A method for preparing pellets from phosphorite powder

Abstract

This invention discloses a method for preparing phosphate rock pellets through pelletizing and roasting. High-calcium and high-silica phosphate rock powders are pretreated and then used together with straw as pelletizing raw materials. After heat treatment, the finished pellets exhibit a concentrated and stable particle size distribution, good permeability, and low pulverization rate under the high-temperature reducing atmosphere of subsequent yellow phosphorus production, significantly reducing dust generation during phosphorus production. Furthermore, the ore produced has high grade, good chemical composition, high strength, and excellent transportability. Its low moisture content and low carbonate content effectively reduce power consumption in subsequent lump ore phosphorus production, improve phosphorus purity, and thus enhance economic efficiency. This method effectively utilizes phosphate rock powder resources, alleviating the raw material shortage problem for yellow phosphorus enterprises. It also effectively reduces raw material costs and saves land resources, aligning with national industrial policies and resource development strategies, and holding significant importance for yellow phosphorus production in my country.

Description

Technical Field

[0001] This invention relates to methods for producing and processing phosphate rock, specifically to a method for preparing phosphate rock pellets by pelletizing and roasting phosphate rock powder, belonging to the field of phosphate rock production and processing technology. Background Technology

[0002] Currently, the main process for producing yellow phosphorus from phosphate rock is the electric furnace method: natural phosphate rock lumps are heated together with a reducing agent in an electric furnace. The reducing agent's reducing properties at high temperatures cause elemental phosphorus to escape as yellow phosphorus vapor. The yellow phosphorus vapor is then cooled and collected to obtain yellow phosphorus. However, this process has high requirements for the phosphate rock raw materials. Generally, the phosphate rock entering the furnace must have uniform particle size, low moisture and carbonate content, a P2O5 content higher than 20%, and a certain thermal strength. To meet production needs, Chinese yellow phosphorus producers mainly use lumpy phosphate rock as raw material.

[0003] With the increasing depletion of high-quality phosphate rock, the amount of high-quality phosphate rock available for yellow phosphorus production is also decreasing, leading to a growing shortage of natural phosphate rock resources and a rising market price. Solving the problem of ore supply for yellow phosphorus production is urgent and has become crucial to ensuring the normal production of yellow phosphorus enterprises.

[0004] At the same time, during the production process of obtaining natural phosphate rock lumps, enterprises will inevitably generate a large amount of phosphate rock powder. This part of high-quality phosphate rock powder cannot be directly used for electric furnace phosphorus production, resulting in the idleness of high-quality phosphate rock resources and waste of resources. On the other hand, a large amount of phosphate rock powder that cannot be directly used for the production of yellow phosphorus is stockpiled in the yard, occupying a lot of space and also causing waste of land resources. Summary of the Invention

[0005] To address the problems in existing technologies, such as the shortage of phosphate rock ore for yellow phosphorus production and the underutilization of high-quality phosphate rock powder during the production of natural phosphate rock ore, leading to resource waste, this invention provides a method for preparing pellets by phosphate rock powder pelletizing and roasting. This method involves pre-treating high-calcium and high-silica phosphate rock powder and then using it together with straw as pelletizing raw materials. The resulting green pellets, after heat treatment, can meet the requirements for yellow phosphorus production. This method effectively utilizes phosphate rock powder resources, alleviating the raw material shortage problem for yellow phosphorus enterprises. Furthermore, it effectively reduces raw material costs and saves land resources, aligning with national industrial policies and resource development strategies, and is of great significance to yellow phosphorus production in my country.

[0006] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is specifically described as follows.

[0007] A method for preparing phosphate rock pellets by pelletizing and roasting, the method comprising the following steps:

[0008] 1) Mix high-calcium phosphate rock powder and high-silica phosphate rock powder to obtain mixed phosphate rock powder. Then grind the mixed phosphate rock powder to obtain fine phosphate rock powder.

[0009] 2) Mix the fine phosphate rock powder with biomass straw to obtain a mixture.

[0010] 3) Add rice slurry to part of the mixture for granulation to obtain phosphate rock pellets.

