A method for preparing super-large size ultra-thin kaolinite nanosheets by pressurized intercalation exfoliation

Abstract

The application relates to the technical field of non-metallic ore processing, and particularly discloses a method for preparing super-large-size super-thin kaolinite nanosheets through pressurized intercalation and peeling, which comprises the following steps: removing impurities from kaolin; performing interlayer intercalation pretreatment on the kaolin through an intercalation agent to obtain kaolin intercalation compound slurry; stirring the kaolin intercalation compound slurry with a macromolecular dispersion solution to obtain kaolin composite ore slurry in a dispersed state; adding medium-low pressure carbon dioxide gas and performing stirring treatment under pressure for a period of time; rapidly discharging the ore slurry from the flexible container after rapid pressure relief to obtain peeled kaolin ore slurry; and finally performing thermodynamic stability treatment on the powder through sedimentation classification, centrifugation, washing and freeze-drying treatment to obtain super-large-size super-thin kaolin nanosheet powder, specifically, the kaolin nanosheet powder is in a sheet-like morphology, has super-large sheet layer size (3-6 mu m), a high height-diameter ratio (200-400) and low sheet layer thickness (8-15 nm).

Description

Technical Field

[0001] This invention belongs to the field of non-metallic mineral processing technology, specifically relating to a method for preparing ultra-large-sized, ultra-thin kaolinite nanosheets by pressure intercalation and exfoliation. Background Technology

[0002] Kaolin is a common natural mineral with broad application prospects in industries such as ceramics, coatings, rubber, concrete, and refractory materials. Particularly in high-end fields like aerospace and energy, kaolin with its unique layered structure can significantly improve the surface and interfacial performance of ceramics. In recent years, the development of military hemostatic materials and aerospace molecular sieves has placed higher demands on the layer size of ultrathin kaolin. Research shows that larger-sized ultrathin kaolin can improve the hemostatic speed of military hemostatic materials and enhance the strength of aerospace molecular sieve microspheres.

[0003] Kaolinite, the main component of kaolin, is a 1:1 type layered silicate mineral composed of tetrahedral layers of silicon-oxygen and octahedral layers of aluminum-oxygen. The layers are linked by hydrogen bonds and generally exist in a book-like stacked structure. The average size of its natural lamellae is approximately 4-10 μm, with a thickness of about 50-200 nm. Intercalation and exfoliation processing of these stacked kaolinites can significantly improve the aspect ratio and specific surface area of ​​kaolin, thereby obtaining a natural ore raw material with excellent interfacial composite capabilities.

[0004] However, the research on efficient kaolin stripping has always been a challenge in the kaolin industry. Currently, the main processes include physical stripping, chemical intercalation stripping, and the combined use of physical and chemical methods.

[0005] Physical exfoliation processes such as ball milling and sand milling have been commonly used in my country's kaolin industry for decades. However, they suffer from drawbacks such as significant flake damage, low aspect ratio, large flake thickness, and low specific surface area. Taking the kaolin production of several leading Chinese kaolin enterprises as an example, the sand milling process currently used, while increasing the specific surface area and decreasing the particle size of kaolin with increasing grinding time, significantly damages the flake particles and gradually exposes iron impurities under high-speed grinding. This results in problems such as low aspect ratio, insufficient flake thickness, and gradual darkening of kaolin powder, which affect the whiteness, purity, and mechanical properties of ceramics, such as compressive strength and flexural strength. Guo et al. (China Nonmetallic Minerals. 2013, 5, 36-38) used a GJ5×2 double-groove high-intensity mixing mill (375 rpm) and a GXMB500 high-efficiency grinding mill with large-sized grinding media (1.5-2.5 mm zirconia ceramic balls) at low speed (480 rpm) to grind Longyan kaolin for 2 hours, obtaining grade 60 and 70 super kaolin products. The content of -2 μm could only be increased from 25.1% in the original ore to over 60% and 70%, while its natural whiteness decreased significantly. Zhang et al. (Applied Clay Science. 2017, 147, 117–122) used small-sized grinding media (1.2 mm zirconia ceramic balls) at high speed (2000 rpm) for 2 hours and found that the kaolin's lamellae structure was severely broken and the aspect ratio did not decrease significantly. In addition, in the 1990s, ultrafine peeling and homogenizing machines were developed both domestically and internationally for the ultrafine processing of kaolin. For example, Pan Yecai et al. (Non-metallic Minerals, 1997, 03, 48-50) used a high-pressure homogenizer (working pressure 20-70 MPa) to spray kaolin slurry at high speed onto a specially designed target, achieving ultrafine crushing through intense collisions between particles and the target, and between particles themselves. However, this process was phased out due to poor peeling effect and easy equipment wear caused by particle collisions. In general, low-speed grinding and peeling suffers from problems such as low grinding efficiency and thicker kaolin flakes, while high-speed mechanical ball milling with small-sized media suffers from severe flake breakage and low aspect ratio after grinding and peeling.

