Preparation method of bonded permanent ferrite

Abstract

The present invention relates to the field of magnetic materials and discloses a method for preparing bonded permanent ferrite, comprising: a) densifying iron oxide and strontium carbonate to obtain a dense material; b) pelletizing the dense material while spraying it with a strontium chloride recovery solution to obtain pellets; c) sintering, cooling, and crushing to obtain a coarse powder; and d) wet ball milling, filter pressing, drying, tempering, and cooling. The method recovers strontium chloride-containing wastewater to obtain a high-concentration strontium chloride recovery solution, which is then used to pelletize the bonded permanent ferrite. This method significantly improves the utilization rate of strontium resources, effectively reduces strontium resource waste, and significantly lowers costs. Furthermore, by further optimizing the parameters of the strontium chloride recovery solution and the bonded permanent ferrite preparation process, the method minimizes the negative impact of the strontium chloride recovery solution on the production and performance of the bonded permanent ferrite.

Description

Technical Field

[0001] The present invention relates to the field of magnetic materials, and in particular to a method for preparing bonded permanent ferrite. Background Art

[0002] Bonded permanent ferrites are made by thoroughly mixing permanent ferrite powder with adhesives (such as rubber, thermoplastic resin, or thermosetting resin), lubricants, and reinforcing agents, followed by molding and curing. Bonded permanent ferrites address the poor flexibility and plasticity of sintered permanent ferrites and are increasingly being used in industries such as motors.

[0003] Bonded permanent magnet ferrites are mostly strontium ferrites. The main raw material of strontium is strontium carbonate. The reserves of celestite, the raw ore of strontium carbonate, are not abundant in my country, and most of them are of low grade. This leads to a high proportion of strontium carbonate in the raw material cost.

[0004] During production, the applicant discovered that the concentration of strontium chloride in wastewater discharged from bonded permanent ferrite production can reach approximately 3%. After wastewater treatment, a large amount of strontium remains in the solid waste, requiring harmless disposal. Recycling this strontium chloride as a raw material would significantly save large-scale enterprises.

[0005] Patent CN202310732992.6 discloses a bonded ferrite magnetic powder for calendering, its preparation method, and application. The preparation method comprises the following steps: thoroughly mixing strontium carbonate, strontium chloride, and iron red, pelletizing, and obtaining pellets; dividing the pellets into first and second pellets, and independently sintering and grinding them to obtain fine-grained pellets with an average particle size of 0.2 μm to 0.4 μm and coarse-grained pellets with an average particle size of 1.6 μm to 2.0 μm; mixing the fine and coarse pellets in a mass ratio of 10% to 30%:1, drying, sequentially annealing, and surface treating, and then drying and crushing to obtain bonded ferrite magnetic powder; the surface treatment agent includes an acetylene surfactant. However, this solution does not involve the recycling of strontium chloride. Summary of the Invention

[0006] To address the above-mentioned technical problems, the present invention provides a method for preparing bonded permanent ferrite magnets. The method recovers strontium chloride-containing wastewater to obtain a high-concentration strontium chloride recovery solution, which is then used to form pellets to ultimately produce bonded permanent ferrite magnets. This method significantly improves strontium resource utilization, effectively reduces strontium resource waste, and significantly lowers costs. Furthermore, by further optimizing the parameters of the strontium chloride recovery solution and the bonded permanent ferrite magnet preparation process, the present invention minimizes the negative impact of the strontium chloride recovery solution on the production and performance of the bonded permanent ferrite magnets.

[0007] The specific technical solution of the present invention is as follows:

[0008] In a first aspect, the present invention provides a preparation method for preparing bonded permanent magnet ferrite by recycling strontium from wastewater, which comprises the following steps:

[0009] a) Densify iron oxide red and strontium carbonate to obtain a densified material.

[0010] b) Pelletize the densified material under the condition of spraying a strontium chloride recovery solution to obtain a pelletized material.

[0011] c) Sinter the pelletized material to obtain a pre-sintered pellet ball; the pre-sintered pellet ball exchanges heat with cooling water in a heat exchange kiln and is crushed to obtain a coarse powder.

[0012] d) Wet ball-mill the coarse powder to obtain a slurry, which is subjected to pressure filtration, drying, tempering, and cooling to obtain a bonded permanent magnet ferrite.

[0013] The present invention recovers a high-concentration strontium chloride recovery solution from wastewater containing strontium chloride, then sprays the strontium chloride recovery solution during the pelletizing process of the iron-strontium densified material to obtain a pelletized material, and finally obtains a bonded permanent magnet ferrite through a series of post-treatments such as sintering. The method of the present invention fully realizes the recycling of strontium resources, can effectively reduce the waste of strontium resources, and greatly reduces costs.

[0014] During the R & D process of the present invention, it is found that when applying the strontium chloride recovery solution to the preparation of bonded permanent magnet ferrite, the following technical problems need to be considered: (1) When using the strontium chloride recovery solution for pelletizing, problems such as precipitation blockage need to be considered in production, as well as the influence of impurity metal ions on the product performance. The impurity metal ions are mainly sodium, magnesium, manganese, chromium and other ions (metal ions such as iron and calcium that can undergo solid-phase reactions to form ferrite phases are not regarded as impurities); (2) The influence of the strontium chloride recovery solution on the strength of the pelletized material for pelletizing; (3) The influence of the strontium chloride content in the pelletized material on the subsequent sintering atmosphere; (4) The influence of the pelletized material for pelletizing with the strontium chloride recovery solution on the strength of the pre-sintered pellet ball after firing, and thus the subsequent influence on dry grinding and fine grinding, etc. These are a systematic problem.

[0015] After a series of studies, the present invention finally gives the following solutions:

[0016] (1) The present invention strictly controls the temperature and pH of the strontium chloride recovery solution at 25 - 50 °C and pH = 7 - 9 respectively, and strictly controls the strontium chloride concentration at 16 - 22 wt%. The present invention finds that by controlling the temperature and pH of the strontium chloride recovery solution within the above ranges, the problem of precipitate blockage can be effectively solved; the temperature of the strontium chloride recovery solution should not be too high, as too high a temperature will not only cause heat waste but also lead to a decrease in the strength of the spherical materials; if the pH is too low, strontium carbonate is prone to decomposition, resulting in insufficient strength of the spherical materials and easy disintegration; conversely, if the pH is too high, free strontium ions, calcium ions, etc. in the strontium chloride recovery solution are prone to precipitation, blocking the spray nozzles (in the prior art, most use tap water to form spheres or solutions prepared with pure substance additives to form spheres, so there is no need to consider the problem of precipitation of impurity metal elements in the solution in the present invention). In addition, when the concentration of impurity ions in the wastewater is too high, the content of impurities and strontium chloride is controlled by dilution or by simultaneously supplementing strontium chloride.

