A method for preparing sponge iron from red mud with zero carbon

Abstract

The present invention discloses a method for preparing sponge iron from red mud with zero carbon content. Hydrogen is used as a reducing agent and fluidizing gas, and low-temperature fluidized solid-state reduction of iron oxide in the red mud is performed to metallic iron. High-activity sponge iron is obtained by magnetic separation, and the metallization rate of the sponge iron is ≥90%. Hydrogen combustion is used to provide the heat required by the system, and the only combustion product is water vapor, achieving zero carbon emissions from the system. A high-speed gas-solid stirring fluidized bed with built-in bottom-extending multi-layer stirring paddles is used to achieve efficient drying, dehydration, dispersion, and transportation of the red mud. Heat exchange between cold hydrogen and the hot reduction raw material is performed to improve the energy utilization rate of the system. The process of the present invention has simple equipment, easy operation, low energy consumption, can process high-moisture and high-viscosity red mud materials, has a wide range of raw material applications, has zero carbon emissions, and is environmentally friendly. It can achieve large-scale, clean, and efficient preparation of high-activity sponge iron from red mud, and has good economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of chemical nonferrous metallurgy and environmental protection, and in particular to a method for preparing sponge iron from red mud with zero carbon. Background Art

[0002] Red mud is an industrial solid waste generated during the alkaline leaching of bauxite to produce alumina. It is characterized by high alkalinity, high moisture content, high viscosity, and radioactivity. Existing disposal methods primarily rely on dry damming and stockpiling, which not only consumes significant land resources but also poses significant safety hazards and harm to surrounding soil and water resources over long periods of storage. Red mud contains a high iron content and can be used as a secondary resource for iron recovery. Separating and recovering the iron in red mud is a key approach to its resource utilization and reduction.

[0003] Chinese patent application CN102628097A discloses a method for preparing iron ore concentrate by treating red mud with reduction and magnetization in a fluidized bed. The red mud is dried and preheated in a drum, and then magnetized, reduced, and roasted in a circulating fluidized bed using reducing gas of a certain composition to obtain iron ore concentrate with an iron grade of 61%-65%. Although this method can recover iron resources from red mud, drum drying is only suitable for low-moisture, low-viscosity red mud. High-moisture, high-viscosity red mud easily agglomerates and sticks to the wall during drum drying, making continuous operation difficult. Chinese patent application CN107523686A discloses an apparatus for preparing iron ore concentrate by suspension roasting of red mud. The red mud is first dried and broken up into red mud ore powder with a moisture content of less than 15%. The red mud is then subjected to fluidized preheating, fluidized oxidation, fluidized reduction, and cooling magnetic separation to obtain iron ore concentrate with an iron grade of 50%-68%. This solution can achieve an iron recovery rate of 60-90% in red mud. However, it uses room-temperature water for indirect heat exchange to cool the heat-reduced raw material, failing to effectively recycle the preheated heat-reduced raw material within the system, resulting in a waste of system energy. In addition, the invention does not specifically describe the method for drying and breaking up the red mud, making it difficult to effectively utilize the high-moisture, high-viscosity red mud.

[0004] Chinese patent application CN102839249A discloses a method for producing iron ore concentrate by directly reducing high-iron red mud in a rotary hearth furnace. The red mud is dried in a chain grate using preheated air to a moisture content of less than 12%. The red mud is then mixed with coke or coal powder and pressed into green pellets. The green pellets are dried, screened, and pressed into pellets of 8-12 mm. The pellets are then fed into a rotary kiln and reduced and roasted at 1000-1400°C. The roasted product is cooled, crushed, and magnetically separated to produce iron ore concentrate with an iron grade greater than 60%. Chinese patent application CN103805726A discloses a method for comprehensively utilizing high-iron red mud using a rotary hearth furnace pelletized iron process. The high-iron red mud, coal powder or coke powder, and a certain amount of additives are mixed and pelletized. The pellets are then reduced and roasted in a rotary hearth furnace at 1350-1450°C. The roasted product is cooled, crushed, and magnetically separated to produce pelletized iron. Chinese patent application CN107254583A discloses a method for comprehensive utilization of red mud based on direct reduction roasting and magnetic separation in a rotary kiln. The method uses red mud as raw material, coal powder as a reducing agent, titanomagnetite as an additive, starch and bentonite as binders to make balls, dry them, and place the dry balls in a rotary kiln at 1280-1300°C for direct reduction roasting. The roasted products are cooled and magnetically separated to obtain direct reduced iron with an iron grade higher than 92%. The above technical solutions achieve the recovery of iron resources in red mud through reduction roasting. However, they all use coal powder or coke powder as a reducing agent, which results in high carbon dioxide emissions during the roasting process and introduces other impurities into the roasted products. In addition, the reduction roasting temperatures of the above inventions are all above 1000°C, resulting in high energy consumption.

