An apparatus and method for co-production of high purity magnesium oxide and metallic magnesium

Abstract

The application provides a device and a method for co-production of high-purity magnesium oxide and metal magnesium. The method comprises: subjecting low-hydrated magnesium chloride to a first pyrolysis reaction to generate crude magnesium oxide and a first pyrolysis tail gas; purifying the crude magnesium oxide to obtain a high-purity magnesium oxide product; converting hydrogen chloride gas in the first pyrolysis tail gas into concentrated hydrochloric acid; subjecting the low-hydrated magnesium chloride and / or bischofite to a complexation reaction with the concentrated hydrochloric acid to generate a complex; subjecting the complex to a second pyrolysis reaction to generate electrolytic-grade anhydrous magnesium chloride and a second pyrolysis tail gas; and using the electrolytic-grade anhydrous magnesium chloride to perform electrolysis to obtain a metal magnesium product and chlorine. The method provided by the application can significantly reduce energy consumption by preparing electrolytic-grade anhydrous magnesium chloride through a hydrochloric acid complex pyrolysis method; and while realizing co-production of high-purity magnesium oxide and metal magnesium, the method also realizes internal circulation of chlorine elements.

Description

Technical Field

[0001] This invention belongs to the field of salt lake resource utilization technology, specifically relating to an apparatus and method for co-producing high-purity magnesium oxide and metallic magnesium. Background Technology

[0002] In the process of extracting potassium and lithium from salt lakes, approximately 10 tons of magnesium chloride hydrate (MgCl2·6H2O) are generated for every ton of potassium fertilizer produced. Due to technological limitations, the comprehensive utilization rate of magnesium resources in salt lakes has long been less than 2%, and large quantities of magnesium chloride hydrate are stockpiled in the form of "magnesium hazard," causing serious resource waste and environmental pollution. Existing single-product routes that only produce magnesium oxide or only produce metallic magnesium cannot achieve the high-value tiered utilization of magnesium, let alone incorporate chlorine into the circular economy system.

[0003] Secondly, in the preparation of magnesium oxide, the traditional pyrolysis process of magnesium chloride has problems such as high pyrolysis temperature (usually above 900℃), easy overburning of products, and low purity (mostly below 95%). Meanwhile, existing metallic magnesium electrolysis processes generally use diaphragm-less molten salt electrolytic cells. The chlorine gas produced at the anode and the liquid metallic magnesium produced at the cathode contact in the same electrolysis chamber, undergoing a reverse reaction to produce magnesium chloride. This results in low current efficiency (e.g., only 75%~80%), low metallic magnesium purity (e.g., only 98.5%~99.0%), and a high risk of chlorine leakage, causing serious environmental pollution. Graphite anodes are consumed quickly, have a short lifespan, and emit greenhouse gases such as carbon dioxide and carbon tetrafluoride. In existing technologies, magnesium oxide production and metallic magnesium production operate independently. The hydrogen chloride in the pyrolysis tail gas and the chlorine gas produced as a byproduct of electrolysis are not utilized synergistically. Chlorine cannot circulate within the system, requiring the purchase of hydrochloric acid for magnesium chloride solution preparation. Simultaneously, chlorine gas is either discharged externally or treated inefficiently, increasing production costs and environmental burden. Summary of the Invention

[0004] To solve all or part of the above-mentioned technical problems, the present invention provides the following technical solutions: A first aspect of the present invention provides a method for co-producing high-purity magnesium oxide and metallic magnesium, comprising: Step A: Allow low-hydrated magnesium chloride to undergo the first pyrolysis reaction to produce crude magnesium oxide and the first pyrolysis tail gas; Step B: Purify the crude magnesium oxide to obtain a high-purity magnesium oxide product; Step C: Convert the hydrogen chloride gas in the first pyrolysis tail gas into concentrated hydrochloric acid; Step D: Perform a complexation reaction between low-hydrated magnesium chloride and / or magnesium chloride hydrate and the concentrated hydrochloric acid obtained in step C to generate a complex, wherein the chemical formula of the complex is MgCl2·xHCl·yH2O, x=0.5~2, y=1~4; Step E: The complex is subjected to a second pyrolysis reaction to generate electrolytic-grade anhydrous magnesium chloride and a second pyrolysis tail gas; Step F: Electrolysis is performed using the electrolytic-grade anhydrous magnesium chloride to produce metallic magnesium and chlorine gas.

[0005] In existing technologies, the magnesium oxide preparation route and the metallic magnesium electrolysis route operate independently. Magnesium chloride can only be converted into either magnesium oxide or metallic magnesium, failing to achieve the cascade utilization of the same raw material. The method provided by this invention uses low-hydrated magnesium chloride as raw material to simultaneously produce two high-value products: high-purity magnesium oxide and high-quality metallic magnesium. This increases the comprehensive utilization rate of magnesium resources by more than 30% compared to single-product routes. In some embodiments, the purity of high-purity magnesium oxide can reach over 98%, and the purity of metallic magnesium can reach over 99.5%.

[0006] The method provided by this invention reacts low-hydrated magnesium chloride with concentrated hydrochloric acid to form a complex. Due to the weak bond between HCl and MgCl2 in the complex, the second pyrolysis reaction can be carried out at low temperatures. Compared with the existing technology where deep dehydration of electrolytic-grade anhydrous magnesium chloride requires high temperatures of 400℃~600℃, this method significantly reduces energy consumption. The concentrated hydrochloric acid required for the complexation reaction comes from hydrogen chloride in the tail gas of the first pyrolysis, realizing the internal circulation of hydrogen chloride.

[0007] In some embodiments, the low-hydrated magnesium chloride used in steps A and D is obtained from magnesium chloride hydrate, a byproduct of salt lakes, through pre-dehydration.

[0008] In some embodiments, step A specifically includes: causing low-hydrated magnesium chloride to undergo the first pyrolysis reaction in a fluidized state, wherein the temperature of the first pyrolysis reaction is 600℃~900℃, preferably 650℃~800℃.

[0009] In some embodiments, step B specifically includes: sequentially washing, filtering, drying, and classifying the crude magnesium oxide to obtain the high-purity magnesium oxide product. The obtained high-purity magnesium oxide product has a purity of over 98%, a particle size D50 of 5μm~50μm, and a specific surface area of ​​10m². 2 / g~50m 2 / g.

[0010] In some embodiments, step C specifically includes: using deionized water to absorb hydrogen chloride gas in the first pyrolysis tail gas in multiple stages to obtain concentrated hydrochloric acid with a concentration of more than 35 wt%.

[0011] In some embodiments, step D includes: mixing low-hydrated magnesium chloride and / or magnesium chloride hydrate with concentrated hydrochloric acid, wherein the amount of concentrated hydrochloric acid is such that the molar ratio of chloride ions to magnesium ions is 4:1 or higher, and carrying out a complexation reaction at 80°C to 120°C.

