A method of pelletizing for catalytic carbon reduction of magnesium

Abstract

A ball making method for catalytic carbon reduction of magnesium smelting, comprising the following steps: 1) raw material preparation, raw material, comprising: calcined lime, carbonaceous reducing agent and carbonaceous catalyst, fineness of 50-300 mesh, total fineness of powder not more than 300 mesh; 2) pitch preheating, negative pressure preheating treatment is carried out on pitch powder, preheating temperature is not more than its softening point, absolute pressure is 10-100 Pa, preheating time is 2-5 hours; 3) mixing, adding the pitch powder after negative pressure preheating treatment into the raw material, the overall fineness after mixing is not more than 300 mesh, the mass ratio of pitch powder in raw material is 3-15%, and stirring and mixing are carried out; 4) ball pressing, adding the mixed powder into a ball press, ball forming pressure is 100-200 MPa, and molding is carried out. The present application solves the environmental and equipment pollution problems caused by pitch smoke in the prior art; no water is added in the ball making process, and no other impurities are introduced, and the bonding process does not need heating.

Description

Technical Field

[0001] This invention relates to primary magnesium smelting technology, specifically to a pelletizing method for catalytic carbon reduction magnesium smelting. Background Technology

[0002] Currently, my country's primary magnesium smelting is mainly based on the Pidgeon process, which accounts for more than 90% of the country's primary magnesium production and more than 85% of the world's primary magnesium production.

[0003] Existing primary magnesium smelting methods include the Pidgeon process, carbothermal magnesium smelting technology, and catalytic carbothermal process. my country's primary magnesium smelting mainly uses the Pidgeon process; however, the Pidgeon process has high energy consumption and large CO2 emissions.

[0004] Compared to the Pidgeon process, the carbothermic magnesium smelting method can significantly reduce energy consumption and generate waste residue pollutants. However, due to the reverse reaction between magnesium vapor and CO and the safety issues of the mixed gas, there are currently no industrial-scale production facilities operating in the carbothermic magnesium smelting method.

[0005] Regardless of whether it is the traditional Pidgeon process, carbothermal magnesium smelting technology, or catalytic carbothermal magnesium smelting technology, all three are solid-phase reactions. That is, the raw materials for smelting need to be ground into powder with a sufficiently fine particle size, mixed according to the process ratio requirements, and then prepared (pressed) into pellets of a certain strength and shape to increase the contact between materials and promote the reaction.

[0006] The differences in the pelletizing process of the three smelting schemes are as follows:

[0007] The Pidgeon process for magnesium production primarily uses calcined dolomite (hereinafter referred to as "calcined dolomite") and ferrosilicon as raw materials. The technology for briquetting calcined dolomite and ferrosilicon is relatively mature, and there are already mature briquetting equipment available on the market. Because calcined dolomite and ferrosilicon have a good bonding degree, no external binder is required; the powdered materials can be bound together solely through mechanical action.

[0008] The carbothermic process for magnesium smelting primarily uses calcined magnesite and coke as raw materials, and its reaction equation is MgO. (s) +C (s) →Mg (g) +CO (g) Unlike the Pidgeon process, the reducing agent in carbon reduction is coke, not 75# ferrosilicon. Coke has a larger specific surface area, lower density, and much greater fluidity than ferrosilicon. It is precisely because of its greater fluidity that pressing coke together with calcined magnesite presents certain challenges.

[0009] Catalytic carbon reduction for magnesium smelting is a novel magnesium smelting technology. Its reaction equation is as follows:

[0010]

[0011] As can be seen from the reaction equation, in addition to calcined white metal and coke, a carbonaceous catalyst was added to the main components of the reaction raw materials, further reducing the intercalation effect of the calcined white metal. Experiments confirmed that after mixing these three substances, the angle of repose formed by natural accumulation is less than 40 degrees, indicating high fluidity, making it impossible to bind them together through mechanical action alone. Therefore, in the catalytic carbon reduction magnesium smelting process, the inability to directly press the raw materials into pellets is the first major challenge faced by this method.

