System and method for recovering alkali by carbonizing red mud

Abstract

A system and method for recovering alkali by carbonizing red mud. The method comprises: adding water and an additive into red mud, and carrying out slurry mixing to obtain a red mud slurry; introducing CO2-containing flue gas into the red mud slurry for carbonization reaction, and then carrying out solid-liquid separation and washing to respectively obtain carbonized red mud and a dilute alkali liquor; carrying out evaporation and concentration on the dilute alkali liquor, carrying out alkali concentration regulation, then introducing CO2 flue gas, and adding a sodium bicarbonate seed crystal for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate; carrying out solid-liquid separation on the mixed slurry to respectively obtain a sodium bicarbonate product and a concentrated alkali liquor; and returning to the step of alkali concentration regulation and / or carbonization and crystallization to treat the concentrated alkali liquor.

Description

A system and method for recovering alkali from red mud carbonization

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202310760149.9 filed on June 26, 2023, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to the field of solid waste resource recovery, and in particular to a system and method for recovering alkali by carbonizing red mud. Background Art

[0004] Red mud is a highly alkaline solid waste generated during alumina production. Its pH typically ranges from 10 to 13, and its alkali content, calculated as the mass percentage of Na2O, ranges from 2% to 13%. The alkaline mineral composition of red mud is complex, consisting of soluble alkali and chemically bound alkali. The chemically bound alkali exists in a stable form within the mud, which is the primary reason for the difficulty in dealkalization.

[0005] Currently, the commonly used dealkali methods include water washing, acid leaching, salt leaching, lime method, calcification carbonization method, hydrothermal method, seawater neutralization method, acid gas neutralization method, biological dealkali method, etc. However, they have the following disadvantages:

[0006] (1) The water washing method can only remove free alkali. Although it is a common red mud washing method used by alumina companies, it can only remove free alkali in the red mud.

[0007] (2) Although the acid leaching method can remove free alkali and chemically bound alkali during the treatment process, it also causes the leaching of metals such as iron, aluminum, calcium, and magnesium in the red mud, resulting in a complex composition of the acid leaching solution, which in turn makes the treatment difficult.

[0008] (3) Salt leaching will produce complex salt solutions while removing alkaline components.

[0009] (4) The lime method can effectively remove alkali from red mud, but since Na needs to be replaced by Ca in lime, the Ca / Na mass ratio needs to be above 4, which is not very economical. In addition, the addition of a large amount of lime will further increase the amount of solid waste.

[0010] (5) Seawater neutralization is restricted by geographical location and environmental protection policies and cannot be widely used and promoted.

[0011] (6) Microbial treatment of red mud de-alkalization has the advantages of being green and low-carbon. However, this technology is expensive and difficult to apply on a large scale in industry.

[0012] (7) The acid gas neutralization method uses acid gases such as SO2 and CO2 to react with alkaline substances in red mud to achieve red mud dealkalization. It not only reduces acid gas emissions but also can achieve red mud dealkalization. However, there is no industrial application at present. The main reasons are low efficiency of acid gas dealkalization and high cost of recovering dilute alkali in the solution.

[0013] Therefore, how to provide a system and method for recovering alkali by carbonizing red mud to reduce the cost of recovering dilute alkali solution through carbonization reaction of CO2 gas, while improving the dealkalization efficiency of acidic gas, is a technical problem that urgently needs to be solved.

[0014] Summary of the Invention

[0015] The present disclosure provides a system and method for recovering alkali by carbonizing red mud, so as to solve the technical problems of low efficiency of acid gas de-alkali and high cost of dilute alkali recovery in the acid gas neutralization method in the prior art.

[0016] According to a first aspect of the present disclosure, a method for recovering alkali by carbonizing red mud is provided, the method comprising: adding water and additives to red mud, and performing slurry adjustment to obtain red mud slurry; introducing CO2-containing flue gas into the red mud slurry for carbonization reaction, and then performing solid-liquid separation and washing to obtain carbonized red mud and dilute alkali solution, respectively; evaporating and concentrating the dilute alkali solution, and adjusting the alkali concentration, and then introducing CO2 flue gas and adding sodium bicarbonate seeds for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate; performing solid-liquid separation on the mixed slurry to obtain a sodium bicarbonate product and a concentrated alkali solution, respectively; and returning the concentrated alkali solution to the alkali concentration adjustment and / or the carbonization crystallization to achieve recycling of the alkali solution.

