Preparation method of high-tap-density iron phosphate

Abstract

The invention provides a preparation method of high-tap-density iron phosphate, which comprises the following steps: S1, carrying out precipitation reaction by using a ferrous sulfate solution as a precipitation reaction kettle bottom solution, carrying out primary filter pressing and washing on obtained precipitation slurry, recovering iron phosphate particles subjected to penetrating filtration, and returning the iron phosphate particles as precipitation seed crystals to the precipitation reaction kettle bottom solution; step S2, pulping the primary washing filter cake to obtain pulping slurry, aging to obtain aged slurry, carrying out secondary filter pressing and washing on the aged slurry, recycling iron phosphate particles subjected to penetrating filtration, and returning the iron phosphate particles to the pulping slurry as aging seed crystals; and S3, drying, calcining and crushing the secondarily washed filter cake to obtain the anhydrous iron phosphate. According to the method, the iron phosphate material lost by penetration filtration in the iron phosphate preparation process is recycled and is added into the reaction kettle as seed crystals for precipitation and aging reaction, and the prepared iron phosphate is relatively large in primary particle size and wide in particle size distribution, so that the iron phosphate with high tap density is prepared by taking the iron phosphate material as a raw material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of new energy battery materials, in particular to a preparation method of high-tap-density iron phosphate. BACKGROUND

[0002] As a key precursor of lithium iron phosphate, a positive electrode material of lithium ion batteries, the physical properties of iron phosphate, such as primary particle morphology, size and particle size distribution, have a decisive influence on the performance of the final lithium iron phosphate. The tap density is an important indicator to measure the compaction performance of iron phosphate powder, which directly affects the tap density of the lithium iron phosphate positive electrode sheet, and further affects the energy density, rate performance and cycle life of the battery. Studies have shown that the larger the primary particle size of iron phosphate and the wider the particle size distribution, the higher the tap density, so that a more tightly packed positive electrode material structure can be formed during the subsequent sintering of lithium iron phosphate, thereby improving the compaction density of the electrode sheet. The lithium iron phosphate electrode with high tap density can reduce the proportion of non-active substances such as conductive agents and binders, increase the active material loading, and ultimately optimize the volume energy density and power output of the battery.

[0003] At present, the main method for preparing iron phosphate in industry is co-precipitation, which is easy to produce a large number of fine particles due to spontaneous nucleation, resulting in low tap density of iron phosphate and affecting the compaction performance of subsequent lithium iron phosphate. In addition, during the production of iron phosphate, when the filter cake layer is not formed on the filter cloth of the plate and frame filter press during the pressure filtration and washing of the iron phosphate slurry, the small particle size portion of the slurry will have a phenomenon of filter penetration, resulting in an increase in the solid content of the filtrate, which reduces the yield of iron phosphate; at the same time, when the filtrate is treated as waste water, the presence of iron phosphate solids increases the difficulty of water treatment.

[0004] In view of the above-mentioned defects in the industrial production of iron phosphate, the present application is proposed. SUMMARY

[0005] The present application aims to overcome the shortcomings of the prior art and provide a preparation method of high-tap-density iron phosphate. Based on the seed-induced iron phosphate particle control technology, the lost iron phosphate microcrystals in the filter penetration are recovered as seeds to effectively increase the primary particle size of iron phosphate and widen the particle size distribution. The conversion of waste microcrystals into functional seeds not only solves the particle control problem of traditional processes, but also realizes efficient resource utilization, providing a low-cost and high-benefit solution for the industrial production of high-performance iron phosphate.

[0006] In order to achieve the above-mentioned purposes of the present application, the following technical solutions are adopted: A preparation method of high-tap-density iron phosphate, comprising the following steps: Step S1, the ferrous sulfate solution is used as the bottom liquid A of the precipitation reactor, mixed with the phosphate and the oxidizing agent to carry out the precipitation reaction, to obtain the precipitation slurry B for the first pressure filtration and washing, and the filtered iron phosphate particles are recovered and returned to the bottom liquid A of the precipitation reactor as the precipitation seed; Step S2, the first washing filter cake C is slurried to obtain the slurry G, and the aged slurry H is obtained after aging, for the second pressure filtration and washing, and the filtered iron phosphate particles are recovered and returned to the slurry G as the aging seed; Step S3, the second washing filter cake I is dried, calcined and crushed to obtain the anhydrous iron phosphate.

