Anhydrous magnesium chloride and preparation method thereof

Abstract

The invention provides anhydrous magnesium chloride and a preparation method thereof, and the preparation method comprises the following steps: mixing MgCl2. NH2O and ammonium chloride, carrying out ball milling, tabletting and granulating the mixed material, and heating and sintering the obtained flaky particles to obtain the anhydrous magnesium chloride, wherein n is an integer, and 0 < n < = 6. The water-containing magnesium chloride and the ammonium chloride can form an alternately coated sandwich structure through the pretreatment modes of ball milling and tabletting granulation, so that hydrogen chloride gas and ammonia gas generated during heating decomposition are diffused from the inside of the flaky particles to the outside, and meanwhile, the water-containing magnesium chloride in the particles can be fully exposed in a hydrogen chloride atmosphere; mgO generated in the sintering process is reduced; according to the tabletting and granulating method, large pores can exist among the flaky particles, generated water molecules can be taken away from a heating system from the pores existing among the flaky particles along with gas circulation in the heating and sintering process, and dehydration is better achieved. Meanwhile, the method is more beneficial to model selection of dehydration equipment.

Description

Technical Field

[0001] The invention relates to the technical field of chemical industry, and in particular to anhydrous magnesium chloride and a preparation method thereof. Background Art

[0002] Hydrated magnesium chloride (MgCl2·nH2O) is a substance that becomes more hygroscopic and more easily deliquescent as n decreases. It absorbs moisture from the air at room temperature and turns into magnesium chloride hexahydrate, which is an important raw material for the manufacture of anhydrous magnesium chloride and magnesium metal.

[0003] At present, the methods for preparing anhydrous magnesium chloride by dehydrating hydrated magnesium chloride mainly include: dehydration under hydrogen chloride protective atmosphere, chlorine melting chlorination dehydration, hydrogen chloride melting chlorination dehydration, ammonium carnallite dehydration, and organic solvent and ammonia complex dehydration. Among them, the method for preparing anhydrous magnesium chloride by dehydrating ammonium carnallite (MgCl2·NH4Cl·6H2O) is suitable for areas rich in magnesium resources, but the method for preparing anhydrous magnesium chloride by simply mixing magnesium chloride and ammonium chloride and then heating and dehydrating has the problems of insufficient raw material utilization and magnesium recovery rate and high MgO content in the product.

[0004] This invention is proposed in order to further improve the raw material utilization rate and magnesium recovery rate when preparing anhydrous magnesium chloride using hydrous magnesium chloride, and to reduce the content of MgO in the prepared anhydrous magnesium chloride. Summary of the invention

[0005] The main purpose of the present invention is to provide anhydrous magnesium chloride and a preparation method thereof, so as to solve the problems of low raw material utilization rate, low magnesium recovery rate and high MgO content in the product when preparing anhydrous magnesium chloride in the prior art.

[0006] In order to solve the above problems, the present invention provides a method for preparing anhydrous magnesium chloride, which comprises the following steps: step (1), mixing MgCl2·nH2O and ammonium chloride and ball milling to obtain a mixed material; step (2), subjecting the mixed material to tabletting and granulation treatment to obtain flaky particles; step (3), heating and sintering the flaky particles to obtain anhydrous magnesium chloride; wherein n is an integer, and 0<n≤6.

[0007] Furthermore, n in MgCl2·nH2O is an integer, and 0<n≤3.

[0008] Furthermore, the diameter of the flaky particles is 5 to 10 mm, and the thickness is 2 to 4 mm; preferably, the pressure when forming the flaky particles is 10 to 15 kN.

[0009] Furthermore, the particle size of the mixed material after ball milling is 200-400 meshes.

[0010] Further, the weight ratio of MgCl2·nH2O to ammonium chloride is (0.1-10):1, preferably, the weight ratio of MgCl2·nH2O to ammonium chloride is (3-8):1.

[0011] Furthermore, the heating and sintering in step (3) includes a first stage heating and sintering and a second stage heating and sintering. The first stage heating and sintering is to heat the temperature to 135-180°C at a heating rate of 5-10°C / min and keep the temperature for 0.5-1h; the second stage heating and sintering is to heat the temperature to 230-300°C at a heating rate of 20-30°C / min and keep the temperature for 0.5-1h.

