A red mud-based carbon dioxide capture sorbent and a method of making the same

Abstract

The present application relates to the field of environmental protection material and carbon capture technology, in particular to a kind of red mud-based carbon dioxide capture adsorbent and its preparation method.It is composed of the following components by weight: activated red mud 60~80 parts;Alkali metal modification component 15~30 parts;Porous carrier 5~10 parts;Binder 3~8 parts;Auxiliary activator 2~5 parts.Activated red mud is obtained by removing iron from bayer process red mud by magnetic separation to iron content≤5wt%, then drying, calcining and crushing.The preparation method includes raw material pretreatment, mixing and dispersion, molding, activation and cooling.The obtained adsorbent has a static adsorption capacity for CO2≥2.8mmol / g, a 20-cycle retention rate≥90%, a compressive strength≥8MPa, and a raw material cost of 800~1200 yuan / t, realizing high-value utilization of red mud and low-cost carbon capture, and being suitable for flue gas CO2 capture in power generation, steel, coal chemical industry and other industries.

Description

Technical Field

[0001] This invention relates to the field of environmental protection materials and carbon capture technology, specifically to a red mud-based carbon dioxide capture adsorbent and its preparation method. Background Technology

[0002] With the global climate change problem becoming increasingly severe, carbon dioxide (CO2) emission reduction has become an international consensus. Industrial flue gas (especially from thermal power, steel, and coal chemical industries) is a major source of CO2 emissions. Solid adsorption methods have become a research hotspot in CO2 capture technology due to their advantages such as relatively low energy consumption, low equipment corrosivity, and simple operation.

[0003] Red mud is a highly alkaline industrial solid waste generated during alumina production, with huge annual emissions. Its storage occupies a large amount of land and poses environmental safety risks. Achieving high-value comprehensive utilization of red mud, especially its conversion into CO2 capture adsorbents, can both dispose of solid waste and reduce carbon capture costs, possessing significant economic and social value. Therefore, some research has been conducted in this field on the preparation of adsorbents using red mud as a raw material.

[0004] Chinese patent document CN116173892A discloses "a modified red mud-based adsorbent and its preparation method and application," which involves acid modification, alkali precipitation, aging, and calcination to modify red mud, followed by loading MgO via impregnation. The resulting adsorbent is used for carbon dioxide adsorption. However, this technical solution has the following shortcomings: First, the process is extremely complex, requiring multiple steps such as acid modification, alkali precipitation, aging, first calcination, impregnation, and second calcination, and involves corrosive chemical reagents such as nitric acid and ammonia, resulting in high energy consumption and cost, which is not conducive to industrial promotion. Second, the optimal saturated adsorption capacity measured in the examples is only 4.77 mg / g (approximately 0.11 mmol / g after conversion), which is low and difficult to meet the actual needs of industrial flue gas treatment. Third, this technology does not involve the molding process of the adsorbent, and the resulting material is in powder form, lacking sufficient mechanical strength and regular morphology, making it impossible to directly fill into fixed-bed or fluidized-bed reactors, thus limiting its application in actual carbon capture engineering. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention provides a red mud-based carbon dioxide capture adsorbent and its preparation method, which is a CO2 capture adsorbent that can use red mud as raw material, has a relatively simple process, low cost, and has both high adsorption capacity and good molding stability.

[0006] To achieve the above objectives, the present invention employs the following technical solution: A red mud-based carbon dioxide capture and adsorbent is composed of the following components in parts by weight: 60-80 parts activated red mud; 15-30 parts alkali metal modified components; 5-10 parts porous carrier; 3-8 parts binder; and 2-5 parts activator. The activated red mud is obtained by magnetic separation of Bayer process red mud to remove iron to an iron content of ≤5 wt%, followed by drying, calcination, and pulverization.

[0007] Furthermore, the Bayer process red mud contains ≥25wt% CaO and ≥15wt% Fe2O3; the alkali metal modifying component is at least one of sodium hydroxide, sodium carbonate, and potassium carbonate, with a purity ≥98wt%; and the porous carrier has a specific surface area ≥500m². 2 / g, selected from at least one of activated carbon, zeolite or mesoporous silica.