[0017] (2) The present invention controls the moisture content of the spherical materials at 10 - 15 wt%; and simultaneously controls its diameter at 8 - 20 mm, with the volume difference of the spherical materials not exceeding 20%. The present invention finds that by limiting the diameter of the spherical materials obtained by pelletizing within the above ranges, the spherical materials can have high strength; in the present invention, in addition to considering the conventional uniformity inside and outside the spherical materials for the solid-phase reaction during sintering, the influence brought by strontium chloride also needs to be considered. If the diameter of the spherical materials is too large, the strength of the spheres will decrease, and if the diameter of the spherical materials is too small, the contact surface area will be too large, resulting in a poor atmosphere between the spherical materials. As described above, the large introduction of chloride ions and the poor atmosphere between the spherical materials will lead to poor performance. By controlling the moisture content of the spherical materials at 10 - 15 wt%, the uniformity of strontium chloride in the spherical materials can be ensured. In the present invention, the level of the moisture content of the spherical materials will not only affect the strength of the spherical materials in the drying section of the sintering device (rotary kiln) and the adhesion between the spherical materials and the kiln wall and between the spherical materials, but also affect the iron-strontium molar ratio of the spherical materials. If the moisture content is too high, it means that the content of strontium chloride is too high and the iron-strontium molar ratio is low, and vice versa if the moisture content is too low, which will cause large fluctuations in the properties of the materials. The properties of the bonded permanent ferrite prepared by the present invention can reach or even be better than those of the products directly produced by dry or wet methods using strontium chloride, which benefits from the comprehensive control of the moisture content of the spherical materials, the concentration and pH of the strontium chloride recovery solution, making the distribution of strontium chloride in the spherical materials more uniform.

[0018] (3) The present invention controls the sintering conditions at an oxygen concentration of 16 - 22%, an air flow rate of 5 - 8 m / s, a temperature of 1100 - 1200 °C, and a time of 60 - 120 min. The present invention finds that by controlling the oxygen content and air flow rate during sintering within the above conditions, the product performance can be effectively improved (in conventional production, the chloride ions in iron red are the monitoring indicators, and too high chloride ions will lead to performance deviation, and the present invention method introduces a large amount of chloride ions, so higher requirements are imposed on the atmosphere conditions).

[0019] Preferably, in step a), the molar ratio of iron to strontium in the iron oxide red and strontium carbonate is 5.0 - 5.8∶1.

[0020] Preferably, in step a), the densification treatment is as follows: the iron oxide red and strontium carbonate are mixed by a plowshare mixer and then introduced into a dry ball mill for ball milling and densification, and the densification time is 30 - 120 min.

[0021] Preferably, in step b), the preparation method of the strontium chloride recovery solution is as follows:

[0022] 1) The wastewater containing 2 - 4 wt% strontium chloride is concentrated to 40 - 60% by volume by the first steam at 100 - 130 °C to obtain a concentrated solution A and the second steam at 80 - 100 °C.

[0023] 2) The concentrated solution A is concentrated to 20 - 30% by volume by the second steam to obtain a concentrated solution B and the third steam at 70 - 80 °C.

[0024] 3) The concentrated solution B is concentrated by the third steam to a strontium chloride concentration of 16 - 22 wt% to obtain the strontium chloride recovery solution.

[0025] Preferably, step 1) is carried out in the first heat exchange concentration device, the first heat exchange concentration device is heated by the first steam, and the first steam is obtained by heat exchange of the cooling water in step c); step 2) is carried out in the second heat exchange concentration device, and the second heat exchange concentration device is heated by the second steam; step 3) is carried out in the third heat exchange concentration device, and the third heat exchange concentration device is heated by the third steam.

[0026] The present invention concentrates the wastewater containing strontium chloride into a high-concentration strontium chloride recovery solution through a triple heat exchange concentration device. Among them, the steam used in the triple heat exchange concentration device is obtained by recovering the heat energy in the pre-burned material balls. In the conventional technology, after the pre-burned material balls are cooled with cooling water, the heat energy obtained by the cooling water is only used for ordinary flushing, and there is often a large surplus, resulting in waste. In this solution, the heat energy of the pre-burned material balls is extremely high, and it is relatively difficult to directly utilize this part of the heat energy. If the pre-burned material balls are directly selected as the heat source to concentrate the wastewater, the requirements for the equipment are relatively high (the temperature of the material balls is about 900 °C. Under this temperature condition, the service life of conventional metals is not long and they are prone to failure. If ceramics are selected, impurities are likely to be introduced). Therefore, in this solution, a self-modified heat exchange kiln is used to realize the heat energy exchange between the pre-burned material balls and the cooling water, and the heat energy is used in the form of steam to heat the wastewater, realizing the concentration of the production wastewater and recycling it for production. To further recover heat energy more efficiently, the wastewater concentration is divided into three-stage evaporation: in the first stage, the first steam generated by the heat exchange kiln is used for heating, and the wastewater is concentrated to 40-60% of the original volume; in the second stage, the second steam generated by the wastewater concentration in the first stage and the hot water condensed from the heat dissipation of the first steam are used for heating, and the wastewater is concentrated to 20-30% of the original volume; in the third stage, the third steam generated by the wastewater concentration in the second stage is used for heating, and the wastewater is concentrated to the target concentration, and the impurity content and temperature are ensured. This solution can reduce the equipment pressure, and at the same time, the heating uniformity of the steam is better, which can ensure the uniform heating during the concentration process. And it is divided into three times of concentration, which can better utilize the waste heat.

[0027] Preferably, the content of impurity metals in the wastewater containing 2-4 wt% strontium chloride is less than 0.2 wt%; the content of impurity metals in the strontium chloride recovery solution is less than 2 wt%.

[0028] Too high content of impurity metals will affect the product performance. Therefore, it is necessary to control the content of impurity metals in the wastewater and the strontium chloride recovery solution.