[0012] Furthermore, the tableting granulation method is at least one of dry extrusion granulation and stirring granulation.

[0013] Furthermore, the heating equipment during heating is at least one of a vertical kiln, a tunnel kiln and a rotary calcining kiln.

[0014] Furthermore, the hydrogen chloride gas and ammonia gas generated by heating are recovered to prepare ammonium chloride, and the preferred recovery method is wet absorption.

[0015] According to another aspect of the present invention, anhydrous magnesium chloride is also provided. The anhydrous magnesium chloride is prepared by the above preparation method. The water content of the anhydrous magnesium chloride is as low as 0.50%, and the content of magnesium oxide in the anhydrous magnesium chloride is as low as 0.11%.

[0016] The present invention provides a method for preparing anhydrous magnesium chloride. The preparation method firstly ball-mills a mixture of MgCl2·nH2O and ammonium chloride so that the ammonium chloride can be uniformly dispersed in the MgCl2·nH2O; then, flaky particles are obtained by tabletting and granulating; and finally, the obtained flaky particles are heated and sintered to obtain anhydrous magnesium chloride. The pretreatment methods of ball milling and tabletting and granulating can make the hydrous magnesium chloride and ammonium chloride form an alternately coated sandwich structure. The special structure can make the hydrogen chloride gas and ammonia gas generated by the ammonium chloride during heating and decomposition diffuse from the inside to the outside of the flaky particles, so that the hydrous magnesium chloride in the particles can be fully exposed to the hydrogen chloride gas atmosphere, thereby reducing the generation of MgO in the sintering process and effectively reducing the content of MgO in the anhydrous magnesium chloride; in addition, the tabletting and granulating method can make larger pores between the flaky particles. In the process of heating and sintering the flaky particles, the water molecules in the system can be taken away from the heating system from the pores between the flaky particles along with the gas circulation, thereby better achieving the purpose of dehydration. At the same time, the above-mentioned method for processing raw materials when preparing anhydrous magnesium chloride is also more conducive to the selection of dehydration equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 The cross-sectional schematic diagram of the sandwich structure formed by MgCl2·nH2O and ammonium chloride proposed in the present invention is shown. DETAILED DESCRIPTION

[0019] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0020] As described in the background technology section, there are many methods for preparing anhydrous magnesium chloride using hydrous magnesium chloride, such as dehydration under hydrogen chloride protective atmosphere, chlorine melting chlorination dehydration, hydrogen chloride melting chlorination dehydration, ammonium carnallite dehydration, organic solvent and ammonia complex dehydration, etc. However, the existing method of preparing anhydrous magnesium chloride by simply mixing hydrous magnesium chloride with ammonium chloride and then heating and dehydrating has the problems of low raw material utilization, insufficient magnesium recovery rate and high MgO content in the product, and has high requirements for the selection of dehydration equipment.

[0021] In order to solve the above problems, the present invention provides a method for preparing anhydrous magnesium chloride, which comprises the following steps: step (1), mixing MgCl2·nH2O and ammonium chloride and ball milling to obtain a mixed material; step (2), subjecting the mixed material to tabletting and granulation treatment to obtain flaky particles; step (3), heating and sintering the flaky particles to obtain anhydrous magnesium chloride; wherein n is an integer, and 0<n≤6.

[0022] In the preparation method of the present invention, MgCl2·nH2O and ammonium chloride are first mixed, and then the two raw materials are fully mixed by ball milling so that the ammonium chloride can be evenly dispersed in the MgCl2·nH2O to obtain a mixture containing MgCl2·nH2O and ammonium chloride; the mixture is then subjected to tabletting and granulation treatment to form the mixture into flaky particles; and the flaky particles are subjected to a heating and sintering process to remove water molecules contained in the molecules to obtain anhydrous magnesium chloride.

