Method for preparing iron phosphate at low cost
By recycling secondary filter press washing wastewater as a hot water resource to promote the ferric phosphate crystallization process, the problems of resource waste and insufficient performance in traditional ferric phosphate production are solved, and high-quality ferric phosphate is produced at low cost and high efficiency.
Patent Information
- Application Number
- CN202511270812.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-05
- Publication Date
- 2025-12-05
AI Technical Summary
Traditional lithium iron phosphate production processes suffer from high water and heat consumption, high production costs, and insufficient product performance. In particular, the waste of heat energy and low water utilization rate of secondary filter press washing wastewater affect the performance of lithium iron phosphate cathode materials.
By recycling secondary filter washing wastewater as a hot water resource for use in the iron phosphate production process, including heating pulping and aging, and combining it with trace amounts of phosphate ions to participate in crystal growth, a triple utilization of water, heat resources and trace components is achieved, promoting the iron phosphate crystallization process.
It enables the recycling of water, heat, and phosphorus resources, reduces production costs, shortens the production cycle, increases the tap density and crystallinity of iron phosphate products, and improves production efficiency.
Smart Images
Figure CN121063501A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of battery cathode material, in particular to a method for preparing iron phosphate as a lithium ion battery cathode material precursor. BACKGROUND
[0002] The two-step method for producing iron phosphate commonly used in the industry mainly includes oxidation synthesis, pressure filtration washing, crystal transformation aging, secondary washing, and drying and calcination. In this process, a large amount of hot desalted water is usually used in the washing process to ensure the effective removal of impurity ions. According to industry standards, high-quality battery-grade iron phosphate requires sulfur content to be less than 0.1%, which makes the washing process one of the key links to determine product quality.
[0003] In the prior art, the secondary pressure filtration washing (referred to as "secondary washing") produces wastewater with the following characteristics: high temperature and containing trace amounts of phosphate. There are mainly three ways to handle these wastewaters in the industry: one is to send them directly to a wastewater treatment station for neutralization and precipitation treatment; the second is to purify them through a multi-stage membrane system (such as reverse osmosis) and then reuse them as desalted water; the third is to evaporate and concentrate to recover the sulfate salts therein. These methods achieve wastewater treatment, but all have obvious defects: (1) Energy waste: the secondary washing wastewater contains a large amount of residual heat, and the traditional treatment method results in the complete loss of this heat energy; (2) Low water resource utilization rate: even if membrane treatment and reuse technology is used, a large amount of electrical energy is needed for desalination treatment, and the desalted water reuse rate is usually not more than 70%; (3) Effective components are not utilized: the trace amounts of phosphate in the secondary washing wastewater are considered as impurities to be removed in the traditional process, but in fact, the 500-900 ppm of phosphorus in the secondary washing wastewater can participate in the growth process of iron phosphate crystals under appropriate conditions.
[0004] There are two key technical bottlenecks in the production process of iron phosphate: one is the high consumption of water and heat resources, resulting in high production costs; the other is the difficulty in further improving the tap density of the product, which affects the performance of the subsequent lithium iron phosphate cathode material. In the traditional process, the use of fresh desalted water for slurry beating and aging, which is an important link affecting the growth of iron phosphate crystals, not only has high cost, but also is not conducive to the repair of crystal defects and the densification growth of particles due to the "too pure" water quality.
[0005] Therefore, the present application is proposed. SUMMARY
[0006] The application aims at the problems of serious resource waste and product performance to be improved in the traditional iron phosphate production process, and provides a method for preparing iron phosphate at low cost, realizes triple recycling and recycling of water resources, heat energy and phosphorus resources, greatly reduces the production cost, and effectively promotes the crystallization process of iron phosphate, thereby shortening the whole production cycle, accelerating the growth rate of crystal nucleus and promoting the uniform growth of particles, and effectively improving the tap density of iron phosphate product.
[0007] In order to achieve the above-mentioned purpose of the application, the following technical scheme is adopted: A method for preparing iron phosphate at low cost comprises the following steps: Step S1, preparing iron phosphate slurry through a precipitation reaction, and performing liquid-solid separation; Step S2, performing primary water washing on the separated solid product; Step S3, adding water to the primary-washed solid product to make slurry, aging the slurry, and performing solid-liquid separation on the aged slurry; Step S4, performing secondary water washing on the separated solid product, collecting secondary washing water, and recycling the secondary washing water to the preparation of subsequent batches of iron phosphate; Step S5, drying and calcining the secondary-washed solid product to obtain iron phosphate finished product.
[0008] Further, the secondary washing water in step S4 is recycled to the primary water washing process and the slurry making process in the preparation of subsequent batches of iron phosphate.
