Determination of Stibnite Sulfur in Ores and Minerals J. A. TSCHERNIKHOV
AND
TATIANA A. USPENSKAYA, Rare Elements Research Institute, SIoscow, U. S. S. K.
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a solution finally distinctly acid (1 t o 2 per cent of free concentrated acid by volume). Titrate excess iodine with 0.1 N sodium thiosulfate, using starch indicator.
HE selective determination of sulfur present as antimony trisulfide in stibnite is impossible by drastic oxidation methods-. g., Cushman's bromine and acetic acid method (S), or sodium peroxide or carbonate-nitrate fusion (1)which yield results for total sulfur. Interference by free sulfur, sulfate sulfur, and acid-insoluble sulfides is avoided in the evolution procedure of McNabb and Wagner (6). This method is satisfactory for pure natural stibnite or for antimony sulfide obtained by liquation of ores, but when applied to low-grade ores which contain considerable amounts of other metallic sulfides partly or wholly decomposed by hydrochloric acid (galena, cinnabar, copper glance) it yields results which include sulfur from these impurities. McNabb and Wagner (6) suggested the separate determination of alkali-insoluble sulfide impurities in the residue from extraction of stibnite with hot aqueous sodium hydroxide, but if applied to low-grade ores this method would be unduly laborious and would not exclude interference by sulfide impurities soluble in alkali. The authors attempted the determination of sulfur present as antimony sulfide (and as other sulfides soluble in alkali and decomposable by hydrochloric acid) by extraction with hot aqueous alkali, acidification of the filtered extract, and application of the evolution procedure to the reprecipitated sulfides. Results were irregular and as much as 10 per cent low, no doubt because of air oxidation of the dissolved sulfo salts. The method described below permits the direct determination of sulfur present as alkali-soluble sulfide. The sample is extracted with hot sodium hydroxide solution, and the resulting solution of antimonite and thioantimonite reduced by aluminum powder. This precipitates metallic antimony and leaves sulfur in solution as sulfide ion, the hydrogen incidentally liberated preventing air-oxidation. The sulfide sulfur is determined iodometrically by pouring the solution into a measured excess of standard iodine solution suitably acidified and titration of excess iodine with standard thiosulfate. The reactions involved are:
With rich ores a too prolonged grinding should be avoided, or air oxidation of some sulfide sulfur may occur. This precaution was not observed to be necessary with lean ores. The quantity of aluminum required varies, much of the metal being dissolved with evolution of hydrogen. The reaction is less vigorous and is more readily controlled if aluminum foil is used. Aluminum powder acts more rapidly, producing considerable effervescence, which may become excessive if the powder is too fine. If the sodium hydroxide contains traces of oxidized chlorine compounds the solutions should be treated with aluminum powder before use. A blank test of the excess titration (last paragraph of procedure) showed no consumption of iodine when a sodium hydroxide solution reduced with aluminum was added to the acidified iodine solution and the iodine titrated with thiosulfate. The procedure described requires about 2.5 hours.
Tests of the NIethod APPLICATIONTO PURESTIBKITE. The accuracy of the method was tested by trials with a specimen of pure stibnite containing not more than traces of foreign sulfides, and analyzed also by the evolution method. The latter was used in a modified form, the hydrogen sulfide being absorbed in cadmium acetate solution, and sulfide sulfur determined by addition of potassium iodide and titration with 0.1 N permanganate; this avoided filtration of cadmium sulfide and the subsequent shaking with acidified iodine solution (6). Results by both methods appear in Table I. TABLE I. DETERMINATION OF SULFIDE SULFURIN PURE STIBNITE Modified Evolution Method
++ 60H= -SbSa + %boa + 3Hz0 %bOI + 2A1" + 60H- = 2 'A103 + 2Sb" + 3Hz0 + 3s35- + 3 1 2 = 35' + 61-
%
Sb&
28.05 28.09 28.17 27.99 27.95 Av. 28.05
'SbS3
Procedure Weigh out sufficient sample (200-mesh) to yield not over
Proposed Method
% 28.00 27.98 28.20 27.85 28.10 28.05
EFFECTIVENESS OF ALKALIEXTRACTION FOR SEPARATION ANTIMONYSULFIDEFROM FOREIGN SULFIDES. The
0.03 t o 0.04 gram of sulfide sulfur (about 0.2 gram of pure stibnite to 2 grams of low-grade ores). Transfer to a porcelain or alkaliresistant beaker, add 20 cc. of 2 N sodium hydroxide, and boil for 20 to 26 minutes. Record the uantities of alkali used here and in subsequent operations, so t?at the quantity of acid reuired for final acidification may be estimated. Decant the
OF
specificity of the new method with respect to antimony sulfide in low-grade ores was tested (1) by examination of the behavior of various foreign sulfides in the alkali-extraction procedure, (2) by qualitative study of the effects of alkali extraction applied to artificial mixtures of stibnite and other sulfides, and (3) by actual determination of stibnite sulfur in such mixtures by the proposed method. 1. Solubility of Some Mineral Sulfides in Hot Aqueous Alkali. Cinnabar, copper glance, galena molybdenite, zinc blende, and pyrite were found to be unattacfred by hot aqueous alkali. By combined action of alkali and aluminum powder or foil the first three sulfides were completely decomposed, sodium sulfide being formed and the metal precipitated. The same treatment decomposed pyrite with difficulty and incompletely, with removal of only one atom of sulfur. Molybdenite and zinc blende were unattacked.