[0008] Further, the binder is at least one of silica sol, polyvinyl alcohol, or carboxymethyl cellulose; when the binder is silica sol, its solid content is ≥30wt%; when the binder is polyvinyl alcohol, its degree of polymerization is 1700~2000; when the binder is carboxymethyl cellulose, its degree of substitution is 0.7~1.2.

[0009] Furthermore, the activator is one or more of hydrogen peroxide, citric acid, and oxalic acid.

[0010] Furthermore, the activated red mud has a particle size ≥100 mesh and a moisture content ≤1%; the porous carrier, alkali metal modified component, binder and activator all have a particle size of 120~200 mesh.

[0011] Furthermore, the adsorbent has a static adsorption capacity of ≥2.8 mmol / g for CO2 at 25℃ and 1 atm, a compressive strength of ≥8 MPa, and an adsorption capacity retention rate of ≥90% after 20 adsorption-desorption cycles.

[0012] A method for preparing a red mud-based carbon dioxide capture and adsorbent includes the following steps: (1) Raw material pretreatment: Bayer process red mud is dried at 150~200℃ to a moisture content of ≤1%, then calcined at 500~700℃ for 1.5~2.5h, and pulverized to 100~150 mesh to obtain activated red mud; alkali metal modified components, porous carriers, binders and activators are pulverized to 120~200 mesh for later use.

[0013] (2) Mixing and dispersing: Weigh each raw material according to the ratio, mix them evenly, and add 3%~5% of deionized water in batches during the mixing process, while controlling the material temperature to ≤40℃, to obtain a mixed slurry.

[0014] (3) Molding process: The mixed slurry is made into particles with a particle size of 2~5mm, or pressed into sheet blanks under a pressure of 15~25MPa for 10~20s.

[0015] (4) Activation treatment: The formed blank is placed in an inert atmosphere and heated to 300-500℃ at a rate of 4-6℃ / min, and kept at the temperature for 2-4 hours for activation; (5) Cooling treatment: After activation, the red mud-based carbon dioxide capture and adsorbent is cooled to room temperature at a rate of ≤10℃ / min in air atmosphere to obtain the red mud-based carbon dioxide capture and adsorbent.

[0016] Further, in step (2), the mixing is carried out using a double helical conical mixer with a rotation speed of 200~300 r / min and a mixing time of 20~30 min, and deionized water is added 3~5 times; in step (3), the particles are obtained by a rotary granulator, and the diameter of the sheet-like blank is 3~6 mm and the thickness is 1~2 mm.

[0017] Furthermore, the inert atmosphere mentioned in step (4) is N2, and the gas flow rate is controlled at 0.5~1.0L / min.

[0018] Compared with existing methods, the beneficial effects of the present invention are: 1. Significantly improved adsorption capacity, achieving synergistic physical-chemical adsorption. This invention significantly improves the adsorption capacity of the adsorbent for CO2 through a synergistic mechanism of "directed activation of red mud, alkali metal modification and enhancement, porous carrier structure optimization, and performance regulation of the activator".

[0019] First, after drying and calcination, the hydroxides in the red mud are converted into more reactive alkaline oxides (such as CaO), significantly enhancing the chemisorption sites for CO2. Simultaneously, the magnetic separation process reduces the competitive adsorption of iron components. Second, the alkali metal modified components react with SiO2 and Al2O3 in the red mud to form aluminosilicate compounds, which then effectively load OH groups onto the red mud surface. - CO3 2- The presence of alkaline active sites significantly enhances the chemisorption capacity for acidic CO2 gas; furthermore, the porous support, acting as a structural framework, increases the overall specific surface area of ​​the adsorbent to 350–600 m². 2 / g provides abundant diffusion pathways and physical adsorption interfaces for CO2 molecules; finally, the activator oxidizes and removes impurities from the surface of the red mud, forms complexes with metal ions, and decomposes during calcination to generate additional microporous structures, thus optimizing the pore size distribution. The synergistic effect of the above components forms a dual capture mechanism of "chemical adsorption as the main factor and physical adsorption as the auxiliary factor".

[0020] Experimental verification (see Example 1) shows that the adsorbent prepared by the method of this invention has a static adsorption capacity of 3.2 mmol / g for CO2 at 25°C and 1 atm (Example 1), with a minimum of 2.8 mmol / g (Example 3). In contrast, the adsorption capacity of existing red mud-based CO2 adsorbents is typically less than 2.0 mmol / g, demonstrating a significant improvement in adsorption capacity.

