A red mud-based biochar, a preparation method thereof and application thereof in improving dewatering performance of red mud

Abstract

The present application relates to the technical field of solid waste resource utilization, and particularly relates to a red mud-based biochar, a preparation method thereof and application of the red mud-based biochar in improving the dewatering performance of red mud.The present application adopts a 'composite activator activation + low-temperature pyrolysis' process, does not need to add a large amount of chemical modification reagent, and simultaneously utilizes the synergistic effect of red mud and biomass compared with the existing high-temperature pyrolysis process at 600-1000 DEG C, so that the biochar has both porous structure and magnetism, and the problem of existing biochar pollution and insufficient activity is solved.Meanwhile, the present application combines red mud (waste) and agricultural waste biomass to prepare biochar, which is used for dewatering of red mud, realizes 'treating mud with mud', the biochar can be recycled and reused through magnetism, greatly reduces the treatment cost, promotes the resource utilization and reduction of red mud, and conforms to the green and environmentally-friendly development concept.

Description

Technical Field

[0001] This invention relates to the field of solid waste resource utilization technology, and in particular to a red mud-based biochar, its preparation method, and its application in improving the dewatering performance of red mud. Background Technology

[0002] The information disclosed in the background section of this invention is intended only to enhance the understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] Red mud is an industrial solid waste generated during alumina production. It is characterized by high alkalinity, high water content, fine particles, large specific surface area, and dense pore structure, making dewatering difficult. Existing red mud dewatering processes mostly employ mechanical pressure filtration combined with inorganic / polymer filter aids for conditioning. However, these processes suffer from problems such as filter cake compression and deformation clogging filtration channels, low dewatering efficiency, high filter aid costs, and the potential for secondary pollution.

[0004] In existing technologies, red mud can be combined with biomass to prepare biochar, which is mostly used for wastewater adsorption or soil remediation. However, existing processes have many drawbacks, such as high pyrolysis temperature; the use of chemical reagents for modification, which generates a large amount of wastewater; and unreasonable raw material ratios, resulting in poor biochar activity. Summary of the Invention

[0005] In view of this, the present invention provides a red mud-based biochar, its preparation method, and its application in improving the dewatering performance of red mud. The present invention solves the defects of low red mud dewatering efficiency, secondary pollution, and the complex preparation process and limited application of red mud-based biochar, realizing the integration of red mud resource utilization and dewatering treatment, reducing treatment costs, and improving dewatering effect.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: In a first aspect, the present invention provides a method for preparing red mud-based biochar, comprising the following steps: Mix red mud powder and biomass powder evenly, add composite activator, and stir to obtain a mixture; The mixture is pyrolyzed under an inert atmosphere to obtain red mud-based biochar.

[0007] Furthermore, the biomass is selected from agricultural waste biomass, preferably at least one of corn stalks, rice husks, and sawdust; more preferably corn stalks.

[0008] Furthermore, the method also includes a pretreatment step, specifically: washing the red mud until the pH is 8.5-9.5, drying, pulverizing, and sieving to obtain red mud powder; pulverizing and drying the biomass to obtain biomass powder.

[0009] Furthermore, the red mud is dried to constant weight at 105-110 ℃, pulverized, and passed through a 100-120 mesh sieve; the biomass is pulverized to 20-40 mesh and dried to constant weight at 80-85 ℃.

[0010] Furthermore, the mass ratio of red mud powder to biomass powder is 0.4-0.6:1.

[0011] Furthermore, the composite activator is Fe2O3 and K2CO3, with a mass ratio of Fe2O3 to K2CO3 of 5-7:1.

[0012] Furthermore, the amount of composite activator added is 3-8% of the total mass of red mud and biomass.

[0013] Furthermore, the inert atmosphere is nitrogen or argon.

[0014] Furthermore, the pyrolysis temperature is 350-450 ℃, the heating rate is 5-8 ℃ / min, and the pyrolysis holding time is 2-3h.

