A method for the continuous synthesis of iron phosphate

Abstract

The application discloses a method for continuously synthesizing iron phosphate, and relates to the technical field of continuous production of iron phosphate. The method comprises the following steps: preparing a mixed solution of ferrous salt solution, phosphate and hydrogen peroxide; continuously adding the ferrous salt solution into a first-stage reaction kettle in a series reaction kettle, wherein the series reaction kettle comprises at least two reaction kettles which are sequentially connected in series, continuously adding the mixed solution into each-stage reaction kettle in the series reaction kettle, and controlling the molar ratio of P / Fe in each-stage reaction kettle; after the reaction is completed, the slurry is pressure-filtered, the filter cake is washed, water is added to the filter cake to form a slurry, the pH value of the slurry is adjusted by using phosphoric acid, and a first-stage slurry is obtained; the first-stage slurry is continuously fed into two-stage series aging kettles, and a second-stage slurry after aging is obtained; the second-stage slurry is pressure-filtered to obtain a filter cake, and the filter cake is washed; and finally, the filter cake is dried and calcined to obtain anhydrous iron phosphate. The above-mentioned process is stable and reliable, the particle size and specific surface of the iron phosphate product are suitable and have small fluctuation, the Fe / P is stable, the product has good consistency, and the production efficiency is high.

Description

Technical Field

[0001] This invention relates to the field of continuous production technology of ferric phosphate, and specifically to a method for continuous synthesis of ferric phosphate. Background Technology

[0002] With the rapid development of new energy, the demand for lithium iron phosphate cathode materials is increasing. As a precursor of lithium iron phosphate cathode materials, iron phosphate is also in high demand and has increasingly stringent requirements.

[0003] Currently, the production of ferric phosphate in the industry mainly adopts batch processes. For example, CN114477120A discloses a method for preparing ferric phosphate, which involves mixing ferrous sulfate and phosphoric acid, oxidizing with hydrogen peroxide, adjusting the pH with ammonia, carrying out a co-precipitation reaction, and aging at a high temperature to prepare the ferric phosphate precursor. This method cannot achieve continuous production, has low production efficiency, and high energy consumption. CN111348637A discloses another method for preparing ferric phosphate, which similarly involves mixing ferrous sulfate and phosphoric acid, oxidizing with hydrogen peroxide, and adjusting the pH with excess sodium hydroxide to obtain the ferric phosphate product. This method has low capacity and a large amount of washing water. In summary, the batch process for producing ferric phosphate results in low production efficiency, unreliable product stability and uniformity, and high energy consumption.

[0004] To overcome the drawbacks of intermittent production, the ferric phosphate process has gradually evolved towards continuous production. For example, patent CN117263154A discloses a method for the continuous production of ferric phosphate and its application, in which phosphorus source, iron source, and pH adjuster are continuously added to the reactor in a parallel flow, and the material is discharged from the reactor via overflow. However, having all the reactants in one reactor leads to severe backmixing, resulting in a large and uneven particle size range in the slurry. Furthermore, the parallel addition of phosphorus source, iron source, and pH adjuster to the reactor results in uneven and uncontrollable particle size in the product, failing to meet the diverse demands of downstream markets. Patent CN116534824A also describes a continuous oxidation process for preparing ferric phosphate, also using overflow discharge. Hydrogen peroxide is added to multiple overflow tanks, and the amount of hydrogen peroxide added to each overflow tank is controlled to regulate the reaction temperature, thereby controlling the nucleation rate and crystal growth rate. The continuous overflow discharge also has a serious backmixing problem. In addition, the reaction process involves the reaction of monoammonium phosphate and ferrous sulfate to produce ferrous phosphate first, and then oxidize the ferrous phosphate to ferric phosphate. The reaction process is not easy to control. The ferrous phosphate precipitation is incomplete, and when it is oxidized to ferric phosphate, some ammonium ions and other impurity ions will be trapped, which will affect the purity of the product.

