Electrolytic magnesium preparation method and device

Abstract

The invention discloses a preparation method and device of electrolytic magnesium, and belongs to the technical field of metal smelting. According to the method, a nickel ferrite-based eutectic ceramic inert anode and liquid metal lead or / and tin alloy are adopted as a cathode, and an industrial MgO raw material is electrolyzed in a MgF2-CaF2-LiF molten electrolyte at the temperature of 800-900 DEG C; after the magnesium-lead-tin alloy is generated through electrolysis, the high density of the metal lead-tin alloy is used for achieving effective isolation of the vacuum chamber and the electrolytic bath, and then the metal pure magnesium is obtained through online vacuum distillation separation by means of the vapor pressure difference of the metal lead-tin alloy and magnesium. According to the method, zero carbon emission in the electrolysis process can be achieved, and the used nickel ferrite-based eutectic ceramic anode can greatly improve the electrolysis current efficiency and the corrosion resistance; by adopting the lead-tin cathode liquid electrode, the production cost can be reduced; and the mode of separating the metal magnesium through online distillation can reduce the distillation energy consumption, and has remarkable environmental protection benefits and economic benefits.

Description

Technical Field

[0001] This invention belongs to the field of non-ferrous metal electrolytic metallurgy technology, specifically relating to a "zero-carbon" electrolytic magnesium preparation method and dedicated device based on inert anode and online separation technology. Background Technology

[0002] Magnesium, as a lightweight and high-strength metallic material, is widely used in aerospace, new energy vehicles, energy storage equipment, and other fields. Currently, the main industrial methods for producing magnesium include electrolysis and thermal reduction (such as the Pidgeon process). Electrolysis holds a dominant position due to its advantages in large-scale production; however, traditional electrolysis processes have low energy efficiency in magnesium separation. In traditional processes, the distillation separation of magnesium alloys often employs batch-based offline processing, consuming up to 4.3 kWh / kg Mg. Furthermore, the energy from electrolysis and distillation processes cannot be utilized in a cascade manner, resulting in significant energy waste. Summary of the Invention

[0003] In view of the defects or deficiencies of the prior art, the present invention provides a method for preparing electrolytic magnesium.

[0004] Therefore, the method provided by the present invention includes: using nickel ferrite-based eutectic ceramic as the anode, liquid metallic lead or liquid metallic tin or a mixture of both located below the electrolytic cell as the cathode, and electrolyzing a molten electrolyte composed of MgF2, CaF2, LiF and MgO in the electrolytic cell under normal pressure and 800-900℃ conditions, forming an alloy liquid in the cathode, wherein the alloy liquid is a magnesium-lead alloy or a magnesium-tin alloy or a magnesium-lead-tin alloy liquid, and the alloy liquid is located below the molten electrolyte; After the magnesium reaches the target concentration in the cathode, the alloy liquid at 800-900℃ is transported to a distillation chamber at 1-100Pa and 700-1000℃ to distill off metallic magnesium. Then, the pressure difference between the distillation chamber and the electrolytic cell is adjusted so that the remaining liquid metal at 800-900℃ after distillation flows back to the electrolytic cell to continue electrolytic processing. The mass percentage of magnesium oxide added to the electrolyte is 2 wt%-6 wt%.

[0005] An alternative approach is to use nickel ferrite-based eutectic ceramic anodes made by mixing 80-90 wt% nickel ferrite, 2-10% NiO, 2-10 wt% oxidizing agent and 2-10 wt% conductive agent, melting the mixture at 1600-1850℃ for 1-2 hours, and then cooling and solidifying it. The oxidizing agent is usually ferric phosphate powder, and the conductive agent is usually molybdenum disilicide powder.

[0006] An optional solution is that the mass percentages of each component of the electrolyte are: 20-50 wt% magnesium fluoride, 30-50 wt% calcium fluoride, 10-25 wt% lithium fluoride, and 2-6 wt% magnesium oxide.

[0007] An alternative approach is to arrange the cathode and anode vertically in the electrolytic cell during electrolysis, with an electrode spacing of 1-5 cm, a cell voltage of 3-6 V, and a current density of 0.3-2 A / cm² passing through the anode working surface.

