A method for preparing a particle size controllable iron phosphate by using mother liquor to recover iron phosphate dust

Abstract

The application provides a method for preparing controllable-size iron phosphate by recycling mother liquor and iron phosphate dust collection material, and comprises the following steps: S1: washing and drying the iron phosphate dust collection material, and then performing first roasting, mixing the obtained roasting material with iron phosphate synthesis mother liquor to prepare pulp, and performing solid-liquid separation to obtain anti-dissolution metal solution; S2: mixing the anti-dissolution metal solution with iron phosphate slag acid-dissolution metal solution, adjusting the molar ratio of Fe / P in the obtained mixed solution to (0.75-0.95):1, and adjusting the molar ratio of S / Fe to (1-1.3):1 to obtain mixed iron phosphate solution; S3: heating the mixed iron phosphate solution, adding seed additives in the heating process, and performing heat preservation after the heating is completed to obtain iron phosphate slurry, and performing solid-liquid separation on the iron phosphate slurry, and performing second roasting on the obtained solid phase to obtain anhydrous iron phosphate. The application realizes stable and controllable particle size of the anhydrous iron phosphate by regulation means, and recycles waste materials generated in the iron phosphate production process, and realizes the resource utilization of the waste materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of iron phosphate synthesis, and particularly relates to a method for preparing iron phosphate with controllable particle size by recycling mother liquor from iron phosphate dust collection material. BACKGROUND

[0002] Currently, in the new energy power lithium battery industry, developing a battery with low cost, long service life and safe and fast charging has become two key technologies. The lithium iron phosphate battery has great application potential and market prospect in the energy storage and power application fields due to its advantages in safety, environmental protection and first-level technology applicability. However, the cost of the lithium iron phosphate battery is relatively high, and the cost of the battery is mainly derived from the high cost of the positive electrode material. In order to reduce the cost of the battery material, the synthesis of the iron phosphate precursor of the positive electrode material is optimized and improved.

[0003] The current existing synthesis method of iron phosphate is sodium method: ferrous sulfate, sodium hydroxide, phosphoric acid and hydrogen peroxide. In the production process, sodium sulfate with high concentration is produced, the by-product has low value, and the treatment cost will restrict the production of iron phosphate. Therefore, how to prepare iron phosphate with low cost and excellent performance is crucial for lithium iron phosphate. As the precursor of the lithium iron phosphate battery, the performance index of the iron phosphate has a great influence on the performance of the lithium iron phosphate battery, and the particle size of the iron phosphate also has a certain influence on the grinding processing efficiency of the lithium iron phosphate.

[0004] In the recycling process of the mother liquor for synthesizing iron phosphate by the ammonium method / sodium method, calcium hydrogen phosphate is added to mix slurry, sulfuric acid is added to the slurry, and then the slurry is filtered for multiple times, calcium hydrogen phosphate is added, ammonia water or sodium hydroxide is added to adjust the pH value, and the slurry is filtered to obtain calcium sulfate gypsum. However, this method needs to introduce additional calcium element, and a new process needs to be added for wastewater treatment, which increases the treatment cost. In the whole production system, the P element cannot be fully recycled and utilized, and the cost of wastewater treatment is also high.

[0005] In the normal production process of iron phosphate, the main component of the bag dust collecting material of the rotary kiln is anhydrous iron phosphate carrying a large amount of flue gas and part of the un-successful diphosphate iron phosphate; the diphosphate and anhydrous iron phosphate cannot be utilized due to high S element content, unqualified BET and small particle size, or agglomeration. The main treatment method for the bag dust collecting material of the rotary kiln at present is: (1) the bag dust collecting material of the rotary kiln is collected through a bin and then returned to the front end for acid dissolution reaction with sulfuric acid, the anhydrous iron phosphate in the bag dust collecting material is dissolved to obtain an iron phosphate solution, and then the diphosphate iron phosphate is obtained through a synthesis method. This method can obtain a product with stable specific surface and particle size. However, the S content in the metal liquid is high due to the large amount of flue gas attached to the surface of the bag dust collecting material, the S content in the synthesized diphosphate iron phosphate is high, and the S cannot be completely removed in the calcination process. In this method, the main component of the bag dust collecting material of the rotary kiln is anhydrous iron phosphate carrying a large amount of flue gas and part of the un-successful diphosphate iron phosphate. In the whole sulfuric acid dissolution process, the diphosphate iron phosphate cannot be completely dissolved, and the remaining diphosphate iron phosphate material cannot be recovered. The complete separation cannot be achieved, and the pressure filtration efficiency is reduced in the dissolution pressure filtration process, which affects the production rhythm. (2) The bag dust collecting material of the rotary kiln is screened and then slurried by adding water to obtain anhydrous iron phosphate filter cake. The anhydrous iron phosphate filter cake and a phosphoric acid solution are mixed, heated, recrystallized, and diphosphate iron phosphate is obtained. Then, the diphosphate iron phosphate is separated from the liquid to obtain diphosphate iron phosphate filter cake. Then, the diphosphate iron phosphate filter cake is dried and calcined to obtain anhydrous iron phosphate. However, a large amount of high-concentration phosphoric acid needs to be added in the process of dissolving the bag dust collecting material to dissolve the diphosphate iron phosphate, and the auxiliary material consumption is large. In this process, the acidity of the mother liquor is greatly reduced after the dissolution is completed, and the mother liquor cannot be recovered. There is a large amount of phosphoric acid in the mother liquor, which causes serious waste of phosphorus resources, and the complete recovery of waste materials and waste water cannot be achieved. SUMMARY

[0006] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a method for preparing particle size controllable iron phosphate by recycling mother liquor from iron phosphate dust collecting material, wherein the mother liquor is completely recycled for dissolving and calcining the dust collecting material, and the particle size of the anhydrous iron phosphate is stably controllable through regulation means.

[0007] According to a first aspect of the present application, a method for preparing particle size controllable iron phosphate by recycling mother liquor from iron phosphate dust collecting material is proposed, comprising the following steps:

[0008] S1: washing and drying the iron phosphate dust collecting material, then calcining once, mixing the obtained calcined material with the iron phosphate synthesis mother liquor to prepare slurry, and then separating the solid and liquid to obtain an anti-dissolution metal solution;

[0009] S2: mixing the reverse-solubilized metal solution with the phosphorus-iron slag acid-solubilized metal solution, adjusting the Fe / P molar ratio in the obtained mixed phosphorus-iron solution to (0.75-0.95):1 and the S / Fe molar ratio to (1-1.3):1, to obtain a mixed phosphorus-iron solution;

[0010] S3: heating the mixed phosphorus-iron solution, adding a seed additive during the heating process, and performing heat preservation after the heating process is completed, to obtain an iron phosphate slurry, and performing solid-liquid separation on the iron phosphate slurry, and performing secondary calcination on the obtained solid phase, to obtain anhydrous iron phosphate.

