A method for vacuum rapid carbothermal reduction of metallic magnesium

Abstract

The application provides a method for vacuum rapid carbothermic reduction of magnesium metal, belonging to the technical field of non-ferrous metal magnesium metallurgy, and comprises the following steps: taking carbonaceous material as a reducing agent and taking oxide containing magnesium oxide as smelting raw material, sequentially performing batching, mixing and ball milling treatment, and then preparing a powdery reducing material with a particle size of not more than 100 µm; placing the powdery reducing material in a conductive mold, and then integrally feeding the powdery reducing material into a vacuum reduction furnace; after the vacuum reduction furnace is closed, starting a vacuum system, controlling the vacuum degree in the furnace to be 10-300 Pa, controlling the reduction temperature of the powdery reducing material to be 1100-1400 ℃, and synchronously applying an electric current density of 2-40 A / cm 2 The direct current or alternating current and the axial mechanical pressure of 5-50 MPa rely on the multi-field deep coupling to induce the traditional slow-speed thermal diffusion carbothermic reduction reaction to be converted into a self-sustaining self-propagating chain reduction reaction; the sample temperature and the overflow magnesium vapor flow are monitored in real time, the real-time data obtained through the monitoring are used to dynamically adjust the power supply current parameters and the mechanical applied pressure.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous magnesium metallurgy technology, specifically relating to a method for rapid vacuum carbothermic reduction of metallic magnesium. Background Technology

[0002] Magnesium, as the lightest structural metal, has wide applications in aerospace, automotive manufacturing, and electronics due to its excellent properties. Among various magnesium smelting processes, the vacuum carbothermal reduction method is considered a key development direction for the industry due to its significant advantages such as wide availability of raw materials, low smelting costs, and low carbon footprint. However, the traditional vacuum carbothermal reduction process has inherent technical bottlenecks that severely restrict its industrial application: First, the reaction kinetics are slow, resulting in low production efficiency: This process relies on an external heat source to drive the solid-phase reaction through thermal diffusion, leading to a single batch reduction cycle of several hours, high energy consumption, and low production capacity. Second, the reduction is incomplete, resulting in low resource utilization: During the reaction, the material easily becomes porous, leading to deterioration of heat and mass transfer, insufficient reduction of magnesium oxide, and high residual magnesium content in the smelting residue. Third, the process is unstable, posing safety hazards: The large amount of magnesium vapor and carbon monoxide gas generated during the reaction can easily cause "spraying," which not only contaminates the product and clogs pipelines but also poses serious safety risks.

[0003] To address these issues, some improvements have been attempted in existing technologies. For example, some studies have introduced electric field-assisted heating to improve the thermal efficiency of the reaction system; others have used mechanical pressure to pre-form the raw materials to improve the contact conditions between particles.

[0004] However, the aforementioned technologies are all improvements or simple combinations of single factors, failing to achieve deep synergistic coupling of multiple physical fields, and therefore cannot fundamentally overcome the limitations of traditional processes. They can only slightly shorten the reaction time or only slightly improve the reduction rate, and cannot simultaneously achieve the comprehensive effects of second-level rapid reduction, ultra-high reduction rate, and stable process without material spraying. Those skilled in the art generally believe that carbothermic reduction of metallic magnesium requires prolonged, continuous high-temperature external heating; the instantaneous self-propagating reaction cannot achieve deep reduction. Furthermore, the synergistic effect of the electric field and high-pressure mechanical pressure will disrupt the stability of the reaction system, making it unsuitable for magnesium smelting conditions.

[0005] Therefore, there is an urgent need to develop a new magnesium smelting process that can overcome the above-mentioned technical bottlenecks and achieve rapid, efficient, and safe reduction of metallic magnesium. Summary of the Invention

[0006] Based on the above-mentioned technical problems, the purpose of this invention is to provide a method for rapid vacuum carbothermic reduction of metallic magnesium, which can simultaneously achieve rapid reduction, ensure a high reduction rate, and maintain a stable reduction process without material spraying.

