Disclosure of Invention
The first problem to be solved by the invention is to provide a preparation method of phosphate ore micro-powder pellets.
In order to solve the first technical problem of the invention, the preparation method of the phosphate ore micro-powder pellet comprises the following steps:
a. uniformly mixing an organic binder, water and powdered rock phosphate according to a mass ratio of 0.2-0.6: 10-15: 100 to obtain a mixed material; the mass ratio of the organic binder to the water to the ground phosphate rock is preferably 0.4-0.6: 12-15: 100;
b. pressing the mixed material into balls at 6-12 MPa to obtain phosphate ore micro powder green pellets; the diameter of the phosphorite micro powder green pellets is preferably 8-30 mm;
c. and drying the phosphate ore micro powder green pellets to obtain phosphate ore micro powder pellets.
Preferably, the organic binder is polyvinyl alcohol, sodium carboxymethylcellulose or methylcellulose, preferably polyvinyl alcohol.
Preferably, the particle size composition range of the ground phosphate rock is as follows: 5-15 wt% of particle size larger than or equal to 74 μm, 50-80 wt% of particle size smaller than 38 μm and smaller than 74 μm, and 15-35 wt% of particle size smaller than or equal to 38 μm.
Preferably, the step a includes the following steps: dissolving the organic binder in water to obtain an organic binder aqueous solution, and uniformly mixing the organic binder aqueous solution and the powdered rock phosphate.
Preferably, the temperature of the organic binder dissolved in water is controlled to be 75-90 ℃.
Preferably, the method for uniformly mixing the organic binder aqueous solution and the ground phosphate rock is to stir and mix for 15-20 minutes.
Preferably, before the ball pressing in the step b, the mixed material is compacted to obtain a compacted material.
Preferably, the drying temperature in the step c is 120-220 ℃, and the drying time is 20-60 minutes.
The industrial waste heat of yellow phosphorus enterprises is utilized, so that the waste heat is utilized, and the effects of energy conservation and emission reduction can be realized. Therefore, preferably, the heat used for drying in step c is from industrial waste heat of yellow phosphorus production.
The second problem to be solved by the invention is to provide the phosphate ore micro-powder pellets.
In order to solve the second technical problem, the phosphate ore micro-powder pellets are prepared by the method. Compared with the phosphate ore micro-powder pellets prepared by the prior method, the pellets prepared by the method of the invention do not generate pulverization phenomenon after falling, and can be broken into a plurality of parts after falling for many times, but the mass of the broken parts with the diameter less than 5mm is less than 5 percent of the total mass of the pellets, so that the amount of returned material pressed pellets is very small.
Further, the compression strength of the phosphorite micro powder pellets is 135-2000N/pellet, the falling strength of the phosphorite micro powder pellets is 44-500 times/pellet at a distance of 50cm from the rubber plate, and the falling strength of the phosphorite micro powder pellets is 3-15 times/pellet at a distance of 150cm from the rubber plate; preferably, the compression strength of the phosphorite micro-powder pellets is 1374-2000N/pellet, the falling strength of the phosphorite micro-powder pellets is 408-500 times/pellet at a distance of 50cm from the rubber plate, and the falling strength of the phosphorite micro-powder pellets is 8-15 times/pellet at a distance of 150cm from the rubber plate.
Has the advantages that:
1. the binder of the invention has less consumption, and does not affect the phosphorite grade of the subsequent process. Meanwhile, the prepared phosphate ore micro-powder pellets have high strength and wide application prospect.
2. In addition, the binder is less in use type, small in use amount and low in pelletizing cost.
3. The invention utilizes the industrial waste heat of yellow phosphorus enterprises, so that the waste heat is utilized, and the effects of energy conservation and emission reduction are achieved.
4. The invention firstly carries out compaction treatment on the mixture and then carries out roller pressure forming, the obtained phosphate rock micro-powder pellets have high balling rate, the material return quantity is reduced, and the cost is reduced again.
5. The invention has simple preparation process, less required equipment and low cost.
Detailed Description
In order to solve the first technical problem of the invention, the preparation method of the phosphate ore micro-powder pellet comprises the following steps:
a. uniformly mixing an organic binder, water and powdered rock phosphate according to a mass ratio of 0.2-0.6: 10-15: 100 to obtain a mixed material; the mass ratio of the organic binder to the water to the ground phosphate rock is preferably 0.4-0.6: 12-15: 100;
b. pressing the mixed material into balls at 6-12 MPa to obtain phosphate ore micro powder green pellets; the diameter of the phosphorite micro powder green pellets is preferably 8-30 mm;
c. and drying the phosphate ore micro powder green pellets to obtain phosphate ore micro powder pellets.
and a, uniformly mixing the materials in the step a by adopting conventional mixing modes such as stirring, shaking and the like, for example, uniformly mixing and stirring the materials by adopting a mixer.
