Iron red and pretreatment process thereof, permanent magnet ferrite and preparation method and application thereof

Abstract

The application belongs to the technical field of permanent magnet ferrite preparation, and particularly relates to iron red and a pretreatment process thereof, a permanent magnet ferrite and a preparation method and application thereof. The application provides a pretreatment process of iron red, comprising the following steps: (1) adjusting the pH value of an iron red solution to 9-10 and drying; (2) performing heat treatment on the dried powder to obtain pretreated iron red; the temperature of the heat treatment is 800-900 DEG C, and the oxygen volume content is greater than or equal to 20% during the heat treatment; and the D50 of the pretreated iron red is 1+ / -0.2 microns. The iron red pretreated by the pretreatment process has large apparent density, high purity and few impurities.

Description

Technical Field

[0001] This invention belongs to the field of permanent magnet ferrite preparation technology, specifically relating to iron oxide red and its pretreatment process, permanent magnet ferrite and its preparation method and application. Background Technology

[0002] The loose packing density of powder particles is affected by factors such as particle size, particle shape, and particle specific surface area. Specifically, (1) when the particle size is large, the friction between particles is small, and the loose packing density is large; when the particle size is small, the cohesive force between particles makes it easy for particles to agglomerate, and the loose packing density is small; (2) the rougher the particle surface or the more irregular the particle shape, the greater the friction between particles and the smaller the loose packing density; the more irregular the particle shape or the smaller the particle size, the larger the specific surface area of ​​the particles, which increases the adsorption force between particles, making it easy for them to agglomerate and the loose packing density becomes smaller. Therefore, in order to improve the loose packing density of the powder, it is necessary to perform surface modification on powder particles with large surface area, irregular shape, fine particle size, and easy agglomeration; for non-spherical irregular powder particles, the powder shape is adjusted by ball milling or vibratory milling.

[0003] Iron oxide, also known as red iron oxide, is the main raw material and source of magnetism for permanent magnet ferrites. Its purity, impurities, and loose packing density play a decisive role in the performance of permanent magnet ferrites. Currently, the common process for preparing red iron oxide is the pickling solution spray roasting process, also known as the Roots process. This process uses waste pickling solution (mainly FeCl2) from steel rolling mills as raw material and produces red iron oxide as a byproduct through spray roasting equipment. In existing technologies, red iron oxide prepared by steel mills is often used to prepare permanent magnet ferrites. However, due to the constraints of different steel mills on preparation processes, steel types, and environmental protection requirements, the purity, impurities, and loose packing density of the red iron oxide produced vary. The purity, impurities, and loose packing density of red iron oxide all play a decisive role in the performance of the permanent magnet ferrites produced. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defects of low purity, many impurities and low loose packing density of iron red in the prior art, which result in low magnetic properties and magnetic flux of the permanent magnet ferrite. Thus, the present invention provides iron red and its pretreatment process, permanent magnet ferrite and its preparation method and application.

[0005] To this end, the present invention provides the following technical solution.

[0006] This invention provides a pretreatment process for iron oxide red, comprising the following steps:

[0007] (1) Adjust the pH of the iron oxide red solution to 9-10 and dry it;

[0008] (2) The dried powder is heat-treated to obtain pretreated iron red; the heat treatment temperature is 800-900℃, and the oxygen volume content during the heat treatment is ≥20%;

[0009] The D50 of the pretreated iron oxide red was 1 ± 0.2 μm.

[0010] Oxygen volume content refers to the volume ratio of oxygen in the mixed atmosphere during heat treatment. The oxygen flow rate can ensure the oxygen volume content.

