CN112899728B - Ammonium carnallite dehydration material and method for preparing magnesium electrolyte melt by using same - Google Patents
Ammonium carnallite dehydration material and method for preparing magnesium electrolyte melt by using same Download PDFInfo
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Abstract
The invention discloses an ammonium carnallite dehydration materialnNH4Cl•MgCl2•mH2O and a method for preparing a magnesium electrolyte melt by using the same, the preparation method comprising the steps of: (a) preparing a chloride melt by taking alkali metal chloride as a raw material; (b) placing the ammonium carnallite dehydrated material on the chloride melt and forming a solid material column; (c) heating the ammonium carnallite dehydrated material to form a magnesium electrolyte melt. The ammonium carnallite dehydrated material is easy to dehydrate in the heating process and can form a certain material structure at different temperatures, and the method for preparing the magnesium electrolyte melt can efficiently remove water in the dehydrated material, control hydrolysate, organic matters and other impurities in the material to be at an extremely low level, and meet the requirements of most advanced multi-electrode electrolytic cell electrolysis.
Description
Technical Field
The invention relates to the technical field of preparation of inorganic materials, in particular to an ammonium carnallite dehydrated material and a method for preparing a magnesium electrolyte melt based on the ammonium carnallite dehydrated material.
Background
China has abundant liquid magnesium resources, such as magnesium chloride hexahydrate (MgCl) in waste brine discharged annually in the process of producing potash fertilizer in Qinghai salt lake2·6H2O) content reaches 2400-3600 ten thousand tons. A large number ofThe magnesium chloride hexahydrate has the resource of being stocked everywhere to form the magnesium hazard in the local, and the opening and the utilization of the magnesium chloride hexahydrate are urgent and become the hot spots concerned by government departments and various circles of society. The method is an effective way for realizing high-efficiency high-value utilization of magnesium chloride hexahydrate. However, since part of the crystal water in magnesium chloride hexahydrate has a strong binding ability with magnesium chloride, it is easily hydrolyzed during its removal by heating, resulting in hydrolysis products (MgOHCl and MgO) which are seriously harmful to electrolysis. To reduce hydrolysis during heating, magnesium chloride hexahydrate is typically synthesized as ammonium carnallite (NH)4Cl·MgCl2·6H2O), and then dehydrating by utilizing the characteristic of small binding capacity of magnesium chloride and crystal water in the double salt. Therefore, ammonium carnallite dehydration is one of the most long and constantly studied methods for preparing high purity electrolytic magnesium melts (or high purity anhydrous magnesium chloride). The method has been studied by well-known companies and research institutions such as dao wu chemical, kaiser aluminum, and the whole soviet al research institute, and many patents have been published.
The high-purity magnesium electrolyte melt (or high-purity anhydrous magnesium chloride) is a key link of the electrolytic magnesium preparation process. The current methods for preparing high-purity magnesium electrolyte melt (or high-purity anhydrous magnesium chloride) by using ammonium carnallite comprise the following steps:
(1) the low-water ammonium carnallite is used for preparing anhydrous magnesium chloride by an ammonia method. The principle and the specific operating procedure of this method are described in patent US3798314 by Yuichi Suzukaw: low water ammonium carnallite (NH) first4Cl• MgCl2•nH2O, n= 0.5-4) at 110 ℃ -160 ℃, the product of the preliminary dehydration reacts with ammonia gas at 200 ℃ -400 ℃ to generate ammonium ammine carnallite NH4Cl•MgCl2•nNH3（n= 0.2-3). The ammonium ammine carnallite is calcined at 712-900 deg.C for a period of time to obtain anhydrous magnesium chloride. The method has the advantages that the process is simple, and the prepared anhydrous magnesium chloride can be directly used for electrolytic smelting of magnesium. Has the disadvantages of large ammonia consumption and high energy consumptionAnd the separation and purification of ammonia gas in the tail gas are difficult.
(2) Preparing anhydrous magnesium chloride by a gas-solid reaction method. Zhongning Bo at the university of Central and south (see: Zhongning Bo, Chenbaizhen, who is new and fast, Li Yi-an-good. ammonium carnallite gas-solid reaction method for preparing anhydrous magnesium chloride. applied chemistry, 2005, 22 (8): 874-: the ammonium carnallite is synthesized by taking bischofite in a salt lake and ammonium chloride as a byproduct for producing magnesite as raw materials and mixing the raw materials according to the molar ratio of 1:1 of magnesium chloride to the ammonium chloride under certain conditions. Dehydrating ammonium carnallite at 160 deg.C for 4 hours to produce low water ammonium carnallite (NH)4Cl•MgCl2•nH2O, n= 0.5-1), mixing low-water ammonium carnallite and solid ammonium chloride according to the mass ratio of 1:4, and enabling NH in the reaction system to be at high temperature3The partial pressure reaches more than 30.5kPa, and the anhydrous magnesium chloride is obtained by dehydration at 410 ℃ and calcination at 710 ℃ respectively. The method has the advantages of simple process equipment and low energy consumption. The disadvantages are that the dosage of ammonium chloride is large, the production cost is very high, and the ammonium chloride is easy to block the pipeline in the production process.
