A method for synthesizing k-cha zeolite from lithium slag

Abstract

This invention belongs to the field of zeolite preparation technology, specifically relating to a method for synthesizing K-CHA zeolite from lithium slag. The method involves aging and crystallizing impurity-removed lithium slag, followed by centrifugation, washing with deionized water, and drying to obtain K-CHA zeolite. This invention synthesizes K-CHA zeolite with a "sunflower" morphology via a simple hydrothermal method, broadening the acquisition pathways of raw materials for zeolite molecular sieve production, reducing the cost of zeolite synthesis, and realizing the resource utilization and high-value utilization of lithium slag.

Description

Technical Field

[0001] This invention belongs to the field of zeolite preparation technology, specifically relating to a method for synthesizing K-CHA zeolite from lithium slag. Background Technology

[0002] Lithium slag is an industrial silica-alumina waste residue generated during the production of lithium salts such as lithium carbonate from lithium-containing ores (spodumene, lepidolite, etc.). With the explosive growth of the lithium-ion battery industry and the rise of energy storage devices, my country's lithium consumption has increased by an average of over 18% annually, resulting in annual lithium slag emissions exceeding 15 million tons. Lithium slag contains large amounts of SiO2 and Al2O3, and small amounts of CaO and Fe2O3, among other chemical components. As a cement admixture, it has long been the primary method of resource utilization for lithium slag. However, with the implementation of the mandatory national standard "General Portland Cement" (GB 175-2023), this large-scale disposal channel is no longer suitable. The large-scale disposal of lithium slag through stockpiling or landfill not only occupies land resources, but the potential impact of residual sulfides and harmful elements in the slag on the surrounding soil and water environment cannot be ignored.

[0003] CHA zeolite is a microporous zeolite molecular sieve with an eight-membered ring three-dimensional channel structure and a pore size of 0.38 nm × 0.38 nm. It is formed by the orderly and stable formation of an eight-membered ring ellipsoidal cage and a three-dimensional intersecting pore framework structure through the intersection of oxygen atoms in aluminum-oxygen tetrahedra (AlO4) and silicon-oxygen tetrahedra (SiO4). Benefiting from its unique structure of small pore size and large cavity, CHA zeolite molecular sieves exhibit excellent properties in methanol-to-olefins catalysis, selective catalytic reduction of nitrogen oxides by ammonia, and adsorption and separation of CH4, N2, and CO2. It has wide applications in the chemical industry and environmental remediation, and possesses significant economic and research value. Due to the limited resources of natural mineral CHA zeolite, the artificial synthesis of CHA zeolite molecular sieves using silica-alumina reagents is currently the mainstream method.

[0004] Lithium slag, coal gangue, and other silicon-aluminum-containing industrial solid wastes, due to their high total silicon and aluminum content, possess natural technical and cost advantages in the artificial synthesis of CHA zeolite molecular sieves. Subsequently, various technical solutions for preparing CHA zeolite from silicon-aluminum-containing industrial solid wastes have emerged, but these solutions suffer from the following technical drawbacks:

[0005] 1. Industrial solid waste containing silicon and aluminum needs to be roasted and activated;

[0006] 2. External reagents are required, such as silicon sources and aluminum sources, to match the target silicon-to-aluminum ratio;

[0007] 3. Seed crystals are required;

[0008] For example, in the patent technology solution of publication number CN119306228A, silicon source, aluminum source and sodium source are used as raw materials. After aging, NaY molecular sieve directing agent is obtained and mixed with silicon source and aluminum source to form a gel. After crystallization, separation and washing, chalcogenide with CHA structure is obtained.

[0009] The patent technology scheme published in CN111282542A uses natural calcium-rich STI zeolite powder as raw material, which is roasted at high temperature, seed crystals are added, and K,Ca-CHA zeolite is hydrothermally synthesized in KOH aqueous solution.

