INDUSTRIAL A N D ENGINEERING CHEMISTRY
July 15, 1931
331
Availability of Phosphoric Acid in Ammoniated Superphosphates Proposed Method for Estimation' K. Kitsuta and Robt. M. Salter OHIO AGRICULTURALEXPERIMENTAL STATION, WOOSTBR,OHIO
Maximum solubility of phosphoric acid was obtained P20,of b o t h s u p e r p h o s from the water-insoluble residues of the ammoniated phates a n d a m m o n i a t e d t h e superphosphate superphosphates when 0.1 gram of the sample was used superphosphates of varying ammoniation process in 100 cc. of citrate solution for 30 minutes at 65' C. ammonia content were deterby the f e r t i l i z e r i n d u s t r y Similar results were obtained using a 2-gram sample mined, using 2.0, 1 .O, 0.5, 0.2, makes desirable a full knowlin 100 cc. of citrate solution containing 4 grams of and 0.1 gram of sample per edge of the chemistry of the ammonium oxalate and digesting for 2 to 4 hours. 100 cc. of citrate s o l u t i o n . process and of the economic Attempts to shorten the time of digestion to 30 The data are presented in value of the product. The minutes by addition of larger quantities of ammonium Table 11. It is observed that present report deals with the oxalate were successful with highly ammoniated superthe amount of citrate-insoluresults of s t u d i e s , by both phosphates, but the method does not apply well to ble Pz05decreases with a rechemical and plant methods, ammoniated superphosphates which contain less than duction in the weight of samof the availability of phos2.5 per cent ammonia. ple taken. With m a t e r i a l phoric acid in ammoniated containing 2.6 per cent and superphosphates of v a r y i n g There was no noticeable decrease in the availability less of ammonia, varying the of the Pz06of ammoniated superphosphates to buckdegrees of ammoniation. sample weight does not wheat and barley when the material contained as high Considerable work has been change the amount of availdone recently by Keenen (e), as 6.2 per cent ammonia. able P,Or. owine to the fact Ross and his associates (6,7), and Howes and Jacobs (4), and Buie (3) has carried out ex- that although there is some increase -in-'waterrsoluble PzO~ periments on cotton. It is known that with increase in am- with smaller samples, this is accompanied by a corresponding moniation there occurs a decrease in the content of avail- decrease in citrate-soluble PzO5. With ammoniation above this point there is observed a rapid increase in citrate-soluble able PzObas measured by the present official method (1). The Association of Official Agricultural Chemists ten- PzOs as the sample size decreases, especially in the most highly tatively approved a change in the present method (6)for ammoniated materials, while the water-soluble PzOa does not determining water-soluble and citrate-insoluble PzOr in change appreciably. The proportions of available P z O ~to fertilizer, whereby the sample taken for both is reduced to the total Pz05 are shown in Table 111. 1 gram and the time of digestion with citrate solution inand Citrate-Insoluble PZOSof Ammoniated creased to 1 hour. However, this change cannot go into effect Table I-Water-Soluble Superphosphates by Offlcial Method before it is officially adopted by the Association. The probability of such action being taken'at next year's meeting will depend upon the results of further referee work already planned. % % % % % % ..
HE rapid adoption of
T
1' 2.5 3b 46 5b
Experimental Procedure PREPARATION O F AMMONIATED SUPERPHOSPHATES-Ammoniated superphosphates of different degrees of ammoniation were prepared in two ways. I n one case the calculated amounts of dilute aqueous ammonia were introduced into a jar containing the superphosphate, after which the material was well mixed, dried, and ground. The second method employed consisted in introducing the calculated amount of ammonia gas from an ammonia generator into an evacuated flask containing the superphosphate, with thorough shaking during the ammoniation process. Samples of these ammoniated superphosphates of equal ammonia content prepared by the two methods showed by analysis nearly the same amounts of water-soluble and citrate-insoluble PZO6, as illustrated in Table I. Accordingly i t was believed unnecessary to use both materials in the availability studies. Hence only ammoniated superphosphates prepared by the first method were employed. EFFECTS OF VARYING WEIGHTOF SAMPLE ADDEDTO 100 cc. OF CITRATESoLuTIoN-Water-soluble and citrate-insoluble 1 Received April 15, 1931. Presented before the Division of Agricultural and Food Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 to April 3, 1931.
