A high-purity montmorillonite purification process

Abstract

The present invention discloses a high-purity montmorillonite purification process, belonging to the technical field of material purification and processing, which includes the following steps: Step S1, preparing materials for natural sedimentation; Step S2, preparing materials for modified sedimentation; Step S3, preparing preliminarily purified materials; Step S4, preparing high-purity montmorillonite; In the present invention, the materials for natural sedimentation and the modification treatment agent are subjected to wet grinding and dry grinding. The modification treatment agent contains a silica sol structure and a graft-modified lignin structure. The silica sol structure contains an inorganic polymer with polyvalent negative charges, which has special reaction ability and adsorption effect on aluminum ions, breaking the "I"-shaped association-based overlapping structure in the montmorillonite structure. The graft-modified lignin structure not only plays a role in viscosity reduction, but also contains multiple hydroxyl groups, which are easy to establish strong hydrogen bonds on the surface of alumina. The grafted oxyether groups thereon are also easy to produce ionic affinity with the surface of oxygen-containing colloids, improving the purity and yield of montmorillonite purified from natural bentonite.

Description

Technical Field

[0001] The present invention relates to the technical field of material purification and processing, and particularly to a high-purity montmorillonite purification process. Background Art

[0002] Natural bentonite is widely used in the fields of casting, medicine, civil engineering, environmental protection, etc. due to its good water absorption and swelling properties, impermeability and suspension stability. The main component of natural bentonite is montmorillonite, which is often accompanied by impurities such as quartz, feldspar and calcite. The content of montmorillonite cannot meet the requirements of the pharmaceutical, food and daily chemical industries, so it needs to be purified.

[0003] Most of the bentonite types in China are mainly calcium-based bentonite. The natural bentonite beneficiation and purification processes mainly include dry method and wet method. The dry processing process is mainly raw ore drying → grinding → classification. The fine particle size is the montmorillonite concentrate, and the coarse particle size is the tailings (coarse sand). The dry process is usually used for bentonite with a montmorillonite content in the raw ore greater than 80% and coarser impurity minerals. The raw ore with a lower montmorillonite content mainly adopts the wet purification process. The wet purification mainly includes pulp dispersion, coarse sand separation, centrifugal purification or natural sedimentation, suspension drying, product grinding and other links. The natural sedimentation process takes a long time and has low production efficiency. The high-speed centrifugation process has high production efficiency, but high energy consumption and high production cost. It is the main process for producing high-value-added bentonite products at present. At the same time, in natural bentonite, cristobalite generally forms a wrapped structure with montmorillonite. Montmorillonite swells when encountering water, and the viscosity of the slurry increases, which is more unfavorable for the separation of fine-grained cristobalite. Therefore, how to promote the separation of cristobalite and montmorillonite in natural bentonite is the key problem to be solved in improving the purification of montmorillonite from natural bentonite. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-purity montmorillonite purification process to solve the problems raised in the background art.

[0005] To achieve the above purpose, the present invention provides the following technical solutions:

[0006] A high-purity montmorillonite purification process includes the following steps:

[0007] Step S1, preparing materials for natural sedimentation: adding natural bentonite into water to prepare a slurry with a mass fraction of 10%, then performing hydraulic classification to obtain classified bottom sand and classified overflow slurry respectively, collecting the classified overflow slurry at the end, drying it at 105°C for 2 - 3 h to obtain materials for natural sedimentation, wherein the dosage ratio of natural bentonite to water is 30 - 40 kg:300 - 400 L;

[0008] Step S2: Preparation of modified sedimentation materials: Add natural sedimentation materials and a modification treatment agent into the mixed solution a of absolute ethanol and water, and perform wet ball milling for 6 - 8 h at a rotation speed of 800 rpm using a planetary ball mill. Then centrifuge, wash with water by centrifugation 2 - 4 times, dry, and then perform dry milling for 15 min at a rotation speed of 500 rpm in the planetary ball mill. After passing through an 800 - mesh sieve and a 1250 - mesh sieve in sequence, the modified sedimentation materials are obtained. Among them, the dosage ratio of the natural sedimentation materials, the modification treatment agent, and the mixed solution a is 200 - 300 g: 5 - 10 g: 4 L. In the mixed solution a, the dosage ratio of absolute ethanol and deionized water is 3 L: 1 L. During the above reaction process, through wet grinding and dry grinding, the modification treatment agent can fully contact the natural sedimentation materials;