[0005] Therefore, there is an urgent need to find a method that can stably control the particle size of iron phosphate products in order to meet the ever-increasing market demand. Summary of the Invention

[0006] The purpose of this invention is to provide a method for the continuous synthesis of ferric phosphate, which solves the problem of poor product consistency caused by the difficulty in controlling the production of ferric phosphate in existing processes.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for continuous synthesis of iron phosphate, characterized by comprising the following steps:

[0008] S1. Prepare ferrous sulfate solution and a mixed solution of phosphate and hydrogen peroxide;

[0009] S2. Ferrous sulfate solution is continuously added to the first stage reactor in a series reactor, which includes at least two reactors connected in series. The mixed solution is continuously added to each stage reactor in the series reactor, and the P / Fe molar ratio in each stage reactor is controlled to be 0.4 to 0.95:1. The slurry in the previous stage reactor is pumped from the bottom of the reactor into the next stage reactor.

[0010] S3. After the reaction is complete, the slurry is filtered, the filter cake is washed, water is added to adjust the slurry, and the pH value is adjusted with phosphoric acid to obtain the first-grade slurry;

[0011] S4. The primary slurry is continuously fed into two aging tanks connected in series. The slurry in the primary aging tank is pumped from the bottom of the tank into the secondary aging tank. The aging temperature and time in the aging tank are controlled to obtain the aged secondary slurry.

[0012] S5. The aged secondary slurry is subjected to pressure filtration to obtain filter cake. The filter cake is washed, and the conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0013] S6. The filter cake is dried at 100-120°C and calcined at 570-590°C to obtain anhydrous ferric phosphate.

[0014] A further technical solution is that the concentration of Fe in the ferrous sulfate solution is 0.90 mol / L to 1.30 mol / L.

[0015] A further technical solution is that the mixed solution is prepared by preparing a phosphate solution with a phosphorus content of 5.4% to 6.3%, adjusting the pH to 6.8 to 7.3 with an alkaline solution, and then adding hydrogen peroxide to make the hydrogen peroxide concentration 3.5% to 4.0%.

[0016] A further technical solution is that the phosphate is one or more of phosphoric acid, diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate; and the alkaline solution is ammonia or sodium hydroxide.

[0017] A further technical solution is that the series-connected reactor consists of two reactors connected in series. The P / Fe molar ratio in the first-stage reactor is 0.4–0.7:1; the P / Fe molar ratio in the second-stage reactor is 0.7–0.95:1; the temperature in the first-stage reactor is controlled at 30°C–45°C; the temperature in the second-stage reactor is controlled at 50°C–55°C; and the residence time of the slurry in each reactor is 40–60 minutes.

[0018] A further technical solution is that the series-connected reactor consists of three reactors connected in series. The P / Fe molar ratio in the first-stage reactor is 0.4–0.6:1; the P / Fe molar ratio in the second-stage reactor is 0.6–0.8:1; and the P / Fe molar ratio in the third-stage reactor is 0.8–0.95:1. The temperature in the first-stage reactor is controlled at 30°C–40°C; the temperature in the second-stage reactor is controlled at 45°C–50°C; and the temperature in the third-stage reactor is controlled at 50°C–55°C. The residence time of the slurry in each reactor is 30–45 minutes.

[0019] The purpose of controlling the phosphorus-to-iron ratio in each stage of the reactor is to control the number of iron phosphate crystal nuclei generated. If the phosphorus-to-iron molar ratio is too high, there are many crystal nuclei, making them difficult to grow, but they are very prone to agglomeration, resulting in larger particle sizes. Conversely, if the phosphorus-to-iron molar ratio is too low, there are fewer crystal nuclei, making them easier to grow, also resulting in larger particle sizes, but requiring a longer time. Both excessively high and low phosphorus-to-iron molar ratios make it difficult to control the consistency of the finished product. Therefore, precise control of the P / Fe molar ratio in each reactor is particularly important to control the final particle size of the finished product.

[0020] A further technical solution is that in step S3, the filter cake is slurried with water to a solid content of 10% to 15%, phosphoric acid is added to control the pH of the slurry to 1.5 to 2.3, the iron-phosphorus ratio of the final product is adjusted, and the crystal form is controlled to age and turn white under these conditions.

