Method for comprehensive utilization of red mud greenification

Abstract

This invention relates to the field of clean utilization of solid waste and discloses a method for the green and comprehensive utilization of red mud. The method includes the following steps: dehydrating the red mud and pelletizing it to obtain red mud pellets; drying the red mud pellets at 300℃~400℃; adding the dried red mud pellets to an electric arc furnace and heating them to 1550℃~1600℃ to melt them, forming a molten pool; introducing reducing gas hydrogen into the molten pool to generate molten iron and slag; using the molten iron for steelmaking or casting; and using the slag for water quenching to separate and extract Al2O3, TiO2, Fe2O3, and SiO2. This invention reduces red mud with hydrogen, resulting in no CO2 emissions, clean and pollution-free production. After iron extraction, various substances are extracted from the slag, achieving high recovery rates, low costs, and good economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of clean utilization of solid waste, and in particular relates to a method for the green and comprehensive utilization of red mud. Background Technology

[0002] Red mud is a solid waste generated during alumina production. It is called red mud because it contains a large amount of Fe₂O₃, giving it its red color. The main components of red mud are Fe₂O₃, Al₂O₃, SiO₂, TiO₂, NaOH, and CaO, along with small amounts of oxides of gallium, germanium, vanadium, scandium, and rare earth elements. The accumulation of red mud not only occupies large amounts of land but also causes environmental pollution.

[0003] In order to solve the problem of red mud pollution, people have studied many methods for treating red mud, but due to high cost and poor efficiency, they have not been applied, and some methods even cause secondary pollution. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned problems by providing a green and comprehensive utilization method for red mud that does not cause environmental pollution and has good economic benefits.

[0005] To achieve the above objectives, the technical solution adopted by this invention is as follows: A method for the comprehensive utilization of red mud for greening, comprising the following steps:

[0006] (1) Dehydrate the red mud and form it into balls to obtain red mud pellets;

[0007] (2) Dry the red mud pellets at 300℃~400℃;

[0008] (3) Add the dried red mud pellets to the electric arc furnace and heat them to 1550℃~1600℃ to melt them and form a molten pool. Blow hydrogen into the molten pool to smelt and generate molten iron and slag. The amount of hydrogen added is 100% more than the amount of hydrogen required to completely reduce the iron oxides in the molten pool.

[0009] (4) Molten iron is used for steelmaking or casting, and slag is used for separation and extraction of Al2O3, TiO2, Fe2O3 and SiO2 after water quenching;

[0010] When H2 is introduced into the molten pool of an electric arc furnace, the following chemical reaction occurs:

[0011] Fe₂O₃ + 3H₂ = 2Fe + 3H₂O

[0012] FeO + H2 = Fe + H2O

[0013] Among them, Al2O3, SiO2, TiO2 and some FeO form slag, and Na2O in the red mud enters the flue dust;

[0014] (5) The flue gas generated in the electric arc furnace is introduced into the combustion chamber, and air is introduced into the combustion chamber to burn hydrogen. The heat from the flue gas and the heat generated from the combustion of H2 are used to generate electricity; the chemical reaction that occurs in the combustion chamber is as follows:

[0015] 2H₂ + O₂ = 2H₂O

[0016] (6) The dust generated in the electric arc furnace is recovered by the dust removal system and then water-immersed to allow the Na2O in the dust to react with water to generate NaOH that is soluble in water. The solid slag and NaOH-containing filtrate are obtained by filtration. The solid slag is returned to step (1) for recycling. After the NaOH content in the filtrate reaches a certain concentration, it is evaporated and crystallized to obtain NaOH product.

[0017] The Na₂O in it dissolves in water and undergoes a chemical reaction:

[0018] Na₂O + H₂O = 2NaOH

[0019] NaOH is used in subsequent processes.

[0020] Preferably, in step (1), the red mud is dehydrated to a moisture content of 10%, and the pellet size is 20mm to 30mm.

[0021] Preferably, in step (2), the pellets are dried to a moisture content of less than 1%.

