Method for recycling and preparing iron phosphate from iron phosphate-containing collected dust material, and use of iron phosphate

Abstract

A method for recycling and preparing iron phosphate from an iron phosphate-containing collected dust material, comprising the following steps: sieving an iron phosphate-containing collected dust material, adding water to form a slurry, and carrying out filtering to obtain an anhydrous iron phosphate filter cake; preparing a slurry from the anhydrous iron phosphate filter cake and a phosphoric acid solution, and carrying out heating, recrystallization, and solid-liquid separation to obtain an iron phosphate dihydrate filter cake; and drying and roasting the iron phosphate dihydrate filter cake to obtain anhydrous iron phosphate. The anhydrous iron phosphate prepared using the method has a high tap density, a small particle size, a large specific surface area, and a low impurity content, can effectively improve the electrochemical performance of a battery, and has a wide application prospect.

Description

A method for recovering iron phosphate dust and preparing iron phosphate and its application Technical Field

[0001] The present invention relates to the field of waste utilization technology, and in particular to a method for recovering iron phosphate dust to prepare iron phosphate and its application. Background Art

[0002] Lithium iron phosphate batteries are widely used in new energy battery materials due to their high safety and cycle life of over 2,000 cycles. As the cost of new energy vehicles continues to decline, lithium iron phosphate's market share in the power battery market continues to climb. The importance of iron phosphate as a precursor to lithium iron phosphate 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 threshold for preparing iron phosphate is low, high-purity, high-impurity, and stable iron phosphate remains relatively scarce.

[0003] Currently, manufacturers primarily use rotary kilns for sulfur removal during production. During rotary kiln operation, a large amount of flue gas, carrying material, is drawn into the dust collection bin under negative pressure, generating a significant amount of dust. Due to differences in process and equipment, dust collection accounts for approximately 3-10% of total production capacity. While some manufacturers have reduced dust generation through rotary kiln modifications and sintering process adjustments, this proportion remains significant. During the negative pressure extraction of sulfur-laden flue gas and dust into the dust collection bin, the flue gas cannot be removed promptly, and due to inherent issues with the ferric phosphate material, a significant amount of sulfur accumulates in the dust collection, altering the physical properties of the ferric phosphate and preventing it from flowing into the product as a normal material.

[0004] At present, the mainstream processing technology of dust removal materials is as follows: (1) the dust removal materials after removing the flue gas are directly returned to the kiln for re-sintering. During the sintering process, the materials are mixed with normal materials and flow into the finished product. However, due to the high sulfur content, S is difficult to be completely removed, resulting in a higher S content in the product end than that of the material without dust addition. In addition, due to the secondary sintering of this part of the material, the moisture content, specific surface area, tap density, etc. of the product will change significantly, resulting in deviation of the finished product indicators. (2) Some manufacturers dissolve the dust removal materials with sulfuric acid and then precipitate them by raising the pH with alkaline solution to synthesize iron phosphate. Although this process makes it easier to maintain product consistency, it still has the disadvantages of cumbersome processing, long process and high cost. Efficiently recycling iron phosphate dust collection materials to prepare iron phosphate can effectively reduce resource waste, reduce costs and increase corporate benefits, which is in line with the strategic planning of sustainable development.

[0005] Summary of the Invention

[0006] The purpose of this article is to overcome the shortcomings of the existing technology and provide a method for recovering iron phosphate dust to prepare iron phosphate and its application. The anhydrous iron phosphate prepared in this article has high tap density, small particle size, large specific surface area, low impurity content, and an ideal molar ratio of Fe and P. Its application in the preparation of battery materials can effectively improve the electrochemical performance of the battery and has broad application prospects.

[0007] To achieve the above objectives, the technical solutions adopted in this paper are:

[0008] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0009] The ferric phosphate dust collection material is sieved, water is added to prepare a slurry, and filtered to obtain an anhydrous ferric phosphate filter cake;

[0010] The anhydrous ferric phosphate filter cake is mixed with a phosphoric acid solution to form a slurry, heated, recrystallized, and solid-liquid separated to obtain a dihydrate ferric phosphate filter cake;

[0011] The ferric phosphate dihydrate filter cake is dried and calcined to obtain anhydrous ferric phosphate.

