WO1981000711A1 - Fertilizer material from apatite - Google Patents

Fertilizer material from apatite Download PDF

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Publication number
WO1981000711A1
WO1981000711A1 PCT/GB1980/000139 GB8000139W WO8100711A1 WO 1981000711 A1 WO1981000711 A1 WO 1981000711A1 GB 8000139 W GB8000139 W GB 8000139W WO 8100711 A1 WO8100711 A1 WO 8100711A1
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Prior art keywords
apatite
roasting
molar ratio
alkali metal
fertilizer material
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PCT/GB1980/000139
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French (fr)
Inventor
F Glasser
R Gunawardane
Original Assignee
Nat Res Dev
F Glasser
R Gunawardane
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Nat Res Dev, F Glasser, R Gunawardane filed Critical Nat Res Dev
Priority to AT80901660T priority Critical patent/ATE7892T1/en
Priority to DE8080901660T priority patent/DE3068215D1/en
Publication of WO1981000711A1 publication Critical patent/WO1981000711A1/en

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    • C—CHEMISTRY; METALLURGY
    • C05—FERTILISERS; MANUFACTURE THEREOF
    • C05B—PHOSPHATIC FERTILISERS
    • C05B13/00—Fertilisers produced by pyrogenic processes from phosphatic materials
    • C05B13/02—Fertilisers produced by pyrogenic processes from phosphatic materials from rock phosphates

