Composite purification method and application of low-grade bentonite

Abstract

The application discloses a composite purification method of low-grade bentonite and application. The composite purification method comprises the following steps: mixing low-grade bentonite with water to prepare a slurry; uniformly mixing the slurry with a first dispersant solution and standing and settling to obtain a first purified liquid; uniformly mixing the first purified liquid with a second dispersant solution, centrifuging at a first centrifugal speed for a first time length, and obtaining a second purified liquid; uniformly mixing the second purified liquid with a third dispersant solution, centrifuging at a second centrifugal speed for a second time length, and obtaining a third purified liquid; and uniformly mixing the third purified liquid with a fourth dispersant solution or a dispersant, centrifuging at a third centrifugal speed for a third time length, and obtaining a fourth purified liquid. In the composite purification method, the dispersant is added in a gradient mode, and multiple centrifugal separation modes are combined, so that the utilization rate of raw materials is ensured, and the purification efficiency and the purity of the final product are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of separation and purification technology, specifically relating to a composite purification method and application of low-grade bentonite. Background Technology

[0002] Bentonite, also known as bentonite rock or bentonite clay, is a clay rock with montmorillonite as its main component. It is widely used in 24 fields, including metallurgy, casting, chemical industry, ceramics, oil drilling, construction, and national defense, and is known as "the clay with a thousand uses".

[0003] On the one hand, although my country has abundant bentonite resources, most of them are calcium-based bentonite with low grades. The montmorillonite content is generally only between 30% and 80%, or even lower, classifying them as medium- to low-grade bentonite deposits. Moreover, due to the presence of large amounts of non-clay minerals such as quartz and feldspar, their development and utilization levels are relatively low. Therefore, effectively utilizing China's abundant low-grade bentonite resources to develop high-value-added montmorillonite products and expand my country's application in the field of high-purity bentonite has broad development prospects.

[0004] On the other hand, although my country has large bentonite reserves, their varying locations and the influence of local climate and geographical conditions result in significant differences in bentonite product quality across different regions. Therefore, research on the development and application of bentonite is regionally specific. Xinjiang is rich in bentonite resources, with total bentonite deposits containing montmorillonite as the main component estimated at approximately 5.945 × 10⁻⁶ tons. 9 The Korla alkali zone is one of the super-large bentonite deposits, but its in-depth research and development are currently limited, so Korla bentonite has not been fully utilized.

[0005] Furthermore, research and practical applications have revealed that Korzite bentonite, which has been used as backfill material and engineering barrier material for radioactive waste disposal, has a low montmorillonite content (mostly 30-50%), classifying it as low-grade bentonite. It is characterized by poor physicochemical properties and fine-grained impurity minerals, particularly the fine particle size of which makes purification difficult. Therefore, to improve the utilization rate and application efficiency of Korzite bentonite mineral resources, high-efficiency and high-benefit purification treatment is necessary.

[0006] Based on the varying montmorillonite content, bentonite purification methods can be broadly categorized into dry and wet methods. The dry method utilizes the fact that impurity minerals in natural bentonite generally have larger particle sizes, hardness, and density. Impurities are separated through a stepwise sedimentation process, resulting in higher-purity bentonite. This method is simple to operate and has a large processing capacity, but it causes significant air pollution and is not suitable for ultrafine particles with similar particle sizes to montmorillonite. Therefore, it is rarely used in industrial production. The wet method uses water as the primary medium. Various external forces (gravity, centrifugal force, etc.) are applied, utilizing the density difference between montmorillonite and impurities (montmorillonite density 2–2.2, quartz and other impurities density around 2.6), and the principle that montmorillonite can disperse sufficiently in an aqueous medium, to separate the impurities from the montmorillonite, achieving purification. For medium- to low-grade bentonite with a montmorillonite content of 30-80% in the raw ore, or for bentonite with relatively small feldspar and quartz particle sizes, wet purification is often used to obtain bentonite with higher purity. Wet purification methods are further divided into natural sedimentation, flocculation, high-speed centrifugation, and secondary classification methods, depending on the specific purification process.

