Process for directly reducing iron and separating iron and aluminum from aluminum oxide red mud

Abstract

The invention provides a process for directly reducing iron and separating iron and aluminum from aluminum oxide red mud, and relates to the technical field of comprehensive utilization of metallurgical solid waste such as red mud and carbon dioxide CCUS. According to the process for directly reducing iron and separating iron from aluminum by using aluminum oxide red mud, solid wastes such as red mud, secondary aluminum ash or other sodium-based additives, metallurgical slag and the like are used as raw materials, and are mixed and granulated after being reasonably matched with a catalyst. Roasting in a gas semi-suspension oxidation kiln; and the roasted material enters a self-gravity closed electric heating reduction kiln to be calcined by taking biomass as fuel. CO gas generated by calcination is used as fuel of the fuel gas semi-suspension oxidation kiln. After calcination, under the protection of excessive CO gas, the high metallization ratio of 95% or above is achieved, iron and aluminum are separated, the material cooled to about 200 DEG C is leached with water, the levigated material enters a magnetic separator, solid-liquid separation and solid-phase magnetic separation of metal iron are achieved, and titanium concentrate and slag are separated.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive utilization of metallurgical solid wastes such as red mud and carbon dioxide CCUS technology, specifically a process for directly reducing iron with alumina red mud and separating iron and aluminum. Background Art

[0002] The aluminum industry produces red mud during the extraction of alumina. Alumina production processes include the Bayer process, the modified Bayer process, the sintering process, and the Bayer-sintering combined process. Bayer red mud is characterized by high contents of iron, aluminum, silicon, and sodium oxides; modified Bayer red mud is primarily composed of silicon, aluminum, iron, calcium, and sodium oxides; sintering red mud is characterized by high contents of calcium, aluminum, silicon, and sodium oxides; and the Bayer-sintering combined process has similar composition and output to the sintering process. Generally, the production of one ton of aluminum requires approximately two tons of alumina, while the production of one ton of alumina generates 1 to 1.8 tons of red mud. Bayer red mud, in particular, contains abundant iron resources, making it an ideal raw material for steel production. However, due to its high sodium oxide content and limited utilization, it is difficult to use in large quantities in bulk building materials such as cement and concrete. It is only used in sintering or pelletizing processes, and actual utilization is very limited (<5% of the total sintering / pelleting material). Currently, the main method for disposing of high-iron red mud is still landfill. Due to the high alkalinity, fine particle size, and complex composition of red mud, a large amount of iron metal resources cannot be properly utilized and are lost without cause. This also wastes land resources where they are stored. Furthermore, red mud is alkaline, and the alkali in it is dissolved by rainwater, easily contaminating surface water and groundwater, impacting the environment. Therefore, minimizing the production and harm of red mud and achieving multi-channel, large-scale resource utilization is urgent.

[0003] The extraction methods of iron from red mud can be mainly divided into direct magnetic separation, wet separation extraction and reduction-magnetic separation fire extraction.

[0004] The magnetic separation method has a simple process, is easy to operate, and has low cost. It is currently the main engineering application method, but the overall iron recovery rate is less than 55%, and the resulting concentrate has a low grade, so it can only be used as a primary selection method.

[0005] Wet extraction primarily involves acid leaching. Due to the high alkalinity of red mud, a large amount of acid is consumed during the extraction process to neutralize the alkali in the mud. Existing research primarily uses hydrochloric acid, sulfuric acid, and oxalic acid. While wet extraction yields high iron recovery rates, the subsequent separation of iron from other metals increases costs. Oxalic acid is a preferred choice for wet extraction in industrial applications due to its high selectivity for iron in red mud.

[0006] The reduction-magnetic separation method involves mixing red mud with a reducing agent and, at high temperatures, converting the weakly magnetic iron-containing minerals present in the mud into strongly magnetic minerals or iron metal. This is then followed by magnetic separation and enrichment. This method, a form of pyrometallurgy, involves extensive research into iron recovery from red mud, resulting in a relatively mature process. However, this method also has drawbacks such as high energy consumption and waste gas generation. Summary of the Invention

[0007] (1) Technical problems solved

[0008] To address the shortcomings of the existing technology, the present invention provides a process for the direct reduction of iron from alumina red mud and the separation of iron and aluminum. This process utilizes a dual rotary kiln pyrometallurgical process to perform oxidation and reduction in oxidizing and reducing environments, respectively. Chlorine generated during the pyrometallurgical process is simultaneously recovered to produce dilute hydrochloric acid for self-use. CO₂ is captured for self-use in the carbonization of sodium alkali to form sodium carbonate. Acidification is then performed to convert the aluminum-containing weak base into products such as aluminum chloride. This process achieves carbon fixation and separation while simultaneously extracting iron through the pyrometallurgical process. Heat, CO₂, and chlorine are recovered for use in the process itself. CO₂ in the flue gas is captured for self-use in the carbonization process. Combined with desulfurization, denitrification, and dust removal, this process effectively reduces waste gas emissions.

