Process for the regeneration of iron phosphate waste

Abstract

The present disclosure belongs to the technical field of resource recycling and battery materials, and particularly relates to a regeneration method of iron phosphate waste, comprising the following steps: (1) calcining the iron phosphate waste, mixing the calcined iron phosphate waste with an acid solution and an oxidizing agent, and heating to perform a hydrothermal reaction; (2) performing solid-liquid separation on slurry obtained in the step (1), and obtaining regenerated iron phosphate after washing and sintering of the obtained solid phase.

Description

Technical Field

[0001] This disclosure belongs to the field of resource recycling and battery materials technology, and specifically relates to a method for regenerating iron phosphate waste. Background Technology

[0002] Currently, the main types of batteries used in new energy vehicles on the market are lithium iron phosphate batteries, lithium iron manganese phosphate batteries, lithium cobalt oxide batteries, and ternary lithium batteries. Among them, lithium iron phosphate batteries occupy the majority of the new energy vehicle battery market due to their good thermal stability, inexpensive raw materials, and good cycle performance. Iron phosphate is an important precursor for lithium iron phosphate, and its quality directly determines the performance of lithium iron phosphate. For example, excessive sulfur content in iron phosphate can affect the formation of spherical lithium iron phosphate particles and make small lithium iron phosphate particles prone to agglomeration, increasing the internal resistance of the material and leading to a significant reduction in battery capacity and cycle performance. High concentrations of metal impurity ions in iron phosphate not only cause a decrease in the reversible specific capacity of lithium-ion batteries, but the precipitation of metal impurity ions can also prevent the formation of an effective passivation layer on the graphite electrode surface, damaging the entire battery. Currently, the mainstream synthesis methods for iron phosphate on the market are mainly divided into six processes: sodium method, ammonium method, iron powder method, fertilizer phosphoric acid method, iron oxide red method, and dicalcium phosphate method. These six processes have high requirements for the purity of raw materials, resulting in higher production costs. Furthermore, most of these processes require pH adjustment, leading to corresponding environmental treatment costs, low environmental benefits, and relatively complex processes. Therefore, developing low-cost, high-quality ferric phosphate is urgently needed.

[0003] During the production of ferric phosphate, some ferric phosphate waste that cannot be directly reused may be generated due to process errors, experiments, equipment failures, human errors, and testing. If this ferric phosphate waste is not utilized and is treated as solid waste, it will be both wasteful and environmentally unfriendly. Therefore, it is very necessary to recycle and reuse ferric phosphate waste.

[0004] This application addresses the problems of complex processes, low environmental benefits, and high product impurities in existing technologies for regenerating iron phosphate from waste phosphate, proposing a method for regenerating iron phosphate waste to provide technical support and theoretical basis for this process. Summary of the Invention

[0005] This disclosure aims to address at least one of the technical problems existing in the related art. To this end, this disclosure proposes a method for regenerating iron phosphate waste, which is environmentally friendly and produces iron phosphate products with high crystallinity and extremely low impurity content, meeting the standards for battery-grade iron phosphate.

[0006] The above-mentioned technical objective of this disclosure is achieved through the following technical solution:

[0007] A method for regenerating ferric phosphate waste includes the following steps: (1) calcining the ferric phosphate waste and mixing it with an acid solution and an oxidant to form a mixture, heating it to carry out a hydrothermal reaction to obtain a slurry; (2) separating the solid and liquid phases of the slurry obtained in step (1), and washing and sintering the obtained solid phase to obtain regenerated ferric phosphate.

[0008] In one embodiment, the iron phosphate waste is further subjected to grinding and sieving.

[0009] In one embodiment, the sieving process refers to passing the material through a 50-150 mesh sieve.

[0010] In one embodiment, the sieving process refers to passing the material through a 60-100 mesh sieve.

[0011] In one embodiment, in step (1), the calcination temperature is 150-500°C and the calcination time is 1-5 hours.

[0012] In one embodiment, in step (1), the calcination temperature is 200-450°C and the calcination time is 2-4 hours.

[0013] In one embodiment, in step (1), the acid solution includes a phosphoric acid solution and other inorganic acid solutions, wherein the molar ratio of phosphoric acid to other inorganic acids in the acid solution is (1-7):(5-10).

