Regeneration method for 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 for iron phosphate waste. The regeneration method comprises the following steps: (1) calcining iron phosphate waste, then mixing the calcined iron phosphate waste with an acid solution and an oxidizing agent, and heating the mixture to perform a hydrothermal reaction; and (2) subjecting the slurry obtained by the reaction in step (1) to solid-liquid separation, and washing and sintering the obtained solid phase to obtain regenerated iron phosphate.

Description

A method for regenerating iron phosphate waste Technical Field

[0001] The present disclosure belongs to the field of resource recycling and battery material technology, and in particular relates to a regeneration method for iron phosphate waste. Background Art

[0002] Currently, the main types of batteries used in new energy vehicles on the market are lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), lithium cobalt oxide (LCO), and ternary lithium batteries. LFP batteries, due to their excellent thermal stability, low raw material costs, and superior cycle performance, dominate the new energy vehicle battery market. Iron phosphate is a key precursor to LFP, and its quality directly determines its performance. For example, excessive sulfur content in LFP can affect the formation of LFP spherical particles and cause small LFP particles to agglomerate, increasing the material's internal resistance and significantly reducing battery capacity and cycle performance. High concentrations of metal impurities in LFP not only reduce the reversible specific capacity of lithium-ion batteries, but the precipitation of these metal impurities can also prevent the formation of an effective passivation layer on the graphite electrode surface, damaging the entire battery. Currently, the mainstream LFP synthesis methods available are divided into six processes: the sodium method, the ammonium method, the iron powder method, the fertilizer phosphoric acid method, the red iron oxide method, and the calcium hydrogen phosphate method. These six processes require high raw material purity, resulting in higher production costs. Moreover, most of these processes require pH adjustment, which leads to corresponding environmental treatment costs, low environmental benefits and relatively complex processes. Therefore, the development of low-cost, high-quality iron phosphate is urgent.

[0003] During the production process of iron phosphate, some iron phosphate waste that cannot be directly reused will be generated due to process errors, experiments, equipment failures, human errors, testing and other reasons. If these iron phosphate wastes are not utilized and treated as solid waste, it will be a waste and not environmentally friendly. Therefore, it is very necessary to recycle and reuse the iron phosphate waste.

[0004] This application proposes a regeneration method for iron phosphate waste to address the problems of complex process, low environmental benefits and high product impurities in the existing technology for regenerating iron phosphate waste into iron phosphate, in order to provide technical support and theoretical basis for the regeneration of iron phosphate waste into iron phosphate.

[0005] Summary of the Invention

[0006] The present disclosure aims to address at least one of the technical problems in the related art. To this end, the present disclosure provides a method for regenerating waste iron phosphate, which is environmentally friendly and produces an iron phosphate product with high crystallinity and extremely low impurity content, meeting the standards for battery-grade iron phosphate.

[0007] The above technical objectives of the present disclosure are achieved through the following technical solutions:

[0008] A method for regenerating waste iron phosphate comprises the following steps: (1) calcining the waste iron phosphate and mixing it with an acid solution and an oxidant to form a mixture, heating it for hydrothermal reaction, and obtaining a slurry; and (2) subjecting the slurry obtained in step (1) to solid-liquid separation, and washing and sintering the obtained solid phase to obtain regenerated iron phosphate.

[0009] In one embodiment, the waste iron phosphate is further ground and sieved.

[0010] In one embodiment, the screening process refers to passing through a 50-150 mesh sieve.

[0011] In one embodiment, the screening process refers to passing through a 60-100 mesh sieve.

[0012] In one embodiment, in step (1), the calcination temperature is 150-500° C., and the calcination time is 1-5 hours.

[0013] In one embodiment, in step (1), the calcination temperature is 200-450° C., and the calcination time is 2-4 hours.

[0014] In one embodiment, in step (1), the acid solution includes a phosphoric acid solution and another inorganic acid solution, and the molar ratio of the phosphoric acid to the other inorganic acid in the acid solution is (1-7):(5-10).

[0015] In one embodiment, in step (1), the acid solution includes a phosphoric acid solution and another inorganic acid solution, and the molar ratio of the phosphoric acid to the other inorganic acid in the acid solution is (1-5):(5-9).

[0016] In one embodiment, the acid solution contains H + The concentration is 1-10mol / L.

[0017] In one embodiment, the acid solution contains H + The concentration is 1-8mol / L.

[0018] In one embodiment, the other inorganic acid is at least one of hydrochloric acid and sulfuric acid.

[0019] In one embodiment, in step (1), the oxidant is hydrogen peroxide.

[0020] In one embodiment, the mass concentration of the hydrogen peroxide is 1%-15%.

[0021] In one embodiment, the mass concentration of the hydrogen peroxide is 3%-10%.

[0022] In one embodiment, in step (1), the mixing ratio of the calcined ferric phosphate waste, the acid solution, and the oxidant is 1 g: 1-5 mL: 1-3 mL.

