Method for recovering and preparing iron phosphate from iron phosphate dust collecting material and application thereof

Abstract

This paper discloses a method for preparing ferric phosphate from ferric phosphate dust and its application, belonging to the field of waste utilization technology. The method includes the following steps: sieving the ferric phosphate dust, adding water to make a slurry, filtering to obtain anhydrous ferric phosphate filter cake; preparing a slurry with the anhydrous ferric phosphate filter cake in a phosphoric acid solution, heating, recrystallizing, and separating the solid and liquid to obtain a dihydrate ferric phosphate filter cake; drying and calcining the dihydrate ferric phosphate filter cake to obtain anhydrous ferric phosphate. The anhydrous ferric phosphate prepared in this paper has high tap density, small particle size, large specific surface area, and low impurity content, which can effectively improve the electrochemical performance of batteries and has broad application prospects.

Description

Technical Field

[0001] This article relates to the field of waste utilization technology, specifically to a method for recovering and preparing ferric phosphate from ferric phosphate dust and its application. Background Technology

[0002] Lithium iron phosphate (LFP) batteries are widely used in new energy battery materials due to their high safety and cycle life exceeding 2000 cycles. With the continuous reduction in the cost of new energy vehicles, LFP's market share in the power battery market is constantly rising. The performance importance of iron phosphate as a precursor to LFP cathode materials is self-evident. Currently, due to differences in raw materials and processes for preparing iron phosphate, there are significant differences between iron phosphate products. Although the production threshold for iron phosphate is not high, high-purity iron phosphate with high impurity content and stable performance remains relatively scarce.

[0003] Currently, most manufacturers use rotary kilns for sulfur removal during production. During operation, the rotary kiln generates a large amount of flue gas carrying materials, which is then drawn into the dust collection silo under negative pressure, producing a significant amount of dust. Due to differences in processes and equipment, this dust accounts for approximately 3-10% of the total production capacity. Although some manufacturers have reduced dust generation through modifications to their rotary kilns and adjustments to their sintering processes, the proportion remains substantial. During the negative pressure extraction of sulfur-containing flue gas and dust into the dust collection silo, the inability to promptly remove the flue gas and the inherent properties of ferric phosphate lead to a significant accumulation of sulfur in the dust collection material. This alters the physical properties of the ferric phosphate, preventing it from flowing into the product end as a normal material.

[0004] The mainstream processing technology for dust collectors is as follows: (1) The dust collectors after the flue gas is removed are directly returned to the kiln for re-sintering. During the sintering process, normal materials are mixed and flow into the finished product. However, due to the high sulfur content, S is difficult to completely remove, resulting in a higher S content in the product compared to the material without dust collectors. Furthermore, this part of the material undergoes secondary sintering, which leads to significant changes in the product's moisture content, specific surface area, and tap density, causing deviations in the finished product's indicators. (2) Some manufacturers use sulfuric acid to dissolve the dust collectors and then use alkaline solution to increase the pH and precipitate them for iron phosphate synthesis. Although this process makes it easier to maintain product consistency, it still has the disadvantages of being cumbersome, having a long process, and being costly. The efficient recovery and preparation of iron phosphate dust collectors into iron phosphate can effectively reduce resource waste, lower costs, and increase corporate profits, which is in line with the strategic planning of sustainable development. Summary of the Invention

[0005] The purpose of this paper is to overcome the shortcomings of existing technologies and provide a method for preparing iron phosphate from iron phosphate dust and its application. The anhydrous iron phosphate prepared in this paper has high tap density, small particle size, large specific surface area, and low impurity content. At the same time, the Fe / P molar ratio is ideal. When applied to the preparation of battery materials, it can effectively improve the electrochemical performance of batteries and has broad application prospects.

[0006] To achieve the above objectives, the technical solution adopted in this paper is as follows:

[0007] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0008] The ferric phosphate dust collector is sieved, water is added to make a slurry, and then filtered to obtain anhydrous ferric phosphate filter cake.