[0007] The specific technical solution is as follows: A method for rapid carbothermic reduction of metallic magnesium in a vacuum includes the following steps: S1: Using carbonaceous materials as reducing agents and magnesium oxide-containing oxides as smelting raw materials, the raw materials are successively processed through batching, mixing and ball milling to obtain powdered reducing raw materials with a particle size of no more than 100µm. S2: Place the powdered reducing material inside the conductive mold and send it into the vacuum reduction furnace as a whole; S3: After sealing the vacuum reduction furnace, start the vacuum system and control the vacuum level inside the furnace to 10~300Pa. Control the reduction temperature of the powdered reducing material to 1100~1400℃, and simultaneously apply a current density of 2~40A / cm to the powdered reducing material. 2 Direct current or alternating current, along with axial mechanical pressure of 5~50MPa, induces the traditional slow thermal diffusion carbothermic reduction reaction to transform into a self-sustaining self-propagating chain reduction reaction through deep multi-field coupling. S4: The sample temperature and the flow rate of overflowing magnesium vapor are monitored in real time throughout the reduction process. Based on the real-time data obtained from the monitoring, the power supply current parameters and the mechanical pressure are dynamically adjusted to maintain the stable and continuous self-propagating chain reduction reaction. S5: The magnesium vapor generated by the reaction enters the condensation zone to cool and crystallize, obtaining metallic magnesium. After the reaction is completed, the vacuum in the furnace is broken to complete the single reduction operation.

[0008] In addition, the method for rapid carbothermic reduction of metallic magnesium in vacuum provided by the present invention may also have the following additional technical features: In the above technical solution, the carbonaceous material is one or more of graphite, semi-coke, coke, and anthracite; the oxide containing magnesium oxide is any one of light-burned magnesium oxide, calcined dolomite powder, calcined magnesia powder, and waste magnesium brick powder.

[0009] In the above technical solution, during the batching step, the carbonaceous material is proportioned in excess of 5% to 20% magnesium oxide stoichiometric ratio.

[0010] In the above technical solution, the self-propagating chain reduction reaction time is controlled at 30~120 seconds.

[0011] In the above technical solution, the direction of DC or AC power supply is consistent with the direction of application of the axial mechanical pressure.

[0012] The above technical solution also includes a security system, which includes: Raw material pretreatment safety: Mixing, ball milling, and placing the powdered raw materials into the conductive mold are all carried out under an inert atmosphere to avoid oxidation and spontaneous combustion of the powder at room temperature; Gas phase control: Carbon monoxide gas generated by the self-propagating chain reduction reaction is collected in a unified manner through a closed pipeline and treated for harmlessness or recycled; the furnace body is maintained in a slightly negative pressure state to prevent the leakage of toxic and flammable gases. Magnesium vapor condensation explosion-proof: The condensation zone adopts a gradient temperature control mode, with the temperature of the first-stage condensation zone controlled at 660-700℃, so that magnesium vapor is preferentially liquefied into liquid magnesium, reducing the generation of ultrafine active magnesium powder; the condensation system is equipped with an argon inert gas device and an explosion relief device to prevent magnesium dust explosion. Interlock protection: The vacuum degree, oxygen content in the furnace, temperature, pressure and current are set with multiple safety interlocks. When vacuum leakage, over-temperature, over-pressure or current abnormality occurs, the power supply and pressure loading are automatically cut off and the emergency protection program is activated. Safety procedures for starting and stopping the machine: Before breaking the vacuum, first fill the furnace with high-purity argon gas for gas replacement, and check that the oxygen content in the furnace is <0.1% before opening the lid.

