December, 1930
INDUSTRIAL A N D ENGILVEERING CHEMISTRY
fluids which deviated the nearest straight line was drawn, the error in no case exceeding 10 per cent and then only in the extremes of temperature. For the gas-viscosity chart (Figure 1),two logarithmically scaled lines of temperature and viscosity were placed close and parallel to each other. The temperature line was scaled in degrees Kelvin, but marked off in corresponding degrees Centigrade and Fahrenheit. Points on the chart were located RS follows: Temperature and viscosity values were taken for two points from the straight line chosen t o represent the variation of viscosity with temperature for each gas. Lines were then drawn through the corresponding values on the temperature and viscosity scales of the chart. The intersection of these lines determined a point characteristic of the fluid. A line from a point on the chart, drawn through a temperature value, will cross the viscosity line a t the value for that temperature. Fourteen gases and two mixtures are given. For liquids (Figure 2), the same procedure was followed, but in this case the points fell between the viscosity and temperature scales because liquids decrease in viscosity with rise in temperature. Forty liquids are given.
1385
All data are for atmospheric pressure. The viscosity of gases is theoretically independent of pressure, and for moderate ranges of pressure this is true. For “permanent” gases the atmospheric pressure values can probably be used t o 100 atmospheres without appreciable error. For liquids such as water the atmospheric pressure values can be used up to about 500 atmospheres. iidditions to either chart may easily be made by following the method outlined, provided data are available for the fluid in question. L i t e r a t u r e Cited a n d Bibliography for Viscosity D a t a (1) Bingham and Jackson, Bur. Standards, Sci. Paper 298, 73 (1917). (2) Cocks, J . SOC.C k m . I d . , 48, 279T (1929). (3) Herschel, Oil Gas J . , 25,135 (1926); J. IND. E m . CHEM.,14,715 (1922). ( 4 ) International Critical Tables, Vol. V. (5) Kaye and Laby, Physical a n d Chemical Constants, 1918. (6) Landolt-Bornstein Tabellen, 1923, 5. A d a g e , Band I ; 1937, 5. A d a g e , Erster Erganzungsband mit Generalregister. (7) Martin, “Treatise on Chemical Engineering,” 1928. (8) Ravenscroft, IND. ENG. CHEW, 21, 1203 (1929). (9) Rhodes a n d Barbour, IND. E N G . CHEM.,15, 850 (1923). (10) Smithsonian Tables, 1920.
ComDosition of Citrate-Insoluble Residues from Superphosphates and Ammoniated Superphosphates’ A
K. D. Jacob, W. L. Hill, W. H. Ross, a n d L. F. Rader, Jr. FERTILIZER A N D FIXED NITROGEN INVESTIGATIONS, BUREAU OP CHEMISTRY A N D SOILS,WASH:XGTON, D. C.
UPERPHOSPHATES always contain a small quantity of phosphoric acid that is insoluble in neutral ammonium citrate solution according to the official method of analysis (1). So far as the writers know, the nature of this citrate-insoluble phosphoric acid has never been thoroughly investigated, but it seems to be the general opinion that it is present principally as undecomposed phosphate rock. When superphosphates are treated with relatively large quantities of ammonia, the percentage of citrate-insoluble phosphoric acid increases to a degree approximately dependent upon the quantity of ammonia added. I n this case it is known that a large portion of the citrate-insoluble phosphoric acid is combined as calcium phosphates, particularly tricalcium phosphate, but it is not known whether the iron, aluminum, and fluorine compounds always present in commercial superphosphate play an important part in the formation of citrate-insoluble phosphoric acid. The present paper gives the results of a study of thecomposition of the citrate-insoluble residues obtained from eleven samples of superphosphates and ammoniated superphosphates.
S
P h o s p h a t e Materials Used
Florida Pebble Superphosphate, No. 1037. This was a well cured commercial material manufactured in the usual manner. Ammoniated Florida Pebble Superphosphate, No. 1036. This material, which contained 5.76 per cent ammonia, was prepared experimentally on a semi-commercial scale from the same batch of superphosphate from which sample No. 1037 was obtained. Florida Pebble Superphosphate, No. 1060. This material, which is sold under the trade name of “Oberphos,” was prepared commercially by a special patented process. Ammoniated Florida Pebble Superphosphate, 17-0. 1050. This 1 Received September 22, 1930. Presented a s a part of the symposium on “Action of Ammonium Citrate on Superphosphates” before t h e Division of Fertilizer Chemistry a t t h e 80th Meeting of t h e American Chemical Society, Cincinnati, Ohio, September S t o 12, 1930.
material, which contained 4.97 per cent ammonia, was prepared experimentally from the same batch of superphosphate from which sample No. 1060 was obtained. Florida Pebble “Den” Superphosphate, N o . 1073. This material was obtained by artificially drying freshly manufactured commercial superphosphate in order to prevent further conversion of citrate-insoluble phosphoric acid into soluble forms. Tennessee Brown-Rock Superphosphate, No. 1066. This was a well cured commercial material manufactured in the usual rnanner. Ammoniated Tennessee Brown-Rock Superphosphate, No. 1067. This material, which contained 4.35 per cent ammonia, was prepared experimentally from the same batch of superphosphate from which sample No. 1066 was obtained. Tennessee Brown-Rock “Den” Superphosphate, No. 1087. This material was obtained by artificially drying freshly manufactured commercial superphosphate. Tennessee Brown-Rock Triple Superphosphate, No. 1059. This material was manufactured several years ago and probably differs somewhat in its composition and properties from the same type of material manufactured a t present. Ammoniated Tennessee Brown-Rock Triple Superphosphate, X o . 1039. This material, which contained 7.51 per cent ammonia, was prepared experimentally from recently manufactured triple superphosphate. Idaho Triple Superphosphate, N o . 1061. This was a recently manufactured commercial product. M e t h o d of Determining Citrate-Insoluble Phosphoric Acid
When tricalcium phosphate and highly ammoniated superphosphates are treated with neutral ammonium citrate solution according to the official method, clear filtrates cannot be obtained because a portion of the phosphate goes into the colloidal condition and passes through the filter paper, thus resulting in low values for citrate-insoluble phosphoric acid. Clear filtrates from such materials were obtained, however, by the use of short Pasteur-Chamberland filter tubes (grade F). Duplicate results were in excellent agreement and, in the case of phosphates which filtered clear through paper, the method gave results that checked closely
INDUSTRIAL AND ENGINEERING CHEMISTRY
1386
of O r i o i n a l P h o s p h a t e s a
T a b l e I-Composition SAMPLE
1037 1036 1060 1050 1073 1066 1067 1087 1059 1039 1061 287 a
PHOSPHATE MATERIAL
P e r cent 9.12 4.02 2.05 3 03 0.06 6.51 2.34 1.01 4.83 5.76 2 79 2 16
Florida Debble SuoeruhosDhate A m m o n s t e d F l o h d a pebble superphosphate Florida pebble superphosphate Ammoniated Florida pebble superphosphate Florida pebble “den” superphosphate Tennessee brown-rock superphosphate Ammoniated Tennessee brown-rock superphosphate Tennessee brown-rock “den” superphosphate Tennessee brown-rock triple superphosphate Ammoniated Tennessee brown-rock triple superphosphate Idaho triple superphosphate Tricalcium phosphate (Eimer and Amend)
P e r cent 5:76
4:j7
..
