Method for preparing titanium-doped iron phosphate from titanium dioxide byproduct ferrous sulfate

Abstract

The invention discloses a method for preparing titanium-doped iron phosphate from a titanium dioxide by-product ferrous sulfate, which comprises the following steps: (1) heating and dissolving the titanium dioxide by-product ferrous sulfate in a solvent to form a ferrous sulfate supersaturated solution; (2) adding a precipitant into the ferrous sulfate supersaturated solution for reaction, and cooling to separate out a mixed solid of ferrous sulfate crystals and titanium-containing precipitates after the reaction is finished; (3) taking the saturated ferrous sulfate mother liquor as a solvent, repeating the step (1) and the step (2), and combining the mixed solid obtained by repeating each time and the mixed solid in the step (2) to obtain a total mixed solid; and (4) dissolving the total mixed solid with sulfuric acid to form an iron-titanium solution, sequentially adding phosphoric acid, hydrogen peroxide and phosphorus salt into the iron-titanium solution, mixing, filtering to obtain a titanium-doped iron phosphate precursor, and heating, aging, filtering, washing, drying and calcining the titanium-doped iron phosphate precursor to obtain the titanium-doped iron phosphate product.

Description

Technical Field

[0001] This invention belongs to the field of titanium dioxide by-product recycling, and particularly relates to a method for preparing titanium-doped ferric phosphate from ferrous sulfate, a by-product of titanium dioxide. Background Technology

[0002] With the continuous development of the new energy industry, the demand for lithium iron phosphate (LFP) cathode materials is expected to surge. Currently, LFP manufacturers use titanium doping during production to improve the electrochemical and cycle performance of LFP materials. The most common method is to add titanium dioxide during the batching stage, followed by sand milling and spraying, and then diffusion of titanium into the LFP lattice under high-temperature conditions during calcination. This method requires significant thermal energy and efficient grinding to ensure uniform titanium doping. Another method of titanium doping in LFP involves introducing titanium-containing compounds as ions during the LFP preparation process. This method does not consume a large amount of thermal energy, and the co-precipitation process in a homogeneous solution allows for more uniform titanium incorporation, which is beneficial for improving LFP performance.

[0003] Currently, most manufacturers of ferric phosphate use ferrous sulfate, a byproduct of titanium dioxide, as the iron source. Therefore, this byproduct contains a large amount of titanium. However, most manufacturers treat this titanium as an impurity, removing it along with other impurity ions by adding alkali, iron powder, or phosphoric acid, resulting in a waste of titanium resources. Alternatively, they directly oxidize the ferrous sulfate byproduct of titanium dioxide to obtain titanium-doped ferric phosphate. For example, CN120841464A discloses a method for preparing titanium-doped ferric phosphate using ferrous sulfate byproducts. This method involves dissolving the ferrous sulfate byproduct of titanium dioxide, adding phosphoric acid, oxidizing it with hydrogen peroxide, adjusting the pH with sodium carbonate, collecting the filtrate, and obtaining a solution containing ferrous sulfate and titanium oxysulfate, thus obtaining titanium-doped ferric phosphate. However, the removal efficiency for other impurity metal ions was not investigated. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing titanium-doped iron phosphate from ferrous sulfate, a byproduct of titanium dioxide, with high titanium element recovery rate and low impurity metal ion content.

[0005] Technical solution: The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, as described in this invention includes the following steps:

[0006] (1) Dissolve ferrous sulfate, a byproduct of titanium dioxide, in a solvent by heating to form a supersaturated ferrous sulfate solution;

[0007] (2) Add a precipitant to the supersaturated ferrous sulfate solution and react. After the reaction is completed, cool down to precipitate the precipitate. Separate the solid and liquid to obtain a mixed solid of ferrous sulfate crystals and titanium-containing precipitate and a saturated mother liquor of ferrous sulfate.

[0008] (3) Using the saturated mother liquor of ferrous sulfate as a solvent, repeat steps (1) and (2). Each time, ferrous sulfate crystals and titanium-containing precipitate mixed solids and saturated mother liquor of ferrous sulfate are obtained. The mixed solids obtained in each repetition and the mixed solids in step (2) are combined as the total mixed solids.

