A high-efficiency recovery and washing method for phosphate particles

Abstract

This invention discloses a highly efficient method for recovering and washing phosphate particles, relating to the field of compound separation and processing technology. This invention utilizes a dielectric electrophoresis field to achieve initial enrichment and purification by leveraging the differences in macroscopic physical properties (dielectric constant, conductivity) between phosphate and major impurities. This significantly reduces the impurity load and complexity of the subsequent processing system. In the pre-purified system, a selective surface modifier is introduced. This modifier, through molecular design, can specifically recognize and adsorb onto the surface of phosphate particles. By altering their surface hydrophilicity / hydrophobicity or Zeta potential, it creates and amplifies the differences in surface chemical properties between phosphate and residual impurities with similar dielectric properties. This cascade strategy of physical field coarse separation creating a favorable environment and chemical modification fine separation amplifying the differences provides a selective basis for subsequent separation processes based on surface property differences, thereby enabling the efficient separation of impurities with similar physical properties that are difficult to separate using traditional methods.

Description

Technical Field

[0001] This invention relates to the field of compound separation and processing technology, specifically to a method for efficient recovery and washing of phosphate particles. Background Technology

[0002] Phosphate is an indispensable basic raw material for modern agriculture and the chemical industry, and its purity directly affects the quality and performance of downstream products. In the wet-process phosphoric acid production or phosphate rock processing, the generated phosphate particles often coexist with various impurities such as silica, aluminates, iron and magnesium compounds, and organic matter. To obtain high-purity phosphate products, these impurities must be effectively separated through a washing process. However, phosphate particles and some impurities are extremely similar in physical properties such as particle size and density, posing a significant challenge to traditional separation methods based on differences in gravity or centrifugal force. Developing efficient and highly selective deep washing technology has become a bottleneck that the industry urgently needs to overcome.

[0003] Currently, industrial phosphate washing methods mostly rely on multi-stage countercurrent decantation, hydrocyclone classification, or belt filter washing. These methods essentially remove impurities through hydraulic scouring and solid-liquid displacement. They are effective for impurities with properties vastly different from the target product, but their separation efficiency drops sharply for impurities with similar physicochemical properties. To improve selectivity, existing technologies have made numerous attempts:

[0004] The flotation method uses the difference in surface hydrophilicity and hydrophobicity to separate substances by adding collectors and frothers, but it introduces new chemical reagents, contaminates the product, and makes wastewater treatment complicated.

[0005] While immersion in acid or alkali can dissolve some impurities, it can also lead to localized dissolution and loss of the target phosphate, as well as corrosion of equipment and the generation of large amounts of saline wastewater.

[0006] In addition, some improved physical methods, such as enhanced hydraulic shearing or high-temperature washing, are often energy-intensive and have limited effectiveness in eliminating lattice inclusions or tightly adsorbed impurities on the particle surface.

[0007] Therefore, existing technologies generally suffer from the dilemma of simultaneously achieving high separation accuracy, chemical reagent residues, and resource recovery rates. There is a need for a method that actively identifies and separates particles of different components, achieving enhanced sorting at the microscopic scale. This would overcome the purity bottleneck of traditional processes and simultaneously realize efficient resource recovery and a green, low-carbon process. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a highly efficient method for the recovery and washing of phosphate particles. This method utilizes a dielectric electrophoresis field to leverage the differences in macroscopic physical properties (dielectric constant, conductivity) between phosphate and major impurities to achieve initial enrichment and purification, significantly reducing the impurity load and complexity of subsequent processing systems. In the pre-purified system, a selective surface modifier is introduced. This modifier, through molecular design, can specifically recognize and adsorb onto the surface of phosphate particles. By altering their surface hydrophilicity / hydrophobicity or Zeta potential, it creates and amplifies the differences in surface chemical properties between phosphate and residual impurities with similar dielectric properties. This cascade strategy of creating a favorable environment through physical field coarse separation and amplifying differences through chemical modification provides a selective basis for subsequent separation processes based on surface property differences, thereby enabling the efficient separation of impurities with similar physical properties that are difficult to separate using traditional methods.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for efficient recovery and washing of phosphate particles, the specific steps of which are as follows:

[0010] S100. Preparation of pre-sorted suspension: Add the phosphate particles containing impurities into the washing reactor, mix with the washing liquid at a solid-liquid mass ratio of 1:3-1:5, adjust the solid content to 5%-30%, and adjust the conductivity to 1-1000μS / cm to obtain the pre-sorted suspension.