And b, the ball pressing machine in the step can adopt a ball pressing machine, such as a rolling ball machine.
Preferably, the organic binder is polyvinyl alcohol, sodium carboxymethylcellulose or methylcellulose, preferably polyvinyl alcohol.
Preferably, the particle size composition range of the ground phosphate rock is as follows: 5-15 wt% of particle size larger than or equal to 74 μm, 50-80 wt% of particle size smaller than 38 μm and smaller than 74 μm, and 15-35 wt% of particle size smaller than or equal to 38 μm.
Preferably, the step a includes the following steps: dissolving the organic binder in water to obtain an organic binder aqueous solution, and uniformly mixing the organic binder aqueous solution and the powdered rock phosphate.
Preferably, the temperature of the organic binder dissolved in water is controlled to be 75-90 ℃.
Preferably, the method for uniformly mixing the organic binder aqueous solution and the ground phosphate rock is to stir and mix for 15-20 minutes.
Preferably, before the ball pressing in the step b, the mixed material is compacted to obtain a compacted material.
Preferably, the drying temperature in the step c is 120-220 ℃, and the drying time is 20-60 minutes.
The industrial waste heat of yellow phosphorus enterprises is utilized, so that the waste heat is utilized, and the effects of energy conservation and emission reduction can be realized. Therefore, preferably, the heat used for drying in step c is from industrial waste heat of yellow phosphorus production.
Compared with the phosphorite micropowder pellets prepared by the conventional method, the pellets prepared by the method cannot generate a pulverization phenomenon after falling, and can be broken into a plurality of parts after falling for many times, but the mass of the broken parts with the diameter less than 5mm is less than 5 percent of the total mass of the pellets, so that the returned pellet pressing amount is very small.
Further, the compression strength of the phosphorite micro powder pellets is 135-2000N/pellet, the falling strength of the phosphorite micro powder pellets is 44-500 times/pellet at a distance of 50cm from the rubber plate, and the falling strength of the phosphorite micro powder pellets is 3-15 times/pellet at a distance of 150cm from the rubber plate; preferably, the compression strength of the phosphorite micro-powder pellets is 1374-2000N/pellet, the falling strength of the phosphorite micro-powder pellets is 408-500 times/pellet at a distance of 50cm from the rubber plate, and the falling strength of the phosphorite micro-powder pellets is 8-15 times/pellet at a distance of 150cm from the rubber plate.
The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.
Example 1
1000kg of phosphorite micro powder, 2kg of required organic binder and 100kg of water. Namely: the mass ratio of the phosphorite micro powder to the organic binder to the water is 100:0.2: 10.
The preparation method of the phosphate ore micro-powder pellets shown in figure 1 comprises the following steps:
(1) 2kg of polyvinyl alcohol dry powder and 100kg of water were mixed uniformly at 80 ℃ to obtain 102kg of an organic binder aqueous solution.