[0022] Preferably, the method for preparing Al2O3, TiO2, Fe2O3 and SiO2 by separating and extracting them after water quenching of the slag is as follows:

[0023] S1: After water quenching, the slag is ground into powder with a particle size of 80μm, then dehydrated to a water content of 10%, and ammonium sulfate is added to mix and pelletize.

[0024] S2: Heat the pellets formed in step S1 to 400℃~500℃ and calcine for 1 hour; the chemical reactions that occur during the calcine process are as follows:

[0025] Fe2O3+3(NH4)2SO4=Fe2(SO4)3+6NH3↑+3H2O

[0026] FeO+(NH4)2SO4=FeSO4+2NH3↑+H2O

[0027] Al2O3+3(NH4)2SO4=Al2(SO4)3++6NH3↑+3H2O

[0028] TiO2+(NH4)2SO4=TiOSO4+2NH3↑+H2O

[0029] The SiO2 in the slag does not participate in the reaction, and the NH3 produced by the reaction is recovered and used in subsequent processes;

[0030] S3: Add water to the clinker produced by roasting and dissolve it. The liquid-solid mass ratio of water to clinker is 3:1. The dissolution time is 1 hour. Filter the dissolved material to obtain filter residue SiO2 and filtrate A containing Al2(SO4)3, Fe2(SO4)3, FeSO4, and TiOSO4.

[0031] S4: Add reducing agent iron filings to filtrate A, react for 4 hours to reduce ferric iron in the filtrate to ferrous iron, remove the iron filings, and obtain a solution; the chemical reaction is as follows:

[0032] Fe 3+ +Fe=2Fe 2+

[0033] S5: The solution is heated to 110℃ to hydrolyze titanium oxysulfate, producing metatitanic acid precipitate. The precipitate is filtered to obtain solid metatitanic acid and filtrate B. The solid metatitanic acid is calcined at 1000℃ to obtain anatase TiO2 product. The hydrolysis reaction that occurs is as follows:

[0034] TiOSO4 + 2H2O = H2TiO3↓ + H2SO4

[0035] The chemical reaction that occurs during calcination is as follows:

[0036] H₂TiO₃=TiO₂+H₂O

[0037] S6: Ammonia gas is introduced into filtrate B to adjust the pH to 6, generating Al(OH)3 precipitate. After filtration, solid Al(OH)3 and filtrate C are obtained. The chemical reaction that occurs is:

[0038] Al2(SO4)3+6NH3+3H2O=2AlOH)3↓+3(NH4)2SO4

[0039] S7: Continue to pass ammonia gas into filtrate C to adjust the pH to 7, generating Fe(OH)2 precipitate. Filter to obtain solid Fe(OH)2 and filtrate D, which is a solution containing ammonium sulfate. Calcinate the solid Fe(OH)2 in air at 500℃ to obtain Fe2O3 product; the chemical reaction that occurs is as follows:

[0040] FeSO4+2NH3+2H2O=Fe(OH)2↓+(NH4)2SO4

[0041] 2Fe(OH)₂ + 1 / 2O₂ = Fe₂O₃ + 2H₂O

[0042] S8: The solid Al(OH)3 obtained in step S6 is added to a NaOH solution with a concentration of 150 g / L and a temperature of 60 °C, until the Al(OH)3 dissolves to saturation, generating a sodium aluminate solution; the chemical reaction that occurs is as follows:

[0043] Al(OH)3 + NaOH = NaAlO2 + 2H2O

[0044] S9: After the sodium aluminate solution is filtered to remove impurities, a small amount of Al(OH)3 is added to the solution as a seed crystal to precipitate pure Al(OH)3. After filtration, Al(OH)3 crystals and mother liquor containing NaOH and NaAlO2 are obtained. The Al(OH)3 crystals are calcined at 1300℃ to obtain Al2O3 product. The mother liquor is returned to step S8 for recycling.

[0045] S10: The filtrate D is evaporated and dehydrated to obtain ammonium sulfate crystals, which are then returned to step S1 for recycling.

