A method for preparing low-viscosity basic ferric phosphate slurry and its product

Abstract

This invention discloses a method for preparing low-viscosity basic ferric phosphate slurry and its product. The preparation method is as follows: ferrous salt solution and phosphate salt solution are prepared and simultaneously added to a reaction vessel to obtain basic ferrous phosphate slurry; an oxidant and a viscosity reducer are added for an oxidation reaction to obtain low-viscosity basic ferric phosphate slurry; the viscosity reducer is 5027W dispersant, anionic surfactant, sodium pyrophosphate, sodium hexametaphosphate, or chromium-free lignin sulfonate. This invention controls the crystal nucleation and growth rate through stepwise feeding, combined with the electrostatic and steric effects of the viscosity reducer, inducing primary particles to form a spherical structure and inhibiting agglomeration. The resulting slurry has a primary particle size of 55-80 nm, a secondary particle size of 7-10 μm, a viscosity ≤15.0 mPa·s, and a sedimentation efficiency P of 1.00-2.00. This slurry has good fluidity, and the anhydrous ferric phosphate prepared by subsequent crystal transformation has high purity, which is beneficial for improving ferric phosphate production efficiency and equipment lifespan.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material technology, specifically to a method for preparing low-viscosity basic iron phosphate slurry and its product. Background Technology

[0002] Iron phosphate (FePO4) is a key precursor material for the preparation of lithium iron phosphate cathode materials. Industrially, the production method for iron phosphate used in battery materials is the co-precipitation method. Ferrous sulfate, phosphate salts, hydrogen peroxide, and ammonia are added to a reaction vessel and stirred to form a slurry. This slurry is transferred between the synthesis, washing, and conversion processes in the wet process of iron phosphate production via pumps and pipelines. The viscosity and flowability of the iron phosphate slurry are crucial to iron phosphate production. A high-quality iron phosphate slurry is easy to stir and disperse, has a fast transfer speed, low viscosity, and is less prone to scaling on equipment surfaces, greatly improving production efficiency. Conversely, a high-viscosity iron phosphate slurry reduces production efficiency. Related patents for improving the physical properties of iron phosphate materials are as follows: CN118545688B, titled "An Iron Phosphate Material and Its Preparation Method and Application," discloses a method for improving the hardness of iron phosphate. An iron phosphate material is prepared by adding a surfactant, and this material possesses four characteristics: 1. Specific pore volume V... p At 0.72cm 3 The following characteristics are observed: 1. The particle size distribution is between 1.28 cm / g and 1.28 cm / g; 2. The average aspect ratio of the primary particles does not exceed 3.5; 3. The hardness index of the iron phosphate material is 0.98-3.57; 4. The equivalent particle size of the primary particles is 254 nm-411 nm; 5. The D50 of the secondary particles is 8.74 μm-10.28 μm. These characteristics result in an iron phosphate material with a loose structure and low overall hardness. When used to prepare cathode materials, this improves the efficiency of grinding with lithium sources, reduces machine wear, and produces cathode materials with good electrochemical performance.

[0003] Currently, the synthesis method for battery-grade iron phosphate is the co-precipitation method. Iron salt solution, phosphate salt solution, pH adjustment, and oxidant come into contact in a reactor, leading to rapid nucleation. The nucleation rate exceeds the growth rate, forming nano-sized basic iron phosphate particles, resulting in a high viscosity of the basic iron phosphate slurry. This affects iron phosphate production efficiency. During continuous production, the high-viscosity slurry is more likely to adhere to the reactor and pipe walls, forming scale and requiring periodic shutdowns for cleaning. The increased flow resistance of the high-viscosity slurry damages the pump impeller, resulting in shorter equipment lifespan. Furthermore, the high-viscosity slurry has a high Reynolds number, making diffusion difficult and mixing efficiency low. During the crystallization reaction to form dihydrate iron phosphate, this affects the purity of the iron phosphate, resulting in poor performance after lithium iron phosphate production.