(2) Adding an organic binder aqueous solution into 1000kg of phosphorite micropowder, and then uniformly mixing and stirring for 15min by a mixer to obtain 1102kg of mixed material;
(3) compacting the obtained mixed material on compacting equipment to obtain a compacted material;
(4) pelletizing and molding the compacted material by using a double-roller ball press, and setting the pressure to be 10Mpa to obtain phosphorite micropowder green pellets with the diameter of 8-30 mm;
(5) and (3) burning tail gas generated in the production of yellow phosphorus, pumping high-temperature air generated by burning waste heat in a combustion chamber to a pellet drying chamber through an air pumping system, and drying the phosphorite micropowder green pellets at the drying temperature of 180 ℃ for 60min to obtain the high-strength phosphorite micropowder pellets. The compressive strength of the obtained phosphate ore micro powder green pellets is 35N/pellet, the falling strength of the phosphate ore micro powder green pellets is 8 times/pellet when the phosphate ore micro powder green pellets are 50cm away from a rubber plate, the phosphate ore micro powder green pellets are broken into a plurality of blocks after the phosphate ore micro powder green pellets fall for 9 times when the phosphate ore micro powder green pellets are 50cm away from the rubber plate, wherein the mass of the phosphate ore micro powder green pellets with the diameter; the compression strength of the dried phosphate rock micro powder agglomerate is 135N/ball, the falling strength of the phosphate rock micro powder agglomerate is 44 times/ball 50cm away from the rubber plate, the phosphate rock micro powder agglomerate falls 45 times away from the rubber plate and is broken into 5 parts, wherein the mass of the phosphate rock micro powder agglomerate with the diameter less than 5mm is 1 percent of the total mass of the pellet; the falling strength of 150cm away from the rubber plate is 3 times per pellet, and the pellet is broken into a plurality of block parts after falling for 4 times of 150cm away from the rubber plate, wherein the mass of the pellet with the diameter less than 5mm is 0 percent of the total mass of the pellet. It can be seen that the pellets of this example do not produce a pulverization phenomenon after falling, and the pellets will break into several parts after falling for many times, and the mass of the broken parts with the diameter less than 5mm is less than 5% of the total mass of the pellets.
Example 2
1000kg of phosphorite micro powder, 3kg of required organic binder and 120kg of water. Namely: the mass ratio of the phosphorite micro powder to the organic binder to the water is 100:0.3: 12.
The preparation method of the phosphate ore micro-powder pellets comprises the following steps:
(1) uniformly mixing 3kg of polyvinyl alcohol dry powder and 120kg of water at 85 ℃ to obtain 123kg of organic binder aqueous solution;
(2) adding the organic binder aqueous solution into 1000kg of phosphorite micropowder, and then uniformly mixing and stirring for 20min by a mixer to obtain 1123kg of mixed material;
(3) compacting the mixed material on compacting equipment to obtain a compacted material;
(4) pelletizing and molding the compacted material by using a double-roller ball press, and setting the pressure to be 8Mpa to obtain phosphorite micropowder green pellets with the diameter of 8-30 mm;
(5) and (3) burning tail gas generated in the production of yellow phosphorus, pumping high-temperature air generated by burning waste heat in a combustion chamber to a pellet drying chamber through an air pumping system, and drying the phosphorite micropowder green pellets at the drying temperature of 120 ℃ for 60min to obtain the high-strength phosphorite micropowder pellets.
The compressive strength of the obtained phosphate ore micro powder green pellets is 45N/pellet, the falling strength of the phosphate ore micro powder green pellets is 14 times/pellet when the phosphate ore micro powder green pellets are 50cm away from a rubber plate, the phosphate ore micro powder green pellets are broken into 4 pieces after falling for 15 times when the phosphate ore micro powder green pellets are 50cm away from the rubber plate, wherein the mass of the phosphate ore micro powder green pellets with the diameter less than 5mm is 3 percent of the; the compression strength of the dried phosphate rock micro-powder agglomerate is 466N/ball, the falling strength of the dried phosphate rock micro-powder agglomerate is 285 times/ball 50cm away from the rubber plate, and the dried phosphate rock micro-powder agglomerate falls 286 times away from the rubber plate and is broken into 4 parts, wherein the mass of the phosphate rock micro-powder agglomerate with the diameter less than 5mm is 0 percent of the total mass of the pellet; the falling strength of 150cm away from the rubber plate is 5 times per pellet, and the pellet is broken into 4 parts after falling for 6 times of 150cm away from the rubber plate, wherein the mass of the pellet with the diameter of less than 5mm is 0 percent of the total mass of the pellet. It can be seen that the pellets of this example do not produce a pulverization phenomenon after falling, and the pellets will break into several parts after falling for many times, and the mass of the broken parts with the diameter less than 5mm is less than 5% of the total mass of the pellets.
Example 3
1000kg of phosphorite micro powder, 5kg of required organic binder and 140kg of water. Namely: the mass ratio of the phosphorite micro powder to the organic binder to the water is 100:0.5: 14.
