Preparation method of high-purity iron oxide red

Abstract

The invention belongs to the technical field of preparation of iron oxide red, and discloses a preparation method of high-purity iron oxide red, which comprises the following specific steps: step 1, preparing a refined ferrous iron source solution, and accurately weighing industrial-grade ferrous sulfate heptahydrate (FeSO4. 7H2O) crystals; a low-defect alpha-FeC2O4 precursor is constructed by utilizing a hydrothermal crystallization technology, so that the risk that impurity ions are introduced in traditional acid pickling is fundamentally avoided, meanwhile, self-purification of the precursor is realized, the oxidation process at the initial stage of calcination is accurately controlled through a nitrogen and carbon dioxide mixed atmosphere, lattice distortion is effectively inhibited, and the preparation method is simple and convenient to operate. Lattice oxygen dynamic reconstruction is achieved through oxygen-argon alternate treatment, surface hydroxyl adsorption is thoroughly eliminated, the thermal stability and weather resistance of the product are greatly enhanced, supercritical CO2 flow state purification is adopted to replace water washing, residual impurities are efficiently removed, meanwhile, the risks of powder agglomeration and secondary pollution are avoided, and the method is suitable for industrial production. And high fluidity and excellent dispersibility of the product are ensured.

Description

Technical Field

[0001] The invention belongs to the technical field of iron oxide red preparation, and specifically relates to a method for preparing high-purity iron oxide red. Background Art

[0002] Iron oxide red (α-Fe2O3) is an important inorganic red pigment and functional material. Due to its excellent tinting strength, hiding power, weather resistance, chemical stability and non-toxic and environmentally friendly properties, it is widely used in many fields such as coatings, plastics, rubber, building materials, electronic materials, catalyst carriers and magnetic materials.

[0003] With the continuous improvement of material performance requirements in high-end application fields, more stringent requirements are put forward for the purity, crystal structure integrity, particle size distribution uniformity and micromorphology control of red iron oxide. The impurity ion content needs to be strictly controlled to avoid adverse effects on the performance of the final product. At present, the main methods for large-scale industrial preparation of red iron oxide include precipitation, roasting and hydrothermal synthesis. There are still some limitations in the pursuit of high purity. First, the precursors obtained by traditional precipitation or direct roasting often contain a variety of soluble ionic impurities. In order to achieve high purity, it is usually necessary to rely on repeated water washing or even strong acid washing for impurity removal. This process is not only cumbersome, water-consuming and energy-consuming, but also very easy to introduce new impurity ions, causing serious agglomeration of precursor particles, which is difficult to disperse subsequently, affecting the dispersibility and particle size distribution of the final product; secondly, in the conversion of ferrous ions to trivalent iron, During the oxidation stage, especially in the initial stage of high-temperature calcination, if the oxidizing atmosphere or temperature is not properly controlled, it is very easy to induce lattice distortion or produce non-stoichiometric defect structures, resulting in incomplete crystal form, hue deviation and performance degradation; furthermore, the conventional calcination process is prone to excessive particle growth or sintering due to local overheating or uneven atmosphere at high temperatures, resulting in a widening of the particle size distribution or even agglomeration, making it difficult to obtain uniform nano or submicron products; in addition, the surface of iron oxide particles is prone to adsorbing hydroxyl groups (-OH) or combining with water during the preparation process to form surface active sites, which not only affects the stability of the product, but may also cause adverse side reactions in subsequent applications; finally, even after multiple washing steps, residual trace impurities may be wrapped in the lattice or form refractory materials during high-temperature calcination, which is difficult to completely remove, becoming a bottleneck that further restricts the iron content of the product, so it needs to be improved. Summary of the Invention

[0004] In view of the deficiencies in the prior art, the present invention provides a method for preparing high-purity iron oxide red, which has the advantage of high purity.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing high-purity iron oxide red, the specific steps of which are as follows:

[0006] Step 1: Prepare refined ferrous iron source solution

[0007] Accurately weigh industrial-grade ferrous sulfate heptahydrate (FeSO4·7H2O) crystals and place them in a reaction vessel. Pour deionized water into the vessel and start the agitator at a speed between 350 and 400 rpm to prepare a saturated solution. Maintain the temperature at 65°C until all FeSO4·7H2O crystals are completely dissolved to form a uniform light green solution. According to a preset stoichiometric ratio, weigh food-grade oxalic acid (H2C2O4) powder and slowly and in batches add it to the saturated solution. Observe that the solution gradually changes from light green to turbidity and eventually forms a large amount of light yellow to yellow-brown ferrous oxalate (FeC2O4) precipitate. Continue stirring until no soluble divalent iron ions remain in the solution.

