CALCIUM METAPHOSPHATE CHEMICAL COMPOSITION AND PROPERTIES’
T
HE phosphatic components of all rock formations, animal residues, and commercial fertilizers occur in the ortho form, and evaluations have been made on the basis of the ortho pentoxide, PzOa. Only recently has it become important to consider the fertilizer possibilities of the meta forms, such as those that have been produced in the semi-works plant at Wilson Dam by the Chemical Engineering Division of the Tennessee Valley Authority. The technical aspects of the process and equipment used will be presented later by members of that division. Briefly, the metaphosphates of the present study were made by burning elemental phosphorus and passing the hot reaction products into beds of Tennessee phosphate rock. By the injection of two moles of PZOE, the 3CaO.PzOs ortho relation that exists in phosphate rock is changed to the metaphosphate, Ca(PO&, or Ca0.Pz05. The resultant melt is delivered into shallow pans, the cooled product having the appearance and characteristics of glass, with color ranges from light straw to dark brown. An alternative is the direct delivery of the melt into water. This rapid cooling causes the melt to sliver and imparts distinct chemical properties to the metaphosphate. The literature pertaining to calcium metaphosphate is comparatively scant, but it is uniformly stated that Ca(PO& is slightly soluble in water and in dilute acids. It would be erroneous and misleading, however, to assume that the semi-works products of the present contribution have chemical properties and fertilizer possibilities identical with reagent grades of calcium metaphosphate. The findings are therefore presented primarily as a pilot study of variant types of a product not hitherto developed as a possible phosphatic manure. The larger lumps of the melt, or “glass,” exhibit no hygroscopic tendency when exposed to indoor atmosphere. When finely ground, however, the glass may show a marked tendency to absorb moisture and become gummy or sticky upon exposure to humidity. Upon further exposure to ordinary atmosphere, the gummy material assumes a white surface coating that progresses inward until the entire mass becomes a dry white material, probably the monohydrate, Ca(PO&HzO. I n the processing of raw phosphate rock to obtain a product that is substantially Ca(POJ2, it is difficult to attain the exact CaO.PZ05 proportion. All of the present products contained P& in excess of that proportion and were therefore inherently acidic. They gave small water-soluble values by the conventional official leaching technic (1); but extended aqueous extractions of some of the products gave solutions of high phosphate content. The phosphorus contents of the solid phases and all analytical values for both meta and ortho solutes will be expressed as PzO5.
The fertilizer industry is based upon the usage of different types of orthophosphates, with a definite trend toward more concentrated products. Until recently, the properties and nutrient values of other forms have been dealt with almost solely in academic approach. The possible production of calcium metaphosphates from phosphate rock raises the question of their chemical properties and the adaptability of conventional analytical procedures in the evaluation of the new materials. The present study was directed toward the determination of the properties of a glassy type of metaphosphate, made by burning phosphorus and passing the hot reaction products into beds of phosphate rock to give a melt that is substantially
and not until orthophosphoric acid is formed by digestion
with the nitric acid of the reagent solution.” The adaptability of the official methods (1) to analysis of metaphosphates was first tried on a calcium metaphosphate prepared in the laboratory. No combination of conditions of time, temperature, agitation, and nitric acid imposed in the analytical systems of the alternative procedures was adequate to effect complete transition of the dissolved PO3 to PO,. There were marked disparities between the solubilities registered by aqueous leaching and by aqueous extractions. Moreover, practically identical values for citrateinsoluble PzOI were obtained from unleached charges and leached residues of the metaphosphate by 1-hour 65” C. digestions with neutral ammonium citrate of 1.09 specific gravity. An erroneous idea of the respective fractions of PzOssoluble in water and in ammonium citrate would therefore be obtained by the use of the conventional official methods. I n all subsequent determinations for absolute values, the filtered aqueous extracts were therefore hydrolyzed by bringing the analytical aliquots of the extracts nearly to the boiling point with supplements of 5 ml. of concentrated nitric acid for a minimal period of 15 minutes; the boiled solutions were cooled before the introduction of the molybdate reagent and the 30-minute agitation a t room temperature. In some instances the direct precipitation with ammonium molybdate was used in successive analyses to measure the progress of transition of POa to POr and in other cases the MoOa precipitations were made upon undigested and digested aliquots in parallel.
