Method for producing lithium-based bentonite by dry method

Abstract

The invention discloses a method for producing lithium-based bentonite by a dry method, which comprises the following steps: crushing sodium-based bentonite, and mixing the crushed sodium-based bentonite with a lithium salt to obtain a mixture; placing the mixture in a twin-screw extruder for sectional mechanical activation to obtain an activated material; carrying out gradient temperature field roasting treatment on the activated material; and crushing the roasted product to obtain the lithium-based bentonite. According to the method, the lithium-based bentonite is prepared through dry-method efficient modification by means of segmented activation, composite additive synergy and gradient temperature field roasting, washing and drying steps are not needed in the preparation process, energy consumption is low, the process is short, and efficient preparation of the bentonite is achieved.

Description

Technical Field

[0001] This invention relates to the field of bentonite preparation technology, and specifically to a dry method for producing lithium-based bentonite. Background Technology

[0002] Lithium-based bentonite, as a high-performance clay mineral material, is widely used in oil drilling, environmental adsorption, and high-end coatings. Currently, the mainstream production method for lithium-based bentonite in the industry is the wet process: mixing sodium-based bentonite with a lithium salt solution, followed by stirring, washing, and drying to obtain the lithium-based product. However, this process has significant drawbacks: 1. It consumes a huge amount of water and generates a large amount of lithium-containing wastewater, resulting in high treatment costs; 2. The drying process requires a large amount of heat energy, leading to persistently high production costs; 3. The process is lengthy, requires significant equipment investment, and is difficult to adapt to the demands of rapid, large-scale production.

[0003] In addition, some dry process explorations have attempted to directly mix and roast lithium salts with bentonite, but due to the insufficient activation of the interlayer structure of montmorillonite and the low lithium-ion exchange efficiency, the product performance is unstable and difficult to industrialize.

[0004] Therefore, it is of great significance to research and develop a dry process to reduce the heat and water consumption in the wet process, achieve green manufacturing, improve the exchange of lithium ions with sodium ions between montmorillonite layers in an aqueous solution-free environment, and avoid the destruction of montmorillonite structure during calcination to ensure product performance. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by providing a dry method for producing lithium-based bentonite. Through segmented activation, synergistic effects of composite additives, and gradient temperature field calcination, a dry method for efficiently modifying and preparing lithium-based bentonite is achieved. The process requires no water washing, has low energy consumption, and a short process flow, thus realizing the efficient preparation of bentonite.

[0006] To address the aforementioned technical problems, this invention provides a dry method for producing lithium-based bentonite, comprising the following steps:

[0007] S1. Sodium-based bentonite is pulverized and then mixed with lithium salt to obtain a mixture;

[0008] S2. The mixture is placed in a twin-screw extruder for mechanical activation to obtain an activated material;

[0009] The temperature of the first stage is 80-120℃; the temperature of the second stage is 150-180℃, and a composite additive, citric acid and silane coupling agent, is added in the second stage.

[0010] S3. The activated material is subjected to gradient temperature field calcination treatment;

[0011] The temperature in the first zone is 250-300℃, the temperature in the second zone is 350-450℃, and the temperature in the third zone is 150-200℃.

[0012] S4. The product from S3 calcination is pulverized to obtain the lithium-based bentonite.

[0013] This invention utilizes a twin-screw extruder for segmented activation: the first segment breaks the interlayer hydrogen bonds of montmorillonite through shear force; the second segment introduces a composite additive to further open the interlayer channels. Citric acid in the composite additive lowers the lithium salt decomposition temperature through chelation, while a silane coupling agent inserts into the montmorillonite interlayer to form a molecular wedge structure. Specifically, the inorganic-loving groups, such as siloxy groups, and the organic-loving groups contained in the silane coupling agent molecule, under the mechanical activation of the twin-screw extruder, allow the siloxy groups to form hydrogen bonds or covalent bonds with the silicon-oxygen tetrahedra between the montmorillonite layers, while the organic groups at the other end extend outwards and insert into the interlayer gaps of montmorillonite, thus opening up the originally tightly stacked montmorillonite sheets. The two work together to expand the interlayer spacing, providing channels for lithium ion diffusion and significantly improving exchange efficiency. The combination of citric acid and the silane coupling agent both lowers the lithium salt activation temperature and protects the montmorillonite structure.