4:35
..
7 il ,.
..
Per cent 0.61 0.58 0.54 0.45 0.98 0.73 0 87 1.31 2.84 3.10 1.77
..
Per cent Per cent 0.80 25.08 0.93 26.56 1.11 28.45 1.16 28.08 0.66 32.45 2.06 27.84 1.96 28.04 1.66 28 90 3.51 17.28 2.86 16.57 0.91 22.82 .. 49.50
Per cent 1=’er cent P e r cent 18.90 1.62 28.54 18.67 1.66 28.94 20.59 2.31 29.10 19,54 2 25 27.95 22.22 0.80 33.45 19.41 1.62 30.24 19.25 1.59 30.28 0.91 31.70 21.97 2.22 6.02 44.07 44.96 3.02 3.67 45.58 1.98 3.66 .. 40.86
Results are not calculated t o t h e basis of constant weight a t 105’ C. P h o s p h o r i c Acid in O r i g i n a l P h o s p h a t e s
T a b l e 11-Citrate-Insoluble
P?O
PzO DISSOLVED BY 100 cc. SOLS. CITRATE
CITRATE-ISSOLUbLE
SAMPLE
PHOSPHATE MATERIAL
1037 1036
Florida pebble superphosphate Ammoniated Florida pebble superphosphate 1060 Florida pebble superphosphate 1050 Ammoniated Florida pebble superphosphate 1073 Florida pebble “den” superphosphate 1066 Tennessee brown-rock superphosphate 1067 Ammoniated Tennessee brown-rock superphosphate 1087 Tennessee brown-rock “den” superphosphate 1059 Tennessee brown-rock triple superphosphate 1039 Ammoniated Tennessee brown-rock triple superphosphate 1061 Idaho triple superphosphate 915a Florida waste-pond phosphate 287‘ Tricalcium phosphate (Eimer and Amend) a
Vol. 22, s o . 12
Sample ground t o 100 mesh for analysis,
WaterTotal insoluble
Per
Per
cent
cent
IVt. of sample
RATIO OF WEIGHTS OF P20, DISSOLVED BY 100 SOLV. c c . CITRATE
Wi. of samole 0 5 g.
L o g . 1.5,s.
Wt. of sample 2.0 g
0.5g.
Log.
1 5g.
Per cent 0.25
Per
Pev
cent
cent
Mg.
0.27
.Ma. 7 2
Mg.
0.28
14 6
21.5
Afd 28 8
1.00 2 . 0 3
2.99
4.00
93.3 24.0
125.4 35.7
147 4 46 8
1.00 1.00
2.50 2.83
2.94 3.71
2.og
0 5g. 1 o g . 1 5 g . 2 og.
18.90
1.71
Per cent 0.28
18.67 20.59
11.03 3.48
1.02 0.96
1 70 1.08
2.67 1.10
3.66 1.14
50.1 11.6
19.54 22 22 19 41
13.67 17.76 5 22
2.95 3.19 0.22
5.01 3.35 0.19
6.24 3.35 0.35
7.15 3.41 0.28
53.6 72 9 23.0
8 6 . 6 111.5 1 4 4 . 1 216.2 50.3 73.1
130 4 287 0 98 8
1.00 1.62 2.08 2.43 1 . 0 0 1 . 9 8 2.97 3 . 9 4 1.00 2 . 0 1 2 . 9 2 3 . 9 5
1.86 1.90
19.25
11.38
0.33
1.11
2.55
3.76
55.3
102.7
132 5
152 4
1 00
1.86
2.40
21.97
5 86
1.21
1.30
1.33
1.42
22.3
43.6
65.0
84 8
1.00
1.96
2.91
3.80
44.07
11.18
1.5s
1.53
1.47
48.1
96.0
144.8
191 2
100
2 00
3 01
4.04
44.96 45.58 23.05
25.41 8 58 23.05
1
1.56
1.11 1 41 3 51 3 80 2 1 . 8 2 22.39
1 61 3 93 ..,
1 88 3 80 22 78
121.5 240.0 25 4 47 8 6 2 6.6
357.0 69.8
...
470 6 95 6 5 4
100 1 00 1 00
1 98 2 . 9 4 3 . 8 7 1 . 8 8 2 . 7 5 3.76 1.05 . . 0.87
40 86
40 86
1
14 54
28 40
31 17
131 6
186.9
193 8
109
1 31
23.60
172.6
1 42
2 76
1.47
Other samples ground t o 20 mesh.