[0007] Further, in step S1, the first washing filtrate D and the first washing water E are respectively filtered through the microporous filter, back-flushed to obtain the dilute precipitation slurry F, and the dilute precipitation slurry F is returned to the bottom liquid A of the precipitation reactor as the precipitation seed.

[0008] Further, in step S2, the second washing filtrate J and the second washing water K are respectively filtered through the microporous filter, back-flushed to obtain the dilute aging slurry L, and the dilute aging slurry L is returned to the slurry G as the aging seed.

[0009] Further, in step S1, the water washing in the first pressure filtration and washing is to the conductivity < 1500 μs / cm to obtain the first washing water E, and in step S2, the water washing in the second pressure filtration and washing is to the conductivity < 500 μs / cm to obtain the second washing water K.

[0010] Further, in step S1, the filtration precision of the microporous filter membrane entered by the first washing filtrate D and the first washing water E is 0.5-1 µm, and in step S2, the filtration precision of the microporous filter membrane entered by the second washing filtrate J and the second washing water K is 0.5-1 µm.

[0011] Further, in step S1, the concentration of the dilute precipitation slurry F is 0.01-0.4 wt%, and in step S2, the concentration of the dilute aging slurry L is 0.01-0.4 wt%.

[0012] Further, in step S1, the addition proportion of the precipitation seed is 1%-5% of the theoretical output mass of iron phosphate, and in step S2, the addition proportion of the aging seed is 1%-5% of the theoretical output mass of iron phosphate.

[0013] Further, in step S1, the pH of the ferrous sulfate solution is 2.0-2.2, the iron content C (Fe 2+ ) = 50-60 g / L, the precipitation reaction time is 0.5-2.5 h, and the reaction temperature is 45-70 ℃.

[0014] Further, in step S2, the acid added in the aging reaction is 85 wt% phosphoric acid, the aging reaction time is 1-3 h, and the aging temperature is 90-100 ℃.

[0015] Compared with the prior art, the present application has the following advantages: 1. The preparation method of high tap density iron phosphate in the present application recycles the iron phosphate microcrystalline particles lost during the filtration and washing process, and the recycled iron phosphate particles have the same crystal structure as the target product, which can be used as ideal seeds to promote the heterogeneous nucleation and directional growth of iron phosphate particles, effectively increase the size of the primary particles of iron phosphate, reduce the generation of small particles caused by spontaneous nucleation, broaden the particle size distribution, thereby increasing the tap density of iron phosphate material, and obtaining iron phosphate finished product with tap density ≥1.05 g / cm 3 ; On the other hand, when the obtained seeds are used to further grow iron phosphate material, they provide growth sites for iron phosphate, which can greatly accelerate the reaction rate and reduce energy consumption.

[0016] 2. The present application effectively improves the overall yield of iron phosphate, reduces raw material waste, and reduces the comprehensive production cost by recycling the iron phosphate particles lost during the first filtration and washing and the second plate and frame filtration and washing, and the process is compatible with existing industrial equipment and easy to promote.

[0017] 3. After recycling the filtration solids in the iron phosphate mother liquor and washing water, the suspended solids content of the wastewater is effectively reduced, the subsequent sewage treatment load is greatly reduced, and green production is realized. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or prior art description. Obviously, the drawings described below are some embodiments of the present application, and those skilled in the art can also obtain other drawings according to these drawings without creative labor.