[0012] In the industrial sector, binders are generally classified into two main categories: inorganic binders and organic binders. Common inorganic binders include sodium silicate, potassium silicate, bentonite, fluorite powder, montmorillonite, clay, sodium carbonate, sodium hydroxide, cement, and silica fume. Commonly used organic binders include wheat flour, cassava flour, molasses waste liquor, tar, pulp, and polyvinyl alcohol.

[0013] In the metallurgical industry, inorganic binders contain metallic impurities that can contaminate smelting products or adversely affect the metal smelting process. Organic binders, on the other hand, present the following three problems:

[0014] ① For example, natural binders such as wheat flour and cassava flour have high hydrogen and oxygen content. At high temperatures, they will undergo condensation reactions to generate water vapor, which will not only react with carbonaceous reducing agents and catalysts to generate CO and H2 gases, consuming a large amount of reducing agents, but also react with the generated metallic Mg vapor to generate MgO, which will seriously reduce the efficiency of catalytic carbon reduction in magnesium smelting.

[0015] ②Most organic binders undergo condensation reactions at high temperatures, and the generated gas escapes, which increases the distance between solid particles, making it difficult for carbonaceous reducing agents to diffuse into the calcined white material for chemical reactions.

[0016] ③ Organic binders such as asphalt tar also have the problem of volatile pollution. For example, the softening point of ultra-high temperature asphalt can reach 150℃, but under high temperature (160-180℃) conditions, its saturated and aromatic components will sublimate first to form asphalt fumes. In the presence of oxygen, the output of asphalt fumes will increase by 9 times, polluting the exhaust pipes and forming oil stains or clogging the exhaust ports.

[0017] In addition, when the pellets for the catalytic carbon reduction magnesium smelting process are put into the tank, the tank wall temperature is around 1000℃. Ordinary binders cannot withstand this temperature, and the pellets will break or pulverize during the throwing process, such as starch-based binders.

[0018] Chinese patent CN114737055A discloses "High-purity composite binder for metallurgical pellets and its application method" and Chinese patent CN103484665A discloses "Method for producing metallurgical composite pellets using different binders and two-stage pelletizing methods". Although the binders described have good bonding performance and high-temperature stability, they contain a certain amount of silicon. Silicon oxides will react with the main raw materials in the catalytic carbothermic magnesium smelting process, calcined white powder, carbonaceous reducing agent, and carbonaceous catalyst, generating SiO2 gas pollution products and increasing energy consumption. In addition, this method requires the addition of a certain amount of water during use. The main raw material in the catalytic carbothermic magnesium smelting process, calcined white powder, readily reacts with water to generate Ca(OH)2 and Mg(OH)2. Under smelting conditions, it will decompose into water vapor, which will not only react with carbonaceous reducing agent and catalyst to generate CO and H2 gas, consuming a large amount of reducing agent, but also react with the generated metallic Mg vapor to generate MgO, seriously reducing the efficiency of catalytic carbothermic magnesium smelting. Therefore, this method cannot be applied to the catalytic carbothermic magnesium smelting pelletizing process.

[0019] Chinese patent CN201210265655.2 discloses "A method for pressing and sintering high-purity silicon dioxide," which proposes a method for forming blanks by bonding SiO2 powder with coal tar pitch. This method can effectively agglomerate powdered SiO2 and achieve a certain strength. However, this method cannot avoid the pollution from pitch fumes generated during subsequent smelting processes, and it requires the addition of water during blank formation, which reacts with the raw materials. Therefore, this method cannot be applied to the granulation process of catalytic carbothermic magnesium smelting.