[0009] Step S3: Preparation of preliminarily purified materials: Add the modified sedimentation materials into deionized water, stir magnetically for 6 - 8 h, let stand for 6 - 8 h, take the supernatant, and dry to obtain the preliminarily purified materials. Among them, the dosage ratio of the natural sedimentation materials and deionized water is 60 - 80 g: 800 - 1000 mL. During the above process, as the sedimentation time increases, the particles with larger particle sizes have a faster sedimentation speed, while bentonite hydrates and expands after being fully dispersed and suspends in the supernatant. At the same time, the modification treatment agent contains a lignin graft copolymer structure. Since this copolymer has both anionic groups and cationic groups, the rigid chain of lignin and the grafted flexible branched chains bridge and flocculate the large particles suspended in bentonite, shortening the natural sedimentation time;

[0010] Step S4: Preparation of high - purity montmorillonite: Grind the preliminarily purified materials to 0.074 mm using a sample preparation machine, then add the mixed solution b of deionized water and sodium hexametaphosphate, stir at a rotation speed of 2000 rpm for 0.8 - 1 h, perform high - speed centrifugal purification, take the supernatant after centrifugation, dry it at 105 °C, cool to room temperature, and grind through a 200 - mesh sieve to obtain high - purity montmorillonite. Among them, the dosage ratio of the preliminarily purified materials and the mixed solution b is 40 - 50 g: 600 - 800 mL. In the mixed solution b, the dosage ratio of deionized water and sodium hexametaphosphate is 600 - 800 mL: 0.2 - 0.3 g. During the above reaction process, using sodium hexametaphosphate as a dispersant, high - purity montmorillonite is obtained through stirring dispersion and centrifugal separation.

[0011] Further, in step S1, for hydraulic classification, a series of four groups of small - cone - angle hydrocyclone groups with diameters of Ф150 mm, Ф75 mm, Ф25 mm, and Ф10 mm are used for hydraulic classification.

[0012] Further, in step S4, the specific parameters during the high - speed centrifugal purification process are that the centrifugal rotation speed range is 2500 - 3500 rpm, the centrifugal time is 10 - 30 min, and the number of centrifugations is 2 - 10 times.

[0013] Further, a preparation method of a modification treatment agent includes the following steps:

[0014] Add tetraethyl orthosilicate and absolute ethanol into a reaction kettle, heat up to 30 °C, while stirring, dropwise add 2-3 wt% ammonia water solution to adjust the pH value to 8-10. After the dropping is completed, react for 2 h, then add pure graft-modified lignin, heat up to 50 °C and stir and react for 4-6 h, cool to room temperature to obtain the modification treatment agent. Among them, the dosage ratio of tetraethyl orthosilicate, absolute ethanol and pure graft-modified lignin is 15-18 mL: 5-8 mL: 0.05-0.15 g. Using tetraethyl orthosilicate as the precursor, hydrolysis and condensation reactions occur under alkaline conditions to obtain the modification treatment agent.

[0015] Further, a preparation method of pure graft-modified lignin includes the following steps:

[0016] Step A1: At room temperature, dissolve lignin in 0.5 M sodium hydroxide solution, while stirring, dropwise add a mixed solution a of allyl glycidyl ether and absolute ethanol, control to finish dropping within 30 min. After the dropping is completed, heat up to 60-70 °C and stir and react for 5-6 h. Under reduced pressure, distill off the excessive allyl glycidyl ether in the reaction solution, adjust the pH to neutral with 1 M hydrochloric acid, then wash with absolute ethanol and deionized water 3-5 times in sequence, and dry at 60 °C for 12-16 h to obtain modified lignin containing unsaturated double bonds. Among them, the dosage ratio of lignin, 0.5 M sodium hydroxide solution and mixed solution c is 18-24 g: 100-120 mL: 160-200 mL. In the mixed solution c, the dosage ratio of allyl glycidyl ether and absolute ethanol is 14-20 g: 160-200 mL. During the above reaction process, under alkaline conditions, the hydroxyl group on lignin and the epoxy group on allyl glycidyl ether undergo a ring-opening reaction to obtain modified lignin containing unsaturated double bonds;

