阅读说明：本技术 一种提纯硫酸亚铁和制备磷酸铁的方法 (Method for purifying ferrous sulfate and preparing iron phosphate ) 是由 郭春燕 张现峰 李宗群 郑桂富 徐善龙 郭晓燕 于 2021-07-30 设计创作，主要内容包括：本发明提供了一种提纯硫酸亚铁和制备磷酸铁的方法。所述提纯硫酸亚铁的方法包括：将硫酸法钛白粉副产物溶于水中,加入抗坏血酸,并用硫酸调节pH至1-2.5,混合,固液分离；向液相中加入络合剂,以及硫化物和/或草酸盐,混合反应,固液分离；向液相中加入磷酸,混合,沉淀,固液分离,得到提纯的硫酸亚铁溶液。所述制备磷酸铁的方法包括：将上述提纯的硫酸亚铁溶液与磷酸盐和双氧水混合反应,固体产物干燥,焙烧后得到磷酸铁。本发明提供的方法制备的磷酸铁纯度高,杂元素含量低,满足电池级磷酸铁的性能要求。(The invention provides a method for purifying ferrous sulfate and preparing ferric phosphate. The method for purifying the ferrous sulfate comprises the following steps: dissolving the sulfuric acid method titanium dioxide byproduct in water, adding ascorbic acid, adjusting pH to 1-2.5 with sulfuric acid, mixing, and performing solid-liquid separation; adding a complexing agent and sulfide and/or oxalate into a liquid phase, carrying out mixed reaction, and carrying out solid-liquid separation; adding phosphoric acid into the liquid phase, mixing, precipitating, and performing solid-liquid separation to obtain a purified ferrous sulfate solution. The method for preparing the iron phosphate comprises the following steps: and mixing the purified ferrous sulfate solution with phosphate and hydrogen peroxide for reaction, drying a solid product, and roasting to obtain the iron phosphate. The iron phosphate prepared by the method provided by the invention has high purity and low content of impurity elements, and meets the performance requirements of battery-grade iron phosphate.)

1. A method of purifying ferrous sulfate, the method comprising the steps of:

(1) dissolving the sulfuric acid method titanium dioxide byproduct in water, adding ascorbic acid, adjusting pH to 1-2.5 with sulfuric acid, mixing, and performing solid-liquid separation;

(2) adding a complexing agent and sulfide and/or oxalate into the liquid phase obtained in the step (1), mixing and reacting, and carrying out solid-liquid separation;

(3) and (3) adding phosphoric acid into the liquid phase obtained in the step (2), mixing, precipitating, and carrying out solid-liquid separation to obtain a purified ferrous sulfate solution.

2. The method according to claim 1, wherein the mass ratio of the ascorbic acid to the sulfuric acid process titanium dioxide by-product in step (1) is 0.2-3.0: 300;

preferably, the concentration of the sulfuric acid in the step (1) is 10 to 30 wt%;

preferably, the temperature of the mixing in the step (1) is 10-30 ℃ and the time is 20-60 min;

preferably, the molar ratio of the complexing agent to Ti ions in the sulfuric acid process titanium dioxide byproduct in the step (2) is 1-10: 1;

preferably, the complexing agent is cetyl trimethyl ammonium bromide and/or sodium dodecyl benzene sulfonate;

preferably, the ratio of the mole number of the sulfide and/or oxalate in the step (2) to the total mole number of Co ions, Ni ions, Cu ions, Pb ions and Mn ions in the titanium dioxide byproduct of the sulfuric acid method is 4-20: 1;

preferably, the sulfide in step (2) is selected from one or a combination of at least two of sodium sulfide, ferrous sulfide and ammonium sulfide, and is further preferably sodium sulfide;

preferably, the oxalate salt in step (2) is sodium oxalate;

preferably, the reaction in the step (2) is carried out at the temperature of 10-30 ℃ for 0.5-2 h;

preferably, the ratio of the mole number of the phosphoric acid in the step (3) to the total mole number of Al ions, Ca ions, Cd ions, Pb ions, Mg ions, Cr ions, Cu ions and Zn ions in the titanium dioxide by-product by the sulfuric acid method is 0.6-10: 1;

preferably, the temperature of the mixing in the step (3) is 10-100 ℃, and the time is 10-30 min;

preferably, the precipitation in step (3) is a standing precipitation;

preferably, the standing and precipitating time is 3-12 h;

preferably, the mixing in steps (1) to (3) is carried out under stirring conditions.

