Process for the preparation of low-sulfur ferric phosphate

Abstract

The application provides a preparation method of low-sulfur ferric phosphate, which comprises the following steps: (1) preparing an acidic sulfate solution containing iron ions and phosphate ions, and controlling the iron-phosphorus molar ratio in the acidic sulfate solution to be 0.01-10 and the phosphorus-sulfur molar ratio to be 0.01-10; (2) adding a crystal seed after the acidic sulfate solution is heated to perform crystallization, or adding a crystal seed to the acidic sulfate solution and then heating to perform crystallization; (3) after the crystallization is completed, liquid-solid separation is performed to obtain a post-crystallization liquid and ferric phosphate solids; (4) the ferric phosphate solids are calcined to obtain the low-sulfur ferric phosphate; and the sulfur content of the low-sulfur ferric phosphate is less than or equal to 200 ppm. The preparation method is simple in operation, low in preparation cost, free of harmful substances in the preparation process, and environmentally friendly.

Description

Technical Field

[0001] This invention relates to the field of ferric phosphate preparation technology, and in particular to a method for preparing low-sulfur ferric phosphate. Background Technology

[0002] Iron phosphate is widely used not only as a raw material for producing lithium iron phosphate, the positive electrode material for lithium-ion batteries, but also as a molluscicide in organic agriculture and as a base coating in paints. There are various methods for producing iron phosphate. Battery-grade iron phosphate has extremely high requirements for impurities and demanding requirements for basic raw materials. Currently, high-purity phosphoric acid or phosphates are usually reacted with iron salts. However, the cost of these high-purity raw materials is very high.

[0003] CN110482514A discloses a method for preparing battery-grade anhydrous iron phosphate. This method uses cold-rolled iron plate scraps and / or reduced iron powder from mineral processing as the iron source to prepare a ferrous solution, or uses ferrous sulfate, a byproduct of the sulfuric acid process for titanium dioxide production, to prepare a ferrous solution. After removing impurities with a flocculant, the ferrous ions are oxidized to ferric ions, which are then mixed with a phosphate ion-containing solution. A dispersant is added, and a crystallization reaction is performed to obtain iron phosphate crystals. The iron phosphate crystals are then dried and calcined to obtain battery-grade anhydrous iron phosphate. This preparation method utilizes low-cost cold-rolled iron plate scraps, reduced iron powder from mineral processing, or ferrous sulfate, a byproduct of the sulfuric acid process for titanium dioxide production, as the iron source. Impurities are removed by flocculant precipitation, followed by crystallization to prepare battery-grade iron phosphate. The raw material cost is low, the product purity is high, the tap density is high, and it has a spherical structure, making it suitable as a precursor for high-tap-density lithium iron phosphate.

[0004] CN111252750A discloses a method for preparing ferric phosphate and alumina from aluminum phosphate slag. The method includes the following steps: dissolving aluminum phosphate slag in an alkaline solution, followed by solid-liquid separation and crystallization to obtain phosphate crystals and an aluminate solution; dissolving the phosphate crystals, adding a calcium-containing solution to react and generate calcium phosphate precipitate, then adding concentrated sulfuric acid to the calcium phosphate precipitate, followed by solid-liquid separation to obtain a phosphoric acid solution, adding an iron source and an oxidant to react and obtain ferric phosphate; the aluminate solution is then seeded and calcined to obtain alumina. This method uses aluminum phosphate slag as raw material, dissolving and separating phosphate and aluminum salts using an alkaline solution, then extracting phosphorus from the phosphates to prepare ferric phosphate, and seeding aluminum from the aluminum salts to prepare alumina. The recovery rates of phosphorus and aluminum are both higher than 96%, which not only fully utilizes the phosphorus and aluminum in the aluminum phosphate slag, but also allows the treated slag to be directly landfilled, offering the advantages of being environmentally friendly and pollution-free.

[0005] CN102683674A discloses a method for preparing a nano-sized iron phosphate precursor and a method for preparing ultrafine nano-sized lithium iron phosphate electrode material using the prepared precursor. First, a nano-sized iron phosphate precursor is prepared, and then the nano-sized precursor is used to prepare even smaller ultrafine nano-sized lithium iron phosphate cathode material. The production process is simple, and the obtained nano-precursor plays a crucial role in the further preparation of finer nano-spherical or near-spherical lithium iron phosphate particles. The electrode material made from the prepared precursor exhibits excellent performance, including high capacity, high-rate discharge capacity, good voltage plateau characteristics, and long cycle life.