[0006] Chemical intercalation and exfoliation involves inserting small-molecule or large-molecule intercalating agents, such as dimethyl sulfoxide, potassium acetate, and urea, into the intercalation spaces of kaolin, followed by controlled exfoliation through agent removal. Chinese patent CN100404626C uses a mixture of kaolin and potassium acetate for grinding and intercalation, followed by water washing to obtain ultrafine kaolin; however, the resulting kaolin has the drawback of insufficient sheet thickness. Chinese patent CN101746768B uses chemical intercalation, grinding, and spray drying to obtain hexagonal sheet-like exfoliated kaolin crystals with an aspect ratio between 10 and 30:1 and a sheet thickness of less than 200 nm. Liu et al. (Applied Clay Science. 2016, 124-125, 175-182) used DMSO-intercalated kaolin as a precursor and significantly increased its specific surface area from 9.98 μm² in the raw ore through methanol grafting and long-chain macromolecular substitution. 2 / g increased to 50.9m 2 / g, however, the product obtained by this method is tubular kaolin nanotubes. Overall, using chemical intercalation and peeling process alone has problems such as the product having thicker sheets or curling into nanotubes.

[0007] Regarding the combined mechanical-assisted physicochemical intercalation and exfoliation process, Zhang et al. (Applied Clay Science. 2017, 147, 117–122) obtained kaolin with a maximum aspect ratio of 14.2 and relatively large sheet thickness through potassium acetate intercalation and high-speed grinding exfoliation. Chinese patent CN1994961A, through potassium acetate intercalation and ultrasonic exfoliation, obtained kaolin with an average sheet thickness of 30.27-79.3 nm. Li Xiaoxu et al. (Applied Chemical Industry. 2012, 41, 2103-2105) used a mixed-static intercalation and ultrasonic exfoliation method to obtain kaolin with a sheet thickness of 15.22 nm. Chinese patent CN1398925A prepared an ultrafine kaolin using multiple chemical intercalation and mechanical grinding exfoliation methods, obtaining 20% ​​nano-sized kaolin with a size below 100 nm. Fu et al. (Applied Surface Science, 2023, 635, 157778, patent CN115784249B) obtained ultrathin kaolin nanosheets with large size (1.3 μm), high aspect ratio (130:1), and low sheet thickness (<10 nm) by intercalation, low-speed abrasion, high-shear dispersion, and freeze-drying.

[0008] Overall, existing mechanically assisted intercalation and stripping processes such as ball milling, ultrasonication, and high-shear dispersion still suffer from problems such as kaolin sheet breakage and low stripping efficiency. The average size of individual kaolin crystal sheets after stripping is generally much smaller than 2μm, which cannot meet the demand for larger-sized ultrathin kaolin for high-end new materials such as military hemostatic materials and molecular sieve microspheres.

[0009] In summary, the current kaolin nanosheet processing technology, which simultaneously meets the requirements of a sheet size greater than 2μm, a sheet thickness less than 20nm, and an aspect ratio greater than 100:1, remains the bottleneck for high-end kaolin raw materials. Summary of the Invention

[0010] The purpose of this invention is to address the shortcomings of the prior art by providing a method for preparing ultra-large and ultra-thin kaolinite nanosheets through pressure intercalation and exfoliation. By synergistic coupling of chemical intercalation, macromolecular composite dispersion, and medium- and low-pressure gas intercalation processes, a kaolinite nanosheet with excellent versatility, ultra-large sheet size, thin sheet thickness, and high aspect ratio is finally obtained.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] The first objective of this invention is to provide a method for preparing ultra-large-sized, ultra-thin kaolinite nanosheets by pressure intercalation and exfoliation, comprising the following steps:

[0013] S1. Grind and pulverize the kaolin ore by ball milling and sieving to obtain kaolin after impurity removal, and set it aside for later use;

[0014] S2. Mix the purified kaolin, intercalating agent and water, stir at a certain temperature for a certain time, and centrifuge to obtain the kaolin intercalation complex.

[0015] S3. Preparation of kaolin composite slurry;

[0016] Add hydrochloric acid solution to a container, heat to a certain temperature, add a certain amount of cellulose and dispersant, and stir for a certain time using a high shear flow field dispersion device to obtain a macromolecular dispersion solution. Add the kaolin intercalation complex described in step S2 to the macromolecular dispersion solution and stir for a certain time to obtain a dispersed kaolin composite slurry.

[0017] S4. Pressure intercalation stripping;

[0018] The kaolin composite slurry described in step S3 is added to a high-pressure container, the container is sealed, medium and low pressure carbon dioxide gas is added and subjected to high shear stirring or ultrasonic treatment under pressure conditions for a period of time, and then the pressure is quickly released. The kaolin composite slurry is quickly sprayed from the Laval nozzle of the high-pressure valve into a flexible container to obtain flaked kaolin slurry.

