Quantitative Separation of Small Amounts of Zinc from Material Rich in Iron FRANKLIN 6. HILLS,Experimental Plant, Colorado School of Mines, Golden, Colo.
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N TECHNICAL analyses zinc is usually determined by the volumetric ferrocyanide method in which the iron is separated by precipitation with ammonium hydroxide, and the manganese by the addition of bromine or ammonium persulfate to the ammoniacal solution. This method is mpid and accurate in skilled hands. However, the separation of iron and manganese from zinc is open to criticism, because of the retention of zinc in the iron and manganese precipitates. When dealing with the usual ores and nietallurgical products, this difficulty is overcome by dissolving the washed precipitate in hydrochloric acid and repeating the precipitation, and by adding ammonium chloride to the solution before each precipitation of iron with ammonium hydroxide (3, 4). If only a few tenths of a per rent of zinc are to be separated from a relatively large amount of iron, the above method of separation is not satisfactory. Precipitation of zinc as zinc sulfide from a solution made slightly acid with sulfuric or formic acid (2) gives a good separation of zinc from iron and manganese when dealing with ordinary ores. It is difficult, however, to obtain the careful adjustment of acidity necessary when minute amounts of zinc are to be separated from large amounts of iron. The following method has been developed to overcome these objections: Weigh 5 grams of material into a 400-cc. beaker PROCEDURE. and decompose with hydrochloric acid, with the addition of nitric acid if sulfides are present. After decomposition,evaporate to dryness and bake. Cool, add about 10 cc. of hydrochloric acid, and warm gently until all soluble matter is dissolved. Filter, and wash the insoluble material free from chlorides. Neutralize the excess hydrochloric acid with ammonium hydroxide, leaving the solution sufficiently acid to prevent hydrolysis of the iron. Add an excess of a sodium citrate solution, prepared by dissolving 1 pound (453.6 grams) of sodium citrate and 20 grams of citric acid in sufficient water to make one liter of solution. It is not possible t o state the exact quantity of sodium citrate which will meet all conditions, as this depends upon the amount of iron, and on the excess hydrochloric acid present. In general from 20 to 50 cc. of the solution are required. There should be enough hydrochloric acid to prevent the formation of any precipitate upon the addition of the sodium citrate solution, and enough sodium citrate solution to react with the excess hydrochloric acid. Dilute to 250 to 300 cc. and pass hydrogen sulfide through the cold solution until it is thoroughly saturated and the precipitate coagulates. Filter and dissolve the precipitate with hot dilute nitric acid into the beaker used for the recipitation. Evaporate to dryness and bake. Cool, dissolve t i e residue in hydrochloric acid, add about 6 grams of ammonium chloride, and proceed by any of the usual methods for the determination of zinc.
A small amount of iron or manganese, in case of a manganese ore, will accompany the sulfide precipitate and may be separated by the usual methods. The amount is so small as to cause no serious difficulty. Lead and copper are precipitated quantitatively with the zinc. This separation may be found useful for the determination of lead and copper in lowgrade products, such as mill tailings, Nickel is not precipitated from a cold solution, and from a warm solution the precipitation is slow. This method was used for the separation of nickel and zinc by Crookes ( I ) , who passed hydrogen sulfide through the cold solution, and stated that a small amount of nickel may be precipitated by long treatment with hydrogen sulfide.
Cobalt is precipitated. A single experiment on material free from nickel and low in cobalt gave a quantitative separation. When tried on material carrying about 5 per cent each of cobalt and nickel, it was not so successful. The cobalt precipitated slowly and required long treatment with hydrogen sulfide to complete the precipitation. As a result of this long treatment, some nickel accompanied the cobalt precipitate, which seems to verify the statement of Crookes, mentioned above. To test the accuracy of the separation the following work was done: Five grams of Bureau of Standards Crescent iron ore, containing 58.6 per cent of iron, were treated as described. To the filtrate from the insoluble material was added 0.0161 gram of c. P. zinc, dissolvedin dilute hydrochloric acid. After completing the separation as outlined, 0.0160 gram of zinc was recovered. Five grams of a manganese concentrate, containing about 44 per cent of manganese, were treated as described, and t o the filtrate from the insoluble material 0.0145 gram of zinc was added. After completing the separation, 0.0140 gram of zinc was recov-
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A flotation tailing, low in zinc and carrying approximately 35 per cent of iron, gave the following results by this method: 0.25, 0.25, 0.25, 0.24, 0.26, 0.26, and 0.26 per cent of zinc.
LITERATURE CITED (1) Crookes, “Select Methods,” 2nd ed., p. 249, Longmans, 1886. (2) Fales and Ware, J . Am. Chem. SOC.,41, 487 (1919). (3) Hillebrand and Lundell, “Applied Inorganic Analysis,” p. 329, Wiley, 1929. (4) Low, A. H., “Technical Methods of Ore Analysis,” 10th ed., p. 257, Wiley, 1927. RECEIVED January 17, 1933.
Air Pressure for Blast Lamps G. W. THIESSEN AND J. E. WERTZ Monmouth College, Monmouth, Ill.
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HE amateur glass blower, who has no means of obtaining an air-pressure pump and tank, may improvise an efficient substitute from a second-hand vacuum sweeper. By dismantling the unnecessary accessories and removing the dust plate, a very compact apparatus results, which may easily be stored in a table drawer, t o allow more working room. By using a large rubber stopper, in which a Y-tube is inserted, in the manifold where the dust bag is ordinarily clamped, three blast lamps can be easily supported, and even four, if necessary. If an oxygen generator is set up and fed into the intake, the flame produced is very suitable for working Pyrex glass. This apparatus may be used for igniting crucibles or for any other work where air pressure is requisite. It should be as easy to improvise as the Muencke blower of Robey (1)and perhaps more convenient to use. A rheostat in series with the motor and the original snap switch fastened firmly to the bench are useful accessories. LITERATURE CITED (1) Robey, R. F., IND. ENG.CKEM.Anal. Ed., 5 , 148 (1933). RECEIVED March 24, 1933.
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