Method for extracting iron by online direct reduction of electric furnace steel slag

Abstract

A method for extracting iron by online direct reduction of electric furnace steel slag, relating to the technical field of metallurgy. The method comprises the following steps: (1) placing a slag pot below a furnace before normal smelting and slag discharging of the electric furnace, and high-temperature steel slag flowing out from a door of the electric furnace; (2) adding aluminum ash balls into the slag pot along with slag flow; (3) under flow impact brought by the molten slag flow entering the slag pot, performing online mixing and reduction on the steel slag and the aluminum ash balls to obtain mixed molten slag containing metal iron drops; (4) performing cooling after the slap pot is filled with the molten slag, taking out a metal iron lump settled at the bottom of the slag pot, and recovering residual metal iron beads in the slag through magnetic separation to obtain a Fe-Mn crude alloy; and using, as a cement raw material, tailings which are used as a typical CaO-SiO2-Al2O3 metallurgical slag system. By means of the method, online convenient treatment of high-temperature electric furnace slag in a slag pot can be directly achieved, sensible heat of the molten electric furnace slag is fully utilized without additionally supplementing heat, the added value of an obtained Fe-Mn crude alloy product is high, and recycling of resources is achieved to the maximum extent.

Description

On-line direct reduction method for iron extraction from electric furnace slag Technical Field

[0001] The invention belongs to the technical field of metallurgy, and in particular relates to an online direct reduction method for iron extraction using electric furnace slag. Background Art

[0002] Electric arc furnace (EAF) shortened steelmaking is a trend in steelmaking. Electric furnace slag is a byproduct of the EAF steelmaking process and is produced in significant quantities, accounting for approximately 5-15% of total steelmaking production when using scrap steel as the raw material. EAF slag is chemically divided into oxidized slag and reduced slag. Oxidized slag, produced in EAFs, accounts for 70% of the total slag. Oxidized slag contains 10-25% FeO. The high-temperature molten slag, discharged at a temperature of approximately 1673-1873K, contains a significant amount of physical heat. With the increase in EAF steel production, EAF slag emissions have also increased annually. The discharge of large amounts of EAF slag not only occupies land and pollutes the environment, but offline processing also results in a significant waste of high-temperature sensible heat resources and valuable elements such as metallic iron.

[0003] Currently, most steel mills handle electric furnace slag by hot pouring from the furnace using electric tank cars. Some also use tank cars to transport the liquid slag to an intermediate slag yard for hot pouring or condensation before dumping the slag in a tank. Alternatively, they directly pour the slag on the underground floor, cool it with water, and then transport it by car. While the carbon thermal reduction of molten steel slag treatment method proposed by some scholars can achieve iron resource extraction from electric furnace molten steel slag, the carbon thermal reduction reaction is endothermic and requires an external heat source to maintain the reduction reaction, which increases energy consumption. Furthermore, the increased viscosity of the slag during the reaction makes it difficult for the reduction reaction and the sedimentation of the metallic iron droplets to proceed fully. Furthermore, carbon thermal reduction increases carbon dioxide emissions, which does not meet the development requirements of low-carbon metallurgy.

[0004] Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide an online direct reduction iron extraction method for electric furnace steel slag, which directly processes the slag flow generated during the electric furnace smelting process online, fully considering the economic efficiency of online convenient processing, sensible heat utilization of molten steel slag and iron resource recovery.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The invention discloses an online direct reduction method for iron extraction from electric furnace steel slag. Aluminum ash balls are added to the molten slag flow during the electric furnace slag flow to reduce the slag to obtain a mixed slag containing metallic iron droplets. After cooling, the metallic iron beads are recovered to obtain a crude iron-manganese alloy.

[0008] Optionally, slag is flowed multiple times during the electric furnace smelting process, and the aluminum ash balls are added to the molten slag flow during at least one of the slag flow processes.

[0009] Optionally, when the electric furnace is slagging, a slag pot is placed under the furnace, aluminum ash balls are added into the slag pot, and the molten slag flow reacts with the aluminum ash balls in the slag pot.

[0010] Optionally, the slag pot is filled with mixed slag and then cooled to recover the metal iron balls.

[0011] Optionally, remove the metal lump at the bottom of the slag pot after cooling.

[0012] Optionally, magnetic separation is used to recover the metal iron beads.

[0013] Optionally, the tailings after recovering the metal iron beads are used as a CaO-SiO2-Al2O3 metallurgical slag system as a cement raw material.

[0014] Optionally, the composition of the slag stream includes SiO2: 10-20%, (CaO+MgO): 45-60%, Al2O3: 2-4%, FeO: 0-25%, MnO: 10%, and P2O5: 0.4-0.6% by mass percentage.

