METHOD FOR OBTAINING A GRANULATED PHOSPHATE FERTILISER AND PHOSPHATE FERTILISER OBTAINED

Abstract

The invention provides a method for obtaining a granulated phosphate fertiliser, as a phosphorus source, for direct use in agriculture, from the natural raw materials phosphate rock, a carbon source, a metabolic inducer of phosphorus-solubilising microorganisms and water.

Claims

1. A method for obtaining a granulated phosphate fertiliser which comprises the steps of: i) granulating ground phosphate rock in a granulator, the ground phosphate rock having a particle size between 100 and 500 μm and a humidity between 1 and 2%, a natural carbon source in ground state with a particle size between 0.1 and 1 mm and a humidity of 25 to 35%, a metabolic inducer of phosphorus-solubilising microorganisms and water to obtain a granulate; ii) drying the granulate obtained in step i) by means of a stream of hot air progressively heated from 50° C. to 290° C., avoiding rapid evaporation of the water, with a granule outlet temperature of 50° C. to obtain a dry granulate; iii) cooling the dry granulate by means of a stream of dry air at room temperature in the range of 20° C. to 25° C. to obtain cooled granules; iv) sieving the cooled granules for removing non-granulated raw material and deteriorated granules to obtain granules with a particle size having an average diameter between 1.5 mm and 3.5 mm; v) drying the granules obtained by step iv) by direct heating at a temperature of 300° C. for reducing humidity of the granulate to a maximum of 2%, with a granule outlet temperature of 40° C. to obtain a granulate; vi) cooling the granulate obtained by step v) by means of a stream of dry air at room temperature in the range of 20° C. to 25° C.; vii) optionally, adding 10.sup.5 ucf/g of additional phosphorus-solubilising microorganisms of the genus bacillus or pseudomonas after step i); viii) sieving the granulate obtained by step vii) to obtain granules with an average particle size between 2 mm and 4 mm.

2. The method according to claim 1, wherein, in step i), starting materials are introduced into the granulator in a proportion of 50-80% by weight of phosphate rock, 20-40% by weight of natural carbon source, 3%-7% of the metabolic inducer of phosphorus-solubilising microorganisms, the metabolic inducer of phosphorous-solubilising microorganisms being in liquid form and the water in a proportion by weight of at least 10%.

3. The method according to claim 2, wherein the metabolic inducer of phosphorus-solubilising microorganisms is used in a proportion between 5% and 7%.

4. The method according to claim 1, wherein the phosphate rock has the following characteristics: TABLE-US-00004 Chemical analysis On dry sample pH 8.43 Humidity 65° C.  3.36% Humidity 105° C.  3.57% Total P.sub.2O.sub.5 (gravimetry) 25-40% P.sub.2O.sub.5 ammonium citrate solution  2.09% P.sub.2O.sub.5 2% citric acid solution 15.77% P.sub.2O.sub.5 2% formic acid solution 30.52% Total CaO 53.13% Total Fe  0.08% SO.sub.3  0.22% Cl  0.04% Neutralising value 36.31%

5. The method according to claim 1, wherein the natural carbon source is selected from leonardite, black coal, anthracite or lignite.

6. The method according to claim 5, wherein the natural carbon source is leonardite with the following characteristics: TABLE-US-00005 Average pH 3.27 Humidity 28.68% Organic matter 29.56% K.sub.2O 0.2% Humic extracts 25-38% Humic acids 17-30% Fulvic acids 15-25% Al  0.17% Fe 0.3% Na  0.25% Si  0.34% MgO  0.41% CaO  1.47%

7. A granulated phosphate fertiliser obtained according to the method according to claim 1, containing 25% of total P.sub.2O.sub.5 with humic acids.

8. An organic amendment for direct use on agricultural and forest soils comprising the fertiliser according to claim 7 and/or for being mixed with other materials in order to obtain a complex fertilising product or an organo-mineral fertiliser.

Description

DETAILED DESCRIPTION

[0027] According to the first aspect, the invention provides a method for obtaining a granulated phosphate fertiliser which includes the steps of: [0028] i) Granulating ground phosphate rock in a granulator with a particle size between 100 and 500 μm and a humidity between 1 and 2%, a natural carbon source in ground state with a particle size between 0.1 and 1 mm and a humidity of 25 to 35%, a metabolic inducer of phosphorus-solubilising microorganisms and water; [0029] ii) Drying the granulate obtained in step i) by means of a stream of hot air progressively heated from 50° C. to 290° C., avoiding rapid evaporation of the water, with a granule outlet temperature of 50° C.; [0030] iii) Cooling the dry granulate by means of a stream of dry air at room temperature, from 20° C. to 25° C.; [0031] iv) Sieving the cooled granules removing the non-granulated raw material and deteriorated granules to obtain granules with a particle size (average diameter) between 1.5 mm and 3.5 mm; [0032] v) Drying the granulate by direct heating at a temperature of 300° C., reducing the humidity of the granulate to a maximum of 2%, with a granule outlet temperature of 40° C.; [0033] vi) Cooling the granulate by means of a stream of dry air at room temperature, from 20° C. to 25° C.; [0034] vii) Optionally, adding 10.sup.5 ucf/g of additional phosphorus-solubilising microorganisms of the genus bacillus or pseudomonas; [0035] viii) Sieving the granulate to obtain granules with an average particle size between 2 mm and 4 mm.