[0011] 4) According to the set pelletizing index, add water to the phosphate rock pellets and the remaining mixture to pelletize them, and obtain large phosphate rock pellets.

[0012] 5) After heat treatment, the large phosphate rock pellets are used to obtain finished pellets.

[0013] Preferably, in step 1), the high-calcium phosphate rock powder is a phosphate rock powder with a P2O5 content of no more than 15 wt% and a CaO content of no less than 40 wt%. More preferably, it is a phosphate rock powder with a P2O5 content of 10-15 wt% and a CaO content of 45-55 wt%.

[0014] In this invention, the chemical composition of high-calcium phosphate rock powder is generally as follows: P2O5 content is 10-15%, SiO2 content is 10%-15%, CaO content is 40%-55%, Fe2O3 content is 0.5%-1%, Al2O3 content is 3%-5%, MgO content is 1%-2%, F content is 0.1%-0.3%, and S content is 0.5%-0.8%.

[0015] Preferably, in step 1), the high-silica phosphate rock powder is a phosphate rock powder with a P2O5 content of no more than 15 wt% and a SiO2 content of no less than 40 wt%. More preferably, it is a phosphate rock powder with a P2O5 content of 10-15 wt% and a SiO2 content of 45-55 wt%.

[0016] In this invention, the chemical composition of the high-silica phosphate rock powder is generally as follows: P2O5 content is 10-15%, SiO2 content is 40%-55%, CaO content is 20%-25%, Fe2O3 content is 0.5%-1%, Al2O3 content is 3%-5%, MgO content is 1%-2%, F content is 0.1%-0.3%, and S content is 0.5%-0.8%.

[0017] Preferably, in step 1), the mixing mass ratio of high-calcium phosphate rock powder to high-silica phosphate rock powder is 1.2-1.6:1, and more preferably 1.3-1.45:1.

[0018] Preferably, in step 1), both high-calcium phosphate rock powder and high-silica phosphate rock powder require pretreatment before mixing. Specifically, the pretreatment involves washing each powder 1-8 times, preferably 3-5 times. The liquid-to-solid mass ratio during each wash is 1-4:1, preferably 2-3:1. After washing, the powders are then filtered and rapidly dried.

[0019] Preferably, in step 1), the rapid drying specifically employs a rapid hot airflow or microwave rapid drying. The purpose of rapid drying is twofold: first, to shorten the drying time and save time; and second, to prevent partial mineral crystallization within the mineral powder, which could affect subsequent crushing.

[0020] Preferably, the moisture content of the rapidly dried high-calcium phosphate rock powder and the high-silica phosphate rock powder is 6-10% each, and more preferably 8-9%.

[0021] Preferably, in step 1), the grinding process specifically involves using a ball mill, rod mill, or autogenous mill.

[0022] Preferably, in step 1), the particle size of the fine phosphate rock powder is not greater than 0.15 mm, and more preferably not greater than 0.125 mm.

[0023] Preferably, in step 2), the mixing mass ratio of the fine phosphate rock powder to the biomass straw is 88-93:7-12, and more preferably 90-92:8-10.

[0024] Preferably, in step 2), the biomass straw is straw pellets with a particle size of no more than 5 mm, and more preferably straw pellets with a particle size of no more than 3 mm. More preferably, the straw pellets are soaked and dried in a calcium hydroxide solution before mixing. The concentration of the calcium hydroxide solution is 0.01-0.2 mol / L, preferably 0.02-0.1 mol / L.

[0025] In this invention, the straw includes, but is not limited to, corn straw, sorghum straw, rice straw, reed straw, etc.

[0026] Preferably, in step 3), the rice slurry is prepared by crushing and grinding cooked rice, then mixing it with water. The concentration of the rice slurry is 1-10 g / L, preferably 2-8 g / L. The amount of rice slurry added is 5-10% of the mass of the mixture, preferably 7-8%.

[0027] Preferably, in step 3), the particle size of the phosphate rock pellets is 5-10 mm, more preferably 6-8 mm.

