Chemical Reactions in Fertilizer Mixtures Reactions of Calcined Phosphate with Ammonium
Sulfate and Superphosphate' ITRATE-soluble p h o s p h a t e KENNETH C. BEESON AND K. D. JACOB present. Thus a constant r a t i o o f 0.7478 part of ammonium sulfate to 1 can be obtained by heating Bureau of Chemistry and Soils, part of calcined phosphate was mainsilica-bearing phosphate rock U. S. Department of Agriculture, tained in these mixtures. No filler was at 1400" C. in the presence of water Washington, D. C. added to any of the incomplete mixtures. On the other hand, the availvapor (8, 10, 11, 13, 1.4, 16). The defluorinated product ( c a l c i n e d able phosphoric oxide in the superphosphate, as well as that in the calcined hosphate, was taken phosphate) is only slightly soluble in water (7) and is basic in into consideration in pre aring all the compEte fertilizer mixtures reaction. Its solubility in neutral ammonium Citrate solution and sufficient filler (sa& was added to give calculated values of depends among other things on (a) the extent to which the 6, 12, and 6 per cent for the total nitrogen, available phosphoric fluorine is volatilized from the phosphate rock, ( b ) the rate a t oxide, and available potash (KzO), respectively; hence the ratio of ammonium sulfate to calcined phosphate increased as the rowhich the product is cooled, and (C> the fineness Of the portion of super hosphate to calcined phosphate increased. $he The results of greenhouse experiments (3, 6, 16) indicate, in particle sizes o t t h e materials, except those in the particle-size general, that properly prepared calcined phosphate is as experiments (Figures 6 and 7) were -80 mesh for the ammonium sulfate,Calcined Phosphate, and Potassium chloride, -40 mesh for effective as superphosphate in promoting the growth of plants. The greater portion of the phosphatic fertilizer used in this the superphosphate9and -" mesh for the country is applied to the soil in mixtures with other fertilizing materials, Thus only about 20 per cent of the annual doTABLEI. COMPOSITION OB CALCINED PHOSPHATES AND mestic production of superphosphate is sold as such direct to SUPERPHOSPHATE farmers, the remainder being marketed in the form of mixed -"-" fertilizer. It is important, therefore, to have information on Citrate-insol. Original Sample the behavior of new phosphatic materials when they are in mechani- ground SamParticle Water- cal to -200 contact with nitrogenous and potassic materials and other ple Material Size' Total sol. fraction meshb F constituents of mixed fertilizers. This paper gives the results Mesh % % % % % of a study of the reactions of calcined phosphate with am1374 Calcinedphosphatee -80 35.16 ... 3.96 3.44 0.15 monium sulfate and ordinary superphosphate in various mix2.64 0 , 0 5 1478 Calcined phosphatec 20 to 40 37.31 .. . 9.63 60to80 37.12 ... 5.63 4.92 0.15 tures and under different conditions of storage. 100to150 37.05 ... 4.46 4.29 0.13
C
1403 Superphosphate
Materials and Method The calcined phos hates were prepared experimentally in direct, oil-fired rotary klns by heating commercial grades of Tennessee brown-rock phosphate at approximately 1400' C. Calcined phosphate 1374 was used in all the ex eriments except those in which the effect of particle size was stugied (Figures 6 and 7 ) . The su erphosphate was prepared commercially from Florida land-peible phosphate. The ammonium sulfate was a moisturefree c. P. salt containing 20.86 per cent of nitrogen. The potassium chloride was a moisture- and magnesium-free low-grade material containing KC1 66.0, CaS04.2Hz0 11.9, h a c 1 17.0, and material insoluble in dilute hydrochloric acid 1.64 per cent. Partial chemical analyses of the superphosphate and the calcined phosphates are given in Table I. The differences in the results for citrate-insoluble phosphorus in the mechanical fractions of calcined phosphate 1478 are caused principally by the effects of particle size rather than by differences in the chemical composition (7). With the exception of the particle-size experiments (Figures 6 and 7 ) , the mixtures containing only phosphatic materials and ammonium sulfate were prepared in the proportion of 1 part of total nitrogen to 2 parts of available phosphoric oxide ( P 2 0 6 ) derived from the calcined phosphate, disregarding the available phosphoric oxide in the superphosphate when this material was
-80d 20.56 20.19 24.49 22.76 60to80 19.98 18.03 100 t o 150 20.17 18.09 20to40
0.24 0.11 0.14 0.13
.. .. .. ..