[0009] Anhydrous ferric phosphate filter cake was mixed with phosphoric acid solution to form a slurry, heated, recrystallized, and separated into solid and liquid to obtain ferric phosphate dihydrate filter cake.

[0010] The filter cake of ferric phosphate dihydrate was dried and calcined to obtain anhydrous ferric phosphate.

[0011] This paper creatively uses sieving to remove large particles of foreign matter from the ferric phosphate dust collection material. Then, water is added to make a slurry, which is then filtered to remove sulfur impurities and other metal impurities. Phosphoric acid solution is then added, and the reaction process is controlled in the phosphoric acid solution, where dissolution and crystallization occur simultaneously. By controlling the rates of these two processes, the dust collection material produced in the production process is recrystallized to obtain high-purity ferric phosphate, thus achieving one-step, efficient, and low-cost impurity separation. Finally, the product is dried and calcined to obtain anhydrous ferric phosphate.

[0012] In one embodiment, the iron phosphate dust collector contains 1-6% sulfur and has a molar ratio of 0.96-1.00 for Fe and P.

[0013] In one embodiment, the material-to-liquid ratio during the water-based pulping process is 1g:(2-4)mL. Within this range, the removal effect on impurities is better.

[0014] In one embodiment, the concentration of the phosphoric acid solution is 0.01 to 1 mol / L.

[0015] In one embodiment, the concentration of the phosphoric acid solution is 0.05–0.35 mol / L. The inventors of this paper have found in extensive research that the concentration of the phosphoric acid solution has a significant impact on the effect. If the concentration is too low, the purpose of dissolution and crystallization cannot be achieved. If the concentration is too high, the product has a large BET, small particle size, is difficult to filter, is prone to clogging the filter screen during sieving, has a high water content, and poor batch stability. Therefore, it is not suitable to use such a solution and may even cause the particles to break, resulting in a reduction in particle size. Therefore, in this paper, it is necessary to strictly control the concentration of the phosphoric acid solution.

[0016] Meanwhile, other acids cannot achieve the purpose of phosphorus supplementation. For example, hydrochloric acid solution cannot achieve the purpose of phosphorus supplementation and will also introduce chloride ions. If sulfuric acid solution is used, it cannot achieve the purpose of phosphorus supplementation. Recrystallization in sulfuric acid solution will result in more sulfate ions not being removed due to the high concentration of sulfate ions in the solution.

[0017] In one embodiment, the molar ratio of Fe, P, and S in the slurry is 1.0:(1.0-1.5):(0.01-0.1); and / or

[0018] The solid content of the slurry is 5-30 wt%.

[0019] The molar ratio of Fe, P, and S is 1.0:(1.0-1.5):(0.01-0.1). Within this range, the presence of excess P is beneficial for the recrystallization of iron phosphate.

[0020] In one embodiment, the recrystallization temperature is 60–95°C, and the recrystallization time is 0.5–6 hours.

[0021] In one embodiment, the recrystallization temperature is 80–90°C, and the recrystallization time is 2–4 hours.

[0022] In one embodiment, the heating rate is 6–15 °C / h.

[0023] In one embodiment, the roasting specifically involves: first roasting at 200–500°C for 0–90 min, then roasting at 200–700°C for 0–90 min, and finally roasting at 500–700°C for 30–120 min.

[0024] This paper adopts a three-step calcination method. During calcination at 200-500℃, the water of crystallization is removed first, followed by sulfur removal. The process of removing the water of crystallization will generate a porous structure, which is more conducive to the subsequent sintering and sulfur removal. The porous structure can improve the product's BET (Best Before Temperature). In the one-step sintering process, the dehydration and sulfur removal processes occur simultaneously, resulting in a slightly worse sulfur removal effect and also leading to a deterioration in performance.

