CN115626619B - Preparation method of battery-grade ferric phosphate - Google Patents

Abstract

The invention discloses a preparation method of battery-grade ferric phosphate, which comprises the following steps: (1) mixing ferrous sulfate with wet process phosphoric acid; (2) Adding sulfate precipitant until the pH value of the solution is 0.3-0.8, reacting at 30-40deg.C for 0.5-3 hr, filtering, and collecting filtrate; (3) Adding sulfate radical precipitant into the filtrate again until the pH value of the solution is 1.8-2.2, reacting for 0.5-3h at 30-60 ℃, filtering, and collecting filtrate; (4) Adding an oxidant into the filtrate for oxidation, adding a pH regulator to control the pH value of the solution to be 1.2-1.6, heating to 90-95 ℃, carrying out solid-liquid separation to obtain crude ferric phosphate, washing, drying and calcining to obtain a ferric phosphate product. The method provided by the invention is suitable for removing sulfate ions in a reaction system by adopting a two-step desulfurization method by taking waste liquid of ferrous sulfate as a raw material, so that the sulfur content of the obtained ferric phosphate product is lower.

Description

Preparation method of battery-grade ferric phosphate

Technical Field

The invention belongs to the technical field of iron phosphate preparation, and particularly relates to a preparation method of battery-grade iron phosphate.

Background

With the rapid development of new energy automobiles, the demand of power lithium ion batteries is continuously increasing, wherein lithium iron phosphate (LiFePO ₄ ) Is considered to be the most ideal positive electrode material for lithium ion batteries. At present, ferric phosphate is mostly adopted as a precursor raw material for preparing lithium iron phosphate, and the quality and purity of a ferric phosphate product are highDirectly affecting the quality of the lithium iron phosphate.

The iron phosphate used to prepare lithium iron phosphate is known in the art as battery grade iron phosphate. Because of the extremely high impurity requirements of battery grade ferric phosphate, which is demanding for the base stock, high purity phosphoric acid or phosphate and ferric salt are typically used for reaction, however, the cost of the high purity raw materials is very high. Therefore, there is a need for a preparation method capable of greatly reducing the cost of iron phosphate, thereby reducing the production cost of lithium ion batteries.

With the development of the iron phosphate manufacturing industry, inexpensive iron and phosphorus sources are becoming a focus of attention of the skilled artisan.

Currently, the iron source used for preparing battery-grade ferric phosphate generally adopts a sulfate form, and the main flow process using ferrous sulfate as the iron source can be divided into an ammonium salt process and a sodium salt process according to the difference of the neutralizer and other cations used. The mother liquor after preparing ferric phosphate by ammonium salt method and sodium salt method contains a large amount of Na ⁺ And NH ₄ ⁺ The subsequent mother liquor is difficult to treat; and a reaction system for preparing ferric phosphate by using ferric sulfate or ferrous sulfate as an iron source contains a large amount of SO ₄ ^2- So that part of sulfate radical is carried in the prepared ferric phosphate dihydrate to influence the purity of the product. Therefore, it is necessary to react SO in the reaction system before forming iron phosphate ₄ ^2- Purifying to maximize SO avoidance ₄ ^2- Influence on the iron phosphate product. In the prior art, SO in a reaction system of ferric phosphate is rarely existed ₄ ^2- Report of clearance.

Wet process phosphoric acid is the most commonly used phosphorus source for the preparation of iron phosphate. The wet phosphoric acid is phosphoric acid containing various impurities obtained by decomposing phosphorite with sulfuric acid or hydrochloric acid and other strong acids and performing liquid-solid separation. Wet phosphoric acid is low in cost and wide in source, but raw wet phosphoric acid contains Ca, mg, al, fe, F and other impurities, and further purification is needed if the raw wet phosphoric acid is used for producing battery-grade ferric phosphate.