[0012] This article creatively screens the iron phosphate dust collection material to remove large particles of foreign matter in the slag material. Then, water is added to make a pulp and filtered to remove sulfur impurities and some other metal impurities. Then, a phosphoric acid solution is added to control the reaction process 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 iron phosphate, thereby achieving one-step efficient and low-cost separation of impurities. Finally, the product, anhydrous iron phosphate, is obtained by drying and roasting.

[0013] In one embodiment, the S content in the ferric phosphate dust collecting material is 1-6%, and the molar ratio of Fe to P is 0.96-1.00.

[0014] In one embodiment, the solid-liquid ratio during the water-addition slurrying is 1 g: (2-4) mL. Within this range, the impurity removal effect is better.

[0015] In one embodiment, the concentration of the phosphoric acid solution is 0.01-1 mol / L.

[0016] In one embodiment, the concentration of the phosphoric acid solution is 0.05 to 0.35 mol / L. The inventors of this article have found in a large number of studies 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 BET is too large, the particle size is too small, the filtration is difficult, the filter screen is easily clogged during screening, the water content is high, and the product batch stability is poor. Therefore, it is not suitable to use it and may even cause the particles to break, resulting in a reduction in particle size. Therefore, in this article, the concentration of the phosphoric acid solution needs to be strictly controlled.

[0017] At the same time, if other acids are used, the purpose of phosphorus replenishment cannot be achieved. For example, if hydrochloric acid solution is used, the purpose of phosphorus replenishment cannot be achieved, and chloride ions will be introduced. If sulfuric acid solution is used, the purpose of phosphorus replenishment cannot be achieved. Recrystallization in sulfuric acid solution will cause more sulfate to be unable to be removed due to the high concentration of sulfate solution.

[0018] 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

[0019] The solid content of the slurry is 5-30 wt%.

[0020] The molar ratio of Fe, P, and S is 1.0:(1.0-1.5):(0.01-0.1). When the molar ratio of Fe, P, and S is within this range, the presence of excess P is beneficial to the recrystallization of iron phosphate.

[0021] In one embodiment, the recrystallization temperature is 60-95° C., and the recrystallization time is 0.5-6 h.

[0022] In one embodiment, the recrystallization temperature is 80-90° C., and the recrystallization time is 2-4 hours.

[0023] In one embodiment, the heating rate is 6-15° C. / h.

[0024] In one embodiment, the calcination is specifically as follows: first calcining at 200-500° C. for (0-90) min, then calcining at 200-700° C. for (0-90) min, and finally calcining at 500-700° C. for (30-120) min.

[0025] This paper adopts a three-step calcination method. When calcining at 200-500℃, the crystallization water is removed first and then the S is removed. The crystallization water removal process will produce a porous structure, which is more conducive to the subsequent sintering and S removal. The porous structure can improve the BET of the product. The one-step sintering, dehydration and S removal processes occur simultaneously, and the S content removal effect is slightly worse, which also leads to poor performance.

[0026] In one embodiment, the calcination is specifically as follows: first calcining at 200-300°C for (10-90) min, then calcining at 400-550°C for (10-90) min, and finally calcining at 600-700°C for (30-120) min.

[0027] This article also provides an anhydrous ferric phosphate prepared by the above-mentioned preparation method, wherein the D50 of the anhydrous ferric phosphate is 5 to 12 μm and the tap density is 0.70 to 1.00 g / cm 3 , with a specific surface area of ​​5 to 8 m2 / g, impurity content ≤500ppm.

[0028] The anhydrous iron phosphate prepared in this article has high tap density, small particle size, large specific surface area, low impurity content, and an ideal molar ratio of Fe and P. Its application in the preparation of battery materials can effectively improve the electrochemical performance of the battery and has broad application prospects.

[0029] In one embodiment, the D50 of the anhydrous ferric phosphate is 9-12 μm and the tap density is 0.85-1.00 g / cm 3 , with a specific surface area of ​​6.5 to 8 m 2 / g, impurity content ≤300ppm.

[0030] In one embodiment, the molar ratio of Fe to P in the anhydrous ferric phosphate is 0.9 to 1.0.

[0031] In one embodiment, the molar ratio of Fe to P in the anhydrous ferric phosphate is 0.94 to 0.98.

[0032] This article also provides an application of anhydrous iron phosphate in the preparation of battery materials.