The solubility of the phosphoric acid of the original phosphates in neutral ammonium citrate solution was determined on 0 . 5 , 1.0-, 1.5,and 2.0-gram samples using 100 cc. of citrate solution in each case. Similar determinations were also made on samples of Eimer and Amend’s tricalcium phosphate and Florida “waste-pond” phosphate. The latter is a natural material obtained in connection with the preparation of Florida hard-rock phosphate for the market, and contains a considerable quantity of colloidal phosphate ( 7 ) . The results of these determinations (Table 11) show that in the case of tricalcium phosphate and the ammoniated superphosphates there was a progressive and significant decrease in the percentage of citrate-insoluble phosphoric acid when 100 cc. of citrate solution were used and the weight of sample taken for analysis was decreased by 0.5gram steps from 2.0 grams to 0.5 gram. On the other hand, decreasing the ratio of sample to citrate solution did not effect significant decreases in the percentage of citrateinsoluble phosphoric acid in Florida waste-pond phosphate Composition and Citrate Solubility of Original Phosphates and the non-ammoniated superphosphates. Thomas ( I O ) Figures showing the composition of the original phosphates obtained similar results on superphosphate, but he reports with respect to the most important constituents are given that the citrate-insoluble phosphoric acid in acidulated in Table I. Silica was not determined, since it is present garbage tankage decreases as the weight of sample taken principally as quartz and probably has no effect on the prop- for analysis decreases. Also Haskins (4) has shown that erties of the phosphates. The “den’’ superphosphates, in the case of precipitated phosphate (dicalcium phosphate) Nos. 1073 and 1087, had been artificially dried, which re- a significant decrease in the percentage of citrate-insoluble sulted in loss of a portion of the fluorine by volatilization. phosphoric acid is obtained by reducing the weight of sample for analysis from 2 grams to 1 gram. 2 T h e potentiometric pH measurements were kindly made b y E. F. The solubility of water-insoluble phosphates in neutral Snyder, of t h e Soil Fertility Division. with those obtained by the use of filter paper. The use of these tubes for the determination of citrate-insoluble phosphoric acid will be described in detail in a later paper. Except for the method of filtration. the official procedure for citrate-insoluble phosphoric acid was followed as closely as possible on all samples. The weighed samples of superphates and ammoniated superphosphates were thoroughly washed with cold water prior to the citrate digestion in order to remove water-soluble phosphoric acid. Austin ( 2 ) has shown that in the case of superphosphates incomplete removal of the water-soluble phosphoric acid results in high values for citrate-insoluble phosphoric acid. For the determination of citrate-insoluble phosphoric acid the superphosphates and ammoniated superphosphates were ground to pass a 20-mesh sieve. The neutral ammonium citrate solution was carefully prepared according to the official method ( I ) , using phenol red as an indicator. The pH values of the several solutions used varied from 6.95 to 7.00 as determined potentiometrically using the hydrogen electrode.2
December, 1930
I N D USTRIA L AND ENGINE E RI NG CHEMIS T R Y ORIGISALPHOSPHATE
Sample
1037 1036 1036b 1060 1050 lO5Ob 1073 1066 1067 1087 1059 1039 1061 287b.c
Type
Florida pebble superphosphate Ammoniated Florida pebble Superphosphate Ammoniated Florida pebble superphosphate Florida pebble superphosphate Ammoniated Florida pebble superphosphate Ammoniated Florida pebble superphosphate Florida pebble "den" superphosphate Tennessee brown-rock superphosphate Ammoniated Tennessee brown-rock superphosphate Tennessee brown-rock "den" superphosphate Tennessee broxn-rock triple superpho7phate Ammoniated Tennessee brown-rock triple superphosphate Idaho triple superphosphate Tricalcium nhosphate (Eimer and Amend)
CITRATE-ISSOLCBLE RESID~ES Sample
\Teighta
1065 1063 1064 1086 1051 1062 1098 1069 1071 1090 1089 1088 lOi2 1117
Grams 33.28 61.59 48.53 47.96 119.15 73.11 73.16 2% 83 52.73 49.16 25.96 39 79 7 2 04 42 11
Oven-dry weights, not calculated t o constant weight a t 10.5' C . b Extracted in t h e proportion of 0.5 gram of phobphate material t o 100 cc. of citrate solution. 3.0 grams of phosphate t o 100 cc. of citrate solution. C 110 grams taken for extraction. d Determined by analysis of small samples using official method. a
ammonium citrate solution, as determined by the official method, is dependent upon a t least four factors-namely, (1) the chemical nature of the phosphate; ( 2 ) the total quantity of water-insoluble phosphoric acid in the sampk for analysis; (3) the quantity of other citrate-soluble salts. such as calcium sulfate, present; and (4) the physical condition of the phosphate. All these factors must be taken into consideration in comparing the results given in Table 11. These factors vary considerably and cannot be controlled in the case of different commercial products prepared by different processes from different types of phosphate rock. Consequently it is practically impossible to reduce the results given in Table I1 to a strictly comparable basis which will permit of drawing definite conclusions as to the relative solubilities in neutral ammonium citrate solution of the phosphoric acid in the water-insoluble phosphate compounds. Comparison of the ratios of the weights of phosphoric acid dissolved from 0.5-, 1.0-, 1.5-, and 2.0-gram samples by 100 cc. of citrate solution shows that in the case of the ordinary superphosphates, the triple superphosphates, and the ammoniated triple superphosphate the weight of phosphoric acid dissolved was directly proportional to the weight of sample taken for analysis. This indicates that within the range of the weights of sample used the weight of phosphoric acid dissolved did not reach the maximum quantity that can be dissolved from the phosphates under the conditions of the determination. I n the case of the ammoniated ordinary superphosphates, however, the weight of phosphoric acid going into solution was not directly proportional to the weight of sample when more than 1 gram of material was taken for analysis. This indicates that as the weight of sample is increased beyond 1 gram the weight of phosphoric acid dissolved approaches the maximum quantity that can be dissolved from these phosphates under the conditions of the determination. The maximum quantity of phosphoric acid was dissolved from the Florida waste-pond phosphate when only 0.5 gram was taken for analysis. Increasing the weight of the sample beyond 1 gram did not greatly increase the quantity of phosphoric acid dissolved from tricalcium phosphate. Large-Scale Preparation of Citrate-Insoluble Residues