[0021] 2. Excellent cycle stability, meeting the requirements of long-term industrial operation. This invention achieves excellent cycle stability through precise compounding of adsorbent components and optimization of activation process.

[0022] The binder forms a stable bond and rigid skeleton structure between particles, effectively solving the pulverization problem that easily occurs in red mud materials during molding and preventing cracking caused by volume shrinkage and expansion of the adsorbent during multiple adsorption-desorption cycles. At the same time, the activator adjusts the surface pH value to a suitable range of 9-11, balancing the adsorption and desorption process of CO2 and avoiding irreversible occupation of active sites. In addition, the skeleton support of the porous carrier further alleviates the volume shrinkage phenomenon during the reaction process and ensures the integrity of the structure.

[0023] Experimental verification (see Example 2) shows that the adsorbent prepared by this invention retains an adsorption capacity of up to 92% after 20 adsorption-desorption cycles. In contrast, similar adsorbents in the prior art typically retain only about 75% after ten cycles. The cycle stability of this invention is significantly better, meeting the industrial requirements of continuous, long-cycle operation in industries such as thermal power and steel.

[0024] 3. Successfully achieved industrial molding, with mechanical strength meeting filling requirements. This invention systematically solves the molding problem of red mud-based adsorbents by introducing a binder and optimizing the molding process.

[0025] This invention employs a synergistic blend of inorganic binders (silica sol) and organic binders (polyvinyl alcohol, carboxymethyl cellulose). After calcination, the silica sol dehydrates and condenses to form a rigid ceramic bridging framework, while the organic binders provide shaping and initial tack strength at low temperatures. Together, they construct a three-dimensional network framework between particles. Combined with a tableting pressure of 15–25 MPa or a rotary granulation process, the resulting adsorbent exhibits a regular geometric morphology and excellent mechanical properties.

[0026] Experimental verification (see Examples 1-3) shows that the compressive strength of the adsorbent of the present invention reaches 8.2~10.2MPa, which is far higher than the basic requirements for the mechanical strength of adsorbents in industrial fixed bed or fluidized bed reactors (usually ≥5MPa).

[0027] 4. Raw material costs are significantly reduced, enabling high-value utilization of solid waste. This invention uses Bayer red mud as the core raw material, accounting for as much as 60% to 80%, achieving the environmental protection goal of "treating waste with waste".

[0028] From the perspective of solid waste disposal: each ton of adsorbent can consume 0.6~0.8 tons of red mud (see Examples 1-3), which effectively alleviates the land occupation and environmental pollution problems caused by red mud stockpiling and transforms "industrial pollutants" into high-value-added carbon capture materials.

[0029] From an economic cost perspective, the raw material cost of the adsorbent of this invention is only 800-1200 yuan / t (see Examples 1-3: Example 1 is 950 yuan / t, Example 2 is 1050 yuan / t, and Example 3 is 820 yuan / t). In contrast, the raw material cost of traditional amine-functionalized adsorbents is typically as high as 2000-3000 yuan / t, meaning this invention reduces costs by more than 60%. Furthermore, the preparation process of this invention does not require complex equipment, further reducing equipment investment and operating energy consumption.

[0030] 5. Strong resistance to water vapor interference, adaptable to actual industrial flue gas conditions. This invention effectively removes water-absorbing impurities and water of crystallization from the surface of red mud through activation treatment. Simultaneously, the porous carrier possesses certain hydrophobic properties, and the dense framework formed by the binder reduces the channels for water vapor to diffuse into the particles. These structural features enable the adsorbent of this invention to maintain a stable CO2 capture capacity even under humid conditions.

[0031] Experimental verification (see Examples 1-3) shows that under flue gas conditions with humidity of 5%~10%, the adsorption capacity fluctuation of the adsorbent of the present invention is ≤10% (7% fluctuation in Example 1, 8% fluctuation in Example 2, and 5% fluctuation in Example 3). This means that the adsorbent of the present invention does not require additional dehumidification pretreatment of industrial flue gas and can be directly adapted to existing emission conditions, significantly reducing the supporting cost and operating energy consumption of carbon capture systems.