[0009] (2) Technical solution

[0010] To achieve the above objectives, the present invention is implemented through the following technical solutions: A process for direct reduction of iron from alumina red mud and separation of iron and aluminum, comprising:

[0011] S1. Calcination in oxidizing environment:

[0012] Red mud, secondary aluminum ash, solid waste of metallurgical slag, iron ore concentrate, and other sodium-based additives are used as raw materials. After being mixed with catalysts in a reasonable proportion, they are granulated and dried using the waste heat from the kiln in the system. After that, they are put into a gas-fired semi-suspension oxidation kiln, using CO as fuel, and roasted in oxygen-enriched or pure oxygen at around 750°C. The main reaction formula is:

[0013] 2Fe(OH)3→Fe2O3+3H2O

[0014] 4FeO+O2→2Fe2O3

[0015] CaCO3→CaO+CO2↑

[0016] MgCO3→MgO+CO2↑

[0017] CaO+SiO2→CaSiO3

[0018] CaO+Fe2O3→CaFe2O4

[0019] 4Al+3O2→2Al2O3

[0020] 2AlN+3O2→2Al2O3+2NO↑

[0021] 2NaCl+SiO2+H2O→Na2SiO3+2HCl↑

[0022] CaAl2O4+SiO2→CaAl2Si2O8

[0023] 3Al2O3+2SiO2→3Al2O3·2SiO2

[0024] 2AlN+3H2O→Al2O3+2NH3↑

[0025] 2NaOH→Na2O+H2O

[0026] Na2CO3+SiO2→Na2SiO3+CO2↑

[0027] NaAlSiO4+CaO→Ca(AlSiO4)2+Na2O

[0028] 2Na3AlF6→6NaF+Al2F6

[0029] 2NaF+SiO2→Na2SiO3+F2↑;

[0030] S2. Acid and carbon recovery:

[0031] The flue gas generated by S1 roasting is first dried by the waste heat in the drying chamber, and then subjected to dust removal, desulfurization and denitrification. The hydrochloric acid is recovered and reused for acidification. CO2 is captured at the end and used for carbonization reaction in the subsequent process. The tail gas is discharged after harmless treatment.

[0032] S3. Calcination under reducing environment:

[0033] After S1 roasting, the material enters the gravity-enclosed electric heating reduction kiln, using biomass or C as fuel, and calcined at 1050-1350℃ for about 60 minutes. The material in the gravity-enclosed electric heating reduction kiln undergoes a uniform multipolar solid-phase reaction in a dispersed or semi-suspended form under gravity. The calcination process is controlled by an intelligent control system. The main reaction formulas are:

[0034] Fe2O3+3C→4Fe+3CO2↑

[0035] Fe2O3+3C→2Fe+3CO↑

[0036] CaFe2O4+2C→CaO+2Fe+2CO2↑

[0037] Na2O+Al2O3→2NaAlO2;

[0038] S4. Waste heat utilization:

[0039] The CO gas generated by calcining excess C-based fuel in a gravity-fed, sealed, electrically heated reduction kiln is used as fuel for a gas-fired semi-suspension oxidation kiln after heat exchange in a waste heat boiler. The excess CO, approximately 15%, enters the gas-fired power generation system, and the calcination steam is sent to the steam power generation system or other heat-using units.

[0040] S5. Water immersion treatment:

[0041] The calcined material after heat exchange in the waste heat boiler is leached with water, ground in a tower mill, and then enters a wet magnetic separator for solid-liquid separation;

[0042] S6, magnetic separation of iron and titanium:

[0043] Solid phase magnetic separation of metallic iron and separation of titanium concentrate from slag 1, which is a tailing rich in CaO (MgO) and a small amount of SiO2 and Al2O3 components;

[0044] S7, liquid phase reprocessing:

[0045] The liquid phase separated by magnetic separation is mainly composed of water-soluble sodium metaaluminate Na2AlO2 and sodium silicate SiO2·Na2O.