[0019] S5. Dilute the kaolin slurry obtained in step S4 with water, let it settle for a period of time, take the upper layer of slurry, centrifuge it, wash it with water several times, add deionized water, mix it well, freeze it quickly, and then freeze-dry it for a certain period of time to obtain large-size ultrathin kaolin nanosheet powder.

[0020] Furthermore, in step S1, the kaolin ore is flaky kaolin, and the origin is selected from Beihai, Maoming or Inner Mongolia; the mesh size used for sieving is 200~400 mesh.

[0021] Furthermore, in step S2, the mass ratio of the purified kaolin to water is 1:1~10, the mass ratio of the purified kaolin to the intercalating agent is 1:0.05~0.4, the stirring temperature is 25~120℃, and the stirring time is 1~72h.

[0022] Furthermore, the intercalating agent is any one of dimethyl sulfoxide, potassium acetate, and urea.

[0023] Furthermore, in step S3, the concentration of the hydrochloric acid solution is 0.1~6M, the temperature is 0~150℃, and the stirring time is 1~30min; the mass ratio of kaolin intercalation complex, cellulose, and dispersant is 1:(0.01~0.2):(0.001~0.01), the stirring temperature is 0~150℃, the stirring time is 1~30min, the linear velocity of the flow field of the high shear flow field dispersion device is greater than 30m / s, and the concentration of kaolin slurry in the solution is 0.1~20wt%.

[0024] Furthermore, in step S4, the pressure of the medium-low pressure carbon dioxide gas is 0.2~10MPa; the linear velocity of the flow field of the high-shear stirring device is greater than 30m / s, and the stirring time is 0.1~1h; the power density of the ultrasonic treatment device is 0.01~0.1kw / L solution, and the stirring time is 0.1~15min; the slurry outflow velocity at the Laval inlet of the high-pressure valve is 20~1000m / s; and the Rockwell hardness HRR of the flexible container is less than 80.

[0025] Furthermore, in step S5, the mass ratio of the kaolin slurry to water is 1:50~200, the settling time is 1~12h, and the number of washing cycles is 1~4.

[0026] Furthermore, in step S5, the centrifugation speed is 3000~10000 rpm, the rapid freezing time is 1~30 min, and the freezing temperature is -50~-20℃.

[0027] A second objective of this invention is to provide ultra-large-sized, ultra-thin kaolin nanosheets prepared according to the above-described preparation method, wherein the average size of the ultra-thin kaolin nanosheets is 3-6 μm, the average thickness is 8-15 nm, and the aspect ratio is 200-400.

[0028] The third objective of this invention is the application of the ultra-large-size ultrathin kaolin nanosheets prepared by the above-described method, or the large-size ultrathin kaolin nanosheets described above, in hemostatic materials and aerospace molecular sieves.

[0029] Compared with the prior art, the beneficial effects of the technical solution provided by the present invention are as follows:

[0030] (1) Conventional sand milling and ultrasonic peeling processes, with increasing peeling time, significantly damage the kaolin lamellae particles, resulting in severe lamellae damage, low aspect ratio, or gradual blackening of the kaolin powder. This method weakens the interlayer forces of kaolin using an intercalating agent, then employs a macromolecular composite dispersion process to pre-disperse and composite the kaolin lamellae in the slurry. Subsequently, while pre-disintegrating the stacked structure, it significantly reduces the damage to the kaolin lamellae structure. Then, gas intercalation and peeling between the kaolin lamellae are achieved through the intercalation effect of medium- and low-pressure CO2, and rapid depressurization further achieves effective separation of the kaolin lamellae. Finally, low-temperature shaping of the nano-lamellae structure is achieved through freeze-drying. The synergistic coupling of these processes yields ultra-large-sized, ultra-thin kaolin.

[0031] (2) The present invention has a significant effect on the exfoliation of kaolin. According to the intercalation exfoliation process of the present invention, ultra-large and ultra-thin kaolin nanosheets with an average sheet size of more than 3 μm and a thickness of about 10 nm can be obtained. The relevant indicators are far higher than those of other current mechanical exfoliation and chemical intercalation exfoliation methods. The above results have been confirmed by macroscopic (X-ray diffraction XRD pattern) and microscopic (scanning electron microscope SEM pattern) characterization tests. The mechanical properties such as compressive strength of ceramic microspheres prepared with it as raw material are significantly improved.

[0032] (3) The ultrathin kaolin obtained by the present invention has a sheet size greater than 3~6μm, which exceeds the size of platelets (2~4μm). This can promote platelet aggregation and significantly shorten the hemostasis time, and is expected to break through the bottleneck of hemostasis performance of kaolin powder. Attached Figure Description

[0033] Figure 1 A process flow diagram for the preparation of ultra-large-size, ultra-thin kaolin nanosheets provided in this embodiment of the invention;

[0034] Figure 2 XRD patterns of the final products provided in Embodiments 1, 2 and Comparative Example 1 of the present invention;

[0035] Figure 3 SEM image of kaolin nanosheets from Example 1;

[0036] Figure 4 This is a mapping diagram of the elemental distribution of the sample in Example 1. Detailed Implementation

[0037] To make the present invention easier to understand, specific embodiments are described below to further illustrate the invention. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical terms used below have the same meaning as understood by those skilled in the art; unless otherwise specified, the raw materials and reagents involved herein can be purchased commercially or obtained by known methods.