(3) Fluidization dehydration is combined with molten salt deammoniation. The 20 th century 70 s Zhengzhou light metals institute used the process to prepare electrolyte melts for magnesium electrolysis. Researchers take brine as a raw material, and the brine is firstly added with CaCl2Remove sulfur and CaSO4Brine and NH of4Cl is acted to synthesize the ammonium carnallite solution. When the temperature of the ammonium carnallite liquid is raised to 80-90 ℃, compressed air is sprayed into the fluidized granulation furnace through a nozzle for subsequent treatment, and the bed temperature is controlled at 185 ℃. Then, the material is added into a fluidized drying furnace for dehydration at the bed temperature of 190 ℃ and 220 ℃ to prepare H in the dehydrated material2O content 4.3wt.%, NH4Cl content 29.8 wt.%. The dehydrated material is added into a melting tank containing various chlorides at 700 ℃, so that the material is heated and melted on the surface of the molten salt to obtain a melt containing anhydrous magnesium chloride. The ammonium chloride in the material is decomposed into ammonia gas and hydrogen chloride, and the ammonia gas and the hydrogen chloride are pumped into the empty tower together with air to realize recovery. However, the recovery rate of ammonium chloride in the production process by using the method is only about 70 percent, which results in higher production cost. In addition to this, water is present in the chloride meltThe content of magnesium oxide in the decomposition product reaches about 1wt percent, which is more than 0.5wt percent required by industrial production.
In summary, the above-mentioned method for preparing high-purity electrolytic magnesium melt has the following common problems: (1) the dehydration protection mechanism is single, resulting in high hydrolysate content. The process only utilizes the characteristic that an ammonium carnallite compound salt molecular mechanism is easy to dehydrate at low temperature (only one dehydration mechanism), can not effectively inhibit hydrolysis of medium-temperature and high-temperature materials, and can not utilize the most advanced multipole slot (the content of the hydrolysis product is required to be less than 0.05 wt.%); (2) and the impurities and organic matters cannot be removed. Organic matters and other impurities (such as Si, Al, Ti and the like) in the materials have very serious influence on the electrolytic process, so that the content of the electrolyte melt is very strict. The problem cannot be solved by the existing method due to the lack of research on the decomposition mechanism and the decomposition kinetics of the ammonium chloride; (3) one heat transfer mode has low heat transfer efficiency. The ammonium carnallite dehydrated material is not suitable for introducing a large amount of air in the high-temperature heating and deammoniation process, the method only transfers heat by the heat conduction mode of high-temperature chloride melt, the heat transfer efficiency is low, and the large-scale industrial production of the process is hindered.
Disclosure of Invention
The technical problem to be solved by the invention is to provide an ammonium carnallite dehydrated material and a method for preparing magnesium electrolyte melt by taking the ammonium carnallite dehydrated material as a reaction starting material or an intermediate product aiming at the defects of the prior art. The ammonium carnallite dehydrated material is not easy to hydrolyze in the heating process and can form a unique material sintering structure at different temperature sections, so that the high-purity magnesium electrolyte melt can be prepared by taking the ammonium carnallite dehydrated material as a raw material under relatively simple process conditions.
In order to solve the above technical problems, the present invention comprises:
an ammonium carnallite dehydration material with the molecular formula ofnNH4Cl•MgCl2•mH2O，n=0.5-1.4，m=0-0.6, having a particle size distribution of: 18-32 wt% for material larger than 1.43mm, and 0.9-1.43mm for material17-25wt.%, 0.3-0.9mm 45-62wt.%, 0.1-0.3mm 2-10 wt.%;
further, the formula isnNH4Cl•MgCl2•mH2O，n=0.6-1.2，m=0.1-0.5, having a particle size distribution of: 19-29wt.% for materials larger than 1.43mm, 19-23wt.% for materials 0.9-1.43mm, 46-59wt.% for materials 0.3-0.9mm, and 3-8wt.% for materials 0.1-0.3 mm.
Further, the formula isnNH4Cl•MgCl2•mH2O，n=0.7-1.0，m=0.2-0.4, having a particle size distribution of: 20-27wt.% for materials larger than 1.43mm, 20-23wt.% for materials 0.9-1.43mm, 47-56wt.% for materials 0.3-0.9mm, and 3-7wt.% for materials 0.1-0.3 mm.
A method of making a magnesium electrolyte melt using the ammonium carnallite dewatered material of claim, comprising the steps of:
(a) preparing a chloride melt by taking alkali metal chloride as a raw material;
(b) placing the ammonium carnallite dehydrated material on the chloride melt and forming a solid material column;
(c) heating the ammonium carnallite dehydrated material to form a magnesium electrolyte melt.
Further, in the step (a), the alkali metal chloride is selected from any one of the group consisting of: potassium chloride; sodium chloride; potassium chloride and sodium chloride; potassium chloride, sodium chloride and anhydrous magnesium chloride; potassium chloride, sodium chloride and anhydrous calcium chloride; potassium chloride, sodium chloride, anhydrous magnesium chloride and anhydrous calcium chloride.
Further, in the step (a), the temperature of the chloride melt is 650-800 ℃.
Further, in the step (b), the ratio of the height of the ammonium carnallite dehydrated material column to the diameter thereof is 0.02-80.00, and the ratio of the diameter of the ammonium carnallite dehydrated material column to the diameter of the chloride melt material is 0.02-1.00.
