A method for producing metallic magnesium from magnesia hydrate

Abstract

This invention relates to the field of magnesium chloride electrolysis technology and discloses a method for producing metallic magnesium from magnesium chloride hydrate. The method includes the following steps: (1) subjecting magnesium chloride hydrate to first-stage phase change dehydration, second-stage phase change dehydration and third-stage phase change dehydration sequentially to obtain low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5%; (2) melting the low-hydrated magnesium chloride at 720-750℃, then chlorinating the melted product in the presence of a carbon-containing reducing agent and a chlorine-containing gas, and then purifying it to obtain magnesium chloride melt, wherein the temperature of the chlorination treatment and the temperature of the purification treatment are not lower than the temperature of the melting treatment; (3) electrolyzing the magnesium chloride melt. This method has a simple process flow, is easy to operate, and can electrolyze to obtain metallic magnesium liquid with a purity equal to or higher than 99.9%.

Description

Technical Field

[0001] This invention relates to the field of electrolytic magnesium chloride technology, and specifically to a method for producing metallic magnesium from magnesium chloride hydrate. Background Technology

[0002] Currently, there are two main methods for producing metallic magnesium: the thermal reduction method (Pidgren process) and the molten salt electrolysis method. The thermal reduction method uses different reducing agents (ferrosilicon, carbon, etc.) to reduce magnesium from its compounds at high temperatures to obtain metallic magnesium. The molten salt electrolysis method involves passing a direct current through a ternary or quaternary molten salt electrolyte to electrolyze magnesium chloride in the molten salt to obtain metallic magnesium. Currently, the Pidgren process is the mainstream production method. However, the survival and further sustainable development of magnesium smelting using the Pidgren process face significant constraints, mainly manifested in: low automation, high labor intensity, high ore consumption, large waste emissions, and high carbon emissions. With increasingly stringent environmental protection requirements, the industry urgently needs to accelerate its green transformation and embark on a path of high-quality development. In contrast, the electrolysis method offers a continuous production process, high automation, and good product quality uniformity, better meeting the requirements of industrialized, large-scale, modernized, and green production, and aligning with sustainable development, making it the future direction for metallic magnesium production. However, the molten salt electrolysis method for producing metallic magnesium currently suffers from problems such as dependence on specific resources, stringent raw material requirements, high energy consumption, equipment corrosion, and high maintenance costs. Summary of the Invention

[0003] The purpose of this invention is to overcome the problems of existing molten salt electrolysis methods for producing metallic magnesium, such as dependence on specific resources, stringent raw material requirements, and high energy consumption. This invention provides a method for producing metallic magnesium from magnesium chloride, which uses magnesium chloride as a raw material and achieves qualified electrolytic raw material through multi-stage heating, dehydration, and melting. The entire process is green and environmentally friendly with a simple process flow, and can electrolyze to obtain high-purity metallic magnesium liquid.

[0004] To achieve the above objectives, the present invention provides a method for producing metallic magnesium from magnesium chloride, the method comprising the following steps: (1) Magnesium chloride was subjected to first-stage phase change dehydration, second-stage phase change dehydration and third-stage phase change dehydration in sequence to obtain low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5%. (2) The low-hydrated magnesium chloride is melted at 720-750℃, and then the melted product is chlorinated in the presence of carbon-containing reducing substances and chlorine-containing gas, and then purified to obtain magnesium chloride melt. The temperature of the chlorination treatment and the temperature of the purification treatment are not lower than the temperature of the melt treatment. (3) Electrolyze the magnesium chloride melt.

[0005] Preferably, in step (1), the first-stage phase change dehydration, the second-stage phase change dehydration, and the third-stage phase change dehydration are carried out in the same dehydration device.

[0006] Preferably, the dehydration device is a rotary reactor.

[0007] Preferably, in step (1), the first-stage phase change dehydration, the second-stage phase change dehydration, and the third-stage phase change dehydration are all carried out in the presence of hydrogen chloride.