[0008] An alternative approach is to dissolve the electrolytically produced magnesium metal into the liquid lead and tin in any mass ratio. A 1:1 ratio is preferred.

[0009] An alternative is to set the target magnesium concentration in the alloy liquid at 10-30 wt%.

[0010] An alternative is to adjust the pressure difference between the distillation chamber and the electrolytic cell to maintain it at 50-100 Pa so that the remaining liquid metal at 800-900℃ after distillation flows back to the electrolytic cell.

[0011] This invention utilizes the high density of metallic lead and / or tin to effectively isolate the vacuum chamber from the atmospheric pressure electrolytic cell, and then utilizes the vapor pressure difference between magnesium and lead-tin liquid metals to achieve online vacuum distillation separation of pure metallic magnesium, ultimately achieving "zero carbon" emissions in the magnesium electrolysis process.

[0012] The online distillation system integrated in this invention utilizes the physical heat of the liquid metal during electrolysis. The online distillation energy consumption is 0.8-0.9 kWh / kg Mg, a reduction of 79-81% compared to traditional offline distillation (energy consumption reduction exceeding 50%), and can be controlled to below 1 kWh / kg Mg. Furthermore, through vacuum distillation separation, the purity of the magnesium product can reach over 99.95%, meeting the industrial first-grade product standard.

[0013] Replacing tin (approximately 200,000 yuan / ton) with metallic lead (approximately 15,000 yuan / ton) as cathode material can reduce cathode material costs by more than 50%; at the same time, lead and tin can be recycled, further controlling costs.

[0014] This invention uses a nickel ferrite-based eutectic ceramic inert anode to replace the traditional carbon anode. The anode product during electrolysis is oxygen instead of CO2, completely eliminating carbon emissions. Compared with the Pidgeon process, CO2 emissions can be reduced by 42 tons per ton of magnesium, and CO2 emissions can be reduced by 24.3 tons per ton compared with the traditional electrolysis method. Furthermore, using a nickel ferrite-based inert anode, the magnesium electrolysis current efficiency can reach up to 93%, which is superior to the existing known levels. At the same time, the nickel ferrite-based eutectic ceramic anode has good resistance to molten salt corrosion (corrosion rate in fluoride salts at 850℃ <0.9mm / year) and conductivity (conductivity >50S / cm). The MgF2-CaF2-LiF electrolyte has suitable viscosity (7-8mPa·s) and conductivity in the 800-900℃ range, ensuring the stable operation of the electrolysis process.

[0015] The present invention also provides an electrolytic magnesium apparatus for implementing the above method. The apparatus includes an electrolytic cell and a distillation chamber. A nickel ferrite-based eutectic ceramic inert anode is disposed above the electrolytic cell and connected to the positive terminal of a power supply. A liquid cathode is placed at the bottom of the electrolytic cell and connected to the negative terminal of a power supply. An electrolyte is located above the liquid cathode in the electrolytic cell, and the anode is immersed in the electrolyte to form an electric circuit. The liquid anode in the cathode region is sealed and connected to the distillation chamber through a corrosion-resistant and high-temperature-resistant guide tube.

[0016] In a further embodiment, the device also includes a vacuum regulation device (such as a pressure control valve, a vacuum sensor, and a vacuum pump) for regulating the pressure difference between the distillation chamber and the electrolytic cell. The guide tube is a silicon nitride ceramic guide tube. Attached Figure Description

[0017] Figure 1 is a schematic diagram of the device structure of the present invention. The components in the figure are labeled as follows: 1 - Electrolytic cell; 2 - Electrolytic cell liner; 3 - Electrolytic cell insulation layer; 4 - Electrolytic cell outer wall; 5 - Heating device; 6 - Electrolyte; 7 - Anode; 8 - Liquid cathode; 9 - Guide pipe; 10 - Heater; 11 - Distillation chamber; 12 - Pure magnesium collector (condenser); 13 - Vacuum pump; 14 - Cathode guide rod; 15 - Anode guide rod; 16 - Power supply; 17 - Electrolyte feed port.

[0018] Figure 2 The results of energy dispersive spectroscopy (EDS) analysis of the magnesium-lead alloy synthesized in the examples are shown.

