Electric nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and synchronously recovering ammonium sulfate as well as use method and application of electric nanofiltration device

Abstract

The invention relates to an electrical nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and synchronously recovering ammonium sulfate and a using method and application thereof.The electrical nanofiltration device comprises an electrical nanofiltration membrane assembly of an anode plate, an electrical nanofiltration unit and a cathode plate which are sequentially arranged, and an anode / cathode chamber is formed between the anode / cathode plate and the electrical nanofiltration unit; the anode plate and the cathode plate are respectively connected with an anode and a cathode of a direct-current power supply; the electric nanofiltration unit comprises a first anion exchange membrane, an electric drive nanofiltration membrane and a second anion exchange membrane which are sequentially arranged in parallel; the electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer which is positioned on the surface of one side of the polyacrylonitrile-based membrane and contains primary amine and secondary amine groups. According to the method, RE < 3 + > and NH4 < + > are selectively separated by utilizing the steric hindrance and electrostatic repulsion effect of the electrically driven nanofiltration membrane, and SO4 < 2-> directionally moves to pass through the anion exchange membrane in combination with an electric field, so that ammonium sulfate is recycled.

Description

Technical Field

[0001] The invention relates to the technical field of solution separation and purification, and in particular to an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, and a use method and purpose of the device. Background Art

[0002] At present, ionic adsorption rare earth ores account for 15% of the world's rare earth reserves and provide more than 90% of heavy rare earths. The main mining process is in-situ leaching, in which ammonium sulfate and other ammonium salts are used as leaching agents to extract rare earth leaching solutions through ion exchange. The amount of leaching agent is determined by the volume of the ore or the amount of rare earth resources. The "Technical Specifications for In-situ Leaching of Ionic Rare Earth Minerals" points out: "The amount of leaching agent is determined based on the volume of the ore, and 1% to 2% of ammonium sulfate is added at a solid-liquid volume ratio of 1:0.33." However, in the actual mining process, people often increase the concentration and amount of ammonium sulfate leaching agent to improve the leaching efficiency of ionic rare earths. Therefore, ionic rare earth tailings also contain a lot of ammonium sulfate. Free ammonium sulfate is leached from the mine under rainwater leaching, and replaces rare earth ions and other metal ions downstream, and then flows to the environmental water system, resulting in excessive metal and ammonia nitrogen concentrations, which poses a great threat to ecological safety. Sampling of river water in some rare earth mining areas in Gannan, Jiangxi Province, the analysis results show that the concentration of rare earth in the water is in the range of 2-100mg / L, and the ammonia nitrogen concentration is in the range of 20-300mg / L, accounting for the vast majority of the water, of which the ammonia nitrogen concentration far exceeds the 15mg / L standard required by the "Ionic Rare Earth Mining Water Pollutant Emission Standard" (DB36 / 1016-2018) and the "Rare Earth Industry Pollutant Emission Standard" (GB26451-2011). If rare earth wastewater can be treated in an efficient and environmentally friendly way and the rare earth elements and ammonium sulfate in it can be recovered, turning rare earth wastewater into treasure, it can not only avoid water pollution but also improve the overall economic benefits.

[0003] Traditional treatment measures for rare earth wastewater include rare earth recovery and ammonia nitrogen treatment. From a technical analysis, there are many feasible methods to choose from for simply recovering rare earth from wastewater or simply treating ammonia nitrogen in wastewater, but the difficulty lies in how to recover rare earth and ammonia nitrogen at a lower cost. At present, the main treatment methods for ammonia nitrogen in ionic rare earth tailings wastewater include physical and chemical methods, chemical methods and biological methods. The defect of the stripping method is that it requires very high alkalinity, and the NH3 produced needs to be absorbed and treated to prevent pollution. After the treatment, acid is needed to neutralize the excess alkali, so its cost is very high and its efficiency is low; the liquid membrane method uses the difference in ion concentration on both sides of the liquid membrane as a driving force, but the pressure difference on both sides of the membrane makes it easy for the water phase on both sides to leak, which seriously reduces the treatment effect of the wastewater; the separation principle of the chemical precipitation method is that the chemical substances are separated by crystallization and precipitation due to different solubility. Not only is the cost high, but the treatment effect is also poor. It is difficult to achieve the effluent index through one treatment; the microalgae adsorption method absorbs ammonia nitrogen and phosphorus in the wastewater as nutrients through microalgae and uses CO2 in the air for photoautotrophy. It is low-cost and environmentally friendly, but its denitrification efficiency is greatly affected by the environment such as temperature. The above ammonia nitrogen treatment methods only treat ammonia nitrogen as "waste" and ignore the possibility of turning ammonia nitrogen into treasure and resource utilization. Therefore, the treatment of ammonia nitrogen should also be developed towards the goals of economy, environmental protection and efficiency.