[0032] 6. The preparation process is simple and suitable for industrial-scale promotion. This invention employs a five-step process of "pretreatment—mixing and dispersion—forming—activation—cooling," which is simple, has a wide operating window, and low equipment requirements. Compared with existing technologies that require complex steps such as acid modification, alkali precipitation, aging, multiple calcination, and impregnation loading, the process of this invention is significantly simplified, does not require the use of corrosive chemical reagents, is easy to achieve continuous industrial production, and has good technical and economic advantages. Detailed Implementation

[0033] This invention discloses a red mud-based carbon dioxide capture and adsorbent and its preparation method. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments, and those skilled in the art can obviously make modifications or appropriate alterations and combinations to the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0034] This invention utilizes a complete process route of "red mud pretreatment—mixing and dispersion—molding—activation—cooling" to prepare a high-performance carbon dioxide capture adsorbent using red mud as the base material, compounded with alkali metal modified components, porous carriers, binders, and activators. Precise control of process parameters ensures the adsorbent's performance and molding stability. The specific technical solution is as follows: (I) Technical requirements for adsorbent components and raw materials This adsorbent is precisely formulated from five key components—activated red mud, alkali metal modified components, porous carrier, binder, and activator—in a specific mass ratio. Each type of raw material must strictly meet the following technical requirements: 1. Red mud Red mud produced by the Bayer process for electrolytic aluminum must be used, with a CaO content of not less than 25 wt% and an Fe2O3 content of not less than 15 wt%. It must also undergo magnetic separation to remove iron, and the final iron content must be strictly controlled below 5 wt%.

[0035] 2. Alkali metal modified components It can be one or more of sodium hydroxide, sodium carbonate, and potassium carbonate, and the purity of the raw materials shall not be less than 98 wt% to ensure the chemical modification effect.

[0036] 3. Porous carrier At least one of activated carbon, zeolite, or mesoporous silica can be used, with a specific surface area of ​​at least 500 m². 2 / g or higher, to ensure good physical adsorption and diffusion properties.

[0037] 4. Adhesive The binder includes at least one of silica sol, polyvinyl alcohol, or carboxymethyl cellulose. The silica sol must have a solid content of at least 30 wt%; the degree of polymerization of polyvinyl alcohol should be strictly controlled between 1700 and 2000, within which it can be completely dissolved in warm water at 60-80°C, forming a solution with moderate viscosity capable of uniformly coating the red mud particles, and the compressive strength of the molded product ≥ 8 MPa. When the binder is carboxymethyl cellulose, its degree of substitution is 0.7-1.2, and its 2% aqueous solution has a viscosity of 200-800 mPa·s at 25°C.

[0038] 5. Activating agent One or more of hydrogen peroxide, citric acid, and oxalic acid can be used to help improve the surface properties and reactivity of materials.

[0039] 6. Component mass ratio The components, by mass percentage, are as follows: activated red mud 60%–80%, alkali metal modified components 15%–30%, porous carrier 5%–10%, binder 3%–8%, and activator 2%–5%. This ratio must be strictly followed to ensure the overall performance of the adsorbent.

[0040] (II) Adsorbent Preparation Process 1. Raw material pretreatment The red mud raw material is dried at 150~200℃ to reduce its moisture content to below 1%, then calcined at 500~700℃ for 1.5~2.5h, and then pulverized to achieve a particle size of 100~150 mesh to finally obtain activated red mud; the alkali metal modified component, porous carrier, binder and activator need to be pulverized to 120~200 mesh for later use.

[0041] 2. Mixing and dispersing Accurately weigh each raw material according to the predetermined mass ratio and put them into a double helix conical mixer. Mix at a speed of 200~300 r / min for 20~30 min. During the process, add 3%~5% of deionized water, which accounts for 3%~5% of the total mass of the material, in 3~5 batches. Strictly control the material temperature to not exceed 40℃. Finally, a uniform mixed slurry is obtained.

[0042] 3. Molding process The mixed slurry is fed into a rotary granulator to produce uniform granules with a particle size of 2-5 mm; or a tablet press is used to press the tablets into sheet-like preforms with a diameter of 3-6 mm and a thickness of 1-2 mm by holding them under a pressure of 15-25 MPa for 10-20 seconds.

