Properties of Diammonium Phosphate Fertilizer PRODUCEL) BY SATURATOR PROCESS H. L. THOIIZPSON’, PHILIP ;MILLER2, F. H. DOLE3, AND -4BRAHARl KhPLAN4 Tennessee Valley Authority, Wilson Dam, Ala.
r)iammonium phosphate, produced from anhydrous ammonia and electric-furnace phosphoric acid in a pilot plant using a new, saturator-type process, consisted of aggregates of thin tabular crystals bonded by a film of fine crystals. The product contained 0 to 5% of monoammonium phosphate, but otherwise was substantially free of impurities. Laboratory tests showed the product to be strong enough to withstand ordinary fertilizer handling without excessive degradation, satisfactorily nonhygroscopic, satisfactorily drillable, and suitably stable with r e s p r r t to loss of ammonia by volatilization under normal
conditions of temperature and humidity. Laboratory and field tests on use of the diammonium phosphate in fertilizer mixtures showed that a diammonium phosphatepotassium chloride mixture was compatible with ammonium sulfate, sodium nitrate, and normal and concentrated superphosphates i n all proportions tested; properties of the resultant mixtures were satisfactory. Mixtures containing ammonium nitrate caked excessively, and those containing calcium cyanamide or high proportions of ammonium nitrate or urea suffered significant ammonia losses.
D
relative humidities above its hygroscopic point. The same authors investigated the drillability, under varying conditions of humidity and temperature, of diammonium phosphate prepared from ammonia and a solution of commercial monosalt and concluded that it was as satisfactory in this respect as ammonium sulfate but less satisfactory than monoammonium phosphate. In an experimental study of methods for producing ammonium phosphates from anhydrous ammonia and electric-furnace phosphoric acid, both of which are produced by TVA a t Wilson Dam, Ala., there was developed through the pilot plant stage a simplified saturator-type process in which either monoammonium or diammonium phosphate could be produced, The simplification was significant with respect to the manufacture of the latter salt because relatively simple means for producing monoammonium phosphate have been known for a long time. The purpose of the present work was to investigate the physical and fertilizer properties, including compatibility with other fertilizer salts, of diammonium phosphate produced in the saturator pilot plant. The principal check material used was monoammonium phosphate that also was prepared in the pilot plant. Monoanlmonium phosphate is a well-known and widely used fertilizer that is regarded as having premium fertilizer properties. Although it would have been desirable to test the experimentally produced diammonium phosphate further against samples produced by other methods, such as the German product, these samples were not available and a relatively small number of comparisons with reagent grade salt had to suffice.
IllMMONIUM phosphate [(NHJPHPO~; 21.2% nitrogen and 53.8% phosphorus pentoxide1 has not enjoyed wide usage in this country as a fertilizer; this may be attributed at least in part to the poor behavior of some diammonium phosphate mixtures that have been used in the past and to unfavorable reports on important fertilizer properties of the salt. Most of the diammonium phosphate that has been used in this country wm imported from Germany before World War I1 in the form of granulated nitrogen-phosphorus pentoxide-potassium oxide mixtures (Nitrophoska), prepared by adding a hot concentrated solution of ammonium nitrate t o a dry mixture of diammonium phosphate and potassium chloride or sulfate and cooling the mixture in granulating equipment ( 4 , 80). The