[0021] A further technical solution is to control the temperature in each stage of the aging reactor at 90℃~95℃, and control the residence time of the slurry in each stage of the aging reactor at 90min~120min; using aging reactors in series results in higher utilization and higher output, and the obtained slurry particles are more uniform, with better stability and consistency.

[0022] A further technical solution is that the continuous synthesis apparatus for ferric phosphate using the method includes a control system, a ferrous sulfate solution storage tank, and a mixed solution storage tank. The outlet of the ferrous sulfate solution storage tank is connected to the first-stage reactor in a series reactor. The outlet of the mixed solution storage tank is connected to each stage of the series reactor. The bottom outlet of the previous stage reactor in the series reactor is connected to the inlet of the next stage reactor via a pump. The outlet of the last stage reactor in the series reactor is connected in sequence to the first filter press and the slurry preparation tank. The slurry preparation tank is connected in sequence to a two-stage series aging reactor, a second filter press, a dryer, a calcination device, a screening device, a finished product weighing device, a cooling device, and a packaging device. The coarse material outlet of the screening device is connected to the crushing device.

[0023] A further technical solution is that the top of the reactor is equipped with a slurry inlet, a mixed solution inlet, and a drive motor. The output end of the drive motor is connected to the stirring device inside the reactor. Steam pipes are installed in the middle and bottom of the reactor. A temperature sensor is also installed inside the reactor. The temperature sensor, drive motor, and control system are connected to the control system.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] 1. In the continuous synthesis process, the ferrous sulfate iron source solution is continuously fed, while the mixed solution of phosphorus source and hydrogen peroxide enters the reaction system at multiple points. The reaction slurry then continuously flows through each stage of the reactor. Due to the presence of hydrogen peroxide, the iron source solution and phosphorus source solution undergo both metathesis and oxidation reactions. The entire process is exothermic. By controlling the phosphorus-iron molar ratio, reaction temperature, and residence time in each reactor, the nucleation rate and crystal growth rate of ferric hydrogen phosphate can be controlled, thereby obtaining ferric phosphate products with suitable primary particle size. By controlling the feed ratio of the mixed solution in each reactor, the P / Fe molar ratio in each reactor can be controlled, ultimately obtaining products with different particle sizes to meet the needs of different markets. In addition, in each stage of the reactor, the metathesis and oxidation reactions occur simultaneously, avoiding the inclusion of impurity ions during precipitation, resulting in high product purity.

[0026] 2. The above methods and apparatus make it easier to control the temperature and reaction completion of the reactor. The bottom discharge and series connection of the reactor effectively avoid back mixing in the reactor, resulting in a more uniform particle size distribution of the finished product.

[0027] 3. The continuous synthesis process of iron phosphate used in this invention is stable and reliable. The iron phosphate product has suitable particle size and specific surface area with small fluctuations, stable Fe / P ratio, good product consistency, high production efficiency, and the yield of the same volume reactor is increased by more than 3 times, while the production cost is significantly reduced. Attached Figure Description

[0028] Figure 1 This is a process flow diagram of the present invention.

[0029] Figure 2 SEM image of the synthesis of iron phosphate in Example 2 of this invention. Figure 1 .

[0030] Figure 3 SEM image of the synthesis of iron phosphate in Example 2 of this invention. Figure 2 .

[0031] Figure 4 This is the XRD pattern of iron phosphate synthesized in Example 2 of the present invention.

[0032] Figure 5 This is a block diagram illustrating the structural principle of the device of the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0034] Example 1

[0035] The continuous synthesis of iron phosphate was achieved using two reactors connected in series. The specific steps are as follows:

[0036] Prepare ferrous sulfate solution and a mixed solution of phosphate and hydrogen peroxide:

[0037] The Fe concentration in the ferrous sulfate solution was 0.966 mol / L (ferrous sulfate heptahydrate, pH 3.0 ± 0.4); the mixed solution was prepared by preparing a phosphate (monoammonium phosphate) solution with a phosphorus content of 5.52%, adjusting the pH to 7.05 with alkaline solution, and then adding hydrogen peroxide to make the hydrogen peroxide concentration 3.82%.