[0025] In one embodiment, the roasting specifically involves: first roasting at 200–300°C for (10–90) min, then roasting at 400–550°C for (10–90) min, and finally roasting at 600–700°C for (30–120) min.

[0026] This article also provides anhydrous ferric phosphate, prepared by the method described above. The anhydrous ferric phosphate has a D50 of 5–12 μm and a tap density of 0.70–1.00 g / cm³. 3 Specific surface area is 5-8 m²2 / g, impurity content ≤500ppm.

[0027] The anhydrous iron phosphate prepared in this paper has high tap density, small particle size, large specific surface area, and low impurity content. At the same time, the Fe / P molar ratio is ideal. Its application in the preparation of battery materials can effectively improve the electrochemical performance of batteries and has broad application prospects.

[0028] In one embodiment, the anhydrous ferric phosphate has a D50 of 9–12 μm and a tap density of 0.85–1.00 g / cm³. 3 Specific surface area is 6.5–8 m² 2 / g, impurity content ≤300ppm.

[0029] In one embodiment, the molar ratio of Fe to P in the anhydrous ferric phosphate is 0.9 to 1.0.

[0030] In one embodiment, the molar ratio of Fe to P in the anhydrous ferric phosphate is 0.94 to 0.98.

[0031] This article also provides an application of anhydrous iron phosphate in the preparation of battery materials.

[0032] The beneficial effects of this paper are as follows: (1) In this paper, the ferric phosphate dust collection material is sieved. Sieving can remove large particles of foreign matter in the slag. Then, water is added to make slurry and filtered to remove S impurities and some other metal impurities. Then, phosphoric acid solution is added and the reaction process is controlled in the phosphoric acid solution. Dissolution and crystallization occur simultaneously. By controlling the rates of the two, the dust collection material generated in the production process is recrystallized to obtain high-purity ferric phosphate, thereby achieving one-step efficient and low-cost separation of impurities. Finally, it is dried and calcined to obtain the product anhydrous ferric phosphate; (2) The anhydrous ferric phosphate prepared in this paper has high tap density, small particle size, large specific surface area, and low impurity content. At the same time, the molar ratio of Fe to P is ideal. Compared with the existing ferric phosphate, it has higher purity and extremely low impurity content, which is far superior to the requirements of commercially available battery-grade ferric phosphate. Applying it to the preparation of battery materials can effectively improve the electrochemical performance of batteries and has broad application prospects. (3) The recrystallization process used in this paper does not require the addition of alkali solution to increase pH to precipitate iron phosphate. During the high-temperature phosphating and washing process, the phosphoric acid solution has a certain driving force to recrystallize into iron phosphate dihydrate, and no impurities are introduced during the recrystallization process. Therefore, it is of great significance for the recycling and treatment of iron phosphate dust with high impurity content. (4) By occupying sulfate sites in the dust by the phosphate ions in the phosphoric acid solution, the adjustment range of iron-phosphorus ratio can be broadened, so that there is more room for adjustment in the preparation process of lithium iron phosphate. Attached Figure Description

[0033] Figure 1The image shows a SEM image of the iron phosphate dihydrate powder prepared in Example 1.

[0034] Figure 2 The image shows the XRD pattern of the iron phosphate dihydrate powder prepared in Example 1.

[0035] Figure 3 The image shows a SEM image of the iron phosphate dihydrate powder prepared in Comparative Example 1.

[0036] Figure 4 The image shows the XRD pattern of the iron phosphate dihydrate powder prepared in Comparative Example 1.

[0037] Figure 5 The image shows the SEM image of the iron phosphate dihydrate powder prepared in Comparative Example 2. Detailed Implementation

[0038] To make the objectives, technical solutions, and advantages of the embodiments described herein clearer, the technical solutions in the embodiments will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments described herein, and not all of them. Based on the embodiments described herein, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this document.

[0039] Unless otherwise specified, all experimental reagents and instruments used in this paper are commonly used reagents and instruments.

