Sodium monofluorophosphate as well as preparation method and application thereof

Abstract

The invention provides sodium monofluorophosphate as well as a preparation method and application thereof, and belongs to the technical field of inorganic material preparation. The preparation method of the sodium monofluorophosphate comprises the following steps: mixing reaction raw materials and activated aluminum oxide, and calcining at 500-800 DEG C to prepare the sodium monofluorophosphate, wherein the reaction raw materials comprise sodium dihydrogen phosphate and sodium fluoride; the mass ratio of the reaction raw materials to the activated aluminum oxide is (1-1.5): 1. By controlling the mass ratio of the activated aluminum oxide to the reaction raw materials, the content of free fluorine in the sodium monofluorophosphate can be remarkably reduced. Wherein sodium dihydrogen phosphate and sodium fluoride which are low in cost are used as reaction raw materials, the reaction speed is high, the preparation process is simple and environmentally friendly, and in the reaction process, activated aluminum oxide is adopted for adsorption and the dosage of the activated aluminum oxide is adjusted, so that the content of free fluorine and other metal impurities can be remarkably reduced, and the purity of sodium monofluorophosphate is improved.

Description

Technical Field

[0001] This application relates to the field of inorganic material preparation technology, and in particular to sodium monofluorophosphate, its preparation method and application. Background Technology

[0002] Sodium monofluorophosphate (Na2PO3F) is a white crystalline powder with a melting point of about 626℃. It is easily soluble in water and has strong hygroscopic properties. In toothpaste production, it is used as an anti-caries agent, desensitizing additive, bactericide, and preservative. It can also be used as a cleaning agent for metal surface oxides, a food additive, and a corrosion inhibitor.

[0003] Sodium monofluorophosphate used in toothpaste industry should meet the following requirements: purity not less than 95.0%, free fluoride content less than 0.68%, and pH between 6.5 and 8.0. High free fluoride content can seriously affect dental and bone health, and even cause fluorosis. However, traditional sodium monofluorophosphate preparation processes still suffer from high levels of impurities such as free fluoride in the product, which can easily cause environmental pollution. Therefore, further improvements to the sodium monofluorophosphate preparation process are urgently needed. Summary of the Invention

[0004] Therefore, the main purpose of this application is to provide sodium monofluorophosphate, its preparation method and application, so as to reduce the free fluorine content in sodium monofluorophosphate and improve the purity of sodium monofluorophosphate. The preparation process of sodium monofluorophosphate is simple and environmentally friendly.

[0005] The first aspect of this application provides a method for preparing sodium monofluorophosphate, comprising the following steps:

[0006] Sodium monofluorophosphate is prepared by mixing the reactants and activated alumina and calcining them at 500-800℃.

[0007] The reaction raw materials include sodium dihydrogen phosphate and sodium fluoride;

[0008] The mass ratio of the reaction raw materials to activated alumina is (1-1.5):1.

[0009] In some embodiments, the activated alumina satisfies the following conditions: particle size of 1-10 mm; average particle size of 1.5-9.5 mm.

[0010] In some embodiments, the activated alumina comprises particles in the following mass fractions:

[0011] 20%-40% of particles have a diameter of 1-4mm;

[0012] 20%-40% of particles have a diameter of 5-6 mm; and

[0013] 20%-40% of the particles have a diameter of 7-10mm.

[0014] In some embodiments, the activated alumina comprises particles in the following mass fractions:

[0015] 15%-35% of particles with a diameter of 1-2 mm;

[0016] 15%-35% of particles with a diameter of 3-4 mm;

[0017] 15%-35% of particles with a diameter of 5-6mm

[0018] 15%-35% of particles with a diameter of 7-8 mm; and

[0019] 15%-35% of particles with a diameter of 9-10mm.

[0020] In some embodiments, the calcination conditions include: a gaseous atmosphere including air, oxygen, or nitrogen; and a time of 0.1-12 hours.

[0021] In some embodiments, the molar ratio of sodium dihydrogen phosphate to sodium fluoride is 1:(0.8-2).

[0022] In some embodiments, the reaction raw materials and activated alumina are dried before being mixed.

