Method for preparing battery grade ferrous sulfate from titanium dioxide by-product ferrous sulfate

Abstract

The invention discloses a method for preparing battery-grade ferrous sulfate from a titanium dioxide byproduct ferrous sulfate, which comprises the following steps: (1) heating and dissolving the titanium dioxide byproduct ferrous sulfate in a solvent to form a ferrous sulfate supersaturated solution; (2) sequentially adding iron powder and sulfuric acid into the ferrous sulfate supersaturated solution, and carrying out reduction reaction; (3) adding a chelating agent into the solution obtained in the step (2), mixing, filtering, cooling, and carrying out solid-liquid separation to obtain recrystallized ferrous sulfate crystals and recrystallized saturated mother liquor; and (4) heating and dissolving the recrystallized ferrous sulfate crystal into a supersaturated solution by using a solvent, cooling and crystallizing, and repeating the recrystallization step to obtain the battery-grade ferrous sulfate. According to the method, a chemical chelation method and a recrystallization method are combined, sodium lignin sulfonate is added into the mother liquor as a chelating agent before the first recrystallization, the sodium lignin sulfonate and metal impurity ions form a stable compound, meanwhile, enrichment of the impurity ions in the mother liquor circulation process is avoided, and the purity of ferrous sulfate crystals is improved.

Description

Technical Field

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

[0002] Ferrous sulfate heptahydrate is a major byproduct in the production of titanium dioxide and is widely used in industries such as chemicals and new energy. However, this byproduct contains a large amount of impurity metal elements such as Mn, Mg, Ti, Al, and Co, and cannot be used directly in the production of chemicals and new energy products. It needs to be purified before it can be used.

[0003] Currently, the main methods for purifying ferrous sulfate, a byproduct of titanium dioxide production, are chemical precipitation and recrystallization. Chemical precipitation primarily removes impurity ions by adding fluorides, sulfides, phosphoric acid, or alkalis. For example, CN107640790A uses ammonia and flocculants to precipitate impurity ions and prepare high-purity ferrous sulfate crystals, but its effectiveness in removing impurity ions is limited. Recrystallization utilizes the solubility difference between ferrous sulfate and other impurity ions, employing a heating-dissolution and cooling-crystallization process to precipitate ferrous sulfate as crystals from the solution. However, traditional recrystallization methods typically require lowering the temperature to around 5°C to ensure a high ferrous sulfate precipitation rate, increasing energy costs. Furthermore, one or two recrystallization cycles cannot completely remove impurity ions, leaving the finished ferrous sulfate product with a high impurity ion content, failing to meet the requirements for battery-grade ferrous sulfate. Summary of the Invention

[0004] Purpose of the invention: The purpose of this invention is to provide a method for preparing battery-grade ferrous sulfate from ferrous sulfate, a byproduct of titanium dioxide.

[0005] Technical solution: The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to the present 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 iron powder and sulfuric acid sequentially to the supersaturated ferrous sulfate solution to induce a reduction reaction;

[0008] (3) Add a chelating agent to the solution obtained in step (2), mix, filter and cool, and separate the solid and liquid to obtain recrystallized ferrous sulfate crystals and recrystallized saturated mother liquor;

[0009] (4) The recrystallized ferrous sulfate crystals are dissolved in a solvent by heating to form a supersaturated solution, and then cooled to crystallize. The recrystallization step is repeated to obtain battery-grade ferrous sulfate.

[0010] In step (1), the mass ratio of the titanium dioxide byproduct ferrous sulfate to the solvent is 1-3:1, which can control the concentration of impurity ions Al, Mn, Mg and Ti at an appropriate level while forming a stable supersaturated ferrous sulfate solution, and keep the co-precipitation of impurity ions at a low level during the crystallization process, thereby reducing the impurity ion content in ferrous sulfate.

[0011] In step (1), the heating and dissolving temperature is 50-70℃. Within this temperature range, the solubility of ferrous sulfate is effectively increased, thereby increasing the precipitation rate of ferrous sulfate during the cooling process. However, excessively high heating temperatures will cause ferrous sulfate heptahydrate to lose its water of crystallization and transform into ferrous sulfate monohydrate, reducing solubility and increasing heating energy consumption.

[0012] 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.

[0013] In step (2), the amount of iron powder added is 1-2% of the mass of ferrous sulfate, a byproduct of titanium dioxide, and is used to reduce the ferric iron in the ferrous sulfate byproduct of titanium dioxide, so as to avoid the ferric ions reacting with the chelating agent to reduce the removal rate of impurity ions and cause excessive impurity ions to be introduced during the recrystallization process.