[0011] It should be noted that the "Fe / P molar ratio" and "S / Fe molar ratio" in the present application refer to the molar ratio of corresponding elements, rather than the molar ratio between single substances.

[0012] In some embodiments, in step S1, the iron phosphate dust collection material includes anhydrous iron phosphate and dihydrate iron phosphate, and the sulfur content of the iron phosphate dust collection material is 10,000-20,000 ppm.

[0013] In some preferred embodiments, the iron phosphate dust collection material is a rotary kiln bag dust collection material in a sintering process of iron phosphate. The dust collection material is collected after back blowing of a bag-type dust collector, and mainly includes two components, one being anhydrous iron phosphate, accounting for about 70%, and the other being dihydrate iron phosphate which is not completely transformed during calcination, accounting for about 30%.

[0014] In some embodiments, in step S1, the washing process includes: preparing a slurry by adding water to the iron phosphate dust collection material, controlling the solid content of the slurry to be 25%-35%, and then performing pressure filtration washing to obtain a dust collection filter cake. The impurities with high S content attached to the surface of the iron phosphate dust collection material can be removed through washing.

[0015] In some embodiments, in step S1, the temperature of the primary calcination is 500-600℃, and the time is 1-2 h. The dry dust collection filter cake is calcined to obtain anhydrous iron phosphate with uniform particle size and complete crystal transformation. The BET of the anhydrous iron phosphate is abnormal, and it cannot be directly used. The anhydrous iron phosphate can be dissolved and reused by using a phosphorus-iron synthesis mother liquor with strong acidity.

[0016] In some embodiments, in step S1, the pH of the phosphorus-iron synthesis mother liquor is less than 1; and / or, the solid content of the slurry is controlled to be 10%-25% during the mixing and slurry preparation process.

[0017] In some embodiments, in step S1, the S content of the phosphorus-iron synthesis mother liquor is greater than 40 g / L.

[0018] In some preferred embodiments, step S1 further comprises heating the mixed pulp slurry to a temperature of 40-60°C, and stirring the mixed pulp slurry at a speed of 200-400 r / min for 8-10 h.

[0019] In some embodiments, in step S2, the reverse-solubilized metal solution is mixed with the phosphorus-iron slag acid-solubilized metal solution at a volume ratio of 1:4 to 1:2; the phosphorus-iron slag acid-solubilized metal solution has a Fe / P molar ratio of (0.75-0.95):1 and a S / Fe molar ratio of (1-1.3):1. The phosphorus-iron slag acid-solubilized metal solution can be a metal solution obtained by acid-solubilizing and impurity-removing the lithium extraction residue of lithium iron phosphate.

[0020] In some embodiments, the phosphorus-iron slag acid-solubilized metal solution has a Fe content of 65-75 g / L and a P content of 45-55 g / L.

[0021] In some embodiments, in step S2, the Fe / P molar ratio of the obtained mixed solution is adjusted to (0.75-0.95):1 and the S / Fe molar ratio is adjusted to (1-1.3):1, which comprises: adjusting the Fe / P molar ratio of the system to (0.75-0.95):1 using phosphoric acid with a mass fraction of 70%-85%, and adjusting the S / Fe molar ratio of the system to (1-1.3):1 using concentrated sulfuric acid with a mass fraction of about 98%. In the mixed phosphorus-iron solution, the phosphate can be slightly excessive to increase the precipitation rate of iron, and the excess phosphoric acid in the mother liquor can be recycled by mother liquor recovery in the subsequent process. The Fe / P molar ratio can be any one of 0.75, 0.8, 0.85, 0.9, 0.95 or any value between any two of them. The S / Fe molar ratio can be adjusted to control the particle size of the iron phosphate, and the particle size of the iron phosphate generated in the subsequent step gradually decreases with the increase of the S / Fe molar ratio. The S / Fe molar ratio can be any one of 1.02, 1.08, 1.13, 1.18, 1.23 or any value between any two of them.

[0022] In some embodiments, in step S2, the Fe concentration in the mixed phosphorus-iron solution is 60-75 g / L. The Fe concentration in the mixed phosphorus-iron solution can be any one of 65 g / L, 70 g / L, 72 g / L, 75 g / L or any value between any two of them.

[0023] In some embodiments, in step S3, the process of temperature rising comprises: rising the temperature to 85-95℃ at a rate of 10-30℃ / h, and then keeping the temperature for 10-20h. The rising rate can be any one of 10℃ / h, 15℃ / h, 20℃ / h, 30℃ / h or any value between any two of them; the temperature for synthesizing iron phosphate is 85-95℃, and can be any one of 85℃, 90℃, 95℃ or any value between any two of them; the keeping time can be any one of 10h, 15h, 20h or any value between any two of them. Controlling the rising rate in the range can control the particle size D50 of the product iron phosphate to be 3.5-6.5μm, otherwise the particle size may deviate.

[0024] In some embodiments, in step S3, the seed additive is added when the mixed phosphorus iron solution is heated to 50-60℃.

[0025] In some embodiments, in step S3, the seed additive is iron phosphate slurry with a solid content of 20%-40%; and / or, the particle size D50 of the seed additive is 1-1.5μm. The solid content of the seed additive can be any one of 25%, 30%, 35%, 40% or any value between any two of them.

[0026] In some embodiments, in step S3, the mass of the seed additive is 5%-20% of the mass of the mixed phosphorus iron solution.

[0027] In some embodiments, in step S3, the solid-liquid separation comprises primary pressure filtration washing and secondary pressure filtration washing.

[0028] In some embodiments, the solid phase of the primary pressure filtration washing is used to prepare the seed additive. The seed additive is prepared from the iron phosphate dihydrate generated in the process of temperature rising, and internal circulation of the seed can be realized.

[0029] In some embodiments, in step S3, the seed additive is obtained by: after primary pressure filtration washing of the iron phosphate slurry, obtaining iron phosphate filter cake, adding water to prepare secondary slurry, and then sand milling the secondary slurry to obtain the seed additive. The solid content of the secondary slurry is 20%-40%, and the rotation speed of the sand milling is 300-500r / min. Using the seed additive obtained by sand milling the slurry of iron phosphate dihydrate synthesized in the later stage to induce the synthesis of iron phosphate in this time can avoid the introduction of impurities and reduce the cost of auxiliary materials.

[0030] In some embodiments, in step S3, after the solid-liquid separation of the iron phosphate slurry, the obtained mother liquor is used to prepare slurry from the calcined material in step S1.

[0031] In some embodiments, in step S3, the solid-liquid separation process comprises multiple times of washing and filtering the iron phosphate slurry with washing water, and the volume ratio of the iron phosphate slurry to the washing water is (1:1) to (1:3) each time, until the pH of the washing water after washing is greater than or equal to 3.

[0032] In some embodiments, in step S3, before the secondary calcination, the solid phase obtained by the solid-liquid separation is further dried, and the drying temperature is 120 to 150 DEG C. The specific drying temperature can be any one of 120 DEG C, 130 DEG C, 140 DEG C, 150 DEG C or any value between any two of them.

