Calcium phosphate pellet and preparation method thereof

Abstract

The invention relates to a calcium phosphate pellet and a preparation method thereof.The calcium phosphate pellet is prepared through the following steps that calcium phosphate is ground and screened, the calcium phosphate is screened through 40-mesh, 60-mesh and 100-mesh screens respectively, and calcium phosphate powder mixtures with different granularities are obtained and marked as first materials; adding the first material and the auxiliary powder into a mixer, and uniformly mixing to obtain a second material; adding a binder into the second material, and uniformly mixing to obtain a mixture I; adding a carbon source into the mixture I, uniformly mixing, uniformly adding industrial water through a spraying device, and uniformly mixing to obtain a mixture II; pelletizing the second mixture through a material pressing machine, and then sequentially performing curing treatment, roasting treatment and cooling treatment to obtain the calcium phosphate pellets. The prepared calcium phosphate pellets are high in compressive strength and high in green pellet forming rate, the bulk density of calcium phosphate products is greatly reduced, transportation and storage are convenient, the roasting temperature in the preparation method is low, and energy consumption is greatly reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of inorganic phosphorus chemical product processing, and particularly relates to a calcium phosphate pellet and a preparation method thereof. Background Art

[0002] Currently, calcium phosphate products in the phosphorus chemical industry are generally available in powder form. The fineness of the powder can easily lead to dust pollution during production and packaging, as well as blockage of transport pipelines during powder delivery, which reduces industrial production efficiency. To ensure convenient storage and transportation of calcium phosphate salts and meet the production needs of phosphorus chemical products and other related products, the calcium phosphate powder is generally prepared into pellets for external sale. Sometimes, in hot and humid regions where the phosphorus chemical industry is located, calcium phosphate salt products are dried to a moisture content of less than 2.5% for long-distance transportation and storage to prevent water absorption and denaturation of the raw materials. However, this low moisture content makes it difficult for the pellets to form effectively in the pelletizing tray and also affects the compressive strength of the green pellets.

[0003] Traditional pelletizing methods include briquetting and pelletizing. Brilling involves uniformly mixing all required materials, pressing them into pellets using a double-roller briquetting machine, and then drying them to form finished pellets. However, the briquetting process places strict demands on the selection and ratio of powder additives and binders. This high ratio of powder additives to binders often results in pellets clinging to each other. Furthermore, existing calcium phosphate pellets suffer from low pelletization rates and low compressive strength, resulting in secondary losses of raw materials and energy consumption, hindering the widespread application of calcium phosphate products.

[0004] This preparation method is also applicable to the pelletizing process of phosphate rock powder and is economical. Compared with the phosphate concentrate powder pelletizing method and phosphate concentrate powder pellets disclosed in Chinese patent CN118108195A, the phosphate concentrate powder pellets contain a high silica content of 17.6%, and the introduction of impurities such as potassium chloride causes the pellets to stick together. The pelletizing process involves adding water to the powdered material and a certain amount of additives to moisten and mix them thoroughly, then using a disc pelletizer. Through simple reciprocating rolling, the pellets continuously grow into round pellets as the disc pelletizer rotates. The resulting raw pellets are then calcined at high temperature to obtain finished pellets. The pelletizing process requires further screening of pellets that do not meet the required size. These pellets must be re-pelletized in the disc pelletizer, which is time-consuming and labor-intensive. Furthermore, the pelletizing process requires calcination at temperatures exceeding 1000°C to increase compressive strength, consuming a large amount of energy.

[0005] Chinese patent CN118125400A discloses a method for preparing yellow phosphorus, in which green phosphate ore pellets are dried and preheated three times, and the preheated material is roasted at 1100-1350°C for 0.2-5 hours. The preheating and roasting processes consume a large amount of electricity and energy. In addition, the pelletizing technology has disadvantages such as difficulty in controlling pellet size, uneven distribution of pellet components, and difficulty in measuring pellet dosage during use. Summary of the Invention

[0006] The present invention aims to provide a calcium phosphate pellet and a preparation method thereof. The prepared calcium phosphate pellet has high compressive strength and a high green ball formation rate, greatly reduces the bulk density of the calcium phosphate product, is convenient for transportation and storage, and can be used for the pelletization of phosphate rock powder. In addition, the roasting temperature in the preparation method is low, which greatly reduces energy consumption.