[0009] Further, the method for collecting the secondary washing water in step S4 is to collect the front-stage secondary washing water and the rear-stage secondary washing water according to the water washing time, the front-stage secondary washing water is recycled to the primary water washing process in the preparation of subsequent batches of iron phosphate, and the rear-stage secondary washing water is recycled to the slurry making process in the preparation of subsequent batches of iron phosphate.
[0010] Further, the total secondary water washing time T in step S4 is 0.5T-0.8T, and the remaining time is the secondary rear-stage water washing time.
[0011] Further, the precipitation reaction in step S1 comprises the following steps: Step S1.1, using a weakly acidic phosphate as raw material to prepare a phosphate solution with a phosphorus content of 1.8%-4.5%; Step S1.2, configuring a ferrous solution with a divalent iron concentration of 50-85g / L ferrous solution; Step S1.3, according to the molar ratio of iron element to phosphorus element nFe:nP of 0.8-1.3:1, adding the ferrous solution and the phosphate solution into a reaction kettle according to the flow ratio of 1:0.7-1.2, and the feeding time is 40min-80min; Step S1.4, hydrogen peroxide is added to the mixed solution to perform an oxidation synthesis reaction, the reaction temperature is 50-80 DEG C, and the reaction time is 30-120 min, so that a phosphoric acid iron slurry with uniform phosphoric acid iron precipitate is prepared.
[0012] Further, the phosphate in step S1.1 uses phosphorus source, which is one or more of phosphoric acid, disodium hydrogen phosphate, and sodium dihydrogen phosphate.
[0013] Further, the ferrous solution in step S1.2 is one or both of ferrous sulfate solution and ferrous chloride solution.
[0014] Further, in step S2, the water is washed once to less than 2-4 mS / cm.
[0015] Further, in step S4, the total time T of the second water washing is 150-250 min.
[0016] Further, in step S4, the second water washing is to less than 0.5 mS / cm.
[0017] Further, in step S4, the second water washing uses fresh desalted water at 60-65 DEG C.
[0018] Further, in step S3, the water is added to the slurry tank, the solid product after the first washing is slurried and homogenized, the homogenized slurry is added to a reaction kettle with a heating device, phosphoric acid is added to adjust the pH value of the slurry to 1.5-1.8, the temperature is raised at a rate of 0.3-1 DEG C / min to 90-95 DEG C, and after the slurry color becomes white, the temperature is maintained for 1-2 h to obtain an aging slurry; the slurry concentration is controlled at 8-20%, and the slurry time is controlled at 1-3 h.
[0019] Further, in step S5, the drying is flash drying, and the mixing temperature of the flash drying is controlled at 100-140 DEG C.
[0020] Further, in step S5, the calcination temperature is 580-720 DEG C, and the calcination time is 2-4 h.
[0021] Compared with the prior art, the present application has the following advantages: 1. The present application recycles the second washing water and uses it as hot water resource for the first washing and slurry process in the production of phosphoric acid iron, breaking the mode of directly discharging the second washing water in traditional production, realizing resource recycling and cyclic utilization, effectively reducing production cost, and reducing environmental protection pressure.
[0022] 2. The present application directly uses a part of the hot water generated by the second pressure filtration washing in the slurry aging process of the subsequent batch without complicated purification treatment, and uses another part of the hot water for the first washing, realizing the triple utilization of water, heat resource and trace effective components.
[0023] 3. The present application adopts hot water beating to age, which utilizes the heat carried by hot water itself to accelerate the reaction rate, and on the other hand, the trace amount of phosphorus component in the second washing water participates in the aging process to regulate crystallization. Compared with the traditional process steps, it can more effectively promote the crystallization process of iron phosphate, thereby shortening the entire production cycle, improving production efficiency, and reducing production cost.
[0024] 4. The present application introduces more thermal motion energy by hot water beating, which intensifies the disordered movement of ions in the solution, i.e. the increase of the entropy of the system. This makes the process of iron phosphate forming crystal nucleus easier, and the growth rate of the crystal nucleus accelerates. At the same time, the suitable temperature provided by hot water provides stable kinetic conditions for the growth of crystal nucleus, which is conducive to the ordered growth of iron phosphate crystals according to certain crystal faces and unit cells, and finally obtains iron phosphate products with uniform particles and good crystallinity. BRIEF DESCRIPTION OF DRAWINGS
[0025] In order to more clearly illustrate the technical solutions in the specific embodiments or prior art of the present application, the drawings needed to be used in the description of the specific embodiments or prior art will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.