[0038] To address the technical problems of low aspect ratio, insufficient thickness, and powder blackening and severe flaking caused by excessive grinding in existing kaolin peeling processes, this invention provides a method for preparing ultrathin kaolin nanosheets. Through the synergistic coupling of chemical intercalation, low-speed ball milling in large-size media, and high-shear flow field dispersion processes, a highly versatile method for ultrathin nano-processing of kaolin with large flask size, thin flask thickness, high aspect ratio, and high specific surface area is finally obtained.

[0039] The principle of the preparation method of this invention is as follows: The original idea of ​​this invention comes from the inventor's first discovery in in-situ XRD testing that low- and medium-pressure carbon dioxide gas can enter the interlayer of intercalated kaolin and promote the separation of kaolin sheet layers under certain conditions. Based on the above discovery, this invention promotes the synergistic effect of the intercalating agent, dispersant and kaolin interface by regulating the movement of low- and medium-pressure carbon dioxide gas between kaolin layers, so that the kaolin sheet layers are dissociated while avoiding the destruction of large-size sheet structures. Then, through the synergistic coupling effect of rapid dispersion in a high-shear flow field and freeze-drying process, the efficient exfoliation and stabilization of the kaolin sheet structure are achieved.

[0040] It should be noted that the medium- and low-pressure carbon dioxide gas dispersion exfoliation utilizes dissolved carbon dioxide gas molecules in the slurry to enter the intercalated kaolin layers, and the kaolin sheet structure is exfoliated by rapid pressure relief; the rapid ejection from the Laval nozzle can further promote the dispersion of kaolin nanosheets in the gas-liquid miscible mixture; the flexible container can prevent the kaolin nanosheets from breaking during the collision with the container.

[0041] The technical solution of this application is described below by way of example.

[0042] This invention provides a method for preparing large-size ultrathin kaolin nanosheets. Specifically, the large-size ultrathin kaolin nanosheets are kaolin nanosheet powders with well-preserved sheet-like morphology and possessing ultra-large sheet size (3~6 μm), high aspect ratio (200~400), and low sheet thickness (8~15 nm). The process flow diagram is shown below. Figure 1 As shown, it includes the following steps:

[0043] Step 1: Remove impurities from kaolin

[0044] The raw kaolin ore is ball-milled and sieved to obtain kaolin (kaolin concentrate) after impurity removal.

[0045] Step 2: Preparation of Kaolin Intercalation Composite Slurry

[0046] Weigh the purified kaolin (kaolin concentrate), intercalating agent and water into a container, mix them, stir at a certain temperature for a certain time, and centrifuge to obtain the kaolin intercalation complex.

[0047] Step 3: Macromolecular Complex Dispersion

[0048] Hydrochloric acid solution is added to a container and heated to a certain temperature. A certain amount of cellulose and dispersant are added. After stirring for a certain time using a high-shear flow field dispersion device, a macromolecular dispersion solution is obtained. The above-mentioned kaolin intercalation complex is added to the solution, and stirring is continued for a certain time to obtain a dispersed kaolin composite slurry.

[0049] Step 4: Intercalation and stripping of medium and low pressure gas

[0050] Kaolin composite slurry is added to a high-pressure container, the container is sealed, medium- and low-pressure carbon dioxide gas is added, and high-shear stirring or ultrasonic treatment is carried out under pressure conditions for a period of time. Then, the pressure is quickly released, and the slurry is rapidly sprayed from the Laval nozzle of the high-pressure valve into a flexible container to obtain flaked kaolin slurry.

[0051] Step 5: Sedimentation classification, centrifugation, washing, and freeze drying

[0052] Large-sized ultrathin kaolin nanosheet crystals were obtained by sedimentation, centrifugation, washing, and freeze-drying of the slurry.

[0053] Preferably, in step 1, the kaolin ore includes any one of the producing areas of Beihai, Maoming, and Inner Mongolia; the mesh size used for sieving is 200-400 mesh.

[0054] Preferably, in step 2, the mass ratio of the purified kaolin to water is 1:1 to 10, the mass ratio of the purified kaolin to the intercalating agent is 1:0.05 to 0.4, the stirring temperature is 25 to 120°C, and the stirring time is 1 to 72 hours.

[0055] Preferably, in step 3, the concentration of the hydrochloric acid solution is 0.1~6M, the temperature is 0~150℃, and the stirring time is 1~30min; the mass ratio of kaolin intercalation material, cellulose, and dispersant is 1:0.01-0.2:0.001-0.01, the stirring temperature is 0~150℃, the stirring time is 1~30min, and the concentration of kaolin slurry in the solution is 0.1~20wt%; the linear velocity of the flow field in the high shear flow field dispersion device is >30m / s.