[0014] In step (2), the amount of sulfuric acid added is to adjust the pH of the supersaturated ferrous sulfate solution to 0.5-1.5. The addition of sulfuric acid can lower the pH of the system, avoid the generation of ferric hydroxide and inhibit the oxidation of ferrous ions. The lower pH can also effectively inhibit the introduction of impurity ions during the crystallization process of ferrous sulfate, thereby improving the purity of ferrous sulfate. In addition, sulfate ions can reduce the solubility of ferrous sulfate during the subsequent recrystallization process, thereby increasing the precipitation rate of ferrous sulfate.

[0015] In step (2), the reduction reaction time is 0.5-1.5h. Too short a mixing time can easily lead to insufficient reduction of ferric ions by iron powder, resulting in residual ferric ions; too long a reaction time will increase energy consumption and time costs.

[0016] In step (3), the chelating agent is sodium lignosulfonate. The sulfonic acid group in its structure can attract metal impurity ions such as Ti, Mn, and Mg in the solution through electrostatic attraction. At the same time, the phenolic hydroxyl and alcoholic hydroxyl groups it contains can further chelate with the metal impurity ions to form a stable compound and precipitate it out of the solution, thereby reducing the content of metal impurity ions in the solution. The polymer skeleton of sodium lignosulfonate can maintain its stability in an acidic environment, avoid the redissolution of metal ions, and improve the purity of the recrystallized ferrous sulfate crystals.

[0017] Preferably, in step (3), the sodium lignosulfonate is dissolved in pure water to form an aqueous solution of sodium lignosulfonate, and then added to the solution obtained in step (2) to improve its dispersibility in the solution, so that it can fully contact the metal impurity ions and improve the impurity removal efficiency.

[0018] In step (3), the amount of chelating agent added is 1-3% of the mass of ferrous sulfate, a byproduct of titanium dioxide. When the amount of chelating agent is insufficient, the effect of removing metal impurity ions such as Ti, Mn, and Mg is limited. When too much chelating agent is added, the excess reaction sites will react with ferrous ions, resulting in a waste of ferrous ions and chelating agent resources.

[0019] In step (3), the filtration is hot filtration, and the hot filtration temperature is ≥45℃ to avoid the precipitation of ferrous sulfate crystals.

[0020] Preferably, in step (3), the mixing time is 1-3 hours. When the mixing time is too short, the chelating agent does not come into sufficient contact with the metal impurity ions and cannot effectively remove metal impurity ions such as Ti, Mn, and Mg.

[0021] Preferably, in step (3), the cooling is natural cooling to 20-30°C. A higher cooling endpoint temperature means lower energy consumption and is beneficial to reducing energy consumption in the next heating process. At the same time, the natural cooling process is slow, which is beneficial to avoid the precipitation of impurity elements.

[0022] Preferably, in step (3), the cooling process can be moderately stirred to prevent the ferrous sulfate crystals from becoming too large and encapsulating too many impurity ions.

[0023] Preferably, in step (3), the recrystallization of ferrous sulfate crystals further includes a washing process, wherein the washing reagent is water or ethanol, to wash away the residual mother liquor on the surface of the ferrous sulfate crystals.

[0024] Preferably, in step (3), the first recrystallization saturated mother liquor is diluted with ethanol as a poor solvent, so that the ferrous sulfate in it precipitates out naturally and the mother liquor is discarded; or the first recrystallization saturated mother liquor is diluted with pure water and precipitated with ammonia or phosphoric acid, the precipitate is used for the preparation of ferric phosphate and the mother liquor is discarded.

[0025] In step (4), the number of repeated recrystallization steps is greater than or equal to 3 times, and when the total recrystallization is N, the saturated mother liquor obtained in the N+1th recrystallization is used to dissolve the ferrous sulfate crystals obtained in the N-1th recrystallization in the next round of preparation of battery-grade ferrous sulfate; wherein the saturated mother liquor obtained in the second recrystallization is used to dissolve the titanium dioxide by-product ferrous sulfate in step (1) in the next round of preparation of battery-grade ferrous sulfate; the repeated use is used to remove the metal impurity ions co-precipitated by the ferrous sulfate crystals during the recrystallization process, thereby improving the purity of the ferrous sulfate crystals; the gradient recycling of the mother liquor can effectively avoid the enrichment of impurity ions during the mother liquor recycling process, and improve the utilization rate of iron ions and reduce costs.