[0026] Figure 1 Process flow chart of the method for preparing iron phosphate at low cost of the present application; Figure 2 SEM image of iron phosphate finished product of Example 1 of the present application; Figure 3 SEM image of iron phosphate finished product of Example 2 of the present application; Figure 4 SEM image of iron phosphate finished product of Example 3 of the present application; Figure 5 SEM image of iron phosphate finished product of Comparative Example 1 of the present application; Figure 6 SEM image of iron phosphate finished product of Comparative Example 2 of the present application; Figure 7 SEM image of iron phosphate finished product of Comparative Example 3 of the present application; Figure 8 SEM image of iron phosphate finished product of Comparative Example 4 of the present application. DETAILED DESCRIPTION
[0027] The technical solutions of the present application will be clearly and completely described below in combination with the drawings and specific embodiments, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application. If the specific conditions are not specified in the embodiments, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be purchased on the market.
[0028] A method for preparing iron phosphate at low cost, comprising the following steps: Step S1, preparing iron phosphate slurry by precipitation reaction, and performing liquid-solid separation; Step S2, performing one-time water washing on the separated solid product; Step S3, adding water to the one-time washed solid product to make pulp, aging the pulp, and performing solid-liquid separation on the aged pulp; Step S4, performing two-time water washing on the separated solid product, collecting the two-time washing water, and recycling the two-time washing water to the one-time water washing process and the pulp making process in the preparation of iron phosphate in the subsequent batch; Step S5, drying and calcining the two-time washed solid product to obtain iron phosphate finished product.
[0029] Preferably, the temperature of the two-time washing water collected in step S4 is 60-65°C, including but not limited to 60°C, 61°C, 62°C, 63°C, 64°C, and 65°C; and the temperature of the two-time washing water recycled is 55-60°C, including but not limited to 55°C, 56°C, 57°C, 58°C, 59°C, and 60°C; Preferably, the method for collecting the two-time washing water in step S4 is to collect the two-time washing front water and the two-time washing rear water according to the water washing time, the two-time washing front water is recycled to the one-time water washing process in the preparation of iron phosphate in the subsequent batch, and the two-time washing rear water is recycled to the pulp making process in the preparation of iron phosphate in the subsequent batch; preferably, in step S4, 60-65°C fresh desalted water is added to the two-time washing front water, the temperature of the fresh desalted water includes but is not limited to 60°C, 61°C, 62°C, 63°C, 64°C, and 65°C, and the fresh desalted water is recycled to the one-time water washing process in the preparation of iron phosphate in the subsequent batch; the addition amount of the fresh desalted water in the one-time water washing process is the addition amount for one-time water washing to the qualified conductivity; Preferably, in step S4, no fresh desalted water is added to the two-time washing rear water, and the two-time washing rear water is recycled to the pulp making process in the preparation of iron phosphate in the subsequent batch, i.e., the pulp making process uses the two-time washing rear water entirely; Preferably, the total time T of the second washing in step S4 is 150-250 min, including but not limited to 150 min, 160 min, 170 min, 180 min, 190 min, 200 min, 210 min, 220 min, 230 min, 240 min, 250 min, the first-stage water washing time before the second washing is 0.5T-0.8T, including but not limited to 0.5T, 0.6T, 0.7T, 0.8T, and the remaining time is the second-stage water washing time after the second washing; in the second washing process, the trace amount of phosphate in the first-stage water and the second-stage water is significantly different, showing a distribution characteristic of high in the first stage and low in the second stage. With the progress of the washing process, the impurity content in the second-stage water gradually decreases, and the washing process can effectively remove the impurities. Although the impurity content in the first-stage water before the second washing is higher than that in the second-stage water after the second washing, compared with the high impurity content of the filter cake after the first washing, the first-stage water before the second washing still belongs to the washing liquid with low impurity concentration, which can be reused in the first washing process to remove the impurities introduced in the precipitation reaction process. The second-stage water after the second washing has very low impurity content, which meets the water quality requirement of the beating process, and can be reused in the beating process, avoiding the accumulation of impurities in the final product, so as to realize the cascade utilization of water resources and effective control of impurities in the production process; Preferably, the fresh desalted water used in the second water washing in step S4 is at a temperature of 60-65°C, including but not limited to 60°C, 61°C, 62°C, 63°C, 64°C, 65°C; Preferably, the precipitation reaction in step S1 comprises the following steps: Step S1.1, a weakly acidic phosphate salt is used as a raw material to prepare a phosphate salt