[0004] Membrane separation technology is an efficient and environmentally friendly separation method. At present, the membrane processes that can achieve ion separation mainly include pressure-driven nanofiltration, electrodialysis and electric-driven nanofiltration. The traditional pressure-driven nanofiltration process uses pressure as the driving force. The pore size and charge density of the nanofiltration membrane surface are adjustable. It can selectively separate ions of different sizes and valence states through its steric hindrance and electrostatic repulsion synergistic effect, but SO4 2- It is not possible to efficiently pass through the nanofiltration membrane, so it is impossible to separate ammonium sulfate and rare earth sulfate. The electrodialysis process uses the electric field as the driving force. The anion exchange membrane and the selective cation exchange membrane are arranged alternately in the membrane stack. Under the action of the electric field, the anions and cations migrate to the anion exchange membrane and the selective cation exchange membrane in the electrodialysis membrane stack respectively. The selective cation exchange membrane can selectively pass NH4 + , thus achieving the purpose of separation. Since selective cation exchange membranes generally operate at relatively low currents or voltages, the target ion separation efficiency is also greatly limited.

[0005] Therefore, how to provide a simple device and method to achieve the NH4 + Rapid and efficient separation of rare earth ions to avoid ammonia nitrogen pollution and separation of SO4 2- Therefore, the recovery and reuse of ammonium sulfate has become an urgent problem to be solved. Summary of the invention

[0006] In order to solve the above technical problems, the present invention provides an electric nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, and its use method and purpose. The electric nanofiltration device of the present invention adopts an electrically driven nanofiltration membrane and an anion exchange membrane and combines the effect of a direct current electric field to apply the electric drive technology to the rare earth ions (RE 404) in rare earth wastewater. 3+ ) and ammonium ions (NH4 + ) by using the steric hindrance and electrostatic repulsion effect of electrically driven nanofiltration membranes to separate RE 3+ With NH4 + Selectively separate and remove SO4 in rare earth wastewater under the action of electric field 2- Directional movement through the anion exchange membrane will also occur, thereby realizing the recovery of ammonium sulfate. Therefore, the present invention can quickly, efficiently and environmentally friendly treat rare earth wastewater, and simultaneously realize the recovery and reuse of ammonium sulfate.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, the electro-nanofiltration device comprising an electro-nanofiltration membrane assembly, the electro-nanofiltration membrane assembly comprising an anode plate, an electro-nanofiltration unit and a cathode plate arranged in sequence, an anode chamber is formed between the anode plate and the electro-nanofiltration unit, a cathode chamber is formed between the cathode plate and the electro-nanofiltration unit, the anode plate is connected to the positive electrode of a direct current power supply, and the cathode plate is connected to the negative electrode of the direct current power supply;

[0009] The electric nanofiltration unit comprises 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, wherein the selective separation layer contains a primary amine group and a secondary amine group.