[0046] Preferably, in S1, the catalyst is a mixture of water glass, sodium metasilicate and chloride-containing salt, wherein the chloride-containing salt accounts for more than 30%.

[0047] Preferably, in said S1, the concentration of the flue gas generated by roasting when captured by the CO2 capture system should be greater than 99.9%.

[0048] Preferably, in S1, the semi-suspension oxidation kiln has the function of semi-suspension of the material and automatic material turning in a dispersed manner, so as to facilitate gas-solid reaction, solid-solid reaction and sufficient heat exchange. The combustion-supporting gas of the semi-suspension oxidation kiln should be blown with pure oxygen, which can facilitate the full progress of the oxidation reaction.

[0049] Preferably, the gravity-enclosed, electrically heated reduction kiln in S3 features automatic material turnover and full sealing. This prevents oxygen from entering the oxidation reaction while allowing the excess C-based fuel to fully reduce the iron oxides to metallic iron. The amount of reducing agent C added should be at least 10% in excess, which also facilitates the full recovery of CO for use in pure oxygen roasting in the semi-suspension oxidation kiln in S1.

[0050] Preferably, in said S4, the materials that have been roasted / calcined in the gravity-fed closed electric heating reduction kiln are protected by excess CO gas, and when the temperature of the CO protective gas drops to about 200°C, the obtained reduced metallic iron and other solid-phase materials are subjected to water immersion treatment, and the excess CO is used as the protective gas to achieve the protective effect on the reduced metallic iron, preventing the reduced metallic iron from being reoxidized in the waste heat boiler after leaving the kiln and before water immersion, controlling the metallization rate of the reduced metallic iron to above 95%, and ensuring that the Al2O3 content in the reduced metallic iron is within 2%.

[0051] Preferably, the slag 1 in the S6 has extremely low P and S, a moderate melting point, and a good slag-making effect, and can be prepared into an excellent steelmaking auxiliary material.

[0052] (3) Beneficial effects

[0053] The present invention provides a process for direct reduction of iron from alumina red mud and separation of iron and aluminum, which has the following beneficial effects:

[0054] The company uses a double rotary kiln pyrometallurgical process to oxidize and reduce red mud and other materials. It also recovers chlorine generated during the pyrometallurgical process to produce dilute hydrochloric acid for its own use. It captures CO2 for carbonization of sodium alkali to sodium carbonate. Acidification converts aluminum-containing weak alkali into products such as aluminum chloride. While extracting iron through pyrometallurgy, it also achieves carbon fixation and separation. It also effectively recovers heat, CO, and chlorine for its own acidification production process. It captures CO2 from flue gas for carbonization in its own process. Combined with end-of-line desulfurization, denitrification, and dust removal, it effectively reduces waste gas emissions. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0056] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0057] Example:

[0058] like Figure 1 As shown, an embodiment of the present invention provides a process for directly reducing iron from alumina red mud and separating iron and aluminum, comprising:

[0059] S1. Calcination in oxidizing environment:

[0060] Red mud, secondary aluminum ash, metallurgical slag and other solid wastes, iron ore concentrate, and other sodium-based additives are used as raw materials. After being mixed with catalysts in a reasonable proportion and granulated, they are dried using the waste heat from the kiln in the system and then enter the gas-fired semi-suspension oxidation kiln. The CO generated by the gravity-fed closed electric heating reduction kiln in S3 is used as fuel (explained below, forming a cycle), and they are roasted in oxygen-enriched or pure oxygen at around 750°C. The main reaction formulas are:

[0061] 2Fe(OH)3→Fe2O3+3H2O

[0062] 4FeO+O2→2Fe2O3

[0063] CaCO3→CaO+CO2↑

[0064] MgCO3→MgO+CO2↑

[0065] CaO+SiO2→CaSiO3

[0066] CaO+Fe2O3→CaFe2O4

[0067] 4Al+3O2→2Al2O3

[0068] 2AlN+3O2→2Al2O3+2NO↑

[0069] 2NaCl+SiO2+H2O→Na2SiO3+2HCl↑

[0070] CaAl2O4+SiO2→CaAl2Si2O8

[0071] 3Al2O3+2SiO2→3Al2O3·2SiO2

[0072] 2AlN+3H2O→Al2O3+2NH3↑

[0073] 2NaOH→Na2O+H2O

[0074] Na2CO3+SiO2→Na2SiO3+CO2↑

[0075] NaAlSiO4+CaO→Ca(AlSiO4)2+Na2O

[0076] 2Na3AlF6→6NaF+Al2F6

[0077] 2NaF+SiO2→Na2SiO3+F2↑.