[0008] Preferably, in step (1), the temperature T1 of the first-stage phase change dehydration, the temperature T2 of the second-stage phase change dehydration, and the temperature T3 of the third-stage phase change dehydration satisfy: T1≤T2<T3.

[0009] Preferably, the difference between T2 and T1 is 0-140, and more preferably 50-80.

[0010] Preferably, the difference between T3 and T2 is 110-200, and more preferably 150-180.

[0011] Preferably, in step (1), the temperature of the first-stage phase change dehydration is 100-180℃.

[0012] Preferably, in step (1), the temperature of the secondary phase change dehydration is 180-240℃.

[0013] Preferably, in step (1), the temperature of the three-stage phase change dehydration is 350-380℃.

[0014] Preferably, in step (2), the temperature difference between the chlorination treatment and the melting treatment is 20-30°C.

[0015] Preferably, in step (2), the temperature difference between the purification treatment and the chlorination treatment is 20-30°C.

[0016] Preferably, in step (2), the chlorination treatment temperature is 750-780℃.

[0017] Preferably, in step (2), the temperature of the purification treatment is 780-800℃.

[0018] Preferably, in step (2), the carbon-containing reducing substance is selected from one or more of carbon monoxide, methane, petroleum coke and coke.

[0019] Preferably, in step (2), the chlorine-containing gas is selected from one or more of chlorine, hydrogen chloride, and a mixture of chlorine and air.

[0020] Preferably, in step (2), the magnesium oxide content in the magnesium chloride melt is <0.2%.

[0021] Compared with the prior art, the technical solution of the present invention has the following advantages: The method described in this invention can prepare metallic magnesium using magnesium chloride as raw material, eliminating the need for the traditional three-stage dehydration process of granulation, air drying, and hydrogen chloride drying. The three-stage dehydration is completed directly in the same dehydration unit, resulting in a simpler process, easier equipment operation, and lower costs. To avoid excessive sulfate and boron ions in the final raw material entering the electrolytic cell, the method described in this invention effectively removes sulfate, boron ions, and other organic impurities under high-temperature conditions through melting, chlorination, and purification. The process is simple and easy to control, removing the strict limitations on raw materials imposed by traditional molten salt electrolysis. Compared to the traditional process of using barium ions to remove sulfate ions followed by inorganic membrane filtration to remove boron ions, the process is simpler. Furthermore, it avoids the problem of barium sulfate precipitate particles not being completely filtered out, which could damage the subsequent inorganic membrane. This results in the final electrolytic preparation of metallic magnesium solution with a purity equal to or higher than 99.9%. Detailed Implementation

[0022] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0023] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0024] This invention provides a method for producing metallic magnesium from hydrated magnesium chloride, the method comprising the following steps: (1) Magnesium chloride was subjected to first-stage phase change dehydration, second-stage phase change dehydration and third-stage phase change dehydration in sequence to obtain low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5%. (2) The low-hydrated magnesium chloride is melted at 720-750℃, and then the melted product is chlorinated in the presence of carbon-containing reducing substances and chlorine-containing gas, and then purified to obtain magnesium chloride melt. The temperature of the chlorination treatment and the temperature of the purification treatment are not lower than the temperature of the melt treatment. (3) Electrolyze the magnesium chloride melt.

[0025] In this invention, the magnesium chloride is the magnesium chloride conventionally understood in the art. It can be obtained by refining salt lake brine and then naturally sun-drying it, or by calcining and / or acid leaching and / or evaporation of dolomite or serpentine.