In order to obtain sufficient quantities of citrate-insoluble residues for a study of their chemical composition and properties, 500-gram samples of the phosphates were extracted in the proportion of 2 grams to 100 cc. of ammonium citrate solution. Extractions were also made on tricalcium phos-
1387
Fraction of original phosphate
Per cent 6 7 12.3 9.7 9 6 23.8 14.6 14 6 4 10 9 5 8 14 3s
6 6 s 2 0 4 3
CITRATE-ISSOLUBLE 1'20, I N 500 G R A M S ORIGINAL PHOSPHATE^
Total
Gvams 0 . ti2 11.42 6.89 5 17 32.22 15 29 17.10 1 24 10 11.3 6 40 4 10 18 16
1
,
55 i4 46
"9
Grams 1 3.5 18 30 5 10 5 70 35 7.5 14 7 5 17 05 1.40 18.80 10 7 35 9 40 19 00 16 00
-
, i l l other extractions were made in t h e proportion of
phate (110 grams) and the ammoniated Florida pebble Superphosphates, Sos. 1036 and 1050, in the proportion of 0.5 gram of material to 100 cc. of citrate solution. The method used for the large-scale extractions v a s as follows: The sample of phosphate was vashed by suction on Buchner funnels with cold water in the proportion of 250 cc. to 2 grams of material in order to remove water-soluble phosphoric acid. (Washing was omitted in the case of the tricalcium phosphate.) The damp water-insoluble residue was immediately separated as completely as possible from the filter paper and quickly added to the proper quantity of ammonium citrate solution which had been heated to 65" C. in a large enamel-lined, steam-jacketed kettle equipped with a mechanical stirrer. The sample was digested a t 65" c. with constant stirring for 30 minutes. The stirrer was then stopped and twenty-four Pasteur-Chamberland filter tubes (grade F) attached to metal manifolds each carrying six tubes, were lowered into the kettle and the solution was removed by suction. The residue was washed seven or eight times with water a t 65" C. until the washings totaled 250 cp. per 2 grams of the original phosphate. The material in the kettle was maintained a t a temperature of 65" C. until washing was completed. The time required to filter the citrate solution when 500-gram samples were digested in the proportion of 2 grams per 100 cc. ranged from 22 minutes in the case of Tennessee brown-rock triple superphosphate, No. 1059, to 2.25 hours for ammoniated Florida pebble superphosphate, No. 1036. Likewise the time required to wash the residues with hot water ranged from 1.1 hours in the case of No. 1059 to 4.5 hours for No. 1036. I n all cases the ammoniated superphosphates required a longer time for filtering and washing than the non-ammoniated materials. The pH values of the citrate solutions used for these extractions ranged from 6.95 to 7.00. After the washing of the citrate-insoluble residue with hot water was completed, the filter tubes were lifted from the kettle and the very fine material adhering to them was carefully removed by rubbing and washing. Upon evaporation of the aqueous suspension on the steam bath the fine material was deposited as horny scales, resembling in a general way those obtained when aqueous suspensions of natural colloidal phosphates (4) are evaporated to dryness. In addition to the material adhering to the tubes, a quantity of relatively coarse material remained in the kettle. This was removed separately and dried a t a temperature of approximately 90" C. Finally, the two fractions were combined, after being weighed separately, and ground to pass a 100-mesh sieve for analysis. The entire operation was performed carefully in order to duplicate as closely as possible
I S D CSTRIAL Aij'D ENGINEERING CHE-WISTRY
1388
T a b l e IV-Composition ORIGINALPHOSPHATE Sample
1087 1059 1039 1061 287d
Florida pebble superphosphate Ammoniated Florida pebble superphosphate Ammoniated Florida pebble superphosphate Florida Debble SuaerohosDhate Ammoniated FloAdapebble superphosphate Ammoniated Florida pebble superphosphate Florida pebble "den" superphosphate Tennessee brown-rock superphosphate Ammoniated Tennessee brown-rock suDerphosphate Tennesseebrown-rock"den"superphosphate Tennessee brown-rock triple superphosphate Ammoniated Tennessee brown-rock triple superphosphate Idaho triple superphosphate Tricalcium phosphate (Eimer a n d Amend)
CITRATE-IXSOLUBLE RESIUUES~ Ignition loss Sam- Total Lossat a t 1000° C. A12036 FelOa CaO ple N 105'C. after drying total a t 105' C.
I 1037 1036 1036d 1060 1050 1050d 1073 1066 1067
of C i t r a t e - I n s o l u b l e R e s i d u e s
I
Type
Vol. 22, No. 12
Per cent
Per cent
Per cent 6.10
Per cent
Per cent
Per cent
Per cent
Per cent 95.4 99.4 98.4 96.6 99.2 98.4 98.3 97.5
1 . 0 7 2 9 . 6 1 20.72 1 . 0 8 2 . 6 8 3 2 . 0 0.83 19.89 1 3 . 0 1 1 . 1 2 2 . 8 5 5 9 . 3 1 . 4 8 1 6 . 2 3 17.13 0.00 2 . 5 3 4 4 . 5
1.03 1.78 2.13
96.4 99.4 94.6
26.98 0.00 25.63 0.00 38.68 ,,
1.97 4.21
96.1 93.1 96.9
1071 0 . 1 7 1 . 4 9 1090 0.11 0 . 3 7 1088 .. 0.71
9.47 4.64 11.45
0.35 0.24 3.74
1068 0 . 4 7 1072 0 . 1 3 .. 1117
11.78 5.86 6.50
1.97 3.84 0.42 0.58
.
Per
3.39 1.69 0.88 3.83 2.12 1.58 1.21 2.08
6.25 5.70 7.75 7.75 7.32 4.82 10.88
,
Per
otalc
1 0 0 0 ~c.
3.50 79.8 3.10 43.9 1.95 54.7 4.90 55.3 4.00 23.3 3.15 36.5 2 . 9 3 36.7 2.1771.4
0.54 1.33 0.19 1.60 0.23 1.86 0.60 1 . 0 7 0.54 0.66 0.54 0.87 0.28 0.87 0.893.00
2.15 0.33 1.74
Per cent
F lost by
sio2 ignition at
ploj soln, so3in 1:4 HCI
,,
cent cent 6.54 1 . 8 5 0.00 27.12 18.54 0 . 5 8 20.23 14.19 0 . 1 9 20.35 10.77 0 . 1 4 37.32 27.04 1 . 1 7 29.79 20.92 0 . 8 2 3 0 . 6 5 23.37 0 . 6 9 5.21 5.450.10
24.25 41.30 49.99
Per cent
2.11 25.8 6.37 20.3 ,,
..
, .
