Method for remanufacturing by using defective iron phosphate
Through high-temperature sulfuric acid swelling and phosphorus iron source conversion treatment, the problem of impurity wrapping in defective iron phosphate is solved, and the preparation of qualified iron phosphate is achieved, and the product quality and inventory utilization rate are improved.
Patent Information
- Application Number
- CN202410142109.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-01-31
- Publication Date
- 2025-08-01
AI Technical Summary
In the prior art, defective iron phosphate cannot be processed in traditional ways due to impurities and magnetic substances being wrapped in materials, resulting in unqualified products, occupying inventory and affecting the product morphology and specific surface area.
The defective iron phosphate is swelled at high temperature using sulfuric acid, combined with the conversion treatment of the phosphorus source and the iron source, and through the filtration and calcination steps, impurities are removed and the iron-phosphorus ratio is adjusted to prepare qualified iron phosphate.
Effectively reduce sulfate residues, ensure the iron-phosphorus ratio, prepare iron phosphate that meets the requirements, improve product quality and reduce inventory occupation.
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Figure CN120398015A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of iron phosphate production, and particularly to a method for remanufacturing defective iron phosphate. Background Art
[0002] During the production of general iron phosphate using the co - precipitation method, due to unstable control of parameters and abnormal equipment, the product indicators are unstable, and magnetic foreign matters or other impurities will be mixed in, resulting in the final sintered product not meeting the indicators and being judged as unqualified iron phosphate. This part of the unqualified iron phosphate cannot remove impurities through traditional washing and calcination, and washing and then calcining the sintered iron phosphate slurry will affect the product morphology and specific surface area.
[0003] In the case of initial startup or equipment abnormalities, iron phosphate products with unqualified magnetic substance or impurity content may be produced. The traditional washing method cannot wash out the impurities wrapped in the materials, resulting in a large amount of washing water or inability to handle. This leads to unqualified iron phosphate products occupying inventory.
[0004] Therefore, this application proposes a method for remanufacturing defective iron phosphate. Summary of the Invention
[0005] In order to overcome the deficiencies of the prior art, the present invention provides a method for remanufacturing defective iron phosphate. In this method, sulfuric acid is used to swell defective iron phosphate at high temperature, and through the addition of phosphorus source and iron source for conversion treatment, the residual sulfate can be reduced, and the iron - phosphorus ratio can be guaranteed, so as to prepare iron phosphate with qualified magnetic substances.
[0006] The technical solution adopted by the present invention to solve its technical problems is as follows:
[0007] On the one hand, this application provides a method for remanufacturing defective iron phosphate, including the following steps:
[0008] At ≥75 °C, sulfuric acid is used to carry out a swelling reaction on defective iron phosphate; when the particle size D50 of the insoluble matter in the swelling reaction liquid < 7 μm, the swelling reaction ends;
[0009] After the swelling reaction ends, the swelling reaction liquid is filtered; in the swelling reaction liquid, materials with a particle size > 5 μm are returned to the dissolution tank, and materials with a particle size ≤ 5 μm are filtered again with the filtrate to obtain a primary filtrate and a primary filter cake;
[0010] The primary filter cake undergoes pulp washing, conversion treatment, filtration, and calcination to obtain qualified iron phosphate.
[0011] Preferably, the defective iron phosphate is iron phosphate with a magnetic substance > 2 ppm.
[0012] Preferably, the addition amount of sulfuric acid is 20% sulfuric acid based on the iron molar content in the defective iron phosphate.
[0013] Preferably, when carrying out the swelling reaction, the pH of the swelling reaction feed liquid is 1.2 - 1.3.
[0014] Preferably, the swelling reaction is carried out at 85 - 90 °C.
[0015] Preferably, the pulp washing is to add the primary filter cake and water into the pulp washing tank for pulp washing.
[0016] Preferably, the conversion treatment is to mix the pulp washing feed liquid obtained by pulp washing, a phosphorus source and an iron source, and carry out conversion at 90 - 95 °C for 1 - 2 h.