[0011] The iron oxide red obtained after pretreatment using the pretreatment process of this invention has high purity, low impurities, and high bulk density. By first adjusting the pH value of the iron oxide red solution to 9-10, the acid radical ions in the iron oxide red can be effectively reduced, avoiding equipment corrosion and effectively reducing costs. The heat treatment at 800-900℃ of this invention can further remove most of the acid radical ions in the iron oxide red, resulting in a lower Cl content in the final pretreated iron oxide red. - ≤0.05%, SO3 2- ≤0.1%; while controlling the oxygen volume content during heat treatment to ≥20% can avoid the volatilization of the aforementioned acid radicals affecting the kiln atmosphere, which would prevent ferrous ions from being completely oxidized to ferric ions, resulting in more impurities, a decrease in the purity of iron oxide, and a lower loose packing density.

[0012] In one optional embodiment, in step (1), the iron oxide solution comprises iron oxide and water, and the mass ratio of iron oxide to water is 1:(1-3); as an example, the mass ratio of iron oxide to water can be 1:1, 1:1.3, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3 or within any two of the above values.

[0013] In an optional embodiment, in step (1), the iron oxide red solution further includes a first surfactant;

[0014] In one optional embodiment, in step (2), the oxygen volume content during the heat treatment is 20-22%;

[0015] In one optional implementation, in step (2), the oxygen flow rate during the heat treatment is 1-5 L / h; as an example, the oxygen flow rate can be 1 L / h, 2 L / h, 3 L / h, 4 L / h, 5 L / h or within any two of the above values.

[0016] In one alternative implementation, the reagent for adjusting the pH value includes an alkaline substance.

[0017] In one alternative embodiment, the alkaline substance includes at least one of ammonia and aluminum hydroxide;

[0018] In one optional embodiment, the first surfactant includes at least one of sodium oleate, calcium silicate, and calcium gluconate;

[0019] In one optional embodiment, the amount of the first surfactant added is 0.1-0.6 wt%, based on the mass of the iron oxide red. As an example, the amount of the first surfactant added can be 0.1 wt%, 0.15 wt%, 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, or within any two of the above values.

[0020] In an optional embodiment, step (1) further includes at least one of sodium hexametaphosphate, sodium citrate, and sodium carboxymethyl cellulose.

[0021] Preferably, based on the mass of the iron oxide red, the total amount of at least one of sodium hexametaphosphate, sodium citrate, and sodium carboxymethyl cellulose added is 0.1-0.3 wt%.

[0022] In one optional implementation, in step (1), the drying temperature is 100-140°C; as an example, the drying temperature can be 100°C, 110°C, 120°C, 130°C, 140°C or within any two of the above values.

[0023] In one optional embodiment, the process further includes ultrasonic water washing before drying;

[0024] In one alternative implementation, step (2) involves a heat treatment time of 1-2 hours.

[0025] In one optional embodiment, a second surfactant is added and vibratory milling is performed after the heat treatment;

[0026] Preferably, the second surfactant comprises calcium stearate;

[0027] Preferably, the amount of the second surfactant added is 0.1-0.2 wt%, based on the mass of the heat-treated iron oxide red.

[0028] Preferably, the vibratory grinding time is 2-3 minutes;

[0029] In one alternative embodiment, the vibratory mill is then passed through a 200-mesh sieve and a 20-mesh sieve; the purpose of this is to remove ultrafine particles and large particles.

[0030] The present invention also provides an iron oxide red obtained by the above-described pretreatment process;

[0031] Preferably, the Fe2O3 content in the iron oxide is ≥99.3wt%;

[0032] Preferably, the FeO content in the iron oxide red is ≤0.05wt%.

[0033] Preferably, the iron oxide red contains Cl - Content ≤0.05wt%;

[0034] Preferably, the loose bulk density of the iron oxide is ≥0.6 g / cm³. 3 .

[0035] The present invention also provides a method for preparing permanent magnet ferrite, wherein iron oxide, lanthanide, strontium oxide, barium oxide, calcium oxide and cobalt oxide are mixed and sintered to obtain permanent magnet ferrite;

[0036] The iron oxide red is prepared according to the above-mentioned pretreatment process;

[0037] Preferably, the lanthanide includes at least one of lanthanum oxide and lanthanum hydroxide;

[0038] Preferably, the lanthanide is lanthanum hydroxide.

