Method for preparing tricalcium phosphate with high citric acid solubility in melt crystal control crystallization mode

Abstract

The invention relates to the technical field of tricalcium phosphate production, and particularly discloses a method for preparing tricalcium phosphate with high citric acid solubility in a melting crystal control crystallization mode, which comprises the following steps: step 1, uniformly mixing phosphate concentrate, a phosphoric acid-containing phase and sodium salt according to a certain proportion, and then adding the mixture into a smelting furnace; 2, smelting is conducted in a smelting furnace in the mode of fuel injection and strong oxidation combustion, the smelting temperature ranges from 1450 DEG C to 1600 DEG C, and the peroxy coefficient of strong oxidation combustion is not smaller than 1; 3, smelting in the smelting furnace in the step 2 is completed, molten slag in a molten state is discharged out of the smelting furnace, and the discharged molten slag is subjected to crystal control crystallization granulation treatment to obtain clean molten slag; and step 4, grinding the clean slag in the step 3 to obtain a defluorinated tricalcium phosphate product. The technical problems that in the prior art, in the production of tricalcium phosphate, the quality of a melting defluorination method is not stable enough, and a calcination defluorination method is long in technological process and high in calcination energy consumption are solved.

Description

Technical Field

[0001] The invention relates to the technical field of tricalcium phosphate production, and in particular to a method for preparing high-citrate-soluble tricalcium phosphate by a melt-controlled crystallization method. Background Art

[0002] Tricalcium phosphate, with the chemical formula of Ca3(PO4)2, is a white, odorless powder with good stability and solubility. When dissolved in water, it produces calcium ions and phosphate ions that are easily absorbed by humans and animals. Therefore, it shows the potential to become a nutritional enhancer in the food processing and feed industries. However, one of the main raw materials for the preparation of tricalcium phosphate is phosphate rock. Phosphate rock usually contains a certain amount of fluoride, which may enter the tricalcium phosphate product during the preparation process. Fluoride is an element that is harmful to the body of animals or humans. If the fluoride content in tricalcium phosphate is too high, the safety and compliance of the product cannot be ensured.

[0003] In order to ensure the safety and compliance of tricalcium phosphate, defluorination treatment is carried out during production. The production process of feed-grade tricalcium phosphate generally adopts high-temperature defluorination. The main processes are melting defluorination and calcination defluorination. The melting defluorination method uses phosphate rock as raw material, adds quartz sand and other fluxes, and melts at high temperature (generally 1350-1500°C). When melting, calcium fluorophosphate reacts with silicon dioxide in quartz sand to form tricalcium phosphate and calcium silicate. At this time, fluorine escapes from the molten ore in the form of compounds such as HF and SiF4, thereby producing qualified defluorinated tricalcium phosphate. In order to accelerate the escape of fluorine, water vapor is usually used to fix the product in the form of α-type tricalcium phosphate glass. During the solidification process of the material, gaseous compounds such as HF and SiF4 will escape quickly, so it is also called hydrothermal method. The sintering method also uses phosphate rock as raw material, adds phosphoric acid, a small amount of silica and soda ash, sodium sulfate and other fluxes, and uses the high-temperature calcination zone of a rotary kiln to melt the surface of the material. Under high temperature, the fluorine in the phosphate rock reacts with compounds such as phosphoric acid in the ingredients to generate volatile fluorides such as HF and SiF4. These fluorides leave the material with the flow of gas in the furnace to achieve defluorination. Since phosphoric acid is used, it is also called the acid heat method.

[0004] In order to improve the solubility of materials, the melting method mainly uses high-silicon phosphate ore. The defluorinated tricalcium phosphate fertilizer produced is of low quality and has many impurities. As a feed-grade product, the quality is not stable enough, and the production energy consumption is high. The calcination defluorination method has problems such as long process flow, high calcination energy consumption, easy ring formation, and difficult control of defluorination and dearsenicization process. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization, so as to solve the technical problems mentioned above in the prior art of tricalcium phosphate production that the quality of the melt defluorination method is not stable enough, and the calcination defluorination method has a long process flow and high calcination energy consumption.