[0056] Preferably, in step 4, the pressure of the medium-low pressure carbon dioxide gas is 0.2~10MPa; the linear velocity of the flow field of the high-shear stirring device is >30m / s, and the stirring time is 0.1~1h; the power density of the ultrasonic treatment device is 0.01~0.1kw / L solution, and the stirring time is 0.1~15min; the slurry outflow velocity at the Laval inlet of the high-pressure valve is 20~1000m / s; and the Rockwell hardness HRR of the flexible container is <80.

[0057] Preferably, in step 5, the concentration of the diluted kaolin slurry is 0.1~10wt%, the settling time is 1~12h, the number of washing cycles is 1~4, the rapid freezing time is 1~30min, and the freezing temperature is -50~-20℃; the centrifugation speed is 3000~10000rpm.

[0058] The following describes, in conjunction with specific embodiments and comparative examples, an exemplary method for preparing large-size ultrathin kaolin nanosheets provided in this application.

[0059] Example 1

[0060] This embodiment provides a method for preparing ultra-large-sized, ultra-thin kaolinite nanosheets by pressure intercalation and exfoliation. The specific steps are as follows:

[0061] Step 1: Remove impurities from kaolin

[0062] The raw kaolin ore from Beihai was ball-milled into powder and passed through a 200-mesh sieve to obtain kaolin after impurity removal.

[0063] Step 2: Preparation of Kaolin Intercalation Composite Slurry

[0064] Weigh 2 kg of purified kaolin and 10 L of DMSO solution with 10% water into a container, stir and mix, stir at 60℃ for 12 h, and centrifuge the slurry to obtain kaolin intercalation composite slurry.

[0065] Step 3: Macromolecular Complex Dispersion

[0066] Add 40L of 0.5M hydrochloric acid solution to a container and heat to 80℃. Add 50g of cellulose and 5g of sodium hexametaphosphate dispersant. Stir for 15min using a high-shear flow field dispersion device to obtain a macromolecular dispersion solution. Add 1kg of kaolin intercalation complex to the solution and continue stirring for 5min.

[0067] Step 4: Intercalation and stripping of medium and low pressure gas

[0068] Dispersed kaolin slurry was added to a high-pressure container, the container was sealed, and medium-low pressure carbon dioxide gas was added. The mixture was then subjected to high-shear stirring for 15 minutes at a pressure of 5 MPa and a temperature of 40°C. The pressure was then quickly released, and the slurry was rapidly ejected from the Laval nozzle of the high-pressure valve into a flexible container to obtain flaked kaolin slurry.

[0069] Step 5: Sedimentation classification, centrifugation, washing, and drying.

[0070] After the kaolin slurry was peeled, the concentration was diluted to 0.5 wt%. After settling for 3 hours, the upper half of the slurry was centrifuged at 8000 rpm and washed twice with water. After washing, it was rapidly frozen at -20℃ for 5 minutes and then freeze-dried to obtain Beihai kaolin nanosheet powder.

[0071] Example 2

[0072] Step 1: Remove impurities from kaolin

[0073] The raw kaolin ore from Beihai was ball-milled into powder and passed through a 200-mesh sieve to obtain kaolin after impurity removal.

[0074] Step 2: Preparation of Kaolin Intercalation Composite Slurry

[0075] Weigh 2 kg of purified kaolin and 10 L of DMSO solution with 10% water into a container, stir and mix, stir at 60℃ for 12 h, and centrifuge the slurry to obtain kaolin intercalation composite slurry.

[0076] Step 3: Macromolecular Complex Dispersion

[0077] Add 40L of 0.1M hydrochloric acid solution to a container and heat to 60℃. Add 50g of cellulose and 5g of sodium hexametaphosphate dispersant. Stir for 15min using a high-shear flow field dispersion device to obtain a macromolecular dispersion solution. Add 1kg of kaolin intercalation complex to the solution and continue stirring for 5min.

[0078] Step 4: Intercalation and stripping of medium and low pressure gas

[0079] Dispersed kaolin slurry was added to a high-pressure container, the container was sealed, and medium-low pressure carbon dioxide gas was added. The mixture was ultrasonically treated for 15 minutes at 10 MPa pressure and 40°C temperature. Then the pressure was quickly released, and the slurry was rapidly ejected from the Laval nozzle of the high-pressure valve into a flexible container to obtain flaked kaolin slurry.

[0080] Step 5: Sedimentation classification, centrifugation, washing, and drying.

[0081] After the kaolin slurry was peeled, the concentration was diluted to 0.5 wt%. After settling for 6 hours, the upper half of the slurry was centrifuged at 8000 rpm and washed twice with water. After washing, it was rapidly frozen at -20℃ for 5 minutes and then freeze-dried to obtain Beihai kaolin nanosheet powder.