[0006] However, the above methods are costly and produce ferric phosphate with high sulfur content, limiting the large-scale application of ferric phosphate. Therefore, there is an urgent need to develop a simple and low-cost method for preparing low-sulfur ferric phosphate. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for preparing low-sulfur ferric phosphate. The method involves adding seed crystals to an acidic sulfate solution to induce crystallization, followed by solid-liquid separation and calcination to obtain low-sulfur ferric phosphate. The preparation method is simple to operate, does not produce harmful substances during the preparation process, and is environmentally friendly.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] This invention provides a method for preparing low-sulfur ferric phosphate, the method comprising the following steps:

[0010] (1) Prepare an acidic sulfate solution containing iron ions and phosphate ions, and control the iron-phosphorus molar ratio in the acidic sulfate solution to be 0.01-10 and the phosphorus-sulfur molar ratio to be 0.01-10;

[0011] (2) The acidic sulfate solution is heated and then seed crystals are added to crystallize; or seed crystals are added to the acidic sulfate solution and then heated to crystallize.

[0012] (3) After the crystallization is completed, liquid-solid separation is performed to obtain the crystallized liquid and iron phosphate solid;

[0013] (4) The solid iron phosphate is calcined to obtain the low-sulfur iron phosphate; the sulfur content of the low-sulfur iron phosphate is ≤200ppm.

[0014] The method for preparing low-sulfur ferric phosphate according to this invention involves adding seed crystals to an acidic sulfate solution with an iron-to-phosphorus molar ratio of 0.01–10 and a phosphorus-to-sulfur molar ratio of 0.01–10, followed by heated crystallization to obtain ferric phosphate with a sulfur content ≤200 ppm. When the iron-to-phosphorus molar ratio is below 0.01, the iron-to-phosphorus ratio in the ferric phosphate will not meet battery-grade standards; when the iron-to-phosphorus molar ratio is above 10, it will also not meet battery-grade standards; when the phosphorus-to-sulfur molar ratio is below 0.01, the sulfur content in the resulting ferric phosphate will be too high, failing to meet the requirements for battery preparation; when the phosphorus-to-sulfur molar ratio is above 10, the precipitation efficiency of ferric phosphate will decrease, and complexation precipitation will easily occur, which is detrimental to the subsequent technical control of ferric phosphate-related indicators. The preparation method described in this invention is simple to operate, low in cost, and does not produce any harmful substances during the process, making it environmentally friendly and suitable for industrial application.

[0015] The sulfur content of the low-sulfur ferric phosphate described in this invention is ≤200ppm, for example, it can be 200ppm, 190ppm, 170ppm, 150ppm, 100ppm or 50ppm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0016] Preferably, the iron ions in step (1) are ferric ions.

[0017] Preferably, the method for preparing the acidic sulfate solution includes: dissolving a water-soluble iron source and a phosphorus source in water; or dissolving iron and phosphorus-containing materials in sulfuric acid solution; or dissolving water-insoluble iron and phosphorus sources in sulfuric acid solution.

[0018] Preferably, the water-soluble iron source includes ferric sulfate and / or ferrous sulfate.

[0019] Preferably, the phosphorus source includes one or a combination of at least two of the following: phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, or ammonium phosphate. Typical but non-limiting combinations include combinations of phosphoric acid and sodium dihydrogen phosphate, combinations of sodium monohydrogen phosphate and trisodium phosphate, combinations of potassium dihydrogen phosphate and potassium monohydrogen phosphate, combinations of tripotassium phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate, or combinations of ammonium phosphate, sodium dihydrogen phosphate, and sodium monohydrogen phosphate.

[0020] Preferably, the iron and phosphorus-containing materials include one or a combination of at least two of the following: iron phosphate, ferrous phosphate, lithium iron phosphate, iron phosphate, waste lithium iron phosphate black powder, or iron-phosphorus slag after lithium extraction from waste lithium iron phosphate black powder. Typical but not limited combinations include a combination of iron phosphate and ferrous phosphate, a combination of lithium iron phosphate and iron phosphate, a combination of waste lithium iron phosphate black powder and iron phosphate, or a combination of ferrous phosphate, lithium iron phosphate, and waste lithium iron phosphate black powder.

[0021] Preferably, the water-insoluble iron source includes one or a combination of at least two of the following: iron powder, iron filings, ferrous oxide, ferrous oxide, ferric oxide, ferric carbonate, ferrous sulfide, ferric hydroxide, ferrous hydroxide, ferric oxalate, ferrous oxalate, waste containing the above iron sources, or pyrite slag. Typical but not limited combinations include combinations of iron powder and iron filings, combinations of ferrous oxide and ferric carbonate, combinations of ferrous sulfide and ferric hydroxide, or combinations of ferrous hydroxide, ferric oxalate, and ferrous oxalate.