[0011] S200, Dielectrophoretic pre-sorting: The pre-sorted suspension is flowed through a sorting region with a non-uniform high-frequency alternating electric field applied. By utilizing the difference in dielectric constant and conductivity between phosphate particles and impurity particles, phosphate particles are enriched in the low-gradient electric field region, while impurity particles migrate and aggregate in the high-gradient electric field region. The low-gradient electric field region is collected to obtain a pre-sorted suspension enriched with phosphate particles.

[0012] S300, In-situ surface modification: Add a selective surface modifier to the pre-sorted suspension and stir and mix at 10-50°C for 1-15 minutes to allow the selective surface modifier to adsorb onto the surface of phosphate particles, thereby specifically changing the surface hydrophilicity / hydrophobicity and surface Zeta potential of the phosphate particles to obtain a modified suspension.

[0013] S400, Dynamic membrane separation and washing: The modified suspension is subjected to dynamic membrane separation, using the formed dynamic membrane layer as the separation interface. Based on the surface property difference of S300, phosphate particles preferentially penetrate the dynamic membrane layer, while impurity particles are retained. At the same time, the penetrated phosphate particles are countercurrently washed to obtain phosphate concentrate slurry.

[0014] S500, Post-processing: The phosphate concentrate slurry is dehydrated to obtain a high-purity phosphate product, and the impurity-rich retentate generated by the S400 dynamic membrane separation operation is collected.

[0015] Furthermore, in S100, the washing liquid is water, dilute acid solution, or dilute alkali solution, and the conductivity is adjusted by adding electrolyte and dilution.

[0016] Furthermore, the working principle of the S200 dielectrophoretic pre-sorting is as follows: the pre-sorted suspension is controlled to pass through the sorting region in the form of a thin laminar flow. By adjusting the frequency and field strength gradient of the non-uniform high-frequency alternating electric field, phosphate particles are enriched in the region with a weak electric field strength gradient and collected as the pre-sorted suspension, while impurity particles are enriched in the region with a strong electric field strength gradient and discharged as the impurity enrichment liquid. The frequency of the non-uniform high-frequency alternating electric field is 50kHz-10MHz, and the field strength gradient is 106-108V / m. 2 .

[0017] Furthermore, in S300, the selective surface modifier is one or more of a biodegradable nonionic surfactant, cationic surfactant, or zwitterionic surfactant, and the amount of the selective surface modifier added is 0.1%-0.3% of the mass of the phosphate particle raw material in the pre-sorted suspension.

[0018] Furthermore, in S300, the specific changes are as follows: the surface contact angle of the phosphate particles is increased by 10°-60°, the absolute value of the surface Zeta potential of the phosphate particles is increased by 10mV-40mV, and the change in the surface properties of the impurity particles is less than 50% of the change in the phosphate particles.

[0019] Furthermore, in S400, the dynamic membrane separation operation is carried out in a dynamic membrane filter, which uses a porous screen, sintered metal, or fabric as the base membrane.

[0020] The dynamic membrane layer is formed in situ on the surface of the base membrane by fine particles of the modified suspension in S300.

[0021] Furthermore, in S400, the countercurrent washing of the penetrated phosphate particles specifically involves: introducing washing liquid from the permeation side of the dynamic membrane layer, and rinsing and replacing the phosphate particles in a flow direction opposite to the penetration direction of the phosphate particles, with a washing time of 20-30 minutes and a washing liquid to phosphate particle mass ratio of 1:1-5:1.

[0022] Furthermore, the phosphate particles are at least one of monoammonium phosphate, diammonium phosphate, calcium dihydrogen phosphate, and calcium hydrogen phosphate;

[0023] The impurity particles include at least one of silicon dioxide, silicates, aluminates, iron compounds, magnesium compounds, and organic matter.