-
in t h e proportion of 2.0
the analytical results obtained for citrate-insoluble phosphoric acid in the original samples. The yields of citrate-insoluble residues obtained from 500 grams of the original phosphates by the large-scale extractions (Table 111) ranged from 22.83 grams in the case of Tennessee brown-rock superphosphate, No. 1066, to 119.15 grams for ammoniated Florida pebble superphosphate, No. 1050, extracted in the proportion of 2 grams to 100 cc. of citrate solution, corresponding, respectively, to 4.6 and 23.8 per cent of the weight of the original phosphates. Except in the case of the Tennessee brown-rock triple superphosphate. ammoniation resulted in a significant increase in the weight of material adhering to the filter tubes, as compared with the weight of the same fraction obtained from the original non-ammoniated superphosphate. I n the case of the tricalcium phosphate practically all of the residue was deposited on the filter tubes in the form of a gelatinous, sticky material. The total quantity of phosphoric acid obtained in the residues from the large-scale extractions ranged from 46 to 133 per cent of the citrat'e-insoluble phosphoric acid determined by the official method using 0.5- to 2.0-gram samples of the original phosphate for analysis. With six of the samples the results obtained by the large-scale extractions checked to *10 per cent of the values calculated from the analyses of the original phosphates. Results obtained by duplicate large-scale extractions on four samples agreed within an average of 8 per cent, the minimum variation between duplicate runs being 0.8 per cent and the maximum 22 per cent. I n the case of two samples which gave excellent duplicate results the average recovery of phosphoric acid in the residues was only 50 to 70 per cent. Consequently it seems that the rather wide variations from the theoretical recoveries obtained on some samples were probably due to differences in the physical condition and the chemical nature of the original phosphates rather than to a lack of uniformity in carrying out the large-scale extractions. Composition of Citrate-Insoluble Residues I n addition to the constituents determined in the original phosphates, the citrate-insoluble residues were analyzed for silica and loss on ignition at 1000" C. The results are given in Table IV. It was found that when the residues were ignited at 1000° C. 38 to 97 per cent of the fluorine was lost. Fluorine was
determined in the ignited residues by the volatilization method (9) and also by a modification of the lead chlorofluoride method3 developed by Hoffman and Lundell (6) for fluorine in glass and enamels. Since the results by the two methods agree very well, it seems quite certain that the loss of fluorine was not an apparent one caused by failure of the methods to account for all the fluorine in the ignited residues, and that the fluorine was actually volatilized from the residues. Although a positive statement as to the form or forms in which all the fluorine was driven off, cannot be made, further experiments showed that only a portion was volatilized as silicon tetrafluoride. Hawley ( 5 ) has shown that significant losses of fluorine occur upon heating mixtures of calcium fluoride and iron pyrite. The residues were not analyzed for pyrite, but it was undoubtedly present, since it usually occurs in phosphate rock in small quantities and would be concentrated to a considerable extent in the citrateinsoluble residues. Because of the inability to distribute properly the fluorine lost by ignition, the results given in Table IV are corrected simply for loss of fluorine as such, although it is certain that no elementary fluorine was volatilized. The constituents determined in the residues totaled 93.1 to 99.4 per cent. Any undetermined elements which were present in the original phosphate rock, and which were neither volatilized nor converted into compounds entirely soluble in water and ammonium citrate solution during the processing of the phosphate rock, would be concentrated in the citrate-insoluble residues. Additional analyses on residues 1063 and 1068 showed the presence of appreciable quantities of sodium, potassium, titanium, magnesium, and manganese. The residues also contained sulfur, which was insoluble in 1:4 hydrochloric acid but which was driven off on ignition, indicating the presence of either organic or pyritic sulfur or both. The nitrogen was present almost entirely in organic combination, none of the residues containing more than a trace of ammonia. The distribution of phosphoric acid in the fine and coarse particles was determined in the case of residues from Florida pebble superphosphate, No. 1037, and ammoniated pebble superphosphate, No. 1036, 500 grams of each material being extracted in the proportion of 2 grams to 100 cc. of citrate solution. Special care was taken to separate the fine material adhering to the filter tubes as completely as possible a T h e details of this modification a n d its application t o the analysis of phosphate rock a n d phosphatic slag will be published later.
December, 1930
IXDUSTRIAL AND ENGINEERING CHEMISTRY
ORICISAL PHOSPHATE RESIDUE Sample
1037 1036 1036" 1060 1050 1050" 1073 1066 1067 1087 1059 1039 1061 2870
Type
Florida pebble superphosphate Ammoniated Florida pebble superphosphate Ammoniated Florida pebble superphosphate Florida pebble superphosphate Ammoniated Florida pebble superphosphate Ammoniated Florida pebble superphosphate Florida pebble "den" superphosphate Tennessee brown-rock suueruhosuhate Ammoniated Tennessee drokn-rdck superphosphate Tennessee brown-rock "den" superphosphate Tennessee brown-rock triple superphosphate Ammoniated Tennessee brown-rock triple superphosphate Idaho triple superphosphate Tricalcium phosphate (Eimer and Amend)
a Extracted in t h e proportion of 0.5 gram
,
from the coarse particles. The results reduced to constant weight a t 105" C. were as follows: TOTAL PzOj IN FISE MATERIAL Per cent Per cent 19.30 24.7 1.48 47.2
COARSERESIDUE Weight PzOs
Grams 50.51 25.64
FRACTIONOF CONSTITUENTS OF ORIGINALPHOSPHATES REXAISISC I K CITRATE-INSOLUBLE RESIDUES A1203
FelOa
CaO
P20,
Per cent
Pev cent
Per cent
Per cent
5.9 4.0 3.9 10.7 28.6 17.6 4.2 5 6 4.3
11.1 21.2 19.4 9.2 13.6 11.0 19.3 6.7 5 s 4.9 2.2 10.7 9.2
1.7 12.6 7.4 6.7 31.7 15.5 13 5 0 9 11 1 6.8 4 9 11.6 26.1 38.7
1.8
6.8 5.1 3.4
..
of phosphate material to 100 cc. of citrate solution.
2.0 grams of phosphate t o 100 cc. of citrate solution.
ORIGIS.4L F I N ERESIDUE P H O S P H A T Weight ~ PzO: Grams Per cent 1036 15.14 21.15 1037 7.95 4.27
1065 1063 1064 1086 1051 1062 1088 10R9 1071 1090 1089 1068 1072 1117
The results show that a considerable portion of the phosphoric acid in the residues was in a very fine state of division. The greater portion of the organic matter present in the original phosphates was recovered in the fine residues. hficroscopical examination of the residues showed that, in the case of the non-ammoniated superphosphates and triple superphosphates, the coarse particles consisted largely of quartz, while in the case of the residues from the ammoniated ordinary superphosphates a considerable quantity of coarse more or less porous granules was present. The appearance of these granules indicated that the citrate solution had penetrated into the interior of the particlm and dissolved out a portion of the material, leaving behind a skeleton of material that was difficultly soluble in ammonium citrate solution. This can be explained by the non-uniform conversion of the monocalcium phosphate in the particles into di- and tricalcium phosphates during the process of treating the original superphosphates with ammonia, the tendency being to form a surface coating of difficultly soluble tricalcium phosphate. The non-siliceous particles in the residues from the non-ammoniated materials did not in general show pronounced pitting or erosion. The results given in Table V show that in all cases, except Florida pebble superphosphate No. 1060 and the ammoniated material prepared therefrom, only 1.8 to 6.8 per cent of the original alumina remained in the citrate-insoluble residues. Also, except in the case of Florida pebble superphosphate No. 1060, ammoniation did not increase the percentage of original alumina remaining in the residues. The percentages of original iron remaining in the residues varied considerably, being in general increased by ammoniation. The percentages of the original calcium and phosphorus remaining in the residues varied considerably and were increased by ammoniation. It is interesting t o note that the figures for these elements parallel each other closely in the case of the individual materials, except the ammoniated and non-ammoniated triple superphosphates. The portion of the original sulfur, soluble in 1: 4 hydrochloric acid, remaining in the residues ranged from zero to 1 per cent. I n general, ammoniation decreased the solubility of the fluorine when the extractions were made in the proportion of 2 grams to 100 cc. of citrate solution, but when the extractions
1389
..