3. Method according to claim 1 or 2, characterized in that it comprises the following steps:

(1) dissolving the sulfuric acid method titanium dioxide byproduct in water, adding ascorbic acid, adjusting pH to 1-2.5 with 10-30 wt% sulfuric acid, stirring at 10-30 deg.C for 20-60min, and filtering;

(2) adding a complexing agent and sodium sulfide and/or sodium oxalate into the filtrate obtained in the step (1), stirring and reacting for 0.5-2h at the temperature of 10-30 ℃, and filtering;

(3) and (3) adding phosphoric acid into the filtrate obtained in the step (2), heating to boil, stirring for 10-30min, standing for precipitation for 3-6h, and filtering to obtain a purified ferrous sulfate solution.

4. A method for producing iron phosphate, comprising the steps of:

(1) preparing a ferrous sulfate solution using the method of any one of claims 1-3;

(2) mixing the ferrous sulfate solution obtained in the step (1) with phosphate and hydrogen peroxide for reaction, and carrying out solid-liquid separation;

(3) and (3) drying and roasting the solid product obtained in the step (2) to obtain the iron phosphate.

5. The method according to claim 4, wherein the phosphate in step (2) is (NH)₄)₂HPO₄And/or NH₄H₂PO₄；

Preferably, Fe in step (2)²⁺With added PO₄ ^3-In a molar ratio of 0.95-1.05: 1;

preferably, Fe in step (2)²⁺With addition of H₂O₂In a molar ratio of 0.95-1.05: 1;

preferably, the reaction in the step (2) is carried out at the temperature of 75-95 ℃ for 1-3 h;

preferably, the drying temperature in the step (3) is 60-80 ℃, and the time is 4-12 h;

preferably, the temperature of the roasting in the step (3) is 500-.

6. Method according to claim 4 or 5, characterized in that it comprises the following steps:

(1) preparing a ferrous sulfate solution using the method of any one of claims 1-3;

(2) adding a mixed solution of phosphate and hydrogen peroxide into the ferrous sulfate solution obtained in the step (1), wherein Fe²⁺With added PO₄ ^3-In a molar ratio of 0.95-1.05:1, Fe²⁺With addition of H₂O₂The molar ratio of 0.95-1.05:1, stirring and reacting for 1-3h at the temperature of 75-95 ℃, cooling and filtering;

(3) and (3) drying the solid product obtained in the step (2) at 60-80 ℃ for 4-12h, roasting at 500-800 ℃ for 1-3h, and grinding to obtain the iron phosphate.

7. Iron phosphate prepared by the method of any one of claims 4 to 6.

8. The use of the iron phosphate according to claim 7 in the preparation of a lithium iron phosphate positive electrode material.

9. A preparation method of a lithium iron phosphate positive electrode material, which is characterized by comprising the step of preparing iron phosphate by using the method of any one of claims 4 to 6.

10. The lithium iron phosphate positive electrode material prepared by the preparation method of claim 9.

Technical Field

The invention belongs to the technical field of inorganic materials, and particularly relates to a method for purifying ferrous sulfate and preparing iron phosphate.

Background

Titanium dioxide, i.e. titanium dioxide, is an important inorganic pigment. The industrial preparation process of titanium dioxide mainly comprises a sulfuric acid method and a chlorination method, wherein the main byproduct for preparing the titanium dioxide by the sulfuric acid method is ferrous sulfate. With the annual increase of the production amount of the titanium dioxide, a large amount of by-product ferrous sulfate is generated, and a large amount of materials are randomly stacked, so that the environment is polluted and resources are wasted.

Ferrous sulfate is a raw material for preparing iron phosphate, and FePO₄And can also be used as an iron source for preparing the anode material LiFePO of the lithium ion battery₄. With the continuous progress of new energy technology, the development opportunity is provided for the application of the lithium ion battery in the field of energy storage batteries. LiFePO₄The FePO is the lithium ion battery anode material with the most market prospect at present and is used as the precursor of the FePO due to the advantages of long cycle life, low cost, environmental friendliness, high safety and the like₄The advantages of stable structure, low cost, no toxicity and the like are attracting more and more attention. If the ferrous sulfate which is the byproduct of the titanium dioxide produced by the sulfuric acid method is used for preparing the battery-grade iron phosphate, the recycling of resources can be realized, and the problems of environmental pollution and the like can be solved. However, the by-product of the titanium dioxide produced by the sulfuric acid method contains various impurities and has high content, and the by-product cannot be directly used for preparing battery-grade iron phosphate.

