CN115305506A - Method for preparing metal magnesium by molten salt electrolysis - Google Patents
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Abstract
The invention provides a method for preparing metal magnesium by molten salt electrolysis, which adopts an electrolytic cell with an anode chamber and a cathode chamber, wherein the anode chamber and the cathode chamber are separated by liquid alloy. At 650-1000 deg.C, magnesium oxide or magnesium carbonate is continuously added into the electrolytic bath as raw material, and metal magnesium is directly obtained at the cathode. Compared with the current traditional magnesium chloride molten salt electrolysis method, the method has the advantages of low requirement on raw material grade, low price, easy obtainment, no chlorine gas generation, environment friendliness, capability of directly obtaining high-purity metal magnesium, simple process flow, high efficiency, energy conservation and continuous operation, and is a green, environment-friendly and sustainable-development metal magnesium production method.
Description
Technical Field
The invention belongs to the technical field of magnesium metallurgy, and particularly relates to a method for preparing metal magnesium by molten salt electrolysis.
Background
Magnesium is widely used in metallurgy, chemical engineering, mechanical manufacturing, electronic communication, aviation, aerospace and other industries due to its excellent physical and mechanical processing properties. China contains abundant magnesium resources, is the country with the largest magnesium reserve in the world, and is also the world with large production and export of original magnesium.
The current magnesium metal production methods are mainly classified into the following two types:
a thermal reduction method represented by the Pidgeon method; pidgeon smelting equipment adopts a grouped single-vacuum-tank reducing furnace, raw materials (magnesium oxide), slag formers (calcium oxide and fluorite) and a reducing agent (ferrosilicon) are ground, mixed and pressed into balls, a solid-phase reduction reaction is carried out in the reducing furnace to generate magnesium vapor, and the magnesium vapor is condensed and crystallized into crude magnesium. But has the following disadvantages: the production process is characterized by intermittent production and low mechanization degree; the energy consumption for maintaining high temperature, high vacuum and long-period operation required by production is high, and the reduction tank is made of expensive high-temperature-resistant nickel-chromium alloy steel and has short service life; the produced reducing slag does not have a proper treatment process at present, and the risk of environmental pollution exists.
The other is a molten salt electrolysis method which takes anhydrous magnesium chloride as raw material; the fused salt electrolysis method adopts a solution containing magnesium chloride (MgCl) 2 ) Calcium chloride (CaCl) 2 ) Sodium chloride (NaCl), calcium fluoride (CaF) 2 ) The molten salt of (2) is used as electrolyte, and molten salt electrolysis is carried out at 700-740 ℃. The metal magnesium liquid is reduced at the cathode of the electrolytic cell and floats on the surface of the molten salt, and chlorine (Cl) is generated at the graphite anode 2 ). However, anhydrous magnesium chloride needs to be prepared by dehydrating magnesium chloride hexahydrate through a complicated process, and side reactions (MgCl) often easily occur in the dehydration process 2 ·H 2 O = = MgO +2 HCl), magnesium oxide is generated. Therefore, anhydrous magnesium chloride has to be prepared by dehydration under an atmosphere of high concentration of hydrogen chloride. Obviously, such a complicated procedure inevitably leads to an increase in cost, and statistically, the production cost of the anhydrous magnesium chloride raw material accounts for about 50% of the cost of the whole electrolytic method.
In order to reduce the cost of the traditional electrolytic magnesium production method, researchers have conducted a series of research works, specifically listed as follows:
chinese patent CN1070243C and US patent US5593566 disclose a method for preparing metal magnesium and magnesium alloy from hydrous magnesium chloride material or magnesium chloride containing magnesium oxide impurity or directly magnesium oxide as raw material. The method adopts a catalyst containing MgCl 2 As an electrolyte, magnesium oxide is chlorinated in an electrolytic cell (Cl) 2 +C+2MgO＝MgCl 2 +CO 2 )，Dissolving magnesium chloride in the electrolyte to realize fused salt electrolysis by using magnesium oxide as a raw material. The disadvantages are that: (1) The method takes the hydrous magnesium chloride material as the raw material for fused salt electrolysis, hydrogen chloride gas is generated in the electrolysis process, and the equipment is seriously corroded; (2) Magnesium chloride or magnesium oxide containing magnesium oxide impurities is used as a raw material for molten salt electrolysis. In order to ensure the complete chlorination of magnesium oxide during the electrolysis process, chlorine gas must be supplemented from the outside, and the anode graphite participates in the chlorination reaction of magnesium oxide, so that the magnesium oxide is consumed.