[0024] Furthermore, in S500, the impurity-rich retentate generated from the dynamic membrane separation operation is returned to S100 for recycling in order to prepare the pre-sorted suspension.

[0025] Compared with existing technologies, this efficient phosphate particle recovery and washing method has the following advantages:

[0026] This invention utilizes a dielectric electrophoresis field to achieve initial enrichment and purification by leveraging the differences in macroscopic physical properties (dielectric constant and conductivity) between phosphate and major impurities. This significantly reduces the impurity load and complexity of subsequent processing systems. In the pre-purified system, a selective surface modifier is introduced. This agent, through molecular design, can specifically recognize and adsorb onto the surface of phosphate particles. By altering their surface hydrophilicity / hydrophobicity or Zeta potential, it creates and amplifies the differences in surface chemical properties between phosphate and residual impurities with similar dielectric properties. This cascade strategy of using a physical field to create a favorable environment for coarse separation and chemical modification to refine and amplify the differences provides a selective basis for subsequent separation processes based on surface property differences. This enables the efficient separation of impurities with similar physical properties that are difficult to separate using traditional methods.

[0027] In the dynamic membrane separation stage, this invention utilizes phosphate particles with specifically modified surfaces. Under cross-flow filtration conditions, these particles are less likely to adhere tightly to the membrane surface or to each other. Instead, they form a loose, highly porosity, and highly permeable initial dynamic membrane layer. When subsequent suspensions flow through this layer, impurity particles with unchanged or minimally changed surface properties are more easily trapped or adsorbed by the loose layer due to the difference in interaction forces between them and the dynamic membrane material and the base membrane. Meanwhile, modified phosphate particles with similar properties are more easily penetrated. This mechanism allows the separation process to not rely solely on the pore size of the base membrane but also to couple the differences in surface affinity. This achieves high precision trapping of fine impurities while maintaining high filtration flux. At the same time, the dynamic layer formed by the modified particles protects the base membrane, greatly mitigating the risk of impurities directly clogging the membrane pores.

[0028] Other advantages, objectives and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination or study, or may be learned from the practice of the invention. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0030] Figure 1 This is a flowchart illustrating the steps of a method for the efficient recovery and washing of phosphate particles. Detailed Implementation

[0031] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with the accompanying drawings and preferred embodiments, is provided below.

[0032] To address the problems of low separation accuracy, residual chemical reagent pollution, insufficient resource recovery rate, and high energy consumption in existing phosphate washing technologies, this invention focuses on industrial scenarios such as wet-process phosphoric acid production and phosphate rock processing, which require deep purification of phosphate particles such as monoammonium phosphate, diammonium phosphate, and dihydrogen phosphate. In these scenarios, phosphate particles often coexist with impurities such as silica, silicates, aluminates, iron and magnesium compounds, and organic matter. Traditional separation methods based on gravity, centrifugal force, or simple pore size sieving are difficult to overcome the separation bottleneck of impurities with similar physical properties and are prone to causing loss of target products or environmental pollution. This invention aims to achieve efficient recovery and high-precision purification of phosphate particles through a cascade process of "physical field pre-sorting, specific chemical modification, and dynamic membrane precise separation," while also considering the green and low-carbon nature of the process and resource recycling.

[0033] The present invention provides a method for efficient recovery and washing of phosphate particles, such as... Figure 1 As shown, the specific steps of this method are as follows:

[0034] S100. Preparation of pre-sorted suspension: Add the phosphate particles containing impurities into the washing reactor, mix with the washing liquid at a solid-liquid mass ratio of 1:3-1:5, adjust the solid content to 5%-30%, and adjust the conductivity to 1-1000μS / cm to obtain the pre-sorted suspension.

[0035] S200, Dielectrophoretic pre-sorting: The pre-sorted suspension is flowed through a sorting region with a non-uniform high-frequency alternating electric field applied. By utilizing the difference in dielectric constant and conductivity between phosphate particles and impurity particles, phosphate particles are enriched in the low-gradient electric field region, while impurity particles migrate and aggregate in the high-gradient electric field region. The low-gradient electric field region is collected to obtain a pre-sorted suspension enriched with phosphate particles.

