Method for preparing magnesium metal from magnesium oxide

Abstract

The invention discloses a method for preparing magnesium metal from magnesium oxide, and belongs to the field of magnesium metal preparation. The method mainly comprises the following steps: mixing a magnesium oxide raw material and a carbonaceous reducing agent according to a mass ratio of 1: (0.8-1.2), and carrying out preheating treatment under the protection of inert gas at 200-400 DEG C for 1-3 hours; s2, a silicon-based reducing agent is added into the mixture obtained in the step S1, the molar ratio of carbon to silicon is 3: 1-5: 1, a calcium fluoride catalyst accounting for 1-5% of the total mass of the mixture is added, and a composite reduction system is formed. By innovatively designing the synergistic effect of a carbon-silicon composite reduction system and a calcium fluoride catalyst, the efficiency and selectivity of magnesium oxide reduction reaction are remarkably improved, and the reaction activation energy is reduced. A sectional temperature control process is combined with dynamic pressure regulation, so that accurate regulation and control of the reaction process are realized, and the reaction rate and the product stability are effectively balanced. And a nanoscale reducing agent and a graphene-carbon nanotube composite material are adopted, so that the activity of a reaction interface is enhanced.

Description

Technical Field

[0001] This invention relates to the preparation of metallic magnesium, and more particularly to a method for preparing metallic magnesium from magnesium oxide. Background Technology

[0002] Currently, the preparation of metallic magnesium mainly relies on electrolysis and thermal reduction methods. While electrolysis can yield high-purity magnesium, it suffers from high energy consumption and severe equipment corrosion. Traditional thermal reduction methods (such as the silicothermic and carbothermic methods) limit their industrial application due to harsh reaction conditions, low reducing agent utilization, and insufficient product purity. For example, the silicothermic method requires high temperatures (above 1200℃), and the low reactivity of silicon with magnesium oxide leads to low magnesium yields. The carbothermic method easily introduces carbon impurities, requiring additional purification steps. Furthermore, existing technologies often use a single reducing agent, making it difficult to synergistically control reaction kinetics and thermodynamic equilibrium. The catalyst loading method and the control of the gas phase environment of the reaction system have not been fully optimized. These problems not only increase production costs but also lead to significant energy consumption and environmental pollution. Therefore, there is an urgent need to develop an efficient and environmentally friendly method for preparing metallic magnesium, achieving a synergistic improvement in high yield, low energy consumption, and high purity through optimization of the reduction system, catalyst design, and reaction condition control. Summary of the Invention

[0003] Purpose of the invention: The purpose of this invention is to provide a method for preparing metallic magnesium from magnesium oxide, so as to solve the problems of high production cost, energy consumption and environmental pollution in existing methods for preparing metallic magnesium.

[0004] Technical solution: A method for preparing metallic magnesium from magnesium oxide, comprising the following steps:

[0005] S1. Mix magnesium oxide raw material and carbonaceous reducing agent at a mass ratio of 1:0.8-1.2, and preheat under inert gas protection at a temperature of 200-400℃ for 1-3 hours.

[0006] S2. Add a silicon-based reducing agent to the mixture obtained in step S1 to make the molar ratio of carbon to silicon 3:1-5:1, and add calcium fluoride catalyst accounting for 1-5% of the total mass of the mixture to form a composite reduction system.

[0007] S3. Place the composite reduction system in a closed reactor and carry out the reduction reaction under segmented temperature control, specifically including:

[0008] a. Heat the system to 800-900℃ at a heating rate of 5-10℃ / min and hold for 1-2 hours;

[0009] b. Heat the system to 1300-1400℃ at a heating rate of 3-5℃ / min, and hold for 2-4 hours to allow magnesium oxide to undergo a reduction reaction with the composite reducing agent to generate metallic magnesium vapor.

[0010] S4. Cool the magnesium vapor to room temperature using a quenching device to obtain crude magnesium product;

[0011] S5. The crude magnesium product is purified by vacuum distillation at a temperature of 600-700℃ and a pressure of 10-100Pa to obtain magnesium.

[0012] The carbonaceous reducing agent is a graphene-carbon nanotube composite material, the silicon-based reducing agent is nano-silicon powder, and in step S3, a mixture of argon and hydrogen is introduced into the reactor in a volume ratio of 95:5.

[0013] Preferably, the carbonaceous reducing agent in step S1 has a particle size of 10-50 μm and undergoes surface oxidation treatment before preheating. The surface oxidation treatment is carried out in a sulfuric acid-hydrogen peroxide mixture at 60-80°C for 30-60 minutes.

