CN113279022A - Reducing molten salt medium and preparation method thereof - Google Patents

Reducing molten salt medium and preparation method thereof Download PDF

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CN113279022A
CN113279022A CN202110532506.7A CN202110532506A CN113279022A CN 113279022 A CN113279022 A CN 113279022A CN 202110532506 A CN202110532506 A CN 202110532506A CN 113279022 A CN113279022 A CN 113279022A
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molten salt
salt medium
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颜晓勇
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Auyong Advanced Materials Technology Shanghai Co ltd
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    • C25C3/00—Electrolytic production, recovery or refining of metals by electrolysis of melts
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Abstract

The invention relates to the technical field of metal material preparation, and particularly discloses a reducing molten salt medium and a preparation method thereof. The preparation method of the reducing molten salt medium adopts a mixed salt MaOH-Ma2CO3-MaCl as raw material, and MaY-MeY as mixture2Is a molten salt medium flux; mixing MaOH-Ma2CO3-MaClMaOH-Ma2CO3-MaCl is melted to form MaOH-Ma2CO3-MaCl molten salt, the MaOH-Ma2CO3-MaCl molten salt is put into a melted MaY-MeY2 molten salt medium flux, and electrolytic reaction is carried out to obtain the reducing molten salt medium; the reducing molten salt medium is MaY-MeY 2-Ma; wherein Ma represents an alkali metal; me represents an alkaline earth metal; y represents a halogen element. The preparation method can effectively solve the problems of low production efficiency and high energy consumption in the prior art for preparing the metal material.

Description

Reducing molten salt medium and preparation method thereof
Technical Field
The invention relates to the technical field of metal material preparation, in particular to a reducing molten salt medium and a preparation method thereof.
Background
The basic method for extracting valuable metals from minerals comprises the following steps: (1) extracting concentrate with high content of metal oxides or sulfides from minerals by a beneficiation method; (2) converting the concentrate into crude metal by adopting a smelting method, and then refining the crude metal to obtain high-purity metal; or (3) the concentrate is first converted into metal compounds (metal oxides, metal halides, metal sulfides, etc.) and the metal is then produced from these metal compounds. The traditional production of metals from metal compounds relies on: (1) a hydrometallurgical preparation method, (2) a high-temperature chemical preparation method, and (3) an electrochemical preparation method.
Active metal M1Thermally reducing compounds M of another metal2X belongs to one of the high-temperature chemical preparation methods, and the total reaction expression is as follows:
M2X+M1＝M2+M1X (1)
wherein M is1Is an active metal (e.g., alkali metal, alkaline earth metal, Al, Si) used as a reducing agent; m2X is a metal compound, wherein M2Is the metal to be produced, and X is a non-metallic element and may be oxygen, chlorine, fluorine, sulfur, carbon, nitrogen, or the like. And M2In contrast, M1Has a stronger affinity for X, that is, M1Thermodynamic stability ratio M of X2X is high. Thus, the standard reaction free energy change (. DELTA.G ℃) of reaction (1) is always negative. Moreover, reaction (1) is always an exothermic reaction and is therefore referred to as "metallothermic reduction". The metallothermic reduction method has been used industrially to produce certain high purity metals, e.g. magnesium separately thermally reducing TiCl4Or ZrCl4Production of titanium sponge or Zirconium metal (Trans. electrochem. Soc., 1940, 78, 35-47; "Zirconium" CRC Handbook of chem. Phys.4, 2007-2TaF7Sodium reduction produces metallic tantalum powder (us 3012877, 12.12.1961), aluminothermic reduction of a mixture of iron oxide and aluminum vanadium oxide produces ferrovanadium (Minerals eng., 2003, 16, 793-one 805).
The metallothermic reduction method requires the consumption of an excess of the active metal reducing agent M1So that the reaction (1) is carried out completely, and all the active metals themselves are expensive, thereby increasing the production cost of the thermal reduction method. From an economic point of view, the metallothermic reduction process is only suitable for producing metals that are more expensive than the metallic reducing agents. In addition, a large amount of reaction heat is released in the metallothermic reduction process, so that the reaction metal products are mutually sintered in situ to easily form spongy porous particles, and the superfine metal powder cannot be prepared.