Depending on the nature of the rare earth halide in which the magnesium oxide is soluble. US patent nos. 5279716 and 5427657 disclose a molten salt electrolysis process for preparing magnesium metal from magnesium oxide as a raw material. The patent US5279716 electrolyte adopts mixed molten salt containing magnesium chloride and rare earth chloride, and the patent US5427657 electrolyte adopts mixed molten salt containing magnesium fluoride and rare earth fluoride, so that the magnesium metal can be prepared from magnesium oxide raw materials. But has the following disadvantages: (1) The rare earth element (neodymium) as the electrolyte component is expensive and difficult to industrialize. (2) The rare earth chloride as the electrolyte component can be decomposed, so that not only can the electrolyte be lost, but also the obtained product is the rare earth magnesium alloy.
Chinese patent CN1173552A and US patent US5853560 propose a method for producing electrolytic magnesium using mixed chloride-fluoride electrolytes. The electrolyte of the method adopts the mixed molten salt (without rare earth halide) of fluoride containing magnesium fluoride and chloride containing magnesium chloride, and can dissolve a certain amount of magnesium oxide, so that the requirement of magnesium chloride raw materials on the content of impurity magnesium oxide can be relaxed. But has the following disadvantages: (1) molten salt electrolysis with a hydrous magnesium chloride material as a raw material. Hydrogen chloride gas is generated in the electrolysis process, and the equipment is seriously corroded. (2) The intermediate product lithium or calcium generated in the electrolytic process is utilized to indirectly reduce magnesium ions to prepare the metal magnesium, and the current efficiency is low.
Cell type and process research for preparing metal magnesium by direct electrolysis of magnesium oxide in Sha recorded Chang and Cai Anhong, in which MgF is used as electrolyte 2 LiF molten salt, magnesium oxide as raw material to prepare magnesium metal. But has the following disadvantages: the magnesium oxide has low solubility, the electrolyte component magnesium fluoride can be decomposed, and the anode effect phenomenon is easy to occur。
The electrolyte of the method adopts the traditional magnesium chloride fused salt, and the magnesium oxide raw material and carbon powder are mixed to prepare the composite anode, so that the metal magnesium can be prepared. But has the following disadvantages: the composite anode is easy to peel off and slag in the electrolytic process, so that magnesium oxide and carbon slag enter the electrolyte, and the anode effect phenomenon is easy to occur.
The university of Boston in the United states proposes a method for producing metal magnesium by a solid oxygen permeable membrane molten salt electrolysis method (SOM method). The method adopts MgF as electrolyte 2 -LiF-CaF 2 The molten salt system and the solid oxygen permeable membrane are made of CeO 2 -Y 2 O 3 -ZrO 2 ) Magnesium oxide is used as a raw material to prepare the metal magnesium. But has the disadvantages that the solid oxygen permeable membrane has short service life and high manufacturing cost under the corrosion of the high-temperature molten salt, and is difficult to be industrially utilized.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
Aiming at the problems in the field of fused salt electrolytic magnesium in different degrees, the invention aims to provide a method for preparing metal magnesium by using magnesium oxide or magnesium carbonate as a raw material and adopting fused salt electrolysis.
In order to realize the purpose, the technical scheme of the invention is as follows:
the invention provides a method for preparing metal magnesium by molten salt electrolysis, which comprises the following steps:
(1) An anodic oxidation-reduction process: an electrolytic cell with an anode chamber and a cathode chamber is adopted, molten salt is respectively arranged in the anode chamber and the cathode chamber, an anode electrode and a magnesium-containing raw material are placed in the anode chamber, and a cathode electrode is placed in the cathode chamber for electrolytic reaction; the anode chamber and the cathode chamber are separated by liquid alloy, and the cathode electrode and the anode electrode are not in contact with the liquid alloy;
the liquid alloy includes a flux metal and magnesium, the flux metal having a metal activity less than magnesium;
after the electrolysis reaction starts, reducing the magnesium-containing raw material in the anode chamber into metal magnesium and dissolving the metal magnesium in the liquid alloy, and oxidizing oxygen ions in the molten salt in the anode chamber at the anode;
(2) Cathode redox process: because the metal activity of magnesium is higher than that of the flux metal, the metal magnesium in the liquid alloy is further oxidized on the surface of the flux metal to obtain magnesium ions, the magnesium ions in the cathode chamber molten salt are reduced at the cathode, and finally the metal magnesium is prepared at the cathode chamber.
