Phosphate Fertilizers by Calcination Process Experiments with
Phosphate Rock in Very Thin Layers' D. S. REYNOLDS, H. L. MARSHALL, K. D. JACOB, AND L. F.RADER, JR. Bureau of Chemistry and Soils,U. S. Department of Agriculture, Washington, D. C.
A
PRECEDING paper (IO) of this series
showed that, under otherwise comparable conditions, the rate of reaction at high temperatures between water vapor and Florida land-pebble phosphate is markedly affected by the weight or thickness of the furnace charge. I n these experiments the thickness of the charges exceeded that of a single-grain layer of particles, and the rate of reaction decreased with increase in the thickness. The present paper gives the results of a study of the reaction (as indicated by volatilization of the fluorine and citrate solubility of the phosphorus) between water vapor and several types of domestic phosphate rock, for particle sizes between 10 and 80 mesh (1.651 and 0.175 mm.) where the thickness of the charge ranged upward from that of a singlegrain layer.
*
When phosphate rock is heated in a single-grain layer of particles at 1400" C. in the presence of water vapor, the rate of reaction, as indicated by the volatilization of fluorine, usually increases with decrease in particle size. Depending upon the type of rock and the particle size, the greater portion of the fluorine is volatilized during the first 2.5-10 minutes of heating. With certain types of rock (particularly Tennessee brown-rock, Idaho, and Montana phosphates) there is a fairly close relationship between the percentage citrate solubility of the phosphorus and the percentage volatilization of the F; fluorine, whereas with other types (Florida pebble and Florida hard rock) the percentage solubility of the phosphorus is much lower than the percentage volatilization of the F; fluorine. The low ratio of phosphorus solubility t o fluorine volatilization, obtained when single-grain layers of Florida pebble and Florida hard-rock phosphates are heated a t 1400" C., can be markedly increased either by increasing the depth of the charge or by reheating the charge for a short time at 1400" C. in a dry atmosphere.
Composition of Phosphate Rocks The phosphate rocks used in this study were representative of the commercial materials that have been or are now being produced from the respective deposits. In preparing the mechanical fractions, except those of the Tennessee brownrock phosphate, the 10-20, 20-40, and 40-80 mesh particles were separated from individual portions of the original rocks that had been ground to pass lo-, 20-, and 40-mesh sieves, respectively. The 10-20 and 20-40 mesh particles of the Tennessee rock were separated from a sample of the original material that had been ground to pass a 10-mesh sieve; the 40-80 mesh particles were separated from another portion of the original rock that had been ground to pass a 40-mesh sieve. Partial chemical analyses of the samples are given in Table I. THe analyses, except the determination of the particle size of the silica, were made on samples ground to pass a 100-mesh sieve. Commercial phosphate rock is a heterogeneous mixture of phosphatic and nonphosphatic compounds which differ in hardness and in resistance to grinding. The va,riation in 1
For previous papers in this series. see literature citations 8, 10, and 11.
chemical composition with particle size (Table I) is in line with results reported previously from this laboratory (2, 4, IO). Table I shows that, in comparison with the other mechanical fractions of this rock, the 40-80 mesh Montana phosphate was very high in silica. Inasmuch as the fractions of this material were prepared from large lumps of rock, i t is probable that the material from which the 40-80 mesh fraction was prepared was not representative of the original sample. "Coarse" silica-silica coarser than 100 mesh (0.147 mm.) and 200 mesh (0.074 mm.), respectively-in the mechanical fractions was determined in the following manner: In order to separate quickly the silica from the fluorine, a 10gram sample of the rock was treated in a 400-cc. beaker with 100 cc. of hot hydrochloric acid (1 t o 4), boiled for 3 minutes, and immediately diluted with 300 cc. of cold water. The clear liquid was decanted, the addition of cold water and decantation of the clear liquid was repeated three times, and the residue was transferred with water to a 100-mesh or a 200-mesh sieve and washed thoroughly. In order t o effect the solution of additional quantities of nonsiliceous material, the particles remaining on the
JUNE, 1936
INDUSTHIAL AND ENGINEERING CHEMISTRY
sieve were transferred to the original beaker and digested with 50 CC. of hydrochloric acid (1 to 1)on the steam bath for 30 minutes. The residue was filtered on paper, washed with hot hydrochloric acid (1 to 20), ignited in a latinum crucible at 1000' C. for 1.0 hour, and weighed. The sifca content of the ignited residue was determined by evaporation with hydrofluoric and sulfuric acids in the usual manner. I n this paper, as in the previous papers of this series (8,1O, 11'), F A represents the fluorine in excess of that corresponding to the fluorapatite [CaloF2(P04)6]equivalent of the total phosphorus in the phosphate rock. FB and F'B represent the fluorine corresponding to the respective atoms of fluorine in the fluorapatite equivalent of the total phosphorus; for convenience these are designated as the first (FB)and second (FfB)a.toms of fluorine.