[0039] Preferably, the original average particle size of the lanthanide is ≤5 μm, the original average particle size of the strontium oxide is ≤1.5 μm, the original average particle size of the barium oxide is ≤2 μm, the original average particle size of the calcium oxide is ≤2.0 μm, and the original average particle size of the cobalt oxide is ≤3 μm. The above particle sizes are similar to the particle size of the iron oxide red after pretreatment in this invention, which facilitates complete ion displacement reaction during solid-phase reaction, allowing ions to enter the crystal lattice without remaining in the grain boundaries.

[0040] The permanent magnet ferrite prepared by the method of the present invention preferably uses lanthanum hydroxide and pretreated iron oxide to prepare permanent magnet ferrite, which can promote the maximization of the main crystal phase and the densification of the ferrite, and effectively improve the magnetic properties and magnetic flux per unit weight of the prepared permanent magnet ferrite.

[0041] The present invention also provides a permanent magnet ferrite prepared by the above preparation method;

[0042] The molecular formula of the permanent magnet ferrite is Ca. y La x Sr 1-x-y-m Ba m Fe 2n-z Co z Where 0.4≤x≤0.65, 0.2≤y≤0.6, 0≤m≤0.15, 0.2≤z≤0.35, and 5.0≤n≤5.8.

[0043] The present invention also provides a permanent magnet ferrite prepared by the above preparation method or the application of the above permanent magnet ferrite in magnetic materials.

[0044] The technical solution of this invention has the following advantages:

[0045] 1. The pretreatment process for iron oxide red provided by the present invention includes the following steps: (1) adjusting the pH value of the iron oxide red solution to 9-10 and drying it; (2) subjecting the dried powder to heat treatment to obtain pretreated iron oxide red; the heat treatment temperature is 800-900℃, and the oxygen volume content during the heat treatment is ≥20%; the D50 of the pretreated iron oxide red is 1±0.2μm. The iron oxide red pretreated by the pretreatment process of the present invention has a high loose density, high purity, and few impurities. The pretreatment process of the present invention first adjusts the pH value to 9-10, which can effectively reduce the acid radical ions in the iron oxide red obtained by the steel mill and avoid corrosion of equipment; after heat treatment at 800-900℃, most of the acid radical ions are removed, and the final iron oxide red acid radical ion content Cl - ≤0.05%, SO3 2- ≤0.1%. Controlling the oxygen volume content to ≥20% can prevent the volatilization of acid radicals from affecting the kiln atmosphere, which would prevent ferrous ions from being completely oxidized to ferric ions, thus reducing impurities and improving the purity and loose packing density of iron oxide.

[0046] 2. The method for preparing permanent magnet ferrite provided by the present invention preferably uses lanthanum hydroxide as a lanthanide and iron oxide red pretreated by the present invention to produce permanent magnet ferrite, which promotes the densification of ferrite and the maximization of the main crystal phase, and significantly improves the remanence, coercivity, intrinsic coercivity, maximum magnetic energy product and magnetic flux per unit weight of the obtained permanent magnet ferrite. Detailed Implementation

[0047] The following embodiments are provided to better understand the present invention and are not limited to the preferred embodiments described. They do not constitute a limitation on the content and scope of protection of the present invention. Any product that is the same as or similar to the present invention, derived by any person under the guidance of the present invention or by combining the features of the present invention with other prior art, falls within the protection scope of the present invention.

[0048] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0049] The pretreatment process for iron oxide red provided by this invention involves first mixing iron oxide red and water at a mass ratio of 1:(1-3) to form an iron oxide red solution, and simultaneously adding a first surfactant, at least one of sodium hexametaphosphate, sodium citrate, and sodium carboxymethyl cellulose. Based on the mass of iron oxide red, the amount of the first surfactant added is 0.1-0.6 wt%, and the total amount of at least one of sodium hexametaphosphate, sodium citrate, and sodium carboxymethyl cellulose added is 0.1-0.3 wt%. The pH of the iron oxide red solution is adjusted to 9-10 with ammonia or aluminum hydroxide, and then dried at 100-140℃.