[0012] In some embodiments, step D specifically includes: mixing low-hydrated magnesium chloride and / or magnesium chloride hydrate with concentrated hydrochloric acid at a solid-liquid mass ratio of 1:1.5 to 1:3, and reacting at 80°C to 120°C for 1 to 2 hours to form the complex; and the amount of concentrated hydrochloric acid used is such that the molar ratio of all chloride ions to magnesium ions in the reaction system is 4:1 or higher.

[0013] In some embodiments, step E specifically includes: subjecting the complex to the second pyrolysis reaction at 200°C to 300°C for 1 to 2 hours.

[0014] In some embodiments, step F specifically includes: mixing the electrolytic-grade anhydrous magnesium chloride with a flux to prepare a molten salt electrolyte, and performing the electrolysis in a diaphragm electrolytic cell.

[0015] In existing diaphragm-less magnesium electrolysis technology, there is no physical isolation device between the anode and cathode chambers. Chlorine gas evolved at the anode comes into contact with liquid magnesium metal generated at the cathode within the electrolytic cell, resulting in a reverse reaction (Mg + Cl2 → MgCl2). This leads to a current efficiency typically of only 75%–80% and a magnesium metal purity typically of only 98.5%–99.0%. The method provided by this invention uses a diaphragm-type electrolytic cell, completely isolating chlorine gas from liquid magnesium metal and eliminating the reverse reaction. The electrolysis method of this invention can increase the current efficiency to over 85%, the magnesium metal purity to over 99.5%, and the purity of the collected chlorine gas at the anode from 70%–85% to over 95%, facilitating subsequent resource utilization.

[0016] Furthermore, in existing diaphragm-less magnesium electrolysis technology, chlorine gas is prone to leakage if the seal is not tight, causing serious environmental pollution and safety risks. For example, graphite anodes are consumed quickly in a Cl2 atmosphere, with a lifespan of about 6 months, and emit greenhouse gases such as CO2 and CF4. Diaphragm electrolyzers can confine the chlorine gas produced at the anode to the anode chamber, and can collect it in a sealed manner using devices such as chlorine gas collection hoods, effectively eliminating the risk of chlorine gas leakage. At the same time, all the collected high-purity chlorine gas is utilized as a resource, achieving zero chlorine emissions. In addition, inert anodes can be used instead of graphite anodes, avoiding greenhouse gas emissions, making the entire process environmentally friendly.

[0017] In some embodiments, the molten salt electrolyte comprises, by mass percentage, 15wt% to 30wt% of electrolytic-grade anhydrous magnesium chloride, 30wt% to 50wt% of KCl, 20wt% to 40wt% of NaCl, and 0wt% to 15wt% of CaCl2.

[0018] In some embodiments, the molten salt electrolyte further includes a composite additive comprising lithium fluoride and nano-cerium oxide, wherein the amounts of lithium fluoride and nano-cerium oxide are 2wt%~5wt% and 0.1wt%~0.5wt% of the mass of electrolytic-grade anhydrous magnesium chloride, respectively. The composite additive can improve the ionic conductivity of the molten salt and the surface activity of the electrode.

[0019] In some embodiments, the electrolysis is performed using a combination of pulsed current and gradient temperature control. Specifically, this includes: first, placing the flux in a diaphragm electrolytic cell; then, adding the electrolytic-grade anhydrous magnesium chloride at a temperature of 400°C to 500°C to form a molten salt electrolyte; and continuing to raise the temperature to an electrolysis temperature of 650°C to 800°C; and during the electrolysis process, applying a pulsed current with a duty cycle of 10% to 50%, a pulse frequency of 50Hz to 500Hz, and a cathode current density of 0.5A / cm². 2 ~2.0A / cm 2 The electrolysis time is 3-5 hours. The preferred cathode current density is 1.0 A / cm². 2 ~1.5A / cm 2 Using pulsed current can stabilize the electrolysis process, homogenize the temperature field, and suppress side reactions.

[0020] In some embodiments, the method further includes step G: collecting hydrogen chloride from the second pyrolysis tail gas of step E and / or chlorine gas generated in step F, and recycling the hydrogen chloride and / or chlorine gas.

[0021] In some embodiments, the recycling of hydrogen chloride includes: absorbing the hydrogen chloride in the second pyrolysis tail gas into concentrated hydrochloric acid and reusing it in the complexation reaction.

[0022] In some embodiments, the recycling of chlorine includes: using chlorine as a protective gas in the second pyrolysis reaction to prepare magnesium chloride pre-dehydration and / or complexes; and / or using chlorine to prepare hydrochloric acid, which is used for the absorption of the first pyrolysis tail gas; and / or using chlorine to produce chlorinated products.

[0023] In existing processes where magnesium oxide and metallic magnesium operate independently, hydrochloric acid, a byproduct of magnesium oxide pyrolysis, is typically sold as a byproduct, while chlorine, a byproduct of metallic magnesium electrolysis, is usually directly discharged or treated with simple alkaline absorption. Chlorine flows unidirectionally between the two independent systems, failing to form a closed-loop cycle. However, the method for co-producing high-purity magnesium oxide and metallic magnesium provided by this invention can construct a fully closed-loop internal chlorine cycle. Specifically, it establishes a complete chlorine internal circulation system: "hydrated magnesium chloride → low-hydrated magnesium chloride → fluidized bed pyrolysis (first pyrolysis reaction) → hydrochloric acid → complex → electrolytic-grade magnesium chloride → electrolysis → chlorine → reuse," achieving a comprehensive chlorine recycling rate of over 90%.

[0024] The method provided by this invention can significantly reduce overall energy consumption and production costs through multi-step synergy. Specifically, the fluidized bed pyrolysis temperature (first pyrolysis temperature) can be controlled at 600~900℃, which is 100~300℃ lower than existing fixed bed pyrolysis; the complex pyrolysis method for preparing anhydrous magnesium chloride reduces the temperature by 200~300℃ compared to existing deep dehydration methods; the diaphragm electrolysis technology can reduce the DC power consumption per ton of magnesium to below 12,000 kWh, which is more than 11% lower than existing diaphragmless electrolysis (approximately 13,500 kWh / t-Mg); and the cost of purchased hydrochloric acid and chlorine is reduced through internal chlorine recycling. Overall, this invention reduces the comprehensive production cost by approximately 20% compared to existing single-product routes.

[0025] A second aspect of the present invention provides an apparatus for the co-production of high-purity magnesium oxide and metallic magnesium, comprising: The fluidized bed pyrolysis unit includes a first fluidized bed pyrolysis furnace, a gas-solid separation mechanism, a cooling mechanism, and a tail gas absorption mechanism; The complexation reaction and pyrolysis unit, which is connected to the fluidized bed pyrolysis unit, includes a closed complexation reactor, a second fluidized bed pyrolysis furnace, and an HCl recovery mechanism; A diaphragm electrolysis unit, which is connected to a complexation reaction and pyrolysis unit, includes a diaphragm electrolytic cell.

[0026] In some embodiments, the apparatus further includes a low-hydrate magnesium chloride preparation unit for converting magnesium chloride hydrate into low-hydrate magnesium chloride, which includes a filtration mechanism, an evaporation crystallization mechanism, and a pre-dehydration mechanism connected in sequence.

