An electrically driven separation device and an electrically driven separation method

Abstract

This invention relates to an electrically driven separation device and method. The electrically driven separation device includes a membrane stack structure and an anode plate and a cathode plate located on both sides of the membrane stack structure. The membrane stack structure includes an acid-resistant selective nanofiltration membrane disposed in the middle, and anion exchange membranes disposed on both sides of the acid-resistant selective nanofiltration membrane. The acid-resistant selective nanofiltration membrane includes a negatively charged porous support layer and a positively charged separation layer located on one side of the porous support layer. The separation layer includes an interfacial polymerization product of an aqueous phase monomer and an organic phase monomer. The aqueous phase monomer includes monomers containing amine functional groups, and the organic phase monomer includes monomers containing sulfonyl chloride functional groups and / or monomers containing isocyanate functional groups. The device provided by this invention introduces an acid-resistant selective nanofiltration membrane, which, utilizing its size sieving and electrostatic effects, enables the device to achieve efficient separation of different types of ions under electrically driven conditions.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to an electrically driven separation device and an electrically driven separation method. Background Technology

[0002] Rare earth elements, due to their unique physicochemical properties, are widely used in high-precision fields such as luminescence, permanent magnets, catalysis, and superconductivity, and are of significant strategic importance. Currently, extraction is the most common method for rare earth ore mining. Its principle involves using an organic extractant to extract rare earth ions from the liquid solution obtained by leaching rare earth ore, releasing hydrogen ions in the process. Then, after extensive acid washing, the hydrogen ions exchange with rare earth ions again, resulting in the back-extraction of rare earth ions. The entire process requires large amounts of acid and alkali, and the acidity significantly affects the rare earth extraction balance and mining efficiency.

[0003] CN107699718A discloses a method for extracting and separating rare earth elements from rare earth ore leachate, comprising the following steps: leachate collection; leachate pretreatment: the obtained rare earth ore leachate is subjected to solid-liquid separation through a fine sieve; obtaining a rare earth ore leachate free of solids; high-temperature extraction: the obtained rare earth ore leachate free of solids is added to a primary extraction tank for primary extraction, and after high-temperature extraction, a first aqueous phase and a first oil phase are obtained; low-temperature extraction: the first aqueous phase is added to a secondary extraction tank for secondary extraction, and after low-temperature extraction, a second aqueous phase and a second oil phase are obtained; room-temperature extraction: the second aqueous phase is added to a tertiary extraction tank for tertiary extraction, and after room-temperature extraction, rare earth-rich material is obtained. This preparation method is complex, requires control of different temperatures, consumes high energy, has a long extraction time, and the purity of the obtained rare earth material needs further improvement.

[0004] Membrane separation technology offers advantages over traditional separation techniques, including simpler processes, lower energy consumption, and environmental friendliness, making it a promising technology for rare earth separation. CN114150167A discloses a novel membrane-enhanced, saponification-free rare earth extraction and separation technology, proposing the efficient separation of hydrogen ions and rare earth ions in the raffinate using nanofiltration membranes. By using pressure to drive the nanofiltration or reverse osmosis membrane, the acidity in the raffinate is reduced through the selective permeation of hydrogen ions, while retaining rare earth ions, thus promoting a positive shift in the extraction equilibrium. This process eliminates the need for saponification extraction, shortens the extraction process, avoids the input of large amounts of acid and alkali, and reduces the generation of high-salt wastewater, which is of great significance for the economic efficiency of rare earth mining and the ecological protection of mining areas. However, the nanofiltration membranes used in the aforementioned existing technologies have poor acid resistance, affecting the separation of rare earth ions and hydrogen ions under acidic conditions. Furthermore, the use of pressure as the driving force limits the separation efficiency of rare earth ions and hydrogen ions.

[0005] Therefore, in view of the shortcomings of the existing technology, it is an urgent technical problem to be solved to provide a membrane separation device that can achieve efficient separation of hydrogen ions and rare earth ions in rare earth feed liquid and has strong acid resistance. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide an electrically driven separation device and method. The electrically driven separation device provided by the present invention incorporates a specific acid-resistant selective nanofiltration membrane, which, together with anion exchange membranes arranged on both sides, forms a membrane stack structure. Combined with the anode and cathode plates on both sides of the membrane stack structure, the various components interact with each other. Under electrically driven conditions, utilizing the size sieving and electrostatic effects of the acid-resistant selective nanofiltration membrane, it can be used to achieve efficient separation of different types of ions within the feed chamber of the device.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides an electrically driven separation device, the electrically driven separation device comprising a membrane stack structure and an anode plate and a cathode plate located on both sides of the membrane stack structure; the membrane stack structure includes an acid-resistant selective nanofiltration membrane disposed in the middle, and anion exchange membranes disposed on both sides of the acid-resistant selective nanofiltration membrane, wherein the anion exchange membrane closer to the anode plate is a first anion exchange membrane, and the anion exchange membrane closer to the cathode plate is a second anion exchange membrane; a feed chamber is formed between the first anion exchange membrane and the acid-resistant selective nanofiltration membrane; a concentration chamber is formed between the second anion exchange membrane and the acid-resistant selective nanofiltration membrane;

[0009] The acid-resistant selective nanofiltration membrane includes a negatively charged porous support layer and a positively charged separation layer located on one side of the porous support layer; the separation layer includes an interfacial polymerization product of aqueous phase monomers and organic phase monomers.

[0010] The aqueous phase monomer includes monomers containing amino functional groups, and the organic phase monomer includes monomers containing sulfonyl chloride functional groups and / or monomers containing isocyanate functional groups.

[0011] The electrically driven separation device provided by this invention introduces a specific acid-resistant selective nanofiltration membrane, which forms a membrane stack structure with the anion exchange membranes arranged on both sides of the membrane stack structure. Combined with the anode plate and cathode plate on both sides of the membrane stack structure, the various components interact with each other. Under electrically driven conditions, the size sieving and electrostatic effects of the acid-resistant selective nanofiltration membrane are used to achieve efficient separation of different types of ions inside the material in the feed chamber of the device.

[0012] The acid-resistant selective nanofiltration membrane introduced in the electrically driven separation device provided by this invention has a separation layer formed by interfacial polymerization of an aqueous monomer containing positively charged amine functional groups and an organic monomer containing sulfonyl chloride functional groups and / or isocyanate functional groups. This results in a well-structured pore structure in the separation layer, enabling size sieving of substances passing through the membrane. Simultaneously, the positively charged separation layer generates an electrostatic effect, allowing small-radius ions in the feed chamber to pass through the nanofiltration membrane and migrate to the concentration chamber, while preventing larger-radius, more charged ions from passing through the feed chamber and retaining them there. This facilitates efficient separation of different types and radii of ions from the added substances in the feed chamber. The separation process provides the prerequisite for the device to separate small-radius hydrogen ions and large-radius rare earth ions in rare earth feed solutions. In addition, the interfacial polymerization products of amino functional groups and sulfonyl chloride functional groups on the separation layer are polysulfonamides, and the interfacial polymerization products of amino functional groups and isocyanate functional groups are polyureas. Both of these interfacial polymerization products enable the nanofiltration membrane to have strong acid resistance, which can realize the multiple efficient separation of substances in the feed chamber by the electrically driven separation device under strong acid conditions. This enables the device to be used to separate rare earth ions and hydrogen ions in rare earth feed solutions under strong acid conditions, and can improve the separation stability of the device for repeated recycling under acid conditions.

[0013] Preferably, the acid-resistant selective nanofiltration membrane is positioned with the separation layer facing the feed chamber.

[0014] Preferably, the molecular weight cutoff of the positively charged separation layer is 100-400 Da, such as 100 Da, 150 Da, 200 Da, 250 Da, 300 Da, 350 Da, or 400 Da.

[0015] Preferably, the degree of crosslinking of the positively charged separation layer is 50-90%, such as 50%, 60%, 70%, 80% or 90%.

