Colorimetric Determination of Aluminum in Iron Ore and Steel J O I E S L. K-iSSNER A N D B I d R l i ALICE OZIER School of C h e m i s t r y . .lletallccrgy, and Ceramics, Cnirersity of ,4lubuma, Cnicersity, - 4 1 ~ . The time required for an accurate colorimetric determination of aluminum in steel and iron ore has been shortened. The method makes use of the fact that hj drogen peroxide will form peroxidized compounds with titanium, \ anadium, etc., but will not oxidize iron in the ferrocqanide complex. Muminuin quinolate has been quantitatively extracted with chloroform from ammoniacal solutions containing tartrate, potassium cyanide, and hydrogen peroxide at pII 9. The method makes possible determination of aluminum in the presence of most elements commonly found in steel-copper, nickel, zinc, cadmium, iron, titanium, banadium, 7irconium, uranium, manganese, chromium, molq hrlenum, and tin.
T
1112 yellom color formed by tlie chloroform extract of aluminum quinolat,e was first used hy Alexander ( 1 )as a basis for estimating aluminum. The method has been studied by Moellcr ( I , $ ) , niodified by Gentry and Sherrington ( 3 ) and, after most of the intei.fering elements have been removed with a mercury catliode, adapted to steel by TPiberley and Bassett ( 1 7 ) . BJ-using an ammoniacal solution containing hydrogen pel'oxide, 1,undell and Knov-les (13) determined aluminum gravimetrically as aluminum quinolate in the presence of titanium, tantaluni, columbium, vanadium, and molybdenum. Lang and Reifei, (9) determined aluminum in the prrs:rnc.e of iron, by using an animoniacal solution containing tartrate and potassium cyanide. IIeczko ( 5 ) estendtd this last procedure to include iron, c o l d t , nickel, molybdenum, copper, and chromium. The authors combined these two techniques and devrloped a direct gmvimetric method for aluminum ( 8 ) in the pi'esenre of all the elements ronimonly associated with aluminum in thr mised hydrosides ( 1 2 ) . In the prest,nt pappi' they have adapted this gravimetric procedure (8) t,o ail estraction colorimetric method for the determination of aluminuni in step1 and iron ore. The analysis of synthetic samples as well as several Bureau of Standai,ds samples indicates that the piwision x r i d armracy of this nietliod are good. REAGEVTS A N D EQUII'>IEST
8-Quinolinol, 2%. Dissolve 2.0 grams of xnxlytical l,engriit 8quinolinol in 100 ml. of chloroform. Potassium cyanide, analytical reagent. Sodium sulfite, a saturated solution in watcli'. Hydrogen peroxide, 3y0,reagent gr:ule. Tartaric acid, analytical reagent. Socliuni carbonate, analytical reagent. Stantlard aluminum solution. Dissolve 2.1 1 1 gi'anis of analytical reagent potassium aluminum sult':ite, Kv.+( SO4)?.24H?O, in 1 liter of water and stnndal,dize l)y amnionin precipitation ant1 ignition to the oxide. First working standard. Dilute 25 ml. of the standard to 500 nil. (1 ml. = 0.0061 mg. of aluminum ). Second working standartl. Pipet 25 nil. of the standard into :i 100-ml. benkcr, add 5 nil. of 70% perchloric ncitl, evaporate to fumes, fume for approsim:itrly 5 minutes ( I T ) , cool, add distilled water, tmnsfer to 50O-nil. volumetric flnsk, ~ n ddilute to the 11Klrk.
Chloroform, reagent grade. l k k m a n quartz spectrophotometer, IIodel DT-. ui~rinentrwere made in 1-em. cells. Hrckninn pH meter, latioratory 3Ioclel G.
-111 mcas-
PROCEDURE FOR STEELS \\ cJigh out I-gram samples into 250-1111. beakers, and add 5 nil of v:nter, 5 ml of nitric acid (specific giavity 1 42), and 10 nil. of TOc( perchloric acid I.:vaporate t o fume3 a n d then fume for
approximately 5 minutes (17'); cool, add 100 ml. of water, and filter into a 500-ml. volumetric flask. Wash the insoluble residue with a hot 1% solution of hydrochloric acid and then with hot water. (Collect the washings in the volumetric flask.) To recover any aluminum that might be retained in the residue, volatilize the silica by treating the residue with hydrofluoric and sulfuric acids; fuse the residue with 2 grams of sodium carbonate; leach the melt with water, heat to boiling, filter, acidify the solution, and add to the reserved filtrate. Dilute the sample to 500 ml. Then pipet a 5-ml. aliquot into a 100-ml. beaker and dilute to about 25 ml. For high-chromium steels, or other steels that will not dissolve by the above procedure, add 10 ml. of nitric acid (epecific gravity 1.42) and 5-ml. portions of hydrochloric acid (specific ravity 1.19) until the sample dissolves. Heat the sample after eact addition of hydrochloric acid. Add 15 ml. of 70 to 72% perchloric acid and fume until the sample turns orange. Dissolve the salts with 75 to 100 ml. of water, filter, and recover the aluminum in the insoluble residue. If a steel contains l e s than 0.0S70 aluminum, it. is necessary to decrease the concent1,ation of the interfering elements in t,he sample by mercury cathode separation. Dissolve a sample containing 0.01 to 0.02 mg. of aluminum in either nitric acid or nitric and hydrochloric acids, add 30 ml. of 1 to 1 sulfuric acid, evaporate to fumes of sulfur trioside, and fume for 1 or 2 minutes. Cool, add 50 to 75 ml. of water, warm until the salts dissolve, filter into a 250-ml. volumetric flask, and recover any aluminum that might be retainrd in the residue. Transfer a 25-ml. aliquot to an electrolytic beaker, and electrolyze at about 5 amperes using a mercury cathode 10 to 12 sq. cm. in area. The cell and technique used were essentially those described by Johnson and coworkers ( 7 ) , except that the solution was stirred by placing a magnetic stirrer under the beaker and a small iron-in-glass agitator in the beaker. Usually one 20-minute electrolysis interval is sufficient; however, two 20-minute electrolysis intervals were required for 0.4 gram of Bureau of Standards sample 55b. The mercury was changed after each interval. \+lien the aliquot taken for the extraction contains more than 0.017 mg. of titanium, evaporate the electrolyzed solution and make a sodium carbonate fusion as described by Parks and Lykken ( 1 5 ) . T o the 25-ml. aliquot, containing 0.01 to 0.15 mg. of aluminum, and to 25 nil. of water to be used as the blank, add 0.2 gram of tartaric acid and 1 ml. of 3% hydrogen peroxide solution; let at,and for about 5 minutes, then add 5 ml. of a saturated solution of sodium sulfite. A4fter approximately 3 minutes add 1.3 grams of potassium cyanide dissolved in about 5 ml. of water, heat to TO" to 80" C., and cool to 25' to 30" C. Add 2 grams of ammonium nitrate and adjust the p H to 8.9 f 0.3 with either ammonium hydroxide or hydrochloric acid. (The pH of the solution is usually within the above limits.) Transfer to a 125ml. separatory funnel, add 5 ml. of the 8-quinolinol solution. shake the mixture for 2 minutes, let it stand for 2 minutes, and d r a x off the chloroform layer into a 50-ml. volumetric flask. Extract threr more times (a total of 20 ml. of the 8-quinolinol solution is used) and dilutc) the extract to 50 ml. with chloroform. 31easui.e the optical dciisity at, 389 i i i w on a spectrophotometer and determine the amount of aluminum from a previously prepared calibration curve. Thrl optical clensity hns heeri found to remain constant for 10 1ioui.s or mor
