Process for the preparation of anhydrous iron phosphate

Abstract

The application provides a preparation method of anhydrous ferric phosphate, and the preparation method comprises the following steps: (1) mixing an iron-containing raw material and a phosphorus-containing raw material to obtain solution A; (2) adding solution A and an oxidant B into a bottom liquid C, and then adding a pH regulator D to obtain a mixed liquid; (3) after the mixed liquid is subjected to a heating reaction, liquid-solid separation is performed to obtain a post-reaction liquid E and a ferric phosphate polyhydrate; and (4) after the ferric phosphate polyhydrate is subjected to aging in an aging liquid F, calcination treatment is performed to obtain the anhydrous ferric phosphate. The preparation method is simple in operation and low in preparation cost, the physical properties of the anhydrous ferric phosphate can be well controlled by adjusting process parameters and operation steps, no harmful substances are generated in the preparation process, and the preparation method is environment-friendly.

Description

Technical Field

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

[0002] Anhydrous ferric phosphate has the molecular formula FePO4. Existing methods for preparing ferric phosphate mainly include: (1) High-temperature roasting method, which involves directly calcining basic ferric ammonium phosphate at 550-700℃ to obtain ferric phosphate. The advantage of the high-temperature roasting method is that the process is simple and convenient, and easy to operate. The disadvantage is that the synthesis cycle is long, the energy consumption is high, and the relatively expensive basic ferric ammonium phosphate is required as raw material, resulting in high production costs; (2) Liquid-phase precipitation method, which involves adding iron and phosphorus sources into a reaction vessel to react. By adjusting the pH value of the system, ferric phosphate solid precipitate is generated in the system. Then, through a series of washing, filtering, drying, and pulverizing processes, the final ferric phosphate product is obtained. The ferric phosphate produced by the liquid-phase precipitation method has a uniform composition and fine particles. However, because the precipitate is not easy to wash, the impurity content of the product is relatively high.

[0003] CN102491302A discloses a battery-grade iron phosphate and its preparation method. This battery-grade iron phosphate is an anhydrous iron phosphate with an orthorhombic crystal structure. The preparation method involves an oxidative precipitation method using air as an oxidant. An aqueous solution of a mixture of divalent iron salt and phosphoric acid or phosphate is added, along with a pH adjuster solution. Air is then introduced, and the mixture is stirred to generate a crystalline complex containing ammonium, hydroxide, and water of crystallization. The resulting product is then obtained through solid-liquid separation, washing, drying, and calcination. This battery-grade iron phosphate is an ideal raw material for preparing lithium iron phosphate, the cathode material for lithium-ion batteries.

[0004] CN106586996A discloses a method for synthesizing anhydrous iron phosphate. The method involves adding 115-127 parts by weight of phosphoric acid to 350 parts by weight of deionized water to prepare a phosphoric acid solution. Then, 80 parts by weight of iron oxide powder are added under stirring. After mixing, the solution is ball-milled in a nano-sand mill. The reaction temperature during ball milling is controlled at 60-80℃. After ball milling for a certain time, a ball-milled suspension with a particle size distribution D50 less than 100nm is obtained. The material is then removed, and the obtained ball-milled suspension is spray-dried at 180-220℃ to obtain spherical precursor powder. Finally, the obtained spherical precursor powder is calcined in air at 700-800℃ for 2-6 hours to obtain anhydrous iron phosphate material.

[0005] CN111377426A discloses a method for preparing anhydrous iron phosphate nanoparticles, comprising: adding iron powder to a phosphoric acid solution, heating to approximately 40°C, maintaining the temperature, adding an oxidant, continuing to maintain the temperature, filtering to obtain a brownish-red filtrate; adding an oxidant to the filtrate and stirring at room temperature; then filtering, washing, and drying to obtain a pale yellow powder; and treating the powder at a high temperature of 500°C–700°C to obtain anhydrous iron phosphate nanoparticles. The oxidation of ferrous ions is completed at room temperature, and iron phosphate does not require crystallization aging, further reducing the cost of preparing iron phosphate.

[0006] However, the above-mentioned methods for preparing ferric phosphate cannot control the physical properties of anhydrous ferric phosphate. Summary of the Invention

[0007] To address the aforementioned technical problems, this invention provides a method for preparing anhydrous iron phosphate. By adjusting process parameters and operating steps, the physical properties of anhydrous iron phosphate can be controlled to obtain anhydrous iron phosphate with small particle size, large specific surface area, and high tap density, making it suitable as a raw material for lithium-ion battery cathode materials.

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

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

[0010] (1) Mix the iron-containing raw material and the phosphorus-containing raw material to obtain solution A;

[0011] (2) After adding solution A and oxidant B to the base solution C at the same time, add pH adjuster D to obtain a mixed solution;

[0012] (3) After the mixture is heated and reacted, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate;

[0013] (4) After aging the ferric phosphate polyhydrate in aging solution F, it is calcined to obtain anhydrous ferric phosphate.

