A settling agent for reducing the solid content of a wet-process phosphoric acid, a settling method, and a settling system

Abstract

This invention provides a flocculant, a flocculant method, and a flocculant system for reducing the solid content of wet-process phosphoric acid, relating to the field of wet-process phosphoric acid purification technology. It solves the technical problems of existing phosphoric acid storage facilities having large flocculant spaces, limited flocculant effect, and long flocculant time. The invention includes preliminary flocculant formation: phosphoric acid and agent A (V1 by volume of phosphoric acid) are added to the first flocculant device, stirred, and then allowed to stand for clarification for 8-12 hours, with V1 = 0.47 L-0.59 L / m³. 3 Secondary sedimentation: Agent B, with a volume of phosphoric acid of V2, is simultaneously added to the second sedimentation device. After sedimentation for 10 hours, the clarification of the phosphoric acid is observed, and the phosphoric acid is discharged. V2 = 0.8 - V1. This invention divides phosphoric acid sedimentation into two steps and two sets of sedimentation devices, ensuring sedimentation effect and reducing sedimentation space without increasing sedimentation time. Simultaneously with the introduction of phosphoric acid into the second sedimentation device, it is thoroughly mixed with Agent B, eliminating the need for a mixing device in the second sedimentation device and saving mixing time.

Description

Technical Field

[0001] This invention relates to the field of wet-process phosphoric acid purification technology, and more specifically, to a flocculant, a flocculant method, and a flocculant system for reducing the solid content of wet-process phosphoric acid. Background Technology

[0002] In the production of wet-process phosphoric acid, especially that produced from medium- and low-grade phosphate rock, a large amount of solid matter precipitates after concentration. Further precipitation occurs as the acid temperature decreases. Combined with the carbonization of organic matter during phosphate rock leaching and the abrasion of the graphite evaporator by the phosphoric acid material during concentration, the solid content in crude phosphoric acid from the 50% P2O5 wet-process process reaches over 5%. These solids are collectively referred to as sludge. The presence of sludge is highly detrimental to the transportation, storage, and further refining of phosphoric acid, therefore it must be removed. In the production of phosphate compound fertilizers, the quality of phosphoric acid has a significant impact on subsequent production. With the continuous decline in phosphate rock quality, existing facilities and methods are no longer sufficient to provide high-quality phosphoric acid for downstream production.

[0003] Traditionally, natural sedimentation is used, allowing solid particles to settle naturally under gravity. However, this process requires large sedimentation equipment, takes anywhere from half a month to a month, and only relatively large solid particles settle out of the acid, leaving a solid content still greater than 1%. If filtration is used, the high viscosity of crude phosphoric acid and the small size of the solid particles in the acid significantly reduce filtration strength, leading to difficulties or even failure in filtration. Various flocculants can be used for sedimentation, including starch, tannins, cellulose, sodium alginate, polyacrylamide and its derivatives, carboxymethyl cellulose, etc. When used in the sedimentation of concentrated crude phosphoric acid, these flocculants result in incomplete sedimentation, excessively high bottom liquid levels, and the inability to obtain clarified phosphoric acid. Because of the high viscosity of crude phosphoric acid, flocculants have difficulty adsorbing sludge particles; even if they do, bridging makes the sludge very loose, resulting in excessively high bottom liquid levels.

[0004] Therefore, a flocculant and method for rapidly reducing the solid content of wet-process phosphoric acid, as proposed in patent publication CN114671419A, uses an organic carboxylic acid-based flocculant to rapidly reduce the solid content of crude phosphoric acid during the wet-process phosphoric acid purification process. This method exhibits high flocculant efficiency and good results, effectively solving problems such as slow and incomplete settling of solid particles in existing wet-process phosphoric acid processes, excessively high bottom liquid height due to loose sludge, and the inability to obtain clarified phosphoric acid. However, this flocculant and method require a large phosphoric acid storage and settling space, resulting in a long settling time. Summary of the Invention

[0005] This invention provides a sedimentation method and sedimentation system for reducing the solid content of wet-process phosphate, in order to solve the technical problems of existing phosphate storage having large sedimentation space, limited sedimentation effect, and long sedimentation time.

