Coal gangue-based porous adsorption material as well as preparation method and application thereof

Abstract

The invention discloses a coal gangue-based porous adsorption material as well as a preparation method and application thereof, and belongs to the technical field of solid waste recycling and porous functional materials. The material is prepared by taking coal gangue as a main raw material through powder forming and heat treatment. The method is characterized in that one-way pressing forming is adopted and combined with a fibrous or sheet-shaped pore forming agent with the length-diameter ratio, so that the pore forming agent is directionally arranged in the pressing process, finally, an elongated pore structure preferentially oriented in the pressing direction is formed in the material, and the fluid permeability of the material in different directions shows remarkable anisotropy. The material has high porosity, appropriate mechanical strength and excellent directional mass transfer capacity. The method is simple in process and low in cost, and high-value utilization of the coal gangue is realized. The prepared material is particularly suitable for a fixed bed or a filtering device to treat industrial wastewater, and when the main flowing direction of the wastewater is consistent with the pore orientation of the material, the bed pressure drop can be effectively reduced, and the pollutant adsorption rate and the treatment capacity can be improved.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization and porous functional materials technology, specifically to a coal gangue-based porous adsorbent material, its preparation method, and its application in wastewater treatment. Background Technology

[0002] Coal gangue is a large-scale solid waste generated during coal mining and washing. It is mainly composed of silica-alumina minerals such as kaolinite, illite, and quartz, and is characterized by its large reserves, wide availability, and relatively stable composition. Long-term, large-scale stockpiling of coal gangue not only occupies land resources but also easily causes environmental problems such as heavy metal leaching and acidic wastewater discharge. Therefore, the resource-based and high-value utilization of coal gangue is of significant environmental and economic importance.

[0003] Numerous studies have utilized coal gangue to prepare porous and environmentally functional materials. One typical method involves extracting silicon and aluminum sources from coal gangue through processes such as calcination, acid leaching, alkali fusion, and hydrothermal synthesis to prepare porous silicon-based materials or molecular sieves for the adsorption or catalytic reactions of organic pollutants. These materials typically exist in powder form, with a pore structure dominated by micropores or mesopores, and the pores are basically randomly distributed in space. Although they possess a certain specific surface area, they require shaping when used as adsorbents, and the mass transfer resistance within the shaped body is high. Another type of research uses coal gangue powder, foaming agents, and other raw materials, obtaining porous blocks through high-temperature foaming or sintering with the addition of pore-forming agents, for use in building materials or simple filter media. While these materials exhibit a macroscopic porous structure, their pore network is mostly isotropic, and they generally face the challenges of balancing porosity and mechanical strength, as well as uncontrollable pore structure.

[0004] It is particularly noteworthy that the complex composition (coexistence of multiple minerals), poor plasticity, and significant differences in sintering behavior among different components of coal gangue make controlling the pore structure during molding and sintering exceptionally difficult. Directly using pore-forming agents (such as spherical pore-forming agents) and molding processes (such as unidirectional pressing) commonly found in conventional porous ceramics often fails to create a uniform, interconnected, and oriented pore structure within the coal gangue matrix. Common drawbacks include: poor compatibility between the pore-forming agent and the matrix leading to pore wall defects; easy collapse or excessive shrinkage of pores during sintering; and the resulting material exhibiting a macroscopically random pore distribution with no significant difference in permeability and mass transfer performance in different directions, failing to meet the requirements for low flow resistance and high mass transfer efficiency in directional flow adsorption applications.

[0005] In the fields of graphene-based materials, porous metal materials, and some high-end ceramics, studies have been conducted on constructing anisotropic channels using precision methods such as cryogenic casting and directional templates, demonstrating the importance of structural orientation in improving mass transfer efficiency. However, these methods are typically complex, costly, and heavily reliant on raw materials with high purity or specific physicochemical properties, making them incompatible with coal gangue solid waste systems, which exhibit large compositional fluctuations and low added value.