[0014] The method for preparing anhydrous ferric phosphate described in this invention achieves synergistic control of the particle size and specific surface area of ​​ferric phosphate hydrate by simultaneously adding solution A and oxidant B to the base solution C. The pH is then adjusted to obtain a mixed solution, which is heated to obtain ferric phosphate polyhydrate. Further aging and calcination are then performed to obtain anhydrous ferric phosphate. The preparation method of this invention is simple to operate, low in cost, and yields anhydrous ferric phosphate with excellent physical properties. No harmful substances are generated during the preparation process, making it environmentally friendly.

[0015] Preferably, the iron-containing raw material in step (1) includes a water-soluble iron source and a water-insoluble iron source.

[0016] Preferably, the water-soluble iron source includes any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride, wherein typical but non-limiting combinations include a combination of ferrous sulfate and ferrous nitrate, a combination of ferrous chloride and ferrous sulfate, or a combination of ferrous nitrate and ferrous chloride.

[0017] Preferably, the water-insoluble iron source includes any one or a combination of at least two of the following: iron powder, iron filings, ferrous oxide, ferric carbonate, ferrous sulfide, ferrous hydroxide, ferrous oxalate, waste containing the above iron sources, or pyrite slag. Typical but non-limiting combinations include combinations of iron powder and iron filings, combinations of ferrous oxide and ferric carbonate, combinations of ferrous sulfide and ferrous hydroxide, or combinations of ferrous oxalate and iron powder.

[0018] Preferably, the phosphorus-containing raw material includes any 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, ammonium phosphate, ferrous phosphate, iron phosphate, lithium-extracting iron-phosphorus slag, or lithium iron phosphate black powder. 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, or combinations of tripotassium phosphate and ammonium dihydrogen phosphate.

[0019] Preferably, the total concentration of ferrous ions in solution A is 0.01 to 3 mol / L, for example, it can be 0.01 mol / L, 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0020] Preferably, the base liquid C in step (2) comprises water.

[0021] Preferably, the oxidant B comprises any one or a combination of at least two of oxygen, ozone, air, hydrogen peroxide, sodium chlorate, sodium hypochlorite, or potassium sodium ammonium persulfate, wherein typical but non-limiting combinations include a combination of oxygen and ozone, a combination of air and hydrogen peroxide, a combination of sodium chlorate and sodium hypochlorite, or a combination of potassium sodium ammonium persulfate and oxygen.

[0022] Preferably, the amount of oxidant B is 0.5 to 5 times the theoretical amount of ferrous oxide, for example, it can be 0.5 times, 1 time, 1.5 times, 2 times, 3 times, 4 times or 5 times, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0023] Preferably, the time for adding solution A to the base solution C is from 10 min to 72 h, for example, it can be 10 min, 15 min, 20 min, 30 min, 45 min, 1 h, 3 h, 5 h, 10 h, 20 h, 50 h or 72 h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] Preferably, the oxidant B is added to the base solution C at a time of 10 min to 72 h, for example, 10 min, 15 min, 20 min, 30 min, 45 min, 1 h, 3 h, 5 h, 10 h, 20 h, 50 h or 72 h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] In this invention, it is preferable that the time for adding solution A to the base solution C is equal to the time for adding oxidant B to the base solution C, which has the advantage of stabilizing the physical properties of the ferric phosphate product. When the time for adding solution A to the base solution C is not equal to the time for adding oxidant B to the base solution C, it will lead to a decrease in the consistency of the product's physical properties.

[0026] Preferably, the pH adjuster D in step (2) comprises any one or a combination of at least two of the following: sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, lithium hydroxide, lithium carbonate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, ammonia, ammonium bicarbonate, ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ferric hydroxide, ferrous hydroxide, ferric oxide, ferric carbonate, iron powder or iron filings. Typical but non-limiting combinations include combinations of sodium hydroxide and sodium carbonate, combinations of sodium bicarbonate and potassium hydroxide, combinations of potassium carbonate and potassium bicarbonate, combinations of lithium hydroxide and lithium carbonate, combinations of lithium phosphate and lithium monohydrogen phosphate, combinations of lithium dihydrogen phosphate and sodium phosphate, or combinations of sodium monohydrogen phosphate and sodium dihydrogen phosphate.

[0027] Preferably, the pH value of the mixture is 1.5 to 5, for example, it can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] The present invention preferably uses a mixed solution with a pH value of 1.5 to 5, which has the advantage of improving the precipitation efficiency and quality of ferric phosphate. When the pH value of the mixed solution is low, the precipitation efficiency will be low; when the pH value of the mixed solution is high, a large amount of ferric hydroxide will be generated.