[0014] This invention employs a gradient temperature field calcination process. The first region is preheated to promote the decomposition of lithium salt into active lithium ions. The second region is the core temperature zone, where lithium ions exchange with sodium ions between the montmorillonite layers. The third region stabilizes the crystal structure. The gradient temperature field design avoids the montmorillonite lattice distortion caused by traditional single-temperature zone calcination. At the same time, the middle temperature zone is precisely controlled below the montmorillonite dehydroxylation temperature to preserve the activity of the layered structure.

[0015] The dry process of this invention eliminates the need for washing and multiple drying steps, significantly reducing total energy consumption compared to traditional wet processes. Water consumption is zero, production costs are reduced by more than 30%, and the process is shorter.

[0016] Furthermore, in S1, the mass ratio of sodium-based bentonite to lithium salt is (10-15):1.

[0017] Furthermore, in S1, the lithium salt is lithium carbonate and / or lithium chloride.

[0018] Furthermore, in S2, the mass of the composite additive is 1-3% of the mass of sodium-based bentonite.

[0019] Furthermore, in S2, the mass ratio of citric acid to silane coupling agent is (1-2):1.

[0020] Furthermore, in S3, the residence time of the activated material in the first region is 30-40 min, the residence time in the second region is 1-1.5 h, and the residence time in the third region is 20-30 min.

[0021] Furthermore, in S4, the pulverization is completed by a collision air jet mill, which performs primary screening of the pulverized material through a built-in turbine classifier.

[0022] Furthermore, S4 also includes: secondary screening of the material after primary screening using a vibrating screen.

[0023] Furthermore, in S4, the pulverization is carried out to D90≤5μm.

[0024] Furthermore, in S1, the pulverization process is carried out to a particle size of 200-300 mesh.

[0025] The beneficial effects of this invention are:

[0026] This invention achieves efficient dry modification and preparation of lithium-based bentonite through segmented activation, synergistic effects of composite additives, and gradient temperature field calcination. The preparation process requires no water washing or drying steps, has low energy consumption and a short process, and achieves efficient preparation of bentonite. Attached Figure Description

[0027] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a flowchart of the dry method for producing lithium-based bentonite according to the present invention. Detailed Implementation

[0029] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Reference Figure 1 As shown, this embodiment provides a dry method for producing lithium-based bentonite, including the following steps:

[0031] S1. Sodium-based bentonite is pulverized and then mixed with lithium salt to obtain a mixture;

[0032] S2. The mixture is placed in a twin-screw extruder for mechanical activation to obtain an activated material;

[0033] The temperature of the first stage is 80-120℃; the temperature of the second stage is 150-180℃, and a composite additive, citric acid and silane coupling agent, is added in the second stage.

[0034] S3. The activated material is subjected to gradient temperature field calcination treatment;

[0035] The temperature in the first zone is 250-300℃, the temperature in the second zone is 350-450℃, and the temperature in the third zone is 150-200℃.

[0036] S4. The product from S3 calcination is pulverized to obtain the lithium-based bentonite.

[0037] In this embodiment, the twin-screw extruder undergoes a segmented activation process: the first segment breaks the interlayer hydrogen bonds of montmorillonite through shear force; the second segment introduces a composite additive to further open the interlayer channels. Citric acid in the composite additive lowers the lithium salt decomposition temperature through chelation, while a silane coupling agent inserts into the interlayer of montmorillonite to form a molecular wedge structure. That is, the inorganic-loving groups, such as siloxy groups, and the organic-loving groups contained in the silane coupling agent molecule structure, under the mechanical activation of the twin-screw extruder, allow the siloxy groups to form hydrogen bonds or covalent bonds with the silicon-oxygen tetrahedra between the montmorillonite layers, while the organic groups at the other end extend outward and insert into the interlayer gaps of montmorillonite, opening up the originally tightly stacked montmorillonite sheets. The two work together to expand the interlayer spacing, providing channels for lithium ion diffusion and significantly improving the exchange efficiency. The combination of citric acid and silane coupling agent not only lowers the lithium salt activation temperature but also protects the montmorillonite structure. Through gradient temperature field calcination, the first zone is preheated to promote the decomposition of lithium salt into active lithium ions. The second zone is the core temperature zone, where lithium ions exchange with sodium ions between the montmorillonite layers. The third zone stabilizes the crystal structure. The gradient temperature field design avoids the montmorillonite lattice distortion caused by traditional single-temperature zone calcination. At the same time, the middle temperature zone is precisely controlled below the montmorillonite dehydroxylation temperature to preserve the activity of the layered structure. The dry process eliminates the need for washing and multiple drying steps, significantly reducing total energy consumption compared to traditional wet processes. Water consumption is zero, production costs are reduced by more than 30%, and the process is shorter.

