Mixed Perchloric-Phosphoric Acids as Solvents for Iron Ores CHARLES A. GOETZ Department
of
and
EARL
Chemistry, lowa State
P. WADSWORTH, JR. College, Amos, lowa
Perchloric and phosphoric acids and mixtures of these acids were studied as solvents for iron ores. The mixture consisting of equal volumes of the two acids was found to be the most satisfactory, and superior to hydrochloric acid. Nearly all iron ores were dissolved in 10 minutes. The iron in the resultant solution, containing an excess of the two acids, was reduced using the Jones (amalgamated zinc) reductor; the reduced iron was titrated directly with permanganate or cerium(1V) sulfate.
T
HE hydrochloric acid method for the dissolution of iron
ores suffers from several pronounced disadvantages. The hydrochloric acid must be kept just below the boiling point to prevent mechanical loss or deposition of iron( 111) oxide or chloride on the walls of the vessel. This deposit is sometimes difficult to redissolve even with hot dilute hydrochloric acid. If the Jones reductor is to be used, it is necessary to remove hydrochloric acid by evaporation with sulfuric acid, because hydrochloric acid causes excessive evolution of hydrogen and results in frequent blocks in the reductor. Evaporation with sulfuric acid often results in the formation of anhydrous iron( 111) sulfate that is difficult to redissolve. When an appreciable amount of silica is present in the ores, hydrochloric acid usually does not remove all of the iron. A sodium carbonate fusion or a hydrofluoric acid treatment is then necessary to obtain all of the iron in soluble form. Each of the above factors tends to give low results and to prolong the time for completing an analysis. The method for analysis presented here is believed to be superior to the hydrochloric acid method in that it is less timeconsuming and less subject t o errors. The ore is rapidly dissolved by gently boiling i-iith a mixture consisting of equal volumes of 72% perchloric acid and 85% phosphoric acid. After being diluted with distilled water and boiled briefly to distill off the chlorine, the cooled solution is passed through the reductor and titrated with permanganate or cerium(1V) sulfate solution. When the method is well organized, it is possible to perform a complete analysis in less than 30 minutes. REAGENTS
electrolytic iron (Hach Chemical Co.) can be used for standardization. A 0.025M solution was used (G. FredFERROIN ISDICATOR. erick Smith Chemical Co.). PROCEDURE
Keigh into a 500-ml. dry Erlenmeyer flask about 0.3 to 0.35 gram of the ore. Add about 20 ml. of the premixed ore solvent and swirl the flask to disperse the ore. Place a refluxing still head ( I ) in the neck of the flask and heat on a burner or hot plate adjusted so that the acids boil gently. In about 10 minutes, or after the iron is dissolved, cool the flask and contents enough so that about 70 ml. of water can be added without causing the water to boil excessively. Boil for about 2 minutes to remove dissolved chlorine; cool and add about 30 ml. of 1 to 1 sulfuric acid. Pass the cool solution through the Jones reductor a t a rate of about 50 to 60 ml. per minute, using suction on the receiving flask if necessary. Add about 0.2 gram of sodium carbonate to the receiving flask before starting the reduction process. This reacts with some of the acid to liberate carbon dioxide, which prevents air oxidation of the iron. Wash the last of the iron solution through the reductor column, using three 25-ml. portions of 1 to 20 dilute sulfuric acid solution and finally three 25-ml. portions of distilled water. Titrate the iron(I1) in the receiving flask using either standard permanganate or cerium(1V) sulfate solution. Ferroin indicator is used with cerium(1V) sulfate; rapid stirring is necessary in this titration to prevent the formation of insoluble cerium(1V) phosphate. EXPERIMENTAL
Dissolution Studies. Boiling perchloric acid (727,) alone failed to dissolve the ores rapidly. Boiling phosphoric acid (85%) gave rapid dissolution, but the silica was converted to a gelatinous form which plugged the Jones reductor so that it became inoperative. An additional disadvantage of phosphoric acid alone was that an insoluble iron(II1) phosphate \+-asoccasionally formed. B mixture of 3 volumes of i 2 % perchloric acid and 1 volume of 85% phosphoric acid was found to give more rapid dissolution than perchloric acid alone, but was not so rapid as phosphoric acid alone. The use of 1volume of perchloric acid with 3 volumes of phosphoric acid gave very rapid dissolution but was almost as unsatisfactory as phosphoric acid alone. Equal volumes of perchloric and phosphoric acids resulted in rapid dissolution of the ores but did not give the objectionable form of silica and insoluble iron(II1) phosphate in any case.
