Ultrafine whitening high-viscosity-concentration kaolin as well as preparation method and application thereof

Abstract

The invention relates to the field of kaolin preparation, and discloses ultrafine whitened high-viscosity-concentration kaolin and a preparation method and application thereof.The preparation method comprises the steps that kaolin raw ore is subjected to pulping dispersion, sand and impurity removal, magnetic separation iron removal, bleaching treatment and calcination treatment, and pretreated kaolin is obtained; pulping and dispersing the pretreated kaolin; carrying out spray drying and sintering on the kaolin suspension slurry; pulping kaolin microsphere particles, uniformly stirring, adding sodium hexametaphosphate, adjusting the pH value of the system to 9-10, heating to 70-85 DEG C, dropwise adding a sodium metaaluminate solution and a dilute sulphuric acid solution in a parallel flow manner, keeping the pH value of the system, stirring, reacting, and aging to obtain alumina coated kaolin; the preparation method comprises the following steps: putting alumina-coated kaolin into a tetraethyl orthosilicate impregnation liquid, uniformly impregnating, drying and roasting, adding the prepared product into a ceramic coating, and endowing the coating with high hardness, high bonding strength, excellent wear resistance, excellent corrosion resistance and excellent fire resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of kaolin preparation, and particularly relates to ultrafine whitening high-viscosity concentration kaolin and a preparation method and application thereof. Background Art

[0002] Kaolin is physically soft and fine, appearing as a white powder. However, powdered kaolin is a product of purification. Actual mined kaolin is often of low purity and contaminated with natural impurities, resulting in a gray or brown color. Not only does it lack the pristine whiteness of pure kaolin, but its chemical properties also suffer, impacting its effectiveness and performance. The excellent refractory properties of pure kaolin determine its excellent chemical properties. Kaolin used in chemical production often requires purification and whitening.

[0003] Thermal spraying of ceramic materials is a new type of surface treatment and surface strengthening professional technology with wide practical application. It has excellent properties that many metal materials cannot match, so it has developed rapidly and played an increasingly important role in many fields. Plasma spraying, as a type of thermal spraying, has become a major surface technology for preparing ceramic coatings due to its advantages of low cost, high deposition efficiency, ease of large-area preparation, and strong adaptability. Kaolin is one of the important raw materials for ceramic materials. The limited interface bonding and intrinsic brittleness of kaolin used in the preparation of ceramic coatings using plasma spraying kaolin limit the significant improvement of various properties such as corrosion resistance, mechanical properties, and bonding strength, thereby restricting the large-scale application of plasma sprayed ceramic coatings in industry. Summary of the Invention

[0004] In order to solve the deficiencies mentioned in the above background technology, the purpose of the present invention is to provide an ultra-fine whitened high-viscosity concentration kaolin and its preparation method and application, so that the prepared ceramic coating has high hardness, good bonding strength, wear resistance, corrosion resistance and fire resistance.

[0005] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing ultrafine whitened high-viscosity kaolin comprises the following steps: S1, preparing pretreated kaolin by pulping and dispersing the kaolin ore, removing sand and impurities, removing iron by magnetic separation, bleaching, and calcining; S2. Prepare a kaolin slurry by adding pretreated kaolin to deionized water, add sodium hexametaphosphate to the kaolin slurry, ultrasonically vibrate the slurry, let it stand, and then filter to obtain a kaolin suspension slurry; S3, spray drying and sintering the kaolin suspension slurry to prepare kaolin microsphere particles; S4. Take kaolin microsphere particles and dissolve them in deionized water, beat and stir them evenly, add sodium hexametaphosphate, use sodium hydroxide to adjust the pH value of the system to 9-10, heat to 70-85°C, and add sodium metaaluminate solution and dilute sulfuric acid solution dropwise to maintain the pH value of the system. Stir and react for 0.5-1h. After the reaction is completed, age for 24-28h, filter, wash, and dry to prepare alumina-coated kaolin; S5. Prepare an impregnation solution of tetraethyl orthosilicate using ethanol as a solvent, with a mass fraction of 5% based on silicon oxide. Place the alumina-coated kaolin in the impregnation solution, impregnate it evenly, dry it at 100-120°C for 20-24 hours, and then calcine it at 550-600°C for 2-4 hours to prepare ultrafine, whitened, and high-viscosity concentrated kaolin.