[0023] In particular, in the preparation method of anhydrous magnesium chloride proposed in the present invention, the mixed material is subjected to ball milling and tableting and granulation treatment. Different from the conventional method of preparing anhydrous magnesium chloride by simply mixing hydrous magnesium chloride and ammonium chloride and then thermally dehydrating them, in the method for preparing anhydrous magnesium chloride described in the present invention, after the hydrated magnesium chloride and ammonium chloride are mixed, they are not only ball milled to make the two raw materials mixed more evenly, but also the mixed material after ball milling is tableted and granulated by tableting and granulation. The above-mentioned method of pretreating the raw materials for preparing anhydrous magnesium chloride can not only significantly reduce the water content in the prepared anhydrous magnesium chloride, but also effectively reduce the MgO content therein. The reasons are as follows. First, the pretreatment method of tableting and granulation after ball milling can make the hydrous magnesium chloride and ammonium chloride raw materials form an alternatingly coated sandwich structure (the cross-sectional schematic diagram is shown in FIG. 2 ). Figure 1 As shown), this sandwich structure can make the hydrogen chloride gas and ammonia produced by ammonium chloride when heated and decomposed diffuse from the inside of the flaky particles to the outside, so that the hydrous magnesium chloride in the particles can be fully exposed to the hydrogen chloride gas atmosphere during the heating and sintering process, and then the MgO produced during the heating and sintering process can be effectively reduced, and the content of MgO in the anhydrous magnesium chloride can be reduced. Second, the method of tableting and granulation after ball milling and mixing is conducive to the subsequent sintering process. There are large pores between the formed flaky particles. During the heating and sintering process, the water molecules in the system can be taken away from the heating system along with the ammonia and hydrogen chloride gas through the pores existing between the flaky particles, so as to better achieve the purpose of dehydration. Third, the pretreatment method of tableting and granulation after ball milling and mixing of hydrous magnesium chloride and ammonium chloride can effectively avoid the bonding between the sintering raw materials caused by the inability to remove the water molecules produced by sintering in time, the bonding of the sintering raw materials to the sintering equipment, and the situation that the heating and sintering process cannot be further carried out caused by the bonding, and further improve the dehydration effect of hydrous magnesium chloride. At the same time, the above-mentioned method for pretreating raw materials when preparing anhydrous magnesium chloride is also more conducive to the selection of dehydration equipment.

[0024] In summary, the method for preparing anhydrous magnesium chloride according to the present invention can not only make the hydrous magnesium chloride and ammonium chloride fully and alternately coated to form a sandwich structure, but also increase the gap between the magnesium chloride and the ammonium chloride during the sintering process, effectively avoid the adhesion of the hydrous magnesium chloride and the ammonium chloride during the sintering process, improve the quality of the prepared anhydrous magnesium chloride from multiple perspectives, make the dehydration process of the hydrous magnesium chloride more thorough, effectively reduce the water content in the prepared anhydrous magnesium chloride and improve the purity of the anhydrous magnesium chloride.

[0025] In a preferred embodiment, n in MgCl2·nH2O is an integer, and 0<n≤3. In the process of preparing anhydrous magnesium chloride, the present invention pre-treats the mixture of hydrated magnesium chloride and ammonium chloride, performs ball milling and tableting and granulation treatment on it. When n in MgCl2·nH2O is an integer, and 0<n≤3, it is more conducive to the tableting and granulation operation of the present invention.

[0026] In a preferred embodiment, the sheet diameter of the flaky particles is 5 to 10 mm and the thickness is 2 to 4 mm. The flaky particles formed by tableting and granulation can, on the one hand, diffuse the hydrogen chloride gas and ammonia generated by ammonium chloride when it is heated and decomposed from the inside of the flaky particles to the outside, so that the hydrous magnesium chloride in the particles can be fully exposed to the hydrogen chloride gas atmosphere, and on the other hand, the gaps between the flaky particles can provide a channel for water molecules to leave the system. When the sheet diameter of the flaky particles is controlled to be 5 to 10 mm and the thickness is 2 to 4 mm, the above two effects can be better exerted. Preferably, the pressure when forming the flaky particles is 10 to 15 kN, and the pressure when tableting is controlled within the above range, so that the obtained flaky particles have a more suitable density, which is conducive to tableting, and is also conducive to the diffusion of hydrogen chloride gas and ammonia generated by ammonium chloride when it is heated and decomposed from the inside of the flaky particles to the outside, so that the hydrous magnesium chloride in the particles can be more fully exposed to the hydrogen chloride gas atmosphere.

