Method for preparing iron phosphate with low impurity and high iron-phosphorus ratio from waste iron phosphate

Abstract

The invention discloses a method for preparing iron phosphate with low impurity and high iron-phosphorus ratio from waste iron phosphate. The method comprises the following steps: S1, adding unqualified waste iron phosphate into acid liquor, and dissolving to form iron and phosphorus liquor; s2, adjusting the pH value of the iron and phosphorus solution to 1.5-2.1 to form an amorphous iron phosphate yellow solid, filtering, washing, and pulping to form a slurry; s3, adding substances required for increasing the iron-phosphorus ratio and a phosphorus source required for crystal transformation into the slurry, and aging at 95 DEG C for 2 hours to obtain iron phosphate dihydrate with high iron-phosphorus ratio and low impurity; and S4, carrying out heat treatment on the iron phosphate dihydrate at 550-650 DEG C to obtain an anhydrous iron phosphate finished product with low impurity and high iron-phosphorus ratio. The method has the beneficial effects that 1, the method for recovering the waste iron phosphate to prepare the iron phosphate with low impurity and high iron-phosphorus ratio is provided; and 2, lithium iron phosphate prepared from the obtained iron phosphate is excellent in electrical performance. And 3, the invention provides a method for greatly reducing the impurity content while increasing the iron-phosphorus ratio in the preparation process of iron phosphate.

Description

Technical Field

[0001] The present invention relates to the field of battery positive electrode material processing, and in particular to a method for preparing low-impurity ferric phosphate with a high iron-phosphorus ratio from waste ferric phosphate. Background Art

[0002] The gradual expansion of China's iron phosphate industry's production capacity is primarily driven by the rapid growth of the new energy vehicle market and increasing demand for energy storage. With the global adoption of electric vehicles, demand for lithium iron phosphate batteries, a battery material known for its safety and long cycle life, has surged. Furthermore, government policy support for the new energy and environmental protection industries has driven advancements in iron phosphate material technology and the improvement of the industry chain. Numerous companies have increased investment, expanded production scale, and improved production processes and product quality, significantly boosting the industry's overall production capacity to meet growing market demand.

[0003] As production capacity continues to expand, it is also accompanied by many problems, such as iron phosphate producing a large amount of "start-up materials" during the production process. These substandard products cannot meet the demand of downstream customers for product quality on the one hand, and the lithium iron phosphate prepared by them cannot meet the requirements in terms of electrical performance and safety performance on the other hand. The regeneration method of iron phosphate waste explained by patents CN110683528 B and CN110980677 B is simply to recycle the waste iron phosphate. The obtained finished product anhydrous iron phosphate has a low iron-phosphorus ratio and high impurities, which is not conducive to the performance of electrical performance. For example, a method for preparing battery-grade iron phosphate using iron phosphate waste as described in patent CN118929601 A has complex steps and the prepared finished product has large primary particles. Therefore, it is very necessary to urgently recycle such discarded materials into qualified products. Summary of the Invention

[0004] In order to solve the technical bottleneck of the existing waste iron phosphate recovery, the present invention aims to use waste iron phosphate as raw material and prepare it into iron phosphate with low impurities and high iron-phosphorus ratio through treatment.

[0005] Technical solution: A method of preparing low-impurity, high-iron-phosphorus ratio ferric phosphate from waste ferric phosphate of the present invention comprises the following steps: Step (1): Dissolve the unqualified waste iron phosphate in acid solution to form iron and phosphorus solution.

[0006] Step (2): Adjust the pH of the iron and phosphorus solutions to form amorphous iron phosphate, which is then filtered, washed, and beaten to form a slurry.

[0007] Step (3): Adding a substance required for increasing the iron-phosphorus ratio and a phosphorus source required for crystallization into the amorphous iron phosphate slurry, and aging at 95° C. for 2 h to obtain dihydrate iron phosphate with a high iron-phosphorus ratio and low impurities.

[0008] Step (4): heat-treating the dihydrated ferric phosphate at 550°C to 650°C to obtain an anhydrous ferric phosphate product with low impurities and high iron-phosphorus ratio.

[0009] Furthermore, the unqualified waste ferric phosphate described in step (1) contains one or more of magnetism, specific surface area, iron content, phosphorus content, moisture, particle size and impurity content that exceeds the standard and does not meet product requirements.