[0020] Chinese patent CN201310408006.8 discloses "A composite binder for hot-pressed iron coke and its preparation method," which proposes a method for preparing a binder with asphalt as the main component. Although the binder prepared by this method has good bonding performance, its manufacturing process is complex. During the manufacturing process, the asphalt softens, and it is impossible to maintain the powder state. After the reaction, the material needs to be cooled before being crushed separately to obtain a powdered binder. Furthermore, under the reaction conditions of this method, it is difficult to remove volatiles from the asphalt, making it impossible to avoid asphalt fume pollution during subsequent smelting. The iron-containing raw materials added to this binder are red mud and oily sludge, which are iron oxides. They play a dispersing role in the binder, and their high content can supplement the smelting raw materials and increase iron production during iron smelting. However, for the catalytic carbon reduction smelting process, the presence of a large amount of iron oxides will seriously reduce the reduction efficiency of metallic magnesium. In addition, the binder prepared by this method can only be used in the hot pressing balling process and cannot achieve a bonding effect at room temperature, increasing the manufacturing difficulty. In summary, this method cannot be applied to the catalytic carbothermic magnesium smelting pelletizing process.

[0021] In summary, most existing metallurgical binders and pelletizing methods suffer from problems such as metal contamination, generation of flue gas contaminants, reduced smelting efficiency, and the need to add water during the manufacturing process (consuming reducing agent and reducing reduction rate). They cannot be applied to the pelletizing process of the catalytic carbothermic magnesium smelting method. Furthermore, no detailed research results or patents have been found that solve the pelletizing problems of the catalytic carbon reduction method. Summary of the Invention

[0022] The purpose of this invention is to propose a pelletizing method for catalytic carbon reduction magnesium smelting, which solves the environmental and equipment pollution problems caused by asphalt fumes in the prior art; moreover, no water needs to be added during the pelletizing process, and no other impurities are introduced, and the bonding process does not require heating; at the same time, the pellets can be bonded at room temperature without reducing the reduction efficiency of the catalytic carbon reduction magnesium smelting process; in addition, the obtained pellets can also supplement the carbonaceous reducing agent in the catalytic carbon reduction magnesium smelting process.

[0023] To achieve the above objectives, the technical solution of the present invention is as follows:

[0024] A method for making pellets for catalytic carbon reduction of magnesium includes the following steps:

[0025] 1) Raw material preparation

[0026] Raw materials include: calcined white powder with a fineness of 50-300 mesh, carbonaceous reducing agent and carbonaceous catalyst, both with a fineness of 100-300 mesh; the overall fineness of the powder does not exceed 300 mesh.

[0027] 2) Asphalt preheating

[0028] The asphalt powder is subjected to negative pressure preheating treatment. The preheating temperature does not exceed its softening point (150℃), the absolute pressure is 10~100Pa, and the preheating time is 2~5 hours.

[0029] 3) Mixing

[0030] Add the asphalt powder that has undergone negative pressure preheating to the raw meal obtained in step 1), and after mixing, the overall fineness should not exceed 300 mesh. The asphalt powder accounts for 3 to 15% of the raw meal mass. Stir and mix.

[0031] 4) Pressing the ball

[0032] The mixed powder is added to a briquetting machine, and the briquetting pressure is 100-200 MPa to form the briquetting material.

[0033] Preferably, the fixed carbon content in the asphalt powder is 55-65%, and the softening point is not lower than 150°C.

[0034] Preferably, in step 2), argon gas or gas N2 is introduced.

[0035] Preferably, in step 3), the calcined white content in the raw material is 40-60% by mass.

[0036] Preferably, in step 3), 0.2-1% of β-resin is added, with a fineness not exceeding 150 mesh; preferably, the H:C molar ratio in the β-resin is less than 0.45.

[0037] Preferably, the carbonaceous reducing agent is graphite, coke, semi-coke, coal, or a mixture of any two or more of the foregoing.

[0038] Preferably, the carbonaceous catalyst is a metal carbide, such as calcium carbide.