high initial temperature of the mixture in this procedure was thought t o result in some loss of ammonia from diamnionium phosphate (80). Most of the Nitrophoslras were characterized by relatively high ammonium nitrate content and nitrogen-phosphorus pentoxide ratio. Therefore, they were hygroscopic and tended to cake and become undrillable unless handled with special care (80). The production of Nitrophoslra from diammonium phosphate was discontinued by the Germans several years ago because of the unsatisfactory physical properties of the product and its tendency t o decompose during handling ( I S ) . The properties of diamnioniuin phosphate Chat may affect its use as a fertilizer in this country by itself or in ungranulated mixtures are not well established, although a number of miscellaneous properties of general interest have been reported (5,6, 9-11, 16, 16, 19, 83’). It is nonpoisonous, nonexplosive, and nonflainmable (it is used as a flame-proofing agent). Several authors have referred qualitatively to the instability of the salt, Collings (8) stated that. it has not been used as extensively as the monosalt “because of its unstable nature and its poor physical condition.” Ross, Mehring, and Merz (1’9)observed that it loscs ammonia when moistened with water and concluded that for this reason, and because i t is less convenient t o prepare than t,he monosalt, it would find limited application in this country unlcss mixed with acidic materials. Mehring and Cumings (1.5) reported that it lost ammonia and bcc:tnie paqty when exposed to ’
Present address. Mississippi Chemiual Corporation, Leland, Miss. * Present address, H. K. Ferguson Company, S o w York, N. Y. , a Present address, Mathieson Alkali Corporation, Niagara Falls, II‘.Y ‘ Present address, Standard Provision Cnmunny. Biriiiingham. Ala. 1
485
I’IIOPERTIES OF SATURATOR-PRODUCED DIAiMMONIUiVf
PHOSPHATE
The process by which diammonium phosphate (DAP) was produced in the present work was of a continuous, single stage, saturator type similar in many respects to comrnonly used methods For manufacturing by-product ammonium sulfate. Gaseous ammonia and strong phosphoric acid were fed continuously, at an ammonia-phosphoric acid mole ratio Of substantially 2.0, correspondmg to diammonium phosphate, into a saturated solution of ammonium phosphate a t ahoul 60’ diammonium phosphate crystallized out of the solution and was recovered by settling, centrifuging, washing, and drying. The ammonia-phosphoric acid mole ratio in the solution was maintained as low as was feasible without precipitating monoam-
c.;
486
,o
INDUSTRIAL AND ENGINEERING CHEMISTRY
COts?RESSED
325-MESH (TYLER)
__ - _ _ - ~~
SCREEN
CON1-A'NINC FdNNEL
'""""3
PLATE
Figure 1.
~
SAMPLE
STEEL
SHEET- METALHOUSING
-
\GLASS
\
I
Diagram of Apparatus Lsed for Shatter Tests
monium phosphate. In practice, this ratio was about 1.6, which corresponded to a pI-1 of about 6.0. This feature of the process was critical in preventing formation of traces of the unstable triammonium salt and in minimizing the ammonia content of vapors escaping from the saturator. The diammonium phosphate crystals precipitated from this solution were n-et ivith a film of the rclat>ivelymore acidic iiiot,her liquor, a portion of vhich \vas displaced by v-ater during washing and the remainder c lized on the surface of the diarnmoiiium phosphate e Further mshing would completely remove the film, but nt o this extent was not necessary and was not practiced.
Vol. 41, No. 3
condition was air velocity, and a t the velocity used, there were satisfactorily significant differences in break-up of samples of different materials and different screen analyses as ~ e l as l satislactory reproducilility of result,s.