[0040] In the examples and comparative examples, the elemental content of the iron phosphate dust collectors used was tested using an ICP-AES instrument. The iron phosphate dust collectors contained 32.55% Fe, 18.59% P, a Fe / P molar ratio of 0.971, 41,700 ppm S, 65 ppm Ni, 25 ppm Co, 2 ppm Mn, and 5 ppm Zn.

[0041] In this article, the technical features described in an open-ended manner include both closed technical solutions composed of the listed features and open technical solutions that include the listed features.

[0042] In this document, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when a range refers to an integer, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0043] Example 1

[0044] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0045] (1) Solution preparation: After preparing 0.20 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0046] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0047] The sulfur content in the slurry after pulping was 10.14 g / L, and the sulfur content in the dried filter cake was 10420 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0048] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.32:0.06.

[0049] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0050] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0051] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 60 min, then at 450°C for 60 min, and finally at 650°C for 90 min to obtain anhydrous ferric phosphate.

[0052] The SEM and XRD images of the ferric phosphate dihydrate powder prepared in this embodiment are shown below. Figure 1 , Figure 2 As shown. Figure 1 It can be seen that the prepared ferric phosphate dihydrate has a micro-nano composite structure, with fine primary particles that aggregate into secondary particles, exhibiting good particle size distribution and dispersibility; Figure 2 It can be seen that the iron phosphate dihydrate prepared in Example 1 has high phase purity, good crystallinity, and no other impurities were found.

[0053] Example 2

[0054] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0055] (1) Solution preparation: After preparing 0.10 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0056] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0057] The sulfur content in the slurry after pulping was 10.56 g / L, and the sulfur content in the dried filter cake was 9170 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0058] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.18:0.06.

[0059] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 12°C, and the slurry was stirred at 350 rpm for 4 hours to recrystallize and obtain a white slurry.

[0060] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0061] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 90 min, then at 450°C for 60 min, and finally at 650°C for 60 min to obtain anhydrous ferric phosphate.

[0062] Example 3

[0063] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0064] (1) Solution preparation: After preparing 0.05 mol / L dilute phosphoric acid, the solution is heated to 35℃ to obtain 5000L of the target phosphoric acid solution;

[0065] (2) 600 kg of dust collection material was sieved through a 100-mesh screen to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 3 g: 10 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0066] The sulfur content in the slurry after pulping was 7.316 g / L, and the sulfur content in the dried filter cake was 9251 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0067] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.10:0.05.

[0068] (4) Recrystallization: The yellow slurry from step (3) was heated to 90°C at a heating rate of 9°C, and the slurry was stirred at 350 rpm for 4 hours to recrystallize and obtain a white slurry.

[0069] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0070] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 90 min, then at 450°C for 60 min, and finally at 650°C for 60 min to obtain anhydrous ferric phosphate.

[0071] Example 4

[0072] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0073] (1) Solution preparation: After preparing 0.10 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0074] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0075] The sulfur content in the slurry after pulping was 9.73 g / L, and the sulfur content in the dried filter cake was 10051 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0076] (3) Ingredients: The filter cake after step (2) is unloaded and put into 5000L of dilute phosphoric acid solution. Stir for 25 minutes to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.06:0.06.

[0077] (4) Recrystallization: The yellow slurry from step (3) was heated to 90°C at a heating rate of 9°C, and the slurry was stirred at 350 rpm for 4 hours to recrystallize and obtain a white slurry.

[0078] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0079] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 300℃ for 30 min, then at 550℃ for 60 min, and finally at 700℃ for 120 min to obtain anhydrous ferric phosphate.

[0080] Example 5

[0081] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0082] (1) Solution preparation: After preparing 0.13 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0083] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0084] The sulfur content in the slurry after pulping was 10.42 g / L, and the sulfur content in the dried filter cake was 9208 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0085] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 20min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.21:0.05.

[0086] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 3 hours to obtain a white slurry.