[0046] Preferably, the method for preparing Al2O3, TiO2, Fe2O3 and SiO2 by separating and extracting them after water quenching of the slag is as follows:

[0047] S1: After water quenching, the slag is ground into powder with a particle size of 80μm, then dehydrated to a moisture content of less than 1%, and mixed with an 80% sulfuric acid solution to form pellets;

[0048] S2: Heat the pellets formed in step S1 to 400℃~500℃ and calcine for 1 hour; the chemical reaction that occurs is as follows:

[0049] Fe₂O₃ + 3H₂SO₄ = Fe₂(SO₄)₃ + 3H₂O

[0050] FeO + H₂SO₄ = FeSO₄ + H₂O

[0051] Al₂O₃ + 3H₂SO₄ = Al₂(SO₄)₃ + 3H₂O

[0052] TiO2 + H2SO4 = TiOSO4 + H2O

[0053] H₂SO₄ = H₂O + SO₃

[0054] SiO2 does not participate in the reaction. The SO3 produced by the reaction is absorbed by dilute sulfuric acid, and the generated H2SO4 is returned to the feed.

[0055] S3: Add water to the clinker produced by roasting and dissolve it. The liquid-solid mass ratio of water to clinker is 3:1 and the dissolution time is 1 hour. Filter the dissolved material to obtain filter residue SiO2 and filtrate A containing Al2(SO4)3, Fe2(SO4)3, FeSO4, TiOSO4 and (NH4)2SO4.

[0056] S4: Add NaOH to filtrate A to adjust the pH to 3, generating Fe(OH)3 precipitate. Filter to obtain solid Fe(OH)3 and filtrate B; the chemical reaction is as follows:

[0057] Fe2(SO4)3+6NaOH=2Fe(OH)3↓+3Na2SO4

[0058] Fe(OH)3 is heated to 600℃ and calcined to obtain Fe2O3, which undergoes the following chemical reaction:

[0059] 2Fe(OH)3=Fe2O3+3H2O

[0060] S5: Add NaOH to filtrate B to adjust the pH to 6, forming Al(OH)3 precipitate. Filter to obtain solid Al(OH)3 and filtrate C; the chemical reaction is as follows:

[0061] Al2(SO4)3+6NaOH=2Al(OH)3↓+3Na2SO4

[0062] S6: Continue adding NaOH to filtrate C to adjust the pH to 7, generating Fe(OH)2 precipitate. Filter to obtain solid Fe(OH)2 and filtrate D. Filtrate D is a solution containing titanium oxysulfate and sodium sulfate. The chemical reaction that occurs is as follows:

[0063] FeSO4+2NaOH=Fe(OH)2↓+Na2SO4

[0064] Solid Fe(OH)₂ was calcined in air at 500°C to obtain Fe₂O₃ product; the chemical reaction that occurred was as follows:

[0065] 2Fe(OH)₂ + 1 / 2O₂ = Fe₂O₃ + 2H₂O

[0066] S7: Add NaOH to filtrate D to adjust the pH to 8.5, producing H2TiO3 precipitate and Na2SO4 solution. Filter to obtain solid H2TiO3 and filtrate E, which is sodium sulfate solution. The chemical reaction that occurs is as follows:

[0067] TiOSO4+2NaOH=H2TiO3↓+Na2SO4

[0068] When solid H₂TiO₃ is calcined at 1000℃, the following chemical reaction occurs:

[0069] H₂TiO₃=TiO₂+H₂O

[0070] Obtain anatase TiO2 product;

[0071] S8: The solid Al(OH)3 obtained in step S5 is added to a NaOH solution with a concentration of 150 g / L and a temperature of 60 °C, until the Al(OH)3 dissolves to saturation, generating a sodium aluminate solution; the chemical reaction that occurs is as follows:

[0072] Al(OH)3 + NaOH = NaAlO2 + 2H2O

[0073] S9: After the sodium aluminate solution is filtered to remove impurities, CO2 is introduced into the sodium aluminate solution to adjust the pH value to above 7, resulting in Al(OH)3 precipitate and Na2CO3 solution. After filtration, solid Al(OH)3 and filtrate F containing Na2CO3 are obtained. CaO is added to filtrate F to produce CaCO3 precipitate and NaOH solution. After filtration, light CaCO3 product and NaOH solution are obtained. The NaOH solution is returned to step S8 for recycling.