At present, FePO₄The preparation method mainly comprises a coprecipitation method, a hydrothermal method, a spray drying method and the like. The coprecipitation method is to dissolve an iron source and a phosphorus source and then add themPrecipitating the compound, washing, drying and calcining to obtain FePO₄. The hydrothermal method is to carry out reaction under the conditions of high temperature and high pressure, and indissolvable substances can be dissolved and recrystallized, so that the aim of generating products is fulfilled. However, this method requires a high temperature and a high pressure, and has a high requirement for the pressure resistance of the reaction vessel, so that this method is energy-intensive and does not have the advantage of mass production. The dryer used in the spray drying method belongs to a convection type dryer, and the heat efficiency is lower.

CN 109775679a proposes a preparation method of iron phosphate for high-purity high-compaction lithium iron phosphate: the method comprises the steps of utilizing ferrous sulfate which is a byproduct of titanium dioxide as a raw material, generating a precipitate through the reaction of a sulfide and ferric hydroxide, removing impurities in the ferrous sulfate, and preparing ferric phosphate by using a ferric hydroxide filter cake. CN 108101016A discloses a method for preparing lithium iron phosphate from a byproduct ferrous sulfate of titanium white, which comprises the steps of purifying the ferrous sulfate byproduct of titanium white in a sulfuric acid process by using sodium sulfide, and reacting with phosphoric acid and hydrogen peroxide to prepare iron phosphate. However, the content of impurity elements in the iron phosphate obtained by the method is still high, the process is complex, the energy consumption is high, the cost is high, the separation efficiency is low, and an improved preparation method of battery-grade iron phosphate is to be researched so as to meet the use requirement of the lithium ion battery anode material.

Disclosure of Invention

Aiming at the defects in the prior art, the invention aims to provide a method for purifying ferrous sulfate and preparing iron phosphate. The iron phosphate prepared by the method has high purity and low content of impurity elements, and meets the performance requirements of battery-grade iron phosphate.

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

in a first aspect, the present invention provides a method of purifying ferrous sulfate, the method comprising the steps of:

(1) dissolving the titanium dioxide byproduct obtained by the sulfuric acid process in water, adding ascorbic acid, adjusting pH to 1-2.5 (such as 1, 1.2, 1.5, 1.8, 2, 2.2 or 2.5) with sulfuric acid, mixing, and performing solid-liquid separation;

(2) adding a complexing agent and sulfide and/or oxalate into the liquid phase obtained in the step (1), mixing and reacting, and carrying out solid-liquid separation;

(3) and (3) adding phosphoric acid into the liquid phase obtained in the step (2), mixing, precipitating, and carrying out solid-liquid separation to obtain a purified ferrous sulfate solution.

The sulfuric acid process titanium dioxide byproduct is a byproduct for preparing titanium dioxide industrially by a sulfuric acid process, and the main component of the byproduct is ferrous sulfate.

In some embodiments of the present invention, the content of ferrous sulfate in the sulfuric acid process titanium dioxide byproduct is 95-99.5 wt%.

In some embodiments of the present invention, the sulfuric acid process titanium dioxide byproduct contains one or more impurity metal ions selected from Al, Ca, Cd, Co, Cr, Mg, Mn, Na, Ni, Pb, Ti, Cu, and Zn.

In some embodiments of the invention, the impurity metal ions in the by-product are each present in an amount of 1.0 × 10^-8～1.0×10^-4In the range of mol/g.

In some embodiments of the invention, the total content of impurity metal ions in the by-product is 1.0 × 10^-5～1.0×10^-3In the range of mol/g.

The invention uses ascorbic acid to prevent Fe²⁺Is oxidized into Fe³⁺Increase Fe²⁺Utilization ratio of (1), reduction of Fe³⁺Interference on subsequent impurity removal processes; the four impurity removing agents of sulfuric acid, complexing agent, sulfide and/or oxalate and phosphoric acid are used for removing impurities, other metal elements in the sulfuric acid method titanium dioxide byproduct can be fully removed, the obtained ferrous sulfate solution has high purity, and the requirement for producing battery-grade iron phosphate can be met.

In the invention, the sulfuric acid is used for adjusting the pH on one hand and removing a part of Pb in the solution as an impurity removing agent on the other hand²⁺And Ca²⁺. The pH value is adjusted to 1-2.5 in the step (1), which is helpful for fully removing impurities and improving the purity of the finally prepared iron phosphate. If the pH is too high, the sulfuric acid is on the one hand directed towards Pb²⁺And Ca²⁺On the other hand, the second addition of phosphoric acid results in PO₄ ^3-For Pb²⁺、Ca²⁺、Mg²⁺The removal of (A) is insufficient, and the amount of sulfuric acid added is too small, Fe²⁺Is easy to be further oxidized to generate Fe³⁺Ions, forming hydroxide precipitates; if the pH is too low, the subsequent addition of sulfide is not favorable for generating metal sulfide precipitate, Co²⁺、Ni²⁺、Pb²⁺And Mn²⁺And the generated sulfide is not completely precipitated, and impurity ions are not sufficiently removed.