[0017] More preferably, the filtration is to use a plate and frame filter press to carry out pressure filtration and washing on the conversion feed liquid obtained after the conversion treatment.
[0018] More preferably, the calcination is to calcine the secondary filter cake obtained after pressure filtration and washing at 550 °C to 600 °C to obtain iron phosphate.
[0019] On the other hand, the present application provides an iron phosphate prepared by the method described above.
[0020] The beneficial effects of the present invention are as follows:
[0021] 1. In the method described in the present application, sulfuric acid is used to carry out a swelling treatment on defective iron phosphate at high temperature, and an iron source and a phosphorus source are added after pulp washing, which can reduce the sulfate residue in the iron phosphate and ensure the iron - phosphorus ratio of the iron phosphate, and can prepare qualified iron phosphate with the magnetic substance meeting the requirements.
[0022] 2. In the method described in the present application, through swelling and conversion treatment of defective iron phosphate, the structure of the iron phosphate crystal can be recombined secondarily to obtain high - grade iron phosphate, which has important significance for the de - inventory and value - addition of defective iron phosphate and its application. BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The present invention will be further described below with reference to the drawings and embodiments.
[0024] Figure 1 is a process flow chart of a method for remanufacturing using defective iron phosphate in the present application;
[0025] Figure 2 is a summary chart of the performance detection of the iron phosphate prepared in Examples 1 - 4 and Comparative Examples 1 - 2 in the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0026] As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items. The terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the present invention. As used herein, the singular forms "a", "an", "one" and "the" are also intended to include the plural forms unless the context clearly indicates otherwise. Further understanding, when "comprising" is used in this specification, it specifies the stated features, integers, steps, operations, elements and / or components, but does not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.
[0027] The inventors found that in defective iron phosphate, due to magnetic substances (such as > 2 ppm) or impurities being wrapped in the material, and iron phosphate does not dissolve in sulfuric acid solution or phosphoric acid solution, and cannot be processed by traditional methods;
[0028] For this reason, the present application provides a method for remanufacturing using defective iron phosphate as shown in Figure 1 shown, including the following steps:
[0029] In a dissolution kettle, at a temperature of ≥ 75 °C, use sulfuric acid to perform a swelling treatment on defective iron phosphate;
[0030] When performing the swelling treatment, the pH of the swelling reaction liquor is 1.2 - 1.3; after the swelling treatment ends, detect that the particle size D50 of the insoluble matter in the swelling reaction liquor < 7 μm, and stop the swelling reaction;
[0031] If the particle size of the insoluble matter in the swelling reaction liquor does not reach D50 < 7 μm, continue the swelling treatment for 30 - 60 min.
[0032] After the swelling treatment ends, use a centrifuge (the aperture of the filter cloth is 5 μm) for filtration; the material with a particle size > 5 μm is returned to the dissolution kettle,
[0033] The material with a particle size ≤ 5 μm enters a plate and frame filter press (the aperture of the filter cloth is 4 - 5 μm) for filtration along with the centrifugal filtrate to obtain a primary filtrate and a primary filter cake. According to the detection index of the primary filtrate, part of the primary filtrate is returned to the dissolution kettle, and the rest is discharged; the primary filter cake and purified water are transferred to a pulp washing tank for pulp washing, and ferrous sulfate is used as the iron source, and monoammonium phosphate or phosphoric acid is used as the phosphorus source, and converted at 90 - 95 °C for 1 - 2 h.
[0034] Use a plate and frame filter press for pressure filtration and washing, and the qualified filter cake after washing is calcined at 550 °C - 600 °C to obtain iron phosphate.
