Method for reducing magnetism in nanoscale titanium dioxide production

Abstract

The application discloses a method for reducing magnetism in nanoscale titanium dioxide production and belongs to the technical field of titanium dioxide manufacturing. The method comprises the following steps: raw material pretreatment, heat treatment under an oxygen-rich atmosphere, inert atmosphere nanomachining, deep physical impurity removal and chemical washing and purification. The method prevents pollution from the source by using high-purity raw materials and inert material equipment, prevents defects by using an oxygen-rich atmosphere in the early stage, and prevents pollution by using inertness in the later stage. The core strategy realizes the whole-process blocking of magnetism generation. In the nanocrystallization crushing stage, the method completely isolates the reaction between the high-activity nanoscale newborn surface and the environmental medium by designing an ultralow-oxygen inert atmosphere and low-temperature conditions, prevents the generation of secondary defects caused by friction heat and surface activity, and locks the previous process results. Furthermore, the method actively provides an oxygen source from the crystal growth source by heat treatment under an oxygen-rich atmosphere (O2>=25%), effectively fills oxygen vacancies and oxidizes them, and fundamentally eliminates lattice defects.

Description

Technical Field

[0001] This invention relates to the field of titanium dioxide manufacturing technology, and more particularly to a method for reducing magnetism in the production of nano-sized titanium dioxide. Background Technology

[0002] Nanoscale titanium dioxide is widely used in new energy batteries, high-end catalysts, functional coatings, and electronic ceramics due to its excellent photocatalytic properties, high specific surface area, and unique surface effects. However, the presence of magnetic materials in these products has become a key bottleneck restricting their application in high-performance fields.

[0003] Magnetic impurities mainly originate from two sources: firstly, exogenous impurities, such as magnetic metal particles like iron (Fe), cobalt (Co), and nickel (Ni) introduced from production equipment wear and tear or raw materials; secondly, more concealed and difficult-to-remove endogenous defects, namely oxygen vacancies generated during crystal growth or post-processing due to an oxygen-deficient environment, and the associated trivalent titanium ions. These intrinsic defects are more pronounced in nanomaterials due to their enormous specific surface area, and can introduce room-temperature ferromagnetism, severely impacting product performance. Currently, physical magnetic separation is commonly used in industry to remove exogenous ferromagnetic particles, but it is ineffective for non-ferromagnetic paramagnetic materials (such as some iron-containing compounds) and particles within the crystal lattice. There is no way to address the defects; if the conventional high-temperature calcination process is carried out in an uncontrolled atmosphere such as air, the local reducing environment may actually exacerbate the generation of oxygen vacancies.

[0004] Furthermore, during the process of pulverizing primary products to the nanoscale, the surface activity of the newly formed particles is extremely high, making them highly susceptible to interaction with water vapor or organic matter in the environment. They are induced to be reduced by frictional heat, generating new surface defects and leading to "secondary magnetization".

[0005] Based on this, a method for reducing magnetism in the production of nano-sized titanium dioxide is proposed. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that in the process of crushing primary products to the nanoscale, the surface activity of the newly formed particles is extremely high, which makes them very easy to react with water vapor or organic matter in the environment, and they are induced to be reduced by frictional heat, resulting in new surface defects and "secondary magnetization". The invention proposes a method to reduce the magnetism in the production of nanoscale titanium dioxide.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for reducing magnetism in the production of nano-sized titanium dioxide includes the following steps: S1. Raw material pretreatment: Using a titanium source with a purity of ≥99.9%, a titanium precursor slurry is obtained through hydrolysis in a reactor made of inert material; S2. Heat treatment under oxygen-enriched atmosphere: After solid-liquid separation and washing of the titanium precursor slurry obtained in step S1, it is placed in a controlled atmosphere heat treatment device, and a flowing mixed gas with an oxygen content of not less than 25% by volume is introduced. Crystallization heat treatment is carried out in the temperature range of 400°C to 650°C for 1 to 6 hours to obtain primary titanium dioxide powder. S3. Inert Atmosphere Nanoprocessing: The primary titanium dioxide powder obtained in step S2 is fed into an airflow pulverizing system using inert gas as the pulverizing medium and atmosphere protection. The oxygen content of the working atmosphere in the system is maintained below 10 ppm, and the temperature of the pulverizing chamber is controlled below 50°C by a cooling system. Ultrafine pulverization and classification are performed to obtain a powder with a specific surface area of ​​5 m². 2 / g to 100m 2 / g, with a median particle size D50 in the range of 10nm to 100nm; S4. Deep physical impurity removal: The nano-titanium dioxide powder obtained in step S3 is subjected to iron removal treatment through a sorting device equipped with a high gradient magnetic medium. The working magnetic field strength of the sorting device is 1.0T to 2.5T.

