An electrofiltration nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, along with its usage and applications.

Abstract

This invention relates to an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, as well as its usage and applications. The electro-nanofiltration device comprises an electro-nanofiltration membrane assembly consisting of an anode plate, an electro-nanofiltration unit, and a cathode plate arranged sequentially. An anode / cathode chamber is formed between the anode / cathode plate and the electro-nanofiltration unit. The anode plate and cathode plate are respectively connected to the positive and negative terminals of a DC power supply. The electro-nanofiltration unit comprises a first anion exchange membrane, an electrically driven nanofiltration membrane, and a second anion exchange membrane arranged in parallel. The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer containing primary and secondary amine groups on one side of the polyacrylonitrile-based membrane. This invention utilizes the steric hindrance and electrostatic repulsion effect of the electrically driven nanofiltration membrane to achieve the separation of rare earth and ammonium sulfate ions. 3+ With NH4 + Selective separation is achieved by combining an electric field with SO4. 2‑ Ammonium sulfate is recovered by directional movement through anion exchange membrane.

Description

Technical Field

[0001] This invention relates to the field of solution separation and purification technology, and in particular to an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, as well as its usage and applications. Background Technology

[0002] Currently, ion-adsorbed rare earth deposits account for 15% of global rare earth reserves and provide over 90% of heavy rare earth elements. The main mining process is in-situ leaching, which primarily uses ammonium salts such as ammonium sulfate as leaching agents to extract rare earth leachate through ion exchange. The amount of leaching agent used is determined by the volume of the ore or the amount of rare earth resources. The "Technical Specification for In-situ Leaching Mining of Ion-Adsorbed Rare Earth Mines" states that "the amount of leaching agent is determined based on the ore volume, with 1%–2% ammonium sulfate added at a solid-liquid volume ratio of 1:0.33." However, in actual mining, the concentration and amount of ammonium sulfate leaching agent are often increased to improve the leaching efficiency of ion-adsorbed rare earths. Therefore, ion-adsorbed rare earth tailings still contain a significant amount of ammonium sulfate. This free ammonium sulfate is leached from the ore by rainwater and displaces rare earth ions and other metal ions downstream, subsequently flowing into environmental water systems. This results in excessive concentrations of metals and ammonia nitrogen, posing a significant threat to ecological safety. Sampling of river water from some rare earth mining areas in southern Jiangxi Province revealed that the concentration of rare earth elements in the water ranged from 2 to 100 mg / L, while the concentration of ammonia nitrogen ranged from 20 to 300 mg / L. The majority of the water samples contained ammonia nitrogen concentrations far exceeding the 15 mg / L limit set by the "Discharge Standard of Pollutants for Ionic Rare Earth Mining" (DB36 / 1016-2018) and the "Discharge Standard of Pollutants for Rare Earth Industry" (GB26451-2011). If rare earth wastewater can be treated efficiently and environmentally, and the rare earth elements and ammonium sulfate recovered, turning this wastewater into a valuable resource, it would not only prevent water pollution but also improve overall economic benefits.

[0003] Traditional rare earth wastewater treatment methods include rare earth recovery and ammonia nitrogen treatment. Technically, there are many feasible methods for recovering rare earth from wastewater or treating ammonia nitrogen from wastewater alone. However, the challenge lies in simultaneously recovering both rare earth and ammonia nitrogen at a relatively low cost. Currently, the main methods for treating ammonia nitrogen in ion-adsorption rare earth tailings wastewater include physicochemical methods, chemical methods, and biological methods. The air stripping method has drawbacks: it requires high alkalinity, and the generated NH3 needs to be absorbed to prevent pollution. After treatment, acid is needed to neutralize excess alkali, resulting in high cost and low efficiency. The liquid membrane method utilizes the ion concentration difference across the membrane, but the pressure difference makes leakage in the aqueous phase on both sides prone to occur, severely reducing the wastewater treatment effect. Chemical precipitation separates chemical substances based on their different solubilities through crystallization and precipitation; it is not only costly but also ineffective, rarely achieving effluent standards with a single treatment. Microalgae adsorption uses microalgae to absorb ammonia nitrogen and phosphorus from wastewater as nutrients and utilizes CO2 from the air for photoautotrophication; it is low-cost and environmentally friendly, but its denitrification efficiency is greatly affected by environmental factors such as temperature. All these ammonia nitrogen treatment methods treat ammonia nitrogen merely as "waste," neglecting the possibility of turning it into a valuable resource. Therefore, ammonia nitrogen treatment should develop towards economic, environmentally friendly, and efficient goals.

[0004] Membrane separation technology is a highly efficient and environmentally friendly separation method. Currently, membrane processes capable of ion separation mainly include pressure-driven nanofiltration, electrodialysis, and electro-driven nanofiltration. Traditional pressure-driven nanofiltration uses pressure as the driving force; the pore size and charge density of the nanofiltration membrane surface are adjustable, allowing for selective separation of ions of different sizes and valence states through the synergistic effect of steric hindrance and electrostatic repulsion. However, SO42-... 2- Nanofiltration membranes cannot efficiently permeate, therefore they cannot separate ammonium sulfate and rare earth sulfate. Electrodialysis is driven by an electric field, with anion exchange membranes and selective cation exchange membranes alternating in the membrane stack. Under the influence of the electric field, anions and cations migrate directionally towards the anion exchange membranes and selective cation exchange membranes, respectively. The selective cation exchange membrane can selectively permeate NH4+. + This achieves the purpose of separation. However, since selective cation exchange membranes generally operate at relatively low currents or voltages, the separation efficiency of target ions is greatly limited.