Patent document CN 202110746350.2 discloses a method for preparing battery-grade ferric phosphate, wherein the iron source of ferric phosphate is ferrous sulfate, the phosphorus source is wet-process phosphoric acid, and the skilled person selects to use the wet-process phosphoric acid firstMixing and curing the acid and the alkaline compound, and purifying wet phosphoric acid to obtain a phosphorus clear solution; oxidizing ferrous sulfate to ferric sulfate; ferric sulfate reacts with the phosphorus clear solution to obtain ferric phosphate slurry, and the ferric phosphate is obtained through liquid-solid separation. Firstly, in the technical scheme, alkaline compounds such as ammonia water, sodium hydroxide, potassium hydroxide and the like are selected, so that the mother solution after the preparation of the ferric phosphate contains a large amount of Na ⁺ 、NH ₄ ⁺ Increasing the difficulty for the subsequent mother liquor treatment. Secondly, the reaction system of ferric sulfate and phosphorus clear solution contains a large amount of SO ₄ ^2- This results in an increase in sulfur content in the resulting iron phosphate product, affecting the quality of the iron phosphate product.

Disclosure of Invention

In order to avoid SO in the reaction system when ferric salt or ferrous salt of sulfuric acid system is used as iron source ₄ ^2- Influence on ferric phosphate products, the preparation method provided by the invention comprises the steps of firstly adding a sulfate radical precipitator and SO in a reaction system ₄ ^2- The reaction generates precipitate, SO that SO in the system is firstly carried out before the ferric phosphate product is formed ₄ ^2- And purifying to obtain the iron phosphate product with lower sulfur impurity content. Furthermore, the sulfate radical precipitator used in the invention can precipitate and separate partial impurities in the wet-process phosphoric acid, such as F ions and the like, and can prepare the ferric phosphate product with low impurity content on the basis of no impurity removal treatment on the wet-process phosphoric acid.

In the process of iron phosphate product precipitation, the technical staff skillfully utilizes the principle that the pH values are different when iron phosphate and ferrous phosphate are precipitated, namely, the solubility of the iron phosphate is low, the pH value of a large amount of precipitation is 1.2-1.6, the ferrous phosphate has higher solubility below the pH value of 2.0, and the iron phosphate begins to be precipitated in the form of a precipitate only around 2.2. The invention takes ferrous sulfate as the raw material to prepare Fe ²⁺ Desulfurizing (1.8-2.2) at a relatively high pH while removing part of the impurities; SO in the waiting system ₄ ^2- And after removing part of impurities, regulating the pH value of the system to be 1.2-1.6, so that ferric phosphate is separated out. Under the condition that the pH value is 1.2-1.6, the solubility of other impurity ions is large, and the impurity ions cannot be synchronously separated out with the ferric phosphate, so the method has the advantages thatThe iron phosphate product prepared by the method has low impurity content.

The invention comprises the following technical scheme:

the invention provides a preparation method of battery-grade ferric phosphate, which comprises the following steps:

(1) Mixing ferrous sulfate and wet phosphoric acid according to the ratio of n Fe/P of 0.85-1.1;

(2) Adding sulfate precipitant until the pH value of the solution is 0.3-0.8, reacting at 30-40deg.C for 0.5-3 hr, filtering, and collecting filtrate;

(3) Adding sulfate radical precipitant into the filtrate until the pH value of the solution is 1.8-2.2, reacting for 0.5-3h at 30-60 ℃, filtering, and collecting filtrate;

(4) Adding an oxidant into the filtrate for oxidation, adding a pH regulator to control the pH value of the solution to be 1.2-1.6, heating to 90-95 ℃, carrying out solid-liquid separation to obtain crude ferric phosphate, washing, drying and calcining to obtain a ferric phosphate product.

The iron in the ferrous sulfate in the step (1) exists in the form of 2-valent iron ions.

In a specific embodiment of the invention, the ferrous sulfate is prepared by the following method: adding a reducing agent into an iron source solution containing ferrous sulfate and/or ferric sulfate for reduction, so that Fe is all Fe ²⁺ Morphology exists.

The reducing agent is selected from FeS, H ₂ S、SO ₃ One or more of the reducing Fe powder.

In a specific embodiment of the invention, the reducing agent is a reducing Fe powder.