[0010] The patent technology in publication number CN118343790A adopts a three-stage hydrothermal method, which involves mixing calcined coal gangue with an alkaline solution and hydrothermally heating it to obtain octahedral zeolite or sodalite. Then, by adding an external silicon source and an organic template agent, the alkaline solution and octahedral zeolite or sodalite are mixed evenly and hydrothermally heated to obtain chabazite. Finally, the chabazite is mixed with a salt solution and water bathed more than three times to obtain coal gangue-based chabazite.

[0011] The aforementioned technical solutions mostly employ calcination activation, or use chemical reagents as raw materials, or require the addition of chemical reagents and silicon sources on top of using solid waste as raw materials, or adopt seed crystal-induced crystallization, resulting in complex procedures and high costs. Therefore, how to significantly reduce the production cost of CHA zeolite has become one of the research hotspots in this field. Summary of the Invention

[0012] The technical problem to be solved by the present invention is to provide a low-cost method for synthesizing K-CHA zeolite from lithium slag.

[0013] The method for synthesizing K-CHA zeolite from lithium slag according to the present invention includes the following steps:

[0014] a. Aging: The lithium residue after impurity removal is mixed with KOH and an aqueous solution to obtain a suspension; or the lithium residue after impurity removal is mixed with a KOH solution to obtain a suspension.

[0015] The suspension was subjected to hydrothermal reaction at 100~120℃ for 2~50 hours, followed by cooling to obtain the silica-alumina gel precursor.

[0016] The KOH concentration in the suspension is 0.2~1.0 M, and the solid-liquid ratio is 1:50~200 g / mL;

[0017] b. Crystallization: CTAB (hexadecyltrimethylammonium bromide in this invention) and anhydrous EtOH (ethanol in this invention) are added to the suspension or silica-alumina gel precursor obtained in step a. After stirring evenly, a hydrothermal reaction is carried out in the crystallization stage.

[0018] Among them, based on SiO2 in the lithium residue removed in step a, the molar ratio is CTAB:SiO2 = 0.01~0.06, EtOH:SiO2 = 0.05~0.2, the hydrothermal reaction temperature in the crystallization stage is 140~160℃, and the hydrothermal reaction time in the crystallization stage is 20~110 hours.

[0019] The products obtained from steps c and b are centrifuged, washed with deionized water, and dried to obtain K-CHA zeolite.

[0020] The method for synthesizing K-CHA zeolite from lithium slag of the present invention, wherein the lithium slag in step a is lithium slag after lithium extraction by sulfuric acid leaching of spodumene to remove impurities such as Ca and S; the lithium slag particle size is ≤200 mesh; and the Si / Al molar ratio is 2~2.5. The impurity removal method can be a conventional impurity removal method in the art.

[0021] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, step a involves a hydrothermal reaction of the suspension at 100-110°C for 2-30 hours.

[0022] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, the KOH concentration in the suspension in step a is 0.2~0.7 M, and the solid-liquid ratio is 1:50~100 g / mL.

[0023] More preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, the concentration of KOH in the suspension in step a is 0.2~0.5 M, and the hydrothermal reaction time is 2~10 hours.

[0024] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, in step b, EtOH: SiO2 = 0.05~0.2.

[0025] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, in step b, CTAB: SiO2 = 0.02~0.04, EtOH: SiO2 = 0.05~0.1, and the hydrothermal reaction time in the crystallization stage is 20~70 hours.

[0026] More preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, in step b, CTAB: SiO2 = 0.02~0.03 and the hydrothermal reaction time is 20~45 hours.

[0027] The present invention has the following beneficial effects:

[0028] 1. The process is simple and has a good cost advantage. This invention adopts a low-temperature hydrothermal activation method, which completely avoids the high energy consumption process of traditional high-temperature roasting, and the energy consumption of the process is significantly reduced. At the same time, it uses lithium slag as the only silicon and aluminum source, without the need to add any external silicon, aluminum chemicals and seed crystals, resulting in low raw material costs and an extremely simple process route.

[0029] 2. A new approach to the high-value utilization of lithium slag has been pioneered. The process of preparing high-value-added zeolite molecular sieve products from industrial solid waste lithium slag has achieved efficient and high-value utilization of the silicon and aluminum components in lithium slag, providing a new approach with industrial potential for the resource utilization of lithium slag.