[0005] Therefore, how to provide a simple device and method to remove NH4 from rare earth wastewater is a key objective. + Rapid and efficient separation of rare earth ions, avoiding ammonia nitrogen pollution, and separation of SO4. 2- Therefore, the recycling and reuse of ammonium sulfate has become an urgent problem to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, along with its usage and applications. This electro-nanofiltration device employs an electrically driven nanofiltration membrane and an anion exchange membrane, combined with a direct current electric field, to apply electro-driven technology to rare earth ions (REs) in rare earth wastewater. 3+ ) and ammonium ions (NH4) + Rapid and efficient selective separation of REs utilizes the steric hindrance and electrostatic repulsion effect of electrically driven nanofiltration membranes. 3+ With NH4 + Selective separation is performed, and SO4 in rare earth wastewater is separated under the action of an electric field. 2- It also undergoes directional migration through the anion exchange membrane, thereby achieving the recovery of ammonium sulfate. Therefore, this invention can treat rare earth wastewater quickly, efficiently, and environmentally, while simultaneously recovering and reusing ammonium sulfate.

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

[0008] In a first aspect, the present invention provides an electro-nanofiltration device for simultaneously recovering ammonium sulfate by separating rare earth and ammonium ions from rare earth wastewater. The electro-nanofiltration device includes an electro-nanofiltration membrane assembly, which includes an anode plate, an electro-nanofiltration unit, and a cathode plate arranged sequentially. An anode chamber is formed between the anode plate and the electro-nanofiltration unit, and a cathode chamber is formed between the cathode plate and the electro-nanofiltration unit. The anode plate is connected to the positive terminal of a DC power supply, and the cathode plate is connected to the negative terminal of the DC power supply.

[0009] The electro-nanofiltration unit includes a first anion exchange membrane, an electrically driven nanofiltration membrane, and a second anion exchange membrane arranged in parallel in sequence.

[0010] The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on one side surface of the polyacrylonitrile-based membrane, the selective separation layer containing primary amine groups and secondary amine groups.

[0011] In this invention, the spatial steric hindrance and electrostatic repulsion effect of the electrically driven nanofiltration membrane in the electro-nanofiltration device are first utilized to achieve rapid and efficient removal of REs from rare earth wastewater. 3+ With NH4 + Selective separation is achieved because the surface of the electrically driven nanofiltration membrane contains primary and secondary amine groups, while the rare earth wastewater is weakly acidic. During the contact between the rare earth wastewater and the electrically driven nanofiltration membrane, the primary and secondary amine groups on the membrane surface are protonated, resulting in a positive charge on the membrane surface. Since the rare earth elements in the wastewater are all trivalent positively charged, NH4+... +As a lower valence state monovalent positive charge, the electrically driven nanofiltration membrane surface exhibits stronger electrostatic repulsion towards the higher valence state trivalent positive charge. Therefore, under the combined effects of steric hindrance and electrostatic repulsion, NH4+... + It is easier to pass through the electrically driven nanofiltration membrane into the concentration chamber, while RE 3+ Still within the desalination chamber, selective separation of the two is achieved; simultaneously, under the influence of a DC electric field, SO4 in the rare earth wastewater... 2- SO42- will pass through the anion exchange membrane into the anode and cathode chambers of the electrode chamber. 2- It will then pass through the anion exchange membrane into the concentration chamber, thus NH4 + and SO4 2- All of these are collected in the concentration chamber to obtain enriched ammonium sulfate, thereby realizing the recycling and reuse of ammonium sulfate.

[0012] As a preferred embodiment of the present invention, the synergistic effect of the pore size and surface charge of the electrically driven nanofiltration membrane enables the separation of RE from rare earth wastewater. 3+ and NH4 + .

[0013] This invention, based on the presence of primary and secondary amine groups on the surface of the electrically driven nanofiltration membrane, further modulates the pore size and surface charge of the membrane. Under the synergistic effect of steric hindrance and electrostatics, NH4... + Maintaining efficient transmembrane mass transfer, while for RE 3+ The retention rate was further improved, thereby increasing RE 3+ With NH4 + Separation efficiency.

[0014] The electrically driven nanofiltration membrane has a molecular weight cutoff of 170 Da to 350 Da, such as 170 Da, 180 Da, 185 Da, 188 Da, 190 Da, 200 Da, 220 Da, 250 Da, 280 Da, 300 Da, 320 Da, or 350 Da.

[0015] Preferably, the electro-nanofiltration membrane assembly includes at least one set of electro-nanofiltration units.

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

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

[0018] Preferably, the compartment between the first anion exchange membrane and the electrically driven nanofiltration membrane is a desalination chamber.

[0019] Preferably, the compartment between the second anion exchange membrane and the electrically driven nanofiltration membrane is a concentration chamber.

[0020] As a preferred embodiment of the present invention, the outlet of the desalination chamber storage component is connected to the inlet of the desalination chamber, and the outlet of the desalination chamber is connected to the inlet of the desalination chamber storage component.

[0021] Preferably, the outlet of the liquid storage component in the concentration chamber is connected to the inlet of the concentration chamber, and the outlet of the concentration chamber is connected to the inlet of the liquid storage component in the concentration chamber.

[0022] Preferably, the outlet of the electrolyte storage component is connected to the inlet of the anode chamber, the outlet of the anode chamber is connected to the inlet of the cathode chamber, and the outlet of the cathode chamber is connected to the inlet of the electrolyte storage component.

[0023] In this invention, the anode chamber and the cathode chamber are connected, which facilitates the removal of SO4 from rare earth wastewater. 2- The separation and transport of ammonium sulfate are then used to recover the ammonium sulfate.

[0024] It should be noted that the material of the connecting tube used for connection is not specifically required or limited in this invention. Any type commonly used by those skilled in the art is applicable to this invention, such as latex tubing.

[0025] As a preferred embodiment of the present invention, a flow rate control unit is provided at the outlet of the desalination chamber storage component, the outlet of the concentration chamber storage component, and the outlet of the electrolyte storage component.

