Extraction of Mg and Al using LF smelting slag

Abstract

The present invention discloses a method for extracting Mg and Al using LF refined slag, which includes the steps of: a) pouring the LF refined slag after casting molten steel from a ladle into a slag tank, placing it in a vacuum chamber, adding a reducing agent to the LF refined slag and mixing it to obtain a mixed reaction raw material; and b) heating the mixed reaction raw material in the slag tank after evacuation to react, and condensing and recovering the generated gaseous Mg and Al at the cooling end outside the vacuum chamber to obtain solid Mg and Al. The method of the present invention uses LF refined slag as a raw material and effectively utilizes its residual heat to produce high added value Mg and Al, which not only solves the problem of greening the LF refined steel slag, but also avoids the disadvantages of Mg production by traditional thermal reduction method, and the recovered Mg and Al can be reused in steel production, which can bring higher economic benefits and solve the difficult problem of large-scale use of LF refined steel slag.

Description

[Technical field]

[0001] The present invention relates to the technical field of steel furnace slag utilization, and specifically to a method for extracting Mg and Al using LF smelting slag. [Background technology]

[0002] The ladle top slag after LF refining has the characteristics of high basicity, good metallurgical properties, appropriate composition, and fast slagging. Although the sulfur content in the furnace slag of some lots is high, the sulfur in the furnace slag of most lots is not saturated, and it can be returned to the refining process for secondary or tertiary use.

[0003] At present, scholars at home and abroad have conducted a lot of research on the recycling and reuse process of LF smelting slag, but there is no steel enterprise that can recycle and reuse all of the LF smelting slag, and the current recycling utilization rate is less than 20%. LF slag that cannot be recycled is put into a slag tank and transported to a slag yard, and is finally disposed of together with converter slag and electric furnace slag. Since steel slag contains P, the ore blending is limited and it can hardly be used for sintering. After recovering metallic Fe, the powder residue can only be piled up, which occupies and pollutes land. Steel slag is discarded in large quantities or used as a raw material for the production of low value-added products such as cement. The accumulation causes powderization and intense dust generation, which is unfavorable to environmental protection and leads to resource waste. It brings serious problems to the social environment and is also a major obstacle to social progress and economic development.

[0004] Therefore, there is a demand for a method for recycling and reusing LF refining slag that can solve the shortcomings of low reuse rate of LF refining slag, its tendency to generate dust due to accumulation, severe environmental pollution, and its low added value use, and that can recycle and reuse LF refining slag with high added value and ultimately achieve the goals of recycling production and zero emissions, while saving energy and reducing emissions. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made based on the inventors' discovery and recognition of the following facts and problems. The conventional research methods for recycling and reusing LF refining slag have several deficiencies, which are mainly evident in the following points: (1) Regarding the recycling process of hot refining slag, many steel companies have conducted tests to recover the heat value of steel slag remaining after refining, but due to constraints such as factory buildings, lifting equipment, product outlines and production systems, the recycling rate of hot slag is low. (2) If the refining slag is cooled, crushed and reused in a solid state, its heat value is not fully utilized, and the cooled slag raw material is used in the next cycle, which slows down the slag formation rate and is disadvantageous to energy conservation. (3) The desulfurization technology for LF refining slag using the thermal oxidation method is difficult to implement due to production space restrictions, and it is difficult to guarantee high-temperature gas at a temperature of 1300 to 1450°C. (4) Desulfurization using solid hydrothermal leaching wastes a large amount of cooling water and the heat of the steel slag during the treatment process, and also causes secondary pollution.

[0006] The main industrial smelting methods for magnesium include electrolysis, carbothermal reduction, Pigeon process, and Magneterm semi-continuous magnesium smelting. Among them, carbothermal reduction magnesium smelting was only used in factories in the 1930s and 1940s, and currently the predominant industrial methods around the world are electrolysis and Pigeon process. Until the mid-1990s, production by electrolysis accounted for more than 80% of the world's magnesium production, while production by the Pigeon and Magneterm processes was only about 20%. Since the beginning of the 21st century, production by the Magneterm process has almost stopped and production by the electrolysis process has also been greatly reduced, but production by the Pigeon process accounts for more than 80% of the world's production.