[0006] Therefore, a long-standing technical challenge in the field of coal gangue resource utilization is how to effectively control the microstructure of porous materials, particularly by introducing anisotropic pore structures that facilitate directional fluid transport, while utilizing simple and low-cost solid waste treatment processes. This would overcome the bottleneck of low mass transfer efficiency in traditional coal gangue porous materials during adsorption applications. Currently, there are no publicly reported cases of successfully constructing monolithic porous adsorbent materials with significant anisotropic permeability in a coal gangue matrix using a simple unidirectional pressing process combined with a specific pore-forming agent. Summary of the Invention

[0007] To address the aforementioned problems, the present invention aims to overcome the shortcomings of existing coal gangue-based porous materials, which often exhibit random isotropic pore structures, making it difficult to simultaneously achieve high porosity, anisotropic mass transfer performance, and sufficient mechanical strength. The invention provides a coal gangue-based porous adsorbent material, its preparation method, and its applications. By utilizing unidirectional pressing of coal gangue powder and the directional arrangement of fibrous pore-forming agents, directional channels are constructed primarily along the pressing direction, enabling controllable adjustment of the anisotropic pore structure. This reduces bed pressure drop and improves mass transfer efficiency and adsorption performance in applications such as wastewater treatment.

[0008] A porous adsorbent material based on coal gangue, the technical solution of which is as follows: 1. A porous adsorbent material based on coal gangue, characterized in that: The coal gangue-based porous adsorbent material is made from coal gangue powder through powder forming and heat treatment to create pores, and is in the form of an integral block or component. The coal gangue-based porous adsorbent material has an interconnected porous structure with an overall porosity of 30-60% and a bulk density of 0.4-1.5 g / cm³. The porous structure comprises elongated pores preferentially oriented in a single direction; The porous structure is anisotropic, and the ratio of its average pore diameter in the preferred orientation direction to the average pore diameter in at least one direction perpendicular to that direction is 1.5 to 5. The compressive strength of the material in the preferred orientation direction is 5–20 MPa; The permeability coefficient along the preferred orientation direction is 1.5 to 5 times that of the permeability coefficient perpendicular to that direction.

[0009] In the above or some embodiments, the coal gangue-based porous adsorbent material is composed of the following components by mass percentage: 70-95% coal gangue, 5-30% binder phase and / or sintering aid.

[0010] In the above or some embodiments, the specific surface area of ​​the coal gangue-based porous adsorbent material is 5-50 m² / g, and the saturated adsorption capacity for organic dye aqueous solutions is 20-200 mg / g.

[0011] In the above or some embodiments, the ratio of the average pore size in the preferred orientation direction to the average pore size in at least one direction perpendicular to that direction is 2 to 4, and the ratio of the permeability coefficients is 2 to 4.

[0012] A method for preparing the coal gangue-based porous adsorbent material is also disclosed, comprising the following steps: (1) Raw material preparation: The coal gangue is crushed and ground to obtain coal gangue powder with an average particle size of 1 to 100 μm; (2) Preparation of molding material: A fibrous and / or flake-shaped pore-forming agent with an aspect ratio is added to the coal gangue powder and mixed evenly to obtain a molding material. The mass fraction of the pore-forming agent in the molding material is 5-30 wt%. (3) Unidirectional pressing molding: The molding material obtained in step (2) is placed in a rigid mold and a unidirectional pressure of 20 to 200 MPa is applied in the predetermined direction for pressing. The pressure is held for 5 to 60 seconds to obtain coal gangue green billet. (4) Heat treatment to create pores: The coal gangue green is heat-treated in an air atmosphere or an inert atmosphere, heated to 600-1100°C at a heating rate of 1-10°C / min, and held for 1-4 hours to allow the pore-forming agent to decompose, burn and / or volatilize and be discharged to form pores, thereby obtaining a coal gangue-based porous adsorbent material.

[0013] In the above or some embodiments, the coal gangue in step (1) is further subjected to pre-calcination treatment before grinding. The pre-calcination temperature is 500-900℃, the holding time is 0.5-3h, and the median particle size D50 of the coal gangue powder after grinding is 5-20μm.

[0014] In the above or some embodiments, the fibrous pore-forming agent in step (2) is selected from one or more of cellulose fiber, wood pulp fiber, and polypropylene fiber. The length of the fibrous pore-forming agent is 0.5-5 mm, the diameter is 20-100 μm, the aspect ratio is 10-50, and the mass fraction is 8-20 wt% of the total mass of the molding material.