solution with a phosphorus content of 1.8%-4.5%, including but not limited to 1.8%, 2.1%, 2.4%, 2.7%, 3%, 3.3%, 3.6%, 3.9%, 4.2%, 4.5%; Step S1.2, the ferrous solution is configured to have a divalent iron concentration of 50-85 g / L, including but not limited to 50 g / L, 55 g / L, 60 g / L, 65 g / L, 70 g / L, 75 g / L, 80 g / L, 85 g / L; Step S1.3, the ferrous solution and the phosphate salt solution are added into a reaction kettle at a flow ratio of 1:0.7-1.2, including but not limited to 1:0.7, 1:0.75, 1:0.8, 1:0.85, 1:0.9, 1:0.95, 1:1, 1:1.15, 1:1.2, at a molar ratio of iron element to phosphorus element nFe:nP of 0.8-1.3:1, including but not limited to 0.8:1, 0.9:1, 1:1, 1.1:1, 1.2:1, 1.3:1, for 40-80 min, including but not limited to 40 min, 45 min, 50 min, 55 min, 60 min, 65 min, 70 min, 75 min, 80 min. Step S1.4, hydrogen peroxide is added to the mixed solution for oxidation synthesis reaction, the reaction temperature is 50-80℃, including but not limited to 50℃, 55℃, 60℃, 65℃, 70℃, 75℃, 80℃, the reaction time is 30-120min, including but not limited to 30min, 40min, 50min, 60min, 70min, 80min, 90min, 100min, 110min, 120min, and the iron phosphate slurry with uniform iron phosphate precipitate is prepared; Preferably, the phosphate salt in step S1.1 uses one or more of phosphoric acid, disodium hydrogen phosphate, and sodium dihydrogen phosphate as the phosphorus source; Preferably, the ferrous solution in step S1.2 is one or both of ferrous sulfate solution and ferrous chloride solution; Preferably, in step S2, the first water washing is to less than 2-4mS / cm, including but not limited to less than 2mS / cm, 3mS / cm, 4mS / cm; Preferably, in step S4, the second water washing is to less than 0.5mS / cm; Preferably, in step S3, the water addition, slurry making, and aging method is as follows: water is added to the slurry making tank, the solid product after the first washing is slurry made and homogenized, the homogenized slurry is added to a reaction kettle with heating device, phosphoric acid is added to adjust the slurry pH value to 1.5-1.8, including but not limited to 1.5, 1.6, 1.7, 1.8, the temperature is raised to 90-95℃ at a temperature rise rate of 0.3-1℃ / min, the temperature rise rate includes but is not limited to 0.3℃ / min, 0.4℃ / min, 0.5℃ / min, 0.6℃ / min, 0.7℃ / min, 0.8℃ / min, 0.9℃ / min, 1℃ / min, the temperature rise to a temperature includes but is not limited to 91℃, 92℃, 93℃, 94℃, 95℃, after the slurry color becomes white, the temperature is kept for 1-2h, including but not limited to 1h, 1h10min, 1h20min, 1h30min, 1h40min, 1h50min, 2h, to obtain the aged slurry; the slurry concentration is controlled at 8-20%, including but not limited to 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, and the slurry making time is controlled at 1-3h, including but not limited to 1h, 1.5h, 2h, 2.5h, 3h; Preferably, the step S5 drying is flash drying, the mixed temperature of the flash is controlled at 100-140℃, including but not limited to 100℃, 110℃, 120℃, 140℃; the calcination temperature is 580-720℃, including but not limited to 580℃, 600℃, 620℃, 640℃, 660℃, 680℃, 700℃, 720℃, and the calcination time is 2-4h, including but not limited to 2h, 2.5h, 3h, 3.5h, 4h.
[0030] Example 1 1. Sodium dihydrogen phosphate is used to prepare a phosphate solution with a phosphorus content of 2.5%; ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 65 g / L; 2. The ferrous solution and the phosphate solution are added to the reaction kettle according to the molar ratio of iron element to phosphorus element of 0.9:1, and the flow ratio of 1:0.85, the feeding is completed in 70 min, 1.5 times excess hydrogen peroxide is added to the reaction kettle for oxidation, the reaction temperature is controlled at 50℃, and the reaction is continued for 45 min to obtain a precipitate slurry; 3. The precipitate slurry is solid-liquid separated and washed once with 60℃ two-washing front-stage water and 65℃ fresh desalted water, and the washing is stopped when the final conductivity is less than 3 mS / cm to obtain a first washing filter cake; 4. According to the beating consistency of 10%, two-washing rear-stage water is added to the beater tank, and the obtained first washing filter cake is added to the beater tank for uniform pulp dispersion, and stirred for 1.5h to obtain a beating slurry; 5. The beating slurry is added to the reaction kettle, and after adjusting the pH to 1.7 by adding phosphoric acid, the temperature is raised, the temperature rising rate is controlled at 0.7℃ / min, and the temperature is raised to 90℃, then the slurry color becomes white, and the temperature is kept for 1.5h to obtain an aging slurry; 6. The aging slurry is solid-liquid separated, and washed twice with 65℃ hot fresh desalted water, the washing time is 200 min, and the washing is stopped when the final conductivity is less than 0.5 mS / cm; the washing water is collected, the washing water collected in the first 160 min is collected as two-washing front-stage water, and the washing water collected in the last 40 min is collected as two-washing rear-stage water; the two-washing front-stage water is reused in the first washing process of the subsequent batch of iron phosphate preparation, and the two-washing rear-stage water is reused in the beating and aging process of the subsequent batch of iron phosphate preparation; 7. The obtained two-washing filter cake is flash dried, the mixed temperature of the flash is controlled at 120℃ to obtain iron phosphate dihydrate, and the iron phosphate dihydrate is calcined at a temperature of 630℃ for 3h to obtain iron phosphate finished product.