[0017] According to a second aspect of the present disclosure, a system for recovering alkali from carbonized red mud is provided, the system being adapted to the method described in the first aspect, the system comprising: a red mud slurrying unit, the red mud slurrying unit comprising a red mud metering and conveying device, a water replenishing device, an additive dosing device, a slurrying tank, and a slurry pump, the discharge ports of the red mud metering and conveying device, the water replenishing device, and the additive dosing device being respectively connected to the feed port of the slurrying tank, and the discharge port of the slurrying tank being connected to the feed port of the slurry pump; a flue gas pretreatment unit The flue gas pretreatment unit includes a drainage pipe, a flue gas compressor, a flue gas retention tank and a flue gas conveying device, the air outlet of the drainage pipe is connected to the air inlet of the flue gas compressor, the air outlet of the flue gas compressor is connected to the air inlet of the flue gas retention tank, and the flue gas conveying device is connected to the air outlet of the flue gas retention tank; the carbonization reaction unit includes a carbonization reactor, an exhaust pipe and a discharge pump, the feed port of the carbonization reactor is connected to the discharge port of the slurry pump, the air inlet of the carbonization reactor is connected to the discharge port of the slurry pump, and the air inlet of the carbonization reactor is connected to the discharge port of the slurry pump. The gas outlet of the flue gas conveying device is connected to the exhaust pipe, and the discharge port of the carbonization reactor is connected to the feed port of the discharge pump; a solid-liquid separation and washing unit, the solid-liquid separation and washing unit includes a solid-liquid separation and washing device and a dilute alkali solution delivery pump, the discharge port of the discharge pump is connected to the feed port of the solid-liquid separation and washing device, and the liquid outlet of the solid-liquid separation device is connected to the dilute alkali solution delivery pump; and an alkali recovery unit, the alkali recovery unit includes an evaporator, an alkali solution mixing tank, a carbonization reactor, and a discharge port of the carbonization reactor. The crystallizer and separator, the liquid outlet of the dilute alkali solution delivery pump is connected to the liquid inlet of the evaporator, the material outlet of the evaporator is connected to the material inlet of the alkali solution mixing tank or the slurry mixing tank, the liquid outlet of the alkali solution mixing tank is connected to the liquid inlet of the carbonization crystallizer, the air inlet of the carbonization crystallizer is connected to the flue gas conveying device, and the material outlet of the carbonization crystallizer is connected to the separator to achieve separation of the sodium bicarbonate product and the concentrated alkali solution, and the liquid outlet of the separator is respectively connected to the alkali solution mixing tank and the slurry mixing tank. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] To more clearly illustrate the technical solutions in the embodiments of the present disclosure, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present disclosure, and those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0019] In order to more completely understand the present disclosure and its beneficial effects, the following description will be given in conjunction with the accompanying drawings. In the following description, the same reference numerals represent the same parts.

[0020] FIG1 is a schematic flow diagram of a method for recovering alkali by carbonizing red mud according to some embodiments of the present disclosure;

[0021] FIG2 is a detailed schematic diagram of a method for recovering alkali by carbonizing red mud according to some embodiments of the present disclosure;

[0022] FIG3 is a logic diagram of a system for recovering alkali from red mud carbonization according to some embodiments of the present disclosure; and

[0023] FIG4 is a schematic diagram of a system structure for recovering alkali from red mud carbonization according to some embodiments of the present disclosure;

[0024] In the attached drawings: 1. Red mud metering and conveying device; 2. Water replenishing device; 3. Additive dosing device; 4. Slurry mixing tank; 5. Slurry pump; 6. Drainage pipe; 7. Flue gas compressor; 8. Flue gas retention tank; 9. Flue gas conveying device; 10. Carbonization reactor; 11. Automatic controller; 12. Flue gas detection device; 13. Exhaust pipe; 14. Discharge pump; 15. Solid-liquid separation and washing device; 16. Dilute alkali solution conveying pump; 17. Evaporator; 18. Steam-water separator; 19. Alkali solution mixing tank; 20. Carbonization crystallizer; 21. Separator. DETAILED DESCRIPTION

[0025] To make the purpose, technical solutions, and advantages of the embodiments of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the drawings in some embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present disclosure.

[0026] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present disclosure can be purchased from the market or prepared by existing methods.

[0027] Figure 1 is a schematic flow diagram of a method for recovering alkali by carbonizing red mud according to some embodiments of the present disclosure. As shown in Figure 1, a method for recovering alkali by carbonizing red mud provided by an embodiment of the present disclosure includes: step S1. adding water and additives to red mud and performing slurry adjustment to obtain red mud slurry; step S2. introducing CO2-containing flue gas into the red mud slurry for carbonization reaction, followed by solid-liquid separation and washing to obtain carbonized red mud and dilute alkali solution, respectively; step S3. evaporating and concentrating the dilute alkali solution, adjusting the alkali concentration, introducing CO2 flue gas and adding sodium bicarbonate seeds for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate; step S4. performing solid-liquid separation on the mixed slurry to obtain a sodium bicarbonate product and a concentrated alkali solution, respectively; and step S5. returning the concentrated alkali solution to the alkali concentration adjustment and / or carbonization crystallization process to achieve recycling of the alkali solution.

[0028] In some optional embodiments, the mass ratio of the additive to the red mud dry weight may be 0.1% to 10%.