Further, in the step (c), the heating mode of the ammonium carnallite dehydration material is as follows: firstly, the temperature is maintained at 250-180 ℃ for 0.1-3.0 hours, then the temperature is maintained at 350-480 ℃ for 0.05-4.5 hours, then the temperature is maintained at 500-620 ℃ for 0.2-4.0 hours, and finally the temperature is maintained at 650-800 ℃ for 0.1-5.0 hours.
Further, in the step (c), the sum of partial pressures of ammonia gas and hydrogen chloride released by decomposing ammonium chloride above the ammonium carnallite dehydrated material in the heating process is 5-150 kp.
Further, in the step (c), the ammonium carnallite dehydrated material sequentially has dehydration, conversion and impurity removal, organic matter removal and molten salt protection stages in the heating process to prepare a magnesium electrolyte melt; and recovering the ammonium chloride escaped from the heating process of the ammonium carnallite dehydrated material, and adding the ammonium chloride into the ammonium carnallite dehydrated material again to realize reutilization, wherein the ammonia released from the conversion reaction of the hydrolysis product is absorbed.
The invention has the beneficial effects that:
the invention has the following advantages: (1) three dehydration protection mechanisms are combined to realize the whole-course protection of the materials. By utilizing the material structure characteristics in the heating process of the ammonium carnallite dehydrated material and controlling the heating process, the dehydrated material is subjected to three dehydration protection mechanisms of low-temperature dehydration, medium-temperature hydrolysate conversion and high-temperature melt protection, the content of the hydrolysate in the product is ensured to be less than 0.05wt%, and the most advanced multi-polar tank can be utilized for electrolytic magnesium production; (2) can remove impurities and organic matters. By utilizing the sintering structures of different stages of the heating process of the ammonium carnallite dehydration material and controlling the decomposition rate of the ammonium chloride heating process, gaseous ammonium chloride or hydrogen chloride chemically reacts with impurities (such as Ti, Fe, Al and the like which have the greatest influence on electrolytic magnesium) and organic matters to generate corresponding gaseous chloride to escape, thereby meeting the requirements of removing impurities and organic matters; (3) the two heat transfer modes have high heat transfer efficiency. The ammonium chloride is ensured to be in contact with the high-temperature melt for a certain time by controlling the melting rate of the dehydrated material, so that the ammonia gas and the hydrogen chloride gas released by decomposing the ammonium chloride have higher temperature. Through controlling the distribution mode of the dehydrated material and utilizing the difference of the escape rates of the decomposition products of the ammonium chloride, the ammonia gas and the hydrogen chloride carry out convection heat transfer on the upper material in the whole process (a bottom melt heat conduction mode is also provided), and the heat conduction efficiency is high.
Drawings
FIG. 1 is a schematic diagram of a process for preparing a high purity magnesium electrolyte melt using the ammonium carnallite dehydrated material of the present invention as a starting material;
FIG. 2 is a drawing of the low water ammonium carnallite 1.2NH produced by the process of the present invention4Cl•MgCl2•0.5H2An XRD pattern of O;
FIG. 3 shows the reaction of potassium chloride and 1.2NH with the process of the invention4Cl•MgCl2•0.5H2An XRD (X-ray diffraction) spectrum of the high-purity electrolyte melt prepared by taking O as a raw material;
FIG. 4 shows the reaction of sodium chloride and 1.0NH with the process of the invention4Cl•MgCl2•0.6H2An XRD (X-ray diffraction) spectrum of the high-purity electrolyte melt prepared by taking O as a raw material;
FIG. 5 shows the reaction of sodium chloride, potassium chloride and 1.4NH with the process of the present invention4Cl•MgCl2•0H2An XRD (X-ray diffraction) spectrum of the high-purity electrolyte melt prepared by taking O as a raw material;
FIG. 6 shows the reaction of sodium chloride, potassium chloride and calcium chloride with 0.9NH using the process of the present invention4Cl•MgCl2•0.4H2And O is the XRD pattern of the high-purity electrolyte melt prepared by the raw material.
Detailed Description
For the purpose of promoting an understanding of the invention, reference will now be made in detail to the present embodiments of the invention, examples of which are illustrated in the accompanying drawings. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The invention provides an ammonium carnallite dehydration material, the molecular formula of which isnNH4Cl•MgCl2•mH2O，n=0.5-1.4，m=0-0.6, having a particle size distribution of: 18-32wt.% for materials larger than 1.43mm, 17-25wt.% for materials 0.9-1.43mm, 45-62wt.% for materials 0.3-0.9mm, and 2-10wt.% for materials 0.1-0.3 mm.
Further, the formula isnNH4Cl•MgCl2•mH2O，n=0.6-1.2，m=0.1-0.5, pellets thereofThe degree distribution is as follows: 19-29wt.% for materials larger than 1.43mm, 19-23wt.% for materials 0.9-1.43mm, 46-59wt.% for materials 0.3-0.9mm, and 3-8wt.% for materials 0.1-0.3 mm.
Further, the formula isnNH4Cl•MgCl2•mH2O，n=0.7-1.0，m=0.2-0.4, having a particle size distribution of: 20-27wt.% for materials larger than 1.43mm, 20-23wt.% for materials 0.9-1.43mm, 47-56wt.% for materials 0.3-0.9mm, and 3-7wt.% for materials 0.1-0.3 mm.