[0029] Preferably, after adding pH adjuster D to the base liquid C, seed crystal #1 is also added, which has the advantage of further improving the physical properties of the product.

[0030] Preferably, the seed crystal #1 comprises iron phosphate polyhydrate.

[0031] Preferably, the amount of the No. 1 seed crystal added is 0.1 to 200 g / L, for example, it can be 0.1 g / L, 0.5 g / L, 1 g / L, 5 g / L, 10 g / L, 50 g / L, 100 g / L, 150 g / L or 200 g / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0032] The preferred dosage of the No. 1 seed crystal in this invention is 0.1–200 g / L, which has the advantage of stably controlling the physical properties of the iron phosphate product. Insufficient dosage of the No. 1 seed crystal will result in a poorer control effect; excessive dosage will lead to a significant increase in production costs.

[0033] Preferably, the heating reaction temperature in step (3) is 20 to 200°C, for example, it can be 20°C, 50°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] Preferably, the heating reaction time is 0.1 to 72 hours, for example, it can be 0.1 hours, 0.5 hours, 1 hour, 3 hours, 5 hours, 10 hours, 20 hours, 40 hours, 50 hours or 72 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0035] Preferably, the first stirring is performed during the heating reaction.

[0036] Preferably, the speed of the first stirring is 5 to 1000 rpm, for example, it can be 5 rpm, 10 rpm, 20 rpm, 50 rpm, 100 rpm, 200 rpm, 500 rpm, 800 rpm, 900 rpm or 1000 rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0037] Preferably, the reaction liquid E described in step (3) is recycled as the bottom liquid C in step (2), which has the advantage of reducing the discharge of saline wastewater.

[0038] Preferably, the iron phosphate polyhydrate is recycled as seed crystal #1 in step (2), which has the advantage of reducing production energy consumption.

[0039] Preferably, during the aging process described in step (4), a No. 2 seed crystal with a particle size D50 ≤ 15 μm is added. For example, it can be 15 μm, 13 μm, 10 μm, 8 μm, 5 μm, 2 μm or 1 μm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0040] In this invention, it is preferable to add seed crystals of size 2 with a particle size D50 ≤ 15 μm during the aging process. Controlling the particle size of seed crystals of size 2 has the effect of stabilizing the physical properties of iron phosphate products.

[0041] Preferably, the seed crystal #2 comprises iron phosphate dihydrate.

[0042] Preferably, the method for grinding the No. 2 seed crystal includes any one or a combination of at least two of stirring milling, ball milling, sand milling or air jet milling, wherein typical but non-limiting combinations include a combination of stirring milling and ball milling, a combination of sand milling and air jet milling or a combination of ball milling and sand milling.

[0043] Preferably, the stirring mill, ball mill, or sand milling method includes either dry milling or wet milling.

[0044] Preferably, the medium for wet milling includes any one or a combination of at least two of methanol, ethanol, propanol, water, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, acetic acid, or citric acid, wherein typical but non-limiting combinations include combinations of methanol and ethanol, propanol and water, hydrochloric acid and sulfuric acid, phosphoric acid and nitric acid, or acetic acid and citric acid.

[0045] Preferably, the liquid-to-solid ratio of the medium to the material during the wet milling process is (1-20):1mL / g, for example, it can be 1:1mL / g, 3:1mL / g, 5:1mL / g, 10:1mL / g, 12:1mL / g, 15:1mL / g, 18:1mL / g or 20:1mL / g, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the aging solution F comprises water or an acidic solution.

[0047] Preferably, the acidic solution comprises any one or a combination of at least two of phosphoric acid, nitric acid, hydrochloric acid, or sulfuric acid, wherein typical but non-limiting combinations include combinations of phosphoric acid and nitric acid, combinations of hydrochloric acid and sulfuric acid, combinations of phosphoric acid and nitric acid, or combinations of hydrochloric acid and sulfuric acid.

[0048] Preferably, the hydrogen ion concentration in the acidic solution is 0.1 to 3 mol / L, for example, it can be 0.1 mol / L, 0.3 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L or 3 mol / L, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0049] Preferably, the aging temperature is 40 to 200°C, for example, it can be 40°C, 50°C, 80°C, 100°C, 120°C, 150°C, 180°C or 200°C, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the aging time is 0.1 to 72 hours, for example, it can be 0.1 hours, 0.5 hours, 1 hour, 3 hours, 5 hours, 10 hours, 20 hours, 40 hours, 50 hours or 72 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0051] Preferably, a second stirring is required during the aging process.