[0038] Continuous synthesis steps: Ferrous sulfate solution is continuously pumped into the first-stage reactor. A phosphorus source mixture with a P content of 5.52%, pH of 7.05, and hydrogen peroxide content of 3.82% is continuously pumped into the first-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.53:1, the reaction temperature is controlled at 35℃, and the residence time is 40 min.

[0039] After the reaction is completed, the slurry in the first-stage reactor is continuously pumped from the bottom into the second-stage reactor using a pump. At the same time, the phosphorus source mixed solution is continuously added to the second-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.88:1, the reaction temperature is controlled at 45℃, the residence time is 50min, and the synthesized slurry is sent for pressure filtration and washing.

[0040] Filter cake preparation and pH adjustment: The obtained filter cake is prepared with water to form a slurry with a solid content of 12%, and phosphoric acid is added at the same time to adjust the pH of the slurry to 1.85 to obtain the first-grade slurry.

[0041] Continuous aging step: The obtained primary slurry is continuously pumped into the first-stage aging reactor, the reaction temperature is controlled at 90℃ and the residence time is 60min. The slurry in the first-stage aging reactor is continuously pumped from the bottom of the reactor into the second-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min, to obtain the secondary slurry.

[0042] Filtration and washing process: The secondary slurry is subjected to pressure filtration to separate the filter cake, and the filter cake is washed. The conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0043] Drying and calcination process: The washed and qualified filter cake is dried at 110°C and calcined at 580°C to obtain anhydrous ferric phosphate.

[0044] Tests showed that the iron-to-phosphorus ratio was 0.971 and the specific surface concentration was 5.85m. 2 / g, particle size D 10 1.20μm, D 50 2.69μm, D 90 8.78μm, D MAX 29.79 μm, tap density 0.61 g / cm³ 3 .

[0045] Example 2

[0046] The continuous synthesis of iron phosphate was achieved using three reactors connected in series. The specific steps are as follows:

[0047] Prepare ferrous sulfate solution and a mixed solution of phosphate and hydrogen peroxide:

[0048] The Fe concentration in the ferrous sulfate solution was 0.964 mol / L (ferrous sulfate heptahydrate, pH 3.0 ± 0.4); the mixed solution was prepared by preparing a phosphate (diammonium phosphate) solution with a phosphorus content of 6.02%, adjusting the pH to 7.05 with alkaline solution, and then adding hydrogen peroxide to make the hydrogen peroxide concentration 3.88%.

[0049] Continuous synthesis steps: The iron salt solution is continuously pumped into the first-stage reactor, and a mixed solution of phosphorus source with P content of 6.02%, pH of 7.05, and hydrogen peroxide content of 3.88% is continuously pumped into the first-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.44:1, the reaction temperature is controlled at 38℃, and the residence time is 30min.

[0050] After the reaction is completed, the slurry in the first-stage reactor is continuously pumped from the bottom into the second-stage reactor using a pump. At the same time, the phosphorus source mixed solution is continuously added to the second-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.71:1, the reaction temperature is controlled at 48℃, and the residence time is 35min.

[0051] After the reaction is completed, the slurry in the second-stage reactor is continuously pumped from the bottom into the third-stage reactor, while the phosphorus source mixed solution is continuously added to the third-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.85:1, the reaction temperature is controlled at 54℃, the residence time is 40min, and the synthesized slurry is sent for pressure filtration and washing.

[0052] Filter cake preparation and pH adjustment steps: The obtained filter cake is prepared with water to form a slurry with a solid content of 12%, and the pH of the slurry is adjusted to 1.85 with phosphoric acid to obtain the first-grade slurry.

[0053] Continuous aging step: The obtained primary slurry is continuously pumped into the first-stage aging reactor, the reaction temperature is controlled at 92℃ and the residence time is 100min. The slurry in the first-stage aging reactor is continuously pumped from the bottom of the reactor into the second-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min, to obtain the secondary slurry.

[0054] Filtration and washing process: The secondary slurry is subjected to pressure filtration to separate the filter cake, and the filter cake is washed. The conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0055] Drying and calcination process: The washed and qualified filter cake is dried at 110°C and calcined at 580°C to obtain anhydrous ferric phosphate.