[0031] Example 2 1. Sodium dihydrogen phosphate is used to prepare a phosphate solution with a phosphorus content of 2.0%; ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 60 g / L; 2. The ferrous solution and the phosphate solution are added into the reactor according to the molar ratio of iron element to phosphorus element of 1.1:1 and the flow ratio of 1:1, the feeding is completed in 60 min, 1.5 times excess hydrogen peroxide is added into the reactor for oxidation, the reaction temperature is controlled at 60°C, and the reaction is continued for 30 min to obtain a precipitate slurry; 3. The precipitate slurry is subjected to solid-liquid separation, and then once water washing is performed using two-washing front-stage water at a temperature of 55°C and fresh desalted water at 60°C, the water washing is continued until the terminal conductivity is less than 2 mS / cm to obtain a first-washing filter cake; 4. The two-washing rear-stage water is added into a beating tank according to a beating consistency of 15%, and the obtained first-washing filter cake is added into the beating tank for uniform slurry dispersion, and stirring is performed for 1 h to obtain a beating slurry; 5. The beating slurry is added into the reactor, and then phosphoric acid is added to adjust the pH to 1.7, and then the temperature is raised at a rate of 0.5°C / min, and the temperature is raised to 90°C, and then the slurry color becomes white, and then the temperature is kept for 1 h to obtain an aging slurry; 6. The aging slurry is subjected to solid-liquid separation, and then twice water washing is performed using hot fresh desalted water at 60°C, the water washing time is 160 min, and the water washing is continued until the terminal conductivity is less than 0.5 mS / cm; the washing water is collected, the washing water collected in the first 120 min of the water washing time is collected as two-washing front-stage water, and the washing water collected in the last 40 min of the water washing time is collected as two-washing rear-stage water; the two-washing front-stage water is reused in the first water washing process of the preparation of the subsequent batch of iron phosphate, and the two-washing rear-stage water is reused in the beating and aging process of the preparation of the subsequent batch of iron phosphate; 7. The obtained two-washing filter cake is subjected to flash drying, the mixed temperature of the flash drying is controlled at 110°C to obtain iron phosphate dihydrate, and the iron phosphate dihydrate is calcined at a temperature of 650°C for 2.5 h to obtain iron phosphate finished product.
[0032] Example 3 1. A phosphate solution with a phosphorus content of 2.2% is prepared by using sodium dihydrogen phosphate; ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 50 g / L; 2. The ferrous solution and the phosphate solution are added into the reactor according to the molar ratio of iron element to phosphorus element of 1:1 and the flow ratio of 1:1, the feeding is completed in 70 min, 1.5 times excess hydrogen peroxide is added into the reactor for oxidation, the reaction temperature is controlled at 60°C, and the reaction is continued for 45 min to obtain a precipitate slurry; 3. The precipitate slurry is subjected to solid-liquid separation, and then once water washing is performed using two-washing front-stage water at a temperature of 57°C and fresh desalted water at 62°C, the water washing is continued until the terminal conductivity is less than 4 mS / cm to obtain a first-washing filter cake; 4. The two-washing rear-stage water is added into a beating tank according to a beating consistency of 15%, and the obtained first-washing filter cake is added into the beating tank for uniform slurry dispersion, and stirring is performed for 1.5 h to obtain a beating slurry; 5. The pulp slurry is added to the reaction kettle, and phosphoric acid is added to adjust the pH to 1.7, and then the temperature is raised at a rate of 1°C / min to 90°C. After the color of the slurry becomes white, the temperature is maintained for 1.5 h to obtain an aging slurry; 6. The aging slurry is solid-liquid separated, and fresh desalted water at 62°C is used for secondary water washing for 240 min until the final conductivity is less than 0.5 mS / cm. The second washing water is collected, and the water collected before 190 min is collected as the first part of the second washing water, and the water collected after 50 min is collected as the second part of the second washing water. The first part of the second washing water is reused in the first washing process of the subsequent batch of iron phosphate preparation, and the second part of the second washing water is reused in the beating and aging process of the subsequent batch of iron phosphate preparation; 7. The obtained second washing filter cake is flash dried, and the mixed temperature of the flash drying is controlled at 115°C to obtain iron phosphate dihydrate, which is calcined at a temperature of 600°C for 3 h to obtain the finished product of iron phosphate.