[0008] Step 2: Purification of precursor by directional recrystallization

[0009] A Buchner funnel is connected to a vacuum filtration device to filter and separate all FeC2O4 precipitates in the reaction mixture of step 1, and the mother liquor is removed to obtain a wet filter cake; the filter cake is transferred to a clean container and washed with high-purity deionized water that has been preheated and thermostatted at 60°C as a washing medium; after washing, the pure wet FeC2O4 filter cake is collected and quantitatively transferred to the inner liner of a pressure-resistant and corrosion-resistant autoclave, ultrapure water is added to the inner liner, and the ratio of the mass of the solid wet filter cake to the volume of the ultrapure water is adjusted to 1:8 to form a uniform suspension; the autoclave is sealed, and the contents are heated to 160°C at a constant heating rate of 5°C / min. At this temperature, the system pressure is maintained in the range of 0.5 to 0.7 MPa, the stirrer is stirred at 60 rpm, and a constant temperature crystallization treatment is performed for 4 hours to complete the directional dissolution-recrystallization process of the FeC2O4 to obtain high-purity, low-defect α-FeC2O4 microcrystals;

[0010] Step 3: Precursor micromorphology control

[0011] The α-FeC2O4 microcrystals after crystallization treatment in the high-pressure reactor in step 2 are cooled to below 90°C, the reactor is opened and the high-purity α-FeC2O4 microcrystal suspension is taken out, and immediately filtered and separated using a polytetrafluoroethylene filter membrane with a pore size of 0.45 μm; the obtained high-purity α-FeC2O4 wet microcrystals are quickly transferred to a sealed glove box operating room filled with high-purity nitrogen, placed on a clean quartz tray, and under a protective atmosphere of continuous high-purity nitrogen, the cooling rate is controlled to be 1°C / min to steadily reduce the material temperature to an ambient temperature of 25°C, and the α-FeC2O4 microcrystals that have completed cooling are transferred to a vacuum drying oven for drying, and finally an anhydrous α-FeC2O4 precursor powder with a specific hexagonal flake micromorphology and a crystal water content of less than 0.1wt% is obtained;

[0012] Step 4: Controlled atmosphere thermal conversion reaction

[0013] Weigh the anhydrous α-FeC2O4 precursor powder prepared in step 3, spread it flat on a quartz boat dedicated to a tubular atmosphere furnace, push the charged quartz boat into the center of the constant temperature zone of the tubular furnace, and strictly seal the furnace tube system; first, continuously introduce a preset ratio of high-purity nitrogen and carbon dioxide mixed protective gas into the furnace tube, and increase the temperature of the material in the furnace from room temperature to 350°C at a constant rate of 3°C / min, and maintain the constant temperature at this temperature point for 2 hours to allow α-FeC2O4 to complete the initial decomposition and form an intermediate phase product. After the constant temperature is reached, the gas source is immediately switched to a pure oxygen flow, and the heating rate is controlled to 2°C / min under a pure oxygen atmosphere, and the temperature of the material in the furnace is increased from 350°C to a final calcination temperature of 750°C, and calcined at 750°C for 3 hours to ensure that the precursor is completely converted into α-Fe2O3 crystals with a hematite structure;

[0014] Step 5: Lattice oxygen dynamic balance treatment

[0015] At the end of the calcination at 750°C in step 4, the temperature of the central constant temperature zone of the tube furnace was maintained at 750°C. The gas introduced into the furnace was immediately switched from pure oxygen to high-purity argon at a steady flow rate of 50 mL / min for 10 minutes. After the argon treatment was completed, the flow rate was immediately reversed and switched back to pure oxygen at the same flow rate for the same 10 minutes. The oxygen and argon gas were alternately treated in a cycle. After all the alternating treatments were completed, the temperature and pure oxygen atmosphere were maintained at 750°C, and the temperature of the material in the furnace was lowered to 300°C at a temperature control rate of 1°C / min.