Further, the raw material containing magnesium is magnesium oxide (MgO grade is more than or equal to 75 percent) or magnesium carbonate (MgCO) 3 The grade is more than or equal to 80 percent), and magnesium carbonate can be decomposed to generate magnesium oxide under the electrolysis condition of 650-1000 ℃.
The anode electrode is made of graphite or inert materials, and preferably, a graphite rod is adopted as the anode electrode.
The inert material comprises an oxide ceramic material (e.g., doped SnO) 2 Surface coating SnO 2 、CaRuO 3 ) Metallic materials (e.g., pt), cermet composites (e.g., ni-NiO-NiFe) 2 O 4 )
The anode chamber molten salt is selected from one or more of calcium chloride, barium chloride, sodium chloride, potassium chloride, lithium chloride, rubidium chloride, cesium chloride, calcium fluoride, lithium fluoride, sodium fluoride and potassium fluoride. Preferably, the electrolyte in the anode chamber adopts (46.7 at%) NaCl-CaCl 2 (53.3at％)。
Furthermore, the cathode electrode is made of stainless steel, tungsten or molybdenum. The cathode electrode material does not react with magnesium metal to form an alloy and does not melt at the electrolysis temperature of the invention. Preferably, the cathode electrode is a stainless steel rod, since stainless steel is inexpensive and readily available.
The cathode chamber molten salt is one or more selected from sodium chloride, potassium chloride, lithium chloride, calcium chloride, barium chloride, lithium fluoride, sodium fluoride and potassium fluoride, and magnesium chloride and/or magnesium fluoride are dissolved in the cathode chamber molten salt. The content of magnesium chloride and/or magnesium fluoride in the cathode chamber molten salt is 5-40 wt%, magnesium ions in the molten salt are guaranteed to be discharged preferentially to separate out magnesium metal, and the density of the molten salt is larger than that of the liquid magnesium metal, so that the liquid magnesium metal is guaranteed to float on the upper surface of the molten salt. Preferably MgCl is used in the cathode compartment 2 (18wt％)-NaCl(38wt％)-KCl(29wt％)-CaCl 2 (15 wt%) molten salt.
The magnesium metal in the liquid alloy, and the magnesium chloride and/or magnesium fluoride in the cathode chamber molten salt act as follows: when the electrolytic reaction starts, no magnesium ions in the electrolyte of the cathode chamber are reduced to generate simple magnesium, and a large voltage is applied to ensure that the current densities of the cathode and the anode reach the required value. In order to ensure the electrolytic reaction to proceed smoothly, a certain amount of magnesium metal needs to be contained in the liquid alloy, and magnesium halide is added into the electrolyte of the cathode chamber. Thus, the redox reaction in the liquid alloy and the cathode chamber can be smoothly carried out, and an electric field passage is formed in the electrolytic cell.
In the electrolytic reaction, the cathode current density is 0.01-2.5A/cm 2 The current density of the anode is 0.01-5A/cm 2 。
Further, the liquid alloy is added to the bottom of the cell, ensuring that it separates the anode and cathode compartments. Further, the flux metal is selected from one or more of copper, zinc, lead, tin, bismuth, silver, gallium, indium and other metal elements. Since the metal activity of the above metals is lower than that of magnesium, magnesium atoms in the liquid alloy are oxidized into magnesium ions on the surface of the flux metal during electrolysis, and the flux metal itself does not undergo redox reaction. The liquid alloy is preferably a liquid copper magnesium alloy Cu (50 at%) -Mg (50 at%).
The liquid alloy comprises the following components in proportion: firstly, the working temperature of the electrolytic bath is determined, and then the metal components in the liquid alloy are determined. According to the alloy phase diagram of magnesium and flux metal, determining the proportion of the magnesium and the flux metal, ensuring that the selected alloy components are in a molten state at the temperature and the density is more than 0.2g/cm of the molten salt density 3 The above.
Furthermore, after the electrolytic reaction is finished, the purity of the metal magnesium obtained at the cathode is more than or equal to 99.90 percent.