[0026] It should be noted that the flow rate control unit described in this invention can be a set, which controls the overall flow rate of each solution entering the desalination chamber, concentration chamber, and anode chamber, or it can be multiple sets, which independently control the flow rate of each solution entering the desalination chamber, concentration chamber, and anode chamber. The equipment of the flow rate control unit is not subject to specific requirements or special limitations. Any flow rate control equipment commonly used by those skilled in the art is applicable to this invention, such as a peristaltic pump.

[0027] As a preferred embodiment of the present invention, the desalination chamber liquid storage component is a desalination chamber liquid storage tank, the concentration chamber liquid storage component is a concentration chamber liquid storage tank, and the electrolyte liquid storage component is an electrolyte liquid storage tank.

[0028] Preferably, the first anion exchange membrane and the second anion exchange membrane are each independently a non-selective anion exchange membrane.

[0029] It should be noted that the first anion exchange membrane, the second anion exchange membrane, and the electrically driven nanofiltration membrane of the present invention are each fixed using a support plate with a certain thickness (allowing ions to pass through the membrane into the corresponding compartment). Specifically, the first anion exchange membrane covers the right side of the hollow portion of the support plate, with the inlet and outlet of the anode compartment located at the bottom and top of the support plate, respectively, and communicating with the hollow portion of the support plate to facilitate solution entry and exit; the electrically driven nanofiltration membrane covers the right side of the hollow portion of the support plate, with the inlet and outlet of the desalination compartment located at the bottom and top of the support plate, respectively, and communicating with the hollow portion of the support plate to facilitate solution entry and exit; and the second anion exchange membrane covers the right side of the hollow portion of the support plate, with the inlet and outlet of the concentration compartment located at the bottom and top of the support plate, respectively, and communicating with the hollow portion of the support plate to facilitate solution entry and exit.

[0030] In a second aspect, the present invention also provides a method for simultaneously recovering ammonium sulfate from rare earth wastewater by separating rare earth and ammonium ions using the electro-nanofiltration device described in the first aspect, the method comprising the following steps:

[0031] Rare earth wastewater is introduced into a desalination chamber, and an auxiliary electrolyte solution is introduced into a concentration chamber. The electrolyte solution is then introduced into both the anode and cathode chambers. Under the influence of a direct current electric field, the NH4+ in the rare earth wastewater... + The SO4 in the rare earth wastewater enters the concentration chamber from the desalination chamber via an electrically driven nanofiltration membrane. 2- The ammonium sulfate is separated from rare earth and ammonium ions and simultaneously recovered. The ammonium sulfate is then passed through the first anion exchange membrane from the desalination chamber to the anode chamber, then through the cathode chamber, and finally through the second anion exchange membrane from the cathode chamber to the concentration chamber.

[0032] The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on one side surface of the polyacrylonitrile-based membrane, the selective separation layer containing primary amine groups and secondary amine groups.

[0033] In this invention, by utilizing electric drive technology in conjunction with the use of an electrically driven nanofiltration membrane, RE can be achieved. 3+ With NH4 + The method of this invention provides rapid and efficient selective separation. It can withstand higher voltage and current, thereby improving separation efficiency. It has advantages such as high efficiency and environmental friendliness, and has great application potential in the treatment of rare earth wastewater.

[0034] As a preferred technical solution of the present invention, the rare earth wastewater includes a mixed solution of rare earth sulfate solution and ammonium sulfate solution.

[0035] Preferably, in the mixed solution of rare earth sulfate solution and ammonium sulfate solution, the rare earth sulfate solution includes lanthanum sulfate solution, samarium sulfate solution and ytterbium sulfate solution.

[0036] Preferably, the concentration of the rare earth sulfate solution is 0.005 mol / L to 0.03 mol / L, such as 0.005 mol / L, 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.025 mol / L, or 0.03 mol / L.

[0037] Preferably, in the mixed solution of rare earth sulfate solution and ammonium sulfate solution, the concentration of ammonium sulfate solution is 0.005 mol / L-0.12 mol / L, such as 0.005 mol / L, 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.04 mol / L, 0.06 mol / L, 0.08 mol / L, 0.10 mol / L or 0.12 mol / L, etc.

[0038] Preferably, the auxiliary electrolyte solution comprises an ammonium sulfate solution.

[0039] Preferably, the concentration of the auxiliary electrolyte solution is 0.005 mol / L to 0.05 mol / L, such as 0.005 mol / L, 0.01 mol / L, 0.015 mol / L, 0.02 mol / L, 0.03 mol / L, 0.04 mol / L, or 0.05 mol / L.

[0040] Preferably, the electrolyte solution comprises sodium sulfate solution and / or potassium sulfate solution.

[0041] Preferably, the concentration of the electrolyte solution is 0.2 mol / L to 0.4 mol / L, such as 0.2 mol / L, 0.3 mol / L, or 0.4 mol / L.

[0042] As a preferred technical solution of the present invention, the operating temperature range of the method is 10℃-30℃, such as 10℃, 15℃, 20℃, 25℃ or 30℃.

[0043] Preferably, the current of the DC electric field is 0.1A-0.3A, such as 0.1A, 0.2A or 0.3A.

[0044] Preferably, the voltage of the DC electric field is 1V-10V, such as 1V, 4V, 6V, 8V or 10V.

[0045] As a preferred embodiment of the present invention, the rare earth wastewater in the desalination chamber, the auxiliary electrolyte solution in the concentration chamber, and the electrolyte solutions in the anode chamber and the cathode chamber are each in an independent circulating state, and the three have the same flow rate.

[0046] Preferably, the flow rate is 10L / h-30L / h, such as 10L / h, 15L / h, 20L / h, 25L / h or 30L / h.

