A method for preparing white carbon black

Abstract

The present invention relates to a method for preparing silica, belonging to the technical field of silica preparation. In the method for preparing silica of the present invention, fluosilicic acid and an ammoniating agent are first reacted to prepare a mixed material, and the mixed material is a gel-like crystal seed. Then, by controlling the pressure of aging and pressure filtration during solid-liquid separation, silica with stable quality and a relatively large specific surface area is obtained. The greater the pressure of pressure filtration, the closer the tissue structure of the silica, the smaller the specific surface area, and the smaller the difference in the specific surface area of the silica between batches, that is, the better the stability; the smaller the pressure of pressure filtration, the lower the filtration efficiency, and the loose tissue structure of the silica, the larger the specific surface area, but the greater the difference in the specific surface area of the silica between batches, that is, the poor stability. When the pressure of pressure filtration is 0.5-0.7 MPa, silica with a specific surface area of 185±15 m<supgt;2< / supgt> / g can be obtained, and the difference between batches is small, meeting the use requirements of the high-end field of rubber tires.

Description

Technical Field

[0001] The present invention relates to a method for preparing silica white, belonging to the technical field of silica white preparation. Background Art

[0002] Silica white, also known as hydrated silicon dioxide with the chemical formula SiO2·nH2O, has been widely used in multiple fields such as plastics, rubber, papermaking, coatings, dyes, and inks due to its excellent chemical stability, electrical insulation, and high specific surface area. The commonly used synthesis methods of silica white are the gas-phase method and the precipitation method. Among them, the precipitation method has significant cost advantages and is the focus of attention of domestic and foreign scholars and the industrial community.

[0003] The traditional mainstream precipitation process (Na2SiO3 + 2H + =SiO2·nH2O + 2Na + + H2O) uses sodium silicate (Na2SiO3) as the raw material, reacts with hydrochloric acid or sulfuric acid, and obtains silica white through precipitation, filtration, washing, drying, and calcination processes under certain temperature, time, and pressure conditions. In addition, due to its lower cost advantage, the process of synthesizing silica white using cheap fluorosilicic acid by-produced from phosphate fertilizer (H2SiF6 + 6NH4OH=6NH4F + SiO2·nH2O, n = 4) has attracted much attention.

[0004] The specific surface area is an important index of silica white powder, and its stability between production batches (i.e., the stability of the specific surface area of silica white prepared in different batches) determines whether silica white can be used in high-end fields such as rubber tires. Rubber tire enterprises require that the specific surface area of high-dispersion silica white in different batches is 185 ± 15 m 2 / g (170 - 190 m 2 / g), that is, based on 185 m 2 / g, the error of the specific surface area of silica white between batches is within 15 m 2 / g, which poses an important challenge to silica white production enterprises, especially those using fluorosilicic acid as the raw material to produce silica white (new process). When synthesizing silica white using traditional methods or the new process, the primary crystal size and pore structure (micropores, mesopores, and macropores) of silica white are important factors determining the specific surface area. Therefore, for enterprises producing silica white using traditional methods, in order to obtain a certain specific surface area (185 ± 15 m 2For the silica white produced by the new process ((g)), it is necessary to control the raw material concentration, feeding rate, silica white synthesis temperature, stirring frequency and speed of the key device to ensure that the primary crystal grains of the synthesized silica white are <50 nm and have a rich and reasonable pore structure distribution at the same time. However, for enterprises producing silica white by the new process, it is more difficult to achieve stable and controllable specific surface area between batches. This is because fluorine has strong polarity, and the fluoride ions with stronger electronegativity in fluosilicic acid and the oxygen ions in silica white will have a competitive binding effect with silicon ions, thus affecting the crystallization and self-dispersibility of silica white.

[0005] Chinese patent document CN103073040B discloses a production method for co-producing calcium fluoride and silica white. The method disclosed in this patent document starts from the by-product fluosilicic acid of wet-process phosphoric acid, and continuously reacts fluosilicic acid with ammonia in a tubular reactor. The generated slurry is aged and filtered to obtain ammonium fluoride filtrate and silica white filter cake; the silica white filter cake is washed and dried to obtain silica white. The silica white prepared by this patent document has high content, small particle size, large specific surface area and excellent reinforcing performance, but the specific surface area of the silica white prepared in different batches varies greatly. Summary of the Invention

[0006] The purpose of the present invention is to provide a preparation method for silica white, which can solve the problem of poor specific surface area stability when using fluosilicic acid to prepare silica white at present.