[0006] In order to solve the above problems, the technical solution adopted by the present invention is as follows: A method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization comprises the following steps:

[0007] Step 1, mixing the phosphate concentrate and the phosphoric acid phase in a certain proportion, mixing evenly, and then adding the mixture into a smelting furnace;

[0008] After the phosphate concentrate and phosphoric acid are mixed, the P content must be controlled to be 15% to 18.5%, and the SiO2 content must be controlled to be 3% to 10%;

[0009] Step 2, smelting is performed in a smelting furnace by injecting fuel and strong oxidizing combustion, the smelting temperature is 1450-1600° C., and the excess oxygen coefficient of the strong oxidizing combustion is not less than 1;

[0010] Step 3, the slag in the molten state after smelting in the smelting furnace in step 2 is discharged from the smelting furnace, and the discharged slag is subjected to a crystal-controlled crystallization and granulation treatment by gas quenching cooling to obtain clean slag;

[0011] Step 4: Grind the clean slag in step 3 to obtain the defluorinated tricalcium phosphate product.

[0012] The beneficial effects of this embodiment are:

[0013] 1. In the production of tricalcium phosphate in the prior art, the quality of the melting defluorination method is not stable enough, the quality of the defluorinated tricalcium phosphate fertilizer produced is low, there are many impurities, the quality of the feed-grade product is not stable enough, and the production energy consumption is high; the calcination defluorination method has the problems of long process flow, high calcination energy consumption, easy ring formation, and difficult control of the defluorination and arsenic removal process. The present application adopts the combustion mode of strong oxidation and fuel injection to strengthen the melting defluorination method, and the phosphate concentrate mixture (sodium salt-phosphoric acid-phosphate concentrate) is quickly melted, and the high temperature, stirring and combustion are used to achieve the purpose of efficient defluorination and arsenic removal. Compared with the calcination defluorination method, the process flow is short and the energy consumption is low; compared with the melting defluorination method, the present application produces clean slag with up-to-standard calcium and phosphorus content and less harmful elements. After testing, the slag of the present application has F≤0.18%, As≤0.0010%, which fully meets the product index requirements of feed-grade defluorinated tricalcium phosphate (tricalcium phosphate (TCP)), and the content of other heavy metal elements does not exceed the standard.

[0014] 2. When the present application is applied to production, it is found that the P recovery rate of the present application is ≥ 98%. Its P recovery rate is higher than that of the prior art. Through analysis, it is found that the present application adopts a combustion method of strong oxidation injection fuel, and the excess oxygen coefficient in the smelting furnace is designed to be greater than 1. While the calorific value of the fuel is fully utilized to melt the material, after the fuel and the combustibles in the material are completely burned, some residual oxygen remains in the slag. The high residual oxygen content in the slag can inhibit the reduction and volatilization of P, thus unexpectedly producing a technical effect of further improving the P recovery rate.

[0015] Furthermore, in the gas quenching cooling and crystallization granulation process in step 3, water mist of 3-25% of the mass of the slag is added for auxiliary cooling, and a water mist and gas quenching and crystallization granulation process is formed by using the water mist and gas quenching process.

[0016] The use of water mist quenching enables the present application to have the following technical effects:

[0017] 1. The gas used for water mist quenching in the present application contains a large amount of atomized tiny water droplets. These tiny water droplets have a large surface area and evaporate quickly. They can quickly absorb the surrounding heat and quickly cool the molten casting. The molten casting is subjected to the thermal expansion and contraction effect during the rapid cooling process. The temperature difference between the inside and the outside will cause uneven volume shrinkage, thereby generating huge internal stress, causing the slag to directly break into small particles, thereby reducing the grinding pressure for subsequent grinding.

[0018] 2. At the beginning of water mist quenching, due to its small volume and large surface area, water mist quickly vaporizes into water vapor after absorbing heat in contact with the molten cast, forming a high-pressure environment. At this time, the temperature of the slag is still very high, at above 1000°C, so a short high-temperature and high-pressure environment will be formed on the surface of the slag. Under the high-temperature and high-pressure environment, part of the water mist can be in a supercritical state for a short time to form a supercritical fluid. The high fluidity and diffusion capacity of the supercritical fluid formed by the water mist enable the supercritical water mist to penetrate into the interior and gaps of the sample matrix, increasing the probability and speed of contact with the object to be tested. In addition, the slag is cracked or broken into small particles due to internal stress, and the water mist can more easily take away the residual fluorine (in the form of compounds such as HF and SiF4) in the slag, further realizing the removal of fluorine.