Definitions

  • This invention relates to making a fertilizer material from apatite.
  • Apatite is an insoluble phosphorus-containing mineral, approximating to Ca 5 (PO 4 ) 3 (F,OH,CI,1 ⁇ 2CO 3 ), and the phosphate content must be rendered soluble for fertilizer use.
  • Apatite the most abundant terrestial form of phosphorus, is conventionally treated with a strong acid such as nitric or sulphuric acid to render the phosphate soluble. This requires a capital-intensive industry.
  • apatite Another known way of treating apatite is the 'Rhenania process' described in British Patent Specification 301022.
  • the apatite is mixed with Na 2 CO 3 to give a molar ratio of
  • the reactants are ground together and calcined in a rotary kiln at 1100C - 1200C for approximately 2 hours. Fluorine is said to be retained in the process, although steam is sometimes admitted to the kiln before 1000C is reached in an attempt to remove at least part of the fluorine.
  • the sintered product may be used directly as a slow- release source of P or it may be subsequently extracted with hot aqueous Na 2 CO 3 solution, giving either Na 3 PO 4 or Ca 3 (PO 4 ) 2 .
  • Rhenania process and without using acid without using acid. Sri Lanka is understood to have an indigenous alkali (NaOH) industry. (although it does also produce hydrochloric acid, this is not a suitable acid for treating apatite.)
  • the alkali is readily convertible to sodium carbonate.
  • siliceous material and this is also widely available as quartz, sand or potash felspar (an alkali metal aluminosilicate). Addition of the last-named in small proportions also has the advantage of introducing available K 2 O, and the same might be said of mica.
  • the present invention is a method of making a fertilizer material from apatite, by roasting apatite at up to
  • apatite (as P 2 O 5 ): alkali metal is 1: at least 3 and in the presence of sufficient siliceous material to keep the free-lime content of the fertilizer material below 2 weight % and to inhibit formation of tetracalcium phosphate.
  • the molar ratio apatite : alkali metal is preferably from
  • the molar ratio apatite : siliceous material is preferably from 1:0.75 to 1:1.0.
  • the roasting temperature is preferably below 1000C, and desirably at least 800C, more preferably at least 85OC, most preferably from 880C to 950C, for example 900C.
  • the duration of roasting need not exceed 2 hours, and is preferably at least 1 hour.
  • the apatite, the siliceous material and the carbonate and/or aluminosilicate are pressed together (e.g. pelletised) before the roasting. This appears to enhance the rate of reaction.
  • the invention extends to the fertilizer material made as set forth above, optionally admixed with other agriculturally acceptable components.
  • the reasons for avoiding excessive free lime and tetracalcium phosphate are as follows: Free lime is capable of causing skin burns, reacts with moisture thereby causing caking and may make the fertilizer, and hence the soil, too alkaline.
  • the phosphate in tetracalcium phosphate Ca 4 P 2 O 9 is all soluble, i.e. it is at first sight an ideal fertilizer material.
  • Ca 4 P 2 O 9 is liable to conversion in the presence of water vapour, which is likely in a fossil- fuel-fired tunnel kiln, to CaO (or Ca(OH) 2 ) plus insoluble hydroxyapatite, one of the very materials which the present invention was devised to solubilise.
  • the quantities of Na 2 0/K 2 0 and SiO 2 are desirably the minimum, as an excess would result in too much dilution of the phosphate phases.
  • a way of determining these is to consider the CaO- and P 2 O 5 -rich regions of the system CaO-Na 2 O-P 2 O 5 -SiO 2 .
  • the plane of compositions lying between Ca 2 SiO 4 , Ca 3 (PO 4 ) 2 and CaNaPO 4 just fulfils the condition that CaO and Ca 4 P 2 0 9 should be absent and, furthermore, we find that this plane of compositions constitutes a true ternary system at subsolidus temperatures. Its position within the quaternary system is shown in the accompanying drawing.