[0010] Furthermore, the acid used in the acid dissolution in step (1) is one or more of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, and oxalic acid, preferably sulfuric acid. The required concentration is 1-3 mol / L, preferably 1.5-2 mol / L.

[0011] Furthermore, as described in step (2), the substance for adjusting the pH of the iron and phosphorus solution is sodium hydroxide, ammonium phosphate, and ammonia water, one or more of which is preferably ammonia water, and the pH range is 1.5~2.1.

[0012] Furthermore, the substance required to improve the iron-phosphorus ratio as described in step (3) is ammonium bisulfate, ammonium sulfate, ferric sulfate, ferric chloride, ferric nitrate, preferably a mixture of ferric sulfate and ammonium bisulfate.

[0013] Furthermore, the phosphorus source required for the crystallization in step (3) is monoammonium phosphate, phosphoric acid, or monosodium phosphate, preferably phosphoric acid.

[0014] Furthermore, after adding the substance required to increase the iron-phosphorus ratio and the phosphorus source required for crystallization, the molar ratio of total iron to total phosphorus in the amorphous ferric phosphate slurry is 1.1-2.0.

[0015] Advantages of the present invention: The present invention provides a method for preparing low-impurity, high-iron-phosphorus ratio iron phosphate from waste iron phosphate. 1. It provides a method for recycling waste iron phosphate to produce low-impurity, high-iron-phosphorus ratio iron phosphate. 2. The iron phosphate obtained by this method can produce lithium iron phosphate with excellent battery performance. 3. It provides a method for increasing the iron-phosphorus ratio and reducing impurities during the iron phosphate preparation process. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the SEM image of ferric phosphate dihydrate in Example 1.

[0017] Figure 2 This is the SEM image of anhydrous ferric phosphate in Example 1.

[0018] Figure 3 The XRD pattern of anhydrous ferric phosphate in Example 1 is Figure 4 This is the electrical performance diagram of lithium iron phosphate. DETAILED DESCRIPTION

[0019] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to normal conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified by the manufacturer are conventional products that can be purchased commercially.

[0020] <Example 1> 2000 g of unqualified waste iron phosphate was put into 5L, 1.5mol / L sulfuric acid solution to dissolve it into iron and phosphorus liquid. The pH of the iron and phosphorus liquid was adjusted to 1.6 with ammonia water to form amorphous iron phosphate, which was filtered, washed, and beaten to form a slurry with an iron phosphate concentration of 1.5mol / L. Iron sulfate with a molar mass fraction of 5% of the total iron and 10% ammonium bisulfate solution and 0.5 times the total iron molar amount of phosphoric acid were added to the above iron phosphate slurry. After aging at 95℃ for 2h, dihydrate iron phosphate with a high iron-phosphorus ratio and low impurities was obtained. The SEM image is shown as follows: Figure 1 As shown in the figure, after the dihydrated iron phosphate is heat treated at 600℃ for 2 hours, the anhydrous iron phosphate with low impurities and high iron-phosphorus ratio is obtained. The SEM and XRD patterns of the finished product are shown in the figure. Figure 2 and 3 shown.

[0021] Preparation of lithium iron phosphate Take 1000 g of the finished iron phosphate product of Example 1, 252 g of lithium carbonate, 36 g of sucrose, 90 g of PEG, 4 g of TiO2, and 1000 ml of water, and sand grind to a particle size D50 = 0.42 ± 0.05 μm. The spray-dried powder is sintered at 785 ° C in a box furnace in a nitrogen atmosphere for 10 h with a heating rate of 2 ° C / min.

[0022] Preparation of lithium-ion button batteries: The lithium manganese iron phosphate prepared by the above method is air flow crushed and used as the positive electrode active material. The positive electrode active material: SP (superconducting carbon black): PVDF (polyvinylidene fluoride) is slurried in a mass ratio of 90:5:5, coated on a 20μm thick aluminum foil, and then dried, rolled, die-cut, and punched into positive electrode sheets. A lithium sheet is used as the negative electrode, a PE material diaphragm is used, and 80μL of electrolyte is added. The electrochemical performance tests of the batteries prepared above are respectively carried out, specifically: the button batteries prepared above are tested using a blue electric tester; the prepared button batteries are placed in an incubator at 25°C for charge and discharge tests, the voltage range is 2.0-4.2V, 0.1C charge and discharge activation for one cycle, and then charged and discharged in a constant current and constant voltage manner. The electrical performance diagram is as follows Figure 4 shown.