[0022] Preferably, when the water-soluble and insoluble iron source is divalent, the acidic sulfate solution obtained in the preparation needs to be oxidized. The oxidant is any one or a combination of at least two of air, oxygen, ozone or hydrogen peroxide. Typical but not limited combinations include the combination of air and oxygen, the combination of ozone and hydrogen peroxide, or the combination of air, oxygen and hydrogen peroxide.

[0023] Preferably, the phosphorus source used to regulate the iron-phosphorus molar ratio is one or a combination of at least two of the following: phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, and ammonium phosphate. Typical but non-limiting combinations include combinations of phosphoric acid and sodium dihydrogen phosphate, combinations of sodium monohydrogen phosphate and trisodium phosphate, combinations of potassium dihydrogen phosphate and potassium monohydrogen phosphate, combinations of tripotassium phosphate, ammonium dihydrogen phosphate, and ammonium monohydrogen phosphate, or combinations of ammonium phosphate, sodium dihydrogen phosphate, and sodium monohydrogen phosphate.

[0024] Preferably, the sulfur source used to regulate the sulfur-phosphorus molar ratio is one or a combination of at least two of sulfuric acid, sodium sulfate, potassium sulfate, or ammonium sulfate, wherein typical but not limited combinations include a combination of sulfuric acid and sodium sulfate, a combination of potassium sulfate and ammonium sulfate, or a combination of sodium sulfate, potassium sulfate, and sodium sulfate.

[0025] Preferably, the total iron ion concentration in the acidic sulfate solution in step (1) is 0.1 to 3 mol / L, for example, it can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L or 3 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0026] Preferably, the seed crystals in step (2) have a particle size of less than 20 μm, such as 20 μm, 19 μm, 17 μm, 15 μm, 12 μm or 10 μm, but are not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0027] The preferred particle size of the seed crystals in this invention is below 20 μm, which has the advantages of effectively reducing the sulfur content in ferric phosphate and effectively improving the precipitation efficiency of ferric phosphate dihydrate.

[0028] Preferably, the seed crystals comprise ferric phosphate dihydrate and / or anhydrous ferric phosphate.

[0029] Preferably, the amount of seed crystal added is 0.1 to 500 g / L, for example, it can be 0.1 g / L, 1 g / L, 10 g / L, 50 g / L, 100 g / L, 200 g / L, 300 g / L or 500 g / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] The preferred addition amount of the seed crystals in this invention is 0.1–500 g / L, which has the advantage of improving the recovery efficiency of low-sulfur iron phosphate.

[0031] Preferably, the method of adding the seed crystal in step (2) includes directly adding the seed crystal solid or adding the seed crystal slurry.

[0032] Preferably, the seed slurry includes a slurry obtained by mixing seed crystals with water; or a slurry obtained by wet milling seed crystals; or a slurry obtained by aging seed crystals in phosphoric acid medium after wet milling.

[0033] Preferably, the concentration of the phosphoric acid medium is 0 to 1 mol / L, for example, it can be 0 mol / L, 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 0.8 mol / L or 1 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the aging temperature is 40 to 200°C, for example, it can be 40°C, 80°C, 100°C, 120°C, 150°C or 200°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the aging time is 0.1 to 100 hours, for example, it can be 0.1 hours, 1 hour, 10 hours, 50 hours, 80 hours or 100 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0036] Preferably, the crystallization temperature in step (2) is 40 to 200°C, for example, it can be 40°C, 80°C, 100°C, 120°C, 150°C or 200°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the crystallization time is 0.1 to 72 hours, for example, it can be 0.1 hours, 1 hour, 5 hours, 20 hours, 40 hours or 72 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0038] Preferably, step (3) further includes washing and drying the ferric phosphate solid sequentially after solid-liquid separation.

[0039] The solid-liquid separation described in this invention is not limited, and any method known to those skilled in the art for solid-liquid separation can be used, such as filtration, sedimentation, or centrifugation.

[0040] Preferably, the calcination temperature in step (4) is 100 to 900°C, for example, it can be 100°C, 200°C, 500°C, 700°C, 800°C or 900°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] Preferably, the calcination time is 0.1 to 20 hours, for example, it can be 0.1 hours, 1 hour, 5 hours, 10 hours, 15 hours or 20 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0042] Preferably, the calcination atmosphere in step (4) includes a non-reducing atmosphere.