[0009] (4) The total mixed solid is dissolved in sulfuric acid to form an iron-titanium solution. Phosphoric acid, hydrogen peroxide and phosphate salt are added to the iron-titanium solution in sequence. After mixing, a titanium-doped iron phosphate precursor is obtained. The titanium-doped iron phosphate precursor is heated, aged, filtered, washed, dried and calcined to obtain the titanium-doped iron phosphate product.

[0010] In step (1), the mass ratio of the titanium dioxide byproduct ferrous sulfate to the solvent is 1-3:1. During the first cycle, the solvent is water, which can form a stable supersaturated ferrous sulfate solution while controlling the concentration of impurity ions such as Al, Mn, Mg, and Ti at an appropriate level. This ensures that the precipitation of impurity ions during the recrystallization of ferrous sulfate is within a controllable range, thereby effectively regulating the content of titanium and other impurities in the recrystallized ferrous sulfate. The heating and dissolution temperature is 50-70℃. Within this temperature range, the solubility of ferrous sulfate is effectively increased, thereby improving the precipitation rate of ferrous sulfate during the cooling process. However, excessively high heating temperatures will cause heptahydrate ferrous sulfate to lose its water of crystallization and transform into monohydrate ferrous sulfate, reducing solubility and increasing heating energy consumption.

[0011] Preferably, in step (1), the heating and dissolving time is 0.5-1.5h, and a suitable stirring time can make the ferrous sulfate fully dissolve.

[0012] In step (2), the precipitant is p-aminobenzoarsic acid, and its addition amount is 0.5-2% of the mass of ferrous sulfate by-product of titanium dioxide. p-Aminobenzoarsic acid is used to cause titanium elements to precipitate together in the form of titanium p-aminobenzoic acid precipitate during the recrystallization process of ferrous sulfate supersaturated solution. In acidic environment, some active sites of p-aminobenzoarsic acid are occupied by hydrogen ions, and its remaining active sites will preferentially combine with high-valence titanium ions to form precipitates. Therefore, it does not have enough active sites to trigger the precipitation of Al, Mn, Mg and other ions, so that the impurity ions remain in the saturated mother liquor of ferrous sulfate, realizing the efficient enrichment of ferrous ions and titanium ions, laying the foundation for the subsequent preparation of high-purity titanium-doped iron phosphate. The reaction time is 0.5-1h. Too short a reaction time will easily lead to insufficient reaction, while too long a reaction time will increase the amount of precipitation of other impurity ions, and at the same time increase energy consumption and time cost.

[0013] Preferably, in step (2), after the p-aminobenzoarsic acid is dissolved in pure water to form an aqueous solution of p-aminobenzoarsic acid, it is added to the supersaturated ferrous sulfate solution to improve its dispersibility in the supersaturated ferrous sulfate solution, so that the precipitate precipitated in the subsequent cooling precipitation process is more uniform.

[0014] In step (2), the cooling is uniform cooling at a rate of 0.2-1℃ / min, so that the solution is cooled to 25-28℃. Too fast a cooling rate can easily cause a large amount of crystals to precipitate out quickly, resulting in too many impurity ions being wrapped in the ferrous sulfate crystals during the recrystallization process.

[0015] In step (3), the repetition is repeated 4-6 times. The obtained saturated ferrous sulfate mother liquor is repeatedly used to dissolve ferrous sulfate, a byproduct of titanium dioxide. During the mother liquor circulation process, Ti element is continuously enriched, thereby controlling the amount of titanium doping. However, Al, Mn, Mg and other ions will also accumulate in the mother liquor as the number of cycles increases, resulting in an increase in the impurity content in the recrystallized ferrous sulfate crystals. Therefore, the number of mother liquor cycles should not be too high.

[0016] Preferably, in step (3), the concentration of ferrous sulfate crystals in the iron-containing solution is 1-2 mol / L. A suitable iron source concentration can control the nucleation rate, crystal size, and particle morphology of ferric phosphate crystals, thereby controlling the specific surface area and tap density of ferric phosphate.