[0019] Figure 1 It is a process route diagram of the preparation method of high tap density iron phosphate in the present application. Figure 2 It is a particle size distribution diagram of the precipitation slurry of Example 1 and Comparative Example 1 of the present application. Figure 3 It is a particle size distribution diagram of the precipitation slurry of Example 2 and Comparative Example 2 of the present application. Figure 4 It is a particle size distribution diagram of the precipitation slurry of Example 3 and Comparative Example 3 of the present application. Figure 5 It is a particle size distribution diagram of the aging slurry of Example 1 and Comparative Example 1 of the present application. Figure 6 It is a particle size distribution diagram of the aging slurry of Example 2 and Comparative Example 2 of the present application. Figure 7Particle size distribution graph of the aged slurry of Example 3 and Comparative Example 3 of the present application; Figure 8 Particle size distribution graph of the anhydrous iron phosphate product of Example 1 and Comparative Example 1 of the present application; Figure 9 Particle size distribution graph of the anhydrous iron phosphate product of Example 2 and Comparative Example 2 of the present application; Figure 10 Particle size distribution graph of the anhydrous iron phosphate product of Example 3 and Comparative Example 3 of the present application. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described clearly and completely 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, rather than 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 of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application. The specific conditions are not specified in the embodiments, and are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not specified by the manufacturer, and are all conventional products that can be purchased on the market.

[0021] A preparation method of high tap density iron phosphate, comprising the following steps: In step S1, a ferrous sulfate solution is used as a bottom liquid A of a precipitation reactor, a phosphate is mixed with an oxidizing agent, and then is added to the ferrous sulfate solution for a precipitation reaction to obtain a precipitation slurry B. The precipitation slurry B is subjected to primary pressure filtration and washing to obtain a primary filter cake C, a primary filtrate D, a primary washing water E, and the iron phosphate particles filtered in the primary pressure filtration and washing are recovered and returned to the bottom liquid A of the precipitation reactor as precipitation seeds. The lost iron phosphate material in the primary plate and frame pressure filtration and washing process during the preparation of the iron phosphate is recovered as the precipitation seeds and is added to the reactor. Most of the iron phosphate continues to grow on the basis of the seeds during the synthesis, and a part of the iron phosphate also nucleates. After the reaction is completed, the primary particles of the prepared iron phosphate are large, and the particle size distribution is wide. The high tap density iron phosphate is prepared by using the above material as the raw material. Preferably, the precipitation slurry B is subjected to solid-liquid separation by using a plate and frame pressure filtration to obtain the primary filter cake C and the primary filtrate D, and the water washing is continued until the conductivity is less than 1500 μs / cm. The obtained washing water is the primary washing water E. Preferably, the primary filtrate D and the primary washing water E are respectively filtered by a microporous filter, and backwashing is performed to obtain a precipitation dilute slurry F. The precipitation dilute slurry F is returned to the bottom liquid A of the precipitation reactor as the precipitation seeds. Preferably, the precipitation dilute slurry F is collected in a beating tank as the precipitation seeds, and the filtrate filtered by the microporous filter is subjected to sewage treatment. Preferably, the microfiltration filter membrane filtration precision is 0.5-1 µm; Preferably, the concentration of the precipitated dilute slurry F is 0.01-0.4 wt%; Preferably, the proportion of the precipitated seed crystal is 1%-5% of the theoretical output of the mass of the iron phosphate; Preferably, the raw material of the ferrous sulfate solution is a titanium white powder by-product, preferably a ferrous sulfate solution obtained by removing impurities and purifying a titanium white powder by-product rutile mother liquor; Preferably, the pH of the ferrous sulfate solution is 2.0-2.2, and the iron content C(Fe 2+ )=50-60 g / L; Preferably, the phosphorus source used in the precipitation reaction of the phosphate is phosphoric acid, and the phosphate solution is prepared by mixing the phosphoric acid with liquid alkali and desalted water, the pH of the phosphate solution is controlled to be 7.0, and the phosphate solution is mixed with an oxidizing agent; Preferably, the oxidizing agent is hydrogen peroxide; Preferably, the precipitation reaction time is 0.5-2.5 h, and the reaction temperature is 45-70 °C; Step S2, the obtained first washing filter cake C is slurried with water to obtain a slurry G, and the slurry H is obtained after aging, the aged slurry H is subjected to secondary pressure filtration and washing to obtain a second washing filter cake I, a second washing filtrate J, a second washing water K, and the ferrous phosphate particles filtered in the secondary pressure filtration and washing are recovered and returned to the slurry G as aging seed crystals; Preferably, the secondary pressure filtration uses a plate and frame filter to separate the solid and liquid, to obtain the second washing filter cake I and the second washing filtrate J, and the water washing is continued until the conductivity is <500 µs / cm, and the obtained washing water is the second washing water K; Preferably, the second washing filtrate J and the second washing water K are respectively filtered through a microfiltration filter, backwashing to obtain an aged dilute slurry L, and the aged dilute slurry L is returned to the slurry G as the aging seed crystal; Preferably, the aged dilute slurry L is collected in a slurry tank as the aging seed crystal, and the filtrate filtered through the microfiltration filter is subjected to sewage treatment; Preferably, the microfiltration filter membrane filtration precision is 0.5-1 µm; Preferably, the concentration of the aged dilute slurry L is 0.01-0.4 wt%; Preferably, the proportion of the aging seed crystal is 1%-5% of the theoretical output of the mass of the iron phosphate; Preferably, the acid added in the aging reaction is 85 wt% phosphoric acid, the aging reaction time is 1-3 h, and the aging temperature is 90-100 °C; Step S3, the second washing filter cake I is dried, calcined, and pulverized to obtain anhydrous iron phosphate; Preferably, the drying method is flash drying.