[0017] Step A2: Ultrasonically disperse the modified lignin in anhydrous DMF. Under nitrogen protection, heat it to 50 - 70 °C, add the emulsion, and continuously stir and react for 8 - 12 h. Cool it to room temperature, perform suction filtration, wash it several times with water, and dry it to obtain the crude graft-modified lignin. Among them, the dosage ratio of the modified lignin, anhydrous DMF, and the emulsion is 10 - 20 g : 80 - 160 mL : 100 mL. The emulsion is prepared by mixing acrylamide, emulsifier, initiator, and solvent according to the dosage ratio of 10 - 14 g : 0.5 - 1.5 g : 1 - 2 g : 100 mL. The emulsifier is polyoxyethylene ether, the solvent is a mixture of deionized water and ethanol in a mass ratio of 9 : 1, and the initiator is composed of sodium persulfate and sodium sulfite in a mass ratio of 2 : 1. In the above reaction, through the action of the initiator, the modified lignin undergoes a graft polymerization reaction with acrylamide to achieve the grafting of polyacrylamide chains onto the lignin molecular chain, which not only further improves the viscosity-reducing performance of the modified lignin but also lays a foundation for subsequent reactions;

[0018] Step A3: Add the crude graft-modified lignin and anhydrous DMF into a Soxhlet extractor, reflux and react for 16 - 18 h, then add a mixed solution d of ethanol and glacial acetic acid, and continue to reflux and react for 12 - 16 h to obtain an extract. Dry the extract to a constant weight to obtain the pure graft-modified lignin. Among them, the dosage ratio of the crude graft-modified lignin, anhydrous DMF, and the mixed solution d is 8 - 10 g : 90 - 100 mL : 24 mL. In the mixed solution d, the dosage ratio of absolute ethanol and glacial acetic acid is 18 mL : 6 mL. In the above process, through two consecutive extraction treatments, the homopolymers in the crude graft-modified lignin can be removed, and the purity of the graft-modified lignin is improved.

[0019] Further, the natural bentonite is Liaoning Jianping natural bentonite.

[0020] Compared with the prior art, the present invention has the following beneficial effects: In order to improve the purity and yield of montmorillonite extracted from sodium-based bentonite, in the present invention, the materials for natural sedimentation and the modification treatment agent are subjected to wet grinding and dry grinding. The modification treatment agent contains a silica sol structure and a graft-modified lignin structure. The silica sol structure contains inorganic polymers with polyvalent negative charges, which have special reaction ability and adsorption effect on aluminum ions, breaking the "I"-shaped association-based overlapping structure in the montmorillonite structure, so that the solid impurities supported or wrapped by this association are fully released. The graft-modified lignin structure contains multiple hydroxyl groups, which are easy to establish strong hydrogen bonds on the surface of alumina, and the grafted oxyether groups thereon are also easy to produce ionic affinity with the surface of oxygen-containing colloids. The hydrogen bonds and affinity make the modified lignin structure easily adsorbed on the surface of montmorillonite molecules to form a polymer protective film, surrounding the montmorillonite molecules. At the same time, the modified lignin also contains a polyacrylamide chain with zwitterions. Therefore, through grinding, the colloids with the same charge are close to each other, with electrostatic repulsion and the steric hindrance effect of the polymer, and they repel each other, further eliminating the "I"-shaped structure, making the fine-grained cristobalite impurities lose support and separate from the montmorillonite particles, playing a dispersing role and improving the purity of montmorillonite. At the same time, the lignin structure in the modification treatment agent can not only play a role in viscosity reduction, but also the rigid chain and grafted flexible branched chains on its own structure can flocculate and sediment the large particles suspended in the bentonite through bridging action, improving the extraction yield. Detailed implementation manners

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0022] The raw materials used in this application are natural bentonite from Jianping, Liaoning. The physical properties of this natural bentonite are shown in Table 1:

[0023] Table 1

[0024]

[0025] Example 1

[0026] Preferably, this embodiment provides a preparation method for pure graft-modified lignin, including the following steps:

[0027] Step A1: At room temperature, dissolve 21 g of lignin in 110 mL of 0.5 M sodium hydroxide solution. While stirring, dropwise add a mixture c of 17 g of allyl glycidyl ether and 180 mL of absolute ethanol, and control to finish dropping within 30 min. After the dropping is completed, raise the temperature to 65 °C and stir and react for 5.5 h. Remove the excessive allyl glycidyl ether in the reaction solution by vacuum distillation. Adjust the pH to neutral with 1 M hydrochloric acid, then wash 4 times with absolute ethanol and deionized water in sequence, and dry at 60 °C for 14 h to obtain modified lignin containing unsaturated double bonds;

[0028] Step A2: Ultrasonically disperse 15 g of modified lignin in 120 mL of anhydrous DMF. Under nitrogen protection, heat to 60 °C, add 100 mL of emulsion, and continuously stir and react for 10 h. Cool to room temperature, filter by suction, wash several times with water, and dry to obtain the crude grafted starch product. Among them, the emulsion is composed of acrylamide, emulsifier, initiator and solvent in a dosage ratio of 12 g:1 g:1.5 g:100 mL. The emulsifier is polyoxyethylene ether, the solvent is a mixture of deionized water and ethanol in a mass ratio of 9:1, and the initiator is composed of sodium persulfate and sodium sulfite in a mass ratio of 2:1;

[0029] Step A3: Add 9 g of the crude grafted modified lignin product and 95 mL of anhydrous DMF to a Soxhlet extractor, reflux and react for 17 h, then add a mixture d of 18 mL of absolute ethanol and 6 mL of glacial acetic acid, and continue to reflux and react for 12 - 16 h to obtain an extract. Dry the extract to a constant weight to obtain the pure grafted modified lignin product.

[0030] Example 2

[0031] Preferably, the present example provides a preparation method of a modified treatment agent, including the following steps:

[0032] Add 16.5 mL of tetraethyl orthosilicate and 6.5 mL of absolute ethanol to a reaction kettle, raise the temperature to 30 °C, while stirring, dropwise add 2.5 wt% ammonia water solution to adjust the pH value to 9. After the dropping is completed, react for 2 h, then add the pure grafted modified lignin product prepared in Example 1, raise the temperature to 50 °C and stir and react for 5 h, and cool to room temperature to obtain the modified treatment agent.

[0033] Example 3

[0034] The present example provides a high-purity montmorillonite purification process, including the following steps:

[0035] Step S1: Preparation of materials for natural sedimentation: Add 30 kg of natural bentonite to 300 L of water to prepare a pulp with a mass fraction of 10%. Then, perform hydraulic classification through a series of hydrocyclone groups with small cone angles of φ150 mm, φ75 mm, φ25 mm, and φ10 mm to obtain classified sand and classified overflow pulp respectively. Collect the classified overflow pulp obtained at the φ10 mm hydrocyclone group with a small cone angle, and then dry it at 105 °C for 2 h to obtain the materials for natural sedimentation;

[0036] Step S2: Preparation of modified sedimentation materials: Add 200 g of the materials for natural sedimentation and 5 g of the modified treatment agent prepared in Example 2 to a mixed solution a of 3 L of absolute ethanol and 1 L of water. Wet ball-mill at a speed of 800 rpm for 6 h using a planetary ball mill, centrifuge, wash twice with water by centrifugation, dry, and then dry-mill at a speed of 500 rpm in the planetary ball mill for 15 min. Pass through an 800-mesh sieve and a 1250-mesh sieve in sequence to obtain the modified sedimentation materials;

[0037] Step S3: Preparation of preliminary purified materials: Add 60 g of the modified sedimentation materials to 800 mL of deionized water, stir magnetically for 6 h, let stand for 6 h, take the supernatant, and dry to obtain the preliminary purified materials;

[0038] Step S4: Preparation of high-purity montmorillonite: Grind 40 g of the preliminary purified materials to 0.074 mm using a sample preparation machine, then add a mixed solution b of 600 mL of deionized water and 0.2 g of sodium hexametaphosphate, stir at a speed of 2000 rpm for 0.8 h, then centrifuge at a speed of 2500 rpm for 10 min, repeat the above centrifugation operation twice, take the centrifuged supernatant, dry it at 105 °C, cool to room temperature, grind it through a 200-mesh sieve to obtain high-purity montmorillonite.

