Determination of Germanium in Minerals and Solutions R , C. AITKENHEID A h D A . R . 3IIDDLETON, Purdue University, Lafayette, Ind.
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F T H E numerous elements n hich are detrimental
sequent removal of excess hydrofluoric acid by evaporation n i t h perchloiic or sulfuric acid may lead to another loss of germanium, apparently through the formation of the insoluble form of germanium dioxide described by lluller and Blank (6) and confirmed by Laubengayer and Morton (3). Experiments showed that the former loss occurred TF lien GeF6-n as too rapidly decomposed; the latter while strong acids were being heated to fuming. Thus n e seem to be confronted by a dilemma. If the acids are fumed too rapidly, germanium seems to be lost as gerinanium fluoride; if n e raise the temperature slon ly to avoid this loss, germanium has more opportunity to pass into tlie insoluble rutile form of the oxide. The authors ha\-e found that the insoluble form dissolves readily in hot dilute alkali if a little sodium sulfide is present. A sinal1 crystal of sodium sulfide nonahydrate is sufficient. The thiogermanate ion is not decomposed by a small excess of mineral acid, a fact that permits a t this point separation of germanium from any arsenic or antimony nhich may be present. Most methods proposed for the separation of germanium from arsenic and antimony are based upon distillation of germanium chloride with hydrochloric acid and simultaneous oxidation of the arsenic and antimony to nonvolatile compounds. The authors have found that tlie presence of finely divided copper in the distillation flask precipitates arsenic and antimony. It is common practice in the electrolytic zinc industry to add copper sulfate to solutions before purifying n i t h zinc dust. The precipitated copper has a specific effect on the removal of arsenic and antimony from solution, 11-hich is probably due to the formation of arsenides and antiinonides of copper. This led the authors to try the effect of copper on arsenic and antimony in strong hydrochloric acid solutions.
to the electrolysis of zinc, germanium IS the most elusive and one of the most trouLlesonie I t s noxious effect n a s pointed out in 1930 by Tainton (Q), n h o stated that 0 1 ing. per liter of electrolyte produces noticeahle reduction of ciirrent efficiency. I n zinc plants wheie cyclic leaching is used germanium is partially precipitated in the neutral leach, but this precipitate is partly dissolved in the acid leach Thus a considerable load of germaniuiii accumulates before equililjrium is reached, nlien the solution may contain seT-era1 milligrams per liter of the element. Members of the nietallurgical staff of the Anaconda Copper Mining Co. ( 2 ) stated in 1920: “the zinc deposit was nearly ideal, until the first of December n h e n it began to show signs of surface corrosion. The character of the deposit gradually changed until its resemblance to the arsenic deposit in the test cell could no longer be mistaken; but the chemists reported no arsenic in solution.” Undoubtedly tlie source of the trouble T? as germanium. The single potential of Zn, Zn++ is gii-en by Lenis (4) and associates as 0.7581. The electrolysis of zinc from acid solution is possible only because zinc has a high hydrogen overvoltage, and the noxious effects of impurities are due to their lowering the hydrogen overvoltage. The injurious impurities are in two distinct regions in the periodic table: The eighth group metals-namely, iron, cobalt, nickel, and the platinum metals-along n i t h tlie 1B family occupy one region. The other includes metalloids n-hich form gaseous hydridesnamely, arsenic, antimony, tin, germanium, selenium, and tellurium. I n zinc electrolysis the impurities which may be present are iron, cobalt, nickel, copper, germanium, arsenic, and antimony. There are sensitil e chemical tests for all these elements except germanium. For this reason a t least one large zinc plant has installed a quartz spectrograph. I n 1928 one of the authors n-as confronted by the problem of eliminating germanium from solutions and was handicapped by lack of a qualitative test for that element, capable of detecting 0.1 ing. or less. A frequently employed method, precipitation of v hite germanium sulfide and confirmation as potassium fluogermanate, sparingly solulile in hydrofluoric acid solution, is incapable of detecting much less than 1 mg. of germanium. Kliile analyzing minerals by the methods of Soyes and Bray (S), the lack of sensitiiity of the sulfidefluogernianate test again hecaine evident. The iiiethods presented in this paper, developed from research undertaken by the writeis to iinprol e on previous methods of gernianium analysis. comprise the follon ing features:
Several grams of chopped copper foil were added t o 50 ml. of hydrochloric acid containing 100 mg. of arsenic trioxide. The copper vias immediately blackened. After standing for 15 minutes the copper and acid mere distilled together, and the distillate nas made 6 h- in acid and saturated with hydrogen sulfide. KO arsenic sulfide v a s visible. The above test was repeated using 100 mg. of antimony trioxide in place of arsenic trioxide. Antimony behaves like arsenic. Fifty milligrams of germanium dioxide, 100 mg. of arsenic trioxide, and 100 mg. of antimony trioxide were diytilled in the apparatu- qhonn in Figure 1. On qaturation of the distillate 111th hydrogen sulfide chaI acteristic n hite germanium sulfide precipitated. The recovery vias 98 per cent. Subsequent TI ork showed that the precipitation of arsenic n i t h copper foil is not complete enough to give a blank Marsh test. Precipitated copper, which is much more reactive because of its finely dilided state, was therefore substituted. When much arsenic is present, a preliminary precipitation hefore distillation removes all except traces which are precipitated in the subsequent distillation in the presence of copper. I n the authors‘ first experiments on distillation, refluxing was employed solely to prolong the action of copper. 91though it was expected that gernianiuni chloridr TT ould return to the flask, all the gernianium escaped from the condenser. Lundin (6, p. 152) has noted that germanium chloride is very difficult to condense and that correct concentration of hydrochloric acid is important, and advises a concentration
Treatment of solids with hydrofluoric, nitric, and sulfuric acids and subsequent extraction with sodium sulfide. Use of metallic copper to precipitate arsenic and antimony. Fractional dibtillation m ith hydrochloric acid, thus reducing the volume of the distillate to 10 per cent of the original volume. A modification of the Marsh test for traces of germanium \Thich is capable of detecting 0 001 mg A gravimetric method for larger amounts by evaporating the hydrochloric acid distillate n ith hydrofluoric, sulfuric, and perchloric acids v, hich gives germanium dioxide direct11 N ithout precipitation by h j drogen sulfide and subsequent ignition. Tlrhen bringing minerals into solution, the use of hydrofluoric acid cannot be avoided. Silica holds u p germanium, as noted by Lundin (6) and verified b y the authors, involving possible loss of germanium as germanium fluoride. The sub633
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slightly less than the constant-boiling mixture in order to condense all vapors passing into the condenser. It occurred to the authors that by using a concentration somewhat greater than constant-boiling and refluxing, germanium chloride and hydrogen chloride would pass out of the condenser; if water absorbed these vapors completely, the germanium could be collected into a small volume. The passage of air bubbles through the apparatus a t the beginning of distillation caused a slight loss, which was avoided b y sweeping all the air out of the apparatus with hydrogen chloride before introducing the germanium-containing solution. Oxidation during distillation involves either passing chlorine through the solution being distilled, or adding potassium permanganate or other reagents which generate chlorine. Loss of germanium seems to be inevitable whenever insoluble gases are allowed to bubble through the receiving liquid. This raises a n objection to the use of oxidants in the distillation and constitutes a valid argument for the use of copper which also reduces the decided tendency to bump during distillation. Comparison of hIarsh tube deposits of more than 0.1 nig. is inaccurate. Gravimetric determination is facilitated and precipitation as germanium sulfide avoided by taking advantage of the stability of the fluogermanate ion. When hydrogen chloride-germanium chloride solution is slonly evaporated with hydrofluoric acid in presence of both perchloric and sulfuric acids, no germanium is volatilized. With hydrofluoric and perchloric acids, three experiments gave 97 per cent recovery. With hydrofluoric and sulfuric acids three experiments gave 99 per cent recovery. When both perchloric and sulfuric acids were used, two experiments gave 100 per cent recovery. Why the two latter acids used together are more effective in retaining germanium is not obvious; presumably the relative stability of GeC16-- and GeF6-- is involved. Possibly at the lower fuming temperature of perchloric acid GeF6-- is not entirely decomposed and germanium fluoride is lost during the subsequent ignition to the oxide. When sulfuric acid is used the rise in temperature is more rapid and germanium chloride may escape if the conversion of GeCls-- to GeF6-- has not yet been completed. hIiiller and Smith (7) studied the application of the Marsh test to germanium and reported on the effectiveness of various hydrogen generators, concluding that a 2 per cent sodium amalgam gives the best results and that zinc and hydrochloric acid are not satisfactory. Since the latter is the generator most convenient when the germanium has been collected in a small volume of hydrochloric acid solution, the authors thoroughly investigated it. Results of many experiments showed that as little as 0.001 mg. could be detected, but only when the following conditions were exactly maintained : 1. The zinc must be in finely divided flaky form and previously proved to be absolutely free from arsenic and germanium. Not all electrolytic zinc is sufficiently pure. The preparation of satisfactory zinc is described below. 2. Concentrated and not dilute hydrochloric acid must be used. The germanium must be in fairly concentrated hydrochloric acid and must fall in drops directly upon the zinc. 3. The germanium must have been separated from all contaminating elements by previous distillation.