Sources of the iron source solution include, but are not limited to, ferrous sulfate solution obtained by dissolving ferrous sulfate heptahydrate crystals, ferrous sulfate solution obtained by reacting iron with sulfuric acid, sulfate slag solution, solution of sulfuric acid acidolysis waste iron, and pyrite cinder acid solution.

In the specific embodiment of the invention, the iron source solution is a solution formed after acidolysis of waste iron by sulfuric acid, and the iron source in the solution is Fe ²⁺ 、Fe ³⁺ Is a combination of (a) and (b). The preparation method provided by the inventionThe concentration of the positive impurity ions in the iron source solution is not particularly limited, and as for the cations in the acidic solution, only the pH in the solution is raised to precipitate. The impurity cation part in the iron source can be removed along with the calcium sulfate, and the unremoved impurity ions exist in the form of ions all the time when the subsequent pH value is reduced to 1.2-1.6, so that the generated ferric phosphate product is not influenced.

The wet process phosphoric acid is H with certain impurity content obtained by decomposing phosphorite with sulfuric acid ₃ PO ₄ A solution.

The sulfate radical precipitant of the invention comprises calcium carbonate or mineral substances with the calcium carbonate content more than or equal to 5 percent, lime (CaO) and lime milk (Ca (OH) ₂ ) One or more of calcium phosphate and calcium hydrophosphate, wherein the mineral with the content of calcium carbonate more than or equal to 5 percent comprises, but is not limited to, limestone, marble and calcite.

In the test process, technicians find that when the sulfate radical precipitator is lime, the lime has stronger alkalinity, so that the system local alkalinity is too strong to generate ferric hydroxide flocculent precipitate, iron loss is caused, and the sulfate radical removal efficiency is affected. Thus, in a most preferred embodiment of the invention, the sulfate precipitant is calcium carbonate.

The advantage of the invention is that the calcium sulfate produced by precipitation is industrial building gypsum, which can be directly used for selling without any treatment, thus reducing the production cost of the target product ferric phosphate.

With the addition of sulfate precipitants (for example, calcium carbonate) in the step (2), calcium ions and sulfate ions form calcium sulfate precipitates, and the calcium sulfate is separated in a filtering mode. At this time, most sulfate ions in the reaction system are removed, calcium carbonate is continuously added into the filtrate, the pH of the system is raised, the precipitation reaction is carried out more thoroughly in the forward direction, and the deep removal of sulfate ions can be realized (as shown in step 3). At the moment, the pH value of the reaction system is less than 2.2, the ferrous phosphate does not precipitate, and the formed calcium sulfate precipitate is continuously present in the reaction system in the form of solution and is separated in a filtering mode.

The oxidant in the step (4) is selected from one or more than two of hydrogen peroxide, ozone, air, sodium peroxide and ammonium persulfate.

In a preferred embodiment of the present invention, the oxidizing agent is hydrogen peroxide.

And (4) adding an oxidant into the system to oxidize ferrous phosphate into ferric phosphate, wherein the reaction equation is as follows: 2Fe ²⁺ +2H ₂ PO ₄ -+H ₂ O ₂ +2H ₂ O→2FePO ₄ ·2H ₂ O↓+2H ⁺ The pH of the reaction system is lowered due to the generation of the oxidation process, and meanwhile, the ferric phosphate precipitation consumes water in the system, so that the pH of the reaction system is further lowered. When the pH value of the system is less than 1.2, ferric phosphate cannot be precipitated, so that an alkaline pH regulator is required to be added into the system to control the pH value of the system to be 1.2-1.6, and normal precipitation of ferric phosphate is ensured.

The pH regulator used in the invention is selected from one or more than two of water, ammonia water and sodium hydroxide. Since ammonia water contains N and sodium hydroxide contains Na, other impurity elements are introduced into the system, and the most preferable pH regulator of the invention is selected from water.

"nFe/P" as used herein means the molar mass ratio of Fe to P.