The preparation method of the phosphate ore micro-powder pellets comprises the following steps:
(1) uniformly mixing 5kg of polyvinyl alcohol dry powder and 140kg of water at 75 ℃ to obtain 145kg of organic binder aqueous solution;
(2) adding the aqueous solution of the organic binder into 1000kg of phosphorite micropowder, and then uniformly mixing and stirring for 20min by a mixer to obtain 1145kg of mixed material;
(3) compacting the mixed material on compacting equipment to obtain a compacted material;
(4) pelletizing and molding the compacted material by using a double-roller ball press, and setting the pressure to be 7Mpa to obtain phosphorite micropowder green pellets with the diameter of 8-30 mm;
(5) and (3) burning tail gas generated in the production of yellow phosphorus, pumping high-temperature air generated by burning waste heat in a combustion chamber to a pellet drying chamber through an air pumping system, and drying the phosphorite micropowder green pellets at the drying temperature of 160 ℃ for 50min to obtain the high-strength phosphorite micropowder pellets.
The compressive strength of the obtained phosphate ore micro powder green pellets is 156N/ball, the falling strength of the phosphate ore micro powder green pellets is 124 times/ball 50cm away from the rubber plate, the phosphate ore micro powder green pellets are broken into 4 blocks after falling for 125 times 50cm away from the rubber plate, wherein the mass of the phosphate ore micro powder green pellets with the diameter less than 5mm is 0 percent of the total mass of the pellets; the compression strength of the dried phosphate rock micro-powder agglomerate exceeds 1867N/ball, the falling strength of 50cm away from the rubber plate is 435 times/ball, the dried phosphate rock micro-powder agglomerate falls 436 times away from the rubber plate 50cm, and the phosphate rock micro-powder agglomerate is broken into 2 parts, wherein the mass of the phosphate rock micro-powder agglomerate with the diameter less than 5mm is 0 percent of the total mass of the pellet; the falling strength of 150cm from the rubber plate is 8 times per pellet, and the pellet is broken into 4 parts after falling for 9 times of 150cm from the rubber plate, wherein the mass of the pellet with the diameter of less than 5mm is 0 percent of the total mass of the pellet. It can be seen that the pellets of this example do not produce a pulverization phenomenon after falling, and the pellets will break into several parts after falling for many times, and the mass of the broken parts with the diameter less than 5mm is less than 5% of the total mass of the pellets.
Example 4
The mass ratio of the phosphorite micro powder to the organic binder to the water is 100:0.6:14, namely: 1000kg of phosphorite micro powder, 6kg of required organic binder and 140kg of water.
The method comprises the following steps:
(1) uniformly mixing 6kg of polyvinyl alcohol organic binder dry powder and 140kg of water at 90 ℃ to obtain 146kg of organic binder aqueous solution;
(2) adding the aqueous solution of the organic binder into 1000kg of phosphorite micropowder, and then uniformly mixing and stirring for 20min by a mixer to obtain 1146kg of mixed material;
(3) compacting the mixed material on compacting equipment to obtain a compacted material;
(4) pelletizing and molding the compacted material by using a double-roller ball press, and setting the pressure to be 8Mpa to obtain phosphorite micropowder green pellets with the diameter of 8-30 mm;
(5) and (3) burning tail gas generated in the production of yellow phosphorus, pumping high-temperature air generated by burning waste heat in a combustion chamber to a pellet drying chamber through an air pumping system, and drying the phosphorite micropowder green pellets at the drying temperature of 180 ℃ for 50min to obtain the high-strength phosphorite micropowder pellets.
The compressive strength of the obtained phosphate ore micro powder green pellets is 189N/ball, the falling strength of the phosphate ore micro powder green pellets is 276 times per ball when the phosphate ore micro powder green pellets are 50cm away from a rubber plate, the phosphate ore micro powder green pellets are broken into 3 pieces after falling 277 times when the phosphate ore micro powder green pellets are 50cm away from the rubber plate, wherein the mass of the phosphate ore micro powder green pellets with the diameter less than 5mm is 0 percent of the total mass; the compression strength of the dried phosphate rock micro-powder agglomerate exceeds 2000N/ball, the falling strength of 50cm away from the rubber plate exceeds 500 times/ball, and the dried phosphate rock micro-powder agglomerate still does not crack after falling for 501 times away from the rubber plate, wherein the mass of the diameter of less than 5mm is 0 percent of the total mass of the pellet; the falling strength of 150cm away from the rubber plate is 15 times per pellet, and the pellet is broken into 4 parts after falling for 16 times of 150cm away from the rubber plate, wherein the mass of the pellet with the diameter of less than 5mm is 0 percent of the total mass of the pellet. It can be seen that the pellets of this example do not produce a pulverization phenomenon after falling, and the pellets will break into several parts after falling for many times, and the mass of the broken parts with the diameter less than 5mm is less than 5% of the total mass of the pellets.