[0023] In some embodiments, the step of drying the reactants and activated alumina specifically includes:

[0024] The reactants are spray-dried under the following conditions: inlet air temperature 100-200°C; outlet air temperature 100-150°C; and inlet air volume 0.1-1 m³ / min. 3 / h;

[0025] The activated alumina is dried at a temperature of 100-300℃ for 0.5-36 hours.

[0026] In a second aspect of this application, a sodium monofluorophosphate is provided, prepared by the method for preparing sodium monofluorophosphate described in the first aspect; wherein the free fluorine content in the sodium monofluorophosphate is 0.048-0.072 mmol / L.

[0027] The third aspect of this application provides a method for preparing sodium monofluorophosphate as described in the first aspect or the application of sodium monofluorophosphate as described in the second aspect in toothpaste.

[0028] Compared with traditional technologies, this application has at least the following beneficial effects:

[0029] This application demonstrates a significant reduction in the free fluorine content of sodium monofluorophosphate by controlling the mass ratio of activated alumina to the reaction raw materials. The preparation process of sodium monofluorophosphate is simple, environmentally friendly, and does not involve the use of hazardous reagents. Specifically, using low-cost sodium dihydrogen phosphate and sodium fluoride as reaction raw materials results in a rapid reaction rate. During the reaction, activated alumina is used for adsorption; adjusting the amount of activated alumina significantly reduces the content of free fluorine and other metallic impurities, thereby improving the purity of sodium monofluorophosphate. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the embodiments and examples. These embodiments and examples are for illustrative purposes only and are not intended to limit the scope of the present application. The purpose of providing these embodiments and examples is to enable a more thorough and comprehensive understanding of the disclosure of the present application. It should also be understood that the present application can be implemented in many different forms and is not limited to the embodiments and examples described herein. Those skilled in the art can make various modifications or alterations without departing from the spirit of the present application, and the equivalent forms obtained also fall within the protection scope of the present application. Furthermore, numerous specific details are set forth in the following description to provide a fuller understanding of the present application. It should be understood that the present application can be implemented without one or more of these details.

[0031] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0032] In view of the problem that the traditional preparation process of sodium monofluorophosphate still has the problem of high content of impurities such as free fluorine in the product, which can easily cause environmental pollution, this application uses sodium dihydrogen phosphate and sodium fluoride as reaction raw materials and controls the mass ratio of activated alumina to reaction raw materials, which can significantly reduce the content of free fluorine in sodium monofluorophosphate and improve the purity of sodium monofluorophosphate. At the same time, the preparation process of sodium monofluorophosphate is simple and environmentally friendly.

[0033] The first aspect of this application provides a method for preparing sodium monofluorophosphate, comprising the following steps:

[0034] Sodium monofluorophosphate is prepared by mixing the reactants and activated alumina and calcining them at 500-800℃.

[0035] The reaction raw materials include sodium dihydrogen phosphate and sodium fluoride;

[0036] The mass ratio of the reaction raw materials to activated alumina is (1-1.5):1.

[0037] During calcination at 500-800℃, NaH2PO4 undergoes dehydration condensation and reacts with NaF to form Na2PO3F. The chemical reaction formula is as follows:

[0038] NaH2PO4 + NaF → Na2PO3F + H2O.

[0039] This application demonstrates a significant reduction in the free fluorine content of sodium monofluorophosphate by controlling the mass ratio of activated alumina to the reaction raw materials. Specifically, using low-cost sodium dihydrogen phosphate and sodium fluoride as reaction raw materials results in a rapid reaction rate, a simple preparation process, and environmental friendliness. During the reaction, activated alumina is used for adsorption; adjusting the amount of activated alumina significantly reduces the content of free fluorine and other metallic impurities, thereby improving the purity of sodium monofluorophosphate.

[0040] In some embodiments, the activated alumina meets the following conditions: particle size of 1.5-10 mm; average particle size of 1.5-9.5 mm.

[0041] In some embodiments, the activated alumina comprises particles in the following mass fractions:

[0042] 20%-40% of particles have a diameter of 1-4mm;

[0043] 20%-40% of particles have a diameter of 5-6 mm; and

[0044] 20%-40% of the particles have a diameter of 7-10mm.