[0038] In a preferred embodiment, in S1, the mass ratio of sodium-based bentonite to lithium salt is (10-15):1, the lithium salt is lithium carbonate and / or lithium chloride, and the pulverization process is carried out to a particle size of 200-300 mesh.

[0039] In a preferred embodiment, in S2, the mass of the composite additive is 1-3% of the mass of sodium-based bentonite, and the mass ratio of citric acid to silane coupling agent is (1-2):1.

[0040] In a preferred embodiment, in S3, the residence time of the activated material in the first region is 30-40 min, the residence time in the second region is 1-1.5 h, and the residence time in the third region is 20-30 min.

[0041] In a preferred embodiment, in S4, the pulverization is completed by a collision-type air jet mill, which performs primary screening of the pulverized material by a built-in turbine classifier; it also includes: performing secondary screening of the material after primary screening by a vibrating screen; the pulverization is completed to D90≤5μm.

[0042] Example 1

[0043] This embodiment relates to a dry method for producing lithium-based bentonite, comprising the following steps:

[0044] (1) Raw material pretreatment: Sodium-based bentonite is crushed to 250 mesh and mixed with lithium carbonate at a mass ratio of sodium-based bentonite: lithium carbonate = 12:1 to obtain a mixture;

[0045] (2) Segmented activation treatment: The mixture obtained in step (1) is placed in a twin-screw extruder for segmented activation treatment. The temperature of the first segment is controlled at 100℃ and the screw speed is 180r / min. The temperature of the second segment is 160℃, and a composite additive is introduced. The amount added is 2% of the mass of sodium bentonite, and the mass ratio of citric acid to silane coupling agent is 1.5:1.

[0046] (3) Gradient temperature field roasting: The activated material obtained in step (2) is sent into a multi-layer roasting furnace for gradient temperature field roasting. The upper layer is preheated at 300℃ and held for 35 minutes, the middle layer is held at 400℃ for 1.2 hours, and the lower layer is cooled at 180℃ for 25 minutes.

[0047] (4) Crushing and grading: The product from the gradient temperature field roasting in step (3) is crushed to D90 = 4μm by a collision airflow pulverizer. The crushed material is then screened by a built-in turbine classifier and then screened by a vibrating screen to obtain the finished product.

[0048] Example 2

[0049] This embodiment relates to a dry method for producing lithium-based bentonite, comprising the following steps:

[0050] (1) Raw material pretreatment: Sodium-based bentonite is crushed to 200 mesh and mixed with lithium chloride at a mass ratio of sodium-based bentonite: lithium chloride = 10:1 to obtain a mixture;

[0051] (2) Segmented activation treatment: The mixture obtained in step (1) is placed in a twin-screw extruder for segmented activation treatment. The temperature of the first segment is controlled at 80°C and the screw speed is 150 r / min. The temperature of the second segment is 150°C, and a composite additive is introduced. The amount added is 1% of the mass of sodium bentonite, and the mass ratio of citric acid to silane coupling agent is 1:1.

[0052] (3) Gradient temperature field roasting: The activated material obtained in step (2) is sent into a multi-layer roasting furnace for gradient temperature field roasting. The upper layer is preheated at 250℃ for 30 minutes, the middle layer is kept at 350℃ for 1 hour, and the lower layer is cooled at 150℃ for 20 minutes.

[0053] (4) Crushing and grading: The product from the gradient temperature field roasting in step (3) is crushed to D90 = 5μm by a collision airflow pulverizer. The crushed material is then screened by a built-in turbine classifier and then screened by a vibrating screen to obtain the finished product.

[0054] Example 3

[0055] This embodiment relates to a dry method for producing lithium-based bentonite, comprising the following steps:

[0056] (1) Raw material pretreatment: Sodium-based bentonite is crushed to 300 mesh and mixed with lithium carbonate at a mass ratio of sodium-based bentonite: lithium carbonate = 15:1 to obtain a mixture;

[0057] (2) Segmented activation treatment: The mixture obtained in step (1) is placed in a twin-screw extruder for segmented activation treatment. The temperature of the first segment is controlled at 120°C and the screw speed is 200 r / min. The temperature of the second segment is 180°C, and a composite additive is introduced. The amount added is 3% of the mass of sodium bentonite, and the mass ratio of citric acid to silane coupling agent is 2:1.