[0036] S300, In-situ surface modification: Add a selective surface modifier to the pre-sorted suspension and stir and mix at 10-50°C for 1-15 minutes to allow the selective surface modifier to adsorb onto the surface of phosphate particles, thereby specifically changing the surface hydrophilicity / hydrophobicity and surface Zeta potential of the phosphate particles to obtain a modified suspension.

[0037] S400, Dynamic membrane separation and washing: The modified suspension is subjected to dynamic membrane separation, using the formed dynamic membrane layer as the separation interface. Based on the surface property difference of S300, phosphate particles preferentially penetrate the dynamic membrane layer, while impurity particles are retained. At the same time, the penetrated phosphate particles are countercurrently washed to obtain phosphate concentrate slurry.

[0038] S500, Post-processing: The phosphate concentrate slurry is dehydrated to obtain a high-purity phosphate product, and the impurity-rich retentate generated by the S400 dynamic membrane separation operation is collected.

[0039] Example 1

[0040] This embodiment targets calcium dihydrogen phosphate particles containing composite impurities (silica + organic matter). It employs a synergistic process of dielectric electrophoretic pre-sorting, in-situ surface modification, dynamic membrane separation, and countercurrent washing. By optimizing electric field parameters, selecting non-ionic selective surface modifiers, and matching dynamic membrane separation conditions, it achieves efficient recovery and high-purity purification of calcium dihydrogen phosphate particles, making it suitable for composite impurity scenarios in actual industrial production.

[0041] In the specific implementation process:

[0042] S100. Preparation of pre-sorted suspension: Add the calcium dihydrogen phosphate granules containing impurities (silica mass fraction 2.3%, organic matter mass fraction 1.1%) to the washing reactor, mix with deionized water (washing liquid) at a solid-liquid mass ratio of 1:4, stir at a speed of 200 r / min, adjust the solid content to 15%, and adjust the conductivity to 500 μS / cm by adding potassium chloride electrolyte to obtain a uniform pre-sorted suspension.

[0043] S200, Dielectrophoretic Pre-sorting: The pre-sorting suspension is controlled to flow through the sorting area in a thin laminar flow with a thickness of 1.0 mm. A titanium alloy ring electrode and a central electrode are set in the sorting area, and a non-uniform high-frequency alternating electric field is applied with a frequency of 5 MHz and a field strength gradient of 5 × 10⁻⁶. 7 V / m 2 By utilizing the difference in dielectric properties between calcium dihydrogen phosphate particles and silica and organic matter, calcium dihydrogen phosphate particles are enriched in the low electric field gradient region, while impurity particles migrate and aggregate in the high electric field gradient region. The material in the low electric field gradient region is collected to obtain a pre-sorted suspension, while the impurity enrichment liquid is discharged.

[0044] S300, In-situ Surface Modification: A selective surface modifier (biodegradable nonionic surfactant modified starch) is added to the pre-sorted suspension at a rate of 0.2% of the mass of the calcium dihydrogen phosphate particles in the pre-sorted suspension. The system temperature is controlled at 30°C, and the mixture is stirred at a rate of 150 r / min for 8 minutes to allow the modified starch to be specifically adsorbed onto the surface of the calcium dihydrogen phosphate particles. The surface contact angle of the calcium dihydrogen phosphate particles is measured to increase from 35° to 62°, and the absolute value of the surface Zeta potential increases from 18 mV to 39 mV. The changes in the surface contact angle and Zeta potential between silica and organic matter are both less than 10%, thus obtaining a modified suspension.

[0045] S400, Dynamic Membrane Separation and Washing: The modified suspension is pumped into a dynamic membrane filtration device, which uses a porous screen with a pore size of 0.2 μm as the base membrane. Fine impurity particles and a small amount of modifier molecules in the modified suspension form a dynamic membrane layer in situ on the surface of the base membrane. The filtration pressure is controlled at 0.12 MPa and the cross-flow rate is 1.2 m / s. Deionized water is introduced from the permeate side of the dynamic membrane layer and washed countercurrently in the opposite direction to the penetration direction of the calcium dihydrogen phosphate particles. The mass ratio of washing liquid to calcium dihydrogen phosphate particles is 3:1, and the washing time is 25 min to obtain calcium dihydrogen phosphate concentrate slurry.

