A method for preparing ferric hydroxyphosphate from titanium dioxide byproducts

Abstract

This invention provides a method for preparing ferric hydroxyphosphate from titanium dioxide byproducts. The method includes: dissolving ferrous sulfate, a byproduct of titanium dioxide production, adding phosphoric acid and iron powder for purification, and filtering to obtain a purified ferrous sulfate solution; adding appropriate amounts of phosphoric acid, hydrogen peroxide, ammonium dihydrogen phosphate solution, and ammonia to the ferrous sulfate solution and reacting for a period of time to form a mixed slurry; repeatedly washing and filtering the mixed slurry to form a ferric hydroxyphosphate precursor; flash drying, sintering, pulverizing, mixing, and then packaging the ferric hydroxyphosphate product. According to this invention, the method for preparing ferric hydroxyphosphate from titanium dioxide byproducts yields a ferric hydroxyphosphate product with advantages such as low cost, low impurity content, and excellent performance. Furthermore, this method has low equipment requirements, a simple process flow, and improves production efficiency, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the technical field of lithium-ion battery cathode material preparation methods, and specifically to a method for preparing hydroxyferric phosphate from titanium dioxide byproducts. Background Technology

[0002] With increasing public awareness of environmental protection and strong government support for new energy, lithium-ion batteries have gradually become widely used power storage devices. Lithium iron phosphate (LFP) batteries, due to their advantages such as good safety performance, long cycle life, and low price, are widely used in new energy vehicles and energy storage. Furthermore, because they do not contain precious metals or rare elements, their raw materials are abundant, and they cause relatively little environmental pollution, LFP batteries are gradually showing renewed vitality. Iron phosphate is a crucial precursor in the preparation of lithium iron phosphate, and its performance determines the main properties of lithium iron phosphate. Therefore, the preparation of high-performance iron phosphate is of great significance for reducing costs throughout the entire lithium iron phosphate battery industry chain.

[0003] Meanwhile, my country's titanium dioxide enterprises currently produce over 3 million tons of titanium dioxide. The main production methods for titanium dioxide are the sulfuric acid process and the chloride process. The sulfuric acid process is adopted by most titanium dioxide producers due to its relatively simple production process and lower requirements for titanium concentrate grade. For every ton of titanium dioxide produced by the sulfuric acid process, approximately 3.5 to 4 tons of ferrous sulfate byproduct are generated. Because it contains impurities such as Mn, Mg, Al, Ti, and Si, it cannot be directly utilized and has long been piled up as solid waste. Such a large amount of ferrous sulfate byproduct not only affects the environment but also wastes iron resources, significantly hindering the development of the titanium dioxide industry. Due to the long-term accumulation of waste, some of the ferrous sulfate is oxidized by air into ferric oxide, ferric hydroxide, and basic ferric sulfate.

[0004] If this ferrous sulfate byproduct can be fully utilized to manufacture lithium iron phosphate materials, it will not only significantly reduce the production cost of titanium dioxide and enable the comprehensive utilization of iron resources, but also solve the environmental pollution problem caused by ferrous sulfate, a byproduct of titanium dioxide. Summary of the Invention

[0005] In view of the above, the present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, the present invention proposes a method for preparing hydroxyferric phosphate from titanium dioxide byproducts and its application. This method uses ferrous sulfate, a byproduct of titanium dioxide, as a material to prepare hydroxyferric phosphate with high raw material utilization, low impurity content, and high product purity under normal temperature and pressure. Furthermore, the method is simple, efficient, and cost-effective, making it suitable for large-scale industrial production.

[0006] Therefore, this invention provides a method for preparing ferric hydroxyphosphate from titanium dioxide byproducts. The method includes: dissolving ferrous sulfate, a byproduct of titanium dioxide, adding phosphoric acid and iron powder for purification, and filtering to obtain a purified ferrous sulfate solution; adding an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower its pH value; adding hydrogen peroxide, ammonium dihydrogen phosphate solution, and ammonia to the ferrous sulfate solution and reacting for a period of time to form a mixed slurry; repeatedly washing and filtering the mixed slurry to form a ferric hydroxyphosphate precursor; flash drying the ferric hydroxyphosphate precursor in a flash evaporator and sintering it at high temperature for a period of time; pulverizing the sintered material using a mechanical mill, mixing it with a ribbon mixer, and then packaging it to obtain the finished ferric hydroxyphosphate product.

[0007] Preferably, the purification reaction temperature is 40℃, the reaction pH is 2.2-2.5, and the reaction time is 1h.

