Determination of Tin with Mercuric Chloride J. G. FAIRCHILD, Geological Survey, U. S. D e p a r t m e n t of the Interior, Washington, D. C.
Tin can be determined by weighing the mercurous chloride formed on adding stannous chloride to mercuric chloride. With pure tin solutions the procedure is rapid and accurate and is applicable over a range from 0.1 to over 70 per cent tin. The present paper describes the necessary procedures as applied to concentrates, cassiterite ores, and ores containing complex tin sulfides. It is especially suited for tin in low-grade ore.
T
H E most common method of determining tin is that in which stannic chloride is reduced by a metal and the resulting stannous chloride is titrated with a standard solution of iodine. The reducing metal may be lead (6),antimony (6),iron (4),or nickel (2). Tin may also be precipitated with cupferron in a fluoborate solution and weighed as the oxide ( I ) , a method that separates tin from lead, bismuth, copper, and antimony. Various separcc tions of tin from other metals are listed by Hillebrand and Lundell (3),but only a few of these refer to combinations found in ores. The method of determining tin described in the present paper is an application of the well-known qualitative reaction between stannous chloride and mercuric chloride, which also serves to s e p arate tin from most other metals. The precipitated mercurous chloride is allowed to settle half an hour or more, filtered off on a Gooch crucible, washed, dried a t 105" C., and weighed. Weight of mercurous chloride X 0.2514 equals weight of tin, a very favorable factor. Another good feature of the method is that the tin gives visible evidence of its presence, whereas in the volumetric method it is not always certain that only tin is being titrated. The directions that follow refer more particularly to the procedures necessary to bring different types of tin ores into solution and the subsequent preparation of stannous chloride by reduction with zinc. The tin and excess zinc are finally dissolved in hydrochloric acid and mercurous chloride is determined w described above.
filtrate in a 250-ml. volumetric flask. The residue may contain about 1 per cent of the tin. Fuse it with cyanide as before. Digest the second metallic residue with the main solution of stannous chloride in the beaker, adding a little concentrated hydrochloric acid if necessary. Cool and filter this solution into the volumetric flask, washing the beaker and filter with dilute acid. Dilute the tin solution to exactly 250 ml., shake thoroughly, and transfer 25 ml., representing 0.1 gram of sample, into a 125-ml. Erlenmeyer flask. Add 2 grams of 20-mesh zinc to the sli htly inclined flask. Close the flask with a 1-hole rubber stopper &ted with a glass tube having a small outlet and two enlarged bulbs in the middle to aid in condensing steam as the flask is heated. This outfit is designed to effect reduction of the tin with exclusion of air. Zinc reduces the tin to a sponge which floats after a time. At this oint add 0.3 gram more of zinc and 12 ml. of concentrated hy&ochloric acid. Finally heat the flask gently until all the zinc and tin are dissolved, while maintaining a continuous outward pressure of steam. Next close the capillary outlet with another rod and rubber tube connection. Cool the flask in running water, release the vacuum, and quickly pour the stannous chloride solution into 30 ml. of mercuric chloride solution containing 1 gram of mercuric chloride, a twofold weight for 0.1 gram of tin. The beaker for precipitation may be 150-ml. size. After rinsing out all the tin solution, the volume in the beaker will be about 120 ml. Let the precipitate settle 30 minutes or more, then filter it by suction into a prepared Gooch crucible. Wash the beaker and crucible three times with 1 to 4 hydrochloric acid, then three times with hot water. This washing removes a few milligrams of lead chloride generally derived from the zinc. Dry for half an hour a t 105' C. Weigh and heat for 15 minutes further to check the weight. The drying of mercurous chloride should not be unduly prolonged: Per cent of Sn = weight of HgCl X 0.02514 X 10 X 100 Results obtained on various samples are shown in Table I. Nos. 1 to 4 are tests of the method made on Bureau of Standards Sample No. 42-C, which contains 99.99+ per cent of tin. Nos. 5 ahd 6, 7 and 8, and 9 and 10 represent three different concentrates run in duplicate. The agreement is satisfactory for the quantity of sample taken.
Tin in Cassiterite Ores Digest 4 grams of the pulp on the steam bath for several hours in a platinum dish with 20 ml. of 1 to 1 sulfuric acid and 15 ml. of hydrofluoric acid. Cover the dish with a larger one. After an hour remove the cover and let the solution evaporate overnight. Heat to fumes, dilute with water, and again concentrate to fumes of sulfur trioxide. Add 40 ml. of 1 to 1 nitric acid and heat until solution is practically complete. Transfer the mixture to a 600-ml. beaker, dilute to 400 ml., and heat to simmering for an hour or more. Filter off any insoluble matter, wash with hot dilute nitric acid, and fuse the ignited residue once only with sodium cyanide as described above. Make up any stannous chloride recovered to 100 ml. and determine tin in 25 or 50 ml., accordin to the richness of the ore. This method will handle most s d d e material low in antimony or copper.