[0026] Preferably, in step (4), the solvent used for heating and dissolving during the final recrystallization is water.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant effects: (1) Combining chemical chelation and recrystallization, a chelating agent is added to the mother liquor before the first recrystallization to effectively remove metal impurity ions and improve the purity of ferrous sulfate crystals; (2) Using sodium lignosulfonate as a chelating agent, it forms a stable compound with metal impurity ions such as Ti, Mn, and Mg, which can be separated by simple filtration, reducing the impurity ion content in the mother liquor and keeping the impurity ions in the finished ferrous sulfate at an extremely low level; (3) Using mother liquor gradient circulation, it effectively avoids the enrichment of impurity ions during the mother liquor circulation process; (4) Using a lower heating temperature and a higher cooling endpoint temperature during multiple recrystallization processes reduces the energy consumption cost of the recrystallization process. Attached Figure Description

[0028] Figure 1 This is a flowchart of the present invention;

[0029] Figure 2 The image shows the XRD pattern of the battery-grade ferrous sulfate prepared in Example 1. Detailed Implementation

[0030] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings.

[0031] Example 1

[0032] The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate as described in this embodiment includes the following steps:

[0033] (1) Weigh 3000g of titanium dioxide byproduct ferrous sulfate, add 1000g of pure water, heat to 70℃, stir for 1.5h until the raw material is completely dissolved to form a supersaturated ferrous sulfate solution;

[0034] (2) Add 60g of iron powder to the supersaturated ferrous sulfate solution, stir for 1.5h to allow it to undergo a reduction reaction, and then add sulfuric acid to adjust the pH to 0.5;

[0035] (3) Add an aqueous solution containing 45g of sodium lignosulfonate to the solution obtained in step (2), stir for 1 hour, filter the solution while it is hot, and let the filtrate cool naturally to 30°C, stirring moderately during the cooling process. After cooling, separate the solid and liquid to obtain ferrous sulfate crystals and saturated mother liquor from the first recrystallization. Use a small amount of pure water or ethanol to wash away the residual mother liquor on the surface of the ferrous sulfate crystals. After precipitating ferrous sulfate crystals from the saturated mother liquor from the first recrystallization using ethanol as a poor solvent, discard the mother liquor.

[0036] (4) The recrystallized ferrous sulfate crystals are dissolved in pure water by heating to form a supersaturated solution, then cooled and crystallized. This recrystallization is repeated three times. The resulting fourth recrystallized ferrous sulfate crystal is battery-grade ferrous sulfate, and its XRD pattern is shown below. Figure 2 As shown. In the three repeated recrystallization processes, the saturated mother liquor of the second recrystallization, the ferrous sulfate crystals of the second recrystallization, the saturated mother liquor of the third recrystallization, the ferrous sulfate crystals of the third recrystallization, the saturated mother liquor of the fourth recrystallization, and the ferrous sulfate crystals of the fourth recrystallization are obtained. The saturated mother liquors of the second, third, and fourth recrystallizations can be used for the mother liquor gradient cycle of the next round of preparing battery-grade ferrous sulfate. Specifically, in the next round of preparing battery-grade ferrous sulfate, the saturated mother liquor of the second recrystallization in the first round is used as a solvent to dissolve the titanium dioxide byproduct ferrous sulfate in step (1); in step (4), the ferrous sulfate crystals of the first recrystallization are dissolved in the saturated mother liquor of the third recrystallization in the first round and then recrystallized for the second time; the ferrous sulfate crystals of the second recrystallization are dissolved in the saturated mother liquor of the fourth recrystallization in the first round and then recrystallized for the third time; the ferrous sulfate crystals of the third recrystallization are dissolved in pure water and then recrystallized for the fourth time.

[0037] Example 2

[0038] The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate as described in this embodiment includes the following steps:

[0039] Weigh 2000g of ferrous sulfate, a byproduct of titanium dioxide, add 1000g of the saturated mother liquor from the second recrystallization in Example 1, heat to 60°C, and stir for 1 hour until the raw material is completely dissolved to form a supersaturated ferrous sulfate solution.

[0040] Add 30g of iron powder to the supersaturated ferrous sulfate solution and stir for 1 hour to allow a reduction reaction to occur. Then add sulfuric acid to adjust the pH to 1.0.