[0019] Figure 3 The XRD pattern of the tin-magnesium alloy obtained after 6 hours of electrolysis in the example is shown. Detailed Implementation

[0020] Unless otherwise specified, the scientific and technical terms used in this article are intended for understanding by those skilled in the art.

[0021] The anode material described in this invention can be the material synthesized using ZL202311818746.9 or the anode material provided by this invention. This invention uses nickel ferrite-based eutectic ceramic as the inert anode and liquid metal lead and / or tin as the cathode; the anode and cathode are arranged vertically, and the electrolysis temperature is maintained at 800-900℃. In a preferred embodiment, the electrode spacing is controlled to be 1-5cm; the cell voltage is 3-6V, and the current density is 0.3-2A / cm²; during electrolysis, MgO dissociates into Mg in the electrolyte. 2+ and O 2- Mg 2+ At the cathode, it gains electrons and is reduced to metallic magnesium, which then dissolves in liquid lead-tin to form a liquid metal alloy. 2- O2 is generated at the anode by electron loss; the alloy liquid formed in the cathode region enters the vacuum distillation chamber through a guide tube. Under conditions of vacuum degree 1-100 Pa and temperature 700-800℃, the vapor pressure difference between magnesium and lead / tin is utilized (magnesium vapor pressure is about 1 kPa and lead vapor pressure is 10 kPa at 700℃). -4 kPa, tin vapor pressure 10 -7 The magnesium is preferentially evaporated and condensed into high-purity metallic magnesium in the condenser (kPa). The separated liquid lead-tin is deposited at the bottom of the distillation chamber. The pressure difference between the vacuum chamber and the electrolytic cell is maintained at 50-100Pa by the vacuum degree regulating device. Under the combined action of suction and gravity, the liquid lead-tin returns to the cathode area of ​​the electrolytic cell through the silicon nitride ceramic guide tube, realizing a closed loop circulation.

[0022] join Figure 1 As shown, the electrolytic magnesium apparatus for implementing the method of the present invention includes an electrolytic cell 1 and a distillation chamber 11, the bottoms of which are connected by a high-temperature and corrosion-resistant guide pipe 9 (such as a silicon nitride ceramic guide pipe); wherein, an anode 7 is provided at the top of the electrolytic cell, a liquid cathode 8 (i.e., liquid lead and / or tin) is provided at the bottom of the electrolytic cell, and a molten electrolyte 6 is contained in the electrolytic cell, with the electrolyte located above the liquid cathode and the anode extending into the electrolyte.

[0023] In further proposals, such as Figure 1 As shown, the outer wall 4 of the electrolytic cell is lined with a corrosion-resistant and high-temperature-resistant inner lining 2, and an insulation layer 3 is provided between the outer wall 4 and the inner lining 2. A heating device 5 is also provided outside the electrolytic cell. The anode is connected to a power supply 16 via an anode guide rod 15, and the cathode is connected to a power supply via a cathode guide rod 14. For convenient feeding, an electrolyte feeding port 17 is provided above the electrolytic cell. A heater 10 is provided outside the distillation chamber, and a pure magnesium collector (condenser) 12 is provided at the top (the condenser temperature is controlled at 300-400℃). A vacuum pump 13 is used to adjust the pressure difference between the distillation chamber and the electrolytic cell.

[0024] In some schemes, renewable power sources are selected: providing zero-carbon electricity such as solar and wind power for the electrolysis process, with an output voltage adjustment range of 3-6V to match the cell voltage requirements.

[0025] In the preferred embodiment, the electrolyte feeding port is equipped with a high-temperature resistant sealing cap (such as one made of silicon nitride ceramic) and a screw feeder. The feeding rate can be adjusted by a PLC in conjunction with the electrolysis current (e.g., when the current is 1A / cm², the feeding rate is 0.5kg / h) to prevent electrolyte evaporation and air entry during electrolysis.

[0026] The present invention will be further explained and illustrated below with reference to the embodiments.