[0007] The technical solution adopted by the present invention to solve the above problems is: a calcium phosphate pellet, the raw materials of the calcium phosphate pellet include calcium phosphate powder, auxiliary powder, binder, industrial water and carbon source, and the calcium phosphate powder is a mixture of 40 mesh calcium phosphate powder, 60 mesh calcium phosphate powder and 100 mesh calcium phosphate powder.

[0008] Preferably, the additive powder comprises silica and limestone, with the silica mass ratio being 0.5-2.5% (compared to the total mass of all materials) and the limestone mass ratio being 0.5-2.5% (compared to the total mass of all materials). The silica and calcium oxide in the additive powder are used to improve the lack of adhesion of the calcium phosphate powder. In the resulting calcium phosphate pellets, calcium silicate is produced through hydration, cross-linking the calcium phosphate at the molecular level and overcoming the difficulty of calcium phosphate pelletization. The combined action of silica and calcium oxide on the surface corrects the problem of the calcium phosphate raw material being too small in particle size or too much fine powder, thereby increasing the permeability of the pellets.

[0009] Preferably, the binder is at least one of clay, kaolin, alumina, and bentonite. Adding a binder can adjust the moisture content of the pellet material, significantly increase the viscosity of the solution between the particles in the raw ball, and produce strong chemical adsorption on the particle surface, thereby enhancing the hydrophilicity of the particle surface, thereby increasing the corresponding chemical reaction energy, viscous reaction energy, and capillary attraction energy, so that the components in the pellet interact more fully during the curing process, which is beneficial to improving the compressive strength of the raw ball. Among them, kaolin and alumina provide rigidity to the pellets, and the selected powder particle size range is large, which can regulate the internal pores of the calcium phosphate salt, so that the resulting calcium phosphate salt pellets do not explode at a high temperature of 1000°C and have certain compressive resistance and wear resistance; clay fully utilizes the low fineness and smoothness of the powder on the outside of the calcium phosphate salt, wrapping a large number of coarse particles as the outer layer, overcoming the difficulties of calcium phosphate salt pelletizing technology.

[0010] Preferably, the carbon source is at least one of coke powder, maltose, and cyclodextrin. The addition of the carbon source ensures that the carbon dioxide and water in the pellets are consumed during the pellet roasting process or when the pellets are subsequently used as sintering raw materials, and maintains a reducing environment for the pellets at high temperatures, thereby preventing changes in the properties of the pellets.

[0011] A method for preparing calcium phosphate pellets comprises the following steps: Step 1: Grind and sieve the calcium phosphate salt, respectively passing it through 40-mesh, 60-mesh, and 100-mesh sieves to obtain calcium phosphate powders of different particle sizes, which are recorded as the first material; Step 2: Add the first material and the powder additive into a mixer and mix them evenly to obtain the second material; Step 3: Adding a binder to the second material and mixing uniformly to obtain a first mixture; Step 4: Add the carbon source to the mixture 1 and mix evenly, then evenly add industrial water through a spray device and mix evenly to obtain the mixture 2; Step 5: The mixed material 2 is pelletized by a press, and then subjected to curing treatment, roasting treatment, and cooling treatment in sequence to obtain calcium phosphate pellets.

[0012] Preferably, in step 2, the amount of the powder additive added is 1-5% of the total mass of all materials.

[0013] Preferably, in step 3, the amount of the binder added is 0.1-1.5% of the total mass of all materials. The binder can increase the ball formation rate and pellet performance of the calcium phosphate salt. If the binder dosage is too low, there will be insufficient bonding between the mixed materials, resulting in poor pellet strength and low ball formation rate, which will not meet the subsequent product recycling production standards; if the binder dosage is too high, the finished balls will stick to the ball pressing device, making demolding difficult and increasing costs.