[0026] In the method described in this invention, in step (1), in the presence of hydrogen chloride gas, the magnesium chloride is dehydrated by a first-stage phase change, converting MgCl2·6H2O to MgCl2·4H2O; by a second-stage phase change, converting MgCl2·4H2O to MgCl2·2H2O; and by a third-stage phase change, converting MgCl2·2H2O to MgCl2·0.3H2O. The presence of hydrogen chloride inhibits the water absorption and hydrolysis of magnesium chloride, as well as the decomposition of basic magnesium chloride, ultimately yielding low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5%. In step (2), the low-hydrated magnesium chloride is melted at 720-750℃ to form a molten state, and then in the presence of carbon-containing reducing substances and chlorine-containing gas... The product after molten treatment is subjected to chlorination. Based on the presence of carbon-containing reducing substances and chlorine-containing gas, the magnesium oxide and basic magnesium chloride in the molten state react to obtain magnesium chloride and remove other organic impurities. In step (3), through further purification treatment, the unreacted magnesium oxide in the molten magnesium chloride further precipitates and is further separated from the molten magnesium chloride. After these three steps in step (2), the magnesium oxide content in the final magnesium chloride melt is <0.2%, and impurities such as sulfate ions and boron elements are also removed, and finally qualified magnesium chloride melt that can be used for electrolysis is obtained. In step (3), the above qualified magnesium chloride melt is electrolyzed to obtain metallic magnesium liquid with a purity equal to or higher than 99.9%. The whole process is simple and easy to operate.

[0027] In a preferred embodiment, in step (1), the first-stage phase change dehydration, the second-stage phase change dehydration, and the third-stage phase change dehydration are carried out in the same dehydration device; based on this, the method of the present invention can complete the dehydration of magnesium chloride in a single dehydration device, without the need for the traditional three-stage dehydration process of granulation, air drying, and hydrogen chloride drying. The entire step (1) is convenient to operate and the process is simple; in a further preferred embodiment, the dehydration device is a rotary reactor.

[0028] In a further preferred embodiment, the rotary reactor is equipped with a scraper plate, which can prevent the product obtained in step (1) from sticking to the wall and improve the recovery rate.

[0029] In the method described in this invention, in step (1), the first-stage phase change dehydration, the second-stage phase change dehydration, and the third-stage phase change dehydration are all carried out in the presence of hydrogen chloride; based on this, the water absorption and hydrolysis of magnesium chloride and the decomposition of basic magnesium chloride are suppressed, and finally, low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5% is obtained.

[0030] In a preferred embodiment, in step (1), the temperature T1 of the first-stage phase change dehydration, the temperature T2 of the second-stage phase change dehydration, and the temperature T3 of the third-stage phase change dehydration satisfy: T1≤T2<T3; based on this, the stepwise dehydration of magnesium chloride can be completed to obtain low-hydrated magnesium chloride with a water content of <5%.

[0031] In a preferred embodiment, in order to further improve the dehydration of magnesium chloride, the difference between T2 and T1 is 0-140, preferably 50-80.

[0032] In a preferred embodiment, in order to further improve the dehydration of magnesium chloride, the difference between T3 and T2 is 110-200, preferably 150-180.

[0033] In a preferred embodiment, in order to further increase the amount of water removed by the first-stage phase change of magnesium chloride, the temperature of the first-stage phase change dehydration in step (1) is 100-180°C.

[0034] In a preferred embodiment, in order to further increase the dehydration amount of the secondary phase change of magnesium chloride, the temperature of the secondary phase change dehydration in step (1) is 180-240℃.

[0035] In a preferred embodiment, in order to further improve the dehydration of the three-stage phase change of magnesium chloride, the temperature of the three-stage phase change dehydration in step (1) is 350-380℃.

[0036] In a preferred embodiment, in order to improve the purity of the magnesium chloride melt and reduce the influence of magnesium oxide, basic magnesium chloride and other impurities, the temperature difference between the chlorination treatment and the melting treatment in step (2) is 20-30°C.

[0037] In a preferred embodiment, in order to further improve the purity of the magnesium chloride melt and reduce the influence of magnesium oxide, basic magnesium chloride and other impurities, the temperature difference between the purification treatment and the chlorination treatment in step (2) is 20-30°C.

[0038] In a preferred embodiment, in step (2), the chlorination treatment temperature is 750-780°C.

[0039] In a preferred embodiment, the temperature of the purification process in step (2) is 780-800℃.

[0040] In a preferred embodiment, in order to further improve the purity of the magnesium chloride melt and reduce the influence of magnesium oxide, basic magnesium chloride and other impurities, in step (2), the carbon-containing reducing substance is selected from one or more of carbon monoxide, methane, petroleum coke and coke.