In the metallothermic reduction method, alkali metal (Ma) and alkaline earth metal (Me) have been widely used as reducing agents in the metallothermic reduction method to prepare various metals, with the main disadvantages of: (1) the price of alkali metal and alkaline earth metal is high, so that the cost of the reduction process is high; (2) due to the chemical activity of alkali metals and alkaline earth metals, the direct use of these metal reducing agents causes operational risks, high safety management requirements and great difficulty; (3) the thermal reduction process releases a large amount of reaction heat, which is easy to cause the local sintering of reaction products, (4) because alkali metal and alkaline earth metal have strong volatility at high temperature, the chemical erosion to the furnace lining material is easy to occur; (5) the production process is complex; 6) the production period is long and the cost is high; (7) the process energy consumption is large; (8) the process is a batch production process, and is difficult to realize continuity or semi-continuity.
Alkali metals have a much lower melting point than alkaline earth metals, but only a slightly lower boiling point than alkaline earth metals. Thus, alkali metals are more suitable for thermal reduction processes with lower reduction temperatures, e.g. below 700 ℃, while alkaline earth metals are more suitable for thermal reduction with higher reduction temperatures, e.g. above 750 ℃. The biggest advantage of the low-temperature metal thermal reduction is that the method can greatly reduce the heat energy loss in the process, and simultaneously effectively reduce the partial sintering degree of the product, so that the structural performance of the product is more consistent.
Molten salts are widely used as reaction media in thermal reduction of alkali or alkaline earth metals. For example, U.S. patent No. 4992096, 12/2/1991 discloses a method for producing CaCl2The rare earth metal and the alloy thereof are prepared by the calcium thermal reduction of rare earth metal chloride in a molten salt medium. In CaCl2Preparation of rare earth metals and alloys by thermal reduction of rare earth metal oxides with calcium in NaCl molten salt medium (US4578242, 3/25/1986) in CaCl2Preparation of rare earth metals and their alloys by thermal reduction of rare earth metal fluorides with calcium in molten salt medium (US patent 5314526, 24/5/1994), MgCl2-NdCl3Magnesiothermic reduction of UO in molten salt medium2And other actinide metal oxides (US590337, 3/1/1994), in CaCl2-CaF2Thermal reduction of TiO by calcium in molten salt medium2Or ZrO2Preparation of metallic titanium or zirconium (US6117208, 9/12/2000), thermal reduction of Ta with sodium in alkali and alkaline-earth chlorides2O5And Nb2O5Preparation of metallic tantalum and niobium (CN1410209A, 2003)Year 4, month 16). The main advantages of the molten salt medium are:
(i) the fused salt medium has good heat transfer performance, is easy to maintain the uniformity of the temperature of the medium, can effectively reduce the local sintering of a reduction product, and is beneficial to ensuring the consistency of the performance of the product;
(ii) alkali and alkaline earth metals have certain solubility in molten halide, and certain thermal reduction reaction byproducts (alkaline earth metal oxide MeO) have equivalent solubility in molten halide salt, so that the properties are favorable for direct contact of an alkali metal reducing agent and oxide MO, and the reaction speed is accelerated.
However, the above-mentioned metallothermic reduction process directly employs calcium or sodium in metallic form as a reducing agent. Therefore, the temperature of the molten metal is controlled,
despite the use of molten salt media, the above-mentioned disadvantages (1), (2), (5), (6), (7) and (8) of the alkali metal and alkaline earth metal thermal reduction methods are still not overcome.
Patent CN105274576B discloses a method for preparing metal by continuous reduction in molten salt medium, aiming at the defects existing in the prior art that oxide MO is thermally reduced by alkali metal in molten salt medium, so as to solve or overcome the following disadvantages:
(i) the alkali metal reducing agent in metallic form is replaced by a specially selected alkaline earth metal oxide MeO/alkali metal halide MaY mixture: the defects of complex operation and danger caused by the existing method of directly adding the alkali metal reducing agent are overcome; the problems of high safety management requirements and high difficulty in alkali metal treatment and operation are solved;
(ii) auxiliary electrolysis of alkaline earth metal oxide MeO-containing molten salt medium to generate and regenerate alkali metal reducing agent in situ: the problem that the prior alkali metal thermal reduction excessively uses an alkali metal reducing agent is solved; overcomes the defect that the existing batch production process of metal thermal reduction is difficult to realize continuity.
However, in the actual production process, the method of patent CN105274576B has the problems of low production efficiency and high energy consumption.
Disclosure of Invention
The present invention aims to solve at least to some extent one of the technical problems indicated in the background.