[0036] Preferably, in step i) of the method of the invention the starting materials are introduced into the granulator in a proportion of 50-80% by weight of phosphate rock, 20-40% by weight of a natural carbon source, a metabolic inducer of phosphorus-solubilising microorganisms in a proportion between 3% and 7% and water in a proportion by weight of at least 10%.

[0037] In step i) of the method described, the metabolic inducer is provided to favour the growth of phosphorus-solubilising microorganisms, both of those present in the soil, and those optionally provided in step vii) of the method and, thereby improving the solubilisation of phosphorus by these in the granule. To this end, metabolic inducers can be selected from known metabolic inducers, such as amino acids, monosaccharides, disaccharides and natural organic acids, for example citric acid, gluconic acid or lactic acid. Preferably, the metabolic inducers are applied as liquids to the granulate and in a proportion of between 5% and 7%, sufficient for the biostimulation of the microorganisms, but insufficient for the direct solubilisation of phosphorus.

[0038] It should be noted that the first drying step ii) of the granulate is carried out by means of a stream of hot air progressively heated from 50° C. to 290° C. This progressive heating, without using vein burners and flame front, enables a gradual dissipation of the humidity avoiding rapid water vaporisation, which can cause breakage or the appearance of cracks in the granules. Likewise, in the cooling step iii) the passage of a stream of dry air at room temperature enables a progressive cooling of the granule and facilitates a first curing thereof, already giving it a certain hardness and avoiding agglomeration or caking thereof.

[0039] In a preferred embodiment of the invention, phosphate rock is selected from phosphate rock with the following characteristics:

TABLE-US-00001 Chemical analysis On dry sample ph 8.43 Humidity 65° C  3.36% Humidity 105° C  3.57% Total P.sub.2O.sub.5 (gravimetry) 25-40% P.sub.2O.sub.5 ammonium citrate solution  2.09% P.sub.2O.sub.5 2% citric acid solution 15.77% P.sub.2O.sub.5 2% formic acid solution 30.52% Total CaO 53.13% Total Fe  0.08% SO.sub.3  0.22% Cl  0.04% Neutralising value 36.31%

[0040] Phosphoric rocks with these features come for example from Morocco and Western Sahara.

[0041] In another preferred embodiment of the invention, the natural carbon source is selected from leonardite, with the following characteristics:

TABLE-US-00002 Average pH 3.27 Humidity 28.68% Organic matter 29.56% K.sub.2O 0.2% Humic extracts 25-38% Humic acids 17-30% Fulvic acids 15-25% Al  0.17% Fe 0.3% Na  0.25% Si  0.34% MgO  0.41% CaO  1.47%

[0042] Leonardite with these characteristics comes for example from the province of Teruel, although they can be used from any other origin.

[0043] The invention also relates to the biological fertiliser obtained by means of the aforementioned method, a fertiliser which contains a high proportion of available phosphorus and suitable for the use thereof as an organic amendment in agricultural and forest soils and/or for being mixed with other materials in order to obtain an organo-mineral fertiliser.

[0044] The phosphate fertiliser granules obtained contain 25% of total P.sub.2O.sub.5 with humic acids and have a high hardness, much higher than that obtained in direct acid-free granulation processes, between 6 and 15 times higher, and dose to that obtained with known acid granulation processes.

[0045] In this regard, in the context of the present invention, hardness is resistance to breakage, abrasion and impact. Thus, high hardness prevents the fertiliser granules from breaking during handling, storage and distribution processes and the resistance thereof to abrasion prevents the formation of powder. This hardness variable of a granule is of vital importance in granulated products, since these are transferred in different steps until they are dosed, steps during which the granule may deteriorate due to low hardness.

[0046] To check the hardness of the granules, a test to measure the same was carried out with a granulate obtained by means of a conventional acid-free granulation method, a conventional granulation process in the presence of acid and the process described herein.

[0047] The hardness checking process was carried out with a hardness tester wherein the granule is arranged and a force is exerted on it, indicating what the breaking force is until the destruction of the granule. In this test, several samples of granules were taken at random, they were compressed and the breaking hardness was measured.

[0048] The results are shown in the following table, wherein the average values of the samples are shown:

TABLE-US-00003 Conventional Granulation Conventional acid-free according to the granulation with granulation invention acid T (s) Force (N/cm.sup.2) P2 Force (N/cm.sup.2) Force (N/cm.sup.2) P3 1 0.1 1.1 1.8 2 0.2 1.2 1.9 3 0.1 1.13 1.9 4 0.1 0.1 0.1

[0049] The invention also provides the use of the granulated phosphate fertiliser obtained according to the method of the invention as an organic amendment in agricultural and forest soils and/or for being mixed with other materials in order to obtain a complex fertilising product or an organo-mineral fertiliser.

[0050] In a usage example, the field dosage of the granulated phosphate fertiliser depends on the type of crop, for example, for a cereal between 150 kg/ha and 300 kg/ha and for a corn between 500 kg/ha and 700 kg/ha.