JPH0122239B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a granular fertilizer containing condensed phosphate. Specifically, the present invention relates to a method for producing a condensed phosphate-containing granular fertilizer that is difficult to disintegrate and powder, has a high utilization rate of phosphate fertilizer components, and has an acidic soil improvement effect.

In Japan, where the climate is warm and rainy, the leaching of bases from soils is intense, and acidic soils are widely distributed throughout the country.

Acidification of soil not only reduces the utilization of fertilizer components by crops, but also causes various physiological disorders in crops, so various acidic soil improvement materials have been developed. Regarding fertilizer effectiveness, phosphoric acid fertilizer components are listed as having a markedly reduced fertilizer effect in acidic soils, and various forms of phosphoric acid fertilizers have been proposed from the perspective of improving their utilization rate, but they also have the effect of improving acidic soils. Basic phosphate fertilizer can be said to be one of the desirable forms.

Currently commercially available phosphate fertilizers mainly contain phosphoric acid in the form of orthophosphates, which, when applied, remove iron from the soil,
Because it quickly combines with aluminum and other substances and becomes available, its utilization rate for crops is extremely low.

On the other hand, phosphoric acid fertilizers containing condensed phosphates prevent or delay orthophosphates from becoming indispensable because the condensed phosphates have a metal-moderating effect. In addition to increasing the utilization rate, condensed phosphate can be expected to be used as a slow-release phosphate fertilizer.

A method for producing a phosphoric acid fertilizer containing condensed phosphoric acid for such purposes is to heat-treat a mixture of an alkali metal or ammonium phosphate and an alkaline earth metal phosphate at a temperature of 105 to 250°C. (Japanese Patent Publication No. 43-22218) is known, but it is possible to prepare and mix an alkali metal or ammonium phosphate and an alkaline earth metal phosphate separately, and then heat-treat the mixture in a number of steps. This is not an advantageous method for producing fertilizers, and even if one attempts to produce granular fertilizers, it is difficult to obtain granular fertilizers with high granule hardness.

In view of the above circumstances, the present inventors have conducted intensive research to industrially advantageously produce a granular phosphoric acid fertilizer with excellent fertilizing effect and ease of handling. By using a highly concentrated phosphoric acid solution, granulating it while reacting under specific conditions, and then heating and drying it, it is difficult to disintegrate, hard to powder, has a high content of condensed phosphates, has fertilizing properties, and has excellent acidity. The present invention was completed by discovering that it is possible to produce a granular fertilizer with excellent soil improvement effects.

That is, the present invention aims to industrially advantageously produce a condensed phosphate-containing granular fertilizer with excellent fertilizer effect and ease of handling. component, soluble magnesium as MgO
A basic substance containing 10% by weight or more of soluble silicon and 5% by weight or more of soluble silicon as SiO ₂ and a phosphoric acid concentration of
35 to 55% by weight of phosphoric acid solution as P ₂ O ₅ , A/MO = 0.3 to 1.0 ...... [] (In the formula, A indicates the number of moles of P ₂ O ₅ in the phosphoric acid solution, MO
represents the number of moles of soluble alkaline earth metal in the basic substance in terms of oxide. ) into a granulator at the ratio shown in
This is achieved by granulating the resulting granules while reacting at a temperature of 100°C to 170°C, and subsequently heating and drying the resulting granules until the temperature of the granules reaches 100 to 170°C.

The present invention will be explained in detail below.

The basic substance used as a raw material in the present invention is mainly composed of soluble alkaline earth metal and soluble silicon, and the total amount thereof is 50% by weight or more in terms of oxide (MgO + CaO + SiO ₂ ), preferably 70% by weight or more. It is desirable that the amount is at least % by weight.

Soluble magnesium in basic substances is MgO
It is necessary that the content is 10% by weight or more, preferably 15% by weight or more. If the amount of soluble magnesium is small, high temperatures are required for condensation of phosphate, making it impossible to industrially advantageously produce a granular fertilizer containing condensed phosphate at a relatively low temperature.

Further, the soluble silicon in the basic substance needs to be at least 5% by weight as SiO ₂ , preferably at least 10% by weight. If the amount of soluble silicon is small, the hardness of the resulting granular fertilizer will be low, which is not preferable.