6b
71, 8b 9.2 lor 110 12e 13c 140 150
0.000 0.729 1.496 2.601 3.706 5.024 6.171 7.276 0.731 1.377 2.363 4 046 5.027 5.974 6.994 I
24.52 24.55 24.46 23.51 23.23 22.83 22.54 22.29 23.38 22.81 22.83 21.70 21.33 21.81 21.48
le.-76 11.90 11.55 10.63 11.89 8.93 6.17 3.55 14.29 13.04 10.68 8.25 6.29 6.69 5.30
23.49 23.73 23.31 22.02 19.18 14.66 13.00 11.76 21.74 20.81 18.88 15.44 13.38 13.34 11.75
6.73 11.83 11.76 11.39 7.29 5.73 6.83 8.21 7.45 7.77 8.20 7.19 7.09 7.65 6.45
a
Not ammoniated.
c
Ammoniated by passing ammonia gas into
1.03 0.82 1.15 1.49 4.05 8.17 9.54 10.53 1.64 2.00 3.96 6.26 7.95 8.48 9.73
superphosphate. superphosphate.
b Ammoniated by addition of aqueous ammonia to
Table 11-Effect of Varying the Weigh of Water-Soluble and Citi
-
CITRATE-INSOLUBLE PZOP
WATER-SOLUBLE PZOS SAU
of Sample in Determination :e-Insoluble PSOS
Weight sample used (grams)
Weight sample used (grams)
PLI
1 2 3 4 5 6 7 8
-
2.0
1.0
0.5
0.2
0.1
%
%
%
%
%
16.76 11.90 11.55 10.63 11.89 8.93 ,6.17 3.55
12.87 12.11 10.64 11.70 9.00 6.17 3.63
13.05 12.36 11.02 12.21 9.24 6.40 3.82
13.52 13.39 11.88 12.72 9.81 6.85 4 53
17.96 14.72 14.25 12.78 13.49 9.98 7.49 4.99
2.0
% 1.03 0.82 1.15 1.49 4.05 8.17 9.54 10.53
1 . 0 0 . 5 0 . 2 0.1
%
%
%
%
0.93 1.23 1.74 2.60 4.57 4.40 5.31
0.68 0.89 1.22 1.47 2.09 2.19 3.28
0.80 1.07 1.51 1.41 1.58 1.27 1.92
0.63 0.54 0.69 0.69 0.81 0.86 0.83 1.05
332
ANALYTICAL EDITION
EFFECT OF REMOVAL OF SOLUBLE CALCIUM DURIXG DIGESTION WITH CITRATE SOLUTION-From the above facts it would appear that solubility in citrate solution may involve a reversible reaction which may be thought of as a double decomposition of water-insoluble calcium phosphates and ammonium citrate producing soluble calcium citrate and ammonium phosphates. Accumulation of calcium citrate tends to retard the reaction until it attains a state of equilibrium. of Varying t h e Weights of Sample i n Determination of Available P a 0 6
Table 111-Effect
AVAILABLEPzOs AS PERCENTOF TOTAL PZOS Weight sample used (grams)
SAMPLE NHs
%
0.00
2.0
1.0
0.5
%
%
%
I
0.73 1.50 2.60 3.71 5.02 6.17 7.28
0.2
% 96.8 95.6 93.6 93.9 93.1 94.4 91.4
2.6 per cent of ammonia. All samples containing more than this amount of ammonia showed decided decrease in citrateinsoluble P206when ammonium oxalate was added to the citrate solution, these decreases being progressively larger as the amount of ammonium oxalate was increased from 1 to 10 grams. Table V-Effect of Addition of Varying Weights of A m m o n i u m Oxalate to Citrate Solution of Citrate-Insoluble PzOl
SAMPLE
I
CITRATE-INSOLUBLE PzOa
j
Weight of ammonium oxalate added (grams)a
-I
None
FOR
-I
I
VARYINO WEIGHTS OF SAMPLE
3
4
6
10
Ammonium oxalate added to 100 cc. citrate solution; time of digestion, 30 minutes Q