In a most preferred embodiment of the present invention, the method for preparing battery grade ferric phosphate comprises the steps of:

(1) Will contain Fe ²⁺ And/or Fe ³⁺ Adding the iron source solution into a reduction tank, and adding a reducing agent to ensure that Fe in the solution is Fe ²⁺ Morphology exists;

(2) Introducing the reduced solution into a desulfurization tank, adding wet phosphoric acid according to the proportion of n Fe/P of 0.85-1.1, adding calcium carbonate until the pH value of the solution is 0.3-0.8, reacting for 0.5-3h at 30-40 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 1.8-2.2, reacting for 0.5-3h at the temperature of 30-60 ℃, filtering, and collecting the filtrate;

(3) Introducing the filtrate into an oxidation tank, adding an oxidant for full oxidation, adding water to control the pH value of the solution to be 1.2-1.6, heating to 90-95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate;

(4) Washing the crude ferric phosphate by using pure water until the conductivity of the washing water is lower than 500us/cm;

(5) And (5) drying and calcining to obtain the iron phosphate product.

The preparation method of the iron phosphate provided by the invention has the following advantages:

(1) To avoid SO ₄ ^2- Influence on ferric phosphate products, the technical staff adopts a two-step desulfurization method, firstly, sulfate radical precipitant is added into a reaction system, the pH value of the system is controlled to be 0.3-0.8, and the precipitant and SO in the system are used ₄ ^2- The reaction generates gypsum, and in order to realize deep desulfurization, a precipitator is continuously added into the filtrate, SO that SO in the system is deeply removed before the ferric phosphate product is formed ₄ ^2- The content of sulfur impurities in the obtained ferric phosphate product is lower;

(2) The method provided by the invention is suitable for the treatment of iron ions (Fe ²⁺ ) The method is a waste liquid of an iron source, and utilizes the principle that the pH values are different when ferric phosphate and ferrous phosphate are separated out, so that the reaction system forms ferrous phosphate under the condition of higher pH and simultaneously removes sulfate ions in the system deeply, then the ferrous phosphate is oxidized into ferric phosphate, the pH value of the system is reduced to separate out the ferric phosphate, and thus, synchronous separation of impurity ions during separation of the ferric phosphate can be avoided;

(3) In addition, in the traditional iron phosphate preparation method, iron phosphate formed in a reaction system with excessive sulfate ions is not easy to remove Ca, mg and the like in the product, a large amount of pure water is required to be used for washing, and 30-50 tons of wastewater can be produced by producing one ton of anhydrous iron phosphate product. The preparation method provided by the invention firstly removes sulfate ions in the reaction system, and can greatly reduce the consumption of washing water.

Drawings

FIG. 1 is a flow chart of a battery grade ferric phosphate preparation process

FIG. 2A photograph of iron phosphate dihydrate electron microscope (2 ten thousand times)

FIG. 3A photograph of iron phosphate dihydrate electron microscope (20 ten thousand times)

FIG. 4A photograph of ferric phosphate anhydride (2 ten thousand times) of the present invention prepared in example 1

FIG. 5A photograph of ferric phosphate anhydride (20 ten thousand times)

Detailed Description

The technical solutions of the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only some embodiments of the present invention, but not all. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

The wet process phosphoric acid composition used in the examples of the present invention is shown in the following table:

TABLE 1 Wet phosphoric acid composition Table

The iron source used in the embodiment of the invention is sulfuric acid acidolysis waste iron solution obtained as a byproduct of a certain factory, and the components are shown in the following table:

TABLE 2 iron source solution composition table

Preparation of battery grade ferric phosphate

Example 1

S1: according to the technological process of figure 1 of the specification, the iron source solution shown above is added into a reduction tank, and the reducing iron powder is added to ensure that Fe in the solution is all Fe ²⁺ Morphology exists;

s2: introducing the reduced solution into a desulfurization tank, adding wet phosphoric acid according to the proportion of n Fe/P of 1.1, adding calcium carbonate until the pH value of the solution is 0.3, reacting for 0.5h at 35 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 1.8, reacting for 1h at the temperature of 40 ℃, filtering, and collecting the filtrate;

s3: introducing the filtrate into an oxidation tank, adding hydrogen peroxide for full oxidation, adding water to control the pH value of the solution to be 1.2, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate;

s4: washing the crude ferric phosphate by using pure water until the conductivity of the washing water is lower than 500us/cm;

s5: and (5) drying and calcining to obtain the iron phosphate product.