[0047] As a preferred technical solution of the present invention, the method includes the following steps:

[0048] Rare earth wastewater is introduced into the desalination chamber of an electrofiltration nanofiltration unit, and an auxiliary electrolyte solution is introduced into the concentration chamber. The electrolyte solutions are then introduced into the anode and cathode chambers of the unit. The rare earth wastewater in the desalination chamber, the auxiliary electrolyte solution in the concentration chamber, and the electrolyte solutions in the anode and cathode chambers all flow at the same rate, independently at 10 L / h-30 L / h. Under a DC electric field with a current of 0.1 A-0.3 A and a voltage of 1 V-10 V at a temperature of 10℃-30℃, the NH4+ in the rare earth wastewater... + The electrically driven nanofiltration membrane of the aforementioned electro-nanofiltration device enters the concentration chamber from the desalination chamber, where SO4 in the rare earth wastewater is removed. 2- The ammonium sulfate is separated from rare earth and ammonium ions and simultaneously recovered. The ammonium sulfate is then passed through the first anion exchange membrane from the desalination chamber to the anode chamber, then through the cathode chamber, and finally through the second anion exchange membrane from the cathode chamber to the concentration chamber.

[0049] The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on the surface of the polyacrylonitrile-based membrane, the surface of the selective separation layer containing primary amine groups and secondary amine groups.

[0050] It should be noted that the method for preparing the electrically driven nanofiltration membrane described in this invention is a conventional method, which can be adapted and adjusted according to actual needs.

[0051] For example, the present invention provides a method for preparing an electrically driven nanofiltration membrane, the method comprising the following steps:

[0052] A polyacrylonitrile-based membrane treated by hydrolysis and acidification is fixed in a mold and immersed in an aqueous solution at 15℃-30℃ for 1 min-10 min. An organic solution at 15℃-30℃ is poured in and immersed in the membrane after immersion in the aqueous solution for 1 min-5 min to induce an interfacial polymerization reaction. The membrane obtained after the interfacial polymerization reaction is placed in an oven and dried to obtain an electrically driven nanofiltration membrane.

[0053] Preferably, the aqueous solution comprises, by mass fraction of 100wt%, 0.4wt%-2.0wt% of an aqueous monomer, such as 0.4wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2.0wt%; 0.1wt%-0.5wt% of a surfactant, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, or 0.5wt%; and the balance being water.

[0054] Preferably, the organic phase solution comprises, by mass fraction of 100wt%, 0.1wt%-1.0wt% of organic phase monomers, such as 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt%, or 1.0wt%, and the balance being organic solvent.

[0055] Preferably, the aqueous monomer comprises any one or a combination of at least two of polyethyleneimine, piperazine, or m-phenylenediamine.

[0056] Preferably, the surfactant comprises sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfate.

[0057] Preferably, the organic phase monomer includes any one or a combination of at least two of pyromellitic chloroformyl chloride, phthaloyl chloride, or terephthaloyl chloride.

[0058] Thirdly, the present invention also provides an application of an electro-nanofiltration device, the application of which includes using the electro-nanofiltration device as described in the first aspect to separate rare earth and ammonium ions from rare earth wastewater and simultaneously recover ammonium sulfate.

[0059] Compared with the prior art, the present invention has at least the following beneficial effects:

[0060] 1) The electro-nanofiltration device of the present invention employs an electrically driven nanofiltration membrane and an anion exchange membrane, combined with the effect of a DC electric field, to apply electro-driven technology to RE. 3+ With NH4 + The selective separation process allows for the recovery and reuse of ammonium sulfate, reducing the emission of ammonia nitrogen pollutants from rare earth wastewater.

[0061] 2) This invention can significantly improve the treatment efficiency and resource utilization rate of rare earth wastewater, and is particularly beneficial for La... 3+ 、Sm 3+ and Yb 3+ The retention rates were as high as 99.01%-99.57%, 98.91%-99.37%, and 98.77%-99.39%, respectively, for NH4. + The retention rate was 19.97%-30.09%, NH4 + For La 3+ 、Sm3+ and Yb 3+ The permeability selective separation coefficients can reach 402.1-637.2, 364.5-414.2 and 320.9-456.8 respectively, which have high separation efficiency. The method of the present invention has broad application prospects in the field of rare earth tailwater treatment. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the process for separating rare earth and ammonium ions and simultaneously recovering ammonium sulfate from rare earth wastewater using an electro-nanofiltration device in Embodiment 1 of the present invention.

[0063] Wherein, 1-anode plate; 2-electro-nanofiltration unit; 201-first anion exchange membrane; 202-electrically driven nanofiltration membrane; 203-second anion exchange membrane; 3-cathode plate; 4-anode chamber; 5-cathode chamber; 6-DC power supply; 7-desalination chamber; 8-concentration chamber; 9-desalination chamber storage component; 10-concentration chamber storage component; 11-electrolyte storage component; 12-flow rate control unit; 13-anode chamber inlet; 14-anode chamber outlet; 15-desalination chamber inlet; 16-desalination chamber outlet; 17-concentration chamber inlet; 18-concentration chamber outlet; 19-cathode chamber inlet; 20-cathode chamber outlet.

[0064] Figure 2 This is a schematic diagram of the separation and movement of ions in the electro-nanofiltration device used in Embodiment 1 of the present invention.

[0065] Figure 3 This is a SEM image of the surface of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention.

[0066] Figure 4 This is a cross-sectional SEM image of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention.

[0067] Figure 5 This is a surface Zeta potential diagram of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention at different pH values.

[0068] Figure 6 This is a schematic diagram of the process for separating rare earth and ammonium ions from rare earth wastewater using a pressure-driven cross-flow nanofiltration device, as described in Comparative Example 2 of the present invention.

[0069] Among them, 21-rare earth wastewater storage tank; 22-diaphragm pump; 23-first valve; 24-first pressure gauge; 25-membrane; 26-membrane module; 27-second valve; 28-second pressure gauge; 29-filtrate collection tank; 30-bypass valve.

[0070] Figure 7 The electrically driven nanofiltration membrane provided in Embodiment 1 of this invention demonstrates its stability in La2000 experiments. 3+ 、Sm3+ Yb 3+ and NH4 + The graph shows the change in retention rate with the number of cycles. Detailed Implementation

[0071] 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.