[0006] The embodiments of the present invention are achieved through the following technical solutions:

[0007] A sedimentation method for reducing the solid content of wet-process phosphate includes the following steps:

[0008] S1: Emptying preparation;

[0009] S2: Preliminary sedimentation: Add agent A with a volume of V1 to the phosphoric acid for sedimentation, where V1 is 0.47 L / m³ based on the volume of phosphoric acid. 3 ~0.59L / m 3 ;

[0010] S3: Secondary sedimentation: After the initial sedimentation, agent B with a volume of V2 is added to the phosphoric acid for further sedimentation, where V2 is 0.8 L / m³ based on the volume of phosphoric acid. 3 -V1;

[0011] Agent A is an aqueous solution prepared by mixing organic carboxylic acids and anionic surfactants at a mass ratio of 1:5 to 7; Agent B is an aqueous solution prepared by mixing organic carboxylic acids and anionic surfactants at a mass ratio of 1:2 to 3.

[0012] Preferably, step S1 further includes the following specific steps: adjusting the liquid level of the primary sedimentation device to drop below 30%, and adjusting the liquid level of the secondary sedimentation device to drop below 10%.

[0013] Preferably, step S3 further includes the following specific steps: sampling and observing the clarification of phosphoric acid at three different liquid levels in the secondary sedimentation device; collecting the upper clear liquid and the lower precipitate upwards and downwards respectively according to the clarification status, and leaving the middle turbid liquid in the secondary sedimentation device; the sampling heights are 65%, 40%, and 22% of the liquid level.

[0014] Preferably, in step S3, the flow rate of phosphoric acid introduced into the secondary sedimentation device after the initial sedimentation does not exceed 300 m / s. 3 / h.

[0015] A settling agent for a wet-process phosphate solids content sedimentation method includes Agent A for initial sedimentation and Agent B for secondary sedimentation. Agent A is an aqueous solution with a total mass concentration of 30-50% prepared by organic carboxylic acid and anionic surfactant at a mass ratio of 1:5-7. Agent B is an aqueous solution with a total mass concentration of 20-40% prepared by organic carboxylic acid and anionic surfactant at a mass ratio of 1:2-3.

[0016] Preferably, the organic carboxylic acid in agents A and B is at least one of benzoic acid, o-hydroxybenzoic acid, salicylic acid, and dodecanoic acid.

[0017] Preferably, the anionic surfactants in Agent A and Agent B are at least two of polyacrylate, carboxymethyl cellulose, alkylbenzene sulfonic acid and its sodium salt, carboxyl-modified polyacrylamide, and sodium dodecyl sulfonate.

[0018] A sedimentation system employing the aforementioned method for reducing the solid content of wet-process phosphoric acid includes a first sedimentation device for initial sedimentation of phosphoric acid, a second sedimentation device for secondary sedimentation of the phosphoric acid, a first metering pump for adding agent A, a second metering pump for adding agent B, and a lift pump for introducing the initially sedimented phosphoric acid into the second sedimentation device, wherein the lift pump is connected to the second metering pump.

[0019] Preferably, it further includes a first ton container and a second ton container for providing the A agent and the B agent respectively. The first ton container and the second ton container are respectively connected to the first metering pump and the second metering pump through a first control valve and a second control valve. The first metering pump and the second metering pump are respectively connected to the first settling device and the lifting pump through a third control valve and a fourth control valve. The first settling device is connected to the lifting pump through a fifth control valve. The lifting pump is connected to the second settling device through a sixth control valve.

[0020] Preferably, the first sedimentation device is provided with a stirring device for stirring phosphoric acid and a driving device for driving the stirring device; the second sedimentation device is provided with an upper outlet for discharging clear liquid and a lower outlet for discharging precipitate.

[0021] By adopting this technical solution, the sedimentation process is divided into two steps. Sedimentation agent A and agent B with the same composition but different proportions are designed for different steps. Phosphoric acid sedimentation is divided into two steps and two sets of sedimentation devices. Without increasing the sedimentation time, the sedimentation effect is guaranteed and the sedimentation space is reduced.

[0022] Specific chemical interactions between organic carboxylic acids and crude phosphoric acid particles, such as complexation, ion adsorption, and exchange, lead to the charge neutralization and instability of the particles. As the chemisorption force on the particle surface increases, the charge neutralization and instability capabilities also strengthen, making it easier for suspended crude phosphoric acid particles to aggregate after instability, thus promoting sedimentation.