1.74
.. ... .
5 -80 mesh = -0.175 mm.; 20 to 40 mesh = 0.833 to 0.381 mm.: 60 to 80 mesh = 0.221 to 0.175 mm.; 100 to 150 mesh = 0.147 to 0.104 mm. b -200 mesh = -0.074 mm. 0 Moisture-free material. d Contained 3.30 per cent free Hap04 and 7.38 per cent free water, both determined by the ether-extractron method (6).
The mixtures were prepared and stored in such quantity that the entire sample, the ingredients of which were weighed individually for each sample, could be used for analysis, thus eliminating errors in sampling and obviating corrections for change in weight during storage. The samples were placed in small straight-sided vials of uniform size, and the open vials were stored under bell jars at constant temperature (30' C.) and humidity. Air, a t the corresponding temperature and humidity, was continuously passed over the vials to remove any ammonia liberated from the samples. Samples that were likely to lose ammonia during storage were segregated from the others. The superphosphate contained only a small quantity of waterand citrate-insoluble phosphorus whereas the phosphorm in the calcined phosphate was practically insoluble in water but mostly soluble in neutral ammonium citrate solution. Therefore it was thought that a better comparison of the changes in the solubility of the phosphorus would be obtained by using analytical samples containing 1gram of the original calcined phosphate than by using
1 Previous papers in this series appeared in IND. ENQ.CHEM., 26, 992 (1934); 29, 61,705,1176 (1937).
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305
evolved gases without altering appreciably the moisture content of the samples. At the end of 84 days the samples were removed from the bottles, dried in the laboratory atmosphere, and analyzed. No nitrogen was lost from the moisture-free mixture and only a trace from that containing 1 per cent of water. However, 8 to 10 Time - D a y s per cent of the nitrogen was FROM MIXTURES OF CALCINED PHOSPHATE WITH AMMONIUM FIGURE1. Loss OF NITROGEN lost from the mixtures that SULFATE AND WITH AMMONIUM SULFATE AND POTASSIUM CHLORIDE contained 3 to 7 per cent of water. As shown in Figure 2, the percentage of total nitrogen lost from an initially moisture-free mixture of calcined phosphate, k? 20 superphosphate (0.2 part per 1.0 part of calcined phosphate), %: % Q and ammonium sulfate depends to a marked extent 011 the FIGURE 2. Loss OF NITROGEN relative proportion of the mixture exposed to the atmosphere. FROM DIFFERENT WEIGHTS OF A MIXTURE OF CALCINED Loss of Nitrogen from Mixtures of Ammonium PHOSPHATE, SUPERPHOSPHATE, Sulfate with Synthetic Calcium Phosphat.es 2? AND AMMONIUM SULFATE HAV5 ING A CONSTANT AREA OF According to Hill et al. (4) a-tricalcium phosphate is the EXPOSED SURFACE predominant constituent of rapidly cooled calcined phosphate. Storage at 79.2 per cent relative humidity for 84 days. As shown in Table 11, serious loss of nitrogen occurs when 0 5.5 11.0 Depth of Sample - Mm. mixtures of ammonium sulfate with pure a-tricalcium phosphate or with synthetic materials containing this compound are stored in open vials. The loss is small with /3-tricaLcium 1-gram samples of the mixtures as specified in the official methods phosphate, and no loss occurs with hydroxyapatite. It apof analyrjis (1). Accordingly, the phosphorus determinations, except those in the particle-size experiments (Figures 6 and 7) pears, therefore, that the loss of nitrogen from mixtures of were made on samples containing 1 gram of calcined phosphate. ammonium sulfate and cdcined phosphate is caused princiComparative determinations showed that the adopted procedure, pally by reaction between the former and the a-tricalcium phosas would be expected, gives somewhat lower values for the soluphate in the latter. Calcined phosphate also reacts readily bility of the phosphorus in water and citrate solution than does the official method. The divergence increases as the ratio of superphosphate to calcined phosphate in the mixture increases. The nitrogen and phosphorus determinations were made in duplicate and triplicate, respectively. The samples were not reground after storage, but in some cases the degree of caking Mixtures of calcined phosphate and was such that it was necessary t o crush the sample prior to its extraction with water and citrate solution. The citrate digesammonium sulfate lose nitrogen when tions were made in the presence of filter-paper pulp (7).