[0082] Comparative Example 1

[0083] Beihai kaolin ore.

[0084] Comparative Example 2

[0085] Step 1: Remove impurities from kaolin

[0086] The raw kaolin ore from Beihai was ball-milled into powder and passed through a 200-mesh sieve to obtain kaolin after impurity removal.

[0087] Step 2: Grinding

[0088] Different masses of medium balls with a particle size of 0.6-0.8 mm (small size) and impurity-removed kaolin were weighed and added to a sand mill for high-speed grinding (2000 r) for 3 hours to obtain ultrafine nano-sized kaolin.

[0089] Comparative Example 3

[0090] Reference (Applied Clay Science. 2017, 147, 117–122)

[0091] Step 1: Remove impurities from kaolin

[0092] The raw kaolin ore from Zhangjiakou was ball-milled into powder and passed through a 200-mesh sieve.

[0093] Step 2: Intercalation

[0094] 100g of raw kaolin ore was mixed with 200g of saturated aqueous solution of potassium acetate, heated to 60℃ and stirred for three days to obtain an intercalation complex.

[0095] Step 3: Grinding

[0096] After intercalation, the intercalated kaolin was ground using a GF-1100 multifunctional experimental disperser (Shenzhen Shuangye Machinery Co., Ltd.). 300g of intercalated kaolin slurry was placed in a 2L grinding tank, and 300g of zirconium balls with a particle size of 1.2mm were added. The slurry was ground at 2000rpm for 2 hours at room temperature, and then the kaolin slurry was separated from the zirconium balls using a sieve. The resulting suspension was repeatedly centrifuged and washed until potassium acetate was completely deintercalated. The ground kaolin was then redispersed with deionized water and sodium polyacrylate dispersant, and allowed to settle for 3 hours. The supernatant suspension was then collected and allowed to settle to obtain the ground kaolin.

[0097] Comparative Example 4

[0098] (1) Preparation of kaolin intercalation complex

[0099] Kaolin and potassium acetate were weighed in a 1:1 mass ratio, added to a mortar, mixed and ground evenly with deionized water, transferred to a polytetrafluoroethylene container, sealed, and allowed to stand at a certain temperature for 24 hours. The mixture was then removed, washed with anhydrous ethanol to remove residual potassium acetate from the surface of the kaolin, centrifuged, and dried at 70°C for 24 hours to obtain the kaolin-potassium acetate intercalation complex.

[0100] (2) Ultrasonic stripping

[0101] Add 1g of kaolin-potassium acetate intercalation complex to 100mL of distilled water and sonicate or stir for 10min.

[0102] (3) Centrifugation, washing, and oven drying

[0103] After centrifugation, the kaolin slurry was washed twice with anhydrous ethanol and dried at 70°C for 24 hours to obtain the sample.

[0104] Comparative Example 5

[0105] This comparative example is based on patent CN201010183343.8.

[0106] Step 1: Remove impurities from kaolin

[0107] Coal-series kaolin is mechanically crushed to a particle size of less than 43 micrometers.

[0108] Step 2: Preparation of the kaolin / dimethyl sulfoxide intercalation composite

[0109] Distilled water and dimethyl sulfoxide (DMSO) were mixed in a volume ratio of 1:15 to prepare a mixed solution. Then, kaolin and DMSO solution were mixed in a mass ratio of 1:10. After stirring continuously at 50°C for 4 hours, the mixture was filtered. The precipitate was washed with anhydrous ethanol, filtered, and dried to obtain the kaolin / dimethyl sulfoxide intercalation composite.

[0110] Step 3: Preparation of kaolin / urea intercalation complex

[0111] The kaolin / dimethyl sulfoxide intercalation complex was mixed with a urea solution of 11 mol / L at a mass ratio of 1:12 and reacted at 20°C with stirring for 2 h. After filtration, washing with distilled water, filtration again, and drying, the kaolin / urea intercalation complex was obtained.

[0112] Step 4: Grinding

[0113] Kaolin / urea intercalation complex, zirconium silicate grinding media balls, and saturated urea solution were placed in a peeler at a volume ratio of 1:2.5:0.8 and mechanically peeled for 4 hours. After washing, centrifugation, and drying, the mixture was ready for use.

[0114] Step 5: Calcination

[0115] The mechanically ground kaolin / urea intercalation composite was heat-treated at 160℃ for 0.5h.

[0116] Step 6: Ultrasound

[0117] After heat treatment, the sample was ultrasonically treated in 95℃ distilled water for 0.5 hours, then filtered and dried; after being dispersed using a high-speed mixer, kaolin flake crystals were obtained.

[0118] Comparative Example 6

[0119] This comparative example is based on patent CN202211633704.3.

[0120] Step 1: Remove impurities from kaolin

[0121] The raw kaolin ore from Beihai was ball-milled into powder and passed through a 200-mesh sieve to obtain kaolin after impurity removal.

