July 15, 1929
INDUSTRIAL AND ENGINEERJNG CHEMISTRY
163
Determination of Iron Oxides in Acid Steel Furnace Slags‘ Revised Methods George T. Dougherty AMERICANSTEEL FOUNDRIES, CHICAGO, ILL.
H E recent appearance of two papers on the determination of ferrous iron in silicate rocks (2, 3)“ has led the writer to believe that his revised method for iron oxides in acid slags from open-hearth and electric steel furnaces, origiiially published in 1921 (1) may be of interest t o many chemists having to deal with this or other kinds of silicates. Since the publication of the earlier paper several important details have been changed which increase the convenience of manipulation and the accuracy of the results. These open-hearth slags run 27 to 37 per cent of FeO, much higher than in any of the minerals enumerated by the authors of the papers mentioned above, and are largely refractory to ordinary acids without hydrofluoric acid added. Acid electric furnace slags may contain from 9 to 32 per cent of FeO. The lead test tube described below is inexpensive and is easily made to order in any non-ferrous foundry, in batches of four or more.
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Method for Ferrous Oxide
Start a carbon dioxide generator in vigorous operation to drive air out of the generating flask connecting with a wash bottle. Heat a 10- to 15-cm. (4- to 6-inch) sand bath rather strongly with a Bunsen flame. The writer employs a lead test tube 10 or 11 cm. (4or 41/2 inches) high, 2.5 em. (1 inch) inside diameter, walls 3 mm. (l/8 inch), capacity 50 to 60 cc. Weigh into the lead tube 0.5 gram of a 100- or 200-mesh sample, from which any particles of metallic iron have previously been removed with a magnet. Add 5 cc. of cold boiled distilled water, and shake a little. Support the lead tube (in the sand bath) by a “buret” clamp fastened to the vertical rod on an iron retort stand, and cover the tube with a two-hole S o . 5 or 51/2 rubber stopper. Leave one of the holes open for a vent, and connect the other hole with the carbon dioxide generator in operation through a bent glass tubing. If glass tubing is used, it must be not less than 9 mm. (3/8 inch) bore t o avoid a possible clogging a t the outlet with silicon fluoride. A lead tubing, if obtainable, is much better, for it will not clog or wear thin and crack as a glass tubing does in time. Heat enough to make steam come out in plenty and not lazily. Disconnect the stopper and pour in 10 cc. of 1:l sulfuric acid from a glass beaker or graduate and then 5 cc. of 48 per cent hydrofluoric acid from a 25-cc. lipped Bakelite graduate. Stopper again and continue to run in carbon dioxide gas but a t a reduced rate. Heat for 20 minutes a t a little lower temperature than before. Avoid a boiling over or too rapid evaporation by judiciously moving the flame farther from the center of the sand bath. The sample should be fully decomposed in 20 minutes. Transfer the hot lead tube with the stopper on and lean it slightly on the edge of a sheet copper box nearly full of cold hydrant water, with carbon dioxide still running in. When the tube is cold, remove the two-hole stopper, add 20 cc. of cold boiled distilled water, and cover tightly with a solid No. 5l/, or 6 rubber stopper. Let the tube stand again after a little whirling in the cold water bath until perfectly cold. Have ready a 500-cc. casserole containing 200 or 250 cc. of cold distilled water and 25 cc. of a saturated (5 per cent) solution of boric acid. Add the contents of the lead tube, rinsing it out with cold water and scrubbing out with a policeReceived April 6, 1929. * Italic numbers in parenthesis refer to literature cited a t end of article. 1
man any ferrous sulfate that may be deposited a t the bottom of the tube. Stir well. Titrate with standard potassium permanganate. Calculate the iron found to ferrous oxide. A prepared solution of boric acid is preferable to the solid boric acid usually added by other chemists as this is not easily dissolved in the time before titrating. Method for Ferric Oxide or Total Iron
The same kind of lead tube is employed, but with a onehole rubber stopper, and it is not connected with a carbon dioxide generator. Use same quantity of sample and of water and 1:1sulfuric acid and hydrofluoric acid as for the determination of ferrous oxide. Cover and boil for 20 minutes, cool in the cold water bath, add 20 cc. of cold distilled water, and after cooling transfer the contents of the tube with rinsings into a 400-cc. beaker containing 50 cc. cold mater and 15 cc. of 1:2 sulfuric acid. Add 3 grams of 20-mesh C. P. zinc. When all the zinc is dissolved, filter off, on a rapid filtering S. & S. KO.589 “black ribbon” filter, the dark cloud of impurities (lead, etc.) precipitated from the meshed zinc and the lead tube, and wash five times with cold water into a 500-cc. casserole containing about 200-cc. of cold water. Put a stick of C. P. zinc in the casserole. After a few minutes of action with the zinc to reduce any iron re-oxidized while filtering, withdraw the stick zinc and rinse it. Add 25 cc. of a 5 per cent boric acid solution, stir well, and titrate with standard potassium permanganate (1 cc. = 0.01 gram Fe). Deduct the number of cubic centimeters of potassium permanganate corresponding to ferrous oxide in a 0.5-gram sample which has been obtained elsewhere and also 0.1 cc. for a blank. Figure the remaining iron to ferric oxide. Add 15 cc. of water to the 0.5-gram sample in a 50-cc. platinum or palau crucible (or 10 or 12 cc. water in a 35-cc. crucible) followed by 10 cc. of 1:l sulfuric acid and 5 cc. of hydrofluoric acid. Twenty minutes’ good heat on the hot plate effects a complete decomposition of the sample to a bright, clear solution. If a boiling over occurs from an excessive heat, the crucible must be washed out and dried. Proceed with a fresh sample, etc., and keep the crucible on a cooler place on the hot plate. Take the crucible off after 20 minutes’ heating, and add a t once 10 cc. of cold water t o redissolve or prevent a white deposit of iron sulfate when cooling down. When cool, finish with the procedure as described for ferric oxide after using the lead tube. The cloud of impurities from the meshed zinc must be filtered off (it can always be noticed on the filter), as it disturbs the titration and renders the end point rather transitory. The c. P. stick zinc, unless thinned by much use, does not yield any iron or other impurities. Old and thinned zinc sticks must be avoided, because impurities are more concentrated in them and are liable to vitiate the results appreciably. Boric acid must not be added until the stick zinc has been taken out. Ferric oxide in acid open-hearth slags ranges from a mere trace up to 2 per cent. Literature Cited (1) Dougherty, Chemist-Analyst, No. 32 (January (2) Sarver, J . A m . Chem SOC.,49, 1472 (1927). (3) Soule, l b z d , 60, 1691 (1928).
15, 1921).