[0029] By controlling the mass ratio of the additive to the dry weight of red mud to 0.1% to 10%, the additive can be fully absorbed into the red mud, and water is added to stir the red mud to form a slurry, which promotes the uniform distribution of the additive in the red mud, so that the subsequent CO2 flue gas can be evenly mixed with the red mud slurry, and the absorption and storage capacity of the red mud slurry for CO2 is improved through the absorbent, thereby improving the dealkalization efficiency of the red mud slurry by CO2 flue gas.

[0030] In some optional embodiments, the additive may include at least one of ammonia, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate, ethanolamine, N-methyldiethanolamine, triethanolamine, 3-methylaminopropylamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N-methyldiethanolamine, N,N-diethylaminoethanol and piperazine.

[0031] By controlling the type of additive to include at least one of ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate, ethanolamine, N-methyldiethanolamine, triethanolamine, 3-methylaminopropylamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N-methyldiethanolamine, N,N-diethylaminoethanol and piperazine, the additive can be made to have the ability to absorb and store CO2, thereby effectively improving the reaction efficiency of the alkaline substances in the red mud slurry with the CO2 flue gas to obtain carbonized red mud.

[0032] In some optional embodiments, the temperature of the carbonization reaction is 25° C. to 150° C., and the pressure of the carbonization reaction is 0.1 MPa to 3.0 MPa.

[0033] By controlling the temperature of the carbonization reaction to 25°C to 150°C and the pressure of the carbonization reaction to 0.1MPa to 3.0MPa, the CO2 flue gas can react completely with the alkaline substances in the red mud slurry, thereby improving the dealkalization efficiency of the red mud slurry by the acidic gas CO2.

[0034] In some optional embodiments, the reaction temperature of the carbonization crystallization is 20°C to 60°C.

[0035] By controlling the reaction temperature of carbonization crystallization to 20°C to 60°C, the CO2 flue gas and the dilute alkali solution after evaporation and concentration can react completely, and by adding sodium bicarbonate seed crystals, the sodium bicarbonate in the solution can be precipitated, thereby obtaining a mixed slurry containing sodium bicarbonate.

[0036] FIG2 is a detailed schematic flow diagram of a method for recovering alkali by carbonizing red mud according to some embodiments of the present disclosure. As shown in FIG2 , in some optional embodiments, the dilute alkali solution is evaporated and concentrated, and the alkali concentration is adjusted, followed by the introduction of CO2 flue gas and the addition of sodium bicarbonate seed crystals for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate, including the following steps:

[0037] S301. The dilute alkali solution is evaporated and concentrated to obtain concentrated alkali solution and CO2-containing steam;

[0038] S302. Adjusting the alkali concentration of the concentrated alkali solution, CO2 flue gas was introduced and sodium bicarbonate seed crystals were added for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate;

[0039] S303. The CO2-containing steam is subjected to steam-water separation to obtain high-concentration CO2 gas and distilled water, respectively;

[0040] S304. Returning the distilled water to the slurry to achieve water recycling; and

[0041] S305. The high-concentration CO2 gas is mixed with the CO2 flue gas, and then returned to the carbonization crystallization to achieve the recycling of CO2 gas.

[0042] By separating the CO2-containing steam obtained by evaporation and concentration, and then recycling the separated high-concentration CO2 gas and distilled water respectively, the recovery cost of the dilute alkali solution can be effectively reduced.

[0043] FIG3 is a logic diagram of a system for recovering alkali by carbonizing red mud according to some embodiments of the present disclosure, and FIG4 is a structural diagram of a system for recovering alkali by carbonizing red mud according to some embodiments of the present disclosure. As shown in FIG3 and FIG4, the embodiments of the present disclosure further provide a system for recovering alkali by carbonizing red mud, the system being adapted to the method, the system comprising: a red mud slurrying unit, the red mud slurrying unit comprising a red mud metering and conveying device 1, a water replenishing device 2, an additive dosing device 3, a slurrying tank 4 and a slurry pump 5, the discharge ports of the red mud metering and conveying device 1, the water replenishing device 2 and the additive dosing device 3 being respectively connected to the feed port of the slurrying tank 4, the discharge port of the slurrying tank 4 being connected to the feed port of the slurry pump 5; a flue gas pretreatment unit, the flue gas pretreatment unit It includes a drainage pipe 6, a flue gas compressor 7, a flue gas retention tank 8 and a flue gas conveying device 9, the air outlet of the drainage pipe 6 is connected to the air inlet of the flue gas compressor 7, the air outlet of the flue gas compressor 7 is connected to the air inlet of the flue gas retention tank 8, and the flue gas conveying device 9 is connected to the air outlet of the flue gas retention tank 8; a carbonization reaction unit, the carbonization reaction unit includes a carbonization reactor 10, an exhaust pipe 13 and a discharge pump 14, the feed port of the carbonization reactor 10 is connected to the discharge port of the slurry pump 5, and the air inlet of the carbonization reactor 10 is connected to the flue gas conveying device 9 The gas outlet of the carbonization reactor 10 is connected to the exhaust pipe 13, and the discharge port of the carbonization reactor 10 is connected to the feed port of the discharge pump 14; a solid-liquid separation and washing unit, the solid-liquid separation and washing unit includes a solid-liquid separation and washing device 15 and a dilute alkali solution delivery pump 16, the discharge port of the discharge pump 14 is connected to the feed port of the solid-liquid separation and washing device 15, and the liquid outlet of the solid-liquid separation device is connected to the dilute alkali solution delivery pump 16; and an alkali recovery unit, the alkali recovery unit includes an evaporator 17, an alkali solution mixing tank 19, a carbonization crystallizer 20 and a separation The device 21, the liquid outlet of the dilute alkali solution delivery pump 16 is connected to the liquid inlet of the evaporator 17, the discharge port of the evaporator 17 is connected to the feed port of the alkali solution mixing tank 19 or the slurry mixing tank 4, the liquid outlet of the alkali solution mixing tank 19 is connected to the liquid inlet of the carbonization crystallizer 20, the air inlet of the carbonization crystallizer 20 is connected to the flue gas delivery device 9, and the discharge port of the carbonization crystallizer 20 is connected to the separator 21 to achieve separation of the sodium bicarbonate product and the concentrated alkali solution, and the liquid outlet of the separator 21 is respectively connected to the alkali solution mixing tank 19 and the slurry mixing tank 4.