The inventor finds that the components of the ammonium carnallite dehydrated material have the following effects through a great deal of research: in a certain distribution mode and a heating process, the ratio of the hydrogen chloride partial pressure to the water vapor partial pressure in the dehydration material of the component can easily reach more than 3.0, so that the dehydration material is not easy to hydrolyze in a large amount of dehydration processes; the ammonium carnallite dehydrated material has the following functions of particle size distribution: (1) reducing hydrolysis during dewatering. When the materials with different particle sizes meet a certain mass fraction and are mixed, the porosity of the dehydrated material is reduced and the tortuosity coefficient is increased at low temperature, so that the partial pressure ratio of hydrogen chloride and water vapor in the materials is greatly increased, and the dehydration is facilitated; (2) beneficial to hydrolysate conversion and impurity removal. Along with the proceeding of the dehydration and deammoniation process, the particle size of the dehydrated material is reduced by 0.3-0.6 times, so that the porosity of the material is further reduced and the tortuosity coefficient is further increased at the intermediate temperature, and the resistance of escaping hydrogen chloride and ammonia gas is greatly increased, so that the hydrogen chloride and the ammonia gas can be uniformly distributed in the material and fully contacted with hydrolysate and impurities, and the conversion of the hydrolysate and the chloridizing escaping of other impurities in the material are facilitated; (3) reducing high temperature hydrolysis. The dehydrated materials with different particle sizes have different melting points, so that fine particles with lower melting points in the high-temperature dehydrated materials are gradually melted and connect the surrounding materials to form a sintered structure with lower porosity, thereby greatly increasing the mass transfer resistance of oxygen-containing gas in the air entering the materials and reducing the hydrolysis of the high-temperature materials; (4) by controlling the mass percentages of different granularities in the materials, the speed of the dehydrated materials melted into the chloride melt can be effectively controlled, so that the materials are protected by high-temperature molten salt immediately after the ammonium chloride is released, certain reaction time for conversion, impurity removal and organic matter removal is ensured, and the purpose of preparing the high-purity magnesium electrolyte melt is achieved.
The ammonium chloride in the ammonium carnallite dehydration material has the following functions: (1) in the low-temperature dehydration stage, the ammonium chloride in the ammonium carnallite dehydration material can weaken the binding force of crystal water and magnesium chloride, thereby being beneficial to dehydration and reducing the generation amount of hydrolysate; (2) in the medium-temperature conversion impurity removal stage, the ammonium chloride can react with the existing hydrolysis products (MgOHCl and MgO) and impurities (such as Ti, Al, Fe and the like which have the greatest influence on electrolytic magnesium) in the dehydrated material to generate anhydrous magnesium chloride which enters the material and allows chlorides of other impurities to escape, so that conversion and impurity removal are realized; (3) in the medium-high temperature organic matter removing stage, ammonium chloride can react with organic matter carbonization products to generate volatile substances and carry out material removal by hydrogen chloride and ammonia gas released by decomposing the ammonium chloride; (4) convection mass transfer and increased heat transfer efficiency. The bottom chloride melt can transfer heat of the bottom chloride melt to hydrogen chloride and ammonia gas released by decomposition of ammonium chloride in a heat conduction mode, and the heat of the two gases is transferred to the solid material in an ascending process through convection heat transfer. Through reasonable cloth mode, can realize ammonia convection heat transfer in earlier stage and later stage hydrogen chloride convection heat transfer, realize the whole convection heat transfer of heating.
As shown in fig. 1, the method for preparing the magnesium electrolyte melt by using the ammonium carnallite dehydrated material provided by the invention comprises the following specific preparation processes:
(a) potassium chloride; sodium chloride; potassium chloride and sodium chloride; potassium chloride, sodium chloride and anhydrous magnesium chloride; potassium chloride, sodium chloride and anhydrous calcium chloride; any one of potassium chloride, sodium chloride, anhydrous magnesium chloride and anhydrous calcium chloride is taken as a raw material, and the chloride melt with the temperature of 650-800 ℃ is prepared by heating.
Preferably, the temperature of the chloride melt is 670-780 ℃; further preferably, the temperature of the chloride melt is 680-750 ℃.
(b) Placing the ammonium carnallite dehydrated material on the chloride melt, and distributing in the following manner: the ratio of the height of the column of the ammonium carnallite dehydrated material to the diameter thereof is 0.02-80.00, and the ratio of the diameter of the column of the ammonium carnallite dehydrated material to the diameter of the chloride melt material is 0.02-1.00.
Preferably, the ratio of the height of the column of ammonium carnallite dewatered feed to its diameter is from 0.50 to 60.00; further preferably, the ammonium carnallite dewatered feed column and its diameter ratio are in the range of 1.00 to 30.00.
Preferably, the ratio of the diameter of the ammonium carnallite dehydrated feed column to the diameter of the chloride melt feed is 0.05-0.85; further preferably, the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 0.10 to 0.70.
(c) The ammonium carnallite dehydration material column is firstly insulated for 0.1 to 3.0 hours at the temperature of 250-.