[0056] Among them, the iron-to-phosphorus ratio was 0.968, and the specific gravity was 7.56m. 2 / g, particle size D 10 1.13μm, D 50 1.85μm, D 90 4.22μm, D MAX 27.45μm, tap density 0.65g / cm³ 3 Products such as Figure 2-4 As shown, by Figure 4 It can be determined that it is anhydrous ferric phosphate, and the SEM image shows that the product particles are evenly distributed.

[0057] Example 3

[0058] The continuous synthesis of iron phosphate was achieved using three reactors connected in series. The specific steps are as follows:

[0059] Prepare ferrous sulfate solution and a mixed solution of phosphate and hydrogen peroxide:

[0060] The Fe concentration in the ferrous sulfate solution was 1.16 mol / L (ferrous sulfate heptahydrate, pH 3.0 ± 0.4); the mixed solution was prepared by preparing a phosphate solution (a 1:1 mixture of monoammonium phosphate and diammonium phosphate) with a phosphorus content of 5.68%, adjusting the pH to 7.10 with alkali, and then adding hydrogen peroxide to make the hydrogen peroxide concentration 4.06%.

[0061] Continuous synthesis steps: The iron salt solution is continuously pumped into the first-stage reactor, and the phosphorus source mixed solution is continuously pumped into the first-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.53:1, the reaction temperature is controlled at 36℃, and the residence time is 30min.

[0062] After the reaction is completed, the slurry in the first-stage reactor is continuously pumped from the bottom into the second-stage reactor, while the phosphorus source mixed solution is continuously added to the second-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.68:1, the reaction temperature is controlled at 45℃, and the residence time is 35min.

[0063] After the reaction is completed, the slurry in the second-stage reactor is continuously pumped from the bottom of the reactor into the third-stage reactor. At the same time, the phosphorus source mixed solution is continuously added to the third-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.88:1, the reaction temperature is controlled at 50℃, the residence time is controlled at 40min, and the synthesized slurry is sent to the pressure filter for washing.

[0064] Filter cake preparation and pH adjustment steps: The obtained filter cake is prepared with water to form a slurry with a solid content of 12%, and the pH of the slurry is adjusted to 1.85 with phosphoric acid to obtain the first-grade slurry.

[0065] Continuous aging step: The obtained primary slurry is continuously pumped into the first-stage aging reactor, the reaction temperature is controlled at 90℃ and the residence time is 120min. The slurry in the first-stage aging reactor is continuously pumped from the bottom of the reactor into the second-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min, to obtain the secondary slurry.

[0066] Filtration and washing process: The secondary slurry is subjected to pressure filtration to separate the filter cake, and the filter cake is washed. The conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0067] Drying and calcination process: The washed and qualified filter cake is dried at 110°C and calcined at 580°C to obtain anhydrous ferric phosphate.

[0068] Among them, the iron-to-phosphorus ratio is 0.965, and the specific gravity is 8.80m. 2 / g, particle size D 10 1.32μm, D 50 1.77μm, D 90 5.43μm, D MAX28.23μm, tapped density 0.62g / cm 3 .

[0069] Example 4

[0070] The continuous synthesis of iron phosphate was achieved using three reactors connected in series. The specific steps are as follows:

[0071] Prepare ferrous sulfate solution and a mixed solution of phosphate and hydrogen peroxide:

[0072] The Fe concentration in the ferrous sulfate solution was 1.02 mol / L (ferrous sulfate heptahydrate, pH 3.0 ± 0.4); the mixed solution was prepared by preparing a phosphate solution (a 1:1 mixture of monoammonium phosphate and diammonium phosphate) with a phosphorus content of 5.80%, adjusting the pH to 7.10 with alkali, and then adding hydrogen peroxide to make the hydrogen peroxide concentration 3.95%.

[0073] Continuous synthesis steps: The iron salt solution is continuously pumped into the first-stage reactor, and the phosphorus source mixed solution is continuously pumped into the first-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.62:1, the reaction temperature is controlled at 38℃, and the residence time is 30min.

