CN113772647B

CN113772647B - High-purity iron phosphate and method for preparing high-purity iron phosphate by adopting multistage purification method

Info

Publication number: CN113772647B
Application number: CN202111057642.1A
Authority: CN
Inventors: 罗显明; 付全军; 何丰; 秦正伟; 宫东杰; 曹宇
Original assignee: Sichuan Lomon Phosphorous Chemistry Co ltd
Current assignee: Sichuan Lomon Phosphorous Chemistry Co ltd
Priority date: 2021-09-09
Filing date: 2021-09-09
Publication date: 2023-03-21
Anticipated expiration: 2041-09-09
Also published as: CN113772647A

Abstract

The invention belongs to the field of new energy batteries, and particularly relates to a method for preparing high-purity iron phosphate by adopting a multistage purification method, which comprises the following steps: s1, adding a potassium-containing compound into a monoammonium phosphate solution for reaction, and filtering to obtain a primary clear liquid after the reaction is finished; the monoammonium phosphate solution is prepared by adding pure water into industrial monoammonium solid or monoammonium phosphate clear liquid; s2, adding a chelating agent into the primary clear liquid prepared in the step S1 for reaction to prepare a secondary clear liquid; s3, reacting the secondary clear liquid prepared in the step S2 with a ferrous sulfate solution in the presence of an oxidant to prepare iron phosphate slurry; and S4, washing and drying the iron phosphate slurry after the reaction in the step S3 to obtain an iron phosphate product. The method is simple and easy to implement, and the purity of the iron phosphate is greatly improved; the application also provides the high-purity iron phosphate prepared by the preparation method, the contents of calcium, magnesium, potassium and sodium impurities are all lower than 15ppm, and the prepared lithium iron phosphate can be effectively ensured to have good safety and stability.

Description

High-purity iron phosphate and method for preparing high-purity iron phosphate by adopting multistage purification method

Technical Field

The invention relates to the field of new energy battery materials, in particular to high-purity iron phosphate and a method for preparing the high-purity iron phosphate by adopting a multi-stage purification method.

Background

Under the background of 'carbon peak reaching' and 'carbon neutralization', the reconstruction of an energy system in China is imperative. With the support of the country to the new energy industry, the new energy automobile and photovoltaic industry enter a rapid development stage, the market promotion effect is gradually enhanced, and the demand is continuously promoted, so that the rapid increase of the product demand of each subdivision in each link at the upstream of the industrial chain is driven. In order to meet the global demand of rapidly increasing power batteries and energy storage, main new energy enterprises in the world are greatly expanded, and the demand of upstream raw materials is increased at a high speed; meanwhile, in order to improve the stability and the safety of the product, the requirements on the quality indexes of the raw materials are continuously improved.

Lithium iron phosphate is a main anode material of a lithium battery, and iron phosphate is a raw material of the lithium iron phosphate, a traditional phosphorus chemical product has new activity due to the requirement of a new energy lithium battery material, the phosphorus chemical product for electronics taking "phosphate rock-phosphate-iron phosphate-lithium iron phosphate" as a route receives more and more attention, and the product quality of the iron phosphate directly affects the stability and safety of the lithium iron phosphate.

The technical method for preparing iron phosphate disclosed in the prior art comprises the following steps:

(1) Ferrous sulfate + industrial monoammonium phosphate oxidation method: reacting ferrous sulfate with iron to remove impurities to obtain a ferrous sulfate solution, dissolving industrial monoammonium phosphate by pure water, adding hydrogen peroxide, mixing the ferrous sulfate solution and the industrial monoammonium phosphate solution, precipitating to obtain a crude ferric phosphate product, aging and pulping to obtain ferric phosphate dihydrate, and drying and calcining to obtain the ferric phosphate product.

(2) Iron, iron oxide + phosphoric acid oxidation: for example, patent 201710635752.9 discloses a process for preparing battery grade high purity nano iron phosphate, which comprises the steps of using a mixture formed by iron powder and iron oxide as an iron source, using phosphoric acid as a phosphorus source to prepare ferrous phosphate mother liquor, then adding hydrogen peroxide to prepare a crude iron phosphate product, finally washing the crude iron phosphate product by using distilled water and ethanol, and drying the washed product to obtain the iron phosphate.