[0013] The vacuum rapid carbothermic reduction method for metallic magnesium of the present invention has the following advantages compared with the prior art: 1. Through the deep organic coupling of vacuum degree, reduction temperature, AC and DC electric fields, axial mechanical pressure, limited raw material particle size and temperature, and magnesium vapor flow closed-loop control, the traditional thermal diffusion rate-controlled carbothermal reduction reaction that relies on long-term high-temperature external heating is transformed into a self-sustaining self-propagating chain reduction reaction. This shortens the reduction cycle of the traditional process from several hours to 30 to 120 seconds, increasing production efficiency by hundreds of times and making it suitable for large-scale continuous industrial production.

[0014] 2. Through the synergistic effect of deep multi-field coupling, the dead zone of heat and mass transfer in the reaction process is eliminated, so that the magnesium oxide reduction conversion rate can stably reach 95% or above.

[0015] 3. By simultaneously applying an axial mechanical pressure of 5 to 50 MPa to the powdered reducing material, the powdered reducing material is kept in a dense state throughout the reaction process, effectively suppressing the spraying problem caused by the loose material and the instantaneous generation of a large amount of magnesium vapor and carbon monoxide.

[0016] 4. By monitoring the sample temperature and the flow rate of overflowing magnesium vapor in real time throughout the reduction process, and dynamically adjusting the power supply current parameters and the mechanical pressure based on the real-time data, a closed-loop control system of "monitoring-feedback-adjustment" is formed, which effectively avoids problems such as local overheating, reaction interruption and incomplete reduction, and ensures the long-term operational stability of the process. Attached Figure Description

[0017] Figure 1 The graph shows the changes in parameters such as temperature, pressure, pressure head displacement, current, and vacuum during the thermal reduction process of this invention.

[0018] Figure 2The image shows the XRD pattern of the carbothermic rapid reduction of magnesium powder according to the present invention.

[0019] Figure 3 This is an energy dispersive spectroscopy (EDS) spectrum of magnesium oxide content in magnesium slag according to the present invention. Detailed Implementation

[0020] The following are specific implementation cases and appendices. Figure 1-3 The present invention will be further described, but the present invention is not limited to these embodiments.

[0021] A method for rapid carbothermic reduction of metallic magnesium in a vacuum includes the following steps: S1: Using carbonaceous materials as reducing agents and magnesium oxide-containing oxides as smelting raw materials, the raw materials are successively processed through batching, mixing and ball milling to obtain powdered reducing raw materials with a particle size of no more than 100µm. S2: Place the powdered reducing material inside the conductive mold and send it into the vacuum reduction furnace as a whole; S3: After sealing the vacuum reduction furnace, start the vacuum system and control the vacuum level inside the furnace to 10~300Pa. Control the reduction temperature of the powdered reducing material to 1100~1400℃, and simultaneously apply a current density of 2~40A / cm to the powdered reducing material. 2 Direct current or alternating current, along with axial mechanical pressure of 5~50MPa, induces the traditional slow thermal diffusion carbothermic reduction reaction to transform into a self-sustaining self-propagating chain reduction reaction through deep multi-field coupling. S4: The sample temperature and the flow rate of overflowing magnesium vapor are monitored in real time throughout the reduction process. Based on the real-time data obtained from the monitoring, the power supply current parameters and the mechanical pressure are dynamically adjusted to maintain the stable and continuous self-propagating chain reduction reaction. S5: The magnesium vapor generated by the reaction enters the condensation zone to cool and crystallize, obtaining metallic magnesium. After the reaction is completed, the vacuum in the furnace is broken to complete the single reduction operation.

[0022] By controlling the vacuum level inside the furnace to 10~300Pa, the saturated partial pressure of magnesium vapor is reduced, providing a thermodynamic basis for the rapid overflow of gaseous magnesium, while isolating air to prevent the oxidation of raw materials.

[0023] In step S1, the prepared raw materials are fed into a mixing device for uniform mixing, and then fed into a ball mill for fine processing to obtain powdered raw materials with a particle size of no more than 100µm.