[0078] S2. Acid and carbon recovery:

[0079] The flue gas generated by the S1 roasting is first dried in the drying chamber by waste heat, then subjected to dust removal, desulfurization, and denitrification. The hydrochloric acid is recovered and reused for acidification. CO2 is captured at the end and used for carbonization reactions in subsequent processes. The tail gas is then discharged after being harmlessly treated.

[0080] S3. Calcination under reducing environment:

[0081] After S1 roasting, the material enters the gravity-enclosed electric heating reduction kiln, using biomass or C as fuel, and is calcined at around 1050°C (the maximum temperature should not exceed 1350°C) for about 60 minutes. The material in the gravity-enclosed electric heating reduction kiln undergoes a uniform multipolar solid-phase reaction in a dispersed or semi-suspended form under gravity. The calcination process needs to be controlled by an intelligent control system to achieve intelligent control of temperature adjustment and calcination time, which is beneficial to reducing and controlling the formation of crust in the kiln. The main reaction formulas are:

[0082] Fe2O3+3C→4Fe+3CO2↑

[0083] Fe2O3+3C→2Fe+3CO↑

[0084] CaFe2O4+2C→CaO+2Fe+2CO2↑

[0085] Na2O+Al2O3→2NaAlO2.

[0086] S4. Waste heat utilization:

[0087] Excess C-based fuel is calcined in a gravity-fed, sealed, electrically heated reduction kiln, generating CO2 that is then used as fuel in a gas-fired semi-suspension oxidation kiln after heat exchange in a waste heat boiler. Approximately 15% of the excess CO enters the gas-fired power generation system, where it acts as a shielding gas for reducing metallic iron, preventing or halting its reoxidation at high temperatures. The CO shielding gas temperature is then controlled to drop to approximately 200°C before the material enters S5. The calcined steam is then delivered to the steam power generation system or other heat-consuming units.

[0088] S5. Water immersion treatment:

[0089] The calcined material after heat exchange in the waste heat boiler is leached with water, ground in a tower mill, and then enters a wet magnetic separator for solid-liquid separation.

[0090] S6, magnetic separation of iron and titanium:

[0091] Solid-phase magnetic separation removes metallic iron and separates the titanium concentrate from the slag, which is a tailing rich in CaO (MgO) and small amounts of SiO2, Al2O3 and other components.

[0092] S7, liquid phase reprocessing:

[0093] The liquid phase separated by magnetic separation is mainly composed of water-soluble sodium metaaluminate Na2AlO2 and sodium silicate SiO2·Na2O.

[0094] In the process verification test, the red mud used had good uniformity, and its representative components were:

[0095]

[0096] Through the verification test results, the 1 million tons / year dry basis red mud green low-carbon demonstration project related to the construction of the above-mentioned alumina red mud direct reduction of iron and iron-aluminum separation process system can produce 350,000 tons of reduced metallic iron and 110,000 tons of titanium concentrate annually, and the aluminum content in the reduced metallic iron is less than 2%, basically achieving iron-aluminum separation. The composition range of the produced reduced metallic iron is:

[0097] TFe <![CDATA[Al2O3]]> <![CDATA[SiO2]]> FeO C S P ＞95 ＜2 ＜1 ＜2 ＜2 0.01 0.01

[0098] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A process for direct reduction of iron from alumina red mud and separation of iron and aluminum, characterized by: include: S1. Calcination in oxidizing environment: Red mud, secondary aluminum ash, solid waste of metallurgical slag, iron ore concentrate, and other sodium-based additives are used as raw materials. After being mixed with catalysts in a reasonable proportion, they are granulated and dried using the waste heat from the kiln in the system. After that, they are put into a gas-fired semi-suspension oxidation kiln, using CO as fuel, and roasted in oxygen-enriched or pure oxygen at around 750°C. The main reaction formula is: 2Fe(OH)3→Fe2O3+3H2O 4FeO+O2→2Fe2O3 CaCO3→CaO+CO2↑ MgCO3→MgO+CO2↑ CaO+SiO2→CaSiO3 CaO+Fe2O3→CaFe2O4 4Al+3O2→2Al2O3 2AlN+3O2→2Al2O3+2NO↑ 2NaCl+SiO2+H2O→Na2SiO3+2HCl↑ CaAl2O4+SiO2→CaAl2Si2O8 3Al2O3+2SiO2→3Al2O3·2SiO2 2AlN+3H2O→Al2O3+2NH3↑ 2NaOH→Na2O+H2O Na2CO3+SiO2→Na2SiO3+CO2↑ NaAlSiO4+CaO→Ca(AlSiO4)2+Na2O 2Na3AlF6→6NaF+Al2F6 2NaF+SiO2→Na2SiO3+F2↑; S2. Acid and carbon recovery: The flue gas generated by S1 roasting is first dried by the waste heat in the drying chamber, and then subjected to dust removal, desulfurization and denitrification. The hydrochloric acid is recovered and reused for acidification. CO2 is captured at the end and used for carbonization reaction in the subsequent process. The tail gas is discharged after harmless treatment. S3. Calcination under reducing environment: After S1 roasting, the material enters the gravity-enclosed electric heating reduction kiln, using biomass or C as fuel, and calcined at 1050-1350℃ for about 60 minutes. The material in the gravity-enclosed electric heating reduction kiln undergoes a uniform multipolar solid-phase reaction in a dispersed or semi-suspended form under gravity. The calcination process is controlled by an intelligent control system. The main reaction formulas are: Fe2O3+3C→4Fe+3CO2↑ Fe2O3+3C→2Fe+3CO↑ CaFe2O4+2C→CaO+2Fe+2CO2↑ Na2O+Al2O3→2NaAlO2; S4. Waste heat utilization: The CO gas generated by calcining excess C-based fuel in a gravity-fed, sealed, electrically heated reduction kiln is used as fuel for a gas-fired semi-suspension oxidation kiln after heat exchange in a waste heat boiler. The excess CO, approximately 15%, enters the gas-fired power generation system, and the calcination steam is sent to the steam power generation system or other heat-using units. S5. Water immersion treatment: The calcined material after heat exchange in the waste heat boiler is leached with water, ground in a tower mill, and then enters a wet magnetic separator for solid-liquid separation; S6, magnetic separation of iron and titanium: Solid phase magnetic separation of metallic iron and separation of titanium concentrate from slag, which is tailings rich in CaO (MgO) and a small amount of SiO2 and Al2O3 components; S7, liquid phase reprocessing: The liquid phase separated by magnetic separation is mainly composed of water-soluble sodium metaaluminate Na2AlO2 and sodium silicate SiO2·Na2O.

2. The process for direct reduction of iron from alumina red mud and separation of iron and aluminum according to claim 1, characterized in that: In the above-mentioned S1, the catalyst is a mixture of water glass, sodium metasilicate and chloride-containing salt, wherein the chloride-containing salt accounts for more than 30%.

3. The process for direct reduction of iron from alumina red mud and separation of iron and aluminum according to claim 1, characterized in that: In the above S1, the concentration of the flue gas generated by roasting is greater than 99.9% when it is captured by the CO2 capture system.

4. The process for direct reduction of iron from alumina red mud and separation of iron and aluminum according to claim 1, characterized in that: In the above S1, the semi-suspension oxidation kiln has the properties of semi-suspension of materials and dispersion-type automatic material turning, and the combustion-supporting gas of the semi-suspension oxidation kiln is pure oxygen blown in.

5. The process for direct reduction of iron from alumina red mud and separation of iron and aluminum according to claim 1, characterized in that: In S3, the gravity-sealed electric heating reduction kiln has automatic material turning and full sealing properties. While preventing oxygen from entering and causing oxidation reaction, the excess C-based fuel fully reduces the iron oxides into metallic iron; the amount of reducing agent C added is more than 10% in excess.

6. The process for direct reduction of iron from alumina red mud and separation of iron and aluminum according to claim 1, characterized in that: In the above S4, the material that has been roasted / calcined in the gravity-fed closed electric heating reduction kiln is protected by excess CO gas, and when the temperature of the CO protective gas drops to about 200°C, the solid phase material of the reduced metallic iron obtained is subjected to water immersion treatment. The excess CO is used as the protective gas to achieve the protective effect on the reduced metallic iron, preventing the reduced metallic iron from being reoxidized in the waste heat boiler after leaving the kiln and before being immersed in water, controlling the metallization rate of the reduced metallic iron to above 95%, and ensuring that the Al2O3 content in the reduced metallic iron is within 2%.

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