[0006] Preferably, the preparation method of pretreated kaolin in step S1 specifically comprises the following steps: (1) The kaolin ore is coarsely crushed by a grinding mill and then transported to a slurry machine, and deionized water and sodium hexametaphosphate are added to the slurry machine to form a slurry with a concentration of 20-40%; (2) Desanding the initial slurry to remove coarse impurities to obtain slurry; (3) transporting the slurry to a high gradient magnetic separator for iron removal to obtain iron-removed slurry; (4) Add sulfuric acid with a concentration of 2-4 mol / L to the iron removal slurry to adjust the pH value of the iron removal slurry to 2-3. After the adjustment is completed, add 0.1-0.2 wt% of hydrosulfite and stir evenly. Then add 0.1-0.15 wt% of oxalic acid for complexation, filter and wash with water to obtain a bleached slurry; (5) The bleached slurry is filtered through a filter press, dried and ground, and the ground powder obtained is evenly mixed with sodium chloride and calcined at 1000-1200°C for 1-1.5 hours to prepare pretreated kaolin.

[0007] Preferably, the particle size of the pretreated kaolin is 2-5 μm.

[0008] Preferably, the solid content of the kaolin slurry is 25-30%; the mass of the sodium hexametaphosphate is 0.1-0.3% of the mass of the pretreated kaolin.

[0009] Preferably, the process parameters of the spray drying are: spray pressure of 1.2 MPa and inlet temperature of 140°C.

[0010] Preferably, the sintering process parameters are: first heating to 850-900°C, cooling and then heating to 1100-1200°C and keeping warm for 1-1.5 hours, cooling again and then heating to 1100-1200°C and keeping warm for 3.5-4 hours.

[0011] Preferably, the concentration of the kaolin microsphere particles is 175-200 g / L; the mass of the sodium hexametaphosphate is 0.1-0.3% of the mass of the kaolin microsphere particles.

[0012] Preferably, the concentration of the sodium metaaluminate solution is 1-2 mol / L; the concentration of the dilute sulfuric acid solution is 0.5-1 mol / L; and the coating amount of the alumina-coated kaolin is 3-4%.

[0013] An ultrafine whitening high-viscosity concentration kaolin is prepared by the above-mentioned preparation method.

[0014] An application of the ultrafine, whitened, high-viscosity concentrated kaolin according to claim 1, wherein the ultrafine, whitened, high-viscosity concentrated kaolin is applied to spray-formed ceramic coatings.

