ANALYTICAL EDITION
June 15, 1943
O F I R O N IN THE EXTR.4CTION LfETHOD TABLE IT. DISTRIBUTION OF ANALYSIS
% F e as Fen08 (a)
Sample 18 19
20
In extract 0.24 0.24 0.35
Total Fe as % Fen02 Direct analysis of catalyst ( a ) -k ( b ) 1.98 1 87 1.90 1 90 2.40 2.23
(b)
I n extracted residue 1.74 1.66 2.06
“dry box”. The sinall fraction i5 transferred to a glass container for analysis. The analytical sample is taken b y inserting a test tube (holding 20 or 50 grams under the sampling conditions) into the bottle to the bottom, thereby removing a reasonably representative portion of the material for transfer t o the weighing bottle.
subsequent argentiometric estimation of chloride, give reproducible results representing 92 to 96 per cent of the total chloride content. Reproducible but l o x results for the chloride content of bauxite-supported aluminum chloride catalysts may be obtained by mater-extracting the catalysts by a standardized procedure. The method indicates 90 to 93 per cent of the total chloride content of the sample. The total chloride content of the catalyst may be determined b y a combination of the tn-0 methods: standard extraction of the original sample plus standard distillation of the ground residue from the extraction. Either the extraction or the distillation method is proposed as a satisfactory routine procedure. The combination method may be used when i t is essential to know the absolute chloride content.
Summary Decomposition of the catalyst with sulfuric acid and removal of the liberated hydrochloric acid b y distillation, ivith
387
Literature Cited (1)
Kolthoff and Furman, “Volumetric Analysis”, Vol. 2, pp. 218, 244, New York, John Wiley & Sons, 1929.
Determination of Iron In the Presence of Chromium and Titanium with the Jones Reductor F. S. GRIMALDI, R. E. STEVENS, A N D M .K. CARRON Geological Survey, U. S. Department of t h e Interior, Washington, D. C.
Sulfuric acid solutions of titanous and chromous sulfates, obtained by passage through the Jones reductor, are oxidized by aeration for from 5 to 10 minutes in the presence of a trace of copper sulfate as a catalyst. Ferrous sulfate is essentially unosidized
T
HE Jones (6) reductor was originally proposed as a
rapid and convenient device for the reduction of ferric to ferrous salts, prior to titration with a standardized solution of an oxidizing agent. The solution to be reduced is preferably a sulfuric acid solution, because side reactions that may occur in the presence of hydrochloric acid are thereby avoided in the ensuing titration. Although the Jones reductor is convenient, several elements other than iron are also reduced b y zinc, and various methods have been proposed to eliminate the effect of these interfering elements. Previous studies have dealt mainly with the interference of titanium. The stability to air-oxidation of ferrous sulfate in sulfuric acid solution was studied by Baskerville and Stevenson (Z), who showed that practically no oxidation of the ferrous sulfate occurred after 3 hours of aeration. They observed also that the presence of cobalt, chromium, copper, and titanium salts had no effect upon the air-oxidation of the ferrous sulfate. Thornton and Roseman (8) studied the preferential oxidation by air of titanous sulfate in the presence of ferrous sulfate. Their results were good, but they suggest that “the procedure is most apt t o succeed when the iron is equal to, or preponderates over, the titanium’’. Gooch and Nexton ( 4 ) used bismuth trioxide for the
and is titrated with permanganate after aeration. Best results are obtained by using 0.0003 millimole of copper sulfate in about 300 ml. of solution. Larger quantities of copper sulfate lead to slightly low results when both chromium and titanium are present.