[0072] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0073] The method for preparing the electrically driven nanofiltration membrane used in the specific embodiments of this invention includes the following steps:

[0074] A hydrolyzed and acidified polyacrylonitrile-based membrane was fixed in a mold and immersed in an aqueous solution of 0.4wt%-2.0wt% polyethyleneimine (molecular weight 600 Da) and 0.1wt% sodium dodecyl sulfate at 25°C for 5 min. Excess solution was removed. A hexane solution containing 0.1wt% trimesoyl chloride at 25°C was poured in and brought into contact with the membrane after immersion in the aqueous solution for 3 min to induce interfacial polymerization. Excess solution was removed, and the membrane was rinsed with hexane to remove unreacted monomers. The membrane was then dried in a 70°C oven for 10 min to obtain an electrically driven nanofiltration membrane. The content of polyethyleneimine can be adaptively selected and adjusted according to the required pore size and surface charge.

[0075] Example 1

[0076] This embodiment provides an electro-nanofiltration device and its method for simultaneously recovering ammonium sulfate from rare earth wastewater by separating rare earth and ammonium ions. The electro-nanofiltration device includes an electro-nanofiltration membrane assembly, which includes an anode plate 1, an electro-nanofiltration unit 2, and a cathode plate 3 arranged sequentially. An anode chamber 4 is formed between the anode plate 1 and the electro-nanofiltration unit 2, and a cathode chamber 5 is formed between the cathode plate 3 and the electro-nanofiltration unit 2. The anode plate 1 is connected to the positive terminal of a DC power supply 6, and the cathode plate 3 is connected to the negative terminal of the DC power supply 6.

[0077] The electro-nanofiltration membrane assembly includes at least one set of electro-nanofiltration units 2. Each electro-nanofiltration unit 2 includes a first anion exchange membrane 201, an electrically driven nanofiltration membrane 202, and a second anion exchange membrane 203 arranged in parallel in sequence. The anode chamber 4 is a compartment formed by the anode plate 1 and the first anion exchange membrane 201. The cathode chamber 5 is a compartment formed by the cathode plate 3 and the second anion exchange membrane 203. The compartment between the first anion exchange membrane 201 and the electrically driven nanofiltration membrane 202 is a desalination chamber 7, and the compartment between the second anion exchange membrane 203 and the electrically driven nanofiltration membrane 202 is a concentration chamber 8.

[0078] The outlet of the desalination chamber storage component 9 is connected to the inlet 15 of the desalination chamber 7, the outlet 16 of the desalination chamber 7 is connected to the inlet of the desalination chamber storage component 9, the outlet of the concentration chamber storage component 10 is connected to the inlet 17 of the concentration chamber 8, the outlet 18 of the concentration chamber 8 is connected to the inlet of the concentration chamber storage component 10, the outlet of the electrolyte storage component 11 is connected to the inlet 13 of the anode chamber 4, the outlet 14 of the anode chamber 4 is connected to the inlet 19 of the cathode chamber 5, and the outlet 20 of the cathode chamber 5 is connected to the inlet of the electrolyte storage component 11.

[0079] A set of flow rate control units 12 are provided at the outlet of the desalination chamber storage component 9, the outlet of the concentration chamber storage component 10, and the outlet of the electrolyte storage component 11.

[0080] The electrically driven nanofiltration membrane comprises a polyacrylonitrile base membrane and a selective separation layer located on the surface of the polyacrylonitrile base membrane. The surface of the selective separation layer contains primary amine groups and secondary amine groups. By adjusting the concentration of polyethyleneimine to 0.6 wt%, the molecular weight cutoff of the electrically driven nanofiltration membrane is 185 Da.

[0081] Figure 1 This diagram illustrates a process flow chart of the method for separating rare earth and ammonium ions and simultaneously recovering ammonium sulfate from rare earth wastewater using an electro-nanofiltration device, as described in Embodiment 1 of the present invention. Figure 2 The diagram shows the separation and movement of ions in the electro-nanofiltration device used in Embodiment 1 of the present invention. In this diagram, the desalination chamber storage component 9 is a desalination chamber storage tank, the concentration chamber storage component is a concentration chamber storage tank, the electrolyte storage component is an electrolyte storage tank, and the flow rate control unit 12 is a peristaltic pump.

[0082] The method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate includes the following steps:

[0083] Rare earth wastewater (a mixed solution of rare earth sulfate solution and ammonium sulfate solution, wherein the concentration of rare earth sulfate solution is 0.03 mol / L and the concentration of ammonium sulfate solution is 0.05 mol / L, and the rare earth sulfate solution includes lanthanum sulfate solution, samarium sulfate solution and ytterbium sulfate solution) is introduced into the desalination chamber from the outlet of the desalination chamber storage tank through a peristaltic pump at a flow rate of 20 L / h, and then circulated back to the desalination chamber storage tank from the outlet of the desalination chamber, so that the rare earth wastewater is kept in a state of continuous circulation.

[0084] A 0.02 mol / L ammonium sulfate solution is introduced into the concentration chamber from the outlet of the concentration chamber storage tank using a peristaltic pump at a flow rate of 20 L / h, and then circulated back to the concentration chamber storage tank from the outlet of the concentration chamber, keeping the ammonium sulfate solution in a state of continuous circulation.

[0085] A 0.3 mol / L sodium sulfate solution is introduced into the anode chamber from the outlet of the electrolyte storage tank at a flow rate of 20 L / h using a peristaltic pump. The solution then enters the cathode chamber through the outlet of the anode chamber and the inlet of the cathode chamber, and finally circulates back to the electrolyte storage tank from the outlet of the cathode chamber. The sodium sulfate solution is kept in a state of circulation to complete the feeding process.