[0015] Beneficial effects of the present invention: The present invention purifies the kaolin ore through pulping and dispersion, sand and impurity removal, magnetic separation and iron removal, bleaching treatment, and calcination treatment. The whiteness and comprehensive performance of the prepared pretreated kaolin are improved, and it has a high utilization value. The present invention spray-dries the pretreated kaolin to prepare micron-sized ceramic microspheres, and adopts a secondary sintering method to prepare kaolin microsphere particles with excellent strength, hardness, and dispersibility. Then, the kaolin microsphere particles are used as the core and sodium aluminate is used as the coating agent to prepare alumina-coated kaolin with a core-shell structure. Subsequently, it is modified with an impregnation solution of tetraethyl orthosilicate and calcined to prepare ultra-fine whitened high-viscosity concentration kaolin, wherein the alumina serves as an intermediate layer and has good chemical compatibility with the kaolin microsphere particles and the silicon dioxide subsequently generated by tetraethyl orthosilicate, which can reduce interface defects and enhance the bonding strength between particles in the coating. At the same time, the silanol formed by the tetraethyl orthosilicate modification will replace the surface of the alumina. Aluminum hydroxyl groups form Al-O-Si bonds, improving interfacial bonding strength and mechanical properties, and alumina coating can improve the fluidity and dispersibility of spherical kaolin microsphere particles, making the particle distribution more uniform during injection molding and the coating density higher. In addition, the nano-scale silica coating formed on the surface of the alumina coating after the hydrolysis of tetraethyl orthosilicate further densifies the coating structure, which can effectively block the penetration of corrosive media. In addition, the ultra-fine whitening high-viscosity concentration kaolin prepared by the present invention is spherical in shape. When used as a reinforcing material for the coating, it can overcome the anisotropy of irregular-shaped reinforcing materials such as needle-shaped, fibrous, spindle-shaped, and sheet-shaped, reduce the stress concentration generated at the sharp corners, and improve the strength and plasticity of the matrix. The ultra-fine whitening high-viscosity concentration kaolin prepared by the present invention can be used in injection-molded ceramic coatings, giving the coating excellent wear resistance, bonding strength, fire resistance, corrosion resistance, and high hardness. DETAILED DESCRIPTION

[0016] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0017] Example 1 A method for preparing pretreated kaolin comprises the following steps: (1) The kaolin ore is coarsely crushed by a grinding mill and then transported to a slurry machine. Deionized water and sodium hexametaphosphate (0.1% by weight of the kaolin ore) are added to the slurry machine to form a 30% concentration of slurry. (2) Desanding the initial slurry to remove coarse impurities to obtain slurry; (3) transporting the slurry to a high gradient magnetic separator for two iron removals to obtain iron-removed slurry; (4) Add 3 mol / L sulfuric acid to the iron removal slurry to adjust the pH value of the iron removal slurry to 3. After the adjustment is completed, add 0.2 wt% of hydrosulfite and stir evenly. Then add 0.15 wt% of oxalic acid for complexation, filter and wash with water to obtain a bleached slurry; (5) The bleached slurry was filtered through a filter press, dried and ground, and the ground powder was mixed evenly with sodium chloride, and calcined at 1200°C for 1.5 hours. The amount of sodium chloride added was 1.5 wt% of the ground powder to prepare pretreated kaolin.

[0018] Example 2 A method for preparing ultrafine whitening high viscosity kaolin comprises the following steps: S1. The pretreated kaolin prepared in Example 1 was added to deionized water to prepare a kaolin slurry with a solid content of 25%, and sodium hexametaphosphate (0.1% by mass of the pretreated kaolin) was added to the kaolin slurry, and the mixture was stirred and dispersed uniformly. The obtained suspension was then poured into a ball mill and ball milled, followed by ultrasonic oscillation for 0.5 h. Finally, the mixture was allowed to stand for 1 h and then filtered to obtain a kaolin suspension slurry. S2. The kaolin suspension slurry was spray dried and sintered at a spray pressure of 1.2 MPa and an inlet temperature of 140° C. The sintering process parameters were as follows: first heating to 850° C., then cooling and heating to 1120° C. and keeping the temperature for 1.5 h, then cooling again and heating to 1120° C. and keeping the temperature for 4 h, with a heating rate of 5° C. / min, to prepare kaolin microsphere particles; S3, take kaolin microsphere particles and dissolve them in deionized water, beat and stir them evenly to obtain a slurry with a concentration of 180g / L, add sodium hexametaphosphate (0.1% by weight of the kaolin microsphere particles), use sodium hydroxide to adjust the pH value of the system to 10, heat to 75°C, and add 1mol / L sodium metaaluminate solution and 0.5mol / L dilute sulfuric acid solution dropwise in parallel, with a coating amount of 3%, maintain the pH value of the system, stir and react for 0.5h, age for 24h after the reaction is completed, filter, wash, and dry to prepare alumina-coated kaolin; S4. Prepare an impregnation solution of tetraethyl orthosilicate using ethanol as a solvent, with a mass fraction of 5% based on silicon oxide. Place the alumina-coated kaolin in the impregnation solution, impregnate it evenly, dry it at 120°C for 24 hours, and then calcine it at 550°C for 4 hours to prepare ultrafine, whitened, and high-viscosity concentrated kaolin.

