Rate of Dolomite Reactions in Mixed Fertilizers F. G. KEENEN AND W. A. MORGAN E. I. du Pont de Nemours & Company, Inc., Wilmington, Del.
phosphate. The rates of these reactions were primarily dependent upon temperature and doubled for each 13" C. rise. They were so slow below 43" C. as t o be of no practical significance except in fertilizer stored longer than 6 months. Loss of available P20j occurred in proportion t o time and temperature of storage, degree of ammoniation, and concentration of P206. Quantity of dolomite was of little importance, since 75-100 pounds per ton sufficed for complete reaction of monoammonium phosphate in 8-10 per cent PZO, fertilizers, and nonacid-forming mixtures usually contain considerably more. Storage of commercial ammoniated mixed fertilizers containing dolomite a t temperatures substantially above 43" C. should be avoided for more than a few weeks.
The recent appreciation of dolomite as a suitable soil-neutralizing agent and source of magnesia has brought about its widespread use in commercial mixed fertilizers and created new problems in their production. Loss of available P20i was encountered in some instances during storage of dolomite mixtures, but rates and factors controlling dolomite reactions remained undefined. Two reactions occurred during storage of ammoniated mixed fertilizers containing dolomite under commercial conditions. Dolomite reacted with monoammonium phosphate, converting a portion of it to diammonium phosphate and substantially reducing water-soluble Pz06,but not causing loss of available Pz05. The loss resulted from secondary reactions involving diammonium phosphate, calcium sulfate, and dicalcium
T
HE tendency for commercial fertilizers to be acid forming in their soil reactions has increased materially during the past decade (8). Realization by agronomists and fertilizer manufacturers of the potential danger ahead if this increase was not counteracted in some way led to widespread production of nonacid-forming fertilizers. This was achieved by incorporating cofiect proportion of pulverized dolomitic limestone in the complete fertilizer mixtures; dolomitic rather than calcic limestone was chosen to obtain the beneficial effects of magnesium and a less active form of limestone for admixture with available forms of PZ05. The introduction of a new and chemically active material in to commercial fertilizer mixtures, which are subjected to such varying treatment in storage and handling, naturally presented new problems to the trade. The nature of dolomitic reactions and factors controlling them were practically unknown two years ago when the demand for nonacid-forming goods suddenly appeared. The trouble encountered in some cases, especially loss of available Pzo5 in factory-stored dolomite mixtures, as a result of not knowing how to handle fertilizers containing dolomite, has unfortunately discouraged some producers almost to the point of returning to the manufacture of acid-forming goods. Incorporation of dolomite should not be a troublesome operation if information along the lines presented in this paper is applied by the trade. Ordinary calcic limestone has been used for many years to neutralize free acid in superphosphate, thereby improving .the condition of the goods as well as preventing destruction of the bags and distributing equipment. Experience led to
the general impression that limestone added beyond the point of neutralization caused excessive losses of available Pz05. The difference between dolomitic (MgC03.CaC03) and ordinary calcic (CaC03) limestones in their effect upon available P~o5in superphosphate and triple superphosphate was not realized until demonstrated by MacIntire and coworkers (6, 6,7). The advantage of dolomite was that a t least a portion of the phosphate with which it reacted became citrate-soluble magnesium phosphates. Any calcium carbonate in excess of that combined as pure dolomite significantly decreased the advantages over ordinary calcic limestone (6, 7). MacIntire also investigated the analytical aspects of available PZOS determination in the presence of limestone (4). Although dolomite was relatively ineffective, calcite caused a significant change in the solvent power of ammonium citrate solution for dicalcium phosphate. Beeson and Ross (1) made extensive studies of monoammonium phosphate reactions with both dolomitic and calcic limestones under widely varying conditions of temperature, moisture, and ratios of components. The equations proposed indicated the formation of diammonium phosphate with no loss of available Pz05 at ordinary temperatures (30' C. or 86" F.). 'Subsequent experiments (9)were extended to 6 - 8 4 mixtures where dolomite activity was found related to particle size. Losses of available PZOs during storage a t 60' C. (140' F.) were attributed to thermal effects upon phosphate equilibria, not to dolomite. In the foregoing investigations, experiments in one case 197
INDUSTRIAL AND ENGINEERING CHEMISTRY
198
VOL. 29, NO. 2
as nearly factory conditions as could be reproduced in the laboratory.
