Method and device for realizing carbon sequestration of red mud under supercritical condition

Abstract

The invention discloses a method and a device for realizing red mud carbon sequestration under supercritical conditions, and relates to the technical field of red mud carbon sequestration, the method comprises a red mud pretreatment step, an ultrasonic cavitation crushing step and a microchannel mixing reaction step, the device comprises a pretreatment unit, an ultrasonic crushing module, a micro-channel mixing module, a gradient reaction tower, a temperature and pressure control system, a multi-stage reciprocating compressor and an external circulating pump. An ultrasonication area is arranged at the top, a honeycomb-shaped micro-channel mixing module is integrated in the middle, a gradient temperature reaction tower is arranged at the bottom, a baffle plate is arranged for strengthening mass transfer, and after a carbon sequestration reaction is completed, slurry returns to the reaction area through a circulating pump; the particle size of the red mud is reduced to 1-5 [mu] m through the ultrasonic-microchannel synergistic effect, and three-phase mixing of the red mud and supercritical CO2 is completed within 0.5 s; meanwhile, a porous supported calcium-magnesium composite catalyst is adopted, the confinement effect and hydrophobicity of a carrier are utilized, the carbon sequestration efficiency is improved to 95% or above, and the problem of silicate side reaction caused by too strong alkalinity is solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of red mud carbon fixation, and particularly relates to a method and device for realizing red mud carbon fixation under supercritical conditions. BACKGROUND

[0002] Red mud is an industrial solid waste produced in the process of alumina production. It has the characteristics of strong alkalinity, heavy metal content, high viscosity and fine particle size. Long-term stacking will not only occupy a large amount of land, but also pollute water and soil. Therefore, a large amount of red mud is a solid waste that needs to be treated and urgently needs to be resourcefully utilized. The traditional landfill, stacking or neutralization method has the problems of high carbon emission and potential waste of red mud resources. The supercritical CO2 technology reacts supercritical CO2 with the alkaline components in the red mud to generate stable carbonates, realizes the goal of "waste carbon fixation", and has the functions of carbon sequestration and harmless utilization of red mud. SUMMARY

[0003] The main purpose of the present application is to provide a method and device for realizing red mud carbon fixation under supercritical conditions, which can solve the problem of red mud resource treatment.

[0004] To achieve the above purpose, the present application provides a method for realizing red mud carbon fixation under supercritical conditions, which comprises the following steps: S1, washing and drying the red mud to remove free water, and then crushing the dried red mud to form a dry red mud powder which is mixed with deionized water in a certain proportion; S2, pressurizing CO2 to a supercritical pressure and a supercritical temperature; S3, ultrasonic crushing of the slurry obtained in step S1, cavitation crushing by an ultrasonic array to reduce the particle size of the red mud; S4, three-phase mixing of the crushed slurry, pressurized supercritical CO2 of step S2 and a porous supported catalyst in a honeycomb-shaped microchannel, and the mixing time is ≤0.5 seconds; S5, the mixed material enters a gradient reaction tower to perform a carbon fixation reaction under the condition of segmented temperature control and then is cooled.

[0005] As a further improvement of the present application, the drying temperature in step S1 is T1, 100℃≤ T1<120℃, the dried red mud is crushed to 150-200 mesh, and the red mud is mixed with deionized water in a liquid-solid ratio of 8-10:1 after crushing.

[0006] As a further improvement of the present application, the supercritical CO2 reaction pressure in step S2 is P1, 10MPa<P1≤25MPa, and the supercritical CO2 reaction temperature in step S3 is T2, 35℃<T2 ≤ 80℃.

[0007] As a further improvement of the present application, the ultrasonic crushing in step S3 uses a piezoelectric ceramic transducer with a frequency of 40 kHz, and the amplitude is dynamically adjusted in a range of 10-100%, so that the particle size of the red mud is reduced to 1-5 μm.

[0008] As a further improvement of the present application, the porous supported catalyst added in step S4 is added in an amount of 2-10 wt% based on the mass of the dry red mud.