[0014] Preferably, in step 4, the amount of the carbon source added is 0.2-1% of the total mass of all materials, and the amount of industrial water added is not more than 5% of the total mass of all materials. The amount of industrial water added affects the ball formation rate and pellet performance of the raw balls. The calcium phosphate powders are more likely to adhere to each other due to the increase in film water. At the same time, the film water acts as a lubricant, increasing the mutual sliding between the particles, which can improve the falling strength of the raw balls. If the industrial water content is too little, the binder cannot be fully dissolved, reducing the adhesion between the calcium phosphate powders; if the industrial water content is too much, the adsorption force between the calcium phosphate particles is reduced, the adhesion of the binder per unit volume is reduced, and the compressive strength of the pellets is reduced. At the same time, the water content is too much, causing the pellets to stick to the ball pressing device and cannot be demoulded smoothly.

[0015] Preferably, in step five, the curing temperature is 40-80°C, and the curing time is 30-120min; the roasting temperature is 400-600°C, and the roasting time is 15-60min; the cooling temperature is room temperature, and the cooling time is 18min. Among them, the curing temperature and roasting temperature affect the dry ball compressive strength. The temperature will affect the adhesion between the binder and the mineral powder and the volatilization of the binder itself. The curing time is appropriate to increase the combination of moisture and binder inside the pellet, increase the interaction between the mineral powders, and improve the overall performance of the pellet. The roasting temperature and time have a greater impact on the dry ball compressive strength. The compressive strength increases with the extension of the roasting time. After the roasting time increases, the amount of melted and resolidified material inside the pellet increases, the granular calcium hydrogen phosphate powder decreases, the distance between the materials decreases, and the interaction is more sufficient, thereby making the internal structure of the pellet more compact. However, the continuous increase in roasting time and temperature will lead to the problem of increased power consumption.

[0016] Compared with the prior art, the advantages of the present invention are: (1) The temperature in the curing and roasting stages of the calcium phosphate pellet preparation method of the present invention is significantly reduced, and through a reasonable raw material ratio, not only can the compressive strength and pelletization rate of the calcium phosphate pellet be significantly improved, but also the chemical composition is stable and the impurity content is low, which greatly reduces the bulk density of the calcium phosphate product, facilitates transportation and storage, and greatly reduces power and energy losses, thereby reducing costs.

[0017] (2) In the preparation method of calcium phosphate pellets of the present invention, calcium phosphate raw materials with different coarse and fine particles are obtained by grinding and screening. During the pelletizing process, the particles of different coarse and fine particles are closely arranged, the molecular interaction force is strong, and the pelletizing property is good.

[0018] (3) The addition of a carbon source to the raw material of the calcium phosphate pellets of the present invention is beneficial to the improvement of the reducibility, and the addition of silicon dioxide and calcium oxide as auxiliary powders has the same composition as the raw material of the calcium phosphate, does not introduce impurities, and the impurity content of the prepared pellets is low. In addition, the amount of binder added in the present invention is low and the materials are simple and easy to obtain. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The figure is a process flow chart of calcium phosphate pellets of the present invention.

[0020] Figure 2 This is a picture of the finished product of calcium phosphate pellets in Example 3 of the present invention. DETAILED DESCRIPTION

[0021] The present invention will be described in further detail below with reference to the accompanying drawings and embodiments.

[0022] like Figure 1 As shown, this is a process flow chart of the calcium phosphate pellets of the present invention.

[0023] The percentages of powder additives, binders, carbon sources and industrial water added are based on the total mass of all materials. Example 1

[0024] (1) Grinding and screening the calcium phosphate salt, respectively passing through 40-mesh, 60-mesh, and 100-mesh sieves to obtain a mixture of calcium phosphate powders of different particle sizes, and mixing the three powders in a mass ratio of 1:1:1 to obtain the first material.

[0025] (2) Adding silicon dioxide and calcium oxide as powdering agents to the first material, and mixing them evenly in a mixer to obtain a second material, wherein the mass percentage of the first material is 93.1%, the mass percentage of silicon dioxide is 0.5%, and the mass percentage of calcium oxide is 0.5%.

[0026] (3) Add 0.5% by weight of clay to the second material, mix well, and obtain a mixture 1.

[0027] (4) Add 0.4% by weight of carbon source to mixture 1 and mix evenly, then spray 5% by weight of industrial water evenly through a spraying device, and mix evenly to obtain mixture 2.