  • Table 1 records the results of solubility determinations made on pure single-phase preparations. For present purposes availability is defined by the relation:
  • phase A is not completely soluble unless it too contains silica in solid solution; Phase A is explained in the footnote to Table 3. Both ⁇ and ⁇ Ca 3 (PO 4 ) 2 give less than 100% available P 2 O 5 . Moreover, while
  • Ca 4 P 2 O 9 has 100% availability, it is (as- already mentioned) readily converted to hydroxyapatite by annealing in air, whereby the available P 2 0 5 falls to 20%. Attempts to form a solid solution, substituting two Na + ions for Ca ++ ions, in the hope that Ca 4-x Na 2x P 2 o 9 would be less reactive to water vapour than the Ca 4 P 2 O 9 , were unavailing.
  • CaNa 6 P 2 0 9 was found to be 100% extractable, but is hygroscopic and therefore undesirable.
  • ss solid solution
  • Sri Lanka apatite sample (1) is a sample of pure apatite from the "leached zone" in the deposit at Eppawela, Sri Lanka.
  • Sample (2) is a commercially beneficiated sample of apatite from Eppawela, Sri Lanka.
  • Phase A see footnote to Table 3.
  • the invention will now be described by way of example.
  • the accompanying drawing shows a corner of the quaternary system CaO-Na 2 O-P 2 0 5 -SiO 2 .
  • the plane Ca 3 (PO 4 ) 2 -Ca 2 SiO 4 -CaNaPO 4 has been marked out. Compositions on this plane contain neither CaO nor Ca 4 P 2 O 9 , and accordingly are desirable.
  • Reaction batches were prepared by blending these raw materials and firing following a heating rate of 5C/min at a constant temperature for 2 hours.
  • Table 3 records the results of the annealing treatments. The phases present were determined by X-ray powder diffraction but the limit of detection of unreacted apatite was as high as 5%.
  • SiO 2 fulfils this-rble.
  • apatite : alkali metal from 1:3 to 1:4 gave the most rapid reaction at low temperatures. These batch proportions correspond to a weight percentage of Na 2 CO 3 between 20 and 27%. Some excess sodium carbonate was tolerable. If the optimum proportions of all three components are considered, molar ratios of apatite : Na 2 CO 3 : SiO 2 close to 1:2:1 are favourable for reaction. If the SiO 2 content is reduced slightly below this optimum, for example to 1:2:3 ⁇ 4, a high yield of available phosphorus is obtained, but free CaO is also developed.
  • Examples 1 to 3 are according to the invention.
  • Examples A to J are not according to the invention. It will be seen that few of Examples A to J gave any significant reaction below 1100oC, and of those which did, either inadequate phosphate was solubilised (as H) or free lime and sometimes a hygroscopic product resulted (as C and D).
  • Phase A tricalcium phosphate.
  • Phase A is believed to approximate to Ca 5 Na 2 (PO 4 ) 4 and is the crystalline phase defined by Ando and Matsuno (J. Ando and S..Matsuno, Bull. Chem. Soc. Japan 41 (1968) 342.)
  • Phase A solid solutions may also contain silicon.
  • APPENDIX Determining the 2%-citric-acid-soluble P 2 O 5 in a sample: The sample is ground to pass a 100 mesh BS sieve. A 1.0 g sample is extracted with 100 ml of 2% citric acid in a mechanical shaker operating at 260 oscillations per minute for 30 minutes at 18C. The resultant solution is filtered under vacuum using a sintered glass crucible (porosity No. 4) and the filtrate P 2 0 5 content is determined by the vanadomolybdate method, in which the following reagents are used:
  • Ammonium metavanadate solution prepared by dissolving 1.12 g of ammonium metavanadate in a mixture of 240 ml of concentrated HC10 4 acid and 260 ml of water.
  • Ammonium molybdate solution prepared by dissolving 35 g of ammonium molybdate in 500 ml of water,
  • Standard phosphate solution 0.2 mg/ml P 2 O 5 , prepared by dissolving 0.3835 g of dried potassium dihydrogen phosphate in 1 litre of water. Solutions (i) and (ii) are stable and will keep for some months.
  • the resultant solution is diluted with water in a 100 ml volumetric flask.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Fertilizers (AREA)