[0007] In order to achieve the above purpose, the technical solution adopted by the preparation method for silica white of the present invention is as follows:

[0008] A preparation method for silica white, comprising the following steps:

[0009] (1) Mix fluosilicic acid and an ammoniating agent in water and react to the end point to obtain a mixed material with a pH of 6-7;

[0010] (2) Age the mixed material to obtain an aged material;

[0011] (3) React the aged material with an ammoniating agent to the end point to obtain a mixture with a pH of 7-8, and then perform solid-liquid separation on the mixture. The solid obtained by the solid-liquid separation is silica white; the solid-liquid separation is pressure filtration, and the pressure of the pressure filtration is 0.5-0.7 MPa;

[0012] The ammoniating agent in step (1) and step (3) is independently ammonia water or ammonia gas.

[0013] The preparation method of the silica of the present invention is to first react fluosilicic acid with an ammoniating agent to prepare a mixture, and the mixture is a gel-like seed crystal. Then, by controlling the pressure of aging and pressure filtration during solid-liquid separation, silica with stable quality and a relatively large specific surface area is obtained. Experimental results show that the greater the pressure of pressure filtration, the denser the tissue structure of the silica, the smaller the specific surface area, and the smaller the difference in the specific surface area of the silica between batches, that is, the better the stability; the smaller the pressure of pressure filtration, the lower the filtration efficiency, and the silica has a loose tissue structure and a larger specific surface area, but the difference in the specific surface area of the silica between batches is greater, that is, the stability is poor. When the pressure of pressure filtration is 0.5-0.7 MPa, silica with a specific surface area of 185±15 m 2 / g can be obtained, and the difference between batches is small, meeting the usage requirements of the high-end field of rubber tires.

[0014] Preferably, the aging time is 0.5-8 h. More preferably, the aging time is greater than 0.5 h and not greater than 8 h. For example, the aging time is 3-8 h. The aging effect of the seed crystal means that during the precipitation process, after the precipitation is complete, the solution is allowed to stand for a period of time under certain conditions. The purpose is to enable the components in the solution to fully react during standing or to make the suspended matter settle. Since the solubility of nano-sized primary crystals is greater than that of large crystals, in the same solution, it is a saturated solution for small crystals, but a supersaturated solution for large crystals. At this time, the small crystals deposited on the surface of the large crystals will gradually dissolve, and the large crystals will gradually grow, making the tissue structure of the silica stable and obtaining a moderate and stable specific surface area. Experimental results show that the longer the seed crystal aging time, the more obvious the agglomeration between primary crystals, the smaller the specific surface area of the obtained silica, and the smaller the difference in the specific surface area of the silica between batches, that is, the better the stability; the shorter the aging time, the less obvious the agglomeration of primary crystals, the higher the specific surface area of the obtained silica, but the greater the difference in the specific surface area of the silica between batches, that is, the stability is poor.

[0015] For the convenience of mixing and use and to improve the uniformity of the seed crystal particle size distribution, preferably, the fluosilicic acid is used in the form of a fluosilicic acid solution. Preferably, the mass fraction of the fluosilicic acid solution is 10-35%. If the mass fraction of the fluosilicic acid solution is too large, the specific surface area of the silica will be too low; if the mass fraction of the fluosilicic acid solution is too small, the specific surface area of the silica will be too large.

[0016] For the convenience of use, preferably, the ammoniating agent in steps (1) and (3) is ammonia water. Preferably, the concentration of the ammonia water is 17-340 g / L. If the mass fraction of the ammonia water is too large, the specific surface area of the silica will be too low; if the mass fraction of the ammonia water is too small, the specific surface area of the silica will be too large.

[0017] Preferably, in step (1), the method of the mixing reaction comprises the following steps: introducing ammonia water and a mixed solution into a tubular reactor, and reacting the ammonia water and the mixed solution in the tubular reactor in a flowing state until the end point to obtain the mixed material; the mixed solution mainly consists of ammonia water and a fluorosilicic acid solution, and the pH of the mixed solution is 1-6. For example, the pH of the mixed solution is 2.5-3. Preferably, the temperature of the mixing reaction is 10-60°C. For example, the temperature of the mixing reaction is 50-55°C.

[0018] Preferably, the mixed solution is prepared by a method comprising the following steps: introducing ammonia water and a fluorosilicic acid solution into a tubular reactor, and reacting the ammonia water and the fluorosilicic acid solution in the tubular reactor in a flowing state until the end point to obtain the mixed solution. Preferably, the reaction temperature for preparing the mixed solution is 10-55°C. For example, the reaction temperature for preparing the mixed solution is 45°C.