[0052] Preferably, the second stirring speed is 5 to 1000 rpm, for example, it can be 5 rpm, 10 rpm, 20 rpm, 50 rpm, 100 rpm, 200 rpm, 500 rpm, 800 rpm, 900 rpm or 1000 rpm, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] Preferably, the calcination temperature is 100 to 900°C, for example, it can be 100°C, 150°C, 180°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.

[0054] Preferably, the calcination time is 0.1 to 720 h, for example, it can be 0.1 h, 0.5 h, 1 h, 10 h, 50 h, 100 h, 200 h, 400 h, 500 h or 720 h, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the atmosphere for the calcination treatment includes a non-reducing atmosphere.

[0056] Preferably, the non-reducing atmosphere includes any one or a combination of at least two of the following: oxygen atmosphere, air atmosphere, nitrogen atmosphere, argon atmosphere, helium atmosphere or carbon dioxide atmosphere. Typical but non-limiting combinations include the combination of oxygen atmosphere and air atmosphere, the combination of nitrogen atmosphere and argon atmosphere, the combination of helium atmosphere and carbon dioxide atmosphere, or the combination of oxygen atmosphere and argon atmosphere.

[0057] As a preferred technical solution of the present invention, the preparation method includes the following steps:

[0058] (1) Mix the iron-containing raw material and the phosphorus-containing raw material to obtain solution A;

[0059] The iron-containing raw materials include water-soluble iron sources and water-insoluble iron sources; the water-soluble iron sources include any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride; the water-insoluble iron sources include any one or a combination of at least two of iron powder, iron filings, ferrous oxide, ferric carbonate, ferrous sulfide, ferrous hydroxide, ferrous oxalate, waste containing the above iron sources, or pyrite slag; the phosphorus-containing raw materials include any one or a combination of at least two of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, ferrous phosphate, ferric phosphorus, lithium-extracted iron-phosphorus slag, or lithium iron phosphate black powder.

[0060] The total concentration of ferrous ions in solution A is 0.01–3 mol / L;

[0061] (2) After adding solution A and oxidant B to the bottom solution C at the same time, add pH adjuster D to obtain a mixed solution with a pH value of 1.5 to 5;

[0062] The base liquid C includes water; the oxidant B includes any one or a combination of at least two of oxygen, ozone, air, hydrogen peroxide, sodium chlorate, sodium hypochlorite, or potassium sodium ammonium persulfate.

[0063] The amount of oxidant B used is 0.5 to 5 times the theoretical amount of ferrous oxide; the time for adding solution A to the base solution C is 10 min to 72 h; the time for adding oxidant B to the base solution C is 10 min to 72 h.

[0064] The pH adjuster D includes any one or a combination of at least two of the following: sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, lithium hydroxide, lithium carbonate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, ammonia, ammonium bicarbonate, ammonium phosphate, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ferric hydroxide, ferrous hydroxide, ferric oxide, ferric carbonate, iron powder or iron filings;

[0065] After adding pH adjuster D to the base solution C, ferric phosphate polyhydrate seed crystals (No. 1) were also added; the amount of seed crystals (No. 1) added was 0.1–200 g / L.

[0066] (3) After the mixture is heated at a temperature of 20 to 200°C for 0.1 to 72 hours, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate.

[0067] During the heating reaction, a first stirring is performed at a speed of 5 to 1000 rpm;

[0068] The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2);

[0069] (4) The ferric phosphate polyhydrate is placed in aging solution F and aged at a temperature of 40-200℃ for 0.1-72h, and then calcined at a temperature of 100-900℃ for 0.1-720h to obtain anhydrous ferric phosphate;

[0070] During the aging process, ferric phosphate dihydrate with a particle size D50≤15μm (No. 2 seed crystals) is added.

[0071] The aging solution F includes water or an acidic solution; the acidic solution includes any one or a combination of at least two of phosphoric acid, nitric acid, hydrochloric acid, or sulfuric acid; the hydrogen ion concentration in the acidic solution is 0.1–3 mol / L.

[0072] The aging process requires a second stirring at a speed of 5 to 1000 rpm;

[0073] The atmosphere for the calcination treatment includes a non-reducing atmosphere; the non-reducing atmosphere includes any one or a combination of at least two of the following: oxygen atmosphere, air atmosphere, nitrogen atmosphere, argon atmosphere, helium atmosphere or carbon dioxide atmosphere.

[0074] Compared with the prior art, the present invention has at least the following beneficial effects:

[0075] The present invention provides a method for preparing anhydrous ferric phosphate that is simple to operate, low in cost, and yields anhydrous ferric phosphate with a particle size of less than 5 μm and a specific surface area of ​​up to 9 m². 2 The density is above / g, and the tap density reaches 0.7g / cm³. 3 The above are suitable raw materials for use as cathode materials in lithium-ion batteries. Detailed Implementation

[0076] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0077] 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.

