Method for preparing battery-grade ferric phosphate using waste ferrous chloride solution and its application

Abstract

The present invention relates to the field of waste liquid treatment technology, and in particular, to a method for preparing battery-grade iron phosphate using waste secondary ferrous chloride solution and its application. The method comprises the following steps: adding a metallic iron material to the waste secondary ferrous chloride solution, performing a first impurity removal reaction, and obtaining a first impurity removal liquid; adding a phosphate ion-containing solution and an alkali solution to the first impurity removal liquid, and then performing solid-liquid separation to obtain a ferrous chloride solution; mixing the ferrous chloride solution with a phosphate solution and an oxidant and performing a synthesis reaction, and then performing solid-liquid separation to obtain iron phosphate dihydrate; during the synthesis reaction, the pH of the mixed material is 1.5 to 2.5; and the iron phosphate dihydrate is calcined to obtain the battery-grade iron phosphate. The method uses waste secondary ferrous chloride solution as a raw material to prepare battery-grade iron phosphate, and while the waste secondary ferrous chloride solution is converted into high-value resources, it avoids the pollution of the waste liquid to the environment and reduces the processing cost.

Description

Technical Field

[0001] The invention relates to the technical field of waste liquid treatment, and in particular to a method for preparing battery-grade ferric phosphate by utilizing waste paraferrous chloride solution and application thereof. Background Art

[0002] In the process of producing titanium dioxide by chloride process, a large amount of waste liquid is produced, the main component of which is ferrous chloride, which also contains a large amount of impurity ions such as hydrogen ions, manganese ions, aluminum ions, etc. If the waste liquid is discharged directly without treatment, it is easy to cause environmental pollution. Using treatment agent to treat it before discharge increases the treatment cost on the one hand, and causes waste of resources on the other hand.

[0003] At present, the waste ferrous chloride solution generated in the production process of titanium dioxide by the chloride process is treated by the following method: the waste liquid is neutralized with lime milk to obtain a precipitate whose main component is ferric hydroxide, and the waste residue after separation and washing is directly transported to the slag yard for centralized stacking. The stacking requires a large amount of land, which will increase the stacking cost of the enterprise and have an impact on the environment. Therefore, it is of great significance to provide a method for resource recovery of waste liquid of titanium dioxide by the chloride process.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The first object of the present invention is to provide a method for preparing battery-grade ferric phosphate using waste ferrous chloride solution. The method uses the waste ferrous chloride solution as a raw material to prepare battery-grade ferric phosphate with high added value. While the waste ferrous chloride solution is converted into high-value resources, the waste liquid is prevented from causing pollution to the environment and the processing cost is reduced.

[0006] The second object of the present invention is to provide the use of battery-grade iron phosphate prepared by the method for preparing battery-grade iron phosphate using waste secondary ferrous chloride solution as described above in lithium-ion batteries.

[0007] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0008] The present invention provides a method for preparing battery-grade ferric phosphate by using waste paraferrous chloride solution, comprising the following steps:

[0009] Adding metallic iron material to the waste secondary ferrous chloride solution, performing a first impurity removal reaction, removing iron ions, chromium ions and vanadium ions, and obtaining a first impurity-removed liquid; wherein the waste secondary ferrous chloride solution comprises waste liquid generated in the production process of titanium dioxide by the chloride process, and the main components of the waste secondary ferrous chloride solution include ferrous ions, iron ions, chloride ions, aluminum ions, chromium ions and vanadium ions;

[0010] Adding a phosphate ion-containing solution and an alkali solution to the first impurity-removing liquid to perform a second impurity-removing reaction to remove aluminum ions, chromium ions and vanadium ions to obtain a second impurity-removing liquid; after solid-liquid separation of the second impurity-removing liquid, a ferrous chloride solution is obtained;

[0011] The ferrous chloride solution is mixed with a phosphate solution and an oxidant to undergo a synthesis reaction, followed by solid-liquid separation to obtain ferric phosphate dihydrate; wherein during the synthesis reaction, the pH of the mixture is 1.5 to 2.5;

[0012] The battery-grade iron phosphate is obtained by calcining the iron phosphate dihydrate.