[0074] After the reaction is completed, the slurry in the first-stage reactor is continuously pumped from the bottom into the second-stage reactor, while the phosphorus source mixed solution is continuously added to the second-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.66:1, the reaction temperature is controlled at 48℃, and the residence time is 35min.

[0075] After the reaction is completed, the slurry in the second-stage reactor is continuously pumped from the bottom of the reactor into the third-stage reactor. At the same time, the phosphorus source mixed solution is continuously added to the third-stage reactor. The P / Fe molar ratio of the slurry in the reactor is controlled at 0.88:1, the reaction temperature is controlled at 54℃, the residence time is controlled at 40min, and the synthesized slurry is sent to pressure filter for washing.

[0076] Filter cake preparation and pH adjustment steps: The obtained filter cake is prepared with water to form a slurry with a solid content of 12%, and the pH of the slurry is adjusted to 1.85 with phosphoric acid to obtain the first-grade slurry.

[0077] Continuous aging step: The obtained primary slurry is continuously pumped into the first-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min. The slurry in the first-stage aging reactor is continuously pumped from the bottom of the reactor into the second-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min, to obtain the secondary slurry.

[0078] Filtration and washing process: The secondary slurry is subjected to pressure filtration to separate the filter cake, and the filter cake is washed. The conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0079] Drying and calcination process: The washed and qualified filter cake is dried at 110°C and calcined at 580°C to obtain anhydrous ferric phosphate.

[0080] Among them, the iron-to-phosphorus ratio is 0.966, and the specific gravity is 7.80m. 2 / g, particle size D 10 1.19μm, D 50 2.23μm, D 90 5.18μm, D MAX 20.23μm, tapped 0.70g / cm 3 .

[0081] Comparative Example 1

[0082] Ferric phosphate is prepared using a single reactor and a single-point feeding of a mixed solution.

[0083] Continuous synthesis steps: A solution of iron salt (ferrous sulfate heptahydrate, pH 3.0±0.4) with a Fe concentration of 1.02 mol / L was continuously pumped into the reactor. A mixed solution of phosphorus source with a P content of 5.80%, a pH of 7.10, and a hydrogen peroxide content of 3.95% was also continuously pumped into the reactor to maintain a P / Fe molar ratio of 0.88:1 in the slurry. The reaction temperature was controlled at 50℃ and the residence time was 60 min. After the reaction was completed, the synthesized slurry was sent for pressure filtration and washing.

[0084] Filter cake preparation and pH adjustment steps: The filter cake obtained from the synthesis process is prepared into a slurry with a solid content of 12% by water, and the pH of the slurry is adjusted to 1.85 by phosphoric acid to obtain the first-grade slurry.

[0085] Continuous aging step: The obtained primary slurry is continuously pumped into the aging vessel, the reaction temperature is controlled at 95℃, and the residence time is 90min to obtain the secondary slurry.

[0086] Filtration and washing process: The secondary slurry is subjected to pressure filtration to separate the filter cake and mother liquor. The filter cake is washed, and the conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0087] Drying and calcination process: The washed and qualified filter cake is dried at 110℃ and calcined at 580℃ to obtain anhydrous ferric phosphate with an iron-to-phosphorus ratio of 0.971 and a specific surface area of ​​3.29m. 2 / g, particle size D 10 1.43μm, D 50 4.68μm, D 90 26.10μm, D MAX 30.98μm, tapped 0.98g / cm 3 The product's specific gravity is significantly lower than the industry standard requirement (the industry standard requires a specific gravity of 4m). 2 / g or more).

[0088] Comparative Example 2

[0089] Three reactors connected in series were used. The pH-adjusted phosphate salt solution and iron source solution were continuously fed from the first-stage reactor, and hydrogen peroxide was continuously injected into each reactor. The P / Fe molar ratio of the slurry in the first-stage reactor, the second-stage reactor, and the third-stage reactor was maintained at 0.95:1.