The solubility rate in the present invention is measured in accordance with the Fertilizer Analysis Method (March 1972, published by the Agricultural Technology Research Institute of the Ministry of Agriculture, Forestry and Forestry).
This was done by pouring the solution into a solution, boiling it for 5 minutes, cooling it, adding water to make a total volume of 250 to 500 ml, and quantifying the amount of the solution eluted from the filtered solution.

As the basic substance which is the raw material of the present invention, any substance having the above-mentioned composition can be used, and it may be a mixture obtained by blending so as to satisfy the above-mentioned composition. Specific examples of materials that can be used as raw materials include by-products such as carbide furnace dust, ferronite slag, dolomite or its calcined products, magnesia clinker by-products, and dried or calcined magnesium-containing products obtained by treating pulp effluent. Mineral slag, cement dust, pulverized coal combustion ash (fly ash), serpentine, or mixtures thereof during the production of basic magnesia fertilizer, iron, steel, ferrosilicon, nickel, stainless steel, phosphoric acid, etc., or mixtures thereof. Examples include those to which magnesium compounds such as magnesium hydroxide and magnesium carbonate, and calcium compounds such as slaked lime, quicklime, and calcium carbonate are added.

The phosphoric acid solution needs to have a phosphoric acid concentration of 35 to ₅₅ % by weight as _P2O5 , preferably 40 to 50% by weight. If the phosphoric acid concentration is low, high temperatures are required for condensation of the phosphate, and advantageously, condensed phosphate cannot be obtained. On the other hand, if the phosphoric acid concentration is too high, granulation progresses too much and large lumps are formed, and reactants adhere to the inside of the apparatus, making stable operation difficult, which is not preferable.

The phosphoric acid concentration needs to be adjusted to a predetermined concentration by taking into consideration the amount of water if water is supplied in addition to the phosphoric acid solution when performing granulation while reacting.

The mixing ratio of the basic substance and the phosphoric acid solution is A/MO=0.3~1.0......[] (In the formula, A and MO have the same meaning as in the preceding formula [].) Do it like this. Preferably
It is preferably 0.4 to 0.9, more preferably 0.46 to 0.7.

This blending ratio is correlated with the granulation properties in reaction granulation and the condensation of phosphate during heat drying.
If the above blending ratio is too small, granulation will be difficult to proceed and high temperatures will be required for condensation. On the other hand, if it is too large, condensation will be facilitated, but granulation will progress too much and large lumps will be formed, or reactants will adhere to the inside of the apparatus, which will impede stable operation.

Examples of granulators for performing granulation while reacting include rotating drum type granulators, dish type granulators, paddle mixer type granulators, etc., which are used in the production of chemical fertilizers.

In the present invention, a basic substance is usually charged into a granulator such as the one described above, and granulation is carried out while a phosphoric acid solution is sprayed onto the basic substance and reacted. The temperature at this time is
The temperature should be between room temperature and 80°C, preferably between room temperature and 70°C. If the temperature during reaction granulation is too high,
This is not preferable because the reaction between phosphoric acid and the basic substance progresses and a large amount of phosphate, which is difficult to undergo condensation, is produced.

The granulated product obtained by reaction granulation is subsequently heated and dried.

As a device for heating and drying, a rotary kiln used for manufacturing chemical fertilizers or the like can be used.

The transition from reaction granulation to heat drying must be after grains are formed by reaction granulation, and preferably before the reaction between the basic substance and the phosphoric acid solution is completed. If the temperature is increased before grains are formed, it will not be possible to obtain granular fertilizer with high grain hardness. Furthermore, if the reaction between the basic substance and the phosphoric acid solution is completed, a large amount of phosphate, which is difficult to undergo condensation, will be produced, which is not preferable. Normally, heat drying is preferably carried out within several minutes to 30 minutes, preferably several minutes to 20 minutes after particles are formed by reaction granulation.

The heating drying temperature is 100-170°C for the granulated material.
℃, preferably 110 to 150℃. Usually, hot air at about 300 to 400°C is passed in cocurrent or countercurrent for about 20 to 40 minutes. If the temperature of the granules is less than 100°C, the condensation of the phosphate will not be sufficient and the product aimed at by the present invention will not be obtained. On the other hand, making it too high is not a good idea as it wastes energy.

In addition, the temperature of the granulated material is determined by taking the granulated material into a container,
This is the temperature measured by immediately inserting a thermometer into the center.