In the present tests, pilot plant diammoniuni phosphate was compared ivith monoammonium phosphate made in the same equipment, with reagent grade (c.P.) mono- and diammonium phosphates, and n5th conditioned grained ammonium nitrate fertilizer. Both samples of the monoainmonium phosphate were needlelike in crystal form ivhile the reagent grade disalt was cry+ tallixed as irregular granules. The sample of ammonium nitrate fertilizer, which consi&xl of splierical granules from regular TT'A plant production, had been conditioned by coating the grain first with 1 of a petrolatum-rosin-paraffin mixture and then with about 4% of clay ( 1 7 ) . The size fractions of the samples were prepared by screening n-ithout crushing. For summary comparison of a numher of samples, the apparent fraction of the sample resistiiig shatter entirely and the fraction that shatters t o dust, (arbitrarily taken as - 100-me& material) afford convenient criteria, and Table I presents a summary for samples in the range -14 + I 6 mesh to -35 4-42 mesh. These results indicate that experimentally produced diammonium phosphate resisted shatter somen-hat better than the other ammonium phosphate samples but also dusted to a slightly greater extent except for the limited comparison between it ami the reagent g i d e disalt. The differences ~vcrcsmall in each case, and it, IT^.: ~011eluded that, aggregates of saturator-produced diammonium phosphate crystals would be as satisfactory from the standpoint of particle strength as other particle forms in which the salt may be produced. This is true part'icularly in view of the relative severity of the test. The superiority of ammonium nit,rate both as to shatter resistance and dust formation may be a result of its plasticity (62),and of the sphericity of the granules testod. HYGROSCOPICITY. The effect of the trace of monosalt occurring principally as a film on the surface of the diainmonium phosphate crystals on hygroscopicity (moisture pickup) and visiblci.e., surface-x-etnesa was observed in laboratory tests. Twogram samples of the material, in n-atch glasses, iyere exposed for 24 t,o 7 2 hours a t 30" C. in a small chamber where the I-iuinidity was controlled by providing a large uncovered volume of a saturated salt solution of known vapor pressure. Original moisture content was found by drying separate samples for 5 hours a t BO" C. and moisture absorption was determined by periodic d g h i n g of the samples. A test was usually discontinued when there was no gain in n-eight over a period of several hours. Tcsts were made on unscreened diammonium phosphate from pilot plant production and on selected screen fractions. One test vas made on experimentally produced monoammonium phosphate as a check. Results of these t,ests are shown in Table 11. They igdicate that diammonium phosphate from the saturator did not absorb moisture to a greater extent than did the monosalt a t 50% relative humidity. The +lO-mesh sample of disalt, which was a very small fraction of the total sample from vhich it was scrccned, contained considerably more monoammonium equivalent, pos-
The resulting product contained from a feiv tenths to several per cent of monoammonium phosphate equivalent, mostly distributed on the surface of the particles of the dibasic salt, but Kith an occasional separate crystal. This characteristic m-as believed t o be peculiar to the saturator product, because mo;;t, if not all, of the previously published proeesses for crystallizing diammonium phosphate call for crystallization from solutions having ammonia-phosphoric acid inole ratios very close to 2.0, as deduced from t,he specified pH values, indicator color changes, or the mole ratio itself. The diammonium phosphate product from the saturator process was further characterized by its crystal habit and particle configurat,ion. The individual crystals were thin plates, octagonal in outline and of thickness on the order of 0.1 the equivalent diameter. A typical particle of the product consisted of several of these plate crystals bonded toget,her by a film of crystallized mother