Apparatus and Method The apparatus and general experimental procedure were described in previous papers (IO,11). The charge was heated in a platinum boat 7.6 cm. long, 1.3 cm. wide, and 0.9 cm. deep. The cold charge was placed in the furnace at the initial temperature of the experiment, and the heating period was measured from the time the boat was put in place in the furnace. The boat was withdrawn from the furnace at the maximum temperature of the experiment and was allowed to cool rapidly in the laboratory atmosphere. With the boats used in these experiments, the uantities of rock required to give a layer one grain deep, uniform?.- distributed over the bottom of the boat so that most of the particles made contact with the surrounding particles, amounted to approximately 0.2, 0.4,and 1.0 gram for the 40-80,20-40,and 10-20 mesh particles, respectively. All samples for analysis were ground to pass a 100-mesh sieve. Fluorine was determined by the Willard and Winter method (9, 14). Citrate-insoluble phosphorus was determined by the recently adopted modification (7) of the official neutral ammonium citrate method; the digestions were made in the ratio of 1.0 gram of sample to 100 cc. of citrate solution. In these studies, as well as those on calcined phosphate reported in previous papers (8, 10, I I ) , the citrate digestions were made in the presence of filter-paper pulp (6). The figures representing the total phoshoric oxide content of the product and the percentage of total uorine volatilized from the phosphate rock under the different experimental conditions are omitted from the tables, but they can be calculated easily from the tabulated data.
i
Experiments with Charges One Grain Deep The weights of the individual charges weie 0.5, 0.4, and 0.2 gram for the 10-20, 20-40, and 40-80 mesh materials, respectively. When the charges of 20-40 and 40-80 mesh
679
materials were uniformly distributed over the bottom of t h e boat, most of the particles made contact with the neighboring particles. However, with the 10-20 mesh material the weight of the charge (0.5 gram) was such that the particles made little or no direct contact with each other. In all cases care was taken to limit the depth of the charge to the thickness of a single particle. I n order to obtain sufficient material for analysis, it was necessary to combine the products from nine runs on the 40-80 mesh particles and from four runs each on the other ranges of particle size. It was impracticable to carry out experiments with particles finer than 80 mesh, because of (a) the small quantity of material required for a single-grain layer, (b) the tendency of the finer particles to undergo pronounced sintering and, in some cases, even fusion, and (c) the consequent difficulty in removing the product from the boat. Certain general conclusions coicerning the action of water vapor on phosphate rock in single-grain layers of particles, under comparable experimental conditions, may be drawn from the data given in Table 11. 1. The rate of reaction may vary considerably with different types of rock. 2. For a particular type of rock, the rate of reaction, as indicated by the volatilization of fluorine, usually increases with decrease in particle size and is invariably greater with 40-80 mesh rock than with coarser material. 3. Depending upon the type of rock and the particle size, approximately 20 to 98 per cent of the F'Bfluorine, or approximately 68 to 99 per cent of the total fluorine, is volatilized during the first 2.5-10 minutes of heating at 1400" C., but a marked decrease in the reaction rate usually occurs after that time. 4. In charges heated at 1400' C.there is a fairly close relationship between the percentage citrate solubility of the phosphorus and the percentage volatilization of the F'B fluorine with certain types of rock (particularly Tennessee brown-rock, Idaho, and Montana phosphates), whereas with other types (Florida pebble and Florida hard rock) the percentage solubility of the phosphorus is very much lower than the percentage volatilization of the F'B fluorine.
Furthermore, the ratio between phosphorus solubility and fluorine volatilization is much higher in 40-80 mesh Tennessee brown rock, for example, that has been heated at 1400" C. than in the same rock that has been heated at 1350" C. under otherwise comparable conditions (Table 11). Results obtained with other samples of commercial Florida pebble and Tennessee brown-rock phosphates from widely separated deposits in the respective districts indicate that the reported data are characteristic of the behavior of these types of rock.
TABLE I. COMPOSITION OF PHOSPHATE ROCKS (Results not corrected to the moisture-free basis) SiO2-
.