[0033] The beneficial effects of this paper are as follows: (1) In this paper, the iron phosphate dust material is screened, and the screening can remove large particles of foreign matter in the slag material, and then water is added to make pulp, and filtration can remove S impurities and some other metal impurities, and then phosphoric acid solution is added to control the reaction process in the phosphoric acid solution. Dissolution and crystallization occur simultaneously. By controlling the rates of the two, the dust material generated in the production process is recrystallized to obtain high-purity iron phosphate, thereby realizing one-step efficient and low-cost separation of impurities. Finally, it is dried and roasted to obtain the product anhydrous iron phosphate; (2) The anhydrous iron phosphate prepared in this paper has high tap density, small particle size, large specific surface area, low impurity content, and an ideal molar ratio of Fe and P. Compared with the existing iron phosphate, it has higher purity and extremely low impurity content, which is far better than the requirements of commercially available battery-grade iron phosphate. Its application in the preparation of battery materials can effectively improve the electrochemical performance of the battery and has broad application prospects. (3) The recrystallization process used in this paper does not require the addition of alkaline solution to increase the pH to precipitate iron phosphate. During the high-temperature phosphating washing process, the phosphoric acid solution has a certain driving force to recrystallize into dihydrate iron phosphate, and no impurities are introduced during the recrystallization process. Therefore, it is of great significance for the recovery and treatment of iron phosphate dust collection materials with high impurity content. (4) In this paper, the phosphate groups in the phosphoric acid solution occupy the sulfate sites in the dust collection materials, which can broaden the adjustment range of the iron-phosphorus ratio, allowing for greater adjustment space in the preparation process of lithium iron phosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a SEM image of the ferric phosphate dihydrate powder prepared in Example 1.

[0035] FIG2 is an XRD pattern of the ferric phosphate dihydrate powder prepared in Example 1.

[0036] FIG3 is a SEM image of the ferric phosphate dihydrate powder prepared in Comparative Example 1.

[0037] FIG4 is an XRD pattern of the ferric phosphate dihydrate powder prepared in Comparative Example 1.

[0038] FIG5 is a SEM image of the ferric phosphate dihydrate powder prepared in Comparative Example 2. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the embodiments herein more clear, the technical solutions in the embodiments herein are described clearly and completely below. Obviously, the described embodiments are only a portion of the embodiments herein, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments herein without inventive effort are also within the scope of protection herein.

[0040] Unless otherwise specified, the experimental reagents and instruments involved in the implementation of this article are commonly used reagents and instruments.

[0041] Among them, in the embodiments and comparative examples, the element content of the iron phosphate dust collecting material used was tested by ICP-AES equipment. The Fe content in the iron phosphate dust collecting material was 32.55%, the P content was 18.59%, the molar ratio of Fe and P was 0.971, the S content was 41700 ppm, the Ni content was 65 ppm, the Co content was 25 ppm, the Mn content was 2 ppm, and the Zn content was 5 ppm.

[0042] In this article, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0043] As used herein, when referring to numerical ranges, unless otherwise specified, the numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between such minimum and maximum values. Furthermore, when a range refers to an integer, every integer between the minimum and maximum values ​​of the range is included. In addition, 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 subsumed therein.

[0044] Example 1

[0045] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0046] (1) Liquid preparation: Prepare 0.20 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0047] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0048] The sulfur content in the slurry after pulping was 10.14 g / L, and the sulfur content in the filter cake after drying was 10420 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0049] (3) Preparation: The filter cake treated in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.32:0.06;

[0050] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0051] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0052] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first 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.

[0053] The SEM and XRD patterns of the ferric phosphate dihydrate powder prepared in this example are shown in Figures 1 and 2, respectively. Figure 1 shows that the prepared ferric phosphate dihydrate exhibits a micro-nano composite structure, with relatively fine primary particles accumulated into secondary particles, and good particle size distribution and dispersibility. Figure 2 shows that the ferric phosphate dihydrate prepared in Example 1 has high phase purity, good crystallinity, and no other impurities are found.

[0054] Example 2

[0055] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0056] (1) Solution preparation: Prepare 0.10 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0057] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0058] The sulfur content in the slurry after pulping was 10.56 g / L, and the sulfur content in the filter cake after drying was 9170 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0059] (3) Ingredients: The filter cake after treatment in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.18:0.06;

[0060] (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 a speed of 350 rpm for recrystallization for 4 h to obtain a white slurry;

[0061] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0062] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first 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.