[0009] As a further improvement of the present application, the porous supported catalyst in step S4 is prepared by the following steps: (1) A carrier is synthesized by a sol-gel method using zinc acetate dihydrate, 2-methyl imidazole and methanol. 20 g of zinc acetate dihydrate is dissolved in 400 mL of methanol to form a solution A, and 30 g of 2-methyl imidazole is dissolved in 400 mL of methanol to form a solution B. The solution A and the solution B are quickly mixed, stirred at 25°C for 12 h, and aged for 24 h. The white precipitate is collected by centrifugation, washed with methanol for 3 times, and dried in an oven at 80°C for 12 h to obtain the carrier powder; (2) A calcium nitrate and magnesium nitrate impregnation solution with a total molar mass of 1.5 mol / L is prepared according to a molar ratio of Ca:Mg=2:1. The carrier is impregnated in the impregnation solution to obtain an impregnated carrier; (3) The impregnated carrier is subjected to gradient calcination in a N2 atmosphere. Dehydration is performed at 100-150°C for 1-2 h, nitrate decomposition is performed at 300-400°C for 2-3 h to generate MgO / CaO nanoparticles, and stable oxides are formed in the impregnated carrier at 550-650°C for 3-4 h. Then, the porous supported catalyst is obtained by gas-phase hydrophobic modification with hexamethyldisilazane, and the water contact angle of the porous supported catalyst is >130°, i.e., the porous supported catalyst has strong hydrophobicity.

[0010] As a further improvement of the present application, the honeycomb-shaped microchannel in step S4 is a microchannel mixing module stacked by multiple layers of titanium alloy microchannel plates, and each plate contains 800-4000 regular hexagonal flow channels with a side distance of 50-300 μm.

[0011] As a further improvement of the present application, the temperature of the upper low-temperature zone of the gradient reaction tower in step S5 is 35-50°C, the temperature of the middle middle-temperature zone is 50-65°C, and the temperature of the lower high-temperature zone is 65-80°C.

[0012] The device used in a method for realizing carbon sequestration of red mud under supercritical conditions comprises a red mud drying tower, a ball mill communicated with the red mud drying tower, a mixing outer cylinder arranged at the outlet of the ball mill, a first red mud annular distributor, a second red mud annular distributor and a CO2 annular distributor arranged in the mixing outer cylinder from top to bottom, an ultrasonic transducer and a titanium alloy amplitude lever vertically arranged between the first red mud annular distributor and the second red mud annular distributor, a plurality of multilayer microchannel mixing modules arranged between the second red mud annular distributor and the CO2 annular distributor, a gradient reaction tower arranged below the CO2 annular distributor, a plurality of stages of reciprocating compressors connected to the outside of the CO2 annular distributor, a plurality of groups of baffle plates arranged at intervals in the gradient reaction tower, a pressure relief valve arranged on the outer wall of the gradient reaction tower, a catalyst feeding pipe arranged at the top end of the gradient reaction tower, a water feeding pipe and a red mud feeding pipe communicated with the ball mill arranged on the first red mud annular distributor, a temperature and pressure control system arranged outside the gradient reaction tower, a conical collector arranged at the bottom end of the gradient reaction tower, and a circulating pump connected to the outside of the conical collector and communicated with the top of the gradient reaction tower.

[0013] As a further improvement of the present application, a plurality of nozzles are annularly distributed on the CO2 annular distributor, the nozzles have a diameter of 0.1-0.5 mm, and the nozzles are arranged towards the second red mud annular distributor, so that the CO2 flowing in the CO2 annular distributor flows from the bottom end of the multilayer microchannel mixing module towards the ultrasonic transducer.

[0014] The beneficial effects of the present application are embodied in: 1. The present application can make CO2 maintain high diffusivity of gas under the condition of supercritical CO2, obtain strong solubility of liquid, and also have chemical inertness and mildness, so that it can fully diffuse, fully contact with red mud, react with pore water or alkaline components in red mud to generate carbonate ions, dissolve alkaline metal oxides (such as CaO) in red mud, generate corresponding hydroxides, release soluble divalent metal ions (such as Mg 2+ , Ca 2+ ), and the divalent metal ions react with carbonate ions to generate carbonate precipitates. This process not only realizes the goal of carbon sequestration of red mud, but also reduces the alkalinity of red mud, making good preparation for the subsequent comprehensive utilization of red mud.

[0015] 2. The present application only uses a supercritical CO2 system, does not use supercritical water combined with supercritical CO2, and instead uses a method of adding a porous supported calcium-magnesium composite catalyst. Giving up the use of supercritical water can reduce the energy consumption of the entire reaction, and in order to make water reach a supercritical state, a high temperature and high pressure of >374 DEG C, >22.1 MPa are required, so only using supercritical CO2 can make the entire reaction be realized under relatively mild conditions. The titanate and silicate present in the red mud will compete with the carbonate ions for the soluble divalent cations (such as Ca 2+Mg 2+ Therefore, this invention incorporates a porous supported calcium-magnesium composite catalyst during the reaction to reduce competition between titanates and silicates in red mud, thereby facilitating carbonate precipitation and increasing carbon fixation efficiency. Furthermore, compared to existing technologies, the use of a single calcium-based catalyst results in excessively high local pH due to its strong alkalinity, triggering silicate side reactions (silicates react with alkaline substances to form silicate complexes, consuming alkaline substances and reducing carbonate production, thus affecting carbon fixation efficiency). The composite catalyst used in this invention, with MgO having a slightly lower alkalinity (pH≈10.3) than CaO (pH≈12.5), allows for pH regulation through the addition of a magnesium-based catalyst, reducing byproduct formation and increasing carbon fixation efficiency by over 20%. Moreover, MgO is more stable in a supercritical CO2 environment, and Mg... 2+ With CO3 2+ It has a stronger binding ability and can generate more stable MgCO3 precipitate, resulting in better carbon fixation effect.