[0043] 4. Activation treatment The shaped preform is placed in a tube furnace and activated under a N2 atmosphere. The gas flow rate is controlled at 0.5~1.0L / min, and the temperature is programmed to rise to 300~500℃ at a rate of 4~6℃ / min, and held at that temperature for 2~4 hours to complete the activation process.

[0044] 5. Cooling treatment After activation, the atmosphere is switched to air and the mixture is naturally cooled to room temperature at a rate not exceeding 10°C / min to obtain a stable carbon dioxide capture and adsorbent product.

[0045] (III) Core Mechanism 1. Targeted activation of red mud Drying and roasting effectively remove moisture and organic impurities from red mud, promoting the conversion of hydroxides into more reactive alkaline oxides (such as CaO), significantly enhancing the chemical adsorption sites for CO2. At the same time, magnetic separation for iron removal reduces the competitive adsorption of iron components in the adsorption process, thereby improving the overall adsorption selectivity.

[0046] 2. Alkali metal modification and enhancement Alkali metal components react with SiO2, Al2O3, etc. in red mud to form aluminosilicate compounds, and OH groups are effectively loaded on the surface of the red mud. - CO3 2 It has alkaline active sites, which greatly enhances the chemical adsorption capacity and reaction efficiency for acidic gas CO2.

[0047] 3. Optimization of porous carrier structure Porous materials, acting as a structural framework, significantly increase the overall specific surface area of ​​the adsorbent (typically reaching 350~600 m²). 2 ( / g) provides more diffusion paths and adsorption interfaces for CO2 molecules, while effectively mitigating volume shrinkage during the reaction process and preventing cracking of the molded structure.

[0048] 4. Stable adhesive molding Through the synergistic effect of inorganic and organic binders, a stable bonding force and rigid skeleton structure are formed between particles, effectively solving the pulverization problem that easily occurs in red mud materials during molding, and enabling the adsorbent to achieve a compressive strength of over 8MPa, meeting the mechanical strength requirements for transportation and filling in industrial applications.

[0049] 5. Performance regulation of activators The activator can oxidize and remove impurities from the surface of red mud, form complexes with metal ions, and decompose during the roasting process to generate additional microporous structures, thereby optimizing the pore size distribution of the material. At the same time, it adjusts the surface pH value to a suitable range of 9-11, balances the adsorption and desorption processes, and improves the recycling efficiency.

[0050] Example 1: Preparation of a particulate high-adsorption-capacity carbon dioxide capture adsorbent Raw material ratio: In this embodiment, the activated red mud is 69 parts, the alkali metal modified component (sodium carbonate) is 20 parts, the porous carrier (activated carbon) is 6 parts, the binder (silica sol, solid content 30%) is 3 parts, and the activator (hydrogen peroxide) is 2 parts, totaling 100 parts by weight.

[0051] The specific parameters of the raw materials used are as follows: the red mud is produced by the Bayer process for electrolytic aluminum, with a CaO content of 28wt%, a Fe2O3 content of 18wt%, and an iron content of 3.5wt% after magnetic separation to remove iron; the activated carbon has a specific surface area of ​​600m². 2 / g, sodium carbonate purity 99wt%.

[0052] Preparation process: (1) Raw material pretreatment: The red mud was dried at 180℃ to a moisture content of 0.8%, calcined at 600℃ for 2 hours, and pulverized to 120 mesh to obtain activated red mud; sodium carbonate, activated carbon, silica sol and hydrogen peroxide were pulverized to 150 mesh for later use.

[0053] (2) Mixing and dispersing: Weigh each raw material according to the above ratio, put them into a double helix cone mixer, mix at 250 r / min speed for 25 min, add 4% of deionized water in 4 portions, control the material temperature at 35℃, and obtain a uniform mixed slurry.

[0054] (3) Molding process: The mixed slurry is fed into a rotary granulator to make uniform granules with a particle size of 3-4 mm.

[0055] (4) Activation treatment: Place the billet in a tube furnace and heat it to 400°C at a rate of 5°C / min under N2 atmosphere (gas flow rate 0.8L / min) and keep it at that temperature for 3 hours to complete the activation.