[0014] Preferably, the specific parameters for segmented temperature control in step S3 are as follows: in the 800-900℃ stage, the system pressure is maintained at 10-20kPa; in the 1300-1400℃ stage, the system pressure is adjusted to 5-10kPa by a dynamic vacuum pump.

[0015] Preferably, in step S3, the calcium fluoride catalyst is loaded onto the surface of magnesium oxide via a sol-gel method, with a loading amount of 0.5-2% of the mass of magnesium oxide, and the catalyst particle size is 0.1-0.5 μm.

[0016] Preferably, the quenching device adopts a three-stage cooling system, including: the first stage: the high-temperature zone uses water-cooled copper pipes for radiation cooling; the second stage: the medium-temperature zone uses liquid nitrogen spray cooling; and the third stage: the low-temperature zone uses molecular sieve adsorption cooling.

[0017] Preferably, during the vacuum distillation purification process in step S5, potassium iodide auxiliaries accounting for 0.1-0.5% of the mass of crude magnesium are added to the distillation furnace to promote the volatilization and separation of impurity elements.

[0018] Preferably, the reactor adopts a double-layer graphite crucible structure, with the inner crucible equipped with a graphene heating element and the outer crucible equipped with an electromagnetic stirring device to achieve uniform mixing of materials in the 1300-1400℃ range.

[0019] Preferably, a physical purification step is added between step S4 and step S5, specifically: placing the crude magnesium product in an ultrasonic cleaning tank and cleaning it in an alcohol solution with an ultrasonic frequency of 20-40kHz for 10-30 minutes to remove surface oxides and impurities.

[0020] Beneficial Effects: This invention significantly improves the efficiency and selectivity of the magnesium oxide reduction reaction and reduces the activation energy by innovatively designing a carbon-silicon composite reduction system and leveraging the synergistic effect of a calcium fluoride catalyst. The segmented temperature control process combined with dynamic pressure regulation achieves precise control of the reaction process, effectively balancing the reaction rate and product stability. The use of nanoscale reducing agents and graphene-carbon nanotube composite materials enhances the activity of the reaction interface, while a three-stage quenching system and ultrasonic physical purification process significantly improve the purity of metallic magnesium. Furthermore, the double-layer structure design of the reactor and the introduction of an electromagnetic stirring device further optimize the uniformity of material mixing and reduce local overheating or incomplete reaction. The overall process reduces energy consumption while minimizing carbon emissions and impurity generation, aligning with the development trend of green metallurgy. This invention not only solves the common problems of low reducing agent utilization, high energy consumption, and insufficient purity in traditional methods but also provides an economical and sustainable technical path for the large-scale preparation of metallic magnesium through multi-technology integration and innovation. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0022] To make the technical solution of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0023] Example 1

[0024] A method for preparing metallic magnesium from magnesium oxide, comprising:

[0025] 1. Mix magnesium oxide (50 μm particle size) and graphene-carbon nanotube composite material (30 μm particle size, surface oxidation treatment) at a mass ratio of 1:1.0 and preheat to 300℃ (1.5 h).

[0026] 2. Add nano-silicon powder (particle size 0.2μm) to make the carbon:silicon molar ratio 4:1, and add 3% calcium fluoride catalyst (sol-gel method loading, particle size 0.3μm).

[0027] 3. In a double-layer graphite crucible reactor, the temperature is raised in stages to 850℃ (hold for 1.5h) → 1350℃ (hold for 3h), and the reaction atmosphere is argon-hydrogen (95:5).

[0028] 4. Cool the magnesium vapor using a three-stage quenching system (water cooling → liquid nitrogen → molecular sieve).

[0029] 5. After ultrasonic cleaning (30kHz, 20min), vacuum distillation (650℃, 50Pa) is performed, and 0.3% potassium iodide is added as an auxiliary agent.

[0030] Example 2

[0031] A method for preparing metallic magnesium from magnesium oxide, comprising:

[0032] 1. Magnesium oxide and graphene-carbon nanotube composite material (particle size 20μm, surface oxidation treatment) are mixed at a ratio of 1:0.9 and preheated to 250℃ (2h).

[0033] 2. The particle size of the nano-silicon powder was adjusted to 0.1μm, the carbon:silicon molar ratio was 3.5:1, and the calcium fluoride catalyst was 1.5%.

[0034] 3. The reaction temperature is divided into stages: 800℃ (1h) → 1300℃ (4h), and the pressure is dynamically adjusted from 15kPa to 8kPa.

[0035] 4. Optimization of parameters for the three-stage quenching system: liquid nitrogen injection temperature -196℃.

[0036] 5. Vacuum distillation temperature 600℃, pressure 80Pa, potassium iodide addition 0.2%.