[0007] Thermal reduction is a method for producing metallic magnesium. It mainly uses dolomite, magnesite, etc. as raw materials, which are fired to MgO in a kiln, then a reducing agent is added and heated and reduced to metallic magnesium in a reduction furnace. At home and abroad, it is widely used to smelt magnesium using the Pigeon method, that is, the fired dolomite (MgO, Cao) is used as raw material and ferrosilicon is used as a reducing agent, which are mixed in a certain ratio, crushed into powder, molded into lumps, placed in a reduction tank, heated and reduced in a reduction furnace to obtain magnesium vapor, which is cooled and crystallized into solid magnesium, and then melted into magnesium ingots. The advantage of this method is its simplicity, but the disadvantage is that the raw materials are mixed in a cold state and then heated, consuming a lot of energy during the production process. The dolomite firing process and the magnesium smelting process by thermal reduction are both performed at high temperatures, take a long time, and require the consumption of a large amount of fuel, and since these two processes are performed separately, the fuel consumption and processing costs during the production process are further increased.

[0008] Whether it is the Pidgeon process or the French Magneterm semi-continuous magnesium smelting process, ferrosilicon, especially ferrosilicon containing more than 75% silicon (usually 75 # Ferrosilicon) is used as a reducing agent, MgO-containing ore is used as a magnesium smelting raw material, and these are mixed with a certain ratio of mineralizer (CaF 2 ), crushed and mixed with magnesium oxide, formed into spheres, and then the spherical raw material is placed in a reduction tank, where it is reacted at high temperature and high vacuum (1200°C, 13 Pa) to generate Mg vapor, which is then crystallized to generate metallic Mg. Here, the mineralizer (CaF 2 ) serves to lower the temperature at which a liquid phase appears and thus increase the reaction rate. The chemical reaction by which Si reduces MgO under high temperature and high vacuum conditions is shown in equation (1). 2MgO+Si=SiO 2 +2Mg(gas) (1)

[0009] The disadvantages of producing Mg by the conventional thermal reduction method are as follows: 1) Since dolomite, magnesite, etc. are used as raw materials for production, the mining process destroys the natural ecological environment. 2) Raw materials such as dolomite and magnesite need to be sintered in a kiln to turn them into MgO. The sintering process is carried out at high temperatures and takes a long time, consuming a large amount of fuel. This results in high fuel consumption and processing costs during the production process. 3) In the production process of magnesium smelting by thermal reduction, the raw materials must be mixed at room temperature and then heated from a cold state to a high temperature of 1200-1250°C, which is necessary for the reaction. This takes a long time and also requires a large amount of fuel consumption. Since this is carried out separately from process 1), the fuel consumption and processing costs of the production process increase further. 4) The Pigeon process adopts external heating, and the heat is gradually transferred from the outside to the inside of the reactor, resulting in a long production cycle, large heat loss, and low thermal energy utilization rate. Analysis shows that the thermal energy utilization rate of a typical process is only about 20%. 5) During the production process, there is severe pollution from smoke and dust, which creates a poor working environment and worsens the surrounding ecological environment. 6) CaF for production 2 This requires additional work, which pollutes the environment.

[0010] Aluminum and aluminum alloys are currently one of the most widely used and economical materials. Because aluminum is highly reactive, it can currently only be produced on a large scale by electrolysis. However, the electrolytic process of aluminum is energy intensive and costly, so researchers are looking for different ways to produce aluminum economically.

[0011] The present invention aims to solve at least one of the technical problems in the prior art to some extent. Therefore, in the embodiment of the present invention, a method for extracting Mg and Al using LF refining slag is proposed. This method uses LF refining slag as a raw material and effectively utilizes its residual heat to produce high added value Mg and Al, which not only solves the problem of greening LF refining steel slag, but also avoids the disadvantages of Mg production by the conventional thermal reduction method, and allows the recovered Mg and Al to be reused in steel production, resulting in higher economic benefits and resolving the difficult problem of large-scale use of LF refining steel slag. [Means for solving the problem]

[0012] In an embodiment of the present invention, a method for extracting Mg and Al using LF smelting slag includes the following steps: a. After pouring molten steel, the LF refining slag is poured from the ladle into a slag tank, which is placed in a vacuum chamber, and the LF refining slag is mixed with a reducing agent to obtain a reactive mixed material; b. After evacuation, the reaction mixture material in the slag tank is heated to react, and the generated gaseous Mg and Al are condensed and collected at the cooling end outside the vacuum chamber. Effect of the Invention

[0013] The method for extracting Mg and Al using LF smelting slag in the embodiment of the present invention provides the following advantages and technical effects: 1. In the method according to the embodiment of the present invention, the LF refining slag after casting of molten steel is used as the raw material, so the cost is low, almost zero. In addition, the LF refining slag has a high residual temperature and contains a lot of sensible heat, so the reducing agent is preheated and the MgO, Al in the slag are reduced. 2 O 3 It also provides some of the energy required for the reaction. By supplementing some of the heat, the demand for the reduction reaction can be met, making the most of the heat and saving a lot of energy.