[0041] In a preferred embodiment, in order to further improve the purity of the magnesium chloride melt and reduce the influence of magnesium oxide, basic magnesium chloride and other impurities, in step (2), the chlorine-containing gas is selected from one or more of chlorine, hydrogen chloride and a mixture of chlorine and air.

[0042] In the method described in this invention, in step (2), there are no special requirements for the amount of the carbon-containing reducing substance and the chlorine-containing gas used, as long as the conversion of magnesium oxide and basic magnesium chloride to magnesium chloride can be completed.

[0043] In a preferred embodiment, in step (2), the content of magnesium oxide in the magnesium chloride melt is <0.2%.

[0044] In the method described in this invention, the melting treatment, chlorination treatment and purification treatment in step (2) are carried out in different areas of the same device. In a specific embodiment, the melting treatment, the chlorination treatment and the purification treatment are carried out in a melting furnace.

[0045] In one specific embodiment, the carbon-containing reducing substance and the chlorine-containing gas are injected into the chlorination zone of the melting furnace through a spray gun for chlorination treatment.

[0046] In a further preferred embodiment, the method of the present invention can also realize the recycling of chlorine gas, a byproduct of electrolysis in step (3). Specifically, the chlorine gas generated by electrolysis in step (3) is purified and then transported to the hydrogen chloride synthesis furnace, reacts with hydrogen gas to generate high-temperature hydrogen chloride gas, and is returned to the rotary reactor to realize the recycling of chlorine gas.

[0047] In one specific embodiment, the method of the present invention is implemented in a system comprising a rotary reactor, a melting furnace, and an electrolytic cell arranged in descending order of height. The specific working principle is as follows: The magnesium chloride hydrate enters the rotary reactor, and in the presence of hydrogen chloride, the temperature of the rotary reactor is controlled to carry out primary phase change dehydration at 100-180℃, secondary phase change dehydration at 180-240℃, and tertiary phase change dehydration at 350-380℃, to obtain low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5%. Under the influence of gravity, the low-hydrated magnesium chloride enters the melting furnace and melts at 720-750℃ to form a melt. The melt flows by gravity into the chlorination zone of the melting furnace. Carbon-containing reducing substances and chlorine-containing gases are sprayed into the chlorination zone through a spray gun, and chlorination is carried out at 750-780℃. The chlorinated product then enters the purification zone of the melting furnace and is kept at 780-800℃ for heat preservation and settling. This allows a small amount of magnesium oxide in the melt to naturally settle to the bottom and be discharged from the bottom slag outlet. The upper layer of magnesium chloride melt (magnesium oxide content less than 0.2%) overflows naturally through the ceramic liner into the electrolytic cell for electrolysis.

[0048] The following examples further illustrate the method for producing metallic magnesium from magnesia-hydrate magnesium hydrate according to the present invention. These examples are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operating procedures; however, the scope of protection of the present invention is not limited to the following examples.

[0049] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0050] Example 1 (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 140°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 370°C to obtain low-hydrated magnesium chloride with a water content of 3.45% and a basic magnesium chloride content of 3.69%. (2) The low-hydrated magnesium chloride enters the melting furnace and is melted at 740°C. Then it flows into the chlorination zone by gravity. Petroleum coke and chlorine gas are sprayed into the chlorination zone by spray gun. Chlorination is carried out at 770°C. Then it flows into the purification zone by gravity. It is kept at 790°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 0.09%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 99.97%.

[0051] Example 2 (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 120°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 360°C to obtain low-hydrated magnesium chloride with a water content of 4.21% and a basic magnesium chloride content of 3.67%. (2) The low-hydrated magnesium chloride enters the melting furnace and is melted at 734°C. Then it flows into the chlorination zone by gravity. Petroleum coke and chlorine gas are sprayed into the chlorination zone by spray gun. Chlorination is carried out at 760°C. Then it flows into the purification zone by gravity. It is kept at 790°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 0.11%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 99.94%.

