Bentonite nanocrystallization stripping process and equipment

Abstract

The invention discloses a bentonite nanocrystallization stripping process and bentonite nanocrystallization stripping equipment. The process comprises the following steps: firstly, carrying out three-roller grinding and pulping on a bentonite wet material, and realizing efficient separation and purification of lamellar montmorillonite by utilizing hydraulic cyclone; and high-efficiency and uniform stripping of high-purity montmorillonite is realized through a variable-frequency-low-frequency ultrasonic stepped stripping device with an optimized structure and high-pressure homogenizing equipment in combination with a nanosheet layer floating separation mechanism. On the basis of swelling characteristics and a layered structure of bentonite, customized stripping equipment and a cyclic separation and enrichment strategy are fused, so that the energy utilization efficiency and the stripping efficiency are remarkably improved, and the yield of nanocrystallization products is greatly improved. By regulating and controlling the stripping degree, controllable preparation of a series of nano montmorillonite powder can be realized, the application requirements of high-end materials and high-performance scenes are met, and a key technical support is provided for conversion of clay minerals into high-performance functional materials.

Description

Technical Field

[0001] This invention relates to the field of inorganic non-metallic material processing technology, specifically to a bentonite nano-stripping process and supporting equipment, and in particular to a novel multi-field coupled stripping process and device that integrates mechanical force, gravitational field and cavitation field. Background Technology

[0002] Bentonite's main mineral component is montmorillonite, and its crystal structure is a typical 2:1 type layered silicate, consisting of two layers of silicon-oxygen tetrahedral sheets sandwiching a layer of aluminum (magnesium)-oxygen octahedral sheets. As an important industrial mineral and strategic resource, bentonite plays a crucial role in traditional industries, modern agriculture, daily consumer goods, and high-tech fields due to its unique water absorption and swelling properties, strong adsorption capacity, good binding properties, and controllable ion exchange performance. "Nano-exfoliation" refers to the process of exfoliating the stacked lamellar structure of natural bentonite through physical, chemical, or physicochemical coupling methods to prepare single-layer or few-layer montmorillonite nanosheets. While retaining the original crystal structure, the exfoliated nanosheets exhibit excellent rheological properties, mechanical strength, electrical properties, thermal stability, and barrier properties, becoming a key basic material for constructing high-value-added products such as high-performance nanocomposites, functional coatings, and electronic devices, significantly improving the utilization efficiency and economic value of mineral resources. Therefore, the nano-scraping of bentonite not only achieves a qualitative leap and exponential improvement in material properties, but also greatly expands its application fields and promotes the upgrading of related industries. This technology is a key link in fully releasing the potential value of bentonite, enabling it to transform from a cheap industrial raw material into a high-value-added functional nanomaterial.

[0003] Nanoscale exfoliation of bentonite is a crucial link between traditional mineral resources and cutting-edge nanomaterials technology, possessing significant scientific value and practical importance for promoting the development of high-performance materials and expanding high-end applications. However, current technological pathways for achieving large-scale, low-cost, and high-quality nanoscale exfoliation still face significant challenges, particularly the lack of processes and supporting equipment that combine high efficiency with structural controllability. Traditional mechanical exfoliation methods, such as ball milling and high-pressure homogenization, generally suffer from high energy consumption and severe equipment wear. Furthermore, under high-intensity mechanical shearing and impact, brittle montmorillonite nanosheets are prone to fracture, lattice distortion, and even amorphization, making it difficult to maintain their structural integrity and ideal morphology, thus restricting the performance consistency of the final nanoproducts. Chemical exfoliation pathways, such as ion exchange and intercalation, while improving exfoliation efficiency and reducing energy consumption to some extent, typically rely on large amounts of intercalating agents, modifiers, and organic solvents, resulting in high costs and the introduction of foreign impurities that alter the surface chemical properties of montmorillonite, affecting its intrinsic properties. In addition, the subsequent purification process is complex, leading to environmental burdens and limiting its industrial application prospects. Therefore, developing efficient nano-stripping technology and specialized equipment that are highly compatible with the unique layered structure and mineral characteristics of bentonite, have a simple process flow, controllable product morphology, and complete structure has become a core technological bottleneck that urgently needs to be overcome in this field, so as to promote the innovative application of bentonite-based nanomaterials in high-end fields. Summary of the Invention

[0004] Current bentonite nanofiber exfoliation processes commonly face bottlenecks such as the susceptibility of montmorillonite nanostructures to damage during exfoliation, difficulty in completely removing chemical reagent residues, and low single-layer exfoliation rates and overall yields in large-scale production. To address these issues, this invention proposes a novel multi-field coupled bentonite nanofiber exfoliation process based on the synergistic effects of mechanical, gravitational, and cavitation fields, along with corresponding integrated equipment. This process aims to achieve efficient and non-destructive exfoliation of montmorillonite flakes by precisely controlling the temporal and spatial distribution of multiple physical fields, significantly improving the yield of montmorillonite nanoflakes and the economic efficiency of the production process while avoiding chemical contamination. This process and equipment not only provide a feasible path for the green preparation of high-quality montmorillonite nanomaterials, but their technical concepts and equipment design can also be extended to the nanofiber processing of other clay minerals. Currently, no reports have been found in related research and application fields both domestically and internationally regarding a multi-field coupled process and integrated exfoliation equipment, indicating the significant innovation and broad application prospects of this technology.