In some embodiments of the invention, the mass ratio of the ascorbic acid to the sulfuric acid process titanium dioxide byproduct in step (1) is 0.2-1.5: 300; for example, it may be 0.2:300, 0.3:300, 0.5:300, 0.8:300, 1:300, 1.2:300, 1.3:300, or 1.5:300, etc.

In the present invention, the main function of ascorbic acid is to prevent Fe²⁺Is oxidized into Fe³⁺. If the amount of addition is too small, it is difficult to sufficiently prevent Fe²⁺Oxidation of (2); if the addition amount is too much, unnecessary waste is caused, and the impurities are not beneficial to the purification of the ferrous sulfate.

In some embodiments of the invention, the concentration of sulfuric acid in step (1) is from 10 to 30 wt%; for example, it may be 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, or the like.

The concentration of sulfuric acid in the present invention is preferably in the above range, and if the concentration is too high, there is a possibility that the sulfuric acid will cause oxidation and cause Fe²⁺Oxidation of (2); if the concentration is too low, pH adjustment is not facilitated.

In some embodiments of the invention, the temperature of the mixing in step (1) is 10-30 ℃, for example, 10 ℃, 12 ℃, 15 ℃, 18 ℃, 20 ℃, 22 ℃, 25 ℃, 28 ℃ or 30 ℃ and the like; the time is 20-60min, such as 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min or 60 min.

In some embodiments of the invention, the molar ratio of the complexing agent to the Ti ions in the sulfuric acid process titanium dioxide byproduct in the step (2) is 1-10: 1; for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, or 10:1, etc.

In some embodiments of the invention, the complexing agent is cetyltrimethylammonium bromide and/or sodium dodecylbenzenesulfonate.

In the invention, the complexing agent mainly plays a role in removing Ti ions in the solution. If the amount of addition is too small, Ti ion removal is insufficient; if the addition amount is too much, unnecessary waste is caused, and the impurities are not beneficial to the purification of the ferrous sulfate.

In some embodiments of the invention, the ratio of the number of moles of the sulfide and/or oxalate in step (2) to the total number of moles of Co ions, Ni ions, Cu ions, Pb ions and Mn ions in the titanium dioxide by-product of the sulfuric acid process is 4-20: 1; for example, 4:1, 5:1, 6:1, 8:1, 10:1, 12:1, 13:1, 15:1, 16:1, 18:1, or 20:1, etc.

In some embodiments of the present invention, the sulfide in step (2) is selected from one or a combination of at least two of sodium sulfide, ferrous sulfide and ammonium sulfide, preferably sodium sulfide.

In some embodiments of the invention, the oxalate salt in step (2) is sodium oxalate.

In the invention, the sulfide mainly plays a role in removing Co ions, Ni ions, Cu ions, Pb ions and Mn ions in the solution, and the oxalate mainly plays a role in removing Ni ions and Cu ions in the solution. If the amount of addition is too small, the ion removal is insufficient; if the addition amount is too much, unnecessary waste is caused, and the impurities are not beneficial to the purification of the ferrous sulfate.

In some embodiments of the invention, the temperature of the reaction in step (2) is 10-30 ℃, for example, 10 ℃, 12 ℃, 15 ℃, 18 ℃, 20 ℃, 22 ℃, 25 ℃, 28 ℃ or 30 ℃ and the like; the time is 0.5 to 2 hours, and may be, for example, 0.5 hour, 0.8 hour, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours or the like.

In some embodiments of the invention, the ratio of the number of moles of phosphoric acid in step (3) to the total number of moles of Al ions, Ca ions, Cd ions, Pb ions, Mg ions, Cr ions, Cu ions and Zn ions in the sulfuric acid process titanium dioxide byproduct is 0.6-10: 1; for example, it may be 0.6:1, 0.8:1, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10: 1.

In the invention, the main function of the phosphoric acid is to remove Al ions, Ca ions, Cd ions, Pb ions, Mg ions, Cr ions, Cu ions and Zn ions in the solution. If the amount of addition is too small, the ion removal is insufficient; if the amount of the additive is too large, unnecessary waste is caused.