[0024] In step S2, the powdered reducing material is filled into the high-temperature conductive mold to complete the pre-forming process and meet the requirements of electric field conduction and uniform pressure transmission.

[0025] By controlling the reduction temperature to 1100~1450℃, the optimal reaction window of the multi-field coupling system is matched, which satisfies the basic conditions for reaction start-up and avoids the high energy consumption and equipment damage caused by ultra-high temperature.

[0026] By setting up a DC / AC composite electric field, the raw material lattice is activated in situ through Joule heating, which significantly reduces the activation energy of the reduction reaction and is the core energy source for triggering the self-propagating reaction.

[0027] By setting the mechanical pressure to 5~50MPa, the spacing between powdered raw material particles is reduced, the mass and heat transfer efficiency at the solid-phase interface is enhanced, the reaction is ensured to proceed continuously and stably, the reaction is prevented from being interrupted due to the loosening of materials that is common during the reduction reaction, and the spraying of materials is eliminated.

[0028] By limiting the powder particle size to no more than 100µm, the coupling process of this invention is adapted to balance the three-dimensional channels of electric field conduction, pressure transmission, and magnesium vapor diffusion.

[0029] By controlling the temperature and magnesium vapor flow rate in a closed loop, the entire coupled operating condition is dynamically matched to stabilize the reduction reaction operation.

[0030] Deep reduction can be achieved by stabilizing the smelting temperature at 1100–1400℃, which significantly reduces the reaction temperature compared to traditional processes. Combined with in-situ Joule heating and self-propagating exothermic heating, the external heat source supply is greatly reduced, resulting in a significant decrease in energy consumption per ton of magnesium smelting and lower carbon emissions.

[0031] By eliminating reaction dead zones through multi-field synergy, the magnesium oxide reduction conversion rate is stably maintained at over 95%, the magnesium content in the smelting residue is extremely low, and there is no material spraying phenomenon.

[0032] It supports both DC and AC power supply modes, which can be flexibly switched according to the equipment conditions at the production site; it is compatible with conventional industrial equipment with limited particle size, pressure and vacuum parameters, making it easy to modify and implement.

[0033] In embodiments of the present invention, the carbonaceous material is one or more of graphite, semi-coke, coke, and anthracite; the oxide containing magnesium oxide is any one of lightly calcined magnesium oxide, calcined dolomite powder, calcined magnesia powder, and waste magnesium brick powder.

[0034] In an embodiment of the present invention, during the batching step, the carbonaceous material is batched in an excess of 5% to 20% magnesium oxide stoichiometric ratio.

[0035] In embodiments of the present invention, the self-propagating chain reduction reaction time is controlled to be 30-120 seconds.

[0036] In an embodiment of the present invention, the direction of the direct current or alternating current supply is consistent with the direction of the axial mechanical pressure application.

[0037] In embodiments of the present invention, a security system is also included, the security system comprising: Raw material pretreatment safety: Mixing, ball milling, and placing the powdered raw materials into the conductive mold are all carried out under an inert atmosphere to avoid oxidation and spontaneous combustion of the powder at room temperature; Gas phase control: Carbon monoxide gas generated by the self-propagating chain reduction reaction is collected in a unified manner through a closed pipeline and treated for harmlessness or recycled; the furnace body is maintained in a slightly negative pressure state to prevent the leakage of toxic and flammable gases. Magnesium vapor condensation explosion-proof: The condensation zone adopts a gradient temperature control mode, with the temperature of the first-stage condensation zone controlled at 660-700℃, so that magnesium vapor is preferentially liquefied into liquid magnesium, reducing the generation of ultrafine active magnesium powder; the condensation system is equipped with an argon inert gas device and an explosion relief device to prevent magnesium dust explosion. Interlock protection: The vacuum degree, oxygen content in the furnace, temperature, pressure and current are set with multiple safety interlocks. When vacuum leakage, over-temperature, over-pressure or current abnormality occurs, the power supply and pressure loading are automatically cut off and the emergency protection program is activated. Safety procedures for starting and stopping the machine: Before breaking the vacuum, first fill the furnace with high-purity argon gas for gas replacement, and check that the oxygen content in the furnace is <0.1% before opening the lid.

