Composite bentonite and preparation method thereof

Abstract

The invention relates to the technical field of bentonite, in particular to composite bentonite and a preparation method thereof. The invention relates to a preparation method of composite bentonite, which comprises the following steps: dispersing calcium bentonite in deionized water, stirring and dispersing at a high speed, and removing impurities to obtain bentonite slurry; adding a hydrophilic modified CS-coated BP-SiO2 filler, carrying out ultrasonic-shearing synergistic treatment, then adding a modifier and a cross-linking agent, and then carrying out a mechanochemical grinding reaction; and drying and grinding the obtained product to obtain the multifunctional composite bentonite. According to the composite bentonite provided by the invention, the dispersion effect of the traditional inorganic filler in the bentonite is improved, the agglomeration phenomenon is avoided to form a stable interface structure, and the comprehensive properties such as the interlayer structure, the overall strength, the stability, the water swelling capacity and the suspension property of the composite bentonite are improved.

Description

Technical Field

[0001] This invention relates to the field of bentonite technology, specifically to a composite bentonite and its preparation method. Background Technology

[0002] Bentonite is a natural clay mineral with montmorillonite as its main component. It possesses a unique layered structure and excellent physicochemical properties, such as water absorption and swelling capacity, cation exchange capacity, dispersion and suspension properties, and adsorption capacity. Due to these properties, bentonite is widely used in various fields, including oil drilling, casting, environmental protection, building materials, medicine, and agriculture. For example, in oil drilling, it is used as a drilling fluid diluent and loss-of-hydraulic control agent, effectively carrying drill cuttings, cooling the drill bit, and stabilizing the wellbore. In the environmental field, it can be used in wastewater treatment to adsorb heavy metal ions and organic pollutants in water. In the building materials industry, it is used as an additive to improve the performance of cement and concrete.

[0003] In the preparation of composite bentonite, some traditional inorganic fillers have surface properties that differ significantly from bentonite, leading to agglomeration upon addition and hindering the formation of a stable interfacial structure, thus affecting the performance improvement of the composite bentonite. Furthermore, some modifiers can only improve the dispersibility of bentonite by altering its surface charge, with limited effect on improving properties such as the interlayer structure and water absorption and swelling capacity. During the water absorption and swelling process, the network structure is easily damaged, resulting in a decrease in the overall strength and stability of the composite bentonite, failing to effectively maintain its structural integrity, and thus affecting its water absorption and swelling performance. Based on this, this invention proposes a composite bentonite and its preparation method. Summary of the Invention

[0004] This invention proposes a composite bentonite and its preparation method, which improves the dispersion effect of traditional inorganic fillers in bentonite, avoids agglomeration to form a stable interface structure, and improves the comprehensive properties of composite bentonite, such as interlayer structure, overall strength, stability, water absorption and swelling capacity, and suspension.

[0005] The technical solution of the present invention is as follows: In a first aspect, the present invention provides a method for preparing composite bentonite, comprising the following steps: Calcium-based bentonite was dispersed in deionized water and subjected to high-speed stirring and impurity removal to obtain a bentonite slurry. Hydrophilic modified CS@BP-SiO2 filler was added, and after ultrasonic-shear synergistic treatment, modifiers and crosslinking agents were added, followed by mechanochemical grinding reaction. The resulting product was dried to obtain the multifunctional composite bentonite.

[0006] During high-energy ball milling, intense collisions and friction occur between balls and between balls and the material, generating strong mechanical forces. These forces not only further refine the particles, increasing their specific surface area and reactivity, but also trigger chemical reactions on the particle surface. For example, during grinding, modifiers and crosslinking agents interact mechanically with the surfaces of bentonite and filler particles, promoting their adsorption and reaction on the particle surface, leading to more stable chemical bonds and interfacial structures.