[0015] Furthermore, the pyrolysis process also includes cooling, product crushing, and sieving steps. Specifically, after pyrolysis, the product is naturally cooled to room temperature, crushed, and then sieved through an 80-100 mesh sieve.

[0016] Secondly, the present invention provides red mud-based biochar prepared by the above preparation method.

[0017] Furthermore, the specific surface area of ​​red mud-based biochar is 180-250 m². 2 / g, porosity 45-55%, saturation magnetization 8-15 emu·g -1 .

[0018] Thirdly, the present invention provides the application of the red mud-based biochar described in the second aspect in improving the dewatering performance of red mud.

[0019] Fourthly, the present invention provides a method for dewatering red mud, comprising the following steps: The red mud-based biochar described in the second aspect is added to the red mud slurry, stirred, and mechanically filtered to obtain a dehydrated filter cake.

[0020] Furthermore, the dehydration temperature of red mud is 20-35 ℃.

[0021] Furthermore, the red mud slurry has a water content of 65-75%.

[0022] Furthermore, the amount of red mud-based biochar added is 2-5% of the dry weight of the red mud.

[0023] Furthermore, the stirring time is 15-25 minutes.

[0024] Furthermore, the filtration pressure is 1.0-1.5 MPa, and the filtration time is 20-30 min.

[0025] Furthermore, the red mud-based biochar after pressure filtration can be recovered by magnetic adsorption and reused after drying at 80-100 ℃.

[0026] Compared with the prior art, the present invention has achieved the following beneficial effects: This invention employs a "composite activator activation + low-temperature pyrolysis" process, eliminating the need for large amounts of chemical modifying reagents. Compared to existing high-temperature pyrolysis processes at 600-1000℃, this invention utilizes the synergistic effect of red mud and biomass to create biochar with both porous structure and magnetic properties, solving the problems of high pollution and insufficient activity in existing biochar preparation methods. This invention achieves "treating mud with mud," combining red mud (waste) with agricultural waste biomass to prepare biochar for red mud dehydration. Simultaneously, the biochar can be magnetically recycled and reused, significantly reducing processing costs and promoting the resource-based and reduced-volume utilization of red mud, aligning with the concept of green and environmentally friendly development. The red mud-based biochar preparation process of this invention requires no complex equipment; low-temperature pyrolysis and room-temperature conditioning are simple to operate; raw materials are widely available and inexpensive; it can be directly integrated into existing red mud treatment production lines, facilitating large-scale industrial application. Detailed Implementation

[0027] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0028] This invention provides a method for preparing red mud-based biochar, comprising the following steps: Mix red mud powder and biomass powder evenly, add composite activator, and stir to obtain a mixture; The mixture is pyrolyzed under an inert atmosphere to obtain red mud-based biochar.

[0029] Furthermore, the biomass is selected from agricultural waste biomass, preferably at least one of corn stalks, rice husks, and sawdust; more preferably corn stalks. This invention uses agricultural waste biomass and red mud to prepare biochar, realizing the comprehensive utilization of waste, promoting the resource-based and reduced-volume utilization of red mud, and conforming to the concept of green and environmentally friendly development.

[0030] Furthermore, the method also includes a pretreatment step, specifically: washing the red mud to a pH of 8.5-9.5, drying, pulverizing, and sieving to obtain red mud powder; pulverizing and drying the biomass to obtain biomass powder. The pH of the red mud washing can be any value between 8.5 and 9.5, such as 8.6, 9.0, or 9.2. Washing the red mud to a pH of 8.5-9.5 can remove surface-soluble salts, such as sodium salts, while avoiding the adverse effects of high alkalinity on the pore structure of the subsequently prepared biochar.

[0031] Furthermore, the red mud is dried to constant weight at 105-110 ℃, pulverized, and then passed through a 100-120 mesh sieve; the biomass is pulverized to 20-40 mesh and dried to constant weight at 80-85 ℃. Passing the pulverized red mud through a 100-120 mesh sieve ensures uniform particle size, avoiding both excessively fine particles that would agglomerate and clog pores during pyrolysis, and excessively coarse particles that would result in insufficient contact between the activator and the raw material, and inadequate pore development in the biochar. Pulverizing the biomass to 20-40 mesh ensures uniform heating during pyrolysis, while also guaranteeing thorough mixing with the red mud and activator, avoiding uneven mixing due to excessively large mesh sizes, and excessively small mesh sizes that would lead to rapid weight loss during pyrolysis and collapse of the pore structure. Strict control of the mesh sizes of the red mud and biomass ensures the stability of the porous structure and filtration performance of the biochar.