[0044] By introducing a red mud slurry preparation unit, a flue gas pretreatment unit, a carbonization reaction unit, a solid-liquid separation and washing unit, and an alkali recovery unit, slurry preparation of red mud, water, and additives, as well as carbonization reaction, evaporation concentration, alkali concentration adjustment, and solid-liquid separation can be achieved, thereby achieving complete reaction between alkaline substances in the red mud slurry and CO2 flue gas, and obtaining carbonized red mud. At the same time, the dilute alkali solution can be recovered and utilized, reducing the recovery cost of the dilute alkali solution.

[0045] The system is implemented based on the above method. The specific steps of the method can refer to the above embodiments. Since the system adopts part or all of the technical solutions of the above embodiments, it has at least all the beneficial effects brought by the technical solutions of the above embodiments, which will not be described one by one here.

[0046] In some optional embodiments, the alkali recovery unit further includes a steam-water separator 18, the feed port of the steam-water separator 18 is connected to the gas outlet of the evaporator 17, the gas outlet of the steam-water separator 18 is connected to the gas inlet of the carbonization crystallizer 20, and the liquid outlet of the steam-water separator 18 is connected to the water replenishment device 2 to achieve the recycling of distilled water.

[0047] By introducing a steam-water separator 18 into the alkali recovery unit, the CO2 and water vapor in the CO2-containing steam can be separated by the steam-water separator 18. By limiting the connection method of the steam-water separator 18, the high-concentration CO2 gas and distilled water obtained by the steam-water separator 18 can be further recycled, thereby effectively reducing the recovery cost of the dilute alkali solution.

[0048] In some optional embodiments, the carbonization reaction unit may further include an automatic controller 11 and a flue gas detection device 12, wherein the automatic controller 11 is arranged on the side wall of the carbonization reactor 10, and the flue gas detection device 12 is arranged on the top of the carbonization reactor 10, and the flue gas detection device 12 is connected to the automatic controller 11 via an electrical signal.

[0049] By introducing an automatic controller 11 and a flue gas detection device 12 into the carbonization reaction unit, using the flue gas detection device 12 to detect the concentration of CO2 gas in the carbonization reactor 10, and then analyzing the concentration data through the automatic controller 11, the opening and closing of the exhaust pipe 13 can be effectively controlled, thereby prompting the residual gas in the carbonization reactor 10 to be discharged.

[0050] The technical solutions of the present disclosure are further described below in conjunction with some examples. It should be understood that these examples are intended only to illustrate the present disclosure and are not intended to limit the scope of the present disclosure. Experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national standards. If there are no corresponding national standards, the methods are carried out in accordance with common international standards, conventional conditions, or conditions recommended by the manufacturer.

[0051] Example 1

[0052] The composition of the red mud used is shown in Table 1.

[0053] Table 1 Main chemical composition of red mud (in terms of oxidation state)

[0054] The CO2-containing flue gas used is the flue gas from the roasting furnace of an alumina enterprise. The CO2 content in the flue gas is 19.5%, the O2 content is 15.4%, and the SO2 content is 15mg / m 3 .

[0055] The steps of Example 1 are as follows:

[0056] Red mud, water and additive ammonia water (mass concentration of 20%) are slurried in a red mud slurry mixing unit, the amount of ammonia water added is 10% of the dry weight of the red mud, and the liquid-solid ratio of the obtained red mud slurry is 20:1;

[0057] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 50°C and the carbonization reaction is carried out under atmospheric pressure;

[0058] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0059] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0060] The removal rate of alkali in red mud is 30%, and 36.09 kg of sodium bicarbonate product is recovered per ton of red mud.