[0041] (3) Add an aqueous solution containing 40g of sodium lignosulfonate to the solution obtained in step (2), stir for 2 hours, filter the solution while it is hot, and let the filtrate cool naturally to 20°C, stirring moderately during the cooling process. After cooling, separate the solid and liquid to obtain the first recrystallization ferrous sulfate crystals and the first recrystallization saturated mother liquor. Use a small amount of pure water or ethanol to wash away the residual mother liquor on the surface of the ferrous sulfate crystals. After diluting the first recrystallization saturated mother liquor with pure water, add ammonia water as a precipitant to precipitate the ferrous sulfate crystals, and then discard the mother liquor.

[0042] (4) The recrystallized ferrous sulfate crystals are dissolved in pure water to form a supersaturated solution, then cooled and crystallized. This recrystallization is repeated three times. The resulting fourth recrystallized ferrous sulfate crystals are battery-grade ferrous sulfate. In the three repeated recrystallization processes, the first recrystallized ferrous sulfate crystals are dissolved in the saturated mother liquor from the third recrystallization in Example 1, and then recrystallized a second time to obtain a second saturated mother liquor. The second recrystallized ferrous sulfate crystals are dissolved in the saturated mother liquor from the fourth recrystallization in Example 1, and then recrystallized a third time to obtain a third saturated mother liquor. The third recrystallized ferrous sulfate crystals are dissolved in pure water, and then recrystallized a fourth time to obtain a fourth saturated mother liquor.

[0043] Example 3

[0044] The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate as described in this embodiment includes the following steps:

[0045] (1) Weigh 1000g of ferrous sulfate, a byproduct of titanium dioxide, add 1000g of the second recrystallization saturated mother liquor from Example 2, heat to 50°C, and stir for 0.5h until the raw material is completely dissolved to form a supersaturated ferrous sulfate solution.

[0046] (2) Add 10g of iron powder to the supersaturated ferrous sulfate solution, stir for 0.5h to allow it to undergo a reduction reaction, and then add sulfuric acid to adjust the pH to 1.5;

[0047] (3) Add an aqueous solution containing 10g of sodium lignosulfonate to the solution obtained in step (2), stir for 1 hour, filter the solution while it is hot, and let the filtrate cool naturally to 25°C, stirring moderately during the cooling process. After cooling, separate the solid and liquid to obtain ferrous sulfate crystals and saturated mother liquor from the first recrystallization. Use a small amount of pure water or ethanol to wash away the residual mother liquor on the surface of the ferrous sulfate crystals. After diluting the saturated mother liquor from the first recrystallization with pure water, add phosphoric acid as a precipitant to precipitate the ferrous sulfate crystals, and then discard the mother liquor.

[0048] (4) The recrystallized ferrous sulfate crystals are dissolved in pure water to form a supersaturated solution, then cooled and crystallized. This recrystallization is repeated three times. The resulting fourth recrystallized ferrous sulfate crystals are battery-grade ferrous sulfate. In the three repeated recrystallization processes, the first recrystallized ferrous sulfate crystals are dissolved in the saturated mother liquor from the third recrystallization in Example 2, and then recrystallized a second time to obtain a second saturated mother liquor. The second recrystallized ferrous sulfate crystals are dissolved in the saturated mother liquor from the fourth recrystallization in Example 2, and then recrystallized a third time to obtain a third saturated mother liquor. The third recrystallized ferrous sulfate crystals are dissolved in pure water, and then recrystallized a fourth time to obtain a fourth saturated mother liquor.

[0049] Example 4

[0050] The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate as described in this embodiment includes the following steps:

[0051] (1) Weigh 2000g of ferrous sulfate, a byproduct of titanium dioxide, add 1000g of the saturated mother liquor from the second recrystallization in Example 3, heat to 60°C, and stir for 1 hour until the raw material is completely dissolved to form a supersaturated ferrous sulfate solution.

[0052] (2) Add 30g of iron powder to the supersaturated ferrous sulfate solution, stir for 1h to allow it to undergo a reduction reaction, and then add sulfuric acid to adjust the pH to 1.0;

[0053] (3) Add an aqueous solution containing 40g of sodium lignosulfonate to the solution obtained in step (2), stir for 2 hours, filter the solution while it is hot, and let the filtrate cool naturally to 20°C, stirring moderately during the cooling process. After cooling, separate the solid and liquid to obtain ferrous sulfate crystals and saturated mother liquor from the first recrystallization. Use a small amount of pure water or ethanol to wash away the residual mother liquor on the surface of the ferrous sulfate crystals. After precipitating ferrous sulfate crystals from the saturated mother liquor from the first recrystallization using ethanol as a poor solvent, discard the mother liquor.