[0017] In step (4), the sulfuric acid is dilute sulfuric acid with pH = 0.8-1.2, which ensures that the mixed solid of ferrous sulfate crystals and titanium-containing precipitate is fully dissolved, and that p-aminobenzoic acid exists in the solution in anionic form.

[0018] In step (4), the amount of phosphoric acid added is 0.05-0.15 times the molar amount of ferrous sulfate in the iron-titanium solution. This is used to supplement phosphorus and make iron phosphate have a good iron-phosphorus ratio to ensure the performance of lithium iron phosphate products. At the same time, the addition of phosphoric acid can effectively reduce the pH of the iron-containing solution, thereby inhibiting the hydrolysis and precipitation of titanium and making the titanium doping more uniform.

[0019] In step (4), the amount of hydrogen peroxide added is 0.5-0.7 times the molar amount of ferrous sulfate in the iron-titanium solution, which is used to completely oxidize ferrous ions to iron ions.

[0020] In step (4), the phosphate salt is ammonium dihydrogen phosphate, and its addition amount is 1.0-1.1 times the molar amount of ferrous sulfate in the iron-containing solution. It is used to precipitate iron ions and titanium ions to obtain titanium-doped iron phosphate precursor. p-Aminobenzoic acid is retained in the mother liquor after precipitation in the form of anion, and its volume is large, so it will not enter the titanium-doped iron phosphate lattice during the precipitation process, thus avoiding the introduction of impurity elements.

[0021] Preferably, in step (4), the ammonium dihydrogen phosphate is an aqueous solution with a concentration of 1.5 mol / L. A suitable concentration range can better control the precipitation rate of iron and titanium, thereby making the precipitation more uniform.

[0022] Preferably, in step (4), the mixing temperature is 45-55℃ and the time is 45-75min. Suitable parameters can enable ferric phosphate to have a suitable specific surface area and tap density.

[0023] Further, in step (4), the temperature for heating is 80-95℃ and the time is 30-90min; the aging time is 90-150min; and the calcination conditions are: calcination at 550-600℃ for 2-4h.

[0024] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: (1) The present invention enriches the iron and titanium elements in the titanium dioxide byproduct ferrous sulfate by recrystallization and co-precipitation. In the recrystallization process of ferrous sulfate, p-aminobenzoarsic acid, which selectively precipitates titanium ions, is added as a precipitant, so that other impurity ions remain in the mother liquor, and a mixed solid containing high-purity ferrous sulfate crystals and titanium precipitate is obtained. Moreover, the p-aminobenzoarsic acid has a large volume and will not enter the titanium-doped iron phosphate lattice in the subsequent precipitation process, thus avoiding the introduction of impurity elements in the post-processing process; (2) By controlling the number of mother liquor circulations in the recrystallization process, the concentration of titanium ions in the system can be regulated. The enrichment level, thereby controlling the amount of titanium co-precipitation during the recrystallization process of ferrous sulfate, thereby regulating the amount of titanium doping in iron phosphate; (3) Use dilute sulfuric acid to completely dissolve the mixed solid of ferrous sulfate crystals and titanium precipitate into a homogeneous solution. At this time, p-aminobenzoic acid exists in the solution in the form of anions. Then add phosphoric acid to supplement phosphorus elements and regulate pH to avoid rapid precipitation of titanium ions. After ferrous ions are oxidized to iron ions, add ammonium dihydrogen phosphate solution to make iron and titanium ions precipitate uniformly, improve the uniformity of titanium doping of iron phosphate, improve the performance of titanium doped iron phosphate products, and facilitate the preparation of lithium iron phosphate with high specific surface area and excellent electrochemical performance. Attached Figure Description

[0025] Figure 1 This is a scanning electron microscope (SEM) image of the titanium-doped iron phosphate prepared in Example 1 of the present invention. Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the embodiments and comparative examples. Unless otherwise stated, all reagents used are commercially available and are used directly without purification.

[0027] Example 1

[0028] The method for preparing titanium-doped iron phosphate from ferrous sulfate, a byproduct of titanium dioxide, as described in this embodiment includes the following steps:

[0029] (1) Weigh 2000g of ferrous sulfate, a byproduct of titanium dioxide, add 1000g of pure water, heat to 60℃, and stir for 1h until the solid is completely dissolved to form a supersaturated solution of ferrous sulfate.