[0019] Example 3 A method for preparing ultrafine whitened high-viscosity kaolin comprises the following steps: S1. The pretreated kaolin prepared in Example 1 was added to deionized water to prepare a kaolin slurry with a solid content of 30%, and sodium hexametaphosphate (0.2% by mass of the pretreated kaolin) was added to the kaolin slurry, and the mixture was stirred and dispersed uniformly. The obtained suspension was then poured into a ball mill and ball milled, followed by ultrasonic oscillation for 0.5 h, and finally allowed to stand for 1 h and then filtered to prepare a kaolin suspension slurry; S2. The kaolin suspension slurry was spray dried and sintered at a spray pressure of 1.2 MPa and an inlet temperature of 140° C. The sintering process parameters were as follows: first heating to 900° C., cooling, then heating to 1150° C. and keeping the temperature for 1.5 h, then cooling again, then heating to 1150° C. and keeping the temperature for 4 h, with a heating rate of 5° C. / min, to prepare kaolin microsphere particles; S3, take kaolin microsphere particles and dissolve them in deionized water, beat and stir them evenly to obtain a slurry with a concentration of 200 g / L, add sodium hexametaphosphate (0.2% by mass of kaolin microsphere particles), use sodium hydroxide to adjust the pH value of the system to 10, heat to 80°C, and add 1.5 mol / L sodium metaaluminate solution and 0.5 mol / L dilute sulfuric acid solution dropwise in parallel, with a coating amount of 4%, maintain the pH value of the system, stir and react for 0.5 h, age for 25 h after the reaction is completed, filter, wash, and dry to prepare alumina-coated kaolin; S4. Prepare an impregnation solution of tetraethyl orthosilicate using ethanol as a solvent, with a mass fraction of 5% based on silicon oxide. Place the alumina-coated kaolin in the impregnation solution, impregnate it evenly, dry it at 120°C for 24 hours, and then calcine it at 580°C for 3 hours to prepare ultra-fine, whitened, and high-viscosity concentration kaolin.

[0020] Example 4 A method for preparing ultrafine whitened high-viscosity kaolin comprises the following steps: S1. The pretreated kaolin prepared in Example 1 was added to deionized water to prepare a kaolin slurry with a solid content of 30%, and sodium hexametaphosphate (0.3% by mass of the pretreated kaolin) was added to the kaolin slurry, and the mixture was stirred and dispersed uniformly. The obtained suspension was then poured into a ball mill and ball milled, followed by ultrasonic oscillation for 0.5 h, and finally allowed to stand for 1 h and then filtered to prepare a kaolin suspension slurry; S2. The kaolin suspension slurry was spray dried and sintered at a spray pressure of 1.2 MPa and an inlet temperature of 140°C. The sintering process parameters were as follows: first heating to 900°C, cooling, then heating to 1200°C and holding for 1 hour, cooling again, then heating to 1200°C and holding for 3.5 hours, with a heating rate of 5°C / min, to prepare kaolin microsphere particles. S3, take kaolin microsphere particles and dissolve them in deionized water, beat and stir them evenly to obtain a slurry with a concentration of 200 g / L, add sodium hexametaphosphate (0.3% by mass of the kaolin microsphere particles), use sodium hydroxide to adjust the pH value of the system to 10, heat to 85°C, and add 2 mol / L sodium metaaluminate solution and 1 mol / L dilute sulfuric acid solution dropwise in parallel, with a coating amount of 4%, maintain the pH value of the system, stir and react for 1 hour, age for 27 hours after the reaction is completed, filter, wash, and dry to prepare alumina-coated kaolin; S4. Prepare an impregnation solution of tetraethyl orthosilicate using ethanol as a solvent, with a mass fraction of 5% based on silicon oxide. Place the alumina-coated kaolin in the impregnation solution, impregnate it evenly, dry it at 120°C for 24 hours, and then calcine it at 550°C for 4 hours to prepare ultrafine, whitened, and high-viscosity concentrated kaolin.

