Determination of Small Amounts of
Beryllium in Silicates E. B. SANDELL, University of Minnesota, Minneapolis, Minn.
T
HE amount of beryllium reported by Goldschmidt and his co-workers (2, 3) in certain silicates (e, g., 0.01 to 0.1 per cent of beryllium oxide in nephelite) and silicate rocks (an average of 0.002 per cent of beryllium oxide in 14 granites and 0.003 per cent in 22 leucocratic nepheline syenites) is large enough to permit the expectation t h a t a chemical method might be developed for the determination of these small quantities of the element. Such a method might prove useful in the occasional determination of beryllium in nephelite and other silicates, and even in some silicate rocks, when spectrographic equipment is not available. I n sodium hydroxide solution (7) morin gives a sensitive fluorescence reaction with beryllium, which under the proper conditions can be made practically specific for beryllium (6). I t s sensitivity is greater than t h a t of the quinalizarin reaction ( I ) , which has been used for the determination of small amounts of beryllium in silicates (6). Accordingly, morin has been used as the reagent in the present method. Two methods of determining minute amounts of beryllium in silicates were tried. The first method involved decomposition of the sample with hydrofluoric and perchloric acids, solution of the residue in hydrochloric acid, precipitation of the hydroxides of beryllium, aluminum, iron, etc., with a slight excess of ammonium hydroxide, solution of the precipitate in hydrochloric acid, and finally precipitation of the hydroxyquinolates of aluminum, iron, etc., in the usual manner. A filtrate was thus obtained which it was thought would contain the beryllium originally present. This solution was extracted with chloroform to remove the excess of 8-hydroxyquinoline and traces of aluminum and iron hydroxyquinolates, and then evaporated to dryness. Ammonium salts were destroyed by heating the residue with nitric and hydrochloric acids. The residue was taken up in a little hydrochloric acid, the solution was made alkaline with sodium hydroxide, morin was added, and beryllium was determined by comparing the fluorescent solution with a series of standards. This method failed to give satisfactory results. Only about 50 per cent of the beryllium present could be recovered from a granite containing 0.005 per cent of the element. It appeared that beryllium was not completely precipitated with the hydroxides of aluminum and iron under the conditions described. The presence of beryllium could be demonstrated in the filtrate. Coprecipitation of beryllium with the hydroxyquinolates of aluminum and iron was negligible. Since the procedure described was time-consuming, attempts to improve the recovery of beryllium were not made, and the second method was tried, and found to yield more satisfactory results.
contain less than 0.1 per cent of lithium oxide when 0.2 gram is taken for analysis. Transfer 0.20 gram of the finely powdered sample containing from 0.0002 to 0.0025 per cent of beryllium to a nickel crucible in which 1.0 gram of sodium hydroxide has been fused and allowed to cool. For higher percentages of beryllium the size of sample should be reduced proportionately, but the amount of sodium hydroxide should be maintained at 1.0 gram. Heat to fusion and maintain at a temperature of about 500" C. for 5 minutes or until the sample has been decomposed. Allow the crucible to cool to room temperature, and add 8 to 10 grams of ice. If the melt is green add 2 or 3 drops of alcohol. Disintegration of the melt can be hastened considerably by stirring or agitating the liquid. When disintegration is complete and manganate has been reduced, transfer the mixture to a small (30-ml.) beaker, add sufficient water to make the volume 20 ml., and stir. Filter through a small (7-cm.) retentive filter paper into a 25-mi. volumetric flask. Wash the residue and the paper with small portions of water, make up the filtrate to 25 ml., and mix. Ignite the paper and its contents in a platinum crucible, transfer the residue to a nickel crucible, grind the solid to a fine powder with a glass rod, add 1.0 gram of sodium hydroxide, and fuse as before. Treat the melt as described above and finally make up the filtrate and washings to 25 ml. A third fusion will be unnecessary in most cases, but may be carried out as a precautionary measure. Beryllium is determined separately in the filtrates from the two fusions as follows: Transfer 5 ml. of solution to a 2 x 7 cm. vial. In similar vials, prepare a series of beryllium standards, each containing 0.20 gram of sodium hydroxide and having the same volume as the unknown solution. To each vial add 2.0 ml. of saturated sodium pyrophosphate solution and 0.10 ml. of 0.02 per cent (weight by volume) solution of morin in acetone. If the presence of appreciable amounts of zinc is suspected, add 1ml. of 5 per cent potassium cyanide t o the unknown and standards. Mix, and compare the solutions in ultraviolet light. A screened mercury glow lamp is a satisfactory source of ultraviolet light. The comparison should be made without undue delay because the fluorescence decreases slowly on standing. The unknown solution and the standard showing the same intensity of fluorescence should also shorn very nearly the same intensity of yellow color in daylight when compared against a white background. The comparison can be made in strong daylight (preferably in direct sunlight) against a dark shaded background if the amount of beryllium present in an aliquot is greater than 1 microgram and the solution is entirely free from opalescence or turbidity. In this case the amount of morin added should be increased appropriately.
