reported. The mannitol complex of GeIV has been used as the basis for an alkalimetric (3, 7’-9) and an iodometric (9) titration. Quinolates of molybdogermanic acid have been used for the iodometric ( I ) , vanadometric (6), and alkalimetric (6) determination of germanium. Thiodigermanates have been titrated iodometrically (IO). Reduction of Ge” to Ge“ with zinc in a sulfuric acid solution and titration with potassium permanganate were reported to give approximate results ( 2 ) . Errors were probably due to the formation of Gel&. Reduction of Ce”’ t o Gel1 by sodium hypophosphite and titration with iodine were reported by Ivanov-Emin (4) to give quantitative results; however, the method is cumbersome in the presence of various elements. The following modifications of this method have produced a simple and accurate volumetric procedure for the determination of germanium. ERMANIUM
The germanium is separated from interfering elements by distillation from a n oxidizing solution. The chlorine produced ensures the absence of arsenic in the distillate and aids in the rapid recovery of the germanium. The method of Ivanov-Emin (4) involves distillation of germanium and arsenic, followed by a sulfide precipitation and a preliminary reduction to separate the arsenic from the germanium.
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B
ANALYTICAL CHEMISTRY
N. J.
Germanium is reduced in a 4 to 5N HCI solution in 5 to 10 minutes. The method of Ivanov-Emin (4) re uires a preliminary reduction in 6 N H81 solution for 40 to 50 minutes to remove the arsenic present, followed by a 15- to 20-minute reduction in 61%’ HC1 solution. This acid concentration as indicated by the proposed method is the upper limit for quantitative recoveries of germanium.
tains a thistle tube which extends to the bottom of the flask. The condenser has a tip approximately 20 em. long. The reduction flask is a 500-ml. Erlenmeyer flask capped with a siphon tube that can be immersed in a NaHC03 solution. A heating unit which will Droduce a distillation r a t e of from 3 to ‘5 ml. per minute is recommended.
Germanium is titrated directly with KI03-KI solution to a starch indicator end point. The method of IvanovEmin (4) involves a back-titration of the excess iodine solution with a thiosulfate solution using starch indicator.
Standard Ge Solution. Ignite approximately 5 grams of high purity GeOz a t 800” C. for hour. Cool in a desiccator and transfer 3.458 grams to a 1-liter volumetric flask. Add 15 t o 20 grams of NaOH and 150 t o
Table 1.
REAGENTS
Recovery of Known Amounts of Germanium
Ge Taken, Mg.
Germanium Recovered, Mg.
10.00 25.00 50.00 120.00
9.97, 10.02, 10.02 25.00, 24.95, 25.02 49.95, 49.98, 50.08 120.4, 119.6, 119.8
Error, % ’
AV.
The proposed method is quicker and less subject to error by manipulation than the method of Ivanov-Emin (4). APPARATUS
The distillation apparatus consists of a 500-ml. Erlenmeyer flask connected by a distillation head to a water-cooled condenser. The distillation head con-
-0.3, +0.2, 0.0, -0.2, -0.1, 0.0, $0.3, -0.3, *0.2
$0.2 t0.1 $0.2 -0.2
200 ml. of H20, and heat gently until dissolution is complete. Cool, dilute to the mark with water, and mix. Store in a polyethylene bottle. One milliliter is equivalent t o 2.400 mg. of Ge. Standard KIOa Solution. Transfer 0.4 gram of NazCOa, 3.0 grams of KIOa, and 40 grams of MI to a 1liter flask. Dissolve in water, dilute
Figure 1. Relation of volume of distillate to germanium recovery
ML
DISTILLATE
COLLECTED
distillation apparatus, adjust the volume to 85 to 90 ml., and add approximately 0.3 gram of KMn04. To the receiving flask add 125 ml. of 30% HCl (v./v.), approximately 10 grams of NaHzPOz,N20, and 10 ml. of HBr (48%). Connect the apparatus and add 120 ml. of 12N HC1 through the thistle tube. Start distillation and collect 70 to 75 ml. of distillate. Disconnect the apparatus, rinse the condenser with a minimum amount of water, and remove the receiving flask. Add 1 or 2 boiling stones to the flask and cap with a reduction head. Reduce and titrat'e in the same manner as in the standardization of KI03 solution.