[0054] (4) The recrystallized ferrous sulfate crystals are dissolved in pure water to form a supersaturated solution, then cooled and crystallized. This recrystallization is repeated four times. The resulting fifth recrystallized ferrous sulfate crystal is battery-grade ferrous sulfate. During the four repeated recrystallization processes, the first recrystallized ferrous sulfate crystal is dissolved in the saturated mother liquor from the third recrystallization in Example 3, and then recrystallized a second time to obtain a second recrystallization saturated mother liquor; the second recrystallized ferrous sulfate crystal is dissolved in the saturated mother liquor from the fourth recrystallization in Example 3, and then recrystallized a third time to obtain a third recrystallization saturated mother liquor; the third recrystallized ferrous sulfate crystal is dissolved in pure water, and then recrystallized a fourth time to obtain a fourth recrystallization saturated mother liquor; the fourth recrystallized ferrous sulfate crystal is dissolved in pure water, and then recrystallized a fifth time to obtain a fifth recrystallization saturated mother liquor. In the four repeated recrystallization processes, the following are obtained: second recrystallization saturated mother liquor, second recrystallization ferrous sulfate crystals, third recrystallization saturated mother liquor, third recrystallization ferrous sulfate crystals, fourth recrystallization saturated mother liquor, fourth recrystallization ferrous sulfate crystals, fifth recrystallization saturated mother liquor, and fifth recrystallization ferrous sulfate crystals. The second, third, fourth, and fifth recrystallization saturated mother liquors can be used for the next round of mother liquor gradient recycling to prepare battery-grade ferrous sulfate. Specifically, in the second round of repeated recrystallization, the second recrystallization saturated mother liquor from the first round is used as a solvent to dissolve the titanium dioxide byproduct ferrous sulfate in step (1). In step (4), the first recrystallization ferrous sulfate crystals are dissolved in the third recrystallization saturated mother liquor from the first round and then recrystallized for the second time. The second recrystallization ferrous sulfate crystals are dissolved in the fourth recrystallization saturated mother liquor from the first round and then recrystallized for the third time. The third recrystallization ferrous sulfate crystals are dissolved in the fifth recrystallization saturated mother liquor from the first round and then recrystallized for the fourth time. The fourth recrystallization ferrous sulfate crystals are dissolved in pure water and then recrystallized for the fifth time.

[0055] Comparative Example 1: Compared with Example 2, the number of recrystallizations in step (4) of Comparative Example 1 is repeated twice, and the rest of the operations are the same (that is, after obtaining the first recrystallized ferrous sulfate crystals and the first recrystallization saturated mother liquor in step (4), the first recrystallized ferrous sulfate crystals are dissolved in the third recrystallization saturated mother liquor in Example 1 to form a supersaturated solution, and then cooled to crystallize, and then the second recrystallization is carried out. The obtained second recrystallized ferrous sulfate crystals are dissolved in pure water and then the third recrystallization is carried out. The obtained third recrystallized ferrous sulfate crystals are the ferrous sulfate finished product).

[0056] Comparative Example 2: Compared with Example 2, sodium lignosulfonate was not introduced before the first recrystallization process in Comparative Example 2, and the rest of the operations were the same.

[0057] Comparative Example 3: Compared with Example 2, the recrystallization process in Comparative Example 3 used ammonia as a precipitant, while the rest of the operations were the same.

[0058] Comparative Example 4: Compared with Example 2, the recrystallization process in Comparative Example 4 did not involve the saturated mother liquor being used in stages. Instead, the mother liquor that had already been circulated four times in the same crystallization process was used for recrystallization, and the rest of the operations were the same.

[0059] The ferrous sulfate products obtained in the examples and comparative examples were subjected to ICP testing, and the data are detailed in Table 1.

[0060] Table 1. Detection Results of Ferrous Sulfate Impurity Content in Finished Battery-Grade Products Element content (unit: ppm) raw material Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Co 41.352 3.119 3.210 3.131 0.855 7.542 4.523 1.315 11.472 Cu 3.415 0 0 0 0 0 0.087 0 0 Ni 17.683 0.218 0.124 0.231 0.093 0.961 0.558 0.281 3.328 Al 34.634 0 0 0 0 0 0.45 0 0 Cr 1.325 0 0 0 0 0 0.056 0 0.01 Zn 24.742 0.531 0.213 1.243 0 1.971 0.995 0.632 3.515 Mg 4020.458 2.748 2.851 3.311 1.135 81.762 101.510 18.425 344.197 Mn 885.157 2.235 1.253 2.261 0.215 29.06 48.946 7.813 71.908 Pb 3.382 0.315 0.243 0.613 0 2.100 0.432 0.192 1.818 Ti 2343.257 0.238 0.246 0.662 0 2.461 16.652 0.153 17.175 Na 14.459 0.527 0.423 0.436 0.177 0 7.362 0.117 2.361 K 6.425 0.114 0.314 0.247 0.152 4.121 2.617 0.152 4.067 Ca 65.355 2.057 3.214 3.510 1.263 9.432 9.979 1.352 2.645