[0015] In the above or some embodiments, the unidirectional pressing pressure in step (3) is 80-150 MPa and the holding time is 5-60 s; the heat treatment temperature in step (4) is 700-1000 ℃ and the holding time is 1-3 h.

[0016] The application of coal gangue-based porous adsorbent materials in fixed-bed adsorption columns or filtration modules was also disclosed, and the application methods are as follows: The coal gangue-based porous adsorbent material is processed into columnar, block, or plate-shaped components and filled into a fixed bed or filtration device, so that the main flow direction of the wastewater to be treated is parallel to the preferred orientation direction of the coal gangue-based porous adsorbent material, thereby causing the wastewater to flow along the preferred orientation direction of the internal pores of the material, for treating industrial wastewater containing organic pollutants and / or heavy metal ions.

[0017] In the above or some embodiments, the organic pollutant is at least one of methylene blue, Congo red, and rhodamine B, and the heavy metal ions are Cu²⁺, Pb²⁺, Cd²⁺, and Cr. 6 At least one of ⁺.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects: 1) Simplified process and inexpensive raw materials: This invention uses coal gangue powder as the main raw material. Porous adsorbent materials can be prepared through conventional crushing, unidirectional pressing and heat treatment. There is no need for complicated hydrothermal synthesis, multi-step acid-base activation or expensive organic template agents. The process is simple and low-cost, and suitable for industrial scale-up.

[0019] 2) Constructing a controllable anisotropic pore structure: This invention introduces a "unidirectional pressing + oriented fibrous pore-forming agent" design for the first time in a coal gangue-based porous material system. By controlling the pressing direction and the morphology and content of the fibrous pore-forming agent, the oriented arrangement of the pore-forming agent is achieved during the pressing process. After heat treatment, oriented channels are formed mainly along the pressing direction, resulting in significant differences in the average pore size and permeability coefficient of the material in different directions, thus constructing a controllable anisotropic pore structure.

[0020] 3) Balance between pore structure and mechanical properties: By synergistically optimizing the particle size of coal gangue powder, the amount of pore-forming agent added, the pressing pressure and the heat treatment regime, this invention achieves a compressive strength of 5-20 MPa while maintaining a porosity of 30-60% and significant anisotropy. It takes into account the mass transfer performance and structural stability of porous materials, and avoids the problems of insufficient strength of foamed materials or limited mass transfer performance of highly dense materials.

[0021] 4) Improved directional mass transfer and adsorption performance: Since the direction of the main pores inside the material is consistent with the main flow direction of the fluid, the fluid has lower flow resistance and higher permeability coefficient when flowing along the preferred orientation, which is conducive to improving the mass transfer rate of pollutants to the active sites in the pores, thereby improving the adsorption rate and breakthrough capacity. Compared with porous coal gangue materials with random pore structure, it exhibits lower pressure drop and better adsorption efficiency under similar porosity conditions.

[0022] 5) Significant environmental and economic benefits: This invention realizes the high-value utilization of coal gangue, a low-value solid waste. The prepared porous material can be widely used in environmental governance fields such as industrial wastewater treatment. While reducing the volume and utilizing coal gangue as a resource, it improves the overall performance of the wastewater treatment unit and has good environmental and economic benefits. Attached Figure Description

[0023] Figure 1 This is a schematic flowchart of the preparation method of the coal gangue-based porous adsorbent material of the present invention.

[0024] Figure 2 This is a schematic diagram of the pore structure of the longitudinal section of the material of the present invention.

[0025] Figure 3 This is a schematic diagram of the pore structure of the cross-section of the material of the present invention.

[0026] Figure 4 This is a schematic diagram illustrating the application of the material of the present invention in a fixed bed device. Detailed Implementation

[0027] The technical solution provided by the present invention will be described in more detail below with reference to the accompanying drawings. The description of exemplary embodiments is merely illustrative and should not be construed as limiting this disclosure or its application or use in any way. This disclosure can be implemented in many different forms and is not limited to the embodiments described herein. The preparation and performance of the present invention are further illustrated below through embodiments, and the key features and technical effects of the present invention are verified through experimental examples.