[0056] (5) Cooling treatment: After activation, the atmosphere is switched to air and cooled to room temperature at a rate of 8℃ / min to obtain the granular red mud-based carbon dioxide capture and adsorbent product.

[0057] Performance testing: Testing showed that the adsorbent prepared in this embodiment had a static adsorption capacity of 3.2 mmol / g for CO2 at 25℃ and 1 atm, a compressive strength of 9.5 MPa, and an adsorption capacity fluctuation of 7% at 8% humidity. Each ton of adsorbent consumed 0.7 tons of red mud, with a raw material cost of 950 yuan / ton.

[0058] Example 2: Preparation of sheet-like, cycle-resistant carbon dioxide capture adsorbent Raw material ratio: In this embodiment, the activated red mud is 65 parts, the alkali metal modified component (sodium hydroxide and potassium carbonate compounded in a mass ratio of 1:1) is 19 parts, the porous carrier (zeolite) is 8 parts, the binder (polyvinyl alcohol, degree of polymerization 1800) is 5 parts, and the activator (citric acid) is 3 parts, totaling 100 parts by weight.

[0059] The specific parameters of the raw materials used are as follows: the red mud is produced by the Bayer process for electrolytic aluminum, with a CaO content of 26wt%, a Fe2O3 content of 16wt%, and an iron content of 4.2wt% after magnetic separation to remove iron; the zeolite has a specific surface area of ​​550m². 2 / g; Sodium hydroxide and potassium carbonate are both 98.5wt% pure; Polyvinyl alcohol is completely dissolved in warm water at 70℃.

[0060] Preparation process: (1) Raw material pretreatment: The red mud was dried at 160℃ to a moisture content of 0.9%, calcined at 550℃ for 2.5h, and pulverized to 100 mesh to obtain activated red mud; the alkali metal modified component, zeolite, polyvinyl alcohol and citric acid were pulverized to 180 mesh for later use.

[0061] (2) Mixing and dispersing: Weigh each raw material according to the above ratio, put them into a double helix cone mixer, mix at 220 r / min for 28 min, add 3.5% of deionized water in three portions, control the material temperature at 30℃, and obtain a mixed slurry.

[0062] (3) Molding process: The mixed slurry is placed in a tablet press and pressed for 15 seconds under a pressure of 20MPa to form a sheet blank with a diameter of 4mm and a thickness of 1.5mm.

[0063] (4) Activation treatment: The billet is placed in a tube furnace and heated to 350°C at a rate of 4°C / min under N2 atmosphere (gas flow rate 0.6L / min) and held for 3.5h for activation.

[0064] (5) Cooling treatment: After activation, the carbon dioxide capture and adsorbent is cooled to room temperature at a rate of 7℃ / min in air atmosphere to obtain the finished product of sheet-like red mud-based carbon dioxide capture and adsorbent.

[0065] Performance testing: Testing showed that the adsorbent prepared in this embodiment had a static adsorption capacity of 2.9 mmol / g for CO2 at 25℃ and 1 atm. After 20 adsorption-desorption cycles, the adsorption capacity retention rate was 92%, the compressive strength was 10.2 MPa, and the adsorption capacity fluctuation was 8% under 10% humidity conditions. Each ton of adsorbent consumed 0.65 tons of red mud, and the raw material cost was 1050 yuan / ton.

[0066] Example 3: Preparation of Low-Cost, Large-Scale Carbon Dioxide Capturing Adsorbent Raw material ratio: In this embodiment, the activated red mud is 75 parts, the alkali metal modified component (sodium carbonate) is 15 parts, the porous carrier (mesoporous silica) is 5 parts, the binder (carboxymethyl cellulose and silica sol are compounded in a mass ratio of 1:2, the degree of substitution of carboxymethyl cellulose is 0.9, and the viscosity of 2% aqueous solution at 25°C is 500 mPa·s) is 3 parts, and the co-activator (oxalic acid and hydrogen peroxide are compounded in a mass ratio of 1:1) is 2 parts, totaling 100 parts by weight.

[0067] The specific parameters of the raw materials used are as follows: the red mud is produced by the Bayer process for electrolytic aluminum, with a CaO content of 25wt%, a Fe2O3 content of 15wt%, and an iron content of 4.8wt% after magnetic separation to remove iron; the mesoporous silica has a specific surface area of ​​500m².2 / g; Sodium carbonate purity 98wt%; Silica sol solid content 30wt%.