liquor. The material was different in these respects from that made by previous processes. PARTICLE STRENGTH.For measurement of the strength of diammonium phosphate particles as compared with other fertilizer materials, modified shatter tests were carried out in the apparatus shown in Figure 1. The principal feature of this apparatus was a vertical steel plate against xvhich test particles suspended in a high velocity stream of air could be impinged; means were provided for collecting t,he product and making screen analysis after impingement. Its use has been referred to in a previous article ( 1 8 ) . TABLE I. 8 L \ I l I A R Y O F RESULTS O F XCCELCRATED SHATTER T E S T 5 ON FKRTILIZER hIAl'l>RI.iIS The proccdurc consisted in yG Sample Il-ithin Original Srreen Fraction pouring a 200-gram sample of yo Sample through 100 Ales11 after Tinpa,ct after Impact closely sized material into the ---Ammonium Phosphates---Ammonium Phosphatei--? 3cieeri funnel as rapidly as the air Conditioncd Experi:neiital Conditioned Experimental Fraction products Rea:ent grade hllllnoIllillli stream (at a calculated mean products _Reagent grade alnlllonl,llll Fed, - Di nIono Di hIono nitrate Di Mono Di llono nitrate Mesh velocity of 500 feet per second a t the tube discharge) mould 23.0 21.0 24.0 .., 10.2 4.0 0.2 2.1 .. 6.1 --14 + 1 G 25.4 30.9 25.7 ... 8.F aspirate it; this usually took 7.1 0.1 3.0 ... 12.2 -16 + 2 0 2 8 . 6 8 . 6 . . . . . 9 ,5 3 . 3 0 . 5 . . . . . . Q , 8 -20 +24 about 2 minutes. The sample 29.6 20.,5 , . 26.7 10.9 5.9 1.3 , .. 1.4 16.7 -24 +28 collected in the flask was 29.7 26.0 ,., 19.0 12.1 -2s t 3 2 7.9 0.4 ... 2.0 18.9 34.1 39.9 ... 12.8 13.1 sized, and its screen analy109 1.0 ... 3.7 - 3 2 +35 27.0 38.9 34.3 , . . 8.5 2>.3 10.9 4.1 ... 0.7 11.8 - 3 5 1-42 sis was compared vith the original. The controlling test ,
,
INDUSTRIAL AND ENGINEERING CHEMISTRY
March 1949 TABLE11
Gnscreened Salt hlono DI Di
NHs:HsPOh mole ratio Time Exposed, Hr. 0 2 24 48 72
Total gain
and t,his represents approximately the behavior of ammonium nitrate in the present, .-Ammonium Sulfate S a t d . So1n.tests. In the set of tests with ex81 posure a t 95% relative huScreened Fractions unof Disalt. Mesh midity and 24" C., both amscreened-10 -20 -35 monium phosphates dropped disalt +10 +20 +35 +60 to about 50% of the initial 1 . 9 8 1.84 1.92 1.94 1.98 % drilling rate after 48 hours. 0.62 0 . 4 6 0 . 2 1 0 . 2 7 0 . 2 4 At this time diaminoniurn 0.83 0 . 7 6 0 . 5 1 0 . 4 7 0 . 4 4 1.05 1.96 1.21 0.57 0.84 phosphate had absorbed 2.9% , , . .,. .., , .. .., ., . ... , ., ... .. moisture and the monosalt. 0 . 4 0 1.60 1.00 0 . 3 0 0 . 6 0 1.87,. The tests were continued for 16 days in all, and the results confirmed the relationship between moisture content and drillability shown in Figure 2. Mehring and Cumings (15) found monoammonium phosphate superior to diammonium phosphate in drillability, whereas the present results indicated that the t n o are about equal with respect to withstanding humid atmospheres without impairment of drillability, and that diammonium phosphate is superior a t comparable moisture contents. The screen analysis of the monosalt used by Mehring and Curnings was unusually favorable with respect to particle size and uniformity (98% between 20 and 40 mesh) while the disalt sample had wider particle-size distribution and smaller average particle size (35% -20- 1-40-,43% -40- f80-, and 17% -80- +ZOO- mesh). Diammonium phosphate IS equal in drillability to monoammonium phosphate of comparable particle size and its drillability, therefore, is satisfactory.
c. (*I")
RESULTSO F HYGROSCOPICITY TESTSA T 30' PHOSPHATES FROM PILOT PLANT
Humidity control Calcium Kitrate, --Urea solution Sstd. S o h . Relative humidity, % (approx.) --50--7
1.00
Satd. S o 1 n . p 75 Screened Fractions of Disalt, Mesh $10
1.W
1.98
0.22 0.22
0.23 0.26
0 . 6 5 0.46 0.65 0 . 7 6
1.84
0.45
0.38
7-
0.55 0.43 0.62 0.48 0.40 0.25
0.80
0.80
0.96 0.96
0.15
0.50
...
.
,
.
7
-35 f60
7;:
1.92 1.94 1.98 Moisture Content, 0.21 0.27 0.24 0 . 2 1 0.27 0 . 2 4 0.36 0.42 0.39 0.36 0.44 0.39
.