[0122] Step 2: Preparation of Kaolin Intercalation Composite Slurry

[0123] Accurately weigh 6g of purified kaolin and 60ml of DMSO solution with 10% water into a container, stir and mix, and stir at 60℃ for 12h to obtain kaolin intercalation composite slurry.

[0124] Step 3: Ball milling and peeling

[0125] Weigh out 32g and 5g of medium balls with particle sizes of 1mm and 2mm respectively, along with the above-mentioned kaolin intercalation slurry and sodium hexametaphosphate dispersant with a mass fraction of 5% and add them to a grinding and peeling device. Ball mill for 30min, stop for 5min, and grind and peel the device at 300rpm for a total grinding time of 2h to obtain the DMSO / kaolin intercalation composite.

[0126] Step 4: Disperse and peel the slices

[0127] Add DMSO / kaolin intercalation complex slurry and distilled water, which have been ball-milled and stirred evenly, to a beaker. The flaking and dispersion are carried out using a high-shear flow field dispersion device, wherein the linear velocity of the flow field is >30m / s, and the stirring time is 0.1 to 2h, to obtain flaked kaolin slurry.

[0128] Step 5: Sedimentation classification, centrifugation, washing, and freeze drying

[0129] The kaolin slurry after descaling was diluted at a ratio of 1:100. After settling for 2 hours, the supernatant was centrifuged at 8000 rpm and discarded. The supernatant was then washed three times with alcohol. After washing, 10 ml of deionized water was added, the mixture was shaken well, and the mixture was placed in a freezer at -20°C to freeze. The mixture was then placed in a freeze dryer and freeze-dried for a certain period of time to obtain Beihai kaolin nanosheet powder.

[0130] Comparative Example 7

[0131] The difference from Example 2 is that steps 3 (macromolecule composite dispersion) and 4 (medium and low pressure gas intercalation and stripping) are omitted, while the other steps and parameters are the same as in Example 2.

[0132] Results Detection and Analysis

[0133] The final products of Examples 1, 2, and Comparative Example 1 were subjected to XRD analysis, such as... Figure 2 As shown, the intensity of the kaolinite (001) crystal plane diffraction peak in Examples 1 and 2 using the technology of the present invention is significantly reduced and broadened, indicating that the thickness of the lamellae of the main mineral component (kaolinite) of Beihai kaolinite is significantly reduced after flaking.

[0134] The SEM results of Example 1 are as follows: Figure 3 As shown, compared to the original Beihai ore, its lamellae have been peeled away from the original ordered stacked thick lamellar structure (around 40 nm) into a thin, intact lamellar structure. Statistical analysis of the kaolinite nanosheets in the SEM images shows that the average size of the kaolinite nanosheets is 3-6 μm, the average thickness of the lamellars is 8-11 nm, and the aspect ratio is 200-400. Furthermore, the ultra-large, ultra-thin kaolinite portions exhibit lamellar bending, such as... Figure 3 As shown in the magnified view, the porosity between kaolinite particles is further increased.

[0135] The specific surface area, pore volume, aspect ratio, sheet thickness, and average sheet size of the final products of Examples 1-2 and Comparative Examples 1-7 are shown in Table 1 below.

[0136] Table 1 shows the aspect ratio, sheet thickness, average sheet thickness, specific surface area, and pore volume for each embodiment and comparative example.

[0137]

[0138] Note: (a) The aspect ratio of the sample was obtained by statistical analysis of the size and thickness of the kaolinite lamellae in the high-resolution SEM image of the sample. (b) The lamellae thickness of the sample was obtained by fitting the (001) peak of the XRD data and calculating it according to the Scherrer formula D001=kλ / βCosθ. The data were obtained from quantitative XRD testing at a scanning speed of 1° / min.

[0139] As shown in Table 1, the kaolin obtained in Examples 1-2 of this application, compared with the raw kaolin from Beihai in Comparative Example 1, significantly improved the aspect ratio (up to 400:1) and the thickness of the lamellae (down to about 10 nm), while retaining the lamellae size of natural kaolin (about 4 μm) to the maximum extent, and significantly improved the specific surface area and pore volume (approximately 2 to 5 times higher than the raw ore).

[0140] As can be seen, the aspect ratio, sheet thickness, and sheet size of Examples 1-2 of the present invention are far superior to those of the methods in Comparative Examples 4-7. Data from the corresponding tables of Examples 1 and Comparative Examples 2-7 shows that using grinding, ultrasonic processes, or other methods instead of the medium-low pressure gas intercalation and exfoliation process of this application will lead to the destruction of the sheet structure and a significant decrease in sheet size. Data from the corresponding tables of Examples 1 and Comparative Examples 2 and 6 shows that the dispersion exfoliation method of this application preserves the size of the kaolin sheets more completely, resulting in ultra-large and ultra-thin kaolin nanosheets with sheet sizes greater than 4 μm. Data from the corresponding tables of Examples 1 and Comparative Examples 6 and 7 shows that through the technological improvements and synergistic effects of intercalation, macromolecular composite dispersion, medium-low pressure gas intercalation and exfoliation, and graded drying, this application can significantly reduce the thickness of the kaolin sheets while preserving the large sheet structure, thereby obtaining an ultra-large and ultra-thin kaolin nanosheet powder.