[0043] Preferably, the non-reducing atmosphere includes any one or a combination of at least two of oxygen, air, nitrogen, argon, helium or carbon dioxide, wherein typical but non-limiting combinations include a combination of oxygen and air, a combination of nitrogen and argon, a combination of helium and carbon dioxide, or a combination of oxygen, air and nitrogen.

[0044] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0045] (1) Prepare an acidic sulfate solution containing ferric ions and phosphate ions, and control the iron-phosphorus molar ratio and phosphorus-sulfur molar ratio in the acidic sulfate solution to be 0.01-10;

[0046] The method for preparing the acidic sulfate solution includes: dissolving a water-soluble iron source and a phosphorus source in water; or dissolving an iron- and phosphorus-containing material in a sulfuric acid solution; or dissolving a water-insoluble iron source and a phosphorus source in a sulfuric acid solution; wherein the water-soluble iron source includes ferric sulfate and / or ferrous sulfate; and the phosphorus source includes one or a combination of at least two of the following: phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, or ammonium phosphate; wherein the iron- and phosphorus-containing material is... The materials include one or a combination of at least two of the following: ferric phosphate, ferrous phosphate, lithium iron phosphate, ferric phosphorus, waste lithium iron phosphate black powder, or iron-phosphorus slag after lithium extraction from waste lithium iron phosphate black powder; the water-insoluble iron source includes one or a combination of at least two of the following: iron powder, iron filings, ferric oxide, ferrous oxide, magnetite, ferric carbonate, ferrous sulfide, ferric hydroxide, ferrous hydroxide, ferric oxalate, ferrous oxalate, waste containing the above iron sources, or pyrite slag; the total iron ion concentration in the acidic sulfate solution is 0.1–3 mol / L;

[0047] (2) The acidic sulfate solution is heated and then seed crystals are added to crystallize; or seed crystals are added to the acidic sulfate solution and then heated to crystallize.

[0048] The seed crystals have a particle size of less than 20 μm; the seed crystals include ferric phosphate dihydrate and / or anhydrous ferric phosphate; the amount of seed crystals added is 0.1–500 g / L; the seed crystals are added by directly adding solid seed crystals or adding seed crystal slurry; the seed crystal slurry includes a slurry obtained by mixing seed crystals with water; or a slurry obtained by wet milling seed crystals; or a slurry obtained by wet milling seed crystals and aging them in a phosphoric acid medium with a concentration of 0–1 mol / L at a temperature of 40–200 °C for 0.1–100 h; the crystallization temperature is 40–200 °C; the crystallization time is 0.1–72 h;

[0049] (3) After the crystallization is completed, liquid-solid separation is performed to obtain the crystallized liquid and iron phosphate solid; the iron phosphate solid is washed and dried in sequence.

[0050] (4) The solid iron phosphate is calcined at a temperature of 100 to 900°C for 0.1 to 20 hours to obtain the low-sulfur iron phosphate; the sulfur content of the low-sulfur iron phosphate is ≤200ppm; the calcination atmosphere includes a non-reducing atmosphere; the non-reducing atmosphere includes any one or a combination of at least two of oxygen, air, nitrogen, argon, helium or carbon dioxide.

[0051] Compared with the prior art, the present invention has at least the following beneficial effects:

[0052] The present invention provides a method for preparing low-sulfur ferric phosphate that is simple to operate, low in cost, and can produce ferric phosphate with low sulfur content. The process does not produce any harmful substances, making it a green and environmentally friendly method with the prospect of large-scale application. Attached Figure Description

[0053] Figure 1 This is a process flow diagram of the preparation method of low-sulfur ferric phosphate in a specific embodiment of the present invention. Detailed Implementation

[0054] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0055] The present invention will now be described in further detail. However, the examples described below are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0056] like Figure 1 As shown, this invention provides a specific embodiment of a method for preparing low-sulfur ferric phosphate. Specifically, the preparation method includes the following steps:

[0057] (1) Prepare an acidic sulfate solution containing ferric ions and phosphate ions, and control the iron-phosphorus molar ratio and phosphorus-sulfur molar ratio in the acidic sulfate solution to be 0.01-10;