In some embodiments of the present invention, the temperature of the mixing in step (3) is 10-100 ℃, for example, 10 ℃, 12 ℃, 15 ℃, 18 ℃, 20 ℃, 22 ℃, 25 ℃, 28 ℃, 30 ℃, 35 ℃, 40 ℃, 50 ℃, 60 ℃, 70 ℃, 80 ℃, 90 ℃ or 100 ℃ and the like; the time is 10-30min, such as 10min, 12min, 15min, 18min, 20min, 22min, 25min, 28min or 30 min.

In some embodiments of the invention, the precipitation in step (3) is a standing precipitation.

In some embodiments of the invention, the standing and precipitating time is 3-12 h; for example, it may be 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, or the like.

In some embodiments of the invention, the mixing in steps (1) - (3) is performed under stirring conditions.

In some embodiments of the invention, the method comprises the steps of:

(1) dissolving the sulfuric acid method titanium dioxide byproduct in water, adding ascorbic acid, adjusting pH to 1-2.5 with 10-30 wt% sulfuric acid, stirring at 10-30 deg.C for 20-60min, and filtering;

(2) adding a complexing agent and sodium sulfide and/or sodium oxalate into the filtrate obtained in the step (1), stirring and reacting for 0.5-2h at the temperature of 10-30 ℃, and filtering;

(3) and (3) adding phosphoric acid into the filtrate obtained in the step (2), heating to boil, stirring for 10-30min, standing for precipitation for 3-6h, and filtering to obtain a purified ferrous sulfate solution.

In a second aspect, the present invention provides a method for preparing iron phosphate, the method comprising the steps of:

(1) preparing a ferrous sulfate solution using the method of the first aspect;

(2) mixing the ferrous sulfate solution obtained in the step (1) with phosphate and hydrogen peroxide for reaction, and carrying out solid-liquid separation;

(3) and (3) drying and roasting the solid product obtained in the step (2) to obtain the iron phosphate.

In some embodiments of the invention, the phosphate in step (2) is (NH)₄)₂HPO₄And/or NH₄H₂PO₄。

In some embodiments of the invention, Fe is used in step (2)²⁺With added PO₄ ^3-In a molar ratio of 0.95-1.05: 1; for example, it may be 0.95:1, 0.96:1, 0.98:1, 1:1, 1.02:1, 1.03:1 or 1.05: 1.

In some embodiments of the invention, Fe is used in step (2)²⁺With addition of H₂O₂In a molar ratio of 0.95-1.05: 1; for example, it may be 0.95:1, 0.96:1, 0.98:1, 1:1, 1.02:1, 1.03:1 or 1.05: 1.

In some embodiments of the invention, the temperature of the reaction in step (2) is 75-95 ℃, for example, 75 ℃, 78 ℃, 80 ℃, 82 ℃, 85 ℃, 88 ℃, 90 ℃, 92 ℃ or 95 ℃ and the like; the time is 1-3 h.

In some embodiments of the present invention, the temperature of the drying in step (3) is 60-80 ℃, for example, 60 ℃, 62 ℃, 65 ℃, 68 ℃, 70 ℃, 72 ℃, 75 ℃, 78 ℃ or 80 ℃ and the like; the time is 4 to 12 hours, and may be, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours.

In some embodiments of the present invention, the temperature of the calcination in step (3) is 500-; the time is 1 to 3 hours, and may be, for example, 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, or the like.

In some embodiments of the invention, the method comprises the steps of:

(1) preparing a ferrous sulfate solution using the method of the first aspect;

(2) adding a mixed solution of phosphate and hydrogen peroxide into the ferrous sulfate solution obtained in the step (1)In which Fe²⁺With added PO₄ ^3-In a molar ratio of 0.95-1.05:1, Fe²⁺With addition of H₂O₂The molar ratio of 0.95-1.05:1, stirring and reacting for 1-3h at the temperature of 75-95 ℃, cooling and filtering;

(3) and (3) drying the solid product obtained in the step (2) at 60-80 ℃ for 4-12h, roasting at 500-800 ℃ for 1-3h, and grinding to obtain the iron phosphate.

The grinding method is not particularly limited, and for example, a depolymerization breaker, a screw propulsion feeding system, a rotating drum inlaid with a blade made of non-metallic material can be used for grinding for 5-30min under the conditions of the main shaft rotation speed of 1200-.

In a third aspect, the present invention provides iron phosphate prepared by the method of the second aspect.

In a fourth aspect, the invention provides an application of the iron phosphate according to the third aspect in preparing a lithium iron phosphate positive electrode material.