[0029] Preferably, in step c), the temperature of the pre-burned material balls is 800-1000 °C.

[0030] Preferably, in step c), the average particle size of the coarse powder is 2.0-8.0 μm.

[0031] Preferably, in step d), the mass ratio of the balls, the material and the water in the wet ball milling is 6-10∶1∶1-1.5.

[0032] Preferably, in step d), the average particle size of the coarse powder after wet ball milling is 1.0-2.0 μm.

[0033] Preferably, in step d), the water content of the slurry after pressure filtration is 15-25 wt%, and the water content after drying is <0.6 wt%.

[0034] Preferably, in step d), the tempering temperature is 850-950°C.

[0035] Compared with the prior art, the present invention has the following beneficial effects:

[0036] (1) The present invention recovers strontium chloride-containing wastewater to obtain a high-concentration strontium chloride recovery solution, which is then used to form pellets to ultimately produce bonded permanent ferrite magnets. The method of the present invention significantly improves the utilization rate of strontium resources, effectively reduces strontium resource waste, and can reduce the production cost per ton of bonded permanent ferrite magnets by approximately 5%.

[0037] (2) The present invention further optimizes the parameters of the strontium chloride recovery solution and the preparation process of the bonded permanent magnet ferrite, thereby minimizing the negative impact of the strontium chloride recovery solution on the production and performance of the bonded permanent magnet ferrite.

[0038] (3) The present invention fully utilizes the heat of the pre-burned balls by transforming the traditional cooling kiln into a heat exchange kiln. By converting the heat of the pre-burned balls into steam heat, the wastewater is evaporated and the temperature of the strontium chloride recovery solution output for ball making is guaranteed, thereby effectively improving the utilization of thermal energy and reducing the pressure of wastewater treatment discharge. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a connection diagram of the strontium chloride concentration and recovery device.

[0040] Figure 2 This is a structural diagram of the heat exchange kiln.

[0041] Figure 3 Schematic diagram of the cross section of the heat exchange kiln.

[0042] Figure 4 Schematic diagram of the water inlet of the segmented water-cooling component.

[0043] Figure 5 This is a schematic diagram of the structure of a single heat exchange and concentration device.

[0044] Figure 6 It is a cross-sectional schematic diagram of a single heat exchange and concentration device.

[0045] The reference numerals are as follows: 1 heat exchange kiln, 2 steam generator, 3 first heat exchange concentration device, 4 second heat exchange concentration device, 5 third heat exchange concentration device, 1-1 rotating bearing, 1-2 support, 1-3 kiln body, 1-3-1 spiral guiding plate, 1-4 feed inlet, 1-5 discharge outlet, 1-6 segmented water cooling component, 1-6-1 preheating pipe section, 1-6-2 heating pipe section, 1-6-3 water inlet, 1-6-4 water inlet pipe, 1-6-5 water outlet, 3-1 waste water cavity, 3-2 steam cavity, 3-3 waste water inlet, 3-4 waste water outlet, 3-5 steam inlet, 3-6 condensate water outlet, 3-7 steam outlet. Detailed implementation manners

[0046] The present invention will be further described below in conjunction with embodiments.

[0047] General embodiment

[0048] A preparation method of bonded permanent ferrite includes the following steps:

[0049] a) Densify iron oxide red and strontium carbonate to obtain a densified material.

[0050] In some preferred embodiments, the molar ratio of iron to strontium in the iron oxide red and strontium carbonate is 5.0-5.8∶1.

[0051] In some preferred embodiments, the densification treatment is to mix iron oxide red and strontium carbonate through a plow knife machine and then introduce them into a dry ball mill for ball milling densification, and the densification time is 30-120 min.

[0052] In some preferred embodiments, the purity of the iron oxide red is above 98.5 wt%; the purity of the strontium carbonate is 97.5 wt%.

[0053] b) Pelletize the densified material under the condition of spraying strontium chloride recovery solution to obtain pelletized material.

[0054] In some preferred embodiments, the concentration of the strontium chloride recovery solution is 16-22 wt%, pH = 7-9, and the temperature is 25-50 °C.

[0055] In some preferred embodiments, the moisture content of the pelletized material is 10-15 wt%.

[0056] In some preferred embodiments, the diameter of the pelletized material is 8-20 mm, and the volume difference of the pelletized material does not exceed 20%.

[0057] In some preferred embodiments, the pelletizing is carried out through a pelletizing pan.

[0058] In some preferred embodiments, the preparation method of the strontium chloride recovery solution is as follows:

[0059] 1) The wastewater containing 2-4 wt% strontium chloride is concentrated to 40-60% by volume by the first steam at 100-130 °C to obtain concentrated liquid A and the second steam at 80-100 °C.

[0060] 2) Concentrated liquid A is concentrated to 20-30% by volume by the second steam to obtain concentrated liquid B and the third steam at 70-80 °C.

[0061] 3) Concentrated liquid B is concentrated by the third steam to a strontium chloride concentration of 16-22 wt% to obtain a strontium chloride recovery solution.

[0062] Further preferably, the content of impurity metals in the wastewater containing 2-4 wt% strontium chloride is less than 0.2 wt%; the content of impurity metals in the strontium chloride recovery solution is less than 2 wt%.

[0063] Further preferably, step 1) is carried out in a first heat exchange concentration device, the first heat exchange concentration device is heated by the first steam, and the first steam is obtained by heat exchange of the cooling water in step c); step 2) is carried out in a second heat exchange concentration device, and the second heat exchange concentration device is heated by the second steam; step 3) is carried out in a third heat exchange concentration device, and the third heat exchange concentration device is heated by the third steam.

[0064] c) Sinter the spherical materials to obtain pre-sintered spherical materials; the pre-sintered spherical materials are heat-exchanged with cooling water in a heat exchange kiln and then crushed to obtain coarse powder.

[0065] In some preferred embodiments, the conditions for sintering are: oxygen concentration 16-22%, air flow rate 5-8 m / s, temperature 1100-1200 °C, and time 60-120 min.

[0066] In some preferred embodiments, the temperature of the pre-sintered spherical materials is 800-1000 °C.

[0067] In some preferred embodiments, the average particle size of the coarse powder is 2.0-8.0 μm.