[0008] As a preferred embodiment, in step S2, the flowing mixed gas is a mixture of oxygen and an inert gas at a volume ratio of 1:3 to 4:1; the inert gas is one or more of nitrogen, argon, or helium. The heat treatment is carried out under programmed temperature control, with a heating rate of 2℃ / min to 10℃ / min. After reaching the target temperature, it enters the isothermal crystallization stage.

[0009] As a preferred embodiment, in step S2, the exhaust end of the controllable atmosphere heat treatment device is connected to an online oxygen concentration analyzer for real-time monitoring of the oxygen content in the exhaust gas. The monitoring signal is fed back to the mass flow controller at the air inlet, forming a closed-loop control system that dynamically adjusts the intake ratio of oxygen and inert gas so that the oxygen content fluctuation range in the reaction zone does not exceed ±5% of the set value.

[0010] As a preferred embodiment, in step S3, the airflow pulverizing system is equipped with a pre-gas purification device and an online trace oxygen analyzer. Before entering the pulverizing chamber, the inert gas must be purified by the gas purification device to reduce the oxygen content to below 1 ppm; The online trace oxygen analyzer monitors the oxygen concentration in the grinding chamber in real time. When the monitored value exceeds 10 ppm for 30 seconds, the system automatically alarms and starts a high-flow inert gas flushing program until the oxygen concentration returns to below the set threshold.

[0011] As a preferred embodiment, in step S3, the feed rate, classifier speed and air pressure of the airflow pulverizing system are controlled so that the particle size distribution of the obtained nano-titanium dioxide powder meets the following requirements: particle size D90≤150nm, and particle size distribution span=(D90-D10) / D50≤1.5.

[0012] As a preferred embodiment, after step S4, step S5 is also included: chemical washing and purification; Specifically, the magnetically separated nano-titanium dioxide powder is mixed with a dilute inorganic acid solution or complexing agent solution with a concentration of 0.1 mol / L to 0.5 mol / L at a solid-liquid ratio of 1:5 to 1:15, and stirred and washed at 20°C to 60°C for 10 to 60 minutes. Solid-liquid separation was then performed, and the filter cake was washed with hot deionized water with a resistivity ≥18MΩ·cm until the conductivity of the effluent was ≤10μS / cm. Finally, dry at 80℃ to 120℃ and a vacuum degree of not less than -0.08MPa for 2 to 6 hours.

[0013] As a preferred embodiment, the titanium source is titanium tetrachloride, titanium oxysulfate, tetraisopropyl titanate, or tetrabutyl titanate. The inert material reactor refers to all components that come into contact with materials, and their materials are Hastelloy, polytetrafluoroethylene-lined carbon steel, quartz glass, or high-purity engineering ceramics.

[0014] As a preferred option, a pre-demagnetization and screening process is set before the feed end in step S2: the washed titanium precursor wet filter cake is re-pulped to make the slurry solid content 10% to 30%, and then it is made to flow through a permanent magnet drum with a surface magnetic field strength of not less than 1000 Gauss at a flow rate of 1 to 5 cm / s to adsorb and remove ferromagnetic impurities in the slurry. The slurry is then spray-dried into powder and sieved using a 200-400 mesh vibrating screen to remove any mechanical foreign matter that may be introduced.