Further, the working temperature of the electrolytic cell is 650-1000 ℃, and the electrolytic reaction is carried out in an inert atmosphere, wherein the inert atmosphere is argon or helium.
In one embodiment of the present invention, taking electrolytic magnesium oxide as an example, the reaction process is as follows: the electrolytic cell is electrified to operate at the temperature of 650-1000 DEG CMagnesium oxide added into the anode chamber is reduced into metal magnesium at an interface formed by anode molten salt and liquid alloy, and is dissolved in the liquid alloy to perform a reaction as shown in a formula (1); the oxygen ions combined with the magnesium oxide move to the surface of the anode electrode under the action of an electric field and are oxidized into zero-valent oxygen, and if the anode electrode adopts graphite, the oxygen ions react to generate CO and CO 2 Escape, e.g. by reaction with inert anodes to form O 2 Escape occurs and reactions as shown in formulas (2) and (3) occur. Meanwhile, magnesium atoms in the liquid alloy lose electrons at an interface formed by the liquid alloy and cathode chamber molten salt, and are oxidized into magnesium ions to enter the cathode chamber molten salt to perform a reaction shown as a formula (4). And the magnesium ions in the molten salt in the cathode chamber move to the surface of the cathode electrode under the action of an electric field, and a metal magnesium solution is obtained through reduction and reacts as shown in the formula (5).
Anode chamber reaction liquid alloy interface reaction: mgO +2e - = Mg (liquid alloy) + O 2- (1)
Graphite anode reaction: c + O 2- -2e - ＝CO/CO 2 (2)
Inert anode reaction: 2O of 2- -2e - ＝O 2 (3)
And (3) reacting liquid alloy interface reaction in the cathode chamber: mg (liquid alloy) -2e - ＝Mg 2+ (4)
Steel cathode reaction: mg (Mg) 2+ +2e - ＝Mg (5)
The invention has the beneficial effects that:
the invention provides a method for preparing magnesium metal by molten salt electrolysis, which adopts an electrolytic cell with an anode chamber and a cathode chamber, wherein the anode chamber and the cathode chamber are separated by liquid alloy. At 650-1000 deg.C, magnesium oxide or magnesium carbonate is continuously added into the electrolytic bath as raw material, and metal magnesium is directly obtained at the cathode. Compared with the current traditional magnesium chloride molten salt electrolysis method, the method has the advantages of low requirement on raw material grade, low price, easy obtainment, no chlorine gas generation, environment friendliness, capability of directly obtaining high-purity metal magnesium, simple process flow, high efficiency, energy conservation and continuous operation, and is a green, environment-friendly and sustainable-development metal magnesium production method.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic view of the structure of an electrolytic cell of the present invention.
Wherein, 1-anode electrode; 2-an anode compartment electrolyte; 3-raw material containing magnesium; 4-liquid alloy; 5-cathode compartment electrolyte; 6-a cathode product; 7-a cathode electrode; i, an anode chamber; II-cathode chamber.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the examples given herein without any inventive step, are within the scope of the present invention.
The embodiment of the invention relates to a method for preparing metal magnesium by molten salt electrolysis, which is carried out in an electrolytic cell. As shown in figure 1, the electrolytic bath adopted by the invention comprises an anode chamber I and a cathode chamber II, wherein an anode chamber electrolyte 2, an anode electrode 1 and a magnesium-containing raw material 3 are arranged in the anode chamber I, and a cathode chamber electrolyte 5 and a cathode electrode 7 are arranged in the cathode chamber II. Wherein the anode electrode 1 is made of graphite, the cathode electrode 7 is made of stainless steel, and the anode chamber I and the cathode chamber II are separated by the liquid alloy 4. In the figure 1, a communicated area below an electrolytic bath is filled with liquid alloy 4, and an anode chamber I and a cathode chamber II are respectively arranged above the electrolytic bath. The interface formed by the liquid alloy 4 and the electrolyte defines the area of the anode chamber I and the cathode chamber II, and the cathode electrode 7 and the anode electrode 1 are not in contact with the liquid alloy 4.