[0016] Preferably, a first electrode chamber is formed between the first anion exchange membrane and the anode plate.

[0017] Preferably, a second electrode chamber is formed between the second anion exchange membrane and the cathode plate.

[0018] Preferably, the electrically driven separation device further includes a liquid storage unit, a concentration storage unit, and an electrode storage unit.

[0019] Preferably, the liquid storage unit is connected to the liquid chamber.

[0020] Preferably, the outlet of the liquid storage unit is connected to the inlet of the liquid chamber, and the inlet of the liquid storage unit is connected to the outlet of the liquid chamber.

[0021] Preferably, the concentration chamber storage unit is connected to the concentration chamber.

[0022] Preferably, the outlet of the concentration chamber storage unit is connected to the inlet of the concentration chamber, and the inlet of the concentration chamber storage unit is connected to the outlet of the concentration chamber.

[0023] Preferably, the electrode chamber storage unit is connected to the first electrode chamber.

[0024] Preferably, the electrode chamber storage unit is connected to the second electrode chamber.

[0025] Preferably, the first electrode chamber and the second electrode chamber are connected.

[0026] It should be noted that the present invention does not specifically limit the connection method between the electrode chamber storage unit and the first and second electrode chambers, only ensuring that the three chambers of the electrode chamber storage unit, the first electrode chamber, and the second electrode chamber are interconnected to achieve charge balance between the first and second electrode chambers during use. For example, the outlet of the electrode chamber storage unit is connected to the inlet of the first electrode chamber, the outlet of the first electrode chamber is connected to the inlet of the second electrode chamber, and the outlet of the second electrode chamber is connected to the inlet of the electrode chamber discharge unit; or, the first outlet of the electrode chamber storage unit is connected to the inlet of the first electrode chamber, the outlet of the first electrode chamber is connected to the first inlet of the electrode chamber storage unit, the second outlet of the electrode chamber storage unit is connected to the inlet of the second electrode chamber, and the outlet of the second electrode chamber is connected to the second inlet of the electrode chamber storage unit; or, the outlet of the electrode chamber storage unit is connected sequentially to the inlet of the first electrode chamber and the inlet of the second electrode chamber through the same pipeline, and the outlets of the first and second electrode chambers are connected to the inlet of the second electrode chamber through the same pipeline. Those skilled in the art can choose the appropriate method as needed.

[0027] Preferably, a transmission unit is provided between the outlet of the liquid storage unit and the inlet of the liquid chamber.

[0028] Preferably, a transmission unit is provided between the outlet of the concentration chamber storage unit and the inlet of the concentration chamber.

[0029] Preferably, a transmission unit is provided between the outlet of the electrode chamber storage unit and the inlet of the first electrode chamber and / or the inlet of the second electrode chamber.

[0030] Preferably, the electrically driven separation device further includes an external power supply.

[0031] Preferably, the external power supply is connected to the anode plate and the cathode plate.

[0032] Preferably, the positive terminal of the external power supply is connected to the anode plate.

[0033] Preferably, the negative terminal of the external power supply is connected to the cathode plate.

[0034] Preferably, the monomer containing an amino functional group includes any one or a combination of at least two of polyethyleneimine, piperazine, m-phenylenediamine, p-phenylenediamine, polyethyleneamine, or polyethyleneaniline, with polyethyleneimine being the most preferred.

[0035] This invention selects specific aqueous monomers that have the advantage of strong interfacial polymerization activity. Among them, compared with other aqueous monomers, polyethyleneimine has the advantage of having more amine reaction sites and being positively charged.

[0036] Preferably, the monomer containing the sulfonyl chloride functional group includes benzenetrisulfonyl chloride.

[0037] In this invention, the interfacial polymerization of benzotrisulfonyl chloride containing sulfonyl chloride functional groups and aqueous monomers containing amino functional groups can obtain a separation layer with higher acid resistance. Furthermore, polysulfonamide is obtained on the separation layer by the polymerization of sulfonyl chloride functional groups of organic monomers and amino functional groups of aqueous monomers, which can further improve the acid resistance of nanofiltration membranes.

[0038] Preferably, the monomer containing the isocyanate functional group includes terephthalic diisocyanate.

[0039] In this invention, the interfacial polymerization of terephthalic diisocyanate containing isocyanate functional groups and aqueous monomers containing amino functional groups is selected to obtain a separation layer with a better pore structure. Furthermore, the polymerization of isocyanate functional groups of terephthalic diisocyanate and amino functional groups of aqueous monomers on the separation layer to obtain polyurea can further improve the acid resistance of nanofiltration membranes.

[0040] Preferably, the negatively charged porous support layer comprises an ultrafiltration membrane.

[0041] Preferably, the material of the ultrafiltration membrane includes any one or a combination of at least two of polyacrylonitrile, polycarbonate, polyvinyl chloride, polysulfone, polyethersulfone, sulfonated polyethersulfone, sulfonated polysulfone, or polyvinylidene chloride, with polyacrylonitrile being the most preferred.

[0042] The present invention employs a porous support layer of a specific material in the electrically driven separation device, which can promote the bonding between the base membrane and the separation layer, reduce the membrane surface resistance, and reduce the resistance to hydrogen ion transmembrane mass transfer.

[0043] Preferably, the molecular weight cutoff of the ultrafiltration membrane is 5-100 kDa, such as 5 kDa, 10 kDa, 20 kDa, 30 kDa, 40 kDa, 50 kDa, 60 kDa, 70 kDa, 80 kDa, 90 kDa, or 100 kDa.

[0044] As a preferred embodiment of the present invention, the acid-resistant selective nanofiltration membrane is prepared by the following method, the specific steps of which are as follows:

[0045] (1) Preparation of aqueous solution: Dissolve the aqueous monomer containing amine functional groups and the surfactant in water to obtain an aqueous solution; the aqueous monomer includes monomers containing amine functional groups;

[0046] Preparation of organic phase solution: Mix organic phase monomers with organic solvents, wherein the organic phase monomers include monomers containing sulfonyl chloride functional groups and / or monomers containing isocyanate functional groups to obtain an organic phase solution;

[0047] (2) Interfacial polymerization reaction: The ultrafiltration base membrane is sequentially immersed in the aqueous phase solution and the organic phase solution, and then subjected to heat treatment to obtain the acid-resistant selective nanofiltration membrane.

[0048] The acid-resistant selective nanofiltration membrane obtained by the preparation method provided by the present invention includes a negatively charged porous support layer and a positively charged separation layer located on one side of the porous support layer. The separation layer includes an interfacial polymerization product of aqueous phase monomers and organic phase monomers.

[0049] Preferably, the material of the ultrafiltration membrane includes any one or a combination of at least two of polyacrylonitrile, polycarbonate, polyvinyl chloride, polysulfone, polyethersulfone, sulfonated polysulfone, sulfonated polyethersulfone, or polyvinylidene chloride, with polyacrylonitrile being the most preferred.

[0050] Preferably, the molecular weight cutoff of the ultrafiltration membrane is 5-100 kDa, such as 5 kDa, 10 kDa, 20 kDa, 30 kDa, 40 kDa, 50 kDa, 60 kDa, 70 kDa, 80 kDa, 90 kDa, or 100 kDa.

[0051] Preferably, the concentration of the organic monomer in the organic phase solution is 0.02-0.4 g / L, such as 0.02 g / L, 0.05 g / L, 0.1 g / L, 0.15 g / L, 0.2 g / L, 0.25 g / L, 0.3 g / L, 0.35 g / L, or 0.4 g / L.

[0052] Preferably, the organic solvent includes any one or a combination of at least two of n-hexane, cyclohexane, ethyl acetate, chloroform, or toluene, with n-hexane being the most preferred.

[0053] Preferably, the monomer containing the sulfonyl chloride functional group includes benzenetrisulfonyl chloride.