[0023] <Example 2> 2000g of unqualified waste iron phosphate was dissolved in 5L of 1.5mol / L sulfuric acid to form an iron and phosphorus solution. The pH of the iron and phosphorus solution was adjusted to 2.3 with ammonia water to form an amorphous iron phosphate. The solution was filtered, washed, and beaten to form a slurry with an iron phosphate concentration of 1.5mol / L. To this iron phosphate slurry, 5% iron sulfate and 10% ammonium bisulfate solution with a molar mass fraction of the total iron were added, along with 0.5 times the total iron molar amount of phosphoric acid. After aging at 95°C for 2h, dihydrate iron phosphate with a high iron-to-phosphorus ratio and low impurities was obtained. The dihydrate iron phosphate was heat-treated at 600°C for 2h to obtain an anhydrous iron phosphate product with low impurities and a high iron-to-phosphorus ratio.

[0024] <Example 3> 2000g of unqualified waste iron phosphate was dissolved in 5L of 1.5mol / L sulfuric acid to form an iron and phosphorus solution. The pH of the iron and phosphorus solution was adjusted to 1.6 with ammonia water to form an amorphous iron phosphate. The solution was filtered, washed, and slurried to form a 1.5mol / L iron phosphate slurry. Iron sulfate (10% of the total iron molar mass fraction) and a 10% ammonium bisulfate solution were added to the iron phosphate slurry, along with 0.5 times the total iron molar mass fraction of phosphoric acid. After aging at 95°C for 2h, dihydrate iron phosphate with a high iron-to-phosphorus ratio and low impurities was obtained. The dihydrate iron phosphate was heat-treated at 600°C for 2h to obtain an anhydrous iron phosphate product with low impurities and a high iron-to-phosphorus ratio.

[0025] <Example 4> 2000g of unqualified waste iron phosphate was dissolved in 5L of 1.5mol / L sulfuric acid to form an iron and phosphorus solution. The pH of the iron and phosphorus solution was adjusted to 1.6 with ammonia water to form an amorphous iron phosphate. The solution was filtered, washed, and beaten to form a slurry with an iron phosphate concentration of 1.5mol / L. To this iron phosphate slurry, 5% iron sulfate and 10% ammonium bisulfate solution with a molar mass fraction of the total iron were added, along with 0.25 times the total iron molar amount of phosphoric acid. After aging at 95°C for 2h, dihydrate iron phosphate with a high iron-to-phosphorus ratio and low impurities was obtained. The dihydrate iron phosphate was heat-treated at 600°C for 2h to obtain an anhydrous iron phosphate product with low impurities and a high iron-to-phosphorus ratio.

[0026] <Example 5> 2000g of unqualified waste iron phosphate was dissolved in 5L of 1.5mol / L sulfuric acid to form an iron and phosphorus solution. The pH of the iron and phosphorus solution was adjusted to 1.6 with ammonia water to form an amorphous iron phosphate. The solution was filtered, washed, and slurried to form a 1.5mol / L iron phosphate slurry. Iron sulfate with a molar mass fraction of 5% of the total iron, a 20% ammonium bisulfate solution, and 0.5 times the total iron molar amount of phosphoric acid were added to the iron phosphate slurry. After aging at 95°C for 2h, dihydrate iron phosphate with a high iron-to-phosphorus ratio and low impurities was obtained. The dihydrate iron phosphate was heat-treated at 600°C for 2h to obtain an anhydrous iron phosphate product with low impurities and a high iron-to-phosphorus ratio.

[0027] Comparative Example 1 2000g of unqualified waste iron phosphate was dissolved in 5L of 1.5mol / L sulfuric acid to form an iron and phosphorus solution. The pH of the iron and phosphorus solution was adjusted to 2.0 with ammonia water to form an amorphous iron phosphate. The solution was filtered, washed, and beaten to form a slurry with an iron phosphate concentration of 1.5mol / L. To this iron phosphate slurry, 5% of the total iron molar mass fraction of iron sulfate and 0.5 times the total iron molar amount of phosphoric acid were added. After aging at 95°C for 2h, dihydrate iron phosphate with a high iron-to-phosphorus ratio and low impurities was obtained. The dihydrate iron phosphate was heat treated at 550°C for 2h to obtain an anhydrous iron phosphate product with low impurities and a high iron-to-phosphorus ratio.