[0045] In some embodiments, the mass fraction of particles with a particle size of 1-4 mm in the activated alumina is 20%-40%, which can be 20%, 25%, 30%, 33% or 40%.

[0046] The mass fraction of particles with a diameter of 5-6 mm is 20%-40%, which can be 20%, 25%, 30%, 33% or 40%;

[0047] The mass fraction of particles with a diameter of 7-10 mm is 20%-40%, which can be 20%, 25%, 30%, 33% or 40%.

[0048] The activated alumina described in this application is in the form of spherical particles.

[0049] In some embodiments, the activated alumina comprises particles in the following mass fractions:

[0050] 15%-35% of particles with a diameter of 1-2 mm;

[0051] 15%-35% of particles with a diameter of 3-4 mm;

[0052] 15%-35% of particles with a diameter of 5-6mm

[0053] 15%-35% of particles with a diameter of 7-8 mm; and

[0054] 15%-35% of particles with a diameter of 9-10mm.

[0055] In some embodiments, the mass fraction of particles with a particle size of 1-2 mm in the activated alumina is 15%-35%, and can be 15%, 20%, 25%, 30%, 33% or 35%.

[0056] The mass fraction of particles with a diameter of 3-4 mm is 15%-35%, which can be 15%, 20%, 25%, 30%, 33% or 35%;

[0057] The mass fraction of particles with a diameter of 5-6 mm is 15%-35%, which can be 15%, 20%, 25%, 30%, 33% or 35%;

[0058] The mass fraction of particles with a diameter of 7-8 mm is 15%-35%, which can be 15%, 20%, 25%, 30%, 33% or 35%;

[0059] The mass fraction of particles with a diameter of 9-10 mm is 15%-35%, which can be 15%, 20%, 25%, 30%, 33% or 35%.

[0060] In some embodiments, the calcination conditions include: a temperature of 500-800°C, which can be 500°C, 600°C, 700°C or 800°C; a gas atmosphere including air, oxygen or nitrogen; and a time of 0.1-12h, which can be 0.1h, 0.5h, 1h, 2h, 3h, 5h, 8h, 10h or 12h.

[0061] In some embodiments, the molar ratio of sodium dihydrogen phosphate to sodium fluoride is 1:(0.8-2), which can be 1:0.8, 1:1, 1:1.2, 1:1.5 or 1:2.

[0062] In some embodiments, the reaction raw materials and activated alumina are dried before being mixed.

[0063] In some embodiments, the step of drying the reactants and activated alumina specifically includes:

[0064] The reactants are spray-dried under the following conditions: inlet air temperature of 100-200°C (100°C, 120°C, 140°C, 160°C, 180°C, or 200°C); outlet air temperature of 100-150°C (100°C, 110°C, 120°C, 130°C, 140°C, or 150°C); and inlet air volume of 0.1-1 m³ / min. 3 / h can be 0.1m 3 / h, 0.2m 3 / h, 0.4m 3 / h, 0.6m 3 / h, 0.8m 3 / h or 1m 3 / h;

[0065] The activated alumina is dried at a temperature of 100-300℃ for 0.5-36 hours.

[0066] By spray drying the reaction raw materials, the mixing, impurity removal and drying of materials can be achieved simultaneously during the pretreatment process of spray drying, thereby improving production efficiency.

[0067] In some embodiments, the raw material sodium dihydrogen phosphate is provided by NaH2PO4·2H2O. The NaH2PO4·2H2O is spray-dried to remove its water of crystallization. The chemical reaction formula is as follows:

[0068] NaH2PO4·2H2O→NaH2PO4+2H2O;

[0069] Furthermore, during the calcination process, NaH2PO4 undergoes dehydration condensation and reacts with NaF to form Na2PO3F, as shown in the following chemical reaction formula:

[0070] NaH2PO4 + NaF → Na2PO3F + H2O.

[0071] In some embodiments, the raw material sodium dihydrogen phosphate is provided by industrial-grade NaH2PO4·2H2O, and the test indicators of the industrial-grade NaH2PO4·2H2O meet the standard of "HG / T 2767-2009 Industrial Sodium Dihydrogen Phosphate". Specifically, the mass percentage of NaH2PO4·2H2O should be ≥98%, the mass percentage of iron should be less than 0.05%, the mass percentage of arsenic should be less than 0.01%, and the mass percentage of water-insoluble matter should be ≤0.1%.