Observations as to Methods of Analysis Prescott and Johnson (14) state: “Ammonium molybdate reacts but slowly with meta- or pyrophosphate solutions-
* In collaboration with the Division of Chemical Engineering, Tennessee Valley Authority. 224
FERTILIZERS W. H. MACINTIRE,L. J. HARDIN, AND F. D. OLDHAM The University of Tennessee Agricultural Experiment Station, Knoxville, Tenn.
hydrolysis induced by the additions of either of the three mineral acids to the aliquots of the 48-hour aqueous extracts is evidenced by the first group of analyses. The combined hydrolytic effect of the extracted acidity and the acid supplements is shown by the 95.7 to 97.2 per cent PZOSvalues for the more acidic metaphosphate, contrasted with corresponding values of about 30 per cent for the less acidic product. TABLE11. Pz06EQUIVALENT VALUESOF FILTERED EXTRACTS FROM CALCIUM METAPHOSPHATEa rhCiESTIONS WITH CONTINUOUSLY
AGITATEDSOLVENTS
(Including PO8 to Po4 transitions effected by hot digestion .with addition of concentrated acids) Supp1e mental C-PZOSContent of ExtractsAs % of total Acid Extn. Diges- As % of charge content Period, tion of -A7 443-A 443-B 443-A 443-B Solvent Hours Ext. 1 None 3.6 Trace 5.7 Water 1 3.6 18.0 516 HNOa 1 2 . 4 20 20.5 4.0 None 13.0 2.6 20 HNOs 55.6 87.6 18.5 12.0 24 “Os 87.6 8.5 5.5 55.6 None 17.3 7 . 1 48 11.0 4.6 HNOa 6 1 . 7 2 0 . 0 9 7 . 2 3 0 . 8 48 HC1 19.8 97.0 30.4 48 61.6 48 HzSOd 6 0 . 8 1 9 . 6 9 5 . 7 30.0 None 1 5 . 5 2 0 . 4 0 24.4 3 1 . 4 0.1 N HNOs 24 24 “Os 63.2 64.40 99.5 9 9 . 1 None 11.2 16.40 17.6 2 5 . 5 0.05 N H N O 24 24 “0s 63.2 64.40 99.5 9 9 . 1 None 8.0 4.8 12.6 7.4 1% Hap04 1 1 HNOa 4 0 . 0 3 0 . 2 6 3 . 0 4 6 . 5 None 12.4 10.4 20 19.5 16.0 20 ” 0 3 62.4 63.2 9 8 . 3 97.4 None 2.4 1.4 3.8 2.2 Water CaCOsb 20 “0s 6 . 6 27.1 10.8 20 17.2 Carbonated water, 0.038 N 20 None 12.2 3.4 19.2 5.2 52.4 12.2 82.5 18.6 20 ”0s 20 None 1 . 4 0 Trace 2.2 Satd. CaHz(C0s)z 20 “ 0 8 1.70 1.0 2.7 i:5 COn MgCOsb 20 None 1.6 1.50 2.5 2.3 Water HNOa 1 0 . 6 4 . 6 0 16.7 7.1 20 a 100-mesh fineness, 50% passing 200. constants of 5-gram charge and 1 liter of solvent at room temperature, sa$lples 443-A and 443-B of Table I. b 1 gram per liter.
-
Ca(PO&, with a Pz06 equivalence of 65 per cent. The composition, solubility, and hygroscopicity of the solids, the stability of their solutions, and their tendencies to undergo hydrolysis, as influenced by the CaO:Pz06 ratio and by silica content, were considered for both air-cooled and quenched materials. The comparative tendencies of PO3 and PO4 to undergo fixation by the soil were also recorded. The determined values are considered to be useful as pilot information in the handling of the melts, in the requisite technic for the chemical analysis and evaluation of the final products, and for guidance in the planning of supplemental Neubauer, pot, and agronomic studies.