h a l i n e extract into a small suction filter, and wash the residue by decantation with hot 0.5 N sodium hydroxide, passing this also through the filter. Discard the insoluble residue. To the alkaline filtrate add aluminum powder or foil and heat until reduction is complete; usually 0.3 to 0.6 gram of aluminum will suffice. Allow the recipitate of antimony to settle, and decant the li uid througt the filter. Wash the residue by decantation wit? several portions of hot 0.5 N sodium hydroxide, passing each washing through the filter. The extraction is complete when a drop of the wash-liquid gives a negative test with a drop of lead acetate solution on a spot-plate. Cool the combined alkaline extracts, and pour into a measured excess (20 to 40 cc.) of 0.1 N iodine previously diluted t o 200 cc. and mixed with enough concentrated hydrochloric acid to yield 309
310
INDUSTRIAL AND ENGINEERING CHEMISTRY TABLE11. DETERMINATION OF STIBNITE SULFUR IN MIXTURES OF STIBNITE AND OTHERSULFIDES
Total Weight Stibnite of ----Foreign Sulfides0.i.N 0.1 N Sulfur Sulfur Sample SbzSa pbs CUS HgS FeSz Iodine NazSz08 Found PresentC Gramsn Grama Gram Gram Gram Gram Cc. Cc. % % 1.oooo 0.1986 0.1013 0.10oo 0.1004 0.1007 40.00 7.31 5.23 5.24 1.0000 0,2009 0.1008 0,1000 0.1002 0.0998 40.00 6.32 5.39 5.30 1.0000 0.1894 0.1002 0.0994 0.0996 0.1000 40.00 7.31 5.23 5.26 1.0000 0,2012 0,0998 0,1000 0.0981 0.1005 40.00 7.21 5.25 5.31 1.0000 0.0975 0.0972 0.0963 0.0968 0.1976 25.00 7.66 2.77 2.72 1.0000 0,1000 0.1000 0,0995 0.1004 0.1010 25.00 7.85 2.74 2.72 2.0000 0,0585 0.1003 0.0992 0,0983 1.0000 20.00 6.60 1.07 1.09 2.0000 0.0600 0.1018 0.1027 0.1006 0.9996 20.00 6.10 1.11 1.11 2.0000 0.0595 0.1020 0.1038 0.1000 1.0000 20.00 6.00 1.12 1.10 2.0000 0.0567 0.1015 0.10oo 0.1001 1.00oo 20.00 6.50 1.08 1.07 a Combined sulfides made up to weight indicated by addition of quartz sand. b Specimen contained 25.60 per cent of stibnite sulfur. Includes previously determined traces of sulfur preaent as arsenic and antimony sulfidea in the pyrite and cinnabar added to the samples.
9. Qualitatiue Tests of Hot Alkali Extraction of ArtiJicial
Mixtures ofOf0.2 Stibnite and of stibnite Otherand the selected S u ~ dforeign e s *A mixture gram each sulfide was extracted first with 20 cc. and then again with 10 cc. of boiling 2 N sodium hydroxide, the residues being washed each time with hot 0.5 N sodium hydroxide and tested for antimony. The first extract was tested for presence of the foreign metal, and the second extract was tested also for antimony. To test for mercury there was used the Feigl spot-test (4) with aniline and stannous chloride. Lead, copper, and iron were sought by addition of sodium tartrate and sodium sulfide. To examine for antimony in the second extract there was employed the Clarke and Evans color test (.2) with potassium iodide, pyridine and gum arabic. These tests showed that antimony sulfide was completely dissolved by the first extraction, the second extract being free from antimony as were also the undissolved residues. Sulfides of mercury, copper, lead, and iron were unattacked in the first extraction, tests for these metals in the filtrates being negative. Only traces of lead, copper, and iron mere detected in the second
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extract from mixtures of stibnite with galena, copper glance, or pyrite, respectively, and cinnabar was wholly undissolved. 3. Determination of Stibnite Suljur in Artiricial Mixtures of Stibnite with ‘various Proportions of Foreign &&des. Mixtures of weighed amounts of
stibnite! galena, copper glance, pyrite, and cinnabar were diluted with quartz sand to simulate lowgrade ores, and analyzed by the new method as described. Results are presented in Table 11.