[0008] Preferably, the amount of phosphoric acid added is in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0009] Preferably, the amount of ammonium dihydrogen phosphate added is such that the iron-phosphorus feeding ratio in the mixed slurry satisfies Fe / P = 1.460-1.490 (molar ratio), the reaction time is 2-6 hours, and the reaction temperature is 25-70℃.

[0010] Preferably, step S3 includes: adding excess hydrogen peroxide to the ferrous sulfate solution and continuing oxidation for a certain period of time; dissolving ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and adding it to the oxidized ferrous sulfate solution; adding ammonia to the ferrous sulfate solution to adjust the pH value of the solution to 3.00±0.02, and forming a mixed slurry after reacting for a period of time.

[0011] Preferably, step S3 includes: adding excess hydrogen peroxide to the ferrous sulfate solution and continuing oxidation for a certain period of time; dissolving ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃; adding ammonia water to the ammonium dihydrogen phosphate solution and stirring to mix evenly to form a mixed ammonium phosphate solution; adding the mixed ammonium phosphate solution to the ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, and reacting for a period of time to form a mixed slurry.

[0012] Preferably, step S3 includes: dissolving ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40°C; adding ammonia water to the ammonium dihydrogen phosphate solution and stirring until homogeneous to form a mixed ammonium phosphate solution; adding hydrogen peroxide to the mixed ammonium phosphate solution and stirring until homogeneous to form a mixed solution; adding the above mixed solution to a ferrous sulfate solution, adjusting the pH of the solution to 3.00±0.02, and reacting for a period of time to form a mixed slurry.

[0013] Preferably, the first and second water washes mainly remove impurities Mn and Mg, while the third water wash involves adding a 1:1 diluted ammonia solution to adjust the pH to 6.5-7.0 to remove SO4 impurities. 2- ion.

[0014] Preferably, the flash evaporator is controlled with an inlet air temperature of 220±20℃, an outlet air temperature of 110±5℃, an air atmosphere for sintering, a sintering temperature of 535-560℃, and a sintering time of 4-5h.

[0015] Preferably, during the pulverization process, the particle size is controlled as follows: D10 ≥ 1.0 μm, D50 6-7 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer is controlled at 35 ± 2 Hz, and the mixing time is 1-2 hours.

[0016] The method for preparing hydroxyferric phosphate from titanium dioxide byproducts provided in this invention utilizes ferrous sulfate, a byproduct of titanium dioxide production, reacting it with hydrogen peroxide, ammonium dihydrogen phosphate, and ammonia. The resulting product is then prepared through processes including water washing and pressure filtration, flash drying, high-temperature sintering, and pulverization. Compared to ferric phosphate prepared by traditional methods, the hydroxyferric phosphate prepared by this method does not require an 80-90℃ crystallization synthesis step and is a spherical, small-particle amorphous precursor. During the water washing and purification stage, impurities are less likely to be trapped inside the crystals and are easily washed away, resulting in a low impurity content and high purity in the finished product. Furthermore, the iron-to-phosphorus ratio and specific surface area of ​​the hydroxyferric phosphate generated by this method are adjustable, allowing for high and low iron-to-phosphorus ratios as needed, which is more conducive to the subsequent construction of lithium iron phosphate crystal structures. In addition, this method requires low reaction temperatures and short reaction times, has low equipment requirements, and a simple process flow, improving production efficiency and making it suitable for large-scale industrial production. Attached Figure Description

[0017] Figure 1 A flowchart of a method for preparing hydroxyferric phosphate from titanium dioxide byproducts provided in an embodiment of the present invention;

[0018] Figure 2 A flowchart of the first embodiment of step 3 in the preparation of hydroxyferric phosphate from titanium dioxide byproducts provided in this invention;

[0019] Figure 3A flowchart of the second embodiment of step 3 in the preparation of hydroxyferric phosphate from titanium dioxide byproducts provided in this invention;

[0020] Figure 4 A flowchart of the third embodiment of step 3 in the preparation of hydroxyferric phosphate from titanium dioxide byproducts provided in this invention;

[0021] Figure 5 The external morphology SEM image of ferric hydroxyphosphate prepared by the method for preparing ferric hydroxyphosphate from titanium dioxide byproducts provided in this embodiment of the invention. Detailed Implementation

[0022] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0023] The following disclosure provides numerous different embodiments or examples for implementing various structures of the invention. To simplify the disclosure, specific examples of components and arrangements are described below. These are merely examples and are not intended to limit the invention. Furthermore, reference numerals and / or letters may be repeated in different examples. Such repetition is for simplification and clarity and does not in itself indicate a relationship between the various embodiments and / or arrangements discussed. Additionally, examples of various specific processes and materials are provided in this invention; however, those skilled in the art will recognize the applicability of other processes and / or the use of other materials.