2-3 are electron microscope images of the prepared iron phosphate dihydrate, and the iron phosphate dihydrate can be seen to be in a thin-sheet cake shape; fig. 4-5 are electron microscope images of the prepared iron phosphate anhydrate, and it can be seen that the iron phosphate anhydrate is honeycomb-shaped.

Example 2

The preparation process is identical to example 1, except that: 1, adding calcium carbonate until the pH value of the solution is 0.5 in the step S2, reacting for 0.5h at 35 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 2.0, reacting for 1h at the temperature of 40 ℃, filtering, and collecting the filtrate; 2, adding water to control the pH value of the solution to be 1.4 in the step S3, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate; the other steps are the same as in example 1, and finally the iron phosphate product is obtained.

Example 3

The preparation process is identical to example 1, except that: 1, adding calcium carbonate until the pH value of the solution is 0.8 in the step S2, reacting for 0.5h at 35 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 2.2, reacting for 1h at the temperature of 40 ℃, filtering, and collecting the filtrate; 2, adding water to control the pH value of the solution to be 1.6 in the step S3, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate; the other steps are the same as in example 1, and finally the iron phosphate product is obtained.

Comparative example 1

The preparation process is identical to example 1, except that: 1, adding calcium carbonate until the pH value of the solution is 0.8 in the step S2, reacting for 0.5h at 35 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 2.5, reacting for 1h at the temperature of 40 ℃, filtering, and collecting the filtrate; 2, adding water to control the pH value of the solution to be 1.6 in the step S3, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate; the other steps are the same as in example 1, and finally the iron phosphate product is obtained.

Comparative example 2

The preparation process is identical to example 1, except that: 1, adding calcium carbonate until the pH value of the solution is 0.8 in the step S2, reacting for 0.5h at 35 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 2.2, reacting for 1h at the temperature of 40 ℃, filtering, and collecting the filtrate; 2, adding water to control the pH value of the solution to be 1.8 in the step S3, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate; the other steps are the same as in example 1, and finally the iron phosphate product is obtained.

Comparative example 3

The preparation process is identical to example 1, except that: 1, adding calcium carbonate until the pH value of the solution is 0.8 in the step S2, reacting for 0.5h at 35 ℃, filtering and separating to obtain calcium sulfate and filtrate, and directly introducing the filtrate into an oxidation tank for the next reaction without deep desulfurization of the filtrate; 2, adding water to control the pH value of the solution to be 1.6 in the step S3, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate; the other steps are the same as in example 1, and finally the iron phosphate product is obtained.

Comparative example 4

The preparation process is identical to example 1, except that: 1, adding calcium carbonate until the pH value of the solution is 2.2 in the step S2, reacting for 0.5h at 35 ℃, filtering and separating to obtain calcium sulfate and filtrate, and introducing the filtrate into an oxidation tank for the next reaction; 2, adding water to control the pH value of the solution to be 1.6 in the step S3, heating to 95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate; the other steps are the same as in example 1, and finally the iron phosphate product is obtained.

TABLE 3 control conditions for inventive examples and comparative examples

Effect example 1 iron phosphate product parameter detection

The iron phosphate compositions prepared in examples 1 to 3, comparative examples 1 to 4 of the present invention were examined, and the results are shown in the following table. Wherein, the reference 1 ferric phosphate is a sample provided by a new energy company in Hubei, and is prepared by taking ferrous sulfate and phosphoric acid as raw materials and adjusting the pH value by using NaOH; the reference 2 ferric phosphate is purchased from 10 ten thousand tons of ferric phosphate industrialization device of Chuan Heng company, is prepared by using ferrous sulfate and industrial monoammonium phosphate as raw materials and regulating the pH value by using ammonia water. Meanwhile, the product index obtained by the patent is compared with the national industry standard iron phosphate for HG_T4701-2021 batteries.