[0033] Comparative Example 1 1. A phosphate solution with a phosphorus content of 2.5% is prepared using sodium dihydrogen phosphate. Ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 65 g / L; 2. The ferrous solution and the phosphate solution are added to the reaction kettle at a flow ratio of 1:0.85 according to the molar ratio of iron element to phosphorus element of 0.9:1. The feeding is completed in 70 min, and 1.5 times excess hydrogen peroxide is added to the reaction kettle for oxidation. The reaction temperature is controlled at 50°C, and the reaction is continued for 45 min to obtain a precipitate slurry; 3. The precipitate slurry is solid-liquid separated, and fresh desalted water at a temperature of 65°C is used for first water washing until the final conductivity is less than 3 mS / cm to obtain a first washing filter cake; 4. Fresh desalted water at room temperature of 30°C is added to the beating tank according to a beating concentration of 10%, and the obtained first washing filter cake is added to the beating tank for uniform dispersion and stirring for 1.5 h to obtain a beating slurry; 5. The beating slurry is added to the reaction kettle, and phosphoric acid is added to adjust the pH to 1.7, and then the temperature is raised at a rate of 0.7°C / min to 90°C. After the color of the slurry becomes white, the temperature is maintained for 1.5 h to obtain an aging slurry; 6. The aging slurry is solid-liquid separated, and fresh desalted water at 65°C is used for secondary water washing for 200 min until the final conductivity is less than 0.5 mS / cm to obtain a second washing filter cake; 7. The obtained second washing filter cake is flash dried, and the mixed temperature of the flash drying is controlled at 120°C to obtain iron phosphate dihydrate, which is calcined at a temperature of 630°C for 3 h to obtain the finished product of iron phosphate.
[0034] Comparative Example 2 1. Sodium dihydrogen phosphate is used to prepare a phosphate solution with a phosphorus content of 2.5%; ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 65 g / L; 2. The ferrous solution and the phosphate solution are added to a reaction kettle according to a flow ratio of 1:0.85 at a molar ratio of iron element to phosphorus element of 0.9:1, and the feeding is completed in 70 min; 1.5 times excess hydrogen peroxide is added to the reaction kettle for oxidation, the reaction temperature is controlled at 50°C, and the reaction is continued for 45 min to obtain a precipitate slurry; 3. The precipitate slurry is solid-liquid separated and washed once with two-washing front-stage water at a temperature of 60°C and fresh desalted water at 65°C until the end point conductivity is less than 3 mS / cm to obtain a first-washing filter cake; 4. Fresh desalted water at room temperature of 30°C is added to a beating tank according to a beating concentration of 10%, and the obtained first-washing filter cake is added to the beating tank for uniform pulp dispersion and stirring for 1.5 h to obtain a beating slurry; 5. The beating slurry is added to a reaction kettle, and phosphoric acid is added to adjust the pH to 1.7, and then the temperature is raised at a rate of 0.7°C / min until 90°C; after the color of the slurry becomes white, the temperature is maintained for 1.5 h to obtain an aging slurry; 6. The aging slurry is solid-liquid separated and washed twice with hot fresh desalted water at 65°C for 200 min until the end point conductivity is less than 0.5 mS / cm to obtain a second-washing filter cake; the washing water is collected, and the washing water collected in the first 160 min is collected as second-washing front-stage water, which is reused in the first-washing process until the end point conductivity is less than 3 mS / cm to obtain a first-washing filter cake; 7. The obtained second-washing filter cake is flash dried at a mixed temperature of 120°C to obtain iron phosphate dihydrate, which is calcined at a temperature of 630°C for 3 h to obtain iron phosphate as a finished product.