[0005] In the bentonite nano-scraping process proposed in this invention, the bentonite raw material is first pretreated by wet three-roll milling, hydration, and cyclone desanding. Then, under the synergistic effect of multiple fields including ultrasonic cavitation, gravity field, high-pressure homogenization, and mechanical force, efficient exfoliation of montmorillonite flakes is achieved to obtain nano-montmorillonite. The specific steps are as follows: (1) Pretreatment: Bentonite and water are added to a powder-liquid mixer at a mass ratio of 2:1 and mixed evenly. After three-roll milling, water is added to adjust the slurry to a mass fraction of 10-15%. The mixture is stirred continuously for 4-6 hours to obtain a uniform bentonite slurry. The three-roll milling process parameters are set as follows: the speed ratio of the rear roller, middle roller and front roller is controlled at 1:2.5:7 to 1:3:9; the roller gap between the rear roller and the middle roller is 50-100μm, and the roller gap between the middle roller and the front roller is 15-20μm; the number of grinding times is 2-4.

[0006] During wet three-roll milling, a significant velocity gradient forms in the roller gap area, subjecting bentonite to intense compression, shearing, and tearing forces as it passes through. Multiple milling processes help promote uniform dispersion and performance homogenization of the material components. Simultaneously, by rationally controlling the speed ratio and number of rolling passes, the lamellar structure of montmorillonite in the wet material can be effectively protected from damage during the exfoliation process. After mechanical stirring and three-roll milling, the bentonite particle size decreases, the specific surface area increases and its distribution becomes more uniform, and the interlayer bonding force decreases. This facilitates the rapid penetration of water molecules into the interlayer domains of montmorillonite, promoting full expansion and exfoliation of the crystal layers and significantly accelerating its hydration process. Under these conditions, continuous stirring for 4–6 hours is sufficient to achieve full hydration and uniform dispersion of the bentonite.

[0007] Subsequently, the bentonite slurry was pumped into a primary classification unit consisting of 8–10 parallel hydrocyclones. Each hydrocyclone had an inner diameter of 50 mm and a cone angle of 6°, and was operated at an operating pressure of 0.3 MPa. The mass ratio of overflow to underflow was adjusted to 6:4. The primary overflow directly entered step (2) for lamellae peeling, while the primary underflow (accounting for approximately 40% of the total volume) was sent to a sand mill for further processing. Lamellae particles exhibit a significant shape drag effect when settling in the fluid, especially when their lamellae plane is perpendicular to the settling direction. In the strong turbulence and shear field inside the hydrocyclone, the lamellae particles continuously tumble and change orientation, resulting in an average settling velocity much lower than that of spherical particles of the same size and density. Therefore, larger flaky particles can be equivalent to smaller spherical particles in terms of settling behavior, allowing hydrocyclones to selectively classify particles based on shape differences: preferentially enriching montmorillonite minerals with flaky structures in the overflow, while discharging equiaxed gangue minerals (such as quartz and feldspar) with similar settling properties into the underflow. The diameter, cone angle, and operating pressure of the hydrocyclone are key design and operating parameters affecting its classification performance (including classification purity). Experiments have shown that a hydrocyclone with a 50 mm diameter and a 6° cone angle, operating at 0.3 MPa, can effectively ensure separation accuracy and mineral purity in the overflow. This invention, based on the unique settling behavior of flaky particles in fluids and combined with the excellent shape-selective classification capability of hydrocyclones, achieves efficient enrichment of montmorillonite flaky particles, which are then directly transported to the subsequent stripping process. Furthermore, the primary underflow is fed into a sand mill for further processing, promoting the further dissociation and dispersion of the encapsulated flaky clay minerals and quartz sand. The sand milling product is then classified by a three-stage hydrocyclone, and its overflow is returned to the pulping process in step (1) for recycling, so as to improve the recovery efficiency of the lamellae mineral components and the yield of nano-montmorillonite; the underflow of the three stages is mainly quartz sand, which is used as the tailings discharge system.

[0008] (2) Nanoscale peeling: The primary overflow obtained in step (1) is introduced from the bottom into the variable frequency ultrasonic treatment device, and preliminary peeling is carried out under the combined action of ultrasound and mechanical stirring; after peeling, the slurry enters the bottom of the low frequency ultrasonic treatment device through the overflow pipes on both sides of the top of the inner cavity of the device, and is further peeled under the coupled action of secondary ultrasound and stirring swirl, and finally discharged from the top overflow pipe to obtain nano-montmorillonite. The ultrasonic power density is 100-200 W / L, and the treatment time is 10-20 min.