[0037] Example 3

[0038] A method for preparing metallic magnesium from magnesium oxide, comprising:

[0039] 1. Magnesium oxide and graphene-carbon nanotube composite material (particle size 50μm, surface oxidation treatment) are mixed at a ratio of 1:1.2 and preheated to 400℃ (1h).

[0040] 2. The nano-silicon powder has a particle size of 0.5μm, a carbon:silicon molar ratio of 5:1, and a calcium fluoride catalyst of 5%.

[0041] 3. The reaction temperature is divided into stages: 900℃ (2h) → 1400℃ (2h), and the pressure is 20kPa → 5kPa.

[0042] 4. The three-stage quenching system is equipped with an ultrasonic cleaning tank (40kHz, 10min).

[0043] 5. Vacuum distillation temperature 700℃, pressure 100Pa, potassium iodide addition 0.5%.

[0044] Comparative Example 1

[0045] The traditional silicothermic method is used, without the use of carbonaceous reducing agents and calcium fluoride catalysts. Magnesium oxide is reduced only with nano-silica powder (particle size 0.5μm). The reaction temperature is 1300℃ (single-stage holding for 3h), and the reaction is cooled under normal pressure without a vacuum distillation step.

[0046] Comparative Example 2

[0047] The carbothermal method was used, with graphite powder replacing graphene-carbon nanotube composite material. No silicon-based reducing agent or calcium fluoride catalyst was added. The reaction temperature was 1400℃ (single-stage holding for 4 hours), and after cooling, only conventional acid washing and purification were performed.

[0048] Comparative Example 3

[0049] A segmented temperature control process (800℃→1300℃) was adopted, but a carbon-silicon composite reduction system was not introduced. Only nano-silicon powder (particle size 0.3μm) was used as a single reducing agent, and calcium fluoride catalyst and a three-stage quenching system were not used.

[0050] (1) Magnesium metal yield (%)

[0051] Test method:

[0052] Raw material weighing: Accurately weigh the mass (m1) of magnesium oxide raw material.

[0053] Product collection: After the reaction is complete, collect the crude magnesium product and remove unreacted magnesium oxide and impurities. Weigh the crude magnesium product (m2).

[0054] After purification, weigh the crude magnesium product by vacuum distillation and weigh the pure magnesium (m3).

[0055] Calculation formula: Yield = [m3 / (m1 × theoretical magnesium content)] × 100% (theoretical magnesium content is calculated based on the stoichiometric ratio of magnesium oxide, assuming complete reaction).

[0056] (2) Purity of metallic magnesium (%)

[0057] Test method:

[0058] Spectroscopic analysis: Inductively coupled plasma optical emission spectroscopy (ICP-OES) or X-ray fluorescence spectroscopy (XRF) was used to analyze the content of impurity elements (such as Fe, Al, Si, Ca, etc.) in the magnesium metal samples.

[0059] Purity calculation: Purity = 100% - ∑ (mass percentage of impurity elements).

[0060] (3) Energy consumption (kW·h / kg)

[0061] Test method:

[0062] Power consumption monitoring: Real-time recording of power consumption (kW·h) of equipment such as reactor, vacuum pump, and cooling system during the reaction process.

[0063] Unit energy calculation: Energy consumption = Total electrical energy consumption (kW·h) / Final magnesium metal production (kg).

[0064] Equipment calibration: Power monitoring equipment needs to be calibrated regularly to ensure data accuracy.

[0065] (4) Carbon emissions (kg CO2 / kg)

[0066] Test method:

[0067] Carbon source tracking: Statistically determine the carbon content of carbonaceous reducing agents (such as graphene-carbon nanotube composites) during the reaction process and calculate the theoretical CO2 emissions during complete combustion.

[0068] Environmental monitoring: The actual CO2 emissions in the reaction tail gas are determined by gas chromatography (GC) or infrared absorption method.

[0069] Carbon emission per unit: Carbon emission = Total CO2 emissions (kg) / Final magnesium metal production (kg).

[0070] (5) Impurity element content (ppm)

[0071] Test method:

[0072] Sample preparation: Dissolve pure magnesium metal in dilute nitric acid to prepare the test solution.

[0073] Instrumental analysis: The concentration of impurity elements (such as Fe, Al, Si, Ni, etc.) was determined by inductively coupled plasma mass spectrometry (ICP-MS).

[0074] Unit conversion: Convert the concentration value to mass percentage (ppm). The formula is: Impurity content (ppm) = element mass (μg) / magnesium metal mass (g).

[0075] Test method description:

[0076] Test equipment calibration: All analytical instruments (such as ICP-OES, ICP-MS, and power monitoring instruments) must be calibrated regularly and comply with national metrological standards.