[0035] Comparative Example 3 1. Sodium dihydrogen phosphate is used to prepare a phosphate solution with a phosphorus content of 2.5%; ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 65 g / L; 2. The ferrous solution and the phosphate solution are added to a reaction kettle according to a flow ratio of 1:0.85 at a molar ratio of iron element to phosphorus element of 0.9:1, and the feeding is completed in 70 min; 1.5 times excess hydrogen peroxide is added to the reaction kettle for oxidation, the reaction temperature is controlled at 50°C, and the reaction is continued for 45 min to obtain a precipitate slurry; 3. The precipitate slurry is solid-liquid separated and washed once with fresh desalted water at a temperature of 65°C until the end point conductivity is less than 3 mS / cm to obtain a first-washing filter cake; 4. Second-washing back-stage water is added to a beating tank according to a beating concentration of 10%, and the obtained first-washing filter cake is added to the beating tank for uniform pulp dispersion and stirring for 1.5 h to obtain a beating slurry; 5. The pulp slurry is added to the reaction kettle, and phosphoric acid is added to adjust the pH to 1.7, and then the temperature is raised at a rate of 0.7°C / min to 90°C. After the color of the slurry becomes white, the temperature is maintained for 1.5 h to obtain an aged slurry; 6. The aged slurry is solid-liquid separated, and fresh desalted water at 65°C is used for secondary water washing for 200 min until the end point conductivity is less than 0.5 mS / cm. The second washing water is collected, and the water collected after 40 min of washing is collected as the second washing post water. The second washing post water is reused in the beating and aging process; 7. The obtained second washing filter cake is flash dried, and the mixed temperature of the flash drying is controlled to 120°C to obtain iron phosphate dihydrate. The iron phosphate dihydrate is calcined at a temperature of 630°C for 3 h to obtain the finished product of iron phosphate.
[0036] Comparative Example 4 1. A phosphate solution with a phosphorus content of 2.5% is prepared using sodium dihydrogen phosphate. Ferrous sulfate crystals are dissolved to prepare a ferrous solution with a divalent iron concentration of 65 g / L; 2. The ferrous solution and the phosphate solution are added to the reaction kettle at a flow ratio of 1:0.85 according to the molar ratio of iron element to phosphorus element of 0.9:1. The addition is completed in 70 min, and 1.5 times excess hydrogen peroxide is added to the reaction kettle for oxidation. The reaction temperature is controlled at 50°C, and the reaction is continued for 45 min to obtain a precipitate slurry; 3. The precipitate slurry is solid-liquid separated, and fresh desalted water at a temperature of 65°C is used for primary water washing until the end point conductivity is less than 3 mS / cm to obtain a first washing filter cake; 4. Fresh desalted water at a temperature of 60°C is added to the beating tank according to a beating concentration of 10%, and the obtained first washing filter cake is added to the beating tank for uniform dispersion and stirring for 1.5 h to obtain a beating slurry; 5. The beating slurry is added to the reaction kettle, and phosphoric acid is added to adjust the pH to 1.7, and then the temperature is raised at a rate of 0.7°C / min to 90°C. After the color of the slurry becomes white, the temperature is maintained for 1.5 h to obtain an aged slurry; 6. The aged slurry is solid-liquid separated, and fresh desalted water at 65°C is used for secondary water washing for 200 min until the end point conductivity is less than 0.5 mS / cm. The second washing water is collected, and the water collected after 40 min of washing is collected as the second washing post water. The second washing post water is reused in the beating and aging process; 7. The obtained second washing filter cake is flash dried, and the mixed temperature of the flash drying is controlled to 120°C to obtain iron phosphate dihydrate. The iron phosphate dihydrate is calcined at a temperature of 630°C for 3 h to obtain the finished product of iron phosphate.
[0037] Test Example: I. The process parameters for preparing iron phosphate in Examples 1-3 and Comparative Examples 1-4 are shown in Table 1.
[0038] Table 1 Process parameters for preparing iron phosphate in example 1, 2, 3, and comparative examples 1-4
[0039] In examples 1, 2, and 3, the second washing water is reused for the first washing and beating, on the one hand, water resources are utilized, and on the other hand, due to the high temperature of the reused water, the pulp temperature of the beating material is obviously improved, and the trace amount of phosphate in the washing water promotes the crystal transformation of iron phosphate in advance during the beating process, so that the aging crystal transformation whitening time is reduced, the whitening temperature is lowered, and the production cycle is obviously shortened.
[0040] In comparative example 1, desalted water is used for the first washing, and desalted water at room temperature is used for beating, so that the pulp temperature of the beating material is low, and due to the use of desalted water for beating before aging, there is no trace amount of phosphate to promote the crystal transformation of iron phosphate in advance, and the aging crystal transformation whitening time is long. In comparative example 2, the second washing water is used for the first washing, and desalted water at room temperature is used for beating, compared with comparative example 1, due to the presence of trace amount of phosphorus in the second washing water, the crystal transformation whitening time is short, and the whitening temperature is low.
[0041] As can be seen from the data of examples 1, 2, 3, and comparative examples 1-4, the production cycle can be effectively shortened and the production cost can be reduced by using the scheme described in the application to prepare the iron phosphate material.
[0042] II. The SEM images of the finished iron phosphate products in examples 1, 2, 3, and comparative examples 1-4 are shown in Figures 2-8 .