[0032] Furthermore, the mass ratio of red mud powder to biomass powder is 0.4-0.6:1. This ratio can be any value between 0.4 and 0.6:1, such as 0.45:1, 0.5:1, or 0.55:1. If the red mud content is too low, the biochar skeleton after pyrolysis will lack sufficient strength and have poor filter support; if the content is too high, it will inhibit the development of pores in the biomass pyrolysis, reducing the specific surface area and activity.

[0033] Furthermore, the composite activator is Fe2O3 and K2CO3; the mass ratio of Fe2O3 to K2CO3 is 5-7:1. The mass ratio of Fe2O3 to K2CO3 can be any value between 5-7:1, such as 5.5:1, 6:1, 6.5:1, etc. In the composite activator, Fe2O3 imparts magnetism to the biochar and catalyzes pyrolysis, while K2CO3 is used for chemical activation and pore formation. The two work synergistically to achieve a balance between high specific surface area and recyclability.

[0034] Furthermore, the amount of composite activator added is 3-8% of the total mass of red mud and biomass. The amount of composite activator added can be any value between 3-8% of the total mass of red mud and biomass, such as 4%, 5%, 6%, 7%, etc.

[0035] Furthermore, the inert atmosphere is either nitrogen or argon. Using an inert atmosphere prevents the oxidative combustion of biomass and the activator. O2 in the air reacts with the biomass carbon skeleton, Fe2O3, and K2CO3 during high-temperature pyrolysis, leading to raw material ablation, a significant decrease in biochar yield, and damage to the pore structure and magnetic components. The inert atmosphere provides a reducing environment for Fe2O3 to be reduced to Fe3O4 / α-Fe, preventing further oxidation and loss of magnetism, thus ensuring the magnetic recovery of biochar. The inert atmosphere also inhibits secondary cracking and polymerization of byproducts such as tar, preventing biochar pore blockage and maintaining its specific surface area and filtration performance. Excluding air prevents the accumulation of combustible gases (such as CO and H2) during pyrolysis, thus avoiding the risk of explosion and improving process safety.

[0036] Furthermore, the pyrolysis temperature is 350-450 ℃, the heating rate is 5-8 ℃ / min, and the pyrolysis holding time is 2-3 h. The pyrolysis temperature can be any value between 350-450 ℃, such as 360 ℃, 370 ℃, 380 ℃, 390 ℃, 400 ℃, 410 ℃, 420 ℃, 430 ℃, 440 ℃, etc. The heating rate can be any value between 5-8 ℃ / min, such as 6 ℃ / min, 7 ℃ / min, etc. The pyrolysis holding time can be any value between 2-3 h, such as 2.1 h, 2.2 h, 2.3 h, 2.4 h, 2.5 h, 2.6 h, 2.7 h, 2.8 h, 2.9 h. The pyrolysis temperature, heating rate, and holding time together determine the structure and properties of the biochar. The optimal temperature range is 350-450 ℃. Too low a temperature results in insufficient pyrolysis and reduction, while too high a temperature leads to carbon skeleton collapse and pore destruction. A heating rate of 5-8 ℃ / min ensures uniform heating of the raw materials, avoiding tar residue or localized overheating. A holding time of 2-3 hours ensures a complete reaction while preventing excessive ablation. The pyrolysis temperature of this invention is lower than existing high-temperature pyrolysis processes. During pyrolysis, volatile substances produced by biomass pyrolysis further activate the red mud, while Fe2O3 in the red mud is reduced to magnetic Fe3O4, imparting magnetism to the biochar and facilitating subsequent recycling and reuse. Compared to high-temperature pyrolysis at 600 ℃, the low-temperature process of this invention retains the well-developed pore structure and stable magnetism, resulting in more stable filtration performance, better economic efficiency, and greater industrial application value.