[0015] Optionally, the components of the aluminum ash ball include, by mass percentage, Al: 0.0-30.0%, Al2O3: 30.0-45.0%, SiO2: 25.0-30.0%, Na2O: 1.0-3.0%, MgO: 2.0-3.0%, CaO: 1.0-3.0%, and (FeO+MnO)<1.0%.

[0016] Optionally, the main chemical reactions during the reduction process are: 3(FeO)+2[Al]=3[Fe]+(Al2O3) (1) 3(MnO)+2[Al]=3[Mn]+(Al2O3) (2)

[0017] Optionally, the weight of the added aluminum ash balls is 15.0-30.0% of the weight of the slag flow.

[0018] Optionally, the composition of the iron-manganese crude alloy contains Fe: 55.0-90.0%, Mn: 8.0-45.0%, and the rest is P and other impurities in terms of mass percentage.

[0019] Optionally, the iron reduction rate in the slag stream is ≥ 91.0%.

[0020] Optionally, 0.15 to 0.25 tons of ferromanganese crude alloy is obtained by processing each ton of electric furnace slag.

[0021] The beneficial effects of the present invention are:

[0022] (1) The slag pot containing high-temperature steel slag does not need to be transported, nor does it require additional disposal equipment. The high-temperature electric furnace slag can be directly and conveniently processed online in the slag pot;

[0023] (2) The sensible heat of the molten electric furnace slag is fully utilized, and the movement of the high-temperature slag flow is used to achieve a full mixing reaction between the slag flow and the aluminum ash balls, without the need for additional heat;

[0024] (3) The reaction between aluminum ash and electric furnace slag is an exothermic reaction, which can maintain good fluidity of the slag pool and create good kinetic conditions for the sedimentation of the metal after reduction. The reduction and sedimentation of the metal are sufficient: it can ensure that the iron reduction rate is ≥91.0%, and the sedimentation rate of the crude alloy obtained after sedimentation is ≥92%;

[0025] (4) The iron extraction process using aluminum ash instead of carbon-reduced electric furnace slag has a distinct low-carbon feature and achieves the effect of "treating waste with waste". The obtained Fe-Mn crude alloy product has high added value, and the tailings after iron extraction can be used as cement raw material, realizing the recycling of resources to the greatest extent.

[0026] Other advantages, objects, and features of the present invention will be described in part in the following description and, in part, will be apparent to those skilled in the art upon examination of the following description or may be learned from practice of the present invention. The objects and other advantages of the present invention may be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below with reference to the accompanying drawings, in which:

[0028] FIG1 is a process flow chart of the present invention. DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present invention by means of specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic illustrations of the basic concept of the present invention, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0030] Among them, the accompanying drawings are only for illustrative purposes and represent only schematic diagrams rather than actual pictures, and should not be understood as limiting the present invention. In order to better illustrate the embodiments of the present invention, some parts of the accompanying drawings may be omitted, enlarged or reduced, and do not represent the dimensions of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions may be omitted in the accompanying drawings.

[0031] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if there are terms such as "upper", "lower", "left", "right", "front", "back", etc. indicating directions or positional relationships, they are based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operate in a specific direction. Therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0032] As shown in FIG1 , the present invention provides a method for extracting iron by online direct reduction of electric furnace slag, comprising the following steps:

[0033] Before the slag is normally flowed during smelting in the electric furnace, a slag pot is placed under the furnace. As the smelting progresses, high-temperature steel slag flows out from the furnace door of the electric furnace. The steel slag comprises, by mass percentage, SiO2: 10-20%, (CaO+MgO): 45-60%, Al2O3: 2-4%, FeO: 10-25%, MnO: 5-10%, and P2O5: 0.4-0.6%.

[0034] Aluminum ash balls are added to the slag pot along with the slag flow; the weight of the aluminum ash balls is 15.0-30.0% of the weight of the electric furnace slag; the aluminum ash balls can be added to the slag pot along with the slag flow at one time or in batches; during the smelting process, slag flows multiple times at the electric furnace door, and aluminum ash balls can be added multiple times along with the slag flow; wherein the components of the aluminum ash balls include, by mass percentage, Al: 20.0-30.0%, Al2O3: 30.0-45.0%, SiO2: 25.0-30.0%, Na2O: 1.0-3.0%, MgO: 2.0-3.0%, CaO: 1.0-3.0%, and (FeO+MnO)<1.0%;

[0035] As the molten slag flows into the slag pot, the steel slag and aluminum ash balls are fully mixed and reduced online to obtain a mixed slag containing a large amount of metallic iron droplets.