[0016] 3. The porous supported calcium-magnesium composite catalyst used in this invention is prepared by the sol-gel method and uses zinc acetate dihydrate, 2-methylimidazole and methanol to synthesize the support. 20 g of zinc acetate dihydrate was dissolved in 400 mL of methanol to form solution A. 30 g of 2-methylimidazole was dissolved in 400 mL of methanol to obtain solution B. Solution A and solution B were then rapidly mixed and stirred at 25 °C for 12 h. After standing for 24 h, the white precipitate was collected by centrifugation. The white precipitate was washed three times with methanol and dried in an oven at 80 °C for 12 h to obtain the carrier powder. Calcium nitrate and magnesium nitrate were prepared into a 1.5 mol / L impregnation solution at a Ca:Mg = 2:1 molar ratio, and an equal volume was loaded into the carrier channels. The carrier was calcined at a gradient of 120 °C, 350 °C, and 600 °C under a N2 atmosphere. Calcination at 120 °C for 2 h dehydrated the carrier, and calcination at 350 °C for 3 h decomposed the nitrate ions to generate MgO / CaO nanoparticles. Calcination at 600 °C for 4 h further decomposed the carrier. h forms a stable oxide; finally, it is modified by hexamethyldisilazane in the gas phase to make its water contact angle >130°, that is, it has strong hydrophobicity, which blocks the water erosion in the red mud slurry and prevents the catalyst from deactivating.

[0017] 4. The porous supported calcium-magnesium composite catalyst used in this invention has a support pore size of only 1.2 nm, confining the CaO / MgO active components to the nanoscale and forming a high-density catalytic microreactor. This shortens the CO2 diffusion distance to the nanoscale, significantly increasing the carbon fixation rate. Furthermore, since silicate crystals typically have a diameter greater than 1.5 nm, they are blocked by the support pores, completely eliminating their competing side reactions.

[0018] 5、The reactor of the device adopts ultrasonic crushing, micro-channel mixing and gradient reaction tower combination. The traditional method causes uneven stirring, resulting in a reaction time of more than 30 minutes, and a carbon sequestration rate of only 89.5%. The device crushes the red mud to 1-5 mu by 40 kHz ultrasonic cavitation, and combines the supercritical CO2 turbulent flow in the honeycomb micro-channel to improve the mass transfer efficiency by 60 times, and the reaction time is shortened to less than 10 minutes. At the same time, the three-section gradient temperature control reaction tower (35-80℃ precise partitioning) cooperates with the catalyst of the limited effect, which not only improves the carbon sequestration rate to 95.5%, but also reduces the energy consumption per ton of red mud to only 120 kWh, while the traditional device is as high as 200 kWh, and the side reaction is serious. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The device structure diagram used for the method for realizing red mud carbon sequestration under supercritical conditions; BRIEF DESCRIPTION OF DRAWINGS 1, red mud drying tower; 2, ball mill; 3, mixing outer cylinder; 4, first red mud annular distributor; 5, second red mud annular distributor; 6, CO2 annular distributor; 7, ultrasonic transducer; 8, titanium alloy amplitude bar; 9, multi-layer micro-channel mixing module; 10, gradient reaction tower; 11, multi-stage reciprocating compressor; 12, baffle; 13, pressure relief valve; 14, catalyst feeding pipe; 15, water inlet pipe; 16, red mud feeding pipe; 17, temperature and pressure control system; 18, conical collector; 19, circulating pump; 20, cooling water jacket. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be further described in detail below with reference to the drawings and examples. It should be understood that the described examples are only a part of the examples of the present application, not all examples. The examples in the present application and the features in the examples can be combined with each other without conflict. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor belong to the scope of protection of the present application.