[0019] 3. The content of citric acid-soluble phosphorus and the content of acid-insoluble matter in defluorinated tricalcium phosphate are important indicators of the quality of tricalcium phosphate; citric acid-soluble phosphorus refers to phosphorus that is difficult to dissolve or insoluble in water, but can be dissolved in a solution of citric acid (citric acid) or ammonium citrate with an acidity equivalent to 2%, usually referring to available phosphorus. The higher the percentage of citric acid-soluble phosphorus in the total phosphorus, the better the quality of the tricalcium phosphate. The present application utilizes water mist gas quenching to control crystallization. After gas quenching and cooling, the slag of the present application is directly granulated, so that the citric acid-soluble phosphorus content of the tricalcium phosphate of the present application is higher than that of the prior art. After testing, the citric acid-soluble phosphorus in the present application accounts for ≥95% of the total phosphorus content, and the content of acid-insoluble matter can be reduced to ≤8%;

[0020] Furthermore, sodium salt is also added to the mixture in step 1. After the phosphate concentrate, phosphoric acid-containing phase and sodium salt are mixed, the P content needs to be controlled to be 15% to 18.5%, the SiO2 content to be 3% to 10%, and the Na content to be 2% to 5%.

[0021] Furthermore, the sodium salt can be any one of sodium bicarbonate, sodium carbonate and sodium hydroxide, or a mixture of two or more of them.

[0022] Furthermore, in step 1, the moisture content of the mixture is controlled to be below 15%.

[0023] Furthermore, the excess oxygen coefficient of the strong oxidative combustion in step 2 is 1 to 1.2.

[0024] Furthermore, the phosphoric acid-containing phase is raffinate slag.

[0025] Furthermore, the fuel sprayed in step 2 is powdered fuel or gaseous fuel.

[0026] Furthermore, the injected fuel is pulverized coal. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is an electron microscope image of tricalcium phosphate that has not been treated with crystallization and granulation.

[0028] Figure 2 This is an electron microscope image of tricalcium phosphate treated by water mist quenching and crystallization granulation of the present invention.

[0029] Figure 3 It is a cross-sectional view of the multi-channel water mist spray gun of the present invention. DETAILED DESCRIPTION

[0030] The following is further described in detail through specific implementation methods:

[0031] The reference numerals in the drawings of the specification include: inner channel 1 , first annular gap 2 , second annular gap 3 .

[0032] Implementation example Figure 1-3 As shown:

[0033] Program Overview:

[0034] A method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization comprises the following steps:

[0035] Step 1, mixing phosphate concentrate, phosphoric acid phase and sodium salt in a certain proportion, mixing evenly, and then adding the mixture into a smelting furnace;

[0036] After the phosphate concentrate, phosphoric acid phase and sodium salt are mixed, the P content, SiO2 content and Na content of the phosphate concentrate, phosphoric acid phase and sodium salt need to be controlled to be 15% to 18.5%, 3% to 10% and 2% to 5% respectively;

[0037] Phosphoric acid phase refers to waste acid and residual acid residue containing phosphoric acid produced in phosphorus chemical industry. Sodium salt can be selected from alkaline salts containing sodium ions such as sodium bicarbonate, sodium carbonate and sodium hydroxide. Before mixing, the contents of P and SiO2 in phosphate concentrate and phosphoric acid phase are sampled and determined by testing. Then, the required proportion of phosphate concentrate, phosphoric acid phase and sodium salt is inferred from the P content after mixing: 15% to 18.5%, SiO2 content: 3% to 10%, and Na content: 2% to 5%. Ensure that the contents of P, SiO2 and Na meet the requirements after mixing.

[0038] Step 2, smelting is performed in a smelting furnace by injecting fuel and strong oxidizing combustion, the smelting temperature is 1450-1600° C., and the excess oxygen coefficient of the strong oxidizing combustion is not less than 1;

[0039] The excess oxygen coefficient is the ratio of the oxygen content in the actual combustion process of the fuel to the oxygen content required for complete combustion of the fuel in theory. When the actual oxygen content used is equal to the theoretically required oxygen content, the excess oxygen coefficient is 1. In order to ensure that the excess oxygen coefficient is not less than 1 during smelting in the smelting furnace, oxygen is added to the air according to the design to form oxygen-enriched air, and the oxygen-enriched air is sprayed into the smelting furnace for fuel combustion. The fuel can be selected from powdered fuels or gaseous fuels such as pulverized coal, natural gas, or yellow phosphorus tail gas.

[0040] Step 3, the slag in a molten state after smelting in the smelting furnace in step 2 is discharged from the smelting furnace, and the discharged slag is subjected to a crystal control crystallization granulation treatment to obtain clean slag;

[0041] Crystallization granulation control refers to controlling the cooling temperature rate of molten slag to achieve control of crystal grain size. This application uses compressed air to gas quench the slag. The gas pressure of gas quenching is controlled to 2-5kg, and 100-500 cubic meters of gas are prepared for gas quenching per kilogram of slag mass.