[0007] Bentonite has a complex and diverse composition, with each component having different formation causes and properties. Each purification method has its own advantages and disadvantages. For example, the natural sedimentation method relies on the principle that montmorillonite, as a clay mineral, generally has a smaller particle size than feldspar, quartz, and other detrital minerals, resulting in a slower sedimentation rate. This method requires simple equipment and is low-cost, but it has a long sedimentation time, requires a large area, has low production efficiency, and some impurities cannot be completely removed. High-speed centrifugation and secondary classification methods separate the bentonite suspension through high-speed centrifugal sedimentation, separating finer detrital minerals (feldspar, carbonates, etc.) to obtain a bentonite slurry with a particle size of less than 5 μm. Centrifuges have broad application prospects for the preparation of high-purity bentonite. However, current research generally involves high-grade ore, typically between 60% and 80%, with limited research on bentonite with a purity of 30% to 60%. Therefore, the corresponding purification methods and processes cannot be widely applied to my country's abundant low-grade bentonite ore deposits. Wu Zhansheng et al. used bentonite ore with a grade of 68.5% for centrifugal purification. The liquid-to-solid ratio of the pulp was 14:1, and the pulping time was 80 minutes. Centrifugation at 300 r / min for 10 minutes yielded a product with a montmorillonite content of 95%. Chen Yuanyuan et al. used bentonite ore with a grade of 75% and a pulp concentration of 15%, centrifuging at 2000 r / min for 2 minutes to obtain a high-purity bentonite product with a montmorillonite content of 93.7%. Furthermore, Ma Liang et al. purified bentonite ore with a montmorillonite content of 79% by centrifugation at a solid-to-liquid ratio of 1:12, a centrifuge speed of 1000 r / min, and a dispersant dosage of 0.3%, obtaining a high-purity montmorillonite product with a purity of 94%. The above purification studies generally used bentonite ore with a high montmorillonite content; research on preparing high-purity montmorillonite from low-grade bentonite ore is relatively limited. Therefore, it is an urgent problem to solve the issue of providing a method with high purification efficiency and high engineering benefits for preparing high-purity montmorillonite from low-grade bentonite ore. Summary of the Invention

[0008] The main objective of this invention is to provide a composite purification method and application for low-grade bentonite, so as to overcome the shortcomings of the prior art.

[0009] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0010] This invention provides a method for the composite purification of low-grade bentonite, comprising:

[0011] S1. Mix low-grade bentonite and water evenly in a volume ratio of 1:5 to 1:6 to prepare a slurry;

[0012] S2. The slurry is mixed uniformly with the first dispersant solution until the content of dispersant in the obtained mixture is 0.45wt% to 0.50wt%, and allowed to stand for sedimentation for 20 to 24 hours. Then the sediment is removed to obtain the first purified liquid.

[0013] S3. The first purified liquid and the second dispersant solution are mixed evenly until the content of dispersant in the obtained mixture is 0.55wt% to 0.60wt%. Then, the mixture is centrifuged at the first centrifugation speed for a first time, and then the precipitate is removed to obtain the second purified liquid.

[0014] S4. The second purified liquid and the third dispersant solution are mixed evenly until the content of dispersant in the obtained mixture is 0.65wt% to 0.70wt%. Then, the mixture is centrifuged at the second centrifugation speed for a second time. After that, the precipitate is removed to obtain the third purified liquid.

[0015] S5. The third purified liquid is mixed evenly with the fourth dispersant solution or dispersant until the content of dispersant in the obtained mixture is 0.75wt% to 0.80wt%. Then, it is centrifuged at the third centrifugation speed for a third time, and then the precipitate is removed to obtain the fourth purified liquid.

[0016] The concentrations of the first, second, third, and fourth dispersant solutions increase sequentially, as do the first, second, and third centrifugation speeds, and the first, second, and third centrifugation durations.

[0017] The embodiments of the present invention also provide the application of bentonite prepared by the aforementioned composite purification method in the field of radioactive waste disposal engineering.