The preparation of battery grade iron phosphate by using ferrous phosphate and industrial monoammonium phosphate has become a mainstream process in the industry due to low cost. However, because the phosphorus source adopted in the process is industrial grade monoammonium phosphate (or clear liquid or mother liquid) prepared from wet-process phosphoric acid, a part of impurities carried in the wet-process phosphoric acid inevitably enter the monoammonium phosphate (or clear liquid or mother liquid) and finally enter the iron phosphate product along with the precipitation, and further other crystals are formed in the iron phosphate crystallization process, so that the stability of the iron phosphate crystals is influenced, and the stability and the safety of the lithium iron phosphate material are further influenced.

Patent publication No. CN113104827A discloses a method for preparing battery-grade anhydrous iron phosphate from industrial ammonium phosphate clear liquid or industrial ammonium phosphate mother liquid, and discloses that the industrial ammonium phosphate clear liquid is purified through defluorination, refining and heavy metal removal operations in sequence to prepare iron phosphate with low impurity content. However, the method has the disadvantages of difficult operation, difficult accurate control of pH in the refining process, complex crystal form of production and preparation, unstable impurity content of the obtained product, and high impurity content of the obtained product after repeated tests, and is difficult to achieve the technical effect claimed by the embodiment.

Disclosure of Invention

The invention aims to provide a preparation method of high-purity iron phosphate, which is simple and feasible and greatly improves the purity of the iron phosphate.

The second purpose of the invention is to provide high-purity iron phosphate, the content of calcium, magnesium, manganese, aluminum, potassium, sodium and other impurities of which is lower than 15ppm, particularly the content of potassium can reach below 10ppm, and the prepared lithium iron phosphate can be effectively ensured to have good safety and stability.

In order to achieve the purpose, the invention adopts the technical scheme that:

firstly, the invention provides a method for preparing high-purity iron phosphate by adopting a multistage purification method, which comprises the following steps:

s1, adding a potassium-containing compound into a monoammonium phosphate solution for reaction, and filtering to obtain a primary clear liquid after the reaction is finished; the monoammonium phosphate solution is prepared by adding pure water into industrial monoammonium solid or monoammonium phosphate clear liquid;

s2, adding a chelating agent into the primary clear liquid prepared in the step S1 for reaction to prepare a secondary clear liquid;

s3, reacting the secondary clear liquid obtained in the step S2 with a ferrous sulfate solution in the presence of an oxidant to obtain iron phosphate slurry;

and S4, washing and drying the iron phosphate slurry after the reaction in the step S3 to obtain an iron phosphate product.

Preferably, in step S1, the concentration of the monoammonium phosphate solution is 15 to 25% based on the monoammonium phosphate; the amount of potassium-containing compound added in step S1 is: controlling the total potassium content in the reaction solution of the step S1 to be 0.1-0.5 percent in mass percentage; in the step S1, the potassium-containing compound is at least one of monopotassium phosphate, dipotassium phosphate, potassium carbonate, potassium bicarbonate or potassium hydroxide, and the calcium and magnesium content in the potassium-containing compound is less than 100ppm; the reaction temperature of the step S1 is 40-60 ℃, and the reaction time is 0.5-3 h.

Preferably, in step S2, the chelating agent is added in an amount of: controlling the mass percent of the chelating agent in the reaction solution to be 0.2-0.5%; in step S2, the chelating agent is at least one selected from ethylenediamine tetraacetic acid (EDTA), aminotrimethylenephosphonic Acid (ATMP), hydroxyethylidene diphosphonic acid (HEDP), 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) or 2-hydroxyphosphonoacetic acid (HPAA); the reaction temperature of the step S2 is 40-60 ℃, and the reaction time is 0.5-3 h.

Preferably, in the step S3, the concentration of the ferrous sulfate is 10 to 15%, and the mass fractions of calcium, magnesium, manganese, aluminum, potassium and sodium in the ferrous sulfate solution are all less than 50ppm; step S3, adding a pH regulator and an oxidant into the reaction system at the same time, wherein the adding time is 0.5-2 h; the amount of the oxidant satisfies the following conditions: 1.2 to 1.5 times of the dosage required for completely oxidizing the ferrous sulfate; the dosage of the pH regulator satisfies the following conditions: controlling the pH value of the reaction end point to be 2.0-3.0; preferably, the oxidant is hydrogen peroxide, and the pH regulator is ammonia water or ammonia gas.