[0054] Preferably, the monomer containing the isocyanate functional group includes terephthalic diisocyanate.

[0055] Preferably, the monomer containing an amino functional group includes any one or a combination of at least two of polyethyleneimine, piperazine, m-phenylenediamine, p-phenylenediamine, polyethyleneamine, or polyethyleneaniline, with polyethyleneimine being the most preferred.

[0056] Preferably, the surfactant comprises any one or a combination of at least two of sodium dodecyl sulfonate, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, or hexadecyltrimethylammonium bromide, and is preferably sodium dodecyl sulfonate.

[0057] This invention selects specific surfactants that offer advantages such as controllable aqueous monomer diffusion, altered pore size distribution of the separation layer, and charge loading. Among these, sodium dodecyl sulfonate has the advantage of controlling the diffusion rate and direction of aqueous monomers compared to other surfactants.

[0058] Preferably, the concentration of the aqueous monomer in the aqueous solution is 0-20 g / L, excluding 0, for example, 1 g / L, 2 g / L, 4 g / L, 6 g / L, 8 g / L, 10 g / L, 12 g / L, 14 g / L, 16 g / L, 18 g / L or 20 g / L, etc.

[0059] Preferably, the concentration of the surfactant in the aqueous solution is 0-5 g / L, excluding 0, for example, 1 g / L, 2 g / L, 3 g / L, 4 g / L or 5 g / L.

[0060] Preferably, the reaction time for the ultrafiltration membrane to be immersed in the aqueous solution is 1-20 min, such as 1 min, 2 min, 4 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, or 20 min.

[0061] Preferably, the reaction temperature at which the ultrafiltration membrane is immersed in the aqueous solution is 10-40℃, such as 10℃, 15℃, 20℃, 25℃, 30℃, 35℃, or 40℃.

[0062] Preferably, the ultrafiltration membrane is immersed in an aqueous solution at a reaction humidity of 20-80%, such as 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0063] Preferably, after the ultrafiltration membrane is immersed in the aqueous solution, the immersed ultrafiltration membrane is removed, and the aqueous solution on the surface of the ultrafiltration membrane is removed. Then, after drying, the obtained ultrafiltration membrane is immersed in the organic solution again.

[0064] Preferably, the reaction time for the ultrafiltration membrane to be immersed in the organic phase solution is 1-20 min, such as 1 min, 2 min, 4 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min, or 20 min.

[0065] Preferably, the reaction temperature at which the ultrafiltration membrane is immersed in the organic phase solution is 10-40℃, such as 10℃, 15℃, 20℃, 25℃, 30℃, 35℃ or 40℃.

[0066] Preferably, the ultrafiltration membrane is immersed in an organic phase solution at a reaction humidity of 20-80%, such as 20%, 30%, 40%, 50%, 60%, 70%, or 80%.

[0067] Preferably, after the ultrafiltration membrane is immersed in the organic phase solution, the immersed ultrafiltration membrane is removed, and the organic phase solution on the surface of the ultrafiltration membrane is removed. Then, after drying, the obtained ultrafiltration membrane is subjected to heat treatment.

[0068] Preferably, the heat treatment temperature is 40-100℃, such as 40℃, 50℃, 60℃, 70℃, 80℃, 90℃ or 100℃.

[0069] Preferably, the heat treatment time is 1-20 min, such as 1 min, 2 min, 4 min, 6 min, 8 min, 10 min, 12 min, 14 min, 16 min, 18 min or 20 min.

[0070] Preferably, the ultrafiltration membrane is further activated before being immersed in the aqueous solution.

[0071] Preferably, the activation treatment includes any one or a combination of at least two of hydrolysis, soaking, or filtration.

[0072] Preferably, the specific process for activating the ultrafiltration membrane includes treating the ultrafiltration membrane sequentially with water, alkaline solution, and acid solution.

[0073] Preferably, the water treatment time for the ultrafiltration membrane is 2-24 hours, such as 2 hours, 4 hours, 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours.

[0074] Preferably, the time for treating the ultrafiltration membrane with the alkaline solution is 30-180 min, such as 30 min, 60 min, 90 min, 120 min, 150 min, or 180 min.

[0075] Preferably, the temperature at which the ultrafiltration membrane is treated with the alkaline solution is 10-80°C, such as 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, or 80°C.

[0076] Preferably, the alkaline solution comprises sodium hydroxide solution and / or potassium hydroxide solution.

[0077] Preferably, the concentration of the alkaline solution is 1-3 mol / L, such as 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L.

[0078] Preferably, the time for treating the ultrafiltration membrane with the acid solution is 1-6 hours, such as 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours.

[0079] Preferably, the temperature at which the ultrafiltration membrane is treated with the acid solution is 10-30°C, such as 10°C, 15°C, 20°C, 25°C, or 30°C.

[0080] Preferably, the acid solution includes hydrochloric acid solution and / or sulfuric acid solution.

[0081] Preferably, the concentration of the acid solution is 0.5-3 mol / L, such as 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, or 3 mol / L.

[0082] Preferably, the ultrafiltration membrane after activation treatment is further washed and dried.

[0083] Secondly, the present invention provides an electrically driven separation method based on the electrically driven separation device described in the first aspect, the electrically driven separation method comprising the following steps:

[0084] Rare earth feed solution is introduced into the feed chamber of the electrically driven separation device described in the first aspect. Initial acid solution is introduced into the concentration chamber of the electrically driven separation device. The anode plate and cathode plate of the electrically driven separation device are energized to electrically drive the separation of rare earth ions and hydrogen ions in the rare earth feed solution. Hydrogen ions in the feed chamber migrate to the concentration chamber through the acid-resistant selective nanofiltration membrane, forming concentrated acid solution in the concentration chamber. Rare earth ions in the feed chamber are retained in the feed chamber by the acid-resistant selective nanofiltration membrane, forming a separated rare earth solution in the feed chamber.

[0085] The electro-driven separation method provided by this invention is based on an electro-driven separation device equipped with an acid-resistant selective nanofiltration membrane. The rare earth feed solution is introduced into the feed chamber on one side of the filter membrane, and the initial acid solution is introduced into the concentration chamber on the other side of the filter membrane. By combining the size sieving and electrostatic effect of the acid-resistant selective nanofiltration membrane with the design of the membrane stack structure of the electro-driven separation device, the efficient separation of rare earth ions and hydrogen ions in the rare earth feed solution in the feed chamber can be achieved.

[0086] The working mechanism of the electro-driven separation method provided by this invention is as follows: A rare earth feed solution is introduced into the feed chamber. The hydrogen ions in the rare earth feed solution have a small radius. Under the drive of an electric field, the hydrogen ions can migrate directionally and pass through an acid-resistant selective nanofiltration membrane to complete the transmembrane mass transfer process. The hydrogen ions are transferred to the concentration chamber on the other side of the filter membrane. Simultaneously, anions in the second electrode chamber migrate to the concentration chamber through the second anion exchange membrane under the drive of an electric field, increasing the number of anions in the concentration chamber. Similarly, anions in the feed chamber also migrate to the first electrode chamber through the first anion exchange membrane under the drive of an electric field. As the electrode chambers migrate, the number of anions in the feed chamber decreases. To achieve charge balance between the feed chamber and the concentration chamber, hydrogen ions in the feed chamber continuously migrate to the concentration chamber, forming a high-concentration acid solution. Meanwhile, rare earth ions in the feed chamber, due to their larger radius and stronger charge, are retained in the feed chamber by the size sieving and electrostatic effects of the acid-resistant selective nanofiltration membrane. This achieves efficient separation of rare earth ions and hydrogen ions in the feed chamber, resulting in a rare earth solution with a high rare earth ion content in the feed chamber and a high-concentration concentrated acid solution in the concentration chamber.