[0046] S500, Post-processing: The calcium dihydrogen phosphate concentrate slurry is fed into a horizontal spiral centrifuge for dewatering at a dewatering rate of 3500 r / min for 7 min to obtain high-purity calcium dihydrogen phosphate product; the impurity-rich retentate generated by the dynamic membrane separation operation is collected, and after removing large particulate impurities by plate and frame filtration, it is returned to S100 for recycling to prepare pre-sorted suspension.

[0047] Performance Testing Specifications

[0048] Product purity: The residual amount of impurities such as silica and organic matter in the calcium dihydrogen phosphate product was determined by ion chromatography, and the product purity was calculated.

[0049] Phosphate recovery rate: The recovery rate is calculated by weighing the total mass of calcium dihydrogen phosphate in the raw material and the mass of calcium dihydrogen phosphate in the final product.

[0050] Membrane fouling rate: The membrane fouling rate is calculated by measuring the initial filtration flux of dynamic membrane separation and the filtration flux after 25 minutes of operation, and then calculating the flux decay ratio.

[0051] Impurity removal rate: The mass fractions of silica and organic matter in the raw materials and the corresponding impurities in the products were measured respectively, and the removal rate of a single impurity was calculated.

[0052] Test Results

[0053] In this embodiment, the purity of the high-purity calcium dihydrogen phosphate product is 99.72%, the calcium dihydrogen phosphate recovery rate is 96.3%, the membrane blockage rate after 25 minutes of dynamic membrane separation operation is 4.8%, the silica removal rate is 98.6%, and the organic matter removal rate is 98.2%.

[0054] Example 2

[0055] This embodiment targets monoammonium phosphate particles containing difficult-to-separate impurities (silicates + aluminates). It employs low-gradient electric field parameters, zwitterionic selective surface modifiers, and suitable dynamic membrane separation conditions to verify the effectiveness of the technical solution in the lower limit of parameters and in water-soluble phosphate systems, achieving efficient removal of difficult-to-separate impurities and high recovery rate of monoammonium phosphate.

[0056] In the specific implementation process:

[0057] S100. Preparation of pre-sorted suspension: Add the monoammonium phosphate granular raw material containing impurities (silicate mass fraction 2.8%, aluminate mass fraction 1.5%) to the washing reactor, mix with 0.1mol / L dilute hydrochloric acid solution (washing liquid) at a solid-liquid mass ratio of 1:3, stir at a speed of 180r / min, adjust the solid content to 10%, and adjust the conductivity to 200μS / cm by dilution to obtain a uniform pre-sorted suspension.

[0058] S200, Dielectrophoretic Pre-sorting: The pre-sorting suspension is controlled to flow through the sorting area in a thin laminar flow (thickness 0.8 mm). A titanium alloy ring electrode and a central electrode are set in the sorting area, and a non-uniform high-frequency alternating electric field is applied with a frequency of 1 MHz and a field strength gradient of 2 × 10⁻⁶. 7 V / m 2 By utilizing the difference in dielectric properties between monoammonium phosphate particles and silicates and aluminates, monoammonium phosphate particles are enriched in the low electric field gradient region, while impurity particles migrate and aggregate in the high electric field gradient region. The material in the low electric field gradient region is collected to obtain a pre-sorted suspension, while the impurity enrichment liquid is discharged.

[0059] S300, In-situ Surface Modification: A selective surface modifier (biodegradable zwitterionic surfactant cocamidopropyl betaine) is added to the pre-sorted suspension at a rate of 0.1% of the mass of the monoammonium phosphate particles in the pre-sorted suspension. The system temperature is controlled at 25°C, and the mixture is stirred at a rate of 120 r / min for 5 minutes to allow cocamidopropyl betaine to specifically adsorb onto the surface of the monoammonium phosphate particles. The surface contact angle of the monoammonium phosphate particles is measured to increase from 28° to 55°, and the absolute value of the surface Zeta potential increases from 15 mV to 32 mV. The changes in the surface contact angle and Zeta potential of silicates and aluminates are both less than 8%, thus obtaining a modified suspension.