[0011] In the present invention, the steric hindrance and electrostatic repulsion effect of the electrically driven nanofiltration membrane in the electric nanofiltration device are firstly utilized to quickly and efficiently remove RE in rare earth wastewater. 3+ With NH4 + For selective separation, since the surface of the electro-driven nanofiltration membrane contains primary and secondary amine groups, and the rare earth wastewater is weakly acidic, the primary and secondary amine groups on the surface of the rare earth wastewater will be protonated during the contact between the rare earth wastewater and the electro-driven nanofiltration membrane, so that the surface of the electro-driven nanofiltration membrane presents a positive charge, and the rare earth elements in the rare earth wastewater are all trivalent positively charged, NH4 +The electrostatic repulsion of the NH4+ nanofiltration membrane surface to the 1-valent positive charge with a lower valence is stronger. Therefore, under the action of steric hindrance and electrostatic repulsion, NH4+ + It is easier to enter the concentration chamber through the electrically driven nanofiltration membrane, while RE 3+ Still in the desalination room, the selective separation of the two is achieved; at the same time, under the action of the DC electric field, SO4 2- The SO4 in the cathode chamber will pass through the anion exchange membrane into the anode chamber in the electrode chamber 2- Then it will pass through the anion exchange membrane into the concentration chamber, thus NH4 + and SO4 2- All of them are collected in the concentration chamber to obtain enriched ammonium sulfate, thereby realizing the recovery and reuse of ammonium sulfate.

[0012] As a preferred technical solution of the present invention, the pore size and surface charge of the electrically driven nanofiltration membrane synergistically achieve the separation of RE from rare earth wastewater. 3+ and NH4 + .

[0013] The present invention further regulates the pore size and surface charge of the electrically driven nanofiltration membrane on the basis that the surface of the electrically driven nanofiltration membrane contains primary and secondary amine groups. Under the synergistic effect of steric hindrance and electrostatic effect, NH4 + Maintain efficient transmembrane mass transfer, while for RE 3+ The interception rate is further improved, thereby increasing RE 3+ With NH4 + Separation efficiency.

[0014] The molecular weight cutoff of the electrically driven nanofiltration membrane is 170Da-350Da, for example, 170Da, 180Da, 185Da, 188Da, 190Da, 200Da, 220Da, 250Da, 280Da, 300Da, 320Da or 350Da.

[0015] Preferably, the electro-nanofiltration membrane assembly comprises at least one group 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 compartment.

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

[0020] As a preferred technical solution of the present invention, the outlet of the desalination chamber liquid 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 liquid storage component.

[0021] Preferably, the outlet of the concentration chamber liquid storage member 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 liquid storage member.

[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 the present invention, the anode chamber and the cathode chamber are in a connected state, which is convenient for SO4 2- separation and transmission, and then recovered to obtain ammonium sulfate.

[0024] It should be noted that the present invention does not make any specific requirements or special limitations on the material of the connecting pipe. As long as it is a type commonly used by technicians in this field, it is applicable to the present invention, for example, it can be a latex tube.

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

[0026] It should be noted that the flow rate control unit described in the present invention can be a group that generally controls the flow rate of each solution entering the desalination chamber, the concentrating chamber and the anode chamber, or it can be multiple groups that independently control the flow rate of each solution entering the desalination chamber, the concentrating chamber and the anode chamber; the device of the flow rate control unit is not subject to specific requirements and special limitations, as long as it is a flow rate control device commonly used by technicians in this field, it is applicable to the present invention, for example, it can be a peristaltic pump, etc.

[0027] As a preferred technical solution 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 respectively fixed by a support plate with a hollow space of a certain thickness (so that ions can pass through the membrane into the corresponding compartment), wherein the first anion exchange membrane covers the right side of the hollow position of the support plate, and the inlet and outlet of the anode chamber are respectively located at the bottom and top of the support plate and are connected to the hollow position of the support plate, so as to facilitate the entry and outflow of the solution; the electrically driven nanofiltration membrane covers the right side of the hollow position of the support plate, and the inlet and outlet of the desalination chamber are respectively located at the bottom and top of the support plate and are connected to the hollow position of the support plate, so as to facilitate the entry and outflow of the solution; the second anion exchange membrane covers the right side of the hollow position of the support plate, and the inlet and outlet of the concentration chamber are respectively located at the bottom and top of the support plate and are connected to the hollow position of the support plate, so as to facilitate the entry and outflow of the solution.