[0039] Example 4

[0040] This example provides a high-purity montmorillonite purification process, including the following steps:

[0041] Step S1: Preparation of materials for natural sedimentation: Add 35 kg of natural bentonite to 350 L of water to prepare a pulp with a mass fraction of 10%. Then, perform hydraulic classification through a series of hydrocyclone groups with small cone angles of φ150 mm, φ75 mm, φ25 mm, and φ10 mm to obtain classified sand and classified overflow pulp respectively. Collect the classified overflow pulp obtained at the φ10 mm hydrocyclone group with a small cone angle, and then dry it at 105 °C for 2.5 h to obtain the materials for natural sedimentation;

[0042] Step S2: Preparation of modified sedimentation material: Add 250 g of natural sedimentation material and 7.5 g of the modified treatment agent prepared in Example 2 into 3 L of a mixed solution a of absolute ethanol and 1 L of water. Wet ball mill with a planetary ball mill at a speed of 800 rpm for 7 h, centrifuge, wash 3 times by centrifugation with water, dry, and then dry mill in a planetary ball mill at a speed of 500 rpm for 15 min. After passing through an 800-mesh sieve and a 1250-mesh sieve in sequence, the modified sedimentation material is obtained;

[0043] Step S3: Preparation of preliminarily purified material: Add 70 g of the modified sedimentation material into 900 mL of deionized water, stir magnetically for 7 h, let stand for 7 h, take the supernatant, and dry to obtain the preliminarily purified material;

[0044] Step S4: Preparation of high-purity montmorillonite: Grind 45 g of the preliminarily purified material to 0.074 mm with a sample preparation machine, then add it to a mixed solution b of 700 mL of deionized water and 0.25 g of sodium hexametaphosphate. Stir at a speed of 2000 rpm for 0.9 h, then centrifuge at a speed of 3000 rpm for 20 min. Repeat the above centrifugation operation 6 times. Take the supernatant after centrifugation and dry it at 105 °C, cool to room temperature, grind and pass through a 200-mesh sieve to obtain high-purity montmorillonite.

[0045] Example 5

[0046] This example provides a high-purity montmorillonite purification process, including the following steps:

[0047] Step S1: Preparation of natural sedimentation material: Add 40 kg of natural bentonite into 400 L of water to prepare a pulp with a mass fraction of 10%. Then, perform hydraulic classification through a series of small-cone-angle hydrocyclone groups with diameters of φ150 mm, φ75 mm, φ25 mm, and φ10 mm to obtain classified sand and classified overflow pulp respectively. Collect the classified overflow pulp obtained at the φ10 mm small-cone-angle hydrocyclone group, and then dry it at 105 °C for 3 h to obtain the natural sedimentation material;

[0048] Step S2: Preparation of modified sedimentation material: Add 300 g of natural sedimentation material and 10 g of the modified treatment agent prepared in Example 2 into 3 L of a mixed solution a of absolute ethanol and 1 L of water. Wet ball mill with a planetary ball mill at a speed of 800 rpm for 8 h, centrifuge, wash 4 times by centrifugation with water, dry, and then dry mill in a planetary ball mill at a speed of 500 rpm for 15 min. After passing through an 800-mesh sieve and a 1250-mesh sieve in sequence, the modified sedimentation material is obtained;

[0049] Step S3: Preparation of preliminarily purified material: Add 80 g of the modified sedimentation material into 1000 mL of deionized water, stir magnetically for 8 h, let stand for 8 h, take the supernatant, and dry to obtain the preliminarily purified material;

[0050] Step S4. Preparation of high-purity montmorillonite: Grind 50 g of the initially purified material to 0.074 mm using a sample preparation machine, then add 800 mL of a mixed solution b of deionized water and 0.3 g of sodium hexametaphosphate, stir for 1 h at a rotation speed of 2000 rpm, then centrifuge for 30 min at a rotation speed of 3500 rpm, repeat the above centrifugation operation 10 times, take the supernatant after centrifugation, dry it at 105 °C, cool it to room temperature, and grind it through a 200-mesh sieve to obtain high-purity montmorillonite.

[0051] Comparative Example 1

[0052] Remove acrylamide in Example 1, keep the remaining raw materials and preparation process unchanged, then replace the obtained substance with the graft-modified lignin pure product in Example 2, keep the remaining raw materials and preparation process unchanged, and then replace the obtained substance with the modified treatment agent in Example 4, keep the remaining raw materials and preparation process unchanged.