[0058] The method for preparing the acidic sulfate solution includes: dissolving a water-soluble iron source and a phosphorus source in water; or dissolving an iron- and phosphorus-containing material in a sulfuric acid solution; or dissolving a water-insoluble iron source and a phosphorus source in a sulfuric acid solution; wherein the water-soluble iron source includes ferric sulfate and / or ferrous sulfate; and the phosphorus source includes one or a combination of at least two of the following: phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, or ammonium phosphate; wherein the iron- and phosphorus-containing material is... The materials include one or a combination of at least two of the following: ferric phosphate, ferrous phosphate, lithium iron phosphate, ferric phosphorus, waste lithium iron phosphate black powder, or iron-phosphorus slag after lithium extraction from waste lithium iron phosphate black powder; the water-insoluble iron source includes one or a combination of at least two of the following: iron powder, iron filings, ferric oxide, ferrous oxide, magnetite, ferric carbonate, ferrous sulfide, ferric hydroxide, ferrous hydroxide, ferric oxalate, ferrous oxalate, waste containing the above iron sources, or pyrite slag; the total iron ion concentration in the acidic sulfate solution is 0.1–3 mol / L;

[0059] (2) The acidic sulfate solution is heated and then seed crystals are added to crystallize; or seed crystals are added to the acidic sulfate solution and then heated to crystallize.

[0060] The seed crystals have a particle size of less than 20 μm; the seed crystals include ferric phosphate dihydrate and / or anhydrous ferric phosphate; the amount of seed crystals added is 0.1–500 g / L; the seed crystals are added by directly adding solid seed crystals or adding seed crystal slurry; the seed crystal slurry includes a slurry obtained by mixing seed crystals with water; or a slurry obtained by wet milling seed crystals; or a slurry obtained by wet milling seed crystals and aging them in a phosphoric acid medium with a concentration of 0–1 mol / L at a temperature of 40–200 °C for 0.1–100 h; the crystallization temperature is 40–200 °C; the crystallization time is 0.1–72 h;

[0061] (3) After the crystallization is completed, liquid-solid separation is performed to obtain the crystallized liquid and iron phosphate solid; the iron phosphate solid is washed and dried in sequence.

[0062] (4) The solid iron phosphate is calcined at a temperature of 100 to 900°C for 0.1 to 20 hours to obtain the low-sulfur iron phosphate; the sulfur content of the low-sulfur iron phosphate is ≤200ppm; the calcination atmosphere includes a non-reducing atmosphere; the non-reducing atmosphere includes any one or a combination of at least two of oxygen, air, nitrogen, argon, helium or carbon dioxide.

[0063] Example 1

[0064] This embodiment provides a method for preparing low-sulfur ferric phosphate, the method comprising the following steps:

[0065] (1) Prepare an acidic sulfate solution containing ferric ions and phosphate ions by dissolving water-soluble iron source ferric sulfate and phosphorus source sodium dihydrogen phosphate in water, and control the iron-phosphorus molar ratio in the acidic sulfate solution to be 5 and the phosphorus-sulfur molar ratio to be 7; the total iron ion concentration in the acidic sulfate solution is 1 mol / L.

[0066] (2) After heating the acidic sulfate solution, ferric phosphate dihydrate seed crystals with a particle size of 10 μm were directly added, and crystallization was carried out at 80 °C for 22 h; the amount of seed crystals added was 200 g / L.

[0067] (3) After the crystallization is completed, the crystallized liquid and iron phosphate solid are obtained by centrifugation; the iron phosphate solid is washed and dried in sequence.

[0068] (4) The solid iron phosphate is calcined in an oxygen atmosphere at a temperature of 300°C for 10 hours to obtain the low-sulfur iron phosphate.

[0069] Example 2

[0070] This embodiment provides a method for preparing low-sulfur ferric phosphate, the method comprising the following steps:

[0071] (1) An acidic sulfate solution containing ferric ions and phosphate ions is prepared by dissolving lithium iron phosphate containing iron and phosphorus in sulfuric acid solution, and the iron-phosphorus molar ratio in the acidic sulfate solution is controlled to be 0.9 and the phosphorus-sulfur molar ratio is controlled to be 0.01; the total iron ion concentration in the acidic sulfate solution is 3 mol / L.

[0072] (2) After heating the acidic sulfate solution, add anhydrous ferric phosphate seed crystals with a particle size of 15 μm, and crystallize at 40 °C for 72 h.

[0073] The amount of seed crystals added is 500 g / L; the seed crystals are added by mixing the seed crystals with water to obtain a seed crystal slurry;

[0074] (3) After the crystallization is completed, the liquid after crystallization and the solid iron phosphate are obtained by filtration; the solid iron phosphate is washed and dried in sequence.

[0075] (4) The solid iron phosphate is calcined in an argon atmosphere at a temperature of 900°C for 0.1 h to obtain the low-sulfur iron phosphate.