[0004] In view of this, a method for preparing low-viscosity basic ferric phosphate slurry and its product are proposed. Summary of the Invention

[0005] A method for preparing a low-viscosity basic ferric phosphate slurry includes the following steps: S1. Prepare ferrous salt solution and phosphate salt solution; S2. The ferrous salt solution and the phosphate solution are simultaneously added to the reaction vessel to react and obtain basic ferrous phosphate slurry. S3. Add an oxidant and a viscosity reducer to the basic ferrous phosphate slurry obtained in step S2 to carry out an oxidation reaction and obtain a low-viscosity basic ferrous phosphate slurry. The viscosity reducer is one or more of 5027W dispersant, anionic surfactant, sodium pyrophosphate, sodium hexametaphosphate, or chromium-free lignin sulfonate.

[0006] The iron salt solution is prepared from ferrous salts such as ferrous titanium dioxide (FeSO4), ferrous chloride (FeCl2), ferrous dihydrogen phosphate (Fe(H2PO4)2), and ferrous nitrate (Fe(NO3)2), or is prepared by dissolving solid iron salts such as iron powder and iron slag in acid; the phosphate salt solution is prepared from phosphate salts such as sodium dihydrogen phosphate (NaH2PO4), potassium dihydrogen phosphate (KH2PO4), ammonium monohydrogen phosphate ((NH4)2HPO4), and ammonium dihydrogen phosphate (NH4H2PO4).

[0007] Furthermore, in step S1, the concentration of the ferrous salt solution is 0.8-1.6 mol / L; the concentration of the phosphate salt solution is 1-2 mol / L. In step S2, the feeding rate of the ferrous salt solution is 1.0-3.0 m / s. 3 The feed rate of the phosphate salt solution is 0.67-2.00 m / h. 3 / h.

[0008] Furthermore, in step S3, the oxidant is one or more of hydrogen peroxide, potassium permanganate, sodium hypochlorite, and ozone.

[0009] Moreover, the anionic surfactant is a petroleum sulfonate or a lignin sulfonate.

[0010] Furthermore, in step S3, the oxidant and viscosity reducer are pre-mixed and then simultaneously added to the basic ferrous phosphate slurry.

[0011] Furthermore, in step S3, when the oxidant is hydrogen peroxide, the method for pre-mixing the oxidant and the viscosity reducer is to add the viscosity reducer to the oxidant at a rate of 92-370 L / h.

[0012] Furthermore, in step S3, the mass of the viscosity reducer is 0.05-1% of the molar amount of iron in the ferrous salt; and the addition ratio of the oxidant is 0.55-0.80 times the molar amount of iron in the ferrous salt.

[0013] Furthermore, step S1 also includes adding a pH adjuster to the phosphate salt solution to adjust the pH to 5-8; the pH adjuster is an alkaline substance such as sodium hydroxide (NaOH), ammonia (NH3·H2O), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), or potassium hydroxide (KOH).

[0014] On the other hand, the present invention also discloses a low-viscosity basic ferric phosphate slurry, which is prepared by the above method. The low-viscosity basic ferric phosphate slurry is a secondary particle formed by the agglomeration of primary particles. The particle size of the primary particles is 55nm-80nm, and the particle size of the secondary agglomerates is 7um-10um. The viscosity of the low-viscosity basic ferric phosphate slurry is ≤15.0mPa·s, and the viscosity is measured by a rotational viscometer.

[0015] Furthermore, the settling efficiency P of the low-viscosity basic ferric phosphate slurry is 1.00-2.00, and the settling efficiency is the ratio of the volume of the supernatant V1 to the volume of the sediment V2 after 5 minutes of settling.

[0016] Furthermore, after filtering, washing, pulping, and adding acid, the low-viscosity basic ferric phosphate slurry is pumped into a reaction vessel via a centrifugal pump, where a crystallization reaction occurs at high temperature to obtain ferric phosphate dihydrate slurry. The ferric phosphate dihydrate slurry is then subjected to washing, flash drying, calcination, crushing, sieving, and demagnetization treatments to obtain battery-grade anhydrous ferric phosphate.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention precisely controls the crystal nucleation and growth rate through a stepwise feeding process (first synthesizing the basic ferrous phosphate intermediate, then adding an oxidant and a viscosity reducer). Combined with the electrostatic repulsion and steric hindrance effect of the viscosity reducer, it induces the primary particles to form a nanoscale spherical structure (55-80nm) and inhibits their uncontrollable agglomeration, ultimately forming loose spherical secondary particles (7-10um). This structure effectively reduces the friction between particles, making the viscosity of the basic ferrous phosphate slurry ≤15.0mPa·s, and the sedimentation efficiency P value controlled within the range of 1.00-2.00. The slurry fluidity is significantly better than that of existing processes.