[0037] Furthermore, the pyrolysis process also includes cooling, product crushing, and sieving steps. Specifically, after pyrolysis, the product is naturally cooled to room temperature, crushed, and then sieved through an 80-100 mesh sieve.

[0038] This invention provides red mud-based biochar prepared by the above-described preparation method.

[0039] Furthermore, the specific surface area of ​​red mud-based biochar is 180-250 m².2 / g, porosity 45-55%, saturation magnetization 8-15 emu·g -1 .

[0040] This invention provides the application of the above-mentioned red mud-based biochar in improving the dewatering performance of red mud.

[0041] This invention employs a "composite activator activation + low-temperature pyrolysis" process, eliminating the need for large amounts of chemical modifying agents. Simultaneously, it utilizes the synergistic effect of red mud and biomass to give the biochar both a porous structure and magnetic properties, solving the problems of high pollution and insufficient activity in existing biochar preparation methods. The dehydration effect is significantly superior to existing filter aids. This invention uses red mud and waste agricultural biomass as raw materials to prepare biochar for red mud dehydration, achieving "treating mud with mud." Furthermore, the biochar can be magnetically recovered and reused, significantly reducing processing costs and promoting the resource-based and reduced-volume utilization of red mud, aligning with the concept of green and environmentally friendly development.

[0042] The present invention also provides a method for dehydrating red mud, comprising the following steps: The above-mentioned red mud-based biochar was added to the red mud slurry, stirred, and mechanically filtered to obtain a dehydrated filter cake.

[0043] Furthermore, the red mud dehydration temperature is 20-35 ℃. Red mud dehydration using the red mud-based biochar prepared according to this invention can be carried out at 20-35 ℃, which is considered ambient temperature operation, requiring no additional heating and reducing energy consumption.

[0044] Furthermore, the water content of the red mud slurry is 65-75%. The water content of the red mud slurry can be any value between 65-75%, such as 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, etc., which is suitable for the dewatering treatment of red mud slurry with high water content.

[0045] Furthermore, the amount of red mud-based biochar added is 8-15% of the dry weight of the red mud. The amount of red mud-based biochar added can be any value between 8-15% of the dry weight of the red mud, such as 10%, 11%, 13%, etc.

[0046] Furthermore, the stirring time is 15-25 minutes.

[0047] Furthermore, the filtration pressure is 1.0-1.5 MPa, and the filtration time is 20-30 min.

[0048] Furthermore, the red mud-based biochar after pressure filtration can be recovered by magnetic adsorption and reused after drying at 80-100 ℃. The red mud-based biochar prepared by this invention can still maintain good filtration aid effect (filter cake moisture content ≤30%) after being reused 3-5 times.

[0049] This invention realizes "treating mud with mud", combining red mud (waste) with agricultural waste biomass to prepare biochar, which is used for the dehydration of red mud itself. At the same time, the biochar can be magnetically recycled and reused, which greatly reduces the processing cost and promotes the resource utilization and reduction of red mud, which is in line with the concept of green and environmentally friendly development.

[0050] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0051] Example 1 A method for preparing red mud-based biochar and its application in improving the dewatering performance of red mud are described below: 1. Raw material pretreatment: Bayer red mud was selected, washed with deionized water until pH 9.0, dried in an oven at 105 ℃ to constant weight, pulverized and passed through a 100-mesh sieve to obtain red mud powder; corn stalks were selected, impurities were removed and pulverized to 30 mesh, dried in an oven at 80 ℃ to constant weight to obtain biomass powder.

[0052] 2. Composite activation: Mix red mud powder and corn stalk powder evenly at a mass ratio of 5:10, add composite activator (Fe2O3 and K2CO3 mixed at a mass ratio of 6:1), the amount added is 5% of the total mass of red mud and corn stalk, and stir until it becomes a paste.

