A method for separating the main product from the by-products of a calcium-thermal reduction diffusion reaction

Abstract

The present application belongs to the technical field of magnetic materials, and particularly relates to a method for separating main products and by-products of calcium thermal reduction diffusion reaction, comprising the following steps: crushing calcium thermal reduction diffusion reaction products to obtain powdery products; mixing and dispersing the powdery products with liquid gallium to obtain a first mixture; separating the main products with magnetism from the first mixture by magnetic separation to obtain the main products with magnetism and a second mixture; separating the by-products without magnetism from the second mixture; and screening the separated main products and by-products respectively, separating the residual gallium and recycling the gallium. The method uses liquid gallium as a separation medium, does not cause oxidation and loss of the main products in the separation process, does not introduce new impurities, and the gallium as a separation medium is harmless to the environment and human body and can be recycled.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnetic materials, and particularly relates to a method for separating main products and by-products of calcium thermal reduction diffusion reaction. BACKGROUND

[0002] With the progress of science and technology, rare earth permanent magnetic materials have been widely used in emerging fields such as information communication, energy-saving appliances, new energy vehicles, medical care, aerospace and wind power generation, which will lead to an increasing demand for permanent magnetic materials. At present, Nd-Fe-B, Sm-Co and Sm-Fe-N permanent magnetic materials, due to their excellent magnetic properties, play a crucial role in the market of permanent magnetic materials.

[0003] So far, there are various methods for preparing Nd-Fe-B, Sm-Co and Sm-Fe-N. For example, there are melt rapid quenching method, mechanical alloying method, magnetron sputtering method, powder metallurgy method, thermal deformation method, hydrogenation disproportionation method and calcium thermal reduction diffusion method. Compared with other methods, the calcium thermal reduction diffusion method has the advantages of using rare earth compounds as raw materials instead of pure rare earth metals, and has the characteristics of short process flow and low energy consumption. Therefore, the calcium thermal reduction diffusion technology is also widely used in the manufacture of Nd-Fe-B, Sm-Co and Sm-Fe-N permanent magnetic materials. In 1974, Cech et al. used Ca to reduce rare earth oxides to obtain rare earth elements, and then prepared SmCo5 permanent magnetic materials by diffusion reaction with Co and carried out industrial production. In 1985, Herget first reported the successful preparation of Nd-Fe-B permanent magnetic materials by reducing Nd2O3 by reduction diffusion method. In 1999, Ishikawa et al. of Sumitomo Metal in Japan successfully synthesized Sm-Fe-N magnetic powder with high magnetic properties and low cost by reduction diffusion method.

[0004] The calcium thermal reduction diffusion reaction is to use calcium or calcium hydride as a reducing agent to reduce rare earth compounds to single elements at high temperature, and then the rare earth elements combine with transition metal elements to form rare earth intermetallic compounds, i.e. the main products of the reaction. At the same time, the reaction also forms calcium oxide products, and may also include some salt reaction aids, which can be collectively classified as reaction by-products. After the reaction is completed, the main products need to be separated from the by-products. At present, the solvent dissolution method is commonly used to remove the by-products from the calcium thermal reduction diffusion reaction products. For example, deionized water, dilute acetic acid solution or ammonium chloride methanol solution is used to dissolve calcium oxide, calcium chloride and other by-products, so as to achieve the purpose of separation. However, the above solvent method has problems such as secondary oxidation of the main reaction products, reaction with the solvent to cause loss, etc. In addition, the toxicity and pollution of the solvent to the human body and the environment are also worth paying attention to, such as the application of methanol will cause great environmental burden, which is not conducive to large-scale production. SUMMARY

[0005] The present application aims to provide a method for separating main products and by-products of calcium thermal reduction diffusion reaction, which uses liquid gallium as a separation medium, does not cause oxidation and loss of main products in the separation process, does not introduce new impurities, and at the same time, the gallium as a separation medium is harmless to the environment and human body and can be recycled.

[0006] Specifically, the present application provides the following technical solutions:

[0007] A method for separating main products and by-products of calcium thermal reduction diffusion reaction, comprising the following steps:

[0008] 1) crushing the calcium thermal reduction diffusion reaction product to obtain a powdered product;

[0009] 2) mixing and dispersing the powdered product with liquid gallium to obtain a first mixture;

[0010] 3) separating the reaction main products with magnetism from the first mixture by magnetic separation to obtain the reaction main products with magnetism and a second mixture, respectively;

[0011] 4) separating the reaction by-products without magnetism from the second mixture;

[0012] 5) screening the reaction main products and reaction by-products separated in steps 3) and 4), respectively, to separate and recycle the residual gallium.