In a fifth aspect, the invention provides a preparation method of a lithium iron phosphate positive electrode material, and the preparation method comprises the step of preparing iron phosphate by using the method in the second aspect.

In a sixth aspect, the invention provides a lithium iron phosphate positive electrode material prepared by the preparation method in the fifth aspect.

Compared with the prior art, the invention has the following beneficial effects:

the method provided by the invention is simple, low in energy consumption, low in cost and high in separation efficiency; the prepared iron phosphate contains less than 0.001% of Al, less than 0.0025% of Ca, less than 0.0005% of Cd, less than 0.0005% of Co, less than 0.003% of Cr, less than 0.0005% of Cu, less than 0.003% of Mg, less than 0.0025% of Mn, less than 0.015% of Na, less than 0.0025% of Ni, less than 0.0015% of Pb, less than 0.006% of Ti, less than 0.0015% of Zn, 0.96-0.97% of iron-phosphorus ratio (Fe: P molar ratio), 3.0-5.0 mu m of D50 and 0.6-1.5g/cm of tap density³The specific surface area is 9.5-22m²Per g, high purity, small particle diameter, high tap density, and large specific surface areaThe performance requirements of the battery-grade iron phosphate can be met; the recycling of ferrous sulfate which is a byproduct of titanium dioxide produced by a sulfuric acid method is realized, the problems of resource waste, environmental pollution and the like caused by stacking of the titanium dioxide byproduct are avoided, a method is provided for improving the performance and the quality of the lithium ion battery raw material, and the development requirement of the battery industry is met.

Drawings

FIG. 1 is an X-ray diffraction pattern of iron phosphate provided in example 1;

FIG. 2 is an infrared spectrum of iron phosphate provided in example 1;

figure 3 is a graph of the thermal weight loss of the iron phosphate provided in example 1;

FIG. 4 shows N of iron phosphate provided in example 1₂Adsorption-desorption isotherm diagram.

Detailed Description

The technical scheme of the invention is further explained by the specific implementation mode in combination with the attached drawings. It should be understood by those skilled in the art that the specific embodiments are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.

In the titanium dioxide by-product of the sulfuric acid process adopted in the embodiment of the invention, the ferrous sulfate content is 99.0 wt%, and the impurity element content detected by an inductively coupled plasma emission spectrometer is as follows:

example 1

The present embodiment provides a method for preparing iron phosphate, comprising the steps of:

(1) dissolving 320g of a sulfuric acid method titanium dioxide byproduct in 1L of water, adding 1g of ascorbic acid, adjusting the pH to 2 by using 20 wt% of sulfuric acid, stirring for 30min at 22 ℃, and filtering;

(2) adding 6.6g of hexadecyl trimethyl ammonium bromide and 120mL of 0.5mol/L sodium sulfide solution into the filtrate obtained in the step (1), stirring and reacting at 22 ℃ for 1h, and filtering;

(3) adding 40mL of 1.5mol/L phosphoric acid into the filtrate obtained in the step (2), heating to boiling, stirring for 20min at a rotating speed of 80r/min, standing and precipitating for 6h, and filtering to obtain a purified ferrous sulfate solution;

(4) taking 50mL of the ferrous sulfate solution obtained in the step (3), and adding 1mol/L of (NH)₄)₂HPO₄Mixing the solution with hydrogen peroxide, and adding into the ferrous sulfate solution, wherein Fe²⁺With added PO₄ ^3-In a molar ratio of 1:1, Fe²⁺With addition of H₂O₂The molar ratio of (1: 1), stirring and reacting for 2h at 85 ℃, cooling and filtering;

(5) and (3) drying the solid product obtained in the step (4) at 70 ℃ for 8h, roasting at 600 ℃ for 2h, using a depolymerizing and scattering machine, spirally propelling a feeding system, embedding a non-metal material blade into a rotary drum, and grinding for 20min under the conditions of the main shaft rotation speed of 1200rpm and the classifier rotation speed of 800rpm to obtain a white anhydrous iron phosphate solid.

Adopting X-ray diffraction, infrared spectrum, thermal weight loss (heating rate 10 ℃/min) and isothermal N₂The iron phosphate obtained in example 1 was characterized by adsorption-desorption.