hliiller and Smith (7, p. 1910) when using zinc and acid observed the formation of a brown solid which they thought either a form of elementary germanium or a lower hydride. Bardet and Tchakirian ( 1 ) observed the same substance but thought i t germanium monoxide, stating that with zinc and 25 per cent sulfuric acid they were able to detect 0.1 mg. of germanium b y this precipitate. The authors investigated its formation as a test for germanium. I n 15 ml. of acid
FIGURE 1. DISTILLATION APP.kR.4TUS .4.
300-mi. Erlenmeyer flask Pyrex condenser, 30 cm. long C. Dropping funnel D. Delivery tube with safety bulb and test tube B.
0.1 mg. of germanium gave a distinct precipitate; 0.01 mg. occasionally but not consistently gave a precipitate. The substance seemed to form most readily in 4 to 6 LV hydrochloric acid on addition of a piece of zinc. It forms a t the surface of the zinc but a t once detaches itself, leaving no stain on the zinc. It has a greasy appearance and creeps up the wall of the tube. I t s formation interferes with the generation of germane. C'nder the conditions laid down in 2 i t is not formed, all the germanium being comerted into germanium hydride. By comparison with deposits from known amounts of germanium, the Marsh test is sufficiently quantitative for 0.1 to 0.001 mg. A portion of the hydrogen chloride-germanium chloride distillate containing not more than 0.1 mg. should be taken, as more than 0.1 mg. makes too dense a deposit for accurate comparison. When several milligrams are present gravimetric determination is advisable.
Recommended Methods
A. EXTRACTION OF GERMANIUM MINERALS. Treat 1 pram of the finely ground material-with 10 ml. of nitric acid, 10 ml. of hydrofluoric acid, and 2 ml. of sulfuric acid (1 to 1) in platinum. Moisten sulfide ores with a few drops of water, add the nitric acid gradually until the evolution of nitric oxide has ceased, then add the other acids. Evaporate at low heat, not allowing to boil. Ascertain the absence of hydrofluoric acid by holding a strip of moistened filter paper over the vessel. When white fumes cease to form, the heating has been sufficient. The sulfuric acid should not fume. Wash the contents of the platinum dish into a small beaker. Make basic with 6 N sodium hydroxide, add a crystal (about 0.5 gram) ofsodium sulfide nonahydrate, and boil 15 minutes. Cool, make just acid with sulfuric acid (1 t o l),and allow to stand until the sulfur has coagulated, preferably overnight. Filter and wash once with a little water. Add 1.5 volumes of concentrated hydrochloric acid to 1 volume of the solution and 2 to 3 grams of the copper reagent'. Treat further as under C. B. TREATMENT OF SOLUTIOSS. To a volume of solution expected to contain 0.001 to 0.1 mg. of germanium add 1.5 volumes of concentrated hydrochloric acid and 2 to 3 grams of the copper reagent, Allow to stand for 1 hour. If the copper is noticeably blackened (arsenic, antimony), filter through an acid-hard,ened paper, add more of the copper, and allow to stand 15 minutes longer. Then distill as described under C. C. DISTILLATIOX. Use an apparatus with ground-glass joints similar to that shown in Figure 1. A is a 300-ml. Erlenmeyer flask with the bottom blown out round. The stem of the dropping funnel should be at least 25 cm. (10 inches) long to overcome back ressure. The gooseneck attached to the Liebig condenser shouljhave a safety bulb about 5 cm. (2 inches) in diameter. Transfer the hydrochloric acid solution obtained in A or B to the flask, washing in the copper with hydrochloric acid (1.5 to 1). Before starting the distillation rinse the condenser and delivery tube with concentrated hydrochloric acid to prevent hydrolysis of germanium chloride, place the test tube containing 5 ml. of water in a beaker of ice water, and adjust the delivery tube to extend almost to the bottom. Start the condenser water and heat the contents of the flask slowly to boiling. Continue the distillation until the water in the receiving tube is saturated with hydroFROM
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INALYTICAL EDITION