[0053] Comparative Example 2

[0054] Replace the graft-modified lignin pure product in Example 2 with the modified lignin prepared in step A1 of Example 1, keep the remaining raw materials and preparation process unchanged, then replace the obtained substance with the modified treatment agent in Example 4, keep the remaining raw materials and preparation process unchanged.

[0055] Comparative Example 3

[0056] Remove tetraethyl orthosilicate in Example 2, keep the remaining raw materials and preparation process unchanged, then replace the obtained substance with the modified treatment agent in Example 4, keep the remaining raw materials and preparation process unchanged.

[0057] Comparative Example 4

[0058] Remove the modified treatment agent in Example 4, keep the remaining raw materials and preparation process unchanged.

[0059] Performance detection

[0060] Weigh the montmorillonite prepared in Examples 3 - 5 and Comparative Examples 1 - 4 respectively and conduct performance detection. The main detection index is the detection of the blue absorption amount. The detection is based on GB / T 20973-2007 Bentonite, and the detection method of the blue absorption amount adopts the titration method with a methylene blue standard solution.

[0061] Table 1

[0062] Project Montmorillonite purity (%) Blue adsorption amount (g / 100g) Yield (%) Example 4 99.2 43.52 63.4 Example 5 99.5 43.71 64.2 Example 6 99.3 43.34 62.6 Comparative Example 1 98.2 42.21 60.3 Comparative Example 2 98.6 42.64 61.5 Comparative Example 3 97.8 41.72 62.8 Comparative Example 4 97.4 41.32 59.8

[0063] As can be seen from the data in Table 1, compared with Comparative Examples 1 - 4, the montmorillonite prepared by the process used in Examples 3 - 5 has higher purity and yield.

[0064] Although embodiments of the present invention have been shown and described, it will be understood by those of ordinary skill in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A high-purity montmorillonite purification process, characterized in that: It includes the following steps: Step S1: Add natural bentonite into water to prepare a slurry with a mass fraction of 10%, then perform hydraulic classification to obtain classified sand and classified overflow slurry respectively. Collect the classified overflow slurry at the end, dry it at 105°C for 2 - 3 h to obtain the material for natural sedimentation; Step S2: Add the material for natural sedimentation and the modification agent into the mixed liquid a of anhydrous ethanol and water, wet-mill it in a planetary ball mill at a rotation speed of 800 rpm for 6 - 8 h, centrifuge it, wash it with water by centrifugation for 2 - 4 times, dry it, then dry-mill it in the planetary ball mill at a rotation speed of 500 rpm for 15 min, and pass through an 800-mesh sieve and a 1250-mesh sieve in sequence to obtain the modified sedimentation material; Step S3: Add the modified sedimentation material into deionized water, stir it magnetically for 6 - 8 h, let it stand for 6 - 8 h, take the supernatant, dry it to obtain the preliminary purified material; Step S4: Grind the preliminary purified material to 0.074 mm with a sample preparation machine, then add the mixed liquid b of deionized water and sodium hexametaphosphate, stir it at a rotation speed of 2000 rpm for 0.8 - 1 h, perform high-speed centrifugal purification, take the supernatant after centrifugation, dry it at 105°C, cool it to room temperature, grind it and pass through a 200-mesh sieve to obtain high-purity montmorillonite; The modification agent is prepared by the hydrolysis and condensation reaction of tetraethyl orthosilicate and graft-modified lignin pure product under alkaline conditions; The graft-modified lignin pure product is first obtained by the ring-opening reaction of lignin and allyl glycidyl ether to get modified lignin, then continuing to carry out a free radical polymerization reaction with acrylamide in the emulsion to obtain the crude graft-modified lignin, and finally obtaining it by extraction and purification in a Soxhlet extractor; 2. The high-purity montmorillonite purification process according to claim 1, wherein: The preparation method of the modification agent includes the following steps: Add tetraethyl orthosilicate and anhydrous ethanol into a reaction kettle, heat it to 30°C, adjust the pH value to 8 - 10 by dropwise adding a 2 - 3 wt% ammonia water solution while stirring. After the dropping is completed, react for 2 h, then add the graft-modified lignin pure product, heat it to 50°C and stir and react for 4 - 6 h, cool it to room temperature to obtain the modification agent; 3. A high-purity montmorillonite purification process according to claim 1, characterized in that: The preparation method of the graft-modified lignin pure product includes the following steps: Step A1: At room temperature, dissolve lignin in a 0.5 M sodium hydroxide solution, dropwise add the mixed liquid c of allyl glycidyl ether and anhydrous ethanol while stirring, control to finish dropping within 30 min, after the dropping is completed, heat it to 60 - 70°C, stir and react for 5 - 6 h, perform vacuum distillation to remove the excessive allyl glycidyl ether in the reaction solution, adjust the pH to neutral with 1 M hydrochloric acid, then wash it with anhydrous ethanol and deionized water for 3 - 5 times respectively, and dry it at 60°C for 12 - 16 h to obtain the modified lignin containing unsaturated double bonds; Step A2: Ultrasonically disperse the modified lignin in anhydrous DMF, under nitrogen protection, heat it to 50 - 70°C, add the emulsion, and continuously stir and react for 8 - 12 h, cool it to room temperature, filter it by suction, wash it with water several times, and dry it to obtain the crude graft-modified lignin; Step A3: Add the crude graft-modified lignin and anhydrous DMF into a Soxhlet extractor, reflux for 16 - 18 h, then add the mixed solution d of ethanol and glacial acetic acid, continue refluxing for 12 - 16 h to obtain an extract. Dry the extract to a constant weight to obtain pure graft-modified lignin.