[0030] (2) Weigh 10g of p-aminobenzoarsine (0.5% of the mass of ferrous sulfate by-product of titanium dioxide), dissolve it in pure water, add it to the above supersaturated ferrous sulfate solution, react for 1 hour, and then cool the solution to 25℃ at a rate of 0.5℃ / min. During the cooling process, the mixed solid of ferrous sulfate crystals and p-aminobenzoarsine titanium will continuously precipitate out. After the cooling is completed, the solution is separated into solid and liquid to obtain the mixed solid of ferrous sulfate crystals and p-aminobenzoarsine titanium and the saturated mother liquor of ferrous sulfate.

[0031] (3) Using the saturated mother liquor of ferrous sulfate as a solvent, repeat steps (1) and (2) five times (i.e. crystallize five times). Each time, a mixed solid of ferrous sulfate crystals and titanium p-aminobenzoic acid and saturated mother liquor of ferrous sulfate are obtained. The mixed solid obtained each time and the mixed solid in step (2) are combined as the total mixed solid.

[0032] (4) Dissolve the total mixed solids in dilute sulfuric acid at pH=0.8 to form an iron-titanium solution (with a ferrous ion concentration of 1.5 mol / L). Take 5 L of this iron-titanium solution (7.5 mol of ferrous sulfate) and add 43.24 g of 85% phosphoric acid (0.375 mol, with a molar ratio of 0.05 to ferrous sulfate) and 556 g of 27.5% hydrogen peroxide (4.50 mol, with a molar ratio of 0.6 to ferrous sulfate) sequentially. 5.5 L of 1.5 mol / L ammonium dihydrogen phosphate solution (8.25 mol molar, 1.1 molar ratio of ferrous sulfate) was stirred at 45 °C for 75 min to obtain a titanium-doped ferric phosphate precursor. The precursor was then heated to 95 °C and held for 90 min until the slurry turned white. After aging for another 90 min, the slurry was filtered, washed, and dried to obtain titanium-doped ferric phosphate dihydrate. This dihydrate was calcined at 580 °C for 3 h to obtain anhydrous titanium-doped ferric phosphate. The scanning electron microscope (SEM) image is shown below. Figure 1 As shown.

[0033] Example 2

[0034] The method for preparing titanium-doped iron phosphate from ferrous sulfate, a byproduct of titanium dioxide, as described in this embodiment includes the following steps:

[0035] (1) Weigh 3000g of ferrous sulfate, a byproduct of titanium dioxide, add 1000g of pure water, heat to 70℃, and stir for 1.5h until the solid is completely dissolved to form a supersaturated solution of ferrous sulfate.

[0036] (2) Weigh 30g of p-aminobenzoarsine (1% of the mass of ferrous sulfate by-product of titanium dioxide), dissolve it in pure water, add it to the above supersaturated ferrous sulfate solution, react for 0.75h, and then cool the solution to 28℃ at a rate of 1℃ / min. During the cooling process, the mixed solid of ferrous sulfate crystals and p-aminobenzoarsine titanium will continuously precipitate. After the cooling is completed, the solution is separated into solid and liquid to obtain the mixed solid of ferrous sulfate crystals and p-aminobenzoarsine titanium and the saturated mother liquor of ferrous sulfate.

[0037] (3) Using the saturated mother liquor of ferrous sulfate as a solvent, repeat steps (1) and (2) 5 times. Each time, a mixed solid of ferrous sulfate crystals and titanium p-aminobenzoic acid and saturated mother liquor of ferrous sulfate are obtained. The mixed solid obtained in each repetition and the mixed solid in step (2) are combined as the total mixed solid.