[0068] Preparation process: (1) Raw material pretreatment: Dry the red mud at 200℃ to a moisture content of 0.7%, calcine at 700℃ for 1.5h, and pulverize to 150 mesh to obtain activated red mud; pulverize sodium carbonate, mesoporous silica, carboxymethyl cellulose, silica sol, oxalic acid and hydrogen peroxide to 200 mesh for later use.

[0069] (2) Mixing and dispersing: Weigh each raw material according to the above ratio, put them into a double helix cone mixer, mix at 280 r / min speed for 20 min, add 3% of deionized water in 5 portions, control the material temperature at 38℃, and obtain a mixed slurry.

[0070] (3) Molding process: The mixed slurry is fed into a rotary granulator to make granules with a particle size of 2~3mm, which is suitable for large-scale industrial production.

[0071] (4) Activation treatment: The billet is placed in a tube furnace and heated to 450°C at a rate of 6°C / min under N2 atmosphere (gas flow rate 1.0L / min) and held for 2 hours for activation.

[0072] (5) Cooling treatment: After activation, the carbon dioxide capture adsorbent is cooled to room temperature at a rate of 9℃ / min in air atmosphere to obtain a low-cost red mud-based carbon dioxide capture adsorbent product.

[0073] Performance testing: Testing showed that the adsorbent prepared in this embodiment had a static adsorption capacity of 2.8 mmol / g for CO2 at 25℃ and 1 atm, a compressive strength of 8.2 MPa, and an adsorption capacity fluctuation of 5% at 5% humidity. Each ton of adsorbent consumed 0.8 tons of red mud, with a raw material cost of 820 yuan / ton, which is more than 65% lower than the cost of traditional amine functionalized adsorbents, making it suitable for large-scale flue gas carbon capture scenarios in the thermal power industry.

[0074] The raw material ratios and performance test results of Examples 1-3 above are summarized as follows: In Example 1, the mass percentages of activated red mud, sodium carbonate, activated carbon, silica sol, and hydrogen peroxide were 70%, 20%, 6%, 3%, and 1%, respectively. Its static CO2 adsorption capacity was 3.2 mmol / g, its compressive strength was 9.5 MPa, and its adsorption capacity fluctuated by 7% under 8% humidity conditions. Each ton of adsorbent consumed 0.7 tons of red mud, and the raw material cost was 950 yuan / ton.

[0075] In Example 2, the mass percentages of activated red mud, sodium hydroxide and potassium carbonate compound (mass ratio 1:1), zeolite, polyvinyl alcohol, and citric acid were 65%, 25%, 7%, 2%, and 1%, respectively. Its static CO2 adsorption capacity was 2.9 mmol / g, the adsorption capacity retention rate was 92% after 20 adsorption-desorption cycles, the compressive strength was 10.2 MPa, the adsorption capacity fluctuation was 8% under 10% humidity conditions, 0.65 tons of red mud were consumed per ton of adsorbent, and the raw material cost was 1050 yuan / ton.

[0076] In Example 3, the mass percentages of activated red mud, sodium carbonate, mesoporous silica, a complex of carboxymethyl cellulose and silica sol (mass ratio 1:2), and a complex of oxalic acid and hydrogen peroxide (mass ratio 1:1) were 80%, 15%, 3%, 1.5%, and 0.5%, respectively. Its static CO2 adsorption capacity was 2.8 mmol / g, its compressive strength was 8.2 MPa, and its adsorption capacity fluctuated by 5% under 5% humidity conditions. Each ton of adsorbent consumed 0.8 tons of red mud, and the raw material cost was 820 yuan / ton, representing a cost reduction of over 65% compared to traditional amine-functionalized adsorbents.

[0077] As can be seen from the above embodiments, the red mud-based carbon dioxide capture adsorbent prepared using the technical solution of the present invention has advantages such as high adsorption capacity (≥2.8mmol / g), good mechanical strength (compressive strength ≥8MPa), excellent cycle stability (retention rate ≥90% after 20 cycles), strong resistance to water vapor interference (adsorption capacity fluctuation ≤10% under humidity of 5%~10%), and low raw material cost (≤1050 yuan / t). Moreover, each ton of adsorbent can absorb 0.6~0.8t of red mud, achieving the dual goals of solid waste resource utilization and low-cost carbon capture, and is suitable for industrial promotion and application.