[0024] This invention provides a method for preparing ferric hydroxyphosphate from titanium dioxide byproducts, resulting in ferric hydroxyphosphate with high raw material utilization, low impurity content, and high product purity. Figure 1 As shown, this method includes:

[0025] Step S1: After dissolving the titanium dioxide byproduct ferrous sulfate, add phosphoric acid and iron powder for purification, and filter under pressure to obtain the purified ferrous sulfate solution.

[0026] The purification reaction temperature was 40℃, the reaction pH was 2.2-2.5, and the reaction time was 1 hour.

[0027] Step S2: Add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution;

[0028] The amount of phosphoric acid added is based on a molar ratio of n(Fe):n(phosphoric acid) = 1:0.15.

[0029] Step S3: Add hydrogen peroxide, ammonium dihydrogen phosphate solution and ammonia to ferrous sulfate solution and react for a period of time to form a mixed slurry;

[0030] The amount of ammonium dihydrogen phosphate added is such that the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio: Fe / P=1.460-1.490, the reaction time is 2-6h, and the reaction temperature is 25-70℃.

[0031] In this embodiment of the invention, hydrogen peroxide, ammonium dihydrogen phosphate solution and ammonia can be added to the ferrous sulfate solution sequentially, or they can be mixed and then added to the ferrous sulfate solution.

[0032] Specifically, in the first embodiment of the present invention, as Figure 2 As shown, step S3 includes:

[0033] Step S311: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time;

[0034] The amount of hydrogen peroxide added is based on a molar ratio of n(Fe):n(hydrogen peroxide) = 1:0.8, the oxidation time is 1.5 h, and the oxidation temperature is less than 50℃.

[0035] Step S312: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and add it to the oxidized ferrous sulfate solution;

[0036] Step S313: Add ammonia to the ferrous sulfate solution to adjust the pH of the solution to 3.00±0.02. After reacting for a period of time, a mixed slurry is formed.

[0037] The amount of ammonia added is based on a molar ratio of n(Fe):n(ammonia) = 1:0.488.

[0038] Specifically, in the second embodiment of the present invention, as Figure 3 As shown, step S3 includes:

[0039] Step S321: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time;

[0040] The amount of hydrogen peroxide added is based on a molar ratio of n(Fe):n(hydrogen peroxide) = 1:0.8, the oxidation time is 1.5 h, and the oxidation temperature is less than 50℃.

[0041] Step S322: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃. Add ammonia water to the ammonium dihydrogen phosphate solution and stir to mix evenly to form a mixed ammonium phosphate solution.

[0042] The amount of ammonia added is based on a molar ratio of n(Fe):n(ammonia) = 1:0.539.

[0043] Step S323: Add the ammonium phosphate mixed solution to the ferrous sulfate solution, adjust the pH of the solution to 3.00±0.02, and form a mixed slurry after reacting for a period of time.

[0044] Specifically, in the third embodiment of the present invention, as Figure 4 As shown, step S3 includes:

[0045] Step S331: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃. Then add ammonia water to the ammonium dihydrogen phosphate solution and stir to mix evenly to form a mixed ammonium phosphate solution.

[0046] The amount of ammonia added is based on a molar ratio of n(Fe):n(ammonia) = 1:0.539.

[0047] Step S332: Add hydrogen peroxide to the ammonium phosphate mixed solution, stir and mix evenly to form a mixed solution;

[0048] The amount of hydrogen peroxide added is based on a molar ratio of n(Fe):n(hydrogen peroxide) = 1:0.8.

[0049] Step S333: Add the above mixed solution to the ferrous sulfate solution, adjust the pH of the solution to 3.00±0.02, and form a mixed slurry after reacting for a period of time.

[0050] Step S4: After multiple water washing and pressure filtration of the mixed slurry, a hydroxyferric phosphate precursor is formed;

[0051] The first and second water washes primarily remove impurities Mn and Mg. The third water wash involves adding a 1:1 diluted ammonia solution to adjust the pH to 6.5-7.0, mainly to remove SO42-. 2- ion.