ORE SOLVEST. Equal volumes of 72% perchloric acid (G. Frederick Smith Chemical Co.) and 85% phosphoric acid were mixed. STAXDARD CERIUMUV)SULFATE SOLUTION.A n approximately 0.1N solution was preTable I. Results of Iron Analyses pared using 58 grams per liter % Fe of cerium(1V) hydrogen sulfate Found, (G. Frederick Smith Chemical 4V. dev. No. of dev. from Co.), then standardized against Analyses from Orig. orig. Xational Bureau of Standards KO. Sample Made Found av. anal. anal. a r s e n i o u s o x i d e . Ceric hy0.06 100.0 1 Electrolytic FeQ 8 100.0 0.0 droxide may also be used to 0.08 100.0 Electrolytic Feb 2 +0.1 4 100.1 69.26C 0.07 NBS 27" 3 69.24 -0.12 4 prepare the solution. 0.06 69.26C 69.12 -0.14 4 NBS 27b STANDARDPERMANGANATE 45 0.04 0.00 69.52 s. 9. co., l a 4 69.52 0.01 -0.09 4 51.85 51.94 6 S.S. Co., 18" SOLUTION.An approximately 0.06 50.95 7 9. S. Co..1g5 8 +0.05 51.00 0.1N solution was prepared 0.03 +0.36 69.23 68.87 s. s. co., 2a 5 8 and standardized against pri0.03 4-0.22 55.61 4 9 55.83 s. s. CO., 125 0.02 57.37 +0.16 10 s. s. co., 90 4 57.53 mary standard sodium oxa0.01 4-0.29 60.25 59.96 11 s. s. co., 5A,3 4 late (Mallinckrodt) or Xational ' Permanganate as titrant: standardized against primary standard sodium oxalate. Bureau of Standards arsenious b Cerium(1V) sulfate as titrant: standardized against NBS arsenious oxide. oxide. The method described NBS analysis. Average of four steel companies' results is 69.12%. herein has also indicated that
37s
Found, HC1 method, corrected Si08 ... ...
.. ... ... ...
69: 22
55,80 57.49 60.22
Dev. Fe Found from SilicaCorrected Values
... +O.'Ol 4-0.03
+0.04 +0.03
376
ANALYTICAL CHEMISTRY
I n all the dissolution studies 20 nil. of the solvent and about 0.3 to 0.4 gram of the ore were used in a 500-ml. Erlenmeyer flask. Analytical Results. ELECTROLYTIC IROS. About 0.22-gram samples of primary standard electrolytic iron 1% eie dissolved, and the iron content was determined using the procedure given above. The result of eight consecutive analyses using permanganate as titrant is given as S o . 1 in Table I. No. 2 is the summary result of four consecutive anal) ses using cerium(1V) sulfate solution as the titrant. The results indicate that the over-all procedure for iron is good and that electrolytic iron is a good and convenient primary standard for the solutions. NBS No. 27 ORE AXALYSIS.National Bureau of Standards sample 27 was analyzed using the procedure given above. The results of these analyses are given as S o s . 3 and 4 in the table. The values obtained by this method check very closely with t ose of four steel companies for the same sample. .4SALYSES OF STASD.4RD SAMPLE C O . ORE SAJfPLES (Hach Chemical Co., Ames, IoJva). Seven samples for student analysis used in this laboratory were analyzed using the new procedure, and the results are given in column 4 of the table. The values for these samples given in column 6 were determined by the supplier in the following manner: dissolution of the ore sample in hydrochloric acid, removal of hydrochloric acid by fuming with sulfuric acid, dilution, reduction with Jones reductor, and titration with permanganate. The new method gave good agreement with samples 1, 18, and 19, but only fair agreement with samples 2, 12, 9, and 5.4. The
authors analyzed sample 12 using the regular hydrochloric acid procedure, and obtained a n average for four analyses of 55.66%. This is only 0.05% (1 part in 1000) higher than the results given by the supplier. The supplier's results appeared to be low compared to those obtained by this method only with samples containing moderate to large amounts of silica (Standard Sample Co., 2, 12,9, and 5A). These samples were then analyzed mith hydrochloric acid as the ore solvent, but the silica was filtered off and fused with sodium carbonate. The residue was dissolved in hydrochloric acid and added t o the filtrate. The hydrochloric acid was then fumed off with sulfuric acid and the iron was reduced in the regular manner with the Jones reductor. The results of these analyses are given in column 8 of the table. By comparing the results i n columns 4, 6, and 8 it is evident that the perchloric-phosphoric acid solvent method gives excellent iron removal from the silica and that the conventional hydrochloric method (column 6) gives low results when considerable silica is present. The new procedure has been used in the sophomore quantitative analysis laboratory a t Ioxva State College for the past year with good results. LITERATURE CITED
(1) Smith, G . F., Goetr, C. A., IND. ENG.CHEY.,ASAL. ED.9, 378 (1937). RECEIVED for review August 18, 1955. Accepted November 25, 1955. Presented a t the 16th Midwest Regional Meeting, ACS, Omaha, Neb., November 4 and 5, 1954.