[0060] S400, Dynamic Membrane Separation and Washing: The modified suspension is pumped into a dynamic membrane filtration device, which uses sintered stainless steel (base membrane material) as the base membrane. Fine impurity particles and a small amount of modifier molecules in the modified suspension form a dynamic membrane layer in situ on the base membrane surface. The filtration pressure is controlled at 0.1 MPa and the cross-flow rate is 1.0 m / s. Deionized water is introduced from the permeate side of the dynamic membrane layer and washed countercurrently in the opposite direction to the penetration direction of the monoammonium phosphate particles. The mass ratio of washing liquid to monoammonium phosphate particles is 2:1, and the washing time is 20 min to obtain monoammonium phosphate concentrate slurry.

[0061] S500, Post-processing: The monoammonium phosphate concentrate slurry is fed into a horizontal spiral centrifuge for dewatering at a dewatering rate of 3000 r / min for 6 min to obtain a high-purity monoammonium phosphate product; the impurity-rich retentate generated by the dynamic membrane separation operation is collected, and after removing large particulate impurities by plate and frame filtration, it is returned to S100 for recycling to prepare a pre-sorting suspension.

[0062] The performance test instructions are the same as in Example 1.

[0063] Test results: In this example, the purity of the high-purity monoammonium phosphate product was 99.65%, and the monoammonium phosphate recovery rate was 95.8%; the membrane blockage rate after 20 minutes of dynamic membrane separation was 5.5%; the silicate removal rate was 98.1%, and the aluminate removal rate was 97.8%.

[0064] Example 3

[0065] This embodiment targets dicalcium phosphate particles containing metal impurities (iron oxides + magnesium oxides) (which have weak crystal stability). It employs high gradient electric field parameters, cationic selective surface modifiers, and high-pressure dynamic membrane separation conditions to verify the safety and efficiency of the technical solution within the parameter limits and the metal impurity system, achieving deep removal of metal impurities and high-purity recovery of dicalcium phosphate.

[0066] In the specific implementation process:

[0067] S100. Preparation of pre-sorted suspension: Add the impurity-containing dicalcium phosphate granules (iron oxide mass fraction 2.1%, magnesium oxide mass fraction 1.3%) to the washing reactor, mix with 0.1 mol / L dilute sodium bicarbonate solution (washing liquid) at a solid-liquid mass ratio of 1:5, stir at a speed of 220 r / min, adjust the solid content to 20%, and adjust the conductivity to 800 μS / cm by adding sodium chloride electrolyte to obtain a uniform pre-sorted suspension.

[0068] S200, Dielectrophoretic Pre-sorting: The pre-sorting suspension is controlled to flow through the sorting area in a thin laminar flow (1.2 mm thick). A titanium alloy ring electrode and a central electrode are set in the sorting area, and a non-uniform high-frequency alternating electric field is applied with a frequency of 8 MHz and a field strength gradient of 8 × 10⁻⁶. 7 V / m 2 By utilizing the difference in dielectric properties between dicalcium phosphate particles and iron oxides and magnesium oxides, dicalcium phosphate particles are enriched in the low electric field gradient region, while impurity particles migrate and aggregate in the high electric field gradient region. The material in the low electric field gradient region is collected to obtain a pre-sorted suspension, while the impurity enrichment liquid is discharged.

[0069] S300, In-situ Surface Modification: A selective surface modifier (biodegradable cationic surfactant alkyl glycoside ammonium chloride) is added to the pre-sorted suspension at a rate of 0.3% of the mass of the dicalcium phosphate particles in the pre-sorted suspension. The system temperature is controlled at 40°C, and the mixture is stirred at a rate of 180 r / min for 12 minutes to allow the alkyl glycoside ammonium chloride to be specifically adsorbed onto the surface of the dicalcium phosphate particles. The surface contact angle of the dicalcium phosphate particles is measured to increase from 32° to 78°, and the absolute value of the surface Zeta potential increases from 16 mV to 45 mV. The changes in the surface contact angle and Zeta potential of iron oxide and magnesium oxide are both less than 10%, thus obtaining a modified suspension.