[0028] Unless otherwise specified, the following terms shall have the following meanings in this specification and claims: "Pressure direction" refers to the direction in which pressure is applied to the material during the molding process of this invention. In the preparation process of this invention, a unidirectional pressing method is generally used for molding, and the pressing direction is also the preferred orientation direction of the fibrous pore-forming agent in the material.

[0029] "Perpendicular to the pressing direction" refers to a direction that is substantially perpendicular to the pressing direction. When observing the cross-section of a material, the cross-section obtained by cutting along the pressing direction is called the "longitudinal section," and the cross-section obtained by cutting perpendicular to the pressing direction is called the "cross section."

[0030] The pore structure inside the material of the present invention has significant differences in the pressing direction and the direction perpendicular to the pressing direction: long strip-shaped channels extending along the pressing direction can be observed on the longitudinal section of the material, while point-shaped or short-range pores are mainly observed on the cross section. This difference in pore morphology and size in different directions constitutes the anisotropic pore structure of the present invention.

[0031] When the material of the present invention is used as a fixed bed or plate filter component, it is preferable to keep the main flow direction of the fluid to be treated consistent with the pressing direction, so that the fluid preferentially flows along the elongated channels inside the material, thereby reducing flow resistance and improving mass transfer efficiency.

[0032] It should be noted that the functions of each component in the system of this invention are not singular. For example, after heat treatment, coal gangue powder forms a ceramic bond, constituting the main binder phase; the added fibrous or flake materials mainly function as pore-forming agents, while also playing a role in toughening and temporary bonding during the greening stage, and may have a certain fluxing effect in the early stages of sintering. Therefore, the term 'additive' or 'functional additive' in this invention is a collective term based on its ultimate contribution to the material's structure and performance.

[0033] Example 1: Preparation of coal gangue-based anisotropic porous adsorbent materials (1) Raw material preparation Coal gangue from a certain mining area was selected, crushed to a particle size of less than 5 mm, and pre-calcined in a muffle furnace at 700℃ for 2 hours to remove some organic matter and water of crystallization. The pre-calcined coal gangue was then ball-milled for 2 hours to obtain coal gangue powder with a median particle size D50 of approximately 10 μm.

[0034] (2) Preparation of molding material Weigh 80g of coal gangue powder and add 20g of wood pulp fiber (dry basis). The fiber length is 1-3mm, the diameter is about 30-50μm, the aspect ratio is about 20-60, and the mass fraction of the fiber in the molding material is 20wt%. Add an appropriate amount of water and a small amount of organic binder to the mixture and stir with a planetary mixer for 30min to obtain a uniform wet molding material.

[0035] (3) Unidirectional compression molding The above-mentioned forming material is loaded into a cylindrical rigid mold and pressed for 60 seconds with a pressure of 100MPa using a unidirectional press. The pressing direction is defined as the preferred orientation. After demolding, a cylindrical coal gangue green billet with a diameter of 30mm and a height of 50mm is obtained.

[0036] (4) Heat treatment to create holes The green body was placed in a box furnace and heated to 800℃ at a rate of 5℃ / min in air atmosphere. After holding at this temperature for 2 hours, it was cooled to room temperature with the furnace. During the heat treatment process, the wood pulp fibers decomposed and burned out, and their occupied spaces were transformed into pores. Combined with the different compaction states formed during the unidirectional pressing process, the material formed a pore structure with differences in the parallel pressing direction and the perpendicular direction, thus obtaining a coal gangue-based porous adsorbent material.

[0037] (5) Structural and performance testing The overall porosity of the material, determined by mercury indentation, was approximately 45%, and the bulk density was approximately 0.9 g / cm³. By cutting the sample and performing image analysis at different orientations, the average pore size parallel to the pressing direction was found to be approximately 50 μm, the average pore size perpendicular to the pressing direction was approximately 20 μm, and the average pore size ratio was approximately 2.5.

[0038] Steady-state permeability tests showed that, under the same pressure differential, the permeability coefficient along the compression direction was approximately three times that in the vertical direction. Using a universal testing machine with loading applied along the compression direction, the material's compressive strength was measured to be approximately 10 MPa.