.,
0.15
,
..
0.17
,
.,
0.15
sibly because it consisted of larger aggregates with more inclusions of crystallized mother liquor. This fraction absorbed significantly more water than did the others, and this is attributed to a higher joint solubility of a mixture of mono- and diammonium phosphate. The effect of particle size on rate of moisture pickup either was negligible or was obscured by the compensating effect of slightly lower ammonia-phosphoric acid mole ratios in the fractions of larger particle size. None of the samples appeared visibly wet, except the +lo-mesh fraction (ammonia-phosphoric acid mole ratio 1.84) after exposure a t 80% relative humidity. Analyses of the samples after the hygroscopicity tests indicated that no ammonia had been lost. The conclusion was that the saturator-produced diammonium phosphate should satisfactorily withstand exposure to normal at,mospheres wit,hout excessive absorptiop of moisture. DRILLABILITY. The diammonium phosphate produced in the present work was tested for drillability in equipment that is in common use in the Southeast-a John Blue No. 30 single-row screw-type fertilizer distributor. A similar machine was described in detail by hIehring and Cumings (15) (distributor No. 10). The machine is designed for use with draft animals; in the present tests the 16-inch ground wheel was mechanically driven a t 52 revolutions per minute which corresponds to a linear velocity of 2.5 miles per hour. Fifty-pound samples of the test materials, described in Table 111, were stored in stainless stecl pans in a controlled-atmosphere test room ( 7 ) . The samples were removed from the test room daily long enough for three 6-minute drilling periods in the distributor, which was set a t one of its two lowest feed rates. A composite sample was also obtained for determination of its moisture ,content, bulk density, and, occasionally, chemical composition. Monoammonium phosphate and conditioned ammonium nitrate were selected for comparative tests, the former was considered to represent a readily drillable material and the latter a poorly drillable material, because of its low hygroscopic point. The diammonium phosphate used in the first set of drillability tests, with evposure a t 80% relative humidity and 26.5' C., was contaminated with monosalt and was chosen for the urpose of further increasing the severity of the test conditions [y virtue of the greater hygroscopicity of this mixture. The material used in the second set of tests, a t 95% relative humidity and 24" C., was substantially pure salt with particle-size distribution comparable to that of the former sample. This same sample was concurrently undergoing dissociation tests discussed below. Results of the first serier of tests on the ammonium phosphates are shown in Figure 2 . The drillability of monoammonium phosphate decreased a t a fairly constant rate with moisture content, and a t 2.5% moisture, for example, the drillability rate was only about 45% of the initial. Diammonium phosphate decreased less rapidly a t first, drilling a t 80% of the initial rate a t moisture content of 2.5%, but then its drillability suffered a sharp drop between 3 and 4% moisture. Miller et al. (17) considered that ammonium nitrate was satisfactorily drillable if its rate was not reduced more than 50% after 24 hours under these conditions,
487
ON AxMIIONIU\.I
-
,
Figure 2.