The technical problem to be solved by the invention is realized by the following technical scheme:
the invention provides a preparation method of a reducing molten salt medium, which is a mixed salt MaOH-Ma2CO3-MaCl as raw material, and MaY-MeY as mixture2Is a molten salt medium flux; mixing MaOH-Ma2CO3Melting of-MaCl to form MaOH-Ma2CO3-MaCl molten salt, charging molten MaY-MeY2Carrying out electrolytic reaction in a molten salt medium flux to obtain the reducing molten salt medium;
the reducing molten salt medium is MaY-MeY2-Ma；
Wherein Ma represents an alkali metal; me represents an alkaline earth metal; y represents a halogen element.
The patent CN105274576B is a previous invention of the inventor, and the inventor further found that the method of the patent CN105274576B has a technical problem of low production efficiency in the process of preparing the metal material in actual production; in order to solve the technical problem of low production efficiency, the inventors have conducted a great deal of experimental studies to find the cause of low production efficiency, and finally found that: the method adopting patent CN105274576B is to prepare a reducing molten salt medium by taking a MeO/MaY mixture as a raw material, the speed of dissolving MeO in the molten salt medium near a reaction product by adopting the reducing molten salt medium is too slow, and the viscosity of surrounding molten salt is increased by the undissolved MeO; and the increase of the viscosity of the molten salt leads to the reduction speed reduction, thereby leading to the low production efficiency. Based on the discovery of the reason, the inventor replaces the raw material MeO/MaY in the patent CN105274576B with the raw material MaOH-Ma2CO3The raw material does not contain MeO, so that the content of MeO in the molten salt medium can be effectively reduced, the melting of MeO generated by the reaction is promoted, the content of MeO in the molten salt medium is effectively reduced, and the problem that the speed of dissolving MeO in the molten salt medium is too slow is solved; further successfully overcomes the problem that the method of the patent CN105274576B has low reduction speed and low production efficiency caused by the slow speed of dissolving MeO in a molten salt medium near a reaction product.
The inventor further researches and discovers that the speed of MeO dissolving in a molten salt medium is too slow in the vicinity of a reaction product, and the undissolved MeO increases the viscosity of the surrounding molten salt; the uniformity of the molten salt performance is reduced due to the increase of the viscosity of the molten salt, particularly the heat transfer property of a molten salt medium is reduced, and the structural consistency of a product is easily reduced due to the local or excessive sintering of a metal product; based on the discovery of the reason, the inventor replaces the raw material MeO/MaY in the patent CN105274576B with the raw material MaOH-Ma2CO3The raw material does not contain MeO, so that the content of MeO in the molten salt medium can be effectively reduced, the dissolution of MeO generated by the reaction is promoted, and the problem that the speed of dissolving MeO in the molten salt medium is too slow is solved; further successfully overcomes the problem of poor structural consistency of the product in the method disclosed in the patent CN 105274576B.
The inventor further researches and discovers that the slow dissolving speed of MeO in a molten salt medium in the vicinity of a reaction product causes the increase of energy consumption and production cost. Based on the discovery of the reason, the inventor replaces the raw material MeO/MaY in the patent CN105274576B with the raw material MaOH-Ma2CO3The raw material does not contain MeO, so that the content of MeO in the molten salt medium can be effectively reduced, the dissolution of MeO generated by the reaction is promoted, and the problem that the speed of dissolving MeO in the molten salt medium is too slow is solved; further successfully overcomes the problem of high energy consumption of the method disclosed in the patent CN 105274576B.
The preparation method of the reducing molten salt medium comprises the following specific steps:
mixing MaOH-Ma2CO3-MaCl molten salt put into the reactor with Ma+A container for ion conduction; will then have Ma+The ion-conducting container is filled with molten MaY-MeY2In a flux of molten salt medium, having Ma+Ion-conducting container external direct contact with MaY-MeY2Contact of molten salt medium with flux to make MaOH-Ma2CO3-MaCl fused salt with molten MaY-MeY2The molten salt medium flux is completely isolated;
in MaOH-Ma2CO3-MaCl in molten saltInserting an electronic conductor bar as an inert anode; in MaY-MeY2An electronic conductor bar is inserted into the fused salt medium flux to be used as an inert cathode; forming an "inert anode, MaOH-Ma2CO3-MaCl (anolyte) | Ma+Ionic solid conductor | MaY-MeY2(catholyte), inert cathode "cells;
carrying out electrolytic reaction on the electrolytic cell to obtain the reducing molten salt medium MaY-MeY2-(Ma)。
The inventor adopts the raw material MaOH-Ma2CO3And the further research shows that the dissolution of Ma produced by adopting the method of the Chinese invention patent CN105274576B into the molten salt medium can cause the remarkable increase of the electron conduction ratio of the medium and the reduction of the electrolysis current efficiency, thereby causing the low efficiency of preparing the Ma reducing agent, and finally causing the low production efficiency, the high energy consumption and the high production cost in the production process.