-Finer than:Citrate--Total Particle F as:100 200 Size" Total sol. F FA FA FB F'B Total mesh mesh FezOab Mesh % % % % % % % % % % 2.25 10-20 31.77 3.85 26.4 63.2 36.8 6.80 4.1 2.5 FIa. land pebbled 2.20 20-40 31.77 3.82 25.8 62.9 37.1 6.15 2.7 2.3 1.85 40-80 30.10 4:20 3.77 28.8 64.4 35.6 9.59 1.9 1.4 36.19 .. 3.89 17.0 58.6 41.5 3.07 0.8 0.3 .. Fla. hard rock, Dunnellon 10-20 36.62 3.89 16.0 58.0 42.0 2.29 0.6 0.3 20-40 35.25 3:83 3.62 13.2 66.6 43.4 4.69 0.5 0.4 0:ss 40-80 .. Tenn. brown rock, Wales 10-20 33.46 .. 3.57 16.4 58.2 41.8 7.38 2.9 1.8 34.10 3.64 16.4 58.2 41.8 5.64 2.6 2.1 20-40 34.64 1:99 3.67 15.8 57.9 42.1 6.30 3.3 2.8 3:io 40-80 10-20 31.83 .. 3.22 11.8 65.9 44.1 6.46 6.2 6.3 Idaho, Conda 20-40 32.17 3.35 14.4 57.2 42.8 5.47 5.2 4.9 40-80 33.66 3:73 3.37 11.2 55.6 44.4 3.93 3.8 3.6 0:iio 10-20 35.79 .. 3.77 15.4 57.7 42.3 6.53 3.3 2.8 .. Mont., Garrison 20-40 36.28 3.84 15.8 57.9 42.1 5.32 3.1 2.1 40-80 1.65 28.96 1:99 2.96 12.8 56.4 43.6 22.01 13.2 9.1 10-20 30.56 .. 3.64 25.2 62.6 37.4 6.35 2.8 1.4 Wyo., Cokeville 20-40 30.65 3.58 23 6 61.8 38.2 6.24 1.5 0.6 0.00 2.3 1.6 0:85 40-80 31.29 1108 3.54 21.2 60.6 39.4 a 10-20 mesh = 1.651-0.833 mm.: 20-40 mesh = 0.833-0.381 mm.; Not corrected for Ti. 40-80 mesh = 0.381-0.175 mm. d From a deposit of unknown location. b Total Fe. 0 Approximate figure. Type and Source of Phosphate
-P*o6-
+
..
.. .. ..
Total
AlzOaC
% 0.54 0.53 0.75
..
coz
CaO %
%
45:30
..
.
a:5,
..
0:79
49:87
2:60
1:is
48:88
1126
0:$4
4+:94
2106
1:+3
39:98
0:96
O:i4
48:k
4101
..
..
..
..
...
... ...
...
..
.. ..
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VOL. 28, NO. 6
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE11. ACTION OF WATER VAPOR ON PHOSPHATES IN CHARGES ONE GRAINDEEP [Charges heated a t 1400O C. in water vapor (0.8 gram per minute) and air (120 CC. per nunute) 1 -Compn. of-Product Ratio of Size of CitrateCitrate P z O Soly. ~ Phosphate Time of sol. F',B, Soly. of to F'.B Particles Heating PnOa F Volatilised PzOs Volatilized Meeh Min. % % % % Florida Pebble Phosphate 10-20 10 14.0 0.62 60.9 39.6 0.650 14.3 20 0.35 78.0 40.1 0.514 30 17.5 0.25 84.2 49.5 0.588 10 20-40 11.8 0.48 69.5 33.5 0.482 20 15.5 0.22 0.506 86.3 43.7 30 16.6 0.13 91.9 46.4 0.505 40-80 5 16.4 0.36 75.8 49.0 0.646 10 20.2 0.14 90.7 60.1 0.663 20 24.2 0.07 0.754 95.2 71.8 30 27.9 0.04 97.5 82.0 0.841 Florida Hard-Rock Phosphate 10-20 7.1 1.34 21.7 10 18.5 0.853 20 7.7 1.03 39.8 0.508 20.2 30 9.9 0.81 52.8 25.6 0.485 20-40 10 6.0 1.16 33.1 15.5 0.468 20 6.5 0.83 52.1 0.321 16.7 30 7.6 0.56 67.9 19.4 0.286 