[0014] 2. In the method according to the embodiment of the present invention, Mg and Al are extracted from LF refining slag after casting of molten steel. LF refining slag is an industrial solid waste, and by using it as a substitute for industrial raw materials such as dolomite, magnesite and aluminum ore, waste utilization is realized and non-renewable ore resources are saved.

[0015] 3. The method of the embodiment of the present invention can effectively solve the problem of recycling and reusing LF refined steel slag, realize green processing, and avoid the shortcomings of traditional Mg and Al production technologies. The recovered Mg and Al can be reused in steel production, which brings about higher economic benefits and provides a new direction for the large-scale use of LF refined steel slag. 4. The method of the embodiment of the present invention has a simple process, low cost, energy saving and environmentally friendly properties, and is easy for large-scale industrial application, with broad prospects.

[0016] In some embodiments, in step a, the temperature of the LF refining slag is 1200° C. or higher. In some embodiments, in step a, the reducing agent is FeSi powder. In some embodiments, the FeSi powder has a Si content of 72 wt% to 78 wt%. In some embodiments, in step a, the amount of the FeSi powder added is 20 wt%-30 wt% of the LF refining slag. In some embodiments, in step a, the reducing agent is added in portions to the LF smelting slag. In some embodiments, in the step b, the vacuum chamber has a vacuum degree of 5 to 20 Pa. In some embodiments, in step b, the reaction temperature is 1300 to 1500°C. In some embodiments, in step b, the reaction time is 1 to 3 hours. [Brief description of the drawings]

[0017] [Figure 1] 1 is a flow chart of extracting Mg and Al using LF smelting slag in an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Examples of the present invention will be described in detail below, but these examples are merely illustrative for understanding the present invention and are not intended to limit the present invention. a. After the molten steel is poured into the LF refining slag tank, the LF refining slag is poured from the ladle into the slag tank and placed in the vacuum chamber. The LF refining slag is mixed with the reducing agent to obtain the reactive mixed material. b. After evacuation, the reaction mixture material in the slag tank is heated to react, and the gaseous Mg and Al produced are condensed and collected at the cooling end outside the vacuum chamber.

[0019] In the method of extracting Mg and Al using LF refining slag in the embodiment of the present invention, the LF refining slag after casting of molten steel is used as a raw material, so the cost is low, almost zero. In addition, since the LF refining slag has a high residual temperature and contains a lot of sensible heat, the reducing agent is preheated and the MgO, Al in the slag are extracted. 2 O 3It also provides part of the energy required for the reaction of LF-smelting slag. The demand for the reduction reaction can be met by supplementing a portion of the heat, so that the heat can be fully utilized and a large amount of energy can be saved; In the method of the embodiment of the present invention, Mg and Al are extracted using LF-smelting slag after molten steel casting as a raw material. LF-smelting slag is an industrial solid waste, and by using it as a substitute for the industrial raw materials dolomite, magnesite and aluminum ore, waste utilization is realized and non-renewable ore resources are saved; The method of the embodiment of the present invention can effectively solve the problem of recycling and reuse of LF-smelting steel slag, and can avoid the shortcomings of traditional Mg and Al production technology while realizing green processing, and the recovered Mg and Al can be reused in steel production, which can obtain higher economic benefits and provide a new direction for the large-scale use of LF-smelting steel slag; The method of the embodiment of the present invention has a simple process, low cost, energy-saving and environmentally friendly, and is easy for large-scale industrial application, and has a broad prospect.

[0020] In some embodiments, in step a, the temperature of the LF refining slag is 1200° C. or higher. In the method of the embodiment of the present invention, the LF refining slag after pouring into the molten steel mostly reaches a temperature of 1200° C. or higher, and the residual heat of the LF refining slag, including a large amount of sensible heat, can be used to preheat the reducing agent, and MgO, Al 2 O 3 It can also provide most of the energy required for the reaction, so that the heat content of the LF refining slag can be fully utilized, saving a large amount of energy, and is energy-saving and environmentally friendly.

[0021] In some embodiments, in step a, the reducing agent is FeSi powder. Preferably, the Si content in the FeSi powder is 72wt%-78wt%. More preferably, the amount of the FeSi powder added is 20wt%-30wt% of the LF refining slag. Preferably, the reducing agent is added to the LF refining slag in portions. In the method of the embodiments of the present invention, the amount of the reducing agent added can be optimized to further improve the heat utilization rate of the LF refining slag and increase the extraction recovery rate of Mg and Al.