[0068] d) Wet ball mill the coarse powder to obtain a slurry, and after pressure filtration, drying, tempering, and cooling, obtain a bonded permanent ferrite.

[0069] In some preferred embodiments, the mass ratio of ball materials to water in the wet ball milling is 6-10∶1∶1-1.5.

[0070] In some preferred embodiments, the average particle size of the coarse powder after wet ball milling is 1.0-2.0 μm.

[0071] In some preferred embodiments, the water content of the slurry after pressure filtration is 15-25 wt%, and the water content after drying is <0.6 wt%.

[0072] In some preferred implementation cases, the tempering temperature is 850-950°C.

[0073] In some preferred implementation cases, the strontium chloride recovery solution is prepared by a strontium chloride concentration recovery device, which comprises:

[0074] The heat exchange kiln includes a horizontally arranged and self-rotating kiln body, with a feed inlet and a discharge outlet at both ends of the kiln body, a spiral guide plate inside the kiln body, and a segmented water-cooling component coiled around the surface of the kiln body;

[0075] The steam generator has two interfaces connected to the water inlet and outlet of the segmented water-cooling component, respectively, to realize the collection of hot water and conversion into steam as well as the supply of cooling water (to the segmented water-cooling component);

[0076] The triple heat exchange and concentration device is connected to the steam generator to realize the transportation of steam to the triple heat exchange and concentration device.

[0077] In some preferred embodiments, the kiln body is positioned at an angle of 3-5° to the horizontal and is supported on a support via a rotating bearing. In some preferred embodiments, a feed inlet is located at the lower horizontal end of the kiln body, and a discharge outlet is located at the higher horizontal end of the kiln body. The flow direction of the segmented water-cooling element is opposite to the flow of material within the kiln body. The cooling water moves in a spiral from top to bottom in a horizontal reference frame, while the direction of the pre-sintered pellets is opposite. Therefore, the spiral guide plate is arranged in a counter-spiral arrangement relative to the cooling water in the preheating and heating sections that wind around the outside of the kiln body.

[0078] In some more preferred implementation cases, the segmented water-cooling component includes a preheating pipe section and a heating pipe section according to the horizontal position of the kiln body from high to low; the preheating pipe section is provided with a water inlet, which is connected to the steam generator through a water inlet pipe; the heating pipe section is provided with a water outlet connected to the steam generator.

[0079] In some more preferred implementation cases, the cross-sections of the preheating pipe section and the heating pipe section are semicircular.

[0080] In some more preferred embodiments, the diameter ratio of the preheating pipe section to the heating pipe section is 1.5-2:1, and the number of coils per unit kiln length is 2-3 coils per 10 cm. The above design ratio is to increase the water flow rate in the pipe and improve its heat exchange effect.

[0081] In some more preferred implementation cases, the diameter of the heating pipe section decreases along the direction of water flow.

[0082] In some more preferred embodiments, the triple heat exchange and concentration device includes a first heat exchange and concentration device, a second heat exchange and concentration device, and a third heat exchange and concentration device connected in series in sequence; each heat exchange and concentration device includes a vertical wastewater cavity and a steam cavity wrapped outside the wastewater cavity; a wastewater inlet and a wastewater outlet are respectively provided at the top and bottom of the wastewater cavity; a steam inlet and a condensate outlet are provided at the top of the steam cavity, and a steam outlet is provided at the bottom; the wastewater outlet of the previous heat concentration device is communicated with the wastewater inlet of the next heat concentration device; the steam outlet and the condensate outlet of the previous heat concentration device are communicated with the steam inlet of the next heat concentration device.

[0083] Specific examples and comparative examples

[0084] Example 1

[0085] (a) Ferric oxide with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% are proportioned according to a molar ratio of iron / strontium of 5.4:1. After mixing ferric oxide and strontium carbonate through a plowshare mixer, they are introduced into a dry ball mill for ball milling to be dense. After 60 minutes of densification, a dense material is obtained.

[0086] (b) The dense material is fed into a pelletizing pan, and a strontium chloride recovery solution with a mass concentration of 18%, a temperature of 45°C, and a pH of 7 is sprayed through a spray pipe for pelletizing to obtain pelletized material; the water content of the pelletized material is 12 wt%.

[0087] (c) The pelletized material is fed into a rotary kiln and sintered for 90 minutes under the conditions of an oxygen concentration of 20%, an air flow rate of 7 m / s, and a temperature of 1150°C to obtain a pre-sintered pellet ball at a temperature of 1000°C; the pre-sintered pellet ball is cooled by exchanging heat with cooling water in a heat exchange kiln and then introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0088] (d) The coarse powder is wet ball milled to an average particle size of 1.5 μm to obtain a slurry; after the slurry is pressure filtered and dried, it is tempered at 900°C and then cooled to obtain bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball material to water in wet ball milling is 10:1:1.2; the water content after pressure filtration is 19%, and the water content after drying is <0.6%.

[0089] Combined Figure 1 , Figure 5 and Figure 6 As shown, the preparation method of the strontium chloride recovery solution is:

[0090] (b-1) Introduce 1 volume of the production wastewater with a strontium chloride mass concentration of 3% into the wastewater chamber 3-1 of the first heat exchange and concentration device 3, and evaporate and concentrate it to 0.5 volume to obtain concentrated liquid A and the second steam (concentrated liquid A is exported from the wastewater outlet 3-4); the first heat exchange and concentration device 3 is heated by the first steam, and the first steam is heated by the heat exchange kiln 1 in step (c). Specifically, the hot water in the heat exchange kiln 1 enters the steam generator 2 to generate steam, and the steam enters the steam chamber 3-2 from the steam inlet 3-5 to heat the wastewater chamber 3-1; the temperature of the first steam is 120°C, and the temperature of the second steam is 95°C; the impurity metal content of the production wastewater is 0.12%.

[0091] (b-2) Introduce concentrated liquid A into the wastewater chamber of the second heat exchange and concentration device 4. The second heat exchange and concentration device 4 is heated by the second steam. Specifically, the hot water in the wastewater chamber 3-1 of the first heat exchange and concentration device 3 flows out of the condensate outlet 3-6 and mixes with the steam flowing out of the steam outlet 3-7, and then enters the steam chamber 3-2 of the second heat exchange and concentration device together. After concentrating concentrated liquid A to 0.25 volume, concentrated liquid B and the third steam are obtained, and the temperature of the third steam is 75°C.