[0007] As a further technical solution, the conditions for the ultrasonic-shear synergistic processing are: ultrasonic power of 400-600W, simultaneous mechanical shearing at a rotation speed of 1500-2500 rpm, and processing time of 20-40 minutes.

[0008] As a further technical solution, the mechanochemical grinding reaction is carried out using a high-energy ball mill with a ball-to-material ratio of 8:1-12:1, a rotation speed of 250-350 rpm, and a grinding time of 45-75 min. The material is then passed through a 300-mesh sieve. The drying process is carried out at 80-100℃ until constant weight is achieved.

[0009] As a further technical solution, the composite bentonite comprises the following raw materials in parts by weight: 100 parts of calcium-based bentonite, 15-30 parts of hydrophilic modified CS@BP-SiO2 filler, 8-12 parts of modifier, and 3-5 parts of crosslinking agent.

[0010] As a further technical solution, the preparation method of the hydrophilic modified CS@BP-SiO2 filler includes the following steps: mixing triethyl borate, triethyl phosphate, anhydrous ethanol and water, adding dilute hydrochloric acid dropwise to adjust the pH value and maintain it at 2.5-3.5, stirring at 30-40℃ for 60-90 min to obtain a hydrolysate, adding silica powder, heating to 50-60℃, stirring at 350-450 rpm for 4-5 h, centrifuging, washing and drying, and then calcining at 300-320℃ for 2-3 h to obtain the final product.

[0011] As a further technical solution, the ratio of triethyl borate, triethyl phosphate, anhydrous ethanol, water and silica powder is 75-85mL: 5-15mL: 25-35mL: 3-4.5mL: 20-30g.

[0012] As a further technical solution, the preparation method of the silica powder includes the following steps: dissolving 4.0-6.0g of P123 template agent in 120-160mL of 2.0M hydrochloric acid solution, stirring in a water bath at 40-45℃ until completely dissolved and clear, and slowly adding 9.0-10mL of tetraethyl orthosilicate while stirring at 400-500rpm; after the addition is complete, continuing to stir at a constant temperature for 3-4h; then transferring the mixture to a reaction vessel and carrying out a hydrothermal reaction in an oven at 100-110℃ for 22-24h; filtering, washing with deionized water until the filtrate is neutral, drying at 90-100℃, and then calcining in a muffle furnace at 2℃ / min to 550-600℃ for 5-6h to obtain the final product.

[0013] As a further technical solution, the modifier is an aqueous solution of a mixture of chitosan and hexadecyltrimethylammonium bromide in a weight ratio of 1:2-3, with a mass concentration of 3%-8%.

[0014] As a further technical solution, the crosslinking agent is citric acid.

[0015] Secondly, the present invention proposes a composite bentonite, which is prepared by the method for preparing the composite bentonite.

[0016] The working principle and beneficial effects of this invention are as follows: This invention utilizes hydrophilically modified CS@BP-SiO2 filler to improve the properties of bentonite. Structurally, the surface properties of the hydrophilically modified CS@BP-SiO2 filler are altered, exhibiting enhanced hydrophilicity. When added to calcium-based bentonite slurry, the filler interacts effectively with the surface of bentonite particles. On one hand, the filler's hydrophilicity facilitates dispersion in the bentonite slurry, ensuring sufficient contact with the bentonite particles. On the other hand, the active groups on the filler surface can adsorb or chemically react with the charges or functional groups on the bentonite surface, forming a stable interfacial structure. This interfacial structure helps prevent the aggregation of bentonite particles, increasing particle dispersion and thus improving the suspension properties of the bentonite. Simultaneously, the presence of the hydrophilically modified filler also forms a hydration film around the bentonite particles, enhancing the bentonite's water absorption and swelling capacity, and increasing its swelling volume.