[0018] This invention also provides a buffer / backfill barrier material for use in radioactive waste disposal projects, comprising bentonite prepared by the aforementioned composite purification method.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: The composite purification method of the present invention adopts a gradient addition of dispersant (more in the early stage and less in the later stage), which ensures the efficient separation of coarse particulate impurities in the early stage and the efficient separation of fine particulate impurities in the later stage, and reduces the total amount of dispersant used. Combined with multiple centrifugation separation, the total process time is shortened. Although the total centrifugation time increases, it is not necessary to maintain a high centrifugation speed continuously, which reduces the requirements for equipment. In summary, the method provided by the present invention significantly improves purification efficiency and final product purity while ensuring the utilization rate of raw materials. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is the XRD pattern of high-purity bentonite in Example 3 of the present invention. Detailed Implementation

[0022] In view of the deficiencies of the prior art, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention. The technical solution of this invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0023] Specifically, as one aspect of the technical solution of this invention, a composite purification method for low-grade bentonite includes:

[0024] S1. Mix low-grade bentonite and water evenly in a volume ratio of 1:5 to 1:6 to prepare a slurry;

[0025] S2. The slurry is mixed uniformly with the first dispersant solution until the content of dispersant in the obtained mixture is 0.45wt% to 0.50wt%, and allowed to stand for sedimentation for 20 to 24 hours. Then the sediment is removed to obtain the first purified liquid.

[0026] S3. The first purified liquid and the second dispersant solution are mixed evenly until the content of dispersant in the obtained mixture is 0.55wt% to 0.60wt%. Then, the mixture is centrifuged at the first centrifugation speed for a first time, and then the precipitate is removed to obtain the second purified liquid.

[0027] S4. The second purified liquid and the third dispersant solution are mixed evenly until the content of dispersant in the obtained mixture is 0.65wt% to 0.70wt%. Then, the mixture is centrifuged at the second centrifugation speed for a second time. After that, the precipitate is removed to obtain the third purified liquid.

[0028] S5. The third purified liquid is mixed evenly with the fourth dispersant solution or dispersant until the content of dispersant in the obtained mixture is 0.75wt% to 0.80wt%. Then, it is centrifuged at the third centrifugation speed for a third time, and then the precipitate is removed to obtain the fourth purified liquid.

[0029] The concentrations of the first, second, third, and fourth dispersant solutions increase sequentially, as do the first, second, and third centrifugation speeds, and the first, second, and third centrifugation durations.

[0030] Specifically, the low-grade bentonite is Kolbenzyl bentonite.

[0031] Specifically, the reason for using a dispersant solution in this invention is that adding water at the same time as adding the dispersant can reduce the total amount of water added and reduce the difficulty of subsequent separation.

[0032] In some preferred embodiments, the low-grade bentonite contains ≤50% montmorillonite.

[0033] In some preferred embodiments, the concentrations of the first dispersant solution, the second dispersant solution, and the third dispersant solution are all 0.1 kg / L to 0.15 kg / L.

[0034] In some preferred embodiments, the dispersant includes any one or more combinations of sodium phosphate, water glass, and sodium hexametaphosphate, but is not limited thereto.

[0035] Furthermore, the dispersant is sodium hexametaphosphate.

[0036] In some preferred embodiments, the first centrifugation speed is 1000-1500 r / min, the second centrifugation speed is 1550-2000 r / min, and the third centrifugation speed is 2050-2500 r / min.

[0037] In some preferred embodiments, the first duration is 1 to 2 minutes, the second duration is 2 to 3 minutes, and the third duration is 3 to 5 minutes.

[0038] Specifically, the particle size separated in this invention gradually decreases, thus requiring higher centrifugation speeds and times. However, the total time required for high-speed centrifugation is shortened, preventing excessive montmorillonite from settling with impurity particles, thereby improving raw material utilization.

[0039] In some preferred embodiments, the composite purification method further includes post-processing, which includes sequentially performing a fourth centrifugation, drying, and grinding on the fourth purified liquid.

[0040] Furthermore, the centrifugation speed of the fourth centrifugation process is 4800–5200 r / min, and the centrifugation time is 15–20 min;

[0041] Furthermore, the drying temperature is 102–108°C.

[0042] Furthermore, the montmorillonite content in the bentonite obtained by grinding is ≥80%.

[0043] Another aspect of the present invention provides the application of bentonite prepared by the aforementioned composite purification method in the field of radioactive waste disposal engineering.