[0090] Continuous synthesis steps: A 1.02 mol / L iron salt solution, a 5.80% P solution, a pH 7.10 phosphate salt solution, and a 27.5% hydrogen peroxide solution are continuously pumped into the first-stage synthesis reactor. The reaction temperature in the first-stage reactor is controlled at 38°C, and the slurry residence time is 30 min. The slurry from the first-stage reactor is then pumped into the second-stage synthesis reactor, while the hydrogen peroxide solution is continuously pumped into the second-stage reactor. The reaction temperature in the second-stage reactor is controlled at 48°C, and the residence time is 35 min. The slurry from the second-stage reactor is then pumped into the third-stage synthesis reactor, while the hydrogen peroxide solution is continuously pumped into the third-stage reactor. The reaction temperature in the third-stage reactor is controlled at 54°C, and the residence time is 40 min. The synthesized slurry is then sent for pressure filtration and washing.

[0091] Filter cake preparation and pH adjustment steps: The filter cake obtained from the synthesis process is prepared into a slurry with a solid content of 12% using pure water, and the pH of the slurry is adjusted to 1.85 using phosphoric acid to obtain the first-grade slurry.

[0092] Continuous aging step: The obtained primary slurry is continuously pumped into the first-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min. The slurry in the first-stage aging reactor is continuously pumped into the second-stage aging reactor, the reaction temperature is controlled at 95℃ and the residence time is 60min, to obtain the secondary slurry.

[0093] Filtration and washing process: The secondary slurry is subjected to pressure filtration to separate the filter cake and mother liquor. The filter cake is washed, and the conductivity of the final washing liquid is controlled to be below 2500 μs / cm.

[0094] Drying and calcination process: The washed and qualified filter cake is dried at 110°C and calcined at 580°C to obtain anhydrous ferric phosphate.

[0095] Among them, the iron-to-phosphorus ratio was 0.964, and the specific gravity was 3.68m. 2 / g, particle size D 10 1.34μm, D 50 3.88μm, D 90 20.18μm, D MAX 37.54μm, tapped density 0.86g / cm 3 .

[0096] Comparative Example 2 only added hydrogen peroxide at multiple points, but did not add phosphorus source at multiple points. As can be seen from the finished product, its ratio is still below the industry standard requirements. Therefore, it can be seen that this method does not improve the particle size of the synthetic slurry.

[0097] Example 5

[0098] Figure 5 An apparatus for the continuous synthesis of ferric phosphate is shown, comprising a control system, a ferrous salt solution storage tank, and a mixed solution storage tank. The outlet of the ferrous salt solution storage tank is connected to the first-stage reactor in a series reactor configuration. The outlet of the mixed solution storage tank is connected to each stage of the series reactor configuration. The bottom outlet of the previous stage reactor in the series reactor configuration is connected to the inlet of the next stage reactor via a pump. The outlet of the last stage reactor in the series reactor configuration is sequentially connected to a first filter press and a slurry preparation tank. The slurry preparation tank is sequentially connected to a two-stage series aging reactor, a second filter press, a dryer, a calcination device, a screening device, a finished product weighing device, a cooling device, and a packaging device. The coarse material outlet of the screening device is connected to a crushing device.

[0099] The series-connected reactor can consist of two or more reactors connected in series. Each reactor is equipped with a slurry inlet, a mixed solution inlet, and a drive motor at the top. The output of the drive motor is connected to a stirring device inside the reactor. Steam pipes are installed in the middle and bottom of the reactor. A temperature sensor is also installed inside the reactor, and the temperature sensor, drive motor, and control system are connected via signal connections. The slurry inlet is used for feeding iron source solution or slurry from the previous reactor.

[0100] Although the invention has been described herein with reference to several illustrative embodiments, it should be understood that many other modifications and implementations can be devised by those skilled in the art, which will fall within the scope and spirit of the principles disclosed herein. More specifically, various modifications and improvements can be made to the components or layouts within the scope of the disclosure, drawings, and claims. Besides modifications and improvements to the components or layouts, other uses will be apparent to those skilled in the art.