[0087] It should be noted that the rare earth feed solution chamber used for separation in this invention can be the extract residue obtained after extraction from rare earth ore leaching solution. Obtaining the rare earth feed solution to be separated from rare earth ore leaching solution are all conventional technical solutions and processing methods that can be obtained within a reasonable range by those skilled in the art. This invention is applicable to all of them.

[0088] Preferably, the rare earth solution comprises a rare earth salt solution and an acid reagent.

[0089] Preferably, the total concentration of rare earth ions in the rare earth feed solution is 0.005-0.20 mol / L, such as 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, or 0.20 mol / L.

[0090] Preferably, the concentration of hydrogen ions in the rare earth feed solution is 0.001-0.20 mol / L, such as 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, or 0.20 mol / L.

[0091] Preferably, in the feed chamber, the concentration ratio of the rare earth ions to the hydrogen ions is (0.5-1.5):(0.5-5.0), wherein the rare earth ions are selected from the range of "0.5-1.5", such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, and the hydrogen ions are selected from the range of "0.5-5.0", such as 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, etc.

[0092] This invention regulates the concentration ratio of rare earth ions to hydrogen ions in the feed chamber, which can improve hydrogen ion migration and rare earth ion retention, thereby improving separation efficiency. If the concentration ratio is too low, the amount of rare earth ions added will be relatively low, resulting in a long separation time. If the concentration ratio is too high, the amount of hydrogen ions added will be relatively low, resulting in the hydrogen ion migration reaching its upper limit, a significant increase in pH, and affecting the separation effect of the rare earth feed solution.

[0093] Preferably, the concentration of hydrogen ions in the initial acid solution is 0.001-0.20 mol / L, such as 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, or 0.20 mol / L.

[0094] In the electro-driven separation method provided by this invention, the initial acid solution added to the concentration chamber serves to reduce solution resistance, provide a charge transfer pathway, and maintain a stable electro-driving force required for membrane separation. Adjusting its concentration can regulate the conductivity of the solution in the concentration chamber of the membrane stack. If the concentration of the initial acid solution in the concentration chamber is too low, the separation efficiency will be reduced and the process energy consumption will be increased. If the concentration of the initial acid solution is too high, concentration polarization will occur, affecting the concentration of the initial acid solution.

[0095] Preferably, the volume ratio of the rare earth solution in the feed chamber to the initial acid solution in the concentration chamber is (0.5-1.5):(0.5-5.0), wherein the volume fraction of the rare earth solution in the feed chamber is selected from the range of "0.5-1.5", such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, etc., and the volume fraction of the initial acid solution in the concentration chamber is selected from the range of "0.5-5.0", such as 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0, etc.

[0096] Preferably, the rare earth liquid introduced into the liquid chamber is transferred to the liquid chamber through the rare earth liquid in the liquid chamber storage unit.

[0097] Preferably, the initial acid solution introduced into the concentration chamber is transferred from the initial acid solution in the concentration chamber storage unit to the concentration chamber.

[0098] Preferably, before energizing, a first electrolyte solution is introduced into the first electrode chamber of the electrically driven separation device, and a second electrolyte solution is introduced into the second electrode chamber of the electrically driven separation device.

[0099] Preferably, the volume ratio of the rare earth solution in the feed chamber to the first electrolyte solution in the first electrode chamber is (0.5-1.5):(0.5-1.5), wherein the volume fraction of the rare earth solution in the feed chamber is selected from the range of "0.5-1.5", such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, and the volume fraction of the first electrolyte solution in the first electrode chamber is selected from the range of "0.5-1.5", such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0100] Preferably, the volume ratio of the initial acid solution in the concentration chamber to the second electrolyte solution in the second electrode chamber is (0.5-1.5):(0.5-1.5), wherein the volume fraction of the initial acid solution in the concentration chamber is selected from the range of "0.5-1.5", such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5, and the volume fraction of the second electrolyte solution in the second electrode chamber is selected from the range of "0.5-1.5", such as 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4 or 1.5.

[0101] Preferably, the first electrolyte solution and the second electrolyte solution are independently selected from any one or a combination of at least two of sodium sulfate solution, magnesium sulfate solution, or sulfuric acid solution.

[0102] Preferably, the concentrations of the first electrolyte solution and the second electrolyte solution are independently selected from 0.2-1 mol / L, such as 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, or 1 mol / L.

[0103] Preferably, the introduction of the first electrolyte solution into the first electrode chamber is achieved by transferring the electrolyte solution from the electrode chamber storage unit to the first electrode chamber.

[0104] Preferably, the second electrolyte solution introduced into the second electrode chamber is transferred to the second electrode chamber through the electrolyte solution in the electrode chamber storage unit.

[0105] In this invention, the second electrolyte solution introduced into the second electrode chamber can be directly transferred to the second electrode chamber through the electrode chamber storage unit. That is, the electrolyte solution is transferred to the second electrode chamber through the outlet of the electrode chamber storage unit to the inlet of the second electrode chamber, or the electrolyte solution flows through the outlet of the electrode chamber storage unit, through the inlet of the first electrode chamber, and then to the inlet of the second electrode chamber. Alternatively, the electrolyte solution can be indirectly transferred to the second electrode chamber through the electrode chamber storage unit. That is, the electrolyte solution is transferred from the outlet of the electrode chamber storage unit to the inlet of the first electrode chamber, flows through the interior of the first electrode chamber, and then through the outlet of the first electrode chamber to the inlet of the second electrode chamber.

[0106] Preferably, the first electrolyte solution and the second electrolyte solution have exactly the same composition.

[0107] Preferably, the feed chamber storage unit, the concentration chamber storage unit, and the electrode chamber storage unit transmit rare earth feed solution, initial acid solution, first electrolyte solution, and second electrolyte solution to the feed chamber, concentration chamber, first electrode chamber, and second electrode chamber, respectively, through a transmission unit.

[0108] Preferably, the device used in the transmission unit includes a peristaltic pump.

[0109] Preferably, the transmission unit is set to a transmission speed of 60-120 rpm, such as 60 rpm, 70 rpm, 80 rpm, 90 rpm, 100 rpm, 110 rpm or 120 rpm.

[0110] Preferably, the power supply includes a DC regulated power supply.

[0111] Preferably, the current density of the energized circuit is 1-20 mA / cm². 2 For example, 1mA / cm 2 2mA / cm 2 4mA / cm 2 6mA / cm 2 8mA / cm 2 10mA / cm 2 12mA / cm 2 14mA / cm 2 16mA / cm 2 18mA / cm 2 or 20mA / cm 2 wait.

[0112] The present invention regulates the current density of the energized circuit to control the ion migration rate; if the current density is too low, it will lead to slow ion migration and low separation efficiency; if the current density is too high, it will cause local precipitation of rare earth elements, which may also lead to membrane failure.

[0113] Preferably, the voltage applied is 5-10V, such as 5V, 6V, 7V, 8V, 9V or 10V.

[0114] Preferably, the acid-resistant selective nanofiltration membrane has a permeability of more than 90% for hydrogen ions in the feed chamber, such as 90%, 92%, 94%, 96%, 98%, or 99%.

[0115] Preferably, the acid-resistant selective nanofiltration membrane has a rejection rate of more than 90% for rare earth ions in the feed chamber, such as 90%, 92%, 94%, 96%, 98%, or 99%.

[0116] Compared with the prior art, the present invention has at least the following beneficial effects:

[0117] (1) The electric-driven separation device provided by the present invention introduces a specific acid-resistant selective nanofiltration membrane, which forms a membrane stack structure with the anion exchange membranes set on both sides of the membrane stack structure. Combined with the anode plate and cathode plate on both sides of the membrane stack structure, the various components interact with each other. Under electric drive conditions, the size sieving and electrostatic effect of the acid-resistant selective nanofiltration membrane are used to achieve efficient separation of different types of ions inside the material in the feed chamber of the device.