.'::I-\?._ L
U
Loss of Nitrogen from Mixtures Containing Calcined Phosphate and Ammonium Sulfate The da,tain Figure 1 indicate that a t the temperature of the experiments (30" C . ) the loss of nitrogen from mixtures of calcined phosphate with ammonium sulfate and with ammonium sulfate and potassium chloride increases with the relative humidity of the atmosphere. Under otherwise comparable conditions the rate of loss, a t least during the lirst 2 weeks of storage, from the complete mixtures (Figure 1B) is greater than that from the incomplete mixtures (Figure 1A). Where loss of nitrogen occurred, other comparisons of incomplete mixtures with complete mixtures (Figures 3 and 6) also usually showed greater percentage losses from the latter. Obviously, quite different results might be obtained with mixtures having other N:PzOs:KzOratios, as well as with those in which the potash is derived from potassic materials other than potassium chloride. I n order to determine the effect of the initial moisture content on the loss of nitrogen from 6-12-6 mixtures of calcined phosphate, ammonium sulfate, and potassium chloride, samples containing 0, 1,3, 5, and 7 per cent of water, respectively, were stored in closed bottles a t 30" C. The bottles were connected through narrow tubes to absorption bulbs containing dilute sulfuric acid, thereby permitting the escape of
they are exposed to the atmosphere,, The rate of loss depends on the initial moisture content and the exposed surface of the mixture and on the relative atmos-8 pheric humidity, as well as on the presence of other salts, such as potassium. chloride. Mixtures containing less than 1 per cent of moisture do not lose nitrogen, when they are stored in closed containers. Under atmospheric conditions the loss decreases with increasing additions of superphosphate but is completely prevented only by the addition of more than 1 part of superphosphate per 2 parts of calcined phosphate ; reactions involving a decrease in the availability of the phosphorus occur in such mixtures. Practically no change in the availability of the phosphorus occurs in mixtures containing only calcined phosphate and ammonium sulfate.
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with sodium and potassium carbonates (1'7) and with a n aqueous solution of ammonia and carbon dioxide (12).
Ca3(P0&
+ 3(NH&S04 =
VOL. 30, NO. 3 3CaS04
+ 2NHaH2P04+ 4NHs
I n the mixtures containing superphosphate there was an immediate increase in citrate-insoluble phosphorus and a further increase during storage (Figures 5B, C, and D ) . ForFROM MIXTURESOF AMMONIUM TABLE 11. Loss OF NITROGEN mation of citrate-insoluble phosphorus was considerably enSULFATE WITH SYNTHETIC C.4LCIUM PHOSPHATES hanced by increasing the relative humidity from 79.2 to 90.5 Mixtures containing 0.5 gram of ammonium sulfate and 0.5 gram of per cent (curves b and c). Addition of ammonium sulfate to phosphatic material (original total nitrogen content of mixtures = 10.43 Der cent) stored a t 30' C. a n d 79.2 per cent relative humidity the mixtures usually caused a significant decrease in the citNitrogen Losta-rate solubilityof the phosphorus (graphs a and b), which is not Phosphatic Material 56 days 112 days 168 days unexpected. Thus, it appears that the formation of citrate% % % insoluble phosphorus in such mixtures involves not only re8-Trlcalcium phosphate 0 86 3.93 3.83 11.80 21.00 a-Tricalcium phosphate 12.27 actions between the calcined phosphate and the superphos.., None Hydroxyapatite None phate, but also reactions between the constituents of the >fixture of hydroxyapatite, l O , p a r t s , and quartz flour, 1 p a r t , heated in presence superphosphate and the ammonia liberated by reaction of the of water vapor a t 1400' (2.5 14.67 18.60 19.92 Hydroxyapatite heated alone in d r y air a t ammonium sulfate with the calcined phosphate. It should 1400' C . c 20.30 26.56 27.70 be borne in mind that the