THE RECOVERY OF IODINE AS SODIUM IODIDE FROM WASTE IODIDE SOLUTIONS WALTERD. DUNNER AND K. MASAKI, UNIVERSITY OF UTAH,SALTLAKECITY, UTAH Iodine is among the most expensive of the commonly used laboratory agents and its recovery, in a usable form, from laboratory wastes is a measure of real economy. For several years this laboratory has made it a rule to store waste iodide solutions and a t periodic intervals to recover the iodine by precipitation with chlorine and filtering. The purification of the crude recovered iodine, however, and its conversion into its more useful form of iodide, was a decidedly troublesome matter. We finally hit upon the following method, which we believe is of interest sufficient to warrant publication. Purification of Crude Iodine Crude iodine as recovered from laboratory wastes contains shreds of asbestos, bits of filter paper, etc., in addition to chemical impurities. Since it is also wet, purification by the conventional method of sublimation is difficult and unsatisfactory. Moreover, i t is not easy in the ordinary laboratory to arrange for the sublimation of quantities as large as a kilogram or more. We therefore have adopted a method of dissolving and reprecipitating. The crude iodine precipitated by chlorine is suspended in a convenient quantity of water, and sulfur dioxide passed in until the solution is colorless. This allows the insoluble material to be separated by filtration. The iodine is agai? precipitated by chlorine, filtered and washed by suction in a large Ruchner funnel. This process of solution, filtration, and reprecipitation, is repeated until a sufficient purity has been attained. We have found that three precipitations, after the iirst recovery of the crude material, are usually enough. We found, for instance, that a sample treated in this way showed, on titration against standard thio solution, 95% iodine as contrasted with 93% iodine found in a sample of the resublimed product of one of the leading manufacturers of chemicals. Conversion into Sodium Iodide The conversion of the purified iodine into sodium or potassium iodide is a more troublesome matter than is the purification of the iodine. It cannot be done by direct treatment of the iodine with alkali hydroxide because of the large amount of iodate formed a t the same time. Direct conversion of the iodine into pure hydriodic acid is very difficult, if not impossible. We therefore dissolve the iodine as before with sulfur dioxide. This gives a solution of hydriodic acid, together with an equivalent amount of sulfuric acid, as shown by the equations: In Son 4HIO +2HI H801
+
+
+
It will also contain sulfurous acid, being saturated with SO2. The volume of this solution is measured, and a sample titrated with a standard alkali. 616
VOL.7. No. 3
RECOVERY OF IODINE
617
One hundred cc. of this solution are reserved for later use, and the remainder neutralized with pure lime. The lime should be weighed out, carefully slaked, and the milk of lime added slowly to the acid solntion. This converts the various acids into the corresponding calcium salts, most of the calcium sulfate and calcium acid sulfite being precipitated while the calcium iodide remains in solution. This mixture is allowed to stand a t least an hour or two with frequent shaking or, better, with continual stirring. After enough time has elapsed to insure a complete reaction, the mixture is filtered and the precipitate carefully washed free from iodide. This residue can then be discarded. The filtrate contains the iodine as calcium iodide, along with small amounts of calcium sulfate or bisulfite and possible excess of lime. In order to determine the amount of excess lime, should any be present, the volume of the solution is measured and an appropriate sample, for example 10 cc., taken. To this is addedanexcess (0.250.50 g.) of alkali iodate and the solution titrated with standard acid until the color of iodine appears. This titration is based on the fact that iodide ion and iodate ion do not react unless hydrogen ion also is present. When enough acid has been added to neutralize the excess alkali, the next drop starts the reaction between iodide and iodate. The appearance of iodine is thus the indication of the end-point of the titration. The excess alkalinity is calculated and adjusted by means of the 100-cc. portion previously reserved for this purpose. The next step is to remove the small amount of sulfate which remains in the solution in'the form of calcium sulfate. This is done by adding a solntion of barium iodide until no further turbidity is produced. The total iodide in the solution is now determined preferably either by titration with a standard silver nitrate or by titration with iodate in the presence of strong hydrochloric acid. The calcium salt is then converted to the sodium or potassium salt by addition of the necessary amount of the corresponding carbonate, accurately weighed out. The precipitate of calcium carbonate should be agitated with the solution for an hour or more, then filtered, washed free from iodide and discarded. The solution of alkali iodide is then evaporated to crystallization or preferably to dryness. The salts so obtained are colorless and pure and quite as useful in the laboratory as similar salts purchased from dealers.
N e w Container for Foods. The American Can Company is reported in The Business Week as working with the Eastman Kodak Company in the development of an entirely new type of container for food products which may largely displace glass and metal. The new material is said to be a cellulose compound discovered accidentally by the Eastman laboratories in experimental film work. Although the idea of a cellulose container is not new, this is reported to be the first discovery of a product strong enough to stand up under acids and wear. It is said to he nearly as strong as metal, as transparent as glass, and lighter in weight than either.-Business Chem.