[0033] In some embodiments, in step S3, the secondary calcination temperature is 650 to 750 DEG C, and the time is 40 to 60 min. The secondary calcination temperature can be any one of 650 DEG C, 700 DEG C, 750 DEG C or any value between any two of them.

[0034] In some embodiments, step S3 further comprises screening and removing the magnetic of the anhydrous iron phosphate, and then packing the product.

[0035] According to a second aspect of the present application, an iron phosphate is provided, which is prepared by the method of the first aspect of the present application, and the particle size D50 of the iron phosphate is 3.5 to 6.5 microns.

[0036] According to a third aspect of the present application, the method of the first aspect of the present application is applied in the production of iron phosphate. The present application recovers the calcination dust in the synthesis process of iron phosphate, and completely recovers the mother liquor to prepare the iron phosphate with controllable particle size. The present application recycles the waste generated in the production process of iron phosphate, realizes the resourceization of waste, and reduces the treatment cost of solid waste.

[0037] According to an embodiment of the present application, at least the following beneficial effects are achieved:

[0038] 1. The present application controls the element ratio in the mixed phosphorus-iron solution, and adds a seed additive during the synthesis of iron phosphate, so that the particle size of the iron phosphate product is stable and controllable.

[0039] 2. The present application is a green and environmentally friendly synthesis method for synthesizing iron phosphate by seed induction without introducing other cations. The present application introduces phosphorus-iron slag acid-soluble metal solution as raw material, mixes with the anti-soluble metal solution obtained by dissolving the iron phosphate calcination dust in the iron phosphate synthesis mother liquor, and induces crystallization and synthesis of iron phosphate by seed additive, reduces the process flow, avoids the enrichment of impurities in the mother liquor caused by the introduction of other metal cations in the mother liquor, and solves the problems of the reuse of the mother liquor, the increase of wastewater treatment cost, and the environmental impact of the external treatment.

[0040] 3. Compared with the traditional process, the process adds mother liquor and waste disposal and recovery process, the reverse metal solution after the mother liquor is dissolved in the rotary kiln bag dust collecting material is mixed with the acid soluble metal solution of the phosphorus iron slag, and then the value is adjusted, and the iron phosphate is synthesized again, so that the excess sulfuric acid and phosphoric acid in the mother liquor and the Fe in the waste are recycled and utilized multiple times, and the recovery rate of P and Fe in the production process is improved by reusing the bag dust collecting material, the resources are fully utilized, and the unit production cost is greatly reduced. BRIEF DESCRIPTION OF DRAWINGS

[0041] The application will be further described below in combination with the drawings and examples, in which:

[0042] Figure 1 The SEM image of the anhydrous iron phosphate prepared in Example 1 of the application is enlarged 50,000 times;

[0043] Figure 2 The SEM image of the anhydrous iron phosphate prepared in Example 1 of the application is enlarged 10,000 times;

[0044] Figure 3 The SEM image of the anhydrous iron phosphate prepared in Example 1 of the application is enlarged 5,000 times;

[0045] Figure 4 The SEM image of the anhydrous iron phosphate prepared in Example 1 of the application is enlarged 2,500 times;

[0046] Figure 5 The production process flow chart of Example 1 of the application is shown in the figure;

[0047] Figure 6 The XRD image of the anhydrous iron phosphate prepared in Examples 1-5 of the application is shown in the figure. DETAILED DESCRIPTION

[0048] The concept and technical effects of the application will be described below in combination with examples, so as to fully understand the purpose, features and effects of the application.

[0049] In the following examples, the raw materials, reagents or devices used are commercially available or can be obtained by known methods unless otherwise specified. The bag dust collecting material includes anhydrous iron phosphate (about 67% by mass), dihydrate iron phosphate (about 30% by mass) which is not completely transformed into crystals during the calcination process, and 3% sulfur; the acid soluble metal solution of the phosphorus iron slag is the metal solution after the lithium extraction slag is subjected to acid dissolution and impurity removal, and the main impurities are Al and Cu, the content of Al is 0.2 g / L, and the content of Cu is 10 mg / L.

[0050] Example 1

[0051] The embodiment provides a method for preparing particle size controllable iron phosphate by recycling bag dusting materials of a rotary kiln with mother liquor, as shown in the figure, and specifically comprises the following steps: Figure 5

[0052] (1) The bag dusting materials are slurried with pure water to prepare slurry with a solid content of 32%, and the slurry is stirred in a tank for 4h; the slurred slurry is pumped into a filter press for pressure filtration washing, drying and calcination at 550 DEG C for 2h, to obtain anhydrous iron phosphate with a particle size D50 of 4.8um and a BET of 5.5m 2 / g.

[0053] (2) A volume ratio of 40% of the bottom liquid mother liquor (Fe content is 3g / L, S content is 50g / L, P content is 12g / L, Al content is 0.18g / L, Cu content is 10mg / L) with a pH value of 1 or less is injected into a dissolving tank, and the dusting materials treated by washing, drying and calcination at the front end are added, and after being dispersed completely and uniformly, the remaining volume ratio of 60% of the bottom liquid mother liquor is added for acid dissolution, the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50 DEG C, and the stirring is carried out at a speed of 400r / min for 6h, and after suction filtration, the reverse dissolution metal solution M1 is obtained; the phosphorus iron slag acid dissolution metal liquid N1 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.023) is mixed and stirred with the reverse dissolution metal solution M1 for 4h, the two metal solutions M1:N1 are mixed according to a volume ratio of 1:2, the final Fe concentration is 72g / L, and the P concentration is 49.8g / L, and then the mass fraction of 85% of phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.023 to obtain a mixed phosphorus iron solution Q1.

[0054] (3) The mixed phosphorus iron solution Q1 mixed at the front end is added into a reaction kettle to start heating, the heating rate is controlled to be 10 DEG C / h, the stirring rate of the reaction kettle is 350r / min, when the temperature is increased to 50 DEG C, the crystal seed additive is started to be added, the mass of the crystal seed additive is 10% of the mass of the mixed phosphorus iron solution Q1, the solid content of the crystal seed additive is 28%, and the particle size D50 is 1.0um. The crystal seed additive is added within 30min, and after the temperature is increased to 95 DEG C, the reaction kettle is started to be heat preserved, and the heat preservation time is 20h.

[0055] ​(4) the obtained white powder slurry is run into a diaphragm filter press for primary pressure filtration washing, the volume ratio of the slurry to washing water is 1:2, the mother liquor is collected separately and is used for dissolving the collected dust in step (2), the filter cake after being unloaded can be used for preparing the seed crystal additive in step (3), the filter cake not used for preparing the seed crystal additive is prepared into a slurry and is subjected to secondary pressure filtration washing, the volume ratio of the slurry to washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is conveyed by a belt to a paddle dryer for drying, the drying temperature is 130℃, the time is 1h, the moisture of the material after drying is controlled to be below 0.5%, and then the material is calcined, the calcination temperature of the rotary kiln is controlled to be 700℃, and the residence time of the material in the kiln is 60min, so that anhydrous iron phosphate after complete calcination is obtained. Finally, the anhydrous iron phosphate A1 is obtained by screening and removing magnetism and packaging.