[0072] In some embodiments, the raw material sodium fluoride is provided by industrial-grade sodium fluoride, and the test indicators of the industrial-grade sodium fluoride need to meet the standard of "YS / T 517-2024 Sodium Fluoride". Specifically, the mass percentage content of sodium fluoride should be ≥94%, and the mass percentage content of water-insoluble matter should be ≤3%.

[0073] In some embodiments, the container used in the calcination process is made of at least one of graphite, quartz, stainless steel, and corundum.

[0074] In some embodiments, the reaction raw materials and activated alumina are mixed and then calcined at 500-800°C, specifically including:

[0075] The reactants and activated alumina are mixed and placed in a graphite crucible, then transferred to a calcining furnace and calcined at 500-800℃.

[0076] In some embodiments, after calcination, the process also includes steps of cooling, separating the active alumina, and pulverizing the sodium monofluorophosphate.

[0077] Cooling conditions include: using air cooling and / or water cooling to cool to 0-50℃;

[0078] The specific method of pulverizing sodium monofluorophosphate includes: pulverizing sodium monofluorophosphate by means of mechanical milling; the mechanical milling includes ball milling or air jet milling.

[0079] In some embodiments, the sodium monofluorophosphate has a particle size of less than 5 μm.

[0080] In a second aspect of this application, a sodium monofluorophosphate is provided, prepared by the method for preparing sodium monofluorophosphate described in the first aspect; wherein the free fluorine content in the sodium monofluorophosphate is 0.048-0.072 mmol / L.

[0081] The third aspect of this application provides a method for preparing sodium monofluorophosphate as described in the first aspect or the application of sodium monofluorophosphate as described in the second aspect in toothpaste.

[0082] The embodiments of this application will be described in detail below with reference to examples. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of this application. For experimental methods in the following embodiments where specific conditions are not specified, please refer to the guidelines given in this application, or follow experimental manuals or conventional conditions in the art, or follow the conditions recommended by the manufacturer, or refer to experimental methods known in the art.

[0083] As an example, the sources of raw materials in this application embodiment are as follows:

[0084] Industrial grade sodium dihydrogen phosphate dihydrate: Produced by Guangdong Guanghua Technology Co., Ltd., specification is industrial grade;

[0085] Industrial grade sodium fluoride: Produced by Guangdong Guanghua Technology Co., Ltd., specification is industrial grade;

[0086] Activated alumina particles with a particle size of 1-2 mm: produced by Guangdong Guanghua Technology Co., Ltd., with an average particle size of 1.5 mm;

[0087] Activated alumina particles with a particle size of 3-4 mm: produced by Guangdong Guanghua Technology Co., Ltd., with an average particle size of 3.5 mm;

[0088] Activated alumina particles with a particle size of 5-6 mm: produced by Guangdong Guanghua Technology Co., Ltd., with an average particle size of 5.5 mm;

[0089] Activated alumina particles with a particle size of 7-8 mm: produced by Guangdong Guanghua Technology Co., Ltd., with an average particle size of 7.5 mm;

[0090] Activated alumina particles with a particle size of 9-10 mm: produced by Guangdong Guanghua Technology Co., Ltd., with an average particle size of 9.5 mm.

[0091] Example 1

[0092] The preparation method of sodium monofluorophosphate is as follows:

[0093] Industrial-grade sodium dihydrogen phosphate dihydrate and industrial-grade sodium fluoride were mixed evenly in a molar ratio of 1:0.8, and then spray-dried. The spray-drying conditions included: an inlet air temperature of 150℃, an outlet air temperature of 120℃, and an inlet air volume of 0.5 m³ / s. 3 / h, to obtain the dried reaction raw materials (sodium dihydrogen phosphate and sodium fluoride).

[0094] Activated alumina particles with particle sizes of 1-2 mm, 3-4 mm, 5-6 mm, 7-8 mm and 9-10 mm were mixed in a mass ratio of 1:1:1:1:1 to prepare an activated alumina mixture (particle size of 1-10 mm) containing 5 different particle size specifications for later use.