[0013] Preferably, the metallic iron material comprises elemental iron and / or reduced ilmenite;

[0014] Preferably, during the first impurity removal reaction, the temperature of the mixed material is 20 to 90° C.;

[0015] Preferably, the first impurity removal reaction time is 0.5 to 2 hours;

[0016] Preferably, the first impurity removal reaction is performed until the pH of the mixed material is 2-3.

[0017] Preferably, the solution containing phosphate ions comprises a phosphoric acid solution and / or a phosphate solution; preferably, the phosphate solution comprises at least one of a sodium phosphate solution, a sodium monohydrogen phosphate solution and a disodium hydrogen phosphate solution;

[0018] Preferably, the volume of the solution containing phosphate ions is 0.1% to 0.5% of the volume of the waste ferrous chloride solution.

[0019] Preferably, the alkali solution comprises at least one of an aqueous ammonia solution, a sodium hydroxide solution, a potassium hydroxide solution, a sodium bicarbonate solution and a sodium carbonate solution;

[0020] Preferably, the pH of the mixed material after the alkali solution is added is 4.0-4.5.

[0021] Preferably, during the second impurity removal reaction, the temperature of the mixed material is 20 to 90°C;

[0022] Preferably, the second impurity removal reaction time is 0.5 to 2 hours.

[0023] Preferably, the phosphate solution used in the synthesis reaction comprises sodium monohydrogen phosphate solution and / or disodium hydrogen phosphate solution;

[0024] Preferably, the mass fraction of the phosphate solution used in the synthesis reaction is 8% to 15%.

[0025] Preferably, the oxidant comprises hydrogen peroxide;

[0026] Preferably, the molar ratio of the iron element in the ferrous chloride solution, the phosphorus element in the phosphate and the H2O2 in the hydrogen peroxide is 1:1:1.1-2.

[0027] Preferably, during the synthesis reaction, the temperature of the mixed material is 20 to 95°C;

[0028] Preferably, the synthesis reaction time is 2 to 5 hours.

[0029] Preferably, the calcination temperature is 480-580° C., and the calcination time is 1-4 hours.

[0030] The present invention also provides an application of the battery-grade iron phosphate prepared by the method for preparing battery-grade iron phosphate using waste secondary ferrous chloride solution as described above in a lithium-ion battery.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The method for preparing battery-grade ferric phosphate by using waste secondary ferrous chloride solution provided by the present invention can meet the index requirements of battery-grade ferric phosphate, and can make high-value resource of waste secondary ferrous chloride solution, reduce the pollution of waste liquid to the environment, and reduce the environmental protection pressure of chlorination process production line. DETAILED DESCRIPTION

[0033] The technical scheme of the present invention will be clearly and completely described below in conjunction with specific embodiments, but it will be appreciated by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work, all belong to the scope of protection of the present invention. If specific conditions are not indicated in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0034] In a first aspect, the present invention provides a method for preparing battery-grade ferric phosphate using waste ferrous chloride solution, comprising the following steps:

[0035] Metallic iron material is added to the waste secondary ferrous chloride solution to carry out a first impurity removal reaction to remove iron ions, chromium ions and vanadium ions to obtain a first impurity-removed liquid.

[0036] Among them, the waste secondary ferrous chloride solution includes waste liquid generated in the production process of titanium dioxide by the chloride process. The main components of the waste secondary ferrous chloride solution include ferrous ions (divalent iron ions), trivalent iron ions, chloride ions, aluminum ions, chromium ions and vanadium ions, and also contain a large amount of hydrogen ions.