Preferably, step S4 specifically includes the following steps:

s41, taking the secondary washing filtrate as primary washing water, after washing, performing iron phosphate crystallization, pulping again, and adding industrial phosphoric acid for aging and pulping; the dosage of the washing water for one time is 10 to 20 times of the mass of the solid phase; after washing, adding pure water to adjust the solid content to 10-15% for pulping again; dilute phosphoric acid (H) with the concentration of 3-10% is added in the process of pulping again ₃ PO ₄ Metering) to control the pH value of the reaction system to be 2.0-2.2, so that the most stable compound, namely ferric phosphate dihydrate is formed; after pulping again, the stirring linear velocity is controlled to be 0.5-2 m/s, and stirring is carried out for 1-3 h for aging and pulping.

S42, adopting pure water as secondary washing water, and drying after secondary washing to obtain an iron phosphate product; the dosage of the secondary washing water is 20-30 times of the mass of the solid phase;

s43, the filtrate obtained in the step S42 is secondary washing filtrate, part of the secondary washing filtrate is returned and sequentially washed to be used as primary washing water, the rest part of the secondary washing filtrate enters a wastewater purification system, the filtrate obtained in the step S41 is primary washing filtrate, all the filtrate enters the wastewater purification system, after the wastewater purification system purifies the filtrate, 50-70% of the wastewater is converted into pure water, and the rest 30-50% of the high-concentration wastewater enters a phosphate fertilizer system to be recycled.

The invention also provides the high-purity iron phosphate prepared by the preparation method.

The invention has the beneficial effects that:

1. according to the multistage purification technology provided by the invention, the industrial monoammonium phosphate or the monoammonium phosphate clear solution is further purified, so that the impurity contents of calcium, magnesium, manganese, aluminum, potassium and sodium in the purified monoammonium phosphate are lower, the crystallization precipitation amount of calcium, magnesium, manganese, aluminum, potassium and sodium in the ferric phosphate precipitation process is effectively reduced, the impurities of calcium, magnesium, manganese, aluminum, potassium and sodium can be washed and separated by simple water washing, the impurity contents of calcium, magnesium, manganese, aluminum, potassium and sodium after washing can be reduced to within 15ppm, and the impurity contents are far lower than the limit values of the ions in the current HG/T4701-2014 standard.

2. The invention creatively provides a method for removing potassium ions and sodium ions in monoammonium phosphate or monoammonium phosphate clear liquid by replenishing potassium ions in advance, and the inventor converts impurity ions such as fluosilicate in the potassium-containing complex salt (such as potassium fluosilicate) into potassium-containing complex salt to precipitate and separate out by replenishing the potassium ions in advance, thereby effectively reducing the amount of complex salts such as potassium sodium fluosilicate dissolved in a liquid phase and further reducing the precipitation amount of the complex salts such as potassium sodium fluosilicate in the ferric phosphate precipitation process.

3. The invention also provides a method for selectively reacting the metal impurities such as calcium, magnesium, manganese, aluminum and the like with the chelating agent to form stable soluble substances by adopting a chelation technology, so that the metal impurities such as calcium, magnesium, manganese, aluminum and the like are effectively prevented from forming precipitates in the ferric phosphate precipitation process, and the content of the metal impurities such as calcium, magnesium, manganese, aluminum and the like in the ferric phosphate solid phase is effectively reduced. The method does not select the conventional method for removing the metal impurities such as calcium, magnesium, manganese, aluminum and the like by precipitating, but creatively chelates the metal impurities such as calcium, magnesium, manganese, aluminum and the like so that the metal impurities do not participate in the precipitation process of the ferric phosphate.

4. The invention adds oxidant and pH regulator into the reaction system at the same time, and realizes the Fe control by controlling the feeding amount and the feeding speed ²⁺ To Fe ³⁺ The oxidation rate in the conversion process is controlled, and the generation of Fe is avoided ³⁺ The phenomenon of wrapping caused by too fast crystal growth due to too high concentration is avoided, the condition that chelated calcium, magnesium, manganese and aluminum are brought into the crystal in a small amount due to too fast crystal growth is also avoided, and the stable control on the iron phosphate crystal is realized.

5. According to the method, phosphoric acid is added in the subsequent treatment process for aging treatment, the pH value of a reaction system is controlled to be 2.0-2.2, and other forms (multiple crystal waters) are converted into dihydrate, so that the most stable compound, namely ferric phosphate dihydrate can be formed, the impurity carrying amount is further reduced, the washing is more thorough, and the impurity content in the final product is lower.