[0009] The variable frequency ultrasonic treatment system is equipped with a hexagonal prism-shaped processing cavity, with the following structural design: two sets of ultrasonic probes are arranged along the height direction on each side, with the lower probe group having a frequency of 40kHz and the upper probe group having a frequency of 20kHz, and the output power of a single probe being 2000W; perforated baffles are installed on each side edge; a feed pipe is installed non-through from the center of the top of the cavity, with its outlet end 10-20cm from the bottom cover of the cavity; overflow pipes are installed symmetrically and non-through from both sides of the bottom of the cavity, with their overflow inlets 10-20cm from the top cover; stirrers are symmetrically installed at the bottom of the cavity, with a stirring speed of 30-50 rpm. Under the action of fixed frequency sound waves, a steady-state standing wave field is easily formed in the liquid, resulting in uneven sound pressure distribution; the sound pressure in some nodal areas is always below the cavitation threshold, forming a "cavitation dead zone," causing uneven montmorillonite exfoliation, and even damage to the lamellar structure due to excessive local cavitation. To address this, this invention proposes using multiple ultrasonic probes in a sequence of high-frequency followed by low-frequency operation. This achieves higher cavitation intensity under similar power dissipation conditions and establishes an efficient gradient cavitation peeling field. When the purified bentonite slurry enters the high-frequency ultrasonic treatment zone, the high-frequency ultrasound generates numerous low-energy cavitation bubbles and a densely distributed cavitation effect, causing the tightly packed montmorillonite to initially peel off into a few lamellar structures. Under mechanical stirring and the backflow action of porous baffles, the montmorillonite with fewer lamellar structures gradually floats to the surface and enters the low-frequency ultrasonic treatment zone. The cavitation bubbles generated in this zone have high energy and high cavitation intensity, which can further peel off the montmorillonite lamellars. The peeled montmorillonite floats on the surface of the slurry and enters the subsequent low-frequency ultrasonic peeling equipment through overflow pipes on both sides of the top of the cavity. Therefore, through the above-mentioned variable-frequency ultrasonic stepped treatment, combined with the gradient floating and separation mechanism of lamellars during the peeling process, efficient and uniform peeling of montmorillonite lamellars is achieved, while effectively avoiding damage to the lamellar structure caused by excessive cavitation.

[0010] Subsequently, the montmorillonite slurry treated with frequency conversion ultrasonic stripping was transferred to a low-frequency ultrasonic treatment system for further stripping. This low-frequency ultrasonic stripping device employs a composite cavity structure composed of cylindrical and frustum-shaped sections, specifically configured as follows: six ultrasonic probes with a frequency of 20 kHz are evenly and vertically arranged along the circumference of the cavity's circular top surface, each probe having an output power of 2000 W; porous baffles are installed between adjacent probes to optimize the sound field distribution and guide fluid flow. The feed pipe is installed non-through from the center of the top of the cavity, with its outlet 10–20 cm from the bottom cover; overflow pipes are symmetrically and non-through on both sides of the bottom of the cavity, with the upper edge of the overflow port 10–20 cm from the top cover. A mechanical stirring device is located at the center of the bottom of the cavity, maintaining a stirring speed of 30–50 rpm. When the montmorillonite slurry enters this low-frequency ultrasonic stripping device, the low-frequency, high-power ultrasonic waves generate stronger penetration and a more intense cavitation effect. The resulting strong shock waves and microjets continuously act on the interlayer gaps of montmorillonite, effectively weakening the interlayer forces and promoting further exfoliation of montmorillonite into a few layers or even a single layer structure. Simultaneously, the synergistic effect of mechanical stirring and the backflow caused by the porous baffles promotes the uniform distribution of cavitation energy in the slurry, enhancing the consistency of the treatment. Furthermore, the internal design of the equipment borrows from the structural concept of a hydrocyclone separator, allowing the more fully exfoliated montmorillonite particles to remain suspended in the upper layer of the slurry due to buoyancy and discharged from the system via an overflow pipe; while insufficiently exfoliated particles continue to be subjected to high-intensity ultrasonic action in the strong cavitation zone, gradually achieving exfoliation and floating separation. This structural design not only improves the utilization efficiency of ultrasonic energy but also significantly enhances the exfoliation efficiency of montmorillonite and the overall processing capacity.

[0011] To obtain high-performance nano-montmorillonite, the overflow slurry after secondary ultrasonic treatment is first pumped into a two-stage hydrocyclone for classification. During this stage, the mass ratio of overflow to underflow is controlled at 7:3 to achieve efficient removal of trace quartz sand. The resulting secondary overflow then enters a high-pressure homogenization process for flake removal, with a homogenization pressure ranging from 30 to 60 MPa. Secondary hydrocyclone separation completely removes quartz sand from the ultrasonic flake removal slurry, and the coupled high-pressure homogenization process achieves efficient exfoliation of montmorillonite nanosheets. Both the secondary and tertiary hydrocyclones consist of 6–8 hydrocyclones connected in parallel, each with an inner diameter of 25 mm and a cone angle of 3°, operating at a pressure of 0.3 MPa. Furthermore, the secondary underflow is combined with the primary underflow and then subjected to sand milling with the following process parameters: rotation speed 500–2000 rpm, processing time 10–30 minutes, frequency 30–50 Hz, and grinding media diameter 0.5–2.0 mm. Wet sand milling aims to effectively strip or disperse clay mineral particles in the underflow. After sand milling, the slurry is fed into a three-stage hydrocyclone with an overflow-to-underflow mass ratio of 8:2. The three-stage overflow is returned to the pulping process in step (1) for recycling, while the three-stage underflow is discharged from the system. The wet sand milling treatment combined with three-stage hydrocyclone classification can effectively dissociate and recover clay mineral components in the primary and secondary underflows, allowing them to return to the pulping tank, thereby significantly improving the enrichment efficiency of montmorillonite and the total yield of nano-sized products (≥90%).