[0027] In some embodiments, the gas-solid separation mechanism includes a two-stage cyclone separator and an electrostatic precipitator.

[0028] In some embodiments, the exhaust gas absorption mechanism is a three-stage packed absorption tower.

[0029] In some embodiments, the diaphragm electrolyzer includes an anode chamber, a cathode chamber, and an ion-selective diaphragm disposed between the anode chamber and the cathode chamber.

[0030] The ion-selective membrane can be selected from cation exchange membranes (such as Nafion series membranes), anion exchange membranes, ceramic membranes (such as ZrO2 or Al2O3 porous membranes with a porosity of 30%~60% and an average pore size of 0.1μm~10μm), or composite membranes. A cation exchange membrane is preferred, which allows Mg... 2+ Migration from the anode chamber to the cathode chamber, while preventing Cl from... -The reverse migration from the cathode chamber to the anode chamber completely isolates the anode and cathode reaction zones. The anode in the anode chamber can be an inert metal anode (such as a SnO2-Sb2O3-CeO2 composite anode, a platinum-plated titanium anode, or a vanadium-aluminum alloy anode) or a graphite anode. The cathode in the cathode chamber can be a stainless steel plate, a molybdenum plate, or a tungsten plate; the cathode surface can be coated with a MoSi2 coating to improve corrosion resistance.

[0031] In some embodiments, the diaphragm electrolysis unit further includes an anode chlorine collection mechanism and a cathode magnesium metal collection mechanism. For example, a chlorine collection hood can be installed at the top of the anode chamber of the diaphragm electrolysis cell, and the chlorine collection hood is connected to a chlorine delivery pipeline; a magnesium liquid siphon and a magnesium collection chamber are installed in the cathode chamber. The liquid magnesium metal generated by electrolysis floats to the magnesium collection chamber because its density is lower than that of molten salt, and is extracted periodically or continuously through the siphon.

[0032] In some embodiments, the device further includes a chlorine recycling unit connected to the diaphragm electrolysis unit, which includes a chlorine compression mechanism, a chlorine storage tank, and a hydrogen chloride synthesis mechanism.

[0033] In some embodiments, the device may further include an automated control unit for controlling the material flow rate, temperature, and pressure parameters among the aforementioned units, thereby enabling coordinated operation among the units of the device.

[0034] A third aspect of the present invention provides a method for co-producing high-purity magnesium oxide and metallic magnesium, which employs the apparatus described in any of the above-mentioned technical solutions, comprising: Low-hydrated magnesium chloride is fed into a first fluidized bed pyrolysis furnace for a first pyrolysis reaction. The resulting gas-solid mixture is then separated in the gas-solid separation mechanism to obtain crude magnesium oxide and first pyrolysis tail gas. The crude magnesium oxide is then cooled and purified by a cooling mechanism to obtain a high-purity magnesium oxide product. The first pyrolysis tail gas is then fed into the tail gas absorption mechanism to obtain concentrated hydrochloric acid. The obtained concentrated hydrochloric acid is fed into the closed complex reactor, and low-hydrated magnesium chloride and / or magnesium chloride hydrate are added to carry out a complexation reaction to obtain a complex with the chemical formula MgCl2·xHCl·yH2O, where x=0.5~2 and y=1~4. The complex is then subjected to a second pyrolysis reaction in a second fluidized bed pyrolysis furnace to generate electrolytic-grade anhydrous magnesium chloride and a second pyrolysis tail gas. The second pyrolysis tail gas enters the HCl recovery unit to form concentrated hydrochloric acid, and the recovered concentrated hydrochloric acid is reused in the complexation reaction. The anhydrous magnesium chloride of the electrolytic grade is fed into a diaphragm electrolytic cell for electrolysis to produce metallic magnesium and chlorine gas.

[0035] In some embodiments, the method further includes: sequentially removing impurities from the salt lake byproduct magnesium chloride, evaporating and crystallizing it, and pre-dehydrating it to obtain low-hydrated magnesium chloride with a water content in the range of 1 to 3 parts water of crystallization. The pre-dehydration can be carried out in a protective atmosphere with a hydrogen chloride volume concentration of 5% to 20%.

[0036] For example, magnesium chloride hydrate (MgCl2·6H2O, purity ≥99%), a byproduct of potassium and lithium extraction from salt lakes, is dissolved in deionized water. After filtration to remove mechanical impurities and insoluble matter, it is evaporated and crystallized to obtain pure magnesium chloride hydrate crystals. The magnesium chloride hydrate crystals are then fed into a pre-dehydration device (e.g., a rotary kiln, fluidized bed dehydrator, or microwave dehydration device) and pre-dehydrated at 150℃~250℃ in a protective atmosphere containing hydrogen chloride (HCl volume concentration 5%~20%) for 2~6 hours. During the pre-dehydration process, magnesium chloride hydrate loses some of its water of crystallization, transforming into low-hydrated magnesium chloride (MgCl2·nH2O, n=1~3), with the water content controlled within the range of 1~3 parts water of crystallization. Dehydration is performed using a protective gas containing hydrogen chloride, which inhibits the hydrolysis reaction of magnesium chloride. In an HCl atmosphere, the equilibrium of the magnesium chloride hydrolysis reaction shifts to the left, thereby reducing the formation of impurities such as magnesium oxide and basic magnesium chloride, and improving the purity of low-hydrate magnesium chloride. The pre-dehydrated low-hydrate magnesium chloride is then crushed and sieved for later use.

[0037] In some embodiments, the method specifically includes: continuously feeding the obtained low-hydrate magnesium chloride solid material into a fluidized bed pyrolysis unit via a screw feeder. The bottom of the first fluidized bed pyrolysis furnace is equipped with an air distribution plate. Preheated fluidizing medium (which can be hot nitrogen or superheated steam, with the temperature controlled at 700℃~900℃) enters the furnace from below the air distribution plate, causing the low-hydrate magnesium chloride solid material to be in a boiling fluidized state within the furnace. The furnace body of the first fluidized bed pyrolysis furnace is equipped with a heating device (e.g., electric heating or gas heating) to maintain the pyrolysis temperature within the furnace in the range of 600℃~900℃, preferably 650℃~800℃, so that the low-hydrate magnesium chloride rapidly undergoes a pyrolysis reaction in a fluidized state. The reaction equation is: MgCl2·nH2O → MgO + 2HCl↑ + (n-1)H2O↑ The residence time of the material in the first fluidized bed pyrolysis furnace can be controlled within 10-30 minutes to ensure the full progress of the first pyrolysis reaction. The pyrolysis tail gas containing coarse magnesium oxide powder is discharged from the top of the first fluidized bed pyrolysis furnace and enters a two-stage cyclone separator and electrostatic precipitator for gas-solid separation. The collected solid is coarse magnesium oxide powder, containing a small amount of undecomposed magnesium chloride and impurities. After gas-solid separation, the main components of the pyrolysis tail gas are HCl, H2O, and fluidizing medium gas (N2 or water vapor).