[0052] Example 3 (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 180°C, secondary phase change dehydration at 240°C, and tertiary phase change dehydration at 380°C to obtain low-hydrated magnesium chloride with a water content of 2.94% and a basic magnesium chloride content of 3.26%. (2) The low-hydrated magnesium chloride enters the melting furnace and is melted at 730°C. Then it flows into the chlorination zone by gravity. Coke and chlorine are sprayed into the chlorination zone by spray gun. Chlorination is carried out at 750°C. Then it flows into the purification zone by gravity. It is kept at 780°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 0.14%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 99.93%.

[0053] Example 4 (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 100°C, secondary phase change dehydration at 180°C, and tertiary phase change dehydration at 350°C to obtain low-hydrated magnesium chloride with a water content of 4.78% and a basic magnesium chloride content of 4.55%. (2) The low-hydrated magnesium chloride is melted in a melting furnace at 750°C, and then flows into the chlorination zone by gravity. Carbon monoxide and hydrogen chloride are sprayed into the chlorination zone by a spray gun and chlorinated at 780°C. Then it flows into the purification zone by gravity and is kept at 800°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 0.19%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 99.92%.

[0054] Example 5 The procedure was carried out in accordance with Example 1, except that in step (2), the melting temperature was 720°C, i.e.: (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 140°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 370°C to obtain low-hydrated magnesium chloride with a water content of 3.45% and a basic magnesium chloride content of 3.69%. (2) The low-hydrated magnesium chloride enters the melting furnace and is melted at 720°C. Then it flows into the chlorination zone by gravity. Petroleum coke and chlorine gas are sprayed into the chlorination zone by a spray gun. Chlorination is carried out at 770°C. Then it flows into the purification zone by gravity. It is kept at 790°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 0.52%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 99.91%.

[0055] Example 6 The procedure is carried out in accordance with Example 1, except that in step (2), the purification temperature is 780°C, i.e.: (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 140°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 370°C to obtain low-hydrated magnesium chloride with a water content of 3.45% and a basic magnesium chloride content of 3.69%. (2) The low-hydrated magnesium chloride enters the melting furnace and is melted at 740°C. Then it flows into the chlorination zone by gravity. Petroleum coke and chlorine gas are sprayed into the chlorination zone by spray gun. Chlorination is carried out at 770°C. Then it flows into the purification zone by gravity. It is kept warm and left to stand at 780°C. The upper layer is magnesium chloride melt (magnesium oxide content is 0.65%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 99.90%.

[0056] Comparative Example 1 The procedure is carried out in accordance with Example 1, except that step (1) is omitted, i.e.: (1) Add water-hydrated magnesium chloride to the melting furnace and melt it at 740°C. Then, it flows into the chlorination zone by gravity. Petroleum coke and chlorine gas are sprayed into the chlorination zone by spray gun. Chlorination is carried out at 770°C. Then, it flows into the purification zone by gravity. It is kept at 790°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 79.43%). (2) The magnesium chloride melt flowed into the electrolytic cell by gravity for electrolysis, but it was found that electrolysis could not be carried out.

[0057] Comparative Example 2 The procedure is the same as in Example 1, except that step (2) is omitted, i.e.: (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 140°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 370°C to obtain low-hydrated magnesium chloride (magnesium oxide content of 1.07%) with a water content of 3.45% and a basic magnesium chloride content of 3.69%. (2) The low-hydrated magnesium chloride was directly added to the electrolytic cell for electrolysis, but it was found that electrolysis could not be carried out.

[0058] Comparative Example 3 The procedure is carried out in accordance with Example 1, except that in step (2), petroleum coke is not added during the chlorination process, i.e.: (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 140°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 370°C to obtain low-hydrated magnesium chloride with a water content of 3.45% and a basic magnesium chloride content of 3.69%. (2) The low-hydrated magnesium chloride enters the melting furnace and is melted at 740°C. Then it flows into the chlorination zone by gravity. Chlorine gas is sprayed into the chlorination zone by spray gun and chlorination is carried out at 770°C. Then it flows into the purification zone by gravity and is kept at 790°C and left to stand. The upper layer is magnesium chloride melt (magnesium oxide content is 0.84%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 98.4%.