[0056] The SEM image of the anhydrous iron phosphate prepared in the embodiment is shown in Figures 1-4 It can be seen that the synthesized anhydrous iron phosphate is relatively stable in particle size and morphology.

[0057] The seed crystal additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0μm. The method for preparing the seed crystal additive from the filter cake after primary pressure filtration washing includes the following steps: taking the filter cake after primary pressure filtration washing, mixing uniformly by adding water to prepare a slurry, and then sand grinding. The solid content of the slurry is controlled to be 28% during the preparation of the slurry, the rotation speed of sand grinding is controlled to be 500r / min, and the final particle size D50 is controlled to be 1.0μm during sand grinding, so that the seed crystal additive is obtained for standby.

[0058] Example 2

[0059] The embodiment provides a method for preparing particle size controllable iron phosphate by recycling the rotary kiln bag dust collection material, and specifically includes the following steps:

[0060] (1) the bag dust collection material is prepared into a slurry with a solid content of 32% by mixing with pure water, and is stirred in a tank for 4h; the slurry after preparation is pumped into a filter press for pressure filtration washing, drying and calcination at 550℃ for 2h, so that anhydrous iron phosphate with a particle size D50 of 4.8μm and a BET of 5.5m 2 / g is obtained.

[0061] (2) into the dissolving tank to hit the volume ratio of 40% of the bottom liquid mother liquor (Fe content of 3 g / L, S content of 50 g / L, P content of 12 g / L, Al content of 0.18 g / L, Cu content of 10 mg / L) with pH value below 1, put the dust collection material treated by washing, drying and calcination at the front end, add the remaining volume ratio of 60% of the bottom liquid mother liquor after being dispersed completely and uniformly, control the solid content of the slurry to be 25%, the acid dissolution temperature is 50℃, and the stirring rate is 400r / min for 6h, and then the reverse dissolution metal solution M2 is obtained after filtration; the phosphorus iron slag acid dissolution metal solution N2 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.089) is mixed with the reverse dissolution metal solution M2 for 4h, and the two metal solutions M2:N2 are mixed according to the volume ratio of 1:2, the final Fe concentration is 72g / L, and the P concentration is 49.8g / L, then the mass fraction of 85% of phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.089 to obtain the mixed phosphorus iron solution Q2.

[0062] (3) the mixed phosphorus iron solution Q2 mixed at the front end is added into the reaction kettle to start heating, the heating rate is controlled to be 10℃ / h, the stirring rate of the reaction kettle is 350r / min, when the temperature is raised to 50℃, the seed additive is started to be added, the mass of the seed additive is 10% of the mass of the mixed phosphorus iron solution Q2, the solid content of the seed additive is 28%, and the particle size D50 is 1.0μm. The seed additive is added within 30min, and after the temperature is raised to 95℃, the reaction kettle is started to be heat preserved for 20h.

[0063] (4) the white powder slurry obtained is transported to the diaphragm filter press for primary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:2, the mother liquor is collected separately and is used for dissolving the dust collection material in step (2), the filter cake after unloading can be used for preparing the seed additive in step (3), the filter cake not used for preparing the seed additive is prepared into slurry and then is subjected to secondary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transported to the paddle dryer for drying, the drying temperature is 130℃, the time is 1h, the water content of the material after drying is controlled to be below 0.5%, then the material is calcined, the rotary kiln calcination temperature is controlled to be 700℃, and the material stays in the kiln for 60min to obtain the anhydrous ferric phosphate after complete calcination. The final screening and magnetic separation are carried out to obtain the anhydrous ferric phosphate A2.

[0064] The seed additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0 μm; the method for preparing the seed additive from the filter cake after the first pressure filtration washing comprises: taking the filter cake after the first pressure filtration washing, mixing uniformly by adding water to prepare a slurry, and then sand milling; the solid content of the slurry is controlled to be 28% during the slurry preparation, the sand milling speed is controlled to be 500 r / min, and the final particle size D50 is controlled to be 1.0 μm during the sand milling, thereby obtaining the seed additive for standby use.

[0065] Example 3

[0066] The embodiment provides a method for preparing iron phosphate with controllable particle size by recycling rotary kiln bag dust collection materials, and specifically comprises the following steps:

[0067] (1) The bag dust collection materials are slurried with pure water to prepare a slurry with a solid content of 32%, and the slurry is stirred in a tank for 4 h; the prepared slurry is pumped into a pressure filter for pressure filtration washing, drying and calcination at 550 ℃ for 2 h, thereby obtaining anhydrous iron phosphate with a particle size D50 of 4.8 μm and a BET of 5.5 m 2 / g.

[0068] (2) The bottom liquid mother liquor (Fe content: 3 g / L, S content: 50 g / L, P content: 12 g / L, Al content: 0.18 g / L, Cu content: 10 mg / L) with a volume ratio of 40% and a pH value of less than 1 is injected into a dissolving tank, and the dust collection materials treated by washing, drying and calcination at the front end are added, and then the remaining bottom liquid mother liquor with a volume ratio of 60% is added for acid dissolution after being dispersed completely and uniformly; the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50 ℃, and the stirring speed is 400 r / min for 6 h; after suction filtration, the reverse dissolution metal solution M3 is obtained; the phosphorus iron slag acid dissolution metal liquid N3 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.13) is mixed with the reverse dissolution metal solution M3 for stirring for 4 h, the two metal solutions M3:N3 are mixed according to a volume ratio of 1:2, the final Fe concentration is 72 g / L, and the P concentration is 49.8 g / L, and then the mass fraction of 85% phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.13, thereby obtaining the mixed phosphorus iron solution Q3.

[0069] (3) The mixed phosphorus iron solution Q3 mixed at the front end is added into a reaction kettle to start heating, the heating rate is controlled to be 10 ℃ / h, the stirring speed of the reaction kettle is 350 r / min, the seed additive is added when the temperature is increased to 50 ℃, the mass of the seed additive is 10% of the mass of the mixed phosphorus iron solution Q3, the solid content of the seed additive is 28%, and the particle size D50 is 1.0 μm; the seed additive is added within 30 min, the temperature is increased to 95 ℃, and then the reaction kettle is kept warm, and the keeping warm time is 20 h.

[0070] (4) The obtained white-pink slurry is transported to a diaphragm filter press for a first-stage filter washing. The volume ratio of slurry to wash water is 1:2. The mother liquor is collected separately and reused in step (2) to dissolve the dust. After the filter cake is unloaded, it can be used to prepare the seed crystal additive in step (3). The filter cake not used to prepare the seed crystal additive is pulped and then subjected to a second-stage filter washing. The volume ratio of slurry to wash water is 1:3. After washing, the pH of the wash water is 3. The filter cake is conveyed to a paddle dryer by a belt for drying. The drying temperature is 130℃ and the time is 1h. The moisture content of the material after drying is controlled to be below 0.5%. Then the material is calcined. The rotary kiln calcination temperature is controlled at 700℃ and the material stays in the kiln for 60min to obtain anhydrous ferric phosphate after complete calcination. Finally, it is screened, demagnetized, and packaged to obtain anhydrous ferric phosphate A3.