Taking magnesium-containing raw material 3 as magnesium oxide as an example, under the action of an external direct current voltage, the magnesium oxide in the anode chamber I is continuously reduced and dissolved, the magnesium metal obtained by reduction is dissolved in the liquid alloy 4, and oxygen ions combined with the magnesium oxide are oxidized into zero-valent oxygen on the surface of the anode electrode 1 to further generate CO and CO 2 /O 2 And (4) escaping. Meanwhile, compared with the flux metal, magnesium in the liquid alloy 4 is preferentially oxidized into magnesium ions to enter the cathode chamber molten salt 5, and the magnesium ions move to the surface of the cathode electrode 7 under the action of an electric field to be reduced to obtain a cathode product 6, namely the metal magnesium liquid. Impurities in the magnesium-containing raw material 3 are dissolved and then are retained in the anode chamber I, the liquid alloy 4 and the cathode chamber II.
Example 1
Placing pre-alloyed copper-magnesium alloy ((50 at%) Cu-Mg (50 at%), vacuumizing the electrolytic cell filled with the copper-magnesium alloy, introducing inert gas argon, and keeping the flow of 10mL/min for continuous argon protection after the electrolytic cell is filled with the argon. And then heating the electrolytic cell to 800 ℃, and preserving the heat for 2 hours to ensure that the copper-magnesium alloy in the electrolytic cell is completely melted into liquid, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
NaCl (40 at%) -CaCl 2 (60 at%) molten salt as anode compartment electrolyte, mgCl 2 (18wt％)-NaCl(38wt％)-KCl(29wt％)-CaCl 2 (15 wt%) molten salt was the cathode compartment electrolyte. Adding a magnesium oxide solid material (with the purity of 98%) to an interface formed by molten salt and liquid alloy in an anode chamber, then heating the temperature of the electrolytic cell to 800 ℃, inserting a graphite rod serving as an anode electrode into the molten salt in the anode chamber and inserting a stainless steel rod serving as a cathode electrode into the molten salt in the cathode chamber after the temperature of the electrolytic cell is stable. Electrifying and electrolyzing for 12h under protective atmosphere provided by argon, and controlling anode current density to be 1.2A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.99 percent, and the anode products are CO and CO 2 。
Example 2
The method comprises the steps of placing pre-alloyed zinc-magnesium alloy ((60 at%) Zn-Mg (40 at%)), vacuumizing the electrolytic cell filled with the zinc-magnesium alloy, introducing inert gas argon, and keeping the flow of 30mL/min for continuous argon protection after the electrolytic cell is filled with the argon. And then heating the electrolytic cell to 740 ℃, and preserving the heat for 2 hours to ensure that the zinc-magnesium alloy in the electrolytic cell is completely melted into liquid, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
With (46.7 at%) NaCl-CaCl 2 (53.3 at%) molten salt as the electrolyte in the anode compartment, mgCl 2 (15wt％)-NaCl(40wt％)-KCl(5wt％)-CaCl 2 (40 wt%) molten salt was the cathode compartment electrolyte. Adding magnesium oxide solid material (purity is 75%) to the interface formed by molten salt and liquid alloy in the anode chamber, then heating the temperature of the electrolytic cell to 740 ℃, and after the temperature of the electrolytic cell is stable, adding CaRuO 3 The inert anode of oxide ceramic is inserted into the fused salt of the anode chamber, and the stainless steel bar is used as the cathode electrode and inserted into the fused salt of the cathode chamber. Electrifying and electrolyzing for 16h under the protective atmosphere provided by helium, and controlling the current density of the anode to be 1.0A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.90 percent, and the anode product is O 2 。
Example 3
Placing a pre-alloyed tin-magnesium alloy ((65 at%) Sn-Mg (35 at%)), vacuumizing the electrolytic cell filled with the tin-magnesium alloy, introducing inert gas argon, and keeping the flow of 20mL/min for continuous argon protection after the argon is filled. The cell was then heated to 700 ℃ and held for 2 hours to completely melt the tin-magnesium alloy in the cell to a liquid state, the resulting liquid alloy dividing the cell into an anode chamber and a cathode chamber.