[0050] The dried powder is heat-treated at 800-900℃ for 1-2 hours. During the heat treatment, oxygen is introduced at a rate of 1-5 L / h to control the oxygen volume content to be ≥20%, preferably 20-22%. A second surfactant is added and the powder is vibrated and milled for 2-3 minutes. The powder is then passed through 200-mesh and 20-mesh sieves to remove ultrafine and large particles. The amount of the second surfactant added is 0.1-0.2 wt%, based on the mass of the heat-treated iron oxide red.

[0051] This invention also provides a method for preparing permanent magnet ferrite, which involves mixing pretreated iron oxide, lanthanide, strontium oxide, barium oxide, calcium oxide, and cobalt oxide, and sintering them to obtain permanent magnet ferrite. Preferably, the lanthanide is lanthanum hydroxide, and the particle size is controlled to be similar to that of the pretreated iron oxide, which facilitates complete ion substitution reaction during solid-phase reaction, allowing ions to enter the crystal lattice without remaining in the grain boundaries.

[0052] Example 1

[0053] This embodiment provides a pretreatment process for iron oxide red, including the following steps:

[0054] (1) Mix 1 kg of iron oxide red and 2 kg of deionized water, and add calcium gluconate and sodium hexametaphosphate at the same time. While stirring, add ammonia water to adjust the pH value to 9-10. Wash the solution with ultrasonic water to remove the precipitate, and dry it at 100℃. The amount of sodium hexametaphosphate added is 0.1 wt% based on the mass of iron oxide red, and the amount of calcium gluconate added is 0.3 wt% based on the mass of iron oxide red.

[0055] (2) The dried powder is heat-treated at 850°C for 1.5 h; oxygen is introduced at 1.5 L / h during the heat treatment to make the oxygen volume content 20.5%; calcium stearate is added to the heat-treated powder and the powder is vibrated and ground for 3 min, then passed through a 20-mesh sieve to remove coarse particles and a 200-mesh sieve to remove fine particles to obtain iron oxide red; the amount of calcium stearate added is 0.1 wt% based on the mass of the heat-treated powder.

[0056] The D50 of the iron oxide red is 0.8 μm; the Fe2O3 content is 99.4 wt%, the FeO content is 0.02 wt%, and the Cl content is...- It has a content of 0.05 wt% and a loose bulk density of 0.68 g / cm³. 3 ;

[0057] This embodiment also provides a method for preparing permanent magnet ferrite, including the following steps:

[0058] The iron oxide red, CaCO3 (purity ≥ 98.5 wt%, original average particle size ≤ 2.0 μm), La(OH)3 (purity ≥ 99.2 wt%, original average particle size ≤ 5 μm), Co3O4 (Co content ≥ 72.2%, original average particle size ≤ 3 μm), SrCO3 (purity ≥ 97.2 wt%, original average particle size ≤ 1.5 μm), and BaCO3 (purity ≥ 98 wt%, original average particle size ≤ 2 μm) prepared above are processed according to the following conditions: CaO is the main phase. y La x Sr 1-x-y-m Ba m Fe 2n-z Co z The materials were weighed and mixed according to the ratio of x = 0.479, m = 0.1, y = 0.321, n = 5.5, z = 0.291, and wet ball milled for 5 hours. The D50 after ball milling was 0.8 μm. The materials were dried and sintered in a pit-type sintering furnace at 1240℃ for 3 hours to obtain the pre-sintered permanent magnet ferrite material.

