GB2226308A - Sulphurated product and process for its manufacture - Google Patents

Abstract

In the sulphurated product a support comprising a hard mineral material, natural phosphate, phosphated fertilizer or soil improver is ground and has its pores partly filled with sulphur. For preparing it one starts with the support ground and brought to a temperature of 145???C to which is mixed intensively liquid sulphur during a time sufficient for the sulphur to diffuse in the pores of the grains of the support without stopping them all up completely, then the mixture obtained is cooled. The support may in particular be a soft natural phosphate and/or maerl. <IMAGE>

Description

Sulphurated Product and Process for its Manufacture The present invention concerns a sulphurated product the support of which containing the sulphur is a hard mineral material, a phosphated fertilizer or a soil improver such as maerl. It concerns likewise a method for manufacturing this sulphurated product as well as means for putting the method into effect.

It is well known that sulphur is an important secondary fertilizing element which enters into the composition of amino acid essential to the life of plants.

It is likewise well known that natural phosphates on the basis of calcium phosphates are insoluble minerals. Their utilization by the plants renders their solubilisation necessary. For this purpose chemical processes have already been used consisting of having them attacked by mineral acids and principally sulphuric acid because it comprises the secondary fertilizing element which is sulphur so as to transform them into soluble phosphates such as monocalcium phosphate.

The reaction "natural phosphates and sulphuric acid" may be directly realized in chemical treatment works but these latter are generally relatively heavy and burdensome.

Furthermore this treatment imposes precise characteristics to the treated phosphate and cannot be considered for all phosphate minerals from which there are generally considerable logistic costs for the storing of the phosphates. Finally, the manufacture of sulphuric acid necessitates rich and first quality sulphur. For these reasons it is sought to avoid this method of manufacturing soluble phosphates.

It has also been proposed to use as additive to the natural phosphates, phosphogypsum which is a sulphate by product of the manufacture of phosphoric acid by the wet process. Such compositions of fertilizer are described, for example, in the documents FR-A-2 157683 and US-A-3660068. These compositions however do not give complete satisfaction. In fact, in the countries with heavy rainfall the amount of sulphur in the form of sulphate presents the serious drawback of being cleaned out very rapidly. That is why serious deficiencies are found in the soils of countries such as Ireland, England, New Zealand, Korea etc.

For several years attempts have been made to use a mixture of natural phosphate and sulpur along with acidophilic microorganisms such as bacteria of the "THIOBACILLUS" type to render soluble the natural phosphates directly in the soil on the spot. This solution has the advantage of allowing the use of sulphur or sulphur minerals of second quality.

Furthermore the direct use of the sulphur is less diluting for the formulation of the fertilizer than the addition of sulphur in the form of sulphate. More concentrated fertilizers can therefore be obtained. In particular for countries with heavy rainfall, sulphur has the advantage of being insoluble and its transformation into sulphate in the soil is relatively slow.

Regarding this subject one can, for example, refer to the natural phosphate and sulphur fertilizing compositions described in the documents FR-A-2 595687 and GB-A-2 136789.

In these preparations the sulphur is ground to obtain a kind of powder which is intimately mixed with the phosphates themselves of low granulometry. In practice the grinding of the sulphur is very delicate work and must be carried out in inert atmosphere in order to avoid possible explosions.

Precautions must also be taken when handling the ground sulphur. It is generally necessary to granulate it or at least agglomerate it.

It is obviously necessary to mix intimately sulphur and phosphate if it is desired to facilitate to a maximum the reactions between the sulphates created by oxidation of the sulphur and the phosphate.