[0028] Preferably, in step 4), the pelletizing index is the ratio of the maximum molecular water mass to the maximum capillary water fill value in the pelletizing mixture, where the maximum capillary water fill value is the maximum capillary water mass minus the maximum molecular water mass. Specifically:

[0029]

[0030] Wherein, K is the sphericity index, and the set sphericity index K 定 The value is >0.8, preferably 0.8-0.85, for example, one of 0.81, 0.82, 0.83, 0.84, and 0.85. In this invention, the K value can be appropriately adjusted according to the moisture content and ratio of each raw material so that the final pelletizing mixture reaches K. 定 Requirements.

[0031] Preferably, in step 4), the particle size of the phosphate rock spheres is 15-30 mm, more preferably 18-25 mm. The overall moisture content of the phosphate rock spheres is 6-9%, more preferably 7-8%. More preferably, the moisture content of the outer layer of the phosphate rock spheres is 8-11%, more preferably 9-10%.

[0032] Preferably, in step 5), the heat treatment includes drying, preheating, calcination, and cooling.

[0033] Preferably, the drying process includes pre-drying, re-drying, and deep drying, wherein: the pre-drying temperature is 180-300℃, preferably 200-280℃, and the pre-drying time is 20-60 min, preferably 30-50 min. The re-drying temperature is 350-500℃, preferably 380-450℃, and the re-drying time is 15-40 min, preferably 20-30 min. The deep drying temperature is 500-700℃, preferably 550-650℃, and the deep drying time is 5-30 min, preferably 8-20 min. Preferably, the pre-drying is intermittent microwave drying, and the re-drying and deep drying are both hot air drying.

[0034] Preferably, the preheating temperature is 750-900℃, more preferably 800-850℃, and the preheating time is 5-30 min, more preferably 10-25 min.

[0035] Preferably, the calcination temperature is 1100-1350℃, more preferably 1150-1300℃. The calcination time is 0.1-5h, more preferably 0.2-4h.

[0036] Preferably, the cooling includes pre-cooling and re-cooling, wherein pre-cooling involves cooling the calcined material to 600-800°C, preferably 650-750°C, using room temperature air. Re-cooling involves re-cooling the pre-cooled material to 120-300°C, preferably 150-250°C, using room temperature air.

[0037] Preferably, natural phosphate rock lumps are used as the base material during the heat treatment of the phosphate rock spheres. The particle size of the natural phosphate rock lumps is 15-30 mm, preferably 20-25 mm. The P2O5 content in the natural phosphate rock lumps is 15-25%, preferably 18-20%. The thickness of the base material is 50-85 mm, preferably 60-75 mm. The thickness of the phosphate rock sphere layer is 100-200 mm, preferably 120-180 mm.

[0038] Preferably, the hot air generated from precooling is circulated for preheating. The hot air generated from recooling is circulated for re-drying. The hot air generated from calcination is used for deep drying after dust removal treatment. The hot air generated from re-drying, deep drying, and preheating is discharged after dust removal, desulfurization, and denitrification treatment.

[0039] In this invention, high-calcium phosphate rock powder and high-silica phosphate rock powder are mixed to obtain mixed phosphate rock powder. After grinding, the mixture is further screened to obtain fine phosphate rock powder of the target particle size. The sieve-over-size powder larger than the target particle size is subjected to cyclic grinding.

[0040] In this invention, after pelletizing, the spherical material needs to be screened to select green pellets (large phosphate rock pellets) that meet the particle size requirements for heat treatment. Generally, spherical materials with particle sizes <15mm and >30mm are further crushed and then returned to the mixing step in step 1) for re-mixing. Furthermore, the finished pellets obtained after heat treatment also need to be screened to select finished phosphate pellets that meet the requirements for yellow phosphorus production (generally requiring a pellet particle size of not less than 5mm). Simultaneously, the bulk materials generated in the above screening steps are recovered and returned for batching and briquetting, thereby saving resources and minimizing solid waste emissions. In addition, during the heat treatment process, the dust separated after dust removal from the dried and preheated hot air is also collected. This dust can be humidified and then returned to the batching step to participate in granulation or pelletizing.

