Iodofluoride Method for the Determination of Copper Effects of Antimony, Aluminum, and Calcium WILLIAII R. CROWELL AND AL-AN T. SPIHER University o f California a t Los Angeles, Los Angeles, Calif.
I
K TWO previous communications the authors have pre-
I n the case of the cupric sulfate experiments, the procedure was as follows:
sented results showing the effects of iron and arsenic in the iodofluoride method for the determination of copper, but no data were offered regarding the effects of antimony, aluminum, and calcium ( 1 , Z ) . Foote and Vance in a study of the effect of antimony in their iodoacetate method have shown that low results are obtained if the amount of antimony present is greater than 20 mg. ( 3 ) . I n his method employing bifluoride and biphthalate, Park has stated that aluminum forms a n insoluble fluoride which, when present in large amounts, occludes some copper and slows u p the titration, but has given no experimental results (4). The effect of calcium which may be present in copper ores in large amounts has not yet been considered. The present paper describes results obtained, showing the behavior of these three impurities in the iodofluoride method.
To 25.00 cc. of copper sulfate solution containing 0.1774 gram of copper were added a solution of the impurities and 5.00 cc. of concentrated sulfuric acid. The solution was evaporated to fuming and diluted to 20 cc., followed by addition of ammonium hydroxide until a distinct odor of ammonia was obtained. In all the runs except 6, 7, 12, and 13, 1.5 grams of ammonium bifluoride were then added. In runs 6 and 7, 2 grams of bifluoride were used, while in runs 12 and 13 (,he amount was 2.5 grams. Kext, 20 cc. of 1.5 Jf potassium iodide solution were added and titration with thiosulfate was made with the addition of 2 grams of potassium thiocyanate and starch solution within 1 cc. of the end point. The impurities were in the form of solutions of potassium pyroantimonate, aluminum nitrate, calcium chloride, ferric nitrate, and arsenic acid. In solutions contsining aluminum nitrate it was found necessary to fume with sulfuric acid if satisfactory results \yere to be obtained. Withoul, the fuming the values were decidedly low, even with amounts corresponding to less than 0.1 gram of aluminum. Calcium chloride and ferric nitrate also showed a tendency at times to give slightly lower results unless TABLE I. EFFECTSO F - i P ; T I J I O S Y , A4LUMIXUM,. I S D CALCIEM ON the fuming process was carried out. TITRATION OF CUPRIC SULFATE SOLETIOSS BY IODOFLUOHIDE In runs 10 to 13, inclusive, the calcium sulfate precipitate was METHOD filtered and washed before addition of ammonia and bifluoride, (Copper taken, 0.1774 gram. volume of thiosuliate required, 26.61 cc-.) while in runs 8 and 9 the solutions were not filtered. -Weight of ImpurityMaxiThe procedure followed in the case of cupric: sulfide was the Anti- Alumi- CalNHIHFI Average mum same as in (9),except that in runs 15 and 16, 2.5 grams of biSeries mony num cium Iron Arsenio Added Error Error fluoride were used and the solutions were filtered in the same G r a m Gram Gram Gram Gram Grams % (70 manner as in runs 10 to 13, inclusive. The impurities consisted 1 0.010 0 . 0 0.0 0.0 0.0 1.5 0.05 0.05 (3)O of calcite crystals and solutions of ferric nitrate and arsenic acid. 2 0.020 0.0 0.0 0.0 0.0 1.5 0.00 0 . 