[0023] Anionic surfactants not only reduce the viscosity of crude phosphoric acid and accelerate sedimentation, but also possess a chain-like macromolecular structure with numerous SO4, COOH, and SO3H active functional groups on their long carbon chains. These groups adsorb onto the surface of dispersed crude phosphoric acid particles through electrostatic interactions, hydrogen bonds, or chemical bonds. When other suspended particles come into contact with the overhanging portions of these long carbon chains, similar adhesion occurs. Through the bridging effect of the polymer, particles agglomerate, reducing the number of fine particles and increasing the apparent particle size, thus increasing the sedimentation rate. Some particles interact with the flocculant to form an envelope layer, which traps other particles, filling the gaps and making the envelope layer denser. This leads to rapid stratification with the phosphoric acid, promoting sedimentation.

[0024] In the initial sedimentation, by adjusting and increasing the ratio of anionic surfactants in Agent A, the viscosity of phosphoric acid is effectively reduced first. At the same time, large sludge particles are quickly settled out. After the large sludge particles are settled out, the phosphoric acid is transferred to the second sedimentation device, where Agent B is added for secondary sedimentation. The secondary sedimentation increases the ratio of organic carboxylic acids, which disrupt the stability of phosphoric acid particles and further accelerate the sedimentation speed. With the phosphoric acid viscosity already low, the sedimentation speed of phosphoric acid is accelerated, thus improving the sedimentation effect of phosphoric acid.

[0025] The above sedimentation method and sedimentation agent are achieved through a sedimentation system. The sedimentation system can precisely control the amount of agent A and agent B added while meeting the requirements of two-step sedimentation. At the same time, when phosphoric acid is introduced into the second sedimentation device after the initial sedimentation, it can be fully mixed with agent B. The booster pump plays the role of mixing agent B while delivering phosphoric acid, eliminating the need for the mixing and stirring device of the second sedimentation device and saving the mixing time of the second sedimentation device.

[0026] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects:

[0027] 1. This invention divides phosphoric acid sedimentation into two steps and two sets of sedimentation devices, ensuring sedimentation effect and reducing sedimentation space without increasing sedimentation time;

[0028] 2. In the initial sedimentation of this invention, the viscosity of phosphoric acid is effectively reduced first, and large particles of sludge are quickly settled. After the large particles of sludge are settled, the phosphoric acid is transferred to the second sedimentation device. The secondary sedimentation uses organic carboxylic acids to destroy the stability of the phosphoric acid particles, further accelerating the sedimentation speed. When the viscosity of phosphoric acid is already low, the sedimentation speed of phosphoric acid is accelerated, and the sedimentation effect of phosphoric acid is improved.

[0029] 3. The sedimentation system of the present invention can precisely control the addition amount of agent A and agent B while meeting the requirements of two-step sedimentation. At the same time, when phosphoric acid is introduced into the second sedimentation device after the initial sedimentation, it can be fully mixed with agent B, eliminating the need for the mixing and stirring device of the second sedimentation device and saving the mixing time of the second sedimentation device. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of the sedimentation system for reducing the solid content of wet-process phosphate provided in Embodiment 1 of the present invention.

[0032] Reference numerals: 1-First settling device, 11-Drive device, 12-Agitator, 13-Fifth control valve, 2-Second settling device, 21-Upper discharge outlet, 22-Lower discharge outlet, 3-First metering pump, 31-First control valve, 32-Third control valve, 4-Second metering pump, 41-Second control valve, 42-Fourth control valve, 5-Lifting pump, 51-Sixth control valve, 61-First ton container, 62-Second ton container. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0035] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0036] In the description of this invention, it should be noted that if terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," or "outer" are used to indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product is in use, they are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0037] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0038] Example 1

[0039] A sedimentation method for reducing the solid content of wet-process phosphate includes the following steps:

[0040] S1: Venting preparation: Adjust the liquid level of the first settling device 1 to drop below 30%, and the liquid level of the second settling device 2 to drop below 10%;

[0041] S2: Preliminary sedimentation: Phosphoric acid and phosphoric acid volume were 0.53 L / m³. 3 After adding agent A to the first sedimentation device 1 and stirring, let it stand and clarify for 10 hours;

[0042] S3: Secondary sedimentation: Phosphoric acid from the first sedimentation device 1 is passed into the second sedimentation device 2. The first sedimentation device 1 performs preliminary sedimentation of the next batch of phosphoric acid, while the second sedimentation device 2 simultaneously adds 0.27 L / m³ of phosphoric acid by volume. 3 Agent B is added, and after 10 hours of sedimentation, the phosphoric acid is observed to clarify and then discharged. The second sedimentation device 2 is then used for the secondary sedimentation of the next batch of phosphoric acid.