citrate digestions were made on the a Percentage of the total nitrogen originally present. water-insoluble residues from samples containing 1 gram of 5 a-Tricalcium phosphate is t h e principal constituent. o The constituents are tetracalcium phosphate and principally a-tricalcalcined phosphate. Consequently the values for citratecium phosphate. insoluble phosphorus are higher than would have been obtained had the analyses been made on 1-gram samples of the mixtures. The nature of the citrate-insoluble compound or compounds Effect of Superphosphate on Loss of Nitrogen formed in these mixtures was not investigated. It is interestfrom Mixtures Containing Ammonium ing to note, however, that MacIntire et al. (9) postulate the Sulfate and Calcined Phosphate formation of fluorapatite as the cause of the increase in citLoss of nitrogen from mixtures containing ammonium sulrate-insoluble phosphorus, which frequently occurs when fate and calcined phosphate decreased with increasing addifluorine-containing materials, such as superphosphates, are tions of superphosphate; however, complete elimination of mixed with limestone, calcium silicates, ammonia, or other the loss under all the experimental conditions was effected basic substances. only by the addition of more than 1 part of superphosphate In the mixtures that contained only calcined phosphate t o 2 parts of calcined phosphate (Figures 3 and 6). I n genand superphosphate (Figure 5, curves a ) , the water solubility eral, the losses from mixtures stored a t 79.2 per cent relative of the phosphorus showed a marked decrease immediately humidity were considerably lower than from those stored at after mixing. In general, this was followed by a marked in90.5 per cent relative humidity. crease in the solubility during the first 14 days of storage, alWhen mixtures of calcined phosphate and superphosphate though the values did not reach those calculated from the were aged for 60 days before adding the ammonium sulfate, percentage of water-soluble phosphorus in the original superthe losses of nitrogen were greater than when the three maphosphate. After the first 14 days the solubility decreased terials were mixed simultaneously (Figure 4). The authors slightly to practically constant values a t 28 days. On the have found no satisfactory explanation of this unexpected beother hand, the mixtures containing ammonium sulfate havior. (Figure 5R, C, and D , curves b and c) showed no decrease in water-soluble phosphorus immediately after mixing, but the solubility decreased rapidly thereafter, particularly in the mixChanges in Water-Soluble and Citrate-Insoluble Phosphorus ture containing the larger quantities of superphosphate (Figure 5C and D),and reached the lowest values in 28 to 56 days. Mixtures that contained only calcined phosphate and All the mixtures containing superphosphate formed hard ammonium sulfate showed an insignificant increase in citratecakes when they were wet immediately after preparation. insoluble phosphorus immediately after their preparation, and The water-insoluble residues from these samples were crushed there was no further change in 84 days (Figure 5 A ) . The on the filter with a glass rod prior to the citrate digestion. water-soluble phosphorus showed, however, a gradual but Stored mixtures that were crushed before analysis did not cake small increase throughout the storage period. The increase when they were wet. in water-soluble phosphorus, as well as the loss of ammonia from such mixtures (Figure l),can be represented as occurring in accordance with the equation: '
7 -
P o u n d s to,
SuperphoJphote per
ZOO0 Pounds qf Caloned Phosphate
FIGURE 4. EFFECT OF AGIKG MIXTURES OF CALCINED PHOSPHATE AND SUPERPHOSPHATE BEFORE ADDING AMMONIUM SULFATE (STORED AT 79.2 PER CENTRELATIVE HUMIDITY FOR 84 DAYS) a. Calcined phosphate, superphosPo'nds of Superphospboie per 2000 Pounds of Calcined Phosphate
FIGURE 3. CONTAINING