+ +
Composition and Solubility of Semi-commercial Calcium Metaphosphates The compositions of four of the products studied are indicated by the detailed analyses of Table I. Product 443-A, of high silica content, was the most acidic and most soluble of all the air-cooled products of this and subsequent tables. The data show that the products are essentially calcium metaphosphates and that all products contained POa in excess of the CaO:P206 ratio that would be accounted for by the respective CaO contents. The solubility results of Table I1 were obtained from agitated extractions of 5-gram charges of 100-mesh products per liter of solvent for periods of 1, 20, 24, and 48 hours a t mom temperature. Only limited hydrolysis was induced by the acid content of the precipitant solution. The marked
+
There were, however, wide disparities between the solvent and hydrolytic capacities of the several acidic solvents. The 24-hour extractions with 0.1 and with 0.05 N nitric acid actually dissolved more than 99 per cent of the total Pz06 content of each of the metaphosphates. These two dilute solvent acids induced little, if any, hydrolysis during the extraction of the more acidic metaphosphate; but they induced an appreciable transition in the solutions of low HPOa content that were derived from the less acidic product, 443-B. The one per cent solution of H3P04 showed marked solvent action upon both of the metaphosphates; but the weak ortho acid induced definite hydrolysis only in the extract of the less acidic material, as might be expected from the observations of Dragunov and Rossnovskaya (6) as to the transition of the sodium hexametaphosphate.
CALCIUM METAPHOSPHATES PRODUCED EXPERIMENTALLY AT WILSONDAM TABLEI. ANALYSESOF TYPICAL c
-Samplea-
No.
Melt treatment
-PzOs Total
%
equivalentWater-so1.b
%
CaO
Analytical and Computed Values Plod PZOK equivalent in excess of CaO of 1 : l CaO Ca0:PzOa contente equivalent FezOs
%
63.50 61.70 22.70 1:2.80 65.00 19.20 23.80 1:2.73 66.11 10.20 24.10 1:2.70 56.80 64.77 19.16 1:3.38 71.68’ 28.328 1 :2.53 e 0 Products used in obtaining data of subsequent tables. b Filtered aqueous extracts from 48-hour agitations at 15’ C., 5 grams per liter. 0 Computed rrom the Ca(P0a)z value of determined CaO. d Basis of,silicophosphate, aa SiOvPaOs. Theoretical values for Ca(P0a)I.
443-A 443-B 453 467
A+cooled Air-cooled Air-cooled Quenched
225
57.59 60.38 61.14 48.61
5.91 4.62 3.97 16.16
%
0.40 2.06 0.37 1.07
PZOS
All08
%
2.20 2.36 2.10 0.86
Si02
%
10.30 4.65 5.02 9.60
equivalent of total SiOd
%
24.38 11.01 11.88 22.72
INDUSTRIAL AND ENGINEERING CHEMISTRY
226
p 1 -
,4&5 Of
f/LT€R€D
EXTPACTJ
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VOL. 29, NO. 2
PO3, the solvent being fortified by the concomitant quantity of HPO, extracted from each of the several metaphosphates. The initial values registered by the 0.1 and 0.05 N acids again showed comparable solvent capacities; but subsequently, the greater capacity of the 0.1 N acid to induce hydrolysis was registered consistently. The initial direct-precipitation value registered by the immediate analysis of both of the unboiled dilute acid extracts of quenched high-silica product 457 were about twice as great as those for the three unquenched products. The final P206 values, and also the acidities, of the extracts of the quenched product were the maximal. This is accounted for by a more rapid and greater absolute advent of HPOa because of the greater surface exposed by the quenched solid. Tests with silver nitrate showed the pfesence of orthophosphate in the aqueous solutions of the quenched material, whereas no ortho ions were present in the aqueous extracts of the three unquenched products. The speeds of the transitions of Po3 to PO, in the two cold dilute nitric acid solutions are shown graphically by the curves of Figure 1.