[0078] Example 1

[0079] This embodiment provides a method for preparing anhydrous ferric phosphate, the method comprising the following steps:

[0080] (1) Mix ferrous sulfate, an iron-containing raw material, and sodium dihydrogen phosphate, a phosphorus-containing raw material, to obtain solution A;

[0081] The total concentration of divalent iron ions in solution A is 1 mol / L;

[0082] (2) After adding solution A and oxidant B ozone to the bottom solution C water at the same time, add pH adjuster D sodium hydroxide to obtain a mixed solution with a pH value of 3.

[0083] The amount of oxidant B ozone used is 3 times the theoretical amount of ferrous oxide used; the time for adding solution A to the bottom liquid C water is equal to the time for adding oxidant B ozone to the bottom liquid C water, which is 50 minutes.

[0084] After adding pH adjuster D (sodium hydroxide) to the base solution C (water), ferric phosphate polyhydrate (1# seed crystal) was also added; the amount of 1# seed crystal added was 100 g / L.

[0085] (3) After the mixture is heated at 100°C for 50 hours, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate.

[0086] During the heating reaction, a first stirring at a speed of 500 rpm is performed.

[0087] The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2);

[0088] (4) The ferric phosphate polyhydrate was placed in aging solution F water and aged at 100°C for 22 hours, and then calcined at 300°C for 120 hours to obtain anhydrous ferric phosphate.

[0089] During the aging process, ferric phosphate dihydrate seed crystals with a particle size of 10 μm at the D50 position (2#) are added; the 2# seed crystals are ground by a stirred mill; the stirred milling method is dry milling.

[0090] The aging process requires a second stirring at a speed of 500 rpm; the calcination treatment is performed in an oxygen atmosphere.

[0091] Example 2

[0092] This embodiment provides a method for preparing anhydrous ferric phosphate, the method comprising the following steps:

[0093] (1) Mix ferrous nitrate (containing iron) and potassium dihydrogen phosphate (containing phosphorus) to obtain solution A;

[0094] The total concentration of ferrous ions in solution A is 0.1 mol / L;

[0095] (2) After adding solution A and oxidant B sodium chlorate to the bottom solution C water, add pH adjuster D lithium dihydrogen phosphate to obtain a mixed solution with a pH value of 1.5.

[0096] The amount of oxidant B sodium chlorate used is 1 times the theoretical amount of ferrous oxide used; the time for adding solution A to the base solution C water is equal to the time for adding oxidant B sodium chlorate to the base solution C water, which is 10 minutes.

[0097] After adding the pH adjuster D (lithium dihydrogen phosphate) to the base solution C (water), ferric phosphate polyhydrate (seed crystal #1) was also added; the amount of seed crystal #1 added was 0.1 g / L.

[0098] (3) After the mixture is heated at 200°C for 0.1 h, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate.

[0099] The heating reaction process involves a first stirring at a speed of 1000 rpm;

[0100] The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2);

[0101] (4) The ferric phosphate polyhydrate was aged in nitric acid F at 200°C for 0.1 h, and then calcined at 100°C for 720 h to obtain anhydrous ferric phosphate.

[0102] During the aging process, ferric phosphate dihydrate seed crystals with a particle size D50 of 15 μm are added. The seed crystals are ground by ball milling. The ball milling is wet milling. The medium for wet milling is methanol. The liquid-solid ratio of the medium to the material during wet milling is 1:1 mL / g.

[0103] The hydrogen ion concentration in the nitric acid is 0.1 mol / L; a second stirring at a speed of 5 rpm is required during the aging process; and the atmosphere for the calcination treatment is a helium atmosphere.

[0104] Example 3

[0105] This embodiment provides a method for preparing anhydrous ferric phosphate, the method comprising the following steps:

[0106] (1) Mix ferrous oxalate, an iron-containing raw material, and ammonium hydrogen phosphate, a phosphorus-containing raw material, to obtain solution A;

[0107] The total concentration of divalent iron ions in solution A is 3 mol / L;

[0108] (2) After adding solution A and oxidant B potassium sodium ammonium persulfate to the bottom solution C water, add pH adjuster D ammonia water to obtain a mixed solution with a pH value of 5.

[0109] The amount of oxidant B, potassium sodium ammonium persulfate, is 5 times the theoretical amount of ferrous oxide; the time for adding solution A to the base solution C (water) is equal to the time for adding oxidant B, potassium sodium ammonium persulfate, to the base solution C (water), which is 72 hours.

[0110] After adding pH adjuster D (ammonia) to the base solution C, ferric phosphate polyhydrate (seeded crystal No. 1) was also added; the amount of seed crystal No. 1 added was 200 g / L.

[0111] (3) After the mixture is heated at 20°C for 72 hours, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate.

[0112] During the heating reaction, a first stirring at a speed of 5 rpm is performed.