[0059] The pre-sintered permanent magnet ferrite material was coarsely pulverized to a D50 of 0.5 μm using a dry vibratory mill and passed through a 60-mesh sieve. 500 g of the pre-sintered permanent magnet ferrite powder was weighed and mixed with 2.5 g SiO2, 7.0 g CaCO3, 0.25 g boric acid, and 800 ml deionized water. The mixture was then wet-milled continuously at 80 rpm for 24 h (using 50% φ6.35 mm and 50% φ3.85 mm bearing steel balls, totaling 9 kg). After milling, the slurry had a D50 of 0.65 μm. It was centrifuged and dehydrated until the slurry concentration reached 68%. It was then subjected to ultrasonic treatment for 1 min and pressed into shape at 5 MPa. Simultaneously, a forming magnetic field of 12000 Oe was applied in the pressing direction to obtain a shaped body with a diameter of 43 mm and a height of 10 mm. The body was then heat-treated at 300 °C to remove moisture and sintered in air at a rate of 150 °C / h to 1220 °C for 60 min to obtain permanent magnet ferrite.

[0060] Example 2

[0061] This embodiment provides a method for preparing permanent magnet ferrite, using the iron oxide red obtained in Example 1. The only difference between the preparation method of permanent magnet ferrite in this embodiment and that in Example 1 is that lanthanum oxide is used instead of La(HO)3 (purity ≥99.2wt%, original average particle size ≤5μm).

[0062] Example 3

[0063] This embodiment provides a pretreatment process for iron oxide red, including the following steps:

[0064] (1) Mix 1 kg of iron oxide red and 2 kg of deionized water, and add calcium silicate and sodium citrate at the same time. While stirring, add aluminum hydroxide to adjust the pH value to 9-10. Wash the solution with ultrasonic water to remove the precipitate, and dry it at 140℃. The amount of sodium citrate added is 0.15 wt% based on the mass of iron oxide red, and the amount of calcium silicate added is 0.2 wt% based on the mass of iron oxide red.

[0065] (2) The dried powder is heat-treated at 900℃ for 1 hour; oxygen is introduced at 4L / h during the heat treatment to make the oxygen volume content 22%; calcium stearate is added to the heat-treated powder and the powder is vibrated and ground for 3 minutes, then passed through a 20-mesh sieve to remove coarse particles and a 200-mesh sieve to remove fine particles to obtain iron oxide red; the amount of calcium stearate added is 0.2wt% based on the mass of the heat-treated powder.

[0066] The D50 of the iron oxide red is 0.85 μm; the Fe2O3 content is 99.35 wt%, the FeO content is 0.02 wt%, and the Cl content is... - It has a content of 0.03 wt% and a loose bulk density of 0.7 g / cm³. 3 ;

[0067] This embodiment also provides a method for preparing permanent magnet ferrite, which is carried out according to the method for preparing permanent magnet ferrite provided in Example 1.

[0068] Comparative Example 1

[0069] This comparative example provides a pretreatment process for iron oxide red. Compared with Example 1, the only difference is that in step (1), the pH value of the iron oxide red solution is 8 instead of the pH value of 9-10 of the iron oxide red solution in Example 1.

[0070] In step (2), the dried powder is heat-treated at 200°C for 1.5 hours; instead of Example 1, the dried powder is heat-treated at 850°C for 1.5 hours; the oxygen volume content during the heat treatment is 20.5%.

[0071] The D50 of the iron oxide red is 0.78 μm; the Fe2O3 content is 99.5 wt%, the FeO content is 0.03 wt%, and the Cl content is... - It has a content of 0.03 wt% and a loose bulk density of 0.55 g / cm³. 3 ;

[0072] This comparative example also provides a method for preparing permanent magnet ferrite, which is carried out according to the method for preparing permanent magnet ferrite provided in Example 1.

[0073] As can be seen from the iron oxide red obtained after pretreatment in the comparative example, if the pH value of the iron oxide red solution is not adjusted to be within the range of 9-10, the D50 of the iron oxide red obtained will be too small and the loose density will be too low. The permanent magnet ferrite prepared with this iron oxide red will have poor magnetic properties and low magnetic flux per unit weight.

[0074] Comparative Example 2

[0075] This comparative example provides a method for preparing permanent magnet ferrite. The only difference from Example 1 is that commercially available iron oxide red is used instead of the iron oxide red prepared in Example 1. The specific parameters of the commercially available iron oxide red are as follows: Fe2O3 purity 99.0 wt%, Cl... - 0.4wt%, loose bulk density 0.37g / cm³ 3 The original average particle size is ≤1.0μm;

[0076] Sintering at 1220℃ for 3 hours in a pit-type sintering furnace instead of sintering at 1240℃ for 3 hours in Example 1.