were confined to superphosphate and limestone in the absence of nitrogen compounds, in another to ammonium phosphate and limestone reaction in the absence of superphosphate which contained large amounts of calcium sulfate. Since no significant losses of available P ~ Ocould S be predicted from the reactions so far proposed, the troubles encountered in oommercial fertilizers with dolomite must have been caused by secondary reactions. The present experiments were therefore undertaken with complete fertilizers mixed and stored under
Materials and Storage
At the beginning of this work, the factors considered to be of primary influence upon dolomite reactions were: temperature and time of storage, degree of ammoniation, PzO5 concentration, quantity of dolomite, and moisture content. Less importance was attached to pressure, particle size and composition of the dolomite, and reaction with specific ingredients such as waste products or tankages. This paper discusses only the effects TABLE I. FORMULAS OF EXPERIMENTAL MIXTURES of varying the primary factors; therefore the A Series, 4-8-4 B Series, 4-10-4 c Series, 2-12-2 data and COnclUsions must not be considered as 1.3 1 . 9 2.5 1.1 1 . 6 2 . 1 Free N, % of superphosphate: 1 . 6 2 . 3 3 , o quantitatively applicable to any and all nonacid1350 1350 1350 1120 1120 1120 Super hosphate goo 900 900 100 86 50 75 100 50 75 Urea Xmmonia Liquor A 50 30 75 loo .. forming fertilizers containing dolomite. It should Ammonium sulfate 280 214 168 280 214 168 D ol omite 351 310 267 351 310 267 135 95 82 be considered rather as an effort to outline the 160 160 160 160 160 160 80 80 80 Potassium chloride 39 121 185 300 370 388 limitations within which the probability of satisFiller 259 341 405 factory commercial operations is reasonably Mixture No. 2 3 4 2 3 4 good. Specific cases must be judged upon the peculiar combinations of primary and secondary factors as well as experience in the particular TABLE11. SUMMARY OF ANALYTICAL RESULTS Lb. factory concerned.
1
No.
A -2
NHa Urea N % Insol. PrOa per Weeks Water-Sol PzOs 54' C. 30' C. 43' C.:,5% c. 30' C. 43' T o n Stored 3OOC., 4 3 ' C . 54' Mixture 4-8-4
2
18
0:32
0.36 0.36 0.25 0:30 0.16 0.30 0 . 1 1 0.25
0.2 0.2 0.33 0.90
0.63
0.63
0:5S
0:2
0.2 0.2 0.2 0.24 0.31
0:46
0:62 0.52 0.48
4.26 2.11 1.57 1.16
0.2 0.2 0.2 0.2 0.2
0.2 0.2 0.2 0.30 0.50
0.2 0.40 0.40 1.32
0.77
0.77
5.50 5.50 5.48 5 . 0 0 5 . 4 8 4.90 5.37 4 . 5 1 5.15 ..
0.2 0.2 0.2 0.2 0.2
0.2 0.2 0.2 0.2 0.2
0.2 0.2 0.23 0.23
17 30
9
4.95 4.95 4.95 4 . 2 1 3.24 2 . 0 3 3.61 2 . 6 9 1 . 2 0 3 . 3 0 2.03 0.51 2 . 8 1 1.37 ..
0.2 0.2 0.2 0.2 0.2
0 4 9 17 30
8 . 4 5 8 . 4 5 8.45 8.06 7.91 7.55 8.16 7.66 6.24 7.23 5.45 .. 7156 7.05
0.2 0.2 0.2
0 4 9 17
0.2 0.2
30
7.35 7.35 7.35 7 . 0 5 6 . 8 5 5.88 6.95 6 . 5 2 4.88 5.98 4.26 6:60 5.53
..
0 4 9 17 30
6.60 6.34 6.17 6.86 5.73
6.60 4.26 3.60 3.24
0 4 9 17 30
6.50 6.24 6.19 5161
A-3 (dry) 27 1.5% Hzd
0 4 9 17 30
5.50 5.37 5.48 5.37 5.56
A-3 (wet), 27 10% HzO
0
4
012
..