[0037] The reactions occurring during the first impurity removal reaction process include:

[0038] Fe 3+ +Fe=Fe 2+ ;

[0039] H + +Fe=H2↑+Fe 2+ ;

[0040] 2Cr 6+ +3Fe=3Fe 2+ +2Cr 3+ ;

[0041] V 5+ +Fe=Fe 2+ +V 3+ .

[0042] A phosphate ion-containing solution and an alkali solution are added to the first impurity-removing liquid to perform a second impurity-removing reaction to remove aluminum ions, chromium ions and vanadium ions to obtain a second impurity-removing liquid. After solid-liquid separation, the second impurity-removing liquid is subjected to ferrous chloride solution.

[0043] The present invention not only removes impurities by adding the solution containing phosphate ions, but also increases the filter pressing speed, improves the separation efficiency, and thus improves the yield, thereby solving the problem in the prior art that only alkali solution is added to generate aluminum hydroxide colloid, which leads to difficulty in filtration and low separation efficiency.

[0044] In addition, the concentration of iron will have a certain impact on the performance of the battery-grade iron phosphate. The present invention uses the solution containing phosphate ions to dilute the concentration of iron.

[0045] The reactions occurring during the second impurity removal reaction process include:

[0046] Al 3+ +PO4 3- =AlPO4↓;

[0047] Cr 3+ +3OH - =Cr(OH)3↓;

[0048] V 3+ +3OH - =V(OH)3↓.

[0049] The ferrous chloride solution is mixed with a phosphate solution and an oxidant and subjected to a synthesis reaction, followed by solid-liquid separation to obtain ferric phosphate dihydrate. During the synthesis reaction, the pH of the mixture is 1.5 to 2.5, including but not limited to any one of 1.7, 1.9, 2.0, 2.2, and 2.4 or a range between any two of them.

[0050] The reactions occurring during the synthesis reaction process include:

[0051] 2Fe 2+ +2PO4 3- +4H + +H2O2+2OH-=2FePO4·2H2O.

[0052] In some specific embodiments of the present invention, after the synthesis reaction and solid-liquid separation, a water washing step is further included, wherein the water washing is performed until the conductivity is less than 500 ms / cm.

[0053] The battery-grade iron phosphate is obtained by calcining the iron phosphate dihydrate.

[0054] The reaction occurring during the calcination process includes: FePO4·2H2O=FePO4+2H2O.

[0055] In some specific embodiments of the present invention, after the calcination, a crushing (grinding) step is also included.

[0056] The method for preparing battery-grade ferric phosphate by using waste secondary ferrous chloride solution provided by the present invention can meet the index requirements of battery-grade ferric phosphate, and can make high-value resource of waste secondary ferrous chloride solution, reduce the pollution of waste liquid to the environment, and reduce the environmental protection pressure of chlorination process production line.

[0057] In addition, the above method has the advantages of being simple, easy to implement, short process and easy to achieve mass production.

[0058] In some specific embodiments of the present invention, the mass fraction of HCl in the waste secondary ferrous chloride solution is 2% to 5%, the mass concentration of Fe element is 60 to 100 g / L, the mass concentration of Al element is 6 to 10 g / L, the mass concentration of Cr element is 1 to 2 g / L, and the mass concentration of V element is 1 to 2 g / L.

[0059] Preferably, the metallic iron material comprises elemental iron and / or reduced ilmenite.

[0060] In some specific embodiments of the present invention, the elemental iron includes at least one of iron powder, iron filings and iron sheets.

[0061] Preferably, during the first impurity removal reaction, the temperature of the mixed material is 20-90°C, including but not limited to any one of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or a range between any two of them.

[0062] Preferably, the time of the first impurity removal reaction is 0.5 to 2 hours, including but not limited to any point value of 1 hour, 1.5 hours or any range value between the two.

[0063] Preferably, the pH of the mixed material after the first impurity removal reaction is 2-3, including but not limited to any one of 2.1, 2.2, 2.3, 2.5, 2.7, 2.8, 2.9 or a range between any two of them.