[0027] In a preferred embodiment, the particle size of the mixed material after ball milling is 200-400 meshes. The ball milling operation can make the hydrated magnesium chloride and ammonium chloride mix more evenly, which is conducive to better forming a sandwich structure of alternating coating of hydrated magnesium chloride and ammonium chloride in the subsequent tableting and granulation process. Controlling the particle size of the mixed material after ball milling to 200-400 meshes can better play the role of the sandwich structure in the above sintering process.

[0028] In a preferred embodiment, the weight ratio of MgCl2·nH2O to ammonium chloride is (0.1-10):1. As described above, in the method for preparing anhydrous magnesium chloride of the present invention, the mixture of MgCl2·nH2O and ammonium chloride is ball-milled so that ammonium chloride can be uniformly dispersed in MgCl2·nH2O, and then the flaky particles are obtained by tabletting and granulation. The hydrous magnesium chloride and ammonium chloride in the flaky particles can form an alternately coated sandwich structure, which is beneficial for the hydrous magnesium chloride in the flaky particles to be fully exposed to the hydrogen chloride gas atmosphere during sintering. Preferably, when the weight ratio of MgCl2·nH2O to ammonium chloride is controlled to be (3-8):1, the sandwich structure formed has a better effect and is more conducive to improving the quality of anhydrous magnesium chloride.

[0029] In a preferred embodiment, the heating and sintering in step (3) includes a first stage heating and sintering and a second stage heating and sintering, wherein the first stage heating and sintering is to heat to 135-180°C at a heating rate of 5-10°C / min, and keep the temperature for 0.5-1h; the second stage heating and sintering is to heat to 230-300°C at a heating rate of 20-30°C / min, and keep the temperature for 0.5-1h. In the process of sintering the flaky particles formed by mixing hydrous magnesium chloride and ammonium chloride, ammonium carnallite (MgCl2·NH4Cl·6H2O) will be formed. Since ammonium carnallite carries water molecules, it will be in a relatively viscous state, which will be unfavorable for the sintering process. Therefore, the above situation is avoided by heating in two stages during the sintering process. When the heating methods of the two stages are controlled within the above range, especially when the heating process of the second stage is controlled to heat rapidly, the sintering effect can be better, and the quality of anhydrous magnesium chloride can be further improved.

[0030] In a preferred embodiment, the tableting and granulation method is at least one of dry extrusion granulation and stirring granulation. The method of tableting and granulating the mixture of hydrous magnesium chloride and ammonium chloride can have a beneficial effect on the preparation of anhydrous magnesium chloride. The method of tableting and granulation is not limited, and any method that can achieve the purpose of tableting and granulation in the present invention, such as dry extrusion granulation and stirring granulation, can be used.

[0031] By way of example but not limitation, the heating device during heating is at least one of a vertical kiln, a tunnel kiln and a rotary calcining kiln. In the method for preparing anhydrous magnesium chloride of the present invention, one of the advantages of the method of sintering the mixed hydrous magnesium chloride and ammonium chloride after tableting and granulation is that the selection of dehydration equipment is expanded. The pores between the flaky particles obtained after tableting and granulation make it possible to obtain anhydrous magnesium chloride of good quality regardless of the selected heating equipment, which can effectively reduce the cost of equipment procurement in actual production.

[0032] In a preferred embodiment, the hydrogen chloride gas and ammonia gas generated during heating and sintering are recovered to prepare ammonium chloride, and the preferred recovery method is wet absorption. During the heating and sintering of hydrous magnesium chloride and ammonium chloride, ammonia gas and hydrogen chloride gas are generated, which can be recovered by wet absorption and used as raw materials for producing ammonium chloride, thus realizing resource utilization, further reducing pollution, and being more environmentally friendly.

[0033] According to another aspect of the present invention, an anhydrous magnesium chloride is provided, wherein the water content of the anhydrous magnesium chloride is as low as 0.50%, and the content of magnesium oxide in the anhydrous magnesium chloride is as low as 0.11%. The anhydrous magnesium chloride meets the standards of the "Quality Standards for Anhydrous Magnesium Chloride" and can be directly used in fields with high requirements for the purity of magnesium chloride, such as batteries, energy storage, polymer materials, ceramic materials, drug preparation, and biological experiments.