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

[0031] The rare earth wastewater is introduced into the desalination chamber, the auxiliary electrolyte solution is introduced into the concentration chamber, and the electrolyte solution is introduced into the anode chamber and the cathode chamber respectively; under the action of the DC electric field, the NH4 + The SO4 in the rare earth wastewater enters the concentration chamber through the electrically driven nanofiltration membrane from the desalination chamber. 2- Enter the anode chamber from the desalination chamber through the first anion exchange membrane, then enter the cathode chamber, and enter the concentration chamber from the cathode chamber through the second anion exchange membrane to separate rare earth and ammonium ions and simultaneously recover ammonium sulfate;

[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, wherein the selective separation layer contains a primary amine group and a secondary amine group.

[0033] In the present invention, the use of electric drive technology combined with the use of electric drive nanofiltration membrane can achieve RE 3+ With NH4 + The method of the present invention can withstand a large voltage and current to improve the separation efficiency, has the advantages of high efficiency and environmental friendliness, and has great application potential in treating 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 the rare earth sulfate solution and the ammonium sulfate solution, the rare earth sulfate solution includes a lanthanum sulfate solution, a samarium sulfate solution and a ytterbium sulfate solution.

[0036] Preferably, the concentration of the rare earth sulfate solution is 0.005 mol / L-0.03 mol / L, for example, 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 the rare earth sulfate solution and the ammonium sulfate solution, the concentration of the ammonium sulfate solution is 0.005 mol / L-0.12 mol / L, for example, 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 ammonium sulfate solution.

[0039] Preferably, the concentration of the auxiliary electrolyte solution is 0.005 mol / L-0.05 mol / L, for example, 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 includes sodium sulfate solution and / or potassium sulfate solution.

[0041] Preferably, the concentration of the electrolyte solution is 0.2 mol / L-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, in the method, the operating temperature range is 10°C-30°C, such as 10°C, 15°C, 20°C, 25°C or 30°C.

[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 technical solution 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 independently in a circulating flow state, and the flow rates of the three are the same.

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

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

[0048] The rare earth wastewater is introduced into the desalination chamber of the electro-nanofiltration device, the auxiliary electrolyte solution is introduced into the concentrating chamber of the electro-nanofiltration device, and the electrolyte solution is respectively introduced into the anode chamber and the cathode chamber of the electro-nanofiltration device. The rare earth wastewater in the desalination chamber, the auxiliary electrolyte solution in the concentrating chamber, and the electrolyte solution in the anode chamber and the cathode chamber have the same flow rate, and each flows independently at a flow rate of 10L / h-30L / h. Under the action of a DC electric field at a temperature of 10℃-30℃, a current of 0.1A-0.3A, and a voltage of 1V-10V, NH4 + The SO4 in the rare earth wastewater enters the concentration chamber from the desalination chamber through the electrically driven nanofiltration membrane of the electro-nanofiltration device. 2- Enter the anode chamber from the desalination chamber through the first anion exchange membrane, then enter the cathode chamber, and enter the concentration chamber from the cathode chamber through the second anion exchange membrane to separate rare earth and ammonium ions and simultaneously recover ammonium sulfate;

[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, wherein the surface of the selective separation layer contains primary amine groups and secondary amine groups.

[0050] It should be noted that the method for preparing the electrically driven nanofiltration membrane described in the present invention is a conventional method and can be adaptively selected and adjusted according to actual conditions.

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

[0052] The polyacrylonitrile-based membrane treated by hydrolysis and acidification is fixed in a mold and infiltrated with an aqueous solution at 15°C-30°C for 1min-10min; an organic solution at 15°C-30°C is poured into the membrane in contact with the aqueous solution for 1min-5min to cause an interfacial polymerization reaction; the membrane obtained after the interfacial polymerization reaction is placed in an oven for drying to obtain an electrically driven nanofiltration membrane.

[0053] Preferably, the aqueous phase solution includes 0.4wt%-2.0wt% of aqueous phase monomers, such as 0.4wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt% or 2.0wt%, etc., based on a mass fraction of 100wt%; 0.1wt%-0.5wt% of surfactants, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% or 0.5wt%, etc., and the remainder of water.