[0043] In this embodiment, step S3 further includes the following specific steps:

[0044] Sampling and observation of phosphoric acid clarification at three different liquid levels in the second sedimentation device 2 were conducted. Based on the clarification, the upper clear liquid and the lower precipitate were discharged upwards and downwards respectively for collection, while the middle turbid liquid remained in the second sedimentation device 2.

[0045] In this embodiment, in step S3, the sampling heights are 65%, 40%, and 22% of the liquid level, respectively.

[0046] A sedimentation method for reducing the solid content of wet-process phosphoric acid, wherein in step S3, the flow rate of phosphoric acid from the first sedimentation device 1 into the second sedimentation device 2 is 300 m³ / s. 3 / h.

[0047] A settling agent for a wet-process phosphate solids content sedimentation method includes an agent A for initial sedimentation and an agent B for secondary sedimentation. The agent A is an aqueous solution with a total mass concentration of 30% prepared by organic carboxylic acid and anionic surfactant at a mass ratio of 1:6. The agent B is an aqueous solution with a total mass concentration of 40% prepared by organic carboxylic acid and anionic surfactant at a mass ratio of 1:2.5.

[0048] In this embodiment, the organic carboxylic acid in agents A and B is benzoic acid.

[0049] In this embodiment, the anionic surfactant in Agent A and Agent B is a mixture of polyacrylate and carboxymethyl cellulose.

[0050] A sedimentation system employing the aforementioned method for reducing the solid content of wet-process phosphoric acid includes a first sedimentation device 1 for initial sedimentation of phosphoric acid, a second sedimentation device 2 for secondary sedimentation of the phosphoric acid, a first metering pump 3 for adding agent A, a second metering pump 4 for adding agent B, and a lift pump 5 for introducing the initially sedimented phosphoric acid into the second sedimentation device 2, wherein the lift pump 5 is connected to the second metering pump 4.

[0051] In this embodiment, a first ton container 61 and a second ton container 62 are also included for providing the A agent and the B agent respectively. The first ton container 61 and the second ton container 62 are respectively connected to the first metering pump 3 and the second metering pump 4 through a first control valve 31 and a second control valve 41. The first metering pump 3 and the second metering pump 4 are respectively connected to the first settling device 1 and the lifting pump 5 through a third control valve 32 and a fourth control valve 42. The first settling device 1 is connected to the lifting pump 5 through a fifth control valve 13. The lifting pump 5 is connected to the second settling device 2 through a sixth control valve 51.

[0052] In this embodiment, the first sedimentation device 1 is provided with a stirring device 12 for stirring phosphoric acid and a driving device 11 for driving the stirring device 12; the second sedimentation device 2 is provided with an upper discharge outlet 21 for discharging clear liquid and a lower discharge outlet 22 for discharging precipitate.

[0053] In this embodiment, the volume of the first settling device is 50m³. 3 The second settling device has a volume of 30m³.3 .

[0054] By adopting this technical solution, the sedimentation process is divided into two steps. Sedimentation agent A and agent B with the same composition but different proportions are designed for different steps. Phosphoric acid sedimentation is divided into two steps and two sets of sedimentation devices. Without increasing the sedimentation time, the sedimentation effect is guaranteed and the sedimentation space is reduced.

[0055] Specific chemical interactions between organic carboxylic acids and crude phosphoric acid particles, such as complexation, ion adsorption, and exchange, lead to the charge neutralization and instability of the particles. As the chemisorption force on the particle surface increases, the charge neutralization and instability capabilities also strengthen, making it easier for suspended crude phosphoric acid particles to aggregate after instability, thus promoting sedimentation.