4:87
36
..
0.2 0.2 0.2 0.2 0.2 0.2
4.26 4.26 3 . 8 5 3.19 3.60 3.04 3 . 2 9 2.56 3.24 2.33
A-4
6.50 5.56 4.41 3.70
5.22 5 . 2 2 4.77 3.93 4.26 3.04 3.98 2.21 3.75
0 4 9 17 30
27
5.22 5.19 4.77
6.50 6.09 5.73 5.56 5.22
0 4 9 17 30
A-3
d.
..
0.2 0.2 0.2 0.2 0.33 0.2 0.2 0.60 0.25
0.36 0:33
..
0120
.. ..
..
..
0173 0.70 0.45
0.77 0.53 0:69 0 . 4 7 0.61 0.26 0.58 ..
0.65
0.65
0160
0166 0.59 0.55 0.60 0.52 0.60
0:io
0.63 0.43 0.31 0.17
O:S6
0.65 0.49 0.39 0.30
..
0.60 0.60 0.44 0:50 0.40 0.50 0.40 ..
0.20 0.21 0.25
0.30 0.54
0.2 0.2 0.21 0.30 0.40
0.2 0.34 0.57 0.80
..
0:23
0.2 0.2 0.20 0.34 0.52
0.2 0.44 0.65 1.02
0:51
0.58 0.37 0:60 0.26 0.50 0 . 2 1 0.41
0.2 0.2 0.2 0.2 0.2
0.2 0.2 0.2 0.28 0.43
0.2 0.46 0.70 1.11
0.72
0.72
0168 0.68 0.50
0:63 0.60 0.51
0.2 0.2
0.2 0.2 0.33 0.43 0:ZO 0 . 4 1
0.2 0.21 0.38 0.45
0.2 0.2 0.2
0.2 0.30 0.56 0.89
0.48 0.52
..
Mixture 4-10-4 B-2
B-3
B-4
18
27
36
6.60 6.06 5.48 4.80 4.44
..
012
0.8
0.44
0.44
0:4l 0:iz
0137 0.38 0.28
0.68
0.58
0:67
..
0.44 0.24 0.22 0.18
..
..
0.72 0.41 0.26 0.20
..
Mixture 2-12-2 c-2
c-3
18
27
0
4 9 17 30 0 4 9
9.90 6.24 5.53 5.61
..
0.2
30
0.2 0.2 0.40 .0.45 0129 0.64
0 4 9 17 30
8.40 8.00 7.66 7.33 6.74
8.40 5.48 4.66 4.77
0.2 0.2 0.2 0.2 0 . 3 0 0.6s 0.26 0.60 1 . 0 5 0 . 5 1 0.85 1 . 6 2 .. 0.51 1.05
8.40 7.33 7.00 5.98 5.88
..
..
0.39
0.39 0.39 0.21 0 : 3 s 0.11 0 . 3 3 0.07 0130 0 . 3 1 ..
0:is
..
9.33 6.34 5.53 5.53
-.
36
8:72
9.90 9.13 8.40 7.81 7.51
9.33 9.33 9.18 8.47 8.80 7.10 .. 6.54 7:66 6.20
17
c-4
9.90 9.56 9.36
..
1
0.59
0.59
0166
0:63 0.50 0.38
0:40
0.77 0:73 0.72 0.50
0.59 0.40 0.26 0.13
..
0.77 0.77 0.42 0 : i l 0.26 0.67 0.16 0.54
..