[0113] The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2);

[0114] (4) The ferric phosphate polyhydrate was aged in sulfuric acid F at 40°C for 72 hours and then calcined at 900°C for 0.1 hours to obtain anhydrous ferric phosphate.

[0115] During the aging process, ferric phosphate dihydrate seed crystals with a particle size D50 of 8 μm are added. The seed crystals are ground by sand milling. The sand milling method is wet milling. The medium for wet milling is propanol. The liquid-solid ratio of the medium to the material during wet milling is 5:1 mL / g.

[0116] The sulfuric acid has a hydrogen ion concentration of 3 mol / L; the aging process requires a second stirring at a speed of 1000 rpm; and the calcination process is carried out in a carbon dioxide atmosphere.

[0117] Example 4

[0118] This embodiment provides a method for preparing anhydrous ferric phosphate, the method comprising the following steps:

[0119] (1) Mix the iron-containing raw material and the phosphorus-containing raw material to obtain solution A;

[0120] The total concentration of ferrous ions in solution A is 2.3 mol / L;

[0121] (2) After adding solution A and oxidant B air to the bottom solution C water at the same time, add pH adjuster D ammonium phosphate to obtain a mixed solution with a pH value of 1.5;

[0122] The amount of oxidant B (air) used is 1.5 times the theoretical amount of ferrous oxide used; the time for adding solution A to the base solution C (water) is equal to the time for adding oxidant B (air) to the base solution C (water), which is 2 hours.

[0123] After adding pH adjuster D ammonium phosphate to the base solution C water, ferric phosphate polyhydrate seed crystal No. 1 was also added; the amount of seed crystal No. 1 added was 50 g / L.

[0124] (3) After the mixture is heated at 60°C for 2 hours, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate.

[0125] The heating reaction process involves a first stirring at a speed of 800 rpm;

[0126] The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2);

[0127] (4) The ferric phosphate polyhydrate was placed in an aging solution F phosphoric acid and aged at 70°C for 3 hours, and then calcined at 300°C for 120 hours to obtain anhydrous ferric phosphate.

[0128] During the aging process, ferric phosphate dihydrate seed crystals with a particle size D50 of 11 μm (No. 2) are added; the No. 2 seed crystals are ground by sand milling; the sand milling method is dry milling.

[0129] The hydrogen ion concentration in the phosphoric acid is 2 mol / L; a second stirring at a speed of 30 rpm is required during the aging process; and the atmosphere for the calcination treatment is air.

[0130] Example 5

[0131] This embodiment provides a method for preparing anhydrous ferric phosphate. Except for step (2), in which solution A is added to the base liquid C water for 30 minutes and oxidant B ozone is added to the base liquid C water for 50 minutes, the preparation method is the same as in embodiment 1.

[0132] Example 6

[0133] This embodiment provides a method for preparing anhydrous ferric phosphate. Except for the pH value of the mixture in step (2) being 1, the preparation method is the same as that in Example 1.

[0134] Example 7

[0135] This embodiment provides a method for preparing anhydrous ferric phosphate. Except for the pH value of the mixture in step (2) being 6, the preparation method is the same as that in Example 1.

[0136] Example 8

[0137] This embodiment provides a method for preparing anhydrous iron phosphate. The preparation method is the same as in Example 1 except that step (2) does not involve adding seed crystal #1.

[0138] Example 9

[0139] This embodiment provides a method for preparing anhydrous iron phosphate. Except for the addition of seed crystals with a particle size D50 of 30 μm during the aging process in step (4), the preparation method is the same as in Example 1.

[0140] The particle size of the anhydrous ferric phosphate obtained in the above examples and comparative examples was tested using a laser particle size analyzer.

[0141] The specific surface area of ​​anhydrous ferric phosphate obtained in the above examples and comparative examples was tested using a specific surface area analyzer.

[0142] The tap density of anhydrous ferric phosphate obtained in the above examples and comparative examples was tested using a tap density meter, and the results are shown in Table 1.

[0143] Table 1

[0144] Particle size (μm) <![CDATA[Specific surface area (m 2 / g)]]> <![CDATA[Tap density (g / cm 3 )]]> Example 1 4 10 0.8 Example 2 2 12 0.9 Example 3 5 9 0.7 Example 4 3 11 0.9 Example 5 5 9 0.7 Example 6 6 8 0.7 Example 7 3 11 0.6 Example 8 5 9 0.7 Example 9 7 7 0.6

[0145] As can be seen from Table 1:

[0146] (1) As can be seen from the comprehensive examples 1 to 4, the method for preparing anhydrous iron phosphate provided by the present invention is simple to operate, and the anhydrous iron phosphate prepared has small particle size, large specific surface area, and high tap density, making it suitable as a raw material for lithium-ion battery cathode material.