[0071] The seed additive is a ferric phosphate slurry with a solid content of 28% and a particle size D50 of 1.0 μm. The method for preparing the seed additive using filter cake after one-time pressure filtration and washing includes: taking the filter cake after one-time pressure filtration and washing, mixing it evenly with water, and then sand milling it. During the slurry preparation process, the solid content of the slurry is controlled to be 28%, the sand milling speed is controlled to be 500 r / min, and the final particle size D50 is controlled to be 1.0 μm during the sand milling process to obtain the seed additive for later use.

[0072] Example 4

[0073] This embodiment provides a method for preparing ferric phosphate with controllable particle size by recovering mother liquor from rotary kiln bag filter dust, specifically including the following steps:

[0074] (1) The dust collector material from the bag filter was mixed with pure water to prepare a slurry with a solid content of 32%, which was stirred in a tank for 4 hours. The slurry was then pumped into a filter press for filtration, washing, drying, and calcination at 550℃ for 2 hours to obtain a particle size D50 of 4.8 μm and a BET of 5.5 μm. 2 / g of anhydrous ferric phosphate.

[0075] (2) into the dissolving tank, the volume ratio of the bottom liquid mother liquor (Fe content of 3 g / L, S content of 50 g / L, P content of 12 g / L, Al content of 0.18 g / L, Cu content of 10 mg / L) with pH value below 1 is 40%, the dust collection material treated by washing, drying and calcination at the front end is put in, after being dispersed completely and uniformly, the remaining volume ratio of the bottom liquid mother liquor is 60% to carry out acid dissolution, the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50℃, the stirring rate is 400 r / min, and the stirring time is 6 h, and then the reverse dissolution metal solution M4 is obtained after filtration; the phosphorus iron slag acid dissolution metal solution N4 (molar ratio n(Fe):n(P) = 0.8, n(S):n(Fe) = 1.18) is mixed with the reverse dissolution metal solution M4 and stirred for 4 h, the two kinds of metal solutions M4:N4 are mixed according to the volume ratio of 1:2, the final Fe concentration is 72 g / L, and the P concentration is 49.8 g / L, then the mass fraction of 85% phosphoric acid is used to adjust n(Fe):n(P) = 0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe) = 1.18 to obtain the mixed phosphorus iron solution Q4.

[0076] (3) the mixed phosphorus iron solution Q4 mixed at the front end is added into the reaction kettle to start heating, the heating rate is controlled to be 10℃ / h, the stirring rate of the reaction kettle is 350 r / min, when the temperature is increased to 50℃, the seed additive is started to be added, the mass of the seed additive is 10% of the mass of the mixed phosphorus iron solution Q4, the solid content of the seed additive is 28%, and the particle size D50 is 1.0 μm. The seed additive is added within 30 min, and after the temperature is increased to 95℃, the reaction kettle is started to be heat preserved, and the heat preservation time is 20 h.

[0077] (4) the white powder slurry obtained is transported to a diaphragm filter press to carry out primary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:2, the mother liquor is collected separately and is used for dissolving the dust collection material in step (2), the filter cake after unloading can be used to prepare the seed additive in step (3), the filter cake not used to prepare the seed additive is prepared into slurry and then is carried out secondary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transported to a paddle dryer through a belt to carry out drying, the drying temperature is 130℃, the time is 1 h, the water content of the material after drying is controlled to be below 0.5%, then the material is calcined, the rotary kiln calcination temperature is controlled to be 700℃, and the material stays in the kiln for 60 min to obtain the anhydrous iron phosphate after complete calcination. Finally, the anhydrous iron phosphate A4 is obtained through screening and magnetic removal and packaging.

[0078] The seed additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0 μm; the method for preparing the seed additive from the filter cake after the first pressure filtration washing comprises: taking the filter cake after the first pressure filtration washing, mixing uniformly by adding water to prepare a slurry, and then sand milling; the solid content of the slurry is controlled to be 28% during the slurry preparation, the sand milling speed is controlled to be 500 r / min, and the final particle size D50 is controlled to be 1.0 μm during the sand milling, thereby obtaining the seed additive for standby use.

[0079] Example 5

[0080] The present embodiment provides a method for preparing iron phosphate with controllable particle size by recycling mother liquor and rotary kiln bag dust collection material, which specifically comprises the following steps:

[0081] (1) The bag dust collection material is slurried with pure water to prepare a slurry with a solid content of 32%, and the slurry is stirred in a tank for 4 h; the prepared slurry is pumped into a pressure filter for pressure filtration washing, drying and calcination at 550 ℃ for 2 h, thereby obtaining anhydrous iron phosphate with a particle size D50 of 4.8 μm and a BET of 5.5 m 2 / g.

[0082] (2) The bottom liquid mother liquor (Fe content: 3 g / L, S content: 50 g / L, P content: 12 g / L, Al content: 0.18 g / L, Cu content: 10 mg / L) with a volume ratio of 40% and a pH value of less than 1 is injected into a dissolving tank, and the dust collection material treated by washing, drying and calcination at the front end is added, and then the remaining bottom liquid mother liquor with a volume ratio of 60% is added for acid dissolution after being dispersed completely and uniformly; the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50 ℃, and the stirring speed is 400 r / min for 6 h; after suction filtration, the reverse dissolution metal solution M5 is obtained; the phosphorus iron slag acid dissolution metal solution N5 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.23) is mixed with the reverse dissolution metal solution M5 for 4 h, the two metal solutions M5:N5 are mixed in a volume ratio of 1:2, the final Fe concentration is 72 g / L, and the P concentration is 49.8 g / L, and then the mass fraction of 85% phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.23 to obtain the mixed phosphorus iron solution Q5.

[0083] (3) The mixed phosphorus iron solution Q5 prepared at the front end is added into a reaction kettle to start heating, the heating rate is controlled to be 10 ℃ / h, the stirring speed of the reaction kettle is 350 r / min, the seed additive is added when the temperature is raised to 50 ℃, the mass of the seed additive is 10% of the mass of the mixed phosphorus iron solution Q5, the solid content of the seed additive is 28%, and the particle size D50 is 1.0 μm; the seed additive is added within 30 min, the temperature is raised to 95 ℃, and then the reaction kettle is kept warm for 20 h.