[0059] Comparative Example 4 The implementation is carried out in accordance with Example 1, except that in step (2), no purification treatment is performed, that is: (1) Add magnesium chloride to a rotary reactor in the presence of hydrogen chloride gas, and carry out primary phase change dehydration at 140°C, secondary phase change dehydration at 200°C, and tertiary phase change dehydration at 370°C to obtain low-hydrated magnesium chloride with a water content of 3.45% and a basic magnesium chloride content of 3.69%. (2) The low-hydrated magnesium chloride is fed into a melting furnace and melted at 740°C. Then it flows into the chlorination zone by gravity. Petroleum coke and chlorine gas are sprayed into the chlorination zone by a spray gun and chlorination is carried out at 770°C to obtain magnesium chloride melt (magnesium oxide content is 1.03%). (3) The magnesium chloride melt flows into the electrolytic cell by gravity for electrolysis to obtain a magnesium metal liquid with a purity of 98.2%.

[0060] The results from the examples and comparative examples show that the purity of the magnesium liquid prepared by the method of the present invention is equal to or higher than 99.9%, which meets the standard for electrolytic magnesium liquid (≥99.9%). Moreover, the method described in the present invention is simple and easy to operate.

[0061] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combining the various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing metallic magnesium from hydrated magnesium chloride, characterized in that, The method includes the following steps: (1) Magnesium chloride was subjected to first-stage phase change dehydration, second-stage phase change dehydration and third-stage phase change dehydration in sequence to obtain low-hydrated magnesium chloride with a water content of <5% and a basic magnesium chloride content of <5%. (2) The low-hydrated magnesium chloride is melted at 720-750℃, and then the melted product is chlorinated in the presence of carbon-containing reducing substances and chlorine-containing gas, and then purified to obtain magnesium chloride melt. The temperature of the chlorination treatment and the temperature of the purification treatment are not lower than the temperature of the melt treatment. (3) Electrolyze the magnesium chloride melt.

2. The method according to claim 1, characterized in that, In step (1), the first-stage phase change dehydration, the second-stage phase change dehydration, and the third-stage phase change dehydration are carried out in the same dehydration device; Preferably, the dehydration device is a rotary reactor.

3. The method according to claim 1 or 2, characterized in that, In step (1), the first-stage phase change dehydration, the second-stage phase change dehydration, and the third-stage phase change dehydration are all carried out in the presence of hydrogen chloride.

4. The method according to any one of claims 1-3, characterized in that, In step (1), the temperature T1 of the first-stage phase change dehydration, the temperature T2 of the second-stage phase change dehydration, and the temperature T3 of the third-stage phase change dehydration satisfy: T1≤T2<T3; Preferably, the difference between T2 and T1 is 0-140, and more preferably 50-80; Preferably, the difference between T3 and T2 is 110-200, and more preferably 150-180.

5. The method according to claim 4, characterized in that, In step (1), the temperature of the first-stage phase change dehydration is 100-180℃; and / or The temperature for the secondary phase change dehydration is 180-240℃; and / or The temperature for the three-stage phase change dehydration is 350-380℃.

6. The method according to any one of claims 1-5, characterized in that, In step (2), the temperature difference between the chlorination treatment and the melting treatment is 20-30°C; and / or The temperature difference between the purification treatment and the chlorination treatment is 20-30°C.

7. The method according to claim 6, characterized in that, In step (2), the chlorination treatment temperature is 750-780℃; and / or The purification process is carried out at a temperature of 780-800℃.

8. The method according to any one of claims 1-7, characterized in that, In step (2), the carbon-containing reducing substance is selected from one or more of carbon monoxide, methane, petroleum coke and coke.

9. The method according to any one of claims 1-8, characterized in that, In step (2), the chlorine-containing gas is selected from one or more of chlorine, hydrogen chloride, and a mixture of chlorine and air.

10. The method according to any one of claims 1-9, characterized in that, In step (2), the magnesium oxide content in the magnesium chloride melt is <0.2%.