[0030] 3. The process conditions of the method of the present invention can realize the directional, efficient and controllable synthesis of K-CHA zeolite products with the morphology of "sunflower", and the products have high cleanliness and good purity. Attached Figure Description

[0031] Figure 1 The XRD pattern and SEM morphology of K-CHA zeolite in Example 1 of this invention are shown.

[0032] Figure 2 The XRD pattern and SEM morphology of K-CHA zeolite in Example 2 of this invention are shown.

[0033] Figure 3 The XRD pattern and SEM morphology of K-CHA zeolite in Example 3 of this invention are shown.

[0034] Figure 4 The XRD pattern and SEM morphology of K-CHA zeolite in Example 4 of this invention are shown.

[0035] Figure 5 The XRD pattern and SEM morphology of K-CHA zeolite in Example 5 of this invention are shown.

[0036] Figure 6 The XRD pattern and SEM morphology of Comparative Example 1 of this invention are shown.

[0037] Figure 7 The XRD pattern and SEM morphology of Comparative Example 2 of this invention are shown.

[0038] Figure 8 The XRD pattern and SEM morphology of Comparative Example 3 of this invention are shown.

[0039] Figure 9 The XRD pattern and SEM morphology of Comparative Example 4 of this invention are shown.

[0040] Figure 10 The XRD pattern and SEM morphology of Comparative Example 5 of this invention are shown.

[0041] Figure 11 The images shown are XRD patterns and SEM morphology images of Comparative Example 6 of this invention. Detailed Implementation

[0042] The method for synthesizing K-CHA zeolite from lithium slag according to the present invention includes the following steps:

[0043] a. Aging: The lithium residue after impurity removal is mixed with KOH and an aqueous solution to obtain a suspension; or the lithium residue after impurity removal is mixed with a KOH solution to obtain a suspension.

[0044] The suspension was subjected to hydrothermal reaction at 100~120℃ for 2~50 hours, followed by cooling to obtain the silica-alumina gel precursor.

[0045] The KOH concentration in the suspension is 0.2~1.0 M, and the solid-liquid ratio is 1:50~200 g / mL;

[0046] b. Crystallization: CTAB and anhydrous EtOH are added to the suspension or silica-alumina gel precursor obtained in step a, and after stirring evenly, a hydrothermal reaction is carried out in the crystallization stage.

[0047] Among them, based on SiO2 in the lithium residue removed in step a, the molar ratio is CTAB:SiO2 = 0.01~0.06, EtOH:SiO2 = 0.05~0.2, the hydrothermal reaction temperature in the crystallization stage is 140~160℃, and the hydrothermal reaction time in the crystallization stage is 20~110 hours.

[0048] The products obtained from steps c and b are centrifuged, washed with deionized water, and dried to obtain K-CHA zeolite.

[0049] The present invention discloses a method for synthesizing K-CHA zeolite from lithium slag. In step a, the impurity-removed lithium slag is the lithium slag obtained after lithium extraction via sulfuric acid leaching of spodumene to remove impurities such as Ca and S. The lithium slag particle size is ≤200 mesh, and the Si / Al molar ratio is 2~2.5. The impurity removal method can be a conventional method in the art. The impurity-removed lithium slag can eliminate the severe influence of impurities on the n(SiO2) / n(Al2O3) value and their impact on zeolite crystallization.

[0050] The aging step of this invention aims to restructure and chemically activate lithium slag using KOH solution under relatively mild, low-temperature hydrothermal conditions. KOH dissolves the amorphous silicon-aluminum phase in the lithium slag and disrupts its original crystal structure, transforming the inert silicon-aluminum oxide into highly reactive [SiO4]. 4- and [AlO4] 5- Ionic monomers and oligomers spontaneously assemble to form a silica-aluminate gel network with a specific short-range order (containing structural unit prototypes that match the target CHA topology), providing structural guidance targets and abundant nucleation sites for subsequent crystallization steps.

[0051] In this invention, suspension refers to a solid-liquid mixture formed by dispersing and suspending impurity lithium slag solid particles in a solution.