[0063] Example 3

[0064] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0065] (1) Solution preparation: Prepare 0.05 mol / L dilute phosphoric acid and heat the solution to 35°C to obtain 5000 L of target phosphoric acid solution;

[0066] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 3 g: 10 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0067] The sulfur content in the slurry after pulping was 7.316 g / L, and the sulfur content in the filter cake after drying was 9251 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0068] (3) Ingredients: The filter cake after treatment in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry, in which the molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.10:0.05;

[0069] (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 a speed of 350 rpm for recrystallization for 4 h to obtain a white slurry;

[0070] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0071] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first 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.

[0072] Example 4

[0073] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0074] (1) Solution preparation: Prepare 0.10 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0075] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0076] The sulfur content in the slurry after pulping was 9.73 g / L, and the sulfur content in the filter cake after drying was 10051 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0077] (3) Preparation: The filter cake after treatment in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 25 min to obtain a yellow slurry, in which the molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.06:0.06;

[0078] (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 a speed of 350 rpm for recrystallization for 4 h to obtain a white slurry;

[0079] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0080] (6) After flash drying, filter cake B was dried to obtain dihydrated ferric phosphate powder, which was then placed in a rotary kiln for calcination, first at 300°C for 30 minutes, then at 550°C for 60 minutes, and finally at 700°C for 120 minutes to obtain anhydrous ferric phosphate.

[0081] Example 5

[0082] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0083] (1) Liquid preparation: Prepare 0.13 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0084] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0085] The sulfur content in the slurry after pulping was 10.42 g / L, and the sulfur content in the filter cake after drying was 9208 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0086] (3) Ingredients: The filter cake after treatment in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 20 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.21:0.05;

[0087] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 3 h to obtain a white slurry;

[0088] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0089] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first at 300°C for 90 min, then at 550°C for 60 min, and finally at 700°C for 60 min to obtain anhydrous ferric phosphate.

[0090] Example 6

[0091] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0092] (1) Solution preparation: Prepare 0.01 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0093] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0094] The sulfur content in the slurry after pulping was 9.93 g / L, and the sulfur content in the filter cake after drying was 10609 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0095] (3) Preparation: The filter cake after treatment in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry, in which the molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.05:0.06;

[0096] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0097] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0098] (6) After flash drying, filter cake B was subjected to dihydrate ferric phosphate powder, which was then placed in a rotary kiln for calcination, first 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.

[0099] Example 7

[0100] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0101] (1) Solution preparation: Prepare 1 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0102] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0103] The sulfur content in the slurry after pulping was 10.10 g / L, and the sulfur content in the filter cake after drying was 10129 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0104] (3) Preparation: The filter cake treated in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:2.50:0.06;

[0105] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0106] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0107] (6) After flash drying, filter cake B was dried to obtain dihydrated ferric phosphate powder, which was then placed in a rotary kiln for calcination, first 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.

[0108] Example 8

[0109] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0110] (1) Liquid preparation: Prepare 0.20 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0111] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0112] The sulfur content in the slurry after pulping was 10.49 g / L, and the sulfur content in the filter cake after drying was 9379 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0113] (3) Preparation: The filter cake treated in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.32:0.06;

[0114] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0115] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0116] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first at 200°C for 60 min, then at 500°C for 60 min, and finally at 700°C for 90 min to obtain anhydrous ferric phosphate.

[0117] Comparative Example 1

[0118] The difference between Comparative Example 1 and Example 1 is that no phosphoric acid solution is added in Comparative Example 1, and all other conditions are the same.

[0119] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0120] (1) Liquid preparation: 5000L pure water solution is heated to 40℃;

[0121] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0122] The sulfur content in the slurry after pulping was 10.39 g / L, and the sulfur content in the filter cake after drying was 10810 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0123] (3) Ingredients: The filter cake after treatment in step (2) was discharged and added into 5000 L of pure water solution, and stirred for 15 min to obtain a yellow slurry, in which the molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.03:0.06;

[0124] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0125] (5) solid-liquid separation of the slurry A obtained in step (4) to obtain an iron phosphate filter cake and a filtered mother liquor;

[0126] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first 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.