[0038] In some implementations, the crude magnesium oxide powder is cooled and then fed into a washing tank, where it is washed with deionized water to remove soluble chlorides. After filtration by a plate and frame filter press, drying in a flash dryer, and classification by an air classifier, a high-purity magnesium oxide product is obtained. This high-purity magnesium oxide product has a purity of over 98%, a particle size D50 of 5μm~50μm, and a specific surface area of ​​10m². 2 / g~50m 2 / g.

[0039] In some embodiments, the first pyrolysis tail gas after gas-solid separation is fed into a three-stage packed absorber, where deionized water is used to absorb hydrogen chloride gas from the first pyrolysis tail gas in a countercurrent manner. The operating conditions of the three-stage packed absorber can be: absorption temperature 30℃~50℃, liquid-to-gas ratio 2~5 L / m³. 3 After three stages of absorption, the absorption rate of hydrogen chloride can reach over 99%, yielding industrial concentrated hydrochloric acid with a concentration of over 35 wt%. The exhaust gas discharged from the top of the absorption tower (mainly fluidized medium gas, such as N2) is heated by a heat exchanger and then returned to the fluidized bed pyrolysis furnace for recycling, realizing the recycling of the fluidized medium.

[0040] In some embodiments, the complexation reaction specifically includes: adding low-hydrated magnesium chloride or magnesium chloride hydrate and concentrated hydrochloric acid (concentration above 35%) to a closed complexation reactor equipped with stirring and reflux condensation at a solid-liquid mass ratio of 1:1.5 to 1:3, wherein the amount of concentrated hydrochloric acid is sufficient to ensure Cl - With Mg 2+ The molar ratio of the components is greater than 4:1 to promote the formation of the complex; the reaction is carried out by stirring at 80℃~120℃ for 1~2 hours to proceed with the complexation reaction. The complexation reaction equation is: MgCl2·nH2O + xHCl → MgCl2·xHCl·yH2O + (ny)H2O↑ Where x = 0.5~2, y = 1~4.

[0041] The resulting complex is a white crystalline or semi-solid substance. The water vapor released during the reaction is condensed and discharged after being condensed by a condenser, and the HCl gas is basically not lost due to condensation and reflux.

[0042] In some embodiments, the second pyrolysis reaction specifically includes: transferring the complex solid to a second fluidized bed pyrolysis furnace, and carrying out the second pyrolysis reaction at a temperature of 200°C to 300°C for 1 to 2 hours. The second pyrolysis reaction is as follows: MgCl2·xHCl·yH2O → MgCl2+ xHCl↑ + yH2O↑ Because HCl and MgCl2 are weakly bonded in the complex, the second pyrolysis temperature is significantly lower than that of traditional deep dehydration (400℃~600℃). The exhaust gas produced by pyrolysis is a mixture of HCl and H2O. After cooling to room temperature, the HCl is absorbed by the condensate to form concentrated hydrochloric acid (concentration can reach over 35%). This hydrochloric acid can be directly recycled in the complexation reaction step, realizing the recycling of HCl. The remaining uncondensed HCl gas can be dried and used as a protective gas in other processes, or combined with electrolytic chlorine gas for treatment. The solid product after pyrolysis is electrolytic-grade anhydrous magnesium chloride, with a purity of over 99.5% and a water content of less than 0.1%.

[0043] The complexation pathway enables internal chlorine recycling, with HCl circulating in a closed loop of "complexation-pyrolysis-absorption-recomplexation." The initially added concentrated hydrochloric acid can be reused repeatedly, requiring only periodic replenishment of small amounts of HCl lost due to operational losses. The high-concentration hydrochloric acid obtained from the absorption of pyrolysis tail gas fully meets the acid concentration requirements of the complexation reaction, eliminating the need for additional concentration. This pathway complements the hydrogen chloride produced from the first pyrolysis tail gas and the chlorine produced by electrolysis: the hydrogen chloride from the first pyrolysis tail gas can be used to prepare concentrated hydrochloric acid for the complexation reaction; the electrolyzed chlorine can be used to synthesize HCl to compensate for system losses.

[0044] In some embodiments, the electrolysis includes: adding molten salt electrolyte into a diaphragm electrolytic cell and heating it to 650°C~800°C (preferably 680°C~750°C) to completely melt the molten salt.

[0045] In some embodiments, the electrolysis is performed using a combination of pulsed current and gradient temperature control. Specifically, this includes: first, heating to 400℃~500℃ and adding electrolytic-grade anhydrous magnesium chloride, stirring while heating until completely dissolved to form a molten salt reaction system, and then continuing to heat to an electrolysis temperature of 650℃~800℃; during the electrolysis process, the applied pulsed current duty cycle is 10%~50%, the pulse frequency is 50Hz~500Hz, and the cathode current density is controlled at 0.5A / cm. 2 ~2.0A / cm 2 Preferred 1.0A / cm 2 ~1.5A / cm 2 The electrolysis time is 3 to 5 hours.

[0046] Under the influence of an electric field, an oxidation reaction occurs in the anode chamber, with the following reaction equation: 2Cl - - 2e - → Cl2↑, the generated chlorine gas can escape and be collected from the chlorine gas collection hood at the top of the anode chamber. A reduction reaction occurs in the cathode chamber, the reaction formula is: Mg²⁺ + + 2e -→Mg(l), the generated liquid magnesium metal automatically floats above the molten salt surface because its density (about 1.58 g / cm³) is lower than that of the molten salt electrolyte (about 1.65~1.75 g / cm³). It can be continuously or periodically drawn into the magnesium collection chamber through the magnesium liquid siphon pipe at the top of the cathode chamber. After cooling and casting, a high-quality magnesium metal product is obtained.

[0047] Thanks to the physical isolation of the anode and cathode chambers by the diaphragm and its ion-selective permeability, the chlorine gas generated at the anode and the liquid magnesium metal generated at the cathode are completely prevented from contacting, thus eliminating the reverse reaction (Mg + Cl2 → MgCl2). Therefore, this process can obtain high-quality magnesium metal with a purity of over 99.5%, a current efficiency of over 85%, and a DC power consumption of less than 12,000 kWh per ton of magnesium. The chlorine gas collected in the anode chamber can achieve a purity of over 95%.

[0048] In some embodiments, the method further includes passing the chlorine gas generated by electrolysis into a chlorine gas recycling unit, where it can be recycled after treatment. After compression and freeze-drying to remove moisture and trace impurities, the chlorine gas can be used to synthesize HCl and then reused in the preparation process of electrolytic-grade anhydrous magnesium chloride, or it can be directly used as the dehydration protective gas required for the preparation of low-hydrated magnesium chloride from magnesium chloride in the step of hydrated magnesium chloride, thus realizing the internal recycling of chlorine.