[0053] 3. Low-temperature pyrolysis: The activated mixture was placed in a closed pyrolysis furnace, nitrogen was introduced to purge air, and the heating rate was controlled at 6 ℃ / min, raising the temperature to 400 ℃ and holding it at that temperature for 2.5 h. After naturally cooling to room temperature, it was pulverized through an 80-mesh sieve to remove impurities, yielding red mud-based biochar. Testing showed that the specific surface area of ​​this biochar was 220 m². 2 / g, porosity 50%, saturation magnetization 12 emu·g -1 .

[0054] 4. Application of Red Mud Dehydration: Take 1000 g of red mud slurry with a moisture content of 70% (300 g dry weight), place it in a stirring device, and adjust the temperature to 30 ℃; add 16 g of red mud-based biochar (12% of the dry weight of the red mud), and stir for 20 min; subject the conditioned red mud slurry to mechanical filtration, controlling the filtration pressure at 1.2 MPa and the filtration time at 25 min, to obtain a filter cake; the filter cake moisture content was found to be 27.5%, and the filtration rate was 1.8 mL / (cm³). 2 ·min).

[0055] 5. Biochar recovery and reuse: After pressure filtration, red mud-based biochar is recovered by magnetic adsorption, dried at 90 ℃ and reused. After being reused 5 times, the moisture content of the filter cake is 29.8%, and it still maintains a good filtration aid effect.

[0056] Example 2 A method for preparing red mud-based biochar and its application in improving the dewatering performance of red mud are described below: 1. Raw material pretreatment: Bayer red mud was selected, washed with deionized water until pH 8.5, dried in an oven at 110 ℃ to constant weight, pulverized and passed through a 120-mesh sieve to obtain red mud powder; rice husks were selected, impurities were removed and pulverized to 20 mesh, dried in an oven at 85 ℃ to constant weight to obtain biomass powder.

[0057] 2. Composite activation: Mix red mud powder and rice husk powder evenly at a mass ratio of 4:10, add composite activator (Fe2O3 and K2CO3 mixed at a mass ratio of 5:1), the amount added is 3% of the total mass of red mud and rice husk, and stir until it becomes a paste.

[0058] 3. Low-temperature pyrolysis: The activated mixture was placed in a closed pyrolysis furnace, argon gas was introduced to purge air, and the heating rate was controlled at 5 ℃ / min, raising the temperature to 350 ℃ and holding it at that temperature for 3 h. After naturally cooling to room temperature, the mixture was pulverized through a 100-mesh sieve to remove impurities, yielding red mud-based biochar. Testing showed that the specific surface area of ​​this biochar was 180 m². 2 / g, porosity 45%, saturation magnetization 8 emu·g -1 .

[0059] 4. Red mud dewatering application: Take 1000 g of red mud slurry with a moisture content of 65% (350 g dry weight), place it in a stirring device, and adjust the temperature to 25 ℃; add 28 g of red mud-based biochar (8% of the dry weight of the red mud), and stir for 15 min; subject the conditioned red mud slurry to mechanical filtration, controlling the filtration pressure at 1.0 MPa and the filtration time at 20 min, to obtain a filter cake; the filter cake moisture content was found to be 28.8%, and the filtration rate was 1.6 mL / (cm³). 2 ·min).

[0060] Example 3 A method for preparing red mud-based biochar and its application in improving the dewatering performance of red mud are described below: 1. Raw material pretreatment: Bayer red mud was selected, washed with deionized water until pH 9.5, dried in an oven at 108 ℃ to constant weight, pulverized and passed through a 110-mesh sieve to obtain red mud powder; sawdust was selected, impurities were removed and pulverized to 40 mesh, dried in an oven at 82 ℃ to constant weight to obtain biomass powder.

[0061] 2. Composite activation: Mix red mud powder and sawdust powder evenly at a mass ratio of 6:10, add composite activator (Fe2O3 and K2CO3 mixed at a mass ratio of 7:1), the amount added is 8% of the total mass of red mud and sawdust, and stir until it becomes a paste.