[0027] Example 1: In this embodiment, the electrolyte composition is 38wt% (456kg) magnesium fluoride, 38wt% (456kg) calcium fluoride, 20wt% (240kg) lithium fluoride, and 4wt% (48kg) industrial-grade MgO (92% purity). 12,000kg of lead is loaded into the bottom of the electrolytic cell, and the uniformly mixed electrolyte powder is added above the lead. The heating device heats the electrolyte to 800-900℃ at a heating rate of 5℃ / min and holds it at that temperature for 1.5 hours to ensure that the electrolyte is completely melted and the composition is uniform. Then the electrolysis process begins. Electrolysis parameters: A nickel ferrite-based eutectic ceramic inert anode with dimensions of Φ50mm×200mm (the material prepared in Example 1, ZL202311818746.9) was used. The anode extended 4cm into the electrolyte, and the liquid lead cathode height was 10cm. The electrode spacing was 3cm. Direct current was applied, and the cell voltage was controlled at 4.5V, the current density at the anode working surface was 1A / cm², and the electrolysis temperature was 850℃. After 8 hours of electrolysis, a magnesium-lead alloy containing 25wt% magnesium was transported into the distillation chamber. The distillation chamber was maintained at a vacuum of 10Pa, a distillation temperature of 750℃, and a condenser temperature of 350℃. After approximately 8 hours of distillation, approximately 28.5kg of magnesium was collected in the condenser. Then, the pressure difference between the electrolytic cell and the vacuum chamber is adjusted to maintain around 70 Pa, so that the 750°C liquid lead automatically flows back to the electrolytic cell for the next round of electrolysis.

[0028] Analysis showed that this example produced a total of 120 kg of magnesium-lead alloy. The energy dispersive spectroscopy (EDS) analysis results of the magnesium-lead alloy during the process are shown below. Figure 2As shown in Table 1, 28.5 kg of high-purity magnesium was obtained by distillation. The magnesium content was 99.97 wt% according to atomic absorption spectrometry. The contents of the main impurities are shown in Table 2. The magnesium purity was 99.96%. There was no loss of liquid lead, and the lead was recycled online. The current efficiency was 91% (the theoretical magnesium production is 0.45 g magnesium per hour at 1 ampere current. The theoretical magnesium production is calculated by multiplying the anode current by the electrolysis time and then by 0.45. The current efficiency is obtained by comparing the actual magnesium production). The anode loss was 0.65 mm / year. The electrolysis energy consumption was 3.0 kWh / kg Mg, the distillation energy consumption was 0.8 kWh / kg Mg, and the total energy consumption was 3.9 kWh / kg Mg.

[0029] Table 1

[0030] Table 2

[0031] Example 2: The difference between this embodiment and Embodiment 1 is that the anode preparation method used is as follows: 800g of nickel ferrite, 40g of NiO, 110g of molybdenum disilicide, and 50g of ferric phosphate are dried at 120°C for 2 hours to remove moisture. After mixing, they are ball-milled at 300rpm for 3 hours using a planetary ball mill to ensure a mixing uniformity of ≥95%. Subsequently, they are placed in a cylindrical zirconia crucible and melted at 1750°C for 1 hour. After cooling with the furnace, the outer skin of the crucible is removed, and holes are drilled on the end face and connected to the anode guide rod for later use.

[0032] The electrolyte composition of this embodiment is 30wt% magnesium fluoride, 42wt% calcium fluoride, and 25wt% lithium fluoride, with 3wt% industrial-grade MgO (98% purity) added. The uniformly mixed electrolyte powder is added to the electrolytic cell and heated to 800-900℃ at a heating rate of 5℃ / min. The temperature is maintained for 1.5 hours to ensure that the electrolyte is completely melted and the composition is uniform, and then the electrolysis process begins. Electrolysis parameters: The anode is a nickel ferrite-based eutectic ceramic with dimensions of Φ40mm×150mm, the height of the liquid tin cathode is 15cm, the electrode spacing is 4cm, the cell voltage is 5V, the current density is 1.5A / cm², and the electrolysis temperature is 900℃.

[0033] Distillation conditions: maintain vacuum of 5 Pa, distillation temperature of 800 °C, and condenser temperature of 400 °C.