[0036] After the slag is filled and cooled, the metal lumps settled at the bottom of the slag pot are taken out and the remaining metal iron beads in the slag are recovered by magnetic separation. The final Fe-Mn crude alloy contains Fe: 55.0-90.0% by mass, Mn: 8.0-45.0% by mass, and the rest is impurities such as P; the Fe reduction rate is ≥91.0%;

[0037] 0.15 to 0.25 tons of Fe-Mn crude alloy can be obtained by processing each ton of electric furnace slag; the tailings, as a typical CaO-SiO2-Al2O3 metallurgical slag system, can be used as cement raw material.

[0038] Through the occurrence of the above reactions, the iron oxides and manganese oxides in the molten slag electric furnace slag are continuously reduced to form metallic iron droplets, which are then precipitated to form Fe-Mn coarse alloy.

[0039] Aluminum ash is the cooling product of slag produced during the electrolytic or cast aluminum production process. It primarily contains metallic aluminum and various oxides. Aluminum ash is widely available and produced in large quantities. The electrolytic aluminum process generates 30-50 kg of aluminum ash for every ton of aluminum produced, and another 30-40 kg of aluminum ash is generated during the processing of each ton of aluminum. However, the current utilization rate of aluminum ash is low, and large amounts of aluminum ash are dumped, resulting in a waste of resources and costing hundreds of yuan. Using aluminum ash instead of metallic aluminum and carbon in a slag bath reduction of steel slag not only addresses the cost of reducing agents, but also, as the thermite reaction is exothermic, the continuous dissolution of Al₂O₃ and SiO₂ in the aluminum ash, along with the Al₂O₃ generated by the reduction reaction, into the slag, spontaneously regulating the slag's melting temperature and viscosity. This ensures optimal kinetic conditions for the reduction and metal settling processes, promoting metal aggregation and settling, and slag-metal separation.

[0040] Example 1

[0041] 1. Before the slag is discharged during normal smelting in the electric furnace, a slag pot is placed under the furnace. As the smelting progresses, high-temperature slag flows out from the furnace door. The slag composition, by mass percentage, includes SiO2: 20.0%, CaO: 40.5%, MgO: 5.0%, Al2O3: 4.0%, FeO: 25.0%, MnO: 5.0%, and P2O5: 0.5%.

[0042] 2. Aluminum ash balls are added to the slag pot along with the slag flow; the weight of the aluminum ash balls is 22.8% of the weight of the electric furnace slag; the aluminum ash balls can be added to the slag pot along with the slag flow at one time or in batches; during the smelting process, slag flows multiple times at the electric furnace door, and aluminum ash balls can be added multiple times along with the slag flow; wherein, the composition of the aluminum ash balls includes, by mass percentage, Al: 30.0%, Al2O3: 34.1%, SiO2: 28.0%, Na2O: 2.5%, MgO: 2.5%, CaO: 2.0%, FeO: 0.5%, and MnO: 0.4%.

[0043] 3. As the molten slag flows into the slag pot, the steel slag and aluminum ash balls are fully mixed and reduced online to obtain a mixed slag containing a large amount of metallic iron droplets;

[0044] 4. After the slag pot is filled and cooled, the metal lumps settled at the bottom of the slag pot are removed. After the remaining metal iron beads in the slag are recovered through magnetic separation, the final Fe-Mn crude alloy is obtained, which contains Fe: 83.0% and Mn: 16.0% by mass, and the rest is impurities such as P; the Fe reduction rate is 91.3%;

[0045] 5. 0.21 tons of Fe-Mn crude alloy can be obtained by processing each ton of electric furnace slag; the tailings, as a typical CaO-SiO2-Al2O3 metallurgical slag system, can be used as cement raw material.

[0046] Example 2

[0047] 1. Before the slag is discharged during normal smelting in the electric furnace, a slag pot is placed under the furnace. As the smelting progresses, high-temperature slag flows out from the furnace door. The slag composition, by mass percentage, includes SiO2: 18.0%, CaO: 45.0%, MgO: 6.0%, Al2O3: 4.0%, FeO: 20.0%, MnO: 6.5%, and P2O5: 0.5%.