[0054] Preferably, the organic phase solution comprises 0.1wt%-1.0wt% of organic phase monomer, such as 0.1wt%, 0.3wt%, 0.5wt%, 0.8wt% or 1.0wt%, etc., and the remainder of organic solvent, based on a mass fraction of 100wt%.

[0055] Preferably, the aqueous phase monomer includes any one of polyethyleneimine, piperazine or meta-phenylenediamine, or a combination of at least two thereof.

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

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

[0058] In a third aspect, the present invention further provides a use of an electro-nanofiltration device, 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 electric nanofiltration device of the present invention uses an electrically driven nanofiltration membrane and an anion exchange membrane and combines the effect of a DC electric field to apply the electric drive technology to RE 3+ With NH4 + Selective separation can be used to recover ammonium sulfate for reuse, thereby reducing the emission of ammonia nitrogen pollutants in rare earth wastewater.

[0061] 2) The present invention can significantly improve the treatment efficiency and resource utilization rate of rare earth wastewater, and has a significant impact on La 3+ 、Sm 3+ and Yb 3+ The interception rates of NH4 + The interception rate is 19.97%-30.09%, NH4 + To La 3+ 、Sm3+ and Yb 3+ The permeability selectivity separation coefficients can reach 402.1-637.2, 364.5-414.2 and 320.9-456.8 respectively, with high separation efficiency. The method of the present invention has broad application prospects in the field of rare earth tail water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 1 is a schematic flow chart of a method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate using an electric nanofiltration device in Example 1 of the present invention;

[0063] Among them, 1-anode plate; 2-electric 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 liquid storage component; 10-concentration chamber liquid storage component; 11-electrolyte liquid 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 It is a schematic diagram of the separation and movement of ions in the electric nanofiltration device used in Example 1 of the present invention.

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

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

[0067] Figure 5 3 is a surface Zeta potential diagram of the electrically driven nanofiltration membrane at different pH values ​​in Example 1 of the present invention.

[0068] Figure 6 This is a schematic flow chart of a method for separating rare earth and ammonium ions from rare earth wastewater using a pressure-driven cross-flow nanofiltration device 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-diaphragm; 26-membrane assembly; 27-second valve; 28-second pressure gauge; 29-filtrate collection tank; 30-bypass valve.

[0070] Figure 7 The electric-driven nanofiltration membrane provided in Example 1 of the present invention has a stability test on La 3+ 、Sm3+ , Yb 3+ and NH4 + Variation of retention rate with cycle number. DETAILED DESCRIPTION

[0071] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and through specific implementation methods. However, the following examples are only 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 shall be subject to the claims.

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

[0073] The method for preparing the electrically driven nanofiltration membrane adopted in the specific embodiment of the present invention comprises the following steps:

[0074] The hydrolyzed and acidified polyacrylonitrile-based membrane is fixed in a mold and infiltrated with an aqueous solution of 0.4wt%-2.0wt% polyethyleneimine (molecular weight 600Da) and 0.1wt% sodium dodecyl sulfate at 25°C for 5 minutes, and the excess solution is removed; a 25°C n-hexane solution containing 0.1wt% trimesoyl chloride is poured into the membrane infiltrated with the aqueous solution for 3 minutes, an interfacial polymerization reaction occurs, the excess solution is removed, and the membrane is rinsed with n-hexane to remove unreacted monomers, and then the membrane is placed in a 70°C oven and dried for 10 minutes to obtain an electrically driven nanofiltration membrane, wherein the content of polyethyleneimine can be adaptively selected and adjusted according to the actual pore size and surface charge required.