Claims

1. A method for continuous synthesis of iron phosphate, characterized in that... Includes the following steps: S1. Prepare ferrous salt solution and prepare a mixed solution of phosphate and hydrogen peroxide; S2. A ferrous salt solution is continuously added to the first stage reactor in a series-connected reactor system, which includes at least two reactors connected in series. The mixed solution is continuously added to each stage reactor in the series-connected reactor system. The P / Fe molar ratio in the first stage reactor is 0.4–0.7:1; the P / Fe molar ratio in the second stage reactor is 0.6–0.95:1; the temperature in the first stage reactor is controlled at 30℃–45℃; the temperature in the second stage reactor is controlled at 45℃–55℃; the residence time of the slurry in each stage reactor is 30–60 min; and the slurry in the previous stage reactor is pumped from the bottom of the previous stage reactor into the next stage reactor. S3. After the reaction is complete, the slurry is filtered, the filter cake is washed, water is added to adjust the slurry, and the pH value is adjusted with phosphoric acid to obtain the first-grade slurry; S4. The primary slurry is continuously fed into two aging tanks connected in series. The slurry in the primary aging tank is pumped from the bottom of the tank into the secondary aging tank. The aging temperature and time in the aging tank are controlled to obtain the aged secondary slurry. S5. The aged secondary slurry is subjected to pressure filtration to obtain filter cake. The filter cake is washed, and the conductivity of the final washing liquid is controlled to be below 2500 μs / cm. S6. The filter cake is dried at 100-120℃ and calcined at 570-590℃ to obtain anhydrous ferric phosphate; The apparatus used in the continuous synthesis of ferric phosphate in the method includes a control system, a ferrous salt solution storage tank, and a mixed solution storage tank. The outlet of the ferrous salt solution storage tank is connected to the first-stage reactor in a series reactor, and the outlet of the mixed solution storage tank is connected to each stage of the series reactor. The bottom outlet of the upper-stage reactor in the series reactor is connected to the inlet of the lower-stage reactor via a pump. The outlet of the last-stage reactor in the series reactor is connected in sequence to the first filter press and the slurry preparation tank. The slurry preparation tank is connected in sequence to a two-stage series aging reactor, a second filter press, a dryer, a calcination device, a screening device, a finished product weighing scale, a cooling device, and a packaging device. The coarse material outlet of the screening device is connected to the crushing device.

2. The method for continuous synthesis of iron phosphate according to claim 1, characterized in that: The concentration of Fe in the ferrous salt solution is 0.90 mol / L to 1.30 mol / L.

3. The method for continuous synthesis of iron phosphate according to claim 1, characterized in that: The mixed solution is prepared by preparing a phosphate solution with a phosphorus content of 5.4% to 6.3%, adjusting the pH to 6.8 to 7.3 with an alkaline solution, and then adding hydrogen peroxide to make the hydrogen peroxide concentration 3.5% to 4.0%.

4. The method for continuous synthesis of iron phosphate according to claim 3, characterized in that: The phosphate is one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium phosphate; the alkaline solution is ammonia or sodium hydroxide.

5. The method for continuous synthesis of iron phosphate according to claim 1, characterized in that: The series-connected reactor consists of three reactors connected in series. The P / Fe molar ratio in the third-stage synthesis reactor is 0.8–0.95:

1. The temperature in the first-stage synthesis reactor is controlled at 30°C–40°C. The temperature in the second-stage synthesis reactor is controlled at 45°C–50°C. The temperature in the third-stage synthesis reactor is controlled at 50°C–55°C. The residence time of the slurry in each reactor is 30–45 minutes.

6. The method for continuous synthesis of iron phosphate according to claim 1, characterized in that: In step S3, the filter cake is mixed with water to a solid content of 10% to 15%, and phosphoric acid is added to control the pH of the slurry to 1.5 to 2.

3.

7. The method for continuous synthesis of iron phosphate according to claim 1, characterized in that: The temperature in each aging reactor is controlled at 90℃~95℃, and the residence time of the slurry in each aging reactor is controlled at 90 min~120 min.

8. The method for continuous synthesis of iron phosphate according to claim 1, characterized in that: The reactor is equipped with a slurry inlet, a mixed solution inlet, and a drive motor at the top. The output of the drive motor is connected to the stirring device inside the reactor. Steam pipes are installed in the middle and bottom of the reactor. A temperature sensor is also installed inside the reactor. The temperature sensor, drive motor, and control system are connected to the control system.

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