[0035] Specifically, at a temperature ≥ 75°C, for example, at 85 - 90°C, sulfuric acid is used to carry out a swelling reaction on defective iron phosphate; carrying out the swelling reaction can make the structure of defective iron phosphate become loose, dissolve magnetic substances or impurities, and at high temperature, the magnetic substances react with sulfuric acid, dissolve into ions and then are dissolved out into the swelling reaction feed liquid;
[0036] More specifically, by adding sulfuric acid, for example, concentrated sulfuric acid with a mass concentration of 98%, the pH of the swelling reaction feed liquid is controlled to be 1.2 - 1.3; under the condition of pH being 1.2 - 1.3, the magnetic substances in the defective calcium phosphate in the swelling reaction feed liquid can be dissolved by sulfuric acid.
[0037] Specifically, the defective iron phosphate is defective iron phosphate with D50 < 15μm and a magnetic substance content of 2 - 100 ppm; after the defective iron phosphate undergoes a swelling reaction, the structure of the iron phosphate in the swelling reaction feed liquid becomes loose and the particle size becomes finer. By controlling the particle size of the insoluble substances in the swelling reaction feed liquid to reach D50 < 7μm, and the insoluble substances with a larger particle size need to be returned to the dissolution tank for swelling treatment again to ensure that the magnetic substances in the swelling reaction feed liquid are fully dissolved out through the swelling treatment.
[0038] Specifically, the primary filtrate and the primary filter cake are obtained by filtering through a plate and frame filter press. The primary filtrate contains iron phosphate with a particle size < 2μm; the primary filter cake may contain some iron phosphate and needs to be processed again.
[0039] Specifically, the process of pulp washing is as follows: the primary filter cake is transferred to a pulp washing tank, and purified water 5 - 6 times the weight of the primary filter cake is added, and pulp washing is carried out at 90 - 95°C for 30 min; after the pulp washing is completed, a pulp washing feed liquid is obtained. By reducing the pulp, the sulfate residue in the primary filter cake is reduced.
[0040] Specifically, during the conversion treatment process, ferrous sulfate is used as the iron source and monoammonium phosphate or phosphoric acid is used as the phosphorus source. After the pulp washing feed liquid, the iron source, and the phosphorus source are fully mixed, conversion is carried out at 90 - 95°C for 1 - 2 h, and the iron phosphate with an unqualified iron - phosphorus ratio can be converted into iron phosphate with a qualified iron - phosphorus ratio, further reducing the sulfate residue in the pulp washing filtrate.
[0041] More specifically, the addition amounts of the iron source and the phosphorus source are 1 - 2% and 3 - 5% of the weight of the primary filter cake.
[0042] For the convenience of those skilled in the art to understand, the present invention will be further described below in conjunction with embodiments. The content mentioned in the embodiments does not limit the present invention.
[0043] Example 1
[0044] A method for remanufacturing using defective iron phosphate includes the following steps:
[0045] Prepare the defective lithium iron phosphate finished product to be processed. First, screen it to remove foreign matters therein to obtain the screened defective lithium iron phosphate. According to the weight ratio of the screened defective lithium iron phosphate to demineralized water (distilled water) of 1:2.5, add the demineralized water and the screened defective lithium iron phosphate into a dissolution kettle, and stir and mix them to obtain a defective lithium iron phosphate liquor.
[0046] Among them: the weight of the screened defective lithium iron phosphate is 200 kg, and the weight content of the magnetic substance in the screened defective lithium iron phosphate is 2.33 ppm, and D50 is 10.2 μm.
[0047] Add concentrated sulfuric acid (20% concentrated sulfuric acid of the iron molar content in the screened defective lithium iron phosphate) to the above dissolution kettle, and fully mix it with the defective lithium iron phosphate liquor to obtain a swelling reaction liquor. Control the pH of the swelling reaction liquor to be 1.2 - 1.3; heat it up to 85 °C, keep the swelling reaction liquor at 85 °C for 1 h for swelling reaction; control the particle size D50 of the insoluble matter in the swelling reaction liquor < 7 μm. After the particle size of the insoluble matter meets the requirements, end the swelling reaction.
[0048] If the particle size of the insoluble matter in the swelling reaction liquor does not reach D50 < 7 μm, continue the swelling treatment for 30 min.