[0075] Example 1

[0076] The present embodiment provides an electro-nanofiltration device for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, and a method for using the same. The electro-nanofiltration device includes an electro-nanofiltration membrane assembly, and the electro-nanofiltration membrane assembly includes an anode plate 1, an electro-nanofiltration unit 2, and a cathode plate 3 arranged in sequence, an anode chamber 4 is formed between the anode plate 1 and the electro-nanofiltration unit 2, 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 electrode of a DC power supply 6, and the cathode plate 3 is connected to the negative electrode of the DC power supply 6;

[0077] The electro-nanofiltration membrane assembly includes at least one group of electro-nanofiltration units 2, wherein the 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 liquid 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 liquid storage component 9, the outlet of the concentration chamber liquid 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 liquid storage component 10, the outlet of the electrolyte liquid 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 liquid storage component 11;

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

[0080] The electrically driven nanofiltration membrane includes 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 contains primary amine groups and secondary amine groups. By adjusting the concentration of polyethyleneimine to 0.6wt%, the molecular weight cutoff of the electrically driven nanofiltration membrane is 185Da.

[0081] Figure 1 The schematic flow diagram of the method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate using an electro-nanofiltration device in Example 1 of the present invention is shown. Figure 2 The schematic diagram of the separation and movement of ions in the electro-nanofiltration device used in Example 1 of the present invention is shown, wherein the desalination chamber liquid storage component 9 is a desalination chamber liquid storage tank, the concentration chamber liquid storage component is a concentration chamber liquid storage tank, the electrolyte liquid storage component is an electrolyte liquid 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 comprises the following steps:

[0083] The rare earth wastewater (a mixed solution of rare earth sulfate solution and ammonium sulfate solution, wherein the concentration of the rare earth sulfate solution is 0.03 mol / L, the concentration of the 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 at a flow rate of 20 L / h through a peristaltic pump, and then circulated back to the desalination chamber storage tank from the outlet of the desalination chamber, and the rare earth wastewater is kept in a circulating flow state;

[0084] A 0.02 mol / L ammonium sulfate solution is introduced into the concentration chamber from the outlet of the concentration chamber storage tank through 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, and the ammonium sulfate solution maintains a circulating flow state;

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

[0086] At a temperature of 25°C, under the action of a DC electric field with a constant current of 0.3A and a maximum voltage limit of 10V, NH4 + The SO4 in the rare earth wastewater is transported from the desalination chamber to the concentration chamber through the electrically driven nanofiltration membrane. 2- The NH4 + and SO4 2- All of them are collected in the concentration chamber to recover ammonium sulfate.

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

[0088] Figure 5 The surface Zeta potential diagram of the electrically driven nanofiltration membrane in Example 1 of the present invention at different pH values ​​is shown. It can be seen from the figure that in a lower pH range, the Zeta potential becomes a positive charge, 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 a method for using the same. The electro-nanofiltration device is consistent with that in Embodiment 1.

[0091] The electrically driven nanofiltration membrane includes 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 contains primary amine groups and secondary amine groups. By adjusting the concentration of polyethyleneimine to 0.4wt%, the molecular weight cutoff of the electrically driven nanofiltration membrane is 188Da, and the pH value corresponding to the isoelectric point is 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 a method for using the same. The electro-nanofiltration device is consistent with that in Embodiment 1.

[0095] The electrically driven nanofiltration membrane includes 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 contains primary amine groups and secondary amine groups. By adjusting the concentration of polyethyleneimine to 1.0wt%, the molecular weight cutoff of the electrically driven nanofiltration membrane is 180Da, and the pH value corresponding to the isoelectric point is 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 for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate, and a method of using the same. The electro-nanofiltration device differs from Example 1 in that a commercial polyamide nanofiltration membrane (NFX nanofiltration membrane) is used as the electrically driven nanofiltration membrane, and 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 in the form of data. After testing and calculation, the results show that the electric-driven nanofiltration membrane has a significant effect on the separation of La. 3+ 、Sm 3+ , Yb 3+ and NH4 + The retention rate of NH4 + To La 3+ 、Sm 3+ and Yb 3+ The specific calculation formula of the selectivity separation coefficient is as follows:

[0101] The retention rate (R) of the target ion in the desalination chamber is calculated by the formula:

[0102]

[0103] The calculation formula of the ion flux (J) of the prepared electrically driven nanofiltration membrane under electrical drive is:

[0104]

[0105] Among them, C t and C0 are the concentrations of ions in the desalination chamber at time t and time 0, respectively; V is the volume of the desalination chamber; A m is the effective area of ​​the membrane.