[0022] In some embodiments, in the step b, the vacuum degree of the vacuum chamber is 5-20 Pa, the reaction temperature is 1300-1500°C, and the reaction time is 1-3 hours. In the method of the embodiment of the present invention, the LF refining slag and the reducing agent are reacted in a vacuum environment, so that the residual heat of the LF refining slag can be fully utilized, and all the energy required for the reduction reaction can be achieved by simply replenishing a portion of the heat, and Mg and Al can be extracted using the LF refining slag as a raw material. EXAMPLES

[0023] The present invention will be described in detail below with reference to examples. In a 260t LF at a certain steelmaking plant, the amount of LF refining slag was 3t / furnace, and the temperature of the LF refining slag in the ladle returned after molten steel pouring was 1200-1250℃.

[0024] Example 1 (1) Reducing agent blending: FeSi powder with a Si content of 75 wt% was prepared, and the amount of FeSi powder added was set to 600 kg so that the amount was 20 wt% of the LF refining slag amount. (2) After the molten steel was poured into the LF refining slag, the slag was poured from the ladle into the slag tank and transported to the vacuum chamber. The slag tank was used as a reaction vessel, and the prepared FeSi powder was added in portions to the LF refining slag at a temperature of 1220°C, and then mixed uniformly. (3) The system was evacuated to a vacuum level of 19 Pa (meaning absolute pressure), and the reaction materials in the slag tank were heated to 1500°C in the vacuum chamber and kept at that temperature for 1 hour. The gaseous Mg and Al produced by the reaction were condensed by the suction force of the vacuum system at the cooling end outside the vacuum chamber and were recovered as solid Mg and Al.

[0025] The main components of the LF refining slag before and after the reaction in this example are shown in Table 1. From Table 1, it can be seen that Mg and Al in the LF refining slag were effectively extracted and recovered after the reaction, and the content of MgO was as low as 2.3%, and Al was 0.01%. 2 O 3 It can be seen that the content has decreased to 6.2%.

[0026] [Table 1] Calculations showed that in the method of this example, the recovery rate of Mg was 73% and the recovery rate of Al was 76%.

[0027] Example 2 (1) Reducing agent blending: FeSi powder with a Si content of 78 wt% was prepared, and the amount of FeSi powder added was set at 750 kg so that the amount was 25 wt% of the LF refining slag amount. (2) After the molten steel was poured into the LF slag tank, the LF slag was poured from the ladle into the slag tank and transported to the vacuum chamber. The slag tank was used as a reaction vessel, and the prepared FeSi powder was added in portions to the LF slag at 1210°C, and then mixed uniformly. (3) The system was evacuated to a vacuum level of 15 Pa, and the reaction materials in the slag tank were heated to 1400°C in the vacuum chamber and kept at that temperature for 2 hours. The gaseous magnesium and aluminum produced by the reaction were condensed by the suction force of the vacuum system at the cooling end outside the vacuum chamber and were recovered as solid Mg and Al, respectively.

[0028] The main components of the LF refining slag before and after the reaction in this example are shown in Table 2. From Table 2, it can be seen that Mg and Al in the LF refining slag were effectively extracted and recovered after the reaction, and the content of MgO was as low as 2%, and Al was 0.01%.2 O 3 It can be seen that the content has decreased to 8%.

[0029] [Table 2] Calculations showed that in the method of this example, the recovery rate of Mg was 68% and the recovery rate of Al was 69%.

[0030] Example 3 (1) Reducing agent blending: FeSi powder with a Si content of 72 wt% was prepared, and the amount of FeSi powder added was set to 900 kg so that the amount was 30 wt% of the LF refining slag amount. (2) After the molten steel was poured into the LF slag tank, the LF slag was poured from the ladle into the slag tank and transported to the vacuum chamber. The slag tank was used as a reaction vessel, and the prepared FeSi powder was added in portions to the LF slag at 1210°C, and then mixed uniformly. (3) The system was evacuated to a vacuum level of 6 Pa, and the reaction materials in the slag tank were heated to 1301°C in the vacuum chamber and kept at that temperature for 3 hours. The gaseous magnesium and aluminum produced by the reaction were condensed by the suction force of the vacuum system at the cooling end outside the vacuum chamber and were recovered as solid Mg and Al, respectively.