[0052] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, step a involves a hydrothermal reaction of the suspension at 100-110°C for 2-30 hours.

[0053] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, the KOH concentration in the suspension in step a is 0.2~0.7 M, and the solid-liquid ratio is 1:50~100 g / mL.

[0054] More preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, the concentration of KOH in the suspension in step a is 0.2~0.5 M, and the hydrothermal reaction time is 2~10 hours.

[0055] The crystallization step of this invention serves to drive the precursor gel to undergo directional structural rearrangement and long-range ordering based on the specific structural state of the precursor gel under specific hydrothermal temperature, additive conditions and alkalinity conditions, ultimately transforming it into K-CHA zeolite crystals with a "sunflower" morphology and regular pore structure.

[0056] The inventors of this invention discovered a non-linear synergistic or antagonistic relationship between the process parameters of the aging step (KOH concentration, temperature) and the process parameters of the crystallization step (temperature, time, additives). This is key to achieving directional synthesis without seed induction. When the aging and crystallization temperatures are high (e.g., aging temperature ≥ 110℃ or crystallization temperature ≥ 150℃) and the KOH concentration is 0.2~0.7 M, K... + Structural guiding effect and OH - The mineralization capabilities of CTAB can be precisely synergistic, enabling direct hydrothermal synthesis of K-CHA crystals, in which case the crystallization step can be performed without the addition of EtOH. When the aging and crystallization temperatures are low, and the KOH concentration is less than 0.5 M or greater than 0.7 M, anhydrous ethanol must be used to adjust the synthesis environment to rebuild the crystallization driving force in order to obtain the target product. Ethanol acts as a regulator, assisting CTAB in acting as a "structure-directing agent" by adjusting the gel structure, changing the dielectric environment, and improving dispersion. The appropriate addition of EtOH can be dynamically adjusted according to the aging and crystallization temperatures. At lower temperatures, it is usually necessary to increase the amount appropriately, while at higher temperatures, it can be reduced or even omitted entirely to achieve precise control of the synthesis pathway.

[0057] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, in step b, EtOH: SiO2 = 0.05~0.2:1.

[0058] Preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, in step b, CTAB: SiO2 = 0.02~0.04:1, EtOH: SiO2 = 0.05~0.1:1, and the hydrothermal reaction time in the crystallization stage is 20~70 hours.

[0059] More preferably, in the method for synthesizing K-CHA zeolite from lithium slag of the present invention, in step b, CTAB:SiO2 = 0.02~0.03:1, and the hydrothermal reaction time is 20~45 hours.

[0060] The present invention will be further described below with reference to specific embodiments and comparative examples, but the implementation of the invention is not limited thereto.

[0061] The lithium residue used in the following examples is lithium residue obtained by spodumene sulfuric acid leaching. The lithium residue is mixed with dilute hydrochloric acid solution at a mass ratio of 1:15, stirred in a water bath at 30°C for 0.5 h, and finally filtered, washed and dried.

[0062] The chemical composition and mass percentage of lithium slag and impurity-removed lithium slag were determined by X-ray fluorescence spectrometry (XRF), as shown in Table 1 below.

[0063] Table 1. Chemical composition and mass percentage of lithium slag and impurity-removed lithium slag

[0064]

[0065] Example 1

[0066] Prepare 50 mL of 0.4 M KOH solution, add 0.5 g of lithium residue (after purification), stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 °C for 6 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.063 g of CTAB and 33 μL of anhydrous ethanol (EtOH) to the gel, stir well, and then hydrothermally crystallize at 140 °C for 70 hours. After the reaction, centrifuge, wash with deionized water, and dry to obtain the K-CHA zeolite sample. Figure 1 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 9.4°, 12.9°, 20.6°, 22.9°, and 30.6°, which are completely consistent with the standard CHA structure zeolite pattern, and there are no impurity phase diffraction peaks, indicating that the sample is a pure phase K-CHA zeolite. Scanning electron microscopy (SEM) characterization results ( Figure 1 -b) shows that the zeolite crystal exhibits a typical "sunflower" morphology, with an overall diameter of about 7 μm and a thickness of about 1.8 μm. The crystal surface is composed of uniformly distributed conical protrusions.