Three grades of mixtures, 4-8%, 4-10-4, and 2-12-2, were a m m o n i a t e d with 50, 75, and 100 pounds of UAL-A per ton; additional nitrogen was supplied as ammonium sulfate and sufficient dolomite was added to render each mixture nonacid-forming. Complete formulas are given in Table I. UAL-A signifies Urea Ammonia Liquor A, a crude solution of urea in concentrated aqua ammonia, one of the commercial ammoniating solutions used by the fertilizer industry to treat superphosphate. The solution contained 45.5 per cent total nitrogen of which 15.1per cent was in the form of urea and 30.4 per cent in the form of free or uncombined ammonia. The quantities of UAL-A used in the experimental mixtures corresponded to additions of approximately 18, 27, and 36 pounds of free ammonia. Reactions discussed in this paper were considered typical of mixtures containing equivalent amounts of free ammonia added as anhydrous am. monia, aqua ammonia, or any other commercial ammoniating solution. Trade ex erience during the past several years has indicate$ that reactions in ammoniated fertilizers under comparable storage conditions were independent of the particular solution used to convey the free ammonia and dependent only upon quantity of free ammonia added. The dolomite used in experimental mixtures contained 21.25 er cent magnesia and 46.5 per cent carbon dioxig which made up approximately 97 per cent of the theoretical values for pure dolomite (MgCOsCaCOs). It was ground so that all passed 50-mesh screen and 90 per cent through 100-mesh. Run-of-pile, 18 er cent available PzOs superphosphate, which hazbeen cured to 1.5 per cent free acid and 9 per cent moisture, was used. No organic or protein-containing fillers were included since they might have complicated the analyses and reactions. Five 8-ounce sample bottles filled from the 50pound batches were stored a t each of three temperatures, 30" C. (86" F.), 43" C. (109" F.), and 54" C. (129" F.). The material was tightly packed in the bottles which were closed by rubber stoppers fitted with slit rubber tube valves to release the carbon dioxide evolved from dolomite reactions. One of the five bottles was removed for anal is at chosen intervals during 7-month storage. ?&e moisture content of the samples, around 5-6 per cent at the start, decreased approximately 1 per cent during storage, except a few of the 54" C. samples that showed a 2 per cent decrease after 17 weeks. The influence of moisture content upon dolomite reaction was determined in one mixture (A-3) by storing samples of a portion that had been dried to 1.5 per cent moisture as well as one which had been wetted to 10 per cent moisture. Nitrogen and P205analyses were by Official Methods of the
INDUSTRIAL AND ENGINEERING CHEMISTRY
FEBRUARY, 1937
199
Association of OAcial Agricultural Chemists. The urease method ( 2 ) served t o identify the urea portion of nitrogen present. A summary of all analytical results is given in Table 11.
Dolomite Reactions Indicated by Decrease i n Water-Soluble Pz05 Consideration of the several reactions that might occur in ammoniated superphosphate mixtures containing dolomite indicated two distinct phases not necessarily controlled by the same factors, but one prerequisite to the other. Watersoluble PzO6 in ammoniated superphosphate is present as monoammonium phosphate (3). Beeson and Ross (1) found that monoammonium phosphate and dolomite reacted as follows:
+
+
3NHrH2P04 CaC08.MgCOI = CaHPOd MgNH4P04 (NH4)zHPOa 2COz
4
8
i2
ib
20
24
28
+
+
+ 2Hz0
(1)
This would cause a decrease in water-soluble PgOo but presumably no loss of available Pz05. The diammonium phosphate so produced is a n unstable compound in the presence of calcium phosphates and gypsum, especially in warm moist storage piles (3). Under these conditions it is converted to monoammonium phosphate, and the ammonia so released reacts with the dicalcium phosphate and gypsum: = NHa + NH4HzP04 + 2CaHPO4 + CaS04.2Hz0 = (NH4)zSOd +
(NH4)zHP04 2NH3
CadPOJz
+ 2Hz0
(2)
(3)
Dolomite does not take part in these secondary reactions and the water-soluble Pz06remains unchanged, but the dicalcium has been converted into less soluble tricalcium phosphate. Strictly speaking, therefore, it is not the dolomite but the diammonium phosphate reaction that concerns the fertilizer manufacturer. The distinction between these is developed in subsequent discussion. Quantitative calculations seemed hopeless in this complicated system; however, it was interesting to calculate the dolomite required for reaction 1, assuming dicalcium phosphate and magnesium ammonium phosphate to be waterinsoluble. On this basis each 1 per cent decrease in watersoluble PzOs would require 26 pounds of dolomite per ton of fertilizer. Table I11 contains the results of such calculations for each storage interval and temperature, along with the percentage of dolomite present which had reacted. Figure 1 shows the decrease in water-soluble Pz06 a t various time intervals during storage a t 30", 43", and 54" C. The 2-12-2 (C) series a t 54" C. were the only samples in which complete reaction of the dolomite was indicated by calculation, The curves for 54" C. showed a n abrupt halt in water-soluble PzOE decrease around the eighth week coincident with the calculated disappearance of all dolomite. The water-soluble PZO6remained constant even at this relatively high temperature for 9 weeks after disappearance of the dolomite. Since reversion of P206 continued at a constant rate during the entire 17 weeks, the distinction between dolomite reaction and diammonium phosphate reaction became more evident. It then seemed reasonably safe to consider dolomite entirely responsible for disappearance of watersoluble PzOe under the existing experimental conditions.