[0019] Preferably, the tubular reactor is a plug flow reactor.

[0020] Preferably, the pressure filtration is carried out using a plate and frame filter press. Compared with other pressure filtration equipment, the advantages of using a plate and frame filter press are easy operation, stable operation, flexible filtration area, and easy pressure control. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a process schematic diagram of the preparation method of silica in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] The technical solutions of the present invention will be further described below with reference to specific embodiments.

[0023] Example 1

[0024] The preparation method of silica in this example is as Figure 1 shown, and specifically comprises the following steps:

[0025] (1) A fluorosilicic acid solution with a mass fraction of 10% and ammonia water with a concentration of 34 g / L are fed into a plug flow reactor. The feeding rate of the fluorosilicic acid solution is controlled at 200 g / min, and the feeding rate of the ammonia water is 0.16 L / min. The fluorosilicic acid solution and the ammonia water react while flowing in the plug flow reactor. The reaction temperature is controlled at 45 °C. When the materials flow to a certain position in the plug flow reactor, the reaction reaches the end point, forming a mixed solution with a pH of 2.5. At the same time, ammonia water with a concentration of 34 g / L is fed into the plug flow reactor from this position at a feeding rate of 0.25 L / min. The mixed solution and the fed ammonia water continue to react while flowing in the plug flow reactor. The reaction temperature is controlled at 50 °C. When the materials flow to the outlet of the plug flow reactor, the reaction reaches the end point and flows out of the plug flow reactor, obtaining a mixed material. The pH of the mixed material is 6.5, and the mixed material is in a gel state;

[0026] (2) The mixed material obtained in step (1) is left standing at room temperature for aging. The aging time is 3 h. After the aging is completed, an aged material is obtained;

[0027] (3) Then, the aged material and ammonia water with a concentration of 34 g / L are added to a reaction kettle and stirred until the pH of the materials in the reaction kettle reaches 7.5 and no longer changes. Then, the materials in the reaction kettle are filtered using a plate and frame filter press. The pressure of the plate and frame filter press is 0.5 MPa. Then, the filtered solid is dried until the weight no longer changes, obtaining white carbon black.

[0028] Example 2

[0029] The difference between the preparation method of white carbon black in this example and the preparation method of white carbon black in Example 1 is only that the pressure of the plate and frame filter press in step (3) of the preparation method of white carbon black in this example is 0.7 MPa.

[0030] Example 3

[0031] The difference between the preparation method of white carbon black in this example and the preparation method of white carbon black in Example 1 is only that the aging time in step (2) of the preparation method of white carbon black in this example is 8 h.

[0032] Example 4

[0033] The preparation method of white carbon black in this example specifically includes the following steps:

[0034] (1) A fluorosilicic acid solution with a mass fraction of 35% and ammonia water with a concentration of 34 g / L are introduced into a plug-flow reactor. The flow rate of the fluorosilicic acid solution is controlled at 250 g / min, and the flow rate of the ammonia water is controlled at 0.625 L / min. The fluorosilicic acid solution and the ammonia water react while flowing in the plug-flow reactor. The reaction temperature is controlled at 45 °C. When the materials flow to a certain position in the plug-flow reactor, the reaction reaches the end point, forming a mixed solution with a pH of 2.5. At the same time, ammonia water with a concentration of 34 g / L is introduced into the plug-flow reactor from this position at a flow rate of 1.1 L / min. The mixed solution and the introduced ammonia water continue to react while flowing in the plug-flow reactor. The reaction temperature is controlled at 50 °C. When the materials flow to the outlet of the plug-flow reactor, the reaction reaches the end point and flows out of the plug-flow reactor, obtaining a mixed material. The pH of the mixed material is 6, and the mixed material is in a gel state;

[0035] (2) The mixed material obtained in step (1) is left standing at room temperature for aging. The aging time is 3 h. After aging, an aged material is obtained;

[0036] (3) Then, the aged material and ammonia water with a concentration of 34 g / L are added to a reaction kettle and stirred until the pH of the materials in the reaction kettle reaches 7.5 and no longer changes. Then, the materials in the reaction kettle are filtered using a plate-and-frame filter press. The pressure of the plate-and-frame filter press is 0.7 MPa. Then, the filtered solid is dried until the weight no longer changes, obtaining white carbon black.