5 40-80 7.2 0.88 47.2 19.3 0.409 10 9.7 0.55 67.1 0.385 25.8 15 11.4 0.28 83.2 30.3 0.364 30 18.2 0.21 87.6 48.3 0.551 T'ennessee Brown-Rock Phosphate 10-20 2.5 10.1 1.12 29,; 28.6 0.979 5.0 53.2 0.848 18.8 0.59 62.7 7.5 24.0 0.31 80.6 67.0 0.831 10.0 28.5 0.14 91.1 79.7 0.875 15.0 30.7 0.09 94.3 85.8 0.910 20-40 15.0 2.5 0.88 45.2 41.5 0.918 23.7 5.0 0.39 75.8 65.6 0.864 30.2 7.5 0.11 93.3 83.2 0.892 10.0 32.0 0.04 97.6 88.0 0.902 15.0 33.8 0.03 98.1 92.9 0.947 40-80 2.5 23.5 0.44 73.2 64.0 0.874 5.0 32.0 0.10 93.8 86.9 0.926 7.5 33.2 0.04 97.6 90.0 0.922 10.0 34.8 98.8 0.02 94.3 0.954 40-80" 5.0 14.3 0.48 70.5 39.2 0.556 10.0 21.2 0.17 89.5 57.8 0.646 15.0 24.7 0.07 95.7 67.2 0.702 20.0 27.4 0.04 97.6 74.2 0.760 30.0 29.8 0.05 96.9 80.6 0.832 Idaho Phosphate 10-20 10.0 25.1 0.25 84.4 70.3 0.833 20.0 27.0 0.15 90.7 75.2 0.829 30.0 29.6 0.07 95.7 82.2 0.859 20-40 5.0 25.5 0.38 76.4 70.4 0.921 10.0 27.5 0.22 86.4 75.7 0.876 20.0 30.6 0.10 93.9 83.9 0.894 30.0 32.1 0.07 95.8 87.9 0.918 40-80 2.5 21.5 0.57 66.0 57.0 0.864 5.0 25.9 0.29 82.9 68.5 0.826 10.0 29.0 0.15 91.2 76.3 0.837 15.0 32.1 0.07 95.9 84.3 0.879 Montana Phosphate 10-20 5.0 24.6 0.57 65.7 65.8 1.002 10.0 30.6 0.20 87.9 81.6 0.928 20.0 31.8 0.07 95.7 84.7 0.885 20-40 5.0 27.7 0.44 74.1 72.7 0.981 10.0 29.8 0.25 85.3 78.0 0.914 20.0 32.3 0.14 91.7 84.3 0.919 30.0 33.9 0.08 95.2 88.5 0.930 40-80 2.5 27.4 0.03 97.7 90.4 0.925 5.0 27.8 0.03 97.7 91.8 0.940 Wyoming Phosphate 10-20 5.0 13.8 0.92 40.1 39.8 0.993 10.0 17.4 0.54 65.0 50.4 0.775 20.0 18.7 0.45 70.9 53.9 0.760 30.0 22.4 0.19 87.7 64.6 9.737 20-40 5.0 17.8 0.62 59.7 51.4 0.861 10.0 21.5 0.32 79.3 62.2 0.784 20.0 23.6 0.21 86.4 67.9 0.786 30.0 25.2 0.10 93.5 .~ . 72 .Z 0.772 40-80 2.5 18.1 0.64 59.4 51.3 0.864 5.0 19.5 0.40 74.6 55.2 0.740 7.6 21.1 0.26 83.5 59.6 0.714 15.0 24.6 0.09 94.4 68.9 0.730 a Heated at 1350' C.
*
Effect of ~~~~~~~i~~the Thickness of the Charge Previous results (8)) summarized in Table 111, show t h a t a close agreement exists between the citrate solubility of the phosphorus and the volatilization of the F'E fluorine when comparatively thick charges (2.5 grams, equivalent to a
TABLB111. RATIOOF PERCENTAUE CITRATESOLUBILITY OF TO PERCENTAUE VOLATILIZATION OF F'BFLUORINE PHOSPHORUS IN COMPARATIVELY THICK CHARUES I2.5-gram charges of 40-80 mesh rock heated for 30 minutes at 1400' C. in water vapor (0.8 gram per minute) a n d air (120 cc. per minute)] -Compn. ofRatio of Product Citrate P~OS Total so1 t'o Type or of siOz Citratesol. V:&ilF'B?olaPhosphate in Rock PzOs F ized PzOl tilized
.