[0092] (b-3) Introduce concentrated liquid B into the wastewater chamber of the third heat exchange and concentration device 5. The third heat exchange and concentration device 5 is heated by the third steam. Specifically, the hot water in the wastewater chamber 3-1 of the second heat exchange and concentration device 3 flows out of the condensate outlet 3-6 and mixes with the steam flowing out of the steam outlet 3-7, and then enters the steam chamber 3-2 of the third heat exchange and concentration device together. Concentrate concentrated liquid B to a strontium chloride solution with a mass concentration of 18% to obtain a strontium chloride recovery solution; the impurity metal content of the strontium chloride recovery solution is 0.16%.

[0093] In step (c), combine Figures 2 - 4As shown in the figure, the heat exchange kiln 1 includes a kiln body 1-3 with an angle of 4° to the horizontal line and placed on a bracket 1-2 through a rotating bearing 1-1. A spiral guide plate 1-3-1 is arranged inside the kiln body 1-3. An inlet 1-4 is arranged at the lower end of the horizontal position of the kiln body 1-3, and an outlet 1-5 is arranged at the higher end of the horizontal position of the kiln body 1-3. A segmented water-cooling component 1-6 is fixedly wound around the outer surface of the kiln body 1-3. The segmented water-cooling component 1-6, from high to low in the horizontal position of the kiln body, includes a connected preheating pipe section 1-6-1 and a heating pipe section 1-6-2 wound around the outside of the kiln body 1-3. The preheating pipe section 1-6-1 is provided with a water inlet 1-6-3, and the water inlet 1-6-3 is communicated with a steam generator 2 through a water inlet pipe 1-6-4; the steam generator 2 is connected to the first heat exchange and concentration device 1 in step (b-1); the basic structural principles of the above first heat exchange and concentration device 3, the second heat exchange and concentration device 4, and the third heat exchange and concentration device 5 are similar; the cross-sections of the preheating pipe section 1-6-1 and the heating pipe section 1-6-2 are semi-circular; the pipe diameter ratio of the preheating pipe section 1-6-1 to the heating pipe section 1-6-2 is 1.5∶1, and the number of winding turns per unit kiln body length is 2 turns per 10 cm. In the segmented water-cooling component 1-6, the heating pipe section 1-6-2 is arranged with reduced diameter and dense rows along the water flow direction to improve the heat exchange efficiency. The cooling water moves in a spiral from top to bottom in the horizontal reference system, while the direction of the pre-burned material balls is opposite. Therefore, the spiral guide plate 1-3-1 is arranged in a reverse spiral with respect to the cooling water of the preheating pipe section 1-6-1 and the heating pipe section 1-6-2 wound around the outside of the kiln body. After the pre-burned material balls are cooled, they enter the next process from the outlet material.

[0094] Example 2

[0095] The difference from Example 1 is that the molar ratio of iron to strontium in the feed is different, which is 5∶1; the concentration of the recovered strontium chloride solution is different, which is 22%. The specific steps are as follows:

[0096] (a) Iron oxide red with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% are proportioned according to the molar ratio of iron / strontium of 5∶1. After being mixed by a plowshare machine, the iron oxide red and strontium carbonate are introduced into a dry ball mill for ball milling to be dense. After 60 minutes of densification, a dense material is obtained.

[0097] (b) The dense material is fed into a pelletizing pan, and a recovered strontium chloride solution with a mass concentration of 22%, a temperature of 45°C, and a pH of 7 is sprayed through a spray pipe for pelletizing to obtain pelletized material; the moisture content of the pelletized material is 12 wt%.

[0098] (c) The pelletized material is fed into a rotary kiln and sintered for 90 minutes under the conditions of an oxygen concentration of 20%, an air flow rate of 7 m / s, and a temperature of 1150°C to obtain pre-burned material balls at a temperature of 1000°C; the pre-burned material balls are heat-exchanged and cooled with cooling water in the heat exchange kiln and then introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0099] (d) Wet ball mill the coarse powder to an average particle size of 1.5 μm to obtain a slurry; after the slurry is pressure-filtered and dried, temper it at 900 °C, and after cooling, obtain the bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball to material to water in wet ball milling is 10∶1∶1.2; the water content after pressure filtration is 19%, and the water content after drying is <0.6%.

[0100] Example 3

[0101] The difference from Example 1 is that the molar ratio of iron to strontium in the feed is different, which is 5.8∶1; the concentration of the recycled strontium chloride solution is different, which is 16%. The specific steps are as follows:

[0102] (a) Mix iron red with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% according to a molar ratio of iron / strontium of 5.8∶1. After mixing iron red and strontium carbonate through a plow knife machine, introduce them into a dry ball mill for ball milling to densify. After densifying for 60 minutes, obtain a densified material.

[0103] (b) Feed the densified material into a pelletizing pan, and spray the recycled strontium chloride solution with a mass concentration of 16%, a temperature of 45 °C, and a pH of 7 through a spray pipe to pelletize and obtain pelletized material; the water content of the pelletized material is 12 wt%.

[0104] (c) Feed the pelletized material into a rotary kiln, and sinter it for 90 minutes under the conditions of an oxygen concentration of 20%, an air flow rate of 7 m / s, and a temperature of 1150 °C to obtain a pre-sintered pellet ball at a temperature of 1000 °C; after the pre-sintered pellet ball exchanges heat with cooling water in a heat exchange kiln and cools, introduce it into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0105] (d) Wet ball mill the coarse powder to an average particle size of 1.5 μm to obtain a slurry; after the slurry is pressure-filtered and dried, temper it at 900 °C, and after cooling, obtain the bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball to material to water in wet ball milling is 10∶1∶1.2; the water content after pressure filtration is 19%, and the water content after drying is <0.6%.

[0106] Example 4

[0107] The difference from Example 1 is that the pH of the recycled strontium chloride solution in the feed is different, which is 8. The specific steps are as follows:

[0108] (a) Mix iron red with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% according to a molar ratio of iron / strontium of 5.4∶1. After mixing iron red and strontium carbonate through a plow knife machine, introduce them into a dry ball mill for ball milling to densify. After densifying for 60 minutes, obtain a densified material.