[0021] Comparative Example 1 A method for preparing ultrafine whitening high-viscosity kaolin comprises the following steps: S1. The pretreated kaolin prepared in Example 1 was added to deionized water to prepare a kaolin slurry with a solid content of 30%, and sodium hexametaphosphate (0.3% by mass of the pretreated kaolin) was added to the kaolin slurry, and the mixture was stirred and dispersed uniformly. The obtained suspension was then poured into a ball mill and ball milled, followed by ultrasonic oscillation for 0.5 h, and finally allowed to stand for 1 h and then filtered to prepare a kaolin suspension slurry; S2. The kaolin suspension slurry was spray dried and sintered at a spray pressure of 1.2 MPa and an inlet temperature of 140° C. The sintering process parameters were set as follows: directly heating to 1200° C. and holding for 4 h at a heating rate of 5° C. / min to prepare kaolin microsphere particles; S3, take the kaolin microspheres in deionized water, beat the pulp and stir uniformly to obtain a slurry with a concentration of 200 g / L, add 0.3% sodium hexametaphosphate of the mass of the kaolin microspheres, adjust the pH value of the system to 10 with sodium hydroxide, heat to 85℃, and add 2 mol / L sodium metaaluminate solution and 1 mol / L dilute sulfuric acid solution by parallel flow drop, the coating amount is 4%, keep the pH value of the system, stir for 1 h, after the reaction is completed, age for 27 h, filter, wash and dry to prepare the alumina-coated kaolin; S4, prepare a tetraethyl orthosilicate impregnating solution with ethanol as the solvent, the mass fraction of silicon oxide is 5%, place the alumina-coated kaolin in the impregnating solution, dry at 120℃ for 24 h after uniform impregnation, then calcine at 550℃ for 4 h to prepare the superfined whitening high-viscosity concentration kaolin.

[0022] Comparative Example 2 A preparation method of a superfined whitening high-viscosity concentration kaolin, comprising the following steps: S1, take the pretreated kaolin prepared in Example 1 to prepare a kaolin slurry with a solid content of 30% in deionized water, add 0.3% sodium hexametaphosphate of the mass of the pretreated kaolin to the kaolin slurry, stir and disperse uniformly, then pour the obtained suspension into a ball mill, then ultrasonic oscillation for 0.5 h, finally after standing for 1 h, filter to prepare a kaolin suspension slurry; S2, spray dry and sinter the kaolin suspension slurry, the spray pressure is 1.2 MPa, the inlet temperature is 140℃, the sintering process parameters are set as follows: first heat to 900℃, cool, then heat to 1200℃ and keep for 1 h, cool again, then heat to 1200℃ and keep for 3.5 h, the heating rate is 5℃ / min, to prepare the kaolin microspheres; S3, take the kaolin microspheres in deionized water, beat the pulp and stir uniformly to obtain a slurry with a concentration of 200 g / L, add 0.3% sodium hexametaphosphate of the mass of the kaolin microspheres, adjust the pH value of the system to 10 with sodium hydroxide, heat to 85℃, and add 2 mol / L sodium metaaluminate solution and 1 mol / L dilute sulfuric acid solution by parallel flow drop, the coating amount is 4%, keep the pH value of the system, stir for 1 h, after the reaction is completed, age for 27 h, filter, wash and dry to prepare the superfined whitening high-viscosity concentration kaolin.