[0021] The method for realizing red mud carbon sequestration under supercritical conditions comprises the following steps: S1, after washing the red mud, it is sent into a drying tower to remove free water, and the dried red mud is crushed by a ball mill 2 to form a dried red mud powder, which is then mixed with deionized water in a certain proportion; S2, CO2 is pressurized to supercritical pressure and supercritical temperature in a compressor; S3, the slurry obtained in S1 is sent to an ultrasonic crushing zone, and cavitation crushing is performed by an ultrasonic array to reduce the particle size of the red mud; S4, the crushed slurry, pressurized supercritical CO2 in step S2 and the porous supported catalyst enter the micro-channel mixing module in parallel, three-phase mixing is completed in the honeycomb-shaped micro-channel, and the mixing time is ≤0.5 seconds; S5, the mixed material enters the gradient reaction tower 10, and the carbon sequestration reaction is carried out under the condition of segmented temperature control. After 10 minutes of reaction, the temperature is lowered.

[0022] To ensure that supercritical CO2, porous supported catalyst and crushed slurry are in full contact, see Figure 1 It also includes a red mud drying tower 1, a ball mill 2 communicating with the red mud drying tower 1, a mixing outer cylinder 3 arranged at the outlet of the ball mill 2, a first red mud annular distributor 4, a second red mud annular distributor 5 and a CO2 annular distributor 6 arranged in the mixing outer cylinder 3 from top to bottom, an ultrasonic transducer 7 and a titanium alloy amplitude rod 8 vertically arranged between the first red mud annular distributor 4 and the second red mud annular distributor 5; a plurality of micro-channel mixing modules 9 are arranged between the second red mud annular distributor 5 and the CO2 annular distributor 6; a gradient reaction tower 10 is arranged below the CO2 annular distributor 6, and a multi-stage reciprocating compressor 11 is connected outside the CO2 annular distributor 6; a plurality of groups of baffles 12 are arranged at intervals in the gradient reaction tower 10, a pressure relief valve 13 is arranged on the outer wall of the gradient reaction tower 10, a catalyst feeding pipe 14 is arranged at the top end of the gradient reaction tower 10; a water inlet pipe 15 and a red mud feeding pipe 16 communicating with the ball mill 2 are arranged on the first red mud annular distributor 4; a temperature and pressure control system 17 is arranged outside the gradient reaction tower 10, a conical collector 18 is arranged at the bottom end of the gradient reaction tower 10, a circulating pump 19 is connected outside the conical collector 18, and the circulating pump 19 communicates with the top of the gradient reaction tower 10.

[0023] As shown in the accompanying drawings Figure 1The device of the application comprises a red mud drying tower 1, a ball mill 2, a red mud feeding pipe 16, a water feeding pipe 15, a first red mud annular distributor 4, a second red mud annular distributor 5, an ultrasonic transducer 7, a titanium alloy amplitude rod 8, a catalyst feeding pipe 14, a multi-layer micro-channel mixing module 9, a CO2 annular distributor 6, a gradient reaction tower 10, a baffle 12, a multi-stage reciprocating compressor 11, a pressure relief valve 13, a temperature and pressure control system 17, a circulating pump 19, a cooling water jacket 20, and a conical collector 18. The ultrasonic transducer 7 and the titanium alloy amplitude rod 8 are arranged in a closed tubular structure and vertically placed, with the upper end provided with the red mud feeding pipe 16 and the water feeding pipe 15, which are respectively connected to the dried and crushed red mud and deionized water. The mixture enters the first red mud annular distributor 4 to ensure that the red mud slurry is uniformly fed into the ultrasonic crushing stage. After the ultrasonic crushing, the red mud slurry enters the second red mud annular distributor 5 arranged at the lower end and then uniformly enters the multi-layer micro-channel mixing module 9. The multi-layer micro-channel mixing module 9 is arranged in a closed tubular structure and connected to the ultrasonic crushing module through the second red mud annular distributor 5. The upper end is provided with the catalyst feeding pipe 14, and the lower end is provided with the CO2 annular distributor 6. The catalyst and supercritical CO2 enter the multi-layer micro-channel mixing module 9 through the pipes. The three phases are instantaneously mixed in the micro-channel, and the mixed slurry enters the gradient reaction tower 10 connected below the multi-layer micro-channel mixing module 9. In the upper low-temperature zone (35-50℃) of the gradient reaction tower 10, carbonate nuclei are generated. In the middle temperature zone (50-65℃), crystal growth is promoted. In the lower high-temperature zone (65-80℃), deep carbonation is completed. The temperature is controlled by the temperature and pressure control system 17. The baffle 12 is arranged inside the gradient reaction tower 10, with 8-10 pieces from top to bottom. The pressure relief valve 13 is used to release pressure when the reaction pressure exceeds to ensure safety. The multi-stage reciprocating compressor 11 pressurizes CO2 to the supercritical CO2 reaction pressure and then uniformly inputs the multi-layer micro-channel mixing module 9 through the CO2 annular distributor 6.