[0039] The material was processed into cylinders approximately 50 cm high and 5 cm in diameter, and packed into a vertical fixed bed to treat an initial methylene blue aqueous solution with a mass concentration of 100 mg / L. Under the same bed height and influent flow rate conditions, compared with a comparative porous coal gangue material with an approximately random pore structure, the bed pressure drop of the material in this embodiment was reduced by approximately 30%, and the breakthrough time was prolonged by approximately 20%. The results indicate that the material in this embodiment exhibits significant pore anisotropy in the parallel and perpendicular compression directions, which is beneficial for reducing flow resistance and improving mass transfer and adsorption performance.

[0040] Example 2: Effects of parameter variations on anisotropy and strength Based on Example 1, the amount of fiber added and the pressing pressure were changed to investigate the changes in pore anisotropy and mechanical properties.

[0041] (1) When the fiber mass fraction is reduced to 8wt%, the overall porosity is reduced to about 35%, the average pore size ratio between the parallel pressing direction and the perpendicular direction is reduced to about 1.6, the permeability ratio is about 1.8, the compressive strength of the material is increased to about 15MPa, and the anisotropy still exists but is weakened.

[0042] (2) When the fiber mass fraction is increased to 25wt% and the pressing pressure is kept at 100MPa, the overall porosity increases to about 55%, the average pore size ratio is about 3.0, the permeability ratio is about 4.0, but the compressive strength decreases to about 6MPa.

[0043] (3) When the pressing pressure is increased to 180 MPa and the fiber mass fraction is kept at 20 wt%, the overall porosity drops to about 30%, the average pore size ratio drops to about 1.4, the permeability ratio is about 1.5, and the anisotropy is significantly weakened.

[0044] The results of Example 2 show that the amount of fibrous pore-forming agent and the pressing pressure have a significant impact on the porosity and mechanical properties of the material of the present invention. When the mass fraction of the fibrous pore-forming agent is low, the overall porosity of the material and the number of elongated channels formed along the pressing direction are reduced, but there are still significant differences in the pore morphology observed in the longitudinal and cross sections. The material still has an anisotropic pore structure and relatively high compressive strength, making it suitable for applications with high strength requirements. When the mass fraction of the fibrous pore-forming agent is too high, although the elongated channels in the longitudinal section are more developed and the fluid permeability in the pressing direction is further improved, the compressive strength of the material decreases significantly, which is not conducive to long-term pressure-bearing use.

[0045] Furthermore, when molding under higher pressing pressure, it can be observed that the overall porosity of the material decreases, the width of the elongated channels on the longitudinal section decreases, and the number of pores on the cross section also decreases. This indicates that excessive pressing pressure will compact the pores and weaken the directional pore-forming effect of the fibrous pore-forming agent.

[0046] In summary, by rationally selecting the amount of fibrous pore-forming agent added and the pressing pressure and other process parameters, a balance can be achieved between pore anisotropy, porosity and compressive strength, thereby obtaining coal gangue-based porous materials with both good permeability and mechanical properties.

[0047] Comparative Example 1: Comparison of the effects of spherical pore-forming agent and the method of the present invention This comparative example aims to illustrate that not all pore-forming agents combined with unidirectional pressing can produce a significant anisotropic pore structure in the coal gangue system of this invention. This result demonstrates that even with unidirectional pressing, conventional spherical pore-forming agents alone cannot achieve the permeability anisotropy (ratio ≥ 1.5) defined in claim 1 of this invention, highlighting the crucial role of using fibrous / sheet-like pore-forming agents with specific aspect ratios in solving this technical problem.

[0048] (1) Raw material preparation Same as Example 1.

[0049] (2) Preparation of molding material Weigh 80g of the coal gangue powder obtained in Example 1 and add 20g of polymethyl methacrylate (PMMA) microspheres as a pore-forming agent. The PMMA microspheres have an average particle size of approximately 80μm and a nearly regular spherical shape (length-to-diameter ratio ≈ 1), with a mass fraction of 20wt% in the molding material. Add an equal amount of water and organic binder as in Example 1 and mix thoroughly to obtain the molding material.

[0050] (3) Unidirectional compression molding Unidirectional pressing was performed using the same mold, pressure (100 MPa), and holding time (60 s) as in Example 1 to obtain a cylindrical green body.