[0037] Example 5

[0038] The preparation method of white carbon black in this example specifically includes the following steps:

[0039] (1) A fluorosilicic acid solution with a mass fraction of 25% and ammonia water with a concentration of 17 g / L are introduced into a plug-flow reactor. The flow rate of the fluorosilicic acid solution is controlled at 200 g / min, and the flow rate of the ammonia water is controlled at 0.7 L / min. The fluorosilicic acid solution and the ammonia water react while flowing in the plug-flow reactor. The reaction temperature is controlled at 45 °C. When the materials flow to a certain position in the plug-flow reactor, the reaction reaches the end point, forming a mixed solution with a pH of 3.0. At the same time, ammonia water with a concentration of 17 g / L is introduced into the plug-flow reactor from this position at a flow rate of 1.5 L / min. The mixed solution and the introduced ammonia water continue to react while flowing in the plug-flow reactor. The reaction temperature is controlled at 55 °C. When the materials flow to the outlet of the plug-flow reactor, the reaction reaches the end point and flows out of the plug-flow reactor, obtaining a mixed material. The pH of the mixed material is 7, and the mixed material is in a gel state;

[0040] (2) The mixed material obtained in step (1) is left standing at room temperature for aging. The aging time is 3 h. After aging, an aged material is obtained;

[0041] (3) Then add the aged material and ammonia water with a concentration of 17 g / L into the reaction kettle, stir until the pH of the material in the reaction kettle reaches 8.0 and remains unchanged, then filter the material in the reaction kettle using a plate and frame filter press with a pressure of 0.6 MPa, and then dry the filtered solid until its weight remains unchanged to obtain silica white.

[0042] Example 6

[0043] The preparation method of silica white in this example specifically includes the following steps:

[0044] (1) Feed a fluorosilicic acid solution with a mass fraction of 25% and ammonia water with a concentration of 340 g / L into a plug flow reactor, control the feeding rate of the fluorosilicic acid solution to be 200 g / min and the feeding rate of the ammonia water to be 0.036 L / min. The fluorosilicic acid solution and ammonia water react while flowing in the plug flow reactor, control the reaction temperature to be 45°C. When the material flows to a certain position in the plug flow reactor, the reaction reaches the end point, forming a mixed solution with a pH of 3.0. At the same time, feed ammonia water with a concentration of 340 g / L into the plug flow reactor from this position at a feeding rate of 0.074 L / min. The mixed solution and the fed ammonia water continue to react while flowing in the plug flow reactor, control the reaction temperature to be 55°C. When the material flows to the outlet of the plug flow reactor, the reaction reaches the end point and flows out of the plug flow reactor to obtain a mixed material with a pH of 6.5, and the mixed material is in a gel state;

[0045] (2) Let the mixed material obtained in step (1) stand at room temperature for aging for 3 h. After the aging is completed, obtain the aged material;

[0046] (3) Then add the aged material and ammonia water with a concentration of 340 g / L into the reaction kettle, stir until the pH of the material in the reaction kettle reaches 8.0 and remains unchanged, then filter the material in the reaction kettle using a plate and frame filter press with a pressure of 0.6 MPa, and then dry the filtered solid until its weight remains unchanged to obtain silica white.

[0047] Example 7

[0048] The preparation method of silica white in this example specifically includes the following steps:

[0049] (1) A 25% by mass fluorosilicic acid solution and ammonia water with a concentration of 340 g / L are introduced into a plug flow reactor. The flow rate of the fluorosilicic acid solution is controlled at a certain value, and the flow rate of the ammonia water is 0.036 L / min. The fluorosilicic acid solution and the ammonia water react while flowing in the plug flow reactor. The reaction temperature is controlled at 45 °C. When the material flows to a certain position in the plug flow reactor, the reaction reaches the end point, forming a mixed solution with a pH of 1. At the same time, ammonia water with a concentration of 340 g / L is introduced into the plug flow reactor from this position at a flow rate of 0.074 L / min. The mixed solution and the introduced ammonia water continue to react while flowing in the plug flow reactor. The reaction temperature is controlled at 55 °C. When the material flows to the outlet of the plug flow reactor, the reaction reaches the end point and flows out of the plug flow reactor, obtaining a mixed material. The pH of the mixed material is 6.5, and the mixed material is in a gel state;

[0050] (2) The mixed material obtained in step (1) is left standing at room temperature for aging. The aging time is 3 h. After aging, an aged material is obtained;

[0051] (3) Then, the aged material and ammonia water with a concentration of 340 g / L are added to a reaction kettle and stirred until the pH of the material in the reaction kettle reaches 8.0 and no longer changes. Then, the material in the reaction kettle is filtered using a plate and frame filter press. The pressure of the plate and frame filter press is 0.6 MPa. Then, the solid obtained by filtration is dried until the weight no longer changes, obtaining white carbon black.