[0017] In this invention, the modifier is an aqueous solution of chitosan and hexadecyltrimethylammonium bromide in a weight ratio of 1:2-3. Chitosan is a natural polymer with abundant active groups such as amino and hydroxyl groups. These groups can electrostatically adsorb onto the negative charge on the surface of bentonite, thereby altering the charge distribution on the surface of bentonite particles, increasing the repulsive force between particles, preventing particle agglomeration, and improving the dispersibility of bentonite. Hexadecyltrimethylammonium bromide, as a cationic surfactant, has long-chain alkyl groups that can insert into the interlayer structure of bentonite, expanding the interlayer spacing. Simultaneously, its hydrophilic groups face the aqueous phase, further enhancing the hydrophilicity and dispersibility of bentonite. The synergistic effect of chitosan and hexadecyltrimethylammonium bromide—chitosan primarily improving dispersibility by altering the surface charge of particles, while hexadecyltrimethylammonium bromide plays a role in interlayer structure and surface activity—comprehensively improves the surface modification and dispersion stability of bentonite, thereby enhancing its hydration capacity and suspension properties.

[0018] In this invention, the crosslinking agent plays a role in constructing a stable network structure in the composite bentonite system. Taking citric acid as an example, the citric acid molecule contains multiple carboxyl groups, which can form chemical crosslinking bonds with metal ions on the surface of bentonite and active groups on the surface of hydrophilic modified CS@BP-SiO2 filler. Through these crosslinking bonds, bentonite particles, fillers, and modifiers are linked together to form a three-dimensional network structure. This network structure not only enhances the overall strength and stability of the composite bentonite but also restricts particle movement, further improving dispersibility. Simultaneously, the stable network structure helps maintain the structural integrity of the bentonite during water absorption and swelling, allowing it to better exert its water absorption and swelling performance. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 This embodiment provides a method for preparing composite bentonite, including the following steps: 100g of calcium-based bentonite was dispersed in 800g of deionized water and dispersed by high-speed stirring to remove impurities, resulting in a bentonite slurry. 20g of hydrophilic modified CS@BP-SiO2 filler was added, and the mixture was subjected to ultrasonic mechanical shearing at 500W and 2000rpm for 30min. Then, 10g of modifier and 4g of crosslinking agent were added, followed by a mechanochemical grinding reaction. The mechanochemical grinding reaction was carried out using a high-energy ball mill with a ball-to-material ratio of 10:1, a rotation speed of 300rpm, and a grinding time of 60min. The ground product was then passed through a 300-mesh sieve. The resulting product was dried at 90℃ to constant weight to obtain multifunctional composite bentonite. The preparation method of hydrophilic modified CS@BP-SiO2 filler includes: mixing 80 mL of triethyl borate, 10 mL of triethyl phosphate, 30 mL of anhydrous ethanol and 4 mL of water, adding dilute hydrochloric acid dropwise, adjusting the pH value and maintaining it at 3, stirring at 35℃ for 75 min to obtain hydrolysate, adding 25 g of silica powder, heating to 55℃, stirring at 400 rpm for 4.5 h, centrifuging, washing and drying, and then calcining at 310℃ for 2.5 h to obtain the final product; The preparation method of silica powder includes: dissolving 5.0 g of P123 template agent in 140 mL of 2.0 M hydrochloric acid solution, stirring at 42 °C in a water bath until completely dissolved and clear, and slowly adding 9.5 mL of tetraethyl orthosilicate dropwise while stirring at 450 rpm; after the addition is complete, continue stirring at a constant temperature for 3.5 h; then transfer the mixture to a reaction vessel and carry out a hydrothermal reaction at 105 °C in an oven for 23 h; filter, wash with deionized water until the filtrate is neutral, dry at 95 °C, and calcine in a muffle furnace at 2 °C / min to 580 °C for 5.5 h to obtain the silica powder; The modifier is an aqueous solution of a mixture of chitosan and hexadecyltrimethylammonium bromide in a weight ratio of 1:2.5, with a mass concentration of 5%; the crosslinking agent is citric acid.