[0028] (5) After the mixture is evenly mixed, it is pelletized by a press to obtain calcium phosphate green balls; then it is subjected to curing treatment, roasting treatment, and cooling treatment in sequence to obtain calcium phosphate pellets. Among them, the curing temperature is 40℃, the curing time is 40 minutes, the roasting temperature is 400℃, the constant temperature is 15 minutes, and the cooling temperature is room temperature, and the cooling time is 18 minutes.

[0029] Comparative Example 1 The only difference between Comparative Example 1 and Example 1 is that calcium phosphate powder of the same particle size (calcium phosphate with a 60-mesh sieve) is used as the raw material.

[0030] Specifically: (1) Grind and sieve the calcium phosphate salt, and pass it through a 60-mesh sieve to obtain the calcium phosphate salt with a 60-mesh sieve, which is used as the first material.

[0031] (2) Add silicon dioxide and calcium oxide as powder additives to the first material, and mix them evenly in a mixer to obtain a second material. The mass percentage of the first material is 93.1%, the mass percentage of silicon dioxide is 0.5%, and the mass percentage of calcium oxide is 0.5%.

[0032] (3) Add 0.5% by weight of clay to the second material, mix well, and obtain a mixture 1.

[0033] (4) Add 0.4% by weight of carbon source to mixture 1 and mix evenly, then spray 5% by weight of industrial water evenly through a spraying device, and mix evenly to obtain mixture 2.

[0034] (5) After the mixture is mixed evenly, it is pelletized by a press to obtain calcium phosphate green balls. It is then subjected to curing, roasting, and cooling treatments to obtain calcium phosphate pellets. The curing temperature is 40°C for 40 minutes, and the roasting temperature is 400°C for 15 minutes. Example 2

[0035] (1) Grind and sieve the calcium phosphate salt, and pass it through 40-mesh, 60-mesh, and 100-mesh sieves to obtain a mixture of calcium phosphate powders of different particle sizes. The three powders are mixed in a mass ratio of 0.5:1:1 to obtain the first material.

[0036] (2) Adding silicon dioxide and calcium oxide as powdering agents to the first material, and mixing them evenly in a mixer to obtain a second material, wherein the mass percentage of the first material is 92.4%, the mass percentage of silicon dioxide is 2%, and the mass percentage of calcium oxide is 1.5%.

[0037] (3) Add 0.5% by weight of bentonite to the second material, mix well, and obtain a mixture 1.

[0038] (4) Add 0.4% by mass of carbon source to mixture 1 and mix evenly, then spray 3.2% by mass of industrial water evenly through a spraying device, and mix evenly to obtain mixture 2.

[0039] (5) After the mixture is evenly mixed, it is pelletized by a press to obtain calcium phosphate green balls; then it is cured, roasted, and cooled in sequence to obtain calcium phosphate pellets, wherein the curing temperature is 60°C, the curing time is 30 minutes, the roasting temperature is 400°C, the constant temperature is 15 minutes, the cooling temperature is room temperature, and the cooling time is 18 minutes.

[0040] Comparative Example 2 The difference between Comparative Example 2 and Example 2 is that no powder additive is added.

[0041] (1) Grind and sieve the calcium phosphate salt, pass it through 40-mesh, 60-mesh, and 100-mesh sieves, and obtain a mixture of calcium phosphate salt powders of different particle sizes. The three powders are mixed in a ratio of 0.5:1:1 to obtain the first material.

[0042] (2) Without adding any powder additives to the first material 1, directly use 95.9% of the first material by mass, and mix them evenly in a mixer to obtain the second material.

[0043] (3) Add 0.5% by weight of bentonite to the second material, mix well, and obtain a mixture 1.

[0044] (4) Add 0.4% by mass of carbon source to mixture 1 and mix evenly, then spray 3.2% by mass of industrial water evenly through a spraying device, and mix evenly to obtain mixture 2.

[0045] (5) After the mixture is evenly mixed, it is pelletized by a press to obtain calcium phosphate green balls; then it is cured, roasted, and cooled in sequence to obtain calcium phosphate pellets, wherein the curing temperature is 60°C, the curing time is 30 minutes, the roasting temperature is 400°C, the constant temperature is 15 minutes, the cooling temperature is room temperature, and the cooling time is 18 minutes. Example 3

[0046] (1) Grind and sieve the calcium phosphate salt, pass it through 40-mesh, 60-mesh, and 100-mesh sieves, and obtain a mixture of calcium phosphate salt powders of different particle sizes. The three powders are mixed in a ratio of 1:1:0.5 to obtain the first material.