[0051] (4) Heat treatment to create holes The heat treatment process was the same as in Example 1 (heating to 800°C in air at a rate of 5°C / min, holding for 2 hours, and then cooling in the furnace). During the heat treatment, the PMMA microspheres were almost completely decomposed and volatilized, forming pores.

[0052] (5) Structural and performance testing The same method as in Example 1 was used for testing. The overall porosity of the obtained material was approximately 43%, and the bulk density was approximately 0.92 g / cm³, similar to that of the material in Example 1. Image analysis results showed that the average pore size of the material did not differ significantly between the parallel and perpendicular compression directions, with a pore size ratio of approximately 1.1. Steady-state permeability experiments showed that the ratio of the permeability coefficient along the compression direction to that perpendicular to the compression direction was approximately 1.1, indicating no significant permeability anisotropy. The compressive strength in the compression direction was approximately 12 MPa.

[0053] The material was loaded into the same fixed-bed apparatus as in Example 1 and treated with methylene blue aqueous solution under the same conditions. Test results showed that its bed pressure drop and breakthrough time were comparable to those of ordinary porous coal gangue material with an approximately random pore structure, and it did not exhibit the performance advantages of significantly reduced bed pressure drop and prolonged breakthrough time shown in Example 1.

[0054] The results of Comparative Example 1 show that, under conditions similar to Example 1, simply replacing the pore-forming agent with a spherical pore-forming agent of similar particle size significantly reduces the differences in pore morphology observed in the longitudinal and cross-sectional sections of the resulting material, even when formed using unidirectional pressing. The distribution of pores in all directions tends to be random, making it difficult to form continuous elongated channels extending along the pressing direction. The overall pore structure of the material is approximately isotropic. Compared to Example 1, the comparative example material shows limited improvement in permeability along the pressing direction under the same porosity conditions, and the pressure drop and adsorption behavior during fixed-bed operation do not show significant advantages. These results indicate that unidirectional pressing alone is insufficient to construct a significant anisotropic pore structure in the system of this invention. It is necessary to introduce a fibrous pore-forming agent with a certain aspect ratio into the raw material system, and to obtain a well-developed continuous pore structure along the pressing direction through the combination of unidirectional pressing and heat treatment, thereby achieving the anisotropic permeability and excellent adsorption effect of this invention.

[0055] Example 3: Application in Heavy Metal Wastewater Treatment The coal gangue-based porous adsorbent material prepared in Example 1 was processed into plate-shaped components (100 mm long, 50 mm wide, and 10 mm thick), with the thickness direction being the pressing direction. Multiple plate-shaped components were arranged in parallel and filled into a plate filter, allowing wastewater to flow in from one side of the plate and from the thickness direction to the other side.

[0056] Simulated electroplating wastewater containing Pb²⁺ and Cd²⁺ was used as the treatment target, with a total metal ion concentration of approximately 50 mg / L. Under certain influent flow conditions, the results showed that the concentrations of Pb²⁺ and Cd²⁺ in the effluent could be reduced to below 0.5 mg / L, meeting relevant discharge standards. Furthermore, under the same treatment volume and component arrangement, the pressure drop between the inlet and outlet of the plate filter constructed with the material in this embodiment was significantly lower than that using porous coal gangue granular packing with an approximately random pore structure. This verifies the applicability of the material of this invention in heavy metal wastewater treatment and the beneficial influence of its anisotropic pore structure on the flow and mass transfer processes.

[0057] Those skilled in the art will understand that, without departing from the essential spirit of the present invention, the types of raw materials, powder particle size, type and morphology of fiber pore-forming agent (such as length, diameter, aspect ratio), pressing pressure and heat treatment regime in the above embodiments can be adjusted to obtain materials with different porosities, degrees of anisotropy and mechanical properties. These modifications and adjustments should all be considered to fall within the protection scope of the present invention.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. However, these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A porous adsorbent material based on coal gangue, characterized in that: The coal gangue-based porous adsorbent material is made from coal gangue powder through powder forming and heat treatment to create pores, and is in the form of an integral block or component. The coal gangue-based porous adsorbent material has an interconnected porous structure with an overall porosity of 30-60% and a bulk density of 0.4-1.5 g / cm³. The porous structure comprises elongated pores preferentially oriented in a single direction; The porous structure is anisotropic, and the ratio of its average pore diameter in the preferred orientation direction to the average pore diameter in at least one direction perpendicular to that direction is 1.5 to 5. The compressive strength of the material in the preferred orientation direction is 5–20 MPa; The permeability coefficient along the preferred orientation direction is 1.5 to 5 times that of the permeability coefficient perpendicular to that direction.