EFFECTOF SUPERPHOSPHATE ON Loss OF NITROGENFROM MIXTURES AMMONIUM SVLFATE AND CALCINED PHOSPHATE (STORED FOR 84 DAYS)
phate,
and ammonium sulfate mixed simultaneously. b. Calcined phosphate a n d superphosphate mixed first a n d ammonium sulfate added a h e r 60 days.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Time
307
-Days
FIQURE 5 . CHAXGES IN WATER-SOLUBLE AND CITRATE-INSOLUBLE PHOSPHORUS IN MIXTURES CONTAINING CALCINED PHOSPHATE AND SUPERPHOSPHATE
Effect of Particle Size For the study of the effect of particle size, individual samples of mixtures composed of 20-40, 60-80, and 100-150 mesh particles of the different materials were prepared and stored for 84 days a t 30OC. and 79.2 per c e n t r e 1a t i v e humidity. Calcined phosphate 1478 (Table I) was used in these exp e r i m e n t s . The mixtures differed from those of the preceding experiments in that a ratio of 1 part of total nitrogen to 2 parts of total available phosphoric oxide was used; the available phosphoric oxide in both the calcined phosphate and the superphosphate was taken into consideration. I n the case of pounds of Superphosphate per 2000 Pounds c j Calciqed Phosphofe complete mixtures the analyses for waterFIQURE 6. EFFECTOF PAR~ICLE SIZEO N Loss OF AMMONIA soluble and citrate-insoluble phosphorus were Storage a t 79.2 per cent relative humidity for 84 days. based on 1-gram samples of- the -initial mixture and conformed in every respect with the requirements of the offic i a l m e t h o d (1); the a n a l y s e s of the incomp l e t e m i x t u r e s were m a d e on samples containing the same quant i t i e s of p h o s p h a t i c materials as were present in t h e c o r r e s p o n d i n g complete mixtures, and ----the results were calculated to the basis of 1 gram of the c o m p l e t e m i x t u r e . The results (Figure 7) are expressed a s p e r c e n t a g e of the sample, whereas those in F i g u r e 5 are expressed a s p e r c e n t a g e of the available p h o s p h o r us Pounds of Superphosphate per 2000 Pounds of Caloned Phosphate initially present. In the case of mixFIQERE 7 . EFFECTOF PARTICLE SIZEON CHANGES IN WATER-SOLUBLE AND CITRATE-INSOLUBLE t u r e s containing o n l y PHOSPHORUS ammonium sulfate, Storage a t 79.2 per cent relative humidity for 84 days.
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calcined phosphate, and superphosphate (Figure 6A), the loss of nitrogen increased with the fineness of the particles, whereas in the complete mixtures (Figure 6B) the loss was greater with the 60-80 mesh than with the 100-150 mesh particles. Beeson and Ross (2) also observed that within certain limits the loss of nitrogen from mixtures of monoammonium phosphate and limestone was sometimes greater with larger particles than with smaller ones. Under otherwise comparable conditions, the loss of nitrogen was much greater from the complete mixtures than from the incomplete ones (see also Figures 1and 3). Variation in particle size had comparatively little effect on the percentages of water-soluble phosphorus in otherwise comparable mixtures. Also, for a given range of particle sizes the percentage of water-soluble phosphorus usually remained nearly constant as the ratio of superphosphate to calcined phosphate was increased. Without exception, the complete mixtures (Figure 7, curves b) showed higher percentages of water-soluble phosphorus than did the corresponding incomplete ones (Figure 7, curves a). For comparable mixtures, the differences between the calculated and determined values for citrate-insoluble phosphorus decreased with the particle size of the materials; for a given range of particle sizes there was, in general, little change in the determined values as the ratio of superphosphate to calcined phosphate wasincreasedfrom 1:5to 1:l.
Acknowledgment The authors are indebted to L. F. Rader, Jr., and T. H. Tremearne for assistance in making the phosphorus determinations.