[0049] Compared with existing technologies, the present invention has at least some or all of the following beneficial effects: The method provided by the present invention achieves the co-production of high-purity magnesium oxide and metallic magnesium, while also realizing the recycling of chlorine, solving the technical problems of the existing technology where the two routes are mutually exclusive, resource utilization is low, and chlorine cannot be recycled. Furthermore, the present invention prepares electrolytic-grade anhydrous magnesium chloride through the hydrochloric acid complex pyrolysis method, requiring a lower pyrolysis temperature, which reduces energy consumption, and achieves the tiered high-value utilization of magnesium resources. Attached Figure Description

[0050] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0051] Figure 1 This is a schematic flowchart of the method for co-producing high-purity magnesium oxide and metallic magnesium in Example 1. Detailed Implementation

[0052] The invention will be more fully understood through the following detailed description of its embodiments. The detailed embodiments disclosed herein are merely illustrative, and the invention may be embodied in various forms. Therefore, the specific functional details disclosed herein should not be construed as limiting, but rather as the basis for the claims.

[0053] In addition, unless otherwise specified, all raw materials used in the following embodiments can be purchased from the market or other sources, and all production and testing equipment used are known in the art, as are the testing methods used.

[0054] Example 1 This embodiment provides an apparatus for the co-production of high-purity magnesium oxide and metallic magnesium, comprising: A low-hydrate magnesium chloride preparation unit is used to convert magnesium chloride hydrate into low-hydrate magnesium chloride. It includes a filtration mechanism, an evaporation crystallization mechanism and a pre-dehydration mechanism connected in sequence. The fluidized bed pyrolysis unit includes a first fluidized bed pyrolysis furnace, a gas-solid separation mechanism, a cooling mechanism, and a tail gas absorption mechanism; The complexation reaction and pyrolysis unit, which is connected to the fluidized bed pyrolysis unit, includes a closed complexation reactor, a second fluidized bed pyrolysis furnace, and an HCl recovery mechanism; A diaphragm electrolysis unit, which is connected to a complexation reaction and pyrolysis unit, including a diaphragm electrolytic cell; The chlorine recycling unit, which is connected to the diaphragm electrolysis unit, includes a chlorine compression mechanism, a chlorine storage tank, and a hydrogen chloride synthesis mechanism.

[0055] The gas-solid separation mechanism in the fluidized bed pyrolysis unit includes a two-stage cyclone separator and an electrostatic precipitator; the tail gas absorption mechanism is a three-stage packed absorption tower.

[0056] A diaphragm electrolyzer includes an anode chamber, a cathode chamber, and an ion-selective diaphragm disposed between the anode and cathode chambers. The diaphragm electrolyzer structure used in this embodiment features a Nafion 117 cation exchange membrane between the anode and cathode chambers; the anode is a SnO2-Sb2O3-CeO2 inert anode (mass ratio 88:6:6), and the cathode is a stainless steel plate (coated with a MoSi2 layer). In this embodiment, a chlorine gas collection hood is also installed at the top of the anode chamber, connected to a chlorine gas delivery pipeline; a magnesium liquid siphon and a magnesium collection chamber are also provided in the cathode chamber. The liquid metallic magnesium generated during electrolysis floats to the magnesium collection chamber due to its lower density than molten salt and is extracted through the siphon.

[0057] This embodiment also provides a method for co-producing high-purity magnesium oxide and metallic magnesium, which is implemented using the above-described apparatus. Figure 1 This is a flowchart illustrating the method provided in this embodiment, which specifically includes the following steps: S1: Preparation of low-hydrated magnesium chloride Magnesium chloride hydrous mineral (MgCl2·6H2O, purity 99.2%), a byproduct of potash fertilizer production in the Qarhan Salt Lake of Qinghai Province, was dissolved in deionized water. Mechanical impurities and insoluble matter were removed by filtration, and the solution was evaporated and crystallized to obtain pure magnesium chloride hydrous mineral crystals. These crystals were then fed into a rotary kiln and pre-dehydrated at 200°C for 4 hours under a nitrogen protective atmosphere containing 10% HCl, yielding low-hydrated magnesium chloride MgCl2·xH2O. Testing revealed that the product contained 98.5% MgCl2 (anhydrous) and approximately 18 wt% water (corresponding to approximately 1.2 molecules of water of crystallization).

[0058] S2: Preparation of high-purity magnesium oxide The low-hydrated magnesium chloride obtained in step S1 is crushed and sieved to a particle size of 0.1~0.5mm, and continuously fed into a fluidized bed pyrolysis furnace (furnace inner diameter 0.5m, height 3m) via a screw feeder. Nitrogen gas preheated to 750℃ is used as the fluidizing medium, and the pyrolysis temperature in the furnace is controlled at 750℃ with a material residence time of 15 minutes. The pyrolysis generates pyrolysis tail gas containing coarse magnesium oxide powder.

[0059] The pyrolysis tail gas containing coarse magnesium oxide powder is discharged from the top of the furnace and sequentially enters a two-stage cyclone separator and an electrostatic precipitator for gas-solid separation. The collected coarse magnesium oxide powder is washed with water to remove soluble chlorides, and then subjected to plate and frame filter press, flash drying (105℃), and air classification to obtain high-purity magnesium oxide product. Testing showed that the high-purity magnesium oxide obtained in this example had a purity of 98.6 wt%, a particle size D50 of 12 μm, and a specific surface area of ​​38.5 m². 2 / g.

[0060] The pyrolysis tail gas after gas-solid separation enters a three-stage packed absorption tower, where it is absorbed countercurrently with deionized water at an absorption temperature of 40°C, a liquid-to-gas ratio of 3 L / m³, and an absorption rate of 99.2%, yielding industrial concentrated hydrochloric acid with a concentration of 35.2 wt%. The nitrogen gas discharged from the top of the absorption tower is heated to 700°C by a heat exchanger and then returned to the fluidized bed pyrolysis furnace for recycling.

[0061] S3: Preparation of electrolytic-grade anhydrous magnesium chloride (hydrochloric acid complex pyrolysis method) Take 100 kg of the low-hydrated magnesium chloride prepared in step S1 and add it to a closed complexing reactor equipped with stirring and reflux condensation. Then add 200 L of industrial concentrated hydrochloric acid (35.2 wt%) prepared in step S2. The solid-liquid mass ratio of low-hydrated magnesium chloride to concentrated hydrochloric acid is 1:1.7. The Cl in the reactor... - With Mg 2+ The molar ratio is 4.2:1. Heating to 100℃ and stirring for 1.5 hours produces a white, semi-solid complex with the chemical formula MgCl₂·xHCl·yH₂O (x≈1.2, y≈2.5). During the reaction, water vapor is discharged through a condenser, and HCl is refluxed.

[0062] The complex was transferred to a fluidized bed pyrolysis furnace and pyrolyzed at 250°C for 1.5 hours to decompose the complex and obtain solid electrolytic-grade anhydrous magnesium chloride (purity 99.6 wt%, water content 0.08 wt%, MgO content 0.2 wt%). The pyrolysis tail gas was cooled to room temperature by a water-cooled jacket, and HCl was absorbed by the condensate to form concentrated hydrochloric acid (about 35%), which was directly recycled for the next batch of complexation reaction.