[0052] Step S5: The ferric hydroxyphosphate precursor is flash-dried in a flash evaporator and then sintered at high temperature for a period of time;

[0053] The flash drying of the ferric hydroxyphosphate precursor is to remove free water. The inlet air temperature of the flash evaporator is controlled at 220±20℃, and the outlet air temperature is controlled at 110±5℃. The sintering atmosphere is air, the sintering temperature can be 535-560℃, and the sintering time can be 4-5 hours.

[0054] Step S6: The sintered material is crushed using a mechanical mill, mixed with a ribbon mixer, and then packaged to obtain the finished hydroxyferric phosphate product.

[0055] During the pulverization process, the particle size is controlled as follows: D10 ≥ 1.0 μm, D50 6-7 μm, and D90 ≤ 60 μm. The mixing frequency of the mixer is controlled at 35 ± 2 Hz, and the mixing time can be 1-2 hours.

[0056] The external morphology SEM image of the ferric hydroxyphosphate prepared by this method is shown below. Figure 5 As shown.

[0057] To verify the quality of the ferric hydroxyphosphate prepared from titanium dioxide byproducts provided in the embodiments of the present invention, different batches of ferric hydroxyphosphate were tested, including the following test items and test methods:

[0058] a) Iron content test

[0059] Test principle: In an acidic environment, Fe is reacted with stannous chloride. 3+ Ions reduced to Fe 2+ The ions were then oxidized with mercuric chloride to remove excess stannous chloride, and the Fe was titrated with potassium dichromate standard solution using sodium diphenylamine as an indicator. 2+ ion.

[0060] Test procedure: Weigh 0.25g of sample, digest with perchloric acid, reduce with stannous chloride, oxidize excess stannous chloride with stannous chloride, add a mixture of sulfuric acid and phosphoric acid and sodium diphenylamine sulfonate indicator, titrate with potassium dichromate standard solution to the endpoint, and calculate the iron content in the sample by the volume of potassium dichromate standard solution consumed.

[0061] b) Phosphorus content test

[0062] Test principle: In an acidic medium, orthophosphate reacts with quinoline phosphomolybdate precipitant to form a yellow quinoline phosphomolybdate precipitate. After filtration, washing, drying, and weighing, the phosphorus content in the sample can be calculated.

[0063] Test Procedure: Weigh 0.5g of sample, digest with perchloric acid, and dilute the solution to a 250ml volumetric flask after digestion. Transfer 25ml of the mother liquor to a beaker as the test solution, add 5ml of concentrated nitric acid to adjust the pH, and add boiling deionized water to a total volume of 75mL. Place the beaker on a 270℃ electric heating plate and boil. Add 40ml of quinammolybdate solution and heat until large precipitates form, then remove the beaker. After cooling, filter the precipitate from the beaker into a weighed empty crucible. Place the crucible in an oven and bake at 180±2℃ for 1 hour until constant weight. Remove the crucible and cool it to room temperature in a desiccator, then weigh it. Calculate the phosphorus content in the sample based on the mass of the precipitate.

[0064] c) Impurity element content test

[0065] Test principle: The sample is vaporized and dissociated into atomic state by using a plasma-excited light source. The light emitted by the light source is further ionized into ionic state. The atoms and ions are excited and emit light in the light source. The light emitted by the light source is decomposed into a spectrum arranged by wavelength using a spectroscopic system. The spectrum is detected by photoelectric devices. The wavelength of the spectrum is used for qualitative analysis of the sample, and the intensity of the emitted light is used for quantitative analysis.

[0066] Test procedure: Weigh 0.3g of sample, add perchloric acid for digestion, and after digestion, make up the volume of the solution to 100ml in a volumetric flask. Shake well and test with ICP. Calculate the content of impurity elements in the sample based on the test results.

[0067] d) Specific surface area test

[0068] Test Principle: The sample tube containing the sample is evacuated to a vacuum and placed in a liquid nitrogen (-196℃) environment. Nitrogen gas, pre-measured by a pressure sensor, is introduced into a fixed volume. Within this limited fixed volume (the instrument dead volume measured by the standard tube + the sample tube volume excluding the sample volume (the free space of the sample tube can be measured using helium at room temperature and liquid nitrogen)), the pressure decreases as the sample begins to adsorb gas, until adsorption reaches equilibrium. At the equilibrium pressure, the amount of gas adsorbed is the difference between the amount of gas added and the amount of adsorbed gas remaining in the gas phase. Different relative pressures P / P0 correspond to different amounts of adsorbed gas, na.