VOL. 30, NO. 3
Literature Cited (1) Assoc. Official Agr. Chem., Methods of Analysis, 4th ed., pp. 21-2 (1935). (2) Beeson, K. C., and Ross, W. H., IND.ENG.CHEM.,26, 992-7 (1934). (3) Brown, B. E., Reid, F. R., and Jacob, K. D., Am. Fertilizer, 81, No. 13, 5-7, 27 (1934). (4) Hill, W. L., Hendricks, 8 . B., Jefferson, M. E., and Reynolds, D. S., IND. ENG.CHEM.,29, 1299-1304 (1937). ( 5 ) Hill, W. L., and Jacob, K. D., J. Assoc. Oficial Agr. Chem., 17, 487-505 (1934). (6) Jacob, K. D., Bartholomew, R. P., Brown, B. E., Pierre, W. H., Reid, F. R., and Tidmore, J. W ., J. A g r . Research, 50, 837-48 (1935). (7) Jacob, K. D., Rader, L. F., Jr., and Tremearne, T. H., J . Assoc. Oficial Agr. Chem., 19,449-72 (1936). (8) Jacob, K. D., Reynolds, D. S., and Marshall, H. L., Am. Inst. Mining Met. Engrs., Tech. Publication 695 (1936). (9) MacIntire, W. H., Hardin, L. J., Oldham, F. D., and Hammond, J. W., IND. ENQ.CHEM.,29,758-66 (1937). (10) Marshall, H. L., Reynolds, D. S., Jacob, K. D., and Rader, L. F., Jr., Ibid., 27, 205-9 (1935). (11) Marshall, H. L., Reynolds, D. S., Jacob, K. D., and Tremearne, T. H., Ibid., 29,1294-8 (1937). (12) Meyers, H. H., U.S. Patent 1,760,990 (June 3, 1929). (13) Reynolds, D. S., Jacob, K. D., Marshal, H. L., and Rader, L. F.. Jr.. IND. ENG.CHEM..27. 87-91 (1935). (14) Reynolds, D. S., Jacob, K. D:, and Rader, L. F., Jr., Ibid., 26, 406-12 (1934). (15) Reynolds, D. S., Marshall, H. L., Jacob, K. D., and Rader, L. F., Jr., Ibid., 28, 678-82 (1936). (16) Ross, W. H., and Jacob, K. D., J. Assoc. Ofzcial Agr. Chem., 20, 231-49 (1937). (17) Whittaker, C. W., Adams, J. R., and Jacob, K. D., IND.ENQ. 29, 1144-8 (1937). CHEW:., R E C ~ I V BSeptember D 3, 1937. Presented before the Division of Fertilizer Chemistry a t the 92nd Meeting of t h e American Chemical Society, Pittsburgh, Pa., September 7 t o 11, 1936.
Flammable Limits of Methane Depressed by Methyl Bromide JOHN C. OLSEN AND ALBERT H. GRADDIS’ Polytechnic Institute of Brooklyn, Brooklyn, N. Y.
T
HE use of methyl bromide as a fire extinguishant origi-
nated some fifteen to twenty years ago (19). I n the United States it finds some use in the extinguishing of oil well fires. The fact that the British Government had a marked degree of success using it (14) gave considerable impetus to the industrial application of the compound. Before 1922 or 1923, tests of one sort or another had been carried out to determine the fire-extinguishant efficiency of the various compounds in use, but few of these tests had the desired accuracy or reliability. The first really accurate and reliable work related to fire-extinguishant efficiency was inaugurated by the United States Bureau of Mines a t the Pittsburgh Experiment Station under the direction of G. W. Jones. Since that time the limits of flammability of ninety-seven compounds have been determined by Jones and H. E’. Coward of Sheffield, England. Coward was detailed by the British Safety in Mines Research Board in 1925 to the Pittsburgh Experiment Station. Their work (4) was published in 1928. During this time also, a considerable amount of work was 1
Present address, U.S. Patent Office, Washington, D. C.
being carried out a t the experiment station on the fire-extinguishant qualities of various inert gaseous diluents on methane flames (2, 3,s). Among the curves produced was one covering the use of carbon tetrachloride. Together with dichlorodifluoromethane these curves represented the class of chlorinated hydrocarbons in contrast to the curves of other inerts such as argon, nitrogen, and helium. However, in the case of methyl bromide which further represents the class of halogenated hydrocarbons, no such curve has been determined and plotted. Jones (9) did obtain mixtures of methyl bromide and air which would support combustion, but the flammable limits are very narrow. No actual tests upon the extinguishant efficiency of methyl bromide have been made although the patent literature ( I S ) indicates that it has been used in conjunction with ethyl and methyl chloride to give a highly volatile mixture good for fire extinguishing. With the foregoing facts in mind, it was decided to test methyl bromide in the pure state with regard to its efficiency in extinguishing methane flames so that it could be compared with the previous work of Coward and Hartwell (3).