[0024] Preferably, the outer layer of the ultrasonic crushing module is provided with a cooling water jacket 20 to prevent the temperature from being too high during ultrasonic crushing.

[0025] Preferably, the ultrasonic crushing module is 1.5 m high and 1 m in diameter. The ultrasonic transducer 7 is 300 mm in diameter and 200 mm in length (including the amplitude rod). The cooling water jacket 20 is 2 mm in wall thickness and 8 mm in inner diameter of the interlayer.

[0026] Preferably, the multi-layer micro-channel mixing module 9 is 1.8 m high and 1 m in diameter. The single-layer micro-channel plate is 100 mm thick and 0.98 m in diameter.

[0027] Preferably, the gradient reaction tower 10 is 4 m high and 1 m in diameter. The upper layer is 1.5 m high, the middle layer is 1 m high, and the lower layer is 1.5 m high. The bottom is conical with a taper angle of 45°-60°.

[0028] Preferably, the CO2 annular distributor 6 is annularly distributed with nozzles with a nozzle aperture of 0.1-0.5 mm, and the nozzles are arranged towards the second red mud annular distributor 5, so that the CO2 flowing in the CO2 annular distributor 6 flows from the bottom end of the multi-layer micro-channel mixing module 9 towards the ultrasonic transducer 7.

[0029] Preferably, the pH of the slurry obtained after the S1 step is >10.

[0030] Preferably, the drying tower temperature in S1 is T1, 100℃≤ T1< 120℃, and the dried red mud is crushed to 150-200 mesh by a ball mill 2 and mixed with deionized water at a liquid-solid ratio of 8-10:1.

[0031] The supercritical CO2 reaction pressure in S2 is P1, and the pressure adjustment is an absolute pressure adjustment, and the supercritical CO2 reaction temperature in S3 is T2, 10 MPa < P1≤ 25 MPa, and 35℃ < T2 ≤ 80℃.

[0032] Preferably, the ultrasonic crushing in S3 uses a piezoelectric ceramic transducer with a frequency of 40 kHz, and the amplitude is dynamically adjusted in the range of 10-100%, so that the particle size of the red mud is reduced to 1-5 μm.

[0033] Preferably, the porous supported catalyst in S4 is prepared by the following steps: (1) using a sol-gel method, a carrier is synthesized using zinc acetate dihydrate, 2-methyl imidazole, and methanol. 20 g of zinc acetate dihydrate is dissolved in 400 mL of methanol to form solution A, and 30 g of 2-methyl imidazole is dissolved in 400 mL of methanol to obtain solution B. Solution A and solution B are quickly mixed, stirred at 25℃ for 12 h, and aged for 24 h. The white precipitate is collected by centrifugation, washed with methanol for 3 times, and dried in an oven at 80℃ for 12 h to obtain a carrier powder; (2) calcium nitrate and magnesium nitrate are prepared into an impregnation solution with a total molar mass of 1.5 mol / L at a molar ratio of Ca:Mg=2:1, and the carrier is impregnated in the impregnation solution to obtain an impregnated carrier; (3) the impregnated carrier is placed in an N2 atmosphere and subjected to gradient calcination, dehydrated at 100-150℃ for 1-2 h, decomposed at 300-400℃ for 2-3 h to generate MgO / CaO nanoparticles, and then calcined at 550-650℃ for 3-4 h to form stable oxides in the impregnated carrier, and then subjected to gas-phase hydrophobic modification with hexamethyldisilazane to obtain a porous supported catalyst with a water contact angle >130°, i.e. strong hydrophobicity.

[0034] Preferably, the multi-layer micro-channel mixing module 9 in step S4 is stacked by multi-layer titanium alloy micro-channel plates, and each plate contains 800-4000 regular hexagonal flow channels with a side distance of 50-300 μm.

[0035] Preferably, the addition amount of the porous supported catalyst added in step S4 is 2-10 wt% (calculated based on the mass of the red mud) of the mass of the dry red mud.

[0036] The gradient reaction tower 10 in S5 is provided with baffles 12, and the residence time of the material is extended to 8-10 minutes, and the carbon fixation rate is ≥95%.