[0041] In this invention, the original high-calcium phosphate rock powder and high-silicon phosphate rock powder have relatively coarse particle size and uneven particle size distribution, and cannot be directly used as pelletizing feed. Therefore, it is generally necessary to grind the high-calcium phosphate rock powder and high-silicon phosphate rock powder. Thus, this invention requires grinding the high-calcium phosphate rock powder and high-silicon phosphate rock powder to fine phosphate rock powder with a particle size of no more than 0.15 mm (preferably no more than 1.25 mm).

[0042] In this invention, multiple water washings of phosphate rock powder not only remove sludge and impurities to improve grade, but also disperse and soften the phosphate rock powder, which is beneficial for uniform crushing in the subsequent process. Since the original high-calcium phosphate rock powder and high-silicon phosphate rock powder generally contain sludge and other soluble impurities, they need to be washed multiple times before mixing and grinding to reduce the impurity content of the phosphate rock powder and improve the grade of phosphate rock.

[0043] In this invention, fine phosphate rock powder and biomass straw are mixed and granulated into small balls before being made into large balls. The moisture content of the small balls and the large balls (outer layer) are different. By adopting layered pelletizing, the outer layer of the pellets has high moisture content and the inner layer has low moisture content, which reduces the vapor pressure in the later stage of the pellet drying time and avoids the pellets from bursting in the later stage of drying. At the same time, it also reduces the overall moisture content of the pellets and saves drying energy consumption.

[0044] In this invention, the process of turning green pellets (large phosphate rock pellets) into finished pellets requires transportation and high-temperature heat treatment. During the transportation and distribution process, collisions and compression between pellets are inevitable, and the roasting temperature reaches over 1100℃. This necessitates that the green pellets possess sufficient strength to prevent excessive breakage during transportation and bursting during heat treatment. Therefore, this invention incorporates biomass straw during the formulation process, ensuring its even distribution within the green pellets. This provides diffusion channels for internal moisture during drying, significantly increasing the rate of water vapor escape and effectively preventing bursting caused by rapid evaporation of water molecules at high temperatures. Simultaneously, the fibers of the biomass straw enhance the adhesion between phosphate rock powder particles, improving the strength of the green pellets. Furthermore, the biomass straw provides additional heat during subsequent roasting, aiding in the high-temperature consolidation of the green pellets and further enhancing the physical strength and chemical properties of the finished pellets.

[0045] In this invention, high-calcium phosphate rock and high-silicon phosphate rock are mixed and ground, which greatly expands the range of raw materials. High-silicon phosphate rock has low hardness and is relatively easy to grind, but after fine grinding, it has poor hydrophilicity and a low static pelletizing index (less than 0.25), resulting in weak pelletizing. In contrast, high-calcium phosphate rock has high hardness and is more difficult to grind, but after fine grinding, it has good hydrophilicity and a large static pelletizing index (greater than 0.5), resulting in better pelletizing. The pelletizing index of the phosphate rock fine powder obtained after fine grinding of high-calcium phosphate rock powder and high-silicon phosphate rock powder is generally greater than 0.35, which can meet the green pellet strength requirements without the addition of binders. The combination of high and low hardness allows for material-to-material grinding during the grinding process, reducing grinding energy consumption. At the same time, it can effectively adjust the acidity, and the acidity of the obtained green pellets is greater than 0.85, which can reduce the amount of flux added in subsequent electric furnace phosphorus production.