[0028] Comparative Example 2 2000 g of unqualified waste iron phosphate was added to 5L of 1.5 mol / L sulfuric acid solution to dissolve it into an iron and phosphorus solution. The pH of the iron and phosphorus solution was adjusted to 2.0 with ammonia water to form an amorphous iron phosphate, which was filtered, washed, and beaten to form a slurry with an iron phosphate concentration of 1.5 mol / L. 0.5 times the total iron molar amount of phosphoric acid was added to the above iron phosphate slurry and aged at 95°C for 2 hours to obtain dihydrated iron phosphate with a high iron-to-phosphorus ratio and low impurities. The dihydrated iron phosphate was heat-treated at 550°C for 2 hours to obtain an anhydrous iron phosphate product with low impurities and a high iron-to-phosphorus ratio.

[0029] Table 1 Physical and chemical data of unqualified iron phosphate to be treated

[0030] Table 2 Iron content, phosphorus content and iron-phosphorus ratio of ferric phosphate products

[0031] Table 3 Impurity data of ferric phosphate products

[0032] The above implementation cases are only for illustrating the technical solutions and features of the present invention, and their purpose is to enable people familiar with the technology to implement them better. They cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention are within the scope of protection of the present invention. The ones not described in detail are prior art.

Claims

1. A method for preparing low-impurity, high iron-phosphorus ratio ferric phosphate from waste ferric phosphate, characterized in that: The following steps are involved: S1. Put unqualified waste iron phosphate into acid solution to dissolve it into iron and phosphorus solution; S2. Adjusting the pH of the iron and phosphorus solutions to form amorphous iron phosphate, filtering, washing, and beating to form a slurry; S3. Adding a substance required for increasing the iron-phosphorus ratio and a phosphorus source required for crystallization into the amorphous iron phosphate slurry, and aging at 90-98° C. for 1-5 hours to obtain iron phosphate dihydrate with a high iron-phosphorus ratio and low impurities; S4. Washing and drying the obtained ferric phosphate dihydrate, and heat-treating the mixture at 550° C. to 650° C. to obtain an anhydrous ferric phosphate product with low impurities and high iron-phosphorus ratio.

2. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 1, characterized in that: Unqualified waste iron phosphate refers to iron phosphate that does not meet product specification requirements due to excessive magnetism, specific surface area, iron content, phosphorus content, moisture content, particle size, and impurity content.

3. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 1, characterized in that: The acid used for acid dissolution is one or more of sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid, and oxalic acid.

4. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 3, characterized in that: The acid used for acid dissolution is sulfuric acid, and the required concentration is 1-3 mol / L, preferably 1.5-2 mol / L.

5. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 1, characterized in that: The substance for adjusting the pH of the iron and phosphorus solution is one or more of sodium hydroxide, ammonium phosphate and ammonia water.

6. The method for preparing low-impurity and high-iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 5, characterized in that: The substance used to adjust the pH of iron and phosphorus solutions is ammonia water, and the pH value range is 1.5~2.

1.

7. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 1, characterized in that: The substances required to improve the iron-phosphorus ratio are one or more of ammonium bisulfate, ammonium sulfate, ferric sulfate, ferric chloride and ferric nitrate.

8. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 7, characterized in that: The substance required to increase the iron-phosphorus ratio is a mixture of ferric sulfate and ammonium bisulfate.

9. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 1, characterized in that: The phosphorus source required for crystallization is one or more of monoammonium phosphate, phosphoric acid, and monosodium phosphate.

10. The method for preparing low-impurity and high iron-phosphorus ratio ferric phosphate from waste ferric phosphate according to claim 1, characterized in that: After adding the substances required for increasing the iron-phosphorus ratio and the phosphorus source required for crystallization, the molar ratio of total iron to total phosphorus in the amorphous ferric phosphate slurry is 1.1 to 2.0.

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