[0049] After the swelling reaction ends, cool the swelling reaction liquor to < 75 °C, and filter it using a centrifuge (the aperture of the filter cloth is 5 μm). The insoluble matter with a particle size > 5 μm is returned to the dissolution kettle, and the centrifuged filtrate enters a plate and frame filter press for filtration (the aperture of the filter cloth is 4 - 5 μm) to obtain a primary filtrate and a primary filter cake.
[0050] Transfer the primary filter cake and purified water to a slurry washing tank for slurry washing. The weight ratio of the primary filter cake to the purified water is 1:3, and slurry wash at 90 °C for 30 min; add an iron source and a phosphorus source, and convert at 90 °C for 1 h. After the conversion ends, cool it to room temperature to obtain a conversion liquor. Among them, the addition amounts of the iron source and the phosphorus source are 1% and 3% of the weight of the primary filter cake.
[0051] Use a plate and frame filter press to filter and wash the conversion liquor. The qualified secondary filter cake after washing is calcined at 550 °C to obtain lithium iron phosphate.
[0052] Example 2
[0053] A method for remanufacturing using defective lithium iron phosphate, comprising the following steps:
[0054] Prepare the defective lithium iron phosphate product to be processed. First, screen it to remove foreign matters therein to obtain the screened defective lithium iron phosphate. According to the weight ratio of the screened defective lithium iron phosphate to demineralized water (distilled water) of 1:2.5, add the demineralized water and the screened defective lithium iron phosphate into a dissolution kettle, and stir and mix them to obtain a defective lithium iron phosphate liquor. The weight of the screened defective lithium iron phosphate is 200 kg, and the weight content of magnetic substances in the screened defective lithium iron phosphate is 8.76 ppm, and D50 is 10.2 μm;
[0055] Add concentrated sulfuric acid (20% concentrated sulfuric acid of the iron molar content in the screened defective lithium iron phosphate) to the above dissolution kettle, and fully mix it with the defective lithium iron phosphate liquor to obtain a swelling reaction liquor. Control the pH of the swelling reaction liquor to be 1.2 - 1.3; heat it up to 90 °C, keep the swelling reaction liquor at 90 °C for 1 h for the swelling reaction; control the particle size D50 of the insoluble matters in the swelling reaction liquor to be < 7 μm. After the particle size of the insoluble matters meets the requirements, end the swelling reaction;
[0056] If the particle size of the insoluble matters in the swelling reaction liquor does not reach D50 < 7 μm, continue the swelling treatment for 60 min.
[0057] After the swelling reaction ends, cool the swelling reaction liquor to < 75 °C, and filter it using a centrifuge (the aperture of the filter cloth is 5 μm). The insoluble matters with a particle size > 5 μm are returned to the dissolution kettle, and the centrifuged filtrate enters a plate and frame filter press for filtration (the aperture of the filter cloth is 4 - 5 μm) to obtain a primary filtrate and a primary filter cake;
[0058] Transfer the primary filter cake and purified water to a pulp washing tank for pulp washing. The weight ratio of the primary filter cake to the purified water is 1:3, and pulp wash at 95 °C for 30 min; add an iron source and a phosphorus source, and convert at 95 °C for 2 h. After the conversion ends, cool it to room temperature to obtain a conversion liquor; the addition amounts of the iron source and the phosphorus source are 2% and 5% of the weight of the primary filter cake.
[0059] Use a plate and frame filter press to filter and wash the conversion liquor. The qualified secondary filter cake after washing is calcined at 600 °C to obtain lithium iron phosphate.