[0018] 2. The low-viscosity slurry prepared by this invention has low flow resistance during pipeline transportation and is less prone to scaling on the reactor wall, pipeline wall and pump impeller surface, reducing equipment wear and blockage risk. The anhydrous ferric phosphate prepared by subsequent crystallization using the process of this invention has high purity, which is beneficial to improving the production efficiency of ferric phosphate and the service life of equipment.

[0019] 3. The low-viscosity slurry prepared by this invention mixes more uniformly in the crystallization reaction, with less diffusion resistance, which is beneficial for impurity separation and complete crystal growth. This increases the iron-to-phosphorus ratio (Fe / P) of the iron phosphate dihydrate precursor to 97.00-98.00, which is better than the comparative example (95.58-96.76). The resulting battery-grade anhydrous iron phosphate has high purity and good crystallinity, and inherits the spherical morphology of the precursor. In the subsequent preparation of lithium iron phosphate cathode materials, it has advantages such as high grinding efficiency, low equipment wear, high compaction density, and short lithium-ion diffusion path, thereby improving the battery's capacity, rate performance, and cycle stability.

[0020] 4. The method of the present invention does not require the addition of complex equipment. It can be achieved simply by optimizing the feeding sequence, controlling the flow rate of the oxidant and the amount of viscosity reducer added. It has a wide process window, good reproducibility, and is easy to promote and apply on existing iron phosphate production lines. Attached Figure Description

[0021] Figure 1 SEM image of basic ferric phosphate slurry prepared under the process conditions of Example 1; Figure 2 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 2; Figure 3 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 3; Figure 4 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 4; Figure 5 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 1; Figure 6 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 2; Figure 7 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 3; Figure 8 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 4; Figure 9 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 5. Detailed Implementation

[0022] Example 1 A method for preparing a low-viscosity basic ferric phosphate slurry includes the following steps: (1) Prepare 3 cubic meters of 1.0 mol / L FeSO4 solution and 2 cubic meters of 1.5 mol / L NaH2PO4 solution, and add NaOH to the phosphate salt solution to adjust the pH of the solution to between 7.8 and 8.0; (2) Ferrous sulfate solution and NaH2PO4 solution are simultaneously added to the reactor at a rate of 2m / min. 3 / h, phosphate feed rate 1.33m 3 / h, react for 10min to obtain basic ferrous phosphate slurry; (3) After mixing 2.5 kg of sodium alkyl phosphate sulfonate viscosity reducer with 185 L of industrial hydrogen peroxide with a mass fraction of 27.5%, the mixture is added to the reactor at a rate of 370.90 L / h to generate low viscosity basic ferric phosphate slurry. (4) After filtering, washing, pulping and adding acid, the low-viscosity basic ferric phosphate slurry is transported to the reactor through a centrifugal pump and 316 stainless steel pipeline to obtain ferric phosphate dihydrate slurry. (5) Heat the ferric phosphate dihydrate slurry to 90°C at a uniform rate, keep it at the temperature for 60 minutes and then discharge it. The white slurry E is filtered and washed by a plate and frame filter press. The conductivity is controlled to be <5000μs / cm during the process to obtain ferric phosphate dihydrate filter cake. (6) The filter cake of ferric phosphate dihydrate is conveyed to the flash evaporator by belt, the feed screw frequency is 15Hz, the outlet air temperature is controlled at 155℃, the main stirring frequency is 80Hz, the free water in the filter cake of ferric phosphate dihydrate is removed, and the filter cake is crushed to obtain ferric phosphate dihydrate powder. (7) The dihydrate ferric phosphate slurry is sequentially washed, flash dried, calcined, crushed, sieved and demagnetized to obtain battery-grade anhydrous ferric phosphate.