[0016] Step 6: Passivation and stabilization treatment at room temperature

[0017] The material in step 5 was naturally cooled to 80°C by heat insulation, the heating power of the tube furnace was turned off, and the gas introduced into the furnace was switched from pure oxygen to dry air to perform forced convection cooling on the hot material; the material temperature was closely monitored. When the temperature dropped to 35°C, the gas flow was turned off and the inlet and outlet of the tube furnace were completely sealed. The sealed furnace tube containing α-Fe2O3 powder was transferred as a whole to a constant temperature and humidity environmental box, the ambient temperature was set to 25°C, and the relative humidity of the environment was controlled to be stable within the range of 10%RH. Under these conditions, the material was allowed to stand for 24 hours for equilibrium treatment;

[0018] Step 7: Non-destructive surface cleaning

[0019] The α-Fe2O3 powder after equilibrium in step 6 was quantitatively removed from the constant temperature and humidity environment box and placed in the treatment chamber of the fluidized bed. Supercritical carbon dioxide fluid was continuously introduced into the treatment chamber. The system pressure was precisely controlled to be 12 MPa and the temperature was stabilized at 50°C. The total constant flow circulation treatment time was 120 minutes. After the treatment was completed, the pressure was uniformly released to the normal pressure environment, and the high-purity α-Fe2O3 final product powder that had been deeply purified by supercritical CO2 in the reaction chamber was collected.

[0020] Preferably, when the food-grade oxalic acid (H2C2O4) powder is added to the saturated solution in step 1, stirring is maintained throughout the entire addition process, and the rotation speed is maintained at 350 to 400 rpm.

[0021] Preferably, when the deionized water is used as the washing medium for washing in step 2, the filter cake is thoroughly rinsed three times under suction filtration conditions, and each washing ensures that sufficient deionized water is used to completely immerse the filter cake.

[0022] Preferably, the α-FeC2O4 microcrystals in step 3 are cooled to below 90°C, and the cooling process must be kept steady and slow.

[0023] Preferably, the vacuum drying oven in step three is set to a drying temperature of 80° C., and the α-FeC 2 O 4 microcrystals are continuously dehydrated and dried for 12 hours under a vacuum degree lower than 0.1 kPa.

[0024] Preferably, the washing process in step 2 needs to be protected by nitrogen and the amount of water used each time is ≥ 5 times the mass of the filter cake, and it is prohibited to use tools containing zinc or copper to contact the filter cake.

[0025] Preferably, the total number of cycles of alternating oxygen and argon treatment in step 5 is 9 times, and the total treatment time of the whole process is controlled to be 180 minutes.

[0026] Preferably, the α-FeC2O4 precursor powder in step 4 is spread evenly in a quartz boat, and it is necessary to ensure that the material is laid evenly and the material thickness is controlled within the range of 3 mm.

[0027] Preferably, in the mixed protective gas of high-purity nitrogen and carbon dioxide in step 4, the gas volume flow ratio is nitrogen:carbon dioxide=9:1.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] The hydrothermal crystallization technology is used to construct a low-defect α-FeC2O4 precursor, which fundamentally avoids the risk of introducing impurity ions by traditional acid washing, and at the same time achieves self-purification of the precursor. The oxidation process in the early stage of calcination is precisely controlled by a mixed atmosphere of nitrogen and carbon dioxide, effectively suppressing lattice distortion. The dynamic reconstruction of lattice oxygen is achieved through oxygen-argon alternating treatment, completely eliminating surface hydroxyl adsorption, greatly enhancing the thermal stability and weather resistance of the product. Supercritical CO2 fluid purification is used instead of water washing, which not only efficiently removes residual impurities but also avoids the risks of powder agglomeration and secondary contamination, ensuring the high fluidity and excellent dispersibility of the product. The entire process realizes water-free phase impurity removal throughout the process, greatly reducing water consumption and wastewater, and eliminating the possibility of new impurities introduced by aqueous phase operations, providing process guarantee for obtaining ultra-high purity products. DETAILED DESCRIPTION

[0030] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0031] The present invention provides a method for preparing high-purity iron oxide red, and the specific steps are as follows:

[0032] Step 1: Prepare refined ferrous iron source solution

[0033] Accurately weigh industrial-grade ferrous sulfate heptahydrate (FeSO4·7H2O) crystals and place them in a reaction vessel. Pour deionized water into the vessel and start the agitator at a speed between 350 and 400 rpm to prepare a saturated solution. Maintain the temperature at 65°C until all FeSO4·7H2O crystals are completely dissolved to form a uniform light green solution. According to a preset stoichiometric ratio, weigh food-grade oxalic acid (H2C2O4) powder and slowly and in batches add it to the saturated solution. Observe that the solution gradually changes from light green to turbidity and eventually forms a large amount of light yellow to yellow-brown ferrous oxalate (FeC2O4) precipitate. Continue stirring until no soluble divalent iron ions remain in the solution.