[0061] Depend on Figure 2 It can be seen that the battery-grade ferrous sulfate crystals have high purity, good crystallinity, and peak positions consistent with those on the standard card, and do not contain obvious impurities.

[0062] As can be seen from the data in Table 1, the impurity content in ferrous sulfate after four recrystallizations in Examples 1-3 and five recrystallizations in Example 4 is at an extremely low level, meeting the requirements for battery-grade ferrous sulfate. The gradient circulation of saturated mother liquor in Examples 2-4 can effectively avoid the enrichment of impurity ions, so that the impurity content of ferrous sulfate after recrystallization remains at a low level. The recycling of mother liquor effectively avoids the loss of raw materials.

[0063] In Comparative Example 1, when ferrous sulfate was recrystallized three times, although the impurity content was greatly reduced, there was still a high Mg content, which did not meet the requirements for battery-grade ferrous sulfate.

[0064] Comparative Example 2, which did not contain sodium lignosulfonate, had a higher content of Mg, Mn, and Ti.

[0065] Comparative Example 3 uses ammonia as a purifying agent. Although it can remove most of the impurity ions, the ammonia purifying process increases the pH of the solution, making ferrous ions easier to oxidize to ferric ions and form ferric hydroxide precipitate. This results in a decrease in the ferrous ion concentration in the solution and a decrease in the yield of ferrous sulfate during recrystallization. At the same time, the increase in pH also makes it easier for impurity ions to precipitate, resulting in an increase in the impurity content in the recrystallized ferrous sulfate.

[0066] Comparative Example 4 used mother liquor that had been reused more than four times for recrystallization. Due to the excessive enrichment of impurities Mn, Mg, and Ti ions, the finished ferrous sulfate contained too many Mn, Mg, and Ti ions, which could not meet the requirements for battery-grade ferrous sulfate.

Claims

1. A method for preparing battery-grade ferrous sulfate 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 iron powder and sulfuric acid sequentially to the supersaturated ferrous sulfate solution to induce a reduction reaction; (3) Add a chelating agent to the solution obtained in step (2), mix, filter and cool, and separate the solid and liquid to obtain recrystallized ferrous sulfate crystals and recrystallized saturated mother liquor; (4) The recrystallized ferrous sulfate crystals are dissolved in a solvent by heating to form a supersaturated solution, and then cooled to crystallize. The recrystallization step is repeated to obtain battery-grade ferrous sulfate.

2. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (1), the mass ratio of the titanium dioxide byproduct ferrous sulfate to the solvent is 1-3:

1.

3. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (1), the heating and melting temperature is 50-70℃.

4. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (2), the amount of iron powder added is 1-2% of the mass of ferrous sulfate, a byproduct of titanium dioxide.

5. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (2), the amount of sulfuric acid added is to adjust the pH of the supersaturated ferrous sulfate solution to 0.5-1.

5.

6. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (2), the reduction reaction takes 0.5-1.5 hours.

7. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (3), the chelating agent is sodium lignosulfonate.

8. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1 or 7, characterized in that, In step (3), the amount of chelating agent added is 1-3% of the mass of ferrous sulfate, a byproduct of titanium dioxide.

9. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (3), the filtration is performed while the filter is still hot.

10. The method for preparing battery-grade ferrous sulfate from titanium dioxide byproduct ferrous sulfate according to claim 1, characterized in that, In step (4), the number of repeated recrystallizations is greater than or equal to 3 times, and when the total recrystallization is N, the recrystallization saturated mother liquor obtained in the N+1th time is used to dissolve the ferrous sulfate crystals obtained in the N-1th time in the next round of preparing battery-grade ferrous sulfate; wherein the recrystallization saturated mother liquor obtained in the second time is used to dissolve the titanium dioxide byproduct ferrous sulfate in step (1) in the next round of preparing battery-grade ferrous sulfate.

Images