[0127] The SEM and XRD of the iron phosphate obtained in step (5) of this comparative example are shown in Figures 3 and 4. As can be seen from Figure 4, the anhydrous material is still the main component in the XRD of the dust removal material, and there is no recrystallization to transform into a dihydrate material. At the same time, it can be seen from the morphology of Figure 3 that the treated dust removal material has not completed the crystallization, and the morphology is still the morphology of the original dust removal material, which proves that pure water cannot complete the crystallization and impurity removal of the dust removal material.

[0128] Comparative Example 2

[0129] The difference between Comparative Example 2 and Example 1 is that the concentration of the phosphoric acid solution in Comparative Example 2 is different, and all other aspects are the same.

[0130] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0131] (1) Liquid preparation: Prepare 1.5 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0132] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0133] The sulfur content in the slurry after pulping was 10.63 g / L, and the sulfur content in the filter cake after drying was 8921 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0134] (3) Ingredients: The filter cake after treatment in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:3.18:0.11;

[0135] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0136] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0137] (6) After flash drying, filter cake B was dried to obtain ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first 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.

[0138] The SEM image of the anhydrous ferric phosphate obtained in this comparative example is shown in FIG5 . It can be seen that due to the excessive amount of P, the product BET is too large, the particle size is too small, the filtration is difficult, the filter screen is easily clogged during screening, the moisture content is high, and the product batch stability is poor. Therefore, it is not suitable for use. FIG5 also shows that the particles are broken, resulting in a reduction in particle size.

[0139] Comparative Example 3

[0140] The difference between Comparative Example 3 and Example 1 is that Comparative Example 3 adopts one-step calcination, and the other aspects are the same.

[0141] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0142] (1) Liquid preparation: Prepare 0.20 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0143] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and then slurried at a ratio of material: pure water = 1 g: 2 mL, and filtered to obtain anhydrous ferric phosphate filter cake;

[0144] The sulfur content in the slurry after pulping was 10.14 g / L, and the sulfur content in the filter cake after drying was 10420 ppm, which indicates that the sulfur in the dust collection material cannot be completely washed away and needs to be processed in subsequent steps;

[0145] (3) Preparation: The filter cake treated in step (2) was discharged and added into 5000 L of dilute phosphoric acid solution, and stirred for 15 min to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.32:0.06;

[0146] (4) Recrystallization: The yellow slurry from step (3) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0147] (5) solid-liquid separation of the white slurry A obtained in step (4) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0148] (6) After flash drying, filter cake B was obtained as ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination at 650°C for 180 min to obtain anhydrous ferric phosphate.

[0149] Comparative Example 4

[0150] The difference between Comparative Example 4 and Example 1 is that no water is added to prepare the pulp in Comparative Example 4, and all other aspects are the same.

[0151] A method for recovering ferric phosphate dust to prepare ferric phosphate comprises the following steps:

[0152] (1) Liquid preparation: Prepare 0.20 mol / L dilute phosphoric acid and heat the solution to 40°C to obtain 5000 L of target phosphoric acid solution;

[0153] (2) 600 kg of dust collection material was sieved through a 100-mesh sieve to remove large particles of foreign matter in the slag material, and 5000 L of dilute phosphoric acid solution was added and stirred for 15 minutes to obtain a yellow slurry. The molar ratio of Fe, P, and S in the yellow slurry was 1.00:1.32:0.22;

[0154] (3) Recrystallization: The yellow slurry from step (2) was heated to 85°C at a heating rate of 9°C, and the slurry was stirred at a speed of 350 rpm for recrystallization for 2 h to obtain a white slurry;

[0155] (4) solid-liquid separation of the white slurry A obtained in step (3) to obtain a ferric phosphate dihydrate filter cake and a filtered mother liquor;

[0156] (5) After flash drying, filter cake B was obtained as ferric phosphate dihydrate powder, which was then placed in a rotary kiln for calcination, first 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.

[0157] Test Case

[0158] 1. Table 1 shows the parameters of raw materials, pulping, batching, mother liquor after recrystallization, etc. during the experiments of Examples 1 to 8 and Comparative Examples 1 to 4. The specific data were obtained by ICP-AES analyzer testing.