[0084] (4) The obtained white powder slurry is transported to a diaphragm filter press for primary pressure filtration washing, the volume ratio of the slurry to washing water is 1:2, the mother liquor is collected separately and is used for dissolving the collected dust in step (2), after the filter cake is unloaded, it can be used for preparing the seed additive in step (3), the filter cake which is not used for preparing the seed additive is slurried and then subjected to secondary pressure filtration washing, the volume ratio of the slurry to washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transported by a belt to a paddle-blade dryer for drying, the drying temperature is 130℃, the time is 1h, and the moisture of the material after drying is controlled to be below 0.5%, then the material is calcined, the calcination temperature of the rotary kiln is controlled to be 700℃, and the residence time of the material in the kiln is 60min, to obtain anhydrous iron phosphate after complete calcination. Finally, the anhydrous iron phosphate A5 is obtained by screening and removing magnetism and packaging.

[0085] The seed additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0μm; the method for preparing the seed additive from the filter cake after primary pressure filtration washing includes: taking the filter cake after primary pressure filtration washing, mixing uniformly by adding water to prepare a slurry, and then sand grinding, the solid content of the slurry is controlled to be 28% during the preparation of the slurry, the sand grinding speed is controlled to be 500r / min, and the final particle size D50 is controlled to be 1.0μm during the sand grinding process, to obtain the seed additive for standby.

[0086] Example 6

[0087] The embodiment provides a method for preparing controllable particle size iron phosphate by recycling the mother liquor of the rotary kiln bag dust collection material, and specifically includes the following steps:

[0088] (1) The bag dust collection material is slurried with pure water to prepare a slurry with a solid content of 32%, and is stirred in a tank for 4h; the prepared slurry is pumped into a filter press for pressure filtration washing, drying and calcination at 550℃ for 2h, to obtain anhydrous iron phosphate with a particle size D50 of 4.8μm and a BET of 5.5m 2 / g.

[0089] (2) into the dissolving tank to hit the volume ratio of 40% of the bottom liquid mother liquor (Fe content of about 3g / L, S content of 50g / L, P content of 12g / L, Al content of 0.18g / L, Cu content of 10mg / L) with pH value below 1, put in the front end after washing, drying, calcination treated dust collection material, dispersed completely uniform after adding the remaining volume of 60% of the bottom liquid mother liquor for acid dissolution, control the solid content of the slurry is 25%, the acid dissolution temperature is 50℃, stirring at a rate of 400r / min for 6h, after suction filtration to obtain the reverse dissolution of metal solution M6; the phosphorus iron slag acid dissolution of metal liquid N6 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.18) and the reverse dissolution of metal solution M6 are mixed and stirred for 4h, the two kinds of metal liquid M6:N6 are mixed according to the volume ratio of 1:2, the final Fe concentration is 72g / L, and the P concentration is 49.8g / L, then adjust n(Fe):n(P)=0.8 with 85% mass fraction of phosphoric acid; adjust n(S):n(Fe)=1.18 with 98% concentrated sulfuric acid to obtain the mixed phosphorus iron solution Q6.

[0090] (3) the mixed phosphorus iron solution Q6 mixed in the front end is added into the reaction kettle to start heating, the heating rate is controlled at 30℃ / h, the stirring rate of the reaction kettle is 350r / min, when the temperature rises to 50℃, the seed additive is started to be added, the mass of the seed additive is 10% of the mass of the mixed phosphorus iron solution Q6, the solid content of the seed additive is 28%, and the particle size D50 is 1.0μm. The seed additive is added within 30min, and after the temperature rises to 95℃, the reaction kettle is started to be heat preserved, and the heat preservation time is 20h.

[0091] (4) the white powder slurry obtained is transported to the diaphragm filter press for primary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:2, the mother liquor is collected separately and is used for dissolving the dust collection material in step (2), the filter cake after unloading can be used for preparing the seed additive in step (3), and the filter cake not used for preparing the seed additive is prepared into slurry and then is subjected to secondary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transported to the paddle dryer through the belt for drying, the drying temperature is 130℃, the time is 1h, the water content of the material after drying is controlled below 0.5%, then the material is calcined, the rotary kiln calcination temperature is controlled at 700℃, and the material stays in the kiln for 60min to obtain the anhydrous ferric phosphate after complete calcination. The final screening removes the magnetic package to obtain the anhydrous ferric phosphate A6.

[0092] The seed additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0 μm; the method for preparing the seed additive from the filter cake after the first pressure filtration washing comprises: taking the filter cake after the first pressure filtration washing, mixing uniformly by adding water to prepare a slurry, and then sand grinding; the solid content of the slurry is controlled to be 28% during the preparation of the slurry, the sand grinding speed is controlled to be 500 r / min, and the final particle size D50 is controlled to be 1.0 μm during the sand grinding process, thereby obtaining the seed additive for standby use.

[0093] Comparative Example 1

[0094] The present embodiment provides a method for preparing iron phosphate with controllable particle size by recycling bag dust collecting material of a rotary kiln mother liquor, which is different from the method of Example 4 in that the heating rate in step (3) is 50 ℃ / h, and the method specifically comprises the following steps:

[0095] (1) The bag dust collecting material is slurried with pure water to prepare a slurry with a solid content of 32%, and the slurry is stirred in a tank for 4 h; the slurry after the slurry preparation is pumped into a pressure filter for pressure filtration washing, drying, and calcination at 550 ℃ for 2 h, thereby obtaining anhydrous iron phosphate with a particle size D50 of 4.8 μm and a BET of 5.5 m 2 / g.

[0096] (2) The bottom liquid mother liquor with a volume ratio of 40% (Fe content of about 3 g / L, S content of 50 g / L, P content of 12 g / L, Al content of 0.18 g / L, and Cu content of 10 mg / L) with a pH value of less than 1 is injected into a dissolving tank, and the dust collecting material after washing, drying, and calcination treatment is added, and then the remaining volume ratio of 60% of the bottom liquid mother liquor is added for acid dissolution, the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50 ℃, and the stirring speed is 400 r / min for 6 h; after suction filtration, the reverse dissolution metal solution M7 is obtained; the phosphorus iron slag acid dissolution metal liquid N7 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.18) is mixed with the reverse dissolution metal solution M7 for 4 h, the two metal solutions M7:N7 are mixed in a volume ratio of 1:2, the final Fe concentration is 72 g / L, and the P concentration is 49.8 g / L, and then the mass fraction of 85% of phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.18 to obtain the mixed phosphorus iron solution Q7.

[0097] (3) Start to add the mixed phosphorus iron solution Q7 into the reactor, and control the heating rate at 50 °C / h, the stirring rate at 350 r / min. When the temperature reaches 50 °C, start to add the seed crystal additive, the mass of the seed crystal additive is 10% of the mass of the mixed phosphorus iron solution Q7, the solid content of the seed crystal additive is 28%, and the particle size D50 is 1.0 μm. Control the adding time of the seed crystal additive within 30 min. After the temperature reaches 95 °C, start to heat the reactor, and the heat preservation time is 20 h.