[0060] Example 3
[0061] A method for remanufacturing using defective lithium iron phosphate, comprising the following steps:
[0062] Prepare the defective lithium iron phosphate product to be processed. First, screen it to remove foreign matters therein to obtain the screened defective lithium iron phosphate. According to the weight ratio of the screened defective lithium iron phosphate to demineralized water (distilled water) of 1:2.5, add the demineralized water and the screened defective lithium iron phosphate into a dissolution kettle, and stir and mix them to obtain a defective lithium iron phosphate liquor. The weight of the screened defective lithium iron phosphate is 200 kg, and the weight content of magnetic substances in the screened defective lithium iron phosphate is 3.33 ppm, and D50 is 3.5 μm;
[0063] Concentrated sulfuric acid (20% concentrated sulfuric acid of the iron molar content in the sieved defective iron phosphate) is added to the above-mentioned dissolution kettle and fully mixed with the defective iron phosphate feed liquid to obtain a swelling reaction feed liquid; the pH of the swelling reaction feed liquid is controlled to be 1.2 - 1.3; the temperature is raised to 85 °C, and the swelling reaction feed liquid is kept at 85 °C for 1 h to carry out the swelling reaction; the particle size D50 of the insoluble matter in the swelling reaction feed liquid is controlled to be < 7 μm. After the particle size of the insoluble matter meets the requirements, the swelling reaction is ended;
[0064] If the particle size of the insoluble matter in the swelling reaction feed liquid does not reach D50 < 7 μm, the swelling treatment is continued for 40 min.
[0065] After the swelling reaction is ended, the temperature of the swelling reaction feed liquid is lowered to < 75 °C, and it is filtered using a centrifuge (the pore size of the filter cloth is 5 μm). The insoluble matter with a particle size > 5 μm is returned to the dissolution kettle, and the centrifuged filtrate enters a plate and frame filter press for filtration (the pore size of the filter cloth is 4 - 5 μm) to obtain a primary filtrate and a primary filter cake;
[0066] The primary filter cake and purified water are transferred to a pulp washing tank for pulp washing. The weight ratio of the primary filter cake to the purified water is 1:3, and pulp washing is carried out at 93 °C for 30 min; an iron source and a phosphorus source are added, and conversion is carried out at 95 °C for 1.5 h. After the conversion is ended, the temperature is lowered to room temperature to obtain a conversion feed liquid; the addition amounts of the iron source and the phosphorus source are 1.5% and 4% of the weight of the primary filter cake.
[0067] The conversion feed liquid is pressure - filtered and washed using a plate and frame filter press, and the qualified secondary filter cake is calcined at 580 °C to obtain iron phosphate.
[0068] Example 4
[0069] A method for remanufacturing using defective iron phosphate includes the following steps:
[0070] Prepare the defective iron phosphate finished product to be processed, first sieve to remove foreign matters therein to obtain sieved defective iron phosphate; according to the weight ratio of sieved defective iron phosphate to demineralized water (distilled water) of 1:2.5, add demineralized water and sieved defective iron phosphate to the dissolution kettle and stir and mix to obtain a defective iron phosphate feed liquid; the weight of the sieved defective iron phosphate is 200 kg, the weight content of the magnetic substance in the sieved defective iron phosphate is 3.51 ppm, and D50 is 11.90 μm;
[0071] Add concentrated sulfuric acid (20% concentrated sulfuric acid of the iron molar content in the sieved defective iron phosphate) to the above dissolution kettle, and fully mix it with the defective iron phosphate liquor to obtain a swelling reaction liquor; control the pH of the swelling reaction liquor to be 1.2 - 1.3; heat up to 90 °C, keep the swelling reaction liquor at 90 °C for 1 h for swelling reaction; control the particle size D50 of the insoluble matter in the swelling reaction liquor to be < 7 μm. After the particle size of the insoluble matter meets the requirements, end the swelling reaction;
[0072] If the particle size of the insoluble matter in the swelling reaction liquor does not reach D50 < 7 μm, continue the swelling treatment for 60 min.