Rate of Dolomite Reaction PsOa DBIOBUE FIGURE1. RATEOF WATER-SOLUBLE AT THREETEMPERATUREB
The rate of water-soluble Pz06decrease could therefore be taken as a measure of dolomite reaction rate. The following average decreases in per cent water-soluble P206 were found for the first 8 (1-8) and second 8 weeks (8-16) :
INDUSTRIAL AND ENGINEERJNG CHEMISTRY
200 Temp., O
c.
30 43 54
Series A, % 1-8 8-16 0.5 0.2
2.1 0.9
0.7 0.5
Series B l % 1-8 8-18 0.4 0.2
2.3 0.9
0.7 0.5
Series 1-8 0.6 3.8 1.6
Cp % 8-16 0.4 0.0 0.2
Av.9 %
1-16 0.8 3.2 1.6
The averages over 1 to 16 weeks show that the rate of dolomite reaction was exactly doubled for each rise of 13" C. (24" F.). The degree of ammoniation, although controlling the quantity of water-soluble PZ05 present, had practically no influence upon its rate of decrease. It was noted also that the reaction during the second 8 weeks was only half as fast as the first 8 a t 30" and 43" C., and but one-third a t 54". Series C a t 54" C. is the one in which the dolomite completely reacted during the first 8 weeks.
VOL. 29, NO. 2
storage and cooled a t the end of 8 weeks, it seems reasonable to assume that the insoluble PZ05would have remained a t 0.4-0.6 per cent, since PZOSreversion a t 30" C. was extremely slow.
secondary R~~~~~~~~ causing A~~~~~~~ p2o5 Reversion
Available Pz05has been recognized in the United States as the combined water-soluble and citrate-soluble phosphates; citrate-soluble is that portion dissolved by 100 cc. of a neutral ammonium citrate solution from a 1-gram sample of previously water-washed fertilizer within 1 hour a t 6.5" C. Citrate-soluble phosphates consist primarily of the dicalcium compound (CaHP04) and also TABLE 111. POUNDS OF DOLOMITE PER TON OF FERTILIZER AND PERCENTOF appreciable amounts of precipitated tricalcium TOTAL DOLOMITE CALCULATED TO HAVEREACTED ON BASISOF DECREASE IN [Ca,(pO,),], magnesium, and magnesiumammoWATER-SOLUBLE P206 nium phosphates. All of these are characterized 2--Sample 3 -Sample 4-Storage--Sample by limited solubility in citrate solution so that Time Temp. A series C series A series C series A series C series Weeks o C . Lb. % Lb. % Lb. % Lb. % Lb. % Lb. % i t is possible with the above proportions of sol4 3 0 6 2 8 8 .. . . 4 4 IO 4 io 12 vent and sample to find the same ammoniated 15 3 20 12 4 22 43 10 23 28 10 28 34 54 26 95 70 34 11 78 82 56 .21 78 95 superphosphate showing different availability in 12 or 16 per cent Pz05grades and in 6 or 8 per 8 2 14 10 4 13 9 30 12 14 17 8 19 23 43 19 6 39 29 26 8 58 81 32 12 36 44 cent grades. The following simple calculation 54 55 85 57 99 lo4 70 26 97 showsthemagnitudeof differences involved. An 17 30 . . . ... .. . . . . . 26 10 28 34 average ammoniated superphosphate containing 43 26 7 55 41 32 ib 73 77 44 16 82 76 54 73 21 114 85 78 25 99 104 80 30 94 115 approximatery 12 per cent dicalcium phosphate 30 30 24 7 31 23 9 3 43 45 26 10 43 52 would be used in quantities of 900 pounds per 43 34 10 62 46 39 13 81 86 50 19 88 83 ton for an 8 per cent Pz05grade and 1350 pounds , per ton for a 12 per cent grade. I n one case 108 pounds of dicalcium phosphate would be preDolomite was reactive a t all temperatures within normal sented and in the other 162 pounds, a 50 per cent increase ranges of fertilizer mixing and storage operations, but its in the component of limited