[0023] In one embodiment, in step (1), the mixing ratio of the calcined ferric phosphate waste, the acid solution, and the oxidant is 1 g: 1-4 mL: 1-2 mL.

[0024] 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 1-5 h, and the heating rate is 1-15° C. / min.

[0025] 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 h, and the heating rate is 1-10° C. / min.

[0026] In one embodiment, the mixed material occupies 40%-80% of the volume of the hydrothermal reactor.

[0027] In one embodiment, in step (2), the supernatant obtained after the solid-liquid separation and the washing water can be returned to step (1) for reuse.

[0028] In one embodiment, in step (2), the solid phase is washed until the conductivity of the obtained washing wastewater is less than 500 μs / cm before sintering.

[0029] In one embodiment, in step (2), the sintering temperature is 500-1000° C., and the sintering time is 1-8 hours.

[0030] In one embodiment, in step (2), the sintering temperature is 600-800° C., and the sintering time is 2-6 hours.

[0031] In one embodiment, in step (2), the thickness of the pile during sintering is ≤5 cm.

[0032] In one embodiment, in step (2), the thickness of the pile during sintering is ≤4 cm.

[0033] The beneficial effects of the present disclosure are:

[0034] (1) The regeneration method of the iron phosphate waste disclosed in the present invention does not require the addition of alkaline substances to adjust the pH and nucleation promoters (organic substances) to promote crystallization, so it does not cause problems such as subsequent wastewater treatment difficulties, and has a high environmental impact;

[0035] (2) The regeneration process of the waste iron phosphate disclosed in the present invention is simple. After calcination, the waste iron phosphate is directly synthesized into dihydrated iron phosphate by a hydrothermal method in one step, and then sintered to obtain regenerated iron phosphate, which is convenient for large-scale industrial production.

[0036] (3) The regeneration method of the iron phosphate waste disclosed in the present invention has a triple impurity removal mechanism, and the resulting product has a low impurity content, high crystallinity, and strong performance. The first impurity removal mechanism: under a high temperature and high pressure environment (created by a hydrothermal reactor and hydrogen peroxide, the hydrogen peroxide pyrolyzes during the heating process to produce oxygen, which can further increase the pressure), the acid dissolves the iron phosphate waste more thoroughly, so that the impurities are basically transferred from the solid phase to the liquid phase; the second impurity removal mechanism: under a high temperature and high pressure environment, the chemical substances in the liquid phase are more active and more likely to generate crystals with high crystallinity and few defects. Such crystals with high crystallinity will prevent impurities in the liquid phase from re-entering the solid phase; the third impurity removal mechanism: under a high temperature and high pressure and acidic (phosphoric acid) environment, the generated dihydrate iron phosphate will undergo the dissolution-crystallization phenomenon more frequently, which will transfer the impurities that are doped or wrapped in the crystals and are difficult to remove to the liquid phase and thus be removed. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a schematic diagram of a process of Example 1 of the present disclosure;

[0038] FIG2 is an XRD pattern of the regenerated ferric phosphate obtained in Example 1 of the present disclosure;

[0039] FIG3 is a SEM image of ferric phosphate dihydrate obtained in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0040] The present disclosure is further described below with reference to specific embodiments.

[0041] Example 1:

[0042] A method for regenerating waste iron phosphate, as shown in FIG1 , comprises the following steps:

[0043] (1) Calcinate the ground iron phosphate waste after passing through a 60-mesh sieve at 250°C for 2 h;

[0044] (2) A slurry of calcined iron phosphate waste: acid solution: hydrogen peroxide = 1 g: 3 mL: 2 mL was prepared and placed in a hydrothermal reactor. The slurry accounted for 70% of the volume of the hydrothermal reactor and the reaction was carried out at 150 ° C for 2 h at a heating rate of 5 ° C / min. The acid solution was composed of phosphoric acid and sulfuric acid, and the molar ratio of phosphoric acid to sulfuric acid was 3:7. The H + The concentration is 2 mol / L, and the mass concentration of hydrogen peroxide is 10%;

[0045] (3) The slurry obtained after the hydrothermal reaction in step (2) is separated into solid and liquid, and the obtained solid is washed until the conductivity of the obtained washing wastewater is less than 500us / cm and then dried, and then sintered at 650°C for 2h. The thickness of the pile 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. The XRD pattern of the obtained regenerated iron phosphate is shown in Figure 2. It can be seen from Figure 2 that the generated iron phosphate has no impurity peaks, and the main peak is high and sharp, indicating that it has high crystallinity. The SEM image of the obtained dihydrate iron phosphate is shown in Figure 3. It can be seen from Figure 3 that the generated dihydrate iron phosphate mainly exists in the form of very thin flakes with an average length of about 200nm.