0 0 (3) 0.030 0 . 0 0.0 0.0 0.0 1.5 - 0 . 4 0 (3) - 0 . 4 3 0.0 0.1 0.0 0.0 0.0 1.5 - 0 . 0 3 (4) - 0 . 0 6 0.0 0.2-0.3 0 . 0 0.0 0.0 1.5 - 0 . 0 3 (7) -0.06 0.0 0.2 0.0 0.2 0.0 2.0 (4) -0.09 -0.06 0.0 0.2 0.0 0.2 0.2 2.0 0.06 - 0 . 0 3 (3) 0.0 0.0 0.1 0.0 0.0 1.5 0.12 0 . 0 3 (4) 9 0.0 0.0 0.2 0.0 0.0 1.5 - 0 . 4 4 (4) - 0 . 5 9 10b 0 . 0 0 . 0 0.1-0.2 0.0 0.0 1.5 ( 7 ) 0.11 0.00 llb 0.0 0 . 0 0.3-0.4 0 . 0 0.0 1.5 - 0 . 0 8 (4) - 0 . 1 3 12b 0 . 0 0.0 0.3-0.4 0.2-0.3 0.0 2.5 (4) - 0 . 1 7 -0.05 13b 0.0 0.0 0.3 0.3 0.2 2.5 - 0 . 0 2 (2) - 0 . 0 4 a Numbers in parentheses refer t o number of titrations made. b Calcium sulfate was filtered off before addition of ammonia and bifluoride. 3 4 5 6 7 8
The results indicate the followirig regarding the behavior of antimony, aluminum, and calcium in the determination of copper by t,he iodofluoride method. 1. As in the case of the iodoacetate method, antimony cannot be present in quantities greater than 20 mg. Since the error is probably due to adsorption of copper by antimonic acid during the mineral acid treatment, this result is to be expected. 2. Aluminum as aluminum sulfate can be present in amounts as great as 0.3 gram, aluminum and iron as much as 0.2 gram each, and aluminum, iron, and arsenic as much as 0.2 gram each, with a n average error in the results less than 0.1 per cent. 3. Calcium can be present in amounts as high as 0.4 gram, calcium and iron in amounts as great as 0.3 gram each, and calcium, iron, and arsenic in amourits as great as 0.2 gram of arsenic and 0.3 gram each of iron anti calcium, with a n average error less than 0.1 per cent, provided the calcium sulfate is filtered off and washed before the addition of ammonia and bifluoride. If the amount of calcium present is no greater than 0.1 gram, filtration is unnecessary. The error due t o the presence of calcium is probably caused by adsorption of copper by calcium fluoride produced as a result of a reaction between calcium sulfate and bifluoride.
TABLE 11. EFFECTOF CALCIUM ox AKALYSIS OF CUPRIC SULFIDE (Percentage of copper in t h e sulfide varied from 62.77 t o 62.00) ---Weight of ImpurityNHaFHt .4verage hlaximum Series Calcium Iron Arsenic Added Deviation0 Deviationa Gram Gram Gram Grams % % 14b 0 . 3 - 0 . 4 0.0 0.0 1.5 - 0 . 0 5 (6) -0.16 15b 0.3 0.2-0.3 0.0 2.5 - 0 . 0 9 (3) -0.14 16b 0.20 0.20 0.20 2.5 0 . 0 2 (3) 0.07 Deviations are percentage deviations from per cent of copper obtained in blank runs. b Calcium suliate was filtered off before addition of ammonia and bifluoride. ~~
Experimental Procedure and Results Results are shown in Tables I and 11. Experiments with all three impurities alone and in combination with iron and arsenic were carried out in solutions of cupric sulfate and with calcium alone and in combination with iron and arsenic on samples of cupric sulfide. The materials used, with the exception of the new impurities. were essentially the same as those described in previous articles (1, 2 ) .
Literature Cited W. R.,Hillis, T. E., Rittonberg, S. C., and Evenson, R.F., ISD. ENG.CHEM.,.4nal. E d . , 8, 9 ( 1 9 3 6 ) . (2) Crowell, TT'. R., Silver, S.H., and Spiher, A. T., I b i d . , 10, 80 (1) Crowell,
(1938). (3) Foote, H.
W., and Vance, J. E., I b i d . , 8, 119 ( 1 9 3 6 ) .
(4) Park, B., I b i d . , 3, 77 ( 1 9 3 1 ) .
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