[0061] Example 2

[0062] The steps of Example 2 are as follows:

[0063] Red mud, water and an additive, ammonium carbonate, are mixed in a red mud mixing unit, wherein the amount of ammonium carbonate added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0064] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 50°C and the carbonization reaction is carried out under atmospheric pressure;

[0065] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0066] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0067] The removal rate of alkali in red mud is 35%, and 42.10 kg of sodium bicarbonate product is recovered per ton of red mud.

[0068] Example 3

[0069] The steps of Example 3 are as follows:

[0070] Red mud, water and an additive, ammonium carbonate, are mixed in a red mud mixing unit, wherein the amount of ammonium carbonate added is 5% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0071] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 100°C and the carbonization reaction pressure is 3.0 MPa;

[0072] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0073] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0074] The removal rate of alkali in red mud is 52%, and 62.56 kg of sodium bicarbonate product is recovered per ton of red mud.

[0075] Example 4

[0076] The steps of Example 4 are as follows:

[0077] Red mud, water and an additive, ammonium carbonate, are mixed in a red mud mixing unit, wherein the amount of ammonium carbonate added is 1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 3:1;

[0078] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 80°C and the carbonization reaction pressure is 2.0 MPa;

[0079] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0080] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0081] The removal rate of alkali in red mud is 56%, and 67.37 kg of sodium bicarbonate product is recovered per ton of red mud.

[0082] Example 5

[0083] The steps of Example 5 are as follows:

[0084] Red mud, water and an additive, ammonium carbonate, are mixed in a red mud mixing unit, wherein the amount of ammonium carbonate added is 0.2% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 7:1;

[0085] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 40°C and the carbonization reaction pressure is 0.5 MPa;

[0086] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0087] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0088] The removal rate of alkali in red mud is 51%, and 61.35 kg of sodium bicarbonate product is recovered per ton of red mud.

[0089] Example 6

[0090] The steps of Example 6 are as follows:

[0091] Red mud, water and an additive, ammonium carbonate, are mixed in a red mud mixing unit, wherein the amount of ammonium carbonate added is 0.5% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0092] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0093] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0094] The dilute alkali solution is transferred to the alkali recovery unit, where it is concentrated by evaporation and then fed into a carbonization crystallizer 20 with an adjusted alkali concentration. Carbonization and crystallization are then carried out by introducing a CO2-containing gas. The resulting sodium bicarbonate-containing slurry undergoes solid-liquid separation to produce sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is then returned to the alkali solution preparation tank 19 and the slurry preparation tank 4. The alkali removal rate from the red mud is 60%, and 72.18 kg of sodium bicarbonate product is recovered per ton of red mud.

[0095] Example 7

[0096] The steps of Example 7 are as follows:

[0097] Red mud, water and an additive, ammonium bicarbonate, are slurried in a red mud slurry mixing unit, wherein the amount of ammonium bicarbonate added is 0.6% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0098] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0099] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0100] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0101] The removal rate of alkali in red mud is 61%, and 73.39 kg of sodium bicarbonate product is recovered per ton of red mud.

[0102] Example 8

[0103] The steps of Example 8 are as follows:

[0104] Red mud, water and ammonium chloride as an additive are mixed in a red mud mixing unit, wherein the amount of ammonium chloride added is 0.5% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0105] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 70°C and the carbonization reaction pressure is 1.5 MPa;

[0106] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0107] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0108] The removal rate of alkali in red mud is 58%, and 69.78 kg of sodium bicarbonate product is recovered per ton of red mud.

[0109] Example 9

[0110] The steps of Example 9 are as follows:

[0111] Red mud, water and ammonium sulfate as an additive are mixed in a red mud mixing unit, wherein the amount of ammonium chloride added is 1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 7:1;

[0112] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 80°C and the carbonization reaction pressure is 1.2 MPa;

[0113] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0114] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0115] The removal rate of alkali in red mud is 59.5%, and 71.58 kg of sodium bicarbonate product is recovered per ton of red mud.

[0116] Example 10

[0117] The steps of Example 10 are as follows:

[0118] Red mud, water and ethanolamine as an additive are mixed in a red mud mixing unit, wherein the amount of ethanolamine added is 0.2% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0119] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 40°C and the carbonization reaction pressure is 1.0 MPa;

[0120] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0121] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0122] The removal rate of alkali in red mud is 63%, and 75.79 kg of sodium bicarbonate product is recovered per ton of red mud.

[0123] Example 11

[0124] The steps of Example 11 are as follows:

[0125] Red mud, water and additive N-methyldiethanolamine are slurried in a red mud slurry mixing unit, wherein the amount of N-methyldiethanolamine added is 0.2% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0126] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 40°C and the carbonization reaction pressure is 1.0 MPa;

[0127] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0128] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0129] The removal rate of alkali in red mud is 62%, and 74.59 kg of sodium bicarbonate product is recovered per ton of red mud.