[0046] In this invention, to further improve the strength of the green pellets, the biomass straw undergoes pretreatment before mixing. Specifically, the biomass straw particles are soaked in a calcium hydroxide solution (e.g., 0.01-1 mol / L) for 0.1-5 hours. After soaking, the biomass straw particles are filtered dry before being added to the batch. Because the biomass straw adsorbs calcium hydroxide, it improves the bonding performance with other materials during the batching process, increasing the strength of the green pellets and significantly reducing the breakage rate during handling. Simultaneously, during subsequent heat treatment, the biomass straw decomposes upon heating, releasing carbon dioxide and water. The released carbon dioxide, under the action of water vapor, reacts with the internal calcium hydroxide to form a compound that acts as a binder (the adsorbed calcium hydroxide solidifies internally as calcium carbonate), further improving the bonding strength between the biomass straw and other raw materials. This helps prevent high-temperature cracking while greatly ensuring and enhancing the strength of the finished phosphate rock pellets and reducing the ore fines rate. It should be noted that the amount of biomass straw added should not be too much or too little. Too much addition will reduce the proportion of fine phosphate rock powder, thus reducing the yield. At the same time, too much straw particles will cause more large pores inside the finished phosphate rock pellets after heat treatment, which will easily lead to the collapse and pulverization of the finished phosphate rock pellets, which is not conducive to improving the strength of the finished phosphate rock pellets. On the other hand, if the amount added is too little, it will not be conducive to improving the internal bonding strength of the green pellets, and the green pellets will easily break apart before heat treatment.

[0047] In this invention, when granulating the mixture (phosphate rock pellets), rice slurry is added to improve the granulation effect, resulting in better particle size distribution and stronger pellets. Furthermore, it provides some heat during subsequent roasting, further enhancing the high-temperature consolidation of the green pellets.

[0048] In this invention, the drying process of green pellets involves intermittent microwave drying and two-stage hot air drying. Microwave heating is used first, allowing for simultaneous heating of the internal and external surfaces of the green pellets. This causes both internal and external moisture to vaporize and diffuse outwards simultaneously, preventing cracking due to uneven drying. Furthermore, the three-stage drying process of this invention is a variable-temperature drying method. The drying stages are divided into multiple sections arranged in a sequence from low to high temperature and from long to short time. Compared to conventional drying, this increases the drying speed, shortens the drying time, avoids cracking of the green pellets, and improves their strength.

[0049] In this invention, natural phosphate rock lumps with a grade higher than that of raw pellets are used as a base material. This mixing method can improve the average grade of the finished pellets. At the same time, the metallurgical properties of the natural phosphate rock lumps are further improved after heat treatment. Using natural phosphate rock lumps as a base material increases permeability and protects the roasting equipment. By selecting an appropriate base material thickness, production capacity is also increased.

[0050] In this invention, to reduce heat emissions and save energy, the hot air emitted from each node of the system is selectively recycled based on the characteristics of each operating condition within the system. Specifically, the hot air generated during cooling is recycled to provide heat for processes such as drying and preheating. Furthermore, waste heat is fully recovered through cascade utilization, significantly reducing the energy consumption for additional heating. In addition, this invention can also recycle and reuse various bulk materials and dust generated during the process, realizing the recycling of valuable resources and contributing to environmental protection.

[0051] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0052] 1. This invention couples high-calcium phosphate rock powder and high-silicon phosphate rock powder, which cannot be reused in existing phosphate rock processing, to solve the problem of resource waste caused by the large amount of stockpiled phosphate rock powder in existing phosphate rock processing, as well as the problem of land resource waste caused by large-scale stockpiling. It realizes the efficient reuse of phosphate rock powder as a resource and also greatly saves land resources.

[0053] 2: This invention adds biomass straw during the mixing and pelleting process. Through the bridging effect of biomass straw, the strength of the green pellets is further improved, while the bursting loss of the pellets during heat treatment is greatly reduced. This effectively ensures the quality and yield of the finished lump mineral products. It also helps to accommodate more bulk and powder materials, improves resource recovery efficiency, and reduces environmental pollution.

[0054] 3. The finished pellets obtained by this invention have a concentrated and stable particle size distribution, good permeability, and low pulverization rate under the high-temperature reducing atmosphere of subsequent yellow phosphorus production, which can greatly reduce the amount of dust in phosphorus production. Furthermore, the ore has high grade, good chemical composition, and high strength, facilitating subsequent transportation and exhibiting strong transportability. Its low moisture content and low carbonate content can effectively reduce the power consumption of subsequent lump ore phosphorus production, improve phosphorus purity, and thus enhance economic benefits. Attached Figure Description

[0055] Figure 1 This is a process flow diagram of the method described in this invention. Detailed Implementation

[0056] The technical solution of the present invention will be illustrated below with examples. The scope of protection sought by the present invention includes, but is not limited to, the following embodiments.