Example 5
1000kg of phosphorite micro powder, 4kg of required organic binder and 150kg of water. Namely: the mass ratio of the phosphorite micro powder to the organic binder to the water is 100:0.4: 15.
The method comprises the following steps:
(1) 4kg of polyvinyl alcohol organic binder dry powder and 150kg of water are mixed uniformly at 80 ℃ to obtain 154kg of organic binder aqueous solution.
(2) Adding the aqueous solution of the organic binder into 1000kg of phosphorite micropowder, and then uniformly mixing and stirring for 20min by a mixer to obtain 1154kg of mixed material;
(3) compacting the mixed material on compacting equipment to obtain a compacted material;
(4) pelletizing and molding the compacted material by using a double-roller ball press, and setting the pressure to be 6Mpa to obtain phosphorite micropowder green pellets with the diameter of 8-30 mm;
(5) and (3) burning tail gas generated in the production of yellow phosphorus, pumping high-temperature air generated by burning waste heat in a combustion chamber to a pellet drying chamber through an air pumping system, and drying the phosphorite micropowder green pellets at the drying temperature of 120 ℃ for 60min to obtain the high-strength phosphorite micropowder pellets.
The compressive strength of the obtained phosphate ore micro powder green pellets is 124N/pellet, the falling strength of the phosphate ore micro powder green pellets is 96 times/pellet when the phosphate ore micro powder green pellets are 50cm away from a rubber plate, the phosphate ore micro powder green pellets are broken into 2 parts after the phosphate ore micro powder green pellets fall for 97 times when the phosphate ore micro powder green pellets are 50cm away from the rubber plate, wherein the mass of the phosphate ore micro powder green pellets with the diameter of less than; the compression strength of the dried phosphate rock micro powder agglomerate is 1374N/ball, the falling strength of the phosphate rock micro powder agglomerate is 408 times/ball when the phosphate rock micro powder agglomerate is 50cm away from a rubber plate, the phosphate rock micro powder agglomerate is broken into 4 parts after the phosphate rock micro powder agglomerate falls 409 times when the phosphate rock micro powder agglomerate is 50cm away from the rubber plate, wherein the mass of the phosphate rock micro powder agglomerate with the diameter less than 5mm is 0 percent of the total mass; the falling strength of 150cm from the rubber plate is 8 times per pellet, and the pellet is broken into 3 parts after falling for 9 times of 150cm from the rubber plate, wherein the mass of the pellet with the diameter of less than 5mm is 0 percent of the total mass of the pellet. It can be seen that the pellets of this example do not produce a pulverization phenomenon after falling, and the pellets will break into several parts after falling for many times, and the mass of the broken parts with the diameter less than 5mm is less than 5% of the total mass of the pellets.
Comparative example 1
25g of phosphate rock powder molding adhesive polyvinyl alcohol and 500g of water.
The preparation method of the adhesive comprises the following steps:
(1) heating 500g of water to 65 ℃, adding 25g of polyvinyl alcohol under the stirring condition, stirring at 65 ℃ until the materials are completely dissolved, and cooling to obtain an adhesive A;
adding 2000 g of 100-120 meshes of phosphate rock powder into a mixer, adding 200 g of a binder A component, stirring and mixing for 30min at normal temperature, adding 250 g of a binder B component, stirring and mixing for 30min at normal temperature, sending the uniformly mixed material into a spherical pressure forming device, carrying out pressure forming under the pressure of 3.0MPa to obtain spherical materials with the spherical sizes of phi 20mm, phi 30mm and phi 50mm, and drying for 72 hours under natural conditions to obtain the phosphate rock powder forming material.