[0023] Comparative Example 3 A preparation method of a superfined whitening high-viscosity concentration kaolin, comprising the following steps: S1. The pretreated kaolin prepared in Example 1 was added to deionized water to prepare a kaolin slurry with a solid content of 30%, and sodium hexametaphosphate (0.3% by mass of the pretreated kaolin) was added to the kaolin slurry, and the mixture was stirred and dispersed uniformly. The obtained suspension was then poured into a ball mill and ball milled, followed by ultrasonic oscillation for 0.5 h, and finally allowed to stand for 1 h and then filtered to prepare a kaolin suspension slurry; S2. The kaolin suspension slurry is spray dried and sintered with a spray pressure of 1.2 MPa and an inlet temperature of 140°C. The sintering process parameters are set as follows: first heating to 900°C, then cooling and rapidly heating to 1200°C and keeping warm for 1 hour, then cooling again and heating to 1200°C and keeping warm for 3.5 hours. The heating rate is 5°C / min to prepare ultrafine whitening and high-viscosity concentration kaolin.

[0024] Comparative Example 4 The pretreated kaolin prepared in Example 1 was used.

[0025] Performance testing The kaolin prepared in Examples 2-4 and Comparative Examples 1-4 was used as a spraying raw material, and stainless steel 304 was ultrasonically cleaned with acetone as a substrate. A ceramic coating was prepared by atmospheric plasma spraying technology, and performance testing was performed: the hardness of the coating cross section was tested using a Vickers hardness tester, with a load of 200 g (1.96 N) and a holding time of 15 s. 15 areas of each coating were randomly selected for measurement and the average value was taken; the bonding strength between the coating and the substrate was tested using a universal testing machine according to GB / T 8642-2002 standard; under ambient temperature and relative humidity of 45%, Si3N4 grinding balls (diameter 6.35 mm) were used as a grinding pair, and a wear test was performed on the coating in the ball-disc reciprocating wear mode of a pin-disc friction and wear tester. Before the wear test, the surface of the coating sample was first ground and polished to a roughness of 0.02 μm. The wear test parameters were: 10 N vertical load, 400 r / min rotation speed, and 30 min test time; according to GB / T 9274-1988 was tested for acid and alkali corrosion resistance, with the acid resistance being 10% sulfuric acid solution and the alkali resistance being 10% sodium hydroxide solution. Butane oxide (1200°C) was used as an instantaneous high-temperature heat source, and the coating changes were observed at 2, 4, and 10 minutes of the burning process. The fire resistance performance test was performed, and the data results are shown in Table 1.

[0026] Table 1 Sample performance test results

[0027] As can be seen from the data results in Table 1, the ceramic coatings prepared in Examples 2-4 of the present invention have high hardness and good bonding strength, wear resistance, corrosion resistance, and fire resistance. Among them, in Comparative Example 1, a single sintering process is used, and the hardness measured is significantly lower than that of Examples 2-4. The reason is that the kaolin microsphere particles prepared by the secondary sintering process have better strength and hardness. In Comparative Example 2, tetraethyl orthosilicate is not impregnated, and in Comparative Example 3, tetraethyl orthosilicate is not coated with alumina and impregnated with tetraethyl orthosilicate. The hardness, wear resistance, acid resistance, and alkali resistance of Comparative Example 2-3 are lower than those of Examples 2-4, indicating that alumina coating and tetraethyl orthosilicate modification can synergistically improve mechanical properties and corrosion resistance. The bonding strength of Comparative Example 3 is lower than that of Examples 2-4. In Comparative Example 4, pretreated kaolin is directly used, and the mechanical properties, bonding strength, and corrosion resistance measured are most significantly lower than those of Examples 2-4.