preferential oxidation of the titanium. Their method requires the removal of the excess of bismuth trioxide before the estimation of iron. Brandt (5)used titanium trichloride as the reducing agent for ferric ion, the excess titanium trichloride being destroyed by copper sulfate. In this procedure the cupric ion is reduced to metal by the titanium trichloride and the precipitated copper is filtered off before titrating the iron. That simple air-oxidation of a titanous solution is not dependable is shown by hlcSabb and Skolnik ( 7 ) . Their results corroborate the experience of Margaret D. Foster of this laboratory, who found that in a solution containing titanous salt equivalent to 0.04 gram of titanium dioxide less than three fourths of the titanium was reoxidized to the quadrivalent state after 10 hours of aeration; a solution containing 0.09 gram of titanium dioxide &-asless than nine-tenths converted in the same time. Axt and Leroy ( 1 ) increased the rate of oxidation by using a perforated plate for supplying the air. McSabband Skolnik ( 7 ) found that the addition of 50 ml. of saturated mercuric chloride solution greatly increased the rate of oxidation of titanous sulfate by aeration. The method described below is based on the discovery b y Zintl and Wattenberg (10) that copper in solution catalyzes air-oxidation of titanous ion. This method is applicable for all proportions of iron, titanium, and chromium. Molybdenum and vanadium should be absent.
388
Vol. 15, No. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. DETERMINATION O F IRON Experiment No.
Fe Taken Gram
1 2 3 4 5 6
7 8 9 10
11
12 13 14 15 16 17 18 19 20 21 22 23
0.0315 0.1576 0.0314 0.0314 0,0942 0.2512 0.2512 0.0314 0.0314 0.1256 0.1256 0.0630 0.0314 0,1570 0.0314 0.0315 0,0315 0,1260 0.1577 0.063O 0.1265 0.0316 0.1256
I N THE PRESENCE O F
(3 ml. of 0.0001 M CuSO4 used) TlOz Cr203 Taken Taken Aeration .Win. Gram Gram h-one None 10 None Sone 10 None 0.5000 15 None 3 0.0030 Sone 0,0030 5 None 0 0030 None 0 5000 15 Sone 0.0030 10 Sone 10 0.5000 Sone 10 0.0030 Sone 10 0.5000 0 0 0 0 0 0 0 0 0 0 0 0
0010 0030 0030 3000 1400 0400 1400 0400 0400 0400
2000 0030
0.0010 0.0030 0.1200 0.0‘400 0.1400 0.3000 0.0400 0.0400 0.1400 0.3000 0.0030 0,0030
5 5 10 10 10 10 10 10 10 10 10 20
Apparatus JOKES REDUCTOR, as described and illustrated by Hillebrand and Lundell ( 5 ) . The 20- to 30-mesh zinc is amalgamated with 3 per cent mercury by shaking with a solution of mercuric chloride. Reagents COPPERSULFATE CATALYST.Solution A, 0.25 gram of cupric sulfate pentahydrate in 500 ml. of Mater. Solution B, 0.0001 molar cupric sulfate, 5 ml. of solution A in 100 ml. of water. Solution B should be made up fresh occasionally. POTASSIUX PERRIAKGANATE SOLUTIOX, 0.05 N , aged a t least a week and filtered through asbestos. Standardized against Bureau of Standards sodium oxalate. 0-PHENANTHROLINE INDICATOR ( 9 ) ,0.75 gram of o-phenanthroline monohydrate and 25 ml. of 0.05 ,?; ferrous sulfate diluted to 50 ml.
Procedure Pass the iron solution a t room temperature (about 200 ml., containing 10 ml. of concentrated sulfuric acid) through the Jones reductor a t a rate sufficiently slow to ensure complete reduction (about 100 ml. per minute). Add to the reduced solution 3 ml. of 0.0001 molar copper sulfate and pass through the solution as rapid a stream of air as is possible without loss by splashing. Continue the aeration for 5 minutes after the violet color of titanous sulfate has disappeared. If the violet color is masked by the green of chromium salts, aerate the solution for 10 minutes. If the solution is essentially colorless after reduction aerate for only 5 minutes. After aeration, titrate the solution of ferrous sulfate in the following manner: First prepare an indicator solution by adding 0.05 N potassium permanganate, a portion of a dfop at a time, to a solution containing 1 to 4 drops of the o-phenanthroline indicator in about 10 ml. of 10 per cent sulfuric acid, until the red color just turns to blue. Pour into this indicator solution a portion of the solution to be titrated, and set aside. Titrate the main portion of the solution to the appearance of the permanganate purple color (if much chromium is present the solution becomes gray-green), add the reserved portion, and titrate to the disappearance of the red color of the indicator. Calculate the iron after subtracting a blank determination on the reagents used. In the absence of much chromium the solutions may be titrated, but with less accuracy, without the o-phenanthroline indicator.