Preferably, the heating mode of the ammonium carnallite dehydrated material is as follows: firstly, preserving heat at the temperature of 260-320 ℃ for 0.2-2.8 hours, then preserving heat at the temperature of 360-470 ℃ for 0.1-4.0 hours, then preserving heat at the temperature of 520-610 ℃ for 0.3-3.8 hours, and finally preserving heat at the temperature of 660-780 ℃ for 0.2-4.5 hours; further preferably, the heating mode of the ammonium carnallite dehydrated material is as follows: firstly, the temperature is maintained at 310 ℃ for 0.3-2.5 hours at 270-.
The ammonium carnallite dehydrated material has the sum of partial pressures of ammonia gas and hydrogen chloride released by decomposing ammonium chloride above the ammonium carnallite dehydrated material in the heating process of 5-150 kp. Preferably, the sum of the partial pressures of ammonia gas and hydrogen chloride released by the decomposition of ammonium chloride above the reaction kettle is 8-140 kpa; further preferably, the sum of the partial pressures of ammonia and hydrogen chloride released by the decomposition of ammonium chloride above it is 10 to 100 kpa.
Under the heating mode, the ammonium carnallite dehydrated material is subjected to dehydration, conversion and impurity removal, organic matter removal and molten salt protection in sequence to prepare the high-purity magnesium electrolyte melt. And recovering the ammonium chloride escaped from the heating process of the ammonium carnallite dehydrated material, and adding the ammonium chloride into the ammonium carnallite dehydrated material again to realize reutilization, wherein the ammonia released from the conversion reaction of the hydrolysis product is absorbed.
The mechanism of the above process is as follows: when the ammonium carnallite component is fullFootnNH4Cl•MgCl2•mH2O（n=0.5-1.4，m= 0-0.6) and the particle size distribution of which is 18-32wt.% for > 1.43mm materials, 17-25wt.% for 0.9-1.43mm materials, 45-62wt.% for 0.3-0.9mm materials, and 2-10wt.% for 0.1-0.3mm materials, the decomposition and escape speed of ammonium chloride in the solid material structure and ammonium carnallite can be effectively controlled by selecting the material distribution mode, the heating mode and the partial pressure of ammonia gas and hydrogen chloride above the dehydrated materials, and the reaction mode and hydrolysis kinetics of the materials are further influenced, so that the materials are subjected to dehydration, conversion impurity removal, organic matter removal and molten salt protection in sequence in the heating process. In the low-temperature dehydration stage, the moisture in the dehydrated material is completely dehydrated and is accompanied with the decomposition and release of a small amount of ammonium chloride. The difference of the diffusion coefficients of the hydrogen chloride gas and the ammonia gas ensures that the ammonia gas can greatly dilute the amount of oxygen-containing gas in the material and the partial pressure ratio of the hydrogen chloride to the water vapor in the material reaches more than 3.0, thereby effectively inhibiting the hydrolysis at the stage; in the stage of medium-temperature conversion and impurity removal, the hydrolysate (MgOHCl and MgO) can completely react with ammonium chloride in the dehydrated material at a given temperature and within a given reaction time to be converted into anhydrous magnesium chloride, so that the conversion of the hydrolysate is realized. In addition, the dehydrated material is lightly sintered, and the sintering structure (porosity and tortuosity coefficient) of the dehydrated material enables hydrogen chloride released by decomposition of ammonium chloride to fully react with impurities (such as Al, Fe, Ti and the like which have the greatest influence on electrolytic magnesium) in the dehydrated material to generate corresponding volatile metal chloride, so that the impurity removal of the dehydrated material is realized; in the middle-high temperature organic matter removing stage, the amount of ammonium chloride in the dehydrated material is reduced, the partial pressure of hydrogen chloride and ammonia gas released by decomposition of the ammonium chloride in the dehydrated material is reduced, at the moment, the organic matter in the dehydrated material starts to be carbonized, and the product gas obtained after the carbonization product is further chlorinated and oxidized escapes along with the volatilization of the hydrogen chloride and the ammonia gas, so that the removal of the organic matter is realized; in the high-temperature molten salt protection stage, the decomposition of ammonium chloride is completed, and at the moment, the anhydrous magnesium chloride is easy to hydrolyze at high temperature, and the hydrolysis process is a gas-solid phase reaction. The particle size distribution characteristics and the material distribution mode of the ammonium carnallite dehydrated material ensure that the dehydrated material can be quickly melted into a bottom chloride melt after the ammonium removal is finished, and the high-temperature molten salt is protectedAnd (4) protecting. The dehydrated material is subjected to the above steps to prepare the high-purity magnesium electrolyte melt with low hydrolysis product, low impurity and low organic matter.
The present invention will be described with reference to specific examples.
In the present invention, the content of the hydrolysate is less than 0.05wt% based on 100% of anhydrous magnesium chloride (i.e., the upper limit of the content of the hydrolysate contained in anhydrous magnesium chloride that is acceptable in the most advanced multi-polar electrolytic cells currently used in the electrolytic production of magnesium metal). Therefore, the high-purity electrolytic magnesium electrolyte melt prepared by the method can be directly used for preparing rare metal magnesium by electrolysis of a multi-polar electrolytic cell.
In the invention, the molecular formula of the ammonium carnallite dehydration material is expressed asnNH4Cl•MgCl2•mH2O, which is prepared by dehydration of crystalline ammonium carnallite. In the preparation process of the crystalline ammonium carnallite, the product components are influenced to a certain extent due to the non-equilibrium crystallization processnThe value of (A) deviates from the content of ammonium chloride in the theoretical ammonium carnalliten=1.0-1.5) to cause dehydration of the same in the materialnThe reduction is 0.5-1.4.