[0069] With (P / P0) / (na(1-P / P0)) as the ordinate and P / P0 as the abscissa, the relationship is linear between 0.05 and 0.3 relative pressures. By measuring the amount of nitrogen adsorbed and the relative pressure, the instrument can determine the monolayer saturated adsorption amount of nitrogen on the sample surface. Then, the specific surface area of ​​the sample can be calculated using an empirical formula (model) determined by the properties of the sample.

[0070] Testing process:

[0071] Add a certain amount of sample to the sample tube, heat and degas it in the degassing station for two hours at a degassing temperature of 200℃, and then place it in the test position to start the test.

[0072] e) Particle size testing

[0073] Test principle: Under laser testing, the angle of the scattered light is inversely proportional to the particle diameter, while the intensity of the scattered light decreases logarithmically as the angle increases. The scattered light is imaged by a Fourier lens or inverse Fourier lens. On a focal plane with multiple detectors, the energy distribution of the scattered light is directly related to the particle diameter distribution. By receiving and measuring the energy distribution of the scattered light, the density distribution characteristics of the particles can be obtained.

[0074] Test procedure: The particle size analyzer was turned on and the parameters were set, including a refractive index of 1.692, an absorptivity of 1.0, and water as the dispersion medium with a refractive index of 1.33. The system was then used to prepare the sample by ultrasonic dispersion, and the dispersed sample was added for testing.

[0075] f) Moisture test

[0076] Test principle: Any moisture (free water or water of crystallization) present in the sample undergoes a quantitative reaction with a Karl Fischer reagent of known titer.

[0077] Test procedure: Weigh 0.5g±0.1g of sample into a sample bottle, place the sample bottle in the device and input the sample mass. Once the device temperature rises above 180℃ and the drift value stabilizes below 10, the device will automatically measure and calculate the water content of the sample.

[0078] g) pH value test

[0079] Test principle: The specified indicator electrode and reference electrode are immersed in the same test solution to form a galvanic cell. The electromotive force of the galvanic cell is related to the pH value of the solution. The pH value of the solution can be obtained by measuring the electromotive force of the galvanic cell.

[0080] Test procedure: Weigh 5±0.01g of sample into an Erlenmeyer flask, add 45±0.05g of pure water, stir at 880r / min for 30min on a magnetic stirrer, and then bathe in a constant temperature water bath at 25℃ for 90min. Finally, use a pH meter to test the pH value of the sample.

[0081] The specific test results are shown in Table 1 below.

[0082] Table 1. Test items and test results of different batches of ferric phosphate

[0083]

[0084]

[0085]

[0086] Tests on different batches of ferric hydroxyphosphate prepared from titanium dioxide byproducts provided in this invention embodiment revealed that the ferric hydroxyphosphate prepared by this method has a narrow particle size distribution, uniform particle size, and its specific surface area and pH fully meet the requirements of lithium iron phosphate. Furthermore, it exhibits low impurity content and high purity. Additionally, tests on different batches of finished ferric hydroxyphosphate showed that by changing the iron-phosphorus feeding ratio, ferric hydroxyphosphate products with varying specific surface areas can be prepared, and the iron-phosphorus ratio in the finished product changes depending on the feeding ratio.

[0087] Specifically, when preparing ferric hydroxyphosphate using the method provided by this invention, when the iron-phosphorus feed ratio is controlled to meet the following conditions: Fe / P = 1.460-1.465 (molar ratio), sintering temperature 545℃, and sintering time 5h, the resulting ferric hydroxyphosphate product has an Fe / P ratio of 1.430-1.450 (molar ratio) and a specific surface area of ​​12±2m². 2 / g, which can meet the requirements of low iron-phosphorus ratio and low specific surface area.

[0088] When the iron-phosphorus feed ratio is controlled to meet the requirements of Fe / P = 1.485-1.490 (molar ratio), sintering temperature of 535℃, and sintering time of 5h, the prepared ferric hydroxyphosphate product has a Fe / P ratio of 1.460-1.480 (molar ratio) and a specific surface area of ​​25±5m². 2 / g, which can meet the requirements of high iron-phosphorus ratio and high specific surface area.