[0012] The bentonite nano-stripping equipment for implementing the above process includes a powder-liquid mixer, a three-roll mill, a slurry preparation device, a high-viscosity pump, a primary hydrocyclone, a variable frequency ultrasonic stripping device, a low frequency ultrasonic stripping device, a secondary hydrocyclone, and a high-pressure homogenizer, connected sequentially along the material flow direction; it also includes a circulation system for treating the underflow of the cyclone, the circulation system including a sand mill and a tertiary hydrocyclone; Wherein: the overflow outlet of the first-stage hydrocyclone is connected to the inlet of the variable frequency ultrasonic peeling device; the overflow outlet of the variable frequency ultrasonic peeling device is connected to the inlet of the low-frequency ultrasonic peeling device; the overflow outlet of the low-frequency ultrasonic peeling device can be selectively connected to the inlet of the second-stage hydrocyclone, or directly used as the output end of the nano-montmorillonite product; the overflow outlet of the second-stage hydrocyclone is connected to the high-pressure homogenizer, and the high-pressure homogenizer outlet serves as the output end of the nano-montmorillonite product; the underflow of the second-stage hydrocyclone merges with the underflow of the first-stage hydrocyclone and is sent to the sand mill; the outlet of the sand mill is connected to the inlet of the third-stage hydrocyclone, the overflow of which is returned to the pulping tank for recycling, and the underflow is discharged as tailings.

[0013] Both the variable frequency ultrasonic peeling device and the low frequency ultrasonic peeling device are equipped with porous baffles, non-penetrating feeding / overflowing discharge structures and bottom stirring devices. The ultrasonic probes are arranged in a spatial gradient to form a stepped cavitation field with high frequency first and then low frequency, which promotes the gradual peeling of montmorillonite flakes and their upward migration and overflow.

[0014] Transmission electron microscope (TEM) images of nano-montmorillonite powder obtained in the embodiments of the present invention ( Figure 3 The results show that the microstructure of natural bentonite (Bent) is characterized by a disordered stacking of multilayered sheet-like structures; however, the nano-montmorillonite (NanoMont-U / UH) prepared by the nano-stripping process and equipment developed in this invention exhibits a significantly reduced degree of sheet stacking, with numerous independent single sheets appearing. This demonstrates that under the strong cavitation effect, the interlayer forces of montmorillonite are effectively overcome, achieving efficient sheet exfoliation. Bentonite and nano-montmorillonite were separately dispersed in water (solid content 2%), stirred at 11000 rpm for 20 minutes, and then placed in a 100 mL graduated cylinder. The change in the volume of the suspension over time was recorded. Figure 4 As shown, the suspended volume of bentonite slurry decreased significantly to 15 mL after standing for 1 h, and a clear solid-liquid separation interface appeared after 2 h. In contrast, nano-montmorillonite slurry exhibited excellent suspension stability, with only slight sedimentation after standing for 7 days, indicating that it has broad application prospects in drilling mud, coatings and thixotropic agents.

[0015] XRD spectrum ( Figure 5 a) indicates that, compared to the raw bentonite, the (001) crystal plane diffraction peak of nano-montmorillonite shifts to a lower angle, and the interlayer spacing increases, further verifying that the montmorillonite lamellae are effectively exfoliated. Furthermore, the diffraction peak intensities of albite (27.7°) and quartz (26.56°) are significantly weakened, indicating that higher-density impurity minerals are effectively removed during hydrocyclone separation. FTIR spectra ( Figure 5 (b) No new absorption peaks appeared, indicating that the nano-processing did not damage the layered structure and crystal integrity of montmorillonite. Chemical composition analysis results (Table 1) show that the contents of framework elements such as SiO2, Al2O3, Fe2O3, MgO, CaO, and K2O remained basically unchanged, while the contents of Na2O and SO3 decreased, possibly related to the separation of feldspar minerals or the dissolution of sulfate substances. Furthermore, the specific surface area and pore size distribution results ( Figure 6 Table 2 shows that the specific surface area of ​​nano-montmorillonite is 1.53-2.30 times that of bentonite, and the pore volume is also significantly increased. This indicates that its structure has changed from the original densely stacked multi-layered structure to a structure with fewer or single layers overlapping each other, forming abundant packing pores. This nanosheet structure, high specific surface area, and excellent dispersibility make nano-montmorillonite significantly superior to traditional bentonite in applications such as wastewater treatment, environmental remediation, catalyst support, and polymer composites, and the added value of related products is also greatly improved.