[0070] S400, Dynamic Membrane Separation and Washing: The modified suspension is pumped into a dynamic membrane filtration device, which uses polyester fiber fabric (base membrane material) as the base membrane. Fine impurity particles and a small amount of modifier molecules in the modified suspension form a dynamic membrane layer in situ on the surface of the base membrane. The filtration pressure is controlled at 0.15 MPa and the cross-flow rate is 1.4 m / s. Deionized water is introduced from the permeate side of the dynamic membrane layer and washed in a countercurrent direction opposite to the penetration direction of the dicalcium phosphate particles. The mass ratio of washing liquid to dicalcium phosphate particles is 4:1, and the washing time is 30 min to obtain dicalcium phosphate concentrate slurry.

[0071] S500, Post-processing: The dicalcium phosphate concentrate slurry is fed into a horizontal spiral centrifuge for dewatering at a dewatering rate of 4000 r / min for 8 min to obtain high-purity dicalcium phosphate product; the impurity-rich retentate generated by the dynamic membrane separation operation is collected, and after removing large particulate impurities by plate and frame filtration, it is returned to S100 for recycling to prepare pre-sorted suspension.

[0072] The performance test instructions are the same as in Example 1.

[0073] Test results: In this embodiment, the purity of the high-purity dicalcium phosphate product was 99.81%, and the dicalcium phosphate recovery rate was 96.7%; the membrane blockage rate after 30 minutes of dynamic membrane separation was 4.2%; the iron oxide removal rate was 98.9%, and the magnesium oxide removal rate was 98.5%.

[0074] To visually demonstrate the application effects of the method of the present invention under different phosphate types, impurity compositions, and process parameters, the performance indicators of the above embodiments were tested and statistically analyzed. The specific test results are shown in the table below:

[0075] Product purity (%) 99.72 99.65 99.81 Phosphate recovery rate (%) 96.3 95.8 96.7 Membrane fouling rate (%) 4.8 5.5 4.2 Removal rate of major impurity 1 (%) Silicon dioxide: 98.6 Silicate: 98.1 Iron oxides: 98.9 Removal rate of major impurity 2 (%) Organic matter: 98.2 Aluminate: 97.8 Magnesium oxide: 98.5 Washing time (min) 25 20 30 Washing solution to phosphate mass ratio 3:1 2:1 4:1

[0076] In summary, Examples 1 to 3 cover three typical phosphate particles: calcium dihydrogen phosphate, monoammonium phosphate, and calcium hydrogen phosphate, respectively. They target common industrial impurity systems, including complex impurities (silica + organic matter), difficult-to-separate impurities (silicates + aluminates), and metallic impurities (iron oxides + magnesium oxides). The process parameters cover parameters such as electric field frequency of 1MHz-8MHz, surface modifier addition of 0.1%-0.3%, and filtration pressure of 0.1MPa-0.15MPa, comprehensively verifying the universality and operability of the method of this invention. The test results show that, regardless of the type of phosphate or the composition of impurities, the method of this invention can achieve excellent purification and recovery effects: the product purity is consistently above 99.6%, reaching a maximum of 99.81%; the phosphate recovery rate is not less than 95.8%, avoiding the dissolution loss problem in traditional processes; the membrane fouling rate is controlled at a low level of 4.2%-5.5%, effectively solving the membrane fouling problem of conventional membrane separation; at the same time, the removal rate for different types of impurities exceeds 97.8%, especially demonstrating highly efficient separation capability for impurities of the same particle size and similar density that are difficult to separate by traditional methods.

[0077] Furthermore, the impurity-rich retentate in the embodiments can be recycled for the preparation of pre-sorted suspensions after simple treatment. Combined with biodegradable selective surface modifiers, this achieves the dual goals of resource recycling and environmental protection. In summary, this invention, through a synergistic process of dielectrophoretic pre-sorting, in-situ surface modification, dynamic membrane separation, and countercurrent washing, combines high efficiency, stability, and environmental friendliness.