[0056] Anionic surfactants not only reduce the viscosity of crude phosphoric acid and accelerate sedimentation, but also possess a chain-like macromolecular structure with numerous SO4, COOH, and SO3H active functional groups on their long carbon chains. These groups adsorb onto the surface of dispersed crude phosphoric acid particles through electrostatic interactions, hydrogen bonds, or chemical bonds. When other suspended particles come into contact with the overhanging portions of these long carbon chains, similar adhesion occurs. Through the bridging effect of the polymer, particles agglomerate, reducing the number of fine particles and increasing the apparent particle size, thus increasing the sedimentation rate. Some particles interact with the flocculant to form an envelope layer, which traps other particles, filling the gaps and making the envelope layer denser. This leads to rapid stratification with the phosphoric acid, promoting sedimentation.

[0057] In the initial sedimentation, by adjusting and increasing the ratio of anionic surfactant in Agent A, the viscosity of phosphoric acid is effectively reduced first. At the same time, large sludge particles are quickly settled out. After the large sludge particles are settled out, the phosphoric acid is transferred to the second sedimentation device 2, Agent B is added, and secondary sedimentation is carried out. The secondary sedimentation increases the ratio of organic carboxylic acid. The organic carboxylic acid destroys the stability of phosphoric acid particles, further accelerating the sedimentation speed. When the viscosity of phosphoric acid is already low, the sedimentation speed of phosphoric acid is accelerated, and the sedimentation effect of phosphoric acid is improved.

[0058] The above sedimentation method and sedimentation agent are achieved through a sedimentation system. The sedimentation system can accurately control the amount of agent A and agent B added while meeting the requirements of two-step sedimentation. At the same time, after the initial sedimentation, when phosphoric acid is introduced into the second sedimentation device 2, it can be fully mixed with agent B. The booster pump 5 plays the role of mixing agent B while transporting phosphoric acid, eliminating the need for the mixing and stirring device 12 of the second sedimentation device 2, and saving the mixing time of the second sedimentation device 2.

[0059] Example 2

[0060] The only difference between this embodiment and Embodiment 1 is that, in step S2, phosphoric acid and phosphoric acid volume are 0.59 L / m³. 3 Agent A is added to the first settling device 1;

[0061] In step S3, 0.21 L / m³ of phosphoric acid is simultaneously added to the second settling device 2. 3 Agent B.

[0062] Example 3

[0063] The only difference between this embodiment and Embodiment 1 is that, in step S2, phosphoric acid and phosphoric acid volume are 0.47 L / m³. 3 Agent A is added to the first settling device 1;

[0064] In step S3, 0.33 L / m³ of phosphoric acid is simultaneously added to the second settling device 2. 3 Agent B.

[0065] Example 4

[0066] The only difference between this embodiment and Embodiment 1 is that Agent A is an aqueous solution with a total mass concentration of 30% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:5; and Agent B is an aqueous solution with a total mass concentration of 40% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:3.

[0067] Example 5

[0068] The only difference between this embodiment and Embodiment 1 is that Agent A is an aqueous solution with a total mass concentration of 30% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:7; and Agent B is an aqueous solution with a total mass concentration of 40% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:2.

[0069] Example 6

[0070] The only difference between this embodiment and Embodiment 1 is that Agent A is an aqueous solution with a total mass concentration of 50% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:6; and Agent B is an aqueous solution with a total mass concentration of 20% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:2.5.

[0071] Example 7

[0072] The only difference between this embodiment and Embodiment 1 is that Agent A is an aqueous solution with a total mass concentration of 40% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:6; and Agent B is an aqueous solution with a total mass concentration of 30% prepared by mixing benzoic acid, polyacrylate, and carboxymethyl cellulose in a mass ratio of 1:2.5.

[0073] Comparative Example 1

[0074] The only difference between this comparative example and Example 1 is that the sedimentation was carried out in the same sedimentation device, with Agent A and Agent B added in two separate steps, and each agent was allowed to settle for 10 hours after addition.

[0075] Comparative Example 2

[0076] The only difference between this comparative example and Example 1 is that in this comparative example, the flocculant is not divided into Agent A and Agent B; the same flocculant is used in both sedimentation steps. The flocculant is an aqueous solution with a total mass concentration of 20%, prepared from a mixture of benzoic acid, polyacrylate, and carboxymethyl cellulose at a mass ratio of 1:4. The amount of flocculant added is 0.8 L / m³ based on the volume of phosphoric acid. 3 .