[0048] 2. Aluminum ash balls are added to the slag pot along with the slag flow; the weight of the aluminum ash balls is 20.6% of the weight of the electric furnace slag; the aluminum ash balls can be added to the slag pot along with the slag flow at one time or in batches; during the smelting process, slag flows multiple times at the electric furnace door, and aluminum ash balls can be added multiple times along with the slag flow; wherein, the composition of the aluminum ash balls includes, by mass percentage, Al: 30.0%, Al2O3: 34.1%, SiO2: 28.0%, Na2O: 2.5%, MgO: 2.5%, CaO: 2.0%, FeO: 0.5%, and MnO: 0.4%.

[0049] 3. As the molten slag flows into the slag pot, the steel slag and aluminum ash balls are fully mixed and reduced online to obtain a mixed slag containing a large amount of metallic iron droplets;

[0050] 4. After the slag pot is filled and cooled, the metal lumps settled at the bottom of the slag pot are removed. After the remaining metal iron beads in the slag are recovered through magnetic separation, the final Fe-Mn crude alloy is obtained, which contains Fe: 75.4% and Mn: 23.5% by mass, and the rest is impurities such as P; the Fe reduction rate is 93.5%;

[0051] 5. 0.19 tons of Fe-Mn crude alloy can be obtained by processing each ton of electric furnace slag; the tailings, as a typical CaO-SiO2-Al2O3 metallurgical slag system, can be used as cement raw material.

[0052] Example 3

[0053] 1. Before the slag is discharged during normal smelting in the electric furnace, a slag pot is placed under the furnace. As the smelting progresses, high-temperature slag flows out from the furnace door. The slag composition, by mass percentage, includes SiO2: 18.0%, CaO: 47.5%, MgO: 7.0%, Al2O3: 4.0%, FeO: 15.0%, MnO: 8.0%, and P2O5: 0.5%.

[0054] 2. Aluminum ash balls are added to the slag pot along with the slag flow; the weight of the aluminum ash balls is 18.2% of the weight of the electric furnace slag; the aluminum ash balls can be added to the slag pot along with the slag flow at one time or in batches; during the smelting process, slag flows multiple times at the electric furnace door, and aluminum ash balls can be added multiple times along with the slag flow; wherein, the composition of the aluminum ash balls includes, by mass percentage, Al: 30.0%, Al2O3: 34.1%, SiO2: 28.0%, Na2O: 2.5%, MgO: 2.5%, CaO: 2.0%, FeO: 0.5%, and MnO: 0.4%.

[0055] 3. As the molten slag flows into the slag pot, the steel slag and aluminum ash balls are fully mixed and reduced online to obtain a mixed slag containing a large amount of metallic iron droplets;

[0056] 4. After the slag pot is filled and cooled, the metal lumps settled at the bottom of the slag pot are removed. After the remaining metal iron beads in the slag are recovered through magnetic separation, the final Fe-Mn crude alloy is obtained, which contains Fe: 65.6% and Mn: 33.3% by mass, and the rest is impurities such as P; the Fe reduction rate is 95.8%;

[0057] 5. 0.17 tons of Fe-Mn crude alloy can be obtained by processing each ton of electric furnace slag; the tailings, as a typical CaO-SiO2-Al2O3 metallurgical slag system, can be used as cement raw material.

[0058] Example 4

[0059] 1. Before the slag is discharged during normal smelting in the electric furnace, a slag pot is placed under the furnace. As the smelting progresses, high-temperature slag flows out from the furnace door of the electric furnace. The slag composition, by mass percentage, includes SiO2: 15.0%, CaO: 49.5%, MgO: 9.0%, Al2O3: 4.0%, FeO: 12.0%, MnO: 10.0%, and P2O5: 0.5%.

[0060] 2. Aluminum ash balls are added to the slag pot along with the slag flow; the weight of the aluminum ash balls is 17.6% of the weight of the electric furnace slag; the aluminum ash balls can be added to the slag pot along with the slag flow at one time or in batches; during the smelting process, slag flows multiple times at the electric furnace door, and aluminum ash balls can be added multiple times along with the slag flow; wherein, the composition of the aluminum ash balls includes, by mass percentage, Al: 30.0%, Al2O3: 34.1%, SiO2: 28.0%, Na2O: 2.5%, MgO: 2.5%, CaO: 2.0%, FeO: 0.5%, and MnO: 0.4%.

[0061] 3. As the molten slag flows into the slag pot, the steel slag and aluminum ash balls are fully mixed and reduced online to obtain a mixed slag containing a large amount of metallic iron droplets;

[0062] 4. After the slag pot is filled and cooled, the metal lumps settled at the bottom of the slag pot are removed. After the remaining metal iron beads in the slag are recovered through magnetic separation, the final Fe-Mn crude alloy is obtained, which contains Fe: 55.1% and Mn: 43.8% by mass, and the rest is impurities such as P; the Fe reduction rate is 97.4%;

[0063] 5. 0.16 tons of Fe-Mn crude alloy can be obtained by processing each ton of electric furnace slag; the tailings, as a typical CaO-SiO2-Al2O3 metallurgical slag system, can be used as cement raw material.