[0087] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0088] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 300℃ for 90 min, then at 550℃ for 60 min, and finally at 700℃ for 60 min to obtain anhydrous ferric phosphate.

[0089] Example 6

[0090] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0091] (1) Solution preparation: After preparing 0.01 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of target phosphoric acid solution;

[0092] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0093] The sulfur content in the slurry after pulping was 9.93 g / L, and the sulfur content in the dried filter cake was 10609 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0094] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.05:0.06.

[0095] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0096] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0097] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 60 min, then at 450°C for 60 min, and finally at 650°C for 120 min to obtain anhydrous ferric phosphate.

[0098] Example 7

[0099] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0100] (1) Solution preparation: After preparing 1 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of target phosphoric acid solution;

[0101] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0102] The sulfur content in the slurry after pulping was 10.10 g / L, and the sulfur content in the dried filter cake was 10129 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0103] (3) Ingredients: The filter cake after step (2) is unloaded and put into 5000L of dilute phosphoric acid solution. Stir for 15 minutes to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:2.50:0.06.

[0104] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0105] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0106] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 60 min, then at 450°C for 60 min, and finally at 650°C for 60 min to obtain anhydrous ferric phosphate.

[0107] Example 8

[0108] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0109] (1) Solution preparation: After preparing 0.20 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0110] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0111] The sulfur content in the slurry after pulping was 10.49 g / L, and the sulfur content in the dried filter cake was 9379 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0112] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.32:0.06.

[0113] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0114] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0115] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 200℃ for 60 min, then at 500℃ for 60 min, and finally at 700℃ for 90 min to obtain anhydrous ferric phosphate.

[0116] Comparative Example 1

[0117] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not include phosphoric acid solution, but everything else is the same.

[0118] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0119] (1) Solution preparation: Heat 5000L of pure aqueous solution to 40℃;

[0120] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0121] The sulfur content in the slurry after pulping was 10.39 g / L, and the sulfur content in the dried filter cake was 10810 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0122] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of pure water and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.03:0.06.

[0123] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0124] (5) The slurry A obtained in step (4) is separated into solid and liquid components to obtain ferric phosphate filter cake and mother liquor;

[0125] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 60 min, then at 450°C for 60 min, and finally at 650°C for 90 min to obtain anhydrous ferric phosphate.

[0126] The SEM and XRD results of the iron phosphate obtained in step (5) of this comparative example are as follows: Figure 3 , 4 As shown, Figure 4 It can be seen that the anhydrous material is still the main component in the XRD of the dust collector material, and it has not recrystallized into dihydrate material. Meanwhile, from... Figure 3 The morphology also shows that the treated dust collector material failed to complete the crystallization process, and its morphology remained the same as the original dust collector material, proving that pure water cannot complete the crystallization and impurity removal of the dust collector material.

[0127] Comparative Example 2

[0128] The difference between Comparative Example 2 and Example 1 is that the concentration of the phosphoric acid solution in Comparative Example 2 is different, but everything else is the same.

[0129] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0130] (1) Solution preparation: After preparing 1.5 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of target phosphoric acid solution;

[0131] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0132] The sulfur content in the slurry after pulping was 10.63 g / L, and the sulfur content in the dried filter cake was 8921 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0133] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:3.18:0.11.

[0134] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0135] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0136] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 60 min, then at 450°C for 60 min, and finally at 650°C for 90 min to obtain anhydrous ferric phosphate.

[0137] The SEM image of the anhydrous ferric phosphate obtained in this comparative example is shown below. Figure 5 As shown, excessive P results in a product with a large BET value, small particle size, difficulty in pressure filtration, easy clogging of the filter screen during sieving, high moisture content, and poor batch stability. Therefore, it is not suitable for this method. Figure 5 It can also be seen that the particles were broken, resulting in a reduction in particle size.

[0138] Comparative Example 3

[0139] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 uses a one-step calcination process, but everything else is the same.