Experimental
For the
of the iron standard was established b y reduction in the Jones reductor and titration with permanganate. Fe Colorimetric tests &th hydrogen Found Error peroxide showed titanium to be esGram Gram sentially absent in the iron solution. 0.0317 +0.0002 None 0.1576 The titanium standard was prepared 0.0316 +o. 0002 from reagent grade potassium ti-0.0001 0.0313 -0.0002 0.0940 tanium fluoride (the fluorine being 0.2511 -0.0001 0.2513 +0.0001 expelled by repeated fuming with sul+0.0002 0.0316 furic acid) and the titanium content None 0.0314 -0.0001 0.1255 established grauimetrically. Colori- 0.0002 0.1254 None 0,0630 metric tests with thiocyanate showed None 0.0314 no iron in the titanium solution. -0,0004 0.1566 -0.0001 0.0313 Chromium was added as potassium - 0,0003 0.0312 - 0,0002 0.0313 dichromate solution made from the -0.0001 0.1259 reagent grade salt by direct weight. 0.1573 - 0.0004 0.0628 0.0002 Standardized pipets and burets viere Sone 0.1265 Sone 0.0316 employed. None 0.1256 Preliminarv studies were made to establish” the optimum concentration of copper sulfate to catalyze t h e oxidation. Large concentrations of copper sulfate, up to 1 mole, caused some oxidation of ferrous sulfate when both titanium and chromium were present, giving a maximum error in ten experiments of -0.0010 gram of iron. However, nine experiments in which only chromium or only titanium was present with the iron shon-ed a maximum error of *0.0001 gram of iron. Table I shows the results obtained by adding 3 ml. of 0.0001 molar copper sulfate as catalyst. The results are seen to be accurate in all the experiments made and throughout extreme ranges of composition. Experiments using still less copper sulfate shon-ed someu-hat incomplete oxidation of titanous sulfate after 10 minutes’ aeration. I n the last experiment in Table I the aeration period was increased to 20 minutes and showed no loss in ferrous content through oxidation. I n experiments 3 and 7, in which 0.5 gram of titanium dioxide was taken, the violet titanous sulfate color persisted for 9 minutes; consequently the aeration period was extended to 15 minutec.
CHROhlIUV .4ND TITANIUM
work were made containing known quantities of iron, titanium, and chromium by mixing Various wdumes of standard solutions. The strength
Acknowledgments The writers gratefully acknowledge the cooperation of several members of the Chemical Laboratory of the U. S. Geological Survey. The work was done under the supervision of R. C. Wells, chief chemist, whose review of the manuscript led to many improvements. Margaret D. Foster made available to the writers her experiences with air oxidation of titanous salts. Joseph 31. Axelrod contributed many useful suggestions during the progress of the investigation.
Literature Cited (1) (2)
Axt, M., and Leroy, M., Ing. chim., 24,28 (1940). Baskerville, C., and Stevenson, R., J . Am. Chem. SOC., 33, 1104 (1911).
Brandt, L., Chem.-Ztg., 42,433, 450 (1918). Gooch, F. A,, and Newton, H. O., Am. J . Sci., 23,365 (1907). (5) Hillebrand, W. F., and Lundell, G. E. F., “Applied Inorganic Analysis”, p. 101, New York, John Wiley & Sons, 1929. (6) Jones, Clemens, Trans. Am. I n s t . M i n i n g Engrs., 17, 4 1 1 (1888(3) (4)
89).
McNabb, W. M., and Skolnik, H., IND. ENQ.CHEX.,ANAL.ED., 14.711 (1942). (8) Thornton,‘W. M., Jr., and Roseman, R., J . Am. Chem. Sac., 57, (7)
619 (1935). (9)
Walden, G. H., Jr., Hammett, L. P., and Chapman, R. P., Ibid., 53, 3908 (1931).
(IO) Zintl, E., and Wattenberg, H,, Ber., 56, PUBLIBXED
by permission of the Director,
472 (1923).
u. s. Geological Survey.