Based on the discovery of the reason, the inventor converts MaOH-Ma into MaOH-Ma in the electrolytic process2CO3-MaCl molten salt put into the reactor with Ma+A container for ion conduction; will then have Ma+The ion-conducting container is filled with molten MaY-MeY2In a flux of molten salt medium, having Ma+Ion-conducting container external direct contact with MaY-MeY2Contact of molten salt medium with flux to make MaOH-Ma2CO3-MaCl fused salt with molten MaY-MeY2The molten salt medium flux is completely isolated; forming an "inert anode, MaOH-Ma2CO3-MaCl (anolyte) | Ma+Ionic solid conductor | MaY-MeY2(catholyte), inert cathode "cell. The electrolysis is carried out based on the electrolytic cell, and the defect that MaY-MeY is formed after electrolysis in the Chinese invention patent CN105274576B is overcome2The- (Ma) molten salt medium has the defect of ion/electron mixed conduction, greatly improves the current efficiency of electrolysis, can realize the efficient preparation of the Ma reducing agent, and finally promotes the improvement of the production efficiency and the reduction of energy consumption in the production process.
In addition, an "inert anode, MaOH-Ma is used2CO3-MaCl (anolyte) | Ma+Ionic solid conductor | MaY-MeY2The electrolysis is carried out in an inert cathode electrolytic cell, so that the oxygen and the water vapor of the anode product are completely separated from the alkali metal Ma of the cathode product, and the reverse reaction of the oxygen and the water vapor with the active metal Ma is avoided. By placing an inert cathode on MaY-MeY2Different positions of the molten salt medium flux can ensure that Ma is separated out from the cathode at any required position in the molten salt medium flux and is locally melted into the molten salt medium flux to be diffused to the periphery of the cathode, thereby strengthening the homogenization and thermal reduction MO process of (Ma) in the medium.
Using an "inert anode, MaOH-Ma2CO3-MaCl (anolyte) | Ma+Ionic solid conductor | MaY-MeY2(catholyte), inert cathode "electrolytic cell, raw material MaOH-Ma can be electrolyzed2CO3-MaCl and MaY-MeY2Separated to lead the fused salt medium flux MaY-MeY2The method has no externally added MeO, promotes the dissolution of the generated MeO, and solves the problem of low production efficiency caused by the over-slow speed of dissolving the MeO in the molten salt medium.
In addition, the MaOH-Ma2CO3-MaCl is a molten salt with a low melting point, preferably the eutectic salt MaOH-Ma2CO3-MaCl molten salt.
In addition, the alkali metal is Li, Na or K; the alkaline earth metal is Ca, Sr or Ba; the halogen element is Cl or F.
In addition, the said has Ma+The active material in the ion-conducting container is a solid ion conductor Ma+β-Al2O3。
In addition, the said has Ma+The ion-conducting container is prepared by the following method: will consist of Na2O and Al2O3Na prepared by using raw materials+β-Al2O3The container is immersed in a bath containing Ma+Ion exchange is carried out in the ion molten salt to obtain the compound with Ma+A container for ion conduction;
or, said has Ma+The ion conducting container isMa oxide or carbonate and Al2O3Is prepared from the raw materials.
In addition, the molten salt containing Ma + ions is MaY-MeY2Mixing molten salt; or a halide or nitrate containing Ma + ions.
In addition, the inert cathode and inert anode electron conductor rods may be of the same or different materials.
Further, the material of the electron conductor rod as the inert anode is selected from: a metal, alloy, electroceramic, cermet, or graphite; the material of the electronic conductor bar as the inert cathode is stainless steel, Fe, Ni, Mo, W or the same material as the prepared metal in a chloride molten salt system; in the fluoride fused salt system is Mo, W or the same material as the prepared metal.
In addition, the electrolytic voltage in the electrolytic reaction is controlled to be higher than the actual decomposition voltage of MaOH and lower than Ma2CO3Or higher than Ma, or2CO3Is lower than the actual decomposition voltage of MaCl or higher than the actual decomposition voltage of MaCl.
In addition, the electrolytic voltage in the electrolytic reaction is controlled to be 2.4-2.6V. In the actual production process, the electrolysis voltage of 2.4-2.6V not only ensures the current efficiency of electrolysis and improves the production efficiency, but also ensures that only gas byproduct oxygen is released at the anode, so that the process has the advantages of environmental protection.