[0098] (4) Transfer the obtained white powder slurry to a diaphragm filter press for primary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:2, the mother liquor is collected separately and used for dissolving the collected dust in step (2), the filter cake after being unloaded can be used for preparing the seed crystal additive in step (3), and the filter cake which is not used for preparing the seed crystal additive is prepared into a slurry and then subjected to secondary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transferred to a paddle dryer for drying, the drying temperature is 130 °C, the time is 1 h, and the water content of the material after drying is controlled to be less than 0.5%. Then, the material is calcined, the calcination temperature of the rotary kiln is controlled at 700 °C, and the residence time of the material in the kiln is 60 min, to obtain the anhydrous iron phosphate after complete calcination. Finally, the anhydrous iron phosphate A7 is obtained by screening and removing the magnet.

[0099] The seed crystal additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0 μm. The method for preparing the seed crystal additive from the filter cake after primary pressure filtration washing includes the following steps: taking the filter cake after primary pressure filtration washing, mixing and uniformly preparing a slurry by adding water, sand grinding, controlling the solid content of the slurry to be 28% during the preparation of the slurry, controlling the sand grinding speed to be 500 r / min, and controlling the final particle size D50 to be 1.0 μm during the sand grinding process, to obtain the seed crystal additive for standby use.

[0100] Comparative Example 2

[0101] The present embodiment provides a method for preparing a particle size controllable iron phosphate by recycling the mother liquor of the rotary kiln bag dust collection material, which is different from the embodiment 4 in that the heating rate in step (3) is 50 °C / h, and the seed crystal additive is added at 25 °C. The specific steps include the following steps:

[0102] (1) Prepare a slurry with a solid content of 32% by mixing the bag dust collection material with pure water, and stir in the tank for 4 h. Pump the prepared slurry into a filter press for pressure filtration washing, drying, and calcination at 550 °C for 2 h, to obtain anhydrous iron phosphate with a particle size D50 of 4.8 μm and a BET of 5.5 m 2 / g.

[0103] (2) into the dissolving tank, the volume ratio of the bottom liquid mother liquor (Fe content of about 3 g / L, S content of 50 g / L, P content of 12 g / L, Al content of 0.18 g / L, Cu content of 10 mg / L) with pH value below 1 is 40%, the dust collection material treated by washing, drying and calcination at the front end is put in, after being dispersed completely and uniformly, the remaining volume ratio of the bottom liquid mother liquor is 60% to carry out acid dissolution, the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50°C, the stirring rate is 400 r / min, and the stirring time is 6 h, and then the back-dissolved metal solution M8 is obtained after filtration; the phosphorus iron slag acid-dissolved metal solution N8 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.18) is mixed with the back-dissolved metal solution M8 and stirred for 4 h, the two kinds of metal solutions M8:N8 are mixed according to a volume ratio of 1:2, the final Fe concentration is 72 g / L, and the P concentration is 49.8 g / L, then the mass fraction of 85% phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.18 to obtain the mixed phosphorus iron solution Q8.

[0104] (3) the mixed phosphorus iron solution Q8 mixed at the front end is added into the reaction kettle, the seed additive is started to be added at room temperature (25°C), meanwhile, the temperature is started to be raised, the temperature raising rate is controlled to be 50°C / h, the stirring rate of the reaction kettle is 350 r / min, the mass of the seed additive is 10% of the mass of the mixed phosphorus iron solution Q8, the solid content of the seed additive is 28%, and the particle size D50 is 1.0 μm. The seed additive is added within 30 min, the temperature is raised to 95°C, and then the reaction kettle is started to be kept warm, and the keeping warm time is 20 h.

[0105] (4) the white powder slurry obtained is transported to a diaphragm filter press for primary pressure filtration and washing, the volume ratio of the slurry to the washing water is 1:2, the mother liquor is collected separately and is used for dissolving the dust collection material in step (2), the filter cake after being unloaded can be used for preparing the seed additive in step (3), the filter cake not used for preparing the seed additive is prepared into a slurry and then is subjected to secondary pressure filtration and washing, the volume ratio of the slurry to the washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transported to a paddle dryer through a belt for drying, the drying temperature is 130°C, the time is 1 h, the water content of the material after drying is controlled to be below 0.5%, then the material is calcined, the rotary kiln calcination temperature is controlled to be 700°C, and the material stays in the kiln for 60 min to obtain the anhydrous iron phosphate after complete calcination. Finally, the anhydrous iron phosphate A8 is obtained through screening and magnetic removal and packaging.

[0106] The seed additive is an iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0 μm; the method for preparing the seed additive from the filter cake after the first pressure filtration washing comprises: taking the filter cake after the first pressure filtration washing, mixing uniformly by adding water to prepare a slurry, and then sand grinding, controlling the solid content of the slurry to be 28% during the slurry preparation, controlling the sand grinding speed to be 500 r / min, and controlling the final particle size D50 to be 1.0 μm during the sand grinding, to obtain the seed additive for standby.

[0107] Comparative Example 3

[0108] The embodiment provides a method for preparing iron phosphate with controllable particle size by recycling rotary kiln bag dust collecting material, and the difference from the embodiment 4 is that the heating rate in step (3) is 50 ℃ / h, and the seed additive is added at 90 ℃, and the method specifically comprises the following steps:

[0109] (1) The bag dust collecting material is slurried with pure water to prepare a slurry with a solid content of 32%, and the slurry is stirred in a tank for 4 h; the slurry after the slurry preparation is pumped into a pressure filter for pressure filtration washing, drying and calcination at 550 ℃ for 2 h, to obtain anhydrous iron phosphate with a particle size D50 of 4.8 μm and a BET of 5.5 m 2 / g.

[0110] (2) The bottom liquid mother liquor with a volume ratio of 40% (Fe content is about 3 g / L, S content is 50 g / L, P content is 12 g / L, Al content is 0.18 g / L, and Cu content is 10 mg / L) with a pH value of less than 1 is injected into a dissolving tank, the dust collecting material treated by washing, drying and calcination at the front end is added, and the remaining volume ratio of 60% of the bottom liquid mother liquor is added after being dispersed completely and uniformly, to perform acid dissolution, the solid content of the slurry is controlled to be 25%, the acid dissolution temperature is 50 ℃, and the stirring is performed at a speed of 400 r / min for 6 h, to obtain a reverse dissolution metal solution M9 after suction filtration; the phosphorus iron slag acid dissolution metal liquid N9 (molar ratio n(Fe):n(P)=0.8, n(S):n(Fe)=1.18) is mixed and stirred with the reverse dissolution metal solution M9 for 4 h, the two metal liquids M9:N9 are mixed according to a volume ratio of 1:2, the final Fe concentration is 72 g / L, and the P concentration is 49.8 g / L, and then the mass fraction of 85% of phosphoric acid is used to adjust n(Fe):n(P)=0.8; 98% concentrated sulfuric acid is used to adjust n(S):n(Fe)=1.18 to obtain a mixed phosphorus iron solution Q9.