2. The coal gangue-based porous adsorbent material according to claim 1, characterized in that, Based on the total dry weight of raw materials, it is prepared from the following components: 70-95% coal gangue powder, and 5-30% of one or more additives selected from binders, sintering aids, and pore-forming agents.

3. The coal gangue-based porous adsorbent material according to claim 1 or 2, characterized in that, The specific surface area of ​​the coal gangue-based porous adsorbent material is 5–50 m² / g, and the saturated adsorption capacity for organic dye aqueous solutions is 20–200 mg / g.

4. The coal gangue-based porous adsorbent material according to any one of claims 1 to 3, characterized in that, The ratio of the average pore size in the preferred orientation direction to the average pore size in at least one direction perpendicular to that direction is 2 to 4, and the ratio of the permeability coefficients is 2 to 4.

5. A method for preparing a coal gangue-based porous adsorbent material as described in any one of claims 1 to 4, characterized in that, Includes the following steps: (1) Raw material preparation: The coal gangue is crushed and ground to obtain coal gangue powder with an average particle size of 1 to 100 μm; (2) Preparation of molding material: A fibrous and / or flake-shaped pore-forming agent with an aspect ratio is added to the coal gangue powder and mixed evenly to obtain a molding material. The mass fraction of the pore-forming agent in the molding material is 5-30 wt%. (3) Unidirectional pressing molding: The molding material obtained in step (2) is placed in a rigid mold and a unidirectional pressure of 20 to 200 MPa is applied in the predetermined direction for pressing. The pressure is held for 5 to 60 seconds to obtain coal gangue green billet. (4) Heat treatment to create pores: The coal gangue green is heat-treated in an air atmosphere or an inert atmosphere, heated to 600-1100°C at a heating rate of 1-10°C / min, and held for 1-4 hours to allow the pore-forming agent to decompose, burn and / or volatilize and be discharged to form pores, thereby obtaining a coal gangue-based porous adsorbent material.

6. The preparation method according to claim 5, characterized in that, The coal gangue in step (1) also includes a pre-calcination treatment before grinding. The pre-calcination temperature is 500-900℃, the holding time is 0.5-3h, and the median particle size D50 of the coal gangue powder after grinding is 5-20μm.

7. The preparation method according to claim 5 or 6, characterized in that, The fibrous pore-forming agent in step (2) is selected from one or more of cellulose fiber, wood pulp fiber, and polypropylene fiber. The length of the fibrous pore-forming agent is 0.5-5 mm, the diameter is 20-100 μm, the aspect ratio is 10-50, and the mass fraction is 8-20 wt% of the total mass of the molding material.

8. The preparation method according to any one of claims 5 to 7, characterized in that, The unidirectional pressing pressure in step (3) is 80-150 MPa and the holding time is 5-60 s; the heat treatment temperature in step (4) is 700-1000 ℃ and the holding time is 1-3 h.

9. The application of the coal gangue-based porous adsorbent material according to any one of claims 1 to 4 in the preparation of a fixed-bed adsorption column or filtration module for wastewater treatment, characterized in that, The coal gangue-based porous adsorbent material is processed into columnar, block, or plate-shaped components and filled into a fixed bed or filtration device, so that the main flow direction of the wastewater to be treated is parallel to the preferred orientation direction of the coal gangue-based porous adsorbent material, thereby causing the wastewater to flow along the preferred orientation direction of the internal pores of the material, for treating industrial wastewater containing organic pollutants and / or heavy metal ions.

10. The application according to claim 9, characterized in that, The organic pollutant is at least one of methylene blue, Congo red, and rhodamine B, and the heavy metal ions are Cu²⁺, Pb²⁺, Cd²⁺, and Cr. 6 At least one of ⁺.

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