0.65 12.2 7.4 5,O 33.0 15 7 15.4 1.3 11.4
5 s
2.0 4.8 8.1 3'1 2
so3
F
Per cent Per cent 0.00 14.4 0.25 0.06 0.05 1.00 0.43 0.30 0.02 0.38 0.35 0.00 0.00 0.00
23.0 11.4 30.3 42.4 20.5 53.6 6.1 17.8 30.8 5.9 5.7 46.4
..
All other extractions were made in t h e proportion of
were made in the proportion of 0.5 gram of the ammoniated phosphate to 100 cc. of citrate solution the percentages of original fluorine remaining in the residues were not significantly different from those obtained in the case of the original non-ammoniated superphosphates. Carter (3) has recently shown that calcium fluosilicate is very soluble in water. It is probable that the fluorine dissolved from the original phosphates by water and citrate solution was combined principally as this compound and perhaps also as sodium and potassium fluosilicates. The non-ammoniated superphosphates also contained small quantities of free hydrofluosilicic acid. Solubility of Residues in Ammonium Citrate Solution The solubility of the phosphoric acid of the residues in neutral ammonium citrate solution was determined on 0 . 5 , 1.0-, 1 . 5 , and 2.0-gram samples, using 100 cc. of citrate solution in each case. The residues were ground to 100 mesh for analysis. The results, which are given in Table VI, show that in all cases smaller quantities of phosphoric acid were dissolved from the residues by citrate solution than were dissolved from the corresponding original phosphates under the same conditions. I n the case of the original non-ammoniated superphosphates and triple superphosphates (Table I) reducing the weight of sample from 2.0 grams to 0.5 gram did not result in a significant decrease in the percentages of citrate-insoluble phosphoric acid found by analysis. I n view of this one might expect that only a small and constant quantity of phosphoric acid would be dissolved by treating the residues obtained from these samples with ammonium citrate solution. The results show, however, that the weights of phosphoric acid dissolved vary considerably when the different residues are extracted under the same conditions. Inasmuch as the residues were all ground to 100 mesh and did not contain significant quantities of citrate-soluble compounds other than the phosphates, this indicates that the residues either contained different phosphate compounds or different proportions of several phosphates which did not dissolve in ammonium citrate solution to the same extent. It seems that the latter view is the more nearly correct one. -4s would be expected, the residues from the ammoniated materials extracted .in the proportion of 0.5 and 2.0 grams of material per 100 cc. of citrate solution, respectively, contained much larger quantities of citrate-soluble phosphoric acid than the residues from the corresponding non-ammoniated materials. As in the case of the original material (Table I), the high solubility of the phosphoric acid in the residue from the ammoniated Tennessee brown-rock triple superphosphate indicates that the greater portion of the phosphoric acid
INDUSTRIAL A N D ENGINEBECING CHEMISTRY
L
0
5
VOl. 22,
KO.
12
was in a state of combination quite different from that in the other residues. Comparison of the ratios of the weights of phosphoric acid dissolved from 0.5, l&, 1.5-, and 2.0-gram samples of the resid-ues by 100 cc. of citrate solution shows that in general the weight of phosphoric acid dissolved did not increase in proportion to the weight of sample taken for analysis. The ratios vary considerably and are not constant for residues obtained from a particular type of the orginal phosphates. I n general the results indicate that, as the weight of sample was increased from 0.5 gram to 2.0 grams, the weight of phosphoric acid dissolved rapidly approached the maximum quantity that could be dissolved from the residues under the conditions of the determination. Nature of Phosphate Compounds Present in CitrateInsoluble Residues
Assuming (1) that all the fluorine and hydrochloric acidsoluble sulfur in the citrate-insoluble residues are combined as calcium fluoride and calcium sulfate, respectively, with the remaining calcium combined as phosphates, and (2) that all the iron and aluminum are combined as the normal phosphates with the remaining phosphorus combined as calcium phosphates, the figures given in Table VI1 show that, with two exceptions, the phosphoric acid-lime ratios of these calcium phosphates range from 0.690 to 0.860. The minimum and maximum ratios do not differ greatly from the ratio 0.760 required for the complex calcium phosphates of the type 3Ca3(POJ2.Ca(OH)2 and the ratio 0.844 required for tricalcium phosphate. T a b l e VII-Phosphoric
Acid-Lime R a t i o s of C a l c i u m P H o s p h a t e s in Citrate-Insoluble Residues
ORIGINAL PHOSPHATE
Pz051.v CaO I N RESIDUERESIDUEPzO;-CaO COM- COM- RATIO RES- B I N E D BINED IX CALDUE AS A S CAL- CIUM CALCIUM CIUM PHOSPHOSPHOSPHATE PHATE"
Florida pebble superphosphate Ammoniated Florida pebble superphosphate 1036C Ammoniated Florida pebble superphosphate 1060 Florida pebble superphosphate 1050 Ammoniated Florida pebble superphosphate l05OC Ammoniated Florida pebble superphosphat?, 1073 Florida pebble den" superphosphate 1066 Tennessee brown-rock superphosphate Ammoniated Tennessee brown1067 rock superphosphate 1087 Tennessee brown-rock "den" superphosphate 1059 Tennessee brown-rock triple superphosphate 1039 Ammoniated Tennessee brownrock triple superphosphate 1061 Idaho triple superphosphate 287C Tricalcium phosphate (Eimer and Amend)
1037 1036
d 0
Y
h
1065
PHATEb
Per cent Per cent -0.08 1.38
...
1063
16.85
22.14
0.761
1064 1086
12.22 8.98
17.24 13.02
0.709 0,690
1051
25.70
30.60
0.840
1062
19.39
24.57
0,789
1088
22.20
25,81
0.860
1069
1.54
1.92
0.802
1071
19.28
24.90
0.774
1090
11.94
14.90
0.801
1089
10.59
12.50
0.847
1068 1072
20.82 24.53
21.14 31.91
0.986 0.769
1117
38.68
49.99
0.774
4 Calculated from the figures given in Table IV, assuming t h a t all t h e A1 and F e are combined as AlPOi and FePO4, respectively, and t h a t t h e remaining PzOj is combined with CaO. b Calculated from t h e figures given in Table I V , assuming t h a t all t h e F and S are combined as CaFz and CaSO4, respectively, and t h a t t h e remaining CaO is combined with PzOj. C Extracted in t h e proportion of 0.5 gram of phosphate material t o 100 cc of citrate solution. All other extractions made in t h e proportion of 2.0 grams of phosphate t o 100 cc. of citrate solution.