[0064] Preferably, the solution containing phosphate ions includes a phosphoric acid solution and / or a phosphate solution; wherein the phosphate solution includes at least one of a sodium phosphate solution, a sodium monohydrogen phosphate solution and a disodium hydrogen phosphate solution.

[0065] Preferably, the volume of the solution containing phosphate ions is 0.1% to 0.5% of the volume of the waste ferrous chloride solution, including but not limited to any one of 0.2%, 0.3%, 0.4% or any range between two of them.

[0066] Preferably, the alkali solution includes at least one of an aqueous ammonia solution, a sodium hydroxide solution, a potassium hydroxide solution, a sodium bicarbonate solution and a sodium carbonate solution.

[0067] Preferably, the alkali solution is added in an amount such that the pH of the mixed material is 4.0 to 4.5, including but not limited to any one of 4.1, 4.2, 4.3, 4.4 or a range between any two of them.

[0068] In some specific embodiments of the present invention, the molar concentration of the alkali solution is 0.5-2 mol / L, including but not limited to any one of 0.8 mol / L, 1.0 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L or a range between any two of them.

[0069] In some specific embodiments of the present invention, the alkali solution is added at a uniform speed.

[0070] Preferably, during the second impurity removal reaction, the temperature of the mixed material is 20-90°C, including but not limited to any one of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or a range between any two of them.

[0071] Preferably, the second impurity removal reaction time is 0.5 to 2 hours, including but not limited to any one of 1 hour and 1.5 hours or any range between the two.

[0072] Preferably, the phosphate solution used in the synthesis reaction comprises sodium monohydrogen phosphate solution and / or disodium hydrogen phosphate solution.

[0073] In some specific embodiments of the present invention, the phosphate solution used in the synthesis reaction process can also be a solution obtained by reacting phosphoric acid and sodium hydroxide.

[0074] Preferably, the mass fraction of the phosphate solution used in the synthesis reaction is 8% to 15%, including but not limited to any one of 9%, 10%, 11%, 12%, 13%, 14% or a range between any two of them.

[0075] Preferably, the oxidant comprises hydrogen peroxide, wherein the hydrogen peroxide refers to hydrogen peroxide solution.

[0076] In some specific embodiments of the present invention, the mass fraction of the hydrogen peroxide is 20% to 30%.

[0077] Preferably, the molar ratio of the iron element in the ferrous chloride solution, the phosphorus element in the phosphate and the H2O2 in the hydrogen peroxide is 1:1:1.1-2, including but not limited to any one of 1:1:1.2, 1:1:1.4, 1:1:1.5, 1:1:1.7, 1:1:1.9 or a range between any two of them.

[0078] Preferably, during the synthesis reaction, the temperature of the mixed material is 20-95°C, including but not limited to any one of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or a range between any two of them.

[0079] Preferably, the synthesis reaction time is 2 to 5 hours, including but not limited to any one of 3 hours and 4 hours or any range between the two.

[0080] In some specific embodiments of the present invention, the synthesis reaction includes: first reacting at pH = 1.8 to 2.5 and room temperature (15 to 30° C.) for 1 to 2 hours, then adjusting the pH to 1.5 to 1.8 and heating to 80 to 95° C. for 1 to 3 hours. In this way, battery-grade iron phosphate with better performance can be obtained.

[0081] In some specific embodiments of the present invention, while obtaining the iron phosphate dihydrate, a filtrate containing phosphate ions is also obtained, and the filtrate can be used as a solution containing phosphate ions for the second impurity removal reaction.

[0082] Preferably, the calcination temperature is 480-580°C, including but not limited to any one of 490°C, 500°C, 510°C, 520°C, 530°C, 550°C, 570°C or a range between any two of them.

[0083] The calcination time is 1 to 4 hours, including but not limited to any one of 2 hours and 3 hours or any range between the two.