[0077] Repeatability verification: Each experiment was repeated 3 times, and the average value was taken as the final result to ensure data reliability.

[0078] Environmental conditions were controlled: the experiment was conducted at standard atmospheric pressure (101.3 kPa) and normal temperature (25 ± 2 ℃) to avoid environmental interference.

[0079] Data comparison basis: The comparative data were obtained through the same testing methods to ensure the fairness and scientific nature of the comparison.

[0080] The test results are shown in the table below:

[0081]

[0082] As can be seen from the comparison of the examples and comparative examples, the present invention significantly improves the yield and purity of metallic magnesium through the synergistic effect of the carbon-silicon composite reduction system and the calcium fluoride catalyst, while reducing energy consumption and carbon emissions. Segmented temperature control and dynamic pressure regulation optimize reaction kinetics, while the three-stage quenching system and ultrasonic cleaning process effectively remove impurities, and vacuum distillation further purifies the product. In contrast, traditional methods, due to single reducing agents or process defects, result in low yields, high energy consumption, and insufficient purity. The technical solution of the present invention has significant advantages in reaction efficiency, product quality, and environmental friendliness, providing an innovative path for the green preparation of metallic magnesium.

[0083] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A method for producing metallic magnesium from magnesium oxide, characterized in that, The method comprises the following steps: S1, mixing the magnesium oxide raw material with the carbonaceous reducing agent according to a mass ratio of 1:0.8-1.2, and preheating the mixture under the protection of inert gas, the preheating temperature being 200-400 DEG C, and the duration being 1-3 hours; S2, adding the silicon-based reducing agent to the mixture obtained in step S1, so that the molar ratio of carbon to silicon is 3:1-5:1, and adding 1-5% of calcium fluoride catalyst based on the total mass of the mixture to form a composite reducing system; S3, placing the composite reducing system in a closed reaction furnace, and performing a reduction reaction under staged temperature control, specifically including: a, heating the system to 800-900 DEG C at a heating rate of 5-10 DEG C / min, and maintaining the temperature for 1-2 hours; b, heating the system to 1300-1400 DEG C at a heating rate of 3-5 DEG C / min, and maintaining the temperature for 2-4 hours, so that the magnesium oxide reacts with the composite reducing agent to generate magnesium vapor; S4, cooling the magnesium vapor to room temperature through a quenching device to obtain crude magnesium; S5, vacuum distillation purification of the crude magnesium, the distillation temperature being 600-700 DEG C, and the pressure being 10-100 Pa, to obtain magnesium. In step S3, the carbonaceous reducing agent is graphene-carbon nanotube composite material, the silicon-based reducing agent is nano silicon powder, and a mixed gas of argon and hydrogen is introduced into the reaction furnace, the volume ratio being 95:

5.

2. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, In step S1, the particle size of the carbonaceous reducing agent is 10-50 μm, and the surface of the carbonaceous reducing agent is subjected to oxidation treatment before preheating, the oxidation treatment being performed at 60-80 DEG C for 30-60 minutes using a sulfuric acid-hydrogen peroxide mixed solution.

3. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, In step S3, the specific parameters of the staged temperature control are as follows: in the 800-900 DEG C stage, the pressure of the system is maintained at 10-20 kPa; in the 1300-1400 DEG C stage, the pressure of the system is adjusted to 5-10 kPa by a dynamic vacuum pump.

4. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, In step S3, the calcium fluoride catalyst is loaded on the surface of the magnesium oxide by a sol-gel method, the loading amount being 0.5-2% of the mass of the magnesium oxide, and the particle size of the catalyst being 0.1-0.5 μm.

5. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, The quenching device adopts a three-stage cooling system, including: first stage: high-temperature zone is cooled by radiating water-cooled copper pipes; second stage: medium-temperature zone is cooled by liquid nitrogen injection; third stage: low-temperature zone is cooled by molecular sieve adsorption.

6. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, In the vacuum distillation purification process of step S5, 0.1-0.5% of potassium iodide additive based on the mass of the crude magnesium is added to the distillation furnace to promote the volatilization and separation of impurity elements.

7. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, The reaction furnace adopts a double-layer graphite crucible structure, the inner crucible is provided with a graphene heating element, and the outer crucible is provided with an electromagnetic stirring device, which is used to realize uniform mixing of the materials in the 1300-1400 DEG C stage.

8. The method of producing metallic magnesium from magnesia according to claim 1, characterized by, A physical purification step is added between step S4 and step S5, specifically: the crude magnesium is placed in an ultrasonic cleaning tank, and is cleaned in an alcohol solution for 10-30 minutes by using ultrasonic waves with a frequency of 20-40 kHz to remove surface oxides and impurities.

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