[0067] Example 2

[0068] Prepare 50 mL of 0.4 M KOH solution, add 0.75 g of purified lithium slag, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 °C for 6 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.095 g of CTAB to the gel, stir well, and then hydrothermally crystallize at 160 °C for 25 hours. After the reaction, centrifuge, wash with deionized water, and dry to obtain the K-CHA zeolite sample. Figure 2 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 9.4°, 12.9°, 20.6°, 22.9°, and 30.6°, which are completely consistent with the standard CHA structure zeolite pattern, and there are no impurity phase diffraction peaks, indicating that the sample is a pure phase K-CHA zeolite. Scanning electron microscopy (SEM) characterization results ( Figure 2 -b) shows that the zeolite crystal exhibits a typical "sunflower" morphology, with an overall diameter of about 6 μm and a thickness of about 1.4 μm. The crystal surface is composed of uniformly distributed conical protrusions.

[0069] This embodiment demonstrates that by increasing the reaction temperature during the crystallization stage, under experimental conditions without the addition of anhydrous ethanol, it is possible to achieve precise matching between the precursor gel state and crystallization conditions, thereby achieving efficient and directional synthesis of K-CHA zeolite with a shorter crystallization time.

[0070] Example 3

[0071] Prepare 50 mL of 0.4 M KOH solution, add 0.5 g of purified lithium slag, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 110 ℃ for 4 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.063 g of CTAB to the gel, stir well, and then hydrothermally crystallize at 140 ℃ for 70 hours. After the reaction, centrifuge, wash with deionized water, and dry to obtain the K-CHA zeolite sample. Figure 3 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 9.4°, 12.9°, 20.6°, 22.9°, and 30.6°, which are completely consistent with the standard CHA structure zeolite pattern, and there are no impurity phase diffraction peaks, indicating that the sample is a pure phase K-CHA zeolite. Scanning electron microscopy (SEM) characterization results ( Figure 3 -b) shows that the zeolite crystal exhibits a typical "sunflower" morphology, with an overall diameter of about 8.5 μm and a thickness of about 2 μm. The crystal surface is composed of uniformly distributed conical protrusions.

[0072] This embodiment demonstrates that by increasing the reaction temperature during the aging stage, precise matching of the precursor gel state and crystallization conditions can be achieved under experimental conditions without the addition of anhydrous ethanol, thus enabling efficient and directional synthesis of K-CHA zeolite at a lower crystallization reaction temperature.

[0073] Example 4

[0074] Prepare 50 mL of 0.25 M KOH solution, add 0.25 g of purified lithium slag, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 ℃ for 6 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.032 g of CTAB to the gel, stir well, and then hydrothermally crystallize at 150 ℃ for 40 hours. After the reaction, centrifuge, wash with deionized water, and dry to obtain the K-CHA zeolite sample. Figure 4 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 9.4°, 12.9°, 20.6°, 22.9°, and 30.6°, which are completely consistent with the standard CHA structure zeolite pattern, and there are no impurity phase diffraction peaks, indicating that the sample is a pure phase K-CHA zeolite. Scanning electron microscopy (SEM) characterization results ( Figure 4 -b) shows that the zeolite crystal exhibits a typical "sunflower" morphology with an overall diameter of 7 μm and a thickness of about 1.5 μm. Compared with the sample synthesized under high KOH concentration conditions, the size of the surface cone-shaped morphology units of the crystal obtained in this embodiment is significantly increased, resulting in higher surface roughness and more complex microstructure of the crystal as a whole.

[0075] This embodiment demonstrates that by increasing the reaction temperature during the crystallization stage, under experimental conditions without adding anhydrous ethanol, it is possible to achieve precise matching between the precursor gel state and crystallization conditions, thereby achieving efficient and directional synthesis of K-CHA zeolite with a lower KOH concentration.