chloric acid. If the evolution of hydrogen chloride gas becomes too slow, because the acid in the flask approaches conqtant-hoiling composition, add conrentrated acid dropwise through the funnel. To saturate the Tmter in the receiver should require about 0.5 hour. D. GRAVIMETRIC DETERMINATIOS. The usual method of precipitation as germanium sulfide and conversion to germanium dioxide can be applied. Since the volume of the distillate is ?mall, it ii more convenient to use the follo~vingmethod: Add an equal volume of 27 S hydrofluoric acid to the distillate in a weighed platinum dish. Then add 1 ml. of concentrated sulfuric acid and 1 ml. of 60 per cent perchloric acid, and evaporate on a steam plate, not permitting to boil. Fume the heavy acids slowly to dryness and ignite. Keigh as germanium dioxide. E. MODIFIED MARSHTEST. .I satisfactory apparatus con-istedof a20-cm. (8-inch)ltest tubeasgenerator, carrying a two-hole rubber stopper through which passed the 25-cm. (10-inch) stem of a small dropping funnel and a delivery tube leading to a gaswashing bottle. (The authors used a scrubber provided with a sintered-glass filter, IO.) The scrubbed gas passed through a straight drying tube loosely stuffed with glass 17-001, and then t o the combustion tube. This consisted of Pyrex 0.6 cm. (0.25 inch) in external diameter and 12.5 cm. (5 inches) long, drawn out to a capillary 5 cm. (2 inches) long and about 1mm. in internal diameter at the farther end. Place in the test tube about 5 grams of zinc (free from arsenic and germanium) prepared as described below, and in the dropping funnel 5 ml. of 12 N hydrochloric acid, proved free from arsenic and germanium. Before closing the test tube, make sure that the stem of the funnel is filled to assure free dropping of the acid into the tube. Open the cock in the funnel t o permit the acid to enter at a rate of about 1 drop per second. Close the cock before air enters the stem and test the emerging hydrogen for quiet burning by igniting a tubeful caught under water. If there is no further danger of explosion, slip the combustion tube in place and heat with a Bunsen burner about 1.8 cm. (0.75 inch) before the constriction. Since the Pyrex is heated to incipient softening, the tube should be supported on both sides of the flame. Now add the distillate from C and allow it to flow into the generator at a rate of 1 drop per second. When the distillate has nearly all entered the st’em, add 5 ml. of pure hydrochloric acid t o flush it out,. Allow the action to continue for 15 minutes after all the acid has entered the generator. With pure reagents the stain in the combustion tube is due to germanium. Standard tubes for comparison should be taken through the whole procedure. This test is quantitative for amount,s of germanium between 0.1 and 0.001 mg. If more than 0.1 mg. is present the stain is too heavy to be est’imated.
Accuracy of Methods
MODIFIED MARSHTESTFOR TRACES.The authois h i - e repeatedly carried sniall quantities of germanium, 0.1, 0.01, and 0.001 mg., through this procedure and compared the Marsh tubes with those produced by adding the germanium directly to the Marsh generator. The comparison was good where 0.1 and 0.01 mg. were used. Where only 0.001 mg was taken through the procedure, the stain in the Marsh tube was somewhat dimmer than that produced by the same amount added directly to the generator. For this reason standard tubes should be taken through the whole procedure. GR-4VIhIETRIC METHOD.Two tests taking 50 mg. of germanium dioxide through the procedure showed a recovery of 98 per cent. Preparation of Special Reagents PRECIPITATED COPPER. Dissolve 100 grams of copper sulfate in 1 liter of water. Precipitate the copper with granulated zinc, using some excess. Then acidify with 18 N sulfuric acid to dissolve the excess zinc and boil, adding more acid until the action ceases. The precipitate should be bright red. Decant the acid solution, wash several times with water, transfer to a nidemouthed bottle, and keep covered with water. ARSENIC-AKD GERNANIUM-FREE HYDROCHLORIC ACID. Arsenic-free hydrochloric acid for the Marsh or Gutzeit tests is satisfactory if proved by blank runs.