[0077] Comparative Example 3

[0078] This comparative example provides a pretreatment process for iron oxide red. Compared with Example 1, the only difference is that the oxygen volume content of the heat treatment is 19%, instead of 1.5 L / h of oxygen being introduced during the heat treatment in Example 1, resulting in an oxygen volume content of 20.5%.

[0079] The D50 of the iron oxide red is 0.8 μm; the Fe2O3 content is 99.2 wt%, the FeO content is 0.5 wt%, and the Cl content is... - It has a content of 0.1 wt% and a loose bulk density of 6.2 g / cm³. 3 ;

[0080] This comparative example also provides a method for preparing permanent magnet ferrite, which is carried out according to the method for preparing permanent magnet ferrite provided in Example 1.

[0081] As can be seen from the iron oxide red obtained after pretreatment in the comparative example, if oxygen is not introduced during heat treatment to control the oxygen volume content, the acid radical ions will volatilize and affect the atmosphere inside the kiln. The ferrous ions cannot be completely oxidized to ferric ions, resulting in low purity and many impurities in the iron oxide red. The permanent magnet ferrite made from this iron oxide red has poor magnetic properties and low magnetic flux per unit weight.

[0082] Test case

[0083] The performance of the permanent magnet ferrites prepared in Examples 1-3 and Comparative Examples 1-3 was tested, as follows:

[0084] (1) Detection method of Br: The results were obtained by measuring on a permanent magnet material testing system and are shown in Table 1;

[0085] (2) Hcb detection method: measured on a permanent magnet material testing system, the results are shown in Table 1;

[0086] (3) Hcj detection method: measured on a permanent magnet material testing system, the results are shown in Table 1;

[0087] (4) The detection method of (BH)max: It was measured on a permanent magnet material testing system, and the results are shown in Table 1;

[0088] (5) Magnetic flux detection method: The magnetic flux was detected using a special test fixture. The results are shown in Table 1.

[0089] Table 1. Magnetic properties of permanent magnet ferrites prepared in each embodiment and comparative example.

[0090] serial number Br(Gs) Hcb(Oe) Hcj(Oe) (BH)max(MGOe) magnetic flux per unit weight (Wb) Example 1 4560 4320 5270 5.15 32.54 Example 2 4520 4280 5308 5.05 31.52 Example 3 4534 4267 5356 5.067 31.66 Comparative Example 1 4475 4156 5037 4.89 30.37 Comparative Example 2 4460 4130 4903 4.95 30.25 Comparative Example 3 4431 4045 4758 4.65 29.89

[0091] The iron red pretreated by the pretreatment process of this invention has a high loose density, high purity and few impurities. When the pretreated iron red is used to prepare permanent magnet ferrite, the remanence, coercivity, intrinsic coercivity, maximum magnetic energy product and magnetic flux per unit weight are significantly improved.

[0092] As can be seen from Examples 1 and 2, lanthanum hydroxide is preferred as a lanthanide for preparing permanent magnet ferrites, resulting in permanent magnet ferrites with higher remanence, coercivity, maximum energy product, and magnetic flux per unit weight.

[0093] As can be seen from the comparison between Example 1 and Comparative Example 1, the present invention first controls the pH value of the iron oxide red solution, and then controls the temperature and time of the heat treatment. The iron oxide red prepared can significantly improve the remanence, coercivity, intrinsic coercivity, maximum magnetic energy product and magnetic flux per unit weight of permanent magnet ferrite, resulting in better magnetic properties.

[0094] As can be seen from the comparison between Example 1 and Comparative Example 2, the magnetic properties and magnetic flux per unit weight of the permanent magnet ferrite prepared by using commercially available iron oxide are significantly reduced.