[0058] (3) Gradient temperature field roasting: The activated material obtained in step (2) is sent into a multi-layer roasting furnace for gradient temperature field roasting. The upper layer is preheated at 280℃ for 40 min, the middle layer is kept at 450℃ for 1.5 h, and the lower layer is cooled at 200℃ for 30 min.

[0059] (4) Crushing and grading: The product from the gradient temperature field roasting in step (3) is crushed to D90 = 3μm by a collision airflow pulverizer. The crushed material is then screened by a built-in turbine classifier and then screened by a vibrating screen to obtain the finished product.

[0060] Comparative Example 1

[0061] The difference between this comparative example and Example 1 is that the composite additive uses only citric acid, without adding a silane coupling agent, while other steps and parameters remain unchanged, specifically:

[0062] (1) Raw material pretreatment: Sodium-based bentonite is crushed to 250 mesh and mixed with lithium carbonate at a mass ratio of sodium-based bentonite: lithium carbonate = 12:1 to obtain a mixture;

[0063] (2) Segmented activation treatment: The mixture obtained in step (1) is placed in a twin-screw extruder for segmented activation treatment. The temperature of the first segment is controlled at 100℃ and the screw speed is 180r / min. The temperature of the second segment is 160℃, and the composite auxiliary agent citric acid is introduced, with an addition amount of 2% of the mass of sodium bentonite.

[0064] (3) Gradient temperature field roasting: The activated material obtained in step (2) is sent into a multi-layer roasting furnace for gradient temperature field roasting. The upper layer is preheated at 300℃ and held for 35 minutes, the middle layer is held at 400℃ for 1.2 hours, and the lower layer is cooled at 180℃ for 25 minutes.

[0065] (4) Crushing and grading: The product from the gradient temperature field roasting in step (3) is crushed to D90 = 4μm by a collision airflow pulverizer. The crushed material is then screened by a built-in turbine classifier and then screened by a vibrating screen to obtain the finished product.

[0066] Comparative Example 2

[0067] The difference between this comparative example and Example 1 is that the gradient temperature field calcination process is omitted, while other steps and parameters remain unchanged. Specifically:

[0068] (1) Raw material pretreatment: Sodium-based bentonite is crushed to 250 mesh and mixed with lithium carbonate at a mass ratio of sodium-based bentonite: lithium carbonate = 12:1 to obtain a mixture;

[0069] (2) Segmented activation treatment: The mixture obtained in step (1) is placed in a twin-screw extruder for segmented activation treatment. The temperature of the first segment is controlled at 100℃ and the screw speed is 180r / min. The temperature of the second segment is 160℃, and a composite additive is introduced. The amount added is 2% of the mass of sodium bentonite, and the mass ratio of citric acid to silane coupling agent is 1.5:1.

[0070] (3) Crushing and grading: The segmented activation product of step (2) is crushed to D90 = 4μm by a collision air jet mill. The crushed material is then screened by a built-in turbine classifier and then screened by a vibrating screen to obtain the finished product.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that it does not use gradient temperature field calcination, but uses single-stage temperature calcination. Other steps and parameters remain unchanged, specifically:

[0073] (1) Raw material pretreatment: Sodium-based bentonite is crushed to 250 mesh and mixed with lithium carbonate at a mass ratio of sodium-based bentonite: lithium carbonate = 12:1 to obtain a mixture;

[0074] (2) Segmented activation treatment: The mixture obtained in step (1) is placed in a twin-screw extruder for segmented activation treatment. The temperature of the first segment is controlled at 100℃ and the screw speed is 180r / min. The temperature of the second segment is 160℃, and a composite additive is introduced. The amount added is 2% of the mass of sodium bentonite, and the mass ratio of citric acid to silane coupling agent is 1.5:1.

[0075] (3) Gradient temperature field roasting: The activated material obtained in step (2) is sent into a roasting furnace for roasting at a temperature of 380℃ for 1.5h.

[0076] (4) Crushing and grading: The product from the gradient temperature field roasting in step (3) is crushed to D90 = 4μm by a collision airflow pulverizer. The crushed material is then screened by a built-in turbine classifier and then screened by a vibrating screen to obtain the finished product.