[0037] The working principle and working process of the device are as follows: the red mud is heated to 100-120℃ by the red mud drying tower 1, dried, and then ground to 150-200 mesh by the ball mill 2; the pretreated red mud enters the ultrasonic crushing module through the red mud feeding pipe 16 and the first red mud annular distributor 4, and deionized water is introduced through the water inlet pipe 15; after ultrasonic crushing, the porous supported catalyst enters the multi-layer micro-channel mixing module 9 through the catalyst feeding pipe 14; while the pretreated red mud, the CO2 is pressurized to the required pressure of supercritical CO2 in the multi-stage reciprocating compressor 11, and is uniformly distributed into the multi-layer micro-channel mixing module 9 through the CO2 annular distributor 6; after the above-mentioned materials are introduced into the multi-layer micro-channel mixing module 9, the supercritical CO2, the red mud slurry and the catalyst are instantaneously mixed; the three-phase mixed slurry after mixing enters the gradient reaction tower 10 for gradient temperature reaction, and through the ultrasonic-micro-channel synergistic effect, the particle size of the red mud is reduced to 1-5 μm, and the three-phase mixing is completed within 0.5 seconds with the supercritical CO2; at the same time, the porous supported calcium-magnesium composite catalyst is used, and the confinement effect and hydrophobicity of the carrier are used to improve the carbon fixation efficiency to more than 95%, and the problem of silicate side reaction caused by excessive alkalinity is completely solved; the three-phase mixed slurry after mixing is reacted for a period of time, and the circulating pump 19 is started every period of time to pump out the red mud accumulated in the conical collector 18 and send it back to the upper reaction area of the gradient reaction tower 10 through the return pipe to form material circulation, which not only improves the uniformity of the reaction and the utilization rate of the red mud carbon fixation, but also reduces the corrosion of the device and prolongs the service life of the device; after the reaction is completed, the heating is stopped and the temperature is lowered; when working in the reactor, new red mud and CO2 can also be treated in the red mud drying tower 1, the ball mill 2 and the multi-stage reciprocating compressor 11 to make the whole process continuous.

[0038] The application will be further described below in conjunction with examples.

[0039] Example 1 S1, take the Bayer process red mud of a certain aluminum plant, wash the red mud, dry it at 105℃ for 24h, and crush it by the ball mill 2 to pass through the 150 mesh sieve; S2, CO2 was pressurized to supercritical CO2 reaction pressure in a multi-stage reciprocating compressor 11, and the absolute pressure P1 = 12 MPa was adjusted; S3, the slurry entered an ultrasonic crushing zone (frequency 40 kHz, amplitude 60%), and the red mud particle size was crushed to 4 μm; S4, the crushed slurry and supercritical CO2 entered a multi-layer microchannel mixing module 9, and the mixing time was 0.4 seconds; S5, the mixed material was reacted in a gradient reaction tower 10 (upper layer 38°C / middle layer 55°C / lower layer 70°C), 5 wt% porous supported catalyst was added, and the reaction time was 8 min; After the reaction was completed, the carbon sequestration efficiency was determined by acidolysis-gas chromatography (acidolysis: the red mud sample after reaction was passed through a 200 mesh screen, reacted with hydrochloric acid and shaken, the CO2 generated in the reaction was collected for gas chromatography analysis and quantitative calculation), and the carbon sequestration rate was 94.7%.

[0040] Example 2 S1, the Bayer process red mud from a certain aluminum plant was taken, the red mud was washed, dried at 110°C for 26 h, and crushed by a ball mill 2, and then passed through a 200 mesh screen; S2, CO2 was pressurized to supercritical CO2 reaction pressure in a multi-stage reciprocating compressor 11, and the absolute pressure P1 = 18 MPa was adjusted; S3, the slurry entered an ultrasonic crushing zone (frequency 40 kHz, amplitude 80%), and the red mud particle size was crushed to 2 μm; S4, the crushed slurry and supercritical CO2 entered a multi-layer microchannel mixing module 9, and the mixing time was 0.3 seconds; S5, the mixed material was reacted in a gradient reaction tower 10 (upper layer 42°C / middle layer 58°C / lower layer 75°C), 8 wt% porous supported catalyst was added, and the reaction time was 9 min; After the reaction was completed, the carbon sequestration efficiency was determined by acidolysis-gas chromatography, and the carbon sequestration rate was 96.2%.

[0041] Example 3 S1, the Bayer process red mud from a certain aluminum plant was taken, the red mud was washed, dried at 100°C for 26 h, and crushed by a ball mill 2, and then passed through a 200 mesh screen; S2, CO2 was pressurized to supercritical CO2 reaction pressure in a multi-stage reciprocating compressor 11, and the absolute pressure P1 = 22 MPa was adjusted; S3, the slurry entered an ultrasonic crushing zone (frequency 40 kHz, amplitude 70%), and the red mud particle size was crushed to 1.5 μm; S4, the crushed slurry and supercritical CO2 entered a multi-layer microchannel mixing module 9, and the mixing time was 0.5 seconds; S5, the mixed material is reacted in the gradient reaction tower 10 (upper layer 45°C / middle layer 62°C / lower layer 78°C), 3 wt% porous supported catalyst is added, and the reaction time is 10 min; After the reaction is completed, the carbon sequestration efficiency is determined by using the acidolysis-gas chromatography method, and the carbon sequestration rate is 95.1%.