DAM
OF Po8 TO PO4 FIGURE1. SPEEDO F TRANSITION IN NITRIC ACID SOLUTIONS OF COMMERCIAL METAPHOSPHATES AT = t 2 5 O C .
Solutions made b room-temperature extractions and filtrations. Total Pi06 equivagnt values as per cent of constant 5-gram charges per liter of solvent. Water-quenched totals: in 0 1 N 62.4; i n 0.05 N, 68.4; composite of air-cooled products: in 0.1 N : 63.3; in 0.05 N, 62.3. A Water-quenched product i n 0.1 N acid. B' Water-quenched product in 0.05 N acid. C: Air-cooled product i n 0.1 N acid. D. Air-cooled product in 0.05 N acid.
Effect of Temperature upon Hydrolysis of PO0 in Dilute Nitric Acid
The solvent capacity of carbonated water of 0.038 normality was comparable with that of distilled water for both of the metaphosphates, without indication of hydrolysis. This is of interest in connection with the conclusion of Kitsato (11) t o the effect that an enzyme will induce hydrolysis and the statement of Weissflog and Mengdehl (17) that root hairs convert POa to POb. The extractions of carbonated water saturated with calcium carbonate gave the minimal solute P205values in the 20hour extractions. The CaHz(C03)2solutions, the aqueous suspension of calcium carbonate, and the more concentrated magnesium bicarbonate solution, prevented cumulative acidity by neutralizing any engendered HPOs.
The data of Table IV show the influence of temperature upon the transitions of POI to PO, in 0.1 and 0.05 N nitric acid extracts, obtained by the procedure of Table 111. The analytical aliquots were subjected to 1-hour refluxed digestions a t the four higher temperatures. With rise of temperature a consistent increase in hydrolysis took place; the 0.1 N acid showed consistently the greater hydrolytic effect. The quantity of acid present was insufficient to effect complete hydrolysis in any of the dilute acid systems, including those fortified by 5-ml. additions of the extractant dilute acids and again boiled. The maximal hydrolysis of 87 per cent was registered by the solution of quenched product 457, but approximately one-fifth of this result was attributable to POc engendered during the extraction of the solid.
Speed of Hydrolysis of PO3 in Dilute Nitric Acid
Autohydrolysis of Filtered Aqueous Extracts
Prideaux (15) concluded that depolymerization and hydraThe data of Table V show the autohydrolysis attributable tion take place simultaneously and that in the hydrolysis of to nitric acid engendered during the extractions of two metaHP03 to H3P04there is no evidence of the intermediate formation of H4Pz07. Balareff (2, S), Dragunov (6, 6 ) , and Travers (16') likewise concluded that OF CALCIUM METAPHOBPHATES INTO ORTHOFORMS TABLE111. TRANSITION the transition to HaP04is direct. On the conIN THEIRDILUTE NITRICACID EXTRACTS AT R O O M TEMPERATURE" trary, Holt and Myers (8) and Beons and Kiehl ,--PZOSEquivalent in Exts. of Ca Metaphosphates (4) claimed t o have established the occurrence Days Water-Quenched Product between Air-Cooled Products 467 of the pyrophosphatic form as an intermediate Extn. and 7 4 4 3 - A 7-443-B7 4 5 3 product. Analysisb0.1N O.OdN 0 . 1 N 0.05N 0 . 1 N 0 . 0 5 N 0.1N 0 . 0 5 N 00 17.6 16.0 18.8 16.8 14.4 12.8 33.2 32.4 To determine the speed and extent of hy1 20.8 18.8 20.0 17.2 34.4 33.2 drolysis induced by dilute nitric acid solutions 3 .. .. 24:s 18:O 35.6 33.2 5 27:2 20:4 .. a t room temperature, the four metaphosphates 6 z8:o zi:e 28:4 l9:2 37:2 8 2916 20:s 40.8 3610 of Table I were extracted simultaneously with 9 3i:2 2i:z 28:s 22:4 0.1 and 0.05N nitric acid for 48 hours, the re11 34.2 24.4 3316 25:2 4i:6 38:s 12 3516 26:O 42:s 37:2 sultant filtrates being analyzed immediately and 14 37:6 27:2 36:s Z8:O 37.6 26.8 17 39.2 29.6 40.0 30.0 43.6 39.6 frequently thereafter during a 30-day period, as 18 38:4 28:8 indicated in Table 111. The phosphomolybdate 20 4210 3i:2 4O:o 3i:e 4i:6 33:~ 47:2 42:O 21 precipitations from the unboiled dilute nitric acid 23 43:2 34:8 43:6 33:2 47:2 4214 24 42:4 35:2 extracts were made under uniform conditions26 4512 3418 44:8 3414 47:6 42:4 samestock of precipitant, constant addition of 10 4312 3418 .. .. ,. .. 