[0023] Example 2 The difference between this embodiment and embodiment 1 is that the hydrogen peroxide feeding rate in (3) is 278.18 L / h.

[0024] Example 3 The difference between this embodiment and embodiment 1 is that the mass of the viscosity reducer in (2) is 4.52 kg.

[0025] Example 4 The difference between this embodiment and embodiment 1 is that: (2) the iron salt feeding rate is 2m 3 / h, phosphate feed rate 1m 3 / h.

[0026] Comparative Example 1 The comparative example of this invention differs from Example 1 in that hydrogen peroxide and a viscosity reducer are added to the phosphate salt and simultaneously added to the reaction vessel along with the phosphate salt, including the following steps: (1) Prepare 3 cubic meters of 1.0 mol / L FeSO4 solution and 2 cubic meters of 1.5 mol / L NaH2PO4 solution. Add 185 L of hydrogen peroxide and 2.5 Kg of sodium alkyl phosphate sulfonate to NaH2PO4. After stirring evenly, add NaOH to the phosphate salt solution to adjust the pH of the solution to between 7.8 and 8.0. (2) Ferrous sulfate solution and NaH2PO4 solution are simultaneously added to the reactor at a rate of 2m / min. 3 / h, phosphate feed rate 1.33m 3 / h, react for 10min to obtain conventional basic ferric phosphate slurry; (3) After filtering, washing, pulping and adding acid, the basic ferric phosphate slurry is transported to the reactor through a centrifugal pump and 316 stainless steel pipeline to carry out the conversion reaction to obtain ferric phosphate dihydrate slurry; (4) Heat the ferric phosphate dihydrate slurry to 90°C at a uniform rate, keep it at the temperature for 60 minutes and then discharge it. The white slurry E is filtered and washed by a plate and frame filter press. The conductivity is controlled to be <5000μs / cm during the process to obtain ferric phosphate dihydrate filter cake. (5) The filter cake is conveyed to the flash evaporator by a belt, the feed screw frequency is 15Hz, the outlet air temperature is controlled at 155℃, the main stirring frequency is 80Hz, the free water in the ferric phosphate dihydrate filter cake is removed, and the filter cake is crushed to obtain ferric phosphate dihydrate powder. (6) The dihydrate ferric phosphate slurry is sequentially washed, flash dried, calcined, crushed, screened and demagnetized to obtain battery-grade anhydrous ferric phosphate.

[0027] Comparative Example 2 The difference between this comparative example and Example 1 is that hydrogen peroxide and viscosity reducer are added separately as raw materials, and are simultaneously added to the reactor along with FeSO4 solution and NaH2PO4 solution.

[0028] Comparative Example 3 The difference between this comparative example and Example 1 is that no viscosity reducer was added.

[0029] Comparative Example 4 The difference between this comparative example and Example 1 is that the hydrogen peroxide feeding rate is 556.36 L / h.

[0030] Comparative Example 5 The difference between this comparative example and Example 1 is that the mass of the viscosity reducer added is 18.10 kg.

[0031] Experimental Section The viscosity and physicochemical properties of the slurry in the examples and comparative examples were characterized. The slurry viscosity was tested using a rotational viscometer; the primary and secondary particle sizes were measured and analyzed using scanning electron microscopy and particle size analysis software; and the slurry settling efficiency was obtained by calculating the ratio of the supernatant volume V1 to the sediment volume V2 using settling experiments.

[0032] The slurries and anhydrous ferric phosphate prepared in the examples and comparative examples were subjected to performance tests. The viscosity of the slurries was measured using a rotational viscometer; the microstructure of the samples was observed using a scanning electron microscope (SEM); key physical properties and morphological characteristics are shown in Tables 1 and 2, respectively. Figure 1-9 As shown. Figure 1 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 1. Figure 2 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 2. Figure 3 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 3. Figure 4 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Example 4. Figure 5 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 1. Figure 6 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 2. Figure 7 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 3. Figure 8 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 4. Figure 9 SEM image of the basic ferric phosphate slurry prepared under the process conditions of Comparative Example 5.