[0106] The calculation formula of permeability selectivity separation coefficient (P) is:

[0107]

[0108] in, is the permeability selectivity separation coefficient; and RE 3+ and NH4 + The flux; and They are respectively the time t, the desalination chamber RE 3+ and NH4 + 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 assembly 26, and a first pressure gauge 24 is provided at the outlet of the first valve 23. The membrane assembly 26 is divided into an upper part and a lower part, the outlet of the lower part of the membrane assembly 26 is connected to the inlet of the second valve 27, the outlet of the second valve 27 is connected to an inlet of the rare earth wastewater storage component 21, the outlet of the upper part of the membrane assembly 26 is connected to the filtrate collection tank 29, and a second pressure gauge 28 is provided 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 another inlet of the rare earth wastewater storage tank 21. The diaphragm 25 is a pressure-driven nanofiltration membrane, and the components and structure are consistent with the electrically driven nanofiltration membrane provided in Example 1.

[0111] The method for using the pressure-driven cross-flow nanofiltration device is as follows:

[0112] The pressure-driven cross-flow nanofiltration device was used to conduct a pressure-driven nanofiltration experiment at 25°C and 6 bar. First, the bypass valve and the second valve were opened, and the first valve was closed to allow the rare earth wastewater to circulate back to the rare earth wastewater storage tank through the bypass, and then the first valve was slowly opened to full open to allow the rare earth wastewater to slowly enter the membrane assembly, and finally the bypass valve was adjusted to make the pressure reach 6 bar.

[0113] Pure water was pre-compacted at 6 bar for 1 hour to stabilize the flux of the membrane. After the device was running smoothly, rare earth wastewater was replaced for formal experiments. The rare earth wastewater was transported from the rare earth wastewater storage tank to the lower part of the membrane assembly by a diaphragm pump. At a pressure of 6 bar, the membrane in the membrane assembly was used to ionize the RE in the rare earth wastewater. 3+ and NH4 + The filtrate after separation enters the upper part of the membrane assembly under the action of pressure, and the remaining liquid after separation is retained in the lower part of the membrane assembly and circulated to the rare earth wastewater storage tank. Except for a small amount of filtrate for detection, it is refluxed to the feed tank together with the remaining liquid after separation, thereby maintaining the concentration of the whole system solution constant.

[0114] The separation effect of comparative example 2 is also reflected in the form of data. After testing and calculation, it is found that the pressure-driven nanofiltration membrane has a good separation effect on La 3+ 、Sm 3+ , Yb 3+ and NH4 + The retention rate of NH4 + To La 3+ 、Sm 3+ and Yb 3+ The specific calculation formula of the selectivity separation coefficient is as follows:

[0115] The retention rate (R) of the target ion in the filtrate collection tank is calculated as follows:

[0116]

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

[0118] Selective separation coefficient (S) calculation formula:

[0119]

[0120] in, is the selectivity separation coefficient; and The membrane reacts with NH4 when filtering rare earth wastewater. + and RE 3+ The interception rate.

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

[0122] Figure 7 The results show that the electric driven nanofiltration membrane in Example 1 of the present invention has a certain stability on La 3+ 、Sm 3+ , Yb 3+ and NH4 + The retention rate of the electro-driven nanofiltration membrane varies with the number of cycles. It can be seen from the figure that in the 10-cycle experiment, the retention rate of the electro-driven nanofiltration membrane 3+ 、Sm 3+ , Yb 3+ and NH4 + There is no obvious change and no phenomenon of reduction in retention rate, that is, the electrically driven nanofiltration membrane has good stability.