[0086] At 25°C, under the influence of a constant current of 0.3A and a maximum voltage limit of 10V, the NH4+ in rare earth wastewater... + SO4 in rare earth wastewater enters the concentration chamber from the desalination chamber via an electrically driven nanofiltration membrane. 2- The NH4+ passes through the first anion exchange membrane from the desalination chamber to the anode chamber, then to the cathode chamber, and finally through the second anion exchange membrane from the cathode chamber to the concentration chamber. + and SO4 2- All ammonium sulfate is collected in the concentration chamber for recovery.

[0087] Figure 3 The SEM image of the surface of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention is shown. Figure 4 The figure shows a cross-sectional SEM image of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention. As can be seen from the figure, the membrane surface has a dense network cross-linked structure, and the membrane cross-section has a loose pore structure.

[0088] Figure 5 The surface Zeta potential diagrams of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention at different pH values ​​are shown. As can be seen from the figure, in the lower pH range, the Zeta potential becomes positive, and the pH value corresponding to its isoelectric point is 6.22.

[0089] Example 2

[0090] This embodiment provides an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, and its usage method. The electro-nanofiltration device is consistent with that in Embodiment 1.

[0091] The electrically driven nanofiltration membrane comprises a polyacrylonitrile base membrane and a selective separation layer located on the surface of the polyacrylonitrile base membrane. The surface of the selective separation layer contains primary amine groups and secondary amine groups. By adjusting the concentration of polyethyleneimine to 0.4 wt%, the electrically driven nanofiltration membrane has a molecular weight cutoff of 188 Da and an isoelectric point corresponding to a pH value of 6.00.

[0092] The method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate is consistent with that in Example 1.

[0093] Example 3

[0094] This embodiment provides an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, and its usage method. The electro-nanofiltration device is consistent with that in Embodiment 1.

[0095] The electrically driven nanofiltration membrane comprises a polyacrylonitrile base membrane and a selective separation layer located on the surface of the polyacrylonitrile base membrane. The surface of the selective separation layer contains primary amine groups and secondary amine groups. By adjusting the concentration of polyethyleneimine to 1.0 wt%, the electrically driven nanofiltration membrane has a molecular weight cutoff of 180 Da and an isoelectric point corresponding to a pH value of 6.85.

[0096] The method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate is consistent with that in Example 1.

[0097] Comparative Example 1

[0098] This comparative example provides an electro-nanofiltration device and its method of use for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate. The difference between the electro-nanofiltration device and Example 1 is that a commercially available polyamide nanofiltration membrane (NFX nanofiltration membrane) is used as the electrically driven nanofiltration membrane. The rest of the device is consistent with Example 1.

[0099] The method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate is consistent with that in Example 1.

[0100] The separation effects of Examples 1-3 and Comparative Example 1 are presented using data. Through testing and calculation, the separation efficiency of the electrically driven nanofiltration membrane for La... 3+ 、Sm 3+ Yb 3+ and NH4 + Retention rate of NH4 + For La 3+ 、Sm 3+ and Yb 3+ The selective separation coefficient is calculated using the following formula:

[0101] Formula for calculating the rejection rate (R) of target ions in the desalination chamber:

[0102]

[0103] The formula for calculating the ion flux (J) of the prepared electrically driven nanofiltration membrane under electric drive is as follows:

[0104]

[0105] Among them, C t C0 and C0 represent the ion concentrations in the desalination chamber at times t and 0, respectively; V is the volume of the desalination chamber; A m This represents the effective area of ​​the membrane.

[0106] Formula for calculating the permeability selective separation coefficient (P):

[0107]

[0108] in, The permeability-selective separation coefficient; and They are RE 3+ and NH4 + flux; and These are the desalination chamber RE at time t. 3+ and NH4 + The concentration.

[0109] Comparative Example 2

[0110] This comparative example provides a pressure-driven cross-flow nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater, such as... Figure 6 As shown, in the pressure-driven cross-flow nanofiltration device, the outlet of the rare earth wastewater storage tank 21 is connected to the inlet of the diaphragm pump 22, the outlet of the diaphragm pump 22 is connected to the inlet of the first valve 23, the outlet of the first valve 23 is connected to the inlet of the membrane module 26, and a first pressure gauge 24 is installed at the outlet of the first valve 23. The membrane module 26 is divided into an upper part and a lower part. The outlet of the lower part of the membrane module 26 is connected to the inlet of the second valve 27, the outlet of the second valve 27 is connected to one inlet of the rare earth wastewater storage component 21, the outlet of the upper part of the membrane module 26 is connected to the filtrate collection tank 29, and a second pressure gauge 28 is installed at the outlet of the second valve 27. The outlet of the diaphragm pump 22 is also connected to the inlet of the bypass valve 30, and the outlet of the bypass valve 30 is connected to the other inlet of the rare earth wastewater storage tank 21. The membrane 25 is a pressure-driven nanofiltration membrane, and its composition and structure are consistent with the electrically driven nanofiltration membrane provided in Example 1.

[0111] The pressure-driven cross-flow nanofiltration device is used as follows:

[0112] Pressure-driven nanofiltration experiments were conducted using the aforementioned pressure-driven cross-flow nanofiltration device at 25°C and 6 bar. First, the bypass valve and the second valve were opened, and the first valve was closed, allowing the rare earth wastewater to circulate back to the rare earth wastewater storage tank via the bypass. Then, the first valve was slowly opened to full opening, allowing the rare earth wastewater to slowly enter the membrane module. Finally, the pressure was adjusted to 6 bar by adjusting the bypass valve.

[0113] Pure water was pre-compacted at 6 bar for 1 hour to stabilize the membrane flux. After the device was running smoothly, rare earth wastewater was used for the formal experiment. The rare earth wastewater was pumped from the rare earth wastewater storage tank to the lower part of the membrane module using a diaphragm pump. Under 6 bar pressure, the membrane in the membrane module was used to remove REs from the rare earth wastewater. 3+ and NH4 + Separation is performed, and the separated filtrate enters the upper part of the membrane module under pressure. The remaining liquid after separation is retained in the lower part of the membrane module and circulated to the rare earth wastewater storage tank. Except for a small amount of filtrate used for testing, all of it is returned to the feed tank along with the remaining liquid after separation, thereby maintaining a constant concentration of the solution in the entire system.