Rich Concentrates of Cassiterite The chief impurities may be oxides of iron, rutile, or tourmaline. Fuse 1 gram of 200-mesh material in a porcelain crucible with sodium pyrosulfate. One ram gives a good sample and provides enough solution for 10 3uplicates. Leach the melt with 50 ml. of 1 to 19 nitric acid, rinse into a beaker containing 400 ml. of 1 to 19 nitric acid, and heat to simmerin for at least one hour. This digestion reprecipitates any tin &solved by the fusion. Not more than 0.5 mg. is lost, as shown by careful tests. Filter off the insoluble residue and wash it with hot dilute nitric acid. Dry and ignite the filter in a 30-ml. porcelain crucible. Fill this crucible half full of sodium cyanide, mix well, and fuse gently until all the cyanide is melted and the tin is reduced to metal. A few weak explosions may occur from the carbon monoxide released, so that i t is advisable to hold the crucible in tongs and gently swirl it. When the melt is quiet, heat in the full flame of the Bunsen burner for 2 minutes in ordel, to form visible beads of tin. Cool the melt in a ring around the wall of the crucible to prevent the crucible from cracking. Leach with hot water in a casserole and carefully decant the cyanide solution without filtering into a sink which is being flushed with water. Wash three times in like manner. Dissolve the tin in about 50 ml. of hot 1 to 1 hydrochloric acid and 10 ml. of concentrated sulfuric acid with the casserole covered. Solution of the tin requires several hours' di estion a t about 60' C. Cool the solution of stannous chlorife, filter it into a small beaker, and reserve for a later addition. Wash the residue with 1 to 4 hydrochloric acid and catch the
Typical results are shown in Table I. Nos. 11 and 12 are duplicates on a sample containing some chalcopyrite. Nos. 13 and 14, 15 and 16 are duplicates on ordinary cassiterite ores. No. 19 is a Bolivian tin concentrate, Bureau of Standa d s No. 137, with certified tin 56.64 per cent.
Tin in Complex Sulfides This procedure covers concentrates of the tetrahedrite group [4Cu~S.(Sb,As)zSs]containing some stannite (CurS.FeS.SnSa) or teallite (PbS.SnSz). Digest 2 grams of the finely ground sample in a covered beaker with a little concentrated nitric acid. After the reaction subsides add a little more acid and evaporate on the steam bath nearly to dryness. Add 200 ml. of water and digest until the 625
INDUSTRIAL AND ENGINEERING CHEMISTRY
626
OF TIN IN TABLEI. DETERMINATIONS
VARIOUS
CONCENTRATES, AND ORES
NO.
1 2 3 4
Sample Taken
Sn Found
Error
Qram
Qram
Qram
0.0510 0.0510 0.0816 0.1020 5 0.1000 6 0.1000 7 0.1000 8 0.1000 9 0.2000 10 0.2000 11 1.0000 12 1 .0000 13 1 .0000 14 1.0000 15 1.0000 16 2,0000 17 1.0000 18 1.0000 19 0.2000 a Average of 56.4,56.8,and 57.0.
0.0509 0,0509 0.0812 0.1025 0.0701 0.0700 0.0644 0.0644 0,0812 0.0808 0,0107 0.0110 0.0231 0,0243 0.0492 0.0998 0.0055 0,0099 0.1134
SOLUTIONS,
-0.0001 -0.0001 0.0004 +0.0005
-
....
.... ....
.... ....
.... *... .... .... .... ....
.... ,... .... ....
sn %
.... .... ....
....