[0062] 3. Low-temperature pyrolysis: The activated mixture was placed in a closed pyrolysis furnace, nitrogen was introduced to purge air, and the heating rate was controlled at 8 ℃ / min, raising the temperature to 450 ℃ and holding it at that temperature for 2 h. After naturally cooling to room temperature, the mixture was pulverized through a 90-mesh sieve to remove impurities, yielding red mud-based biochar. Testing showed that the specific surface area of ​​this biochar was 250 m². 2 / g, porosity 55%, saturation magnetization 15 emu·g -1 .

[0063] 4. Application of Red Mud Dehydration: Take 1000 g of red mud slurry with a moisture content of 75% (250 g dry weight), place it in a stirring device, and adjust the temperature to 35 ℃; add 37.5 g of red mud-based biochar (15% of the dry weight of the red mud), and stir for 25 min; subject the conditioned red mud slurry to mechanical filtration, controlling the filtration pressure at 1.5 MPa and the filtration time at 30 min, to obtain a filter cake; the filter cake moisture content was found to be 26.2%, and the filtration rate was 2.0 mL / (cm³). 2 ·min).

[0064] Comparative Example 1 Dehydration is performed using PAC (polyaluminum chloride) filter aid instead of red mud-based biochar.

[0065] 1000 g of red mud slurry with a moisture content of 70% (300 g dry basis) was placed in a stirring device and the temperature was adjusted to 30 ℃. 27 g of PAC (8% of the dry red mud mass) was added and stirred for 20 min. The conditioned red mud slurry was then mechanically filtered, with a filtration pressure of 1.2 MPa and a filtration time of 25 min, yielding a filter cake. The filter cake showed a moisture content of 33.5% and a filtration rate of 1.5 mL / (cm³). 2 ·min).

[0066] Comparative Example 2 No red mud-based biochar used 1000 g of red mud slurry with a moisture content of 70% (300 g dry weight) was placed in a stirring device and the temperature was adjusted to 30 ℃. The red mud slurry was mechanically filtered, with the filtration pressure controlled at 1.2 MPa and the filtration time at 25 min, to obtain a filter cake. The filter cake moisture content was found to be 42%, and the filtration rate was 1.3 mL / (cm). 2 ·min).

[0067] Comparative Example 3 A method for preparing red mud-based biochar and its application in improving the dewatering performance of red mud are described below: 1. Raw material pretreatment: Bayer red mud was selected, washed with deionized water until pH 9.0, dried in an oven at 105 ℃ to constant weight, pulverized and passed through a 100-mesh sieve to obtain red mud powder; corn stalks were selected, impurities were removed and pulverized to 30 mesh, dried in an oven at 80 ℃ to constant weight to obtain biomass powder.

[0068] 2. Compounding: Mix red mud powder and corn stalk powder at a mass ratio of 5:10 to obtain a mixture.

[0069] 3. Low-temperature pyrolysis: The mixture is placed in a closed pyrolysis furnace, nitrogen is introduced to remove air, the heating rate is controlled at 6℃ / min, the temperature is raised to 600℃, and the pyrolysis is maintained at this temperature for 2.5 h; after natural cooling to room temperature, it is crushed and passed through an 80-mesh sieve to remove impurities, and red mud-based biochar is obtained.

[0070] 4. Red mud dewatering application: Take 1000 g of red mud slurry with a moisture content of 70% (300 g dry basis) and place it in a stirring device, adjusting the temperature to 30 ℃; add 27 g of red mud-based biochar (8% of the dry basis of the red mud) and stir for 20 min; mechanically filter the conditioned red mud slurry, controlling the filtration pressure at 1.2 MPa and the filtration time at 25 min to obtain a filter cake; the filter cake moisture content was found to be 31.2%, and the filtration rate was 1.6 mL / (cm³). 2 ·min).

[0071] Comparative Example 4 Compared with Example 1, the difference is that the pyrolysis temperature is 300 °C, and the rest is the same as Example 1.