[0147] (2) It can be seen from the combined examples 1 and 5 that the time when solution A is added to the bottom liquid C water in example 5 is different from the time when oxidant B ozone is added to the bottom liquid C water. This will result in a slight increase in the particle size, a slight decrease in the specific surface area, a slight decrease in the tap density of the prepared anhydrous iron phosphate, and a deterioration in the consistency of the physical properties of anhydrous iron phosphate.

[0148] (3) As can be seen from the combined examples 1 and 6-7, the pH value of the mixture in step (2) of example 6 is relatively low, which leads to a lower precipitation efficiency of the mixture in the heating reaction, an increase in the particle size of the prepared anhydrous ferric phosphate to 6 μm, and a decrease in the specific surface area to 8 m². 2 / g, the tap density decreased to 0.7g / cm³. 3 In Example 7, the pH value of the mixture in step (2) was relatively high, which led to the formation of a large amount of ferric hydroxide. The final anhydrous ferric phosphate particles were 3 μm in size, and the specific surface area was reduced to 11 m². 2 / g, the tap density decreased to 0.6g / cm³. 3 ;

[0149] (4) It can be seen from the combined examples 1 and 8-9 that in Example 8, step (2) without adding seed crystal #1 and in Example 9, step (4) with the addition of seed crystal #2 with a particle size D50 of 30μm during the aging process will both lead to an increase in the particle size, a decrease in the specific surface area, and a decrease in the tap density of the prepared anhydrous iron phosphate.

[0150] 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 anhydrous ferric phosphate, characterized in that, The preparation method includes the following steps: (1) Mixing iron-containing raw materials and phosphorus-containing raw materials yields solution A; (2) After adding solution A and oxidant B to the bottom solution C at the same time, pH adjuster D is added, and seed crystal No. 1 is added to obtain a mixed solution; the time for adding solution A to the bottom solution C is equal to the time for adding oxidant B to the bottom solution C. The pH value of the mixture is 1.5~5; the amount of seed crystal #1 added is 0.1~200g / L; (3) After the mixture is heated and reacted, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate; The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2); (4) After aging the ferric phosphate polyhydrate in aging solution F, it is calcined to obtain anhydrous ferric phosphate; During the aging process, seed crystals of size 2 with a particle size D50 ≤ 15 μm are added; the seed crystals of size 2 include iron phosphate dihydrate.

2. The preparation method according to claim 1, characterized in that, The iron-containing raw materials in step (1) include water-soluble iron sources and water-insoluble iron sources.

3. The preparation method according to claim 2, characterized in that, The water-soluble iron source includes any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride.

4. The preparation method according to claim 2, characterized in that, The water-insoluble iron source includes any one or a combination of at least two of the following: iron powder, iron filings, ferrous oxide, ferric carbonate, ferrous sulfide, ferrous hydroxide, ferrous oxalate, waste containing the above iron sources, or pyrite slag.

5. The preparation method according to claim 1, characterized in that, The phosphorus-containing raw materials include any 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, ammonium phosphate, ferrous phosphate, iron phosphate, iron-phosphorus slag after lithium extraction, or lithium iron phosphate black powder.

6. The preparation method according to claim 1, characterized in that, The total concentration of ferrous ions in solution A is 0.01~3 mol / L.

7. The preparation method according to claim 1, characterized in that, The base liquid C in step (2) includes water.

8. The preparation method according to claim 1, characterized in that, The oxidant B includes any one or a combination of at least two of oxygen, ozone, air, hydrogen peroxide, sodium chlorate, or sodium hypochlorite.

9. The preparation method according to claim 1, characterized in that, The amount of oxidant B used is 0.5 to 5 times the theoretical amount of ferrous oxide.

10. The preparation method according to claim 1, characterized in that, The time for adding solution A to the base solution C is from 10 min to 72 h.

11. The preparation method according to claim 1, characterized in that, The pH adjuster D in step (2) includes any one or a combination of at least two of the following: sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, lithium hydroxide, lithium carbonate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, ammonia, ammonium bicarbonate, ammonium phosphate, ammonium monohydrogen phosphate, or ammonium dihydrogen phosphate.

12. The preparation method according to claim 1, characterized in that, The heating reaction in step (3) is carried out at a temperature of 20~200℃.

13. The preparation method according to claim 1, characterized in that, The heating reaction time is 0.1~72h.

14. The preparation method according to claim 1, characterized in that, The first stirring is carried out during the heating reaction.

15. The preparation method according to claim 14, characterized in that, The first stirring speed is 5~1000 rpm.

16. The preparation method according to claim 1, characterized in that, The aging solution F includes water or an acidic solution.

17. The preparation method according to claim 16, characterized in that, The acidic solution includes any one or a combination of at least two of phosphoric acid, nitric acid, hydrochloric acid, or sulfuric acid.