[0042] Preferably, in the present application, 3-5% of the mass of the slag to be cooled is added to assist cooling during the gas quenching cooling process. When adding water, the added water must first be made into water mist using a water mist device such as a water mist nozzle, and the water mist is added to the compressed air to perform water mist gas quenching. This includes but is not limited to using a multi-channel water mist spray gun for water mist gas quenching, and a multi-channel water mist spray gun such as Figure 3 As shown, the inner channel 1 is high-speed gas atomization; the first annular gap 2 and the second annular gap 3 are mechanical water atomization, and the water mist required by the present application is produced by using high-pressure airflow and annular gaps. Since it is a prior art, it will not be described in detail here.

[0043] Step 4: Grind the clean slag in step 3 to obtain the defluorinated tricalcium phosphate product.

[0044] Example 1

[0045] In this embodiment, the phosphate concentrate of the mixture is high-grade phosphate ore, the phosphoric acid phase is waste phosphoric acid, and the sodium salt is sodium carbonate. After mixing them, the moisture content of the mixture is 10.70%, and the specific composition is shown in Table 1-1. The mixture is added to the oxygen-enriched and enhanced smelting furnace through a belt conveyor for smelting at a smelting temperature of 1500°C to 1550°C.

[0046] The smelting furnace uses pulverized coal as fuel, and the oxygen combustion excess coefficient is 1.2. After the mixture is melted, the molten slag is discharged and water mist quenched under the conditions of gas pressure of 5kg, gas flow of 500m3 per kilogram of slag, and water mist of 25% of the slag mass. After the molten slag is treated with water mist quenching, it is ground to obtain the final product.

[0047] The components of the final product tricalcium phosphate (TCP) are shown in Table 1-2.

[0048] Table 1-1 Chemical composition of mixture 1 wt% (dry basis)

[0049]

[0050] Table 1-2 Chemical composition of tricalcium phosphate (TCP) by weight (dry basis)

[0051]

[0052] Example 2

[0053] The phosphate concentrate of the mixture in Example 2 is low-silicon grade phosphate ore, the phosphoric acid phase is waste phosphoric acid, the sodium salt is sodium bicarbonate, the moisture content of the mixture is 4.66%, and the specific components are shown in Table 2-1. The mixture is added to the oxygen-enriched enhanced smelting furnace via a belt conveyor, and the smelting temperature is 1500℃~1550℃.

[0054] The fuel is pulverized coal, and the oxygen combustion excess coefficient is 1.1. The molten slag is treated with water mist quenching and ground to obtain the final product. The water mist quenching is carried out at a gas pressure of 4kg and a gas flow rate of 300m 3 Water mist quenching is carried out under the condition that the water mist is 10% of the slag mass for every kilogram of slag.

[0055] The components of the final product tricalcium phosphate (TCP) are shown in Table 2-2.

[0056] Table 2-1 Chemical composition of mixture 2 wt% (dry basis)

[0057]

[0058] Table 2-2 Chemical composition of tricalcium phosphate (TCP) by weight (dry basis)

[0059]

[0060] Example 3

[0061] In Example 3, the mixture is high-silicon grade phosphate rock, the acid phase is residual acid slag, the sodium salt is sodium hydroxide, the moisture content of the mixture is 1.51%, and the specific components are shown in Table 3-1. Mixture 3 is added to the oxygen-enriched enhanced smelting furnace via a belt conveyor, and the smelting temperature is 1450℃~1500℃.

[0062] The fuel is pulverized coal, and the oxygen combustion excess coefficient is 1.2. The molten slag is treated with water mist quenching and ground to obtain the final product. The water mist quenching is carried out at a gas pressure of 3kg and a gas flow rate of 200m 3 Water mist quenching is carried out under the condition that the water mist is 5% of the slag mass for every kilogram of slag.

[0063] The components of the final product tricalcium phosphate (TCP) are shown in Table 3-2.

[0064] Table 3-1 Chemical composition of mixture 3 wt% (dry basis)

[0065]

[0066] Table 3-2 Chemical composition of tricalcium phosphate (TCP) by weight (dry basis)

[0067]

[0068] Example 4

[0069] In Example 4, the mixed material is high-silicon grade phosphate ore, the phosphoric acid phase is a mixture of residual acid slag and waste phosphoric acid, no sodium salt is added, and it is a sodium-free product. The moisture content of the mixed material is 5.54%, and the specific composition is shown in Table 4-1. The mixed material is added to the oxygen-enriched enhanced smelting furnace through a belt conveyor, and the smelting temperature is 1450℃~1500℃.