[0089] In summary, the method for preparing hydroxyferric phosphate from titanium dioxide byproducts provided in this invention utilizes ferrous sulfate, a byproduct of titanium dioxide production, reacting it with hydrogen peroxide, ammonium dihydrogen phosphate, and ammonia. The resulting product is then prepared through processes including water washing and pressure filtration, flash drying, high-temperature sintering, and pulverization. Compared to ferric phosphate prepared by traditional methods, the hydroxyferric phosphate prepared by this method does not require an 80-90℃ crystallization synthesis step and is a spherical, small-particle amorphous precursor. During the water washing and purification stage, impurities are less likely to be trapped inside the crystals and are easily washed away, resulting in a low impurity content and high purity in the finished product. Furthermore, the iron-to-phosphorus ratio and specific surface area of ​​the hydroxyferric phosphate generated by this method are adjustable, allowing for high and low iron-to-phosphorus ratios as needed, which is more conducive to the subsequent construction of lithium iron phosphate crystal structures. In addition, this method requires low reaction temperatures and short reaction times, has low equipment requirements, and a simple process flow, improving production efficiency and making it suitable for large-scale industrial production.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0091] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing ferric hydroxyphosphate from titanium dioxide byproducts, characterized in that, The method includes: Step S1: After dissolving the titanium dioxide byproduct ferrous sulfate, add phosphoric acid and iron powder for purification, and filter under pressure to obtain the purified ferrous sulfate solution. Step S2: Add an appropriate amount of phosphoric acid to the ferrous sulfate solution to lower the pH value of the ferrous sulfate solution; Step S3: Add hydrogen peroxide, ammonium dihydrogen phosphate solution and ammonia to ferrous sulfate solution and react for a period of time to form a mixed slurry; Step S4: After multiple water washing and pressure filtration of the mixed slurry, a hydroxyferric phosphate precursor is formed; Step S5: The ferric hydroxyphosphate precursor is flash-dried in a flash evaporator and then sintered at high temperature for a period of time; Step S6: The sintered material is crushed using a mechanical mill, mixed with a ribbon mixer, and then packaged to obtain the finished hydroxyferric phosphate product.

2. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, In step S1, the purification reaction temperature is 40℃, the reaction pH is 2.2-2.5, and the reaction time is 1h.

3. The method for preparing hydroxyferric phosphate from titanium dioxide byproducts according to claim 1, characterized in that, In step S2, the amount of phosphoric acid added is in a molar ratio of n(Fe):n(phosphoric acid) = 1:0.

15.

4. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, In step S3, the amount of ammonium dihydrogen phosphate added is such that the iron-phosphorus feeding ratio in the mixed slurry meets the iron-phosphorus molar ratio: Fe / P = 1.460-1.490, the reaction time is 2-6 hours, and the reaction temperature is 25-70℃.

5. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, Step S3 includes: Step S311: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time; Step S312: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃, and add it to the oxidized ferrous sulfate solution; Step S313: Add ammonia to the ferrous sulfate solution to adjust the pH of the solution to 3.00±0.

02. After reacting for a period of time, a mixed slurry is formed.

6. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, Step S3 includes: Step S321: Add excess hydrogen peroxide to the ferrous sulfate solution and continue oxidation for a certain period of time; Step S322: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃. Then add ammonia water to the ammonium dihydrogen phosphate solution and stir to mix evenly to form a mixed ammonium phosphate solution. Step S323: Add the ammonium phosphate mixed solution to the ferrous sulfate solution, adjust the pH of the solution to 3.00±0.02, and form a mixed slurry after reacting for a period of time.

7. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, Step S3 includes: Step S331: Dissolve ammonium dihydrogen phosphate powder in water to prepare a 30% concentration ammonium dihydrogen phosphate solution at a dissolution temperature of 30-40℃. Then add ammonia water to the ammonium dihydrogen phosphate solution and stir to mix evenly to form a mixed ammonium phosphate solution. Step S332: Add hydrogen peroxide to the ammonium phosphate mixed solution, stir and mix evenly to form a mixed solution; Step S333: Add the above mixed solution to the ferrous sulfate solution, adjust the pH of the solution to 3.00±0.02, and form a mixed slurry after reacting for a period of time.

8. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, In step S4, the first and second water washes mainly remove impurities Mn and Mg. During the third water wash, a 1:1 diluted ammonia solution is added to adjust the pH to 6.5-7.0 to remove SO4 impurities. 2- ion.

9. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, In step S5, the inlet air temperature of the flash evaporator is controlled at 220±20℃, the outlet air temperature is controlled at 110±5℃, the sintering atmosphere is air, the sintering temperature is 535-560℃, and the sintering time is 4-5h.

10. The method for preparing ferric hydroxyphosphate from titanium dioxide byproducts according to claim 1, characterized in that, In step S6, during the crushing process, the particle size is controlled as D10≥1.0μm, D50:6-7μm, D90≤60μm, the mixing frequency of the mixer is controlled at 35±2Hz, and the mixing time is 1-2h.

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