I
I
I
2
I
I
I
3 4 5 MOISTURE CONTENT, %
I
I
I
6
7
8
Effect of Moisture Content on Drillabilities of Ammonium Phosphates
DISSOCIATIOK TENDENCY. Some of the st>udiesrelating to the important question of the dissociation tendency of diammonium phosphate were incidental to other studies, as for instance the hygroscopicity tests, but one series of laboratory tests was directed toward finding some definite condit,ions under which dissociation actually occurred and measuring the amount and rate of ammonia loss under these conditions. The procedure used in these laboratory tests was the same as in the hygroscopicity study, except that multiple samples were used, and individual samples were withdrawn a t intervals for analysis and determination of ammonia loss. Also, higher humidities were used and parallel tests were ruii a t about the same humidity, but with different humidity-control solutions. Tests were run on samples of reagent grade (c.P.) diammonium phosph.ate for comparison. Results of these laboratory tests, shown in Table IV, indicate
488
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 41, No. 3
Beeson ( 2 ) found that disrociation of dry diammonium pliosplia.to a t 60" C. \vas hastcncrl b>-addition of the monosalt. 'The d3-pound sample of pilot plant diammonium phosp1iai.c. Test at ROC4 relative humidit>' xiid 26.2' C Diammoni:im phoal~hate that \vas tested for drillability Before exposure O.RU 1.85 0.7:i 1 4 . 9 60.0 18.7 3 . 7 2.6 2.3 After 28 days' esposore 3.40 1.M 0.8:3 26.4 60.8 11.0 1.2 0.:3 0.3 during exposure t o 95% rela?vlonoammonium phosplia ti: live humidity a t 24.5" C;. Before exposure O.lll ... 0.70 7.0 31.2 3'27 7.4 1.:3 0 4 After 2 1 days' exposure 2.16 0.98 0.54 17,9 aB.2 22.9 2.3 0.2 0 2 wa:, also analyzed for delcotion of ammonia loss. Gairiplt~> Ammonium nitrate (grained, conditioned) +.-71----t c ----2R -+ :: Before exposure 0.05b . . 1 .00 were taken after remixing t,iic> , . .. . . After 2 days' expo:ure 2.0"C 0,870 .. .. rriat,erinl. ltesults arc shown Tests a t 9554 relative humidity m d 24" C Diammoniuni phosphate in Table V. The analyses vary Before exposure 0.20 1.98 After 10 days' exposure 14 7" 1.97 mther widely; this mag b ( x :rttrihuted to difficulties of Monoainmoniuni phosphate . , Before exposure 0.4b O.Y8 sampling arid analyzing w!l After 16 days' ex1xmire 8.4b 0.48 , , .., .. als. The lack of evidence ' Drying loss after 8 hours at 60" C . Drying loss after 2 hours a t 130' C . easurable ammonia loss Average of nine 2-day exposures. d Swelled. may be considered conclusive Screen unalysis not made hilt material ourriparablr i n lpnrticle silt' t o llllii,t,i i . ; i d in ~ J W T ~ O ttA3t. U ~ in view of the large nunibw of malyses made. In comparison with the laboratory te of rriatt:iial \vas handled in this test and thc tenithat dianimoniuni phosphate begins t o lose amiiioiiia at 30' C. r. Both factors probably contributcd towiui when exposed to humidities above its hygroscopic point jabolrt minimizing ammonia loss. Conditions of the present test. \\ 83YG relative humidity) ; the rate and extent of ammonia loss more nearly practical, t,houghthe humidity-temperature combiiia17ei-eabout the same for the esperimentally produced and reagent tion was still somewhat severe, and the results confirm tho congrade dianimonium phosphate samples. Within each set of clusion that diammonium phosphate should be regarded i t 5 R I I tests there appears t o be rough correlation between ammonia adequately stable fertilizer material. loss and the amount of moisture absorbed. The inaterial tested These results are not, in agreement with those of Mehrjng i t n i l in Pet 4 \vas an impure experimental product containing about Cumings ( 2 6 ) who observed that a 20-pound sample of di20y0 monosalt. Although this sample lost less ammonia in proammonium phosphate exposed to 90% humidity at 20" C. for 19 portion t o the amount of water absorbed than the re1e)tivelypure days became liquid and lost ammonia. Their samplc had i ) c ~ : r i d in Set 3 a t about the same humidity, the rate of exposed progressively t o rclative himidities of 40 to SO%, iii moisturc ahsorplion was very much greater because of the greater 10% steps. The original data, as supplied to the authors t1.y solubility of the mixture. Consequently, the ammonia loss over Mehring ( 2 4 , indicated that 13 to 14% of the ammonia wac, lost a given time interval was about the same for the two samples, and but that the loss occurred before ttiid noi. aft,er exposure at 90% therefore the practical va,lue of previous suggestions for stabilizing relative humidity. Their sample, therefore, was exposed to dianinior~umphosphate by admixture with the monosalt ( 2 0 , d l ) high humidity at a n initial ammonia-phosphoric acid mole rat,io is qucstionahlt~. It is interesting to notc in t,his coirnec+tionthat, of 1.73, which would exp1,ziri its rapid absorption of watw arid liquefaction; their sample: would compare with 1 1 1 ~uti(, tmtcd in Sct 4 ol Tat)l(l Il', X o pxplanation of the prior I o z F of ammonia is advanccil. From the result,s of ttic lal)tr ratory hygroscopicity and dirsociation tests and from t i i ~ engiiitx>ringtcst at high hrirniditg, i t appears that relatively ,.. ... pure tiiammoriiuin phoqphate .. tky S!ablt: [(JV \T;d? t
h
c
b
. . I
... 1) .i
2.0 3 .R 8.1
...