[0047] (2) Adding silicon dioxide and calcium oxide as powdering agents to the first material, and mixing them evenly in a mixer to obtain a second material, wherein the mass percentage of the first material is 90.1%, the mass percentage of silicon dioxide is 1.5%, and the mass percentage of calcium oxide is 2.5%.

[0048] (3) Add 0.5% by weight of kaolin, 0.2% by weight of bentonite, and 0.3% by weight of clay to the second material, and mix well to obtain a first mixture.

[0049] (4) Add 0.4% by mass of carbon source to mixture 1 and mix evenly, then spray 4.5% by mass of industrial water evenly through a spraying device, and mix evenly to obtain mixture 2.

[0050] (5) After the mixture is evenly mixed, it is pelletized by a press to obtain calcium phosphate green balls; then it is cured, roasted, and cooled in sequence to obtain calcium phosphate pellets, wherein the curing temperature is 60°C, the curing time is 30 minutes, the roasting temperature is 500°C, the constant temperature is 20 minutes, the cooling temperature is room temperature, and the cooling time is 18 minutes.

[0051] The finished product of calcium phosphate pellets in Example 3 is shown in FIG. Figure 2 As shown, the pellets are cylindrical with a diameter of 5 cm and a height of 15 cm. The surface of the pellets is smooth, the texture is uniform, and the edges of the pellets are neat, indicating that the calcium phosphate raw materials, the auxiliary powder and the binder are mixed relatively evenly, and the pellet particles interact closely.

[0052] Comparative Example 3 The only difference between Comparative Example 3 and Example 3 is that no adhesive is added.

[0053] Specifically: (1) Grind and sieve the calcium phosphate salt, and pass it through 40, 60, and 100 mesh sieves respectively to obtain a mixture of calcium phosphate salt powders with different particle sizes. The three powders are mixed in a mass ratio of 1:1:0.5 to obtain the first material.

[0054] (2) Adding silicon dioxide and calcium oxide as powdering agents to the first material, and mixing them evenly in a mixer to obtain a second material, wherein the mass percentage of the first material is 90.1%, the mass percentage of silicon dioxide is 1.5%, and the mass percentage of calcium oxide is 2.5%.

[0055] (3) Add 1% of the mass of the first material to the second material, mix them evenly, and obtain a mixed material 1.

[0056] (4) Add 0.4% by mass of carbon source to mixture 1 and mix evenly, then spray 4.5% by mass of industrial water evenly through a spraying device, and mix evenly to obtain mixture 2.

[0057] (5) After the mixture is evenly mixed, it is pelletized by a press to obtain calcium phosphate green balls; then it is cured, roasted, and cooled in sequence to obtain calcium phosphate pellets, wherein the curing temperature is 60°C, the curing time is 30 minutes, the roasting temperature is 500°C, the constant temperature is 20 minutes, the cooling temperature is room temperature, and the cooling time is 18 minutes.

[0058] The physical properties of the calcium phosphate pellets obtained in Examples 1-3 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1.

[0059] Table 1

[0060] Comparing the performance of the raw and finished balls in Example 1 with that in Comparative Example 1, it can be seen that after the calcium phosphate raw materials of different particle sizes are mixed in a certain proportion in Example 1, the drop strength of the raw balls and the compressive strength of the finished balls are both improved. This indicates that calcium phosphate salts of different coarse and fine particles are obtained by grinding and screening, and then mixed in a certain proportion before being formed into balls. During the mechanical ball pressing process, the particles of different coarse and fine sizes are arranged more closely, and after curing and roasting, the molecular interaction between the particles and the powder is strong, thereby improving the ball forming performance.