[0109] (b) Feed the compacted material into a pelletizing pan, and spray the strontium chloride recovery solution with a mass concentration of 18%, a temperature of 45 °C, and a pH of 8 through a spray pipe for pelletizing to obtain pelletized material; the water content of the pelletized material is 12 wt%.

[0110] (c) Feed the pelletized material into a rotary kiln, and sinter it for 90 min under the conditions of an oxygen concentration of 20%, an air flow rate of 7 m / s, and a temperature of 1150 °C to obtain pre-sintered pellet balls at a temperature of 1000 °C; the pre-sintered pellet balls are heat-exchanged and cooled with cooling water in a heat-exchange kiln, then introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0111] (d) Wet ball mill the coarse powder to an average particle size of 1.5 μm to obtain slurry; after the slurry is pressure-filtered and dried, temper it at 900 °C, and then cool it to obtain bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball to material to water in wet ball milling is 10:1:1.2; the water content after pressure filtration is 19%, and the water content after drying is <0.6%.

[0112] Example 5

[0113] The difference from Example 1 lies in the different sintering conditions: the pre-sintering oxygen concentration is 16%, and the air speed is 8 m / s. The specific steps are as follows:

[0114] (a) Mix iron red with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% according to a molar ratio of iron / strontium of 5.4:1. After mixing the iron red and strontium carbonate through a plowshare mixer, introduce them into a dry ball mill for ball milling to densify, and obtain compacted material after 60 min of densification.

[0115] (b) Feed the compacted material into a pelletizing pan, and spray the strontium chloride recovery solution with a mass concentration of 18%, a temperature of 45 °C, and a pH of 7 through a spray pipe for pelletizing to obtain pelletized material; the water content of the pelletized material is 12 wt%.

[0116] (c) Feed the pelletized material into a rotary kiln, and sinter it for 90 min under the conditions of an oxygen concentration of 16%, an air flow rate of 8 m / s, and a temperature of 1150 °C to obtain pre-sintered pellet balls at a temperature of 1000 °C; the pre-sintered pellet balls are heat-exchanged and cooled with cooling water in a heat-exchange kiln, then introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0117] (d) Wet ball mill the coarse powder to an average particle size of 1.5 μm to obtain slurry; after the slurry is pressure-filtered and dried, temper it at 900 °C, and then cool it to obtain bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball to material to water in wet ball milling is 10:1:1.2; the water content after pressure filtration is 19%, and the water content after drying is <0.6%.

[0118] Example 6

[0119] It is different from Example 1 in that the sintering conditions are different: the pre-sintering oxygen concentration is 22%, and the air velocity is 5 m / s. The specific steps are as follows:

[0120] (a) Ferric oxide with a mass purity of more than 98.5% and strontium carbonate with a purity of more than 97.5% are proportioned according to a molar ratio of iron / strontium of 5.4:1. The ferric oxide and strontium carbonate are mixed by a plowshare mixer and then introduced into a dry ball mill for ball milling to densify. After 60 minutes of densification, a densified material is obtained.

[0121] (b) The densified material is fed into a pelletizing pan, and a strontium chloride recovery solution with a mass concentration of 18%, a temperature of 45°C, and a pH of 7 is sprayed through a spray pipe for pelletizing to obtain pelletized material; the moisture content of the pelletized material is 12 wt%.

[0122] (c) The pelletized material is fed into a rotary kiln and sintered for 90 minutes under the conditions of an oxygen concentration of 22%, an air flow rate of 5 m / s, and a temperature of 1150°C to obtain pre-sintered pellet balls at a temperature of 1000°C; the pre-sintered pellet balls are heat-exchanged with cooling water in a heat exchange kiln and then introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0123] (d) The coarse powder is wet ball milled to an average particle size of 1.5 μm to obtain a slurry; after the slurry is pressure filtered and dried, it is tempered at 900°C and cooled to obtain bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball material to water in wet ball milling is 10:1:1.2; the moisture content after pressure filtration is 19%, and the moisture content after drying is <0.6%.

[0124] Example 7

[0125] It is different from Example 1 in that the content of strontium chloride in the wastewater is 2.2%, the content of impurity metals is 0.03%, and the content of impurity metals in the strontium chloride recovery solution is 0.09%.

[0126] Example 8

[0127] It is different from Example 1 in that the content of strontium chloride in the wastewater is 4.7%, the content of impurity metals is 0.10%, and the content of impurity metals in the strontium chloride recovery solution is 0.18%.

[0128] Example 9

[0129] It is different from Example 1 in that the temperature of the pre-sintered pellet balls is 900°C, the temperature of the first steam is 110°C, the temperature of the second steam is 90°C, and the temperature of the third steam is 70°C.

[0130] Example 10

[0131] It is different from Example 1 in that the temperature of the pre-sintered pellet balls is 1100°C, the temperature of the first steam is 125°C, the temperature of the second steam is 98°C, and the temperature of the third steam is 76°C.

[0132] Comparative Example 1

[0133] It is different from Example 1 in that a conventional manufacturing process is adopted: strontium chloride is directly added to the pelletizing according to the ratio. The specific steps are as follows:

[0134] (a) Ferric oxide with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% are proportioned according to a molar ratio of iron / strontium of 5.4:1, and then strontium chloride accounting for about 2.16% of the total mass of ferric oxide and strontium carbonate is added. After mixing ferric oxide, strontium carbonate and strontium chloride through a plowshare mixer, they are introduced into a dry ball mill for ball milling to be dense. After 60 minutes of densification, a dense material is obtained.

[0135] (b) The dense material is fed into a pelletizing pan for pelletizing to obtain pellet material; the moisture content of the pellet material is 12 wt%.

[0136] (c) The pellet material is fed into a rotary kiln and sintered for 90 minutes under the conditions of an oxygen concentration of 20%, an air flow rate of 7 m / s, and a temperature of 1150 °C to obtain a pre-sintered pellet ball at a temperature of 1000 °C; the pre-sintered pellet ball is heat-exchanged and cooled with cooling water in a heat exchange kiln and then introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0137] (d) The coarse powder is wet ball milled to an average particle size of 1.5 μm to obtain a slurry; after the slurry is pressure filtered and dried, it is tempered at 900 °C and cooled to obtain bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of the ball material to water in the wet ball milling is 10:1:1.2; the moisture content after pressure filtration is 19%, and the moisture content after drying is <0.6%.

