83
ANALYTICAL EDITION
February 15, 1941
wave length of 450 mp. T h e transmittance at this wave length is determined and from a standard curve t h e percentage of phosphorus is calculated.
Acknowledgment The authors are indebted to Eberbach & Son Co., Ann Arbor, Mich., for the use of the spectrophotometer.
Literature Cited (1) Bogatski, G,, Arch. ~ i ~ ~ 12,~195 h(1938). ~ ~ ~ ~ ~ (2) Misson, G., Chem.-Ztg., 32, 633 (1908). IND.ENQ.CHEM.,Anal. (3) Murray, W. M., and Ashley, S. E. Q,, Ed., 10, 1 (1938). (4) Willard, H. H., and Greathouse, L. H., J. Am. Chem. Soc., 42, 2208 (1920). (5) Zinsadse, C., IND.Ew. CHEM., Anal. Ed., 7, 227, 320 (1935).
Basic Sulfates of Iron and Aluminum in Analytical Separations J. G. FAIRCHILD, C. S. Geological Survey, Washington, D. C.
AS
DESCRIBED in a previous paper (S), a solution of ferric sulfate was used t o form a basic ferric alum with potassium which was thereby separated from cesium. In a similar manner, after the addition of potassium sulfate a n excess of iron can be separated from divalent metals, which are then determined by the usual methods. I n this procedure a basic sulfate of iron and potassium is formed a t a definite p H and at steam bath temperature, 90” C. The precipitation of iron is nearly complete, while divalent metals remain in solution. A small part of a n y aluminum present is also precipitated. Mellor (7) mentions as products of the hydrolysis of ferric alum a few basic sulfates of iron and potassium which vary in composition and are microcrystalline. Krueger ( 5 ) obtains a basic sulfate of iron and ammonium in separating iron from cobalt, nickel, zinc, and manganese. He fails to consider the resence of aluminum and completes the separation of iron as a &asic acetate. Ardagh and Bongard (1) obtain good separations of nickel and zinc from iron and aluminum in a small volume of solution containing a little hydrochloric acid and 5 grams of ammonium chloride, to which strong ammonia is added in excess. Noyes and Bray (9) separate 2 to 50 mg. of nickel or zinc from 100 m of iron very satisfactorily by the above procedure, but with cotalt 1 mg. in 50 is caught in the precipitate of iron. This separation is troublesome and requires repetition, especially when excessive quantities of iron and aluminum are present. Lundell and Knowles (6) find that nickel only may be satisfactorily separated by the Blum method in a single precipitation. The writer has observed that the separation from aluminum is by far the more uncertain. Nickel only can be separated in a faintly acid solution containing ammonium sulfate. Aluminum, like iron, forms a basic sulfate with potassium. A patent on basic alum has been issued to Fleischer (4), who heats a solution of alum above 60” C. in a continuous system. Titanium forms no double sulfate, as tested by experiment. According t o Mellor (8) magnesium, zinc, or manganese may enter the basic sulfate molecule, which resembles alunite in composition but contains the same proportion of potassium sulfate as ordinary alum. Cobalt also fqrms a double sulfate with aluminum. Aluminum may be separated from beryllium by this method satisfactorily without the use of ammonium sulfate. Britton ( 2 ) obtains a 90 per cent separation of aluminum from beryllium as potassium alum.
Procedure Treat a slightly acid solution of ferric sulfate, free from.fluoride, chloride, and nitrate, with potassium acid sulfate and partially neutralize with dilute ammonia until a precipitate be ins to persist. Heat this solution for several hours in a flask yowered directly into the steam bath; a dense, microcrystalline, orange-red precipitate is produced. Potassium sulfate yields a less soluble precipitate than the ammonium salt. The presence of titanium or phosphate renders subsequent filtration slow and the filtrate yellow with too much iron. I n such a case, further neutralize the filtrate and repeat the hydrolysis. About 5 mg. of iron remain in solution. If appreciable quantities of titanium are present, first hydrolyze a t 0.1 N acidity. Proceed in like manner for phosphate after adding titanium sulfate. DETERMINATION OF ZINC AND NICKEL.Place the solution of iron and zinc sulfate in a 500-ml. Kjeldahl flask, add potassium
acid sulfate equal in weight to the ferric oxide probably present, dilute to 300 ml., and slowly add dilute ammonia until a slight permanent precipitate remains. Place a small funnel in the neck of the flask and heat to 90” C. in the steam bath for a t least 4 hours, or overnight. Hydrolysis with a wired-in sto per yields a more granular basic sulfate. Filter while hot. The filtrate should be colorless and have a pH close to 2.8, just yellow to thymol blue. Evaporate the filtrate and wash water to 150 ml. Filter off any precipitate of iron, add methyl orange, and neutralize until the color just remains red, a t a pH of 3.1, which is about right for the precipitation of zinc sulfide. Transfer the solution to an Erlenmeyer flask, add 2 ml. of 5 per cent mercuric chloride solution, and precipitate zinc and mercury with hydrogen sulfide. Ignite the filtered and washed sulfides and weigh as zinc oxide in the usual way. If cobalt or nickel was originally present the precipitation of zinc may require repetition. After removing the greater part of the iron as above, concentrate the filtrate and wash water to 300 ml., add methyl orange, and neutralize the filtrate until faintly red. Add 5 grams of ammonium sulfate and hydrolyze in steam for a t least 4 hours. This second hydrolysis removes more iron, together with half of any aluminum present. Ammonium sulfate keeps nickel in solution. Concentrate the filtrate from aluminum to 150 ml., add 2 grams of tartaric acid, and precipitate nickel with dimethylglyoxime in the usual way. The hydrolysis of ferric sulfate begins at about p H 1.2 and some iron remains in solution at pH 3.4. This figure was first calculated, then verified after t h e hydrolysis by direct determination in a p H meter. As the p H is increased t o 3.8 the basic sulfates become slimy and filter slonly. At p H 3.8 the solubility for either iron or aluminum is still about 5 mg. T h e hydrolysis of aluminum sulfate begins at about pH 2.8 and is one-half complete a t p H 3.1. T h e solubility at 3.4 in terms of aluminum oxide is increased t o 35 mg. in the presence of 10 grams of ammonium sulfate. I n the analysis of meteorites, stainless steel, and some minerals, a few per cent of the divalent metals are present with large percentages of iron or both iron and aluminum. Numerous quantitative tests were made of the behavior of such combinations involving cobalt, nickel, zinc, or beryllium.
Literature Cited (1) Ardagh and Bongard, IND.EXG.CHEM.,16,297 (1924). (2) Britton, J . SOC.Chem. Ind., 41,3491‘ (1922). (3) Fairchild, Am. Mineral., 18, 543 (1933). (4) Fleischer, A. (to Kalunite Co.), U. S. Patent 1,958,083 (May 8, 1934). (5) Krueger, Z.anal. Chem., 114,241-8 (1938). (6) Lundell and Knowles, J . Am. Chem. Soc., 45,676 (1923). (7) Mellor, “Comprehensive Treatise on Inorganic and Theoretical Chemistry”, Vol. V, p. 341, New York. Longmans, Green and Co., 1935. (8) Ibid., Vol. XIV, pp. 3 5 3 4 . (9) Noyes and Bray, “Qualitative Analysis for the Rare Elements”, p. 393, New York, Macmillan Co., 1927. PRESENTED before the Division of Physical and Inorganic Chemistry at the 99th Meeting of the American Chemical Society, Cincinnati, Ohio. Published by permission of the Director, U. S. Geological Survey.
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