%
%
%
%
%
Rocks Containing More than 2 Per Cent Silica Florida land pebble 9.96 31.9 0.02 98.6 93.5 0.948 Florida land pebble 7.44 33.3 0.08 94.9 90.5 0.954 Florida hard rock 4.69 0.22 30.2 80.1 0.925 86.6 Tennessee brown rock4 5.30 0.01 36.1 97.8 0.985 99.3 Tennessee brown rock 4.54 0.01 37.2 99.3 99.7 1.004 Tennessee blue rock 6.48 31.8 0.06 91.6 0.953 96.1 Tennessee kidney 11.52 31.7 0.03 91.9 0.938 98.0 Tennessee white rock 2.55 30.3 0.17 79.3 90.0 0.881 Idaho" 3.93 37.2 0.01 97.9 99.1 0.988 Montana" 22.01 28.9 0.02 95.7 98.2 0.976 Wyoming" 6.00 32.2 0.08 0.956 90.4 94.7 Rooks Containing Lesa t h a n 2 Per Cent Silica Tennessee whiterock 1.67 7.0 0.87 K0.K 17 R 0.352 Morocco 0.74 1.8 i . 4 1 i8:6 -4:s 0.300 Curaeao Island 0.54 11.5 0.43 76.6 27.8 0 a 363 Christmas Island 0.34a 2.8 0.72 61.1 6.7 0.110 Makatea Island 0.34b 2.4 1.18 36.2 5.8 0.160 Nauru Island 0.39b 2.1 1 . 2 3 34.0 5.0 0.147 1.8 1.30 30.4 4.3 Ocean Island 0 . m 0.141 4 The same sample of 40-80 mesh rock was used in the other experiments reported in the present paper. 6 Material insoluble i n 1 t o 1 hydrochloric acid.
thickness of approximately 1.8 mm.) of 40-80 mesh phosphate rock, containing more than 2 per cent of silica, are heated in the presence of water vapor a t 1400" C., and the products are cooled quickly. Under these conditions the ratio of phosphorus solubility to F'E fluorine volatilized ranged from 0.881 to 1.004 and averaged 0:955 with eleven samples of phosphate rock. On the other hand, with seven samples of rock that contained less than 2 per cent of silica, the ratio was only 0.110 to 0.363 and averaged 0.225; with these phosphates the ratio was greatly increased by the addition of silica to the charge. These results) together with those given in Table 11,indicate that the ratio between phosphorus solubility and fluorine volatilization depends) a t least within certain limits, upon both the total silica content of the charge and the extent of the contact surface between the silica and phosphate. If the charge is composed of a heterogeneous mixture of more or less discrete particles of phosphate and silica, it is obvious that the maximum contact surface between the individual particles is not attained in a single-grain layer. As shown in Table IV, a marked increase in the ratio of phosphorus solubility to fluorine volatilization was obtained with 40-80 mesh Florida pebble and hard-rock phosphates merely by increasing the weight of the charge from 0.2 gram (corresponding to a single-grain layer of particles) to 0.4 gram; further small increases in the ratios were obtained by increasing the weight of the charge to 0.8 gram (corresponding to an actual charge thickness of approximately 0.7 mm.). Likewise) increases in the ratios were usually obtained by increasing the charge weights of the other types of phosphate, but the effect was quite small with the Tennessee brown rock. Important increases in the ratios were not obtained by increasing the charge weight beyond 0.8 gram. Also, the maximum phosphorus solubilities and fluorine volatilizations were . . obtained with charges weighing either 0.4 or 0.8 gram. In general, similar results (not shown in the tables) were obtained with the 20-40 mesh fractions) but the increase in the ratio with the charge weight was usually less than with the corresponding 40-80 mesh fractions. No experiments were made with the 10-20 mesh fractions. Within the limits of the total silica contents of the rocks, the data (Tables I to IV) do not indicate a d e h i t e relation-
JUNE, 1936
INDUSTRIAL AND ENGINEERING CHEMISTRY
OF WEIGHTOF CRARUE TABLEIV. EFFEICT [Charges of 40-80 mesh rock heated at 1400eC. in water vapor (0.8gram per minute) and air (120CO. per minute) 1 Y C o m p n . ofRatio of Product Citrate Pa06 Soly. Ci trateF'B Volatil- Soly. of t o F'B sol. T y e or Source of Wt. of ized PnOr Volatilized F Charge Px01 Shosphate ~. Qrame
%
%
%
20.2 0.14 90.7 0.20b 93.3 25.9 0.10 0.40 97.2 29.8 0.04 0.80 90.7 27.8 0.14 1.25 Flotidahardrwko 0.20b 18.2 0.21 87.6 0.40 25.1 0.18 89.4 0.80 27.3 0.21 87.6 1.25 27.3 0.25 86.0 Tennassee brown rockd 0.20b 33.2 0.04 97.6 0.40 34.6 0.04 97.6 0.80 27.2 0.31 81.2 1.25 20.1 0.72 56.1 Idaho d 0.20b 27.4 0.21 87.6 0.40 30.9 0.14 91.7 0.80 29.8 0.21 87.6 1.26 25.7 0.43 74.6 Wyoming6 0.20b 21.7 0.19 88.1 0.40 23.6 0.20 87.3 0.80 25.3 0.24 84.8 1.26 21.8 0.44 72.1 a Char ea heated for 10 minutes. b Dept%of charge = 1 grain (0.381t o 0.175 mm.). * Charges heated for 30 minutes. d Charges heated for 7.5 minutes.