[0021] Example 2 This embodiment provides a method for preparing composite bentonite, including the following steps: 100g of calcium-based bentonite was dispersed in 800g of deionized water and dispersed by high-speed stirring to remove impurities, resulting in a bentonite slurry. 15g of hydrophilic modified CS@BP-SiO2 filler was added, and the mixture was subjected to mechanical shearing at 400W ultrasonic power and 1500rpm for 20min. Then, 8g of modifier and 3g of crosslinking agent were added, followed by a mechanochemical grinding reaction. The mechanochemical grinding reaction was carried out using a high-energy ball mill with a ball-to-material ratio of 8:1, a rotation speed of 250rpm, and a grinding time of 45min. The ground product was then passed through a 300-mesh sieve. The resulting product was dried at 80℃ to constant weight to obtain multifunctional composite bentonite. The preparation method of hydrophilic modified CS@BP-SiO2 filler includes: mixing 75 mL triethyl borate, 5 mL triethyl phosphate, 25 mL anhydrous ethanol and 3 mL water, adding dilute hydrochloric acid dropwise, adjusting the pH value and maintaining it at 3, stirring at 30℃ for 60 min to obtain hydrolysate, adding 20 g silica powder, heating to 50℃, stirring at 350 rpm for 4 h, centrifuging, washing and drying, and then calcining at 300℃ for 2 h to obtain the final product; The preparation method of silica powder includes: dissolving 4.0 g of P123 template agent in 120 mL of 2.0 M hydrochloric acid solution, stirring in a 40 °C water bath until completely dissolved and clear, and slowly adding 9.0 mL of tetraethyl orthosilicate dropwise while stirring at 400 rpm; after the addition is complete, continue stirring at a constant temperature for 3 h; then transfer the mixture to a reaction vessel and carry out a hydrothermal reaction in an oven at 100 °C for 22 h; filter, wash with deionized water until the filtrate is neutral, dry at 90 °C, and then calcine in a muffle furnace at a temperature of 2 °C / min to 550 °C for 5 h to obtain the silica powder; The modifier is an aqueous solution of a mixture of chitosan and hexadecyltrimethylammonium bromide in a weight ratio of 1:2, with a mass concentration of 3%; the crosslinking agent is citric acid.

[0022] Example 3 This embodiment provides a method for preparing composite bentonite, including the following steps: 100g of calcium-based bentonite was dispersed in 800g of deionized water, and the mixture was stirred at high speed to disperse and remove impurities, resulting in a bentonite slurry. 30g of hydrophilic modified CS@BP-SiO2 filler was added, and the mixture was subjected to mechanical shearing at 600W ultrasonic power and 2500rpm for 40min. Then, 12g of modifier and 5g of crosslinking agent were added, followed by a mechanochemical grinding reaction. The mechanochemical grinding reaction was carried out using a high-energy ball mill with a ball-to-material ratio of 12:1, a rotation speed of 350rpm, and a grinding time of 75min. The ground product was then passed through a 300-mesh sieve. The resulting product was dried at 100℃ to constant weight to obtain multifunctional composite bentonite. The preparation method of hydrophilic modified CS@BP-SiO2 filler includes: mixing 85 mL triethyl borate, 15 mL triethyl phosphate, 35 mL anhydrous ethanol and 4.5 mL water, adding dilute hydrochloric acid dropwise to adjust the pH value and maintain it at 3.5, stirring at 40℃ for 90 min to obtain hydrolysate, adding 30 g silica powder, heating to 60℃, stirring at 450 rpm for 5 h, centrifuging, washing and drying, and then calcining at 320℃ for 3 h to obtain the final product; The preparation method of silica powder includes: dissolving 6.0g of P123 template agent in 160mL of 2.0M hydrochloric acid solution, stirring in a 45℃ water bath until completely dissolved and clear, and slowly adding 10mL of tetraethyl orthosilicate while stirring at 500rpm; after the addition is complete, continue stirring at a constant temperature for 4h; then transfer the mixture to a reaction vessel and carry out a hydrothermal reaction in an oven at 110℃ for 24h; filter, wash with deionized water until the filtrate is neutral, dry at 100℃, and then calcine in a muffle furnace at 2℃ / min to 600℃ for 6h to obtain the silica powder; The modifier is an aqueous solution of a mixture of chitosan and hexadecyltrimethylammonium bromide in a weight ratio of 1:3, with a mass concentration of 8%; the crosslinking agent is citric acid.