[0084] In a second aspect, the present invention also provides the use of battery-grade iron phosphate prepared by the method for preparing battery-grade iron phosphate using waste paraferrous chloride solution as described above in lithium-ion batteries.

[0085] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0086] The waste ferrous chloride solution used in the following embodiments and comparative examples of the present invention is the waste liquid (same batch) generated in the production process of titanium dioxide by the chloride process. The content of impurity elements in the waste liquid is shown in Table 1.

[0087] Example 1

[0088] The method for preparing battery-grade ferric phosphate using waste ferrous chloride solution provided in this embodiment comprises the following steps:

[0089] (1) Add iron powder to the waste ferrous chloride solution generated in the production process of titanium dioxide by the chloride process to remove iron ions, chromium ions and vanadium ions, and react at 60° C. for 0.5 h until the pH of the mixture is 2, thereby obtaining a first impurity-removed liquid.

[0090] (2) After adding a sodium phosphate solution (i.e., a solution containing phosphate ions) having a volume of 0.1% of the volume of the waste secondary ferrous chloride solution to the first impurity-removing liquid, a 0.5 mol / L sodium hydroxide solution was pumped into the first impurity-removing liquid using a peristaltic pump to adjust the pH to 4.0, and the mixture was reacted at 60° C. for 0.5 h and then filtered to obtain a purified ferrous chloride solution. After detection and calculation, the iron yield (iron mass in the purified ferrous chloride solution / iron mass in the waste secondary ferrous chloride solution×100%) was 96%.

[0091] (3) To the purified ferrous chloride solution, a sodium monohydrogen phosphate solution with a mass fraction of 10% and a hydrogen peroxide with a mass fraction of 27% are added according to the molar ratio of the iron element in the ferrous chloride solution, the phosphorus element in the phosphate and the H2O2 in the hydrogen peroxide of 1:1:1.5, and at the same time, a sodium hydroxide solution with a mass fraction of 8% is used to control the pH value of the synthesis reaction process to 2.0. After reacting for 1.5 hours, phosphoric acid is added to adjust the solution pH to 1.7, and the temperature is raised to 85° C., and after reacting for 1 hour, filter pressing is performed, and the filter cake (i.e., iron phosphate dihydrate) is washed with water until the conductivity is less than 500 ms / cm, and then the calcination temperature is 480° C., and the calcination time is 4 hours. After calcination, it is crushed to obtain iron phosphate.

[0092] Example 2

[0093] The method for preparing battery-grade ferric phosphate using waste ferrous chloride solution provided in this embodiment comprises the following steps:

[0094] (1) Add reduced titanium to the waste ferrous chloride solution generated in the production process of titanium dioxide by the chloride process, react at 50° C. for 1 hour to remove iron ions, chromium ions and vanadium ions until the pH of the mixture is 3, thereby obtaining a first impurity-removing liquid.

[0095] (2) After adding a disodium hydrogen phosphate solution (i.e., a solution containing phosphate ions) having a volume of 0.2% of the volume of the waste secondary ferrous chloride solution to the first impurity-removing liquid, a 1 mol / L sodium hydroxide solution was pumped into the first impurity-removing liquid using a peristaltic pump to adjust the pH to 4.0, and the mixture was reacted at 50° C. for 1 h and then filtered to obtain a purified ferrous chloride solution. After detection and calculation, the iron yield (the mass of iron in the purified ferrous chloride solution / the mass of iron in the waste secondary ferrous chloride solution×100%) was 95%.

[0096] (3) To the purified ferrous chloride solution, 8% sodium monohydrogen phosphate solution and 30% hydrogen peroxide were added according to the molar ratio of iron in the ferrous chloride solution, phosphorus in the phosphate and H2O2 in the hydrogen peroxide of 1:1:1.7, and 8% sodium hydroxide solution was used to control the pH value of the reaction process to 2.2. After reacting for 1 hour, phosphoric acid was added to adjust the solution pH to 1.9. The temperature was raised to 90° C. and reacted for 1 hour, and then the filter cake was filtered and washed with water until the conductivity was less than 500 ms / cm. The filter cake was then calcined at a temperature of 500° C. for 3 hours. After calcination, the filter cake was crushed to obtain ferric phosphate.