In the present invention, "high purity" in the high purity magnesium electrolyte melt means that the content of hydrolysate, the content of impurities (Ti, Al, Fe) and the content of organic matter in the melt are all less than the upper acceptable limit of an electrolytic cell, i.e. the ratio of hydrolysate to the content of magnesium chloride in the melt is less than 0.05wt.%, the content of Ti in the melt is less than 300ppm, the content of Al in the melt is less than 100ppm, the content of Fe in the melt is less than 200ppm, and the content of organic matter (in terms of C) in the melt is less than 200 ppm.
The products prepared according to the invention were tested according to the following method.
1. Titration method for determining precipitate of sample water solution to determine content of hydrolysate in anhydrous magnesium chloride
The anhydrous magnesium chloride sample obtained was dissolved in water and the aqueous solution was filtered repeatedly at least three times with four sheets of filter paper of a quantitative size phi 90mm until the filtrate was particularly clear. Repeatedly washing the filter paper with deionized water to remove magnesium ions attached to the filter paper, putting the filter paper containing hydrolysate particles into a beaker after washing, adding excessive prepared 1:100 sulfuric acid, heating the beaker on an electric furnace to boil and standing for five minutes to complete the reaction. The solution in the beaker was subjected to EDTA titration to determine the content of magnesium ions, thereby obtaining the content of hydrolysate in anhydrous magnesium chloride.
2. Determination of the Crystal Water content by Karl Fischer titration
The moisture is measured by Karl Fischer titration, and the moisture meter is KF-1B type moisture meter of Shanghai chemical research institute instrument factory (see: "research on preparation of basic magnesium chloride and physical and chemical properties thereof" and "scientific and technical data of salt lake (1980)" ].
3. The phase of each substance was determined by X-ray diffraction (XRD) using an X-ray diffractometer (model: X' Pert PRO MPD; manufacturer: Philips).
4. The contents of Ti, Al, Fe, etc. in the electrolyte melt were measured using an inductively coupled plasma emission spectrometer (Spectrum GX model of PerkinElmer, usa).
5. The organic content of the electrolyte was determined using a total organic carbon-morphological nitrogen analyzer (formals SERIES model of Skalar, netherlands).
Typical but non-limiting examples of the invention are as follows:
example 1
Preparing potassium chloride melt at 800 ℃ by taking 100g of potassium chloride as raw material, and dehydrating 30g of ammonium carnallite into 1.2NH4Cl•MgCl2•0.5H2O (particle size distribution: 20wt.% for > 1.43mm, 20wt.% for 0.9-1.43mm, 50wt.% for 0.3-0.9mm, 10wt.% for 0.1-0.3 mm) was laid on the above potassium chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 0.5, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 0.5. Heating ammonium carnallite dehydrated material at 250 ℃ for 0.5 hour, then at 400 ℃ for 0.1 hour, then at 550 ℃ for 0.5 hour, and finally at 700 ℃ for 1.0 hour, and keeping the sum of partial pressures of ammonia gas and hydrogen chloride above the dehydrated material to be 10kpa in the heating process to prepare the high-purity carnallite dehydrated materialA magnesium electrolyte melt.
The starting materials and the product obtained in example 1 were characterized according to the measurement methods described above. The results are as follows:
XRD analysis was performed on the ammonium carnallite dehydrated feed used and the electrolyte melt prepared, see fig. 2 and 3, respectively. The prepared magnesium electrolyte melt had a hydrolysate content of 0.02wt.%, a Ti content of 86ppm, an Al content of 23ppm, an Fe content of 15ppm, and an organic matter (in terms of C) content of 57 ppm.
Example 2
Preparing sodium chloride melt from 100g of sodium chloride at 800 ℃, and dehydrating 35g of ammonium carnallite into 1.0NH4Cl•MgCl2•0.6H2O (particle size distribution: 18wt.% for > 1.43mm material, 25wt.% for 0.9-1.43mm material, 52wt.% for 0.3-0.9mm material, 5wt.% for 0.1-0.3mm material) was laid on the chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 1.0, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 0.3. Heating the ammonium carnallite dehydrated material at 280 ℃ for 1.5 hours, then at 370 ℃ for 2.0 hours, then at 530 ℃ for 1.0 hour, and finally at 650 ℃ for 0.1 hour, and keeping the sum of partial pressures of ammonia gas and hydrogen chloride above the dehydrated material at 30kpa in the heating process to prepare the high-purity magnesium electrolyte melt.
The product obtained in example 2 was characterized according to the measurement method described above. The results are as follows:
XRD analysis was performed on the prepared electrolyte melts, and each is shown in FIG. 4. The prepared magnesium electrolyte melt had a hydrolysate content of 0.01wt.%, a Ti content of 92ppm, an Al content of 18ppm in the melt, an Fe content of 12ppm in the melt, and an organic matter (in terms of C) content of 64 ppm.