In the present invention, "-" between the components represents the composition, such as the mixed salt MaOH-Ma2CO3-MaCl represents MaOH, Ma2CO3And a mixed salt of MaCl.
The invention also provides a reducing molten salt medium prepared by the preparation method.
Has the advantages that: compared with the prior art, the preparation of the metal material in the reducing molten salt medium has the following advantages: (1) using MaOH-Ma2CO3-MaCl as raw material of alkali metal Ma, convenient for using common metal or alloy to replace expensive noble metal as oxygen inert anodeThe electrode material, the low theoretical decomposition voltage of MaOH is beneficial to reducing the electric energy consumption for preparing Ma; (2) the oxygen and the water vapor of the anode product are completely separated from the alkali metal Ma of the cathode product, so that the reverse reaction of the oxygen and the water vapor with the active metal Ma is avoided; (3) using an "inert anode, MaOH-Na2CO3NaCl (anolyte) | Ma+Ionic solid conductor | MaY-MeY2(cathode electrolyte), inert cathode' electrolytic cell overcomes the defect that MaY-MeY is formed after electrolysis in the Chinese invention patent CN105274576B2The- (Ma) molten salt medium has the defect of ion/electron mixed conduction, so that the current efficiency of auxiliary electrolysis is greatly improved, and the efficient preparation of the Ma reducing agent can be realized; (4) ma separated out from the cathode has extremely high purity; (5) compared with the traditional method of directly adding Ma from the surface of the molten salt medium and then diffusing the Ma downwards to enter the molten salt medium main body, the Ma separated out from the cathode is easy to be directly dissolved to enter the molten salt medium main body, and the volatilization and oxidation loss of the Ma on the surface of the molten salt medium are reduced; (6) by placing an inert cathode on MaY-MeY2Different positions in the fused salt medium flux can ensure that Ma is separated out from the cathode at any required position in the fused salt medium flux and is locally melted into the fused salt medium to be diffused to the periphery of the cathode, thereby strengthening the homogenization and thermal reduction MO process of (Ma) in the medium; (7) the addition of Ma has more accurate controllability, and the defects that Ma in CN105274576B is slowly dissolved in a molten salt medium and (Ma) is slowly and uniformly distributed are avoided; (8) overcomes the defects of scum and flue gas dust formation in the traditional Ma adding process; (9) oxygen and water vapor released by the anode are naturally separated at normal temperature, and valuable oxygen becomes a unique gas byproduct, so that the process has the advantages of environmental protection.
Drawings
FIG. 1 is a schematic diagram of a process for preparing a reducing molten salt medium according to an embodiment of the present invention.
Detailed Description
The present invention is further explained below with reference to specific examples, which are not intended to limit the present invention in any way.
The invention uses an electrochemical method to prepare the reducing agent of alkali metal Ma in situ, and the method decomposes eutectic mixed salt MaOH-Ma through molten salt electrolysis2CO3MaOH, Ma in the-MaCl system2CO3And MaCl. The total electrolytic reactions are represented by the following reactions, respectively:
4(MaOH)＝4(Ma)+O2(g)+2H2O (2a)
2(Ma2CO3)＝4Ma+O2(g)+2CO2(g) (2b)
2(MaCl)＝2Ma+Cl2(g) (2c)
adding Ma into molten MaOH2CO3And the purpose of the MaCl is to properly reduce the activity of MaOH in the mixed molten salt and the melting point of the molten salt.
The thermal reduction of MO by an alkali metal Ma in a reducing molten salt medium to produce a metal M is represented by reaction 3:
MO+2(Ma)+MeY2＝M+2MaY+(MeO) (3)
wherein in the reaction (3), (MeO) is a reaction by-product of the reaction (3), and then dissolved in the reducing MaY-MeY2Formation of MaY-MeY in (Ma) molten salt medium2- (Ma) - (MeO) media. MeY2Also participate in the heat reduction MO reaction of Ma, and MeY exists in a molten salt medium2So that reaction 3 is
Figure BDA0003067506580000071
The value of (A) is more negative, and the thermodynamic driving force of preparing metal M by thermally reducing MO by Ma is further improved. The () above means that the metal or metal oxide is dissolved in the molten salt medium in which it is melted, respectively.