[0052] Example 8

[0053] The preparation method of white carbon black in this example specifically includes the following steps:

[0054] (1) A 25% by mass fluorosilicic acid solution and ammonia water with a concentration of 340 g / L are introduced into a plug flow reactor. The flow rate of the fluorosilicic acid solution is controlled at a certain value, and the flow rate of the ammonia water is 0.036 L / min. The fluorosilicic acid solution and the ammonia water react while flowing in the plug flow reactor. The reaction temperature is controlled at 45 °C. When the material flows to a certain position in the plug flow reactor, the reaction reaches the end point, forming a mixed solution with a pH of 6. At the same time, ammonia water with a concentration of 340 g / L is introduced into the plug flow reactor from this position at a flow rate of 0.074 L / min. The mixed solution and the introduced ammonia water continue to react while flowing in the plug flow reactor. The reaction temperature is controlled at 55 °C. When the material flows to the outlet of the plug flow reactor, the reaction reaches the end point and flows out of the plug flow reactor, obtaining a mixed material. The pH of the mixed material is 6.5, and the mixed material is in a gel state;

[0055] (2) The mixed material obtained in step (1) is left standing at room temperature for aging. The aging time is 3 h. After aging, an aged material is obtained;

[0056] (3) Then add the aged material and ammonia water with a concentration of 340 g / L into the reaction kettle, stir until the pH of the material in the reaction kettle reaches 8.0 and no longer changes, then filter the material in the reaction kettle using a plate-and-frame filter press with a pressure of 0.6 MPa, and then dry the filtered solid until its weight no longer changes to obtain silica white.

[0057] Comparative Example 1

[0058] The difference between the preparation method of silica white in this comparative example and the preparation method of silica white in Example 1 is only that the aging time in step (2) of the preparation method of silica white in this comparative example is 0.5 h.

[0059] Comparative Example 2

[0060] The difference between the preparation method of silica white in this comparative example and the preparation method of silica white in Example 1 is only that the aging time in step (2) of the preparation method of silica white in this comparative example is 8.5 h.

[0061] Comparative Example 3

[0062] The difference between the preparation method of silica white in this example and the preparation method of silica white in Example 1 is only that the pressure of the plate-and-frame filter press in step (3) of the preparation method of silica white in this example is 1.0 MPa.

[0063] Comparative Example 4

[0064] The difference between the preparation method of silica white in this comparative example and the preparation method of silica white in Example 2 is only that the aging time in the preparation method of silica white in this comparative example is 0, that is, no aging is carried out, but the mixture is directly filtered.

[0065] Comparative Example 5

[0066] The difference between the preparation method of silica white in this example and the preparation method of silica white in Example 2 is only that the pressure of the plate-and-frame filter press in step (3) of the preparation method of silica white in this example is 0.3 MPa.

[0067] Comparative Example 6

[0068] The difference between the preparation method of silica white in this comparative example and the preparation method of silica white in Example 4 is only that the pressure of the plate-and-frame filter press in step (3) of the preparation method of silica white in this comparative example is 0.8 MPa.

[0069] Comparative Example 7

[0070] The difference between the preparation method of the silica in this comparative example and that in Example 3 lies only in that in step (1) of the preparation method of the silica in this comparative example, a fluosilicic acid solution with a mass fraction of 40% is used, and the feeding amount of the fluosilicic acid solution is adjusted to ensure that the pH of the mixed solution and the pH of the mixed material are the same as those of the mixed solution and the mixed material in Example 3, respectively.

[0071] Comparative Example 8

[0072] The difference between the preparation method of the silica in this comparative example and that in Example 3 lies only in that in step (1) of the preparation method of the silica in this comparative example, ammonia water with a concentration of 12 g / L is used, and the feeding amount of the ammonia water is adjusted to ensure that the pH of the mixed solution and the pH of the mixed material are the same as those of the mixed solution and the mixed material in Example 3, respectively.

[0073] The mass fraction of the fluosilicic acid solution, the concentration of the ammonia water, the aging time, and the pressure of the plate and frame filter press used in Examples 1-6 and Comparative Examples 1-6 are listed in Table 1.