In the document DE-A-1914453 a preparation of a granulate of hard fertilizer is described resistant to abrasion, containing sulphur, natural phosphate and pulverised organic substances the mixture of which is granulated with water or a solution of binding material. The granulate is heated to the temperature necessary to melt the non-organic substances contained, then cooled. By way of variation it is likewise proposed to use in the first mixing, products of organic origin preferably wet instead of powdered products, the rest of the manufacture being unchanged. In practice, in this preparation the melted sulphur serves as binder which give a product really hard and resistant to wear. In the end grains covered with sulphur are obtained. This is a drawback because one no longer has, at least on the surface the intimate sulphur-phosphate mixture desired.In practice the transformation of the sulphur alone into sulphate leads to an acidification of the soil which may be a drawback.

Finally, in addition to the possible coating of sulphur on the surface, this preparation does not ensure in an obvious manner an intimate mixture in the bulk.

One object of the present invention consists in providing a sulphurated product in which the sulphur is finely divided without having had to grind it mechanically.

Another object of the invention consists in providing a method of preparation of such a sulphurated support and in particular a phosphate fertilizer based on natural phosphate and containing sulphur allowing of obtaining a product in which the phosphate and sulphur mixture is very intimate in the bulk as well as on the surface giving the possibility of slow but practically simultaneous oxidation of the sulphur then of the phosphate whilst limiting the acidification of the soils.

According to one characteristic of the invention, in order to prepare the sulphurated product of the invention one starts from the support ground and brought to a temperature of 1450C to which one mixes intensively liquid sulphur during a time sufficient for the sulphur to diffuse into the pores of the grains of the said support without stopping them up completely, the mixture obtained is then cooled.

According to another characteristic the support is a soft natural phosphate.

According to another characteristic, the support is maerl.

According to another characteristic the support is a mixture of soft phosphate and maerl.

According to another characteristic the soft phosphate is powdered to at least 10% refusal to the sieve 100 ASTM/160 micrometers).

According to another characteristic, the invention concerns the product obtained according to the preparations mentioned above.

The characteristic of the invention mentioned above as well as others will appear more clearly on reading the following description of examples of putting into effect the preparation, the said description being made in relation to the attached drawings in which: Fig. 1 shows diagrammatically an installation for the manufacture of sulphurated phosphates according to the invention; Fig. 2 shows diagrammatically a variation of the installation for the manufacture of sulphurated phosphate according to the invention; and Fig. 3 is a diagram of the acid solubilization principle.

In the installation of Fig. 1 a heating apparatus 1 in which one uses a heating coil 2 driven by a motor 3 comprises an inlet 4 through which is introduced the soft ground phosphate, in inlet 5 through which is introduced solid sulphur and an outlet 6 through which the heated mixture of sulphur and ground phosphate comes out. The apparatus 1 comprises a double casing with an inlet 7 through which it receives steam or other suitable thermal fluid and an outlet 8 through which the steam or the said cooled fluid comes out.

In practice the soft ground phosphate is admitted at the inlet 4 at a temperature higher than 800C. By way of example, if it is a question of soft Algerian or Tunisian soft phosphate it will have been ground to 10% refusal to the sieve of 80 micrometer with a specific surface greater than 20m2 per gram. If it is a question of maerl the specific surface will be 3m2 per gram. It should be observed that at the time of fine grinding of the phosphate or maerl one finds a rather high rise in temperature from 80 to 1000C so that it is of interest in using these products directly at the outlet of the powder in order to effect savings of energy.

The outlet 6 of the apparatus 1 is connected to the inlet 9 of a mixer with double casing 10 which comprises a stirrer 11 driven by a motor 12. An inlet 13 permits of introducing the steam or other equivalent fluid between the two casings and an outlet 14 allows this cooled fluid to escape. A temperature regulation device keeps the mixture in the stirrer at the desired temperature. The outlet 15 of the mixer 10 is connected to the inlet 16 of a cooling apparatus 17 which comprises a cooling coil 18 driven by a motor 19.

The cooling apparatus 17 comprises a cooled product outlet 20, a cold air or water atomized or not inlet 21 and a cooling fuid outlet 22.