TABLE 4 iron phosphate product composition Table

As can be seen from the data in the table, the contents of the components in the iron phosphate products prepared in the embodiments 1-3 of the invention are all within the national standard requirement range, and the iron phosphate products belong to qualified products. Comparative example 3 because there is only one desulfurization step in desulfurization, and the amount of added calcium carbonate controls the pH value of the system to be 0.8, the desulfurization depth is low, and the S content in the prepared iron phosphate product is 560ppm, which is far higher than the national standard requirement. In addition, the technical staff of the invention unexpectedly find that the process for preparing the ferric phosphate by the two-step desulfurization method provided by the invention is more stable, the obtained product parameters are more controllable, the difference among batches is not obvious, the process controllability of the one-step desulfurization method is poor, and although the product parameters of the batch are qualified, the next batch is possibly unqualified.

Effect example 2 reaction System removal efficiency

Test purpose: detecting SO in a reaction system after two-step desulfurization in the preparation process of ferric phosphate ₄ ^2- Concentration.

The test method comprises the following steps: the reaction systems of examples 1-3 and comparative examples 1-4 were examined separately for the solution before desulfurization by adding calcium carbonateMiddle SO ₄ ^2- Concentration of SO in the filtrate before entering the oxidation tank ₄ ^2- The concentrations and results are shown in the following table:

TABLE 5SO ₄ ^2- Removal efficiency

From the above table data, it can be seen that the desulfurization efficiency and iron phosphate yield of the preparation process of examples 1-3 of the present invention simultaneously exhibit higher levels. In the preparation process of comparative example 1, due to the higher pH value of the second-stage desulfurization, part of ferric sulfate is precipitated together with gypsum, and the iron loss is higher. Comparative example 3 has significantly lower desulfurization efficiency than the other groups due to the low desulfurization depth.

Effect example 3 preparation Process washing Water usage

Although the raw materials for preparing the ferric phosphate are the sulfuric acid acidolysis waste iron solution with high impurity content and the wet phosphoric acid, the preparation process provided by the invention has the advantages that even though the raw materials with high impurity content are used, the ferric phosphate product meeting the industry standard can be obtained on the basis of no need of pre-purification. Meanwhile, sulfate radical in the system is removed by the two-step desulfurization method in the earlier stage, and a reasonable pH range is controlled in the process of phosphate radical precipitation, so that the content of impurities in the crude ferric phosphate prepared by the method is low, and the water consumption is greatly reduced in the subsequent process of washing the crude ferric phosphate by pure water.

The following table shows the water usage during washing of crude iron phosphate in the preparation process of inventive examples 1-3, comparative examples 1-4. The results are shown in the following table:

the conventional process refers to a Na method flow published in most documents, and specifically comprises the following steps: purified FeSO ₄ Mixing with commercial phosphoric acid (purified), and reacting with hydrogen peroxide to obtain FePO ₄ And H is ₂ SO ₄ NaOH is added into the slurry to raise the pH value of the slurry to obtain FePO ₄ ·2H ₂ Cake of O and Na ₂ SO ₄ The main synthesis mother liquor, because of the high Na content in the product (below 200 ppm) in the standard, is washed below standard value, and usually about 10 tons of mother liquor and 40 tons of washing water are required for producing 1 ton of anhydrous ferric phosphate.

Table 6 by-product waste water (ton) of preparation process

As can be seen from the water consumption data in the table, the preparation process (examples 1-3) provided by the invention has a small consumption of washing water, and the consumption of washing water is between 30 and 40 tons (containing mother liquor and washing water). The comparative example 2 had a higher pH during precipitation of ferric phosphate, resulting in an increase in impurity ions carried out by the precipitation, and a slight increase in wash water, mainly for pH adjustment, the mother liquor amount of comparative example 2 was 2 times that of the other examples, and the amount of wastewater (mother liquor+wash water) finally produced was 55.2 tons. The iron phosphate of comparative example 3 was not completely desulfurized, so that the impurity content of the iron phosphate product was increased, and the washing water amount was increased. Comparative example 4 was also incomplete desulfurization and the amount of wash water was slightly increased. Most importantly, as can be seen from the data in the table, the iron phosphate preparation process provided by the invention has much less water washing amount than 50 tons of the conventional process, and has obvious progress.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and not for limiting the same; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some or all of the technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit of the invention.