It is certain, however, that all the iron and aluminum are not combined as the phosphates. Residue No. 1063 obtained from ammoniated Florida pebble superphosphate No. 1036 contained 0.28 per cent of iron and aluminum oxides insoluble in 1:l hydrochloric acid and only 0.04 per cent of insoluble phosphoric acid. Residue KO. 1068, obtained
INDUSTRIAL A N D ENGINEERIKG CHEMISTRY
December, 1930
from ammoniated Tennessee brown-rock triple superphosphate, No. 1039, contained 0.28 per cent of iron and aluminum oxides insoluble in 1:l hydrochloric acid and 0.34 per cent of insoluble phosphoric acid. Also, it is quite probable that not all the iron and aluminum which dissolved in 1: 1 hydrochloric acid were combined as the phosphates. This is probably the largest source of error in calculating the ratios which would be correspondingly increased with decrease in the quantities of iron and aluminum combined as the phosphates. I n the case of residue S o . 1065, obtained from Florida pebble superphosphate No. 1037, the phosphoric acid present was not sufficient to combine with all the iron and aluminum, while the residue contained an excess of lime over that required to combine with the fluorine and sulfur, when the phosphoric acid and lime are distributed in the manner used for calculating the ratios given in Table VII. If we assume, however, that only 50 per cent of the iron and aluminum is combined as the phosphates, the phosphoric acid-lime ratio for this residue is not greatly different from the ratios obtained for the other residues, except N o . 1068. It is probable that some of the fluorine is not combined as calcium fluoride, which would result in phosphoric acidlime ratios smaller than those given in Table VII. The writers believe, however, that the error from this source is small and, in general, is more than counterbalanced by the error caused by calculating all the iron and aluminum as the phosphates. Although the results given in Tables I1 and VI show that, in general, neutral ammonium citrate solution dimolves appreciably greater quantities of phosphoric acid from the residues than from the natural Florida phosphate, it seems quite certain that a portion of the phosphoric acid in the residues was present as unattacked phosphate rock. IJ'hen ordinary superphosphates are treated with 4 to 6 per cent of ammonia, as in the case of the ammoniated materials used in this investigation, the greater portion of the original water-soluble phosphoric acid is converted into relatively insoluble compounds, principally the di- and tricalcium phosphates. The reactions resulting in the formation of these compounds may be represented by the simple composite equations :
++
Ca(H2P04)2 2NH3 c a ( H ~ P 0 ~ )4NH3 ~
Cas04 = 2CaHP04 + (NH&SO4 (1) ++ 2CaS04 Ca3(P04)2 + 2(NH4)~S04(2) =
When triple superphosphate is treated with not more than approximately 7 per cent of ammonia, as in the case of the ammoniated Tennessee brown-rock triple superphosphate, No. 1039, the water-insoluble phosphoric acid is present principally as dicalcium phosphate. Ca(HzPOJ2
+ 2"3
=
CaHPO4
+ (NH4)2HI304
(3)
Haskins (4) has shown that precipitated phosphate (dicalcium phosphate) is almost completely soluble when 1 gram of the material is treated with 100 cc. of ammonium citrate solution. The figures given in Table I1 show, however, that only 64 per cent of the phosphoric acid is dissolved from tricalcium phosphate when 0.5 gram of the material is treated with 100 cc. of citrate solution. I n view of this one would expect that the residues obtained by extracting the ammoniated ordinary superphosphates in the proportion of 2 grams to 100 cc. of citrate solution contained considerable tricalcium phosphate and probably some dicalcium phosphate, and also that the residues obtained by extracting the same materials in the proportion of 0.5 gram to 100 cc. of citrate solution contained some tricalcium phosphate but no dicalcium phosphate. Many years ago Warrington (11) observed, however, that tricalcium phosphate hydrolyzes in water to give a product containing
1391
an excess of lime. Lorah, Tartar, and Wood (8) have recently made a more thorough investigation of this reaction and conclude that a product corresponding in composition to hydroxyapatite is finally obtained by prolonged treatment of tricalcium phosphate with large quantities of boiling water. They represent the hydrolysis by the summary equation: lOCaa(PO4)2
+
6H20 = 3[3Ca3(PO&.Ca(OH)2]
+
2H3POa
Considerable hydrolysis occurs when tricalcium phosphate is treated with neutral ammonium citrate solution, as shown by the fact that the phosphoric acid-lime ratio in the residue, Yo. 1117, obtained by extracting tricalcium phosphate, No. 287, in the proportion of 0.5 gram to 100 cc. of citrate solution, mas only 0.774 as compared with the ratio 0.825 in the original material. The residue contained only 0.12 per cent of carbon dioxide. The phosphoric acid-lime ratios in the citrate-insoluble residues obtained when 0 . 5 , 1.0-, 1.5-, and 2.0-gram samples of the tricalcium phosphate were treated with 100 cc. of citrate solution, respectively, were determined, with the following results: WEIGHTOF SAXIPLE FOR CITRATEDIGESTION
PSOrCa0 R AT I O IN CITRATE-INSOLUBLE RESIDUE
Grams 0.5 1.0 1.5
0.760 0.786 0.796 0.792
2.0
These figures show that when 1.5- to 2.0-gram samples of tricalcium phosphate are treated with citrate solution a considerable portion of the phosphoric acid remaining in the insoluble residue is combined as the hydroxyphosphate. With smaller samples larger portions of the citrate-insoluble phosphoric acid were combined as the hydroxyphosphate, the residue consisting entirely of this compound when a 0.5-gram sample was used. On the basis of these results it may be concluded that the residues obtained by extracting the ammoniated ordinary superphosphates in the proportion of 2 grams to 100 cc. of citrate solution contained both tricalcium phosphate and calcium hydroxyphosphate, while those obtained by extracting in the proportion of 0.5 gram to 100 cc. contained calcium hydroxyphosphate and very little, if any, tricalcium phosphate. The high phosphoric acid-lime ratio, 0.986, calculated for the residue, No. 1068, obtained from ammoniated Tennessee brown-rock triple superphosphate, No. 1039, was undoubtedly due to the presence of dicalcium phosphate. The ratio of phosphoric acid to lime in pure dicalcium phosphate is 1.267. None of the results obtained during this investigation indicate that recombination of the tricalcium phosphate and calcium fluoride to give compounds of the type 3Ca3(PO4)2.CaFz occurred either during the ammoniation of the original superphosphates or during the extraction of the ammoniated materials with citrate solution. Conclusions
I-In the case of phosphate rock and non-ammoniated ordinary and triple superphosphates reducing the weight of sample from 2.0 grams to 0.6 gram does not result in a significant decrease in the percentage of citrate-insoluble pliosphoric acid found by analysis when 100 cc. of citrate solution are used in each case. Reducing the weight of sample results, however, in significant decreases in the citrate-insoluble phosphoric acid in tricalcium phosphate and in highly ammoniated ordinary and triple superphosphates. 2-The solubility of water-insoluble phosphates in neutral
1392
.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
ammonium citrate solution is reduced by the presence of calcium sulfate, which is soluble in citrate solution, 3-As determined by the official method of analysis, the citrate solubility of water-insoluble phosphates depends on the type and quantity of phosphate compound, or compounds,. present. 4-Citrate-insoluble residues obtained from ammoniated and non-ammoniated superphosphates and triple superphosphates contain varying quantities of iron, aluminum, calcium, phosphoric acid, and fluorine, but little or no sulfate. &In general, treatment of superphosphates and triple superphosphates with relatively large quantities of ammonia tends to decrease the solubility of the iron in neutral ammonium citrate solution, has little, if any, effect on the solubility of the aluminum, and greatly reduces the solubility of the calcium and phosphoric acid. 6-Citrate-insoluble residues obtained by the large-scale extraction of processed phosphate materials contain varying and, in general, significant quantities of citrate-soluble phosphoric acid as determined by a second treatment with citrate solution. 7-Citrate-insoluble residues obtained from tricalcium phosphate consist wholly, or in part, of calcium hydroxyphosphate, which is less soluble than the original tricalcium phosphate in citrate solution. 8-Citrate-insoluble residues obtained from ammoniated and non-ammoniated superphosphates and triple superphosphates contain iron and aluminum phosphates and unattacked phosphate rock. I n addition to these compounds, residues obtained from highly ammoniated ordinary superphosphates, extracted in the proportion of 2 grams to 100 cc.