The results in Table I1 indicate that the proposed method permits accurate determination Of the sulfur of stibnite in presence of sulfides of lead, copper, iron, and mercury. Free sulfur and arsenic sulfide interfere to whatever extent they are present, and Ordinarily introduce a n inconsiderable error. The new method is recommended for the rapid and accurate determination of stibnite sulfur in stibnite and in low-grade ores containing as impurities other sulfides such as galena, copper glance, cinnabar, and Pyrite- It will Probably yield the sulfur combined with antimony in certain mineral double-sulfides such as livingstonite, boulangerite, and zinkenite.
Literature Cited “Chemisoh-technisch Untersuchungsmethoden,” Band 11, Teil 2, p. 1677, Berlin, Julius Springer, 1932.
(1) Berl-Lunge,
(2) Clarke and Evans, Analvat, 54, 23 (1929). ENQ.CHEM.,10,376 (1918). (3) Cushman, J. IND.
(4)
Feigl, “Qualitative Analyse mit Hilfe von Tiipfelreactionen,” p. 132, Leipzig, Akademische Verlagsgesellschaft m. b. H., 1931.
(5) McNabb and Wagner, IND.ENG.CHEM.,Anal. (6) Ibid., 2, 254 (1930).
Ed., 1, 32
(1929).
RECEIVED July 16, 1934.
Zinc Cobaltinitrite for the Detection of Potassium JANE ADAMS, MARTHA HALL, AND W. F. BAILEY, MacMurray College, Jaclisonville, 111.
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HE reagents commonly used for the qualitative detection of sodium and potassium are not completely satisfactory. Probably the most sensitive are sodium cobaltinitrite for potassium and zinc uranyl acetate for sodium as recommended by Kolthoff (1). If these are used, however, a separate portion must be used for sodium; and if a large amount of potassium is present it must be at least partially removed before use of the sodium reagent. For this purpose, the zinc perchlorate procedure of Reedy (2) is very satisfactory. The purpose of this investigation was to develop a reagent which would retain the sensitivity of the sodium cobaltinitrite reagent without introducing sodium ion and a t the same time leave the filtrate in a state best suited for the use of zinc uranyl acetate for the detection of sodium. Zinc cobaltinitrite should answer the purpose, since the added zinc ion should decrease the solubility of the sodium precipitate by common ion effect. Experimental Throughout the course of the investigation the chemicals used were Baker’s c. P. anal zed. Attempts to prepare zina nitrite were almost entirely witgout avail. Barium nitrite was made by metathesis of sodium nitrite and barium chloride. On dissolving this in a solution of cobalt nitrate and acidifying with acetic acid, a yellow precipitate of barium cobaltinitrite separated, and was converted to zinc cobaltinitrite by shaking with a solu-
tion of zinc sulfate. The resulting solution, however, was too unstable to be practical. Direct preparation of a cobaltinitrite solution was then tried by passing oxides of nitrogen through (1) a solution of cobalt nitrate containing suspended zinc hydroxide, (2) a suspension of zinc and cobalt hydroxides, and (3) a solution of zinc acetate and cobalt acetate. In all cases a darkening resulted and the solution gave a yellow precipitate with potassium nitrate. The third method gave by far the most consistent results. The oxides of nitrogen were made by the action of either dilute sulfuric acid on a solution of. potassium nitrite or concentrated nitric acid on copper, the latter being most convenient. The final method of preparation adopted was t o pass a rapid stream of oxides of nitrogen, made by the action of concentrated nitric acid on copper foil, through a solution saturated with both cobalt acetate and zinc acetate for from 45 to 60 minutes. The resulting dark brown solution was tightly stoppered, allowed to stand overnight, and then decanted from any precipitate. If kept tightly stoppered t o prevent loss of oxides of nitrogen, the solution was as sensitive as ever after 6 weeks; left open to the air, all cobaltinitrite disappeared within a week. T o test the sensitivity of the reagent, solutions containing varying amounts of potassium nitrate were mixed with an equal volume of the reagent. The sensitivity is given in milligrams of cation per milliliter of the resulting solution. Repeated tests showed that 1 mg. of potassium per milliliter gave an immediate yellow precipitate. After standing for 15