[0130] Example 12

[0131] The steps of Example 12 are as follows:

[0132] Red mud, water and triethanolamine as an additive are mixed in a red mud mixing unit, wherein the amount of triethanolamine added is 0.2% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 5:1;

[0133] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 40°C and the carbonization reaction pressure is 1.0 MPa;

[0134] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0135] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0136] The removal rate of alkali in red mud is 64.5%, and 77.60 kg of sodium bicarbonate product is recovered per ton of red mud.

[0137] Example 13

[0138] The steps of Example 13 are as follows:

[0139] Red mud, water and additive 3-methylaminopropylamine are slurried in a red mud slurry mixing unit, wherein the amount of 3-methylaminopropylamine added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0140] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0141] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0142] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0143] The removal rate of alkali in red mud is 60%, and 72.18 kg of sodium bicarbonate product is recovered per ton of red mud.

[0144] Example 14

[0145] The steps of Example 14 are as follows:

[0146] Red mud, water and additive diethylenetriamine are slurried in a red mud slurry mixing unit, wherein the amount of diethylenetriamine added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0147] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0148] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0149] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0150] The removal rate of alkali in red mud is 50%, and 60.15 kg of sodium bicarbonate product is recovered from one ton of red mud.

[0151] Example 15

[0152] The steps of Example 15 are as follows:

[0153] Red mud, water and triethylenetetramine additive are mixed in a red mud mixing unit, wherein the amount of triethylenetetramine added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0154] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0155] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0156] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0157] The removal rate of alkali in red mud is 48%, and 57.74 kg of sodium bicarbonate product is recovered per ton of red mud.

[0158] Example 16

[0159] The steps of Example 16 are as follows:

[0160] Red mud, water and tetraethylene pentamine as an additive are mixed in a red mud mixing unit, wherein the amount of tetraethylene pentamine added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0161] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0162] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0163] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0164] The removal rate of alkali in red mud is 48.6%, and 58.47 kg of sodium bicarbonate product is recovered per ton of red mud.

[0165] Example 17

[0166] The steps of Example 17 are as follows:

[0167] Red mud, water and additive N-methyldiethanolamine are slurried in a red mud slurry mixing unit, wherein the amount of N-methyldiethanolamine added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0168] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0169] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0170] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0171] The removal rate of alkali in red mud is 46.9%, and 56.42 kg of sodium bicarbonate product is recovered per ton of red mud.

[0172] Example 18

[0173] The steps of Example 18 are as follows:

[0174] Red mud, water and additive N,N-diethylaminoethanol are slurried in a red mud slurry mixing unit, wherein the amount of N,N-diethylaminoethanol added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0175] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0176] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0177] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0178] The removal rate of alkali in red mud is 51.7%, and 62.20 kg of sodium bicarbonate product is recovered per ton of red mud.

[0179] Example 19

[0180] The steps of Example 19 are as follows:

[0181] Red mud, water and piperazine as an additive are mixed in a red mud mixing unit, wherein the amount of piperazine added is 0.1% of the dry weight of the red mud, and the liquid-to-solid ratio of the obtained red mud slurry is 10:1;

[0182] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 60°C and the carbonization reaction pressure is 1.5 MPa;

[0183] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0184] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0185] The removal rate of alkali in red mud is 39%, and 46.92 kg of sodium bicarbonate product is recovered per ton of red mud.

[0186] Comparative Example 1

[0187] The steps of Comparative Example 1 are as follows:

[0188] Red mud and water are slurried in a red mud slurry mixing unit, and the liquid-solid ratio of the obtained red mud slurry is 20:1;

[0189] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 50°C and the carbonization reaction is carried out under atmospheric pressure;

[0190] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0191] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0192] The removal rate of alkali in red mud is 16.5%, and 19.85 kg of sodium bicarbonate product is recovered per ton of red mud.

[0193] Comparative Example 2

[0194] The steps of Comparative Example 2 are as follows:

[0195] Red mud and water are mixed in a red mud mixing unit to obtain a red mud slurry with a liquid-solid ratio of 1:1;

[0196] After the red mud slurry reacts with the CO2-containing flue gas in the carbonization reactor 10, the carbonization reaction temperature is 25°C and the carbonization reaction pressure is 3.0 MPa;

[0197] The red mud slurry after the carbonization reaction is washed in a countercurrent manner in a solid-liquid separation and washing unit to obtain carbonized red mud and dilute alkali solution;

[0198] The dilute alkali solution is transferred to the alkali recovery unit, and after evaporation and concentration, the alkali concentration is adjusted and sent to the carbonization crystallizer 20, and CO2-containing gas is introduced for carbonization crystallization. The slurry containing sodium bicarbonate after carbonization and crystallization is subjected to solid-liquid separation to obtain sodium bicarbonate product and concentrated alkali solution. The concentrated alkali solution is returned to the alkali solution preparation tank 19 and the slurry mixing tank 4.