[0022] Example 1 A preparation method of high tap density iron phosphate, comprising the following steps: Step S1, after the impurity removal and purification of the titanium dioxide by-product rutile mother liquor, a ferrous sulfate solution is obtained, which is put into a precipitation reactor as a bottom liquid A for use, the pH of the ferrous sulfate solution is controlled to be 2.0, the iron content C(Fe 2+ ) is 50 g / L; 85% phosphoric acid, 32% liquid alkali and desalted water are mixed to prepare a phosphate solution, the pH of the phosphate solution is controlled to be 7.0, the molar ratio of iron element, phosphorus element and hydrogen peroxide is 1:1:0.75, the phosphate solution and hydrogen peroxide are mixed and then added to the ferrous sulfate solution for a synthesis reaction, the reaction temperature is controlled to be 50°C, the reaction time is 2h, after the reaction is completed, a precipitation slurry B is obtained; the precipitation slurry B is subjected to solid-liquid separation by plate and frame filter pressing to obtain a first washing filter cake C and a first washing filtrate D, and then water washing is continued until the conductivity is less than 1500 μs / cm, the obtained washing water is a first washing washing water E; The first washing filter cake C and the first washing washing water E are respectively filtered by a microporous filter, the filter membrane of the microporous filter has a filtering precision of 0.5 μm, and the filtration and backwashing obtain a precipitation dilute slurry F which is collected in a beating-up tank as a precipitation crystal seed, the concentration of the precipitation dilute slurry F is 0.05wt%, and the obtained filtrate is subjected to sewage treatment; the obtained precipitation crystal seed is returned to the precipitation reactor bottom liquid A and mixed with the ferrous sulfate solution according to 1% of the mass of the theoretical output of iron phosphate; Step S2, the first washing filter cake C is added with water for beating-up to obtain a beating-up slurry G, 85wt% phosphoric acid is added for aging reaction, the aging temperature is 90°C, the aging time is 1.5h, and the obtained slurry is an aging slurry H; the aging slurry H is subjected to solid-liquid separation by plate and frame filter pressing to obtain a second washing filter cake I and a second washing filtrate J, and then water washing is continued until the conductivity is less than 500 μs / cm, the obtained washing water is a second washing washing water K; The second washing filter cake I and the second washing washing water K are respectively filtered by a microporous filter, the filter membrane of the microporous filter has a filtering precision of 0.5 μm, and the filtration and backwashing obtain an aging dilute slurry L which is collected in a beating-up tank as an aging crystal seed, the concentration of the aging dilute slurry L is 0.10wt%, and the obtained filtrate is subjected to sewage treatment; the obtained aging crystal seed is mixed with the beating-up slurry G according to 2% of the mass of the theoretical output of iron phosphate; Step S3, the second washing filter cake I is subjected to flash drying, calcination and crushing to obtain anhydrous iron phosphate product.