[0044] Another aspect of the present invention provides a buffer / backfill barrier material for use in radioactive waste disposal engineering, comprising bentonite prepared by the aforementioned composite purification method.

[0045] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. This embodiment is implemented on the premise of the technical solution of the invention, and provides detailed implementation methods and specific operation processes. However, the protection scope of the present invention is not limited to the following embodiments.

[0046] Unless otherwise specified, the experimental materials used in the examples below can be purchased from conventional biochemical reagent companies.

[0047] Example 1

[0048] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:5.5 to make a slurry.

[0049] (2) The slurry is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the sodium hexametaphosphate content in the obtained mixture is 0.45 wt%, and then allowed to stand for 22 h to settle. After that, the precipitate is removed to obtain the first purified liquid.

[0050] (3) The first purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the content of dispersant in the obtained mixture is 0.55 wt%. Then, it is centrifuged at 1200 r / min for 1.5 min, and the precipitate is removed to obtain the second purified liquid.

[0051] (4) The second purified solution is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the content of dispersant in the obtained mixture is 0.65 wt%. Then, it is centrifuged at 1700 r / min for 2.5 min, and the precipitate is removed to obtain the third purified solution.

[0052] (5) The third purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the content of dispersant in the obtained mixture is 0.75 wt%. Then, it is centrifuged at 2100 r / min for 4 min, and the precipitate is removed to obtain the fourth purified liquid.

[0053] (6) The fourth purified feed liquid is centrifuged at 5000 r / min for 18 min. The separated lower layer of refined soil is dried in an oven at a temperature of 105±3℃. After grinding, it is passed through a 200-mesh sieve and then ground to obtain high-purity bentonite, in which the content of montmorillonite in the high-purity bentonite is 92.4 wt%.

[0054] Comparative Example 1 (different from Example 1 in that it does not use stepped centrifugation)

[0055] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:5.5 to make a slurry.

[0056] (2) The slurry is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the sodium hexametaphosphate content in the obtained mixture is 0.45 wt%, and then allowed to stand for 22 h to settle. After that, the precipitate is removed to obtain the first purified liquid.

[0057] (3) The first purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the content of dispersant in the obtained mixture is 0.8 wt%. The mixture is centrifuged at 2100 r / min for 8 min, and then the precipitate is removed to obtain the second purified liquid.

[0058] (4) The second purified material was centrifuged at 5000 r / min for 18 min. The separated lower layer of refined clay was dried in an oven at 105±3℃. After grinding, it was passed through a 200-mesh sieve and then ground to obtain high-purity bentonite, in which the content of montmorillonite in the high-purity bentonite was 49.7 wt%.

[0059] Comparative Example 2 (different from Example 1 in that: in step (1), the dispersant was directly added to 0.8 wt%)

[0060] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:5.5 to make a slurry.

[0061] (2) The slurry is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the sodium hexametaphosphate content in the obtained mixture is 0.8 wt%, and then allowed to stand for 22 h to settle. After that, the sediment is removed to obtain the first purified liquid.

[0062] (3) Centrifuge the first purified liquid at 1200 r / min for 1.5 min, then remove the precipitate to obtain the second purified liquid;

[0063] (4) Centrifuge the second purified solution at 1700 r / min for 2.5 min, then remove the precipitate to obtain the third purified solution;

[0064] (5) Centrifuge the third purified liquid at 2100 r / min for 4 min, then remove the precipitate to obtain the fourth purified liquid;

[0065] (6) The fourth purified feed liquid is centrifuged at 5000 r / min for 18 min. The separated lower layer of refined soil is dried in an oven at a temperature of 105±3℃. After grinding, it is passed through a 200-mesh sieve and then ground to obtain high-purity bentonite, in which the content of montmorillonite in the high-purity bentonite is 61 wt%.

[0066] Comparative Example 3 (different from Example 1 in that: in step (2), the dispersant was directly added to 0.8 wt%)

[0067] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:5.5 to make a slurry.

[0068] (2) The slurry is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12 kg / L until the sodium hexametaphosphate content in the obtained mixture is 0.45 wt%, and then allowed to stand for 22 h to settle. After that, the precipitate is removed to obtain the first purified liquid.