[0033] From Table 1 and Figure 1-9 As can be seen from Examples 1-4, by adding ferrous salt and phosphate salt simultaneously and precisely controlling the flow rate of hydrogen peroxide, the nucleation and growth of basic ferric phosphate slurry can be controlled. The primary ion size of the basic ferric phosphate particles develops to between 60-120 nm (standard range). The viscosity reducer effectively prevents the aggregation between particles. Under the electrostatic effect and steric hindrance effect, the primary particles spontaneously connect to form loose spheres of uniform size. Therefore, the friction between particles is reduced, and the viscosity of the slurry is reduced. Based on the above particle size and morphology characteristics, the high-performance slurry settling efficiency is between 1.00 and 2.00.

[0034] Specifically, since the hydrogen peroxide feeding rate in Example 2 was lower than that in Example 1, the primary particle nucleation rate in Example 1 was higher than that in Example 2. This indicates that a lower hydrogen peroxide feeding rate is beneficial to the development of primary particles. For basic iron phosphate slurry, an increase in the number of primary particles is beneficial to a decrease in viscosity. For anhydrous iron phosphate materials, the more complete the particle development, the higher the iron-to-phosphorus ratio of the material.

[0035] Therefore, the primary particle size is: Example 1 (60.78 nm) < Example 2 (70.25 nm); Therefore, the secondary particle size is: Example 1 (9.25 μm) > Example 2 (8.23 μm); Therefore, the slurry viscosity is: Example 1 (10.20 mPa·s) > Example 2 (9.85 mPa·s); Therefore, the settling efficiency is: Example 1 (1.32) > Example 2 (1.45). Therefore, the basic ferric phosphate slurry of Examples 1 and 2 were subjected to the same crystallization reaction, and the Fe / P (97.20) of Example 1 was less than that of Example 2 (97.60).

[0036] Specifically, since the amount of viscosity reducer in Example 3 is twice that in Example 1, the experimental data show that the degree of primary particle development first increases and then decreases with the increase of viscosity reducer dosage, while the degree of secondary particle aggregation decreases with the increase of viscosity reducer.

[0037] Therefore, the primary particle size is: Example 3 (55.65 nm) < Example 1 (60.78 nm); Therefore, the secondary particle size is: Example 3 (7.25 μm) > Example 1 (9.25 μm); Therefore, the slurry viscosity was: Example 3 (9.58 mPa·s) < Example 1 (10.20 mPa·s); Therefore, the settling efficiency was: Example 3 (1.58) > Example 1 (1.32). Therefore, the basic ferric phosphate slurry of Examples 1 and 3 were subjected to the same crystallization reaction, and the Fe / P ratio of Example 3 (97.10) was less than that of Example 1 (97.20).

[0038] Specifically, since the iron salt rate in Example 4 is lower than that in Example 1, the reduced feeding rate is beneficial to the development and growth of crystal nuclei.

[0039] Therefore, the particle size in Example 4 (75.74 nm) is greater than that in Example 1 (60.78 nm). Therefore, the secondary particle size: Example 4 (8.95um) < Example 1 (9.25um); Therefore, the slurry viscosity is: Example 4 (7.85 mPa·s) < Example 1 (10.20 mPa·s); Therefore, the settling efficiency was: Example 4 (1.95) > Example 1 (1.32). Therefore, the basic ferric phosphate slurry of Examples 1 and 4 were subjected to the same crystallization reaction, and the Fe / P ratio of Example 4 (97.55) was greater than that of Example 1 (97.20).

[0040] Compared with Examples 1-4, Comparative Examples 1-4 did not control the growth rate of basic ferrous phosphate particles by first adding ferrous salt and phosphate salt to prepare the basic ferrous phosphate slurry intermediate and by controlling the flow rate of hydrogen peroxide. Alternatively, no viscosity reducer was added to promote the reduction of slurry viscosity. Therefore, the key viscosity control indicators of the prepared slurry, such as primary particle size, secondary particle size, slurry viscosity, and sedimentation efficiency, were not within the standard range. From the morphology analysis of the comparative examples, it can be found that some primary particles are flocculent, rather than the nano-spherical particles in the examples. The secondary particles are agglomerated into lumps, rather than the spherical secondary particles in the examples. Therefore, this process scheme did not reduce the viscosity of the slurry.