27 29 4610 34:8 grams of ammonium nitrate, no addition of con30 .. .. 4414 36:O 46:O 35:6 48:4 43:2 centrated nitric acid, and agitation for 30 minAbs.d 63.2 63.2 63.6 62.4 63.2 61.2 62.4 58.4 The eight extractions were made gimultaneously by agitating 5-gram charges in 1 liter utes. Any hydrolysis induced by the requisite of the dilute HN.08 for 48 hours, filtering, and permitting to stand. nitric acid content of the precipitant was conb Mooa precipitations made by the same ammonium molybdate mixture, with 10 grams of ammonium nitrate, no additional nitric acid, and agitation for 30 minutes a t room temperasidered to be a uniform quantity. Each proture. Determinations made immediately after obtaining filtered extracts. gressive increase in PO1 was therefore attributed d Absolute values in extracts subsequent t o effecting complete transitions of POa t o PO6 to the capacity of the designated dilute nitric by addition of concentrated "Os, and boiling for 30 minutes. acid solution to induce hydrolysis of dissolved I
Q
0
FEBRUARY, 1937
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEIV. INFLUENCE OF DIGESTION T~MPERATURE UPON TRANSITION OF CALCIUM META-TO ORTHOPHOSPHATE IN NITRICACIDSOLUTIONS Calcium Meta hos phate MeLs -
8ontent PzOs Equivalent of Filtered
Exts.b of CalSupplemental Digestion cium Metaphosphate Treatments Prior 0.1 N 0.05 N equivat o MoOa Pptn." extns. ertns. No. Type lent 443-A Air-cooled 6 4 . 0 % I hr. at 25' C. 14.8 14.0 1 hr. a t 40° C 16.8 16.4 17.6 16.0 1 hr. a t 60' C. 34.4 26.8 1 hr. a t 80' C. Boiled 41.2 30.8 Boiled after addition of 5 ml. concd. "Os 64.0 63.6 443-B Air-cooled 6 5 . 0 % 1 hr. a t 25' C. 12.8 10.8 1 hr. a t 40' C. 14.0 12.0 1 hr. a t 60' C. 20.0 12.8 30.0 23.2 1 hr. a t 80' C. Boiled 30.8 25.6 6-ml. addition of extn. acid and boiled 52.4 46.0 Boiled after addition of 5 ml. concd. HNOs 64.4 62.4 14.4 12.8 Air-cooled 6 5 . 1 % 1 hr. at 25" C. 453 18.8 1 hr. a t 40" C. 15.6 22.4 1 hr. a t 60' C. 18.8 36.8 26.8 1 hr. a t 80' C. 45.2 31.2 Boiled 5 ml. addition of extn. acid and boiled, 45.4 36.4 Boiled after addition of 61.2 5 ml. concd. "03 63.2 33.2 32.4 Quenched 6 4 . 8 % 1 hr. a t 25' C. 457 33.2 32.4 1 hr. a t 40' C. 36.4 34.0 1 hr. a t 60' C. 44.0 39.6 1 hr. a t SOo C. 50.0 43.6 Boiled 5 ml. addition of extn. acid and boiled 50.8 44.0 Boiled after addition of 58.4 58.4 5 ml. concd. "Os Except for indicated additions of concd. HNOJ and 5 ml. of 0.1 and 0.05 N all of the ammonium phosphoniolybdate precipitations from the filtered e x h o t s were made immediately, with additions of 10 grams NH4NOa. T h e 1-hour digestion of aliquots of the filtered extraots were all made in analytical Erlenmeyer flasks, fitted with reflux condensers. b All 0.1 and 0.05 N extractions were made a t room temperature, constant ratio of 5 grams per liter, with constant agitation for 48 hours. Total
"08
P2ok
curves of Figure 2. Since both extracts gave negative tests for PO4 ions prior t o immediate analysis, the recorded starting points are higher than the true points. The elevations of the initial points are attributed to the transitions induced during the analysis of the systems that contained variants of engendered HPOB and a constant of reagent nitric acid. Nevertheless, since all imposed analytical conditions were constants, the configurations indicate the influence of temperature upon the acceleration of hydrolysis by the HPOa content of the two extracts of divergent pH value and PzOr concentration.