[0016] In summary, the present invention has the following advantages compared with the prior art: 1. This invention develops a bentonite nano-scraping process. The process first involves three-roll differential grinding and pulping of wet bentonite material to promote full hydration and expansion while weakening interlayer bonding. Subsequently, hydraulic cyclone separation and purification of montmorillonite lamellae are achieved. Finally, a specially designed variable-frequency-low-frequency ultrasonic scraping device and a high-pressure homogenizer are used, leveraging the synergistic effects of ultrasonic step-by-step processing and the nano-lamellae flotation separation mechanism, to achieve efficient and uniform peeling of high-purity montmorillonite lamellae, effectively suppressing damage to the lamellae structure caused by excessive cavitation.

[0017] 2. This invention provides a complete set of equipment for bentonite nano-scraping. Based on the layered structure and scraping mechanism of montmorillonite, this equipment integrates a specially designed ultrasonic processing chamber, a high-frequency followed by low-frequency ultrasonic combination mode, bottom feeding and mechanical stirring, top overflow collection of scraped products, and porous baffle backflow, significantly improving ultrasonic energy utilization efficiency and montmorillonite scraping efficiency. Furthermore, the two-stage underflow is sand-milled and then swirled back to the pulping stage, effectively dissociating and recovering clay mineral components, thereby greatly improving the enrichment efficiency of montmorillonite and the total yield of nano-sized products.

[0018] 3. This invention utilizes abundant bentonite as raw material and achieves efficient montmorillonite exfoliation under green conditions without introducing any chemical reagents. Through ultrasonic and high-pressure homogenization, along with multi-mode cyclic synergistic processing, the process is highly efficient. This technology offers excellent controllability, allowing for the adjustment of the montmorillonite exfoliation degree according to application requirements. This enables the controllable preparation of a series of nano-montmorillonite powders, meeting the material needs of high-end fields and high-performance scenarios such as wastewater treatment, environmental remediation, catalyst supports, and polymer composites. It provides key technical support for the transformation of clay minerals into high-performance functional materials and the development of advanced nanomaterials. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the bentonite nano-process flow of the present invention. In the diagram: 1-Powder-liquid mixer, 2-Three-roll mill, 3-Pulping equipment, 4-High viscosity pump, 5-First-stage hydrocyclone classifier, 6-One-way valve, 7-Variable frequency ultrasonic peeling equipment, 8-Low frequency ultrasonic peeling equipment, 9-Second-stage hydrocyclone classifier, 10-Sand mill, 11-Third-stage hydrocyclone classifier, 12-High pressure homogenizer.

[0020] Figure 2 This is a schematic diagram of the ultrasonic peeling equipment (7 and 8) in the nano-scale process of this invention. Figure 2 (a) and (b) are the front view and top view of the variable frequency ultrasonic stripping device, respectively. Figure 2 (c) is a schematic diagram of the multi-hole partition structure used in the variable frequency ultrasonic stripping device and the low frequency ultrasonic stripping device. Figure 2 (d) is a schematic diagram of the ultrasonic generator used in the variable frequency ultrasonic stripping device and the low frequency ultrasonic stripping device. Figure 2 (e) and (f) are the front view and top view of the low-frequency ultrasonic stripping device, respectively. In the figure: 71, 81 - feed pipe, 72, 82 - ultrasonic stripping processing cavity, 73, 83 - ultrasonic probe, 731, 831 - ultrasonic transducer, 732, 832 - ultrasonic amplitude transformer, 74, 84 - porous partition, 741, 841 - pores on the surface of the partition, 75, 85 - overflow pipe, 76, 86 - stirrer.

[0021] Figure 3 These are TEM images of bentonite and nano-montmorillonite prepared using the process of this invention.

[0022] Figure 4 These are digital photographs showing the change in stability of the suspension of bentonite and nano-montmorillonite prepared by the process of this invention over time. From left to right, the slurries are Bent, NanoMent-U-1, NanoMent-U-2, NanoMent-U-3, NanoMent-UH-1, and NanoMent-UH-2.

[0023] Figure 5 These are the XRD and FTIR spectra of bentonite and nano-montmorillonite prepared by the process of this invention.

[0024] Figure 6 These are the adsorption / desorption isotherms and pore size distribution curves of bentonite and nano-montmorillonite prepared by the process of this invention. Detailed Implementation

[0025] The bentonite nano-stripping process and equipment of the present invention will be further described below through typical embodiments.

[0026] like Figure 1 As shown, the bentonite nano-stripping process equipment includes, in sequence along the material flow direction, a powder-liquid mixer 1, a three-roll mill 2, a pulping device 3, a high-viscosity pump 4, a primary hydrocyclone 5, a one-way valve 6, a variable frequency ultrasonic stripping device 7, a low-frequency ultrasonic stripping device 8, a secondary hydrocyclone 9, and a high-pressure homogenizer 12; it also includes a circulation system for treating the underflow of the cyclone, the circulation system including a sand mill 10 and a tertiary hydrocyclone 11; Wherein: the overflow outlet of the primary hydrocyclone 5 is connected to the inlet of the variable frequency ultrasonic peeling device 7; the overflow outlet of the variable frequency ultrasonic peeling device 7 is connected to the inlet of the low frequency ultrasonic peeling device 8; the overflow outlet of the low frequency ultrasonic peeling device 8 can be selectively connected to the inlet of the secondary hydrocyclone 9, or directly used as the output end of the nano-montmorillonite product; the overflow outlet of the secondary hydrocyclone 9 is connected to the high pressure homogenizer 12, and the high pressure homogenizer outlet is used as the output end of the nano-montmorillonite product; the underflow of the secondary hydrocyclone 9 and the underflow of the primary hydrocyclone 5 are merged and sent to the sand mill 10; the outlet of the sand mill 10 is connected to the inlet of the tertiary hydrocyclone 11, the overflow of the hydrocyclone is returned to the pulping tank 3 for recycling, and the underflow is discharged as tailings.