6. The invention adopts a countercurrent washing mode, uses the secondary washing filtrate as the primary washing water, effectively reduces the consumption of the primary washing to the pure water, and reduces the consumption of the pure water by more than 30 percent of the whole system.

7. The excessive phosphorus and potassium elements and the chelating agent supplemented by the method enter a wastewater system and return to a phosphate fertilizer production process along with high-concentration wastewater, wherein the excessive phosphoric acid is directly recycled; the potassium element directly serves as a nutrient element and enters the compound fertilizer, so that the potassium is not wasted; and the chelating agent still keeps certain chelating ability when entering the fertilizer, can be effectively combined with metal cations, improves the water solubility of the fertilizer, is beneficial to the absorption and transformation of crops, and improves the fertilizer efficiency of the product.

Drawings

Fig. 1 is a process flow chart of a method for preparing high-purity iron phosphate by using a multistage purification method in example 1 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the present invention is further described with reference to specific embodiments below. Those not specifically indicated in the examples were carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents used, or those not indicated together with the manufacturer, are conventional products available commercially. All features disclosed in this specification may be combined in any combination, except features or/and steps which are mutually exclusive.

The following examples will give a more complete understanding of the invention to those skilled in the art, but are not intended to limit the invention in any way.

The ferrous sulfate used in the following examples of the application is a same batch of product, wherein the contents of calcium, magnesium, manganese, aluminum, potassium and sodium are respectively 95ppm, 56ppm, 92ppm, 68ppm, 78ppm and 98ppm;

the potassium-containing compounds used in the examples described below are all commercially available laboratory reagents with negligible impurity content;

industrial monoammonium phosphate in the following examples of the application is a product of the same batch, and is added with pure water to prepare a monoammonium phosphate solution A with the concentration of 20 percent (calculated by the monoammonium phosphate);

the industrial monoammonium phosphate clear solutions in the following examples of the application are all products of the same batch, and are added with pure water to prepare a monoammonium phosphate solution B with the concentration of 25 percent (calculated by monoammonium phosphate);

the contents of the components in the monoammonium phosphate solution prepared from the two raw materials are respectively shown in table 1:

TABLE 1 monoammonium phosphate solution content of each component

Example 1

The embodiment provides a method for preparing high-purity iron phosphate by adopting a multistage purification method, which comprises the following steps:

s1, taking 1000ml of monoammonium phosphate solution A, adding potassium carbonate into the monoammonium phosphate solution, and controlling the mass percentage of the total potassium content in the monoammonium phosphate solution to be 0.3%; stirring and reacting for 2h at 50 ℃, and filtering to obtain primary clear liquid after the reaction is finished;

s2, adding EDTA (ethylene diamine tetraacetic acid) with the mass percent of 0.3% into the primary clear liquid prepared in the step S1, and stirring and reacting at 50 ℃ for 2 hours to prepare secondary clear liquid;

s3, mixing the secondary clear liquid prepared in the step S2 with a 15% ferrous sulfate solution; adding hydrogen peroxide and ammonia water simultaneously, wherein the feeding time is controlled to be 1h, the dosage of the hydrogen peroxide is 1.2 times of the theoretical dosage of completely oxidized ferrous sulfate, and the dosage of the ammonia water is used for controlling the pH value of the reaction end point to be 2.8-3.0; obtaining iron phosphate slurry after the reaction is finished;

s41, adopting the secondary washing filtrate as primary washing water, wherein the using amount of the primary washing water is 15 times of the mass of the solid phase; after washing, adding pure water to adjust the solid content to 15%, pulping again, and simultaneously adding diluted phosphoric acid (H) with the concentration of 5% in the pulping process again ₃ PO ₄ Meter); after pulping again, controlling the stirring linear speed to be 2m/s, stirring for 2h, aging and pulping;

s42, adopting pure water as secondary washing water, wherein the using amount of the secondary washing water is 20 times of the mass of the solid phase; drying the mixture to constant weight after secondary washing to obtain an iron phosphate product;

s43, the filtrate obtained in the step S42 is secondary washing filtrate, part of the secondary washing filtrate is returned and sequentially washed to be used as primary washing water, the rest part of the secondary washing filtrate enters a wastewater purification system, the filtrate obtained in the step S41 is primary washing filtrate, all the filtrate enters the wastewater purification system, after the wastewater purification system purifies the filtrate, 70% of the wastewater is converted into pure water, and the rest 30% of the high-concentration wastewater enters a phosphate fertilizer system to be recycled.