2 .3 4.0
7.1
13.2
.. .. .. ...
...
.*.
".,
, . .
.".
...
e. i T h f ! l J cxposcd to relative lnumiditiej l x l o i v i t s hygroscopic point ('F&L:
lV), the dissociation partial prtwure corrwponds ttpparPnilp t,o that of the tliy salt ( 3 ) and ammonia v(ilati1ization at atmo-plicric tcinpcraLures will be negligible. 'Yhcrc, wcre no detectable aniiiionia losses during the previously mentioned hygrosco pttrt,icle-streiigt,l~ during the drillah lmiib-caking tests
March 1949
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
below. On exposure to relative humidities above its hygroscopic point, dissociation pressure is higher, as it will correspond to solutions in equilibrium with the ambient humidity. However, the occurrence of atmospheric humidities of this magnitude at an ambient temperature as high as 30' C. (86" F.) is not common, and a t lower temperatures, where higher relative humidities are expectable, dissociation pressures are substantially decreased. In the present work, the total production of about 75 tons of the salt was stored in bulk and bags, shipped, and tested, without analytical evidence of ammonia loss. Moreover, there was no discernible ammonia odor over the material after it cooled from the drying temperature used in its manufacture (60" to 80" C.)
Time Exposed, Days 0 1 2 3
4
7 8 Y 10
It 13
16
Moisturr Content,
74
Wet Basis 3 1 2.Y 4.0 4.8 6.4 6.5
...
2.02 1.98 2.14 2.03 2.03 1.98 1.97
7.3
8.2 9.0 11.7 10.8
The caking tendency of cxpcrimentally CAKING TENDENCY. produced diammonium phosphate was measured relative to other fertilizer salts by a method adapted from Adams and Ross (1). Samples of test materials were subjected to mechanical pressure in 2-inch diameter test bombs constructed essentially as described by the previous authors, and the cbmpresssive strength of the resultant cakes was taken as the measure of relative caking tendency. The test portions used were such as to yield calces about 1 inch thick ( 1 0 . 2 5 inch).
-
Duplicate cakes of diammonium phosphate (originally 10+6O-mesh) were exposed a t 60-pound per square inch pressure and 30' C. for 14 days. The cakes changed in moisture content from 4.8 to 4.6% and had crushing strengths of 70 and 110 pounds per square inch applied pressure. Monosalt cakes that changed from 2.8 to 1.4% moisture under the same Conditions, including particle-size distribution, had crushing strengths of 60 and 100 pounds per s uare inch. In further tests, in which the temperature was lowerel gradually from 42" to 31 O C. over the 14-day period with other conditions unchanged, the diammoniuin phosphate cakes lost moisture from 2.8 down to 2.4% and both had crushing strengths of 120 pounds per square inch, while monoammonium phosphate cakes that dried from 2.8 to 0.1 % moisture had strengths of 120 and 150 pounds per square inch.
TABLE
VI.