[0034] Step 2: Purification of precursor by directional recrystallization

[0035] A Buchner funnel is connected to a vacuum filtration device to filter and separate all FeC2O4 precipitates in the reaction mixture of step 1, and the mother liquor is removed to obtain a wet filter cake; the filter cake is transferred to a clean container and washed with high-purity deionized water that has been preheated and thermostatted at 60°C as a washing medium; after washing, the pure wet FeC2O4 filter cake is collected and quantitatively transferred to the inner liner of a pressure-resistant and corrosion-resistant autoclave, ultrapure water is added to the inner liner, and the ratio of the mass of the solid wet filter cake to the volume of the ultrapure water is adjusted to 1:8 to form a uniform suspension; the autoclave is sealed, and the contents are heated to 160°C at a constant heating rate of 5°C / min. At this temperature, the system pressure is maintained in the range of 0.5 to 0.7 MPa, the stirrer is stirred at 60 rpm, and a constant temperature crystallization treatment is performed for 4 hours to complete the directional dissolution-recrystallization process of the FeC2O4 to obtain high-purity, low-defect α-FeC2O4 microcrystals;

[0036] Step 3: Precursor micromorphology control

[0037] The α-FeC2O4 microcrystals after crystallization treatment in the high-pressure reactor in step 2 are cooled to below 90°C, the reactor is opened and the high-purity α-FeC2O4 microcrystal suspension is taken out, and immediately filtered and separated using a polytetrafluoroethylene filter membrane with a pore size of 0.45 μm; the obtained high-purity α-FeC2O4 wet microcrystals are quickly transferred to a sealed glove box operating room filled with high-purity nitrogen, placed on a clean quartz tray, and under a protective atmosphere of continuous high-purity nitrogen, the cooling rate is controlled to be 1°C / min to steadily reduce the material temperature to an ambient temperature of 25°C, and the α-FeC2O4 microcrystals that have completed cooling are transferred to a vacuum drying oven for drying, and finally an anhydrous α-FeC2O4 precursor powder with a specific hexagonal flake micromorphology and a crystal water content of less than 0.1wt% is obtained;

[0038] Step 4: Controlled atmosphere thermal conversion reaction

[0039] Weigh the anhydrous α-FeC2O4 precursor powder prepared in step 3, spread it flat on a quartz boat dedicated to a tubular atmosphere furnace, push the charged quartz boat into the center of the constant temperature zone of the tubular furnace, and strictly seal the furnace tube system; first, continuously introduce a preset ratio of high-purity nitrogen and carbon dioxide mixed protective gas into the furnace tube, and increase the temperature of the material in the furnace from room temperature to 350°C at a constant rate of 3°C / min, and maintain the constant temperature at this temperature point for 2 hours to allow α-FeC2O4 to complete the initial decomposition and form an intermediate phase product. After the constant temperature is reached, the gas source is immediately switched to a pure oxygen flow, and the heating rate is controlled to 2°C / min under a pure oxygen atmosphere, and the temperature of the material in the furnace is increased from 350°C to a final calcination temperature of 750°C, and calcined at 750°C for 3 hours to ensure that the precursor is completely converted into α-Fe2O3 crystals with a hematite structure;

[0040] Step 5: Lattice oxygen dynamic balance treatment

[0041] At the end of the calcination at 750°C in step 4, the temperature of the central constant temperature zone of the tube furnace was maintained at 750°C. The gas introduced into the furnace was immediately switched from pure oxygen to high-purity argon at a steady flow rate of 50 mL / min for 10 minutes. After the argon treatment was completed, the flow rate was immediately reversed and switched back to pure oxygen at the same flow rate for the same 10 minutes. The oxygen and argon gas were alternately treated in a cycle. After all the alternating treatments were completed, the temperature and pure oxygen atmosphere were maintained at 750°C, and the temperature of the material in the furnace was lowered to 300°C at a temperature control rate of 1°C / min.