Through detection, the compression strength of the green pellets in the process is 54.7N/ball, the falling strength of the green pellets 50cm away from the rubber plate is 8 times/ball, the green pellets are broken into a plurality of parts after falling for 9 times 50cm away from the rubber plate, wherein the mass of the green pellets with the diameter less than 5mm is 8.4 percent of the total mass of the pellets, the compression strength of the dried phosphate rock pellets is 1458N/ball, the falling strength of the green pellets with the diameter less than 50cm away from the rubber plate is 470 times/ball, the green pellets are broken into 5 parts after falling for 471 times 50cm away from the rubber plate, and the mass of the broken parts with the diameter less than 5mm is 0 percent of the total mass of the; the falling strength of 150cm away from the rubber plate is 2 times per ball, the falling strength of 150cm away from the rubber plate is 3 times, the falling strength is broken into a plurality of parts, and the mass of the broken parts with the diameter less than 5mm is 0 percent of the total mass of the pellets. It can be seen that, although the powdered rock phosphate pellets prepared in comparative example 1 do not generate a pulverization phenomenon after the pellets dried under the static non-stacking condition fall, and can be broken into a plurality of parts after falling for a plurality of times, and the mass of the broken parts with the diameter smaller than 5mm is smaller than 5% of the total mass of the pellets, the green pellets prepared in comparative example 1 only have the compressive strength of 54.7 n/ball, and can be broken into a plurality of parts after falling for 9 times with the distance of 50cm from the rubber plate, wherein the mass with the diameter smaller than 5mm is 8.4% of the total mass of the pellets. The green pellets prepared under the condition can only be statically dried, however, during the actual production of enterprises, the green pellets which are just prepared need to be massively stacked and transported to a drying device, so that falling pulverization and crushing by pellet extrusion can be caused, and the returned material amount is increased, so that the green pellet performance of the comparative example 1 can not meet the actual production requirement. In addition, the binder B is required to be added in the comparative example 1, so that the ground phosphate rock forming process becomes complicated, the operation of workers is inconvenient, the pellet production process is difficult to control, the performance of the pellets is unstable, the grade of the ground phosphate rock pellets is reduced by the additive, the power consumption is increased, and the production cost of yellow phosphorus is increased.
Comparative example 2
1000kg of phosphorite micro powder, 1kg of required organic binder and 150kg of water. Namely: the mass ratio of the phosphorite micro powder to the organic binder to the water is 100:0.1: 15.
The method comprises the following steps:
(1) 1kg of polyvinyl alcohol organic binder dry powder and 150kg of water are mixed uniformly at 80 ℃ to obtain 151kg of organic binder aqueous solution.
(2) Adding the aqueous solution of the organic binder into 1000kg of phosphorite micropowder, and then uniformly mixing and stirring for 20min by a mixer to obtain 1151kg of mixed material;
(3) compacting the mixed material on compacting equipment to obtain a compacted material;
(4) pelletizing and molding the compacted material by using a double-roller ball press, and setting the pressure to be 6Mpa to obtain phosphorite micropowder green pellets with the diameter of 8-30 mm;
(5) and (3) burning tail gas generated in the production of yellow phosphorus, pumping high-temperature air generated by burning waste heat in a combustion chamber to a pellet drying chamber through an air pumping system, and drying the phosphorite micropowder green pellets at the drying temperature of 120 ℃ for 60min to obtain the high-strength phosphorite micropowder pellets.
The compressive strength of the obtained phosphate ore micro powder green pellets is 38.4N/pellet, the falling strength of the phosphate ore micro powder green pellets is 2 times/pellet when the phosphate ore micro powder green pellets are 50cm away from a rubber plate, the phosphate ore micro powder green pellets are broken into 5 parts after falling for 3 times when the phosphate ore micro powder green pellets are 50cm away from the rubber plate, wherein the mass of the phosphate ore micro powder green pellets with the diameter less than 5mm is 14.5 percent of the total; the compression strength of the dried phosphate rock micro powder agglomerate is 374N/ball, the falling strength of the phosphate rock micro powder agglomerate is 18 times/ball when the phosphate rock micro powder agglomerate is 50cm away from the rubber plate, and the phosphate rock micro powder agglomerate is broken into 5 parts after the phosphate rock micro powder agglomerate falls for 19 times when the phosphate rock micro powder agglomerate is 50cm away from the rubber plate, wherein the mass of the phosphate rock micro powder agglomerate with the diameter less than 5mm is 5.8 percent of the; the falling strength of 150cm away from the rubber plate is 1 time/ball, and the falling strength of 150cm away from the rubber plate is 2 times, and the falling strength is broken into 5 parts, wherein the mass of the diameter of less than 5mm is 8.6 percent of the total mass of the pellets. It can be seen that when the proportion of the polyvinyl alcohol dosage, the ground phosphate rock and the water is not in the range of the invention, the pulverization phenomenon is generated after the pellets fall, the pellets can be broken into a plurality of parts after falling for a plurality of times, and the mass of the broken parts with the diameter less than 5mm is more than 5 percent of the total mass of the pellets.