[0074] S10: Filtrate E is a solution containing Na2SO4. Adding NH4HCO3 to filtrate E produces NaHCO3 precipitate and a solution containing ammonium sulfate. Filtration yields NaHCO3 product and filtrate G containing (NH4)2SO4. Dehydrating filtrate G yields ammonium sulfate crystals. The chemical reaction that occurs when NH4HCO3 is added to the Na2SO4 solution is as follows:

[0075] Na2SO4+2NH4HCO3=(NH4)2SO4+2NaHCO3↓

[0076] Preferably, the mass ratio of the slag to ammonium sulfate is 1:2.

[0077] Preferably, the mass ratio of the slag to sulfuric acid is 1:1.5.

[0078] By adopting the above technical solution, the present invention has the following beneficial effects:

[0079] This invention utilizes hydrogen to reduce red mud to recover metallic iron, without CO2 emissions and without causing environmental pollution;

[0080] The method achieves an iron recovery rate of 95%, and the prepared iron meets the People's Republic of China ferrous metallurgical industry standard YB / T5296-2011.

[0081] This invention utilizes the slag from iron extraction to separate and extract Al2O3, TiO2, Fe2O3, and SiO2 products. The recovery rates of Al2O3, TiO2, SiO2, and FeO in the slag reach 98%, 95%, 99%, and 98% respectively. The recovery rate of Na2O entering the flue dust is also 98%, resulting in high added value.

[0082] This invention can fully recover and utilize various elements in red mud with almost no residue. It has a high recovery rate of each element, a high degree of comprehensive utilization, low production cost, and low energy consumption. It is a green and high-value-added method for the comprehensive utilization of red mud. Attached Figure Description

[0083] Figure 1A flowchart of the process for the green and comprehensive utilization of red mud for invention;

[0084] Figure 2 Al2O3, TiO2, and Fe2O3 were separated and extracted from the slag after water quenching according to Method 1. 3、 SiO2 process flow diagram;

[0085] Figure 3 Al2O3, TiO2, and Fe2O3 were separated and extracted from the slag after water quenching, according to method 2. 3、 SiO2 process flow diagram; Detailed Implementation

[0086] The specific embodiments of the present invention will be further described below with reference to examples.

[0087] The red mud used in the following examples is solid waste red mud from the production of alumina in an alumina plant. The composition of the red mud is 56.18% Fe2O3, 18.29% Al2O3, 7.83% SiO2, 7.31% TiO2, 2.31% Na2O, 0.83% CaO, and 7.25% other components.

[0088] Example 1

[0089] A method for the comprehensive green utilization of red mud includes the following steps:

[0090] (1) The red mud is heated to 200°C in a rotary kiln and dried, dehydrated to a moisture content of 10%, and pelletized. The pellet size is 20mm to 30mm to obtain red mud pellets.

[0091] (2) Dry the red mud pellets at 300℃ until the moisture content is less than 1%;

[0092] (3) Add the dried red mud pellets to the electric arc furnace and heat them to 1550℃ to melt them and form a molten pool. Blow hydrogen into the molten pool for smelting. The amount of hydrogen introduced is 100% more than the amount of hydrogen required to completely reduce the iron oxides in the molten pool. Molten iron and slag are generated. After the amount of molten iron and slag reaches a certain amount, the slag is discharged first and then the iron is discharged. The slag is poured into the slag ladle and the molten iron is poured into the molten iron ladle.

[0093] (4) Use molten iron for steelmaking or casting;

[0094] (5) After water quenching, the slag is ground into powder with a particle size of 80μm, then dehydrated to a moisture content of 10%, and ammonium sulfate is added to mix and pelletize; wherein, the particle size of the pellets is 20mm~30mm, and the mass ratio of slag to ammonium sulfate is 1:2.

