ANALYTICAL CHEMISTRY
194 LITERATURE CITED (1) Boggs, M. M.,and Fevold, H. L., Ind. Eng. Chem., 38, 1075-9 (1946). (2) Boyd, J. M., and Peterson, G. T., Ibid., 37,370-3 (1945). (3) Cartwight, c*v I N D . E N G * C H E M . ? h - 4 E~D . , 18, 779-85 (1946). (4) Coulter, S. T., and Jenness, R., Univ. Minn., Agr. Expt. Sta., Tech. Bull. 167 (1945). (5) Dunlop, A. P., Stout‘,P. R . , and Swadesh,S., Ind. Eng. Chem., 38, 705-8 (1946).
(6) Franklin, W. S., “Precision of Measurernent,” pp. 6-10, Lancaster, Pa., Lancaster Press, 1925. (7) Lea, C. H., Moran, T., and Smith, J. A . B., J . Dairy Research, 13, 162-215 (1943). ( 8 ) Stadtman, E. R., Barker, H. 9..Haas, V., Mrak, E. M., and MacKinney, G., Ind. Eng. Chem.,38,3324 (1946). (9) Tarassuk, N. P., FoodInds., 19,781-3 (1947).
RECEIVED November 19, 1947.
Determination of Phosphorus in Iron Ore JAMES L. KASSNER AND MARY ALICE OZIER University of Alabama, Uniuersity, Ala.
HE determination of phosphorus in iron ore is carried out in Tthree steps : solution of the sample, precipitation of the ammonium molybdiphosphate ( 7 ) , and alkalimetric titration of this salt to determine the amount of phosphorus present. This study deals specifically n-ith the second and third steps in this procedure. The solution of the sample is effected by standard procedure. The single-strength citromolybdate solution used in the determination of phosphorus pentoxide in phosphate rock ( 3 ) did not give complete precipitation when used in the determination of phosphorus in iron ore. After considerable experimentation a double-strength citromolybdate solution was prepared and found to be stable. This study has shown that the time required for a complete determination of phosphorus in iron ore can be shortened by using the new double-strength citromolybdate solution and separating the .ammonium molybdiphosphate a t the boiling point. The analysis of several Bureau of Standards samples indicates that the precision and accuracy of the method are good. The new mixed indicator (3)used in the determination of phosphorus pentoxide in phosphate rock is used in determining the end point. REAGENTS AND STANDARD SOLUTIONS
Double-Strength Citromolybdate Solution. Solution A . Dissolve the following reagents in 1400 ml. of water and warm while stirring until solution is complete: 100 grams of ammonium nitrate, 128 grams of citric acid monohydrate, and 136 grams of ammonium molybdate, ( T ~ ” ~ ) & ~ O , O N . ~ H ~ O . Solution B. Dilute 528 ml. of concentrated nitric acid (specific gravity 1.42) with 300 ml. of water. Prepare the citromolybdate solution by pouring Solution A into Solution B. Clear i t as follows: Add 10 to 15 drops of 20Q/,diammonium hydrogen phosphate solution, boil 5 to 10 minutes, allow to stand overnight; then siphon off the clear solution. (Such a solution remained clear 2 years.) The other reagents for this method are essentially those used in the determination of phosphorus pentoxide in phosphate rock
Wash the precipitate with hot water, dissolve in not more than 20 ml. of hot 1 to 2 nitric acid solution, and add it to the reserved filtrate. Dilute the solution to 80 ml., add 100 ml. of double-strength citromolybdate solution, heat to boiling, and keep a t this temperature for 5 to 10 minutes. Remove the solution from the heat and filter immediately. Before transferring the precipitate to a Gooch crucible, wash it three times by decantation with 1% nitric acid solution, using about 5 ml. for each wash. Transfer the precipitate to the crucible and wash it 10 to 12 times with 1% potassium nitrate solution. Place the crucible in the original beaker and dissolve the precipitate in a known volume of 0.1 N sodium hydroxide solution, using about 30 ml. in excess (3). Add 0.5 ml. of the mixed indicator (S) and titrate the solution with 0.1 X nitric acid until it turns yellow. Remove the crucible from the beaker, wash with carbon dioxide-free water, and adjust the volume to about 100 ml. In direct sunlight or in front of an illuminator equipped with a fluorescent daylight Xlazda lamp, back-titrate the solution with 0.1 ,V sodium hydroxide until a purple coloration appears and remains. The percentage of phosphorus is calculated on the basis of: 1 P == 23 NaOH. Data are tabulated in Table I. DISCUSSION AND NOlES ON PROCEDURE
Arsenic seems to interfere more in this procedure than it does when the precipitation is carried out a t a lower temperature by shaking. If arsenic is present, i t should be removed as rerommended by Lundell, Hoffman, and Bright (6). Table I. Sample No.