18. The preparation method according to claim 16, characterized in that, The hydrogen ion concentration in the acidic solution is 0.1~3 mol / L.

19. The preparation method according to claim 1, characterized in that, The aging temperature is 40~200℃.

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

21. The preparation method according to claim 1, characterized in that, A second stirring is required during the aging process.

22. The preparation method according to claim 21, characterized in that, The second stirring speed is 5~1000 rpm.

23. The preparation method according to claim 1, characterized in that, The calcination temperature is 100~900℃.

24. The preparation method according to claim 1, characterized in that, The calcination treatment time is 0.1~720h.

25. The preparation method according to claim 1, characterized in that, The atmosphere for the calcination treatment includes a non-reducing atmosphere.

26. The preparation method according to claim 25, characterized in that, The non-reducing atmosphere includes any one or a combination of at least two of the following: oxygen atmosphere, air atmosphere, nitrogen atmosphere, argon atmosphere, helium atmosphere, or carbon dioxide atmosphere.

27. The preparation method according to claim 1, characterized in that, The preparation method includes the following steps: (1) Mixing iron-containing raw materials and phosphorus-containing raw materials yields solution A; The iron-containing raw materials include water-soluble iron sources and water-insoluble iron sources; the water-soluble iron sources include any one or a combination of at least two of ferrous sulfate, ferrous nitrate, or ferrous chloride; the water-insoluble iron sources include any one or a combination of at least two of iron powder, iron filings, ferrous oxide, ferric carbonate, ferrous sulfide, ferrous hydroxide, ferrous oxalate, waste containing the above iron sources, or pyrite slag; the phosphorus-containing raw materials include any one or a combination of at least two of phosphoric acid, sodium dihydrogen phosphate, sodium monohydrogen phosphate, trisodium phosphate, potassium dihydrogen phosphate, potassium monohydrogen phosphate, tripotassium phosphate, ammonium dihydrogen phosphate, ammonium monohydrogen phosphate, ammonium phosphate, ferrous phosphate, ferric phosphorus, lithium-extracted iron-phosphorus slag, or lithium iron phosphate black powder. The total concentration of ferrous ions in solution A is 0.01~3 mol / L; (2) After adding solution A and oxidant B to the bottom solution C, add pH adjuster D to obtain a mixed solution with a pH value of 1.5~5; The base liquid C includes water; the oxidant B includes any one or a combination of at least two of oxygen, ozone, air, hydrogen peroxide, sodium chlorate, or sodium hypochlorite. The amount of oxidant B used is 0.5 to 5 times the theoretical amount of ferrous oxide; the time for adding solution A to the base solution C is 10 min to 72 h; The pH adjuster D includes any one or a combination of at least two of the following: sodium hydroxide, sodium carbonate, sodium bicarbonate, potassium hydroxide, potassium carbonate, potassium bicarbonate, lithium hydroxide, lithium carbonate, lithium phosphate, lithium monohydrogen phosphate, lithium dihydrogen phosphate, sodium phosphate, sodium monohydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium monohydrogen phosphate, potassium dihydrogen phosphate, ammonia, ammonium bicarbonate, ammonium phosphate, ammonium monohydrogen phosphate, or ammonium dihydrogen phosphate. After adding pH adjuster D to the base solution C, seed crystal #1 is also added; the amount of seed crystal #1 added is 0.1~200g / L; (3) After the mixture is heated at a temperature of 20~200℃ for 0.1~72h, the liquid and solid are separated to obtain the reaction liquid E and ferric phosphate polyhydrate; During the heating reaction, a first stirring is performed at a speed of 5~1000 rpm; The reaction solution E is recycled as the base solution C in step (2); the iron phosphate polyhydrate is recycled as the seed crystal #1 in step (2); (4) The ferric phosphate polyhydrate is placed in aging solution F and aged at a temperature of 40~200℃ for 0.1~72h, and then calcined at a temperature of 100~900℃ for 0.1~720h to obtain anhydrous ferric phosphate; During the aging process, ferric phosphate dihydrate with a particle size D50≤15μm (No. 2 seed crystals) is added. The aging solution F includes water or an acidic solution; the acidic solution includes any one or a combination of at least two of phosphoric acid, nitric acid, hydrochloric acid, or sulfuric acid; the hydrogen ion concentration in the acidic solution is 0.1~3 mol / L; The aging process requires a second stirring at a speed of 5 to 1000 rpm; The atmosphere for the calcination treatment includes a non-reducing atmosphere; the non-reducing atmosphere includes any one or a combination of at least two of the following: oxygen atmosphere, air atmosphere, nitrogen atmosphere, argon atmosphere, helium atmosphere or carbon dioxide atmosphere.