solubility. In the presence of rate of reaction below 43" C. was SO low that for most pracdolomite, magnesium phosphates, and other citrate-soluble tical mixing operations i t can be neglected. It is interesting components of mutual influence on solubilities, this increase to note that the rate of dolomite reaction bears no direct in quantity might indicate an apparent reversion of PnOb in relation to the secondary reactions causing loss of available the 12 per cent grade, although the original material was PZO6. For example, the C series a t 54" C. reacted extremely identical. rapidly with dolomite during the first 8 weeks, but the inThe ammonium phosphate-dolomite reaction (Equation 1) soluble Pz05increased a t the same rate as in the less rapidly does not directly cause loss of available Pz05 except in so reacting A series. Had the c series been removed from 54" far as it may increase the quantity of dicalcium phosphate and magnesium ammonium phosphate in high-grade goods beyond the saturation point of the ammonium citrate solution. Since each mole of diammonium phosphate ultimately can lose a mole of free ammonia, calculations based on Equation 1 show that 100 pounds of dolomite potentially release 9.25 pounds of ammonia in a ton of fertilizer mixture. Equation 3 indicates that 9.25 pounds of ammonia could ) dicalcium convert 38 pounds of PzOj (1.9 per cent P z O ~from to tricalcium phosphate. How much of this would show up as unavailable or insoluble Pz06 would depend largely upon the amount of free ammonia already added (degree of ammoniation), quantity and nature of other p h o s p h a t e s present (grade of 1.2 goods), as well as possible change in pH of the citrate solution by ,.as t h e d o l o m i t e r e s i d u e i n t h e u ? isample. In view of the involved analytirFIGURE 2. INFLUENCE OF 0.8 5 cal aspects of insoluble Pz06 and r TEMPERATURE UPON INm the existence of reactions other SOLUBLE P 2 0 6 AFTER 9than that of diammonium phosAND 1 7 - w E E K STORAGE PERIODS u phate tending toward less soluble phosphates, no calculations or r e a c t i o n mechanisms were attempted except the brief sugges99 tions already made. Consideration L
.
c.
46c
30
r m90m R A rum -9.c.
so
50
'7
43t.
I
I
I
I
I
I
I temperature of storage piles containing highly ammoniated goods should receive special consideration.
Conversion of Urea Nitrogen t o Ammoniacal Nitrogen Urea was not hydrolyzed to a significant extent within 17 weeks in any samples stored a t or below 43" C. (Table 11). Thirty-week storage resulted in 10-20 per cent reaction a t 43" C., and slight changes a t 30" C. Samples a t 54" C. averaged 25 per cent hydrolysis per month; many were as high as 30 per cent the first 4 weeks but s u b s t a n t i a 11y decreasing as time went on. concentration nor degree of amNeither P~OS moniation within the limits of the samples studied was of influence upon this reaction, and moisP ture content had only a slight effect. No loss 48 of total nitrogen was detectable in any sample after 30-week storage a t 43" C. or 17-week a t 54" C., showing that all the ammonia released by urea hydrolysis had been readily absorbed by the phosphates. I n order to retain the maximum amount of nitrogen in the agronomically desirable form of urea, storage over any extended period a t temperatures above 45" C. (113" F.) should be avoided.