[0076] Example 5

[0077] Prepare 50 mL of 0.9 M KOH solution, add 0.5 g of lithium residue (after purification), stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 ℃ for 2 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.063 g of CTAB and 50 μL of anhydrous ethanol (EtOH) to the gel, stir well, and then hydrothermally crystallize at 140 ℃ for 70 hours. After the reaction, centrifuge, wash with deionized water, and dry to obtain the K-CHA zeolite sample. Figure 5As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 9.4°, 12.9°, 20.6°, 22.9°, and 30.6°, which are completely consistent with the standard CHA structure zeolite pattern, and there are no impurity phase diffraction peaks, indicating that the sample is a pure phase K-CHA zeolite. Scanning electron microscopy (SEM) characterization results ( Figure 5 -b) shows that the zeolite crystals exhibit a typical "sunflower" morphology, with an overall diameter of approximately 7.4 μm and a thickness of approximately 2.5 μm. The crystal surface is composed of conical protrusions. A small number of strip-shaped MER crystals are sporadically distributed between the crystal grains.

[0078] Comparative Example 1

[0079] This comparative example adopts the method disclosed in Chinese Patent CN 119503834 A, using KOH as the alkali. The specific steps are as follows: 50 mL of 0.85 M KOH solution is prepared in a round-bottom flask, 0.5 g of lithium residue (after purification) is added, and after stirring evenly, it is transferred to an oil bath and reacted at 90 ℃ for 48 hours, followed by aging at room temperature for 20 minutes to obtain a silica-alumina gel precursor; the gel is then transferred to a hydrothermal reactor and hydrothermally crystallized at 120 ℃ for 45 hours. After the reaction, the product is obtained by filtration, washing with deionized water, and drying. Figure 6 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ values ​​of 20.8°, 23.8°, 25.6°, and 26.7°. The peaks at 20.8° and 26.7° are characteristic diffraction peaks of SiO2, while those at 23.8° and 26.7° are characteristic diffraction peaks of the aluminosilicate mineral KAlSi2O6. Scanning electron microscopy (SEM) characterization results ( Figure 6 -b) shows that the comparative sample exhibits an amorphous morphology with a wide particle size distribution and lacks the regular geometric morphology characteristic of crystalline materials on its surface and overall. The structural and morphological characteristics of this product are significantly different from the typical crystallographic morphology of well-crystallized K-CHA zeolite.

[0080] This comparative example shows that the process design of the present invention cannot be achieved simply by replacing the type of alkali agent in existing methods. Its success depends on the specific condition matching and synergistic effect between steps such as aging and crystallization.

[0081] Comparative Example 2

[0082] Prepare 50 mL of 0.55 M NaOH solution, add 0.5 g of lithium residue (after purification), stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 °C for 5 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.042 g of CTAB and 33 μL of anhydrous ethanol (EtOH) to the gel, stir well, and then hydrothermally crystallize at 160 °C for 70 hours. After the reaction, centrifuge, wash with deionized water, and dry. Figure 7 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 15.7°, 18.2°, 25.8°, 30.5°, 33.2°, and 35.7°, consistent with the standard analcime pattern. Scanning electron microscopy (SEM) characterization results ( Figure 7 -b) shows that the comparative sample has a polyhedral geometry, which is typical of analcime morphology.

[0083] This comparative example shows that in the process system of the present invention, KOH not only provides the alkaline environment required for the reaction as an alkaline source, but also plays an irreplaceable specific structure-guiding role in regulating the gel state of the precursor and guiding the formation of the CHA topology.

[0084] Comparative Example 3

[0085] Prepare 50 mL of 0.4 M KOH solution, add 0.5 g of purified lithium residue, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 °C for 6 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.063 g of CTAB to the gel, stir well, and then hydrothermally crystallize at 140 °C for 70 hours. After the reaction, centrifuge, wash with deionized water, and dry. Figure 8 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ values ​​of 21.5°, 25.6°, 26.7°, 29.5°, and 32.4°. The 26.7° peak is a characteristic diffraction peak of SiO2, while the 21.5°, 25.6°, 29.5°, and 32.4° peaks are characteristic diffraction peaks of the aluminosilicate mineral KAlSi2O6. Scanning electron microscopy (SEM) characterization results ( Figure 8 -b) shows that the comparative sample exhibits an amorphous morphology with a wide particle size distribution and lacks the regular geometric morphology characteristic of crystalline materials, both on the surface and overall. The structural and morphological characteristics of this product are significantly different from those of the well-crystallized "sunflower" K-CHA zeolite.