Claims (9)

1. A method of preparing battery grade ferric phosphate, the method comprising:

(1) Mixing ferrous sulfate and wet phosphoric acid according to the ratio of n Fe/P of 0.85-1.1;

(2) Adding sulfate precipitant until the pH value of the solution is 0.3-0.8, reacting at 30-40deg.C for 0.5-3 hr, filtering, and collecting filtrate;

(3) Adding sulfate radical precipitant into the filtrate until the pH value of the solution is 1.8-2.2, reacting for 0.5-3h at 30-60 ℃, filtering, and collecting filtrate;

(4) Adding an oxidant into the filtrate for oxidation, adding a pH regulator to control the pH value of the solution to be 1.2-1.6, heating to 90-95 ℃, carrying out solid-liquid separation to obtain crude ferric phosphate, washing, drying and calcining to obtain a ferric phosphate product;

iron in the ferrous sulfate in the step (1) exists in the form of 2-valent iron ions, and the ferrous sulfate is prepared by the following method: adding a reducing agent into an iron source solution containing ferrous sulfate and/or ferric sulfate for reduction, so that Fe is all Fe ²⁺ Morphology exists; the reducing agent is selected from FeS, H ₂ S、SO ₃ One or more of the reducing Fe powder.

2. The method according to claim 1, wherein the reducing agent is a reducing Fe powder.

3. The method according to claim 1, wherein the source of the iron source solution is selected from one or a combination of two or more of a ferrous sulfate solution obtained by dissolving a ferrous sulfate crystal heptahydrate, a ferrous sulfate solution obtained by reacting iron with sulfuric acid, a sulfuric acid residue solution, a solution of sulfuric acid hydrolyzed waste iron, and a pyrite cinder acid solution.

4. The preparation method according to claim 1, wherein the sulfate radical precipitant is one or more selected from the group consisting of calcium carbonate, minerals with a calcium carbonate content of 5% or more, lime milk, calcium phosphate, and calcium hydrogen phosphate, and wherein the minerals with a calcium carbonate content of 5% or more are one or more selected from the group consisting of limestone, marble, and calcite.

5. The method according to claim 4, wherein the sulfate-based precipitant is calcium carbonate.

6. The method according to claim 1, wherein the oxidizing agent in the step (4) is one or a combination of two or more selected from hydrogen peroxide, ozone, air, sodium peroxide and ammonium persulfate.

7. The method according to claim 1, wherein the pH adjuster used in the step (4) is one or a combination of two or more selected from the group consisting of water, aqueous ammonia and sodium hydroxide.

8. The method of claim 7, wherein the pH adjuster is selected from the group consisting of water.

9. The method of manufacturing according to claim 1, wherein the method of manufacturing battery grade iron phosphate comprises the steps of:

(1) Will contain Fe ²⁺ And/or Fe ³⁺ Adding the iron source solution into a reduction tank, and adding a reducing agent to ensure that Fe in the solution is Fe ²⁺ Morphology exists;

(2) Introducing the reduced solution into a desulfurization tank, adding wet phosphoric acid according to the proportion of n Fe/P of 0.85-1.1, adding calcium carbonate until the pH value of the solution is 0.3-0.8, reacting for 0.5-3h at 30-40 ℃, and filtering and separating to obtain calcium sulfate and filtrate; continuously adding calcium carbonate into the filtrate until the pH value of the solution is 1.8-2.2, reacting for 0.5-3h at the temperature of 30-60 ℃, filtering, and collecting the filtrate;

(3) Introducing the filtrate into an oxidation tank, adding an oxidant for full oxidation, adding water to control the pH value of the solution to be 1.2-1.6, heating to 90-95 ℃, and carrying out solid-liquid separation to obtain crude ferric phosphate;

(4) Washing the crude ferric phosphate by using pure water until the conductivity of the washing water is lower than 500us/cm;

(5) And (5) drying and calcining to obtain the iron phosphate product.