[0023] Example 2 A preparation method of high tap density iron phosphate, comprising the following steps: Step S1, after the impurity removal and purification of the titanium dioxide by-product rutile mother liquor, a ferrous sulfate solution is obtained, which is put into a precipitation reactor as a bottom liquid A for use, the pH of the ferrous sulfate solution is controlled to be 2.1, the iron content C(Fe2+ ) = 55 g / L; 85% phosphoric acid is mixed with 32% liquid alkali and desalted water to prepare a phosphate solution, the pH of the phosphate solution is controlled at 7.0, the molar ratio of iron element, phosphorus element and hydrogen peroxide is 1:1:0.75, the phosphate solution is mixed with hydrogen peroxide and then added to the ferrous sulfate solution for synthesis reaction, the reaction temperature is controlled at 45°C, the reaction time is 1.5 h, after the reaction is completed, a precipitate slurry B is obtained; the precipitate slurry B is subjected to solid-liquid separation by plate and frame filter pressing to obtain a first washing filter cake C and a first washing filtrate D, and water washing is continued until the conductivity is <1500 μs / cm, and the obtained washing water is a first washing washing water E; The first washing filter cake D and the first washing washing water E are respectively filtered by a microporous filter, the filter membrane of the microporous filter has a filtering precision of 1 μm, and the filtration and backwashing obtain a precipitate dilute slurry F which is collected in a beating-up tank as a precipitate crystal seed, the concentration of the precipitate dilute slurry F is 0.2 wt%, and the obtained filtrate is subjected to sewage treatment; the obtained precipitate crystal seed is returned to the precipitate reaction kettle bottom liquid A and mixed with the ferrous sulfate solution according to 3% of the mass of the theoretical output of iron phosphate; Step S2, the first washing filter cake C is added with water for beating-up to obtain a beating-up slurry G, 85 wt% phosphoric acid is added for aging reaction, the aging temperature is 95°C, the aging time is 3 h, and the obtained slurry is an aging slurry H; the aging slurry H is subjected to solid-liquid separation by plate and frame filter pressing to obtain a second washing filter cake I and a second washing filtrate J, and water washing is continued until the conductivity is <500 μs / cm, and the obtained washing water is a second washing washing water K; The second washing filtrate J and the second washing washing water K are respectively filtered by a microporous filter, the filter membrane of the microporous filter has a filtering precision of 1 μm, and the filtration and backwashing obtain an aging dilute slurry L which is collected in a beating-up tank as an aging crystal seed, the concentration of the aging dilute slurry L is 0.2 wt%, and the obtained filtrate is subjected to sewage treatment; the obtained aging crystal seed is mixed with the beating-up slurry G according to 1% of the mass of the theoretical output of iron phosphate; Step S3, the second washing filter cake I is subjected to flash drying, calcination and crushing to obtain anhydrous iron phosphate products.