Results Obtained with Bureau of Standards Iron Ores Interferences Present Ti02
% 26
vios
7,
0.07
P206
.
Exptl. Value
%
%
0.04
0.115 0 loa 0:10; 0.09
+o,
0.1oc
+O.Ol
0.09c
(5).
27B
0.023
0.004d
0,036-
29
0.99
0.08
1.01
PROCEDURE
Weigh out a 2-gram sample of iron ore into a 150-ml. beaker, add 20 ml. of concentrated hydrochloric acid (specific gravity 1.19) ( 8 ) ,heat the covered solution on a hot plate unOil the ore is dissolved, add 5 to 10 ml. of concentrated nitric acid (specific gravity 1.42) ( 4 ) , add 12 to 15 ml. of 60 to 70y0perchloric acid ( 1 , 2, 11, lb), heat on a hot plate to copious fumes of perchloric acid, and fume a t least 5 minutes to dehydrate the silica. Wash the filter with hot 1%nitric acid solution and then with hot water. Reserve the filtrate. In order to recover any phosphorus that might be retained in the residue, volatilize the silica by treating the residue with an excess of hydrofluoric acid and a small amount of nitric acid (6); fuse the residue with sodium carbonate, leach with warm water, and filter to remove any titanium that might be present. Add to the filtrate from the fusion a little ferric chloride free from phosphorus and precipitate the ferric phosphate with ammonia (IO).
Pro5
Certified Value
Deviatior, 02
+o.oi
f0.01 0.00
0.00
0.03Cia 0 035‘ 0:031! 0.036 0.037c 0.035c
-0.001 -0.001 -0.005 0.000 +0.001 -0.001
1.0Cia
fO.04
1.04a 1.05b 1.04b 1.03c 1.01c
f0.03 f0.04 +0.03 +0.02 +0.03
10 minutes a n d allowed t o stand overnipht before filterinn. * Boiled Boiled 10 minutes and filtered immediately. Boiled 5 minutes a n d filtered imrnediatelp.
a
d e
Per cent vanadium. Per cent phosphorus.
195
V O L U M E 2 2 , N O . 1, J A N U A R Y 1 9 5 0 I11 routine analysis of iron ore a t the mine, any phosphorus re?:tined in the acid-insoluble material is often neglected (9). If titanium is not present this fraction seldom contains more than 0.003% phosphorus (6). The treatment of the sample should be varied according to whether the analysis is being made for wluble, soluble and insoluble, or total phosphorus. Because iron retards the separation of the yellow precipitate n n d forms a complex with citric acid, it is necessary to use a more sho\m in Table I, B. T’ariation in the amount of potassium *.?.anidefrom 0.05 to 0.8 ml. did not affect the magnesium ret-overy. The presence of 0.1 ml. of the 5y0 potassium cyanide ~olutionwas able to eliminate the effect up to 40 micrograms of mpper satisfactorily (Table I, C). Because potassium cyanide alone or potassium cyanide with C’opper has a tendency to intensify the magnesium titan yellow r-olorslightly, it has been found advisable to add copper and potas-ium cyanide to the magnesium standards. Inasmuch as this effect of copper does not increase appreciably over 8 micrograms, it is suggested that 8 micrograms be added to the standards. Thus in the modified procedure both copper and potassium y n i d e are added to the standards and 0.1 ml. of 5 % potassium vyanide is added to all unknown.
T a b l e I. Effect of V a r y i n g Amounts of Copper a n d 5 % P o t a s s i u m C y a n i d e on M a g n e s i u m Recovery
A
(15 micrograms determined in 5 ml. of solution) Copper Present, 5 % Potassium Magnesium Recovery, 70 Y Cyanide, MI. 0 0.0 100 1 0.0 80 2 0.0 57 4 0.0 33 8 0.0 30 16 0.0 30 32 0.0 25
B
16 16 16 16 16
0.05 0.10 0.20 0.40 0.80
107 100 99 100 105
0
C
16 24 32 40
0.10 0.10 0.10 0.10 0.10
100 100 104 104 107