[0069] (3) The first purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.12Kg / L until the content of dispersant in the obtained mixture is 0.8wt%. Then, it is centrifuged at 1200r / min for 1.5min, and the precipitate is removed to obtain the second purified liquid.

[0070] (4) Centrifuge the second purified solution at 1700 r / min for 2.5 min, then remove the precipitate to obtain the third purified solution;

[0071] (5) Centrifuge the third purified liquid at 2100 r / min for 4 min, then remove the precipitate to obtain the fourth purified liquid;

[0072] (6) The fourth purified feed liquid is centrifuged at 5000 r / min for 18 min. The separated lower layer of refined soil is dried in an oven at a temperature of 105±3℃. After grinding, it is passed through a 200-mesh sieve and then ground to obtain high-purity bentonite, in which the content of montmorillonite in the high-purity bentonite is 62wt%.

[0073] Comparative Example 4 (different from Example 1 in that no dispersant was used)

[0074] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:5.5 to make a slurry.

[0075] (2) The slurry was allowed to stand and settle for 22 hours, and then the sediment was removed to obtain the first purified liquid.

[0076] (3) Centrifuge the first purified liquid at 1200 r / min for 1.5 min, then remove the precipitate to obtain the second purified liquid;

[0077] (4) Centrifuge the second purified solution at 1700 r / min for 2.5 min, then remove the precipitate to obtain the third purified solution;

[0078] (5) Centrifuge the third purified liquid at 2100 r / min for 4 min, then remove the precipitate to obtain the fourth purified liquid;

[0079] (6) The fourth purified feed solution is centrifuged at 5000 r / min for 18 min. The separated lower layer of refined soil is dried in an oven at a temperature of 105±3℃. After grinding, it is passed through a 200-mesh sieve and then ground to obtain high-purity bentonite, in which the content of montmorillonite in the high-purity bentonite is 51.3 wt%.

[0080] Example 2

[0081] The method is the same as in Example 1, except that sodium hexametaphosphate is replaced with sodium phosphate, and the montmorillonite content in the obtained high-purity bentonite is 81.6 wt%.

[0082] Example 3

[0083] The method is the same as in Example 1, except that sodium hexametaphosphate is replaced with water glass. The high-purity bentonite obtained contains 84.4 wt% montmorillonite. The XRD pattern of the high-purity bentonite is shown below. Figure 1 As shown.

[0084] Example 4

[0085] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:55 to make a slurry.

[0086] (2) The slurry is mixed uniformly with a sodium hexametaphosphate solution with a concentration of 0.1 kg / L until the sodium hexametaphosphate content in the obtained mixture is 0.48 wt%, and then allowed to stand for 20 h to settle. After that, the precipitate is removed to obtain the first purified liquid.

[0087] (3) The first purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.1 kg / L until the content of dispersant in the obtained mixture is 0.58 wt%. Then, it is centrifuged at 1000 r / min for 2 min, and the precipitate is removed to obtain the second purified liquid.

[0088] (4) The second purified solution is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.1 kg / L until the content of dispersant in the obtained mixture is 0.68 wt%. Then, it is centrifuged at 1550 r / min for 3 min, and the precipitate is removed to obtain the third purified solution.

[0089] (5) The third purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.1 kg / L until the content of dispersant in the obtained mixture is 0.78 wt%. Then, it is centrifuged at 2050 r / min for 5 min, and the precipitate is removed to obtain the fourth purified liquid.

[0090] (6) The fourth purified feed liquid is centrifuged at 4800 r / min for 20 min. The separated lower layer of refined soil is dried in an oven at a temperature of 105±3℃. After grinding, it is passed through a 200-mesh sieve. After grinding, high-purity bentonite is obtained, in which the content of montmorillonite in the high-purity bentonite is 88wt%.

[0091] Example 5

[0092] (1) Mix Kolbenz (low-grade bentonite, in which the content of montmorillonite is ≤50wt%) with water at a volume ratio of 1:6 to make a slurry.