[0076] Example 3

[0077] This embodiment provides a method for preparing low-sulfur ferric phosphate, the method comprising the following steps:

[0078] (1) An acidic sulfate solution containing ferric ions and phosphate ions is prepared by dissolving water-insoluble iron source iron oxide and phosphoric acid source in sulfuric acid solution, and the iron-phosphorus molar ratio and phosphorus-sulfur molar ratio in the acidic sulfate solution are controlled to be 10; the total iron ion concentration in the acidic sulfate solution is 0.1 mol / L.

[0079] (2) Add ferric phosphate dihydrate seed crystals with a particle size of 17 μm directly to the acidic sulfate solution and then heat the solution to crystallize at 200 °C for 0.1 h; the amount of seed crystals added is 0.1 g / L;

[0080] (3) After the crystallization is completed, precipitation is performed to obtain the crystallized liquid and iron phosphate solid; the iron phosphate solid is washed and dried in sequence.

[0081] (4) The solid iron phosphate is calcined in a nitrogen atmosphere at a temperature of 100°C for 10 hours to obtain the low-sulfur iron phosphate.

[0082] Example 4

[0083] This embodiment provides a method for preparing low-sulfur ferric phosphate, the method comprising the following steps:

[0084] (1) An acidic sulfate solution containing ferric ions and phosphate ions is prepared by dissolving the iron and phosphorus-containing waste lithium iron phosphate black powder residue after lithium extraction with sulfuric acid solution, and the iron-phosphorus molar ratio in the acidic sulfate solution is controlled to be 0.5 and the phosphorus-sulfur molar ratio is controlled to be 6.5; the total iron ion concentration in the acidic sulfate solution is 0.9 mol / L.

[0085] (2) Add anhydrous ferric phosphate seed slurry with a particle size of 12 μm to the acidic sulfate solution and then heat it to crystallize at 120°C for 36 h.

[0086] The amount of seed crystals added is 58 g / L; the seed crystal slurry is a slurry obtained by wet grinding of seed crystals and aging at 100°C for 3 hours in a phosphoric acid medium with a concentration of 1 mol / L.

[0087] (3) After the crystallization is completed, the crystallized liquid and iron phosphate solid are obtained by centrifugation; the iron phosphate solid is washed and dried in sequence.

[0088] (4) The solid iron phosphate is calcined in a helium atmosphere at a temperature of 200°C for 13 hours to obtain the low-sulfur iron phosphate.

[0089] Example 5

[0090] This embodiment provides a method for preparing low-sulfur iron phosphate. Except for the seed crystal particle size of 3 μm in step (2), the preparation method is the same as in Example 1.

[0091] Example 6

[0092] This embodiment provides a method for preparing low-sulfur iron phosphate. Except for the addition amount of seed crystals in step (2) being 0.1 g / L, the preparation method is the same as in Example 1.

[0093] Example 7

[0094] This embodiment provides a method for preparing low-sulfur iron phosphate. Except for the addition amount of seed crystals in step (2) being 500 g / L, the preparation method is the same as in Example 1.

[0095] Comparative Example 1

[0096] This comparative example provides a method for preparing low-sulfur iron phosphate. Except for the iron-to-phosphorus molar ratio of 0.001 in the acidic sulfate solution in step (1), the preparation method is the same as in Example 1.

[0097] Comparative Example 2

[0098] This comparative example provides a method for preparing low-sulfur iron phosphate. Except for the iron-to-phosphorus molar ratio of 15 in the acidic sulfate solution in step (1), the preparation method is the same as in Example 1.

[0099] Comparative Example 3

[0100] This comparative example provides a method for preparing low-sulfur iron phosphate. Except for the phosphorus-sulfur molar ratio of 0.001 in the acidic sulfate solution in step (1), the preparation method is the same as in Example 1.

[0101] Comparative Example 4

[0102] This comparative example provides a method for preparing low-sulfur iron phosphate. Except for the phosphorus-sulfur molar ratio of 15 in the acidic sulfate solution in step (1), the preparation method is the same as in Example 1.

[0103] The sulfur content in the low-sulfur iron phosphate prepared in the above examples and comparative examples was determined using a carbon-sulfur analyzer, and the results are shown in Table 1.