EFFECTOF ADDINGAMMONIUMOXALATETO CITRATE SOLUTION UPON SOLUBILITY OF ROCKPHOSPHATE AND TRICALCIUM PHOSPHATE-The rock phosphate used was Superfine Ruhm phosphate and the tricalcium phosphate was Baker and Adamson's c. P. quality. From the results presented in Table VI1 it is observed that adding ammonium oxalate to the citrate solution markedly reduced the amount of insoluble P205of tricalcium phosphate, but had practically no effect on the solubility of the PzOs of the rock phosphate. Table VI-Effect of Supplying Ammoniated Superphosphates t o Buckwheat a n d Barley in Pot Culture upon Yield a n d Phosphoric Acid Recoverya -
~
CITRATE-INSOLUBLE PZOS BY OFFICIALMETHOD EXCEPT FOR MODIFYING TIME O F DIGESTIONA N D ADDITION OF AMMONIUM
0
0.729 1.496 2.601 3.706 5.024 6.171 Unfertilized
BARLEY
BUCKWHEAT
AMMOXIA IN
%
SAMPLENHo
2
%
97.6 97.7 97.0 97.0 96.4 96.2 96.4 95.4
Table IV-Comparison of Effects on Citrate-Insoluble PzOs of Varying t h e Weights of Sample a n d of Addition of A m m o n i u m Oxalate t o Citrate Solution
CITRATE-INSOLUBLE PZOGBY OFFICIALMETHODEXCEPT
1
0.1
An attempt was made to remove the soluble calcium by adding ammonium oxalate to the citrate solution. The results are shown in Table IV. The removal of soluble calcium apparently permitted the reaction to proceed to approximate completion, with effects similar to those from the use of small-size samples. It is noticed that using a 2-gram sample in 100 cc. of citrate solution plus 4 grams of ammonium oxalate, and digesting for 30-minute and 2-hour periods, gave approximately the same percentages of citrate-insoluble PZO5 as with the use of 0.5- and 0.2-gram samples, respectively, in 100 cc. of citrate solution with 30-minute digestion. Using 4 grams of ammonium oxalate to 100 cc. of citrate solution and extending the digestion to 4 hours gave still less citrate-insoluble P205.
I
Vol. 3, No. 3
1
Grams
%
Mg.
13.24 13.97 13.65 14.15 13.04 14.30 13.60 6.89
0.95 0.93 1.01 0.98 0.96 0.89 0.88
124 128 138 138 126 128 120 46
0.68
I
Grams
%
Mg.
2.18 3.26 2.83 3.07 2.69 2.22 2.81 1.00
0.53 0.51 0.54 0.50 0.51 0.47 0.49 0.41
11.5 16.0 14.8 14.9 13.5 10.3 13.4 4.4
OXALATE^
Weight sample used (grams)
2.0
1.0
%
%
4
0.5 0.2 0.1
%
%
%
%
%
%
1.03 1.25 1.55 1.92 2.37 3.97 2.80 3,30
0.97 1.23 1.41 1.42 1.85 1.56 1.84
0.92 0.93 1.16 1.29 1.26 1.39 1.35 1.65
AVAILABILITY OF PZO5 OF AMMONIATED SUPERPHOSPHATE BUCKWHEAT AND BARLEY I N P O T CuLTuRE-Buckwheat and barley were grown in Wooster silt loam in pot culture. Superphosphate and a series of six ammoniated superphosphates varying in ammonia content from 0.73 to 6.17 per 8 cent were applied in such amounts as to carry equivalent I a Ammonium oxalate added, 4 grams, quantities of total P206. The nitrogen supplied in all cultures was made uniform by appropriate additions of ammonium EFFECT OF ADDITION OF VARIOUS AMOUNTS OF AMMONIUMnitrate. Yield of dry matter, percentage content of Pz05 OXALATE TO CITRATESOLUTION-Determinations of citratein the dry matter, and total removal of P205 were determined. insoluble PzO5 were made using increasing amounts of am- The data are presented in Table VI. There is no evidence of monium oxalate, from 1 to 10 grams for 100 cc. of citrate any significant reduction in the availability of the P205 of solution, employing a 2-gram