[0111] (3) Start to add mixed phosphorus iron solution Q9 into the reactor, and start to heat up, control the heating rate at 50℃ / h, the stirring rate of the reactor at 350r / min, when the temperature reaches 90℃, start to add the seed crystal additive, the mass of the seed crystal additive is 10% of the mass of the mixed phosphorus iron solution Q9, the solid content of the seed crystal additive is 28%, and the particle size D50(1) is 1.0μm. Control the adding time of the seed crystal additive within 30min, and start to heat up to 95℃, then start to heat preservation of the reactor, and the heat preservation time is 20h.

[0112] (4) The obtained white powder slurry is transported to the diaphragm filter press for primary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:2, the mother liquor is collected separately and is used for dissolving the collected dust in step (2), the filter cake after unloading can be used for preparing the seed crystal additive in step (3), the filter cake which is not used for preparing the seed crystal additive is prepared into slurry and then is subjected to secondary pressure filtration washing, the volume ratio of the slurry to the washing water is 1:3, and the pH of the washing water after washing is 3. The filter cake is transported to the paddle dryer through the belt for drying, the drying temperature is 130℃, the time is 1h, the water content of the material after drying is controlled to be less than 0.5%, and then the material is calcined, the calcination temperature of the rotary kiln is controlled at 700℃, and the residence time of the material in the kiln is 60min, to obtain the anhydrous iron phosphate after complete calcination. The final screening and magnetic removal are performed to obtain the anhydrous iron phosphate A9.

[0113] The seed crystal additive is the iron phosphate slurry with a solid content of 28% and a particle size D50 of 1.0μm, the method for preparing the seed crystal additive from the filter cake after primary pressure filtration washing comprises the following steps: taking the filter cake after primary pressure filtration washing, mixing uniformly by adding water to prepare slurry, and then sand grinding, the solid content of the slurry is controlled to be 28% during the preparation of the slurry, the sand grinding speed is controlled to be 500r / min, and the final particle size D50 is controlled to be 1.0μm during the sand grinding, to obtain the seed crystal additive for standby.

[0114] Test example

[0115] The iron phosphate prepared by the examples 1-6 and the comparative examples 1-3 is subjected to data detection, and the test results are shown in Table 1:

[0116] Table 1: Iron phosphate detection data table

[0117]

[0118] As can be seen from Examples 1-5, the particle size of the iron phosphate changes more obviously, the particle size can be controlled by the S / Fe molar ratio, the particle size D50 gradually decreases with the increase of the S / Fe molar ratio, and according to the detected data, the Fe and P contents and the Fe / P molar ratio of the obtained iron phosphate product are within the theoretical range (the Fe content is 36.1%-36.7%, the P content is 20.3%-21%, and the Fe / P molar ratio is between 0.97 and 0.99), and there is no obvious difference; the BET and S content indicators are slightly different in Examples 1-5, but are still within the normal range (the BET is between 4 and 7.5 m 2 / g, and the S content is ≤500 ppm).

[0119] As can be seen from Example 4, Example 6 and Comparative Example 1, in the process of synthesizing iron phosphate, increasing the heating rate will increase the particle size D50 of the product, but too fast heating rate will lead to too large particle size D50, and the diffraction peak of the subsequent lithium iron phosphate sintering will be low, which is not conducive to the performance of the material. It can also be seen that too fast heating rate will also make the particle size fluctuation of the product larger, and too large particle size fluctuation will lead to unstable sintering effect in the subsequent lithium iron phosphate sintering process.

[0120] As can be seen from Comparative Example 1, Comparative Example 2 and Comparative Example 3, in the process of synthesizing iron phosphate, the higher the temperature at which the seed additive is added, the higher the particle size D50 of the product, and if the temperature at which the seed additive is added is too high, the particle size fluctuation of the product will also be larger.

[0121] Figure 6 The XRD pattern of the anhydrous iron phosphate prepared in Examples 1-5 can be seen that the crystallinity of the anhydrous iron phosphate prepared by the present application is good.

[0122] The above embodiments of the present application are described in detail, but the present application is not limited to the above embodiments, and various changes can be made within the knowledge of those skilled in the art without departing from the spirit of the present application. In addition, the embodiments of the present application and the features in the embodiments can be combined with each other without conflict.

Claims

1. A method for preparing a particle size controllable ferric phosphate using mother liquor recovery of ferric phosphate dust collector material, characterized by, The method comprises the following steps: S1: washing and drying the iron phosphate dust collection material, then carrying out first roasting, mixing the obtained roasting material with iron phosphate synthesis mother liquor to prepare slurry, and then carrying out solid-liquid separation to obtain anti-dissolution metal solution; S2: mixing the anti-dissolution metal solution with phosphorus iron slag acid-dissolution metal solution, adjusting the molar ratio of Fe / P in the obtained mixed solution to be (0.75-0.95):1 and the molar ratio of S / Fe to be (1-1.3):1 to obtain mixed phosphorus iron solution; S3: heating the mixed phosphorus iron solution, adding seed additive during the heating process, carrying out heat preservation after the heating is completed, obtaining iron phosphate slurry, and carrying out solid-liquid separation on the iron phosphate slurry, then carrying out second roasting on the obtained solid phase to obtain anhydrous iron phosphate; In step S3, the heating process comprises: heating at a rate of 10-30 ℃ / h to 85-95 ℃, and then heat preserving for 10-20 h; the seed additive is added when the temperature of the mixed phosphorus iron solution reaches 50-60 ℃; The seed additive is obtained by the following method: obtaining iron phosphate filter cake by carrying out first pressure filtration washing on the iron phosphate slurry, adding water to prepare secondary slurry, and then carrying out sand milling on the secondary slurry.

2. The method of claim 1, wherein, In step S1, the iron phosphate dust collection material comprises anhydrous iron phosphate and dihydrate iron phosphate, and the sulfur content of the iron phosphate dust collection material is 10000-20000 ppm.

3. The method of claim 1, wherein, In step S1, the pH of the iron phosphate synthesis mother liquor is less than 1; and / or, the solid content of the slurry is controlled to be 10%-25% during the mixing process.

4. The method of claim 1, wherein, In step S2, the anti-dissolution metal solution is mixed with the phosphorus iron slag acid-dissolution metal solution at a volume ratio of 1:4 to 1:2; the molar ratio of Fe / P in the phosphorus iron slag acid-dissolution metal solution is (0.75-0.95):1, and the molar ratio of S / Fe is (1-1.3):

1.

5. The method of claim 1, wherein, In step S2, the concentration of Fe in the mixed phosphorus iron solution is 60-75 g / L.

6. The method of claim 1, wherein, In step S3, the seed additive is an iron phosphate slurry with a solid content of 20%-40%; and / or, the particle size D50 of the seed additive is 1-1.5 μm.

7. The method of claim 1, wherein, In step S3, the mass of the seed additive is 5%-20% of the mass of the mixed phosphorus iron solution.

8. Iron phosphate characterized in that, The iron phosphate is prepared by the method of any one of claims 1-7, and the particle size D50 of the iron phosphate is 3.5-6.5 μm.

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