With (10 at%) KCl- (40 at%) NaCl-CaCl 2 (50 at%) molten salt as the electrolyte in the anode compartment, mgCl 2 (20wt％)-NaCl(50wt％)-CaCl 2 (30 wt%) molten salt was the cathode compartment electrolyte. Adding a magnesium oxide solid material (with the purity of 85%) to an interface formed by molten salt and liquid alloy in an anode chamber, heating the temperature of the electrolytic cell to 700 ℃, inserting a graphite rod serving as an anode electrode into the molten salt in the anode chamber and inserting a stainless steel rod serving as a cathode electrode into the molten salt in the cathode chamber after the temperature of the electrolytic cell is stable. Electrifying and electrolyzing for 14h under protective atmosphere provided by argon, and controlling anode current density to be 1.5A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.94 percent, and the anode product magnesium metal prepared in the cathode chamber has the purity ofPolar products are CO and CO 2 。
Example 4
Placing prealloyed copper-lead-magnesium alloy (Cu (17 at%) - (17.5 at%) Pb-Mg (65.5 at%) on the bottom of the electrolytic bath, vacuumizing the electrolytic bath filled with the copper-lead-magnesium alloy, introducing inert gas argon, keeping the flow of 30mL/min for continuous argon protection after the argon is filled, heating the electrolytic bath to 650 ℃, and preserving the temperature for 2 hours to ensure that the copper-lead-magnesium alloy in the electrolytic bath is completely melted into a liquid state, wherein the formed liquid alloy divides the electrolytic bath into an anode chamber and a cathode chamber.
With (46.7 at%) NaCl-CaCl 2 (53.3 at%) molten salt as the electrolyte in the anode compartment, mgCl 2 (15 wt%) -NaCl (45 wt%) -KCl (40 wt%) molten salt was the cathode compartment electrolyte. Adding magnesium oxide solid material (purity is 90%) to the interface formed by molten salt and liquid alloy in the anode chamber, heating the temperature of the electrolytic bath to 650 ℃, and after the temperature of the electrolytic bath is stable, adding Ni-NiO-NiFe 2 O 4 The inert anode of the metal ceramic is inserted into the fused salt of the anode chamber, and the stainless steel bar is used as the cathode electrode and inserted into the fused salt of the cathode chamber. Electrifying and electrolyzing for 12h under the protective atmosphere provided by argon, and controlling the current density of the anode to be 1.2A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.91 percent, and the anode product is O 2 。
Example 5
Placing pre-alloyed copper-magnesium alloy ((60 at%) Cu-Mg (40 at%)), vacuumizing the electrolytic cell filled with the copper-magnesium alloy, introducing inert gas argon, and keeping the flow of 10mL/min for continuous argon protection after the argon is full. And then heating the electrolytic cell to 900 ℃, and preserving the heat for 1 hour to ensure that the copper-magnesium alloy in the electrolytic cell is completely melted into a liquid state, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
With CaCl 2 (95 at%) -CaO (5 at%) molten salt as electrolyte of anode chamber, mgF 2 (25 at%) -NaF (75 at%) molten salt as cathode compartment electrolyte. Adding magnesium oxide solid material (purity 98%) to the interface formed by molten salt and liquid alloy in the anode chamber, heating the temperature of the electrolytic cell to 1000 deg.C, and stabilizing the temperature of the electrolytic cellThe rod is inserted into the anode chamber fused salt as an anode electrode, and the tungsten rod is inserted into the cathode chamber fused salt as a cathode electrode. Electrifying and electrolyzing for 24h under protective atmosphere provided by argon, and controlling anode current density to be 0.01A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.94 percent, and the anode products are CO and CO 2 。
Example 6
Placing pre-alloyed copper-magnesium alloy ((55 at%) Cu-Mg (45 at%)), vacuumizing the electrolytic cell filled with the copper-magnesium alloy, introducing inert gas argon, and keeping the flow of 50mL/min for continuous argon protection after the argon is filled. And then heating the electrolytic cell to 850 ℃, and preserving the heat for 2 hours to ensure that the copper-magnesium alloy in the electrolytic cell is completely melted into a liquid state, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
With (10 at%) LiCl- (20 at%) NaCl-CaCl 2 (70 at%) molten salt as anode compartment electrolyte, mgF 2 (28.7at％)-CaF 2 (15.2 at%) -LiF (56.1 at%) salt as cathode compartment electrolyte. Adding a magnesium carbonate solid material (with the purity of 95%) to an interface formed by molten salt and liquid alloy in an anode chamber, then heating the temperature of the electrolytic cell to 850 ℃, inserting a graphite rod serving as an anode electrode into the molten salt in the anode chamber and inserting a stainless steel rod serving as a cathode electrode into the molten salt in the cathode chamber after the temperature of the electrolytic cell is stable. Electrifying and electrolyzing for 24h under protective atmosphere provided by argon, and controlling the current density of the anode to be 5A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.90 percent, and the anode product is CO and CO 2 。
