Diammonium p h o s p h a t e reacts with limestone and with dolomite a t ordinary temperature and in the presence of moisture to evolve c a r b o n dioxide and ammonia. The reaction with limestone results in a reversion of a part of the phosphoric acid in the mixture to a citrate-insoluble form. The r e a c t i o n with dolomite gives r i s e t o t h e formation of magnesium ammonium phosphate, with a corresponding d e c r e a s e in water-soluble nitrogen and p h o s p h o r i c a c i d , but the citrate-insoluble phosphoric acid formed in mixtures of dolomite and diammonium phosphate a t ordinary temperatures is relatively small. The citrate-soluble magnesia in an aged mixture of 100 parts of dolomite with 86 parts of diammonium phosphate is about 50 per cent greater than in the original dolomite. The principal p r o d u c t s formed in the reaction of diammonium phosphate with limestone and with dolomite have been determined, and equations are given t o represent these reactions.
Chemical Reactions in
Fertilizer Mixtures Reactions of Diammonium Phosphate with Limestone and with Dolomite KENNETH C. BEESON Fertilizer Research Division, Bureau of Chemistry and Soils, Washington, D. C.
chemical reactions between the components of the mixture. Thus some monoammonium phosphate will form in mixtures containing ammonium sulfate and superphosphate by double decomposition reaction between the former and the monocalcium phosphate in the superphosphate. Monoammonium phosphate is also formed in the ammoniation of superN A PREVIOUS paper ( 2 ) it was shown that in the presphosphate or mixtures containing superphosphate. ence of moisture, monoammonium phosphate reacts with Diammonium phosphate is used to some extent in the limestone a t ordinary temperature to evolve carbon dipreparation of special grades of fertilizers such as the Nitrooxide, regardless of the relative amounts of the reactants inphoska mixtures. It does not occur in the ordinary types of itially present. No decrease in the fertilizer value of the fertilizer mixtures but is formed according to the following mixture occurs as a result of this reaction unless the calcium carbonate in the mixture exceeds one mole per mole of P205, equation when double superphosphate is treated with more than 6 per cent ammonia ( 6 ) : when the reaction taking place may be accompanied by a loss of ammonia as well as a decrease in the availability of the Ca(H2P04), 2NH8 ---f CaHPOd (NH&HP04 phosphoric acid in the mixture. Diammonium phosphate has a physiological acidity (4) It was further shown that in the presence of moisture, monoequivalent to 71 pounds of calcium carbonate per unit of niammonium phosphate reacts with dolomite at ordinary temtrogen or to 75 pounds per 100 pounds of material. The peratures to evolve carbon dioxide, but no loss of ammonia or diammonium phosphate in fertilizer mixtures must therefore reversion of phosphoric acid occurs with any proportion of the be accompanied by a basic material equivalent to about threereactants. Loss of ammonia and reversion of phosphoric acid fourths of its weight of calcium carbonate if the physiological may occur, however, when a mixture of monoammonium phosreaction of the mixture is to remain unchanged. The present phate with an excess of dolomite is maintained for a time a t paper discusses the reactions that take place when such basic about 90" C. materials as limestone and dolomite are added to diammonium Monoammonium phosphate is used as a fertilizer material phosphate and that may impose a limitation on the use of this in the preparation of high-analysis mixtures, and it may also material in fertilizer mixtures. be formed in a wide range of fertilizer mixtures as a result of
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INDUSTRIAL AND ENGINEERING CHEMISTRY
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Experimental Procedure The limestone and used in these tests were the same as those employed in the work reported Previ"usb' (2). The compositions Of the limestone and Of the dolomite were as follows (in per cent) :
Limestone Dolomite
Volatile Moisture Matter 0.14 0.06 0.87 0.08
Acid-Insol. Matter FexOs Nil Nil 9.76 0.56
MgO
CaO
0.11 17.10
55.74
29.01
41.87
The different sized particles of limestone and dolomite used in the tests showed little variation in calcium carbonate equivalent. Analysis of the diammonium phosphate showed a PzOsto NH, ratio of 2.12, whereas the theoretical ratio is 2.09. The pH of its 0.1 M solution was found to be 7.82. APPARATUS.The apparatus and method of studying these reactions were the same as described previously (3). COMPOSITION OF MIXTURES.For the purpose of this study quantities of material were chosen to correspond to the relative amounts indicated by the following tentative equations: 2(NH&HP04 3CaCO3 ----f Cas(PO& 4"s 3coz i3H20 (1) 5(NH&HPO& 3CaCOrMgCO3 3MgNH4P04 CadPOh 7NHa 6CO2 6H2O (2)
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position to monoammonium phosphate and ammonia in from 15 to 30 days a t 60' C., depending upon the proportion of monoammonium phosphate present. Calculations based on the equation derived by Passill6 (3) showed that the equilibrium pressure of ammonia Over moisture-free solid diammonium phosphate is 5.7 mm. a t 90" C. and 0.5 mm. a t 60" 6,
CaCOa COS Eqmvalent 43.76
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99.60 95.22
Effect of Particle Size on Loss of Carbon Dioxide
The losses of carbon dioxide that take place with time from mixturesof 1part diammonium phosphate and 1.14 parts limestone of varying particle size are shown by the curves in Figure 2. These curves indicate that the initial reaction is slower and more uniform than that in corresponding mixtures with monoammonium phosphate (S), and that the daily loss of carbon dioxide did not show any marked decrease until after 20 to 30 days. In the case of monoammonium phosphate-limestone (