[0086] This comparative example shows that under experimental conditions of absence of anhydrous ethanol and low crystallization temperature, the mismatch between the precursor gel state and the crystallization conditions causes CTAB to change from a structure-directing agent to a crystallization inhibitor. Its strong adsorption effect hinders the dissolution-reorganization process of the gel network, thereby inhibiting the formation and crystallization of the CHA topology.

[0087] Comparative Example 4

[0088] Prepare 50 mL of 0.55 M KOH solution, add 0.5 g of purified lithium residue, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 °C for 6 hours, then allow to cool naturally to room temperature to obtain the silica-alumina gel precursor. Then, hydrothermally crystallize at 160 °C for 75 hours. After the reaction, the product is centrifuged, washed with deionized water, and dried. Figure 9 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ of 9.4°, 12.9°, 20.6°, 22.9°, and 30.6°, which are similar to those of standard CHA structure zeolites. Figure 1 The presence of uniform diffraction peaks and the absence of impurity phase diffraction peaks indicate that the sample is a pure-phase K-CHA zeolite. Scanning electron microscopy (SEM) characterization results ( Figure 9 -b) shows that the product morphology exhibits significant heterogeneity, with the main body being amorphous aggregates of a wide size distribution, interspersed with a small number of strip-shaped MER crystals. This morphology is fundamentally different from the well-crystallized and uniformly shaped "sunflower"-shaped K-CHA zeolite crystals.

[0089] This comparative example demonstrates that in the process system of this invention, CTAB is not merely a surfactant, but plays a crucial and irreplaceable structure-directing role. Its absence would prevent the system from effectively guiding the directional assembly of silicon-aluminum species into a "sunflower"-shaped crystal structure, instead causing the reaction to shift towards the more thermodynamically stable amorphous phase or other heterocrystalline paths. This further confirms the necessity of multi-parameter synergistic control in this invention for achieving the directional synthesis of the product.

[0090] Comparative Example 5

[0091] Prepare 50 mL of 0.6 M KOH solution, add 0.5 g of purified lithium residue, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 ℃ for 8 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.063 g of CTAB and 33 μL of anhydrous ethanol (EtOH) to the gel, stir well, and then hydrothermally crystallize at 130 ℃ for 80 hours. After the reaction, centrifuge, wash with deionized water, and dry. Figure 10As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ values ​​of 21.5°, 25.6°, 26.7°, 29.5°, and 32.4°. The 26.7° peak is a characteristic diffraction peak of SiO2, while the 21.5°, 25.6°, 29.5°, and 32.4° peaks are characteristic diffraction peaks of the aluminosilicate mineral KAlSi2O6. Scanning electron microscopy (SEM) characterization results ( Figure 10 -b) shows that the comparative sample is amorphous with a wide particle size distribution and lacks the regular geometric morphology characteristic of crystalline materials on its surface and overall. The structural and morphological characteristics of this product are significantly different from the morphology of well-crystallized "sunflower"-shaped K-CHA zeolite.

[0092] This comparative example shows that when the crystallization temperature deviates from the range defined in the claims of this invention, even with a high KOH concentration and sufficient crystallization time, the reaction still cannot lead to the formation of K-CHA zeolite under the conditions of CTAB and anhydrous ethanol. This indicates that there is a strict matching relationship between the crystallization temperature and the precursor gel state formed during the aging stage; exceeding a reasonable range will lead to instability of the crystallization path, making it impossible to achieve the directional synthesis of the product.