Example 7
Placing pre-alloyed silver-magnesium alloy ((35 at%) Ag-Mg (65 at%)), vacuumizing the electrolytic cell filled with the silver-magnesium alloy, introducing inert gas argon, and keeping the flow of 10mL/min for continuous argon protection after the argon is filled. And then heating the electrolytic cell to 850 ℃, and keeping the temperature for 2 hours to ensure that the silver-magnesium alloy in the electrolytic cell is completely melted into liquid, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
NaCl (10 at%) -CaCl 2 (90 at%) molten salt as the electrolyte in the anode compartment, mgCl 2 (40 wt%) -NaCl (20 wt%) -KCl (40 wt%) molten salt was the cathode compartment electrolyte. Adding a magnesium oxide solid material (with the purity of 75%) to an interface formed by molten salt and liquid alloy in an anode chamber, then heating the temperature of the electrolytic cell to 900 ℃, inserting a graphite rod serving as an anode electrode into the molten salt in the anode chamber and inserting a molybdenum rod serving as a cathode electrode into the molten salt in the cathode chamber after the temperature of the electrolytic cell is stable. Electrifying and electrolyzing for 24h under protective atmosphere provided by argon, and controlling the current density of the anode to be 0.05A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.90 percent, and the anode product is CO and CO 2 。
Example 8
Placing prealloyed gallium-magnesium alloy (70 at percent) Ga-Mg (30 at percent) at the bottom of the electrolytic cell, vacuumizing the electrolytic cell filled with the gallium-magnesium alloy, introducing inert gas argon, and keeping the flow of 10mL/min for continuous argon protection after the argon is filled. And then heating the electrolytic cell to 720 ℃, and preserving the heat for 2 hours to ensure that the gallium-magnesium alloy in the electrolytic cell is completely melted into liquid, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
NaCl (15 at%) -CaCl 2 (85 at%) molten salt as anode compartment electrolyte, mgCl 2 (20wt％)-NaCl(55wt％)-CaCl 2 (25 wt%) molten salt was the cathode compartment electrolyte. Adding a magnesium carbonate solid material (with the purity of 80%) to an interface formed by molten salt and liquid alloy in an anode chamber, then heating the temperature of the electrolytic cell to 850 ℃, inserting a graphite rod serving as an anode electrode into the molten salt in the anode chamber and inserting a tungsten rod serving as a cathode electrode into the molten salt in the cathode chamber after the temperature of the electrolytic cell is stable. Electrifying and electrolyzing for 24h under protective atmosphere provided by argon, and controlling the current density of the anode to be 1.0A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.90 percent, and the anode products are CO and CO 2 。
Example 9
Placing prealloyed indium magnesium alloy (50 at percent In-Mg (50 at percent)) at the bottom of the electrolytic bath, vacuumizing the electrolytic bath filled with the indium magnesium alloy, then introducing inert gas argon, and keeping the flow of 10mL/min for continuous argon protection after the electrolytic bath is filled with the argon. And then heating the electrolytic cell to 700 ℃, and preserving the heat for 2 hours to ensure that the indium-magnesium alloy in the electrolytic cell is completely melted into liquid, and the formed liquid alloy divides the electrolytic cell into an anode chamber and a cathode chamber.
NaCl (50 at%) -CaCl 2 (50 at%) molten salt as anode compartment electrolyte, mgCl 2 (5 wt%) -NaCl (20 wt%) -KCl (75 wt%) molten salt was the cathode compartment electrolyte. Adding a magnesium oxide solid material (with the purity of 85%) to an interface formed by molten salt and liquid alloy in an anode chamber, heating the temperature of the electrolytic cell to 700 ℃, inserting a graphite rod serving as an anode electrode into the molten salt in the anode chamber and inserting a stainless steel rod serving as a cathode electrode into the molten salt in the cathode chamber after the temperature of the electrolytic cell is stable. Electrifying and electrolyzing for 20h under protective atmosphere provided by argon, and controlling the current density of the anode to be 0.8A/cm 2 The purity of the cathode product magnesium metal prepared in the cathode chamber is 99.90 percent, and the anode products are CO and CO 2 。
Comparative example 1
The electrolytic cell shown in FIG. 1 was used. The anode electrode, cathode electrode and molten salt were the same as in example 1 except that no liquid alloy was added, and the molten salts in the cathode and anode chambers were mixed together. Electrolysis was carried out at the same reaction temperature, cathode current density and anode current density as in example 1. After the reaction is finished, the cathode product is analyzed to be a small amount of metal magnesium, and the anode product is chlorine.