[0070] The fuel is natural gas, and the oxygen combustion excess coefficient is 1. The molten slag is gas quenched and ground to obtain the final product. The water mist gas quenching is carried out at a gas pressure of 2kg and a gas flow rate of 100m 3 Water mist quenching is carried out under the condition that the water mist is 3% of the slag mass for every kilogram of slag.

[0071] The components of the final product tricalcium phosphate (TCP) are shown in Table 4-2.

[0072] Table 4-1 Chemical composition of mixture 4 by weight (dry basis)

[0073]

[0074] Table 4-2 Chemical composition of tricalcium phosphate (TCP) by weight (dry basis)

[0075]

[0076] Comparative Example 1

[0077] The difference between the comparative example and the embodiment 1 is that the oxygen combustion excess coefficient of the smelting furnace is 0.8. The specific components of the mixture 5 used are shown in Table 5-1; the components of the final product tricalcium phosphate (TCP) are shown in Table 5-2.

[0078] Table 5-1 Chemical composition of mixture 4 by weight (dry basis)

[0079]

[0080] Table 5-2 Chemical composition of tricalcium phosphate (TCP) by weight (dry basis)

[0081]

[0082]

[0083] Comparison column 2

[0084] The difference between the comparative example and the example 1 is that the molten state of the smelting furnace is cooled by air flow, and the solid slag is formed after cooling for grinding. The specific composition of the mixture 6 used is shown in Table 6-1; the composition of the final product tricalcium phosphate (TCP) is shown in Table 6-2.

[0085] Table 6-1 Chemical composition of mixture 4 by weight (dry basis)

[0086]

[0087] Table 6-2 Chemical composition of tricalcium phosphate (TCP) by weight (dry basis)

[0088]

[0089] Experimental Example-Appearance

[0090] The tricalcium phosphate (TCP) prepared in Example 1 and Comparative Example 2 was scanned by electron microscope, and the results were as follows: Figure 1 , Figure 2 shown.

[0091] The above is only an embodiment of the present invention, and the common knowledge such as the known specific structure and characteristics in the scheme is not described in detail here. It should be pointed out that for those skilled in the art, several deformations and improvements can be made without departing from the structure of the present invention, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization, characterized in that: The following steps are involved: Step 1, mixing the phosphate concentrate and the phosphoric acid phase in a certain proportion, mixing evenly, and then adding the mixture into a smelting furnace; After the phosphate concentrate and phosphoric acid are mixed, the P content must be controlled to be 15% to 18.5%, and the SiO2 content must be controlled to be 3% to 10%; Step 2, smelting is performed in a smelting furnace by injecting fuel and strong oxidizing combustion, the smelting temperature is 1450-1600° C., and the excess oxygen coefficient of the strong oxidizing combustion is not less than 1; Step 3, the slag in the molten state after smelting in the smelting furnace in step 2 is discharged from the smelting furnace, and the discharged slag is subjected to a crystal-controlled crystallization and granulation treatment by gas quenching cooling to obtain clean slag; Step 4: Grind the clean slag in step 3 to obtain the defluorinated tricalcium phosphate product.

2. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 1, characterized in that: In the gas quenching cooling and crystallization granulation process in step 3, 3-25% water mist of the slag mass is added for auxiliary cooling, and a water mist gas quenching and crystallization granulation process is formed by using the water mist and gas quenching process.

3. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 2, characterized in that: Sodium salt is also added to the mixture in step 1. After the phosphate concentrate, phosphoric acid-containing phase and sodium salt are mixed, the P content needs to be controlled to be 15% to 18.5%, the SiO2 content to be 3% to 10%, and the Na content to be 2% to 5%.

4. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 3, characterized in that: The sodium salt can be any one of sodium bicarbonate, sodium carbonate and sodium hydroxide, or a mixture of two or more of them.

5. The method for preparing highly citric acid soluble tricalcium phosphate by melt controlled crystallization according to claim 1, characterized in that: In step 1, the moisture content of the mixture is controlled to be below 15%.

6. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 1, characterized in that: The excess oxygen coefficient of the strong oxidative combustion in step 2 is 1 to 1.

2.

7. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 1, characterized in that: The phosphoric acid-containing phase is raffinate slag.

8. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 1, characterized in that: The fuel sprayed in step 2 is powdered fuel or gaseous fuel.

9. The method for preparing highly citric acid-soluble tricalcium phosphate by melt-controlled crystallization according to claim 8, characterized in that: The injected fuel is pulverized coal.

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