[0057] Example 1

[0058] High-calcium phosphate rock powder (P2O5 content approximately 13.6%, CaO content approximately 47.2%) and high-silica phosphate rock powder (P2O5 content approximately 14.4%, SiO2 content approximately 45.8%) were each subjected to three separate water washing treatments (the liquid-to-solid mass ratio of each water washing was 3:1). Then, they were rapidly dried using microwave to obtain dried high-calcium phosphate rock powder (moisture content approximately 7.9%) and high-silica phosphate rock powder (moisture content approximately 8.0%). The dried high-calcium phosphate rock powder and the dried high-silica phosphate rock powder were mixed evenly at a mass ratio of 5.5:4 to obtain mixed phosphate rock powder. The mixed phosphate rock powder was then ground, and the powder with a particle size of less than or equal to 0.125 mm was collected as fine phosphate rock powder.

[0059] Corn stalks are crushed to a particle size of less than 3 mm to obtain stalk pellets. Then, fine phosphate rock powder and stalk pellets are mixed evenly at a mass ratio of 90:10 to obtain a mixture. Rice slurry with a concentration of 6 g / L and 7.5% of the mixture mass is added to the mixture for granulation to obtain phosphate rock pellets with an average particle size of about 7 mm.

[0060]

[0061] Using phosphate rock pellets as the core, more mixture and water are added to form pellets, resulting in phosphate rock pellets with an average particle size of about 20 mm (the overall moisture content is about 8.2%, and the moisture content of the outer layer of the pellets is about 9.5%).

[0062] Natural lump ore with an average particle size of 22 mm (P2O5 content approximately 20.8%) was laid as the bottom material for the trolley, with a thickness of 70 mm. Then, a layer of green pellets (large phosphate rock pellets) was laid on top of the bottom material, with a thickness of 170 mm. After laying, the mixture layer was dried using microwave at 280℃ for 30 min, followed by drying with hot air at 450℃ for 25 min, and finally drying with hot air at 550℃ for 15 min. After drying, the mixture layer was preheated with hot air at 800℃ for 10 min. After preheating, natural gas (9000 kcal / Nm³) was used... 3 The mixture of phosphate rock and air is then burned to form a calcined layer at 1250℃ for 25 minutes. After calcination, the calcined clinker is cooled to approximately 700℃ using room temperature air, and then further cooled to approximately 180℃ using room temperature hot air. After cooling, the clinker is sieved, and clinker pellets ≥5mm in size are collected as finished phosphate rock pellets.

[0063] Example 2

[0064] Repeat Example 1, except that the dried high-calcium phosphate rock powder and the dried high-silica phosphate rock powder are mixed at a mass ratio of 5:4.

[0065] Example 3

[0066] Repeat Example 1, except that the dried high-calcium phosphate rock powder and the dried high-silica phosphate rock powder are mixed at a mass ratio of 6:4.

[0067] Example 4

[0068] Example 1 was repeated, except that the mass ratio of fine phosphate rock powder to straw pellets was 88:12.

[0069] Example 5

[0070] Example 1 was repeated, except that the mass ratio of fine phosphate rock powder to straw pellets was 92:8.

[0071] Example 6

[0072] Example 1 was repeated, except that before mixing the straw pellets with the phosphate rock powder, the mixture was first soaked in a 0.02 mol / L calcium hydroxide solution for 1 hour and then filtered dry to obtain modified straw pellets.

[0073] Comparative Example 1

[0074] Repeat Example 1, except that only high-calcium phosphate rock powder is used.

[0075] Comparative Example 2

[0076] Repeat Example 1, except that only high-silica phosphate rock powder is used.

[0077] Comparative Example 3

[0078] Repeat Example 1, except that the dried high-calcium phosphate rock powder and the dried high-silica phosphate rock powder are mixed at a mass ratio of 1:1.

[0079] Comparative Example 4

[0080] Repeat Example 1, except that the dried high-calcium phosphate rock powder and the dried high-silica phosphate rock powder are mixed at a mass ratio of 4:5.

[0081] Comparative Example 5

[0082] Repeat Example 1, except that biomass straw was not used.