[0114] The separation effect of Comparative Example 2 is also presented using data. Through testing and calculation, the effect of the pressure-driven nanofiltration membrane on La... 3+ 、Sm 3+ Yb 3+ and NH4 + Retention rate of NH4 + For La 3+ 、Sm 3+ and Yb 3+ The selective separation coefficient is calculated using the following formula:

[0115] Formula for calculating the rejection rate (R) of target ions in the filtrate collection tank:

[0116]

[0117] Among them, C p and C f These are the ion concentrations in the filtrate and the remaining liquid after separation, respectively.

[0118] The formula for calculating the selective separation coefficient (S) is as follows:

[0119]

[0120] in, The selective separation coefficient; and These are the membranes' response to NH4 during the filtration of rare earth wastewater. + and RE 3+ The retention rate.

[0121] The specific data is shown in Table 1.

[0122] Figure 7 This illustrates the effect of the electrically driven nanofiltration membrane in Embodiment 1 of the present invention on La in a stability experiment. 3+ 、Sm 3+ Yb 3+ and NH4 + The graph shows the change in retention rate of the electrically driven nanofiltration membrane with the number of cycles. As can be seen from the graph, in 10 cycles, the retention rate of the membrane for La... 3+ 、Sm 3+ Yb 3+ and NH4 + There were no significant changes, and no decrease in the rejection rate, indicating that the electrically driven nanofiltration membrane has good stability.

[0123] Table 1

[0124]

[0125] The test results show that:

[0126] (1) As can be seen from Examples 1-3, the electro-nanofiltration device of the present invention uses an electrically driven nanofiltration membrane and an anion exchange membrane combined with the effect of a DC electric field to apply electro-driven technology to rare earth wastewater RE 3+ With NH4 + Rapid, efficient, and selective separation of SO42- in rare earth wastewater under the influence of an electric field. 2- It can also undergo directional movement through the anion exchange membrane, enabling the recovery and reuse of ammonium sulfate;

[0127] Furthermore, by further controlling the pore size and surface charge intensity of the electrically driven nanofiltration membrane, the rare earth ion rejection rate can be further increased, thereby enhancing the interaction between rare earth ions and NH4+. + Separation efficiency, further improving NH4 + For La 3+ 、Sm 3+ and Yb 3+ Selective separation coefficient;

[0128] Specifically, for La 3+ 、Sm 3+ and Yb 3+ The retention rates were as high as 99.01%-99.57%, 98.91%-99.37%, and 98.77%-99.39%, respectively, for NH4. + The retention rate was 19.97%-30.09%, NH4 + For La 3+ 、Sm 3+ and Yb 3+The selective separation coefficients can reach 402.1-637.2, 364.5-414.2 and 320.9-456.8 respectively, which can achieve efficient separation of rare earth ions and ammonium ions, and simultaneous efficient recovery of ammonium sulfate.

[0129] (2) As can be seen from Example 1 and Comparative Example 1, using a common commercial polyamide nanofiltration membrane (NFX nanofiltration membrane) as the electrically driven nanofiltration membrane, its effect on RE 3+ With NH4 + The selectivity is much lower than that of the electrically driven nanofiltration membrane prepared by interfacial polymerization in Example 1, and it cannot achieve RE 3+ With NH4 + Highly efficient separation.

[0130] (3) As can be seen from Comparative Example 2, when a conventional pressure-driven cross-flow nanofiltration device is used, it can only achieve RE 3+ With NH4 + Partial separation, NH4 + For La 3+ 、Sm 3+ and Yb 3+ The selective separation coefficient is extremely low, making RE impossible. 3+ With NH4 + Even with efficient separation, ammonium sulfate cannot be recovered simultaneously.

[0131] In summary, the electro-nanofiltration device of this invention employs an electrically driven nanofiltration membrane and an anion exchange membrane combined with the effect of a DC electric field, applying electro-driven technology to rare earth ions (REs) in rare earth wastewater. 3+ ) and ammonium ions (NH4) + Rapid and efficient selective separation of REs utilizes the steric hindrance and electrostatic repulsion effect of electrically driven nanofiltration membranes. 3+ With NH4 + Selective separation is performed, and SO4 in rare earth wastewater is separated under the action of an electric field. 2- It also undergoes directional migration through the anion exchange membrane, thereby achieving the recovery of ammonium sulfate. Therefore, this invention can treat rare earth wastewater quickly, efficiently, and environmentally, while simultaneously recovering and reusing ammonium sulfate.

[0132] 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 electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, characterized in that, The electro-nanofiltration device includes an electro-nanofiltration membrane assembly, which includes an anode plate, an electro-nanofiltration unit, and a cathode plate arranged sequentially. An anode chamber is formed between the anode plate and the electro-nanofiltration unit, and a cathode chamber is formed between the cathode plate and the electro-nanofiltration unit. The anode plate is connected to the positive terminal of a DC power supply, and the cathode plate is connected to the negative terminal of the DC power supply. The electro-nanofiltration unit includes a first anion exchange membrane, an electrically driven nanofiltration membrane, and a second anion exchange membrane arranged in parallel in sequence. The anode chamber is a compartment formed by the anode plate and the first anion exchange membrane, the cathode chamber is a compartment formed by the cathode plate and the second anion exchange membrane, the compartment between the first anion exchange membrane and the electrically driven nanofiltration membrane is a desalination chamber, and the compartment between the second anion exchange membrane and the electrically driven nanofiltration membrane is a concentration chamber. The outlet of the desalination chamber storage component is connected to the inlet of the desalination chamber, and the outlet of the desalination chamber is connected to the inlet of the desalination chamber storage component. The outlet of the concentration chamber storage component is connected to the inlet of the concentration chamber, and the outlet of the concentration chamber is connected to the inlet of the concentration chamber storage component. The outlet of the electrolyte storage component is connected to the inlet of the anode chamber, and the outlet of the anode chamber is connected to the inlet of the cathode chamber. The outlet of the cathode chamber is connected to the inlet of the electrolyte storage component. The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on one side surface of the polyacrylonitrile-based membrane. The selective separation layer contains primary and secondary amine groups. The pore size and surface charge of the electrically driven nanofiltration membrane work synergistically to separate RE from rare earth wastewater. 3+ and NH4 + .