Figure 2. Relation of acid concentration to germanium recovery
EXPERIMENTAL
to the mark with water, and mix. Standardize with standard Ge solution as described below.
15 seconds, (A magnetic stirrer is recommended in the titration.) Calculate the germanium equivalent of the KIOs solution from this titration.
PROCEDURE
Standardization of KIO, Solution. Transfer by pipet 50.0 ml. of standard Ge solution t o a 500-ml. Erlenmeyer flask. Add 170 ml. of 6 N HC1, approximately 5 grams of NaH2P02. HzO, and 1 or 2 boiling stones. Cap Kith a reduction head and mix.
Table II.
Sample 1 2
3
ANALYSIS OF SAMPLES
Samples may be taken into solution by IYaOH-NaZO~fusion, 25% XaOH 5% H202digestion, or HKO~-HZSO~ treatment. Fusions are carried out m nickel crucibles using 5 to 6 grams of NazOz and 1 to 2 grams of NaOH a t a
Results of Assays by Two Analysts
(Per cent Ge found) gnalyst A 8.66, 8.70, 8.68 14.19, 14.19, 14.21 18.99, 19.06, 19.06
Heat to boiling and boil for 6 to 10 minutes. Remove from the heat, place the siphon tube in a beaker of saturated r\TaHC03, and cool t o 15' to 20' C. in a water bath. Remove the reduction head, add 3 to 5 ml. of 0.5% starch solution, and titrate immediately with the HI03 solution to a blue end point which persists for 10 to
Distillation. Figure 1 shows the per cent germanium recovered w. the volume of distillate at a distilling rate of 3.0 ml. per minute. Quantitative distillation is realized after 60 ml. of distillate has been collected. It is necessary to have at least 6N HCI concentration t o obtain a quantitative distillation in this volume. Hydrobromic acid is added to the receiving flask to reduce the chloiine produced and prevent loss of germanium by entrainment. Reduction. Figure 2 shows t h e effect of acid concentration on the reduction of germanium by KaHZPO2.HQO. An acid concentration between 3A: and 6 N RC1 ensures complete reduction. An acid concentration of 4 N to 5N is recommended.
LITERATURE CITED
(1) Alemarin, I. P., Alekseeva, 0. A , , J. A p p l . Chem. Ir. 8. 8. R. 12, 1900 (1939). (2) Bardet, J., Tchakirian, A., Compt. rend. 186, 637 (1928). (3) Cluley, H. J., Analyst 76, 517-22 (19.51 I . (4) Ivanov-Emin, B. W., Zavodskaya Lab. 13, 161 (1947). ( 5 ) Kasarenko, N.A., Vinkovetskaya, 8. Ya., Zhur. Anal. Khim. 11 ( 5 ) , 572-7 \ - - - - I
Analyst B 8.69, 8.68, 8.65 14.21, 14.20, 14.23 19.07, 19.10, 19.07
dull red heat. Concentrates may be taken into solution by boiling with 15 ml. of 25% NaOH solution for 3 to 5 minutes, then adding 30 ml. of 501, H202 and boiling again. Metal samples may be dissolved with a mixture of 15 to 20 ml. of Hn'Oa and 10 ml. of HzS04 and taking to fumes of H2S& Transfer the sample solution to a
(1 956). \ - - - - I
(6) Shakhova, Z. F., hlotorkima, R. K., S'estnilc. &foskov. unio. 12 (2), 183-93 (1957). ( 7 ) Tchakarian, A., Bull. SOC. chim. France 51 (4),846 (1932). (8) Ibid., !? (5), 98 (1943). (9) Tchakirian, A,. Compt. rend. 187, 229 (1928). (10) Willard, H. H., Zuehlke, C. W., IR'D.ENG.CHEM.,ANAL. ED. 16, 322 (1944). RECEIVEDfor reviex ,June 8, 1960. Accepted September 19, 1960.
VOL. 32, NO. 13, DECEMBER 1960
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