[0095] (6) Heat the pellets prepared in step (5) to 500°C and bake for 1 hour;

[0096] (7) The clinker produced by roasting is dissolved in water. The mass ratio of water to clinker liquid to solid is 3:1. The dissolution time is 1 hour. The dissolved substances are filtered and separated to obtain filter residue SiO2 and filtrate A containing Al2(SO4)3, Fe2(SO4)3, FeSO4, TiOSO4 and (NH4)2SO4.

[0097] (8) Add excess 100% reducing agent iron filings to filtrate A, react for 4 hours to reduce ferric iron in the filtrate to ferrous iron, remove the iron filings, and obtain a solution. The amount of iron filings added is sufficient to reduce the Fe in the solution. 3+ All reduced to Fe 2+ One hundred percent excess;

[0098] (9) Heat the solution to 110°C to hydrolyze the titanium oxysulfate to produce metatitanic acid precipitate. The hydrolysis time is 4 hours. Filter to obtain solid metatitanic acid and filtrate B. Calcine the solid metatitanic acid at 1000°C to obtain anatase TiO2 product.

[0099] (10) Ammonia gas was introduced into filtrate B to adjust the pH value to 6, Al(OH)3 precipitate was produced, and the solution was filtered to obtain solid Al(OH)3 and filtrate C.

[0100] (11) Ammonia gas is introduced into filtrate C to adjust the pH value to 7, and Fe(OH)2 precipitate is produced. After filtration, solid Fe(OH)2 and filtrate D are obtained. Filtrate D is a solution containing ammonium sulfate. Solid Fe(OH)2 is calcined in air at 500°C to obtain Fe2O3 product.

[0101] (12) Add the solid Al(OH)3 obtained in step (10) to a NaOH solution with a concentration of 150 g / L to dissolve Al(OH)3 to saturation. The reaction time is 1 hour and the temperature is 60°C to generate sodium aluminate solution.

[0102] (13) After the sodium aluminate solution is filtered to remove impurities, a small amount of Al(OH)3 is added to the solution as a seed crystal. The amount of seed crystal added is 0.2% of the solution mass. Pure Al(OH)3 is precipitated. After filtration, Al(OH)3 crystals and mother liquor containing NaOH and NaAlO2 are obtained. The Al(OH)3 crystals are calcined at 1300℃ to obtain Al2O3 product. The mother liquor is returned to step (12) for recycling.

[0103] (14) Evaporate and dehydrate the filtrate D to obtain ammonium sulfate crystals, and return it to step (5) for recycling;

[0104] (15) The flue gas generated in the electric arc furnace is introduced into the combustion chamber, and air is introduced into the combustion chamber to make hydrogen burn in the combustion chamber. The heat from the flue gas and the heat generated from the combustion of H2 are used to generate electricity.

[0105] (16) The dust generated in the electric arc furnace is recovered by the dust removal system and then water is used to react Na2O in the dust with water to generate NaOH that is soluble in water. The solid slag and NaOH-containing filtrate are obtained by filtration. The solid slag is returned to step (1) for recycling. After the NaOH content in the filtrate reaches a certain concentration, it is evaporated and crystallized to obtain NaOH product.

[0106] This method reduces iron oxides in red mud to metallic iron using hydrogen, achieving an iron recovery rate of 95%. The prepared iron meets the People's Republic of China's ferrous metallurgy industry standard YB / T5296-2011.

[0107] During the iron extraction process of red mud in an electric arc furnace, Na2O in the red mud enters the flue dust, which is then processed to obtain NaOH product.

[0108] After iron extraction, the slag is quenched in water and then separated to obtain Al2O3, TiO2, Fe2O3, and SiO2 products. The recovery rates of Al2O3, TiO2, SiO2, Fe2O3, and FeO in the slag are all 99%. The recovery rate of Na2O entering the flue dust is 98%.

[0109] Example 2

[0110] A method for the comprehensive green utilization of red mud includes the following steps:

[0111] (1) The red mud is heated to 200°C in a rotary kiln and dried. The red mud is dehydrated to a moisture content of 10%, and pelletized. The pellet size is 20mm to 30mm to obtain red mud pellets.