[0063] S4: Preparation of high-quality metallic magnesium by membrane electrolysis Take 20 kg of electrolytic-grade anhydrous magnesium chloride prepared in step S3, mix it with 45 kg of KCl, 25 kg of NaCl, and 10 kg of CaCl2, then add 0.6 kg (3 wt% of the mass of electrolytic-grade anhydrous magnesium chloride) of LiF and 0.06 kg (0.3 wt% of the mass of electrolytic-grade anhydrous magnesium chloride) of nano CeO2, mix them evenly to obtain molten salt electrolyte, add it to a diaphragm electrolytic cell, heat it to 700℃ to completely melt the molten salt electrolyte, and use pulse current electrolysis: duty cycle 30%, frequency 200 Hz, cathode current density 1.2 A / cm², electrolysis time 4 hours.

[0064] Chlorine gas (96.5% purity) is generated in the anode chamber and collected by the top chlorine gas collection hood; liquid magnesium is generated in the cathode chamber, floats to the surface, and is then drawn into the magnesium collection chamber through a siphon. After cooling, it is cast into an ingot to obtain 6.2 kg of magnesium. The magnesium purity is 99.6 wt%, the current efficiency is 88.6%, and the DC power consumption per ton of magnesium is 11,200 kWh.

[0065] S5: Chlorine recycling The chlorine gas collected in step S4 is mixed with hydrogen gas at a volume ratio of 1:1.05 and fed into a hydrogen chloride synthesis furnace to produce HCl. This HCl gas is then mixed with nitrogen gas to prepare a mixed gas containing 10% HCl, which is returned to step S1 as a dehydration protective gas. The remaining chlorine gas is directly fed into the tail gas absorption system of the complexing reactor in step S3 to replenish the HCl loss. The calculated overall chlorine recycling rate is 92.5%.

[0066] Example 2 Example 2 is basically the same as Example 1, except that the following process conditions are slightly different: In step S2: the pyrolysis temperature in the furnace is controlled at 650℃, and the material residence time is 25 minutes; the liquid-to-gas ratio of the three-stage packed absorption tower is adjusted to 5 L / m³, and the absorption temperature is 30℃. The high-purity magnesium oxide obtained in Example 2 has a purity of 98.2 wt%, a particle size D50 of 18 μm, and a specific surface area of ​​28.6 m². 2 / g; The concentration of industrial concentrated hydrochloric acid obtained in step S2 is 36wt%.

[0067] In step S3: 31.5 wt% industrial concentrated hydrochloric acid was used for the complexation reaction, with the solid-liquid mass ratio adjusted to 1:2.5, the reaction temperature at 120℃, and the reaction time at 2 hours. The electrolytic-grade anhydrous magnesium chloride produced after the pyrolysis of the complex had a purity of 99.5 wt%, a water content of 0.12 wt%, and an MgO content of 0.35 wt%.

[0068] In step S4: the electrolysis temperature is adjusted to 650℃, the cathode current density is 0.8 A / cm², the pulse current duty cycle is 20%, and the frequency is 100Hz. The magnesium metal obtained by electrolysis has a purity of 99.5wt%, a current efficiency of 85.2%, and a DC power consumption of 11,800 kWh per ton of magnesium; the chlorine gas purity is 95.2%.

[0069] As in Example 1, chlorine was reused, and the overall chlorine recycling rate was 90.5%.

[0070] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0071] Example 3 Example 3 is basically the same as Example 1, except that the following process conditions are slightly different: In step S3: the complex is pyrolyzed at 200℃ for 2 hours. The resulting electrolytic-grade anhydrous magnesium chloride has a purity of 99.4 wt%, a water content of 0.15 wt%, and an MgO content of 0.4 wt%. The concentrated hydrochloric acid obtained from the absorption of the pyrolysis tail gas has a concentration of 32.5 wt%.

[0072] In step S4: the amount of LiF added was 2 wt% (0.4 kg) of the mass of anhydrous MgCl2, and the amount of CeO2 added was 0.1 wt% (0.02 kg); the electrolysis temperature was 720℃, the cathode current density was 1.5 A / cm², the pulse current duty cycle was 50%, and the frequency was 500 Hz. The magnesium metal obtained by electrolysis had a purity of 99.5 wt%, a current efficiency of 85.8%, and a DC power consumption of 11,600 kWh per ton of magnesium; the chlorine gas purity was 95.5%.

[0073] As in Example 1, chlorine was reused, and the overall chlorine recycling rate was 91.2%.

[0074] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0075] Example 4 Example 4 is basically the same as Example 1, except that the following process conditions are slightly different: In step S1: the pre-dehydration temperature of magnesium chloride is 250℃, the pre-dehydration time is 3 hours, the HCl concentration in the protective gas is 5%, and the resulting low-hydrated magnesium chloride is MgCl2·1.5H2O with a water content of about 12wt%.

[0076] In step S4: No LiF or CeO2 is added to the molten salt electrolyte; the diaphragm in the diaphragm electrolyzer is a ceramic diaphragm (ZrO2 porous membrane, porosity 45%, average pore size 0.5 μm). The electrolysis temperature is 750℃, the cathode current density is 1.8 A / cm², the pulse current duty cycle is 40%, and the frequency is 300 Hz. The purity of the magnesium obtained by electrolysis is 99.5 wt%, the current efficiency is 86.1%, and the DC power consumption per ton of magnesium is 11,500 kWh; the chlorine purity is 95.8%.

[0077] As in Example 1, chlorine was reused, and the overall chlorine recycling rate was 91.8%.

[0078] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0079] Example 5 Example 5 is basically the same as Example 1, except that the following process conditions are slightly different: Instead of performing the pre-dehydration treatment of magnesium chloride in step S1, magnesium chloride (MgCl2·6H2O) is used directly for the complexation reaction in step S3. Step S3 includes: 100 kg of hydrated magnesium chloride (MgCl2·6H2O) was added to 250 L of concentrated industrial hydrochloric acid (35.2 wt%) prepared in step S2, with a solid-liquid mass ratio of 1:2.0. The reaction was carried out at 120℃ for 2 hours to form a complex. The complex was then pyrolyzed at 300℃ for 1 hour. The resulting electrolytic-grade anhydrous magnesium chloride had a purity of 99.3 wt%, a water content of 0.20 wt%, and an MgO content of 0.55 wt%.

[0080] Step S4 is performed in the same way as in Example 1. In this example, the purity of the magnesium metal obtained by electrolysis is 99.4 wt%, the current efficiency is 84.5%, the DC power consumption per ton of magnesium is 12,100 kWh, and the chlorine purity is 95.0%.

[0081] As in Example 1, chlorine was reused, and the overall chlorine recycling rate was 89.5%.