[0097] Example 3

[0098] The method for preparing battery-grade ferric phosphate using waste ferrous chloride solution provided in this embodiment comprises the following steps:

[0099] (1) Add iron scale to the waste ferrous chloride solution generated in the production process of titanium dioxide by the chloride process, react at 70° C. for 2 h to remove iron ions, chromium ions and vanadium ions until the pH of the mixture is 2.5, thereby obtaining a first impurity-removing solution.

[0100] (2) After adding a sodium phosphate solution (i.e., a solution containing phosphate ions) having a volume of 0.1% of the volume of the waste secondary ferrous chloride solution to the first impurity-removing liquid, a 2 mol / L sodium hydroxide solution was pumped into the first impurity-removing liquid using a peristaltic pump to adjust the pH to 4.5, and the mixture was reacted at 70° C. for 0.5 h and then filtered to obtain a purified ferrous chloride solution. After detection and calculation, the iron yield (the mass of iron in the purified ferrous chloride solution / the mass of iron in the waste secondary ferrous chloride solution×100%) was 95%.

[0101] (3) To the purified ferrous chloride solution, a 15% by mass sodium hydrogen phosphate solution and a 25% by mass hydrogen peroxide solution are added according to the molar ratio of the iron element in the ferrous chloride solution, the phosphorus element in the phosphate and the H2O2 in the hydrogen peroxide of 1:1:2, and a 15% by mass sodium hydroxide solution is used to control the pH value of the reaction process to 2.5. After reacting for 2 hours, phosphoric acid is added to adjust the solution pH value to 1.5, and the temperature is raised to 80° C., and after reacting for 2 hours, filter pressing is performed, and water washing is performed until the conductivity is less than 500 ms / cm. The filter cake is then calcined at a calcination temperature of 520° C. and a calcination time of 2 hours. After calcination, the filter cake is crushed to obtain ferric phosphate.

[0102] Comparative Example 1

[0103] The method for preparing battery-grade ferric phosphate using waste ferrous chloride solution provided in this comparative example is basically the same as that in Example 1, except that steps (1) and (2) are not performed, but sodium monohydrogen phosphate solution and hydrogen peroxide are directly added to the waste ferrous chloride solution generated in the production process of titanium dioxide by the chloride process to carry out a synthesis reaction.

[0104] Comparative Example 2

[0105] The method for preparing battery-grade ferric phosphate using waste ferrous chloride solution provided in this comparative example is basically the same as that in Example 1, except that in step (2), no sodium phosphate solution is added.

[0106] After detection and calculation, the iron yield in this comparative example (the mass of iron in the purified ferrous chloride solution / the mass of iron in the waste secondary ferrous chloride solution×100%) is 85%.

[0107] Comparative Example 3

[0108] The method for preparing battery-grade ferric phosphate using waste ferrous chloride solution provided in this comparative example is basically the same as that in Example 1, except that in step (3), a sodium hydroxide solution with a mass fraction of 8% is used to control the pH of the synthesis reaction process to 3.0.

[0109] Experimental Example 1

[0110] The content of impurity elements in the waste secondary ferrous chloride solution generated in the production process of titanium dioxide by the chloride process was detected, and the content of impurity elements in the purified ferrous chloride solution obtained in step (2) of Examples 1 to 3 and Comparative Examples 2 to 3 was detected respectively. The detection results are shown in Table 1.

[0111] Table 1 Impurity element content in each group of purified ferrous chloride solutions

[0112]

[0113]

[0114] As can be seen from Table 1, in step (2) of Comparative Example 2, no sodium phosphate solution was added, and the impurity removal efficiency was reduced.