[0118] (2) The electro-driven separation method provided by the present invention is based on an electro-driven separation device equipped with an acid-resistant selective nanofiltration membrane. The rare earth feed liquid is introduced into the feed chamber on one side of the filter membrane, and the initial acid liquid is introduced into the concentration chamber on the other side of the filter membrane. By combining the size sieving and electrostatic effect of the acid-resistant selective nanofiltration membrane with the design of the membrane stack structure of the electro-driven separation device, the rare earth ions and hydrogen ions in the rare earth feed liquid in the feed chamber can be efficiently separated. Attached Figure Description

[0119] Figure 1 This is a schematic diagram of the structure of the electrically driven separation device provided in Example 1.

[0120] Among them, 1 is an acid-resistant selective nanofiltration membrane; 2 is a first anion exchange membrane; 3 is a second anion exchange membrane; 4 is an anode plate; 5 is a cathode plate; 6 is a feed chamber; 7 is a concentration chamber; 8 is a first electrode chamber; 9 is a second electrode chamber; 10 is a feed chamber storage unit; 11 is a concentration chamber storage unit; and 12 is an electrode chamber storage unit.

[0121] Figure 2 This is a schematic diagram of the mechanism of the electrically driven separation device provided by the present invention in the electrically driven separation method.

[0122] Figure 3 This is a scanning electron microscope image of the separation layer surface in the acid-resistant selective nanofiltration membrane obtained in Example 1.

[0123] Figure 4 This is a scanning electron microscope image of the cross-section of the acid-resistant selective nanofiltration membrane obtained in Example 1. Detailed Implementation

[0124] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0125] Example 1

[0126] This embodiment provides a method for preparing an acid-resistant selective nanofiltration membrane, comprising the following steps:

[0127] S1. Activation of ultrafiltration membrane: A polyacrylonitrile membrane with a molecular weight of 50 kDa was immersed in water for 12 hours, then immersed in a sodium hydroxide solution with a concentration of 1.25 mol / L for 1 hour and kept at 60°C. Then, the ultrafiltration membrane treated with sodium hydroxide solution was placed in hydrochloric acid with a concentration of 1 mol / L and immersed at 20°C for 3 hours. Finally, the acid-treated polyacrylonitrile membrane was rinsed with deionized water to obtain the activated polyacrylonitrile membrane.

[0128] S2. Preparation of aqueous solution: Dissolve polyethyleneimine and sodium dodecyl sulfonate in deionized water and mix thoroughly. The concentration of polyethyleneimine is 10 g / L and the concentration of sodium dodecyl sulfonate is 0.5 g / L to obtain an aqueous solution.

[0129] S3. Prepare the organic phase solution: Dissolve benzotrisulfonyl chloride in n-hexane to obtain an organic phase solution with a concentration of 0.2 g / L.

[0130] S4. Interfacial polymerization reaction: The polyacrylonitrile base membrane activated in step S1 is fixed in an interfacial polymerization mold. The activated polyacrylonitrile base membrane is immersed in the aqueous solution obtained in step S2 and soaked at 30°C for 10 min with a reaction humidity of 60%. The treated polyacrylonitrile base membrane is taken out, washed with deionized water, and then dried for the first time. Then, the product dried for the first time is immersed in the organic solution obtained in step S3 and soaked at 30°C for 5 min with a reaction humidity of 60%. The unreacted monomers are washed with n-hexane to clean the organic solution. Then, the obtained film product is heat-treated at 60°C for 5 min to obtain an acid-resistant selective nanofiltration membrane.

[0131] This embodiment provides an example of using the acid-resistant selective nanofiltration membrane obtained by the above preparation method to assemble an electrically driven separation device. A schematic diagram of the electrically driven separation device is shown below. Figure 1 As shown, specifically, it includes: an acid-resistant selective nanofiltration membrane 1 disposed in the middle region of the electrically driven separation device. The acid-resistant selective nanofiltration membrane 1 includes a negatively charged porous support layer and a positively charged separation layer located on one side of the porous support layer. The porous support layer is composed of a polyacrylonitrile ultrafiltration base membrane with a molecular weight of 50 kDa. The separation layer includes an interfacial polymerization product of polyethyleneimine and benzotrisulfonyl chloride. The molecular weight cutoff of the separation layer is 243 Da, and the degree of crosslinking of the separation layer is 81.82%. A first anion exchange membrane 2 and a second anion exchange membrane 3 are respectively disposed on both sides of the acid-resistant selective nanofiltration membrane 1. The first anion exchange membrane 2 is located away from the acid-resistant selective nanofiltration membrane. An anode plate 4 is disposed on one side of the acid-resistant selective nanofiltration membrane 1, and a cathode plate 5 is disposed on the side of the second anion exchange membrane 3 away from the acid-resistant selective nanofiltration membrane 1. A feed chamber 6 is formed between the first anion exchange membrane 2 and the acid-resistant selective nanofiltration membrane 1, and a concentration chamber 7 is formed between the second anion exchange membrane 3 and the acid-resistant selective nanofiltration membrane 1. The acid-resistant selective nanofiltration membrane 1 is fixed with the separation layer facing the feed chamber 6 and the porous support layer facing the concentration chamber 7. A first electrode chamber 8 is formed between the first anion exchange membrane 2 and the anode plate 4, and a second electrode chamber 9 is formed between the second anion exchange membrane 3 and the cathode plate 5. The anode plate 4 and the cathode plate 5 are respectively connected to the positive and negative terminals of an external power supply.

[0132] The electrically driven separation device also includes a liquid storage unit 10, a concentration storage unit 11, and an electrode storage unit 12. The outlet of the liquid storage unit 10 is connected to the inlet of the liquid storage unit 6 via a pipeline, and the inlet of the liquid storage unit 10 is connected to the outlet of the liquid storage unit 6 via a pipeline. The outlet of the concentration chamber storage unit 11 is connected to the inlet of the concentration chamber 7 via a pipeline, and the inlet of the concentration chamber storage unit 11 is connected to the outlet of the concentration chamber 7 via a pipeline. The outlet of the electrode chamber storage unit 12 is connected to the inlet of the second electrode chamber 9 and the inlet of the first electrode chamber 8 via pipelines, and the outlet of the first electrode chamber 8 and the outlet of the second electrode chamber 9 are connected to the inlet of the electrode chamber storage unit 12 via pipelines. A transfer unit is also provided between the outlet of the liquid storage unit 10 and the inlet of the liquid storage unit 6, between the outlet of the concentration chamber storage unit 11 and the inlet of the concentration chamber 7, and between the outlet of the electrode chamber storage unit 12 and the inlet of the second electrode chamber 9 to transfer the solution in each storage unit to each chamber. The transfer unit uses a peristaltic pump.

[0133] This embodiment also provides an electrically driven separation method based on the above-mentioned electrically driven separation device, which specifically includes the following steps:

[0134] (I) A peristaltic pump is used to transfer the rare earth solution from the storage unit in the feed chamber to the feed chamber of the electrically driven separation device. The specific composition of the rare earth solution is a rare earth sulfate solution, wherein the total concentration of rare earth ions in the solution is 0.01 mol / L, and the rare earth ions include La. 3+ 、Sm 3+ Dy 3+ Yb 3+ and Y 3+ Each component has a concentration of 0.002 mol / L. The concentration of hydrogen ions in the rare earth feed solution is 0.01 mol / L. A peristaltic pump is used to transfer the sulfuric acid solution with a hydrogen ion concentration of 0.01 mol / L from the storage unit of the concentration chamber to the concentration chamber. A peristaltic pump is also used to transfer the sodium sulfate solution with a concentration of 0.4 mol / L from the storage unit of the electrode chamber to the first electrode chamber and the second electrode chamber. The volume ratio of the rare earth feed solution in the feed chamber, the sulfuric acid in the concentration chamber, the sodium sulfate in the first electrode chamber, and the sodium sulfate in the second electrode chamber is 1:1:1:1. The peristaltic pump used for transferring the rare earth feed solution, the sulfuric acid solution, and the electrolyte sodium sulfate solution rotates at 90 rpm.