[0082] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0083] Example 6 Example 6 is essentially the same as Example 1, except that in step S4: the electrolysis temperature is 800℃, the cathode current density is 2.0 A / cm², the pulse current duty cycle is 10%, the frequency is 50Hz, the LiF addition is 5wt% (1.0 kg) of the mass of electrolytic-grade anhydrous magnesium chloride, and the CeO2 addition is 0.5wt% (0.1 kg) of the mass of electrolytic-grade anhydrous magnesium chloride; the electrolysis time is 3 hours. The purity of the electrolyzed metallic magnesium is 99.5wt%, the current efficiency is 85.5%, the DC power consumption per ton of magnesium is 11,900 kWh, and the chlorine purity is 95.3%.

[0084] As in Example 1, chlorine was reused, and the overall chlorine recycling rate was 90.8%.

[0085] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0086] Example 7 Example 7 is essentially the same as Example 1, except that in step S4: LiF and CeO2 are not added to the molten salt electrolyte; the electrolysis temperature is 650℃, the cathode current density is 0.5 A / cm², the pulse current duty cycle is 50%, the frequency is 500Hz, and the electrolysis time is 5 hours. The magnesium metal obtained by electrolysis has a purity of 99.5wt%, a current efficiency of 85.0%, a DC power consumption of 11,700 kWh per ton of magnesium, and a chlorine purity of 95.0%.

[0087] As in Example 1, chlorine was reused, and the overall chlorine recycling rate was 90.2%.

[0088] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0089] Example 8 Example 8 is basically the same as Example 1, except that in step S4 of Example 8, a pulsed current is not used, but DC electrolysis is used instead, with a current density of 1.2 A / cm² and an electrolysis temperature of 700℃. The rest is the same as in Example 1, and will not be described again here.

[0090] In Example 8, the magnesium metal produced by electrolysis had a purity of 99.4%, a current efficiency of 82.5%, a DC power consumption of 12,500 kWh per ton of magnesium, a chlorine purity of 95.0%, and a chlorine comprehensive recycling rate of 91.0%.

[0091] Example 1 uses pulsed current with a current efficiency of 88.6%. Compared with Example 1, the current efficiency of Example 8 is reduced by 6.1%, and the energy consumption is increased by 1,300 kWh / t-Mg.

[0092] Comparative Example 1 Comparative Example 1 provides a method for preparing magnesium oxide without the co-production of metallic magnesium. Comparative Example 1 uses the exact same conditions as steps S1 and S2 of Example 1 to prepare high-purity magnesium oxide and industrial concentrated hydrochloric acid, but skips steps S3, S4, and S5.

[0093] Comparative Example 1 only produced magnesium oxide, with a magnesium resource utilization rate of only 51%, a chlorine element recycling rate of 0%, hydrochloric acid was sold externally, and no chlorine was recovered.

[0094] Comparative Example 2 Comparative Example 2 provides a conventional non-partitioned magnesium electrolysis method that does not co-produce magnesium oxide.

[0095] Comparative Example 2 used an industrial plateless magnesium electrolytic cell, with anhydrous magnesium chloride of the same purity as in Example 1 as the raw material, mixed with KCl, NaCl, and CaCl2 in the same proportion (without LiF and CeO2), and electrolyzed at 700°C under direct current, with a cathode current density of 1.2 A / cm², for 4 hours, and graphite was used as the anode.

[0096] Comparative Example 2 yielded magnesium metal with a purity of 99.0% produced by electrolysis, a current efficiency of 76%, and a DC power consumption of 13,500 kWh per ton of magnesium. Chlorine gas was collected unorganized at the anode with a purity of 78%. Most of the chlorine gas in Comparative Example 2 was absorbed by the alkaline solution before being discharged, resulting in a chlorine recycling rate of 0%.

[0097] Comparative Example 3 Comparative Example 3 uses the same steps S1, S3, S4, and S5 as Example 1, but omits step S2 (i.e., high-purity magnesium oxide is not prepared); the concentrated hydrochloric acid (35% concentration) required for step S3 of Comparative Example 3 needs to be purchased externally.

[0098] The electrolytic-grade anhydrous magnesium chloride prepared in Comparative Example 3 had a purity of 99.6% and a water content of 0.08%. The metallic magnesium purity was 99.5%, the current efficiency was 86.5%, the DC power consumption per ton of magnesium was 11,500 kWh, and the overall chlorine recycling rate was 85.2% (due to the lack of hydrochloric acid replenishment from pyrolysis tail gas, hydrochloric acid needs to be purchased externally periodically). The comprehensive utilization rate of magnesium resources was only 49% (for metallic magnesium products only).

[0099] Comparative Example 4 Comparative Example 4 is basically the same as Example 1, except that step S3 uses a traditional deep dehydration method instead of the complex pyrolysis method. Step S3 of Comparative Example 4 includes: S3: The low-hydrated magnesium chloride (MgCl2·2H2O) obtained in step S1 was directly fed into a fluidized bed deep dehydrator. A dry HCl / N2 mixture (HCl volume concentration 10%) was used as the fluidizing medium and protective gas. Deep dehydration was carried out at 500℃ for 2 hours to obtain electrolytic-grade anhydrous magnesium chloride. Testing showed a purity of 99.4%, a water content of 0.3%, and a MgO content of 0.5%.

[0100] The rest is implemented in the same way as in Example 1, and will not be described again here.

[0101] Comparative Example 4 showed that the purity of the magnesium metal obtained by electrolysis was 99.5%, the current efficiency was 85.2%, the DC power consumption per ton of magnesium was 11,800 kWh, the chlorine purity was 95.5%, and the chlorine comprehensive recycling rate was 90.5%. The comprehensive utilization rate of magnesium resources was 89%.

[0102] Compared to the method in Example 1, which involved preparing a complex followed by pyrolysis at 250°C, Comparative Example 4 required deep dehydration at a higher temperature of 500°C for 2 hours, and the resulting anhydrous magnesium chloride contained 0.5 wt% MgO, indicating a higher MgO content. Furthermore, compared to Example 1, Comparative Example 4 exhibited a lower current efficiency of only 85.2%.

[0103] The effects of the methods described in the above embodiments and comparative examples are summarized in Table 1.

[0104] Table 1. Effects of the methods used in Examples 1-8 and Comparative Examples 1-4 In summary, the method provided by this invention integrates the fluidized bed pyrolysis of low-hydrated magnesium chloride to produce high-purity magnesium oxide with the membrane-type molten salt electrolysis to produce high-quality metallic magnesium. Based on this, a complete closed-loop cycle of chlorine is achieved, solving the technical problems of the existing technology where the two routes are mutually exclusive, resource utilization is low, and chlorine cannot be recycled. Furthermore, the method provided by this invention introduces a hydrochloric acid complex pyrolysis method to prepare electrolytic-grade anhydrous magnesium chloride, which not only reduces energy consumption but also realizes the tiered high-value utilization of magnesium resources.

[0105] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.

[0106] All aspects, embodiments, features, and examples of this invention should be considered illustrative, used to explain and illustrate the invention, but not to limit it. The scope of the invention is defined only by the claims.

[0107] Although the invention has been described with reference to the above embodiments, those skilled in the art will understand that various other changes, omissions, and / or additions can be made without departing from the spirit and scope of the invention, and that substantially equivalents can be substituted for elements in the described embodiments. Therefore, the invention is not intended to be limited to the specific embodiments disclosed, but rather to encompass all embodiments falling within the scope defined by the claims.