[0115] Experimental Example 2

[0116] The element contents of the battery-grade iron phosphates prepared in the above embodiments and comparative examples were respectively detected, and the results are shown in Table 2.

[0117] Table 2 Element content in battery grade iron phosphate

[0118]

[0119] It can be seen from Table 2 that the iron phosphate prepared in each embodiment of the present invention can meet the index requirements of battery-grade iron phosphate.

[0120] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A method for preparing battery-grade ferric phosphate using waste secondary ferrous chloride solution, characterized in that: The steps include: Adding metallic iron material to the waste secondary ferrous chloride solution, performing a first impurity removal reaction, removing iron ions, chromium ions and vanadium ions, and obtaining a first impurity-removed liquid; wherein the waste secondary ferrous chloride solution comprises waste liquid generated in the production process of titanium dioxide by the chloride process, and the main components of the waste secondary ferrous chloride solution include ferrous ions, iron ions, chloride ions, aluminum ions, chromium ions and vanadium ions; Adding a phosphate ion-containing solution and an alkali solution to the first impurity-removing liquid to perform a second impurity-removing reaction to remove aluminum ions, chromium ions and vanadium ions to obtain a second impurity-removing liquid; after solid-liquid separation of the second impurity-removing liquid, a ferrous chloride solution is obtained; The ferrous chloride solution is mixed with a phosphate solution and an oxidant to undergo a synthesis reaction, followed by solid-liquid separation to obtain ferric phosphate dihydrate; wherein during the synthesis reaction, the pH of the mixture is 1.5 to 2.5; The iron phosphate dihydrate is calcined to obtain the battery-grade iron phosphate; The metallic iron material includes elemental iron and / or reduced ilmenite.

2. The method for preparing battery-grade ferric phosphate using waste secondary ferrous chloride solution according to claim 1, characterized in that: During the first impurity removal reaction, the temperature of the mixed material is 20 to 90° C.; And / or, the time of the first impurity removal reaction is 0.5 to 2 hours.

3. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The first impurity removal reaction is performed until the pH of the mixed material is 2-3.

4. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The solution containing phosphate ions includes a phosphoric acid solution and / or a phosphate solution.

5. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 4, characterized in that: The phosphate solution includes at least one of a sodium phosphate solution, a sodium monohydrogen phosphate solution and a disodium hydrogen phosphate solution.

6. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The volume of the solution containing phosphate ions is 0.1% to 0.5% of the volume of the waste secondary ferrous chloride solution.

7. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The alkali solution includes at least one of an aqueous ammonia solution, a sodium hydroxide solution, a potassium hydroxide solution, a sodium bicarbonate solution and a sodium carbonate solution; And / or, the pH of the mixture added with the alkali solution is 4.0-4.

5.

8. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: During the second impurity removal reaction, the temperature of the mixed material is 20 to 90° C.; And / or, the time of the second impurity removal reaction is 0.5 to 2 hours.

9. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The phosphate solution used in the synthesis reaction process includes sodium monohydrogen phosphate solution and / or disodium hydrogen phosphate solution.

10. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The mass fraction of the phosphate solution used in the synthesis reaction is 8% to 15%.

11. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The oxidant includes hydrogen peroxide.

12. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 11, characterized in that: The molar ratio of the iron element in the ferrous chloride solution, the phosphorus element in the phosphate and the H2O2 in the hydrogen peroxide is 1:1:1.1-2.

13. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: During the synthesis reaction, the temperature of the mixed material is 20 to 95°C; And / or, the synthesis reaction time is 2 to 5 hours.

14. The method for preparing battery-grade ferric phosphate using waste paraferrous chloride solution according to claim 1, characterized in that: The calcination temperature is 480-580° C., and the calcination time is 1-4 hours.

15. Use of the battery-grade iron phosphate obtained by the method for preparing battery-grade iron phosphate using waste secondary ferrous chloride solution as claimed in any one of claims 1 to 14 in lithium-ion batteries.

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