[0041] Specifically, since Comparative Example 1 involves the simultaneous addition of ferrous salt, (phosphate salt + hydrogen peroxide + viscosity reducer), the ferrous salt, phosphate salt, and hydrogen peroxide react instantly upon contact to form crystal nuclei, resulting in a nucleation rate greater than the growth rate.

[0042] Therefore, the primary particle size is: Comparative Example 1 (40.24 nm < Example 1 (60.78 nm)). Therefore, the size of the secondary particles is: Comparative Example 1 (2.54 μm) > Example 1 (9.25 μm). Therefore, the slurry viscosity was: Comparative Example 1 (26.32 mPa·s) > Example 1 (10.20 mPa·s). Therefore, the settling efficiency was: Comparative Example 1 (0.55) < Example 1 (1.32). Therefore, the basic iron phosphate slurry of Comparative Example 1 and Example 1 were subjected to the same crystallization reaction. The Fe / P ratio of Comparative Example 1 (96.54) was less than that of Example 1 (97.20).

[0043] Specifically, since Comparative Example 2 uses a four-pronged feeding method involving ferrous salt, phosphate salt, hydrogen peroxide, and viscosity reducer, the nucleation rate of ferrous salt, phosphate salt, hydrogen peroxide, and viscosity reducer is lower than that of the comparative example, but still greater than the nucleation rate of the feeding method in the examples.

[0044] Therefore, the size of the primary particles is: Comparative Example 1 (40.24 nm) < Comparative Example 2 (45.29 nm). Therefore, the size of the secondary particles is: Comparative Example 1 (2.54 μm) < Comparative Example 2 (3.24 μm). Therefore, the viscosity of the slurry is: Comparative Example 1 (26.32 mPa·s) > Comparative Example 2 (22.34 mPa·s). Therefore, the settling efficiency is: Comparative Example 1 (0.55) < Comparative Example 2 (0.59). Therefore, the basic iron phosphate slurry of Comparative Example 1 and Comparative Example 2 were subjected to the same crystallization reaction, and the Fe / P ratio of Comparative Example 1 (96.54) was less than that of Comparative Example 2 (96.76).

[0045] Specifically, since Comparative Example 3 differs from Example 1 in that no viscosity reducer was added, although the primary particles were fully developed and grown, they did not form a loose spherical structure like in the example under the electrostatic effect and steric hindrance of the binder, but instead formed blocky aggregates.

[0046] Therefore, the primary particle size: Comparative Example 3 (65.34 nm) < Example 1 (60.78 nm) Therefore, the secondary particle size is: Comparative Example 3 (15.32 μm) > Example 1 (9.25 μm). Therefore, the slurry viscosity was: Comparative Example 3 (35.28 mPa·s) > Example 1 (10.20 mPa·s). Therefore, the settling efficiency was: Comparative Example 3 (0.68) < Example 1 (1.32). Therefore, the basic iron phosphate slurry of Comparative Example 3 and Example 1 were subjected to the same crystallization reaction. The Fe / P ratio of Comparative Example 3 was 96.23 < that of Example 1 (Fe / P 97.20).

[0047] Specifically, since the difference between Comparative Example 4 and Example 1 is that the hydrogen peroxide feeding rate is twice that of Example 1, the nucleation rate of Comparative Example 4 is faster.

[0048] Therefore, the primary particle size: Comparative Example 4 (30.25 nm) < Example 1 (60.78 nm) Therefore, the size of the secondary particles is: Comparative Example 4 (5.43 μm) < Example 1 (9.25 μm). Therefore, the slurry viscosity was: Comparative Example 4 (28.56 mPa·s) > Example 1 (10.20 mPa·s). Therefore, the settling efficiency was: Comparative Example 4 (0.78 < Example 1 (1.32)). Therefore, the basic iron phosphate slurry of Comparative Example 4 and Example 1 were subjected to the same crystallization reaction. The Fe / P ratio of Comparative Example 4 (96.15) was less than that of Example 1 (97.20).