[0077] Comparative Example 3

[0078] The only difference between this comparative example and Example 1 is that the second sedimentation device is used to remove the precipitate by sedimentation for 10 hours to obtain phosphoric acid.

[0079] The relevant experimental data for the above embodiments and comparative examples are shown in Table 1 below.

[0080] Table 1. Relevant experimental data of Examples 1-7 and Comparative Examples 1-3

[0081]

[0082] The MER values ​​and solid content of the supernatant obtained from the above embodiments and the second sedimentation device 2 of the comparative example are shown in Table 2.

[0083] Table 2. Relevant test data of Examples 1-7 and Comparative Examples 1-3

[0084]

[0085] The value of MER is equal to ((Al2O3%+Fe2O3%+MgO%) / P2O5%).

[0086] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sedimentation method for reducing the solid content of wet-process phosphate, characterized in that: Includes the following steps: S1: Emptying preparation; S2: Preliminary sedimentation: Add agent A with a volume of V1 to the phosphoric acid for sedimentation, where V1 is 0.47 L / m³ based on the volume of phosphoric acid. 3 ~0.59L / m 3 Phosphoric acid is initially settled using a preliminary settling device. S3: Secondary sedimentation: After the initial sedimentation, agent B with a volume of V2 is added to the phosphoric acid for further sedimentation, where V2 is 0.8 L / m³ based on the volume of phosphoric acid. 3 -V1; Secondary sedimentation phosphoric acid uses a secondary sedimentation device; Agent A is an aqueous solution prepared by mixing an organic carboxylic acid and anionic surfactant in a mass ratio of 1:5 to 7; Agent B is an aqueous solution prepared by mixing an organic carboxylic acid and anionic surfactant in a mass ratio of 1:2 to 3; the organic carboxylic acid in Agent A is the same as that in Agent B, and the anionic surfactant in Agent A is the same as that in Agent B.

2. The sedimentation method for reducing the solid content of wet-process phosphate according to claim 1, characterized in that: Step S1 also includes the following specific steps: adjusting the liquid level of the primary sedimentation device to drop below 30%, and adjusting the liquid level of the secondary sedimentation device to drop below 10%.

3. The sedimentation method for reducing the solid content of wet-process phosphate according to claim 1, characterized in that: Step S3 also includes the following specific steps: sampling and observing the clarification of phosphoric acid at three different liquid levels in the secondary sedimentation device; collecting the upper clear liquid and the lower precipitate upwards and downwards respectively according to the clarification status, and leaving the middle turbid liquid in the secondary sedimentation device; the sampling heights are 65%, 40% and 22% of the liquid level.

4. A sedimentation method for reducing the solid content of wet-process phosphate according to any one of claims 1-3, characterized in that: In step S3, the flow rate of phosphoric acid after the initial sedimentation into the secondary sedimentation device does not exceed 300 m / s. 3 / h.

5. A flocculant for a method of reducing the solid content of wet-process phosphate sedimentation, characterized in that: The mixture includes Agent A for initial sedimentation and Agent B for secondary sedimentation as described in any one of claims 1-4, wherein Agent A is an aqueous solution with a total mass concentration of 30%-50% prepared by organic carboxylic acid and anionic surfactant in a mass ratio of 1:5-7; and Agent B is an aqueous solution with a total mass concentration of 20%-40% prepared by organic carboxylic acid and anionic surfactant in a mass ratio of 1:2-3.

6. The flocculant for a method of reducing the solid content of wet-process phosphate sedimentation according to claim 5, characterized in that: The organic carboxylic acid in Agent A and Agent B is at least one of benzoic acid, o-hydroxybenzoic acid, and dodecanoic acid.

7. The flocculant for a method of reducing the solid content of wet-process phosphate sedimentation according to claim 5, characterized in that: The anionic surfactants in Agent A and Agent B are at least two of the following: polyacrylate, carboxymethyl cellulose, alkylbenzene sulfonic acid and its sodium salt, carboxyl-modified polyacrylamide, and sodium dodecyl sulfonate.

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