[0078] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A red mud-based carbon dioxide capture and adsorbent, characterized in that, It consists of the following components in parts by weight: 60-80 parts of activated red mud; Alkali metal modified component 15-30 parts; 5-10 parts of porous carrier; 3-8 parts adhesive; 2-5 parts of activator; The activated red mud is obtained by magnetically separating Bayer process red mud to remove iron until the iron content is ≤5wt%, and then drying, roasting and pulverizing it.

2. The red mud-based carbon dioxide capture and adsorbent according to claim 1, characterized in that, The Bayer process red mud contains ≥25wt% CaO and ≥15wt% Fe2O3. The alkali metal modified component is at least one of sodium hydroxide, sodium carbonate, and potassium carbonate, with a purity ≥98 wt%. The specific surface area of ​​the porous carrier is ≥500m². 2 / g, selected from at least one of activated carbon, zeolite or mesoporous silica.

3. The red mud-based carbon dioxide capture and adsorbent according to claim 1, characterized in that, The adhesive is at least one of silica sol, polyvinyl alcohol, or carboxymethyl cellulose; When the binder is silica sol, its solid content is ≥30 wt%; When the adhesive is polyvinyl alcohol, its degree of polymerization is 1700~2000; When the binder is carboxymethyl cellulose, its degree of substitution is 0.7 to 1.

2.

4. The red mud-based carbon dioxide capture and adsorbent according to claim 1, characterized in that, The activator is one or more of hydrogen peroxide, citric acid, and oxalic acid.

5. The red mud-based carbon dioxide capture and adsorbent according to claim 1, characterized in that, The activated red mud has a particle size ≥100 mesh and a moisture content ≤1%; The porous carrier, alkali metal modified component, binder and activator all have a particle size of 120~200 mesh.

6. A red mud-based carbon dioxide capture and adsorbent according to any one of claims 1-5, characterized in that, The adsorbent has a static adsorption capacity of ≥2.8 mmol / g for CO2 at 25℃ and 1 atm, a compressive strength of ≥8 MPa, and an adsorption capacity retention rate of ≥90% after 20 adsorption-desorption cycles.

7. A method for preparing the red mud-based carbon dioxide capture and adsorbent according to any one of claims 1-6, characterized in that, Includes the following steps: 1) Raw material pretreatment: Bayer process red mud is dried at 150~200℃ to a moisture content of ≤1%, then calcined at 500~700℃ for 1.5~2.5h, and pulverized to 100~150 mesh to obtain activated red mud; The alkali metal modified components, porous carriers, binders, and activators were pulverized to 120-200 mesh for later use. 2) Mixing and dispersing: Weigh each raw material according to the ratio, mix them evenly, and add 3%~5% of deionized water according to the total mass of raw materials in batches during the mixing process, and control the material temperature ≤40℃ to obtain a mixed slurry; 3) Molding process: The mixed slurry is made into particles with a particle size of 2~5mm, or pressed into sheet blanks under a pressure of 15~25MPa for 10~20s; 4) Activation treatment: Place the formed blank in an inert atmosphere and heat it to 300-500℃ at a rate of 4-6℃ / min, and keep it at that temperature for 2-4 hours for activation. 5) Cooling treatment: After activation, the red mud-based carbon dioxide capture and adsorbent is cooled to room temperature at a rate of ≤10℃ / min in air atmosphere to obtain the red mud-based carbon dioxide capture and adsorbent.

8. The method for preparing a red mud-based carbon dioxide capture and adsorbent according to claim 7, characterized in that, The mixing described in step 2) is performed using a double-helix conical mixer at a speed of 200-300 r / min and a mixing time of 20-30 min, with deionized water added in 3-5 batches; The particles described in step 3) are obtained using a rotary granulation mechanism, and the diameter of the sheet-like preform is 3~6mm and the thickness is 1~2mm.

9. The method for preparing a red mud-based carbon dioxide capture and adsorbent according to claim 7, characterized in that, The inert atmosphere mentioned in step 4) is N2, and the gas flow rate is controlled at 0.5~1.0L / min.