[0064] Example 5

[0065] 1. Before the slag is discharged during normal smelting in the electric furnace, a slag pot is placed under the furnace. As the smelting progresses, high-temperature slag flows out from the furnace door. The slag composition, by mass percentage, includes SiO2: 20.0%, CaO: 40.5%, MgO: 5.0%, Al2O3: 4.0%, FeO: 25.0%, MnO: 5.0%, and P2O5: 0.5%.

[0066] 2. Aluminum ash balls are added to the slag pot along with the slag flow; the weight of the aluminum ash balls is 27.6% of the weight of the electric furnace slag; the aluminum ash balls can be added to the slag pot along with the slag flow at one time or in batches; during the smelting process, slag flows multiple times at the electric furnace door, and aluminum ash balls can be added multiple times along with the slag flow; wherein, the composition of the aluminum ash balls includes Al: 25.0%, Al2O3: 36.7%, SiO2: 29.0%, Na2O: 3.0%, MgO: 3.0%, CaO: 2.5%, FeO: 0.6%, and MnO: 0.2% by mass.

[0067] 3. As the molten slag flows into the slag pot, the steel slag and aluminum ash balls are fully mixed and reduced online to obtain a mixed slag containing a large amount of metallic iron droplets;

[0068] 4. After the slag pot is filled and cooled, the metal lumps settled at the bottom of the slag pot are removed. After the remaining metal iron beads in the slag are recovered through magnetic separation, the final Fe-Mn crude alloy is obtained, which contains Fe: 83.0% and Mn: 15.9% by mass, and the rest is impurities such as P; the Fe reduction rate is 92.1%;

[0069] 5. 0.21 tons of Fe-Mn crude alloy can be obtained by processing each ton of electric furnace slag; the tailings, as a typical CaO-SiO2-Al2O3 metallurgical slag system, can be used as cement raw material.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solutions, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for extracting iron by online direct reduction of electric furnace slag, characterized in that: When slag is flowing in an electric furnace, aluminum ash balls are added to the molten slag flow to reduce it to obtain a mixed slag containing metallic iron droplets; after cooling, the metallic iron beads are recovered to obtain a crude iron-manganese alloy.

2. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: There are multiple slag flows during the electric furnace smelting process, and the aluminum ash balls are added to the molten slag flow during at least one of the slag flows.

3. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: When the electric furnace is slag flowing, a slag pot is placed under the furnace, and aluminum ash balls are added into the slag pot. The molten slag flow reacts with the aluminum ash balls in the slag pot.

4. The method for extracting iron by online direct reduction of electric furnace slag according to claim 3, characterized in that: The slag pot is filled with mixed slag and then cooled to recover the metal iron beads.

5. The method for extracting iron by online direct reduction of electric furnace slag according to claim 3, characterized in that: After cooling, remove the metal lump at the bottom of the slag pot.

6. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The metal iron beads are recovered by magnetic separation.

7. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The tailings after recycling the metal iron beads are used as CaO-SiO2-Al2O3 metallurgical slag system as cement raw material.

8. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The components of the slag flow include SiO2: 10-20%, (CaO+MgO): 45-60%, Al2O3: 2-4%, FeO: 10-25%, MnO: 5-10%, and P2O5: 0.4-0.6% by mass percentage.

9. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The components of the aluminum ash ball include Al: 20.0-30.0%, Al2O3: 30.0-45.0%, SiO2: 25.0-30.0%, Na2O: 1.0-3.0%, MgO: 2.0-3.0%, CaO: 1.0-3.0%, and (FeO+MnO)<1.0% by mass percentage.

10. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The main chemical reactions during the reduction process are: 3(FeO)+2[Al]=3[Fe]+(Al2O3) (1) 3(MnO)+2[Al]=3[Mn]+(Al2O3) (2) 11. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The weight of the added aluminum ash balls is 15.0 to 30.0% of the weight of the slag flow.

12. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The composition of the iron-manganese crude alloy is Fe: 55.0-90.0%, Mn: 8.0-45.0%, and the rest is P and other impurities.

13. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: The reduction rate of iron in the slag stream is ≥91.0%.

14. The method for extracting iron by online direct reduction of electric furnace slag according to claim 1, characterized in that: 0.15-0.25 ton of ferromanganese crude alloy can be obtained by processing each ton of electric furnace slag.

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