[0135] (II) A DC regulated power supply is used as the external power source to energize the anode and cathode plates in the electrically driven separation device. The current density is 10 mA / cm². 2The voltage is 7.5V. The rare earth feed solution is electrically driven to separate. The hydrogen ions in the feed chamber migrate to the concentration chamber through the acid-resistant selective nanofiltration membrane, forming a concentrated acid solution. The rare earth ions in the feed chamber are retained in the feed chamber by the acid-resistant selective nanofiltration membrane, forming a separated rare earth solution in the feed chamber.

[0136] Example 2

[0137] The method for preparing the acid-resistant selective nanofiltration membrane provided in this embodiment differs from that in Example 1 only in that the concentration of polyethyleneimine in step S2 is 5 g / L.

[0138] This embodiment also provides an acid-resistant selective nanofiltration membrane obtained by the above preparation method for use in an electrically driven separation device. In this embodiment, the degree of crosslinking of the separation layer in the acid-resistant selective nanofiltration membrane 1 is 76.24%, and the molecular weight cutoff of the separation layer is 287 Da. Except for the change in the acid-resistant selective nanofiltration membrane, the structure of the electrically driven separation device provided in this embodiment is the same as that in Embodiment 1.

[0139] This embodiment also provides an electrically driven separation method based on the above-mentioned electrically driven separation device, which specifically includes the following steps:

[0140] (I) A peristaltic pump is used to transfer the rare earth solution from the storage unit in the feed chamber to the feed chamber of the electrically driven separation device. The specific composition of the rare earth solution is a rare earth sulfate solution, wherein the total concentration of rare earth ions in the solution is 0.015 mol / L, and the rare earth ions include La. 3+ 、Sm 3+ Dy 3+ Yb 3+ and Y 3+ Each component has a concentration of 0.003 mol / L. The concentration of hydrogen ions in the rare earth feed solution is 0.015 mol / L. A peristaltic pump is used to transfer the sulfuric acid solution with a hydrogen ion concentration of 0.015 mol / L from the storage unit of the concentration chamber to the concentration chamber. A peristaltic pump is also used to transfer the sodium sulfate solution with a concentration of 0.3 mol / L from the storage unit of the electrode chamber to the first electrode chamber and the second electrode chamber. The volume ratio of the rare earth feed solution in the feed chamber, the sulfuric acid in the concentration chamber, the sodium sulfate in the first electrode chamber, and the sodium sulfate in the second electrode chamber is 1.1:0.9:1:1. The peristaltic pump used for transferring the rare earth feed solution, the sulfuric acid solution, and the electrolyte sodium sulfate solution has a rotation speed of 120 rpm.

[0141] (II) A DC regulated power supply is used as an external power source to energize the anode and cathode plates in the electrically driven separation device. The current density is 20 mA / cm². 2With an applied voltage of 10V, rare earth feed liquid is electrically driven for separation. Hydrogen ions in the feed liquid chamber migrate to the concentration chamber through an acid-resistant selective nanofiltration membrane, forming a concentrated acid solution in the concentration chamber. Rare earth ions in the feed liquid chamber are blocked and retained in the feed liquid chamber by the acid-resistant selective nanofiltration membrane, forming a separated rare earth solution in the feed liquid chamber.

[0142] Example 3

[0143] The method for preparing the acid-resistant selective nanofiltration membrane provided in this embodiment differs from that in Example 1 only in that the concentration of polyethyleneimine in step S2 is 1 g / L.

[0144] This embodiment also provides an acid-resistant selective nanofiltration membrane obtained by the above preparation method for assembling an electrically driven separation device. The degree of crosslinking of the separation layer in the acid-resistant selective nanofiltration membrane is 65.43%, and the molecular weight cutoff of the separation layer is 364 Da. Except for the change in the acid-resistant selective nanofiltration membrane, the structure of the electrically driven separation device provided in this embodiment is the same as that in Example 1.

[0145] This embodiment also provides an electrically driven separation method based on the above-mentioned electrically driven separation device, which specifically includes the following steps:

[0146] (I) A peristaltic pump is used to transfer the rare earth solution from the storage unit in the feed chamber to the feed chamber of the electrically driven separation device. The specific composition of the rare earth solution is a rare earth sulfate solution, wherein the total concentration of rare earth ions in the rare earth solution is 0.02 mol / L, and the rare earth ions include La. 3+ 、Sm 3+ Dy 3+ Yb 3+ and Y 3+ Each component has a concentration of 0.004 mol / L. The concentration of hydrogen ions in the rare earth feed solution is 0.01 mol / L. A peristaltic pump is used to transfer the sulfuric acid solution with a hydrogen ion concentration of 0.01 mol / L from the storage unit of the concentration chamber to the concentration chamber. A peristaltic pump is also used to transfer the sodium sulfate with a concentration of 0.2 mol / L from the storage unit of the electrode chamber to the first electrode chamber and the second electrode chamber. The volume ratio of the rare earth feed solution in the feed chamber, the sulfuric acid solution in the concentration chamber, the sodium sulfate in the first electrode chamber, and the sodium sulfate in the second electrode chamber is 0.8:1.2:1:1. The peristaltic pump used for transferring the rare earth feed solution, the sulfuric acid solution, and the electrolyte sodium sulfate solution rotates at 90 rpm.

[0147] (II) A DC regulated power supply is used as an external power source to energize the anode and cathode plates in the electrically driven separation device. The current density is 5 mA / cm². 2With an applied voltage of 5V, rare earth feed liquid is electrically driven for separation. Hydrogen ions in the feed liquid chamber migrate to the concentration chamber through an acid-resistant selective nanofiltration membrane, forming a concentrated acid solution in the concentration chamber. Rare earth ions in the feed liquid chamber are blocked and retained in the feed liquid chamber by the acid-resistant selective nanofiltration membrane, forming a separated rare earth solution in the feed liquid chamber.

[0148] Example 4

[0149] The only difference between this embodiment and Example 1 is that in the preparation method of the acid-resistant selective nanofiltration membrane provided in this embodiment, the concentration of benzenetrisulfonyl chloride in step S3 is 0.1 g / L; correspondingly, the acid-resistant selective nanofiltration membrane obtained by this preparation method in this embodiment is used to assemble an electrically driven separation device, the degree of crosslinking of the acid-resistant selective nanofiltration membrane 1 is 78.91%, and the molecular weight cutoff of the separation layer is 251 Da. All other contents are the same as in Example 1.

[0150] Example 5

[0151] The only difference between this embodiment and Example 1 is that in the preparation method of the acid-resistant selective nanofiltration membrane provided in this embodiment, the concentration of benzotrisulfonyl chloride in step S3 is 0.05 g / L; correspondingly, the acid-resistant selective nanofiltration membrane obtained by this preparation method in this embodiment is used to assemble an electrically driven separation device, and the degree of crosslinking of the acid-resistant selective nanofiltration membrane 1 is 79.26%, and the molecular weight cutoff of the separation layer is 269 Da. All other contents are the same as in Example 1.

[0152] Example 6

[0153] The only difference between this embodiment and Example 1 is that in the preparation method of the acid-resistant selective nanofiltration membrane provided in this embodiment, the benzenetrisulfonyl chloride in the organic phase solution in step S3 is replaced with terephthalic diisocyanate at a concentration of 0.2 g / L; correspondingly, the acid-resistant selective nanofiltration membrane obtained by this preparation method in this embodiment is used to assemble an electrically driven separation device, the surface composition of the acid-resistant selective nanofiltration membrane 1 is polyurea, and the molecular weight cutoff of the separation layer is 217 Da. All other contents are the same as in Example 1.

[0154] Example 7

[0155] The only difference between this embodiment and Embodiment 1 is that the hydrogen ion concentration in the feed chamber of the electrically driven separation method provided in this embodiment is 0.0005 mol / L. All other aspects are the same as in Embodiment 1.