sample, and limiting the time any of the ammoniated superphosphates below that of the of digestion to 30 minutes.2 The citrate-insoluble P205, superphosphate itself. Instead there appears some evidence as shown in Table V, showed no decrease through the addition of an increased availability of the Pz06in the ammoniated of ammonium oxalate with materials containing less than superphosphates of low ammonia content. Data obtained by use of the tentative official method which 2 It was observed that 1 gram of ammonium oxalate is soluble in 100 CC. provides for the use of the water-insoluble residue from a 1of citrate solution in the cold, whereas 2 grams are partly insoluble in the cold, but all soluble at 65' C. All crystals of ammonium oxnlate disappeared gram sample and digestion for 1 hour in citrate solution are after digestion with the sample in the citrate solution for 30 minutes, excompared with the results of other methods in Table VIII. cepting when 10 grams of ammonium oxalate were used. In this case a From these data it appears that the tentative official method few large crystals remained undissolved. These dissolved in the first increases phosphorus solubility appreciably, but the increase wash water. 1 2 3 4 5 6 7
0.00 0.73 1.50 2.60 3.71 5.02 6.17 7.28
1.03 0.63 0 . 8 2 0.93 0.68 0.80 0.54 1.15 1.23 0.89.1.07 0.69 1.491.741.221.510.69 4 . 0 5 2.60 1 . 4 7 1 . 4 1 0 . 8 1 8.17 4.57 2.09 1.58 0.86 9 . 5 4 4.40 2.19 1.27 0 . 8 3 10.53 5.31 3.28 1 . 9 2 1 . 0 5 I
TO
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 15, 1931 Table VII-Effect
333
of Time of Digestion a n d Addition of A m m o n i u m Oxalate t o Citrate Solution on Citrate-Insoluble PZOSof Tricalcium Phosphate a n d Rock Phosphate REMARKS
2 2 2 2 2 2 2 2 2 2
Tricalcium phosphate
Rock phosphate
a
45.78 45.78 45.78 45.78 37.03 37.03 37.03 37.03 37.03 37.03
0.83 0.83 0.83 0.83 0.02 0.02 0.02 0.02 0.02
14.44 21.08 15.30 23.32 4.91 4.53 4.64 4.76 4.23 4.23
0.02
of Tentative Official Method with Other Methods
Table VIII-Comparison
AVAILABLE PzOs METHOD
Sample number 1
1-gram sample, 1hourextractiona 2-gram sample, 1/zhourextractionb
1
%
2
%
3
%
4
%
6
%
6
7
8
%
%
%
2 3 . 6 3 2 3 . 6 9 2 3 . 3 8 2 1 . 9 0 2 0 . 3 8 1 7 . 9 0 17.86 17.08 2 3 . 4 9 2 3 . 7 3 2 3 . 3 1 2 2 . 0 2 1 9 . 1 8 1 4 . 6 6 13.00 11.76
2 3 . 8 9 2 4 . 0 1 2 3 . 7 7 2 2 . 8 2 2 2 . 4 1 2 1 . 9 7 2 1 . 7 1 21.24 hourextraction 2-gram sample plus 4 grams ammonium oxalate, 4-hour ex23.60 23.62 2 3 . 3 0 22.22 21.96 21.44 21.19 20.64 traction b
30.50 23.87 29.65 21.63 .32.10 32.48 32.37 32.25 32.78 32.78
Official method'" Official method digested 2 hours Official method: digested 2 hoursa Officialmethod digested 4 hours Official method: digested 4 hoursa
4 grams of ammonium oxalate added.
is not so great as that obtained by using a 0.1-gram sample and 1/2-hour extraction, or a 2-gram sample plus 4 grams of ammonium oxalate and 4-hour extraction.
a
21.91 16.13 24.15 4.93 4.55 4.66 4.78 4.25 4.25
Tentative official method. Present official method.