[0034] The present application is further described in detail below in conjunction with specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in the present application.

[0035] Example 1

[0036] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure of magnesium chloride wrapped with ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0037] Example 2

[0038] MgCl2·3H2O and ammonium chloride are mixed in a weight ratio of 1:2, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a stirring granulation method to prepare flaky particles with a multi-layer sandwich structure of ammonium chloride wrapped with magnesium chloride, wherein the pressure during tableting and granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a tunnel kiln, first heated to 160°C at a heating rate of 8°C / min, and sintered at the temperature for 0.8h; then heated to 270°C at a heating rate of 25°C / min, and sintered at the temperature for 0.8h to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0039] Example 3

[0040] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 2:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the tableting granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a rotary calcining kiln, first heated to 180°C at a heating rate of 10°C / min, and sintered for 0.5h; then heated to 300°C at a heating rate of 30°C / min, and sintered for 0.5h to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0041] Example 4

[0042] The difference from Example 1 is that the molecular formula of hydrous magnesium chloride is MgCl2·6H2O.

[0043] MgCl2·6H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·6H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure of magnesium chloride wrapped with ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0044] Example 5

[0045] The difference from Example 1 is that the molecular formula of hydrous magnesium chloride is MgCl2·H2O.

[0046] MgCl2·H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0047] Example 6

[0048] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 200 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure of magnesium chloride wrapped with ammonium chloride, wherein the pressure during the flaking granulation is 10 kN, the flaky particles have a diameter of 5 mm, and a thickness of 4 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 180°C at a heating rate of 5°C / min, and sintered at the temperature for 0.5h; then heated to 230°C at a heating rate of 20°C / min, and sintered at the temperature for 1h to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0049] Example 7

[0050] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 400 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 15 kN, the flaky particles have a diameter of 10 mm, and a thickness of 4 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 135°C at a heating rate of 10°C / min, and sintered at the temperature for 1 hour; then heated to 300°C at a heating rate of 30°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0051] Example 8

[0052] The difference from Example 1 is that MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 0.1:1.

[0053] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 0.1:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0054] Example 9

[0055] The difference from Example 1 is that MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 10:1.

[0056] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 10:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0057] Example 10

[0058] The difference from Example 1 is that MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 3:1.

[0059] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 3:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0060] Embodiment 11

[0061] The difference from Example 1 is that MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 8:1.

[0062] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 8:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 12 kN, the flaky particles have a diameter of 8 mm, and a thickness of 3 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0063] Example 12

[0064] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 500 meshes; the obtained mixture is subjected to a dry extrusion granulation method to prepare flaky particles with a single-layer sandwich structure in which magnesium chloride wraps ammonium chloride, wherein the pressure during the flaking granulation is 20 kN, the flaky particles have a diameter of 3 mm, and a thickness of 1 mm; the obtained flaky particles are placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered for 1 hour; then heated to 240°C at a heating rate of 5°C / min, and sintered for 1 hour to obtain anhydrous magnesium chloride, and ammonia and hydrogen chloride gases generated during the sintering process are recovered by a wet absorption method for preparing raw material ammonium chloride.

[0065] Comparative Example 1

[0066] MgCl2·3H2O and ammonium chloride are mixed at a weight ratio of 1:1, and ball-milled to obtain a mixture of MgCl2·3H2O and ammonium chloride, wherein the particle size of the mixture is 300 meshes; the obtained mixture is placed in a vertical kiln, first heated to 140°C at a heating rate of 5°C / min, and sintered at the temperature for 1 hour; then heated to 240°C at a heating rate of 20°C / min, and sintered at the temperature for 1 hour, and a large-area bonding phenomenon occurs during the sintering process.

[0067] The moisture content, dehydration rate and MgO content in the anhydrous magnesium chloride prepared in Examples 1 to 12 and Comparative Example 1 were measured, and the results are shown in Table 1.

[0068] The test method is further explained here: Product moisture content: The test of product moisture content is obtained according to "GB / T6283-2008 Determination of water content in chemical products - Karl Fischer method (general method)"; Dehydration rate = m1 / m0, where m1 is the weight of anhydrous magnesium chloride after dehydration, and m0 is the weight of hydrous magnesium chloride before dehydration; Test of MgO content: MgO content is obtained according to the determination method of magnesium oxide content used in "HG / T 2573-2012 Industrial Light Magnesium Oxide".