[0027] The variable frequency ultrasonic stripping device used is equipped with a hexagonal prism-shaped processing cavity, the structure of which is as follows: two sets of ultrasonic probes are arranged along the height direction on each side, the lower probe group has a frequency of 40 kHz, the upper probe group has a frequency of 20 kHz, and the output power of a single probe is 2000W; perforated baffles (pore diameter Φ2 mm, opening rate 30%, distance from cavity wall 500 mm) are installed on each side edge; a feed pipe (inner diameter DN80) is installed non-through from the center of the top of the cavity, and its outlet end is 20 cm from the bottom cover of the cavity; overflow pipes (inner diameter DN50) are installed symmetrically and non-through from both sides of the bottom of the cavity, and their overflow inlets are 10 cm from the top cover; stirrers are symmetrically installed at the bottom of the cavity, and the stirring speed is 50 rpm. The low-frequency ultrasonic stripping device adopts a composite cavity structure spliced ​​from a cylindrical shape (inscribed circle diameter 1200 mm, height 1000 mm) and a frustum shape (upper base radius: lower base radius = 3:1). Its specific configuration is as follows: six ultrasonic probes are evenly and vertically arranged along the circumference of the upper circular top surface of the cavity. The probe frequency is 20 kHz, and the output power of a single probe is 2000W. A perforated partition is set between adjacent probes. A feed pipe is installed non-through from the center of the top of the cavity, and its outlet end is 10 cm away from the bottom cover of the cavity. Overflow pipes are installed symmetrically and non-through from both sides of the bottom of the cavity, and the upper edge of the overflow port is 10 cm away from the top cover. A stirrer is installed at the center of the bottom of the cavity, and the stirring speed is 30 rpm.

[0028] Comparative Example 1 70 kg of bentonite and 35 kg of water were added to a powder-liquid mixer 1 and mixed evenly to obtain a wet material. The wet material was then fed to a three-roll mill 2 for grinding. The speed ratio of the rear, middle, and front rollers was set to 1:3:9, the gap between the rear and middle rollers was 50 μm, and the gap between the middle and front rollers was 20 μm. Grinding was performed four times. The ground material was transferred to a slurry preparation unit 3, where water was added to prepare a slurry with a mass fraction of 10%, and the mixture was continuously stirred for 6 hours. The resulting slurry was pumped into a first-stage hydrocyclone 5 for separation, with the overflow to underflow mass ratio controlled at 6:4. The overflow slurry was collected, filtered through a plate and frame filter press to obtain a filter cake, and then thoroughly dried at 100 °C to finally obtain the bentonite powder product, denoted as Bent.

[0029] Example 1 Nano-montmorillonite was prepared using the bentonite nano-exfoliation process and equipment of the present invention. The specific process steps are as follows: (1) 70 kg of bentonite and 35 kg of water were mixed evenly in a powder-liquid mixer 1 to obtain wet material. The wet material was then conveyed to a three-roll mill 2 for grinding. The speed ratio of the rear roller, middle roller and front roller was set to 1:2.5:7, the roller gap between the rear roller and the middle roller was 100 μm, and the roller gap between the middle roller and the front roller was 15 μm. The grinding was carried out twice. The ground material was transferred to a pulping device 3 (pulping tank), and water was added to prepare a slurry with a mass fraction of 10%. The mixture was stirred continuously for 6 h. The obtained slurry was pumped into a first-stage hydrocyclone 5 through a high-viscosity pump 4 for separation. The overflow and underflow mass ratio was controlled to be 6:4. The first-stage overflow slurry was collected and transferred to the sheet peeling process. The first-stage underflow was sent to a sand mill 10 and processed for 30 minutes at a speed of 500 rpm, a frequency of 30 Hz and a grinding ball diameter of 0.5 mm. The slurry after sand milling is sent into a three-stage hydrocyclone 11, and the overflow to underflow mass ratio is controlled at 8:2. The three-stage overflow is returned to the pulping process for reuse, and the three-stage underflow is discharged from the system. (2) The primary overflow obtained in step (1) is introduced from the bottom into the variable frequency ultrasonic peeling device 7. Under the combined action of ultrasound and mechanical stirring, preliminary peeling is carried out. The ultrasonic power density is 200 W / L and the processing time is 5 min. After preliminary peeling, the slurry enters the bottom of the low frequency ultrasonic peeling device 8 through the overflow pipes on both sides of the top of the inner cavity of the device. Under the conditions of ultrasonic power density of 200 W / L and processing time of 5 min, the layers are further peeled off through the coupling action of secondary ultrasound and stirring swirl. Finally, the overflow slurry is discharged from the top overflow pipe, collected and filtered by plate and frame filter press to obtain filter cake. It is then fully dried at 100 ℃ to obtain nano-montmorillonite powder product, labeled as NanoMont-U-1.