Florida pebble"
% 60.1 76.8 88.8 83.0 48.3 66.4 72.4 72.4 90.0 93.8 73.8 54.8 72.3 81.3 78.6 68.0 60.9 66.2 71.3 61.6
0.663 0.823 0.914 0.916 0.551 0,743 0.826 0.852 0.922 0.961 0.909 0.977 0.825 0.887 0.897 0.913 0.691 0.758 0.841 0.854
ship between either the actual or the relative amounts of "fine" silica (finer than 100 or 200 mesh) and the behavior of the phosphates on calcination. Furthermore, with the possible exception of the Florida hard-rock phosphate, the behavior of the rocks on calcination in single-grain layers does not seem to be correlated with the total silica content of the charge.
Effect of Heating in combinations of Wet and Dry Atmospheres As shown in Table I1 (section on Tennessee brown rock) and elsewhere (IO), a low ratio of phosphorus solubility to fluorine volatilization is usually obtained when either thin or thick layers of phosphate rock are heated in the presence of water vapor a t 1350" C. and lower temperatures. Also, it has been shown (10)that the low ratio obtained when a 0.6gram charge (equivalent to a charge thickness greater than that of a single-grain layer) of 40-80 mesh Florida pebble phosphate is heated a t 1300" C. for 30 minutes, can be greatly increased, without further volatilization of the fluorine, merely by reheating the product for a short time at 1400" C. in a dry atmosphere. Likewise, the ratios obtained by heating single-grain layers of 40-80 mesh Florida pebble, Florida hard-rock, and Wyoming phosphates at 1400" C. in the presence of water vapor were markedly increased by reheating the products for 10 minutes a t 1400" C. in dry air (Table V). Similar results (not given in the tables) were obtained with the 10-20 and 20-40 mesh fractions of these and other phosphates.
Factors Affecting Relation between Phosphorus Solubility and Fluorine Volatilization The available data indicate that hydroxyapatite [Calo(OH)I(PO&] is formed as an intermediate product of the decomposition of fluorapatite [CaloF~(P0,)6]in the reaction between phosphate rock and water vapor a t high temperatures. Pure hydroxyapatite has a low solubility in neutral ammonium citrate solution (Table VI and citations 3, 6,8). In the presence of a high concentration of water vapor, the pure compound is stable at 1400" C. but, when it is mixed with finely divided silica, the phosphorus is readily converted, at this temperature, into the citrate-soluble condition
681
(Table VI and citation 8). According to Bredig, Franck, and Fiildner ( 1 ) , Schleede, Schmidt, and Kindt (I@, and Tromel (13)) when pure hydroxyapatite is heated alone in a dry atmosphere it decomposes a t about 1400" C. into a mixture of tetracalcium phosphate (CadPz09) and a-tricalcium phosphate; the product is almost completely soluble in neutral ammonium citrate solution (Table VI and citation 8). In view of these facts, it seems logical to conclude that the lack of agreement between phosphorus solubility and fluorine volatili~iationin the experiments with single-grain layers (Table 11)is due, a t least in part, to incomplete decomposition of the hydroxyapatite because of insufficient contact between the silica and the phosphate. This conclusion is supported by the fact that the ratio of phosphorus solubility to fluorine volatilization is invariably increased merely by increasing the thickness of the charge beyond that of a singlegrain layer, thereby increasing the surface of contact between the particles (Tables I11 and IV). Further evidence of the presence of hydroxyapatite resides in the fact that the ratio obtained with a single-grain layer of particles is also increased merely by reheating the undisturbed charge for a short time at 1400' C. in a dry atmosphere (Table V). It seems therefore that in the presence of water vapor a high ratio of phosphorus solubility to fluorine volatilization, as well as a high conversion of the phosphorus into the citrate-soluble condition, is dependent, at least in part, on intimate contact of the phosphate with silica, and that the silica functions not only in the volatilization of the fluorine but also in the decomposition of the hydroxyapatite which is formed as an intermediate product. The results given in Table VI show that alumina is as effective as an equal weight of silica in promoting the decomposition of pure hydroxyapatite a t 1400" C. in the presence of water vapor. Also, the decomposition of hydroxyapatite is promoted to a considerable extent by the presence of ferric oxide, but its effect is less than that obtained with silica and
TABLE: V. EFFECT OF HEATINU PHOSPHATE ROCKIN WET AND DRYAIR [0.2-gram charges of 40-80 mesh rock heated initially in water vapor (0.8 gram per minute) and air (120cc. per minute); depth of charge = 1 grain (0.381to 0.175 mm.)]