*
FIGURE 3. RATE'OF INSOLUBLE Pa06INCREASE AT 43"AND 54" C.
of the insoluble PzOb data was limited to practical conclusions which could be drawn from the analytical results as they stood. The relation b e t w e e n i n soluble P205 and temperature a t 9- and 17-week intervals is shown in Figure 2. The change WEEKS in insoluble P206 as storage continued a t 43O and 54" C. up to 30 weeks is shown in Figure 3. The critical storage ternperature for grades below 12 per cent Pz0swas 43" C. This does not mean that there was a sudden change in rate a t that point, but a t lower temperatures the rate had been sufficiently reduced so that the quantity of less soluble phosphates did not build up to the saturation point of the ammonium citrate solution within the particular time interval. Seventeen weeks a t 43" C. were necessary to increase insoluble P205in the A series u p to the point reached in 4 weeks a t 54" C. The constant increase in rate as the temperature rose is shown by the C series in Figure 2. I n this more concentrated P205 mixture, the citrate solution was so nearly saturated a t the start that even small increases in the less soluble forms of P205 were immediately perceptible. The results a t 54" C. seemed erratic compared with those a t lower temperatures. This was due to complications introduced by the slow hydrolysis of urea to ammonia and carbon dioxide, and subsequent reaction of the ammonia so produced: CO(NH2)2 HzO = COz 2s" (4)
+
Influence of Moisture The moisture content was varied in sample A-3, originally containing 5 per cent water, by drying one portion to 1.5 per cent and moistening another to 10 per cent water. The comparative behavior of these samples is shown in Table 11. These data further illustrate the existence of two independent sets of reactions. Water-soluble PzOedecreased -i. e., dolomite reacted-to a much greater extent in the 10 per cent moisture samples, although the citrate-insoluble P205 changed but slightly. It seems probable, therefore, that normal variations in moisture content of mixed fertilizers in commercial operations, say from 5 up to 10 per cent moisture, would have little influence upon Pzo5 reversion or urea hydrolysis. Superphosphate mixtures containing less than 5 per cent moisture would be practically inactive.
Practical Suggestions I n commercial fertilizer mixing operations i t seems advisable to avoid extended storage of ammoniated goods containing dolomite a t temperatures above 45" C. (113" F.). Under existing analytical methods of evaluating available Pz05, considerably greater precautions must be taken to avoid apparent P205reversion in grades containing more than 10 per cent P20s,except where such goods are "bases" to be remixed into lower grades in the same factory. Trade experience during the past one or two seasons has shown t h a t little trouble is encountered in storage piles when the foregoing conditions are met.
+
Discussion of urea decomposition appears in a subsequent section. The exaggerated effect of degree of ammoniation a t 54" C. is due undoubtedly to this urea hydrolysis. For example, 50 pounds of ammoniating liquor introduced 16.3 pounds of urea which a t 50 per cent hydrolysis would produce 4.6 pounds of ammonia, equivalent to an additional 12.5 pounds of ammoniating liquor; whereas 100 pounds Of liquor duced 32.6 pounds of urea, yielding 9.2 pounds of ammonia equivalent to a n additional 25 pounds of liquor. Therefore all No. 4 samples a t 54" C. storage were potentially ammoniated with 125 pounds of liquor and No. 2 with 62.5 pounds, a difference of 62.5 pounds. These same samples stored a t 43" C. or below differed by only 50 pounds of ammoniating so~utionequivalent, as no urea hydrolyzed to free ammonia at these temperatures* Since the temperature Of ammoniated as as quantity Of is higher in proportion to the amount of ammoniating Solution used,
Literature Cited
tl; an,",^^, ' ~ ~~ ~~~ " $; g ~~~ (1934)' j~ ; (3) Keenen, Ibid., 22, 1378 (1930). (4) MacIntire, J. Assoc. 0ficiaZ Agr. Chem., 16,589 (1933). (5) Maohtire, Hardin, and Oldham, IND.ENQ. CHEM.,28, 711 (1936) (6) MaoInti;e and Shaw, Ibid., 24, 1401 (1932). (7) MaoIntire and Shuey, Ibid., 24, 933 (1932). (8) Mehring and Peterson, J. Assoc. Oflcial Agr. Chem., 17, 95-100 (1934). (9) Ross and Beeson, Proc. 1 s t Ann. Meeting Comm. Fertilizers Am. SOC.Agron., 1935, 24-32. R ~ C ~ I VSeptember ED 12, 1936. Presented before the Division of Fertilizer Chemistry at the 92nd Meeting of the American Chemiaal Soaiety. Pittaburgh, Pa., September 7 to 11, 1936.
201