The granulated material taken out from the heating dryer is sieved to separate fine grains and coarse grains into products.

In the present invention, by circulating a part to 9/10 of the granules obtained by heating and drying to the granulator, granulation can be facilitated and stable operation can be achieved. Can be done. There is no particular restriction on the circulation amount of the above particulate matter as long as it is 9/10 or less, but it is usually 1/2.
~9/10, preferably about 2/3 ~ 5/6, and the larger the amount of phosphoric acid solution used, the better the amount of circulation should be increased.

The present invention can be carried out either batchwise or continuously, but industrially it is advantageous to carry out the process continuously while circulating 1/2 to 9/10 of the dry granules to the granulator.

When using the method of the present invention, a granular fertilizer with a high condensed phosphate content and high grain hardness can be produced with easy operation, and the soluble alkaline earth metal in the basic substance and the phosphoric acid in the phosphoric acid solution can be produced. Since the content of condensed phosphate can be arbitrarily adjusted by selecting the blending ratio, phosphoric acid solution concentration, or reaction granulation or heat drying conditions, the industrial value is extremely large.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. In addition, "%" in an Example shows "weight%." Further, the condensed phosphate content is a value obtained by extracting a sample using a 2% aqueous citric acid solution and measuring the extract by liquid chromatography.

Example 1 Carbide furnace dust (soluble MgO28.9%, soluble MgO28.4%, soluble
CaO44.0%, soluble _SiO2 9.5%, particle size 0.1mm or less)
600Kg/hr, Ferronitskel slag (soluble
MgO26.7%, soluble MgO21.1%, soluble CaO11.4
%, soluble _SiO2 44.8%, average particle size 0.3mm) 200Kg/
hr and granules obtained by heat drying described below 8000
Kg/hr is continuously supplied, and the P ₂ O ₅ concentration is 47.7
While spraying 1280Kg/hr of phosphoric acid solution at a temperature of 60~
Pelletization was carried out while reacting at 70°C for an average residence time of 7 minutes.

The granules were continuously introduced into a rotating drum dryer, and hot air at 300°C was flowed in parallel, with an average residence time of 30
Heat drying was performed for 1 minute. The temperature of the granulated material taken out from the dryer was 130°C.

The resulting granules have a particle size of 1.91 to 2.83 mm.
1900Kg/hr was obtained as a product, and the remainder was circulated to the granulator.

The analytical values and grain hardness of the product were as follows.

T-P ₂ O ₅ 32.2% C-P ₂ O ₅ 32.2% W-P ₂ O ₅ 5.8% Condensed phosphoric acid amount 20.5% S-MgO 11.9% C-CaO 15.0% Grain hardness 1.2Kg/grain comparison example 1 Example In step 1, heat drying was carried out by flowing hot air at 150°C in parallel flow, with an average residence time of 30 minutes, and the temperature of the granules
The test was carried out at 90° C., and the other operations were carried out in exactly the same manner as in Example 1. The analytical values and grain hardness of the obtained product were as follows.

T-P ₂ O ₅ 32.2% C-P ₂ O ₅ 32.2% W-P ₂ O ₅ 10.5% Condensed phosphoric acid amount 0.5% S-MgO 11.9% C-CaO 15.0% Grain hardness 1.0Kg/cm ²

Claims (1)

[Claims] 1 Main components are soluble alkaline earth metal and soluble silicon, and soluble magnesium is MgO.
A basic substance containing 10% by weight or more of soluble silicon and 5% by weight or more of soluble silicon as SiO ₂ and a phosphoric acid concentration of
35 to 55% by weight of phosphoric acid solution as P ₂ O ₅ , formula A/MO = 0.3 to 1.0 ...... [] (In the formula, A indicates the number of moles of P ₂ O ₅ in the phosphoric acid solution, MO
represents the number of moles of soluble alkaline earth metal in the basic substance in terms of oxide. ) into a granulator at the ratio shown in
1. A method for producing a condensed phosphate-containing granular fertilizer, which comprises granulating the fertilizer while reacting at a temperature of 100° C., and then heating and drying the obtained granular material until the temperature of the granular material reaches 100 to 170° C. 2. The method for producing a condensed phosphate-containing granular fertilizer according to claim 1, wherein 1/2 to 9/10 of the granular material obtained by heating and drying is circulated to a granulator for reaction granulation.