[0046] Example 2:

[0047] A method for regenerating ferric phosphate waste comprises the following steps:

[0048] (1) Calcinate the ground iron phosphate waste after passing through a 60-mesh sieve at 450°C for 4 hours;

[0049] (2) A slurry was prepared by mixing calcined iron phosphate waste, acid solution, and hydrogen peroxide = 1 g: 3 mL: 2 mL. The mixture was placed in a hydrothermal reactor, with the slurry accounting for 70% of the volume of the reactor. The reaction was carried out at 160°C for 4 h at a heating rate of 5°C / min. The acid solution was composed of phosphoric acid and sulfuric acid, with a molar ratio of phosphoric acid to sulfuric acid of 3:7. The H + The concentration is 2 mol / L, and the mass concentration of hydrogen peroxide is 10%;

[0050] (3) The slurry obtained after the hydrothermal reaction in step (2) is separated into solid and liquid, and the obtained solid is washed until the conductivity of the washing wastewater is less than 500 μS / cm and then dried, and then sintered at 750°C for 4 hours. The thickness of the pile during sintering is ≤4 cm to obtain regenerated iron phosphate. The supernatant obtained after the solid-liquid separation and the washing water can be returned to step (2) for reuse.

[0051] Example 3:

[0052] This embodiment provides a method for regenerating waste iron phosphate, which differs from embodiment 1 only in that the temperature for calcining the waste iron phosphate in step (1) is 300°C.

[0053] Example 4:

[0054] This embodiment provides a method for regenerating waste iron phosphate, which differs from embodiment 1 only in that the temperature for calcining the waste iron phosphate in step (1) is 400°C.

[0055] Example 5:

[0056] This embodiment provides a method for regenerating ferric phosphate waste, which differs from embodiment 1 only in that: in step (2), the H + The concentration is 5mol / L.

[0057] Example 6:

[0058] This embodiment provides a method for regenerating ferric phosphate waste, which differs from embodiment 1 only in that: in step (2), the H + The concentration is 8mol / L.

[0059] Example 7:

[0060] This embodiment provides a method for regenerating iron phosphate waste, which differs from Example 1 only in that the solid sintering time in step (3) is 4 hours.

[0061] Example 8:

[0062] This embodiment provides a method for regenerating iron phosphate waste, which differs from embodiment 1 only in that the solid sintering temperature in step (3) is 750°C.

[0063] Comparative Example 1:

[0064] This embodiment provides a method for regenerating waste iron phosphate, which differs from Example 1 only in that no hydrogen peroxide is added in step (2).

[0065] Test example:

[0066] The relevant parameters of the regenerated ferric phosphate prepared in Examples 1-8 and Comparative Example 1 were tested according to the HG / T 4701-2021 standard. The relevant product parameters are shown in Table 1.

[0067] Table 1: Relevant parameters for regenerated ferric phosphate

[0068] From Table 1 we can see that:

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

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

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

Claims

1. A regeneration method for iron phosphate waste, characterized in that: It includes the following steps: (1) After calcining the iron phosphate waste, it is mixed with an acid solution and an oxidant to form a mixture, and heated for hydrothermal reaction to obtain a slurry; (2) The slurry obtained from the reaction in step (1) is subjected to solid-liquid separation, and the obtained solid phase is washed and sintered to obtain regenerated iron phosphate.

2. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (1), the iron phosphate waste is also subjected to grinding and sieving treatment.

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

4. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (1), the calcination temperature is 150 - 500 °C, and the calcination time is 1 - 5 h.

5. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (1), the acid solution includes a phosphoric acid solution and other inorganic acid solutions, and in the acid solution, the molar ratio of phosphoric acid to other inorganic acids is (1 - 7):(5 - 10).

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

7. The regeneration method for 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 regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (1), the oxidant is hydrogen peroxide.

9. The regeneration method for iron phosphate waste according to claim 8, characterized in that: The mass concentration of the hydrogen peroxide is 1% - 15%.

10. The regeneration method for iron phosphate waste according to claim 9, characterized in that: In step (1), the mixing ratio of the calcined iron phosphate waste, the acid solution and the oxidant is 1 g:1 - 5 mL:1 - 3 mL.

11. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (1), the hydrothermal reaction is carried out in a hydrothermal reaction kettle, the temperature of the hydrothermal reaction is 100 - 200 °C, the time of the hydrothermal reaction is 1 - 5 h, and the heating rate is 1 - 15 °C / min.

12. The regeneration method for iron phosphate waste according to claim 11, characterized in that: The volume of the mixture in the hydrothermal reaction kettle is 40% - 80%.

13. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (2), the supernatant obtained after solid-liquid separation and the washing water for washing can be returned to step (1) for repeated use.

14. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (2), the solid phase is washed until the conductivity of the obtained washing wastewater < 500 us / cm and then sintered.

15. The regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (2), the sintering temperature is 500 - 1000 °C, and the sintering time is 1 - 8 h.

16. A regeneration method for iron phosphate waste according to claim 1, characterized in that: In step (2), the thickness of the stacked material during sintering is ≤ 5 cm.

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