[0028] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0029] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for preparing ultrafine whitening high viscosity kaolin, characterized in that: The following steps are involved: S1, preparing pretreated kaolin by pulping and dispersing the kaolin ore, removing sand and impurities, removing iron by magnetic separation, bleaching, and calcining; S2. Prepare a kaolin slurry by adding pretreated kaolin to deionized water, add sodium hexametaphosphate to the kaolin slurry, ultrasonically vibrate the slurry, let it stand, and then filter to obtain a kaolin suspension slurry; S3, spray drying and sintering the kaolin suspension slurry to prepare kaolin microsphere particles; S4. Take kaolin microsphere particles and dissolve them in deionized water, beat and stir them evenly, add sodium hexametaphosphate, use sodium hydroxide to adjust the pH value of the system to 9-10, heat to 70-85°C, and add sodium metaaluminate solution and dilute sulfuric acid solution dropwise to maintain the pH value of the system. Stir and react for 0.5-1h. After the reaction is completed, age for 24-28h, filter, wash, and dry to prepare alumina-coated kaolin; S5. Prepare an impregnation solution of tetraethyl orthosilicate using ethanol as a solvent, with a mass fraction of 5% based on silicon oxide. Place the alumina-coated kaolin in the impregnation solution, impregnate it evenly, dry it at 100-120°C for 20-24 hours, and then calcine it at 550-600°C for 2-4 hours to prepare ultrafine, whitened, and high-viscosity concentrated kaolin.

2. The method for preparing ultrafine whitening high viscosity kaolin according to claim 1, characterized in that: The preparation method of the pretreated kaolin in step S1 specifically comprises the following steps: (1) The kaolin ore is coarsely crushed by a grinding mill and then transported to a slurry machine, and deionized water and sodium hexametaphosphate are added to the slurry machine to form a slurry with a concentration of 20-40%; (2) Desanding the initial slurry to remove coarse impurities to obtain slurry; (3) transporting the slurry to a high gradient magnetic separator for iron removal to obtain iron-removed slurry; (4) Add sulfuric acid with a concentration of 2-4 mol / L to the iron removal slurry to adjust the pH value of the iron removal slurry to 2-3. After the adjustment is completed, add 0.1-0.2 wt% of hydrosulfite and stir evenly. Then add 0.1-0.15 wt% of oxalic acid for complexation, filter and wash with water to obtain a bleached slurry; (5) The bleached slurry is filtered through a filter press, dried and ground, and the ground powder obtained is evenly mixed with sodium chloride and calcined at 1000-1200°C for 1-1.5 hours to prepare pretreated kaolin.

3. The method for preparing ultrafine whitening high viscosity kaolin according to claim 2, characterized in that: The particle size of the pretreated kaolin is 2-5 μm.

4. The method for preparing ultrafine whitening high viscosity kaolin according to claim 1, characterized in that: The solid content of the kaolin slurry is 25-30%; the mass of the sodium hexametaphosphate is 0.1-0.3% of the mass of the pretreated kaolin.

5. The method for preparing ultrafine whitening high viscosity kaolin according to claim 1, characterized in that: The process parameters of the spray drying are: spray pressure of 1.2 MPa and inlet temperature of 140°C.

6. The method for preparing ultrafine whitened high viscosity kaolin according to claim 1, characterized in that: The sintering process parameters are: first heating to 850-900° C., cooling, then heating to 1100-1200° C. and keeping warm for 1-1.5 hours, cooling again, then heating to 1100-1200° C. and keeping warm for 3.5-4 hours.

7. The method for preparing ultrafine whitened high viscosity kaolin according to claim 1, characterized in that: The concentration of the kaolin microsphere particles is 175-200 g / L; the mass of the sodium hexametaphosphate is 0.1-0.3% of the mass of the kaolin microsphere particles.

8. The method for preparing ultrafine whitened high viscosity kaolin according to claim 1, characterized in that: The concentration of the sodium metaaluminate solution is 1-2 mol / L; the concentration of the dilute sulfuric acid solution is 0.5-1 mol / L; and the coating amount of the alumina-coated kaolin is 3-4%.

9. An ultra-fine whitening high viscosity concentration kaolin, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

10. An application of the ultrafine whitening high viscosity concentration kaolin according to claim 1, characterized in that: The ultrafine whitening high-viscosity concentration kaolin is applied to spray-formed ceramic coatings.

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