[0112] (2) Dry the red mud pellets at 400℃ until the moisture content is less than 1%;

[0113] (3) Add the dried red mud pellets to the electric arc furnace and heat them to 1600℃ to melt them and form a molten pool. Blow hydrogen into the molten pool for smelting. The amount of hydrogen introduced is 100% more than the amount of hydrogen required to completely reduce the iron oxides in the molten pool. Molten iron and slag are generated. After the amount of molten iron and slag reaches a certain amount, the slag is discharged first and then the iron is discharged. The slag is poured into the slag ladle and the molten iron is poured into the molten iron ladle.

[0114] (4) Use molten iron for steelmaking or casting;

[0115] (5) After water quenching the slag, grind it into powder with a particle size of 80μm, then dehydrate it to a moisture content of less than 1%, and add an 80% sulfuric acid solution to mix and pelletize it.

[0116] (6) Heat the pellets prepared in step (5) to 400°C and bake for 1 hour;

[0117] (7) The clinker produced by roasting is dissolved in water. The mass ratio of water to clinker liquid to solid is 3:1. The dissolution time is 1 hour. The dissolved substances are filtered and separated to obtain filter residue SiO2 and filtrate A containing Al2(SO4)3, Fe2(SO4)3, FeSO4 and TiOSO4.

[0118] (8) Add NaOH to filtrate A, adjust the pH value to 3, and Fe(OH)3 precipitate is produced. Filter to obtain solid Fe(OH)3 and filtrate B. Calcine Fe(OH)3 at 600℃ to obtain Fe2O3 product.

[0119] (9) Add NaOH to filtrate B, adjust the pH value to 6, produce Al(OH)3 precipitate, filter, and obtain solid Al(OH)3 and filtrate C;

[0120] (10) Add NaOH to filtrate C, adjust the pH value to 7, produce Fe(OH)2 precipitate, filter, and obtain solid Fe(OH)2 and filtrate D. Calcine solid Fe(OH)2 in air at 500°C to obtain Fe2O3 product.

[0121] (11) Add NaOH to filtrate D and adjust the pH value to 8.5 to produce H2TiO3 precipitate. Filter to obtain solid H2TiO3 and filtrate E. Filtrate E is Na2SO4 solution. Calcine solid H2TiO3 at 1000℃ to obtain anatase TiO2 product.

[0122] (12) Add the solid Al(OH)3 obtained in step (9) to a NaOH solution with a concentration of 150 g / L to dissolve Al(OH)3 to saturation. The reaction time is 1 hour and the temperature is 60°C to generate sodium aluminate solution.

[0123] (13) After the sodium aluminate solution is filtered to remove impurities, CO2 is introduced into the solution to adjust the pH value to 7, resulting in Al(OH)3 precipitate and Na2CO3 solution. After filtration, solid Al(OH)3 and filtrate F containing Na2CO3 are obtained. CaO is added to filtrate F to produce CaCO3 precipitate and NaOH solution. After filtration, light CaCO3 product and NaOH solution are obtained. NaOH solution is returned to step (11) for recycling.

[0124] (14) Filtrate E is a Na2SO4 solution. NH4HCO3 is added to filtrate E, and the reaction produces NaHCO3 precipitate and a solution containing ammonium sulfate. After filtration, NaHCO3 product and filtrate G containing (NH4)2SO4 are obtained. Filtrate G is dehydrated to obtain ammonium sulfate crystals.

[0125] (15) The flue gas generated in the electric arc furnace is introduced into the combustion chamber, and air is introduced into the combustion chamber to make hydrogen burn in the combustion chamber. The heat from the flue gas and the heat generated from the combustion of H2 are used to generate electricity.

[0126] (16) The dust generated in the electric arc furnace is recovered by the dust removal system and then water is used to react Na2O in the dust with water to generate NaOH that is soluble in water. The solid slag and NaOH-containing filtrate are obtained by filtration. The solid slag is returned to step (1) for recycling. After the NaOH content in the filtrate reaches a certain concentration, it is evaporated and crystallized to obtain NaOH product.