[0078] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for efficient recovery and washing of phosphate particles, characterized in that, The specific steps of this method are as follows: S100. Preparation of pre-sorted suspension: Add the phosphate particles containing impurities into the washing reactor, mix with the washing liquid at a solid-liquid mass ratio of 1:3-1:5, adjust the solid content to 5%-30%, and adjust the conductivity to 1-1000μS / cm to obtain the pre-sorted suspension. S200, Dielectrophoretic pre-sorting: The pre-sorted suspension is flowed through a sorting region with a non-uniform high-frequency alternating electric field applied. By utilizing the difference in dielectric constant and conductivity between phosphate particles and impurity particles, phosphate particles are enriched in the low-gradient electric field region, while impurity particles migrate and aggregate in the high-gradient electric field region. The low-gradient electric field region is collected to obtain a pre-sorted suspension enriched with phosphate particles. The working principle of the S200 dielectric electrophoretic pre-sorting is as follows: the pre-sorted suspension is controlled to flow through the sorting region in a thin laminar flow manner. By adjusting the frequency and field strength gradient of the non-uniform high-frequency alternating electric field, phosphate particles are enriched in the weak field strength gradient region and collected as the pre-sorted suspension, while impurity particles are enriched in the strong field strength gradient region and discharged as impurity enriched liquid. The frequency of the non-uniform high-frequency alternating electric field is 50kHz-10MHz, and the field strength gradient is 106-108V / m. 2 ; S300, In-situ surface modification: Add a selective surface modifier to the pre-sorted suspension and stir and mix at 10-50°C for 1-15 minutes to allow the selective surface modifier to adsorb onto the surface of phosphate particles, thereby specifically changing the surface hydrophilicity / hydrophobicity and surface Zeta potential of the phosphate particles to obtain a modified suspension. In S300, the specific changes are: increasing the surface contact angle of phosphate particles by 10°-60°, increasing the absolute value of the surface Zeta potential of phosphate particles by 10mV-40mV, and simultaneously making the change in surface properties of impurity particles less than 50% of the change in phosphate particles; S400, Dynamic membrane separation and washing: The modified suspension is subjected to dynamic membrane separation, using the formed dynamic membrane layer as the separation interface. Based on the surface property difference of S300, phosphate particles preferentially penetrate the dynamic membrane layer, while impurity particles are retained. At the same time, the penetrated phosphate particles are countercurrently washed to obtain phosphate concentrate slurry. S500, Post-processing: The phosphate concentrate slurry is dehydrated to obtain a high-purity phosphate product, and the impurity-rich retentate generated by the S400 dynamic membrane separation operation is collected.

2. The method for efficient recovery and washing of phosphate particles according to claim 1, characterized in that, In S100, the washing liquid is water, dilute acid solution, or dilute alkali solution, and the conductivity is adjusted by adding electrolyte and dilution.

3. The method for efficient recovery and washing of phosphate particles according to claim 1, characterized in that, In step S300, the selective surface modifier is one or more of a biodegradable nonionic surfactant, cationic surfactant, or amphoteric surfactant, and the amount of the selective surface modifier added is 0.1%-0.3% of the mass of the phosphate particle raw material in the pre-sorted suspension.

4. The method for efficient recovery and washing of phosphate particles according to claim 1, characterized in that, In S400, the dynamic membrane separation operation is carried out in a dynamic membrane filter, which uses a porous screen, sintered metal, or fabric as the base membrane. The dynamic membrane layer is formed in situ on the surface of the base membrane by fine particles of the modified suspension in S300.

5. The method for efficient recovery and washing of phosphate particles according to claim 1, characterized in that, In S400, the countercurrent washing of the penetrated phosphate particles specifically involves: introducing the washing solution from the permeation side of the dynamic membrane layer, and rinsing and replacing the phosphate particles in a flow direction opposite to the penetration direction of the phosphate particles. The washing time is 20-30 minutes, and the mass ratio of the washing solution to the phosphate particles is 1:1-5:

1.

6. The method for efficient recovery and washing of phosphate particles according to claim 1, characterized in that, The phosphate particles are at least one of monoammonium phosphate, diammonium phosphate, calcium dihydrogen phosphate, and calcium hydrogen phosphate. The impurity particles include at least one of silicon dioxide, silicates, aluminates, iron compounds, magnesium compounds, and organic matter.

7. The method for efficient recovery and washing of phosphate particles according to claim 1, characterized in that, In step S500, the impurity-rich retentate generated from the dynamic membrane separation operation is returned to step S100 for recycling in order to prepare the pre-sorted suspension.

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