[0199] The removal rate of alkali in red mud is 19%, and 22.86 kg of sodium bicarbonate product is recovered per ton of red mud.

[0200] According to one or more technical solutions of some embodiments of the present disclosure, there are at least the following technical effects or advantages:

[0201] (1) The present invention provides a method for recovering alkali by carbonizing red mud, which increases the absorption and storage capacity of red mud for CO2 gas by introducing additives, thereby improving the efficiency of CO2 gas in removing alkaline substances in red mud slurry. Since the method directly utilizes CO2 gas in flue gas for carbon fixation and conversion, there is no need to separate and concentrate the flue gas CO2, thereby achieving carbon emission reduction.

[0202] (2) According to a method for recovering alkali by carbonizing red mud in some embodiments of the present disclosure, after the red mud is fixed with CO2, the alkalinity of the red mud is significantly reduced, the pH of the leachate is less than 9.0, and the red mud is converted from Class II general industrial solid waste to Class I general industrial solid waste, and the storage and disposal requirements are reduced, which is conducive to subsequent comprehensive utilization.

[0203] (3) According to a method for recovering alkali by carbonizing red mud in some embodiments of the present disclosure, the alkaline substances in the red mud and the CO2 in the flue gas are eventually converted into sodium bicarbonate and can be recovered later, which brings considerable economic benefits to the project and reduces the overall recovery cost of the dilute alkali solution.

[0204] (4) According to some embodiments of the present disclosure, a system for recovering alkali by carbonizing red mud is provided. In the process of recovering alkaline substances in dilute alkali solution, CO2 is recovered by using an alkali recovery unit, thereby realizing the conversion of sodium bicarbonate → sodium carbonate → sodium bicarbonate. Compared with the traditional direct evaporation and crystallization to recover sodium carbonate, the amount of evaporated water is reduced, and the CO2 gas generated in the evaporation process is reused for a second time, thereby further reducing the carbon emissions of the system.

[0205] According to some embodiments of the present disclosure, a method for recovering alkali by carbonizing red mud is disclosed. By first using an absorbent, water, and red mud for slurry mixing, the absorbent can enhance the CO2 absorption and storage capacity in the red mud slurry. At the same time, the slurry mixing method is used to allow the absorbent to be fully mixed with the red mud, prompting the CO2 and the alkaline substances in the red mud to undergo a carbonization reaction. The dilute alkali solution after the carbonization reaction is then evaporated and concentrated, and the alkali concentration is adjusted. CO2 and sodium bicarbonate seeds are then added for carbonization and crystallization. Then, solid-liquid separation is performed to obtain a sodium bicarbonate product and a concentrated alkali solution, thereby recovering excess CO2 using the dilute alkali solution and achieving recycling of the concentrated alkali solution. Therefore, according to some embodiments of the present disclosure, a method for recovering alkali by carbonizing red mud can improve the dealkalization efficiency of the acidic gas CO2 and reduce the cost of recovering the dilute alkali based on the acid gas neutralization method.

[0206] Various embodiments of the present disclosure may be presented in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of the present disclosure; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numbers within the range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0207] In the present disclosure, unless otherwise specified, the directional words used, such as "upper" and "lower", specifically refer to the directions of the drawings in the accompanying drawings. In addition, in the description of the present disclosure, the terms "including", "comprising", etc. mean "including but not limited to". In this article, relational terms such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that there is any such actual relationship or order between these entities or operations. In this article, "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. Wherein A and B can be singular or plural. In this article, "at least one" refers to one or more, and "plurality" refers to two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, "at least one of a, b, or c", or "at least one of a, b and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple.

[0208] The foregoing description is intended only to provide specific embodiments of the present disclosure, intended to enable those skilled in the art to understand and implement the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present disclosure. Therefore, the present disclosure is not to be limited to the embodiments shown herein, but is to be construed in the broadest manner consistent with the principles and novel features claimed herein.

Claims

1. A method for recovering alkali by carbonization of red mud, comprising: adding water and additives to the red mud, and performing slurry adjustment to obtain red mud slurry; Passing CO2-containing flue gas into the red mud slurry for carbonization reaction, and then performing solid-liquid separation and washing to obtain carbonized red mud and dilute alkali solution respectively; The diluted alkali solution is evaporated and concentrated, and the alkali concentration is adjusted, and then CO2 flue gas is introduced and sodium bicarbonate seed crystals are added for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate; Performing solid-liquid separation on the mixed slurry to obtain a sodium bicarbonate product and a concentrated alkali solution respectively; as well as The concentrated alkali solution is returned to the alkali concentration adjustment and / or the carbonization crystallization to achieve recycling of the alkali solution.

2. The method according to claim 1, wherein: The liquid-to-solid ratio of the red mud slurry is 1:1 to 20:

1.

3. The method according to claim 1 or 2, wherein: The mass ratio of the additive to the red mud dry weight is 0.1% to 10%.