[0015] As a preferred option, the final nano-titanium dioxide product obtained in step S3 is subjected to quality testing. The testing indicators and methods include: using a vibrating sample magnetometer to test its saturation magnetization intensity, which is required to be ≤0.2 emu / g; The total content of magnetic metallic impurities of iron, cobalt, and nickel was determined using inductively coupled plasma mass spectrometry, with a requirement of ≤0.1ppm.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. In the nano-pulverization stage, this invention, through the design of an ultra-low oxygen inert atmosphere and low temperature conditions, completely isolates the highly active nano-new surface from the reaction with the environmental medium, preventing the generation of secondary defects caused by frictional heat and surface activity, thus locking in the results of the preceding process; and through oxygen-rich atmosphere (O2≥25%) heat treatment, actively provides an oxygen source from the crystal growth source, effectively filling oxygen vacancies and... Oxidized to This fundamentally eliminates lattice defects.

[0017] 2. This invention eliminates pollution at the source by using high-purity raw materials and inert equipment. Through the core strategy of oxygen enrichment to suppress defects in the front and inertization to prevent pollution in the back, it achieves complete blocking of the magnetic generation process and achieves comprehensive and in-depth removal of exogenous magnetic impurities and surface adsorbates. It breaks through the limitation of traditional methods that can only deal with exogenous impurities and achieves simultaneous and efficient control of internal and exogenous magnetic sources. Attached Figure Description

[0018] Figure 1 This is a flowchart of a method for reducing magnetism in the production of nano-sized titanium dioxide, as proposed in this invention. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0022] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0023] Example, refer to Figure 1A method for reducing magnetism in the production of nano-sized titanium dioxide includes the following steps: Raw material pretreatment: Using a titanium source with a purity of ≥99.9%, a titanium precursor slurry is obtained through hydrolysis in a reactor made of inert material; Heat treatment under oxygen-enriched atmosphere: After solid-liquid separation and washing, the obtained titanium precursor slurry is placed in a controlled atmosphere heat treatment device, and a flowing mixed gas with an oxygen content of not less than 25% by volume is introduced. Crystallization heat treatment is carried out in the temperature range of 400℃ to 650℃ for 1 to 6 hours to obtain primary titanium dioxide powder. Inert atmosphere nanoprocessing: The obtained primary titanium dioxide powder is fed into an airflow milling system using inert gas as the milling medium and atmosphere protection. The oxygen content of the working atmosphere in the system is maintained below 10 ppm, and the temperature of the milling chamber is controlled below 50℃ by a cooling system for ultrafine milling and classification, resulting in a specific surface area of ​​5 m². 2 / g to 100m 2 / g, with a median particle size D50 in the range of 10nm to 100nm; Deep physical impurity removal: The obtained nano-titanium dioxide powder is subjected to iron removal treatment through a sorting device equipped with a high gradient magnetic medium. The working magnetic field strength of the sorting device is 1.0T to 2.5T.

[0024] Chemical washing and purification; Specifically, the magnetically separated nano-titanium dioxide powder is mixed with a dilute inorganic acid solution or complexing agent solution with a concentration of 0.1 mol / L to 0.5 mol / L at a solid-liquid ratio of 1:5 to 1:15, and stirred and washed at 20°C to 60°C for 10 to 60 minutes. Solid-liquid separation was then performed, and the filter cake was washed with hot deionized water with a resistivity ≥18MΩ·cm until the conductivity of the effluent was ≤10μS / cm. Finally, dry at 80℃ to 120℃ and a vacuum degree of not less than -0.08MPa for 2 to 6 hours.

[0025] The flowing gas mixture is composed of oxygen and an inert gas in a volume ratio of 1:3 to 4:1; the inert gas is one or more of nitrogen, argon, or helium. The heat treatment is carried out under programmed temperature control, with a heating rate of 2℃ / min to 10℃ / min. After reaching the target temperature, it enters the isothermal crystallization stage.

[0026] The exhaust end of the controlled atmosphere heat treatment device is connected to an online oxygen concentration analyzer for real-time monitoring of the oxygen content in the exhaust gas. The monitoring signal is fed back to the mass flow controller at the air inlet, forming a closed-loop control system that dynamically adjusts the intake ratio of oxygen and inert gas so that the oxygen content fluctuation range in the reaction zone does not exceed ±5% of the set value.