[0140] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0141] (1) Solution preparation: After preparing 0.20 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0142] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material. Then, the material was slurried with a ratio of material: pure water = 1 g: 2 mL and filtered to obtain anhydrous ferric phosphate filter cake.

[0143] The sulfur content in the slurry after pulping was 10.14 g / L, and the sulfur content in the dried filter cake was 10420 ppm. This indicates that the sulfur in the dust collection material cannot be completely washed away and requires subsequent processing steps.

[0144] (3) Ingredients: The filter cake after step (2) is discharged into 5000L of dilute phosphoric acid solution and stirred for 15min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry is 1.00:1.32:0.06.

[0145] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0146] (5) The white slurry A obtained in step (4) is separated into solid and liquid, yielding ferric phosphate dihydrate filter cake and mother liquor;

[0147] (6) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting at 650°C for 180 min to obtain anhydrous ferric phosphate.

[0148] Comparative Example 4

[0149] The difference between Comparative Example 4 and Example 1 is that Comparative Example 4 does not add water to make pulp, but all other aspects are the same.

[0150] A method for recovering ferric phosphate dust to prepare ferric phosphate includes the following steps:

[0151] (1) Solution preparation: After preparing 0.20 mol / L dilute phosphoric acid, the solution is heated to 40℃ to obtain 5000L of the target phosphoric acid solution;

[0152] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter from the slag material, and 5000 L of dilute phosphoric acid solution was added and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P and S in the yellow slurry was 1.00:1.32:0.22.

[0153] (3) Recrystallization: The yellow slurry from step (2) was heated to 85°C at a heating rate of 9°C and then recrystallized at a stirring speed of 350 rpm for 2 hours to obtain a white slurry.

[0154] (4) The white slurry A obtained in step (3) was separated into solid and liquid components to obtain ferric phosphate dihydrate filter cake and mother liquor;

[0155] (5) After the filter cake B is flash-dried, ferric phosphate dihydrate powder is obtained. Then it is placed in a rotary kiln for roasting. First, it is roasted at 250°C for 60 min, then at 450°C for 60 min, and finally at 650°C for 90 min to obtain anhydrous ferric phosphate.

[0156] Test case

[0157] 1. Table 1 shows the results of parameters such as raw materials, pulping, batching, and mother liquor after recrystallization during the experiments of Examples 1 to 8 and Comparative Examples 1 to 4. The specific data were obtained by testing with an ICP-AES analyzer.

[0158] Table 1

[0159]

[0160]

[0161] As shown in Table 1, the pulping and filtration in step (2) cannot clean the dust collection material. After recrystallization, the Fe content in the mother liquor is less than 1 g / L, and the P content does not match the design amount. It can be seen that some P has entered the crystal lattice of the dust collection material. The S content in the mother liquor proves that the recrystallization process can release sulfate ions from the iron phosphate.

[0162] 2. Table 2 shows the indicators of the anhydrous products synthesized in Examples 1-8 and Comparative Examples 1-4, the content of impurity elements in the recrystallized ferric phosphate products and commercially available products. The specific data were obtained by testing with an ICP-AES equipment.

[0163] Table 2

[0164]

[0165] As shown in Table 2, the impurity content of the ferric phosphate products prepared in the examples is significantly lower than that in Comparative Example 1. The particle size (BET, D50, and TD) of the ferric phosphate after recrystallization in Examples 1-4 is not significantly different from that before improvement, but the Fe / P ratio deviates significantly from the center value, being smaller than the Fe / P ratio before recrystallization. Therefore, recrystallization can adjust the Fe / P ratio in the product, broadening the adjustment range. Comparison with the examples shows that this process can effectively control the Fe / P ratio during recrystallization, which is beneficial for obtaining the optimal Fe / P ratio. Furthermore, in some processes, due to process limitations, products with high Fe / P ratios that cannot be improved (in some processes, Fe / P reaches above 1) can be improved to 0.940–0.980 using this process. Although the ferric phosphate prepared in Comparative Example 2 has a low impurity content, the product has a large BET, small particle size, is difficult to filter, easily clogs the filter screen during sieving, has a high moisture content, and poor batch stability (particle breakage). The ferric phosphate prepared in Comparative Example 3 has an excessively low Fe / P ratio, and the ferric phosphate prepared in Comparative Example 4 has an excessively high impurity content.