Wherein fig. 1 is an X-ray diffraction pattern of the iron phosphate prepared in example 1. The spectrogram is combined with FePO₄The spectrogram and diffraction data of the standard card (01-084-0875) are similar and are trigonal system FePO₄Space group is P3132 and cell parameter is The peak type is sharper, which indicates that the crystallinity of the sample is good; and no other impurity peaks are observed in the graph, which indicates that the ferric phosphate sample prepared by the method is pure-phase FePO₄。

Fig. 2 is an infrared spectrum of the iron phosphate prepared in example 1. From FIG. 2It can be seen that, at 1062cm^-1，1025cm^-1，639cm^-1，593cm^-1Has obvious absorption peak. Wherein 1062cm^-1，1025cm^-1The strong absorption peak comes from PO₄ ^3-Symmetric and antisymmetric stretching vibration of middle P-O bond, 639cm^-1Corresponding to PO₄ ^3-Flexural vibration of middle P-O bond, 593cm^-1The absorption peak is caused by the asymmetric expansion and contraction vibration between ferrites. No stretching vibration peak and bending vibration peak of O-H bond are observed in the spectrogram, which indicates that the prepared FePO₄Contains no crystal water.

Fig. 3 is a graph of the thermal weight loss of the iron phosphate prepared in example 1. The thermogravimetric curve represents the relationship between mass fraction of a substance and temperature change. As can be seen from FIG. 3, FePO prepared in example 1₄It is very stable at high temperatures and only 1.5% weight loss on heating to 1000 c, which is likely to be the loss of free water due to moisture absorption by the sample.

FIG. 4 is N of iron phosphate prepared in example 1₂Adsorption-desorption isotherm diagram. By N₂The adsorption-desorption isotherm test obtains FePO₄BET specific surface area data of, FePO₄The BET calculation result of (A) is 20.04m²(g) description of FePO prepared₄Has larger specific surface area, which is beneficial to preparing the anode material LiFePO of the lithium ion battery₄。

Example 2

The present embodiment provides a method for preparing iron phosphate, comprising the steps of:

(1) dissolving 320g of a sulfuric acid method titanium dioxide byproduct in 1L of water, adding 0.3g of ascorbic acid, adjusting the pH to 1 by using 20 wt% of sulfuric acid, stirring for 20min at 30 ℃, and filtering;

(2) adding 3.0g of sodium dodecyl benzene sulfonate and 80mL of 0.5mol/L ammonium sulfide solution into the filtrate obtained in the step (1), stirring and reacting at 30 ℃ for 0.5h, and filtering;

(3) adding 24mL of 1.5mol/L phosphoric acid into the filtrate obtained in the step (2), heating to 50 ℃, stirring for 10min at the rotating speed of 100r/min, standing for precipitation for 3h, and filtering to obtain a purified ferrous sulfate solution;

(4) taking 50mL of the ferrous sulfate solution obtained in the step (3), and adding 1mol/L of NH₄H₂PO₄Mixing the solution with hydrogen peroxide, and adding into the ferrous sulfate solution, wherein Fe²⁺With added PO₄ ^3-In a molar ratio of 0.95:1, Fe²⁺With addition of H₂O₂The molar ratio of (1) to (2) is 0.95, stirring and reacting for 3h at 75 ℃, cooling and filtering;

(5) and (3) drying the solid product obtained in the step (4) at 80 ℃ for 4h, roasting at 500 ℃ for 3h, using a depolymerizing breaker, spirally propelling a feeding system, embedding a non-metal material blade into a rotary drum, and grinding for 5min under the conditions of the main shaft rotation speed of 1400rpm and the classifier rotation speed of 600rpm to obtain a white anhydrous iron phosphate solid.

Example 3

The present embodiment provides a method for preparing iron phosphate, comprising the steps of:

(1) dissolving 320g of a sulfuric acid method titanium dioxide byproduct in 1L of water, adding 1.6g of ascorbic acid, adjusting the pH to 2.5 by using 20 wt% of sulfuric acid, stirring for 60min at 10 ℃, and filtering;

(2) adding 20g of hexadecyl trimethyl ammonium bromide and 300mL of 0.5mol/L sodium oxalate solution into the filtrate obtained in the step (1), stirring and reacting at 10 ℃ for 2h, and filtering;

(3) adding 80mL of 1.5mol/L phosphoric acid into the filtrate obtained in the step (2), stirring at 10 ℃ for 30min at a rotation speed of 50r/min, standing for precipitation for 12h, and filtering to obtain a purified ferrous sulfate solution;

(4) taking 50mL of the ferrous sulfate solution obtained in the step (3), and adding 1mol/L of (NH)₄)₂HPO₄Mixing the solution with hydrogen peroxide, and adding into the ferrous sulfate solution, wherein Fe²⁺With added PO₄ ^3-In a molar ratio of 1.05:1, Fe²⁺With addition of H₂O₂The molar ratio of (1.05: 1), stirring and reacting for 1h at 95 ℃, cooling and filtering;

(5) and (3) drying the solid product obtained in the step (4) at 60 ℃ for 12h, roasting at 800 ℃ for 1h, using a depolymerizing and scattering machine, spirally propelling a feeding system, embedding a non-metal material blade into a rotary drum, and grinding for 30min under the conditions of the main shaft rotation speed of 1500rpm and the classifier rotation speed of 1000rpm to obtain a white anhydrous iron phosphate solid.