4. The method according to claim 1 or 3, wherein: The additive includes at least one of ammonia water, ammonium carbonate, ammonium bicarbonate, ammonium chloride, ammonium sulfate, ethanolamine, N-methyldiethanolamine, triethanolamine, 3-methylaminopropylamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, N-methyldiethanolamine, N,N-diethylaminoethanol and piperazine.

5. The method according to claim 1, wherein: The temperature of the carbonization reaction is 25° C. to 150° C., and the pressure of the carbonization reaction is 0.1 MPa to 3.0 MPa.

6. The method according to claim 1, wherein: The reaction temperature of the carbonization crystallization is 20°C to 60°C.

7. The method according to claim 1, wherein: The dilute alkali solution is evaporated and concentrated, and the alkali concentration is adjusted, CO2 flue gas is introduced, and sodium bicarbonate seeds are added for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate, comprising the steps of: The diluted alkali solution is evaporated and concentrated to obtain concentrated alkali solution and CO2-containing steam respectively; Adjusting the alkali concentration of the concentrated alkali solution, introducing CO2 flue gas and adding sodium bicarbonate seed crystals for carbonization and crystallization to obtain a mixed slurry containing sodium bicarbonate; Separating the CO2-containing steam into steam and water to obtain high-concentration CO2 gas and distilled water respectively; Returning the distilled water to the slurry preparation to achieve water recycling; The high-concentration CO2 gas is mixed with the CO2 flue gas and then returned to the carbonization crystallization to achieve the recycling of CO2 gas.

8. A system for recovering alkali from red mud carbonization, adapted to the method according to any one of claims 1 to 7, the system comprising: A red mud slurry conditioning unit, the red mud slurry conditioning unit comprising a red mud metering and conveying device (1), a water replenishing device (2), an additive dosing device (3), a slurry conditioning tank (4) and a slurry pump (5), wherein the discharge ports of the red mud metering and conveying device (1), the water replenishing device (2) and the additive dosing device (3) are respectively connected to the feed port of the slurry conditioning tank (4), and the discharge port of the slurry conditioning tank (4) is connected to the feed port of the slurry pump (5); A smoke pretreatment unit, the smoke pretreatment unit comprising a drainage pipe (6), a smoke compressor (7), a smoke retention tank (8) and a smoke conveying device (9), the air outlet of the drainage pipe (6) being connected to the air inlet of the smoke compressor (7), the air outlet of the smoke compressor (7) being connected to the air inlet of the smoke retention tank (8), and the smoke conveying device (9) being connected to the air outlet of the smoke retention tank (8); A carbonization reaction unit, the carbonization reaction unit comprising a carbonization reactor (10), an exhaust pipe (13) and a discharge pump (14), the feed port of the carbonization reactor (10) being connected to the discharge port of the slurry pump (5), the air inlet of the carbonization reactor (10) being connected to the air outlet of the flue gas conveying device (9), the air outlet of the carbonization reactor (10) being connected to the exhaust pipe (13), and the discharge port of the carbonization reactor (10) being connected to the feed port of the discharge pump (14); A solid-liquid separation washing unit, the solid-liquid separation washing unit comprising a solid-liquid separation washing device (15) and a dilute alkali solution delivery pump (16), the discharge port of the discharge pump (14) being connected to the feed port of the solid-liquid separation washing device (15), and the liquid outlet of the solid-liquid separation device being connected to the dilute alkali solution delivery pump (16); and An alkali recovery unit comprises an evaporator (17), an alkali solution mixing tank (19), a carbonization crystallizer (20) and a separator (21); the liquid outlet of the dilute alkali solution delivery pump (16) is connected to the liquid inlet of the evaporator (17); the material outlet of the evaporator (17) is connected to the material inlet of the alkali solution mixing tank (19) or the slurry mixing tank (4); the liquid outlet of the alkali solution mixing tank (19) is connected to the liquid inlet of the carbonization crystallizer (20); the air inlet of the carbonization crystallizer (20) is connected to the flue gas conveying device (9); the material outlet of the carbonization crystallizer (20) is connected to the separator (21) to achieve separation of sodium bicarbonate product and concentrated alkali solution; the liquid outlet of the separator (21) is respectively connected to the alkali solution mixing tank (19) and the slurry mixing tank (4).

9. The system according to claim 8, wherein: The alkali recovery unit further comprises a steam-water separator (18), the feed port of the steam-water separator (18) being connected to the gas outlet of the evaporator (17), the gas outlet of the steam-water separator (18) being connected to the gas inlet of the carbonization crystallizer (20), and the liquid outlet of the steam-water separator (18) being connected to the water replenishment device (2), so as to realize the recycling of distilled water.

10. The system according to claim 8 or 9, wherein: The carbonization reaction unit further comprises an automatic controller (11) and a smoke detection device (12); the automatic controller (11) is arranged on the side wall of the carbonization reactor (10); the smoke detection device (12) is arranged on the top of the carbonization reactor (10); and the smoke detection device (12) is connected to the automatic controller (11) via an electrical signal.

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