[0104] Table 1

[0105] Sulfur content (ppm) Example 1 150 Example 2 50 Example 3 180 Example 4 100 Example 5 120 Example 6 190 Example 7 120 Comparative Example 1 100 Comparative Example 2 190 Comparative Example 3 400 Comparative Example 4 130

[0106] As can be seen from Table 1:

[0107] (1) As can be seen from Examples 1 to 5, the method for preparing low-sulfur iron phosphate provided by the present invention can obtain iron phosphate with low sulfur content and iron-phosphorus ratio that meets the battery grade standard, and no harmful substances are generated during the process.

[0108] (2) As can be seen from Examples 1 and 6-7, the amount of seed crystals added does not affect the sulfur content of ferric phosphate, but it does affect the precipitation efficiency of ferric phosphate during the preparation process. In Example 6, when the amount of seed crystals added was 0.1 g / L, the precipitation efficiency of ferric phosphate was 80%. In Example 7, when the amount of seed crystals added was 500 g / L, the precipitation efficiency of ferric phosphate was 98%. This shows that by limiting the amount of seed crystals added in a specific range, the present invention can achieve a high recovery efficiency of low-sulfur ferric phosphate.

[0109] (3) It can be seen from the combined examples 1 and 2 that the change in the iron-phosphorus molar ratio in the acidic sulfate solution will not affect the sulfur content of iron phosphate. However, when the iron-phosphorus molar ratio in the acidic sulfate solution is not within the range specified in this invention, the iron-phosphorus ratio of the obtained low-sulfur iron phosphate does not meet the battery grade standard of 0.97 to 1.02.

[0110] (4) It can be seen from the comprehensive comparison of Example 1 and Comparative Examples 3-4 that the phosphorus-sulfur molar ratio in the acidic sulfate solution of Comparative Example 3 is less than 0.01, which will result in an excessively high sulfur content in the obtained iron phosphate, which is 400 ppm, and does not meet the requirements for battery preparation; the phosphorus-sulfur molar ratio in the acidic sulfate solution of Comparative Example 4 is higher than 10, which will result in a decrease in the precipitation efficiency of iron phosphate and easy complex precipitation, which is not conducive to the subsequent technical control of iron phosphate related indicators; thus, it is shown that the present invention limits the phosphorus-sulfur molar ratio in the acidic sulfate solution to a specific range in order to ensure that the sulfur content of iron phosphate is low and the recovery efficiency is high.

[0111] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing low-sulfur ferric phosphate, characterized in that, The preparation method includes the following steps: (1) Prepare an acidic sulfate solution containing iron ions and phosphate ions, and control the iron-phosphorus molar ratio in the acidic sulfate solution to be 0.01~10 and the phosphorus-sulfur molar ratio to be 0.01~10; (2) The acidic sulfate solution is heated and seed crystals are added to crystallize; or seed crystals are added to the acidic sulfate solution and the temperature is raised to crystallize. The seed crystals have a particle size of less than 20 μm; The amount of seed crystals added is 0.1~500g / L; (3) After the crystallization is completed, liquid-solid separation is performed to obtain the crystallized liquid and iron phosphate solid; (4) The ferric phosphate solid is calcined to obtain the low-sulfur ferric phosphate; the sulfur content of the low-sulfur ferric phosphate is ≤200ppm.

2. The preparation method according to claim 1, characterized in that, The iron ions mentioned in step (1) are ferric ions.

3. The preparation method according to claim 1, characterized in that, The method for preparing the acidic sulfate solution includes: dissolving water-soluble iron and phosphorus sources in water; or dissolving iron and phosphorus-containing materials in sulfuric acid solution; or dissolving water-insoluble iron and phosphorus sources in sulfuric acid solution.

4. The preparation method according to claim 3, characterized in that, The water-soluble iron source includes ferric sulfate and / or ferrous sulfate.

5. The preparation method according to claim 3, characterized in that, The phosphorus source includes one or a combination of at least two of the following: phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, or ammonium phosphate.

6. The preparation method according to claim 3, characterized in that, The iron and phosphorus-containing materials include one or a combination of at least two of the following: iron phosphate, ferrous phosphate, lithium iron phosphate, iron phosphate, waste lithium iron phosphate black powder, or iron-phosphorus slag after lithium extraction from waste lithium iron phosphate black powder.

7. The preparation method according to claim 3, characterized in that, The water-insoluble iron source includes one or a combination of at least two of the following: iron powder, iron filings, iron oxide, ferrous oxide, iron(II,III) oxide, ferric carbonate, ferrous sulfide, ferric hydroxide, ferrous hydroxide, ferric oxalate, ferrous oxalate, waste containing the above iron sources, or pyrite slag.