[0027] The air jet mill system is equipped with a pre-gas purification device and an online trace oxygen analyzer; Before entering the pulverizing chamber, the inert gas must pass through a gas purification device to reduce the oxygen content to below 1 ppm; The online trace oxygen analyzer monitors the oxygen concentration in the grinding chamber in real time. When the monitored value exceeds 10 ppm for 30 seconds, the system automatically alarms and starts a high-flow inert gas flushing program until the oxygen concentration returns to below the set threshold.

[0028] Control the feed rate, classifier speed and air pressure of the air jet milling system so that the particle size distribution of the obtained nano titanium dioxide powder meets the following requirements: particle size D90≤150nm, and particle size distribution span=(D90-D10) / D50≤1.5.

[0029] The titanium source is titanium tetrachloride, titanium oxysulfate, tetraisopropyl titanate, or tetrabutyl titanate; An inert material reactor refers to all components that come into contact with materials, and their materials are Hastelloy, PTFE-lined carbon steel, quartz glass, or high-purity engineering ceramics.

[0030] Before the feed end in step S2, a pre-demagnetization and screening process is set up: the washed titanium precursor wet filter cake is re-pulped to make the slurry solid content 10% to 30%, and then it is made to flow through a permanent magnet drum with a surface magnetic field strength of not less than 1000 Gauss at a flow rate of 1 to 5 cm / s to adsorb and remove ferromagnetic impurities in the slurry. The slurry is then spray-dried into powder and sieved using a 200-400 mesh vibrating screen to remove any mechanical foreign matter that may be introduced.

[0031] The final nano-titanium dioxide product obtained in step S3 is subjected to quality inspection. The inspection indicators and methods include: using a vibrating sample magnetometer to test its saturation magnetization intensity, which is required to be ≤0.2 emu / g; The total content of magnetic metallic impurities of iron, cobalt, and nickel was determined using inductively coupled plasma mass spectrometry, with a requirement of ≤0.1ppm.

[0032] The present invention will be further illustrated by specific embodiments below, but the present invention is not limited thereto.

[0033] Example 1 Titanium tetrachloride with a purity of 99.99% was used as raw material and hydrolyzed in a PTFE-lined reactor to obtain metatitanic acid slurry.

[0034] After being pressure filtered and washed with water, the slurry is redispersed and pre-demagnetized by a permanent magnet drum (1200 Gauss), then spray-dried and passed through a 325-mesh sieve.

[0035] The sieved precursor powder was loaded into a tube furnace, and a 1:1 O2 / N2 mixture (50% oxygen content) was introduced. The temperature was increased to 500℃ at 5℃ / min, and calcined at this temperature for 3 hours. The oxygen concentration in the furnace was stabilized at (50±1.5)% through a closed-loop control system.

[0036] After calcination, the powder was fed into an airflow milling system. The system was continuously supplied with purified high-purity nitrogen gas with an oxygen content of <1 ppm. During the milling process, the chamber temperature was maintained below 45℃, and the oxygen concentration remained stable at around 5 ppm. By adjusting the parameters, nanoparticles with D50=45nm, D90=78nm, and SPAN=1.2 were obtained.

[0037] The powder was subjected to high-gradient magnetic separation with a magnetic field strength of 2.0T.

[0038] After magnetic separation, the powder was washed with 0.3 mol / L dilute hydrochloric acid at a solid-liquid ratio of 1:10 at 50°C for 40 minutes. After filtration, it was washed with deionized water at 85°C until the conductivity of the filtrate was 8 μS / cm.

[0039] The filter cake was vacuum dried at -0.09 MPa and 100°C for 4 hours to obtain the final product.

[0040] Product testing: Saturation magnetization (VSM): 0.08 emu / g Total magnetic metal content (ICP-MS): Fe+Co+Ni=22ppm surface Scale (XPS): / ( + =1.3% All indicators were better than the control standards.

[0041] Example 2 The steps are basically the same as in Example 1, except that the heat treatment parameters in step 3 are changed: an O2 / N2 mixture with an oxygen content of 30% is introduced, the calcination temperature is 550°C, and the temperature is kept constant for 2 hours.

