GB1570947A - Method of producing calcium phosphates - Google Patents

Description

(54) AN IMPROVED METHOD OF PRODUCING CALCIUM PHOSPHATES (71) We, POLITECHNIKA WARSZAWSKA Pi. Jednosci Robotniczej 1, Warszawa, Poland, a state enterprise organised and existing under the laws of Poland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a method of producing calcium phosphates for use as fertilizer from a raw mineral comprising phosphate rock or apatite.In these raw minerals phosphorus appears in the form of water-insoluble compounds having the apatite structure A5(P04)3Z wherein A is a cation such as calcium, magnesium or strontium and Z is an anion such as F-, Cl-, OH-. Such compounds cannot be taken up by plants.

In the production of phosphatic fertilizer these raw phosphorus compounds become converted into a form which can be taken up by plants, and which is water-soluble or weak-acid-soluble.

A previously proposed method of producing fertilizer consists in agglomerating phosphate rock or apatite with soda, lime and silica, in a rotary furnace at a temperature of from 1100 to 1200"C. Clinker thus produced is then ground in a ball mill. The obtained thermophosphates, known under their trade names such as Thomas slag or super-slag, primarily contain water-insoluble clacium silic-phosphates, which only on secretion of organic acids by the plant roots become converted into a plant-available form. Therefore, Thomas slags and super-slags are fertilizers to be spread in autumn.

Another previously proposed process for producing super-phosphates consists in treating water-insoluble tricalcium-phosphate - bearing raw mineral with a 62-70 % aqueous solution of sulphuric acid. In this process the sulphuric acid has to be produced initially (usually in a contact process), then stored and diluted to the appropriate concentration level. Prior to the production process proper, the raw mineral is carefully ground in a ball mill mixed with the suphuric acid in a mixer and introduced into the process chamber where, in the presence of the sulphuric acid, the water-insoluble tricalcium phosphate becomes converted into a water-soluble compound, gypsum being obtained at the same time as a by-product.The solidified and dried product is disintegrated and, if desired, granulated, and the fertilizer obtained is used in the early spring for quick-growing plants. According to this method, as a result of the sulphuric acid reaction with the raw mineral, about 5 per cent of the phosphorus contained in the raw mineral becomes converted into water-insoluble, but weak-acid-soluble, bi-, tri-, tetra- and higher linear phosphates and cyclic metaphosphates, whereas over 90 per cent of the phsophorus in the raw mineral becomes highly water-soluble monocalcium phosphate.

As the water-insoluble fertilizer ingredients of the superphosphate are slowly soluble in acids, they form the most valuable ingredient of the fertilizer since they offer a sustained supply of phosphorus for the soil surface layer. Their availability is as high as 90 per cent, while - according to the 1968 Procedures published by M. Niklewski and E. Wenglikowski from the College of Economics in Wrocklaw - utilization of water-soluble phosphorus compounds by plants does not exceed some 15 to 26 per cent. Thus, over 75 per cent of the phosphorus contained in the simple superphosphate as obtained in the wet process, remains useless because of its water solubility, and becomes either washed away from the fields by rain water etc., or undergoes a retrogradation process.The same disadvantage is also a feature of the so called triple superphosphate which is more concentrated than the simple one and which is produced by reaction of a phosphoric acid aqueous solution with phosphoric raw material.

It has been previously proposed to produce calcium metaphosphate by a method including reacting gaseous sulphur trioxide with a raw mineral comprising phosphate rock or tricalcium orthophosphate in the presence of a small amount of water which may be introduced as moisture in the raw mineral or as moisture in the gas stream.

According to the present invention a method of producing calcium phosphates includes heating raw mineral comprising phosphate rock or apatite to remove substantially all of the water therefrom, and reacting the substantially water-free raw mineral with gaseous sulphur trioxide in the substantially complete absence of water, For the production of fertilizers by the method of this invention, apatite or phosphoric rock with various initial moisture content and granulation can be used.

The sulphur trioxide can be obtained from any source, and be in gaseous admixture with at least one gas selected from air, sulphur dioxide, nitrogen, oxygen and the Inert gases.

The raw minerals may be ground and dried, and then exposed to the reaction gas. when the sulphur trioxide is in contact with the raw mineral grains which contain or phosphorus, a reaction takes place resulting in water-insoluble bi-, tri-, and tetra-phosphates of calcium, as well as higher condensed linear phosphates and metaphosphates. On separation of the gases, the reaction product in the form of loose, non-hygroscopic and non-lumping powder, is ready for use as a phosphatic fertilizer.

Over 90 per cent of the phsophorus contained in such a fertilizer is available to the plants due to the water-insoluble, but weak-acid-soluble, nature of the phosphorus compounds.

Utilization of phosphorus (as available to the plants) contained in the phosphatic fertilizer produced by the method of this invention can be more than three times as high as that experienced with the simple and triple superphosphates.

An embodiment of the present invention will now be described by way of illustration in the following Example.

Example 1 ton of crude phosphate rock is introduced into a ring-type mill and ground to a granulation of below 0.2 mm. Then, the raw material is dried at a temperature of 350 to 450"C within a drum-type kiln heated with mazout combustion gases, the gas outlet temperature being 120 to 1500C.

The dried material, 865 kg by weight, whose moisture content has been reduced to below 1 per cent, is transferred directly from the kiln into a fluidized-bed reactor where it is contacted with sulphur trioxide, the latter being introduced in the form of a mixture with oxygen and nitrogen, in a proportion of 10:18:72 by volume respectively, the total amount of the introduced gas mixture being 1150 Nm3.