[0093] Comparative Example 6

[0094] Prepare 50 mL of 0.75 M KOH solution, add 0.5 g of purified lithium residue, stir well, and transfer to a hydrothermal reactor. React hydrothermally at 100 °C for 6 hours, then allow to cool naturally to room temperature to obtain a silica-alumina gel precursor. Add 0.063 g of CTAB to the gel, stir well, and then hydrothermally crystallize at 150 °C for 45 hours. After the reaction, centrifuge, wash with deionized water, and dry. Figure 11 As shown in -a, the X-ray diffraction pattern of the obtained product shows characteristic diffraction peaks at 2θ values ​​of 21.5°, 25.6°, 26.7°, 29.5°, and 32.4°. The 26.7° peak is a characteristic diffraction peak of SiO2, while the 21.5°, 25.6°, 29.5°, and 32.4° peaks are characteristic diffraction peaks of the aluminosilicate mineral KAlSi2O6. Scanning electron microscopy (SEM) characterization results ( Figure 11 -b) shows that the comparative sample is amorphous with a wide particle size distribution and lacks the regular geometric morphology characteristic of crystalline materials on its surface and overall. The structural and morphological characteristics of this product are significantly different from the morphology of well-crystallized "sunflower"-shaped K-CHA zeolite.

[0095] This comparative example demonstrates that, under specific precursor gel state and crystallization conditions, the addition of anhydrous ethanol is a key factor in achieving the directed synthesis of K-CHA. The absence of ethanol leads to strong adsorption of CTAB on the gel surface, severely deactivating its reactivity and hindering the necessary dissolution-recrystallization process, causing the system to shift towards the formation of a thermodynamically more stable amorphous mixture.

Claims

1. A method for preparing K-CHA zeolite using lithium slag, characterized in that... Includes the following steps: a. Aging: The lithium residue after impurity removal is mixed with KOH and an aqueous solution to obtain a suspension; or the lithium residue after impurity removal is mixed with KOH solution to obtain a suspension; wherein the Si / Al molar ratio in the lithium residue after impurity removal is 2~2.5; The suspension was subjected to hydrothermal reaction at 100~120℃ for 2~50 hours, followed by cooling to obtain the silica-alumina gel precursor. The KOH concentration in the suspension is 0.2~1.0 M, and the solid-liquid ratio is 1:50~200 g / mL; b. Crystallization: CTAB and anhydrous EtOH are added to the suspension or silica-alumina gel precursor obtained in step a, and after stirring evenly, a hydrothermal reaction is carried out in the crystallization stage. Among them, taking SiO2 in the lithium residue removed in step a as the basis, the molar ratio is CTAB: SiO2 = 0.01~0.06, EtOH: SiO2 = 0.05~0.2, the hydrothermal reaction temperature in the crystallization stage is 140~160℃, and the hydrothermal reaction time in the crystallization stage is 20~110 hours. The products obtained from steps c and b are centrifuged, washed with deionized water, and dried to obtain K-CHA zeolite.

2. The method for preparing K-CHA zeolite using lithium slag according to claim 1, characterized in that: The lithium slag mentioned in step a is the lithium slag after lithium extraction by sulfuric acid leaching of spodumene to remove Ca and S impurities; the particle size of the lithium slag is ≤200 mesh.

3. The method for preparing K-CHA zeolite using lithium slag according to claim 1, characterized in that: In step a, the suspension is subjected to a hydrothermal reaction at 100~110℃ for 2~30 hours.

4. The method for preparing K-CHA zeolite using lithium slag according to claim 1, characterized in that: In step a, the KOH concentration in the suspension is 0.2~0.7 M, and the solid-liquid ratio is 1:50~100 g / mL.

5. The method for preparing K-CHA zeolite using lithium slag according to claim 4, characterized in that: In step a, the KOH concentration in the suspension is 0.2~0.5 M, and the hydrothermal reaction time is 2~10 hours.

6. The method for preparing K-CHA zeolite from lithium slag according to any one of claims 1 to 5, characterized in that: In step b, CTAB: SiO2 = 0.02~0.04, EtOH: SiO2 = 0.05~0.1, and the hydrothermal reaction time in the crystallization stage is 20~70 hours.

7. The method for preparing K-CHA zeolite using lithium slag according to claim 6, characterized in that: In step b, CTAB:SiO2 = 0.02~0.03, and the hydrothermal reaction time is 20~45 hours.

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