[0013] Compared with traditional separation media such as water and dilute acetic acid solution, the use of liquid gallium as a separation medium does not cause oxidation and loss of main products in the separation process, does not introduce new impurities, and at the same time, is harmless to the environment and human body and can be recycled.

[0014] In addition, liquid gallium has a suitable density, which is less than the reaction main products and greater than the reaction by-products, so that after dispersing the calcium thermal reduction diffusion reaction product in liquid gallium, the reaction main products will settle in the liquid gallium, and the reaction by-products will float on the surface of the liquid gallium, i.e. the product separation can be realized by physical action, which is convenient for subsequent magnetic separation.

[0015] Further, the inventors have unexpectedly found that part of the main products in the calcium thermal reduction diffusion reaction product will be wrapped by by-products, and even with ultrasonic and mechanical stirring, it is difficult to disperse the main products from the surface-wrapped by-products, thereby reducing the separation effect. Liquid gallium has a suitable surface tension, which helps to disperse the main and by-products in the wrapped state, and the separation effect is significantly improved.

[0016] As a preferred, in the above method, the particle size of the powdered product is less than 74 μm.

[0017] As a preference, in the above method, the temperature of the liquid gallium is 50-80℃. At this temperature, the liquid gallium does not react with the main product or the by-product.

[0018] In a preferred embodiment, in the above method, the powdered product is mixed and dispersed with the liquid gallium by ultrasonic oscillation and / or mechanical stirring. The dispersion of the product is mainly based on the fact that the density of the main product is higher than that of the liquid gallium, while the density of the by-product is lower than that of the liquid gallium. By ultrasonic oscillation and / or mechanical stirring, the powdered product can be fully contacted and uniformly distributed with the liquid gallium, and the by-product can be dispersed and floated on the surface of the liquid gallium.

[0019] As a preference, in the above method, step 3) is repeated for three to four times to ensure that the magnetic main product is completely separated from the first mixture.

[0020] As a preference, in the above method, step 4) is repeated for three to four times to ensure that the non-magnetic by-product is completely separated from the liquid gallium.

[0021] As a preference, in the above method, in step 5), the screening treatment is specifically as follows: the remaining gallium in the main product or the by-product is heated to a liquid state with fluidity, and then solid-liquid separation is achieved by screening.

[0022] The present application has at least the following beneficial effects:

[0023] (1) The main product and the by-product after the gallium and calcium thermal reduction diffusion reaction do not react, so there is no secondary oxidation and loss of the main product, and no new impurities are introduced.

[0024] (2) As a separation medium, gallium can be recycled 100%, with low separation cost and low energy consumption.

[0025] (3) The separation process is simple to operate, and the by-product separation effect is obvious.

[0026] (4) The equipment used is simple, and there is no environmental pollution, which is conducive to industrial application. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0028] Figure 1 The XRD pattern of the phase composition of the calcium reduction reaction product of the samarium-iron alloy prepared in Example 1 is shown.

[0029] Figure 2 XRD pattern of the main product after separation of the calcium reduction reaction product of the samarium-iron alloy of Example 1.

[0030] Figure 3 XRD pattern of the by-product after separation of the calcium reduction reaction product of the samarium-iron alloy of Example 1.

[0031] Figure 4 XRD comparison before and after separation of the calcium reduction reaction product of the samarium-iron alloy of Example 1. DETAILED DESCRIPTION

[0032] The present application provides a method for separating the main product and by-product of a calcium thermal reduction diffusion reaction, which in a preferred embodiment comprises: in a grinding and crushing step, grinding the calcium thermal reduction diffusion reaction product into fine particles and sieving; in a medium preparation step, melting the metallic gallium and keeping it in a liquid state with good fluidity; in a product dispersion step, using ultrasonic oscillation and mechanical stirring to make the powder fully contact with the liquid gallium; in a magnetic separation step, first separating the main product with magnetism using a magnet, and then separating the by-product from the metallic gallium; and in a sieving and collecting step, further recovering the liquid metallic gallium as the separation medium.

[0033] Main product and by-product of calcium thermal reduction reaction

[0034] The composition system of the main product of the calcium thermal reduction diffusion reaction includes Nd-Fe-B, Sm-Co and Sm-Fe-N permanent magnetic materials, but there is no particular limitation on the specific composition ratio and the content of alloying elements in the specific main product. In addition, the by-product of the calcium thermal reduction diffusion reaction includes calcium oxide, calcium chloride and the like generated in the reduction reaction, as well as calcium chloride, potassium chloride and the like as reaction aids.