[0005] Therefore, given that current process technology is unable to cleanly and efficiently recover iron resources in red mud, the key to achieving large-scale, efficient and clean utilization of iron resources in red mud is to simplify operating procedures and reduce process energy consumption and carbon emissions through process and technological innovation. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the present invention aims to provide a method for preparing sponge iron from red mud with zero carbon.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A method for preparing sponge iron from red mud with zero carbon, comprising the following steps:

[0009] S1. Drying and breaking up process: using preheated tail gas to dry and break up the red mud in a stirred fluidized bed to obtain dried red mud material and dried tail gas;

[0010] S2, preheating process: using hot flue gas to preheat the dust and the dried material obtained in step S1 to obtain preheated material and preheated tail gas, and the preheated tail gas is sent to the drying and scattering process in step S1;

[0011] S3, combustion process: the reduction tail gas and air are burned to obtain hot flue gas, which is sent to the preheating process in step S2;

[0012] S4, reduction process: using hot hydrogen to reduce the preheated material obtained in step S2 to obtain hot-reduced raw material and reduced tail gas, which is fed into the combustion process in step S3;

[0013] S5, cooling process: using cold hydrogen to cool the hot reduction raw material obtained in step S4 to obtain hot hydrogen and cold reduction raw material, and the hot hydrogen is fed into the reduction process in step S4;

[0014] S6, magnetic separation process: the cold-reduced raw material obtained in step S5 is subjected to magnetic separation to obtain high-activity sponge iron and aluminum-containing slag;

[0015] S7, filtering and dust removal process: filtering and dust removal of the dry tail gas obtained in step S1 to obtain tail gas and dust, and the dust is sent to the preheating process in step S2.

[0016] Furthermore, in step S1, the solid mass content of the red mud is 40%-80%.

[0017] Furthermore, in step S1, fluidizing gas is introduced into the bottom of the stirred fluidized bed, and the stirring shaft extends from the center of the bottom of the stirred fluidized bed into the reactor of the stirred fluidized bed; the number of stirring paddle layers set in the part of the stirring shaft extending into the reactor of the stirred fluidized bed is not less than three layers, and is evenly distributed along the axial direction of the stirring shaft.

[0018] Furthermore, in step S1, the rotation speed of the stirring shaft is 100-2000 rpm.

[0019] Furthermore, in step S1, the dried red mud material is subjected to bubbling fluidization or turbulent fluidization in the stirred fluidized bed.

[0020] Furthermore, in step S4, the reduction temperature is 400-600°C, and the preheated material and the heat-reduced material are bubbling fluidized or turbulent fluidized in the fluidized bed used for the reduction process.

[0021] Furthermore, in step S4, the reduction time is 0.5-2h.

[0022] Furthermore, in step S6, the metallization rate of the obtained sponge iron is ≥90%.

[0023] The beneficial effects of the present invention are:

[0024] 1. This invention utilizes low-temperature, solid-state reduction of red mud particles in a fluidized bed with hydrogen to produce sponge iron, eliminating the need for mixing, pelletizing, and drying the raw pellets, resulting in a simple process. The rapid mass and heat transfer between the hydrogen and the fine red mud particles within the fluidized bed results in high reduction efficiency and low energy consumption. Low-temperature reduction effectively prevents particle agglomeration in the fluidized bed, while also resulting in a high-quality, highly active sponge iron product.

[0025] 2. The present invention uses hydrogen combustion to provide the heat required by the system. The only combustion product is water vapor, which can achieve zero carbon emissions for the system.

[0026] 3. This invention uses a high-speed gas-solid agitation fluidized bed with built-in bottom-extending multi-layer agitators to achieve efficient drying, dehydration, dispersion, and transportation of red mud. The high-speed bottom-extending multi-layer agitators can effectively shear and disperse high-moisture and high-viscosity red mud, enhance mass and heat transfer, strengthen drying and dehydration, and effectively crush the dried material. The equipment is simple and easy to operate.

[0027] 4. The present invention has a high waste heat recovery rate, which effectively improves the thermal efficiency of the overall process system;

[0028] 5. In the present invention, the solid phase heat processing processes of red mud drying, breaking up, preheating, transportation and reduction of iron oxides in red mud to metallic iron are all carried out in a gas-solid fluidized bed, which is convenient for continuous operation and large-scale processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart of the methods of various embodiments of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described below in conjunction with the accompanying drawings. It should be noted that this embodiment is based on the technical solution and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to this embodiment.

[0031] Example 1

[0032] This embodiment provides a method for preparing sponge iron from red mud with zero carbon, such as Figure 1 As shown, the following steps are included:

[0033] S1. Drying and Dispersing Process: Red mud with a solids content of 40% is dried and dispersed in a stirred fluidized bed using preheated tail gas to produce dried red mud and dried tail gas. Fluidizing gas is introduced into the bottom of the stirred fluidized bed, and a stirring shaft extends from the center of the bottom of the stirred fluidized bed into the reactor of the stirred fluidized bed. The portion of the stirring shaft extending into the reactor of the stirred fluidized bed is equipped with three layers of stirring paddles evenly distributed along the axis of the stirring shaft. The stirring shaft rotates at 1500 rpm.