Discussion of Results
In the dissolution of water-insoluble calcium phosphates of the ammoniated superphosphates in the ammonium citrate solution, it may be assumed that equilibria are set up between the various ions present (NH4+, Pod---, Ca++, Citrate---) and the undissociated salts corresponding to all possible combinations and in accordance with their several dissociation constants. The solubility product of the ions of the water-insoluble calcium phosphates is apparently too low to permit of their complete solution when 2 grams of sample are employed. Addition of ammonium oxalate, by removing calcium ions as insoluble calcium oxalate, should favor the continued solubility of these materials. It was observed that addition of ammonium oxalate to the citrate solution increased the citrate-insoluble PzO5 slightly when the ammoniation of the samples was less than 2.6 per cent. According to Keenen's analyses and calculations, it appears that the products of the ammoniation reaction up ,to about this point are mono- and dicalcium phosphates and monoammonium phosphate. Using the official method, these are presumably all soluble in the citrate solution. Apparently, however, the solubility of one or more of these constituents is slightly less in the solution containing both ammonium oxalate and ammonium citrate than in a solution containing only the latter salt. Comparing the water-insoluble residues from the ammoniated superphosphates with tricalcium phosphate, it is observed that the addition of ammonium oxalate to the citrate solution produces a much larger relative effect upon the former, even when the ammoniation of the superphosphate is at the maximum point of 7.3 per cent ammonia. This behavior indicates that the water-insoluble PzO~ of ammoniated superphosphates is not identical with precipitated tricalcium phosphate, but that it is much more soluble than the
latter in citrate solution to which ammonium oxalate has been added to remove the soluble calcium. When ammoniated superphosphates are applied to the soil, plants appear to dispose of the soluble calcium liberated from the relatively insoluble calcium phosphates by absorption, with the result that the solution process continues. Thus under field conditions the solubility of the phosphorus is favored by a process not unlike that resulting from the addition of ammonium oxalate to the citrate solution in the laboratory. This is in agreement with Truog's view (8) that plants which can take up abundant calcium can assimilate most phosphorus from relatively insoluble calcium phosphates. It should be added, however, that under field conditions soluble calcium may also be removed by reaction with soluble sulfates and carbonates. One advantage of the addition of ammonium oxalate to the citrate solution is the saving of time of filtration and washing of the citrate-insoluble residue. This process often requires several hours when highly ammoniated superphosphates are used, but when ammonium oxalate is added t o the citrate solution, filtration and washing can be finished in 15 minutes. Possible Methods for Estimation of Citrate-Insoluble Phosphoric Acid
One of the following modifications of the official method would appear worthy of consideration as being perhaps better adapted to measuring the available PZOsin ammoniated superphosphates. (1) Applicable to superphosphates and ammoniated superphosphates. Follow the official method except for the addition of 4 grams of ammonium oxalate to the 100-cc. portion of citrate solution, and digest either 2 or 4 hours instead of 30 minutes. (2) Follow present official method for all superphosphates and ammoniated superphosphate samples which contain less than 2.5 per cent of ammonia. For ammoniated samples which contain over 2.5 per cent ammonia, add 10 grams of crystalline ammonium oxalate to 100 cc. of citrate solution and digest for 30 minutes a t 65" C. It is recognized that this method would be difficult to apply in practice. (3) Follow the official method except for the use of a 0.1or 0.2-gram sample instead of 2 grams. Literature Cited (1) Assocn. Official Agr. Chem., Methods, p. 4 , 1925. (2) Assocn. Official Agr. Chem., Corrections of Methods, J. Assocn. Oficia2 Agr. Chem., 14, 71 (1931). (3) Buie, Phosghorus Digest, 2-6, Feb., 1931. (4) Howes and Jacobs, IND.ENG.CHBM.,Anal. Ed., 3, 70-2 (1931). ( 5 ) Jacob, Hill, Ross, and Rader, IND.ENG.CHEM., 22, 1385-92 (1930). (6) Keenen, I b i d . , 23, 1378-82 (1930). (7) Ross and Jacob, Paper presented at the meeting of the Awocn. Official Agr. Chem., Washington, D. C., October, 1930. (8) Truog, Wis. Agr. Expt. Sta., Res. Bull. 41, 48 (1916).