8. The preparation method according to claim 1, characterized in that, The total iron ion concentration in the acidic sulfate solution in step (1) is 0.1~3 mol / L.

9. The preparation method according to claim 1, characterized in that, The seed crystals in step (2) include ferric phosphate dihydrate and / or anhydrous ferric phosphate.

10. The preparation method according to claim 1, characterized in that, The method of adding the seed crystal in step (2) includes directly adding the seed crystal solid or adding the seed crystal slurry.

11. The preparation method according to claim 10, characterized in that, The seed slurry includes a slurry obtained by mixing seed crystals with water; or a slurry obtained by wet milling seed crystals; or a slurry obtained by aging seed crystals in phosphoric acid medium after wet milling.

12. The preparation method according to claim 11, characterized in that, The concentration of the phosphoric acid medium is 0~1 mol / L.

13. The preparation method according to claim 11, characterized in that, The aging temperature is 40~200℃.

14. The preparation method according to claim 11, characterized in that, The aging time is 0.1 to 100 hours.

15. The preparation method according to claim 1, characterized in that, The crystallization temperature in step (2) is 40~200℃.

16. The preparation method according to claim 1, characterized in that, The crystallization time is 0.1 to 72 hours.

17. The preparation method according to claim 1, characterized in that, Step (3) after solid-liquid separation also includes washing and drying the iron phosphate solid in sequence.

18. The preparation method according to claim 1, characterized in that, The calcination temperature in step (4) is 100~900℃.

19. The preparation method according to claim 1, characterized in that, The calcination treatment time is 0.1~20h.

20. The preparation method according to claim 1, characterized in that, The calcination atmosphere in step (4) includes a non-reducing atmosphere.

21. The preparation method according to claim 20, characterized in that, The non-reducing atmosphere includes any one or a combination of at least two of oxygen, air, nitrogen, argon, helium, or carbon dioxide.

22. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Prepare an acidic sulfate solution containing ferric ions and phosphate ions, and control the iron-phosphorus molar ratio and phosphorus-sulfur molar ratio in the acidic sulfate solution to be 0.01~10; The method for preparing the acidic sulfate solution includes: dissolving a water-soluble iron source and a phosphorus source in water; or dissolving an iron- and phosphorus-containing material in a sulfuric acid solution; or dissolving a water-insoluble iron source and a phosphorus source in a sulfuric acid solution; wherein the water-soluble iron source includes ferric sulfate and / or ferrous sulfate; and the phosphorus source includes one or a combination of at least two of the following: phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, or ammonium phosphate; wherein the iron- and phosphorus-containing material is... The materials include one or a combination of at least two of the following: ferric phosphate, ferrous phosphate, lithium iron phosphate, ferric phosphorus, waste lithium iron phosphate black powder, or iron-phosphorus slag after lithium extraction from waste lithium iron phosphate black powder; the water-insoluble iron source includes one or a combination of at least two of the following: iron powder, iron filings, iron oxide, ferrous oxide, magnetite, ferric carbonate, ferrous sulfide, ferric hydroxide, ferrous hydroxide, ferric oxalate, ferrous oxalate, waste containing the above iron sources, or pyrite slag; the total iron ion concentration in the acidic sulfate solution is 0.1~3 mol / L; (2) The acidic sulfate solution is heated and seed crystals are added to crystallize; or seed crystals are added to the acidic sulfate solution and the temperature is raised to crystallize. The seed crystals have a particle size of less than 20 μm; the seed crystals include ferric phosphate dihydrate and / or anhydrous ferric phosphate; the amount of seed crystals added is 0.1~500 g / L; the seed crystals are added by directly adding solid seed crystals or adding seed crystal slurry; the seed crystal slurry includes a slurry obtained by mixing seed crystals with water; or a slurry obtained by wet milling seed crystals; or a slurry obtained by wet milling seed crystals and aging them in a phosphoric acid medium with a concentration of 0~1 mol / L at a temperature of 40~200℃ for 0.1~100 h; the crystallization temperature is 40~200℃; the crystallization time is 0.1~72 h; (3) After the crystallization is completed, the liquid and iron phosphate solid are obtained by liquid-solid separation; the iron phosphate solid is washed and dried in sequence. (4) The solid iron phosphate is calcined at a temperature of 100~900℃ for 0.1~20h to obtain the low sulfur iron phosphate; the sulfur content of the low sulfur iron phosphate is ≤200ppm; the calcination atmosphere includes a non-reducing atmosphere; the non-reducing atmosphere includes any one or a combination of at least two of oxygen, air, nitrogen, argon, helium or carbon dioxide.

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