[0038] (4) Dissolve the total mixed solids in dilute sulfuric acid at pH=1.0 to form an iron-titanium solution (with a ferrous ion concentration of 1.2 mol / L). Take 5 L of this iron-titanium solution (6 mol of ferrous sulfate) and add 69.18 g of 85% phosphoric acid (0.6 mol, with a molar ratio of 0.1 to ferrous sulfate) and 371 g of 27.5% hydrogen peroxide (3 mol, with a molar ratio of 0.5 to ferrous sulfate). 4.2 L of 1.5 mol / L ammonium dihydrogen phosphate solution (6.3 mol molar, with a molar ratio of 1.05 to ferrous sulfate) was stirred at 50 °C for 60 min to obtain a titanium-doped iron phosphate precursor. The titanium-doped iron phosphate precursor was heated to 80 °C and held for 30 min until the slurry turned white. It was then aged for another 150 min, and after filtration, washing, and drying, titanium-doped iron phosphate dihydrate was obtained. Titanium-doped iron phosphate dihydrate was calcined at 550 °C for 4 h to obtain anhydrous titanium-doped iron phosphate.

[0039] Example 3

[0040] The method for preparing titanium-doped iron phosphate from ferrous sulfate, a byproduct of titanium dioxide, as described in this embodiment includes the following steps:

[0041] (1) Weigh 1000g of ferrous sulfate, a byproduct of titanium dioxide, add 1000g of pure water, heat to 50℃, and stir for 0.5h until the solid is completely dissolved to form a supersaturated solution of ferrous sulfate.

[0042] (2) Weigh 20g of p-aminobenzoarsine (2% of the mass of ferrous sulfate by-product of titanium dioxide), dissolve it in pure water, add it to the above supersaturated ferrous sulfate solution, react for 0.5h, and then cool the solution to 25℃ at a rate of 0.2℃ / min. During the cooling process, the mixed solid of ferrous sulfate crystals and p-aminobenzoarsine titanium will continuously precipitate. After the cooling is completed, the solution is separated into solid and liquid to obtain the mixed solid of ferrous sulfate crystals and p-aminobenzoarsine titanium and the saturated mother liquor of ferrous sulfate.

[0043] (3) Using the saturated mother liquor of ferrous sulfate as a solvent, repeat steps (1) and (2) 5 times. Each time, a mixed solid of ferrous sulfate crystals and titanium p-aminobenzoic acid and saturated mother liquor of ferrous sulfate are obtained. The mixed solid obtained in each repetition and the mixed solid in step (2) are combined as the total mixed solid.

[0044] (4) Dissolve the total mixed solids in dilute sulfuric acid at pH=1.2 to form an iron-titanium solution (where the ferrous ion concentration is 1 mol / L). Take 5 L of this iron-titanium solution (5 mol of ferrous sulfate) and add 86.47 g of 85% phosphoric acid (0.75 mol, with a molar ratio of 0.15 to ferrous sulfate) and 432.7 g of 27.5% hydrogen peroxide (3.5 mol, with a molar ratio of 0.15 to ferrous sulfate). 70) and 3.3 L of 1.5 mol / L ammonium dihydrogen phosphate solution (molar amount of 4.95 mol, molar ratio of ferrous sulfate to ferrous sulfate is 1.0) were stirred at 55 °C for 45 min to obtain titanium-doped iron phosphate precursor. The titanium-doped iron phosphate precursor was heated to 88 °C and kept at that temperature for 60 min until the slurry turned white. It was then aged for another 120 min, and then filtered, washed and dried to obtain dihydrate titanium-doped iron phosphate. The dihydrate titanium-doped iron phosphate was calcined at 600 °C for 2 h to obtain anhydrous titanium-doped iron phosphate.

[0045] Example 4: The difference from Example 1 is that the number of repetitions in step (3) is 4, that is, crystallization four times.

[0046] Example 5: The difference from Example 1 is that the number of repetitions in step (3) is 6, that is, crystallization six times.

[0047] Comparative Example 1: Compared with Example 1, after step (1), an appropriate amount of phosphoric acid was added to the supersaturated solution of ferrous sulfate, a byproduct of titanium dioxide, heated to 55°C and kept warm for 3 hours, and then filtered to obtain a clear ferrous sulfate solution after impurity removal. The clear solution was oxidized with hydrogen peroxide and used as an iron source to prepare iron phosphate, with other conditions being the same.

[0048] Comparative Example 2: Compared with Example 1, no precipitant was added in step (2), and the other steps were the same.