[0014] In one embodiment, in step (1), the acid solution includes a phosphoric acid solution and other inorganic acid solutions, wherein the molar ratio of phosphoric acid to other inorganic acids in the acid solution is (1-5):(5-9).

[0015] In one embodiment, the acid solution contains H + The concentration is 1-10 mol / L.

[0016] In one embodiment, the acid solution contains H + The concentration is 1-8 mol / L.

[0017] In one embodiment, the other inorganic acid is at least one of hydrochloric acid and sulfuric acid.

[0018] In one embodiment, in step (1), the oxidant is hydrogen peroxide.

[0019] In one embodiment, the hydrogen peroxide has a mass concentration of 1%-15%.

[0020] In one embodiment, the hydrogen peroxide has a mass concentration of 3%-10%.

[0021] In one embodiment, in step (1), the mixing ratio of the calcined iron phosphate waste, acid solution and oxidant is 1g:1-5mL:1-3mL.

[0022] In one embodiment, in step (1), the mixing ratio of the calcined iron phosphate waste, acid solution and oxidant is 1g:1-4mL:1-2mL.

[0023] In one embodiment, in step (1), the hydrothermal reaction is carried out in a hydrothermal reactor, the temperature of the hydrothermal reaction is 100-200°C, the time of the hydrothermal reaction is 1-5h, and the heating rate is 1-15°C / min.

[0024] In one embodiment, in step (1), the hydrothermal reaction is carried out in a hydrothermal reactor, the temperature of the hydrothermal reaction is 120-160°C, the time of the hydrothermal reaction is 2-4 hours, and the heating rate is 1-10°C / min.

[0025] In one embodiment, the mixture occupies 40%-80% of the volume of the hydrothermal reactor.

[0026] In one embodiment, in step (2), the supernatant obtained after solid-liquid separation and the washing water can be returned to step (1) for reuse.

[0027] In one embodiment, in step (2), the solid phase is washed until the conductivity of the resulting washing wastewater is <500 μS / cm before sintering.

[0028] In one embodiment, in step (2), the sintering temperature is 500-1000℃ and the sintering time is 1-8h.

[0029] In one embodiment, in step (2), the sintering temperature is 600-800°C and the sintering time is 2-6 hours.

[0030] In one embodiment, in step (2), the thickness of the sintering stockpile is ≤5cm.

[0031] In one embodiment, in step (2), the thickness of the sintering stockpile is ≤4cm.

[0032] The beneficial effects of this disclosure are:

[0033] (1) The regeneration method of iron phosphate waste disclosed herein does not require the addition of alkaline substances to adjust pH or nucleating agents (organic matter) to promote crystallization, thus avoiding problems such as subsequent wastewater treatment difficulties and having a high environmental protection effect;

[0034] (2) The recycling method of iron phosphate waste disclosed herein is simple. After calcination, iron phosphate waste is directly synthesized into iron dihydrate in one step by hydrothermal method, and then sintered to obtain recycled iron phosphate, which is convenient for large-scale industrial production.

[0035] (3) The regeneration method for ferric phosphate waste disclosed herein has a triple impurity removal mechanism, resulting in a product with low impurity content, high crystallinity, and strong performance. The first impurity removal mechanism: Under high temperature and high pressure (created using a hydrothermal reactor and hydrogen peroxide, where hydrogen peroxide pyrolyzes during the heating process to generate oxygen, further increasing the pressure), the acid dissolves the ferric phosphate waste more thoroughly, causing impurities to be transferred from the solid phase to the liquid phase. The second impurity removal mechanism: Under high temperature and high pressure, the chemical substances in the liquid phase are more active, making it easier to generate crystals with high crystallinity and few defects. These highly crystalline crystals will prevent impurities in the liquid phase from re-entering the solid phase. The third impurity removal mechanism: Under high temperature, high pressure, and acidic (phosphoric acid) conditions, the generated dihydrate ferric phosphate will undergo the dissolution-crystallization phenomenon more frequently, transferring impurities that are difficult to remove and are doped or encapsulated in the crystals to the liquid phase for removal. Attached Figure Description

[0036] Figure 1 This is a flowchart illustrating Embodiment 1 of the present disclosure;

[0037] Figure 2 The XRD pattern of the regenerated iron phosphate obtained in Example 1 of this disclosure;

[0038] Figure 3 This is a SEM image of ferric phosphate dihydrate obtained in Example 1 of this disclosure. Detailed Implementation

[0039] The present disclosure will be further described below with reference to specific embodiments.