[0030] Example 2 Nano-montmorillonite was prepared using the bentonite nano-exfoliation process and equipment of the present invention. The specific process steps are as follows: Based on Example 1, the following adjustments were made: In step (2), the primary overflow slurry obtained in step (1) was subjected to frequency conversion-low frequency ultrasonic peeling treatment; the slurry overflowing from the low frequency ultrasonic peeling device 8 after secondary ultrasonic treatment was all passed through the secondary hydrocyclone 9, then flowed into the primary underflow and was sent to the sand mill 10. After sand milling, hydrocyclone classification (tertiary hydrocyclone classifier 11), and pulping (pulping device 3), it was subjected to frequency conversion-low frequency ultrasonic peeling treatment again. That is, after the bentonite raw material was subjected to two consecutive frequency conversion-low frequency ultrasonic peeling treatments, the final product was nano-montmorillonite powder, labeled as NanoMont-U-2.

[0031] Example 3 Nano-montmorillonite was prepared using the bentonite nano-exfoliation process and equipment of the present invention. The specific process steps are as follows: Based on Example 1, the following adjustments were made: In step (2), the primary overflow slurry obtained in step (1) was subjected to frequency-low frequency ultrasonic stripping, wherein the power density and processing time of frequency-low frequency ultrasonic stripping and low frequency ultrasonic stripping were 100W / L and 10 min, respectively, and finally nano-montmorillonite powder product was obtained, labeled as NanoMont-U-3.

[0032] Example 4 Nano-montmorillonite was prepared using the bentonite nano-exfoliation process and equipment of the present invention. The specific process steps are as follows: Based on Example 1, the following adjustments were made: In step (1), the ground material was mixed with water to form a slurry with a mass fraction of 15%; in step (2), the overflow slurry from the low-frequency ultrasonic peeling device 8 after secondary ultrasonic treatment was sent to the secondary hydrocyclone 9, and the mass ratio of overflow to underflow was controlled at 7:3; the secondary overflow was collected and further subjected to high-pressure homogenization peeling at 30 MPa pressure, and the resulting product was denoted as NanoMont-UH-1. The secondary underflow was combined with the primary underflow for a sand milling process, and the ground slurry was introduced into the tertiary hydrocyclone, and the mass ratio of overflow to underflow was controlled at 8:2. The tertiary overflow was returned to the pulping process in step (1) for recycling, and the tertiary underflow was used as the tail material discharge system.

[0033] Example 5 Nano-montmorillonite was prepared using the bentonite nano-exfoliation process and equipment of the present invention. The specific process steps are as follows: Based on Example 1, adjustments were made as follows: In step (1), the ground material was mixed with water to form a slurry with a mass fraction of 15%; in step (2), the bentonite raw material underwent two consecutive frequency-low frequency ultrasonic peeling treatments; the resulting overflow was sent to a secondary hydrocyclone, and the mass ratio of overflow to underflow was controlled at 7:3; the secondary overflow was collected and further subjected to high-pressure homogenization peeling at 60 MPa pressure to obtain nano-montmorillonite, labeled NanoMont-UH-2; the secondary underflow was combined with the primary underflow for a sand milling process, and the ground slurry was introduced into a tertiary hydrocyclone, and the mass ratio of overflow to underflow was controlled at 8:2. The tertiary overflow was returned to the pulping process in step (1) for recycling, and the tertiary underflow was used as a tailings discharge system.

Claims

1. A process for nanosizing and exfoliating bentonite clay, characterized in that Comprise the following steps: (1) Pretreatment: bentonite and water are mixed uniformly according to the mass ratio of 2:1, after three-roll grinding treatment, water is added to prepare a slurry with a mass fraction of 10-15%, and the stirring is continued for 4-6 hours; the obtained slurry is pumped into a first-stage hydrocyclone, the mass ratio of overflow to underflow is controlled to be 6:4, the first-stage overflow is subjected to sheet peeling in step (2), and the first-stage underflow is sent to a sand mill; (2) Nanometerization peeling: the first-stage overflow obtained in step (1) is introduced into the bottom of a variable-frequency ultrasonic peeling equipment, and preliminary peeling is carried out under the synergistic action of ultrasonic and mechanical stirring; after peeling, the slurry is introduced into the bottom of a low-frequency ultrasonic peeling equipment through the overflow pipes on the two sides of the shaft of the inner cavity of the equipment, and further peeling is carried out under the coupling action of secondary ultrasonic and stirring cyclone, and finally the nanometer montmorillonite is obtained through the top overflow pipe; or, the overflow slurry after secondary ultrasonic treatment is sent into a second-stage hydrocyclone, the mass ratio of overflow to underflow is controlled to be 7:3, the second-stage overflow is subjected to high-pressure homogenization peeling treatment to prepare the nanometer montmorillonite; the second-stage underflow and the first-stage underflow are combined for sand milling treatment, and the obtained slurry is sent into a third-stage hydrocyclone, the mass ratio of overflow to underflow is controlled to be 8:2, the third-stage overflow is returned to the slurry preparation process of step (1) for reuse, and the third-stage underflow is discharged from the system. The three-roll grinding process parameters in step (1) are as follows: the speed ratio of the rear roller, the middle roller and the front roller is controlled to be 1:2.5:7-1:3:9; the roller gap of the rear roller and the middle roller is 50-100 μm, and the roller gap of the middle roller and the front roller is 15-20 μm; the material grinding times are 2-4 times.