[0073] After the swelling reaction ends, cool the swelling reaction liquor to < 75 °C, filter it using a centrifuge (the aperture of the filter cloth is 5 μm), return the insoluble matter with a particle size > 5 μm to the dissolution kettle, and the centrifuged filtrate enters a plate and frame filter press for filtration (the aperture of the filter cloth is 4 - 5 μm) to obtain a primary filtrate and a primary filter cake;
[0074] Transfer the primary filter cake and purified water to a pulp washing tank for pulp washing. The weight ratio of the primary filter cake to purified water is 1:3, and pulp wash at 90 °C for 30 min; add an iron source and a phosphorus source, and carry out conversion at 95 °C for 1.5 h. After the conversion ends, cool to room temperature to obtain a conversion liquor; the addition amounts of the iron source and the phosphorus source are 2% and 5% of the weight of the primary filter cake.
[0075] Use a plate and frame filter press to filter and wash the conversion liquor. The qualified secondary filter cake is calcined at 600 °C to obtain iron phosphate.
[0076] Comparative Example 1 (without conversion treatment)
[0077] A method for remanufacturing using defective iron phosphate includes the following steps:
[0078] Prepare the defective iron phosphate finished product to be processed, first sieve to remove foreign matters therein to obtain sieved defective iron phosphate; according to the weight ratio of sieved defective iron phosphate to demineralized water (distilled water) of 1:2.5, add demineralized water and sieved defective iron phosphate to the dissolution kettle, and stir and mix to obtain a defective iron phosphate liquor; the weight of the sieved defective iron phosphate is 200 kg, and the weight content of the magnetic substance in the sieved defective iron phosphate is 3.33 ppm, and D50 is 3.5 μm;
[0079] Add concentrated sulfuric acid (20% concentrated sulfuric acid of the iron molar content in the sieved defective iron phosphate) to the above dissolution kettle, and fully mix it with the defective iron phosphate liquor to obtain a swelling reaction liquor; control the pH of the swelling reaction liquor to be 1.2 - 1.3; heat up to 85 °C, keep the swelling reaction liquor at 85 °C for 1 h for the swelling reaction; control the particle size D50 of the insoluble matter in the swelling reaction liquor to be < 7 μm, and end the swelling reaction after the particle size of the insoluble matter meets the requirements;
[0080] If the particle size of the insoluble matter in the swelling reaction liquor does not reach D50 < 7 μm, continue the swelling treatment for 40 min.
[0081] Cool the swelling reaction liquor to < 75 °C, filter it using a centrifuge (the pore size of the filter cloth is 5 μm), return the insoluble matter with a particle size > 5 μm to the dissolution kettle, and the centrifuged filtrate enters a plate and frame filter press for filtration (the pore size of the filter cloth is 2 μm) to obtain a primary filtrate and a primary filter cake;
[0082] The primary filter cake is calcined at 550 °C to obtain iron phosphate.
[0083] Comparative Example 2 (without swelling treatment)
[0084] A method for remanufacturing using defective iron phosphate includes the following steps:
[0085] Prepare the defective iron phosphate finished product to be processed, first sieve to remove foreign matters therein to obtain sieved defective iron phosphate; according to the weight ratio of sieved defective iron phosphate to demineralized water (distilled water) of 1:2.5, add demineralized water and sieved defective iron phosphate to the dissolution kettle, and stir and mix to obtain a defective iron phosphate liquor; the weight of the sieved defective iron phosphate is 200 kg, and the weight content of the magnetic substance in the sieved defective iron phosphate is 3.33 ppm, and D50 is 3.5 μm;
[0086] Transfer the sieved defective iron phosphate and purified water to a pulp washing tank for pulp washing. The ratio of sieved defective iron phosphate to water is 1:3, and pulp wash at 90 °C for 30 min; add an iron source and a phosphorus source, and convert at 90 °C for 1 h. After the conversion is completed, cool to room temperature to obtain a conversion liquor; the addition amounts of the iron source and the phosphorus source are 1.5% and 4% of the weight of the sieved defective iron phosphate.
[0087] Use a plate and frame filter press to filter and wash the conversion liquor, and calcine the qualified filter cake at 550 °C to obtain iron phosphate.