Vol. 22, No. 12
of citrate solution, contain tricalcium phosphate, calcium hydroxyphosphate and, perhaps, some dicalcium phosphate, but when these materials are extracted in the proportion of 0.5 gram to 100 cc. tricalcium phosphate either is absent or is present only in relatively small quantities. Dicalcium phosphate is the principal phosphate compound present in residues obtained by extracting ammoniated triple superphosphate in the proportion of 2 grams to 100 cc. of citrate solution. Acknowledgment
The writers are indebted to F. G. Keenen, of the Du Pont Ammonia Corporation, and to C. C. Howes, of the Davison Chemical Company, for the majority of the samples of phosphates used in this investigation. Grateful acknowledgment is made to K. C. Beeson, H. L. Marshall, and D. S. Reynolds for their very valuable assistance in the preparation and analysis of the citrate-insoluble residues and the analysis of the original materials. Literature Cited (1) Assocn. Official Agr. Chem., Xethods, p. 4 (1925). (2) Austin, IND. END.CHEM.,16, 1037 (1923). (3) Carter, Ibid., 22, 886 (1930). (4) Haskins, J. Assocn. Oficiol Agr. Chem., 4,64 (1920); 5, 97 (1921). ( 5 ) Hawley, IND. END. CHBM.,18, 573 (1926). (6) Hoffman and Lundell, Bur. Sfondords J. Research, 3, 581 (1929). (7) Jacob, Hill, and Holmes, Colloid Symposium Annual, Vol. VII, p. 195 (1930). (8) Lorah, T a r t a r , and Wood, J. A m . Chem. Soc., 61,1097 (1929). (9) Reynolds, Ross, a n d Jacob, J. Assocn. Oficial Agr. Chem., 11, 225 (1928). (10) Thomas, J. I N D .E N D .CHEM.,9,865 (1917). (11) Warrington, J . Chem. SOC.,19, 296 (1866); ‘26, 983 (1873).
Chemical and Physical Composition of Certain Finely Divided Natural Phosphates from Florida’ W. L.
K. D. Jacob,*L. T. A l e ~ a n d e rand , ~ H. L. Marshall2 BUREAUOF CHEMISTRY AND SOILS, WASHINGTON, D. C.
A study has been made of the chemical and physical verted into new p o n d s . composition of several samples of natural soft and wasteThese “waste-pond” phosthe Florida hard-rock pond phosphates from Florida. The results given in phates, which usually vary in p h o s p h a t e industry, the present paper include data on the physical composhade from white to a straw attention was called to the sition of the samples, effect of temperature on the color, are composed of very soft chalky phosphates (3, 9, physical composition, specific gravity, chemical compofine particles and when wet 10) which occur in considersition of the original phosphates and the mechanical they are quite plastic and able quantities, not only in fractions separated therefrom, and the solubility of the sticky. Upon drying they close association with the phosphoric acid in neutral ammonium citrate and 2 s h r i n k a n d c r a c k in the hard-rock phosphate, but also per cent citric acid solutions. manner c h a r a c t e r i s t i c of in individual deDosits of varimaterials c o n t a i n i n g high able size. Mitson (6) has discussed these phosphates with particular reference to their percentages of colloid. The air-dried lumps, which disdistribution in the Florida hard-rock and land-pebble districts. integrate rapidly when placed in water, usually contain During the process of preparing Florida hard-rock phos- about 18 to 25 per cent phosphoric acid (P205)and 15 to 18 phate for the market the soft phosphate present in the matrix per cent iron and aluminum oxides. The abandoned waste is washed into waste ponds, where it settles out along with ponds in the Florida hard-rock district are estimated to conthe clay and other impurities, the finer particles concentrating tain several million tons of this material. I n this paper the a t points farthest from the entrance to the pond. When fine phosphate deposited in the Florida hard-rock phosphate the ponds become filled with waste material they are allowed waste ponds will be called “waste-pond” phosphate in order to to dry up and the water from the phosphate washers is di- distinguish it from the soft phosphate obtained directly from the natural deposits. 1 Received September 22, 1930. Presented by W. L. Hill, L. T. Owing, in general, to the relatively low content of phosAlexander, and K. D. Jacob before the Division of Fertilizer Chemistry a t t h e 80th Meeting of t h e American Chemical Society, Cincinnati, Ohio, Septemphate and high content of iron and aluminum, it has not been ber 8 t o 12,1930, considered practicable to attempt the conversion of soft 2 Fertilizer Materials and Manufacture Division, Bureau of Chemistry phosphate into superphosphate by treatment with sulfuric and Soils. or other acids. Waggaman (8) and Matson (6) have sug8 Soil Chemistry and Physics Division, Bureau of Chemistry a n d Soils
E
ARLY in the history of