[0039] In the pelletizing method for catalytic carbon reduction magnesium smelting described in this invention:

[0040] 1) Raw material preparation: Calcinated white powder is ground to a fineness of 50–300 mesh, and carbonaceous reducing agent and carbonaceous catalyst are ground to a fineness of 100–300 mesh. The overall fineness of the powder should not exceed 300 mesh. The combined effects of mass transfer diffusion and interfacial diffusion on the reduction reaction mean that both excessively fine and excessively fine raw materials will lead to a decrease in reduction conversion rate. When the raw material is too coarse, the distance between solid particles is too large, which is not conducive to the diffusion of the carbonaceous reducing agent into the calcined white powder for chemical reaction, and easily results in unreacted "nuclei" left due to incomplete reaction. When the raw material fineness is too small, the pellet density is large, and the distance between solid particles is too small, which is not conducive to the diffusion of magnesium vapor generated in the reaction out of the pellets, but is conducive to the diffusion of the carbonaceous reducing agent into the calcined white powder for chemical reaction.

[0041] 2) Asphalt preheating: Asphalt powder is preheated under negative pressure at a temperature not exceeding its softening point (150℃) and an absolute pressure of 10–100 Pa (negative pressure). This lowers the sublimation point of asphalt fumes (saturated and aromatic components) without softening the asphalt (maintaining its powdery state), while simultaneously reducing the oxygen content in the reaction environment, thus reducing asphalt fumes production. Preheating time is 2–5 hours. Preheating the asphalt powder removes saturated and aromatic components (asphalt fumes) in advance, reducing the production of asphalt fumes during the smelting process and minimizing pollution. Since the saturated and aromatic components in asphalt are oil components, they primarily provide fluidity rather than viscosity (adhesion is provided by resins, which are β-resins, also hydrocarbon organic compounds; these resins can be added to improve overall viscosity and carbon content). Therefore, the negative pressure preheating process has no adverse effect on the bonding effect of the aggregate. Furthermore, the carbon content of asphalt powder treated with negative pressure preheating can increase by 3–10%, the softening point by 15–20%, and the adhesion will also be improved.

[0042] 3) Mixing: Add the preheated asphalt powder to the raw meal obtained in step 1). The overall fineness of the mixture should not exceed 300 mesh. The preheated asphalt powder accounts for 3-15% of the raw meal mass. Stir and mix. The asphalt powder has good adsorption and adhesion properties, which can effectively agglomerate the raw meal together during the briquetting process.

[0043] 4) Briquetting: The mixed powder is added to a briquetting machine (at room temperature) at a briquetting pressure of 100-200 MPa and briquetting is performed, achieving a briquetting rate of up to 90%. Too low or too high a briquetting pressure will lead to a decrease in the reduction conversion rate. If the briquetting pressure is too low, the distance between solid particles is too large, which is not conducive to the diffusion of carbonaceous reducing agent atoms into the calcined white metal for chemical reaction, but it is conducive to the diffusion of magnesium vapor generated in the reaction and its overflow from the briquetting pellet. If the briquetting pressure is too high, the distance between solid particles is too small, which is not conducive to the diffusion of magnesium vapor generated in the reaction and its overflow from the briquetting pellet, but it is conducive to the diffusion of carbonaceous reducing agent atoms into the calcined white metal for chemical reaction. Therefore, this invention controls the briquetting pressure at 100-200 MPa, which yields the best effect for the magnesium smelting reduction reaction.

[0044] Preferably, the fixed carbon content in the asphalt powder is 55-65%, and the softening point is not lower than 150℃. A high fixed carbon content results in a large carbon-to-hydrogen ratio, leading to minimal water vapor generation during the smelting process due to pyrolysis, thus having no adverse impact on the smelting process.

[0045] In step 2), the introduction of protective gases such as argon and nitrogen can reduce the oxygen content in the reaction environment, thereby reducing the production of asphalt fumes.