Example 2

This example provides a method for preparing high-purity iron phosphate by using a multi-stage purification method, which is different from example 1 in that:

in the step S1, the addition amount of potassium carbonate is as follows: the mass percentage of the total potassium content in the monoammonium phosphate solution is controlled to be 0.1 percent.

Example 3

in the step S1, the monoammonium phosphate solution A is replaced by a monoammonium phosphate solution B, and the addition amount of potassium carbonate is as follows: the mass percentage of the total potassium content in the monoammonium phosphate solution is controlled to be 0.5 percent.

Example 4

in the step S2, the addition amount of the EDTA is 0.2 percent of the total amount of the primary clear liquid in percentage by mass.

Example 5

in the step S2, the monoammonium phosphate solution A is replaced by the monoammonium phosphate solution B, and the addition amount of the EDTA is 0.5 percent of the total amount of the primary clear liquid in percentage by mass.

Example 6

in step S2, EDTA was replaced with the same amount of ATMP.

Comparative example 1

This comparative example provides a method for preparing high-purity iron phosphate using a multi-stage purification method, which is different from example 1 in that:

in step S1, sodium carbonate is added, and the addition amount is as follows: the mass percentage of the total sodium content in the monoammonium phosphate solution is controlled to be 0.3 percent.

Comparative example 2

the step S2 is: adjusting the pH value of the primary clear liquid prepared in the step S1 to 7.0, reacting for 0.5h, precipitating and filtering to obtain secondary clear liquid; the subsequent reaction was continued in the same manner as in example 1.

Comparative example 3

and step S3, simultaneously adding the secondary clear liquid obtained in the step S2, 15% ferrous sulfate solution, hydrogen peroxide and ammonia water, mixing, and stirring for reacting for 1 hour to obtain the iron phosphate slurry.

Comparative example 4

step S41, using the secondary washing filtrate as primary washing water, wherein the usage amount of the primary washing water is 15 times of the mass of the solid phase; after washing, pulping is not carried out again, and diluted phosphoric acid is not added for aging treatment.

Comparative example 5

The comparative example provides a method for preparing high-purity iron phosphate by adopting a multistage purification method, which comprises the following steps:

s1, fluorine removal: adding 1% of diatomite and 1% of sodium carbonate solution into the clear industrial ammonium phosphate solution to react for 5 hours, and then filtering to obtain a phosphorus-containing solution after fluorine removal;

s2, refining: introducing ammonia gas into the phosphorus-containing solution prepared in the step S1 to adjust the pH value, adjusting the pH value to 6.8, and removing impurities such as calcium, magnesium, manganese, aluminum and the like through a precipitation reaction to obtain a phosphate solution with low impurity ion content;

s3, synthesizing ferric phosphate dihydrate: adding pure water into the refined phosphate solution obtained in the step S2 to dilute the solution to 20% (based on monoammonium phosphate), and adjusting the pH value to obtain a phosphate solution required by the synthesis reaction; dissolving ferrous sulfate crystals in water to prepare a 15% ferrous sulfate solution, and obtaining a sulfate solution required by a synthetic reaction; slowly adding a phosphate solution required by the reaction into a sulfate solution, and synchronously adding hydrogen peroxide and ammonia water, wherein the amount of the hydrogen peroxide is 1.2 times of the mass of the ferrous sulfate, and the amount of the ammonia water is used for controlling the pH value of the reaction end point to be 2.8-3.0 to fully react to obtain synthetic slurry; and (3) carrying out filter pressing on the synthetic slurry, and washing and drying a filter cake to obtain the ferric phosphate dihydrate.

Experiment ofExample (b)

The iron phosphate products prepared in the above examples and comparative examples are subjected to performance tests, and the test method refers to HG/T4701-2014. The test results are shown in table 2:

TABLE 2 test results for various examples and comparative examples

Composition (I)	K/ppm	Na/ppm	Ca/ppm	Mg/ppm	Mn/ppm	Al/ppm
							Example 1	8.15	11.23	12.85	11.82	13.36	11.32
Example 2	10.25	14.35	12.30	11.75	13.58	11.69
							Example 3	7.25	10.56	12.55	12.03	13.84	11.86
Example 4	8.32	11.35	14.32	13.85	14.69	12.96
							Example 5	8.18	11.52	11.20	10.65	11.21	10.10
Example 6	8.20	11.28	12.61	11.62	13.32	11.29
							Comparative example 1	31.21	28.20	13.20	12.10	13.92	12.15
Comparative example 2	9.21	11.62	36.15	52.12	41.25	48.36
							Comparative example 3	8.92	11.35	15.24	14.20	15.21	13.41
Comparative example 4	9.72	12.25	16.12	15.25	16.78	14.52
							Comparative example 5	32.51	29.58	42.28	56.31	43.25	52.31

In conclusion, in the iron phosphate prepared by the method for preparing high-purity iron phosphate by adopting the multistage purification method, the contents of elements such as calcium, magnesium, potassium, sodium, manganese, aluminum and the like are all originally lower than the requirements specified in the existing standard HG/T4701-2014, so that the prepared lithium iron phosphate material has higher stability and safety, and the preparation method is simple and feasible and has good industrial prospect.

The present invention is not limited to the above embodiments, and any structural changes made under the teaching of the present invention shall fall within the protection scope of the present invention, which has the same or similar technical solutions as the present invention.

Claims

1. A method for preparing high-purity iron phosphate by adopting a multistage purification method is characterized by comprising the following steps:

s3, reacting the secondary clear liquid obtained in the step S2 with a ferrous sulfate solution in the presence of an oxidant to obtain iron phosphate slurry; a pH regulator is also added in the step, the pH regulator and the oxidant are simultaneously added into the reaction system, and the adding time is 0.5-2 h;

s4, washing and drying the iron phosphate slurry after the reaction in the step S3 to obtain an iron phosphate product; step S4 specifically includes the following steps:

s41, taking the secondary washing filtrate as primary washing water, after washing, performing iron phosphate crystallization, pulping again, and adding industrial phosphoric acid for aging and pulping;

and S42, adopting pure water as secondary washing water, and drying after secondary washing to obtain the iron phosphate product.

2. The method for preparing high-purity iron phosphate by using a multistage purification method according to claim 1, wherein the amount of the potassium-containing compound added in step S1 is: and controlling the total potassium content in the reaction solution in the step S1 to be 0.1-0.5 percent in percentage by mass.

3. The method for preparing high-purity iron phosphate according to claim 1, wherein the chelating agent is at least one selected from ethylenediamine tetraacetic acid, aminotrimethylenephosphonic acid, hydroxyethylidene diphosphonic acid, 2-phosphonic butane-1,2,4-tricarboxylic acid, and 2-hydroxyphosphonoacetic acid in step S2.

4. The method for preparing high-purity iron phosphate by using a multistage purification method according to claim 3, wherein the chelating agent is added in an amount of 0.2 to 0.5% by mass in step S2.

5. The method for preparing high-purity iron phosphate using a multi-stage purification process according to claim 1,

in the step S1, the reaction temperature is 40-60 ℃, and the reaction time is 0.5-3 h;

in the step S2, the reaction temperature is 40-60 ℃, and the reaction time is 0.5-3 h.

6. The method for preparing high-purity iron phosphate by using a multistage purification method according to any one of claims 1 to 5, wherein the amount of the oxidizing agent used in step S3 is such that: 1.2 to 1.5 times of the dosage required for completely oxidizing the ferrous sulfate; the dosage of the pH regulator satisfies the following conditions: controlling the pH value of the reaction end point to be 2.0-3.0.

7. The method for preparing high-purity iron phosphate using a multi-stage purification process according to claim 6,

in the step S1, the concentration of the monoammonium phosphate solution is 15-25% by weight of monoammonium phosphate;

in the step S3, the concentration of the ferrous sulfate is 10-15%, and the mass fractions of calcium, magnesium, manganese, aluminum, potassium and sodium in the ferrous sulfate solution are all less than 50ppm.

8. The method for preparing high-purity iron phosphate using a multi-stage purification process according to claim 1,

in step S41, the dosage of the washing water for one time is 10 to 20 times of the mass of the solid phase; after washing, adding pure water to adjust the solid content to 10-15% for pulping again; dilute phosphoric acid with the concentration of 3-10% is added in the pulping process again;

in step S42, the amount of the secondary washing water is 20 to 30 times of the mass of the solid phase.

9. The high purity ferric phosphate produced by the method for producing high purity ferric phosphate according to any one of claims 1 to 8 using a multi-stage purification method.