[0127] This method reduces iron oxides in red mud to metallic iron using hydrogen, achieving an iron recovery rate of 95%. The prepared iron meets the People's Republic of China's ferrous metallurgy industry standard YB / T5296-2011.

[0128] After iron extraction, the slag is crushed, water-quenched, and then separated to obtain Al2O3, TiO2, Fe2O3, and SiO2 products. The recovery rates of Al2O3, TiO2, SiO2, Fe2O3, and FeO in the slag reach 98%, 95%, 99%, and 99%, respectively. The recovery rate of Na2O entering the flue dust reaches 98%.

[0129] The above description is a detailed description of the preferred embodiments of the present invention. However, the embodiments are not intended to limit the scope of the patent application of the present invention. All equivalent changes or modifications made under the guidance of the present invention should be considered as patents covered by the present invention.

Claims

1. A method for the comprehensive green utilization of red mud, characterized in that, Includes the following steps: (1) Dehydrate the red mud, form it into pellets, and obtain red mud pellets; (2) Dry the red mud pellets at 300℃~400℃; (3) Add the dried red mud pellets to the electric arc furnace and heat them to 1550℃~1600℃ to melt them and form a molten pool. Introduce reducing gas hydrogen into the molten pool to generate molten iron and slag. The amount of hydrogen added is 100% excess of the amount of hydrogen required to completely reduce the iron oxides in the molten pool. (4) Use molten iron for steelmaking or casting, and use the slag after water quenching to separate the mixed phase of metal oxides and silicon dioxide, and extract each metal oxide in the mixed phase of metal oxides separately, wherein the metal oxide phase is composed of Al2O3, TiO2 and Fe2O3. (5) The flue gas generated in the electric arc furnace is introduced into the combustion chamber, and air is introduced into the combustion chamber to make hydrogen burn in the combustion chamber. The heat from the flue gas and the heat generated from the combustion of H2 are used to generate electricity. (6) The dust generated in the electric arc furnace is recovered by the dust removal system and then water is used to make the Na2O in the dust react with water to generate NaOH that is soluble in water. The solid slag and NaOH-containing filtrate are obtained by filtration. The solid slag is returned to step (1) for recycling. After the NaOH content in the filtrate reaches a certain concentration, it is evaporated and crystallized to obtain NaOH product.

2. The method for comprehensive green utilization of red mud according to claim 1, characterized in that, In step (1), the red mud is dehydrated to a moisture content of 10%, and the pellet size is 20mm~30mm.

3. The method for comprehensive green utilization of red mud according to claim 1, characterized in that, In step (2), the pellets are dried to a moisture content of less than 1%.

4. The method for comprehensive green utilization of red mud according to claim 1, characterized in that, The preparation method for separating and extracting Al2O3, TiO2, Fe2O3 and SiO2 from the slag after water quenching is as follows: S1: After water quenching, the slag is ground into powder with a particle size of 80μm, then dehydrated to a water content of 10%, and ammonium sulfate is added to mix and pelletize. S2: Heat the pellets prepared in step S1 to 400℃~500℃ and bake for 1 hour; S3: Add water to the clinker produced by roasting and dissolve it. The liquid-solid mass ratio of water to clinker is 3:1 and the dissolution time is 1 hour. Filter the dissolved material to obtain filter residue SiO2 and filtrate A containing Al2(SO4)3, Fe2(SO4)3, FeSO4, TiOSO4 and (NH4)2SO4. S4: Add reducing agent iron filings to filtrate A, react for 4 hours to reduce ferric iron in filtrate to ferrous iron, remove the iron filings, and obtain a solution; S5: Heat the solution to 110℃ to hydrolyze titanium oxysulfate to produce metatitanic acid precipitate. Filter to obtain solid metatitanic acid and filtrate B. Calcine the solid metatitanic acid at 1000℃ to obtain anatase TiO2 product. S6: Pass ammonia gas into filtrate B, adjust the pH value to 6, generate Al(OH)3 precipitate, filter, and obtain solid Al(OH)3 and filtrate C; S7: Continue to pass ammonia gas into filtrate C to adjust the pH value to 7, generate Fe(OH)2 precipitate, filter to obtain solid Fe(OH)2 and filtrate D, filtrate D is a solution containing ammonium sulfate, calcine solid Fe(OH)2 in air at 500℃ to obtain Fe2O3 product; S8: Add the solid Al(OH)3 obtained in step S6 to a NaOH solution with a concentration of 150 g / L, and react for 1 hour at a temperature of 60℃ to allow Al(OH)3 to dissolve to saturation and generate sodium aluminate solution. S9: After the sodium aluminate solution is filtered to remove impurities, a small amount of Al(OH)3 is added to the solution as a seed crystal to precipitate pure Al(OH)3. After filtration, Al(OH)3 crystals and mother liquor are obtained. The Al(OH)3 crystals are calcined at 1300℃ to obtain Al2O3 product. The mother liquor is returned to step S8 for recycling. S10: The filtrate D is evaporated and dehydrated to obtain ammonium sulfate crystals, which are then returned to step S1 for recycling.