Abstract

Apatite is conventionally made into a fertilizer material by treatment with a strong acid, requiring capital-intensive industry. Hydroxyapatite is treated above 1100C with alkali but world reserves are problematic. The invention treats apatite at 900C with sodium aluminosilicate/carbonate and siliceous material in quantities to keep the composition in terms of CaO, SiO2, Na2O and P2O5 in or near the ternary system Ca2SiO4 - Ca3(PO4)2 - CaNaPO4.

Description

FERTILIZER MATERIAL FROM APATITE
This invention relates to making a fertilizer material from apatite. Apatite is an insoluble phosphorus-containing mineral, approximating to Ca5(PO4)3(F,OH,CI,½CO3), and the phosphate content must be rendered soluble for fertilizer use. Apatite, the most abundant terrestial form of phosphorus, is conventionally treated with a strong acid such as nitric or sulphuric acid to render the phosphate soluble. This requires a capital-intensive industry.
Another known way of treating apatite is the 'Rhenania process' described in British Patent Specification 301022. The apatite is mixed with Na2CO3 to give a molar ratio of
Na2CO3/P205 ~ 1.0, while at the same time sufficient SiO2 is also added to combine with excess CaO. The reactants are ground together and calcined in a rotary kiln at 1100C - 1200C for approximately 2 hours. Fluorine is said to be retained in the process, although steam is sometimes admitted to the kiln before 1000C is reached in an attempt to remove at least part of the fluorine. The sintered product may be used directly as a slow- release source of P or it may be subsequently extracted with hot aqueous Na2CO3 solution, giving either Na3PO4 or Ca3(PO4)2. This process requires high temperatures, and hydroxy-rich apatite, which is indigenous to central Europe and occurs in a few other regions of the world, some of which are of questionable reliability. Hard mineral apatite (richer in chlorine/fluorine) is widely available in Sri Lanka, India and East Africa and is often a by-product from other mining operations. The present invention seeks to make fertilizer material from such apatite at a lower temperature than the 1100C - 1200C required in the
Rhenania process and without using acid. Sri Lanka is understood to have an indigenous alkali (NaOH) industry. (While it does also produce hydrochloric acid, this is not a suitable acid for treating apatite.) The alkali is readily convertible to sodium carbonate. To make fertilizer material from apatite according to the present invention requires siliceous material, and this is also widely available as quartz, sand or potash felspar (an alkali metal aluminosilicate). Addition of the last-named in small proportions also has the advantage of introducing available K2O, and the same might be said of mica.
Accordingly, the present invention is a method of making a fertilizer material from apatite, by roasting apatite at up to
1100C with a carbonate and/or aluminosilicate of an alkali metal in an amount such that the molar ratio apatite (as P2O5): alkali metal is 1: at least 3 and in the presence of sufficient siliceous material to keep the free-lime content of the fertilizer material below 2 weight % and to inhibit formation of tetracalcium phosphate. The molar ratio apatite : alkali metal is preferably from
1:3 to 1:10, more preferably 1:3 to 1:5, for example.1:4.
The molar ratio apatite : siliceous material (as SiO2) is preferably from 1:0.75 to 1:1.0.
The roasting temperature is preferably below 1000C, and desirably at least 800C, more preferably at least 85OC, most preferably from 880C to 950C, for example 900C. The duration of roasting need not exceed 2 hours, and is preferably at least 1 hour.
Preferably the apatite, the siliceous material and the carbonate and/or aluminosilicate are pressed together (e.g. pelletised) before the roasting. This appears to enhance the rate of reaction.
The invention extends to the fertilizer material made as set forth above, optionally admixed with other agriculturally acceptable components. The reasons for avoiding excessive free lime and tetracalcium phosphate (i.e. why siliceous material is added) are as follows: Free lime is capable of causing skin burns, reacts with moisture thereby causing caking and may make the fertilizer, and hence the soil, too alkaline. The phosphate in tetracalcium phosphate Ca4P2O9 is all soluble, i.e. it is at first sight an ideal fertilizer material. However, Ca4P2O9 is liable to conversion in the presence of water vapour, which is likely in a fossil- fuel-fired tunnel kiln, to CaO (or Ca(OH)2) plus insoluble hydroxyapatite, one of the very materials which the present invention was devised to solubilise.
In practice, the quantities of Na20/K20 and SiO2 (which must be added in order to eliminate the above undesirable phases) are desirably the minimum, as an excess would result in too much dilution of the phosphate phases. A way of determining these is to consider the CaO- and P2O5-rich regions of the system CaO-Na2O-P2O5-SiO2. The plane of compositions lying between Ca2SiO4, Ca3(PO4)2 and CaNaPO4 just fulfils the condition that CaO and Ca4P209should be absent and, furthermore, we find that this plane of compositions constitutes a true ternary system at subsolidus temperatures. Its position within the quaternary system is shown in the accompanying drawing.
Table 1 records the results of solubility determinations made on pure single-phase preparations. For present purposes availability is defined by the relation:
Figure imgf000005_0001
The experimental method for determining the 2%-citric-acid- soluble P2O5 is given in the Appendix. Ground mineral apatite is poorly soluble: typically only 17 - 18% of its P2O5 content is 'available'.
Amongst the phases having 100% available P2O5 are Ca4P2O9, nagelschmidtite, silicocarnotite, rhenanite (a range of solid solutions around CaNaPO4) , and an α Ca2SiO4, solid solution containing typically 30 wt % Ca3(P04)2. The presence of silica in solid solution in rhenanite appears to activate the dissolution of phosphate. Moreover, phase A is not completely soluble unless it too contains silica in solid solution; Phase A is explained in the footnote to Table 3. Both α and β Ca3(PO4 )2 give less than 100% available P2O5. Moreover, while