[0023] Comparative Example 1 Based on Example 1, adjustments were made. Unlike Example 1, hydrophilic modified CS@BP-SiO2 filler was not added in Comparative Example 1.

[0024] Comparative Example 2 Based on Example 1, adjustments were made. Unlike Example 1, Comparative Example 2 used unmodified silica powder instead of hydrophilic modified CS@BP-SiO2 filler. That is, it was obtained according to the preparation method of silica powder in Example 1, but without hydrophilic modification.

[0025] Comparative Example 3 Based on Example 1, adjustments were made. Unlike Example 1, the amount of hydrophilic modified CS@BP-SiO2 filler in Comparative Example 3 was adjusted to 5g.

[0026] Comparative Example 4 Based on Example 1, adjustments were made, except that the amount of modifier used in Comparative Example 4 was adjusted to 2g.

[0027] Comparative Example 5 Based on Example 1, adjustments were made. The difference from Example 1 is that the mechanical-chemical grinding time in Comparative Example 5 was adjusted to 30 min.

[0028] Comparative Example 6 Based on Example 1, the modification was adjusted. Unlike Example 1, the modifier in Comparative Example 6 was a pure chitosan aqueous solution, i.e., hexadecyltrimethylammonium bromide was not used, and the mass concentration was 5%.

[0029] Comparative Example 7 Based on Example 1, adjustments were made. The difference from Example 1 is that the crosslinking agent in Comparative Example 7 was changed to glutaraldehyde.

[0030] Experimental Example: The composite bentonites prepared in Examples 1-3 and Comparative Examples 1-7 were tested as follows: Suspension performance: Referring to the method for determining the apparent viscosity of bentonite slurry in GB / T5005-2010 "Drilling Fluid Materials Specification", 24.0g of the composite bentonite sample to be tested was weighed and slowly added to a stirring cup containing 350mL of deionized water. The mixture was stirred continuously at 10000rpm for 5min using a high-speed stirrer. The stirring cup was then sealed and allowed to stand at 23℃ for 24h. After curing, the mixture was stirred at high speed again for 1min. The bentonite slurry was immediately poured into the sample cup of a rotational viscometer and equilibrated in a constant temperature water bath at 25℃ for 5min. The readings at 600rpm and 300rpm were taken using a six-speed rotational viscometer. The apparent viscosity (AV) was calculated using the following formula: AV(mPa·s)=Φ600 / 2; kinetic-plastic ratio=(Φ300-PV) / PV, where the plastic viscosity PV=Φ600-Φ300. A higher apparent viscosity (AV) value generally indicates better dispersibility and hydration ability of the sample, i.e., better suspension performance.

[0031] 75μm sieve residue: The test was conducted according to GB / T20973-2020 "Bentonite". 10.0g of the composite bentonite sample to be tested was placed in a 75μm standard test sieve. The sample on the sieve was rinsed with a slow stream of water until the water flowed clear. The residue was transferred to a pre-weighed weighing bottle and dried in an oven at 105℃ until constant weight. After cooling to room temperature in a desiccator, it was weighed. 75μm sieve residue (%) = (mass of residue / mass of sample) × 100%; the lower the residue, the finer the sample particle size, the better the dispersibility, and the higher the product quality.