[0069] Table 1

[0070]

[0071]

[0072] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: Embodiments 1 to 12 are to prepare anhydrous magnesium chloride from hydrous magnesium chloride using the preparation method of the present invention, and the dehydration rate of the method is above 98%, and the highest can reach 98.5%. The water content in the prepared anhydrous magnesium chloride and the content of magnesium oxide therein are also in a relatively low range, the water content of anhydrous magnesium chloride is as low as 0.50%, and the content of magnesium oxide in anhydrous magnesium chloride is as low as 0.11%, with good quality. Even if some parameters in the preparation process are controlled outside the preferred range, embodiment 12 still has good effects. The preparation method of the present invention has the advantages of high raw material utilization and high magnesium recovery rate. In addition, the method for treating raw materials in the method for preparing anhydrous magnesium chloride of the present invention is also more conducive to the selection of dehydration equipment, and has good effects on more common heating equipment such as vertical kilns, tunnel kilns and rotary calcining kilns. In Comparative Example 1, only the ball milling method was used, and the tableting and granulation operation mentioned in the present invention was not used. During the sintering process, obvious bonding occurred, which hindered the dehydration process and made it difficult to obtain anhydrous magnesium chloride with good quality. The water content and magnesium oxide content of the obtained anhydrous magnesium chloride were both high.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing anhydrous magnesium chloride, characterized in that, The preparation method comprises the following steps: Step (1), mixing MgCl2·nH2O and ammonium chloride and ball milling to obtain a mixed material; Step (2), subjecting the mixed material to tableting and granulation to obtain flaky particles; Step (3), heating and sintering the flaky particles to obtain the anhydrous magnesium chloride; Wherein n is an integer, and 0<n≤6.

2. The method for preparing anhydrous magnesium chloride according to claim 1, wherein The n in the MgCl2·nH2O is an integer, and 0<n≤3.

3. The preparation method of anhydrous magnesium chloride according to claim 1, characterized in that, The flake particles have a diameter of 5 to 10 mm and a thickness of 2 to 4 mm; Preferably, the pressure when forming the flaky particles is 10-15 kN.

4. The method for preparing anhydrous magnesium chloride according to any one of claims 1 to 3, characterized in that: The particle size of the mixed material after ball milling is 200-400 meshes.

5. The method for preparing anhydrous magnesium chloride according to any one of claims 1 to 3, characterized in that: The weight ratio of the MgCl2·nH2O to the ammonium chloride is (0.1-10):

1. Preferably, the weight ratio of the MgCl2·nH2O to the ammonium chloride is (3-8):

1.

6. The method for preparing anhydrous magnesium chloride according to any one of claims 1 to 3, characterized in that: The heating and sintering in step (3) includes a first stage heating and sintering and a second stage heating and sintering. The first stage heating and sintering is to heat the temperature to 135-180°C at a heating rate of 5-10°C / min and keep the temperature for 0.5-1h. The second stage heating and sintering is to heat the temperature to 230-300°C at a heating rate of 20-30°C / min and keep the temperature for 0.5-1h.

7. The method for preparing anhydrous magnesium chloride according to any one of claims 1 to 3, characterized in that: The tableting granulation method is at least one of dry extrusion granulation and stirring granulation.

8. The method for preparing anhydrous magnesium chloride according to any one of claims 1 to 3, characterized in that: The heating equipment during the heating is at least one of a vertical kiln, a tunnel kiln and a rotary calcining kiln.

9. The method for preparing anhydrous magnesium chloride according to any one of claims 1 to 3, characterized in that: The hydrogen chloride gas and ammonia gas generated by heating are recovered to prepare ammonium chloride, and preferably the recovery method is wet absorption.

10. Anhydrous magnesium chloride, characterized in that The anhydrous magnesium chloride is prepared by the preparation method according to any one of claims 1 to 9, the water content of the anhydrous magnesium chloride is as low as 0.50%, and the content of magnesium oxide in the anhydrous magnesium chloride is as low as 0.11%.

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