4. A high-purity montmorillonite purification process according to claim 2, characterized in that: The dosage ratio of tetraethyl orthosilicate, absolute ethanol and pure graft-modified lignin is 15 - 18 mL: 5 - 8 mL: 0.05 - 0.15 g.

5. A high-purity montmorillonite purification process according to claim 3, characterized in that: In the said step A1, the dosage ratio of lignin, 0.5 M sodium hydroxide solution and mixed solution c is 18 - 24 g: 100 - 120 mL: 160 - 200 mL. In the mixed solution c, the dosage ratio of allyl glycidyl ether and absolute ethanol is 14 - 20 g: 160 - 200 mL.

6. A high-purity montmorillonite purification process according to claim 3, characterized in that: In the said step A2, the dosage ratio of modified lignin, anhydrous DMF and emulsion is 10 - 20 g: 80 - 160 mL: 100 mL. The emulsion is composed of acrylamide, emulsifier, initiator and solvent mixed according to the dosage ratio of 10 - 14 g: 0.5 - 1.5 g: 1 - 2 g: 100 mL. The emulsifier is polyoxyethylene ether, the solvent is composed of deionized water and absolute ethanol mixed according to the mass ratio of 9:1, and the initiator is composed of sodium persulfate and sodium sulfite mixed according to the mass ratio of 2:

1.

7. A high-purity montmorillonite purification process according to claim 3, characterized in that: In the said step A3, the dosage ratio of the crude graft-modified lignin, anhydrous DMF and mixed solution d is 8 - 10 g: 90 - 100 mL: 24 mL. In the mixed solution d, the dosage ratio of absolute ethanol and glacial acetic acid is 18 mL: 6 mL.

8. A high-purity montmorillonite purification process according to claim 1, characterized in that: In the said step S1, the dosage ratio of natural bentonite and water is 30 - 40 kg: 300 - 400 L. Hydrocyclone classification is carried out using a series of four groups of small-cone-angle hydrocyclone groups with diameters of Ф150 mm, Ф75 mm, Ф25 mm, and Ф10 mm for hydrocyclone classification.

9. A high-purity montmorillonite purification process according to claim 1, characterized in that: In the said step S2, the dosage ratio of the natural sedimentation material, modification treatment agent and mixed solution a is 200 - 300 g: 5 - 10 g: 4 L. In the mixed solution a, the dosage ratio of absolute ethanol and deionized water is 3 L: 1 L.

10. A high-purity montmorillonite purification process according to claim 1, characterized in that: In the said step S3, the dosage ratio of the natural sedimentation material and deionized water is 60 - 80 g: 800 - 1000 mL. In the said step S4, the dosage ratio of the initially purified material and mixed solution b is 40 - 50 g: 600 - 800 mL. In the mixed solution b, the dosage ratio of deionized water and sodium hexametaphosphate is 600 - 800 mL: 0.2 - 0.3 g.

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