[0024] Example 3 A preparation method of high-tamping iron phosphate, comprising the following steps: Step S1, a ferrous sulfate solution is obtained after the titanium dioxide by-product rutile mother liquor is impurity-removed and purified, and is placed in a precipitate reaction kettle as a precipitate reaction kettle bottom liquid A for use, the pH of the ferrous sulfate solution is controlled at 2.2, the iron content C (Fe 2+) = 60 g / L; 85% phosphoric acid is mixed with 32% liquid alkali and desalted water to prepare a phosphate solution, the pH of the phosphate solution is controlled to be 7.0, the molar ratio of iron element, phosphorus element and hydrogen peroxide is 1:1:0.75, the phosphate solution is mixed with hydrogen peroxide, and then added to the ferrous sulfate solution for synthesis reaction, the reaction temperature is controlled to be 60°C, the reaction time is 0.5 h, after the reaction is completed, a precipitate slurry B is obtained; the precipitate slurry B is subjected to solid-liquid separation by plate and frame filter pressing to obtain a first washing filter cake C and a first washing filtrate D, and then water washing is continued until the conductivity is <1500 μs / cm, and the washing water obtained is a first washing water E; The first washing filtrate D and the first washing water E are respectively filtered by a micropore filter, the filter membrane of the micropore filter has a filtering precision of 1 μm, and the filtration and backwashing obtain a precipitate dilute slurry F which is collected in a beating tank as a precipitate crystal seed, the concentration of the precipitate dilute slurry F is 0.4 wt%, and the obtained filtrate is subjected to sewage treatment; the obtained precipitate crystal seed is returned to the precipitate reaction kettle bottom liquid A and mixed with the ferrous sulfate solution according to 5% of the mass of the theoretical output of iron phosphate. Step S2, the first washing filter cake C is added with water for beating to obtain a beating slurry G, 85 wt% phosphoric acid is added for aging reaction, the aging temperature is 100°C, the aging time is 1 h, and the obtained slurry is an aging slurry H; the aging slurry H is subjected to solid-liquid separation by plate and frame filter pressing to obtain a second washing filter cake I and a second washing filtrate J, and then water washing is continued until the conductivity is <500 μs / cm, and the washing water obtained is a second washing water K; The second washing filtrate J and the second washing water K are respectively filtered by a micropore filter, the filter membrane of the micropore filter has a filtering precision of 1 μm, and the filtration and backwashing obtain an aging dilute slurry L which is collected in a beating tank as an aging crystal seed, the concentration of the aging dilute slurry L is 0.4 wt%, and the obtained filtrate is subjected to sewage treatment; the obtained aging crystal seed is mixed with the beating slurry G according to 5% of the mass of the theoretical output of iron phosphate. Step S3, the second washing filter cake I is subjected to flash drying, calcination and crushing to obtain anhydrous iron phosphate products.

[0025] Comparative Example 1 The preparation method of the iron phosphate in the present comparative example comprises the following steps: Step S1, a titanium white powder by-product rutile mother liquor is purified by removing impurities to obtain a ferrous sulfate solution which is placed in a precipitate reaction kettle as a precipitate reaction kettle bottom liquid A for use, the pH of the ferrous sulfate solution is controlled to be 2.0, the iron content C (Fe 2+) = 50 g / L; 85% phosphoric acid is mixed with 32% liquid alkali and desalted water to prepare a phosphate solution, the pH of the phosphate solution is controlled at 7.0, the molar ratio of iron element, phosphorus element and hydrogen peroxide is 1:1:0.75, the phosphate solution is mixed with hydrogen peroxide and then added to the ferrous sulfate solution for synthesis reaction, the reaction temperature is controlled at 50°C, the reaction time is 2h, after the reaction is completed, a precipitate slurry B is obtained; the precipitate slurry B is subjected to solid-liquid separation by plate and frame filter pressing to obtain a first washing filter cake C and a first washing filtrate D, and water washing is continued until the conductivity is <1500 us / cm, and the obtained washing water is a first washing washing water E; Step S2, the first washing filter cake C is added with water to obtain a beating slurry G, 85wt% phosphoric acid is added for aging reaction, the aging temperature is 90°C, the aging time is 1.5h, and the obtained slurry is an aging slurry H; the aging slurry H is subjected to solid-liquid separation by plate and frame filter pressing to obtain a second washing filter cake I and a second washing filtrate J, and water washing is continued until the conductivity is <500 us / cm, and the obtained washing water is a second washing washing water K; Step S3, the second washing filter cake I is subjected to flash drying, calcination and crushing to obtain an anhydrous ferric phosphate product.