[0042] Step 6: Passivation and stabilization treatment at room temperature

[0043] The material in step 5 was naturally cooled to 80°C by heat insulation, the heating power of the tube furnace was turned off, and the gas introduced into the furnace was switched from pure oxygen to dry air to perform forced convection cooling on the hot material; the material temperature was closely monitored. When the temperature dropped to 35°C, the gas flow was turned off and the inlet and outlet of the tube furnace were completely sealed. The sealed furnace tube containing α-Fe2O3 powder was transferred as a whole to a constant temperature and humidity environmental box, the ambient temperature was set to 25°C, and the relative humidity of the environment was controlled to be stable within the range of 10%RH. Under these conditions, the material was allowed to stand for 24 hours for equilibrium treatment;

[0044] Step 7: Non-destructive surface cleaning

[0045] The α-Fe2O3 powder after equilibrium in step 6 was quantitatively removed from the constant temperature and humidity environment box and placed in the treatment chamber of the fluidized bed. Supercritical carbon dioxide fluid was continuously introduced into the treatment chamber. The system pressure was precisely controlled to be 12 MPa and the temperature was stabilized at 50°C. The total constant flow circulation treatment time was 120 minutes. After the treatment was completed, the pressure was uniformly released to the normal pressure environment, and the high-purity α-Fe2O3 final product powder that had been deeply purified by supercritical CO2 in the reaction chamber was collected.

[0046] Industrial-grade FeSO4·7H2O reacts with food-grade oxalic acid to form a ferrous oxalate (FeC2O4) precipitate. The filter cake is then washed multiple times with hot deionized water under nitrogen to thoroughly remove impurities. The wet filter cake is then directionally recrystallized in an autoclave to obtain high-purity α-FeC2O4. This is then dried at a controlled cooling rate under nitrogen to obtain an anhydrous α-FeC2O4 precursor powder with a specific hexagonal flake morphology and low crystalline water content. This precursor is then thermally converted in a tube furnace. After calcination, the powder is treated with alternating cycles of pure oxygen and argon at 750°C to optimize lattice oxygen balance. The powder is then forced to cool in dry air and allowed to equilibrate for 24 hours. Finally, the powder is non-destructively cleaned with supercritical CO2 for 120 minutes, and the high-purity α-Fe2O3 final product is obtained after decompression.

[0047] In step 1, when food-grade oxalic acid (H2C2O4) powder is added to the saturated solution, stirring is maintained throughout the entire addition process, and the rotation speed is maintained at 350 to 400 rpm.

[0048] By maintaining stirring while adding the food grade oxalic acid (H2C2O4) powder, ensure that the powder is well dispersed after each addition.

[0049] Wherein, when deionized water is used as the washing medium for washing in step 2, the filter cake is thoroughly rinsed three times under suction filtration conditions, and each washing ensures that sufficient deionized water completely immerses the filter cake.

[0050] The filter cake was rinsed three times with deionized water to completely remove residual sulfate ions and soluble impurities.

[0051] Among them, in step 3, the α-FeC2O4 microcrystals are cooled to below 90°C, and the cooling process must be kept steady and slow.

[0052] By slowly and steadily cooling the α-FeC2O4 microcrystals to below 90°C, crystal defects caused by sudden temperature changes can be avoided.

[0053] In step 3, the drying temperature of the vacuum drying oven is set to 80° C., and the α-FeC2O4 microcrystals are continuously dehydrated and dried for 12 hours under a vacuum degree lower than 0.1 kPa.

[0054] By limiting the drying temperature and dehydration drying time, the water content of α-FeC2O4 microcrystals is ensured to be less than 0.1wt%.

[0055] Among them, the entire washing process in step 2 must be protected by nitrogen and the amount of water used each time must be ≥ 5 times the mass of the filter cake. It is also prohibited to use tools containing zinc or copper to contact the filter cake.

[0056] Filling nitrogen during the washing process can prevent Fe 2+ Oxidation to F 3+ , avoiding the introduction of impure iron phase and reducing the purity of the precursor.

[0057] Among them, the total number of cycles of alternating oxygen and argon treatment in step 5 is 9 times, and the total treatment time of the whole process is controlled to be 180 minutes.

[0058] The total number of alternating oxygen and argon treatments was set to 9 times for a total of 180 minutes to ensure that lattice oxygen defects were fully and repeatedly adjusted, promote the ordering of oxygen vacancies and eliminate local stress, thereby obtaining α-Fe2O3 with a complete lattice and highly stable crystal structure, significantly improving the color fastness and chemical stability of the final product under high temperature and light.