[0042] Example 4 S1, taking the bayer process red mud of an aluminum plant, the red mud is washed, dried at 115°C for 18h, and crushed by a ball mill 2, and then passed through a 160 mesh screen; S2, the CO2 is pressurized to the supercritical CO2 reaction pressure in the multi-stage reciprocating compressor 11, and the absolute pressure P1=15MPa is adjusted; S3, the slurry enters the ultrasonic crushing area (frequency 40 kHz, amplitude 50%), and the red mud particle size is crushed to 4μm; S4, the crushed slurry and the supercritical CO2 enter the multi-layer microchannel mixing module, and the mixing time is 0.6 seconds; S5, the mixed material is reacted in the gradient reaction tower 10 (upper layer 35°C / middle layer 50°C / lower layer 65°C), 10 wt% porous supported catalyst is added, and the reaction time is 8.5 min; After the reaction is completed, the carbon sequestration efficiency is determined by using the acidolysis-gas chromatography method, and the carbon sequestration rate is 94.3%.

[0043] Example 5 S1, taking the bayer process red mud of an aluminum plant, the red mud is washed, dried at 108°C for 22h, and crushed by a ball mill 2, and then passed through a 170 mesh screen; S2, the CO2 is pressurized to the supercritical CO2 reaction pressure in the multi-stage reciprocating compressor 11, and the absolute pressure P1=25MPa is adjusted; S3, the slurry enters the ultrasonic crushing area (frequency 40 kHz, amplitude 90%), and the red mud particle size is crushed to 1μm; S4, the crushed slurry and the supercritical CO2 enter the multi-layer microchannel mixing module 9, and the mixing time is 0.2 seconds; S5, the mixed material is reacted in the gradient reaction tower 10 (upper layer 48°C / middle layer 65°C / lower layer 80°C), 2 wt% porous supported catalyst is added, and the reaction time is 9.5 min; After the reaction is completed, the carbon sequestration efficiency is determined by using the acidolysis-gas chromatography method, and the carbon sequestration rate is 96.8%, Example 6 S1, taking the bayer process red mud of an aluminum plant, the red mud is washed, dried at 112°C for 20h, and crushed by a ball mill 2, and then passed through a 190 mesh screen; S2, the CO2 is pressurized to the supercritical CO2 reaction pressure in the multi-stage reciprocating compressor 11, and the absolute pressure P1=10MPa is adjusted; S3, the slurry enters the ultrasonic crushing zone (frequency 40 kHz, amplitude 75%), and the red mud particle size is crushed to 5 μm; S4, the crushed slurry and supercritical CO2 enter the multi-layer microchannel mixing module, and the mixing time is 0.7 seconds; S5, the mixed material is reacted in the gradient reaction tower 10 (upper layer 40℃ / middle layer 55℃ / lower layer 70℃), 6 wt% porous supported catalyst is added, the reaction time is 10 min, and the circulating pump 19 group returns the material in a proportion of 15%; After the reaction is completed, the carbon sequestration efficiency is determined by acidolysis-gas chromatography, and the carbon sequestration rate is 95.9%.

[0044] Example 7 S1, take the Bayer red mud, the red mud is washed, dried at 105℃ for 24 h, crushed by a ball mill, and sieved through a 150 mesh screen; S2, the CO2 is pressurized to the supercritical CO2 reaction pressure in the multi-stage reciprocating compressor 11, and the absolute pressure P1=20 MPa is adjusted; S3, the slurry enters the ultrasonic crushing zone (frequency 40 kHz, amplitude 85%), and the red mud particle size is crushed to 2.5 μm; S4, the crushed slurry and supercritical CO2 enter the multi-layer microchannel mixing module 9, and the mixing time is 0.4 seconds; S5, the mixed material is reacted in the gradient reaction tower 10 (upper layer 50℃ / middle layer 65℃ / lower layer 80℃), 7 wt% porous supported catalyst is added, and the reaction time is 8 min. After the reaction is completed, the carbon sequestration efficiency is determined by acidolysis-gas chromatography, and the carbon sequestration rate is 95.3%.