[0043] As can be seen from the SEM images of the finished iron phosphate products in comparative examples 1, 2, 3, and comparative examples 1-4, the particles of the iron phosphate product prepared by the application are more uniform, and the crystallinity is better. During the aging process of iron phosphate, the amorphous form of iron phosphate is transformed into white crystal precipitate of dihydrate iron phosphate, and the trace amount of phosphate ions in the second washing water can participate in the formation of the crystal structure of iron phosphate, providing the necessary material basis for crystal growth; and the heat in the second washing water provides a suitable temperature, providing stable kinetic conditions for the growth of crystal nucleus, which is conducive to the ordered growth of iron phosphate crystals according to certain crystal faces and unit cells, and helps to form more regular and complete crystal particles.
Claims
1. A method for low cost production of iron phosphate characterized in that, The method comprises the following steps: Step S1, preparing an iron phosphate slurry by a precipitation reaction, and performing liquid-solid separation; Step S2, performing first water washing on the separated solid product; Step S3, adding water to the first-washed solid product to make a slurry, aging the slurry, and performing solid-liquid separation on the aged slurry; Step S4, performing second water washing on the separated solid product, collecting the second washing water, and recycling the second washing water to the preparation of the iron phosphate in the subsequent batch; Step S5, drying and calcining the second-washed solid product to obtain the finished product of the iron phosphate.
2. The method of claim 1, wherein the low cost production of iron phosphate is characterized by, The second washing water in step S4 is recycled to the first water washing process and the slurry making process in the preparation of the iron phosphate in the subsequent batch.
3. The method of claim 2, wherein the low cost production of iron phosphate is characterized by, In step S4, the method for collecting the second washing water is to collect the first-stage second washing water and the second-stage second washing water according to the water washing time, the first-stage second washing water is recycled to the first water washing process in the preparation of the iron phosphate in the subsequent batch, and the second-stage second washing water is recycled to the slurry making process in the preparation of the iron phosphate in the subsequent batch.
4. The method of claim 3, wherein the low cost production of iron phosphate is characterized by, In step S4, the total second water washing time is T, the first-stage second water washing time is 0.5T-0.8T, and the remaining time is the second-stage second water washing time.
5. The method of claim 1, wherein the low cost production of iron phosphate is characterized by, The precipitation reaction in step S1 comprises the following steps: Step S1.1, using a weakly acidic phosphate as a raw material to prepare a phosphate solution with a phosphorus content of 1.8%-4.5%; Step S1.2, configuring a ferrous solution with a divalent iron concentration of 50-85 g / L; Step S1.3, adding the ferrous solution and the phosphate solution into a reaction kettle according to a flow ratio of 1:0.7-1.2 at an iron element to phosphorus element molar ratio of 0.8-1.3:1, and the feeding time is 40-80 min; Step S1.4, adding hydrogen peroxide into the mixed solution to perform an oxidation synthesis reaction, the reaction temperature is 50-80℃, and the reaction time is 30-120 min, thereby preparing an iron phosphate slurry with uniform iron phosphate precipitates.
6. The method of claim 5, wherein the low cost production of iron phosphate is characterized by, The method comprises at least one of the following technical features: (1) The phosphate in step S1.1 uses one or more of phosphoric acid, disodium hydrogen phosphate, and sodium dihydrogen phosphate as a phosphorus source; (2) The ferrous solution in step S1.2 is one or both of ferrous sulfate solution and ferrous chloride solution.
7. The method of claim 5 or 6, wherein the method is characterized by, The method comprises at least one of the following technical features: (1) The first water washing in step S2 is performed until the conductivity is less than 2-4 mS / cm; (2) The total second water washing time T in step S4 is 150-250 min; (3) The second water washing in step S4 is performed until the conductivity is less than 0.5 mS / cm.
8. The method of claim 7, wherein the low cost production of iron phosphate is characterized by, In step S4, the second water washing is performed using fresh desalted water at 60-65℃.
9. The method of claim 1, wherein the low cost production of iron phosphate is characterized by, In step S3, the method for adding water to make a slurry and aging is as follows: water is added into a slurry making tank, the first-washed solid product is made into a slurry and homogenized, the homogenized slurry is added into a reaction kettle with a heating device, phosphoric acid is added to adjust the pH value of the slurry to 1.5-1.8, the temperature is raised to 90-95℃ at a temperature raising rate of 0.3-1℃ / min, the slurry color becomes white after the temperature is raised, and the temperature is maintained for 1-2 h to obtain an aged slurry; the slurry concentration is controlled to be 8-20%, and the slurry making time is controlled to be 1-3 h.
10. The method of claim 1, wherein the low cost production of iron phosphate is characterized by, The method comprises at least one of the following technical features: (1) The drying in step S5 is flash drying, and the mixed temperature for flash drying is controlled to be 100-140℃. (2) The calcination temperature in step S5 is 580-720 DEG C, and the calcination time is 2-4h.