Claims

1. A method for preparing ferric phosphate from ferric phosphate dust, characterized in that, Includes the following steps: The ferric phosphate dust collector is sieved, water is added to make a slurry, and then filtered to obtain anhydrous ferric phosphate filter cake. Anhydrous ferric phosphate filter cake was mixed with phosphoric acid solution to form a slurry, heated, recrystallized, and separated into solid and liquid to obtain ferric phosphate dihydrate filter cake. The filter cake of ferric phosphate dihydrate was dried and calcined to obtain anhydrous ferric phosphate; The concentration of the phosphoric acid solution is 0.01~1 mol / L; The roasting process is as follows: first roasting at 200~500℃ for t1 min, then roasting at 200~700℃ for t2 min, and finally roasting at 500~700℃ for t3 min, wherein 0 min < t1≤90 min, 0 min < t2≤90 min, and 30 min≤t3≤120 min.

2. The method for preparing ferric phosphate from ferric phosphate dust according to claim 1, characterized in that, The iron phosphate dust collector contains 1-6% sulfur and has a Fe-P molar ratio of 0.96-1.

00.

3. The method for preparing ferric phosphate from ferric phosphate dust according to claim 1, characterized in that, The material-to-liquid ratio during the slurry preparation process is 1g:(2~4)mL.

4. The method for preparing ferric phosphate from ferric phosphate dust according to claim 1, characterized in that, The concentration of the phosphoric acid solution is 0.05~0.35 mol / L.

5. The method for preparing ferric phosphate from ferric phosphate dust according to claim 1, characterized in that, The molar ratio of Fe, P, and S in the slurry is 1.0:(1.0-1.5):(0.01-0.1); and / or The solid content of the slurry is 5-30 wt%.

6. The method for preparing ferric phosphate from ferric phosphate dust according to claim 1, characterized in that, The recrystallization temperature is 60~95℃, and the recrystallization time is 0.5~6h.

7. The method for preparing ferric phosphate from ferric phosphate dust according to claim 6, characterized in that, The recrystallization temperature is 80~90℃, and the recrystallization time is 2~4h.

8. The method for preparing ferric phosphate from ferric phosphate dust according to claim 6, characterized in that, The heating rate is 6~15℃ / h.

9. The method for preparing ferric phosphate from ferric phosphate dust according to claim 1, characterized in that, The roasting process specifically involves: first roasting at 200-300℃ for 10-90 minutes, then roasting at 400-550℃ for 10-90 minutes, and finally roasting at 600-700℃ for 30-120 minutes.

10. Anhydrous ferric phosphate, characterized in that, The anhydrous ferric phosphate is prepared by the preparation method according to any one of claims 1 to 9, wherein the D50 is 5 to 12 μm and the tap density is 0.70 to 1.00 g / cm³. 3 Specific surface area is 5~8m² 2 / g, impurity content ≤500ppm.

11. The anhydrous ferric phosphate according to claim 10, characterized in that, The anhydrous ferric phosphate has a D50 of 9-12 μm and a tap density of 0.85-1.00 g / cm³. 3 Specific surface area is 6.5~8m² 2 / g, impurity content ≤300ppm.

12. The anhydrous ferric phosphate according to claim 10, characterized in that, The molar ratio of Fe to P in the anhydrous ferric phosphate is 0.9 to 1.

0.

13. The use of anhydrous iron phosphate according to any one of claims 10 to 12 in the preparation of battery materials.

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