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nearly constant. The loss in antimony appears to be a function of the temperature; the curve shows that it increases with the finishing temperature with the exception of the jog at 450°C. which, as stated with Table III, is an unexplained experimental accident.
The following conclusions may be drawn from the investigation:
1. The ignition point of stibnite is approximately 200°C. as evidenced by the odor of SO, evolved and its action on litmus paper.
2. There is a sharp visible formation of Sb203 at 336°C. At this point white fumes are evolved.
3. The formation of Sb203 takes place slowly, probably according to the reaction:
Sb2S3 + 90 = Sb2O3 + 3802
4. It is possible to eliminate all the sulphur slightly below 400°C. without a large loss of antimony.
5. Stibnite is oxidized at first to antimony trioxide which begins to change to antimony tetroxide only when all the sulphide has been decomposed.
6. The amount of tetroxide increases as the trioxide decreases, the action being more rapid as the finishing temperature is raised.
7. The loss of antimony during the roast increases with the temperature.
A discussion of the chemical work is given in the paper by W. T. Hall and J. Blatchford, read at this meeting.
(SUBJECT TO REVISION) DISCUSSION OF THIS PAPER IS INVITED. It should preferably be presented in person at the New York meeting, February, 1916, when an abstract of the
paper will be read. If this is impossible, then discussion in writing may be sent to the Editor, American Institute of Mining Engineers, 29 West 39th Street, New York, N. Y., for presentation by the Secretary or other representative of its author. Unless special arrangement is made, the discussion of this paper will close Apr. 1, 1916. Any discussion offered thereafter should preferably be in the form of a new paper.
The Determination of Antimony in the Products Obtained by Roasting
WILLIAM T. HALL,* BOSTON, MASS. AND JOHN BLATCHFORD, † OAK PARK, ILL.
(New York Meeting, February, 1916)
The product obtained by roasting stibnite is likely to contain some unoxidized antimony trisulphide and a mixture of antimony trioxide and antimony tetroxide. It was desired to determine, as accurately as possible, the condition of the antimony as well as the total quantity present. Attempts were made to separate the trisulphide and the two oxides by methods based upon their varying solubilities in different solvents, but no satisfactory results were obtained in this way. It was found, however, that by determining the total antimony content, the antimony present as trioxide, and the antimony present as trisulphide, a good idea of the chemical composition of the roasted product could be obtained.
The total antimony was determined by dissolving the sample in concentrated hydrochloric acid, reducing the antimony entirely to the trivalent condition by means of hydriodic acid and eventually titrating the antimony back to the pentavalent condition by means of iodine in the presence of sodium bicarbonate.1 The details of the procedure are as follows:
Weigh out 0.25 gram of the roasted product into a trapped flask (Fig. 1), add 4 grams of powdered tartaric acid, 2 grams of potassium iodide and 40 c.c. of concentrated hydrochloric acid. Boil the solution gently for 5 min. and then cool to room temperature by shaking the flask while holding it under running water. Then, very carefully discharge the iodine color by the cautious addition of 0.05-normal.sodium thiosulphate solution, adding a little starch toward the last. Nearly neutralize the acid with ammonia solution, but leave the solution distinctly acid.
Pour the slightly acid solution into 200 c.c. of water conAssistant Professor of Analytical Chemistry, Massachusetts Institute of † Analytical Chemist and Metallurgist. F.A. Gooch and u. w. Gruener: American Journal of Science, Series 3, vol.
xlii, p. 213 (1891).
taining an excess of sodium bicarbonate and titrate to a permanent blue color with standard 0.1-normal iodine solution.
The determination of the unchanged antimony sulphide was accomplished by a method corresponding to that used in the determination of sulphur in steel. The sample was dissolved in concentrated hydrochloric acid, the escaping hydrogen sulphide absorbed in an ammoniacal cadmium chloride solution and the sulphur in the precipitated cadmium sulphide determined iodometrically.
Inasmuch as all the antimony present in the roasted stibnite was soluble in concentrated hydrochloric acid, the solution remaining in the evolution flask after the determination of the sulphur could be used for the determination of the trivalent antimony. The details of the procedure are as follows:
To the solution remaining in the evolution flask after the determination of the sulphur, add 4 grams of powdered tartaric acid and carefully dilute with 100 c.c. of water. Carefully add 6-normal ammonia
А. - Shortened OaCl, Tube
B = 400 C.C.Erlenmeyer Flask Fig. 1.-APPARATUS USED IN DETERMINATION OF ANTIMONY IN ROASTED STIBNITE.
solution until the solution is only slightly acid and then pour the solution into a large beaker containing 5 grams of sodium bicarbonate in 200 c.c. of water. Titrate with 0.1-normal iodine solution as in the determination of the total antimony.
In computing the results, it is necessary to remember that antimony tetroxide may be regarded as antimonious antimonate:
2Sb2O4 = Sb2O3 + Sb205. Since antimony pentoxide changes to the tetroxide when heated above 300°, it is fair to assume that each atom of pentavalent antimony found in the analysis corresponds to one molecule of antimony tetroxide. Then from the total quantity of trivalent antimony found, deductions must be made for the amount of tetroxide and for the trisulphide as found by the sulphur determination; the balance is the trivalent antimony corresponding to the quantity of antimony trioxide present.
Comparatively little information concerning the chemical properties
2 A. A. Blair: The Chemical Analysis of Iron, 7th Edition, p. 60. H. Kinder: Stahl und Eisen, vol. xxviii, p. 249 (1908). Massenez: Ibid, vol. xxxii, p. 2089 (1912)