[0046] In step 3), 0.2-1% of β-resin is added, with a fineness not exceeding 150 mesh, and the H:C molar ratio in the β-resin is less than 0.45. β-resin can improve the overall adhesion and carbon content, reduce the proportion of saturated and aromatic components, thereby increasing the strength of the pellets, reducing pollution, and providing more carbon elements for subsequent smelting and reduction reactions.

[0047] Compared with the prior art, the advantages of the present invention are as follows:

[0048] 1) Existing briquetting machines and methods cannot compress raw materials with fine particle size and good flowability;

[0049] 2) Existing organic binders have high hydrogen and oxygen content and a large hydrogen-carbon molar ratio, which will cause adverse side reactions under high-temperature smelting conditions.

[0050] 3) Most existing pelletizing methods that add organic binders (such as asphalt and coal tar) require hot pressing to pelletize, and cannot achieve pelletizing at room temperature;

[0051] 4) Existing inorganic binders contain some metallic impurities, which may react with magnesium smelting raw materials, thus reducing the yield and quality of metallic magnesium.

[0052] 5) Existing composite binders have relatively complex compositions and manufacturing processes, and there is a possibility of interaction with magnesium smelting raw materials, which will reduce the yield and quality of metallic magnesium. At the same time, due to the complexity of the manufacturing process, the production cost is also higher and the production cycle is longer.

[0053] 6) Most existing pelletizing methods require the addition of water for mixing. However, the main raw material in the catalytic carbothermic magnesium smelting process, calcined white metal, readily reacts with water to generate Ca(OH)2 and Mg(OH)2. Under smelting conditions, it decomposes to release water vapor, which not only reacts with carbonaceous reducing agents and catalysts to generate CO and H2 gases, consuming a large amount of reducing agent, but also reacts with the generated metallic Mg vapor to generate MgO, severely reducing the efficiency of catalytic carbothermic magnesium smelting. Therefore, it cannot be applied to the pelletizing process of the catalytic carbothermic magnesium smelting process.

[0054] In view of the above-mentioned deficiencies in the prior art, this invention proposes a method for adding asphalt powder that has undergone negative pressure preheating treatment. By adding the asphalt powder that has undergone negative pressure preheating treatment, the reactants are bound together to achieve the purpose of preparing pellets. Its advantages are:

[0055] 1. The beneficial effects of adding asphalt powder that has undergone negative pressure preheating treatment in this invention are:

[0056] ① Asphalt mainly consists of four components: saturated components, aromatic components, resins, and asphaltenes. During the heating process, two types of reactions occur: aerobic pyrolysis and pyrolysis of heavier components. Aerobic pyrolysis is further divided into three stages: the decomposition of saturated components, aromatic components, and resins. The activation energy for the decomposition of these three components increases sequentially, as does the reaction temperature. The decomposition and sublimation temperatures of saturated components and aromatic components (asphalt fumes) are less than 200℃. Preheating the asphalt powder under negative pressure can remove the saturated and aromatic components, preventing the generation of asphalt fumes that contaminate pipelines during subsequent smelting processes.

[0057] ②The asphalt powder will not melt during the negative pressure preheating process and will remain in powder form;

[0058] ③ Asphalt powder and β-resin decompose at 400–500℃ (the catalytic carbothermic magnesium smelting temperature is 1200–1700℃, much higher than its decomposition temperature). After decomposition, dehydrogenation polymerization can occur, generating more stable macromolecular substances, which supplement the carbonaceous reducing agent in the smelting process. The substances produced by decomposition are methane, aldehydes, hydrocarbons, esters, and ethers, which will not adversely affect the magnesium smelting products or their quality.

[0059] ④ Under the high-temperature conditions of catalytic carbothermic magnesium smelting, asphalt powder and β-resin will undergo heavy component condensation (500-700℃). This stage will cause the carbon polymer remaining from the previous reaction to further condense and carbonize, forming semi-coke. At this time, asphalt and β-resin will be converted into carbon elements that can be used in the catalytic carbon reduction magnesium smelting process to participate in the magnesium smelting process.