[0032] Water absorption and swelling performance: Refer to the "Swelling Capacity" determination method in GB / T20973-2020; weigh 2.00 g of the composite bentonite sample to be tested, dried at 105℃, and slowly and evenly pour it into a stoppered graduated cylinder containing 100 mL of deionized water through a funnel. Allow the sample to settle freely in the water for 2 hours. After 2 hours, directly read the volume of bentonite in the graduated cylinder (in milliliters). The volume read in milliliters is the swelling capacity of the sample. The larger this value, the stronger the water absorption and swelling capacity of the sample, and the better its hydration performance and theoretical bonding performance.

[0033] The results are shown in Table 1 below: Table 1

[0034] Based on the above, it can be seen that Example 1 has the highest parameters, exhibiting the best apparent viscosity, dynamic-to-plastic ratio, plastic viscosity, lowest 75μm sieve residue, and highest swelling capacity. This indicates that optimizing the preparation parameters can significantly improve the suspension, dispersibility, and water absorption and swelling properties of bentonite.

[0035] Comparative Example 1, without the addition of hydrophilic modified CS@BP-SiO2 filler, had the lowest apparent viscosity (15.0 mPa·s) and swelling capacity (20.0 mL), and the highest 75 μm sieve residue (0.50%). The hydrophilic modified CS@BP-SiO2 filler is a key component for improving the dispersibility and hydration performance of bentonite, and its absence leads to a significant reduction in suspension and water absorption swelling capacity.

[0036] Comparative Example 2 used unmodified silica powder instead of the hydrophilic modified filler, and its performance was improved compared to Comparative Example 1, but still far lower than that of Example 1: the apparent viscosity (18.0 mPa·s) and expansion volume (25.0 mL) were lower, while the 75 μm sieve residue (0.30%) was higher. Hydrophilic modification treatment can enhance the hydrophilicity and dispersibility of the filler, while the effect of unmodified silica powder is limited, failing to fully utilize the synergistic effect of the filler.

[0037] In Comparative Example 3, the amount of hydrophilic modified CS@BP-SiO2 filler was reduced to 5g. The apparent viscosity (20.0 mPa·s) and expansion volume (28.0 mL) were lower than those in Example 1, while the 75μm sieve residue (0.25%) was higher. Insufficient filler content cannot effectively improve the structure and properties of bentonite; an appropriate amount of filler is a necessary condition to ensure the composite effect.

[0038] Comparative Example 4: When the amount of modifier was reduced to 2g, the apparent viscosity (22.0 mPa·s) and swelling capacity (26.0 mL) were lower, while the residue on the 75μm sieve (0.20%) was higher. Insufficient amount of modifier (chitosan and hexadecyltrimethylammonium bromide) would affect the surface modification and dispersion stability of bentonite, resulting in reduced hydration capacity and suspension.

[0039] In Comparative Example 5, reducing the mechanochemical grinding time to 30 min resulted in a significant increase in the 75 μm sieve residue (0.40%), while the apparent viscosity (24.0 mPa·s) and expansion volume (28.0 mL) were lower. Insufficient grinding time led to coarser particle size and poor dispersibility; sufficient mechanochemical grinding is crucial to ensuring finer and more uniform particle dispersion.

[0040] Comparative Example 6 used pure chitosan as the modifier, without cetyltrimethylammonium bromide. It had lower apparent viscosity (19.0 mPa·s) and swelling capacity (22.0 mL), but higher residue on the 75 μm sieve (0.35%). Cetyltrimethylammonium bromide, as a cationic surfactant, can enhance the hydrophilicity and dispersibility of bentonite; its absence significantly reduced the modification effect.

[0041] Comparative Example 7 used glutaraldehyde as the crosslinking agent, and its performance was similar to but slightly worse than that of Example 1: the apparent viscosity (26.0 mPa·s) and expansion volume (32.0 mL) were higher, but the 75 μm sieve residue (0.15%) was slightly higher. Citric acid is more suitable as a crosslinking agent for this system, as it can form a stable network structure, while glutaraldehyde may have lower crosslinking efficiency or poor compatibility with the components, resulting in a slight decrease in performance.