[0034] The results showed that after 6 hours of electrolysis, 100 kg of magnesium-tin alloy was obtained, and 24 kg of magnesium was obtained by distillation; the current efficiency was 89%, the anode loss was 0.75 mm / year, the magnesium purity was 99.99%, and tin was recycled online; the electrolysis energy consumption was 3.4 kWh / kg Mg, the distillation energy consumption was 0.9 kWh / kg Mg, and the total energy consumption was 4.2 kWh / kg Mg. Figure 3 The image shows the XRD pattern after the cathodic liquid has cooled, indicating that when magnesium enters the molten tin cathode and cools, it can form a Mg2Sn alloy in the tin.

[0035] Example 3: The difference between this embodiment and Embodiment 1 is that the anode used is prepared as follows: 900g of nickel ferrite, 10g of NiO, 70g of molybdenum disilicide, and 20g of ferric phosphate are dried at 120°C for 2 hours to remove moisture. After mixing, they are ball-milled at 300rpm for 3 hours using a planetary ball mill to ensure a mixing uniformity of ≥95%. Subsequently, they are placed in a cylindrical zirconia crucible and melted at 1800°C for 1 hour. After cooling with the furnace, the outer skin of the crucible is removed, holes are drilled on the end face, and metal guide rods are connected for later use.

[0036] The electrolyte used consists of 48wt% magnesium fluoride, 36wt% calcium fluoride, 10wt% lithium fluoride, and 6wt% industrial-grade MgO (90% purity). Electrolysis parameters: The anode is a nickel ferrite-based eutectic ceramic with dimensions of Φ45mm×180mm, the liquid lead-tin cathode (lead-tin weight ratio of 1:1) is 8cm high; the electrode spacing is 1cm; the cell voltage is 3V, the current density is 0.8A / cm², and the electrolysis temperature is 800℃.

[0037] Distillation conditions: maintain a vacuum of 100 Pa, a distillation temperature of 1000 °C, and a condenser temperature of 300 °C.

[0038] The results showed that after 10 hours of electrolysis, 90 kg of magnesium-lead alloy was obtained, and 19.8 kg of magnesium was obtained through distillation. The current efficiency was 93%, the anode loss was 0.83 mm / year, the magnesium purity was 99.93%, and lead and tin were recycled online. The electrolysis energy consumption was 3.3 kWh / kg Mg, the distillation energy consumption was 0.88 kWh / kg Mg, and the total energy consumption was 4.09 kWh / kg Mg. Because the waste heat from distillation was used to preheat the electrolyte raw material (heating the raw material from room temperature to 400°C, replacing part of the medium-frequency induction heating energy consumption), the heating system energy consumption was reduced by approximately 0.09 kWh / kg Mg, making the actual total energy consumption (4.09 kWh / kg Mg) slightly lower than the theoretical sum (4.18 kWh / kg Mg). The above embodiments demonstrate that this invention, by using a novel inert anode material, optimizing the electrolyte ratio, electrolysis parameters, and distillation conditions, can stably produce high-purity metallic magnesium while achieving the technical goals of zero carbon emissions, low cost, and low energy consumption.

[0039] Comparative Example 1 (Zirconium Oxide SOM Anode): This comparative example uses the same electrolysis parameters as Example 1, except that the anode is replaced with a zirconia SOM anode with dimensions of Φ50mm×200mm.

[0040] Test results show that the current efficiency is 75% (lower than the 91% of the present invention), the anodic corrosion rate is 5.2 mm / year (far higher than the 0.65 mm / year of the present invention), and the anode preparation cost is 220,000 yuan / ton (higher than the 60,000 yuan / ton of the nickel ferrite-based anode of the present invention).

[0041] The cost breakdown of nickel ferrite-based anodes (per ton) is as follows: 850 kg of nickel ferrite raw material × 20,000 yuan / ton = 17,000 yuan, 100 kg of molybdenum disilicide × 80,000 yuan / ton = 8,000 yuan, 50 kg of ferric phosphate × 10,000 yuan / ton = 500 yuan, melting energy consumption (1800℃ × 1 hour) approximately 4,500 yuan, equipment depreciation and labor costs 10,000 yuan, and the total preparation cost is approximately 60,000 yuan / ton; the preparation cost of zirconia SOM anodes reaches 220,000 yuan / ton due to the zirconia raw material (50,000 yuan / ton) and complex sintering process.