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REAGEKT ZINC. The zinc must be free from arsenic, antimony, and germanium. Zinc in suitably small flakes was prepared by the following method: Electrolytic zinc was melted in an assay crucible using ammonium chloride as a flux. When the zinc was well melted and the crucible at a bright red heat, the metal was poured through a 100-ml. Alundum crucible with a 2-mm. hole in the bot’tom and allowed to fall about 6 meters (20 feet) into a bucket of ice water. The impact of the molten zinc on the water causes it to spatter out into thin flakes. If sufficiently pure zinc is not obtainable, met a1 of very high purity can be prepared by electrolysis. Purify 5 liters of zinc sulfate solution containing 100 grams of zinc per liter by the following method: Add sufficient ferric sulfate to give 2 to 3 grams of iron per liter and heat nearly to boiling. Add zinc oxide until the iron is precipitated, then potassium permanganate to permanent pink, boil 15 minutes, and filter. Arsenic, antimony, germanium, and cobalt are removed. To the filtrate add copper sulfate to give a copper content of 1 gram per liter and heat to boi!ing. Add 5 grams of zinc dust per liter, boil 30 minutes, and filter. Electrolyze in a 2-liter battery jar or beaker, using an aluminum cathode LT-ith edges framed with wood to facilitate stripping the zinc. Use two lead anodes having a submerged area twice that of the cathode. The anodes can be suspended by folds over the edge of the jar. Cathode current density should be about 30 amperes per 0.0992 sq. meter (1 square foot). With a submerged cathode area (both sides) of 154.8 sq. cm. (24 square inches) and a current efficiency of 90 per cent, about 6 grams of zinc per hour are deposited. The quality of the deposit is best when the acidity of the electrolyte is about 90 grams per liter of sulfuric acid. Since sulfuric acid may contain arsenic and other impurities, it is preferable to establish optimum acidity through electrolysis. This acidity will have been reached when about 60 grams of zinc have been deposited per liter of electrol>%’e-that is, after 20 hours if 2 liters are being electrolyzed. Thereafter, 6 grams of zinc should be added each hour that the cell is run, by withdrawing 100 ml. of t,he electrolyte and replacing it with 100 ml. of the purified solution. The electrolyte should be titrated occasionally to verify the acidity. The cathode is stripped daily. The deposit is broken up and the flaky form prepared as described above.
Summary Germanium can be accurately tleteriiiined in minerals or solutions by a modified Marsh test when less than 0.1 mg. is present, gravimetrically when larger amounts are involved. Losses of germanium through volatilization as germanium fluoride and through formation of the acid-insoluble form of germanium dioxide are provided against. Modifications of the Marsh test permit the detection of 0.001 mg. of germanium, even when using a zinc-hydrochloric acid generator. The preparation of reagent copper used in the proposed methods and of electrolytic zinc of the high purity essential for the Marsh test for germanium is described.
Literature Cited B a r d e t a n d Tchakirian, Compt. rend., 186, 63?--8 (1528). L a i s t et al., Trcins. -4%. Inst. Mining Met. Engrs., 64, 724 (1920). Laubengayer and M o r t o n , J. Am. Chem. Soc., 54, 2303 (1932). Lewis a n d R a n d a l l , “Thermodynamics,” p. 433, New I’ork, S l c G r a w - H i l l B o o k Co., 1923. Lundin, H a r a l d , Trans. Am. Electrochem. Soc., 63, 149 (1933). Muller and B l a n k , J . Am. C h e n . SOC.,46, 2338 (1924). Muller a n d Smith, Ihid.,44, 1509 (1922). iioyes and B r a y , “Qualitative Analysis of the Rare Elements, New York, M a e m i l l a n Co., 1527. Tainton, U. C., and Clayton, E. T., Trans. Am. Electrochem.
Soc., 57, 278 (1930). Thomas Co., 4.H., Catalog 5998-A,p . 368 (1931).
RECEIVED J u n e 16, 1937. Abstracted from a thesis submitted by M r . Aitkenhead t o the ftLculty of Purdue University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. A copy of the complete thesis may be borrowed from the Purdue University Library through the InterLibrary loan. The quantitative d a t a upon which statements in this paper are based will be found therein.