[0040] Example 1:

[0041] A method for regenerating iron phosphate waste, such as Figure 1 As shown, it includes the following steps:

[0042] (1) Calcining the ferric phosphate waste after grinding and passing through a 60-mesh sieve at 250℃ for 2 hours;

[0043] (2) A slurry was prepared by mixing calcined ferric phosphate waste, acid solution, and hydrogen peroxide in a ratio of 1g:3mL:2mL. This slurry was placed in a hydrothermal reactor, filling 70% of the reactor's volume. The reaction was carried out at 150℃ for 2 hours at a heating rate of 5℃ / min. The acid solution consisted of phosphoric acid and sulfuric acid, with a molar ratio of 3:7. The H+ in the acid solution... + The concentration is 2 mol / L, and the mass concentration of hydrogen peroxide is 10%.

[0044] (3) Separate the solid and liquid components of the slurry obtained after the hydrothermal reaction in step (2). Wash the obtained solid until the conductivity of the washing wastewater is <500 μS / cm, then dry it. Then sinter it at 650℃ for 2 hours. The thickness of the sintering pile should be ≤4cm to obtain regenerated ferric phosphate. The supernatant and washing water obtained after solid-liquid separation can be returned to step (2) for reuse. The XRD pattern of the obtained regenerated ferric phosphate is shown in the figure. Figure 2 As shown, by Figure 2 It can be seen that the generated ferric phosphate has no impurity peaks, and the main peak has a high intensity and sharpness, indicating its high crystallinity. The SEM image of the obtained ferric phosphate dihydrate is shown below. Figure 3 As shown, by Figure 3 It can be seen that the generated iron phosphate dihydrate mainly exists in the form of very thin flakes, with an average length of about 200 nm.

[0045] Example 2:

[0046] A method for regenerating iron phosphate waste includes the following steps:

[0047] (1) The ferric phosphate waste that has been ground and passed through a 60-mesh sieve is calcined at 450℃ for 4 hours;

[0048] (2) A slurry was prepared by mixing calcined ferric phosphate waste, acid solution, and hydrogen peroxide in a ratio of 1g:3mL:2mL. This slurry was placed in a hydrothermal reactor, filling 70% of the reactor's volume. The reactor was reacted at 160℃ for 4 hours at a heating rate of 5℃ / min. The acid solution consisted of phosphoric acid and sulfuric acid, with a molar ratio of 3:7. The H+ in the acid solution... + The concentration is 2 mol / L, and the mass concentration of hydrogen peroxide is 10%.

[0049] (3) Separate the solid and liquid of the slurry obtained after the hydrothermal reaction in step (2). Wash the obtained solid until the conductivity of the washing wastewater is <500us / cm and then dry it. Then sinter it at 750℃ for 4h. The thickness of the slurry during sintering is ≤4cm to obtain regenerated iron phosphate. The supernatant obtained after solid-liquid separation and the washing water can be returned to step (2) for reuse.

[0050] Example 3:

[0051] This embodiment provides a method for regenerating iron phosphate waste, the only difference from embodiment 1 is that the calcination temperature of iron phosphate waste in step (1) is 300°C.

[0052] Example 4:

[0053] This embodiment provides a method for regenerating iron phosphate waste, the only difference from embodiment 1 is that the calcination temperature of iron phosphate waste in step (1) is 400°C.

[0054] Example 5:

[0055] This embodiment provides a method for regenerating iron phosphate waste, the only difference from Embodiment 1 being: the H+ in the acid solution in step (2) + The concentration is 5 mol / L.

[0056] Example 6:

[0057] This embodiment provides a method for regenerating iron phosphate waste, the only difference from Embodiment 1 being: the H+ in the acid solution in step (2) + The concentration is 8 mol / L.

[0058] Example 7:

[0059] This embodiment provides a method for regenerating iron phosphate waste, the only difference from embodiment 1 is that the solid sintering time in step (3) is 4 hours.

[0060] Example 8:

[0061] This embodiment provides a method for regenerating iron phosphate waste, the only difference from embodiment 1 is that the solid sintering temperature in step (3) is 750°C.