M$n. Min. Floridapebble
10 0 10 10 Floridahardrock 15 0 15 10 Wyoming 10 0 10 10 0 120 cc. per minute; dried
%
%
%
%
0.14 90.7 20.2 0.10 93.3 30.0 0.28 83.2 11.4 0.28 83.4 25.1 21.7 0.19 88.1 29.7 0.14 91.1 over phosphorus pentoxide.
60.1 88.2 30.3 66.2 60.9 83.2
0.663 0.945 0.364 0.794 0.691 0.913
TABLEVI. EFFECT OF SILICA, ALUMINA, AND FERRIC OXIDXI ON DECOMPOSITION OF HYDROXYAPATITE: (Charges heated for 30 minutes at 1400O C.: 1.0 gram of hydroxyapatite, 0.1 gram of oxide) Furnace Citrate-Sol. Citrate Soly. Compn. of Charge Atmosphere" &Os of PlOl
%
%
42.4 98.4 Hydroxyapatiteb alone Dry 88.8 34.6 Hydroxyapatite silica Dry Hydroxyapatite alone Wet 4.6 10.8 Hydroxyapatite eilica Wet 34.7 89.1 Hydroxyapatite 4-alumina Wet 36.5 92.3 Hydroxyapatite ferric oxide Wet 17.9 45.7 4 Dry atmosphere = 120 cc. of air per minute, dried over phosphorus pentoxide; wet atmosphere = 0.8 gram of water vapor and 120 00. of air per minute. b The original hydroxyapatite contained: total Pa06 41.30,citrate-soluble PnOs 9.93, CaO 54.72per cent.
+ + +
*
INDUSTRIAL AND ENGINEERING CHEMISTRY
682
alumina. I n these experiments the oxides were ground to pass a 100-mesh sieve and were thoroughly mixed with the hydroxyapatite. The nature of the product obtained when hydroxyapatite is heated in the presence of water vapor and silica, alumina, or ferric oxide has not been determined. Inasmuch as all types of domestic phosphate rock contain small percentages of iron and aluminum, it seems likely that these constituents, a t least in so far as they are present in the form of the free oxides, contribute to the formation of citratesoluble phosphorus when phosphate rock is heated a t high temperatures in the presence of water vapor.
Literature Cited Bredig, M. A,, Franck, H. H., and Fiildner, H., 2. Elektrochem., 38, 158-64 (1932). Hill, W. L., Marshall, H. L., and Jacob, K. D., IND.ENQ. CHEM.,23, 1120-4 (1931). Jacob, K. D., Beeson, K. C . , Rader, L. F., Jr., and Ross, W. H., J . Assoc. Oficial Agr. Chem., 14,263-83 (1931).
VOL. 28, NO. 6
(4) Jacob, K. D., Hill, W. L., Marshall, H. L., and Reynolds, D. S., U. 8. Dept. Agr., Tech. Bull. 364 (1933). ( 5 ) Jacob, K. D., Rader, L. F., Jr., and Ross, FV. H., J . Assoc. Oficia2 Aar. Chem.. 15. 146-62 (1932). (6) Jacob, K. D., Rader,’ L. F., Jr., and Tremearne, T. H., Ibid., 19,No.3 (1936). To be published. (7) Lapp, M. E., Ibid., 15, 66 (1932).