[0045] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for carbon sequestration in red mud under supercritical conditions, characterized in that, The method comprises the following steps: S1, washing and drying the red mud to remove free water, and then crushing the dried red mud to form a dried red mud powder, and then mixing the dried red mud powder with deionized water in a certain proportion; S2, pressurizing CO2 to a supercritical pressure and a supercritical temperature; S3, ultrasonic crushing of the slurry obtained in step S1, cavitation crushing by an ultrasonic array, and reduction of the particle size of the red mud; S4, three-phase mixing of the crushed slurry, pressurized supercritical CO2 of step S2, and a porous supported catalyst in a honeycomb-shaped microchannel, with a mixing time of ≤0.5 seconds; S5, the mixture enters a gradient reaction tower, and a carbon sequestration reaction is carried out under the condition of segmented temperature control, and then the temperature is lowered.

2. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: In step S1, the drying temperature is T1, 100℃≤ T1<120℃, the dried red mud is crushed to 150~200 mesh, and the red mud is mixed with deionized water in a liquid-solid ratio of 8~10:1 after crushing.

3. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: In step S2, the supercritical CO2 reaction pressure is P1, 10MPa<P1≤ 25MPa, and the supercritical CO2 reaction temperature of step S3 is T2, 35℃<T2 ≤ 80℃.

4. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: In step S3, the ultrasonic crushing uses a piezoelectric ceramic transducer with a frequency of 40 kHz, and the amplitude dynamic control range is 10~100%, so that the particle size of the red mud is reduced to 1~5μm.

5. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: In step S4, the addition amount of the porous supported catalyst is 2~10wt% of the mass of the dried red mud powder.

6. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1 or 5, characterized in that: The porous supported catalyst in step S4 is prepared by the following steps: (1) using a sol-gel method, a carrier is synthesized using zinc acetate dihydrate, 2-methylimidazole, and methanol; (2) calcium nitrate and magnesium nitrate are prepared into an impregnation solution with a total molar mass of 1.5mol / L in a Ca:Mg=2:1 molar ratio, the carrier is immersed in the impregnation solution to obtain an impregnated carrier; (3) the impregnated carrier is placed in an N2 atmosphere for gradient calcination, dehydrated at 100~150℃ for 1~2h, decomposed at 300~400℃ for 2~3h to generate MgO / CaO nanoparticles, and then calcined at 550~650℃ for 3~4h to form stable oxides in the impregnated carrier, and then subjected to hexamethyldisilazane gas phase hydrophobic modification to obtain a porous supported catalyst.

7. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: In step S4, the honeycomb-shaped microchannel is a microchannel mixing module stacked by multiple layers of titanium alloy microchannel plates, and each plate contains 800~4000 regular hexagonal flow channels with a side distance of 50~300μm.

8. The method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: In step S5, the temperature of the upper low-temperature zone of the gradient reaction tower is 35~50℃, the temperature of the middle middle-temperature zone is 50~65℃, and the temperature of the lower high-temperature zone is 65~80℃.

9. The device used in the method for realizing carbon sequestration of red mud under supercritical conditions according to claim 1, characterized in that: The application relates to a red mud drying tower, a ball mill communicated with the red mud drying tower, a mixing outer cylinder arranged at the outlet of the ball mill, a first red mud annular distributor, a second red mud annular distributor and a CO2 annular distributor arranged in the mixing outer cylinder from top to bottom, an ultrasonic transducer and a titanium alloy amplitude lever vertically arranged between the first red mud annular distributor and the second red mud annular distributor, a multilayer microchannel mixing module arranged between the second red mud annular distributor and the CO2 annular distributor, a gradient reaction tower arranged below the CO2 annular distributor, a multistage reciprocating compressor connected to the outside of the CO2 annular distributor, a plurality of groups of baffles arranged in the gradient reaction tower at intervals, a pressure relief valve arranged on the outer wall of the gradient reaction tower, a catalyst feeding pipe arranged at the top end of the gradient reaction tower, a water feeding pipe and a red mud feeding pipe communicated with the ball mill arranged on the first red mud annular distributor, a temperature and pressure control system arranged outside the gradient reaction tower, a conical collector arranged at the bottom end of the gradient reaction tower, a circulating pump connected to the outside of the conical collector and communicated with the top of the gradient reaction tower.

10. The device used in the method for realizing carbon sequestration of red mud under supercritical conditions according to claim 9, characterized in that: The CO2 annular distributor is annularly distributed with nozzles, the nozzle caliber is 0.1-0.5 mm, the nozzles are arranged towards the second red mud annular distributor, and the CO2 flowing in the CO2 annular distributor flows from the bottom end of the multilayer microchannel mixing module towards the ultrasonic transducer.

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