[0059] In step 4, the α-FeC2O4 precursor powder is spread evenly in the quartz boat. It is necessary to ensure that the material is laid evenly and the material thickness is controlled within 3 mm.

[0060] By controlling the thickness of the material, it is ensured that the material is heated evenly and the gas can fully penetrate in the constant temperature zone of the tube furnace.

[0061] In the step 4, the gas volume flow ratio of the mixed protective gas of high-purity nitrogen and carbon dioxide is nitrogen:carbon dioxide=9:1.

[0062] The volume flow ratio of nitrogen: carbon dioxide mixed gas is set to 9:1, creating a precisely controlled weak reducing / inert protective atmosphere in the early stage of thermal decomposition, which not only effectively inhibits the premature oxidation of FeC2O4 or unnecessary side reactions, but also ensures its controllable decomposition along the predetermined path.

[0063] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that includes a list of elements includes not only those elements but also other elements not explicitly listed, or elements inherent to such process, method, article, or apparatus.

[0064] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing high-purity iron oxide red, characterized in that, The specific steps are as follows: Step 1: Prepare refined ferrous iron source solution Accurately weigh industrial-grade ferrous sulfate heptahydrate (FeSO4·7H2O) crystals and place them in a reaction vessel. Pour deionized water into the vessel and start the agitator at a speed between 350 and 400 rpm to prepare a saturated solution. Maintain the temperature at 65°C until all FeSO4·7H2O crystals are completely dissolved to form a uniform light green solution. According to a preset stoichiometric ratio, weigh food-grade oxalic acid (H2C2O4) powder and slowly and in batches add it to the saturated solution. Observe that the solution gradually changes from light green to turbidity and eventually forms a large amount of light yellow to yellow-brown ferrous oxalate (FeC2O4) precipitate. Continue stirring until no soluble divalent iron ions remain in the solution. Step 2: Purification of precursor by directional recrystallization Using a Buchner funnel connected to a vacuum filtration device, filter and separate all FeC2O4 precipitates in the reaction mixture of step 1, remove the mother liquor to obtain a wet filter cake; transfer the filter cake to a clean container and wash it with high-purity deionized water that has been preheated and maintained at 60°C as a washing medium; After washing, a pure wet FeC2O4 filter cake is collected and quantitatively transferred to the inner liner of a pressure-resistant and corrosion-resistant high-pressure reactor. Ultrapure water is added to the inner liner, and the ratio of the mass of the solid wet filter cake to the volume of ultrapure water is adjusted to 1:8 to form a uniform suspension. The high-pressure reactor is sealed, and the material in the reactor is heated to 160°C at a constant heating rate of 5°C / min. At this temperature, the system pressure is maintained in the range of 0.5 to 0.7 MPa. The stirrer is stirred at 60 rpm, and a constant temperature crystallization treatment is performed for 4 hours to complete the directional dissolution-recrystallization process of FeC2O4 to obtain high-purity, low-defect α-FeC2O4 microcrystals. Step 3: Precursor micromorphology control The α-FeC2O4 microcrystals after crystallization treatment in the high-pressure reactor in step 2 are cooled to below 90°C, the reactor is opened and the high-purity α-FeC2O4 microcrystal suspension is taken out, and immediately filtered and separated using a polytetrafluoroethylene filter membrane with a pore size of 0.45 μm; the obtained high-purity α-FeC2O4 wet microcrystals are quickly transferred to a sealed glove box operating room filled with high-purity nitrogen, placed on a clean quartz tray, and under a protective atmosphere of continuous high-purity nitrogen, the cooling rate is controlled to be 1°C / min to steadily reduce the material temperature to an ambient temperature of 25°C, and the α-FeC2O4 microcrystals that have completed cooling are transferred to a vacuum drying oven for drying, and finally an anhydrous α-FeC2O4 precursor powder with a specific hexagonal flake micromorphology and a crystal water content of less than 0.1wt% is obtained; Step 4: Controlled atmosphere thermal conversion reaction Weigh the anhydrous α-FeC2O4 precursor powder prepared in step 3, spread it flat on a quartz boat dedicated to a tubular atmosphere furnace, push the charged quartz boat into the center of the constant temperature zone of the tubular furnace, and strictly seal the furnace tube system; first, continuously introduce a preset ratio of high-purity nitrogen and carbon dioxide mixed protective gas into the furnace tube, and increase the temperature of the material in the furnace from room temperature to 350°C at a constant rate of 3°C / min, and maintain the constant temperature at this temperature point for 2 hours to allow α-FeC2O4 to complete the initial decomposition and form an intermediate phase product. After the constant temperature is reached, the gas source is immediately switched to a pure oxygen flow, and the heating rate is controlled to 2°C / min under a pure oxygen atmosphere, and the temperature of the material in the furnace is increased from 350°C to a final calcination temperature of 750°C, and calcined at 750°C for 3 hours to ensure that the precursor is completely converted into α-Fe2O3 crystals with a hematite structure; Step 5: Lattice oxygen dynamic balance treatment At the end of the calcination at 750°C in step 4, the temperature of the central constant temperature zone of the tube furnace was maintained at 750°C. The gas introduced into the furnace was immediately switched from pure oxygen to high-purity argon at a steady flow rate of 50 mL / min for 10 minutes. After the argon treatment was completed, the flow rate was immediately reversed and switched back to pure oxygen at the same flow rate for the same 10 minutes. The oxygen and argon gas were alternately treated in a cycle. After all the alternating treatments were completed, the temperature and pure oxygen atmosphere were maintained at 750°C, and the temperature of the material in the furnace was lowered to 300°C at a temperature control rate of 1°C / min. Step 6: Passivation and stabilization treatment at room temperature The material in step 5 was naturally cooled to 80°C by heat insulation, the heating power of the tube furnace was turned off, and the gas introduced into the furnace was switched from pure oxygen to dry air to perform forced convection cooling on the hot material; the material temperature was closely monitored. When the temperature dropped to 35°C, the gas flow was turned off and the inlet and outlet of the tube furnace were completely sealed. The sealed furnace tube containing α-Fe2O3 powder was transferred as a whole to a constant temperature and humidity environmental box, the ambient temperature was set to 25°C, and the relative humidity of the environment was controlled to be stable within the range of 10%RH. Under these conditions, the material was allowed to stand for 24 hours for equilibrium treatment; Step 7: Non-destructive surface cleaning The α-Fe2O3 powder after equilibrium in step 6 was quantitatively removed from the constant temperature and humidity environment box and placed in the treatment chamber of the fluidized bed. Supercritical carbon dioxide fluid was continuously introduced into the treatment chamber. The system pressure was precisely controlled to be 12 MPa and the temperature was stabilized at 50°C. The total constant flow circulation treatment time was 120 minutes. After the treatment was completed, the pressure was uniformly released to the normal pressure environment, and the high-purity α-Fe2O3 final product powder that had been deeply purified by supercritical CO2 in the reaction chamber was collected.

2. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: When the food-grade oxalic acid (H2C2O4) powder is added to the saturated solution in step 1, stirring is maintained during the entire addition process, maintaining a rotation speed of 350 to 400 rpm.

3. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: When the deionized water is used as the washing medium for washing in step 2, the filter cake is thoroughly rinsed three times under suction filtration conditions, and each washing ensures that sufficient deionized water is used to completely immerse the filter cake.

4. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: In step 3, the α-FeC2O4 microcrystals are cooled to below 90°C, and the cooling process must be kept steady and slow.

5. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: The vacuum drying oven in step 3 is set to a drying temperature of 80° C., and the α-FeC2O4 microcrystals are continuously dehydrated and dried for 12 hours under a vacuum degree lower than 0.1 kPa.

6. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: The entire washing process in step 2 must be protected by nitrogen and the amount of water used each time must be ≥ 5 times the mass of the filter cake. It is prohibited to use tools containing zinc or copper to contact the filter cake.

7. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: The total number of cycles of alternating oxygen and argon treatment in step 5 is 9 times, and the total treatment time of the whole process is controlled to be 180 minutes.

8. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: The α-FeC2O4 precursor powder described in step 4 is spread evenly in a quartz boat. It is necessary to ensure that the material is laid evenly and the material thickness is controlled within 3 mm.

9. A method for preparing high-purity iron oxide red according to claim 1, characterized in that: In the protective gas mixture of high-purity nitrogen and carbon dioxide described in step 4, the gas volume flow ratio is nitrogen:carbon dioxide=9:1.