(8) Marshall, H. L., Reynolds, D. S.,Jacob, K. D.. and Rader. L. F., Jr., IND. ENQ.CHEM.,27, 205-9 (1935). (9) Reynolds, D. S.,J. Assoc. Oflcial A g r . Chem., 17,323-9 (1934). (10) Reynolds, D. S., Jacob, K. D., Marshall, H. L., and Rader, L. F., Jr., IND.ENQ.CHEM.,27, 87-91 (1935). (11) Reynolds, D. S., Jacob, K. D., and Rader, L. F., Jr., Ibid., 26. 406-12 (1934). (12) Schleede, A., Schmidt, W., and Kindt, H., Z . Elektrochem.. 38. 633-41 (1932). (13) Triimel, G . , M i t t . Kaiser-Wilhelm Inst. Eisenforsch. DQsseldorf. 14. 25-34 (1932). (14) Willard, H. H., and Winter, 0. B., IND.ESQ.CHEM., Anal. Ed., 5, 7-10 (1933). RECEIVED April 2, 1936.
GLASS PUMP for Circulation of G a s e s against Moderate Pressures J. C. BALSBAUGH, R. 0. LARSEN,AND D. A. LYON Massachusetts Institute of Technology, Cambridge, Mass.
V
ARIOUS modifications of all-glass, magnetically operated, piston-type circulation pumps have been used successfully by severa1 workers (1, I,3, 4). One similar to that described in the literature (3) was constructed for use in this laboratory. This pump proved to be unsatisfactory since it would not operate against the pressure required (about 70 mm. of mercury). The previous workers stated that 30 em. of water was the maximum head against which this type of pump would be effective. It was found possible to raise this maximum pressure somewhat, but a t the highest pressure the volume displacement was so small as to render the pump useless for the purpose in view, A new pump was constructed and it has been entirely successful. As now in use, it is capable of forcing air against a pressure of 210 111111. of mercury. Further improvements over the other pumps of this type were made by reducing the size, eliminating a troublesome commutator, dispensing with the need for cooling, and increasing the dependability of operation.
Apparatus The essential new feature of this double-acting pump is that the piston and cylinder wall are ground to fit as carefully as the parts of hypodermic glass syringes in common use. Thus the chief objection to the ordinary pump is completely eliminated-namely, leakage of gas between the piston and cylinder wall. ’ The second novel feature is that the usual series of solenoids alternately excited through a commutator is replaced by a single solenoid moving up and down mechanically. This arrangement permits operation a t smaller currents and thereby eliminates the need for cooling: The cylinder, A (Figure l), is made from heavy-walled, 25mm. Pyrex tubing, 18 cm. long and taper-ground at each end to
prevent the piston from sticking during rest periods. The glass piston, B, is 7.5 cm. long and holds a piece of soft iron, C, machined as indicated. The iron is packed in the glass piston with shredded asbestos before sealing. This packing effectively prevents the iron from making actual contact with the glass which might otherwise cause cracking during operation. The solenoid D, is wound with 3500 turns of No. 26 single cotton-covered enameled wire on a brass core with soft iron end plates. The solenoid is operated by a 0.05-horsepower motor, E , through a crank and a 3040-1 worm gear as shown. The stroke length is adjustable by means of a slot in the crank wheel. Mounting the pump vertically minimizes friction and wear on the piston. The valves, F , are emall glass bulbs about 10 mm. in diameter, blown on the end of 4-mm. Pyrex tubing and ground at the base into 7mm. tubing. About 15 mm. of the tubing is left attached to the bulb and drawn to a point. This acts as a guide to obtain effective seating of the valve. These valves are very responsive and will maintain a pressure of 100 mm. of mercury for several hours. The inlet and outlet tubes are connected at G and H, respectively.
Data Two variables control the capacity of the pump-the stroke length and the speed. The data given are for a speed of sixty-four strokes per minute and a stroke length of 55 mm. A current of 0.6 ampere is required to hold the piston in place during operation. The capacity of the pump operating against various pressure heads is as follows: Pressure
-Mm.H o 32 l6 46 58
Volume Cc./min. 2100 1900 1720 1570
’ Pressure
Volume
iMm. Ho 110 122 140 178
Cc./min.
900
740 560
Pressure Mm. Hg 190 202 210
Volume Cc./min. 120 60 16
200
The ratio of maximum inlet to outlet pressure attained by t h e pump is almost exactly the same as the ratio of the total dis-