[0083] Comparative Example 6

[0084] Repeat Example 1, except without washing and rapid drying.

[0085] Result detection

[0086] The finished phosphate rock pellets obtained in each of the above embodiments and comparative examples were subjected to various quality tests, and the test results are shown in the table below:

[0087]

[0088]

Claims

1. A method for preparing phosphate rock pellets by pelletizing and roasting, characterized in that: The method includes the following steps: 1) High-calcium phosphate rock powder and high-silica phosphate rock powder are washed with water 1-8 times respectively. After washing, they are filtered and rapidly dried. The high-calcium phosphate rock powder and high-silica phosphate rock powder are mixed to obtain mixed phosphate rock powder. Then, the mixed phosphate rock powder is ground to obtain fine phosphate rock powder. The high-calcium phosphate rock powder is phosphate rock powder with a P2O5 content of not more than 15 wt% and a CaO content of not less than 40 wt%. The high-silica phosphate rock powder is phosphate rock powder with a P2O5 content of not more than 15 wt% and a SiO2 content of not less than 40 wt%. The mixing mass ratio of high-calcium phosphate rock powder to high-silica phosphate rock powder is 1.2-1.6:

1. 2) The fine phosphate rock powder and biomass straw are mixed to obtain a mixture; the mixing mass ratio of the fine phosphate rock powder to the biomass straw is 88-93:7-12; the straw particles are soaked and filtered dry in calcium hydroxide solution before mixing. 3) Add rice slurry to a portion of the mixture for granulation to obtain phosphate rock pellets; the concentration of the rice slurry is 1-10 g / L; the amount of rice slurry added is 5-10% of the mass of the mixture. 4) According to the set pelletizing index, water is added to the phosphate rock pellets and the remaining mixture to form larger phosphate rock pellets; 5) After heat treatment of the phosphate rock pellets, the finished pellets are obtained.

2. The method according to claim 1, characterized in that: In step 1), the high-calcium phosphate rock powder is phosphate rock powder with a P2O5 content of 10-15 wt% and a CaO content of 45-55 wt%; and / or In step 1), the high-silica phosphate rock powder is phosphate rock powder with a P2O5 content of 10-15wt% and a SiO2 content of 45-55wt%.

3. The method according to claim 1, characterized in that: In step 1), the mixing mass ratio of high-calcium phosphate rock powder to high-silica phosphate rock powder is 1.3-1.45:

1.

4. The method according to claim 1, characterized in that: High-calcium phosphate rock powder and high-silica phosphate rock powder are washed with water 3-5 times respectively; the liquid-solid mass ratio during a single water wash is 1-4:

1.

5. The method according to claim 1, characterized in that: The rapid drying specifically refers to the use of rapid hot airflow or microwave rapid drying.

6. The method according to claim 5, characterized in that: After rapid drying, the moisture content of high-calcium phosphate rock powder and high-silica phosphate rock powder are 6-10% each.

7. The method according to claim 6, characterized in that: After rapid drying, the moisture content of high-calcium phosphate rock powder and high-silica phosphate rock powder are 8-9% each.

8. The method according to claim 1, characterized in that: In step 1), the grinding process specifically involves using ball milling, rod milling, or autogenous milling; the particle size of the fine phosphate rock powder is no greater than 0.15 mm.

9. The method according to claim 8, characterized in that: In step 1), the particle size of the fine phosphate rock powder is no greater than 0.125 mm.

10. The method according to claim 1, characterized in that: In step 2), the mixing mass ratio of the fine phosphate rock powder to the biomass straw is 90-92:8-10.

11. The method according to claim 1, characterized in that: The biomass straw is straw particles with a particle size of no more than 5 mm.

12. The method according to claim 11, characterized in that: The biomass straw is straw particles with a particle size of no more than 3 mm.

13. The method according to claim 1, characterized in that: In step 3), the rice slurry is prepared by crushing and grinding cooked rice and mixing it with water; the concentration of the rice slurry is 2-8 g / L; and the amount of rice slurry added is 7-8% of the mass of the mixture.