[0049] Comparative Example 3: Compared with Example 1, the sulfuric acid pH in step (4) is 2, and the other steps are the same.

[0050] Comparative Example 4: Compared with Example 1, ammonia was used as a precipitant in step (2).

[0051] Comparative Example 5: The difference from Example 1 is that the number of repetitions in step (3) is 1, that is, crystallization once.

[0052] Comparative Example 6: The difference from Example 1 is that the number of repetitions in step (3) is 2, that is, crystallization twice.

[0053] Comparative Example 7: The difference from Example 1 is that the number of repetitions in step (3) is 3, that is, crystallization three times.

[0054] The total ferrous sulfate and total titanium-containing precipitate obtained from the repeated use of saturated ferrous sulfate mother liquor in Examples 1-3 and Comparative Examples 1-4 were prepared into solutions with an iron concentration of 1 mol / L and subjected to ICP detection. The data are detailed in Table 1.

[0055] Table 1. Detection results of impurity content in ferrous sulfate crystals after recrystallization in the examples and comparative examples.

[0056] Depend on Figure 1 It can be seen that the primary particles of the anhydrous titanium-doped iron phosphate prepared in Example 1 of the present invention are small in size, uniform in size, and have good agglomeration. The secondary particles formed by their agglomeration have a loose and porous surface. Therefore, the titanium-doped iron phosphate has good performance.

[0057] As shown in Table 1, Examples 1-5 of this invention employ a combination of recrystallization and co-precipitation to enrich iron and titanium elements. This effectively removes metallic impurities from ferrous sulfate, a byproduct of titanium dioxide production. Simultaneously, due to the addition of the precipitant, titanium p-aminobenzoarsinate co-precipitates during the recrystallization process, resulting in a mixed solid of ferrous sulfate crystals and titanium p-aminobenzoarsinate. Furthermore, Examples 1-3 demonstrate that the titanium ion content in the recrystallized ferrous sulfate increases with the increase in the solid-liquid mass ratio during the feeding process. Comparative Example 1 uses phosphoric acid to remove impurities from the titanium dioxide byproduct ferrous sulfate, resulting in ferrous sulfate containing almost no titanium. Comparative Example 2, lacking a precipitant to precipitate titanium, yields recrystallized ferrous sulfate containing only a small amount of carried-out titanium, resulting in a low content. In Comparative Example 3, the high pH of the sulfuric acid prevents complete dissolution of the titanium-containing precipitate, thus some titanium remains in precipitate form, leading to a slightly lower titanium ion content in the solution. Comparative Example 4 uses ammonia as a precipitant, which cannot selectively precipitate Ti. As a result, impurity ions such as Al, Mn, and Mg all precipitate and enter the ferrous sulfate solution, leading to an excessive impurity content in the titanium-doped ferric phosphate, which fails to meet the requirements.

[0058] The total ferrous sulfate and total titanium precipitate obtained from the repeated use of saturated ferrous sulfate mother liquor in Examples 1, 4, 5 and Comparative Examples 5-7 were prepared into a solution with an iron concentration of 1 mol / L and subjected to ICP detection. The data are detailed in Table 2.

[0059] Table 2. Impurity content of ferrous sulfate crystals prepared by recrystallization from saturated ferrous sulfate mother liquor after different numbers of repetitions.

[0060] As shown in Table 2, with the increase in the number of recrystallization cycles of the saturated ferrous sulfate mother liquor, titanium elements in the mother liquor continuously accumulate, resulting in a continuous increase in the titanium content in the recrystallized ferrous sulfate. Therefore, the number of times the saturated ferrous sulfate mother liquor is recycled can effectively control the titanium content in the recrystallized ferrous sulfate crystals, thereby controlling the amount of titanium doping in titanium-doped ferric phosphate. At the same time, the content of other impurity elements also continuously increases due to enrichment. Therefore, if the number of mother liquor cycles is too high, the impurity element content in the recrystallized ferrous sulfate will be too high to meet the requirements for preparing ferric phosphate.

[0061] The physicochemical properties of the titanium-doped iron phosphate prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are detailed in Table 3.