Example 3
55g of potassium chloride and 45g of sodium chloride are used to prepare a chloride melt at 750 ℃, 40g of ammonium carnallite dehydrate 1.4NH are added4Cl•MgCl2•0H2O (particle size distribution: 30wt.% for materials larger than 1.43mm, 17wt.% for materials 0.9-1.43mm, 51wt.% for materials 0.3-0.9mm, 0.1-0.3 mm)2 wt.%) was laid on top of the chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 10.0, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 0.7. Heating the ammonium carnallite dehydrated material at 300 ℃ for 0.1 hour, then at 350 ℃ for 0.05 hour, then at 500 ℃ for 0.2 hour, and finally at 720 ℃ for 2.0 hours, and keeping the sum of the partial pressures of ammonia gas and hydrogen chloride above the dehydrated material to be 50kpa in the heating process to prepare the high-purity magnesium electrolyte melt.
The product obtained in example 3 was characterized according to the measurement method described above. The results are as follows:
XRD analysis was performed on the prepared electrolyte melts, and each is shown in FIG. 5. The prepared magnesium electrolyte melt had a hydrolysate content of 0.006wt.%, a Ti content of 76ppm, an Al content of 26ppm, an Fe content of 8ppm, and an organic matter (in terms of C) content of 48 ppm.
Example 4
Preparing chloride melt from 50g of potassium chloride, 40g of sodium chloride and 10g of anhydrous magnesium chloride at 680 ℃, and dehydrating 30g of ammonium carnallite 0.5NH4Cl•MgCl2•0.1H2O (particle size distribution: 32wt.% for > 1.43mm material, 18wt.% for 0.9-1.43mm material, 46wt.% for 0.3-0.9mm material, 4wt.% for 0.1-0.3mm material) was laid on the chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 50.0, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 1.00. Heating the ammonium carnallite dehydrated material at 330 ℃ for 2.5 hours, then heating at 450 ℃ for 3.0 hours, then heating at 600 ℃ for 3.5 hours, and finally heating at 800 ℃ for 0.5 hour, and keeping the sum of partial pressures of ammonia gas and hydrogen chloride above the dehydrated material to be 70kpa in the heating process to prepare the high-purity magnesium electrolyte melt.
The product obtained in example 4 was characterized according to the measurement method described above. The results are as follows:
the prepared magnesium electrolyte melt had a hydrolysate content of 0.008wt.%, a Ti content of 60ppm, an Al content of 39ppm, an Fe content of 11ppm, and an organic matter (in terms of C) content of 46 ppm.
Example 5
Preparing chloride melt from 50g of potassium chloride, 35g of sodium chloride and 15g of anhydrous calcium chloride at 710 ℃, and dehydrating 38g of ammonium carnallite 0.9NH4Cl•MgCl2•0.4H2O (particle size distribution: 18wt.% for > 1.43mm material, 25wt.% for 0.9-1.43mm material, 45wt.% for 0.3-0.9mm material, 2wt.% for 0.1-0.3mm material) was laid on the chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 80.0, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 0.02. Heating the ammonium carnallite dehydrated material at 260 ℃ for 3.0 hours, heating at 360 ℃ for 4.5 hours, heating at 620 ℃ for 0.2 hour, and heating at 650 ℃ for 5.0 hours, and keeping the sum of partial pressures of ammonia gas and hydrogen chloride above the dehydrated material to be 100kpa in the heating process to prepare the high-purity magnesium electrolyte melt.
The product obtained in example 5 was characterized according to the measurement method described above. The results are as follows:
XRD analysis was performed on the prepared electrolyte melts, and each is shown in FIG. 6. The prepared magnesium electrolyte melt had a hydrolysate content of 0.01wt.%, a Ti content of 36ppm, an Al content of 30ppm, an Fe content of less than 13ppm, and an organic matter (in terms of C) content of 29 ppm.
Example 6
Preparing chloride melt from 50g of potassium chloride, 30g of sodium chloride, 10g of anhydrous magnesium chloride and 10g of anhydrous calcium chloride at 650 ℃, and dehydrating 38g of ammonium carnallite into 0.7NH4Cl•MgCl2•0.3H2O (particle size distribution: 32wt.% for > 1.43mm material, 17wt.% for 0.9-1.43mm material, 46wt.% for 0.3-0.9mm material, 5wt.% for 0.1-0.3mm material) was laid on the chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 0.02, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 1.00. Heating ammonium carnallite dehydrated material at 290 deg.C for 1.2 hr, then at 480 deg.C for 0.05 hr, then at 600 deg.C for 4.0 hr, and finally at 780 deg.C for 1.5 hr, and maintainingAnd in the heating process, the sum of the partial pressures of ammonia gas and hydrogen chloride above the dehydrated material is 140kpa, and the high-purity magnesium electrolyte melt is prepared.
The product obtained in example 6 was characterized according to the measurement method described above. The results are as follows:
the prepared magnesium electrolyte melt had a hydrolysate content of 0.03wt.%, a Ti content of 38ppm, an Al content of 57ppm in the melt, an Fe content of less than 25ppm in the melt, and an organic matter (in terms of C) content of 59 ppm.