14. The method according to claim 1, characterized in that: The particle size of the phosphate rock pellets is 5-10 mm.

15. The method according to claim 14, characterized in that: The particle size of the phosphate rock pellets is 6-8 mm.

16. The method according to any one of claims 1-15, characterized in that: In step 4), the pelleting index is the ratio of the maximum molecular water mass to the maximum capillary water surplus in the pelleting mixture, where the maximum capillary water surplus is the maximum capillary water mass minus the maximum molecular water mass; specifically: ； Wherein, K is the sphericity index, and the set sphericity index K 定 The value is greater than 0.

8.

17. The method according to claim 16, characterized in that: K 定 The value ranges from 0.8 to 0.

85.

18. The method according to claim 1, characterized in that: The particle size of the phosphate rock pellets is 15-30 mm; the overall moisture content of the phosphate rock pellets is 6-9%.

19. The method according to claim 18, characterized in that: The particle size of the phosphate rock pellets is 18-25 mm; the overall moisture content of the phosphate rock pellets is 7-8%.

20. The method according to claim 18, characterized in that: The moisture content of the outer layer of the phosphate rock spheres is 8-11%.

21. The method according to claim 20, characterized in that: The moisture content of the outer layer of the phosphate rock spheres is 9-10%.

22. The method according to any one of claims 1-15, characterized in that: In step 5), the heat treatment includes drying, preheating, calcination, and cooling.

23. The method according to claim 22, characterized in that: The drying process includes pre-drying, re-drying, and deep drying, wherein: the pre-drying temperature is 180-300℃ and the pre-drying time is 20-60 min; the re-drying temperature is 350-500℃ and the re-drying time is 15-40 min; and the deep drying temperature is 500-700℃ and the deep drying time is 5-30 min.

24. The method according to claim 23, characterized in that: The pre-drying temperature is 200-280℃ and the pre-drying time is 30-50 min; the re-drying temperature is 380-450℃ and the re-drying time is 20-30 min; the deep drying temperature is 550-650℃ and the deep drying time is 8-20 min.

25. The method according to claim 23, characterized in that: Pre-drying is done by intermittent microwave drying, while re-drying and deep drying are both done by hot air drying.

26. The method according to claim 23, characterized in that: The preheating temperature is 750-900℃, and the preheating time is 5-30 minutes.

27. The method according to claim 26, characterized in that: The preheating temperature is 800-850℃, and the preheating time is 10-25 minutes.

28. The method according to claim 26, characterized in that: The roasting temperature is 1100-1350℃; the roasting time is 0.1-5h.

29. The method according to claim 28, characterized in that: The roasting temperature is 1150-1300℃; the roasting time is 0.2-4h.

30. The method according to claim 28, characterized in that: The cooling includes pre-cooling and re-cooling, wherein pre-cooling is cooling the roasted material to 600-800°C using room temperature air; and re-cooling is cooling the pre-cooled material to 120-300°C using room temperature air.

31. The method according to claim 30, characterized in that: Pre-cooling involves cooling the roasted material to 650-750℃ using room temperature air; re-cooling involves further cooling the pre-cooled material to 150-250℃ using room temperature air.

32. The method according to claim 30, characterized in that: In the heat treatment process of phosphate rock spheres, natural phosphate rock lumps are used as the base material; the particle size of the natural phosphate rock lumps is 15-30 mm; the P2O5 content in the natural phosphate rock lumps is 15-25%; the thickness of the base material is 50-85 mm; the thickness of the phosphate rock sphere layer is 100-200 mm; and / or The hot air generated from pre-cooling is circulated as preheating air; the hot air generated from re-cooling is circulated as re-drying air; the hot air generated from roasting is used as deep drying air after dust removal treatment; the hot air generated from re-drying, deep drying and preheating is discharged after dust removal, desulfurization and denitrification treatment.

33. The method according to claim 32, characterized in that: The particle size of the natural phosphate rock lumps is 20-25mm; the P2O5 content in the natural phosphate rock lumps is 18-20%; the thickness of the base material is 60-75mm; and the thickness of the phosphate rock sphere layer is 120-180mm.

Images