[0060] 2. In the pelletizing process of this invention, the pelletizing pressure is 100-200 MPa, which can ensure that the pellet density is 1.8-2.5 t / m³. 3 Within this density range, the magnesium smelting conversion rate is better. According to the experiment, when the pelletizing pressure is below 100MPa, the reduction rate of metallic magnesium is the highest at 87%, when the pelletizing pressure is above 200MPa, the reduction rate of metallic magnesium is the highest at 83%, and when the pelletizing pressure is between 100 and 200MPa, the reduction rate of metallic magnesium can reach more than 95%.

[0061] 3. The briquetting process described in this invention does not require heating the asphalt to soften it; the briquetting effect can be achieved at room temperature.

[0062] 4. The ball-making and adhesive-using processes described in this invention do not require the addition of water. Detailed Implementation

[0063] The present invention will be further described below with reference to the embodiments.

[0064] The parameters for the embodiments of the present invention are shown in Table 1.

[0065] The preparation process of this invention is as follows:

[0066] 1) Raw material preparation

[0067] Raw materials include: calcined white powder with a fineness of 50-300 mesh, coke and calcium carbide with a fineness of 100-300 mesh; the overall fineness of powders shall not exceed 300 mesh.

[0068] 2) Asphalt preheating

[0069] The asphalt powder is subjected to negative pressure preheating treatment. The preheating temperature does not exceed its softening point (150℃), the absolute pressure is 10~100Pa, and the preheating time is 2~5 hours.

[0070] 3) Mixing

[0071] Add the asphalt powder that has undergone negative pressure preheating to the raw meal obtained in step 1), and after mixing, the overall fineness should not exceed 300 mesh. The asphalt powder accounts for 3 to 15% of the raw meal mass. Stir and mix.

[0072] 4) Pressing the ball

[0073] The mixed powder is added to a briquetting machine, and the briquetting pressure is 100-200 MPa to form the briquetting material.

[0074] Table 1

[0075]

Claims

1. A method for making pellets for catalytic carbon reduction of magnesium, characterized in that, Includes the following steps: 1) Raw material preparation Raw materials, including: calcined white powder with a fineness of 50-300 mesh; carbonaceous reducing agent and carbonaceous catalyst, both with a fineness of 100-300 mesh; the total fineness of the raw materials does not exceed 300 mesh; 2) Asphalt preheating The asphalt powder is subjected to negative pressure preheating treatment. The preheating temperature does not exceed its softening point, the absolute pressure is 10-100 Pa, and the preheating time is 2-5 hours. 3) Mixing Add the asphalt powder that has undergone negative pressure preheating to the raw meal obtained in step 1), and after mixing, the overall fineness should not exceed 300 mesh. The asphalt powder accounts for 3 to 15% of the raw meal mass. Stir and mix. 4) Pressing the ball The mixed powder is added to a briquetting machine, and the briquetting pressure is 100-200 MPa to form the briquetting material.

2. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 1, characterized in that, The fixed carbon content in the asphalt powder is 55-65%, and the softening point is not lower than 150℃.

3. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 1, characterized in that, In step 2), argon or nitrogen gas is introduced.

4. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 1, characterized in that, In step 3), add 0.2-1% of β-resin, with a fineness not exceeding 150 mesh.

5. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 4, characterized in that, The H:C molar ratio in the β-resin is less than 0.

45.

6. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 1, characterized in that, In step 1), the calcined white content in the raw material is 40-60% by mass.

7. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 1, characterized in that, The carbonaceous reducing agent is graphite, coke, semi-coke, coal, or a mixture of any two or more of the aforementioned.

8. The pelletizing method for catalytic carbon reduction magnesium smelting as described in claim 1, characterized in that, The carbonaceous catalyst is a metal carbide.

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