[0062] Table 3 Performance Indicators and Impurity Content of Titanium-Doped Ferric Phosphate

[0063] As shown in Table 3, in Examples 1-3, the addition of p-aminobenzoic acid, a precipitant that only precipitates titanium ions, during the recrystallization of ferrous sulfate allowed other impurity ions to remain in the mother liquor. Through a combination of recrystallization and co-precipitation, iron and titanium elements were enriched, resulting in ferric phosphates with high titanium doping content and higher specific surface area, thus effectively improving the performance of ferric phosphate. Comparative Example 1 used ferrous sulfate after impurity removal with phosphoric acid to prepare ferric phosphate, and the finished product contained almost no titanium. In Comparative Example 2, no p-aminobenzoic acid was added during the recrystallization of ferrous sulfate, preventing titanium co-precipitation and significantly reducing the titanium content in the ferric phosphate. This demonstrates that the addition of p-aminobenzoic acid can effectively control the titanium doping content in ferric phosphate. In Comparative Example 3, the pH of the sulfuric acid was too high, failing to completely dissolve the titanium-containing precipitate. Titanium did not enter the ferric phosphate crystals in ionic form, resulting in poor doping uniformity, uneven ferric phosphate grain size, and a low specific surface area. Comparative Example 4 used ammonia as a precipitant, which caused impurity ions such as Al, Mn, and Mg to precipitate together. As a result, the content of impurity ions in titanium-doped iron phosphate increased, and the Al ion content even exceeded the specified range, which could not meet the requirements of titanium-doped iron phosphate products.

Claims

1. A method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide production, characterized in that, Includes the following steps: (1) Dissolve ferrous sulfate, a byproduct of titanium dioxide, in a solvent by heating to form a supersaturated ferrous sulfate solution; (2) Add a precipitant to the supersaturated ferrous sulfate solution and react. After the reaction is completed, cool down to precipitate the precipitate. Separate the solid and liquid to obtain a mixed solid of ferrous sulfate crystals and titanium-containing precipitate and a saturated mother liquor of ferrous sulfate. (3) Using the saturated mother liquor of ferrous sulfate as a solvent, repeat steps (1) and (2). Each time, ferrous sulfate crystals and titanium-containing precipitate mixed solids and saturated mother liquor of ferrous sulfate are obtained. The mixed solids obtained in each repetition and the mixed solids in step (2) are combined as the total mixed solids. (4) The total mixed solid is dissolved in sulfuric acid to form an iron-titanium solution. Phosphoric acid, hydrogen peroxide and phosphate salt are added to the iron-titanium solution in sequence. After mixing, a titanium-doped iron phosphate precursor is obtained. The titanium-doped iron phosphate precursor is heated, aged, filtered, washed, dried and calcined to obtain the titanium-doped iron phosphate product.

2. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (1), the mass ratio of the titanium dioxide byproduct ferrous sulfate to the solvent is 1-3:1, and the heating and dissolving temperature is 50-70℃.

3. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (2), the precipitant is p-aminobenzoic acid, and the amount added is 0.5-2% of the mass of ferrous sulfate, a by-product of titanium dioxide. The reaction time is 0.5-1h.

4. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (2), the cooling is uniform cooling, with a cooling rate of 0.2-1℃ / min.

5. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (3), the repetition is performed 4-6 times.

6. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (4), the sulfuric acid is dilute sulfuric acid with a pH of 0.8-1.

2.

7. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (4), the amount of phosphoric acid added is 0.05-0.15 times the molar amount of ferrous sulfate in the iron-titanium solution.

8. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (4), the amount of hydrogen peroxide added is 0.5-0.7 times the molar amount of ferrous sulfate in the iron-titanium solution.

9. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (4), the phosphate salt is ammonium dihydrogen phosphate, and the amount added is 1.0-1.1 times the molar amount of ferrous sulfate in the iron-titanium solution.

10. The method for preparing titanium-doped ferric phosphate from ferrous sulfate, a byproduct of titanium dioxide, according to claim 1, is characterized in that, In step (4), the mixing conditions are: temperature 45-55℃ and time 45-75min.

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