In practice the temperature of the heating fluid introduced through the inlet 7 into the apparatus 1 must be higher than 1500C and the heating time sufficient for the sulphur which has been introduced solid to become liquid. It should be noted that the sulphur begins to melt about 1150C and that its viscosity goes through a minimum about 1450C. The sulphur then has a viscosity approaching that of fuel oil.

Thus the mixture coming out of the outlet 6 of the apparatus 1 comprises grains of phosphate and liquid sulphur. In the mixer 10 the fluid entering through 13 is at a temperature permitting of maintaining the temperature of the mixture at 1500C. The mixing time is such that the liquid sulphur has fully penetrated into the pores of the grains of phosphate.

The product which comes out of the mixture 10 is cooled to about 1000C in the cooling apparatus 17 to be delivered through the outlet 20 from where it can be conveyed to a granulation apparatus.

In the embodiment of Fig. 2 one has however a heating apparatus 1, a mixer 10 and a cooling apparatus 17. The inlet 5 of the apparatus 1 is not used but a direct inlet 23 of the mixer through which liquid sulphur is introduced.

The operation is substantially the same as that of the example of Fig. 1.

By chemical attack of the compounds delivered at the outlet 20 using dilute hydrochloric acid it has been able to be established that the sulphur was very finely dispersed in the product, the dimension of the particles of sulphur found again after solution of the other constituants being very small. A large percentage of the particles had a dimension below 20 micrometers and there was a notable presence of ultra-fines.

The installation shown in Fig. 3 permits of effecting the acid solubilisation of the product delivered through the outlet 20 of the installations of Figs. 1 and 2. It comprises a reactor 24 provided with a stirrer 25 and in which there are prepared solubilisation liquors by mixing water, mineral acids and ammonium salts, a solubilisation reactor 26 with stirrers 27 in which one causes the outlet product of the reactor 24 to react with the sulphurated product delivered through the outlet 20, a maturing vault 28 the outlet of which is connected, according to the case, to a maturing stocking store 29 or a grannulator workshop 30 in which are added other raw materials and which delivers the granulated finished product.

In the preceding embodiments there is used as support intended to be sulphurated, soft natural phosphate but one could also prepare the sulphurated product by using as support maerl or even mixtures of soft phosphates, maerl or even phosphates, maerl and hard mineral materials.

In a preparation experiment one started from soft natural phosphate having a specific surface of 20m2 per gram, and sulphur 99.5% purity. The finished product contained 10% sulphur. The results mentioned above were obtained.

Among the advantages of the method of the invention can be cited the fact that it permits of only partially filling with sulphur the pores of the support. Thus one can effect subsequently solubilisation reactions of the phosphate by acids or granulation operations. Finally, there is no sticking effect between the grains which permits of preserving a maximum specific surface.

Claims (9)

1. A method of manufacturing a sulphurated product of which the support of the sulphur is of the type comprising natural phosphate, phosphated fertilizer, hard mineral material or soil improver, characterised in that the said support is ground and brought to a temperature of 1450C and in that there is mixed intensively with it liquid sulphur during a time sufficient for the sulphur to diffuse into the pores of the grains of the said support without stopping them all up completely, then the mixture obtained is cooled.

2. Method according to claim 1, characterised in that the support is a soft natural phosphate.

3. Method according to claim 1, characterised in that the support is maerl.

4. Method according to claim 1, characterised in that the support is a mixture of soft phosphates and maerl.

5. Method according to claim 1, characterised in that the support is a mixture of soft phosphates, maerl and a hard and porous mineral material.

6. Method according to claims 2, 4 or 5, characterised in that the soft phosphate is pounded to at least 10% of refusal to the sieve 100 ASTM (160 micrometers).

7. Sulphurated product manufactured according to one of the claims 1 to 6.

8. Sulphurated product manufactured according to one of the claims 1 to 6, characterised in that the mixture obtained is then completely or partly rendered soluble by an acid attack.

9. Product manufactured according to one of the claims 1 to 6, characterised in that the sulphurated product thus obtained undergoes a granulation.