[0026] Comparative Example 2 The preparation method of the ferric phosphate of the present comparative example comprises the following steps: Step S1, a ferrous sulfate solution is obtained by purifying the titanium dioxide by-product rutile mother liquor, and is placed in a precipitation reactor as a bottom liquid A for use, the pH of the ferrous sulfate solution is controlled at 2.1, the iron content C (Fe 2+ ) = 55 g / L; 85% phosphoric acid is mixed with 32% liquid alkali and desalted water to prepare a phosphate solution, the pH of the phosphate solution is controlled at 7.0, the molar ratio of iron element, phosphorus element and hydrogen peroxide is 1:1:0.75, the phosphate solution is mixed with hydrogen peroxide and then added to the ferrous sulfate solution for synthesis reaction, the reaction temperature is controlled at 45°C, the reaction time is 1.5h, after the reaction is completed, a precipitate slurry B is obtained; the precipitate slurry B is subjected to solid-liquid separation by plate and frame filter pressing to obtain a first washing filter cake C and a first washing filtrate D, and water washing is continued until the conductivity is <1500 us / cm, and the obtained washing water is a first washing washing water E; Step S2, the first washing filter cake C is added with water to obtain a beating slurry G, 85wt% phosphoric acid is added for aging reaction, the aging temperature is 90°C, the aging time is 1.5h, and the obtained slurry is an aging slurry H; the aging slurry H is subjected to solid-liquid separation by plate and frame filter pressing to obtain a second washing filter cake I and a second washing filtrate J, and water washing is continued until the conductivity is <500 us / cm, and the obtained washing water is a second washing washing water K; Step S3, the second washing filter cake I is subjected to flash drying, calcination and crushing to obtain an anhydrous ferric phosphate product.

[0027] Comparative Example 3 The comparative method for preparing ferric phosphate includes the following steps: Step S1: After removing impurities from the rutile mother liquor, a byproduct of titanium dioxide production, a ferrous sulfate solution is obtained and placed in the precipitation reactor as the bottom liquid A for later use. The pH of the ferrous sulfate solution is controlled at 2.2, and the iron content C (Fe) is controlled at 2.2. 2+ =60g / L; Prepare a phosphate solution by mixing 85% phosphoric acid with 32% liquid alkali and demineralized water, controlling the pH of the phosphate solution to 7.0, and add the phosphate solution and hydrogen peroxide in a molar ratio of 1:1:0.75 to a ferrous sulfate solution for synthesis reaction, controlling the reaction temperature to 60℃ and the reaction time to 0.5h. After the reaction is completed, a precipitate slurry B is obtained; the precipitate slurry B is separated into solid and liquid by plate and frame filter press to obtain a first-wash filter cake C and a first-wash filtrate D, which are then washed with water until the conductivity is <1500μs / cm, and the resulting wash water is the first-wash wash water E; Step S2: After adding water to the first-wash filter cake C and pulping it to obtain pulp slurry G, add 85wt% phosphoric acid for aging reaction at 100℃ for 1h. The resulting slurry is aged slurry H. Use plate and frame filter press to separate solid and liquid in the aged slurry H to obtain second-wash filter cake I and second-wash filtrate J. Continue washing with water until the conductivity is <500μs / cm. The resulting wash water is second-wash wash water K. Step S3: Flash dry, calcine and pulverize the second-washed filter cake I to obtain anhydrous ferric phosphate product.

[0028] Experimental example: I. Particle size distribution tests were performed on the precipitate slurry B obtained in step S1 of Examples 1-3 using recycled ferric phosphate particles as seed crystals, and the precipitate slurry B obtained in step S1 of Comparative Examples 1-3 without adding seed crystals, to obtain the particle size distribution of the precipitate slurries. Figures 2-4 ; 2. The particle size distribution of the aged slurry H obtained by recycling and using the filtered iron phosphate particles as aging seed crystals in step S2 of Examples 1-3, and the aged slurry H obtained without adding aging seed crystals in step S2 of Comparative Examples 1-3, was tested to obtain the particle size distribution of the aged slurry. Figures 5-7 ; 3. The particle size distribution of the anhydrous ferric phosphate products obtained in step S3 of Examples 1-3 and Comparative Examples 1-3 was tested to obtain the particle size distribution of anhydrous ferric phosphate. Figures 8-10 Table 1 compares the particle size and tap density of anhydrous ferric phosphate products. Table 1. Comparison of particle size and tap density of anhydrous ferric phosphate products from Examples 1-3 and Comparative Examples 1-3.