Ca4P2O9has 100% availability, it is (as- already mentioned) readily converted to hydroxyapatite by annealing in air, whereby the available P205 falls to 20%. Attempts to form a solid solution, substituting two Na+ ions for Ca++ ions, in the hope that Ca4-xNa2xP2o9would be less reactive to water vapour than the Ca4P2O9, were unavailing.
CaNa6P209was found to be 100% extractable, but is hygroscopic and therefore undesirable.
Figure imgf000006_0001
Figure imgf000007_0001
Note: ss = solid solution; Sri Lanka apatite sample (1) is a sample of pure apatite from the "leached zone" in the deposit at Eppawela, Sri Lanka. Sample (2) is a commercially beneficiated sample of apatite from Eppawela, Sri Lanka. For explanation of Phase A, see footnote to Table 3.
As for the influence of halogens, chlorine is almost entirely eliminated during the firing of apatite-containing batches, although most of the fluorine is retained. The fluorine is believed to be present in solid solution in phases which are soluble in citric acid. When these phases are dissolved in citric acid, fluorine is probably present in the solution in the form of fluorosilicate complexes.
The invention will now be described by way of example. The accompanying drawing shows a corner of the quaternary system CaO-Na2O-P205-SiO2. The plane Ca3(PO4)2-Ca2SiO4-CaNaPO4has been marked out. Compositions on this plane contain neither CaO nor Ca4P2O9, and accordingly are desirable.
Mineral apatite (minus 100 mesh BS) was reacted with Na2CO3 and SiO2 (quartz, minus 120 mesh). The apatite was taken from the "leached zone" of the deposit: Table 2 gives a complete analysis typical of the concentrate as well as partial analysis of the particular batch of apatite concentrate used in this study. Microscopically, the apatite occurs as anhedral grains, most of which are monocrystals.
Figure imgf000008_0001
(a) Analysis reported by the Geological Survey Department,
Colombo 2, Sri Lanka (1973). The two samples were believed to be essentially identical.
Reaction batches were prepared by blending these raw materials and firing following a heating rate of 5C/min at a constant temperature for 2 hours. Table 3 records the results of the annealing treatments. The phases present were determined by X-ray powder diffraction but the limit of detection of unreacted apatite was as high as 5%.
In the absence of SiO2, mixtures of apatite and Na2CO3 react to produce large amounts of free CaO. Therefore, as free CaO is deemed to be an undesirable constituent, it is essential to add something to combine with it: SiO2 fulfils this-rble.
Much of the reaction is completed swiftly, even though this apatite is comparatively coarse-grained. As a rough guide, batches having a molar ratio of apatite to Na2CO3 from 1:1.5 to
1:2.0 (i.e. apatite : alkali metal = from 1:3 to 1:4) gave the most rapid reaction at low temperatures. These batch proportions correspond to a weight percentage of Na2CO3 between 20 and 27%. Some excess sodium carbonate was tolerable. If the optimum proportions of all three components are considered, molar ratios of apatite : Na2CO3 : SiO2 close to 1:2:1 are favourable for reaction. If the SiO2 content is reduced slightly below this optimum, for example to 1:2:¾, a high yield of available phosphorus is obtained, but free CaO is also developed. Similarly, reduction of the sodium carbonate content leads to incomplete reaction and the appearance of unreacted apatite which can only be removed by sintering at 1100º - 1300ºC. Table 3 shows the various compositions tried. Examples 1 to 3 are according to the invention. Examples A to J are not according to the invention. It will be seen that few of Examples A to J gave any significant reaction below 1100ºC, and of those which did, either inadequate phosphate was solubilised (as H) or free lime and sometimes a hygroscopic product resulted (as C and D).
The phases present are given roughly in the order: most first.
Figure imgf000009_0002
Figure imgf000009_0001
Figure imgf000010_0001
Figure imgf000011_0001
Abbreviations:- R = Rhenanite, CaNaPO4; F ap = Fluorapatite, Ca5(PO4)3F (all remaining apatite having this composition); tr. = trace, α and β are the high and low temperature forms respectively.
C3P = tricalcium phosphate. Phase A is believed to approximate to Ca5Na2(PO4 )4 and is the crystalline phase defined by Ando and Matsuno (J. Ando and S..Matsuno, Bull. Chem. Soc. Japan 41 (1968) 342.) In the present context, Phase A solid solutions may also contain silicon.
APPENDIX Determining the 2%-citric-acid-soluble P2O5 in a sample: The sample is ground to pass a 100 mesh BS sieve. A 1.0 g sample is extracted with 100 ml of 2% citric acid in a mechanical shaker operating at 260 oscillations per minute for 30 minutes at 18C. The resultant solution is filtered under vacuum using a sintered glass crucible (porosity No. 4) and the filtrate P205 content is determined by the vanadomolybdate method, in which the following reagents are used:
(i) Ammonium metavanadate solution, prepared by dissolving 1.12 g of ammonium metavanadate in a mixture of 240 ml of concentrated HC104 acid and 260 ml of water. (ii) Ammonium molybdate solution, prepared by dissolving 35 g of ammonium molybdate in 500 ml of water, (iii) Standard phosphate solution, 0.2 mg/ml P2O5, prepared by dissolving 0.3835 g of dried potassium dihydrogen phosphate in 1 litre of water. Solutions (i) and (ii) are stable and will keep for some months.
To a 2 ml aliquot of sample filtrate are added 10 ml of the vanadate solution (i) and 10 ml of the molybdate solution (ii) successively, mixing well after the addition of each reagent.
The resultant solution is diluted with water in a 100 ml volumetric flask.
After 30 minutes the absorbance is measured at 460 nm using a Unicam SP 600 colorimeter against a reagent blank solution. The standard phosphate solution (iii) is used in calibration.