[0156] Example 8

[0157] The only difference between this embodiment and Embodiment 1 is that the hydrogen ion concentration in the feed chamber of the electrically driven separation method provided in this embodiment is 2.0 mol / L. All other aspects are the same as in Embodiment 1.

[0158] Example 9

[0159] The only difference between this embodiment and Embodiment 1 is that the current density in the electrically driven separation method provided in this embodiment is 0.5 mA / cm². 2 The rest of the content is the same as in Example 1.

[0160] Example 10

[0161] The only difference between this embodiment and Embodiment 1 is that the current density in the electrically driven separation method provided in this embodiment is 30 mA / cm². 2 The rest of the content is the same as in Example 1.

[0162] Example 11

[0163] The only difference between this embodiment and Embodiment 1 is that in the electrically driven separation method provided in this embodiment, the energizing process in step (II) is replaced by a pressure-driven process. Specifically, the acid-resistant selective nanofiltration membrane obtained in Embodiment 1 is fixed in a pressure-driven conventional cross-flow separation device and used as a separation membrane. After pre-pressurizing with 6 bar for 1 hour, a pressure of 4 bar is applied to the feed chamber as the driving force for membrane separation, separating rare earth ions and hydrogen ions in the rare earth feed solution. All other aspects are the same as in Embodiment 1.

[0164] Comparative Example 1

[0165] The only difference between this comparative example and Example 1 is that the electrically driven separation device provided in this comparative example uses an activated polyacrylonitrile-based membrane to directly replace the acid-resistant selective nanofiltration membrane. All other aspects are the same as in Example 1.

[0166] Comparative Example 2

[0167] The only difference between this comparative example and Example 1 is that in the electrically driven separation device provided in this comparative example, the separation layer of the acid-resistant selective nanofiltration membrane provided in Example 1 is replaced with a selective nanofiltration membrane comprising an interfacial polymerization product of polyethyleneimine and trimesoyl chloride. That is, in the preparation method of the selective nanofiltration membrane provided in this comparative example, the organic phase monomer in the organic phase solution is trimesoyl chloride. All other contents are the same as in Example 1.

[0168] The permeability of hydrogen ions and the total rejection rate of rare earth ions in the feed chamber of the separation process provided in Examples 1-11 and Comparative Examples 1-2 were detected.

[0169] (1) Total retention rate of rare earth ions: The total concentration of rare earth ions in the feed chamber was tested by an inductively coupled plasma emitter. The total concentration of rare earth ions in the initial feed chamber was recorded as A0, and the total concentration of rare earth ions in the feed chamber after electric drive separation was recorded as A1. The total retention rate of rare earth ions was A1 / A0×100%.

[0170] (2) Hydrogen ion permeability: The concentration of hydrogen ions in the feed chamber is measured by pH meter. The initial concentration of hydrogen ions in the feed chamber is recorded as B0, and the concentration of hydrogen ions in the feed chamber after electric separation is recorded as B1. The hydrogen ion permeability is (B0-B1) / B0×100%.

[0171] The test results are shown in Table 1.

[0172] Table 1

[0173] Hydrogen ion transmittance Total Retention Rate of Rare Earth Ions Example 1 95.63％ 99.60％ Example 2 95.10％ 98.28％ Example 3 95.93％ 95.74％ Example 4 96.11％ 97.81％ Example 5 95.73％ 90.74％ Example 6 95.10％ 95.69％ Example 7 50.68％ 99.35％ Example 8 90.52％ 87.96％ Example 9 78.47％ 99.78％ Example 10 96.79％ 84.36％ Example 11 90.06％ 94.85％ Comparative Example 1 91.49％ 71.11％ Comparative Example 2 92.53％ 89.76％

[0174] The test results show that:

[0175] (1) As can be seen from Examples 1 to 6, the electric-driven separation device provided by the present invention introduces a specific acid-resistant selective nanofiltration membrane, which forms a membrane stack structure with the anion exchange membranes set on both sides of the membrane stack structure. Combined with the anode plate and cathode plate on both sides of the membrane stack structure, the various components interact with each other. Under electric drive conditions, the size sieving and electrostatic effect of the acid-resistant selective nanofiltration membrane can be used to achieve efficient separation of rare earth ions and hydrogen ions in rare earth feed liquid.

[0176] Figure 2 A schematic diagram of the electro-driven separation mechanism of the acid-resistant selective nanofiltration membrane is given. As shown in the figure, the positively charged separation layer of the acid-resistant selective nanofiltration membrane faces the rare earth feed liquid in the feed chamber. Under the action of the electric field, small-radius hydrogen ions can pass through the acid-resistant selective nanofiltration membrane, while large-radius rare earth ions are trapped in the feed chamber by the acid-resistant selective nanofiltration membrane, thereby achieving the separation of rare earth ions and hydrogen ions in the feed chamber.

[0177] Figure 3 The image shows a scanning electron microscope (SEM) image of the separation layer surface in the acid-resistant selective nanofiltration membrane obtained in Example 1. As can be seen from the image, the surface of the separation layer of the obtained acid-resistant selective nanofiltration membrane is relatively dense, with a high degree of cross-linking and extremely fine pore structure, which is even not clearly visible in the SEM image. This allows a large number of rare earth ions to be retained in the feed chamber.

[0178] Figure 4The image shows a scanning electron microscope (SEM) image of the cross-section of the acid-resistant selective nanofiltration membrane obtained in Example 1. As can be seen from the image, compared with the macroporous structure of the underlying support layer, the pores and channels of the surface separation layer in the obtained acid-resistant selective nanofiltration membrane are very small, and cannot even be clearly seen in the SEM image. The thickness of the separation layer in the obtained acid-resistant selective nanofiltration membrane is in the range of 69.95±5.17 nm, with good morphology, and can achieve the separation of rare earth ions and hydrogen ions in the rare earth feed solution in the feed chamber.

[0179] (2) By comparing Examples 1 and Examples 7-8, it can be seen that if the concentration of hydrogen ions in the feed chamber is too low, the separation efficiency will be affected; if the concentration of hydrogen ions in the feed chamber is too high, the membrane separation time will be prolonged and the membrane separation effect will be affected.

[0180] (3) By comparing Example 1 and Example 9-10, it can be seen that if the current density of the present invention is too low, the electric driving force will be insufficient and the transmembrane mass transfer efficiency will be low; if the current density is too high, the hydrogen ion mass transfer will be too fast, the system will be greatly affected by pH changes, and in severe cases, rare earth ions will be locally precipitated.

[0181] (4) By comparing Example 1 and Example 11, it can be seen that the electro-driven separation method of the present invention has a better rare earth ion rejection rate and a higher hydrogen ion permeability than the pressure-driven membrane separation technology, and can achieve a better separation effect between rare earth ions and hydrogen ions in rare earth feed liquid.

[0182] (5) By comparing Example 1 with Comparative Example 1, it can be seen that the specific acid-resistant selective nanofiltration membrane used in this invention has a significantly improved retention rate of rare earth ions in rare earth feed solution compared with the original membrane.

[0183] (6) By comparing Example 1 and Comparative Example 2, it can be seen that in the electrically driven separation device provided by the present invention, if the separation layer of the nanofiltration membrane includes the interfacial polymerization product of polyethyleneimine and trimesoyl chloride, that is, the organic monomer of the interfacial polymerization is selected to contain acyl chloride functional groups, the separation layer will be not acid resistant, and hydrolysis will occur after running for a period of time, resulting in membrane failure and thus affecting the overall effect of membrane separation.