[0074] Table 1 The mass fraction of the fluosilicic acid solution, the concentration of the ammonia water, the aging time, and the pressure of the plate and frame filter press used in Examples 1-6 and Comparative Examples 1-6

[0075]

[0076] Experimental Example

[0077] To evaluate the specific surface area of the silica prepared by the preparation methods of the silica in Examples 1-8 and Comparative Examples 1-8 and the difference in the specific surface area of the silica prepared in different batches, the preparation methods of the silica in Examples 1-8 and Comparative Examples 1-8 were repeated 10 times respectively, and then the specific surface area tests were carried out on 3 samples prepared by each method (the specific surface area was tested by the nitrogen adsorption method). During the test, several sampling points were selected from different positions of each sample for testing, and then the specific surface areas tested at different positions selected from the 3 samples prepared by the same method were summarized and expressed in the form of average value ± fluctuation range. The size of the average value represents the size of the specific surface area of the corresponding sample, and the fluctuation range represents the stability of the preparation method of the corresponding sample. The smaller the fluctuation range, the smaller the difference in the specific surface area of the silica prepared in different batches by the corresponding method. The specific surface areas of the silica prepared by different methods are shown in Table 2.

[0078] Table 2 The specific surface areas of the silica prepared by different methods

[0079] Preparation method <![CDATA[Specific surface area (m 2 ·g -1 )]]> Example 1 180±10 Example 2 180±5 Example 3 185±5 Example 4 190±15 Example 5 190±10 Example 6 180±10 Example 7 180±10 Example 8 190±15 Comparative example 1 180±15 Comparative example 2 140±5 Comparative example 3 140±5 Comparative example 4 220±20 Comparative example 5 150±15 Comparative example 6 140±15 Comparative example 7 140±15 Comparative example 8 140±15

[0080] To study the influence of reaction temperature on the experimental results, silica was prepared according to the preparation method of silica in Example 1, except that the temperature for preparing the mixed solution in step (1) was adjusted from 45 °C to 10 °C or 55 °C. It was found that the specific surface area of the prepared silica was the same as that of the silica prepared in Example 1. At the same time, the temperature for the reaction of the mixed solution and ammonia water to prepare the mixed material in step (1) was adjusted from 50 °C to 10 °C or 60 °C. It was found that the specific surface area of the prepared silica was the same as that of the silica prepared in Example 1.

Claims

1. A method for preparing silica, characterized in that, It includes the following steps: (1) Mix fluosilicic acid and an ammoniating agent in water and react until the end point to obtain a mixed material with a pH of 6 - 7; (2) Age the mixed material to obtain an aged material; the aging time is 0.5 - 8 h; (3) React the aged material with an ammoniating agent until the end point to obtain a mixture with a pH of 7 - 8, then perform solid - liquid separation on the mixture, and the solid obtained from the solid - liquid separation is silica white; the solid - liquid separation is pressure filtration, and the pressure of the pressure filtration is 0.5 - 0.7 MPa; The ammoniating agent in step (1) and step (3) is independently ammonia water or ammonia gas.

2. The method for preparing silica as claimed in claim 1, wherein, The aging time is 3 - 8 h.

3. The method for preparing silica as claimed in claim 1 or 2, characterized in that, The fluosilicic acid is used in the form of a fluosilicic acid solution; the mass fraction of the fluosilicic acid solution is 10 - 35%.

4. The method for preparing silica as claimed in claim 1 or 2, characterized in that, The ammoniating agent in step (1) and step (3) is ammonia water; the concentration of the ammonia water is 17 - 340 g / L.

5. The method for preparing silica as claimed in claim 1 or 2, characterized in that, In step (1), the method of the mixing reaction includes the following steps: Pass ammonia water and a mixed solution into a tubular reactor, and react ammonia water and the mixed solution in the tubular reactor in a flowing state until the end point to obtain the mixed material; the mixed solution is mainly composed of ammonia water and a fluosilicic acid solution, and the pH of the mixed solution is 1 - 6.

6. The method for preparing silica as claimed in claim 5, wherein The pH of the mixed solution is 2.5 - 3.

7. The method for preparing silica as claimed in claim 5, characterized in that, The temperature of the mixing reaction is 10 - 60 °C.

8. The preparation method of silica as claimed in claim 5, characterized in that, The mixed solution is obtained by a method including the following steps: Pass ammonia water and a fluosilicic acid solution into a tubular reactor, and react ammonia water and the fluosilicic acid solution in the tubular reactor in a flowing state until the end point to obtain the mixed solution.

9. The method for preparing silica as claimed in claim 8, wherein, The reaction temperature when preparing the mixed solution is 10 - 55 °C.

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