[0095] The reactants and the active alumina mixture were mixed evenly in a mass ratio of 1:1, then placed in a graphite sagger and placed in a calcining furnace for calcination in an air atmosphere at a temperature of 500°C for 0.1 hours.

[0096] After calcination, the liquid material flows out, while the activated alumina remains in the furnace. The liquid material is then cooled to 30°C by forced air cooling and ball milling to prepare sodium monofluorophosphate powder.

[0097] Example 2

[0098] The preparation methods of sodium monofluorophosphate in Example 2 and Example 1 are basically the same, except that the calcination temperature is adjusted to 800°C and sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0099] Example 3

[0100] The preparation method of sodium monofluorophosphate in Example 3 is basically the same as that in Example 1, except that "calcination in an air atmosphere" is replaced with "calcination in a nitrogen atmosphere"; sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0101] Example 4

[0102] The preparation method of sodium monofluorophosphate in Example 4 is basically the same as that in Example 1, except that the calcination time is adjusted to 12h; and sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0103] Example 5

[0104] The preparation method of sodium monofluorophosphate in Example 5 is basically the same as that in Example 1, except that the active alumina mixture is different. Specifically, the preparation method of the active alumina mixture is as follows:

[0105] Activated alumina particles with particle sizes of 1-2 mm, 5-6 mm and 9-10 mm were mixed in a mass ratio of 1:1:1 to prepare an activated alumina mixture (particle size of 1-10 mm) containing three different particle size specifications for later use.

[0106] Sodium monofluorophosphate powder was prepared according to the method in Example 1.

[0107] Example 6

[0108] The preparation method of sodium monofluorophosphate in Example 6 is basically the same as that in Example 1, except that the "active alumina mixture" is replaced with an equal mass of "active alumina with a particle size of 1-2 mm (average particle size of 1.5 mm)"; sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0109] Example 7

[0110] The preparation method of sodium monofluorophosphate in Example 7 is basically the same as that in Example 1, except that the "active alumina mixture" is replaced with an equal mass of "active alumina with a particle size of 5-6 mm (average particle size of 5.5 mm)"; sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0111] Example 8

[0112] The preparation method of sodium monofluorophosphate in Example 8 is basically the same as that in Example 1, except that the "active alumina mixture" is replaced with an equal mass of "active alumina with a particle size of 9-10 mm (average particle size of 9.5 mm)"; sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0113] Example 9

[0114] The preparation method of sodium monofluorophosphate in Example 9 is basically the same as that in Example 1, except that the calcination time is adjusted to 5 hours and sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0115] Comparative Example 1

[0116] The preparation methods of sodium monofluorophosphate in Comparative Example 1 and Example 1 are basically the same, except that the mass ratio of the reaction raw materials and activated alumina is adjusted to 1:2; and sodium monofluorophosphate powder is prepared according to the method of Example 1.

[0117] Comparative Example 2

[0118] The preparation method of sodium monofluorophosphate in Comparative Example 2 is basically the same as that in Example 1, except that the mass ratio of the reaction raw materials and activated alumina is adjusted to 2:1; and sodium monofluorophosphate powder is prepared according to the method in Example 1.

[0119] Sodium monofluorophosphate powders prepared in Examples 1-8 and Comparative Examples 1-2 were tested according to the national standard GB 24567-2009 Sodium monofluorophosphate for toothpaste industry. The test results are shown in Table 1.

[0120] Table 1. Detection results of sodium monofluorophosphate powder

[0121]

[0122]

[0123] " / " indicates that it was not recorded.

[0124] Table 1 shows that, compared with Comparative Examples 1-2, the sodium monofluorophosphate powder prepared in Examples 1-8 of this application exhibits significantly improved purity, significantly reduced free fluoride content, and lower concentrations of arsenic and lead ions. Specifically, the free fluoride content decreased from 0.103-0.126 mmol / L to 0.032-0.072 mmol / L, a reduction of 75%; while the bound fluoride content increased from 4.39 wt%-13.06 wt% to 13.25 wt%-13.41 wt%.