[0049] Specifically, since the difference between Comparative Example 5 and Example 1 is that the amount of viscosity reducer used is 18.1 kg, the addition of excessive viscosity reducer to the synthesis system will affect the nucleation and development of basic ferric phosphate. Therefore, some irregular particles were observed in the microscopic morphology diagram. Under the action of excessive viscosity reducer, the particles were linked together to form larger agglomerates, and the settling rate was greatly increased. However, the particles settled too quickly and deposited during pipeline transportation, which is also not conducive to the crystallization and transportation of the slurry.

[0050] Therefore, the primary particle size: Comparative Example 5 (35.23 nm) < Example 1 (60.78 nm) Therefore, the secondary particle size is: Comparative Example 5 (9.35 μm) > Example 1 (9.25 μm). Therefore, the slurry viscosity was: Comparative Example 5 (38.23 mPa·s) > Example 1 (10.20 mPa·s). Therefore, the settling efficiency was: Comparative Example 5 (3.49) > Example 1 (1.32). Therefore, the basic iron phosphate slurry of Comparative Example 5 and Example 1 were subjected to the same crystallization reaction. The Fe / P ratio of Comparative Example 5 (95.58) was less than that of Example 1 (97.20).

[0051] Table 1 Properties of basic ferric phosphate slurry

Claims

1. A method for preparing a low-viscosity basic ferric phosphate slurry, characterized in that, Includes the following steps: S1. Prepare ferrous salt solution and phosphate salt solution; S2. The ferrous salt solution and the phosphate solution are simultaneously added to the reaction vessel to react and obtain basic ferrous phosphate slurry. S3. Add an oxidant and a viscosity reducer to the basic ferrous phosphate slurry obtained in step S2 to carry out an oxidation reaction and obtain a low-viscosity basic ferrous phosphate slurry. The viscosity reducer is one or more of 5027W dispersant, anionic surfactant, sodium pyrophosphate, sodium hexametaphosphate, or chromium-free lignin sulfonate.

2. The preparation method according to claim 1, characterized in that, In step S1, the concentration of the ferrous salt solution is 0.8-1.6 mol / L; the concentration of the phosphate salt solution is 1-2 mol / L. In step S2, the feeding rate of the ferrous salt solution is 1.0-3.0 m³ / h, and the feeding rate of the phosphate salt solution is 0.67-2.00 m³ / h.

3. The preparation method according to claim 1, characterized in that, In step S3, the oxidant is one or more of hydrogen peroxide, potassium permanganate, sodium hypochlorite, and ozone.

4. The preparation method according to claim 1, characterized in that, In step S3, the anionic surfactant is a petroleum sulfonate or a lignin sulfonate.

5. The preparation method according to claim 3, characterized in that, In step S3, the oxidant and viscosity reducer are premixed and then simultaneously added to the basic ferrous phosphate slurry.

6. The preparation method according to claim 5, characterized in that, In step S3, the oxidant is hydrogen peroxide, and the method for pre-mixing the oxidant and viscosity reducer is to add the viscosity reducer to the oxidant at a rate of 92-370 L / h.

7. The preparation method according to claim 1, characterized in that, In step S3, the mass of the viscosity reducer is 0.05-1% of the molar amount of iron in the ferrous salt; the addition ratio of the oxidant is 0.55-0.80 times the molar amount of iron in the ferrous salt.

8. The preparation method according to claim 1, characterized in that, Step S1 further includes adding a pH adjuster to the phosphate salt solution to adjust the pH to 5-8; the pH adjuster is sodium hydroxide, ammonia, sodium carbonate, potassium carbonate, or potassium hydroxide.

9. A low-viscosity basic ferric phosphate slurry, characterized in that, The low-viscosity basic ferric phosphate slurry is prepared by the method according to any one of claims 1-8, wherein the low-viscosity basic ferric phosphate slurry is a secondary particle formed by primary particle agglomeration, wherein the particle size of the primary particles is 55nm-80nm, and the particle size of the secondary agglomerates is 7um-10um; the viscosity of the low-viscosity basic ferric phosphate slurry is ≤15.0mPa·s.

10. The low-viscosity basic ferric phosphate slurry according to claim 9, characterized in that, The settling efficiency P of the low-viscosity basic ferric phosphate slurry is 1.00-2.00, and the settling efficiency is the ratio of the volume of the supernatant to the volume of the sediment after 5 minutes of settling.

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