[0034] S2, preheating process: using hot flue gas to preheat the dust and the dried material obtained in step S1 to obtain preheated material and preheated tail gas, and the preheated tail gas is sent to the drying and scattering process in step S1;

[0035] S3, combustion process: the reduction tail gas and air are burned to obtain hot flue gas, which is sent to the preheating process in step S2;

[0036] S4, reduction process: using hot hydrogen to reduce the preheated material obtained in step S2 at 450 ° C for 1.5 hours to obtain hot reduction material and reduction tail gas, which is fed into the combustion process in step S3;

[0037] S5, cooling process: using cold hydrogen to cool the hot reduction raw material obtained in step S4 to obtain hot hydrogen and cold reduction raw material, and the hot hydrogen is fed into the reduction process in step S4;

[0038] S6, magnetic separation process: the cold-reduced raw material obtained in step S5 is subjected to magnetic separation to obtain high-activity sponge iron with a metallization rate of 94% and aluminum-containing slag;

[0039] S7, filtering and dust removal process: filtering and dust removal of the dry tail gas obtained in step S1 to obtain tail gas and dust, and the dust is sent to the preheating process in step S2.

[0040] In the above method, the drying, breaking up, preheating and reduction steps are all carried out in a gas-solid fluidized bed.

[0041] Example 2

[0042] The method flow of this embodiment is basically the same as that of Example 1, except that: in step S1, the solid content of the red mud is 80%, and the stirring shaft speed of the stirred fluidized bed is 100 rpm; in step S3, the reduction temperature is 400°C, and the reduction time is 2 hours; in step S6, high-activity sponge iron with a metallization rate of 92% is obtained after magnetic separation.

[0043] Example 3

[0044] The method flow of this embodiment is basically the same as that of Example 1, except that: in step S1, the solid content of the red mud is 40%, the number of stirring paddle layers arranged on the portion of the stirring shaft extending into the stirred fluidized bed reactor is 5, and the stirring shaft rotation speed is 2000 rpm; in step S3, the reduction temperature is 600°C, and the reduction time is 0.5 h; and in step S6, high-activity sponge iron with a metallization rate of 95% is obtained after magnetic separation.

[0045] Example 4

[0046] The method flow of this embodiment is basically the same as that of Example 1, except that: in step S1, the solid content of the red mud is 50%, the number of stirring paddle layers arranged on the portion of the stirring shaft extending into the stirred fluidized bed reactor is 4, and the stirring shaft rotation speed is 1000 rpm; in step S3, the reduction temperature is 500°C, and the reduction time is 1 hour; and in step S6, high-activity sponge iron with a metallization rate of 93% is obtained after magnetic separation.

[0047] Those skilled in the art can make various corresponding changes and modifications based on the above technical solutions and concepts, and all of these changes and modifications should be included in the scope of protection of the claims of the present invention.

Claims

1. A method for preparing sponge iron from red mud with zero carbon, characterized by: The following steps are involved: S1. Drying and breaking up process: using preheated tail gas to dry and break up the red mud in a stirred fluidized bed to obtain dried red mud material and dried tail gas; S2, preheating process: using hot flue gas to preheat the dust and the dried material obtained in step S1 to obtain preheated material and preheated tail gas, and the preheated tail gas is sent to the drying and scattering process in step S1; S3, combustion process: the reduction tail gas and air are burned to obtain hot flue gas, which is sent to the preheating process in step S2; S4, reduction process: using hot hydrogen to reduce the preheated material obtained in step S2 to obtain hot-reduced raw material and reduced tail gas, which is fed into the combustion process in step S3; S5, cooling process: using cold hydrogen to cool the hot reduction raw material obtained in step S4 to obtain hot hydrogen and cold reduction raw material, and the hot hydrogen is fed into the reduction process in step S4; S6, magnetic separation process: the cold-reduced raw material obtained in step S5 is subjected to magnetic separation to obtain high-activity sponge iron and aluminum-containing slag; S7, filtering and dust removal process: filtering and dust removal of the dry tail gas obtained in step S1 to obtain tail gas and dust, and the dust is sent to the preheating process in step S2.

2. The method according to claim 1, characterized in that In step S1, the solid mass content of the red mud is 40%-80%.

3. The method according to claim 1, characterized in that In step S1, fluidizing gas is introduced into the bottom of the stirred fluidized bed, and the stirring shaft extends from the center of the bottom of the stirred fluidized bed into the reactor of the stirred fluidized bed; the number of stirring paddle layers set in the part of the stirring shaft extending into the reactor of the stirred fluidized bed is not less than three layers, and is evenly distributed along the axial direction of the stirring shaft.

4. The method according to claim 3, characterized in that In step S1, the rotation speed of the stirring shaft is 100-2000 rpm.

5. The method according to claim 1, characterized in that In step S1, the dried red mud material is subjected to bubbling fluidization or turbulent fluidization in a stirred fluidized bed.

6. The method according to claim 1, characterized in that In step S4, the reduction temperature is 400-600°C, and the preheated material and the heat-reduced material are bubbling fluidized or turbulent fluidized in the fluidized bed used for the reduction process.

7. The method according to claim 1, characterized in that In step S4, the reduction time is 0.5-2h.

8. The method according to claim 1, characterized in that In step S6, the metallization rate of the obtained sponge iron is ≥90%.

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