The gas being introduced into the reactor has a temperature ranging from 300 to 350eC, and the average reaction time duration is 20 to 30 seconds.

Subsequently, the material is cooled down inside a cooling drum, and transferred into a storage bin, wherefrom it is poured into bags.

A total of 1248 kG of the phosphatic fertilizer is obtained in the form of dry, non-lumping and non-hygroscopic powder of the following composition by weight: - phosphorus (converted to P205) - 23.50/0, this including 2% of water-soluble phosphorus whereof 19.4% is soluble in 2%citric acid; - CaO - 37.2% - SO3 - 34.1% - Si02 - 0.61% - A1203 - 0.31% - Fe203 - 0.02% - MgO - 0.12% - K20 + Na20 - 0.96% - F - 1.6% - U - 0.003% - H20 - 0.4% - free acids - none - elements from raw mineral - remainder WHAT WE CLAIM IS: 1. A method of producing calcium phosphates including heating raw mineral comprising phosphate rock or apatite to remove substantially all of the water therefrom and reacting the substantially water-free raw mineral with gaseous sulphur trioxide in the substantially complete absence of water.

2. A method as claimed in claim 1, wherein the gaseous sulphur trioxide is in a gaseous admixture.

3. A method as claimed in claim 2, wherein the gaseous sulphur trioxide is in admixture with at least one gas selected from air, sulphur dioxide, nitrogen, oxygen and the Inert gases.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. It has been previously proposed to produce calcium metaphosphate by a method including reacting gaseous sulphur trioxide with a raw mineral comprising phosphate rock or tricalcium orthophosphate in the presence of a small amount of water which may be introduced as moisture in the raw mineral or as moisture in the gas stream. According to the present invention a method of producing calcium phosphates includes heating raw mineral comprising phosphate rock or apatite to remove substantially all of the water therefrom, and reacting the substantially water-free raw mineral with gaseous sulphur trioxide in the substantially complete absence of water, For the production of fertilizers by the method of this invention, apatite or phosphoric rock with various initial moisture content and granulation can be used. The sulphur trioxide can be obtained from any source, and be in gaseous admixture with at least one gas selected from air, sulphur dioxide, nitrogen, oxygen and the Inert gases. The raw minerals may be ground and dried, and then exposed to the reaction gas. when the sulphur trioxide is in contact with the raw mineral grains which contain or phosphorus, a reaction takes place resulting in water-insoluble bi-, tri-, and tetra-phosphates of calcium, as well as higher condensed linear phosphates and metaphosphates. On separation of the gases, the reaction product in the form of loose, non-hygroscopic and non-lumping powder, is ready for use as a phosphatic fertilizer. Over 90 per cent of the phsophorus contained in such a fertilizer is available to the plants due to the water-insoluble, but weak-acid-soluble, nature of the phosphorus compounds. Utilization of phosphorus (as available to the plants) contained in the phosphatic fertilizer produced by the method of this invention can be more than three times as high as that experienced with the simple and triple superphosphates. An embodiment of the present invention will now be described by way of illustration in the following Example. Example

1 ton of crude phosphate rock is introduced into a ring-type mill and ground to a granulation of below 0.2 mm. Then, the raw material is dried at a temperature of 350 to 450"C within a drum-type kiln heated with mazout combustion gases, the gas outlet temperature being 120 to 1500C.

The dried material, 865 kg by weight, whose moisture content has been reduced to below 1 per cent, is transferred directly from the kiln into a fluidized-bed reactor where it is contacted with sulphur trioxide, the latter being introduced in the form of a mixture with oxygen and nitrogen, in a proportion of 10:18:72 by volume respectively, the total amount of the introduced gas mixture being 1150 Nm3.

The gas being introduced into the reactor has a temperature ranging from 300 to 350eC, and the average reaction time duration is 20 to 30 seconds.

Subsequently, the material is cooled down inside a cooling drum, and transferred into a storage bin, wherefrom it is poured into bags.

A total of 1248 kG of the phosphatic fertilizer is obtained in the form of dry, non-lumping and non-hygroscopic powder of the following composition by weight: - phosphorus (converted to P205) - 23.50/0, this including 2% of water-soluble phosphorus whereof 19.4% is soluble in 2%citric acid; - CaO - 37.2% - SO3 - 34.1% - Si02 - 0.61% - A1203 - 0.31% - Fe203 - 0.02% - MgO - 0.12% - K20 + Na20 - 0.96% - F - 1.6% - U - 0.003% - H20 - 0.4% - free acids - none - elements from raw mineral - remainder WHAT WE CLAIM IS: 1. A method of producing calcium phosphates including heating raw mineral comprising phosphate rock or apatite to remove substantially all of the water therefrom and reacting the substantially water-free raw mineral with gaseous sulphur trioxide in the substantially complete absence of water.

2. A method as claimed in claim 1, wherein the gaseous sulphur trioxide is in a gaseous admixture.

3. A method as claimed in claim 2, wherein the gaseous sulphur trioxide is in admixture with at least one gas selected from air, sulphur dioxide, nitrogen, oxygen and the Inert gases.

4. A method of producing calcium phosphates, as claimed in claim 1 and substantially as

hereinbefore described with reference to the Example.

5. Calcium phosphates whenever produced by the method according to any of the preceding claims.