[0035] Grinding and crushing process

[0036] The grinding method of the calcium thermal reduction diffusion reaction product is not particularly limited, and manual grinding or mechanical grinding can be used. The maximum particle size d of the powder after grinding should be less than 74 microns, i.e. the powder after grinding can pass through a 200-mesh sieve. Multiple grinding methods can be used, such as multiple sieving methods.

[0037] Medium preparation process

[0038] The medium preparation process is to heat and keep the metallic gallium at a temperature, so that it is in a liquid state with good fluidity. The heating method is not particularly limited, as long as the environment temperature of the liquid metallic gallium is 50-80°C.

[0039] Product dispersion process

[0040] The ground and crushed powder is slowly poured into a container containing liquid gallium, and the product is dispersed mainly by using the fact that the density of the main reaction product is higher than that of the liquid gallium and the density of the by-product is lower than that of the liquid gallium. During the dispersion process, in order to make the reactant powder fully contact with the liquid gallium and uniformly distributed, ultrasonic oscillation and mechanical stirring are used to achieve this, but there is no special requirement for the specific equipment and process parameters of the above operation.

[0041] Magnetic separation process

[0042] The magnetic separation process first uses the fact that the main reaction product alloy has room-temperature ferromagnetism to separate the main reaction product from the by-product and the liquid gallium by using the attractive force of a magnet to provide an external magnetic field. There is no special requirement for the magnet here, and in order to improve the yield of the main reaction product, this process needs to be repeated 3-4 times to ensure that the magnetic main reaction product is completely separated. Subsequently, the non-magnetic by-product is separated from the liquid gallium, and this process is repeated 3-4 times to ensure that the by-product is completely separated; thus, the main product, the by-product, and the liquid gallium as the separation medium are obtained, respectively.

[0043] Screening collection process

[0044] The screening collection process is to further improve the purity of the main reaction product and to recycle the metal gallium as the separation medium to improve its recycling rate. Therefore, after the magnetic separation process is completed, the main reaction product and the by-product are respectively subjected to a screening process (the reaction product or by-product is heated to 80°C and kept for 10 minutes, so that the residual metal gallium becomes a liquid with good fluidity, and then solid-liquid separation is achieved by screening), to remove the residual metal gallium. The final main product alloy powder and by-product powder are obtained, and the screened metal gallium is recycled again.

[0045] The application will be further described below in conjunction with examples, but the application is not limited to the following examples.

[0046] If a specific technique or condition is not specified in the examples, it is performed according to the technique or condition described in the literature in the art or according to the product manual. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be purchased through a regular channel.

[0047] Example 1

[0048] The calcium-thermal reduction and diffusion reaction product for preparing a samarium-iron alloy is taken as the separation object, which contains the main reaction product samarium-iron alloy and the by-products calcium oxide and calcium chloride (the phase composition is as shown in Table 1). Figure 1The reaction product is put into a mortar and ground into powder by manual grinding. The ground powder is sieved by a 800 mesh sieve to ensure that the maximum particle size d of all the powder is less than 15 microns. The gallium is heated to 80°C by water bath heating and kept in liquid state. The ground powder and liquid gallium are poured into a previously prepared beaker in turn. The mixture is subjected to ultrasonic and mechanical stirring. After treatment, the reaction byproduct is observed to float on the surface of the liquid gallium, and the reaction main product is concentrated at the bottom of the beaker. The reaction main product samarium-iron alloy at the bottom of the beaker is slowly absorbed along the wall of the beaker by a magnet and collected into a previously prepared container. The process is repeated 4 times to ensure that the reaction main product is completely separated from the liquid gallium. Subsequently, the reaction byproduct calcium oxide and calcium chloride floating on the surface of the liquid gallium is fished out. The process is repeated 4 times to ensure that the reaction byproduct is completely separated from the liquid gallium. Finally, the collected reaction main product and byproduct are sieved to further improve the purity of the reaction product and recover the residual gallium, to obtain the final reaction main product (the phase composition is as shown in Figure 2 and the byproduct (the phase composition is as shown in Figure 3 The sieved gallium is recycled again.

[0049] Figure 4 The XRD of the calcium reduction reaction product before and after separation is compared. It can be seen from Figure 4 that the method provided by the present application can separate the main product and most of the byproduct. This is important for further separating the main product and byproduct more completely by other methods, while avoiding serious oxidation of the main product.