[0042] Comparative Example 2 (Traditional Carbon Anode): This comparative example uses the same electrolysis parameters as Example 1, except that the anode is replaced with a carbon anode.

[0043] Test results show that the electrolysis process produces 24.3 kg of CO2 per 1 kg of magnesium produced (zero emissions for this invention), with a current efficiency of 78% (lower than 91% for this invention) and an anode loss of 2 mm / year (higher than 0.65 mm / year for this invention). Although the cost of carbon anode raw materials is 40,000 yuan / ton (lower than 60,000 yuan / ton for this invention), it requires an additional carbon emission treatment cost of approximately 500 yuan / ton of magnesium, making the overall cost higher than that of this invention.

Claims

1. A method for preparing electrolytic magnesium, characterized in that, The method includes: using nickel ferrite-based eutectic ceramic as the anode, liquid metallic lead or liquid metallic tin or a mixture of both located below the electrolytic cell as the cathode, and electrolyzing a molten electrolyte composed of MgF2, CaF2, LiF and MgO in the electrolytic cell under normal pressure and 800-900℃ conditions, forming an alloy liquid in the cathode, wherein the alloy liquid is a magnesium-lead alloy or a magnesium-tin alloy or a magnesium-lead-tin alloy liquid, and the alloy liquid is located below the molten electrolyte; After the magnesium reaches the target concentration in the cathode, the alloy liquid at 800-900℃ is transported to a distillation chamber at 1-100Pa and 700-1000℃ to distill off metallic magnesium. Then, the pressure difference between the distillation chamber and the electrolytic cell is adjusted so that the remaining liquid metal at 800-900℃ after distillation flows back to the electrolytic cell to continue electrolytic processing. The mass percentage of magnesium oxide added to the electrolyte is 2wt%-6wt%.

2. The preparation method according to claim 1, characterized in that, The material of the nickel ferrite-based eutectic ceramic anode used is made by mixing 80-90 wt% nickel ferrite, 2-10% NiO, 2-10 wt% oxidizing agent and 2-10 wt% conductive agent, melting at 1600-1850℃ for 1-2 hours, and then cooling and solidifying. The oxidizing agent is usually ferric phosphate powder, and the conductive agent is usually molybdenum disilicide powder.

3. The preparation method according to claim 1, characterized in that, The mass percentages of the electrolyte components are as follows: magnesium fluoride 20-50 wt%, calcium fluoride 30-50 wt%, lithium fluoride 10-25 wt%, and magnesium oxide 2-6 wt%.

4. The preparation method according to claim 1, characterized in that, During electrolysis, the cathode and anode are arranged vertically in the electrolytic cell with a spacing of 1-5 cm. The cell voltage is 3-6 V, and the current density through the anode working surface is 0.3-2 A / cm². 2 .

5. The preparation method according to claim 1, characterized in that, The magnesium produced by electrolysis dissolves into the liquid lead and tin in any mass ratio.

6. The preparation method according to claim 1, characterized in that, The target concentration of magnesium in the alloy liquid is 10-30 wt%.

7. The preparation method according to claim 1, characterized in that, Adjust the pressure difference between the distillation chamber and the electrolytic cell to maintain it at 50-100 Pa so that the remaining liquid metal at 800-900℃ after distillation flows back to the electrolytic cell.

8. An electrolytic magnesium apparatus for implementing the method of any one of claims 1-7, characterized in that, It includes an electrolytic cell and a distillation chamber. A nickel ferrite-based eutectic ceramic inert anode is installed above the electrolytic cell and connected to the positive terminal of the power supply. A liquid cathode is placed at the bottom of the electrolytic cell and connected to the negative terminal of the power supply. The electrolyte is located above the liquid cathode in the electrolytic cell, and the anode is immersed in the electrolyte to form an electric circuit. The liquid anode in the cathode region is sealed and connected to the distillation chamber through a corrosion-resistant and high-temperature-resistant guide tube.

9. The apparatus according to claim 8, characterized in that, The device also includes a vacuum adjustment device for adjusting the pressure difference between the distillation chamber and the electrolytic cell.

10. The apparatus according to claim 8, characterized in that, The flow guide is a silicon nitride ceramic flow guide.

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