[0138] Comparative Example 2

[0139] It is different from Example 1 in that: the production wastewater is directly used for pelletizing. The specific steps are as follows:

[0140] (a) Ferric oxide with a mass purity of more than 98.5% and strontium carbonate with a mass purity of more than 97.5% are proportioned according to a molar ratio of iron / strontium of 5.4:1. After mixing ferric oxide and strontium carbonate through a plowshare mixer, they are introduced into a dry ball mill for ball milling to be dense. After 60 minutes of densification, a dense material is obtained.

[0141] (b) The dense material is fed into a pelletizing pan, and the clear liquid of the production wastewater (i.e., the clear liquid of the wastewater before concentration and recovery in Example 1) is sprayed through a spray pipe for pelletizing to obtain pellet material; the moisture content of the pellet material is 12 wt%.

[0142] (c) Feed the ball material into the rotary kiln and sinter it for 90 min under the conditions of an oxygen concentration of 20%, an air flow rate of 7 m / s, and a temperature of 1150 °C to obtain pre-sintered ball materials at a temperature of 1000 °C; after the pre-sintered ball materials are heat-exchanged and cooled with cooling water in the heat exchange kiln, they are introduced into a dry ball mill for crushing to obtain coarse powder, and the average particle size of the coarse powder is 5.5 μm.

[0143] (d) Wet ball mill the coarse powder to an average particle size of 1.5 μm to obtain a slurry; after the slurry is pressure-filtered and dried, temper it at 900 °C and cool it to obtain bonded permanent magnet ferrite magnetic powder. Among them, the mass ratio of ball material to water in wet ball milling is 10∶1∶1.2; the water content after pressure filtration is 19%, and the water content after drying is <0.6%.

[0144] Comparative Example 3

[0145] The difference from Example 1 is that the concentration of the strontium chloride recovery solution is 25%.

[0146] Comparative Example 4

[0147] The difference from Example 1 is that the concentration of the strontium chloride recovery solution is 12%.

[0148] Comparative Example 5

[0149] The difference from Example 1 is that the water content of the ball material after pelletizing is 18%.

[0150] Comparative Example 6

[0151] The difference from Example 1 is that the water content of the ball material after pelletizing is 9%.

[0152] Comparative Example 7

[0153] The difference from Example 1 is that the pH of the strontium chloride recovery solution is 10.0 and the temperature is 60 °C.

[0154] Comparative Example 8

[0155] The difference from Example 1 is that during the pre-sintering process, the oxygen content in the rotary kiln is 15% and the air flow rate is 4 m / s.

[0156] Comparative Example 9

[0157] The difference from Example 1 is that the temperature of the pre-sintered ball material is 800 °C, the temperature of the first steam is 100 °C, the temperature of the second steam is 82 °C, and the temperature of the third steam is 65 °C.

[0158] Comparative Example 10

[0159] It is different from Example 1 in that: the strontium chloride content in the production wastewater is 1.5%, the impurity metal content in the solution is 0.22%, and the impurity metal content in the recovered strontium chloride solution is 0.31%.

[0160] Performance testing:

[0161] (1) Average particle size: It is detected by a WLP-205A Fisher average particle size analyzer. It is necessary to detect the average particle size of the magnetic powder before and after tempering. The tempering process is: heat preservation at 850°C for 30 minutes. Tempering can eliminate some lattice defects, and at the same time promote the growth of some ultrafine grains, improving the overall performance.

[0162] (2) Compression density: It is obtained by measuring the height after compressing the same weight of magnetic powder to 30 MPa with a cemented carbide mold and converting.

[0163] (3) Rubber mixing: Mix the magnetic powder, rubber binder, and additives in the same proportion and then knead and wrap the roll on an open mill. The roll temperature is 85°C, and the roll gap is adjusted to 2 mm. Knead for 5 minutes to produce a 2-mm film.

[0164] After cooling to room temperature for 15 minutes, put it into a constant temperature oven at 60°C and keep it warm for 1 hour. Fold it 3 times in a calender to produce a 2-mm film. The calender roll temperature is 45°C, and the roll gap is adjusted to 2 mm.

[0165] (4) Magnetic property testing of the film: After cooling the film to room temperature, transfer it to the test room. The test room is kept at a constant temperature of 20 - 23°C. After placing it for 60 minutes, punch out 5 round pieces with a diameter of Φ25.4 mm and stack them into a 10-mm thick sample block to test the performance.

[0166] The samples of each example and Comparative Example 1 were tested, and the results are shown in Table 1.

[0167] Table 1

[0168]

[0169] It can be seen from the data comparison recorded in the above table that:

[0170] The performance of the samples obtained in Examples 1 - 10 can reach or even exceed the performance of the samples obtained by the conventional process (i.e., Comparative Example 1). However, since the wastewater was used to recover strontium chloride in Examples 1 - 10, considering the current price of strontium, the cost can be saved by 3 - 5%.

[0171] The differences between Comparative Example 2 and Example 1 are as follows: The production wastewater is directly used for pelletizing. The composition of the production wastewater is unstable, and the strontium chloride concentration is low. After being used for pelletizing, it will cause large fluctuations in the performance of the finished product during the production process. Moreover, due to the low strontium chloride concentration in the pellet material, the iron-strontium molar ratio is too high, resulting in both low intrinsic and remanence of the film; Similarly, in Comparative Example 4, due to the low strontium chloride concentration in the pellet material, the iron-strontium molar ratio is too high, resulting in poor performance; The differences between Comparative Example 6 and Example 1 are as follows: The moisture content of the pellet material after pelletizing is 9%. It is a high iron-strontium molar ratio formula. In addition, the too low moisture content causes the pellet structure to be loose, and the drying speed is too fast after entering the kiln, making it easy to collapse and break, thus resulting in large performance fluctuations.

[0172] The differences between Comparative Example 3 and Example 1 are as follows: The concentration of the strontium chloride recovery solution is 25%, resulting in too low iron-strontium molar ratio, resulting in low remanence Br but high coercivity Hcj of the film; The differences between Comparative Example 5 and Example 1 are as follows: The moisture content of the pellet material after pelletizing is 18%. It is also a low molar ratio formula, which will also affect the pre-burning process, resulting in too low temperature at the tail end of the kiln and increased gas consumption, so it is not compatible with the current pre-burning process.