Molten salt medium MaY-MeY formed in process of thermally reducing MO by Ma2The oxygen sites of (Ma) - (MaO) are controlled by the (Me)/(MeO) thermodynamic equilibrium and can be expressed by the following reaction:
(Me)+1/2O2(g)＝(MeO) (4)
MaY-MeY2the equilibrium oxygen level of the (Ma) - (MaO) molten salt medium is represented by the following equation:
Figure BDA0003067506580000081
wherein the content of the first and second substances,
Figure BDA0003067506580000084
is MaY-MeY2- (Ma) - (MaO) equilibrium oxygen position of molten salt medium, K is equilibrium constant of reaction (4), aMeOAnd aMeThe activity of MeO and Me, respectively, in the molten salt medium. The lower the oxygen level, the greater the reducing power (or reducibility) of the molten salt medium. Formula 1 shows that at a certain temperature, the molten salt medium MaY-MeY2Equilibrium oxygen sites of (Ma) - (MaO)
Figure BDA0003067506580000082
The ratio is proportional and inversely proportional to the reducing power. When the concentration of (MeO) in the molten salt medium is constant, the concentration of (Ma) in the molten salt medium increases, with a consequent increase in its activity. Increase aMeThe oxygen level of the molten salt medium can be reduced, the reducing capability of the medium is improved, and the Ma thermal reduction MO process is enhanced.
Table 1 shows the respective ratios MaOH, Ma2CO3And MCl as a starting material to prepare Ma thermodynamic data at 550 ℃.
TABLE 1. with MaOH, Ma2CO3And the thermodynamic data of MCl as raw material for preparing the reducing agent of the alkali metal Ma
Figure BDA0003067506580000083
Figure BDA0003067506580000091
As is clear from the data in Table 1, the standard free energy of reaction (2) is changed
Figure BDA0003067506580000092
Positive values indicate that these reactions do not proceed spontaneously, but that the alkali metal salts in table 1 can be decomposed by electrochemical methods, such as molten salt electrolysis. For example, when Ma ═ Na and 550 ℃:
(i) controlling electrolysis cell currentReaction 2a will occur at 2.4-2.6V, NaOH is decomposed: na is precipitated at the cathode, and O is released at the anode2(g) And H2O(g)，
(ii) In the range of about 2.4-3.4V, reactions 2a and b occur simultaneously, NaOH and Na2CO3And is decomposed at the same time: na is precipitated at the cathode, and O is released at the anode2(g)，H2O (g) and CO2(g)，
(iii) Above about 3.5V, reactions 2a, b and c will occur simultaneously, NaOH, Na2CO3And NaCl are decomposed simultaneously: na is precipitated at the cathode, and O is released at the anode2(g)，H2O(g)，CO2(g) And Cl2(g)。
When the molten salt electrolysis is carried out under the conditions, the corresponding loss amount of salt can be continuously added to maintain the molten low-melting-point mixed molten salt MaOH-Ma2CO3The composition of the-MaCl is essentially unchanged.
The thermodynamic analysis results in table 1 provide necessary theoretical basis for the preparation of the reducing agent of alkali metal Ma and the preparation of metal M by thermal reduction of MO by Ma according to the present invention.
The invention specifically adopts a solid ion conduction diaphragm to produce alkali metal Ma under the support of electrolysis, and the Ma is dissolved in a fused salt medium flux MaY-MeY on site2To form a reducing molten salt medium MaY-MeY2- (Ma). A solid ionic conductor is employed that is conductive by cations. At present, Na is a solid ionic conductor widely used in industry+β-Al2O3(Na2O.11Al2O3: about 350 ℃ and 1200 ℃ Na+Conductive) ion conductors (j.inorg. nuclear. chem., 1967, 29, 2453-; phil. trans., 1996, 354, 1595-. The literature reports ease: when Na is present+β-Al2O3The conductor is immersed in molten other alkali metal chloride, nitrate or mixed salts thereof, Na+β-Al2O3Na in (1)+The ions will react with Ma in the molten salt+Ion exchange is carried out on the ions, and Ma can be prepared by immersing in new molten salt for multiple times+β-Al2O3Conductors (J.Inorg.Nucl.chem., 1967, 29, 2453-2475; Solid State Ionics, 1982, 7, 267-281).
The present invention adopts Na in the form of a container for the method+β-Al2O3Conductor in-situ preparation of Ma+β-Al2O3A conductor. Ma obtained by any other existing preparation method+β-Al2O3Conductors can also be used in the present invention.
Example 1 preparation of reducing molten salt Medium
This example uses the mixed salt NaOH-Na2CO3NaCl as raw material and NaCl-CaCl mixture2Is a molten salt medium flux; wherein the mixed salt is NaOH-Na2CO3NaOH and Na in NaCl2CO3And the mass ratio of NaCl is 2: 1. Mixture NaCl-CaCl2Neutralizing NaCl and CaCl2The mass ratio of (A) to (B) is 1: 2.