[0042] The above are merely preferred embodiments of the present invention and are 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 a composite bentonite, characterized by, The method comprises the following steps: The calcium-based bentonite is dispersed in deionized water, high-speed stirring and impurity removal are performed, and a bentonite slurry is obtained; the hydrophilic modified CS@BP-SiO2 filler is added, and then ultrasonic-shearing synergistic treatment is performed; then, a modifier and a crosslinking agent are added, and mechanical-chemical grinding reaction is performed; and finally, the obtained product is dried to obtain the multifunctional composite bentonite.

2. The method of claim 1, wherein the bentonite is prepared by mixing 0.1 to 0.3 parts by weight of the sodium carbonate with 100 parts by weight of the bentonite. The ultrasonic-shearing synergistic treatment is performed at an ultrasonic power of 400-600 W and a mechanical shearing speed of 1500-2500 rpm for 20-40 min.

3. The method for preparing composite bentonite according to claim 1, characterized in that, The mechanical-chemical grinding reaction is performed by using a high-energy ball mill at a ball-to-material ratio of 8:1-12:1 and a rotation speed of 250-350 rpm for 45-75 min, and the product is sieved through a 300-mesh screen after grinding; and the drying is performed at 80-100 ℃ until the weight is constant.

4. The method for preparing composite bentonite according to claim 1, characterized in that, The composite bentonite comprises the following raw materials in parts by weight: 100 parts of calcium-based bentonite, 15-30 parts of the hydrophilic modified CS@BP-SiO2 filler, 8-12 parts of the modifier, and 3-5 parts of the crosslinking agent.

5. The method for preparing composite bentonite according to claim 1, characterized in that, The preparation method of the hydrophilic modified CS@BP-SiO2 filler comprises the following steps: mixing triethyl borate, triethyl phosphate, anhydrous ethanol and water, adding dilute hydrochloric acid dropwise, adjusting and maintaining the pH value at 2.5-3.5, stirring at 30-40 ℃ for 60-90 min to obtain a hydrolysis solution, adding silica powder, heating to 50-60 ℃, stirring at 350-450 rpm for 4-5 h, centrifugal separation, washing and drying, and then calcining at 300-320 ℃ for 2-3 h to obtain the product.

6. The method for preparing composite bentonite according to claim 5, characterized in that, The amount ratio of the triethyl borate, the triethyl phosphate, the anhydrous ethanol, the water and the silica powder is 75-85 mL:5-15 mL:25-35 mL:3-4.5 mL:20-30 g.

7. The method for preparing composite bentonite according to claim 5, characterized in that, The preparation method of the silica powder comprises the following steps: dissolving 4.0-6.0 g of P123 template in 120-160 mL of 2.0 M hydrochloric acid solution, stirring in a 40-45 ℃ water bath until the solution is clear and completely dissolved, slowly adding 9.0-10 mL of tetraethyl orthosilicate dropwise under stirring at 400-500 rpm, continuing constant-temperature stirring for 3-4 h after the addition is completed, transferring the mixture to a reaction kettle, performing hydrothermal reaction at 100-110 ℃ for 22-24 h in an oven, washing with deionized water until the filtrate is neutral, drying at 90-100 ℃, heating to 550-600 ℃ at a rate of 2 ℃ / min in a muffle furnace, and calcining for 5-6 h to obtain the product.

8. The method for preparing composite bentonite according to claim 1, characterized in that, The modifier is an aqueous solution of a mixture of chitosan and cetyltrimethylammonium bromide at a weight ratio of 1:2-3, and the mass concentration is 3%-8%.

9. The method for preparing composite bentonite according to claim 1, characterized in that, The crosslinking agent is citric acid.

10. A composite bentonite, characterized by, The multifunctional composite bentonite is prepared by the method of any one of claims 1-9.

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