Claims

1. A method of making a fertilizer material from apatite, by roasting apatite at up to 1100C with a carbonate and/or aluminosilicate of an alkali metal in an amount such- that the molar ratio apatite (as P205):alkali metal is 1: at least 3 and in the presence of sufficient siliceous material to keep the free-lime content of the fertilizer material below 2 weight % and to inhibit formation of tetracalcium phosphate.
2. A method according to Claim 1 , wherein the molar ratio apatite:alkali metal is from 1:3 to 1:10.
3. A method according to Claim 2, wherein the molar ratio apatite:alkali metal is from 1:3 to 1:5.
4. A method according to any preceding claim, wherein the molar ratio apatite: siliceous material (as SiO ) is. from lsθ.75 to
1:1.0.
5. A method according to any preceding claim, wherein the temperature of roasting the apatite is below 1000C.
6. A method according to any preceding claim, wherein the temperature of roasting the apatite is at least 800C.
7. A method according to Claim 6, wherein the said temperature is at least 850C.
8. A method according to .Claim 7ι wherein the said temperature is from 88OC to 950C.
9. A method according to any preceding claim, wherein the duration of the roasting does not exceed 2 hours.
10. A method according to any preceding claim, wherein the duration of the roasting is at least 1 hour.
11. A method according to any preceding claim, further comprising pressing together the apatite, the siliceous material and the carbonate and/or aluminosilicate before the roasting.
PCT/GB1980/000139 1979-09-07 1980-09-08 Fertilizer material from apatite WO1981000711A1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
AT80901660T ATE7892T1 (en) 1979-09-07 1980-09-08 APATITE-BASED FERTILIZER.
DE8080901660T DE3068215D1 (en) 1979-09-07 1980-09-08 Fertilizer material from apatite

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Application Number Priority Date Filing Date Title
GB7931090 1979-09-07
GB7931090 1979-09-07

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Publication number Priority date Publication date Assignee Title
US5451242A (en) * 1992-10-16 1995-09-19 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Active synthetic soil
US5433766A (en) * 1992-10-16 1995-07-18 The United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration Slow-release fertilizer
ITUB20150913A1 (en) * 2015-05-28 2016-11-28 Bio Eco Active S R L Fertilizer compositions based on an inorganic compound substituted with micro and macro elements

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB301022A (en) * 1927-11-23 1929-07-18 Kali Chemie Ag Process for the production of calcined phosphates
FR1189773A (en) * 1958-01-14 1959-10-06 Potasse & Engrais Chimiques Process for manufacturing phosphopotassium fertilizers
US2916372A (en) * 1955-05-03 1959-12-08 Lurgi Ges Fur Chemie Und Hutte Production of phosphate fertilizers soluble in citric acid
FR1541911A (en) * 1966-11-09 1968-10-11 Kali Chemie Ag Process for obtaining calcined phosphates endowed with a fertilizing activity
FR1559414A (en) * 1967-04-18 1969-03-07
FR2140401A1 (en) * 1971-06-05 1973-01-19 Kali Chemie Ag
FR2382416A1 (en) * 1977-03-02 1978-09-29 Kali Chemie Ag PROCESS FOR THE PRODUCTION OF PHOSPHATE FERTILIZERS

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1799882A (en) * 1924-03-21 1931-04-07 Firm Of Rhenania Ver Chemische Process for producing fertilizer
DE1592685C3 (en) * 1966-11-09 1973-10-04 Kali-Chemie Ag, 3000 Hannover Process for the production of calcined phosphate
DE2606883A1 (en) * 1976-02-20 1977-09-01 Kali Chemie Ag PROCESS FOR THE PRODUCTION OF A CITRATE-SOLUBLE GLUE PHOSPHATE DUCT

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB301022A (en) * 1927-11-23 1929-07-18 Kali Chemie Ag Process for the production of calcined phosphates
US2916372A (en) * 1955-05-03 1959-12-08 Lurgi Ges Fur Chemie Und Hutte Production of phosphate fertilizers soluble in citric acid
FR1189773A (en) * 1958-01-14 1959-10-06 Potasse & Engrais Chimiques Process for manufacturing phosphopotassium fertilizers
FR1541911A (en) * 1966-11-09 1968-10-11 Kali Chemie Ag Process for obtaining calcined phosphates endowed with a fertilizing activity
FR1559414A (en) * 1967-04-18 1969-03-07
FR2140401A1 (en) * 1971-06-05 1973-01-19 Kali Chemie Ag
FR2382416A1 (en) * 1977-03-02 1978-09-29 Kali Chemie Ag PROCESS FOR THE PRODUCTION OF PHOSPHATE FERTILIZERS

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EP0041504A1 (en) 1981-12-16
US4436546A (en) 1984-03-13
JPS56501086A (en) 1981-08-06
DE3068215D1 (en) 1984-07-19
EP0041504B1 (en) 1984-06-13
US4363650A (en) 1982-12-14

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