MATERIALS USED
Identification Material Symbol Sourae N DAP Diammonium phosphate TVA pilot plant 21 .o MAP TVA pilot plant 1 3 . 6 Monoammonium phosphate AN Ammonium nitrate" TVA plant 32.5 .4mmonium sulfate Commercial AS 20.9 Chilean m d i u m nitrate Commercial SN 16.4 CN Commercial Calcium cyanamide 20.0 U Commercial 46.7 Uroa NSP Norinal superphosphate Commercial ... TSP Concentsated superphosphate TVA plant Commercial K Chloride of potash ... Sand Commercial S a Conditioned. Association of Official Agriculniral Chemists solubility.
These test conditions dizered from those preferred by Adams and Itoss, who recommended crushing of the samples to -80mesh, an applied pressure of 12 pounds per square inch, and exposure of 7 days. I n tests carried out in the present work on both of the ammonium phosphates and on ammonium sulfate under Adams and Ross's conditions, the caking induced was negligible (0 t o 5 pounds per square inch) and did not afford comparisons. However, urea and unconditioned ammonium nitrate did cake significantly (200- to 303-pound crushing pressure) under these conditions, and the fact that the ammonium phosphates did not cake to this extent even undrr the more severe conditions first reported above indicates that they mere superior in this respect. Adams and Ross tested the caking tendency of monoammonium phosphate and they found it superior to urea, as well as ammonium sulfate, sodium nitrate, and potassium chloride. The present results indicated that diainmonium phosphate compared favorably with monoammonium phosphate, and it should therefore be satisfactory from the standpoint of caking tendency. C O \ I P A T I R I L I T Y O F DIAMMONIUM PHOSPHATE WITH OTHER F E R T I L I Z E R MATERIALS
1.98 1.97 2.08 2.00 2.03
0.2 1.4
'l'he compatibility relationships between most of the rommonly used fcrtjlizer materials have been reported (8.4, but the characteristics of diammonium phosphate in this respect have received limited attention. Tests made by Beeson ( 2 ) showed that the addition of limestone to diammonium phosphate for the production of physiologically neutral mixtures containing 5% moisture resulted in high ammonia losses a t 30" C. The effect of dolomite 'i?as less pronounced but still signihcant. The effect of moisture content was not studied, though previous tests on monoammonium phosphate (3) had shown substantial differences between mixtures containing 1% moisture and thohe containing 5 or 10%. Temperature has an important effect on dissociation, and in tests a t room temperature (presumably less than 30" C.) MacIntire and Sanders (12) found negligible ammonia losses from 4 to 1 mixtures of 100-mesh calcitic and dolomitic limestones with Nitrophoska that contained about 60% diammonium phosphate. This was true for mixtures that contained 6% moisture as well as for others that were air dry. Tests were made in the present work to study the properties of fertilizer mixtures of varying nitrogen-phosphorus pentoxidepotassium oxide proportions in which diammonium phosphate was a major constituent. The nitrogen-phosphorus pentoxide ratio in these mixtures was adjusted by addition of commonly available nitrogenous or phosphatic fertilizers, and potassium oxide was supplied as commercial potassium chloride. The materials used are described in Table VI. Test mixtures of these materinls are described in groups as follows:
N group, straight nitrogen materials added in varying proportions to a base mixture of 2 parts diammonium phosphate per part of chloride of potash (potassium oxide-phosphorus pentoxide ratio of 0.5) (Table VII).
IN
COMPATIBILITY TESTS 7 -
Composition, %
I _ _ _
...
489
PZOS 53.6 60.0
...
...
Kz0
... ...
..,
...
I..
.., 18:i; 48.6
,..
... ... ...
53.3
Moisture 0.2 1.5 0.6 0.8 0.3 0.6 0.1 5.9 2.8 0.4 0.0
$20 4.4 7.7 21.4
-20 +35 55.5 30.5 55.1
t
c
74.0
19.7
24.3 34.0 1.8 0.1
21.9 15.6 1.6 37.7
