Separation and icroscopic Identification of Gallium in the Presence of Aluminum AARON WOLD, JAMES H. BAIRD, and CHARLES R. HOUGH Hofitra College, Hempstead, N. Y., and Polytechnic Institute of Brooklyn,
Brooklyn,
N. Y.
bath, redissolving the resultant gallium salt three times in 15 ml. of concentrated nitric acid, followed each time by evaporation until acid fumes no longer were detected hy moist. litmus paper.
Present methods for the separations of gallium from aluminum hased upon differences in the solubilities of the hydroxides are difficult to perform because the hydroxides are gelatinous and peptize readily. A procedure has been developed using the technique of ehemical mioroscopy to detect gallium in the presence of aluminum. Acetylaeetone (2,4-pentanedione) will extraot omr 90% of the gallium fmm a 6M hydrochloric acid solution containing both gallium and aluminum. Gallium acetylacetonate ean he transformed from the monoclinic system to the orthorhombic system by heating or by recrystallizing from ethyl acetate. Similar treatment does not change aluminum aeetylaeetonate from the monoclinic system.
method. A solution of aluminum was prepared by dissolving 8.94 grams of reagent grade aluminum chloride hexahydrate in 100 ml. of water. The ncetylaeetone had a boiling range of 133" to 135' C. PROCEDURE
Gallium Acetylacetonate. Gallium hydroxide was precipitated on a slide by the addition of 10% ammonium hydroside to a drop of stock solution of gallium chloride. The gallium hydroxide was washed with water to remove rtmmonium and chloride ions. A
G
ALLIUM can he separated partially from aluminum by the addition of animonia (e), gallium hydroxide being the more soluble of the two. The addition of cesium sulfate gives an alum with both aluminum and gallium (5) of the same crystal habit (a cube, an octahedron, or combination of the two forms). Winchell (7) has reported the refractive indices as 1 . 4 8 6 ~for~ ~ for cesium gallium sulfate. cesium aluminum sulfate and 1.4650~m The differences in their refractive indices would enable identificirtion if good separations could he effected. However, separations of gallium from aluminum hased upon differences in the soluhilities of the hydroxides are often difficult to perform since the hydroxides are gels which are easily peptiaed. The technique described here employs the preparation of cryst$line aluminum and gallium xetylscetonates, which show different optical charaoteristios under certain conditions. (Since completion of this work, Steinhach and Freiser (6) have indicated the general applicahility of acetylscetane extraction to metal separations.) The addition of ammonium acetylacetonate to an aqueous solution of gallium or aluminum chloride neutralized with ammonia produces monoclinic crystals of the acetylacetonates. If the aqueous solution is acid, only the gallium compound will form, aluminum remaining as the chloride. Gallium acetylacetonzte is soluble in excess acetylacetone which can be extracted with ether from acid aqueous solution containing both gallium and aluminum chlorides. The ether layer, which contains the gallium, is treated with dilute ammonium hydroxide t o remove the excess acetylacetone. On evaporation of the ether, gallium aoetylscetonate is obtained. Aluminum acetylacetonate can he obtained from the aqueous layer by adjustment of the pH to 7.2 with dilute ammonia. Monoclinic gallium acetylacetonate can he transformed to the orthorhombic system by heating or by recrystallizing from ethyl acetate. Similar treatment does not change aluminum acetylacetonate from the monoclinic system (I, 4,5).
"
CFigure 1). Analysis, calculated for Gs(C,&O*),. C, 49.08%; H, 5.73%; Ga, 19 09%. Found. C, 49.05%; H, 5.70%; Ga, 19.04%. Aluminum Acetylacetonate. The procedure for gallium repeated with aluminum chloride substiacetylacetonate was reneated acetvlacetonate tuteh for gallium chloride. chlfide. Aluminum acetylacctonate scetylacctonate pretuted cipitated in the same crystal form as was observed for gallium acetylacetonate. Analvsis, calculated for AI(C,H,Os)a. C, 55.61%; H, 6.48%; AI, 8.3i%. Found. C, 55.59%; H, 6.46%; AI, 8.30%.
EXPERIMENTAL
Reagents. A stock solution of gallium (A. D. Mackay, 1nc.i ~"
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tion was Keaied on s"steam bath tobrive off the excess acid. Figure 1. Photomicrograph of Gallium Aeetylacetonate Recrystallized from Aqueous Acetylaeetnno (300 X)
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V O L U M E 26, NO. 3, M A R C H 1 9 5 4 ,
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acetonate which had been recrystallized from ethyl acetate were also placed an the hot stage. It appeared that only the orthorhombic farm was obtained from ethyl acetate solutions. Optical Properties. The refractive indices of aluminum and gallium acetylacetanates m-ere determined with a polarizing microscope using the Becke line technique. The liquids used for these measurements were checked with a refractometer a t ZOO, 25", and 30' C. and the change in refractive index with temperature was caloulated. The crystals were placed on & five-circle universal stage equipped with a speeisl water cell for temperature variation. After rotation to %positionwhich allowed one or more of the critical refractive indices to be measured, the temperature vas varied until the mounting liquid matched that of the crystal. The universal stage was also used to check the value of the angle between the ODtiC &xes. 2 V . which is usudlv obtained from interference fig,x e s . Table I summitriaes the optical properties of aluminum and gallium act:tylacetanittes.