2. The process for nanosizing and exfoliating bentonite clay of claim 1 wherein: The first-stage hydrocyclone in step (1) is composed of 8-10 parallel hydrocyclones with a cylinder inner diameter of 50 mm and a cone angle of 6°, and the operating pressure is 0.3 MPa.

3. The process for nanosizing and exfoliating bentonite clay of claim 1 wherein: The variable-frequency ultrasonic peeling equipment in step (2) is provided with a six-prism-shaped treatment cavity, and the structure design is as follows: two groups of ultrasonic probes are arranged on each side along the height direction, the frequency of the lower probe group is 40 kHz, the frequency of the upper probe group is 20 kHz, the output power of a single probe is 2000 W; a perforated partition plate is installed on each side edge; a feeding pipe is non-penetratingly installed at the center of the top of the cavity, and the outlet end is 10-20 cm away from the bottom cover of the cavity; overflow pipes are symmetrically and non-penetratingly installed on both sides of the bottom of the cavity, and the overflow inlets are 10-20 cm away from the top cover; a stirrer is symmetrically installed at the bottom of the cavity, and the stirring speed is 30-50 rpm.

4. The process of claim 1 wherein: The low-frequency ultrasonic peeling equipment in step (2) adopts a composite cavity structure composed of a cylindrical part and a circular truncated cone part, and the specific configuration is as follows: six ultrasonic probes are uniformly and vertically arranged on the circular top surface of the upper part of the cavity along the circumferential direction, the frequency of the probes is 20 kHz, and the output power of a single probe is 2000 W; a perforated partition plate is arranged between adjacent probes; a feeding pipe is non-penetratingly installed at the center of the top of the cavity, and the outlet end is 10-20 cm away from the bottom cover of the cavity; overflow pipes are symmetrically and non-penetratingly installed on both sides of the bottom of the cavity, and the upper edge of the overflow port is 10-20 cm away from the top cover; a stirrer is installed at the center of the bottom of the cavity, and the stirring speed is 30-50 rpm.

5. The process of claim 1 wherein: ​ 6. The process of claim 1 wherein: The ultrasonic power density of the variable-frequency ultrasonic flaking device and the low-frequency ultrasonic flaking device in step (2) is 100-200 W / L, and the processing time is 5-10 min; when high-pressure homogenization is used, the high-pressure homogenization pressure is 30-60 MPa.

7. The process of claim 1 wherein: The secondary and tertiary hydrocyclones in step (2) are each composed of 6-8 parallel hydrocyclones with an inner diameter of 25 mm and a cone angle of 3°, and the operating pressure is 0.3 MPa.

8. The process of claim 1 wherein: In step (2), the sand milling is performed at 500-2000 rpm for 10-30 min, the frequency is 30-50 Hz, and the diameter of the grinding ball is 0.5-2.0 mm.

9. The process of claim 1 wherein: The ultrasonic treatment in step (2) can be repeatedly performed or cycled, and at least one pass of variable-frequency-low-frequency ultrasonic treatment is performed.

10. An apparatus for nanofluidization and exfoliation of bentonite for carrying out the process according to any one of claims 1 to 9, characterized in that, The system comprises, in sequence along the material flow direction, a powder-liquid mixer, a three-roll mill, a pulping device, a high-viscosity pump, a primary hydrocyclone, a variable-frequency ultrasonic flaking device, a low-frequency ultrasonic flaking device, a secondary hydrocyclone, and a high-pressure homogenization device; the system further comprises a processing system for recycling the cyclone underflow, which comprises a sand mill and a tertiary hydrocyclone. The overflow outlet of the primary hydrocyclone is connected to the inlet of the variable-frequency ultrasonic flaking device; the overflow outlet of the variable-frequency ultrasonic flaking device is connected to the inlet of the low-frequency ultrasonic flaking device; the overflow outlet of the low-frequency ultrasonic flaking device is connected to the inlet of the secondary hydrocyclone, or directly outputs the nanometer montmorillonite product; the overflow outlet of the secondary hydrocyclone is connected to the high-pressure homogenization device, and the nanometer montmorillonite product is output from the discharge outlet of the high-pressure homogenization device. The secondary hydrocyclone underflow is combined with the primary hydrocyclone underflow and then sent to the sand mill; the outlet of the sand mill is connected to the inlet of the tertiary hydrocyclone, the overflow of the tertiary hydrocyclone is returned to the pulping tank for recycling, and the underflow is discharged as tailings.

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