[0077] The performance of the products obtained in the examples and comparative examples was tested, and the results are shown in Table 1:

[0078] Table 1

[0079]

[0080] As shown in Table 1, the embodiments of this invention employ a dry process of segmented activation + synergistic composite additives + gradient temperature calcination to produce lithium-based bentonite. The lithium-ion exchange rate reaches 80%-88%, and the expansion capacity, blue absorption, and gel strength are significantly better than those of the comparative examples. Furthermore, XRD analysis shows that the montmorillonite layered structure is intact, and the product performance is stable. In contrast, Comparative Example 1 does not add a silane coupling agent, and citric acid alone cannot effectively open the interlayer channels, resulting in low exchange efficiency. Comparative Example 2 does not undergo calcination treatment, lacking the ion exchange conditions triggered by calcination, and has almost no modification effect. Comparative Example 3 uses single-temperature calcination treatment, which makes it difficult to simultaneously achieve ion exchange and structural protection within a single temperature zone, leading to local structural damage and performance degradation.

[0081] In summary, the twin-screw extruder of this invention performs segmented activation treatment: the first segment breaks the interlayer hydrogen bonds of montmorillonite through shear force; the second segment introduces a composite additive to further open the interlayer channels. Citric acid in the composite additive lowers the lithium salt decomposition temperature through chelation, and the silane coupling agent inserts into the interlayer of montmorillonite to form a molecular wedge structure. That is, the inorganic-loving groups, such as siloxy groups, and the organic-loving groups contained in the silane coupling agent molecule structure, under the mechanical activation of the twin-screw extruder, allow the siloxy groups to form hydrogen bonds or covalent bonds with the silicon-oxygen tetrahedra between the montmorillonite layers, while the organic groups at the other end extend outward and insert into the interlayer gaps of montmorillonite, opening up the originally tightly stacked montmorillonite sheets. The two work together to expand the interlayer spacing, providing channels for lithium ion diffusion and significantly improving the exchange efficiency. The combination of citric acid and silane coupling agent not only lowers the lithium salt activation temperature but also protects the montmorillonite structure. This invention employs a gradient temperature field calcination process. The first region undergoes preheating to promote the decomposition of lithium salt into active lithium ions. The second region, the core temperature zone, facilitates the exchange of lithium ions with sodium ions between the montmorillonite layers. The third region stabilizes the crystal structure. This gradient temperature field design avoids the montmorillonite lattice distortion caused by traditional single-temperature zone calcination. Simultaneously, the middle temperature zone is precisely controlled below the montmorillonite dehydroxylation temperature, preserving the activity of the layered structure. This invention's dry process eliminates the need for washing and multiple drying stages, significantly reducing total energy consumption compared to traditional wet processes. Water consumption is zero, production costs are reduced by over 30%, and the process is shorter.

[0082] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A method for dry production of lithium-based bentonite, characterized in that, Includes the following steps: S1. Sodium-based bentonite is pulverized and then mixed with lithium salt to obtain a mixture; S2. The mixture is placed in a twin-screw extruder for mechanical activation to obtain an activated material; The temperature of the first stage is 80-120℃; the temperature of the second stage is 150-180℃, and a composite additive, citric acid and silane coupling agent, is added in the second stage. S3. The activated material is subjected to gradient temperature field calcination treatment; The temperature in the first zone is 250-300℃, the temperature in the second zone is 350-450℃, and the temperature in the third zone is 150-200℃. S4. The product from S3 calcination is pulverized to obtain the lithium-based bentonite.

2. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S1, the mass ratio of sodium-based bentonite to lithium salt is (10-15):

1.

3. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S1, the lithium salt is lithium carbonate and / or lithium chloride.

4. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S2, the mass of the composite additive is 1-3% of the mass of sodium-based bentonite.

5. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S2, the mass ratio of citric acid to silane coupling agent is (1-2):

1.

6. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S3, the residence time of the activated material in the first region is 30-40 min, the residence time in the second region is 1-1.5 h, and the residence time in the third region is 20-30 min.

7. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S4, the pulverization is completed by a collision-type air jet mill, which performs primary screening of the pulverized material through a built-in turbine classifier.

8. The method for dry production of lithium-based bentonite as described in claim 7, characterized in that, S4 also includes: secondary screening of the material after primary screening using a vibrating screen.

9. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S4, the material is pulverized to a density of D90 ≤ 5 μm.

10. The method for dry production of lithium-based bentonite as described in claim 1, characterized in that, In S1, the pulverization process is carried out to a particle size of 200-300 mesh.

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