Determination of 6-Ethoxy-1,2-dihydro-2,2,4-trimethylquinoline in Biological Materials E. M. BICKOFF, JACK GUGGOLZ, A. L. LIVINGSTON,
and
Western UtiliZdtiOn Research Branch, Agricultural Research Service,
A fluorometric method has been devised for measurement of the antioxidant 6-ethoxy-1,2-dihydro-2,2,4trimethylquinoline in biological materials in the presence of fluorescing impurities also extracted from tissues by the same method. It is capable of detecting about 0.01 p.p.m. of the antioxidant in a solvent solution. The procedure has proved successful in obtaining approximate analyses of treated alfalfa meal as well as tissues of rats, chicks, and calves employed in chronic toxicity studies. With minor modification, it has been applied in analyses of milk, butter, and eggs from animals fed antioxidant-treated meal.
T
HE effectiveness of 6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline as an antioxidant for carotene in dehydrated alfalfa meal was reported in 19.50 ( 2 ) . This antioxidant is now commercially available and over 30,000 tons of meal were treated with it in 19.54, Feeding tests have shown that its toxicity is low and alfalfa meal treated with the antioxidant for use in poultry feeds is now shipped in interstate commerce, This study required a method of assay for the antioxidant, sufficiently sensitive to permit its detection in animal tissues, eggs, milk, butter, and treated alfalfa meal. REAGENTS AND APPARATUS
The reagents used were reagent grade acetone, diethyl ether, potassium permanganate, and sodium sulfate. The acetone re-
C. R A Y THOMPSON
U. S. Department of
Agriculture, Albany
7 0, Calif.
q:iired redistillation prior to use. Pure-grade iso-octane (99% 2,2,Ctrimethylpentane, Phillips Petroleum Co., Bartlesville, Okla.) was found satisfactory. The instrument used for t h e fluorescence measurements was a Model 12A Coleman photofluorometer Kith a PC-1 filter (480 mp) and a BS-1 filter (435 mp). However, any sensitive photofluorometer used for vitamin assay n-ould be satisfactory if used n-ith comparable filters. Q.iinine sulfate was used as a fluorometric standard. It.was found that 0.06 y per ml. of quinine sulfate in O . 1 N hydrochloric acid had a fluorescence equivalent t o 0.1 y per ml. of the antioxidant. A microcup electrical blender m-as used t'o macerate the tissue samples. ANALYSES
Tissue. A sample of about 2 grams is blended in a microblender cup with 50 ml. of freshly distilled acetone. The homogenate is filtered and an aliquot of 10 to 20 ml. of the filtrate is added to 100 ml. of iso-octane. After the acetone has been removed bv washing the mixture with water, the iso-octane extract is dried over sodium sulfate. Following appropriate dilution, the total fluorescence of the iso-octane solution is determined. Fifteen milliliters of tmheextract, in iso-octane solution is det,ermined. Then 15 ml. of the extract in iso-octane is shaken with 10 ml. of 0.04% potassium permanganate solution for 1 minute, the potassium permanganat,e layer is decanted off, and the isooctane layer is dried over sodium sulfate. The fluorescenee of t h e potassium permanganate-treated iso-octane solution is read and suht,racted from the original reading; the difference is the fluorescence attributable to the ant,iosidant. Milk. To 25 ml. of thoroughly homogenized milk, 25 ml. of a solution containing 1 part of acetone and 3 parts of iso-octane is added. The mixture is shaken vigorously for 1 minute in 8 glass-stoppered bottle and transferred to a 500-ml. separatory funnel. The lower layer ie discarded and the iso-octane layer IS washed r i t h 400-ml. portions of distilled n-ater until all traces of