[0088] Detect the iron - phosphorus ratio and the content of magnetic substances of the iron phosphates prepared in Examples 1 - 4 and Comparative Examples 1 - 2, and summarize the relevant results in Figure 2 as follows:
[0089] Among them: For the detection of the iron-to-phosphorus ratio, the iron and phosphorus in iron phosphate are determined by inductively coupled plasma optical emission spectrometry; for the detection of the content of magnetic substances, the sample to be tested and a magnet are mixed and then placed on a pot mill. The rotation speed of the pot mill is set to 110 r / min and mixed for 30 min; the magnet is separated; concentrated hydrochloric acid and concentrated nitric acid are added to digest and make the volume constant for the separated magnet, and the contents of Fe, Cr, Zn, Ni, and P in the constant-volume solution are determined by an ICP instrument. The contents of Fe, Cr, Zn, Ni, and P are summarized to obtain the content of magnetic substances in the sample to be tested.
[0090] From Figure 2 , it can be seen that after being treated according to Examples 1-4, the content of magnetic substances in the defective iron phosphate is significantly reduced, and the lowest is reduced to 0.06 ppm. Moreover, the conversion rate of the defective iron phosphate into the finished iron phosphate product reaches more than 83%, and the loss of the defective iron phosphate is small; for the iron-to-phosphorus ratio in the defective iron phosphate, after the conversion treatment, the iron-to-phosphorus ratio of the finished product in the iron phosphate becomes qualified (0.969 - 0.970).
[0091] In Comparative Example 1, the defective iron phosphate lacked the conversion treatment, and the obtained iron-to-phosphorus ratio decreased and did not reach the required iron-to-phosphorus ratio (0.969 - 0.970);
[0092] In Comparative Example 2, the defective iron phosphate lacked the swelling treatment, and the amount of magnetic substances removed was small. The obtained finished iron phosphate product still contained a large amount of magnetic substances (reaching 2.30 ppm).
[0093] The above embodiments are the preferred implementation schemes of the present invention. In addition, the present invention can also be implemented in other ways. Any obvious replacement without departing from the concept of the present invention is within the protection scope of the present invention.
Claims
1. A method for remanufacturing using defective lithium iron phosphate, characterized in that, It includes the following steps: At a temperature ≥75°C, use sulfuric acid to carry out a swelling reaction on defective iron phosphate; when the particle size D50 of the insoluble matter in the swelling reaction feed liquid <7 μm, the swelling reaction ends; After the swelling reaction ends, filter the swelling reaction feed liquid; in the swelling reaction feed liquid, the materials with a particle size >5 μm are returned to the dissolution kettle, and the materials with a particle size ≤5 μm are filtered again together with the filtrate to obtain a primary filtrate and a primary filter cake; The primary filter cake undergoes pulp washing, conversion treatment, filtration, and calcination to obtain qualified iron phosphate.
2. The method according to claim 1, characterized in that, The defective iron phosphate is iron phosphate with a magnetic substance >2 ppm.
3. The method according to claim 1, characterized in that, The addition amount of the sulfuric acid is 20% sulfuric acid of the iron molar content in the defective iron phosphate.
4. The method according to claim 1, wherein When carrying out the swelling reaction, the pH of the swelling reaction feed liquid is 1.2 - 1.
3.
5. The method according to claim 1, characterized in that The swelling reaction is carried out at 85 - 90°C.
6. The method according to claim 1, wherein The pulp washing is to add the primary filter cake and water to a pulp washing tank for pulp washing.
7. The method according to claim 1, characterized in that The conversion treatment is to mix the pulp washing feed liquid obtained from pulp washing, a phosphorus source, and an iron source, and carry out conversion at 90 - 95°C for 1 - 2 h.
8. The method according to claim 7, characterized in that, The filtration is to use a plate and frame filter press to carry out pressure filtration and washing on the conversion feed liquid obtained after the conversion treatment.
9. The method according to claim 8, characterized in that, The calcination is to calcine the secondary filter cake obtained after pressure filtration and washing at 550°C - 600°C to obtain iron phosphate.
10. A ferric phosphate, characterized in that, Iron phosphate prepared by the method according to any one of claims 1 - 9.