[0038] Specifically, the furnace door must not be opened directly under high temperature conditions. Example 1

[0039] Graphite was selected as the carbonaceous reducing agent, 10 grams of lightly calcined magnesium oxide was used as the magnesium source, and 6 grams of semi-coke were mixed with magnesium oxide in a molar ratio of 1.15:1. The raw materials were ball-milled after mixing, and the particle size of the powder was controlled to be ≤100μm. The mold is 50mm high and 20mm in diameter. Powder is loaded into the conductive mold and placed in a vacuum reduction furnace. The furnace is evacuated to 60Pa and powered by DC current at a current density of 18A / cm². Simultaneously, an axial mechanical pressure of 45MPa is applied to the reaction material inside the mold, with the pressure direction aligned with the current direction. Temperature and magnesium vapor flow are monitored in real-time and controlled in a closed-loop system. The magnesium vapor flow rate is obtained by measuring the vacuum level within the reduction furnace chamber. The entire process is coupled to trigger a self-propagating reaction. The magnesium oxide content in the reduction slag is measured at reduction times of 30 seconds, 60 seconds, and 180 seconds, and the magnesium oxide reduction rates are calculated to be 40%, 80%, and 95.4%, respectively. The reaction time is controlled by the magnesium vapor flow rate; when the magnesium vapor flow rate decreases from high to zero, the reduction reaction is considered complete under those conditions.

[0040] Specifically, the reduction rate = 100% - the percentage of magnesium oxide weight in the magnesium slag relative to the magnesium oxide content in the raw material.

[0041] Comparative Example 1: The difference between this comparative example and Example 1 is that, without applying pressure, at a current density of 18 A / cm², a sample temperature of 1280°C, and reduction times of 30 seconds, 60 seconds, 180 seconds, and 1800 seconds, the magnesium oxide reduction rates were 2%, 5%, 17%, and 69%, respectively.

[0042] Comparative Example 2: The difference between this comparative example and Example 1 is that after the sample is mixed, it is first molded into a cylindrical sample with a diameter of 40 mm and a length of 50 mm under a pressure of 45 MPa; it is then placed in a vacuum reduction furnace and evacuated to 60 Pa; the temperature of the vacuum furnace is adjusted to 1550℃, and the magnesium oxide reduction rates are 21%, 64%, and 71% for 0.5 hours, 2 hours, and 4 hours, respectively. Example 2

[0043] Semi-coke was used as the reducing agent, and calcined dolomite powder was used as the raw material, with a carbon-to-magnesium ratio of 1.2:1. The particle size of the powder after ball milling was ≤100μm. The vacuum degree inside the furnace was 40Pa, AC power was used with a current density of 25A / cm², the sample reduction temperature was 1320℃, and a mechanical pressure of 55MPa was applied. The reduction time was 48 seconds, and the magnesium oxide reduction rate was 96.4%. The reduction slag was tested as follows: Figure 3 As shown. Example 3

[0044] The sample was prepared using coke and industrial magnesium oxide as raw materials, with a powder particle size ≤100μm; vacuum degree 120Pa, AC power supply, current density 12A / cm², sample reduction temperature 1180℃, mechanical pressure 25MPa; reduction time 59 seconds, magnesium oxide reduction rate 96.3%.