Relation of Particle Size to Aqueous Extraction The data of Table VI show the effect of particle size upon the speed and extent of aqueous extractions for two metaphosphates, markedly different in solubility although almost identical in total Pz05equivalent content. The gritty par-
b wk/
TABLEV. INFLUENCE OF TEMPERATURE UPON AUTOHYDROLYSIB OF AQUEOUS FILTERED EXTRACTS~ OF Two METAPHOSPHATES % PzOs Registered by Aliquots of Exts.c Aged at:
--65" C.-Intervals between Extn. -Room temp.443-A 443-B and Analysisb 443-A 443-B Immediate analysis 16.0 4.6 16.0 4.6 16.2 4.6 35.6 10.8 48 hours 16.8 5.2 42.8 13.6 96 hours 7 days 17.2 6.4 51.2 14.0 17.6 6.5 54.6 16.0 10 days 18.4 6.8 56.8 17.2 13 days 15 days 18.5 6.8 57.4 17.4 a 48-hour extractions 5 grams per liter. b Direct precipitatiod, no " 0 8 added; 10 grams NH4NOa; 30-minute agitation. c Total Pi06 content: 443-A, 62.8 per cent; 443-B, 20.0 per cent.
227
a m
FIGURE 2. SPEED OF AUTOHYDROLYSIS IN ExTRACTS OF Two TYPESOF CALCIUM METAPHOSPHATES
A . Extract 443-A, Concentration 3140 p. p. m.
PzOs, p H C 3, standing qmesoent a t room temperature. B. Extract 443-B, concentration 1000 p. p. m. PzOs, p H 4.2, standing quiescent at room temperature. C. Same as A , standing quiescent a t 65' C. D. Same as B,standing quiescent a t 65O C .
ticles of the dense air-cooled product were decidedly different from the sliver-like separates obtained from the quenched product. The extracts of the quenched material were decidedly more acid than the extracts of the less soluble aircooled product. Direct molybdate precipitations gave negative P z Ovalues ~ for all of the extracts of the air-cooled product, but a definite
phosphates when the aqueous extracts were aged at room temperature and a t 65' C. Both of the cold filtered extracts gave negative tests for orthophosphoric acid a t the beginning of the aging period. The P z O con~ centration of extract 443-A was more than three TABLEVI. INFLUENCE OF FINENESS UPON SOLUBILITY OF METAPHOSPHATES AS MEASURED BY AQUEOUS EXTRACTIONS~ times the concentration of extract 443-B and the P -nOa Content of Charges in Their Aqueous Extractions b two extracts had respective pH values of 2.5 and -MOO* Pptn.c from Air-Cooled-MoOa Pptn.c from Water-Quenched4.2. Product Product -After ,RNOa-After "01Comparable transitions took place in the two Mesh digestiond -Directlydigestiond of As A s % As As 7 ' As As 7' extracts during the 15-day period of aging a t SepapH Di% of of PaOs pH % of of Pz& % of of Pz& r o o m t e m p e r a t u r e . Concordant percentage rates Value rectly charge content Value charge content charge content 6.4 9.9 21.6 33.3 6.4 Trace 1.60 2.4 C3.0 20-50 transitions were also registered by the two ex4.6