[0050] Example 2

[0051] The calcium reduction diffusion reaction product for preparing neodymium iron boron alloy is taken as the separation object, which contains the reaction main product neodymium iron boron alloy and the reaction by-product calcium chloride. The reaction product is placed in a mortar and ground into powder by manual grinding. The ground powder is sieved by a 200-mesh sieve to ensure that the maximum particle size d of all the powder is less than 74 microns. The metallic gallium is heated to 50°C by water bath heating and kept at this temperature to be in liquid state. The ground powder and the liquid gallium are poured into a previously prepared beaker in sequence. The mixture is subjected to ultrasonic and mechanical stirring. After the treatment, the reaction by-product is observed to float on the surface of the liquid gallium, while the reaction main product is concentrated at the bottom of the beaker. The reaction main product neodymium iron boron alloy at the bottom of the beaker is slowly attracted out along the beaker wall by a magnet and collected into a previously prepared container. This process is repeated three times to ensure that the reaction main product is completely separated from the liquid gallium. Subsequently, the reaction by-product calcium chloride floating on the surface of the liquid gallium is fished out. This process is repeated three times to ensure that the reaction by-product is completely separated from the liquid gallium. Finally, the collected reaction main product and reaction by-product are sieved to further improve the purity of the reaction product and recover the residual metallic gallium. The sieved metallic gallium is recycled again.

[0052] Example 3

[0053] The calcium reduction diffusion reaction product for preparing samarium cobalt alloy is taken as the separation object, which contains the reaction main product samarium cobalt alloy and the reaction by-product calcium oxide. The reaction product is placed in a mortar and ground into powder by manual grinding. The ground powder is sieved by a 400-mesh sieve to ensure that the maximum particle size d of all the powder is less than 38 microns. The metallic gallium is heated to 70°C by water bath heating and kept at this temperature to be in liquid state. The ground powder and the liquid gallium are poured into a previously prepared beaker in sequence. The mixture is subjected to ultrasonic and mechanical stirring. After the treatment, the reaction by-product is observed to float on the surface of the liquid gallium, while the reaction main product is concentrated at the bottom of the beaker. The reaction main product samarium cobalt alloy at the bottom of the beaker is slowly attracted out along the beaker wall by a magnet and collected into a previously prepared container. This process is repeated three times to ensure that the reaction main product is completely separated from the liquid gallium. Subsequently, the reaction by-product calcium oxide floating on the surface of the liquid gallium is fished out. This process is repeated three times to ensure that the reaction by-product is completely separated from the liquid gallium. Finally, the collected reaction main product and reaction by-product are sieved to further improve the purity of the reaction product and recover the residual metallic gallium. The sieved metallic gallium is recycled again.

[0054] It should be pointed out finally that the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; and although the present application has been described in detail with reference to the foregoing embodiments, it should be appreciated by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features thereof can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for separating the main product and byproduct of a calcium thermal reduction diffusion reaction, characterized in that, Includes the following steps: 1) The calcium thermal reduction diffusion reaction product is crushed to obtain a powdered product; 2) The powdered product is mixed with liquid gallium metal and dispersed to obtain a first mixture; 3) The magnetic reaction product is separated from the first mixture by magnetic separation to obtain the magnetic reaction product and the second mixture, respectively; 4) To separate the non-magnetic reaction byproducts from the second mixture; 5) The reaction main product and reaction byproduct obtained in steps 3) and 4) are sieved to separate the residual metallic gallium and recycle it.

2. The method for separating the main product and byproduct of the calcium thermal reduction diffusion reaction according to claim 1, characterized in that, The particle size of the powdered product is less than 74 μm.

3. The method for separating the main product and byproduct of the calcium thermal reduction diffusion reaction according to claim 1 or 2, characterized in that, The temperature of the liquid gallium metal is 50~80℃.

4. The method for separating the main product and byproduct of the calcium thermal reduction diffusion reaction according to claim 1 or 2, characterized in that, Repeat step 3) three to four times.

5. The method for separating the main product and byproduct of the calcium thermal reduction diffusion reaction according to claim 1 or 2, characterized in that, Repeat step 4) three to four times.

6. The method for separating the main product and byproduct of the calcium thermal reduction diffusion reaction according to claim 1 or 2, characterized in that, In step 5), the sieving process specifically involves heating the main product or byproduct of the reaction to make the residual gallium metal appear as a fluid liquid, and then achieving solid-liquid separation through sieving.

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