As shown in FIG. 1, (1) will contain NaOH-Na2CO3Na of NaCl starting Material+β-Al2O3Putting NaCl-CaCl into a container2In a molten salt medium, adding Na+β-Al2O3The outside of the container is directly connected with NaCl-CaCl2The molten salt medium is contacted with each other, and NaOH-Na is made2CO3-molten NaCl salt with molten NaCl-CaCl2The molten salt medium flux is completely isolated; (2) when Na is present+β-Al2O3The raw materials in the container are melted to form molten NaOH-Na2CO3After NaCl fused salt, inserting an electronic conductor iron rod into the fused salt as an inert anode; in NaCl-CaCl2An electronic conductor bar made of stainless steel is inserted into the molten salt medium flux to serve as an inert cathode; form an "inert anode, NaOH-Na2CO3NaCl (anolyte) | Na+β-Al2O3|NaCl-CaCl2(catholyte), inert cathode "cells; (3) controlling the voltage of the electrolytic cell within the range of 2.3-2.5V at 600 ℃, and carrying out electrolytic reaction on the electrolytic cell to obtain the reducing molten salt medium.
This example uses eutectic NaOH-Na2CO3NaCl anolyte is raw material of metallic sodium reducing agent, and the cell voltage is controlled in the range of 2.3-2.5V at 600 deg.C, and the auxiliary electrolysis is implemented between inert anode and inert cathode of the cell shown in figure 1, and NaOH is electrochemically decomposed, and NaOH-Na is used under the condition of 2.3-2.5V2CO3Na in NaCl anolyte2CO3NaCl will not participate in the electrode reaction and will act as an electrolyte flux. Oxygen evolution at the anode and production of water vapor, Na from NaOH+Ion from Na+β-Al2O3The inner wall of the container passes through Na+β-Al2O3NaCl-CaCl with container membrane entering the outside of the container2Cathode electrolyte, high-purity Na is separated out from the inert cathode and then is melted into the cathode electrolyte to form NaCl-CaCl with strong reducibility2- (Na) molten salt medium.
Example 2 preparation of reducing molten salt Medium
This example uses the mixed salt KOH-K2CO3KCl is used as raw material, and KCl-CaCl is used as mixture2Is a molten salt medium flux; wherein the mixed salt KOH-K2CO3KOH, K in KCl2CO3And the mass ratio of KCl is 3: 1. Mixture KCl-CaCl2Medium KCl and CaCl2The mass ratio of (A) to (B) is 2: 1.
As shown in FIG. 1, (1) KOH-K is added2CO3Melting of-KCl to form KOH-K2CO3-KCl molten salt, adding K+β-Al2O3In a container; k+β-Al2O3Directly contacting KCl-CaCl outside the container2Molten salt medium flux phase contact, so that KOH-K2CO3-KCl molten salt with molten KCl-KCl2The molten salt medium flux is completely isolated; (2) in KOH-K2CO3Inserting an electronic Ni conductor bar into KCl molten salt as an inert anode; in KCl-KCl2An electronic conductor bar made of stainless steel is inserted into the molten salt medium flux to serve as an inert cathode; form an "inert anode, KOH-K2CO3-KCl (anolyte) | K+β-Al2O3|KCl-CaCl2(catholyte), inert cathode "cells; (3) Controlling the voltage of the electrolytic cell within the range of 2.3-2.5V at 650 ℃, and carrying out electrolytic reaction on the electrolytic cell to obtain KCl-CaCl2- (K) reducing molten salt medium.
Example 3 preparation of reducing molten salt Medium
This example uses the mixed salt LiOH-Li2CO3-LiCl as raw material, and mixture LiCl-CaCl2Is a molten salt medium flux; wherein the mixed salt LiOH-Li2CO3LiOH, Li in LiCl2CO3And the mass ratio of LiCl is 3: 1: 2. Mixture LiCl-CaCl2Neutralizing LiCl and CaCl2The mass ratio of (A) to (B) is 1: 1.75.