In ultraviolet light 0.1 microgram of beryllium gives a slightly stronger fluorescence than a blank under the conditions described. A faint turbidity has no significant effect if the comparison is made in ultraviolet light.
Discussion The results obtained by applying the method are given in Table I. Double fusions were made except in Nos. 8,9, 10,11, and 12. The recovery of beryllium by double fusion is satisfactory in the case of silicates containing relatively small amounts of iron, magnesium, and calcium. Thus good results were obtained in the analyses of the synthetic acid rock and granite in which the sum of ferric, ferrous, magnesium, calcium, and titanium oxides was, respectively, 5.8 and 7.4 per cent. Satisfactory recovery of beryllium could not be obtained in the case of the synthetic basic rock and the diabase in which the sum of ferric, ferrous, magnesium, calcium, and titanium oxides was, respectively, 24 and 25.9 per cent. On the basis of these results, the procedure described should be applicable to silicates such as nephelite or to a typical granite.
Outline of Method The silicate sample is decomposed by fusion n-ith sodium hydroxide, and ice is added to the cold melt. This method of decomposition has been used by Rienacker (6)for the detection of beryllium in silicates, and also for the rough estimation of the element, with quinalizarin as reagent. The mixture is atered after disintegration of the melt, and the insoluble material is washed and re-fused with sodium hydroxide. Beryllium is then determined in aliquot portions of the two filtrates by adding morin and comparing with a standard series in ultraviolet light.
Procedure The following procedure is in general applicable to silicates low (containing less than 10 per cent) in ferric, ferrous, magnesium, calcium, and titanium oxides. The sample must 674
ANALYTICAL EDITION
NOVEMBER 15, 1940
With 0.025 gram of a silicic sample (granite) one fusion yielded a rather good recovery of beryllium. However, when such a small sample is used, the beryllium content of the material should be greater than 0.005 per cent. TABLEI. DETERMINATION OF BERYLLIUM IN SILICATES AFTER DOUBLE F-~SIOS WITH SODIUM HYDROXIDE No.
Sample
Be Present"
Be Found
Error
70
%
%
Synthetic acid rockb (0.2gram) 0.0005 0.0005 0,0000 Synthetic acid rock (0.2 gram) 0.0010 0.0011 iO.0001 Kephelitec (0.2gram) 0.0016 0.0015 0.0000 Granited (0.2gram) 0.0015 0.0015 0.0000 Granite (0.2gFam) 0.0015 0.0014 -0.0001 Granite (0.2 pram) 0.0030 0.0027 -0.0003 7 Granite (0.2 i r a m j 0.0055 0.0050 -0.0005 8 Granite (0.05 gram) 6 0.0025 0.0015 -0.0010 0.0045 0.0040 9 Granite (0.025 gram18 -0.0005 10 Granjte (0.025 gram) a 0.0085 0.0070 -0.0015 11 Granite (0.025 gra?) e 0.021 0.020 -0.001 12 Quartz (0.2 gram) 0.0020 0.0024 $0.0004 13 Svnthetic basic rock/ (0.2 gram) 0.0010 0.0005 -0.0005 0.0010 14 DiabaseV (0.2 gram) 0.0005 -0.0005 15 Diabase (0.2gram) 0.0020 0.0012 -0.0008 16 Synthetic acid rock (0 ,- .2 -. mn -.m ..,l 4, 0.10% Li 0.0000 0.0003 +0.0003 17 Synthetic acid rock (0.2 gram) O . l O ~ oZn 0.0000 0.0000 0.0000 0.0020 0.0022 +0.0002 1s Granited (0.2gram) -t 0.05% c u a Includes Be originally present and that added. b Percentage composition: SiOa 77, AlzOa 17, FetOa 2.1, N g O 1.3, CaO 2.2, TiOn 0.2, PzOa 0.1. MnO 0.1. Contained no Be (