[0072] The filter cake moisture content was found to be 34.6%, and the filtration rate was 1.4 mL / (cm²). 2 (min). After pressure filtration, biochar was recovered by magnetic adsorption. After drying at 90 ℃, it was reused 5 times. The moisture content of the filter cake increased to 38.2%, and the filtration aid effect decreased significantly.

[0073] Comparative Example 5 Compared with Example 1, the difference is that the pyrolysis temperature is 500 °C, and the rest is the same as Example 1.

[0074] The filter cake moisture content was found to be 30.3%, and the filtration rate was 1.6 mL / (cm²). 2 After pressure filtration, biochar was recovered by magnetic adsorption. After drying at 90 °C, it was reused 5 times. The moisture content of the filter cake increased to 32.1%, and the filtration rate decreased to 1.5 mL / (cm³). 2 (min), the filtration effect is somewhat reduced.

[0075] Comparative Example 6 Compared with Example 1, the difference is that potassium carbonate was not used as the composite activator, otherwise it is the same as Example 1.

[0076] The filter cake moisture content was found to be 30.8%, and the filtration rate was 1.5 mL / (cm). 2 After pressure filtration, biochar was recovered by magnetic adsorption. After drying at 90 °C, it was reused five times. The moisture content of the filter cake increased to 33.5%, and the filtration rate decreased to 1.4 mL / (cm³). 2 The filtration effect (min) was significantly worse than that of Example 1.

[0077] Comparative Example 7 Compared with Example 1, the difference is that iron oxide was not used in the composite activator, otherwise it is the same as Example 1.

[0078] The filter cake moisture content was found to be 29.3%, and the filtration rate was 1.5 mL / (cm²). 2 (min). After pressure filtration, an attempt was made to recover the biochar by adsorption with a magnet, but magnetic recovery could not be achieved due to the lack of magnetism.

[0079] Comparative Example 8 Compared with Example 1, the difference is that no composite activator was added, otherwise it is the same as Example 1.

[0080] The filter cake moisture content was found to be 32.5%, and the filtration rate was 1.4 mL / (cm²). 2 (min). After pressure filtration, an attempt was made to recover the biochar by adsorption with a magnet, but magnetic recovery could not be achieved due to the lack of magnetism.

[0081] Comparative Example 9 Compared with Example 1, the only difference is that the heating rate is 2 °C / min.

[0082] The filter cake moisture content was found to be 30.1%, and the filtration rate was 1.5 mL / (cm²). 2 After pressure filtration, biochar was recovered by magnetic adsorption. After drying at 90 °C, it was reused five times. The moisture content of the filter cake increased to 32.8%, and the filtration rate decreased to 1.4 mL / (cm³). 2 (min), and the pyrolysis cycle is extended.

[0083] Comparative Example 10 Compared with Example 1, the only difference is that the heating rate is 10 °C / min.

[0084] The filter cake moisture content was found to be 30.5%, and the filtration rate was 1.5 mL / (cm²). 2 After pressure filtration, biochar was recovered by magnetic adsorption. After drying at 90 °C, it was reused five times. The moisture content of the filter cake increased to 33.2%, and the filtration rate decreased to 1.4 mL / (cm³). 2 Furthermore, localized overheating leads to the breakage of some biochar, resulting in a decrease in recycling efficiency.

[0085] Comparative Example 11 Compared with Example 1, the only difference is that the mass ratio of Fe2O3 to K2CO3 in the composite activator is 8:1.

[0086] The filter cake moisture content was found to be 31.0%, and the filtration rate was 1.45 mL / (cm²). 2 After pressure filtration, biochar was recovered by magnetic adsorption. After drying at 90 °C, it was reused 5 times. The moisture content of the filter cake increased to 34.0%, and the filtration rate decreased to 1.3 mL / (cm³). 2 (min) Due to insufficient K2CO3 activation, the filter aid performance decreased significantly.

[0087] The dehydration results of Examples 1 and Comparative Examples 1-11 are shown in Table 1.