[0184] In summary, the electro-driven separation device provided by this invention introduces a specific acid-resistant selective nanofiltration membrane, which, together with anion exchange membranes arranged on both sides, forms a membrane stack structure. Combined with the anode and cathode plates on both sides of the membrane stack structure, the various components interact. Under electro-driven conditions, utilizing the size sieving and electrostatic effects of the acid-resistant selective nanofiltration membrane, it can be used to achieve efficient separation of different types of ions within the feed chamber of the device. This invention also provides an electro-driven separation method based on this specific electro-driven separation device. Rare earth feed solution is added to the feed chamber on one side of the filter-resistant membrane, and acid is added to the concentration chamber on the other side of the filter-resistant membrane. Through the size sieving and electrostatic effects of the acid-resistant selective nanofiltration membrane combined with the design of the membrane stack structure of the electro-driven separation device, efficient separation of rare earth ions and hydrogen ions in the rare earth feed solution can be achieved.

[0185] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. An electrically driven separation device, characterized in that, The electrically driven separation device includes a membrane stack structure and an anode plate and a cathode plate located on both sides of the membrane stack structure. The membrane stack structure includes an acid-resistant selective nanofiltration membrane disposed in the middle, and anion exchange membranes disposed on both sides of the acid-resistant selective nanofiltration membrane, with the anion exchange membrane closer to the anode plate being the first anion exchange membrane and the anion exchange membrane closer to the cathode plate being the second anion exchange membrane. A feed chamber is formed between the first anion exchange membrane and the acid-resistant selective nanofiltration membrane; a concentration chamber is formed between the second anion exchange membrane and the acid-resistant selective nanofiltration membrane. The acid-resistant selective nanofiltration membrane includes a negatively charged porous support layer and a positively charged separation layer located on one side of the porous support layer; the separation layer includes an interfacial polymerization product of aqueous phase monomers and organic phase monomers. The aqueous phase monomer includes monomers containing amino functional groups, and the organic phase monomer includes monomers containing sulfonyl chloride functional groups and / or monomers containing isocyanate functional groups.

2. The electrically driven separation device according to claim 1, characterized in that, The acid-resistant selective nanofiltration membrane is positioned with the separation layer facing the feed chamber; Preferably, the molecular weight cutoff of the positively charged separation layer is 100-400 Da; Preferably, the degree of crosslinking of the positively charged separation layer is 50-90%; Preferably, a first electrode chamber is formed between the first anion exchange membrane and the anode plate; Preferably, a second electrode chamber is formed between the second anion exchange membrane and the cathode plate; Preferably, the electrically driven separation device further includes a liquid storage unit, a concentration storage unit, and an electrode storage unit; Preferably, the liquid storage unit is connected to the liquid chamber; Preferably, the outlet of the liquid storage unit is connected to the inlet of the liquid chamber, and the inlet of the liquid storage unit is connected to the outlet of the liquid chamber. Preferably, the material storage unit in the concentration chamber is connected to the concentration chamber; Preferably, the outlet of the concentration chamber storage unit is connected to the inlet of the concentration chamber, and the inlet of the concentration chamber storage unit is connected to the outlet of the concentration chamber. Preferably, the electrode chamber storage unit is connected to the first electrode chamber; Preferably, the electrode chamber storage unit is connected to the second electrode chamber; Preferably, the first electrode chamber and the second electrode chamber are connected.

3. The electrically driven separation device according to claim 1 or 2, characterized in that, The electrically driven separation device also includes an external power supply; Preferably, the external power supply is connected to the anode plate and the cathode plate; Preferably, the positive terminal of the external power supply is connected to the anode plate; Preferably, the negative terminal of the external power supply is connected to the cathode plate.

4. The electrically driven separation device according to any one of claims 1-3, characterized in that, The monomer containing an amino functional group includes any one or a combination of at least two of polyethyleneimine, piperazine, m-phenylenediamine, p-phenylenediamine, polyethyleneimine, or polyethyleneaniline, preferably polyethyleneimine; Preferably, the monomer containing the sulfonyl chloride functional group includes benzenetrisulfonyl chloride; Preferably, the monomer containing the isocyanate functional group includes terephthalic diisocyanate.

5. The electrically driven separation device according to any one of claims 1-4, characterized in that, The negatively charged porous support layer includes an ultrafiltration membrane; Preferably, the material of the ultrafiltration membrane includes any one or a combination of at least two of polyacrylonitrile, polycarbonate, polyvinyl chloride, polysulfone, polyethersulfone, sulfonated polyethersulfone, sulfonated polysulfone, or polyvinylidene chloride, with polyacrylonitrile being the preferred material. Preferably, the molecular weight cutoff of the ultrafiltration membrane is 5-100 kDa.

6. An electrically driven separation method based on the electrically driven separation device according to any one of claims 1-5, characterized in that, The electrically driven separation method includes the following steps: Rare earth feed solution is introduced into the feed chamber of the electrically driven separation device according to any one of claims 1-5. Initial acid solution is introduced into the concentration chamber of the electrically driven separation device. The anode plate and cathode plate of the electrically driven separation device are energized to electrically drive the separation of rare earth ions and hydrogen ions in the rare earth feed solution. Hydrogen ions in the feed chamber migrate to the concentration chamber through the acid-resistant selective nanofiltration membrane, forming concentrated acid solution in the concentration chamber. Rare earth ions in the feed chamber are retained in the feed chamber by the acid-resistant selective nanofiltration membrane, forming a separated rare earth solution in the feed chamber.

7. The electrically driven separation method according to claim 6, characterized in that, The rare earth solution includes a rare earth salt solution and an acid reagent; Preferably, the total concentration of rare earth ions in the rare earth feed solution is 0.005-0.20 mol / L; Preferably, the concentration of hydrogen ions in the rare earth feed solution is 0.001-0.20 mol / L; Preferably, the concentration of hydrogen ions in the initial acid solution is 0.001-0.20 mol / L; Preferably, the volume ratio of the rare earth solution in the feed chamber to the initial acid solution in the concentration chamber is (0.5-1.5):(0.5-5.0); Preferably, the rare earth liquid introduced into the liquid chamber is transferred to the liquid chamber through the rare earth liquid in the liquid chamber storage unit; Preferably, the initial acid solution introduced into the concentration chamber is transferred from the initial acid solution in the concentration chamber storage unit to the concentration chamber.

8. The electrically driven separation method according to claim 6 or 7, characterized in that, Before the power is applied, a first electrolyte solution is introduced into the first electrode chamber of the electrically driven separation device, and a second electrolyte solution is introduced into the second electrode chamber of the electrically driven separation device. Preferably, the volume ratio of the rare earth solution in the feed chamber to the first electrolyte solution in the first electrode chamber is (0.5-1.5):(0.5-1.5); Preferably, the volume ratio of the initial acid solution in the concentration chamber to the second electrolyte solution in the second electrode chamber is (0.5-1.5):(0.5-1.5); Preferably, the first electrolyte solution and the second electrolyte solution are independently selected from any one or a combination of at least two of sodium sulfate solution, magnesium sulfate solution, or sulfuric acid solution; Preferably, the concentrations of the first electrolyte solution and the second electrolyte solution are independently selected from 0.2-1 mol / L; Preferably, the first electrolyte solution introduced into the first electrode chamber is transferred to the first electrode chamber through the electrolyte solution in the electrode chamber storage unit; Preferably, the second electrolyte solution introduced into the second electrode chamber is transferred to the second electrode chamber through the electrolyte solution in the electrode chamber storage unit; Preferably, the first electrolyte solution and the second electrolyte solution have exactly the same composition.

9. The electrically driven separation method according to any one of claims 6-8, characterized in that, The power supply includes a DC regulated power supply; Preferably, the current density of the energized circuit is 1-20 mA / cm². 2 ; Preferably, the voltage applied is 5-10V.

10. The electrically driven separation method according to any one of claims 6-9, characterized in that, The acid-resistant selective nanofiltration membrane has a permeability of over 90% for hydrogen ions in the feed chamber. Preferably, the acid-resistant selective nanofiltration membrane has a rejection rate of over 90% for rare earth ions in the feed chamber.

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