[0042] Final product test results: saturation magnetization 0.12 emu / g; total magnetic metal content 28 ppm; surface... The proportion is 1.8%. All indicators still meet the standards, indicating that the process has good adaptability within the parameter range of this invention.

[0043] Comparative Example 1 Compared to Example 1, the heat treatment in step 3 was carried out in static air (oxygen content of about 21%), with other conditions remaining unchanged.

[0044] Final product test results: saturation magnetization 0.45 emu / g; surface The proportion is as high as 8.7%. This indicates that it cannot be effectively suppressed under normal air conditions. The formation of defects leads to a significant increase in intrinsic magnetism.

[0045] Comparative Example 2 Compared with Example 1, the airflow pulverization process in step 4 does not use purified nitrogen protection, but instead uses ordinary compressed air in an open environment for pulverization, while other conditions remain unchanged.

[0046] Final product test results: saturation magnetization 0.31 emu / g; surface The proportion is 4.5%. This indicates that even if a low-defect primary powder is obtained after oxygen-enriched heat treatment, the product surface will still be severely "secondarily contaminated" during subsequent unprotected nano-processing, resulting in new magnetic defects.

[0047] Comparative Example 3 Steps 5 (high gradient magnetic separation) and 6 (acid washing) in Example 1 are omitted, and only step 4 is performed to obtain the powder.

[0048] Final product test results: saturation magnetization 0.25 emu / g; total magnetic metal content as high as 185 ppm; surface... The proportion is 1.5%. This indicates that controlling endogenous defects alone cannot remove exogenous metal impurities, and a combined physicochemical impurity removal step is essential.

[0049] Based on the above embodiments, the following conclusions can be drawn: 1. The key role of oxygen-enriched heat treatment: A direct comparison between Comparative Example 1 and Example 1 shows that simply changing the heat treatment atmosphere from 50% oxygen-enriched to ordinary air significantly reduces endogenous defects in the product. The ratio increased dramatically by nearly seven times, leading to a severe exceedance of the saturation magnetization. This demonstrates that an active high oxygen partial pressure environment is the decisive factor in suppressing lattice defects and reducing intrinsic magnetism.

[0050] 2. The necessity of inert protection during nano-sizing: Comparative Example 2 shows that even with perfect oxygen-enriched heat treatment in the initial stage, if the inert protection is removed (and replaced with air) during the subsequent nano-sizing process, the newly formed surface will be subject to secondary contamination. The proportion and saturation magnetization have rebounded significantly, which confirms that the dual strategy of "suppressing defects at the front end and preventing contamination at the back end" is indispensable.

[0051] 3. Synergistic effect of multi-stage impurity removal system: Comparative Example 3 shows that even if the crystal defects themselves are well controlled ( Although the proportion is only 1.5%, the total amount of exogenous metal impurities soared nearly 9 times after omitting magnetic separation and chemical washing, resulting in excessive saturation magnetization. This highlights that physical magnetic separation and chemical washing are irreplaceable for removing exogenous impurities and must be used in conjunction with defect control processes.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for reducing magnetism in the production of nano-sized titanium dioxide, characterized in that, Includes the following steps: S1. Raw material pretreatment: Using a titanium source with a purity of ≥99.9%, a titanium precursor slurry is obtained through hydrolysis in a reactor made of inert material; S2. Heat treatment under oxygen-enriched atmosphere: After solid-liquid separation and washing of the titanium precursor slurry obtained in step S1, it is placed in a controlled atmosphere heat treatment device, and a flowing mixed gas with an oxygen content of not less than 25% by volume is introduced. Crystallization heat treatment is carried out in the temperature range of 400°C to 650°C for 1 to 6 hours to obtain primary titanium dioxide powder. S3. Inert Atmosphere Nanoprocessing: The primary titanium dioxide powder obtained in step S2 is fed into an airflow pulverizing system using inert gas as the pulverizing medium and atmosphere protection. The oxygen content of the working atmosphere in the system is maintained below 10 ppm, and the temperature of the pulverizing chamber is controlled below 50°C by a cooling system. Ultrafine pulverization and classification are performed to obtain a powder with a specific surface area of ​​5 m². 2 / g to 100m 2 / g, with a median particle size D50 in the range of 10nm to 100nm; S4. Deep physical impurity removal: The nano-titanium dioxide powder obtained in step S3 is subjected to iron removal treatment through a sorting device equipped with a high gradient magnetic medium. The working magnetic field strength of the sorting device is 1.0T to 2.5T.

2. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, In step S2, the flowing mixed gas is a mixture of oxygen and an inert gas at a volume ratio of 1:3 to 4:1; the inert gas is one or more of nitrogen, argon, or helium. The heat treatment is carried out under programmed temperature control, with a heating rate of 2℃ / min to 10℃ / min. After reaching the target temperature, it enters the isothermal crystallization stage.

3. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, In step S2, the exhaust end of the controllable atmosphere heat treatment device is connected to an online oxygen concentration analyzer for real-time monitoring of the oxygen content in the exhaust gas. The monitoring signal is fed back to the mass flow controller at the air inlet, forming a closed-loop control system that dynamically adjusts the intake ratio of oxygen and inert gas so that the oxygen content fluctuation range in the reaction zone does not exceed ±5% of the set value.

4. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, In step S3, the airflow pulverizing system is equipped with a pre-gas purification device and an online trace oxygen analyzer; Before entering the pulverizing chamber, the inert gas must be purified by the gas purification device to reduce the oxygen content to below 1 ppm; The online trace oxygen analyzer monitors the oxygen concentration in the grinding chamber in real time. When the monitored value exceeds 10 ppm for 30 seconds, the system automatically alarms and starts a high-flow inert gas flushing program until the oxygen concentration returns to below the set threshold.

5. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, In step S3, the feed rate, classifier speed and air pressure of the airflow pulverizing system are controlled so that the particle size distribution of the obtained nano-titanium dioxide powder meets the following requirements: particle size D90≤150nm, and particle size distribution span=(D90-D10) / D50≤1.

5.

6. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, Following step S4, step S5 is also included: chemical washing and purification; Specifically, the magnetically separated nano-titanium dioxide powder is mixed with a dilute inorganic acid solution or complexing agent solution with a concentration of 0.1 mol / L to 0.5 mol / L at a solid-liquid ratio of 1:5 to 1:15, and stirred and washed at 20°C to 60°C for 10 to 60 minutes. Solid-liquid separation was then performed, and the filter cake was washed with hot deionized water with a resistivity ≥18MΩ·cm until the conductivity of the effluent was ≤10μS / cm. Finally, dry at 80℃ to 120℃ and a vacuum degree of not less than -0.08MPa for 2 to 6 hours.

7. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, The titanium source is titanium tetrachloride, titanium oxysulfate, tetraisopropyl titanate, or tetrabutyl titanate. The inert material reactor refers to all components that come into contact with materials, and their materials are Hastelloy, polytetrafluoroethylene-lined carbon steel, quartz glass, or high-purity engineering ceramics.

8. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, Before the feed end in step S2, a pre-demagnetization and screening process is set up: the washed titanium precursor wet filter cake is re-pulped to make the slurry solid content 10% to 30%, and then it is made to flow through a permanent magnet drum with a surface magnetic field strength of not less than 1000 Gauss at a flow rate of 1 to 5 cm / s to adsorb and remove ferromagnetic impurities in the slurry. The slurry is then spray-dried into powder and sieved using a 200-400 mesh vibrating screen to remove any mechanical foreign matter that may be introduced.

9. The method for reducing magnetism in the production of nano-sized titanium dioxide according to claim 1, characterized in that, The final nano-titanium dioxide product obtained in step S3 is subjected to quality inspection. The inspection indicators and methods include: using a vibrating sample magnetometer to test its saturation magnetization intensity, which is required to be ≤0.2 emu / g; The total content of magnetic metallic impurities of iron, cobalt, and nickel was determined using inductively coupled plasma mass spectrometry, with a requirement of ≤0.1ppm.

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