2. The electro-nanofiltration device according to claim 1, characterized in that, The electrically driven nanofiltration membrane has a molecular weight cutoff of 170 Da-350 Da.

3. The electro-nanofiltration device according to claim 1, characterized in that, The electro-nanofiltration membrane assembly includes at least one set of electro-nanofiltration units.

4. The electro-nanofiltration device according to claim 1, characterized in that, A flow rate control unit is provided at the outlet of the desalination chamber storage component, the outlet of the concentration chamber storage component, and the outlet of the electrolyte storage component.

5. The electro-nanofiltration device according to claim 1, characterized in that, The desalination chamber storage component is a desalination chamber storage tank, the concentration chamber storage component is a concentration chamber storage tank, and the electrolyte storage component is an electrolyte storage tank.

6. The electro-nanofiltration device according to claim 1, characterized in that, The first anion exchange membrane and the second anion exchange membrane are each independently non-selective anion exchange membranes.

7. A method for separating rare earth elements and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate using the electro-nanofiltration device according to any one of claims 1-6, characterized in that, The method includes the following steps: Rare earth wastewater is introduced into a desalination chamber, and an auxiliary electrolyte solution is introduced into a concentration chamber. The electrolyte solution is then introduced into both the anode and cathode chambers. Under the influence of a direct current electric field, the NH4+ in the rare earth wastewater... + The SO4 in the rare earth wastewater enters the concentration chamber from the desalination chamber via an electrically driven nanofiltration membrane. 2- The ammonium sulfate is separated from rare earth and ammonium ions and simultaneously recovered. The ammonium sulfate is then passed through the first anion exchange membrane from the desalination chamber to the anode chamber, and then through the second anion exchange membrane from the cathode chamber to the concentration chamber. The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on one side surface of the polyacrylonitrile-based membrane, the selective separation layer containing primary amine groups and secondary amine groups.

8. The method according to claim 7, characterized in that, The rare earth wastewater includes a mixed solution of rare earth sulfate solution and ammonium sulfate solution.

9. The method according to claim 8, characterized in that, The mixed solution of rare earth sulfate solution and ammonium sulfate solution includes lanthanum sulfate solution, samarium sulfate solution and ytterbium sulfate solution.

10. The method according to claim 8, characterized in that, The concentration of the rare earth sulfate solution is 0.005 mol / L to 0.03 mol / L.

11. The method according to claim 8, characterized in that, In the mixed solution of rare earth sulfate solution and ammonium sulfate solution, the concentration of ammonium sulfate solution is 0.005 mol / L-0.12 mol / L.

12. The method according to claim 7, characterized in that, The auxiliary electrolyte solution includes an ammonium sulfate solution.

13. The method according to claim 7, characterized in that, The concentration of the auxiliary electrolyte solution is 0.005 mol / L to 0.05 mol / L.

14. The method according to claim 7, characterized in that, The electrolyte solution includes sodium sulfate solution and / or potassium sulfate solution.

15. The method according to claim 7, characterized in that, The concentration of the electrolyte solution is 0.2 mol / L to 0.4 mol / L.

16. The method according to claim 7, characterized in that, In the method, the operating temperature range is 10℃-30℃.

17. The method according to claim 7, characterized in that, The current in the DC electric field is 0.1A-0.3A.

18. The method according to claim 7, characterized in that, The voltage of the DC electric field is 1V-10V.

19. The method according to claim 7, characterized in that, The rare earth wastewater in the desalination chamber, the auxiliary electrolyte solution in the concentration chamber, and the electrolyte solutions in the anode and cathode chambers are each in an independent circulating state, and the three have the same flow rate.

20. The method according to claim 19, characterized in that, The flow rate is 10L / h-30L / h.

21. The method according to claim 7, characterized in that, The method includes the following steps: Rare earth wastewater is introduced into the desalination chamber of an electrofiltration nanofiltration unit, and an auxiliary electrolyte solution is introduced into the concentration chamber. The electrolyte solutions are then introduced into the anode and cathode chambers of the unit. The rare earth wastewater in the desalination chamber, the auxiliary electrolyte solution in the concentration chamber, and the electrolyte solutions in the anode and cathode chambers all flow at the same rate, independently at 10 L / h-30 L / h. Under a DC electric field with a current of 0.1 A-0.3 A and a voltage of 1 V-10 V at a temperature of 10℃-30℃, the NH4+ in the rare earth wastewater... + The electrically driven nanofiltration membrane of the aforementioned electro-nanofiltration device enters the concentration chamber from the desalination chamber, where SO4 in the rare earth wastewater is removed. 2- The ammonium sulfate is separated from rare earth and ammonium ions and simultaneously recovered. The ammonium sulfate is then passed through the first anion exchange membrane from the desalination chamber to the anode chamber, then through the cathode chamber, and finally through the second anion exchange membrane from the cathode chamber to the concentration chamber. The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on the surface of the polyacrylonitrile-based membrane, the surface of which contains primary amine groups and secondary amine groups.

22. The use of an electro-nanofiltration device, characterized in that, The application includes using the electro-nanofiltration device as described in any one of claims 1-6 to separate rare earth and ammonium ions from rare earth wastewater and simultaneously recover ammonium sulfate.

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