Comparative example 1

There is provided a method for preparing iron phosphate, which is different from example 1 in that the pH is adjusted to 3 with sulfuric acid in step (1).

Comparative example 2

There is provided a method for preparing iron phosphate, which is different from example 1 in that the pH is adjusted to 0.5 with sulfuric acid in step (1).

Comparative example 3

There is provided a method for preparing iron phosphate, which is different from example 1 in that cetyltrimethylammonium bromide, a complexing agent, is not added in step (2).

Comparative example 4

There is provided a method for preparing iron phosphate, which is different from example 1 in that the operation of step (1) is replaced with: dissolving 320g of sulfuric acid method titanium dioxide byproduct in 1L of water, adding 30g of iron powder, heating to 90 ℃, stopping heating when the pH value of the solution reaches 4, cooling to normal temperature, and filtering; the subsequent steps were the same as in example 1.

And (3) performance testing:

the iron-phosphorus ratios, particle sizes, tap densities and specific surface areas of the iron phosphates provided in the above examples and comparative examples were measured as follows:

D₅₀particle size: laser particle size analysis;

tap density: analyzing by a tap density meter;

specific surface area: isothermal N₂Adsorption-desorption process.

The results of the above tests are shown in table 1 below:

TABLE 1

Test items	D50Particle size (. mu.m)	Tap density (g/cm)3)	Specific surface area (m)2/g)
				Example 1	4.6	1.0	20.04
Example 2	5	0.6	15.23
				Example 3	3.2	1.5	22.05
Comparative example 1	4.5	1.05	19.59
				Comparative example 2	4.4	1.1	20.35
Comparative example 3	4.5	1.04	18.68
				Comparative example 4	4.0	1.2	21.56

As can be seen from the test results in Table 1, the iron phosphate provided by the invention has a D50 particle size of 3.0-5.0 μm and a tap density of 0.6-1.5g/cm³The specific surface area is 9.5-22m²The phosphate per gram has the advantages of high purity, small particle size, high tap density and large specific surface area, and can meet the performance requirements of battery-grade iron phosphate.

The content (mass percentage) of each element in the iron phosphate provided in the above examples and comparative examples was measured by using an inductively coupled plasma emission spectrometer, and the results are shown in table 2 below:

TABLE 2

In Table 2, < 0.0005% means that the content of this element is below the detection limit.

From the test results in table 2, it can be seen that the iron phosphate provided by the present invention has an iron-to-phosphorus ratio (Fe: P molar ratio) of 0.96 to 0.97, an Al content of < 0.001%, a Ca content of < 0.0025%, a Cd content of < 0.0005%, a Co content of < 0.0005%, a Cr content of < 0.003%, a Cu content of < 0.0005%, a Mg content of < 0.003%, a Mn content of < 0.0025%, a Na content of < 0.015%, a Ni content of < 0.0025%, a Pb content of < 0.0015%, a Ti content of < 0.006%, a Zn content of < 0.0015%, and low impurity elements, and can satisfy the performance requirements of battery grade iron phosphate.

In comparative example 1, the addition of sulfuric acid was insufficient due to the excessively high pH, resulting in an increase in the Ca, Mg, and Pb contents of the resulting iron phosphate, as compared to example 1.

Compared with the example 1, in the comparative example 2, the pH value is too low, so that the subsequent addition of sulfide is not favorable for generating metal sulfide precipitate, and the contents of Co, Ni, Pb and Mn in the obtained iron phosphate are increased.

Compared with example 1, in comparative example 3, Ti cannot be sufficiently removed because no complexing agent is added, thus resulting in a significant increase in Ti content in the obtained iron phosphate.

Compared with example 1, the use of iron powder for preventing oxidation and adjusting pH in comparative example 4 resulted in a significant increase in Mg, Pb, Ca content in the resulting iron phosphate due to the absence of introduced sulfuric acid and the higher pH.

Although the invention has been described in detail hereinabove by way of general description, specific embodiments and experiments, it will be apparent to those skilled in the art that many modifications and improvements can be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.