[0159] Table 1

[0160] As shown in Table 1, the pulping and filtration in step (2) cannot clean the dust collection material. The Fe content in the mother liquor after recrystallization is about 1 g / L or less, and the P content does not meet the designed amount. It can be seen that part of the 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 from the iron phosphate.

[0161] 2. Table 2 shows the indicators of the anhydrous products synthesized in Examples 1 to 8 and Comparative Examples 1 to 4, the impurity element contents of the recrystallized ferric phosphate products and commercially available products. The specific data were obtained by ICP-AES testing.

[0162] Table 2

[0163] As can be seen from Table 2, the impurity content of the iron phosphate product prepared in the embodiment is significantly lower than that in comparative example 1. The particle size BET, D50 and TD of the iron phosphate after recrystallization in Examples 1-4 are not much different from those before improvement, and the Fe / P deviates greatly from the center value, which is smaller than the Fe / P before recrystallization. Therefore, the Fe / P in the product can be adjusted by recrystallization, which broadens the Fe / P adjustment range in the product. Compared with the examples, it can be seen that the Fe / P of the product can be effectively regulated during the recrystallization process of this process, which is conducive to obtaining the optimal Fe / P. In some processes, due to process limitations, the product with high Fe / P and cannot be improved (Fe / P of some processes reaches 1 or more) can be improved to 0.940-0.980 by this process. Although the iron phosphate prepared in comparative example 2 has a low impurity content, the product BET is large, the particle size is small, the filtration is difficult, the filter screen is easily blocked during screening, the water content is high, and the product batch stability is poor (particle breakage). The iron phosphate prepared in comparative example 3 has too low Fe / P, and the iron phosphate prepared in comparative example 4 has too high an impurity content.

Claims

1. A method for preparing ferric phosphate by recycling ferric phosphate dust collection material, characterized in that: The following steps are involved: The iron phosphate dust collecting material is sieved, water is added to make pulp, and filtered to obtain anhydrous iron phosphate filter cake; The anhydrous ferric phosphate filter cake is mixed with a phosphoric acid solution to form a slurry, heated, recrystallized, and solid-liquid separated to obtain a dihydrate ferric phosphate filter cake; The ferric phosphate dihydrate filter cake is dried and calcined to obtain anhydrous ferric phosphate.

2. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 1, characterized in that: The S content in the ferric phosphate dust collecting material is 1-6%, and the molar ratio of Fe to P is 0.96-1.

00.

3. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 1, characterized in that: The solid-liquid ratio during the water-adding slurrying is 1 g: (2-4) mL.

4. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 1, characterized in that: The concentration of the phosphoric acid solution is 0.01-1 mol / L.

5. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 4, characterized in that: The concentration of the phosphoric acid solution is 0.05-0.35 mol / L.

6. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material 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 5-30wt%.

7. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 1, characterized in that: The recrystallization temperature is 60-95° C., and the recrystallization time is 0.5-6 h.

8. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 7, characterized in that: The recrystallization temperature is 80-90° C., and the recrystallization time is 2-4 hours.

9. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 7, characterized in that: The heating rate is 6-15°C / h.

10. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 1, characterized in that: The calcination is specifically as follows: first calcining at 200-500°C for (0-90) min, then calcining at 200-700°C for (0-90) min, and finally calcining at 500-700°C for (30-120) min.

11. The method for preparing ferric phosphate by recycling ferric phosphate dust collection material according to claim 1, characterized in that: The calcination is specifically as follows: first calcining at 200-300°C for (10-90) min, then calcining at 400-550°C for (10-90) min, and finally calcining at 600-700°C for (30-120) min.

12. Anhydrous ferric phosphate, characterized in that: Prepared by the preparation method according to any one of claims 1 to 11, the D50 of the anhydrous ferric phosphate is 5 to 12 μm, and the tap density is 0.70 to 1.00 g / cm 3 , with a specific surface area of ​​5 to 8 m 2 / g, impurity content ≤500ppm.

13. The anhydrous ferric phosphate according to claim 12, characterized in that: The D50 of the anhydrous ferric phosphate is 9-12 μm, and the tap density is 0.85-1.00 g / cm 3 , with a specific surface area of ​​6.5 to 8 m 2 / g, impurity content ≤300ppm.

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

0.

15. Use of the anhydrous ferric phosphate according to any one of claims 12 to 14 in the preparation of battery materials.

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