[0125] Compared to Comparative Examples 1-2, which used reactants and activated alumina in a mass ratio of 1:2 or 2:1, Example 1 used reactants and activated alumina in a mass ratio of 1:1. In the prepared sodium monofluorophosphate powder, the sodium monofluorophosphate content increased from 61.72 wt%-99.29 wt% to 99.60 wt%, and the free fluoride content decreased from 0.103-0.126 mmol / L to 0.040%. This indicates that by adjusting the mass ratio of reactants and activated alumina, this application can significantly reduce the free fluoride content in sodium monofluorophosphate and improve its purity.

[0126] Comparing Examples 1-4, it can be seen that the sodium monofluorophosphate prepared in this application under calcination conditions of 500-800℃, 0.1-12h, and air or nitrogen atmosphere all have high purity and low free fluorine content. Among them, the sodium monofluorophosphate prepared under calcination conditions of 500℃, 0.1h, and nitrogen atmosphere all have higher purity and lower free fluorine content.

[0127] Comparing Examples 1 and 5-8, it can be seen that the sodium monofluorophosphate prepared by this application using activated alumina or a mixture thereof with a particle size of 1-10 mm has high purity and low free fluorine content. In particular, the sodium monofluorophosphate prepared by Example 1 using activated alumina composed of particles with a particle size of 1-2 mm, 3-4 mm, 5-6 mm, 7-8 mm and 9-10 mm at a mass percentage of 20% has even higher purity and lower free fluorine content.

[0128] Comparing Examples 1, 4, and 9, it can be seen that the sodium monofluorophosphate prepared in this application within a calcination time of 0.1-12 h has high purity and low free fluorine content.

[0129] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0130] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing sodium monofluorophosphate, characterized in that, Includes the following steps: Sodium monofluorophosphate is prepared by mixing the reactants and activated alumina and calcining them at 500-800℃. The reaction raw materials include sodium dihydrogen phosphate and sodium fluoride; The mass ratio of the reaction raw materials to activated alumina is (1-1.5):

1.

2. The method for preparing sodium monofluorophosphate according to claim 1, characterized in that, The activated alumina satisfies the following conditions: The particle size is 1-10 mm; the average particle size is 1.5-9.5 mm.

3. The method for preparing sodium monofluorophosphate according to claim 2, characterized in that, The activated alumina comprises particles in the following mass fractions: 20%-40% of particles have a diameter of 1-4mm; 20%-40% of particles have a diameter of 5-6 mm; and 20%-40% of the particles have a diameter of 7-10mm.

4. The method for preparing sodium monofluorophosphate according to claim 2, characterized in that, The activated alumina comprises particles in the following mass fractions: 15%-35% of particles with a diameter of 1-2 mm; 15%-35% of particles with a diameter of 3-4 mm; 15%-35% of particles with a diameter of 5-6mm; 15%-35% of particles with a diameter of 7-8 mm; and 15%-35% of particles with a diameter of 9-10mm.

5. The method for preparing sodium monofluorophosphate according to any one of claims 1-4, characterized in that, The calcination conditions include: a gaseous atmosphere including air, oxygen, or nitrogen; and a time of 0.1-12 hours.

6. The method for preparing sodium monofluorophosphate according to any one of claims 1-4, characterized in that, The molar ratio of sodium dihydrogen phosphate to sodium fluoride is 1:(0.8-2).

7. The method for preparing sodium monofluorophosphate according to any one of claims 1-4, characterized in that, Before mixing the reactants and activated alumina, the process also includes a step of drying the reactants and activated alumina.

8. The method for preparing sodium monofluorophosphate according to claim 7, characterized in that, The specific steps for drying the reaction raw materials and activated alumina include: The reactants are spray-dried under the following conditions: inlet air temperature 100-200°C; outlet air temperature 100-150°C; and inlet air flow rate 0.1-1 m³ / min. 3 / h; The activated alumina is dried at a temperature of 100-300℃ for 0.5-36 hours.

9. A sodium monofluorophosphate, characterized in that, Sodium monofluorophosphate is prepared by the method described in any one of claims 1-8; the free fluorine content in the sodium monofluorophosphate is 0.048-0.072 mmol / L.

10. The method for preparing sodium monofluorophosphate as described in any one of claims 1-8 or the application of sodium monofluorophosphate as described in claim 9 in toothpaste.

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