[0062] Comparative Example 1:

[0063] This embodiment provides a method for regenerating iron phosphate waste, the only difference from embodiment 1 is that hydrogen peroxide is not added in step (2).

[0064] Experimental example:

[0065] According to the HG / T 4701-2021 standard, the relevant parameters of the regenerated iron phosphate prepared in Examples 1-8 and Comparative Example 1 were tested. The relevant product parameters are shown in Table 1.

[0066] Table 1: Relevant parameters of regenerated iron phosphate

[0067]

[0068] As shown in Table 1:

[0069] (1) In the regeneration method of iron phosphate waste disclosed in this invention, hydrogen peroxide plays an important role in removing impurities. Compared with Example 1 (with added hydrogen peroxide), the impurity content of the product in Comparative Example 1 (without added hydrogen peroxide) increased significantly. This is mainly because the hydrogen peroxide in Example 1 can further increase the pressure and strengthen the triple impurity removal mechanism by generating oxygen through pyrolysis during the heating process.

[0070] (2) In the regeneration method of iron phosphate waste disclosed in this invention, the impurities of the product can be further reduced by adjusting the calcination temperature and time, increasing the concentration of the acid solution, and adjusting the sintering temperature and time.

[0071] (3) The regeneration method of iron phosphate waste disclosed herein can effectively separate iron phosphate from impurities (S, Mg, Al, etc.), and the purity of the regenerated iron phosphate is above 99.99 wt%, which can meet the standard of battery-grade iron phosphate.

Claims

1. A method for the regeneration of iron phosphate waste material, characterized in that: The method comprises the following steps: (1) mixing the calcined iron phosphate waste with an acid solution and an oxidizing agent to form a mixture, and heating to perform a hydrothermal reaction to obtain a slurry; (2) performing solid-liquid separation on the slurry obtained in step (1), and washing and sintering the obtained solid phase to obtain regenerated iron phosphate; in step (1), the oxidizing agent is hydrogen peroxide, the mass concentration of the hydrogen peroxide is 1%-15%, the hydrothermal reaction is performed in a hydrothermal reaction kettle, the temperature of the hydrothermal reaction is 100-200 ℃, the time of the hydrothermal reaction is 1-5 h, the heating rate is 1-15 ℃ / min, and the volume of the mixture in the hydrothermal reaction kettle is 40%-80%.

2. The method of regenerating iron phosphate waste material according to claim 1, characterized in that: In step (1), the iron phosphate waste is further subjected to grinding and sieving treatment.

3. A method of regenerating iron phosphate waste according to claim 2, characterized in that: The sieving treatment refers to passing through a 50-150 mesh sieve.

4. The method of claim 1, wherein the iron phosphate waste material is a waste material from a phosphoric acid production process. In step (1), the calcination temperature is 150-500 ℃, and the calcination time is 1-5 h.

5. The method of regeneration of iron phosphate waste material as claimed in claim 1 wherein: In step (1), the acid solution comprises a phosphoric acid solution and other inorganic acid solutions, and the molar ratio of phosphoric acid to other inorganic acids in the acid solution is (1-7):(5-10).

6. A method of regenerating iron phosphate waste according to claim 5, characterized in that: H in the acid solution + The concentration is 1-10 mol / L.

7. A method of regenerating iron phosphate waste according to claim 5, characterized in that: The other inorganic acid is at least one of hydrochloric acid and sulfuric acid.

8. The method of claim 1, wherein the iron phosphate waste material is a waste material from a phosphoric acid production process. In step (1), the mixing ratio of the calcined iron phosphate waste, the acid solution and the oxidizing agent is 1 g:1-5 mL:1-3 mL.

9. The method of claim 1, wherein the iron phosphate waste material is a waste material from a phosphoric acid production process. In step (2), the supernatant obtained after the solid-liquid separation and the washing water used for washing can be returned to step (1) for reuse.

10. The method of claim 1, wherein: In step (2), the solid phase is washed until the conductivity of the washing wastewater is less than 500 us / cm, and then sintered.

11. The method of claim 1, wherein the iron phosphate waste material is a waste material from a phosphoric acid production process. In step (2), the sintering temperature is 500-1000 ℃, and the sintering time is 1-8 h.

12. The method of claim 1, wherein: In step (2), the thickness of the stacked material during sintering is ≤5 cm.

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