[0045] Comparative Example 3: The process employs a vacuum + electric field combination, without matching mechanical pressure, dedicated temperature control, or limited powder particle size; the reduction time is 4.5 hours, the magnesium oxide reduction rate is only 74.6%, and the smelting energy consumption is 3.7 times that of the present invention. It cannot achieve self-propagating rapid deep reduction, which directly proves that simple technology combinations cannot achieve the technical effect of the present invention.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for rapid carbothermic reduction of metallic magnesium in a vacuum, characterized in that, The steps include the following: S1: Using carbonaceous materials as reducing agents and magnesium oxide-containing oxides as smelting raw materials, the raw materials are successively processed through batching, mixing and ball milling to obtain powdered reducing raw materials with a particle size of no more than 100µm. S2: Place the powdered reducing material inside the conductive mold and send it into the vacuum reduction furnace as a whole; S3: After sealing the vacuum reduction furnace, start the vacuum system and control the vacuum level inside the furnace to 10~300Pa. Control the reduction temperature of the powdered reducing material to 1100~1400℃, and simultaneously apply a current density of 2~40A / cm to the powdered reducing material. 2 Direct current or alternating current, along with axial mechanical pressure of 5~50MPa, induces the traditional slow thermal diffusion carbothermic reduction reaction to transform into a self-sustaining self-propagating chain reduction reaction through deep multi-field coupling. S4: The sample temperature and the flow rate of overflowing magnesium vapor are monitored in real time throughout the reduction process. Based on the real-time data obtained from the monitoring, the power supply current parameters and the mechanical pressure are dynamically adjusted to maintain the stable and continuous self-propagating chain reduction reaction. S5: The magnesium vapor generated by the reaction enters the condensation zone to cool and crystallize, obtaining metallic magnesium. After the reaction is completed, the vacuum in the furnace is broken to complete the single reduction operation.

2. The method for rapid carbothermic reduction of metallic magnesium in vacuum according to claim 1, characterized in that, The carbonaceous material is one or more of graphite, semi-coke, coke, and anthracite; the magnesium oxide is any one of lightly calcined magnesium oxide, calcined dolomite powder, calcined magnesia powder, and waste magnesium brick powder.

3. The method for rapid vacuum carbothermic reduction of metallic magnesium according to claim 1, characterized in that, In the batching process, carbonaceous materials are proportioned in excess of magnesium oxide by 5% to 20% according to the stoichiometric ratio.

4. The method for rapid carbothermic reduction of metallic magnesium in vacuum according to claim 1, characterized in that, The self-propagating chain reduction reaction time is controlled between 30 and 120 seconds.

5. The method for rapid vacuum carbothermic reduction of metallic magnesium according to claim 1, characterized in that, The direction of the DC or AC power supply is consistent with the direction of the axial mechanical pressure application.

6. The method for rapid vacuum carbothermic reduction of metallic magnesium according to claim 1, characterized in that, It also includes a security system, which includes: Raw material pretreatment safety: Mixing, ball milling, and placing the powdered raw materials into the conductive mold are all carried out under an inert atmosphere to avoid oxidation and spontaneous combustion of the powder at room temperature; Gas phase control: Carbon monoxide gas generated by the self-propagating chain reduction reaction is collected in a unified manner through a closed pipeline and treated for harmlessness or recycled; the furnace body is maintained in a slightly negative pressure state to prevent the leakage of toxic and flammable gases. Magnesium vapor condensation explosion-proof: The condensation zone adopts a gradient temperature control mode, with the temperature of the first-stage condensation zone controlled at 660-700℃, so that magnesium vapor is preferentially liquefied into liquid magnesium, reducing the generation of ultrafine active magnesium powder; the condensation system is equipped with an argon inert gas device and an explosion relief device to prevent magnesium dust explosion. Interlock protection: The vacuum degree, oxygen content in the furnace, temperature, pressure and current are set with multiple safety interlocks. When vacuum leakage, over-temperature, over-pressure or current abnormality occurs, the power supply and pressure loading are automatically cut off and the emergency protection program is activated. Safety procedures for starting and stopping the machine: Before breaking the vacuum, first fill the furnace with high-purity argon gas for gas replacement, and check that the oxygen content in the furnace is <0.1% before opening the lid.

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