[0031] The main components of the LF refining slag before and after the reaction in this example are shown in Table 3. From Table 3, it can be seen that Mg and Al in the LF refining slag were effectively extracted and recovered after the reaction, and the content of MgO was as low as 1.5%, and Al was 0.01%. 2 O 3 It can be seen that the content has decreased to 7%.

[0032] [Table 3] Calculations showed that in the method of this example, the recovery rate of Mg was 78% and the recovery rate of Al was 73%.

[0033] Comparative Example 1 (1) Reducing agent blending: FeSi powder with a Si content of 75 wt% was prepared, and the amount of FeSi powder added was set to 150 kg so that the amount was 5 wt% of the LF refining slag amount. (2) After the molten steel was poured into the LF slag tank, the LF slag was poured from the ladle into the slag tank and transported to the vacuum chamber. The slag tank was used as a reaction vessel, and the prepared FeSi powder was added in portions to the LF slag at 1210°C, and then mixed uniformly. (3) The system was evacuated until the degree of vacuum reached 19 Pa, and the reaction materials in the slag tank were heated to 1500°C in the vacuum chamber and kept at that temperature for 1 hour. The gaseous magnesium and aluminum produced by the reaction were condensed at the cooling end outside the vacuum chamber by the suction force of the vacuum system and were recovered as solid Mg and Al, respectively.

[0034] The main components of the LF refining slag before and after the reaction in this example are shown in Table 4. From Table 4, it can be seen that Mg and Al in the LF refining slag were effectively extracted and recovered after the reaction, and the content of MgO was as low as 6.7%, and Al was 0.01%. 2 O 3 It can be seen that the content has decreased to 21%.

[0035] [Table 4] Calculations showed that in the method of Comparative Example 1, the recovery rate of Mg was 25%, and the recovery rate of Al was 23%.

[0036] Comparative Example 2 The same method as in Example 3 was used, except that the amount of FeSi powder with a Si content of 78 wt% was added as a reducing agent to be 1050 kg so as to be 35 wt% of the LF refining slag amount. The main components of the LF refining slag before and after reaction are shown in Table 5.

[0037] [Table 5] Calculations showed that in the method of Comparative Example 2, the recovery rate of Mg was 65%, and the recovery rate of Al was 62%.

[0038] In the present invention, the terms "one embodiment", "several embodiments", "examples", "specific examples" or "several examples" mean that the specific features, structures, materials or properties described in the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the meanings of the above terms do not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or properties described may be combined as appropriate in any one or more embodiments or examples. Furthermore, a person skilled in the art may combine different embodiments or examples described in this specification and different features in the embodiments or examples, as long as they are not mutually inconsistent.

[0039] Although the embodiments of the present invention have been shown and described above, it should be understood that the above embodiments are illustrative and do not limit the present invention. Those skilled in the art may change, modify, replace, or change the above embodiments within the scope of the present invention.

Claims

1. A method for extracting Mg and Al using LF smelting slag, comprising the steps of: a) pouring the LF refining slag after casting molten steel from the ladle into a slag tank, placing it in a vacuum chamber, adding a reducing agent to the LF refining slag and mixing it to obtain a mixed reaction raw material; b) After evacuation, the mixed reaction raw materials in the slag tank are heated to react with each other, and the gaseous Mg and Al produced are condensed and collected at the cooling end outside the vacuum chamber.

2. The method for extracting Mg and Al using LF refining slag according to claim 1, characterized in that in step a, the temperature of the LF refining slag is 1200°C or higher.

3. The method for extracting Mg and Al using LF refining slag according to claim 1, characterized in that in step a, the reducing agent is FeSi powder.

4. The method for extracting Mg and Al using LF refining slag according to claim 3, characterized in that the Si content in the FeSi powder is 72 wt% to 78 wt%.

5. The method for extracting Mg and Al using LF refining slag according to claim 3 or 4, characterized in that in step a, the amount of the FeSi powder added is 20 wt % to 30 wt % of the LF refining slag.

6. The method for extracting Mg and Al using LF smelting slag according to claim 1, characterized in that in step a, the reducing agent is added to the LF smelting slag in portions.

7. The method for extracting Mg and Al using LF refining slag according to claim 1, characterized in that in step b, the vacuum degree of the vacuum chamber is 5 to 20 Pa.

8. The method for extracting Mg and Al using LF refining slag according to claim 1, characterized in that in step b, the reaction temperature is 1300-1500°C.

9. The method for extracting Mg and Al using LF refining slag according to claim 1 or 8, characterized in that in step b, the reaction time is 1 to 3 hours.

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