Comparative example 2
The metal alloy was replaced with copper alone and the other reaction conditions were the same as in example 1. The reaction condition needs the temperature above 1083 ℃ to ensure that the metal copper is melted into liquid state, and has the problem that the fused salt volatilizes at high temperature, and needs higher voltage to realize current path, so the electrolysis process is difficult to carry out.
Comparative example 3
The metal alloy was replaced with magnesium alone and the reaction conditions were otherwise the same as in example 1. The magnesium liquid floats on the surface of the fused salt in the cathode and anode chambers, and the fused salt in the cathode and anode chambers is mixed into a whole. In the electrolytic process, the anode reaction is the oxidation of metal magnesium, the cathode reaction is the reduction of magnesium ions, after the electrolytic reaction is finished, the cathode product is the metal magnesium,comparative example 4
Magnesium chloride was not added to the molten salt in the cathode chamber, and the balance was supplemented with sodium chloride, and the other reaction conditions were the same as in example 1. After the electrolysis reaction is finished, the cathode product is analyzed to be metal magnesium with high impurity content, and the purity is 71.5%.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (10)
1. A method for preparing metal magnesium by molten salt electrolysis is characterized by comprising the following steps:
(1) An anode chamber oxidation reduction process: adopting an electrolytic cell with an anode chamber and a cathode chamber, respectively arranging anode chamber electrolyte and cathode chamber electrolyte in the anode chamber and the cathode chamber, placing an anode and a solid magnesium-containing raw material in the anode chamber, and placing a cathode in the cathode chamber for electrolytic reaction; the anode chamber and the cathode chamber are separated by liquid alloy, and the cathode and the anode are not in contact with the liquid alloy;
the liquid alloy includes a flux metal and magnesium metal, the flux metal having a metal activity less than magnesium;
after the electrolysis reaction starts, reducing the magnesium-containing raw material in the anode chamber into metal magnesium and dissolving the metal magnesium in the liquid alloy, and oxidizing oxygen ions in the molten salt in the anode chamber at the anode;
(2) Cathode compartment redox process: and oxidizing the magnesium metal in the liquid alloy into magnesium ions at the interface of the liquid alloy, reducing the magnesium ions in the molten salt in the cathode chamber at the cathode, and preparing the magnesium metal in the cathode chamber.
2. The method of claim 1, wherein the magnesium-containing raw material is magnesium oxide or/and magnesium carbonate.
3. The method of claim 1, wherein the anode is a graphite anode or an inert anode, and the inert anode is an oxide ceramic material, a metallic material, or a cermet material.
4. The method according to claim 1, wherein the anode chamber molten salt is selected from one or more of calcium chloride, barium chloride, sodium chloride, potassium chloride, lithium chloride, calcium fluoride, lithium fluoride, sodium fluoride and potassium fluoride.
5. The method of claim 1, wherein the cathode is stainless steel, tungsten, or molybdenum.
6. The method according to claim 1, wherein the cathode chamber molten salt is selected from one or more of sodium chloride, potassium chloride, lithium chloride, calcium chloride, barium chloride, lithium fluoride, sodium fluoride and potassium fluoride, and is dissolved with magnesium salt which is magnesium chloride or/and magnesium fluoride.
7. The method of claim 6, wherein the magnesium salt is present in the molten salt in the cathode compartment in an amount of 5wt% to 40wt%.
8. The method of claim 1, wherein the flux metal is selected from one or more of copper, zinc, lead, tin, bismuth, silver, gallium, and indium.
9. A process according to any one of claims 1 to 8, characterized in that in said electrolysis reaction, the cathodic current density is between 0.01 and 2.5A/cm 2 The current density of the anode is 0.01-5A/cm 2 。
10. The method according to any one of claims 1 to 8, wherein the operating temperature of the electrolytic cell is 650-1000 ℃, and the electrolysis reaction is carried out in an inert atmosphere, wherein the inert atmosphere is argon or helium.
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| CN117509646A (en) * | 2023-11-13 | 2024-02-06 | 中国科学院广州地球化学研究所 | Preparation method and device of silicon-based nano-micron material |
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