[0029] Depend on Figures 2-10As shown in Table 1, the present application recycles the iron phosphate particles filtered in the first pressure filtration and washing and the second pressure filtration and washing as the precipitation seed and aging seed, which can effectively increase the size of the first iron phosphate particles, broaden the particle size distribution, and thus improve the tap density of the iron phosphate material.

Claims

1. A method for producing a high-density ferric phosphate, characterized by, The method comprises the following steps: Step S1, a ferrous sulfate solution is used as a bottom liquid A of a precipitation reactor, mixed with a phosphate and an oxidizing agent to perform a precipitation reaction, to obtain a precipitation slurry B, which is subjected to primary pressure filtration and washing, and the filtered iron phosphate particles are recovered and returned to the bottom liquid A of the precipitation reactor as precipitation seeds; Step S2, the first washing filter cake C is slurried to obtain a first washing slurry G, which is aged to obtain an aged slurry H, which is subjected to secondary pressure filtration and washing, and the filtered iron phosphate particles are recovered and returned to the first washing slurry G as aging seeds; Step S3, the second washing filter cake I is dried, calcined and crushed to obtain anhydrous iron phosphate.

2. The method of producing high tap density ferric phosphate according to claim 1, characterized by, In step S1, the first washing filtrate D and the first washing water E are filtered through a microporous filter, back-flushed to obtain a dilute precipitation slurry F, which is returned to the bottom liquid A of the precipitation reactor as precipitation seeds.

3. The method of producing high tap density ferric phosphate according to claim 2, characterized by, In step S2, the second washing filtrate J and the second washing water K are filtered through a microporous filter, back-flushed to obtain a dilute aging slurry L, which is returned to the first washing slurry G as aging seeds.

4. The method of producing high tap density ferric phosphate according to claim 3, characterized by, In step S1, the water washing in the primary pressure filtration and washing is performed until the conductivity is less than 1500 μs / cm to obtain the first washing water E, and in step S2, the water washing in the secondary pressure filtration and washing is performed until the conductivity is less than 500 μs / cm to obtain the second washing water K.

5. The method of producing high tap density ferric phosphate according to claim 4, characterized by, In step S1, the microporous filter membrane filtering precision of the first washing filtrate D and the first washing water E is 0.5-1 μm, and in step S2, the microporous filter membrane filtering precision of the second washing filtrate J and the second washing water K is 0.5-1 μm.

6. The method of producing high tap density ferric phosphate according to claim 3 or 5, characterized by, In step S1, the concentration of the dilute precipitation slurry F is 0.01-0.4 wt%, and in step S2, the concentration of the dilute aging slurry L is 0.01-0.4 wt%.

7. The method of producing high tap density ferric phosphate according to claim 1, characterized by, In step S1, the precipitation seeds are added in a proportion of 1%-5% of the theoretical output of iron phosphate, and in step S2, the aging seeds are added in a proportion of 1%-5% of the theoretical output of iron phosphate.

8. The method of producing high tap density ferric phosphate according to claim 1, characterized by, In step S1, the pH of the ferrous sulfate solution is 2.0-2.2, the iron content C (Fe2+) is 50-60 g / L, the precipitation reaction time is 0.5-2.5 h, and the reaction temperature is 45-70 °C.

9. The method of producing high tap density ferric phosphate according to claim 1, characterized by, In step S2, the acid added in the aging reaction is 85 wt% phosphoric acid, the aging reaction time is 1-3 h, and the aging temperature is 90-100 °C.

10. The use of the preparation method according to any one of claims 1-9 in the preparation of iron phosphate from titanium dioxide by-product.

Images