[0093] (2) The slurry is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.15 kg / L until the sodium hexametaphosphate content in the obtained mixture is 0.5 wt%, and allowed to stand for 24 h to settle. Then the sediment is removed to obtain the first purified liquid.

[0094] (3) The first purified liquid is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.15 kg / L until the content of dispersant in the obtained mixture is 0.60 wt%. Then, it is centrifuged at 1500 r / min for 1 min, and the precipitate is removed to obtain the second purified liquid.

[0095] (4) The second purified solution is mixed evenly with a sodium hexametaphosphate solution with a concentration of 0.15 kg / L until the content of dispersant in the obtained mixture is 0.70 wt%. Then, it is centrifuged at 2000 r / min for 2 min, and the precipitate is removed to obtain the third purified solution.

[0096] (5) Mix the third purified liquid with sodium hexametaphosphate until the content of dispersant in the obtained mixture is 0.80 wt%, then centrifuge at 2500 r / min for 3 min, and then remove the precipitate to obtain the fourth purified liquid;

[0097] (6) The fourth purified feed liquid is centrifuged at 5200 r / min for 15 min. The separated lower layer of refined soil is dried in an oven at a temperature of 105±3℃. After grinding, it is passed through a 200-mesh sieve and then ground to obtain high-purity bentonite, in which the content of montmorillonite in the high-purity bentonite is 98.7 wt%.

[0098] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0099] It should be understood that the technical solutions of the present invention are not limited to the specific embodiments described above. Any technical modifications made to the technical solutions of the present invention without departing from the spirit and scope of the claims are within the scope of protection of the present invention.

Claims

1. A method for the composite purification of low-grade bentonite, characterized in that, include: S1. Low-grade bentonite and water are uniformly mixed at a volume ratio of 1:5 to 1:6 to prepare a slurry; wherein the content of montmorillonite in the low-grade bentonite is ≤50%; the low-grade bentonite is Kolbenzyl bentonite. S2. The slurry is mixed uniformly with the first dispersant solution until the content of dispersant in the obtained mixture is 0.45wt%~0.50wt%, and allowed to stand for sedimentation for 20~24h. Then the sediment is removed to obtain the first purified liquid. S3. Mix the first purified liquid with the second dispersant solution until the content of dispersant in the obtained mixture is 0.55wt%~0.60wt%. Then centrifuge at a first centrifugal speed of 1000~1500r / min for a first time of 1~2min. After that, remove the precipitate to obtain the second purified liquid. S4. Mix the second purified liquid with the third dispersant solution until the content of dispersant in the obtained mixture is 0.65wt%~0.70wt%. Then centrifuge at a second centrifugal speed of 1550~2000r / min for a second time of 2~3min. After that, remove the precipitate to obtain the third purified liquid. S5. The third purified liquid is mixed evenly with the fourth dispersant solution or dispersant until the content of dispersant in the obtained mixture is 0.75wt%~0.80wt%. Then, it is centrifuged at a third centrifugation speed of 2050~2500r / min for a third time of 3~5min. After that, the precipitate is removed to obtain the fourth purified liquid. The concentrations of the first, second, third, and fourth dispersant solutions increase sequentially, as do the first, second, and third centrifugation speeds, and the first, second, and third centrifugation durations.

2. The composite purification method according to claim 1, characterized in that: The concentrations of the first dispersant solution, the second dispersant solution, and the third dispersant solution are all 0.1 kg / L to 0.15 kg / L.

3. The composite purification method according to claim 1, characterized in that: The dispersant includes any one or more combinations of sodium phosphate, water glass, and sodium hexametaphosphate.

4. The composite purification method according to claim 3, characterized in that: The dispersant is sodium hexametaphosphate.

5. The composite purification method according to claim 1, characterized in that, It also includes post-processing, which includes sequentially centrifuging, drying, and grinding the fourth purified liquid.

6. The composite purification method according to claim 5, characterized in that, The centrifugation speed for the fourth centrifugation process is 4800~5200 r / min, and the centrifugation time is 15~20 min.

7. The composite purification method according to claim 5, characterized in that, The drying process is carried out at a temperature of 102~108℃.

8. The composite purification method according to claim 5, characterized in that: The bentonite obtained by grinding contains ≥80% montmorillonite.

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