[0088] Table 1. Dehydration results of Example 1 and Comparative Examples 1-11

[0089] As shown in Table 1, the red mud-based biochar prepared in Example 1 of this invention exhibits significantly better dehydration performance than the comparative examples. Comparative Example 1, using PAC filter aid, failed to construct a rigid porous framework, resulting in easily compressed and deformed filter cakes and secondary pollution. Comparative Example 2, without any filter aid, showed extremely poor dehydration performance of the red mud slurry, with a filter cake moisture content as high as 42%. Comparative Example 3, with an excessively high pyrolysis temperature (600℃) and no composite activator, experienced carbon framework collapse and pore shrinkage, resulting in poor dehydration. Comparative Example 4, with an excessively low pyrolysis temperature (300℃), resulted in insufficient pyrolysis, poor pore development, and weak magnetism. Comparative Example 5, with an excessively high pyrolysis temperature (500℃), experienced slight carbon framework collapse, leading to decreased reusability. Comparative Example 6, lacking K2CO3, lacked chemical activation for pore formation, resulting in a low specific surface area. Comparative Example 7, without Fe2O3, resulted in non-magnetic biochar that could not be magnetically recovered. Comparative Example 8, without any activator, exhibited extremely poor porosity, lacked magnetism, and its performance was close to that of untreated red mud. In Comparative Example 9, the heating rate was too slow (2 °C / min), causing tar to clog the pores. In Comparative Example 10, the heating rate was too fast (10 °C / min), resulting in uneven heating, carbon skeleton breakage, and low recovery efficiency. In Comparative Example 11, the Fe₂O₃ to K₂CO₃ mass ratio (8:1) was unbalanced, with insufficient K₂CO₃, weakening the pore-forming effect and resulting in low porosity. The above comparative examples deviated from the optimized range of this invention in terms of pyrolysis temperature, heating rate, activator composition, and dosage, leading to low porosity, small specific surface area, poor magnetic properties, or unstable structure in the biochar, thus resulting in dehydration performance inferior to that of this invention.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing red mud-based biochar, characterized in that, Includes the following steps: Red mud powder and biomass powder are mixed evenly, and a composite activator is added and stirred to obtain a mixture; the mass ratio of red mud powder to biomass powder is 0.4-0.6:1; the amount of composite activator added is 3-8% of the total mass of red mud and biomass. The mixture is pyrolyzed under an inert atmosphere to obtain red mud-based biochar. The composite activator is Fe2O3 and K2CO3; The pyrolysis temperature is 350-450 ℃.

2. The preparation method according to claim 1, characterized in that, The biomass is selected from agricultural waste biomass.

3. The preparation method according to claim 1, characterized in that, The method also includes a pretreatment step, specifically: washing the red mud until the pH is 8.5-9.5, drying, pulverizing, and sieving to obtain red mud powder; pulverizing and drying the biomass to obtain biomass powder.

4. The preparation method according to claim 1, characterized in that, The mass ratio of Fe2O3 to K2CO3 is 5-7:

1.

5. The preparation method according to claim 1, characterized in that, The inert atmosphere is nitrogen or argon.

6. The preparation method according to claim 1, characterized in that, The pyrolysis heating rate is 5-8 ℃ / min, and the pyrolysis holding time is 2-3 h.

7. Red mud-based biochar prepared by the preparation method according to any one of claims 1-6.

8. The application of the red mud-based biochar as described in claim 7 in improving the dewatering performance of red mud.

9. A method for dewatering red mud, characterized in that, Includes the following steps: The red mud-based biochar of claim 7 is added to the red mud slurry, stirred, and mechanically filtered to obtain a dehydrated filter cake.

10. The method as described in claim 9, characterized in that, The dehydration temperature of red mud is 20-35 ℃; or, the water content of red mud slurry is 65-75%. Alternatively, the amount of red mud-based biochar added is 8-15% of the dry weight of the red mud; Alternatively, stir for 15-25 minutes; Alternatively, the filtration pressure is 1.0-1.5 MPa, and the filtration time is 20-30 min; Alternatively, the red mud-based biochar after pressure filtration can be recovered by magnetic adsorption and reused after drying at 80-100 ℃.

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