[0095] As can be seen from the comparison between the examples and Comparative Example 3, the present invention controls the oxygen volume content in the kiln by introducing oxygen, so that a large number of ferrous ions are oxidized to ferric ions, which can significantly improve the magnetic properties and magnetic flux per unit weight of the obtained permanent magnet ferrite. In the comparative example, no oxygen was introduced, and the remanence, coercivity, intrinsic coercivity, maximum energy product and magnetic flux per unit weight of the permanent magnet ferrite obtained by using the iron red pretreated by oxygen were all significantly reduced.

[0096] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A pretreatment process for iron oxide red, characterized in that, Includes the following steps: (1) Adjust the pH of the iron oxide red solution to 9-10 and dry it; (2) The dried powder is heat-treated to obtain pretreated iron red; the heat treatment temperature is 800-900℃, and the oxygen volume content during the heat treatment is ≥20%; The D50 of the pretreated iron oxide red was 1 ± 0.2 μm.

2. The pretreatment process according to claim 1, characterized in that, In step (1), the iron oxide solution comprises iron oxide and water, wherein the mass ratio of iron oxide to water is 1:(1-3); and / or, In step (1), the iron oxide red solution further includes a first surfactant; and / or, In step (2), the oxygen volume content during the heat treatment is 20-22%; and / or, In step (2), during the heat treatment, the oxygen flow rate is 1-5 L / h; and / or, Reagents for adjusting pH include alkaline substances.

3. The pretreatment process according to claim 2, characterized in that, The alkaline substance includes at least one of ammonia and aluminum hydroxide; and / or, The first surfactant includes at least one of sodium oleate, calcium silicate, and calcium gluconate; and / or, Based on the mass of the iron oxide red, the amount of the first surfactant added is 0.1-0.6 wt%.

4. The pretreatment process according to claim 2, characterized in that, In step (1), the iron red solution further includes at least one of sodium hexametaphosphate, sodium citrate, and sodium carboxymethyl cellulose; Preferably, based on the mass of the iron oxide red, the total amount of at least one of sodium hexametaphosphate, sodium citrate, and sodium carboxymethyl cellulose added is 0.1-0.3 wt%.

5. The pretreatment process according to claim 1, characterized in that, In step (1), the drying temperature is 100-140℃; and / or, In step (2), the heat treatment time is 1-2 hours.

6. The pretreatment process according to claim 1, characterized in that, After heat treatment, a second surfactant is added and vibrated during milling. Preferably, the second surfactant comprises calcium stearate; Preferably, the amount of the second surfactant added is 0.1-0.2 wt%, based on the mass of the heat-treated iron oxide red.

7. A red iron oxide obtained by the pretreatment process described in any one of claims 1-6; Preferably, the Fe2O3 content in the iron oxide is ≥99.3wt%; Preferably, the FeO content in the iron oxide red is ≤0.05wt%. Preferably, the iron oxide red contains Cl - Content ≤0.05wt%; Preferably, the loose bulk density of the iron oxide is ≥0.6 g / cm³. 3 .

8. A method for preparing permanent magnet ferrite, characterized in that, Iron oxide red, lanthanide, strontium oxide, barium oxide, calcium oxide, and cobalt oxide are mixed and sintered to obtain permanent magnet ferrite; The iron oxide red is obtained by the pretreatment process according to any one of claims 1-6; Preferably, the lanthanide includes at least one of lanthanum oxide and lanthanum hydroxide; Preferably, the lanthanide is lanthanum hydroxide.

9. The permanent magnet ferrite prepared by the method of claim 8; The molecular formula of the permanent magnet ferrite is Ca. y La x Sr 1-x-y-m Ba m Fe 2n-z Co z Where 0.4≤x≤0.65, 0.2≤y≤0.6, 0≤m≤0.15, 0.2≤z≤0.35, and 5.0≤n≤5.

8.

10. The application of the permanent magnet ferrite prepared by the preparation method of claim 8 or the permanent magnet ferrite of claim 9 in magnetic materials.