5. The method for comprehensive green utilization of red mud according to claim 1, characterized in that, The preparation method for separating and extracting Al2O3, TiO2, Fe2O3 and SiO2 from the slag after water quenching is as follows: S1: After water quenching, the slag is ground into powder with a particle size of 80μm, then dehydrated to a moisture content of less than 1%, and mixed with an 80% sulfuric acid solution to form pellets; S2: Heat the pellets prepared in step S1 to 400℃~500℃ and bake for 1 hour; S3: Add water to the clinker produced by roasting, the water to clinker liquid-solid mass ratio is 3:1, the dissolution time is 1 hour, filter the dissolved material to obtain filter residue SiO2 and filtrate A containing Al2(SO4)3, Fe2(SO4)3, FeSO4 and TiOSO4. S4: Add NaOH to filtrate A to adjust the pH value to 3, and Fe(OH)3 precipitate will be generated. Filter to obtain solid Fe(OH)3 and filtrate B. Calcine Fe(OH)3 at 600℃ to obtain Fe2O3. S5: Add NaOH to filtrate B, adjust the pH to 6, generate Al(OH)3 precipitate, filter, and obtain solid Al(OH)3 and filtrate C; S6: Add NaOH to filtrate C, adjust the pH value to 7, generate Fe(OH)2 precipitate, filter, and obtain solid Fe(OH)2 and filtrate D. Calcine solid Fe(OH)2 in air at 500℃ to obtain Fe2O3 product; S7: Add NaOH to filtrate D to adjust the pH value of filtrate D to 8.5, generate H2TiO3 precipitate, filter to obtain solid H2TiO3 and filtrate E, filtrate E is Na2SO4 solution, calcine solid H2TiO3 at 1000℃ to obtain anatase TiO2 product; S8: Add the solid Al(OH)3 obtained in step S5 to a NaOH solution with a concentration of 150 g / L, at a temperature of 60°C, for a reaction time of 1 hour, so that Al(OH)3 dissolves to saturation and the reaction produces sodium aluminate solution. S9: After the sodium aluminate solution is filtered to remove impurities, CO2 is introduced into the sodium aluminate solution to adjust the pH value to above 7, resulting in Al(OH)3 precipitate and Na2CO3 solution. After filtration, solid Al(OH)3 and filtrate F containing Na2CO3 are obtained. CaO is added to filtrate F to produce CaCO3 precipitate and NaOH solution. After filtration, light CaCO3 product and NaOH solution are obtained. The NaOH solution is returned to step S8 for recycling. S10: Filtrate E is a Na2SO4 solution. NH4HCO3 is added to filtrate E, and the reaction produces NaHCO3 precipitate and a solution containing ammonium sulfate. After filtration, NaHCO3 product and filtrate G containing (NH4)2SO4 are obtained. Filtrate G is dehydrated to obtain ammonium sulfate crystals.

6. A method for the comprehensive green utilization of red mud according to claim 4, characterized in that, The mass ratio of the slag to ammonium sulfate is 1:

2.

7. A method for the comprehensive green utilization of red mud according to claim 5, characterized in that, The mass ratio of the slag to sulfuric acid is 1:1.5.

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