Table I.
_ r. ..-. ...~.. . . . .
AIum inui saet
-- chlorio acid, and 0.01 gram of aluminum per ml. in IN and 6 N hydrochloric acid. Equal volumes ai acetylacetone and combined gallium and aluminum chloride solutions vere placed in a 50-ml. beaker and stirred in a constant temperature bath a t 25.0" C. far varying lengths of time. After removal from the bath, the mixture i m s transferred to a separatory funnel. The
Figure 3.
Photomicrograph of Gallium Acetylaeetonate after Sublimation (300 X )
ANALYTICAL CHEMISTRY
548
rnoromiorograpn o r baiuum xceryracr;wrxate Recrystallized from Ethyl Acetate (300 X )
13zgure a.
Figure 4. Photomicrograph of Aluminum Acetylaeetonate Recrystallized from Ethyl Acetate (300X)
The acetylacet,one-ether mixture was shaken 4 to 5 times r i t h 10 ml. of 0.7M ammonium hydroside. The ether extract was placed in sn evaporating dish from which slightly discolored crystals of gallium aeetylacetonate wcrc obtained. Recrystalliaation from ether or ethanol, in the prasence of norite, gave colorless monoclinic crystals of gallium aeetylacetonate. Aluminum acetylacetonate urns obtained from the aqueous phase by adjustment of the pH to 7.2 with dilute ammonia. LITERATURE CITED
Tahle 11. Percentage of Total Gallium Extracted from Aluminum-Gallium Mixtures HCI. N Gallium Extrsoted, % Mixture A . Snit. concn. of gallium, 0.05 a. gsllium and 0.05 g. aluminum. total volume 10 mi. 6 87" 1 30' Init. concn. of gsllium. 0.05 g. gdlium and Mixture B. 0.05 a. aluminum. tots1 volume 10 m1. 6
1
926 3za
Mixture C. Snit. eoncn. of gallium, 0.005 g. gallium and 0.05 8. aluminum, total volume5 5 ml. 6 85' 1 20'
*After 1 hour. b After two l-hour extractions.
Astbury, W. T., Proe. Rou. Soe. (London), A112, 449 (1926). (2) Charnot. E. AI., and l l a s o n . A. B.. "Handbook of Chemical Miarosannr " Vnl. TT. n. 173. New York. John Wilev 8- Sons. . (1)
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1940.
(3) Ihid.. p. 176. (4) Jaeper, :F. M..Pmc. Aced. Sci. Amslel-da,n. 33, 283 (1930). ( 5 ) Morgan, G. T..and Dre~r-,H. D. K., J . Chom. Soc.. 119, I059 (1'321)
(6) Steinbach, J. F., and Freiser, H., Ax&. C n ~ x ,25, , 881 (1'333). (7) Winchell. A. N., "Xcroscopic Characters of Artificial Inorganic Solid Substances," P. 260, New York, John Wiley & Sons, 1931. REOE~VE for D review July 24. 1953. Aeoepted November 28, 1953. Presented before tho Division of Anhlytiosl Chemistry a t the 124th Meeting of the A ~ s n r c r l iC ~ E M I O A
Quantitative Del Gases-Correct Gases" [ANAL.CHEM.,25, 1718 (1953)1,the statistical quantities a t the end of Tshle I me in error. They should rend'
both the aqueous phaseand the oomhined acetylscetane ether extract was determined by evaporation of the solvents, formation
Sum of differences for all values
=
14.6
Average difference (21 =
0.4 3.1
sidi .. =
1 = 0.77
precipitahg the gallium by the addithn 0fu6% c u p f e r k , and reigniting the cupferrate to the oxide. After removal of the gallium, aluminum was precipitated with &quinalinal in the usual manner and weighed as aluminum oxide. I n each case, two determinations were run (hut not concurrently), RThich agreed to within 2%. Less than 2% of aluminum was found in the acetylncetone-ether extract. Gallium aoetylacetonate wm obtained from the acetylaoetoneether extract hj- the fallowing procedure.
Since the significant, ( 5 % ) t value far 30 degrees of freedom is 2.042, the deviation of the differences from zero is completely negligihle, which is tlie conclusion in the original paper. In the abstract of the paper the standard deviation is given as -0.77 p.p.m. by a typographical error. It should read 0.77 p.p.m. The authors are indebted to William I. Martin far pointing out these errors. LEONARD P. PEPKOFITZ EDWINL. SHIRLEY