70.1 70.0 64.4 64.4 40.6 40.4 1.07 1.10 2.31
“4.99 4;:
0.55 0.49 56.7a
residue settles completely. Filter through a 9-cm. No. 40 Whatman paper, wash the residue with 1 to 1 nitric acid, then transfer it to the filter with hot water. Place the filter in the beaker, cover it with a little concentrated sulfuric acid, and fume with small additions of sodium nitrate until oxidation of the paper is complete, Add a little water and transfer the solution to a large latinum crucible for evaporation with hydrofluoric acid to umes of sulfur trioxide. Dissolve the sulfates of tin, antimony, or possibly lead in 20 ml. of 1 to 4 hydrochloric acid, transfer the solution to a 100-ml. volumetric flask, and make up to volume. The oxides of antimony and tin should not be ignited because they form a solid mixture. Transfer 50 ml. of the solution to the special flask for reduction with 4 to 5 grams of zinc, usin the mossy variety for slow action. Allow the reduction to proceej for half an hour with zinc still in excess, then add 25 ml. of hydrochloric acid and heat to boiling
P
VoL 15, No. 10
for about 5 minutes. Cool quickly with the flask closed, release the vacuum, and filter off antimony and lead on a fast paper, such as S. & S. 597, directly into 15 ml. of mercuric chloride solution with stirring. Wash once with dilute hydrochloric acid. A small precipitate of mercurous chloride settles slowly, Weigh the mercurous chloride and calculate 60 tin as described above.
Nos. 17 and 18, Table I, are duplicates on a sample high in sulfides. No. 18 contained 5.0 mg. of standard tin purposely added in excess of the quantity in the ore. Summary The chief advantages of this method are the use of a small volume of stannous chloride for the precipitation of mercuroua chloride and the simplicity of reducing the tin. Lead and antimony in minor quantities are the only metals likely to interfere, but their relative insolubility in dilute acid after reduction with zinc makes the interference negligible for most ores. This method is more easily controlled than the iodometric, and will handle most types of ore, according to the indicated procedure. Concentrates of 70 per cent tin, or more, are completely reduced by a single fusion with sodium cyanide. Much time is saved by one short reduction. Literature Cited (1) Furman, N.H., IND.ENO.CHEM.,15, 1071 (1923). (2) Hallett, R. L., J. SOC.Chem. I d . ,35, 1087 (191F). (3) Hillebrand, W. F., and Lundell, G . E. F., “Applied Inorganic Analysis”, p. 235,New York, John Wiley & Sons, 1929. (4) Low, A. H., “Technical Methods of Ore Analysis”, 11th ed., p. 241, New York, John Wiley & Sons, 1939. (5) Lundell, G. E. F., and Schemer, J. A., J. IND.ENQ.CHEM.,14. 426 (1922) (6) Stelling, E., Ibid., 16,346(1924). I
PUBLIFJAED by permission of the Director, U. S. Geological Survey.
Determination of Small Amounts of Arsenic, Antimony, and Tin in Lead and Lead Alloys C. L. LUKE,Bell Telephone Laboratories, Inc., New York, N. Y.
A new method for the determination of small amounts of arsenic, antimony, and tin in lead and lead alloys consists of separation of the three metals from the lead by a double coprecipitation with manganese dioxide, reduction of arsenic and
M
ETHODS for the determination of small amounts-i. e., 0.001 to 0.02 per c e n t o f arsenic, antimony, and tin in lead and lead alloys usually call for the preliminary removal of lead as sulfate. This separation is not satisfactory, however, unless hydrofluoric acid is added to ensure complete solution of the three metals (17). If hydrofluoric acid is used, platinum or ceresin vessels are required unless the glassware is known to be arsenic-free. Recently a very accurate method of separating lead from its impurities has been described (4), but it requires special apparatus and is not suitable for rapid analysis. Several years ago a method was developed in these laboratories which hss proved to be very satisfactory for routine analysis of lead alloys (see Table 11). In this method the arsenic, antimony, and tin are separated as hydrated oxides from the nitric acid solution of the alloy by coprecipitation with hydrated manganese dioxide ( 9 , I I ) . After separation from the lead, the metal oxides are converted to sulfates, and arsenic and antimony are reduced
antimony to the trivalent state, separation of the arsenic by distillation as chloride, titration of the arsenic and antimony separately by the method of Gyory, and reduction of tin with lead and titration with standard iodine solution.
to the trivalent state. Arsenic is then separated by diRtillation as chloride, and titrated with standard bromate solution by t h e method of Gyory (8). The solution containing the tin and antimony is diluted with hot water, and the antimony is titrated by the Gyory method. Finally, tin is reduced with lead and titrated with standard iodine solution (9). The method is applicable to the analysis of pig lead and all the usual types of lead alloys except those containing selenium, tellurium, and large amounts of antimony and tin. Methods of analysis employing coprecipitation separations have been developed for the latter alloys, but will not be considered here.
Apparatus The apparatus required for the distillation of arsenic is shown in Fisure 1. It consists of a 500-ml. Erlenmeyer flask with a three-hole rubber stopper carrying a 0.6-cm. (0.25-lnch) glass tube, a thermometer, and a glass capillary pressure regulator