As shown in FIG. 1, (1) LiOH-Li is added2CO3Melting of LiCl to LiOH-Li2CO3-LiCl molten salt, insertion of Li+β-Al2O3In a container; li+β-Al2O3Directly contacting LiCl-CaCl outside the container2Molten salt medium flux contact to LiOH-Li2C03-LiCl molten salt with molten LiCl-LiCl2The molten salt medium flux is completely isolated; (2) in LiOH-Li2CO3-inserting an electron conductor iron rod into the LiCl molten salt as an inert anode; in LiCl-LiCl2An electronic conductor bar made of stainless steel is inserted into the molten salt medium flux to serve as an inert cathode; forming an "inert anode, LiOH-Li2CO3-LiCl (anolyte) | Li+β-Al2O3|LiCl-CaCl2(catholyte), inert cathode "cells; (3) controlling the voltage of the electrolytic cell within the range of 2.9-3.0V at 550 ℃, and carrying out electrolytic reaction on the electrolytic cell to obtain LiCl-CaCl2- (Li) reducing molten salt medium.

Claims (10)

1. The preparation method of the reducing molten salt medium is characterized in that the mixed salt MaOH-Ma is used as the reducing molten salt medium2CO3-MaCl as raw material, and MaY-MeY as mixture2As a molten salt medium flux, adding MaOH-Ma2CO3Melting of-MaCl to form MaOH-Ma2CO3-MaCl molten salt, charging molten MaY-MeY2Carrying out electrolytic reaction in a fused salt medium flux to obtainThe reducing molten salt medium;
the reducing molten salt medium is MaY-MeY2-Ma；
Wherein Ma represents an alkali metal; me represents an alkaline earth metal; y represents a halogen element.
2. The method for preparing a reducing molten salt medium according to claim 1, characterized by comprising the following steps:
mixing MaOH-Ma2CO3-MaCl molten salt put into the reactor with Ma+A container for ion conduction; will then have Ma+The ion-conducting container is filled with molten MaY-MeY2In a flux of molten salt medium, having Ma+Ion-conducting container external direct contact with MaY-MeY2Contact of molten salt medium with flux to make MaOH-Ma2CO3-MaCl fused salt with molten MaY-MeY2The molten salt medium flux is completely isolated;
in MaOH-Ma2CO3Inserting an electron conductor bar into the MaCl molten salt to serve as an inert anode; in MaY-MeY2An electronic conductor bar is inserted into the fused salt medium flux to be used as an inert cathode; forming an "inert anode, MaOH-Ma2CO3-MaCl (anolyte) | Ma+Ionic solid conductor | MaY-MeY2(catholyte), inert cathode "cells;
and carrying out electrolytic reaction on the electrolytic cell to obtain the reducing molten salt medium.
3. The method for preparing reducing molten salt medium according to claim 2, wherein the MaOH-Ma2CO3-MaCl is a molten salt with a low melting point, preferably the eutectic salt MaOH-Ma2CO3-MaCl molten salt.
4. The method for preparing a reducing molten salt medium according to claim 2, wherein the reducing molten salt medium has Ma+The active material in the ion-conducting container is a solid ion conductor Ma+β-Al2O3。
5. The method for preparing a reducing molten salt medium according to claim 2, wherein the reducing molten salt medium has Ma+The ion-conducting container is prepared by the following method: will consist of Na2O and Al2O3Na prepared by using raw materials+β-Al2O3The container is immersed in a bath containing Ma+Ion exchange is carried out in the ion molten salt to obtain the compound with Ma+A container for ion conduction;
or, said has Ma+The ion-conducting container is made of Ma oxide or carbonate and Al2O3Is prepared from the raw materials.
6. The method for preparing a reducing molten salt medium according to claim 4, wherein the medium contains Ma+The ionic molten salt is MaY-MeY2Mixed molten salts, or halides or nitrates containing Ma + ions.
7. A method for preparing a reducing molten salt medium as claimed in claim 2, wherein the inert cathode and inert anode electron conductor rods are of the same or different materials.
8. A method for preparing a reducing molten salt medium according to claim 6, characterized in that the material of the electron conductor rod as the inert anode is selected from: a metal, alloy, electroceramic, cermet, or graphite; the material of the electronic conductor bar as the inert cathode is stainless steel, Fe, Ni, Mo, W or the same material as the prepared metal in a chloride molten salt system; in the fluoride fused salt system is Mo, W or the same material as the prepared metal.
9. The method for preparing reducing molten salt medium according to claim 2, wherein the electrolysis voltage in the electrolysis reaction is controlled to be higher than the actual decomposition voltage of MaOH and lower than Ma2CO3Is actually divided intoDe-potential, or higher than Ma2CO3Is lower than the actual decomposition voltage of MaCl or higher than the actual decomposition voltage of MaCl.
10. A reducing molten salt medium produced by the production method according to any one of claims 1 to 9.
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