[0141] Intercalation using medium- and low-pressure gas is a novel intercalation technology that is completely different from the current domestic and international kaolin intercalation and peeling technologies. It utilizes the principle of using gas as an intercalating agent to promote the peeling of layered materials and can be extended to the intercalation and peeling of other layered materials.

[0142] Where there is no conflict, the above embodiments and features described herein can be combined with each other.

[0143] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing ultra-large-sized, ultra-thin kaolinite nanosheets by pressure intercalation and exfoliation, characterized in that, Includes the following steps: S1. Grind and pulverize the kaolin ore by ball milling and sieving to obtain kaolin after impurity removal, and set it aside for later use; S2. Mix the purified kaolin, intercalating agent and water, stir at a certain temperature for a certain time, and centrifuge to obtain the kaolin intercalation complex. S3. Preparation of kaolin composite slurry; Add hydrochloric acid solution to a container, heat to a certain temperature, add a certain amount of cellulose and dispersant, and stir for a certain time using a high shear flow field dispersion device to obtain a macromolecular dispersion solution. Add the kaolin intercalation complex described in step S2 to the macromolecular dispersion solution and stir for a certain time to obtain a dispersed kaolin composite slurry. S4. Pressure intercalation stripping; The kaolin composite slurry described in step S3 is added to a high-pressure container, the container is sealed, medium-low pressure carbon dioxide gas is added, and high-shear stirring or ultrasonic treatment is performed under pressure conditions for a period of time. Then, the pressure is quickly released, and the kaolin composite slurry is rapidly sprayed from the Laval nozzle of the high-pressure valve into a flexible container to obtain a flaked kaolin slurry. The pressure of the medium-low pressure carbon dioxide gas is 5~10MPa. S5. Dilute the kaolin slurry obtained in step S4 with water, let it settle for a period of time, take the upper layer of slurry, centrifuge it, wash it with water several times, add deionized water, mix it well, freeze it quickly, and then freeze-dry it for a certain period of time to obtain large-size ultrathin kaolin nanosheet powder.

2. The method as described in claim 1, characterized in that, In step S1, the kaolin ore is flaky kaolin, and the origin is selected from Beihai, Maoming or Inner Mongolia; the mesh size used for sieving is 200~400 mesh.

3. The method as described in claim 1, characterized in that, In step S2, the mass ratio of the purified kaolin to water is 1:1~10, the mass ratio of the purified kaolin to the intercalating agent is 1:0.05~0.4, the stirring temperature is 25~120℃, and the stirring time is 1~72h.

4. The method as described in claim 3, characterized in that, The intercalating agent is any one of dimethyl sulfoxide, potassium acetate, and urea.

5. The method as described in claim 1, characterized in that, In step S3, the concentration of the hydrochloric acid solution is 0.1~6M, the heating temperature is 0~150℃, and the stirring time is 1~30min; the mass ratio of kaolin intercalation complex, cellulose, and dispersant is 1:(0.01~0.2):(0.001~0.01), the stirring temperature is 0~150℃, and the stirring time is 1~30min; the linear velocity of the flow field of the high shear flow field dispersion device is greater than 30m / s; and the concentration of kaolin slurry in the solution is 0.1~20wt%.

6. The method as described in claim 1, characterized in that, In step S4, the linear velocity of the flow field of the high-shear stirring device is greater than 30 m / s, and the stirring time is 0.1~1 h; the power density of the ultrasonic treatment device is 0.01~0.1 kW / L solution, and the stirring time is 0.1~15 min; the slurry outflow velocity at the Laval inlet of the high-pressure valve is 20~1000 m / s; and the Rockwell hardness HRR of the flexible container is less than 80.

7. The method as described in claim 1, characterized in that, In step S5, the mass ratio of the kaolin slurry to water is 1:50~200, the settling time is 1~12h, and the number of washing cycles is 1~4.

8. The method as described in claim 7, characterized in that, In step S5, the centrifugation speed is 3000~10000 rpm, the rapid freezing time is 1~30 min, and the freezing temperature is -50~-20℃.

9. The ultra-large size, ultra-thin kaolin nanosheets prepared by the preparation method according to any one of claims 1-8, characterized in that, The large-size ultrathin kaolin nanosheets have an average sheet size of 3~6μm, an average sheet thickness of 8~15nm, and an aspect ratio of 200~400.

10. The application of ultra-large-size ultra-thin kaolin nanosheets prepared by any one of the preparation methods described in claims 1-8 or the large-size ultra-thin kaolin nanosheets described in claim 9 in hemostatic materials and aerospace molecular sieves.

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