Example 7
Preparing a chloride melt from 55g of potassium chloride and 45g of sodium chloride at 720 ℃, and dehydrating 35g of ammonium carnallite into 1.1NH4Cl•MgCl2•0.2H2O (particle size distribution: 18wt.% for > 1.43mm, 17wt.% for 0.9-1.43mm, 62wt.% for 0.3-0.9mm, 3wt.% for 0.1-0.3 mm) is laid on the chloride melt. Wherein the ratio of the height of the column of the ammonium carnallite dehydrated feed to the diameter thereof is 60.0, and the ratio of the diameter of the column of the ammonium carnallite dehydrated feed to the diameter of the chloride melt is 0.5. Heating the ammonium carnallite dehydrated material at 280 ℃ for 2.8 hours, then at 430 ℃ for 4.2 hours, then at 550 ℃ for 1.2 hours, and finally at 680 ℃ for 0.8 hours, and keeping the sum of partial pressures of ammonia gas and hydrogen chloride above the dehydrated material at 150kpa in the heating process to prepare the high-purity magnesium electrolyte melt.
The product obtained in example 7 was characterized according to the measurement method described above. The results are as follows:
the prepared magnesium electrolyte melt had a hydrolysate content of 0.01wt.%, a Ti content of 35ppm, an Al content of 69ppm, an Fe content of less than 19ppm, and an organic matter (in terms of C) content of 45 ppm.
From the results of the above examples, it can be seen that according to the ammonium carnallite dehydrated material and the method for preparing high-purity magnesium electrolyte melt by using the same provided by the invention, the content of hydrolysis products in the electrolyte melt can be controlled below 0.03wt.%, the content of Ti can be controlled below 100ppm, the content of Al in the melt can be controlled below 70ppm, the content of Fe in the melt can be controlled below 20ppm, and the content of organic matters (calculated as C) can be controlled below 70ppm, which are all lower than the upper limit of the application of a multi-pole cell, and the requirements of advanced world magnesium electrolysis process on the electrolyte can be met.
Although the present invention is illustrated by the above examples to show the detailed process parameters and process flows of the present invention, the present invention is not limited to the above detailed process parameters and process flows, i.e., it is not meant that the present invention is necessarily dependent on the above detailed process parameters and process flows to be practiced. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (7)
1. An ammonium carnallite dehydration material is characterized in that: having a molecular formula ofnNH4Cl•MgCl2•mH2O，n=0.5-1.4，m=0-0.6, having a particle size distribution of: 18-32wt.% for materials larger than 1.43mm, 17-25wt.% for materials 0.9-1.43mm, 45-62wt.% for materials 0.3-0.9mm, and 2-10wt.% for materials 0.1-0.3 mm;
2. the ammonium carnallite dehydrated feed of claim 1, wherein: having a molecular formula ofnNH4Cl•MgCl2•mH2O，n=0.6-1.2，m=0.1-0.5, having a particle size distribution of: 19-29wt.% for materials larger than 1.43mm, 19-23wt.% for materials 0.9-1.43mm, 46-59wt.% for materials 0.3-0.9mm, and 3-8wt.% for materials 0.1-0.3 mm.
3. The ammonium carnallite dehydrated feed of claim 1, wherein: having a molecular formula ofnNH4Cl•MgCl2•mH2O，n=0.7-1.0，m=0.2-0.4, having a particle size distribution of: 20-27wt.% for materials larger than 1.43mm, 20-23wt.% for materials 0.9-1.43mm, 47-56wt.% for materials 0.3-0.9mm, and 3-7wt.% for materials 0.1-0.3 mm.
4. A method of producing a magnesium electrolyte melt using the ammonium carnallite dehydrated material as set forth in any one of claims 1 to 3, wherein: the method comprises the following steps:
(a) preparing a chloride melt by taking alkali metal chloride as a raw material;
(b) placing the ammonium carnallite dehydrated material on the chloride melt and forming a solid material column;
the ratio of the height of the ammonium carnallite dehydrated material column to the diameter thereof is 0.02-80.00, and the ratio of the diameter of the ammonium carnallite dehydrated material column to the diameter of the chloride melt material is 0.02-1.00;
(c) heating the ammonium carnallite dehydrated material to form a magnesium electrolyte melt.
The heating mode of the ammonium carnallite dehydration material is as follows: firstly, the temperature is preserved for 0.1 to 3.0 hours at the temperature of 250-;
and in the heating process of the ammonium carnallite dehydration material, the sum of partial pressures of ammonia gas and hydrogen chloride released by decomposing ammonium chloride above the ammonium carnallite dehydration material is 5-150 kp.
5. The method of producing a magnesium electrolyte melt according to claim 4, characterized in that: in the step (a), the alkali metal chloride is any one selected from the group consisting of: potassium chloride; sodium chloride; potassium chloride and sodium chloride; potassium chloride, sodium chloride and anhydrous magnesium chloride; potassium chloride, sodium chloride and anhydrous calcium chloride; potassium chloride, sodium chloride, anhydrous magnesium chloride and anhydrous calcium chloride.
6. The method of producing a magnesium electrolyte melt according to claim 4, characterized in that: in the step (a), the temperature of the chloride melt is 650-800 ℃.
7. The method of producing a magnesium electrolyte melt according to claim 4, characterized in that: in the step (c), the ammonium carnallite dehydrated material sequentially has dehydration, conversion and impurity removal, organic matter removal and molten salt protection stages in the heating process to prepare a magnesium electrolyte melt; and recovering the ammonium chloride escaped from the heating process of the ammonium carnallite dehydrated material, and adding the ammonium chloride into the ammonium carnallite dehydrated material again to realize reutilization, wherein the ammonia released from the conversion reaction of the hydrolysis product is absorbed.
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