Claims

1. A method for co-producing high-purity magnesium oxide and metallic magnesium, characterized in that, include: Step A: Allow low-hydrated magnesium chloride to undergo the first pyrolysis reaction to produce crude magnesium oxide and the first pyrolysis tail gas; Step B: Purify the crude magnesium oxide to obtain a high-purity magnesium oxide product; Step C: Convert the hydrogen chloride gas in the first pyrolysis tail gas into concentrated hydrochloric acid; Step D: Perform a complexation reaction between low-hydrated magnesium chloride and / or magnesium chloride hydrate and the concentrated hydrochloric acid obtained in step C to generate a complex, wherein the chemical formula of the complex is MgCl2·xHCl·yH2O, x=0.5~2, y=1~4; Step E: The complex is subjected to a second pyrolysis reaction to generate electrolytic-grade anhydrous magnesium chloride and a second pyrolysis tail gas; Step F: Electrolysis is performed using the electrolytic-grade anhydrous magnesium chloride to produce metallic magnesium and chlorine gas.

2. The method according to claim 1, characterized in that, The sources of low-hydrated magnesium chloride used in steps A and D include: magnesium chloride by-products from salt lakes, which are obtained through pre-dehydration. And / or, step A specifically includes: causing low-hydrated magnesium chloride to undergo the first pyrolysis reaction in a fluidized state, wherein the temperature of the first pyrolysis reaction is 600℃~900℃; And / or, step D specifically includes: mixing low-hydrated magnesium chloride and / or magnesium chloride hydrate with concentrated hydrochloric acid at a solid-liquid mass ratio of 1:1.5 to 1:3, and reacting at 80℃ to 120℃ for 1 to 2 hours to form the complex; and the amount of concentrated hydrochloric acid used is such that the molar ratio of all chloride ions to magnesium ions in the reaction system is 4:1 or higher.

3. The method according to claim 1, characterized in that, Step E specifically includes: subjecting the complex to the second pyrolysis reaction at 200℃~300℃ for 1~2 hours.

4. The method according to claim 1, characterized in that, Step F specifically includes: mixing the electrolytic-grade anhydrous magnesium chloride with a flux to prepare a molten salt electrolyte, and performing the electrolysis in a diaphragm electrolytic cell.

5. The method according to claim 4, characterized in that, The molten salt electrolyte comprises, by mass percentage, 15wt% to 30wt% of electrolytic-grade anhydrous magnesium chloride, 30wt% to 50wt% of KCl, 20wt% to 40wt% of NaCl, and 0wt% to 15wt% of CaCl2; And / or, the molten salt electrolyte further includes a composite additive, which includes lithium fluoride and nano-cerium oxide, wherein the amounts of lithium fluoride and nano-cerium oxide are 2wt%~5wt% and 0.1wt%~0.5wt% of the mass of electrolytic-grade anhydrous magnesium chloride, respectively. And / or, the electrolysis is carried out using a combination of pulsed current and gradient temperature control, specifically including: first placing the flux in a diaphragm electrolytic cell, adding the electrolytic-grade anhydrous magnesium chloride when the temperature is raised to 400℃~500℃ to form a molten salt electrolyte, and continuing to raise the temperature to an electrolysis temperature of 650℃~800℃; and, during the electrolysis process, the applied pulsed current duty cycle is 10%~50%, the pulse frequency is 50Hz~500Hz, and the cathode current density is 0.5A / cm². 2 ~2.0A / cm 2 The electrolysis time is 3 to 5 hours.

6. The method according to claim 1, characterized in that, It also includes step G: collecting hydrogen chloride from the second pyrolysis tail gas of step E and / or chlorine produced in step F, and recycling the hydrogen chloride and / or chlorine.

7. The method according to claim 7, characterized in that, The recycling of hydrogen chloride includes: absorbing the hydrogen chloride in the second pyrolysis tail gas into concentrated hydrochloric acid, which is then reused in the complexation reaction; And / or, the recycling of chlorine includes: using chlorine as a protective gas in the second pyrolysis reaction for the preparation of magnesium chloride pre-dehydration and / or complex; and / or using chlorine to prepare hydrochloric acid, which is used for the absorption of the first pyrolysis tail gas; and / or using chlorine to produce chlorinated products.

8. An apparatus for the co-production of high-purity magnesium oxide and metallic magnesium, characterized in that, include: The fluidized bed pyrolysis unit includes a first fluidized bed pyrolysis furnace, a gas-solid separation mechanism, a cooling mechanism, and a tail gas absorption mechanism; The complexation reaction and pyrolysis unit, which is connected to the fluidized bed pyrolysis unit, includes a closed complexation reactor, a second fluidized bed pyrolysis furnace, and an HCl recovery mechanism; A diaphragm electrolysis unit, which is connected to a complexation reaction and pyrolysis unit, includes a diaphragm electrolytic cell.

9. The apparatus according to claim 8, characterized in that, It also includes a low-hydrate magnesium chloride preparation unit for converting magnesium chloride hydrate into low-hydrate magnesium chloride, which includes a filtration mechanism, an evaporation crystallization mechanism and a pre-dehydration mechanism connected in sequence. And / or, it also includes a chlorine recycling unit connected to the diaphragm electrolysis unit, which includes a chlorine compression mechanism, a chlorine storage tank and a hydrogen chloride synthesis mechanism; And / or, the diaphragm electrolysis unit further includes an anode chlorine gas collection mechanism and a cathode magnesium metal collection mechanism.

10. A method for co-producing high-purity magnesium oxide and metallic magnesium, characterized in that, The apparatus of claim 8 or 9 comprises: Low-hydrated magnesium chloride is fed into a first fluidized bed pyrolysis furnace for a first pyrolysis reaction. The resulting gas-solid mixture is then separated in the gas-solid separation mechanism to obtain crude magnesium oxide and first pyrolysis tail gas. The crude magnesium oxide is then cooled and purified by a cooling mechanism to obtain a high-purity magnesium oxide product. The first pyrolysis tail gas is then fed into the tail gas absorption mechanism to obtain concentrated hydrochloric acid. The obtained concentrated hydrochloric acid is fed into the closed complex reactor, and low-hydrated magnesium chloride and / or magnesium chloride hydrate are added to carry out a complexation reaction to obtain a complex with the chemical formula MgCl2·xHCl·yH2O, where x=0.5~2 and y=1~4. The complex is then subjected to a second pyrolysis reaction in a second fluidized bed pyrolysis furnace to generate electrolytic-grade anhydrous magnesium chloride and a second pyrolysis tail gas. The second pyrolysis tail gas enters the HCl recovery unit to form concentrated hydrochloric acid, and the recovered concentrated hydrochloric acid is reused in the complexation reaction. The anhydrous magnesium chloride of the electrolytic grade is fed into a diaphragm electrolytic cell for electrolysis to produce metallic magnesium and chlorine gas.

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