[0173] The differences between Comparative Example 7 and Example 1 are as follows: The pH of the strontium chloride recovery solution is 10.0 and the temperature is 60 °C. The temperature of the strontium chloride recovery solution in Comparative Example 7 is too high, and the strength of the pellet material decreases. Analyzing the reason, it may be due to the decrease in the viscosity of water or too fast evaporation; The pH is too high, and the free strontium ions, calcium ions, etc. in the strontium chloride recovery solution decrease, making the iron-strontium molar ratio slightly higher. Moreover, the viscosity of the material reacted in the crushing in step (c) and the fine grinding in step (d) is too high, making the material difficult to disperse evenly, and the orientation degree in the magnetic field decreases, resulting in poor detection performance.

[0174] The differences between Comparative Example 8 and Example 1 are as follows: During the pre-burning process, the oxygen content in the rotary kiln is 15% and the air flow rate is 4 m / s, that is, the solid-phase reaction is in a relatively oxygen-deficient environment. The formation of the ideal ferrite phase requires a sufficient oxygen environment, otherwise it may lead to an increase in side reactions and a significant decrease in coercivity Hcj.

[0175] The differences between Comparative Example 9 and Example 1 are as follows: The temperature of the pre-burned pellet balls is 800 °C, the temperature of the first steam is 100 °C, the temperature of the second steam is 82 °C, and the temperature of the third steam is 65 °C. This comparative example mainly affects the efficiency of strontium chloride recovery. As long as the concentration, temperature, and pH of the sprayed strontium chloride recovery solution are ensured, theoretically, the impact on performance is not significant. However, production is a systematic problem. The too low temperature of the pre-burned pellet balls will lead to a decrease in the subsequent concentration efficiency, and may cause unstable feeding during continuous production. Unstable feeding in the kiln will lead to large fluctuations in performance, and the performance is difficult to predict; The performance of Comparative Example 9 after having a negative impact on production is manifested as overburning of the pre-burned pellet balls and a decrease in the intrinsic properties.

[0176] The difference between Comparative Example 10 and Example 1 lies in that: the strontium chloride content in the production wastewater is 1.5%, the impurity metal content in the solution is 0.22%, and the impurity metal content in the recovered strontium chloride solution is 0.31%. The recovered strontium chloride solution obtained in Comparative Example 10 is not diluted with a high-concentration strontium chloride solution. Therefore, the impurity content is relatively high, the strontium chloride concentration is relatively low, the iron-strontium molar ratio is on the high side, but there are also more impurity ions. Therefore, the intrinsic properties are slightly better than those of Comparative Example 2, and the remanence is lower.

[0177] In summary, in view of the theme purpose of cost saving, the various parameters of this solution are interrelated in production. Without subsequent process correction, the adjustment of parameters will lead to poor product stability and performance indicators.

[0178] The raw materials and equipment used in the present invention are all common raw materials and equipment in the art without special instructions; the methods used in the present invention are all conventional methods in the art without special instructions.

[0179] The above are only the preferred embodiments of the present invention, and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent transformations made to the above embodiments according to the technical essence of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A preparation method of bonded permanent ferrite, characterized in that Including: a) Densifying iron oxide red and strontium carbonate to obtain a densified material; b) Pelletizing the densified material under the condition of spraying a strontium chloride recovery solution to obtain pelletized material with a water content of 10 - 15 wt%; The preparation method of the strontium chloride recovery solution is as follows: 1) Waste water containing 2 - 4 wt% strontium chloride and an impurity metal content of < 0.2 wt% is concentrated to 40 - 60% by volume by first steam at 100 - 130 °C to obtain concentrated liquid A and second steam at 80 - 100 °C; 2) Concentrated liquid A is concentrated to 20 - 30% by volume by second steam to obtain concentrated liquid B and third steam at 70 - 80 °C; 3) Concentrated liquid B is concentrated by third steam to a strontium chloride concentration of 16 - 22 wt% to obtain a strontium chloride recovery solution with a pH of 7 - 9 and a temperature of 25 - 50 °C; c) Sintering the pelletized material at an oxygen concentration of 16 - 22%, an air flow rate of 5 - 8 m / s, and a temperature of 110 - °C for 60 - 120 min to obtain a pre-sintered pelletized material; the pre-sintered pelletized material is heat-exchanged with cooling water in a heat exchange kiln and then crushed to obtain coarse powder; d) Wet ball-milling, pressure-filtering, drying, tempering, and cooling the coarse powder to obtain bonded permanent ferrite.

2. The preparation method according to claim 1, characterized in that: In step a), the molar ratio of iron to strontium in the iron oxide red and strontium carbonate is 5.0 - 5.8:

1.

3. The preparation method according to claim 1 or 2, characterized in that: In step a), the densifying treatment is dry ball-milling densification after mixing the iron oxide red and strontium carbonate, and the densifying time is 30 - 120 min.

4. The preparation method according to claim 1, characterized in that: In step b), the diameter of the pelletized material is 8 - 20 mm, and the volume difference of the pelletized material does not exceed 20%.

5. The preparation method according to claim 4, characterized in that: The impurity metal content in the strontium chloride recovery solution is less than 2 wt%.

6. The preparation method according to claim 4, wherein: Step 1) is carried out in a first heat exchange concentration device, and the first heat exchange concentration device is heated by first steam, and the first steam is obtained by heat-exchanging the cooling water in step c); Step 2) is carried out in a second heat exchange concentration device, and the second heat exchange concentration device is heated by second steam; Step 3) is carried out in a third heat exchange concentration device, and the third heat exchange concentration device is heated by third steam.

7. The preparation method according to claim 1, characterized in that: In step c), the temperature of the pre-sintered pelletized material is 800 - 1000 °C.

8. The preparation method according to claim 1, wherein: In step c), the average particle size of the coarse powder is 2.0 - 8.0 μm.

9. The preparation method according to claim 1, wherein: In step d), The mass ratio of ball material to water in the wet ball-milling is 6 - 10:1:1 - 1.5; The average particle size of the coarse powder after wet ball-milling is 1.0 - 2.0 μm.

10. The preparation method according to claim 1, characterized in that: In step d), The water content of the material after pressure-filtering is 15 - 25 wt%, and the water content of the material after drying is < 0.6 wt%; The temperature of the tempering is 850 - 950 °C.

Images