[0061] Comparing the performance of the raw balls and finished balls in Example 2 with that in Comparative Example 2, it can be seen that the raw ball loss rate in Example 2 with the addition of the powder aid is lower. This shows that the addition of silicon dioxide and calcium oxide can effectively improve the disadvantage of the calcium phosphate powder's lack of adhesion. The principle is that silicon dioxide, calcium oxide, and industrial water hydrate to produce calcium silicate during the pelletizing process, cross-linking the calcium phosphate at the molecular level and significantly improving the calcium phosphate pelletizing efficiency. This patent uses silicon dioxide and calcium oxide as components inherent in the calcium phosphate powder, without introducing external impurities, ensuring uniform composition of the finished balls.

[0062] Comparing the performance of the raw balls and finished balls in Example 3 with that in Comparative Example 3, the addition of a binder can adjust the distribution and content of capillary water and bound water inside the pellets. The binder and industrial water coordinate with each other, which can increase the viscosity of the particles inside the pellets, produce strong chemical adsorption on the particle surface, increase the hydrophilicity of the surface of the internal calcium phosphate powder, silica, calcium oxide, and carbon source, and make the interaction between the components of the pellets more sufficient during the curing process, so that the corresponding chemical action energy, viscous action energy, and capillary attraction energy can be improved, which is conducive to improving the compressive strength of the raw balls. Among them, kaolin and alumina provide rigidity for the pellets, can regulate the internal pores of the calcium phosphate, so that the obtained calcium phosphate pellets do not burst at a high temperature of 1000 ° C and have certain compressive resistance and wear resistance; clay fully utilizes the low fineness and smoothness of its powder outside the calcium phosphate, wraps a large number of coarse particles as the outer layer, overcomes the difficulty of calcium phosphate pelletizing technology, and can prevent the mutual adhesion between pellets, making the demoulding of pellets easier.

[0063] In addition to the above embodiments, the present invention also includes other implementation methods. Any technical solutions formed by equivalent transformation or equivalent replacement should fall within the scope of protection of the claims of the present invention.

Claims

1. A calcium phosphate pellet, characterized in that: The raw materials of the calcium phosphate pellets include calcium phosphate powder, auxiliary powder, binder, industrial water and carbon source. The calcium phosphate powder is a mixture of 40-mesh calcium phosphate powder, 60-mesh calcium phosphate powder and 100-mesh calcium phosphate powder.

2. The calcium phosphate pellet according to claim 1, characterized in that: The auxiliary powder is silicon dioxide and limestone, and the mass ratio of silicon dioxide to limestone is 0.5-2.5:0.5-2.

5.

3. The calcium phosphate pellet according to claim 1, characterized in that: The binder is at least one of clay, kaolin, alumina and bentonite.

4. The calcium phosphate pellet according to claim 1, characterized in that: The carbon source is at least one of coke powder, maltose and cyclodextrin.

5. A method for preparing calcium phosphate pellets according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Grind and sieve the calcium phosphate salt, and pass it through 40, 60, and 100 mesh sieves respectively to obtain a mixture of calcium phosphate powders with different particle sizes, which is recorded as the first material; Step 2: adding the first material and the auxiliary powder into a mixer and mixing them evenly to obtain the second material; Step 3: Add a binder to the second material and mix evenly to obtain a mixed material 1; Step 4: Add the carbon source to the mixture 1 and mix evenly, then evenly add industrial water through a spray device, and mix evenly to obtain the mixture 2; Step 5: Mixture 2 is pelletized by a press, and then subjected to curing, roasting and cooling treatments in sequence to obtain calcium phosphate pellets.

6. The method for preparing calcium phosphate pellets according to claim 5, characterized in that: In step 2, the amount of the powder additive added is 1-5% of the total mass of all materials.

7. The method for preparing calcium phosphate pellets according to claim 5, characterized in that: In step 3, the amount of the binder added is 0.5-1.5% of the total mass of all materials.

8. The method for preparing calcium phosphate pellets according to claim 5, characterized in that: In step 4, the amount of the carbon source added is 0.2-1% of the total mass of all materials, and the amount of industrial water added is not higher than 5% of the total mass of all materials.

9. The method for preparing calcium phosphate pellets according to claim 5, characterized in that: In step 5, the curing temperature is 40-80°C, and the curing time is 30-120 min; the roasting temperature is 400-600°C, and the roasting time is 15-60 min; the cooling temperature is room temperature, and the cooling time is 18 min.

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