[0123] Table 1

[0124]

[0125] The test results show that:

[0126] (1) It can be seen from Examples 1-3 that the electric nanofiltration device of the present invention uses an electrically driven nanofiltration membrane and an anion exchange membrane and combines the effect of a direct current electric field to apply the electric drive technology to RE in rare earth wastewater. 3+ With NH4 + Rapid and efficient selective separation, and under the action of the electric field, SO4 2- Directed movement through the anion exchange membrane will also occur, allowing the recovery of ammonium sulfate for reuse;

[0127] In addition, by further regulating the pore size and surface charge strength of the electrically driven nanofiltration membrane, the rare earth ion retention rate can be further increased, thereby improving the separation of rare earth ions and NH4 + Separation efficiency, further improve NH4 + To La 3+ 、Sm 3+ and Yb 3+ The selectivity separation factor;

[0128] Specifically, for La 3+ 、Sm 3+ and Yb 3+ The interception rates of NH4 + The interception rate is 19.97%-30.09%, NH4 + To La 3+ 、Sm 3+ and Yb 3+The selectivity separation coefficients and can reach 402.1-637.2, 364.5-414.2 and 320.9-456.8 respectively, which can realize the efficient separation of rare earth ions and ammonium ions and the efficient recovery of ammonium sulfate.

[0129] (2) It can be seen from Example 1 and Comparative Example 1 that the common commercial polyamide nanofiltration membrane (NFX nanofiltration membrane) is used as the electrically driven nanofiltration membrane, and 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 RE cannot be achieved. 3+ With NH4 + Efficient separation.

[0130] (3) It can be seen from Comparative Example 2 that when a conventional pressure-driven cross-flow nanofiltration device is used, it can only achieve RE 3+ With NH4 + Partial separation, NH4 + To La 3+ 、Sm 3+ and Yb 3+ The selectivity separation coefficient is extremely low and RE cannot be achieved 3+ With NH4 + It is impossible to separate the ammonium sulfate efficiently and simultaneously recover the ammonium sulfate.

[0131] In summary, the electric nanofiltration device of the present invention adopts an electrically driven nanofiltration membrane and an anion exchange membrane and combines the effect of a direct current electric field to apply the electric drive technology to the rare earth ions (RE) in rare earth wastewater. 3+ ) and ammonium ions (NH4 + ) by using the steric hindrance and electrostatic repulsion effect of electrically driven nanofiltration membranes to separate RE 3+ With NH4 + Selectively separate and remove SO4 in rare earth wastewater under the action of electric field 2- Directional movement through the anion exchange membrane will also occur, thereby realizing the recovery of ammonium sulfate. Therefore, the present invention can quickly, efficiently and environmentally friendly treat rare earth wastewater, and simultaneously realize the recovery and reuse of ammonium sulfate.

[0132] The applicant declares that the above is only a specific implementation mode 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 thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope 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 comprises an electro-nanofiltration membrane assembly, which comprises an anode plate, an electro-nanofiltration unit and a cathode plate which are arranged in sequence, an anode chamber is formed between the anode plate and the electro-nanofiltration unit, a cathode chamber is formed between the cathode plate and the electro-nanofiltration unit, the anode plate is connected to the positive electrode of a DC power supply, and the cathode plate is connected to the negative electrode of the DC power supply; The electric nanofiltration unit comprises a first anion exchange membrane, an electrically driven nanofiltration membrane and a second anion exchange membrane arranged in parallel in sequence; 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, wherein the selective separation layer contains a primary amine group and a secondary amine group.

2. The electro-nanofiltration device according to claim 1, characterized in that: The pore size and surface charge of the electrically driven nanofiltration membrane synergistically achieve separation of RE from rare earth wastewater 3+ and NH4 + ; Preferably, the molecular weight cut-off of the electrically driven nanofiltration membrane is 170Da-350Da; Preferably, the electro-nanofiltration membrane assembly comprises at least one group of electro-nanofiltration units; Preferably, the anode chamber is a compartment formed by the anode plate and the first anion exchange membrane; Preferably, the cathode chamber is a compartment formed by the cathode plate and the second anion exchange membrane; Preferably, the compartment between the first anion exchange membrane and the electrically driven nanofiltration membrane is a desalination compartment; Preferably, the compartment between the second anion exchange membrane and the electrically driven nanofiltration membrane is a concentrating compartment.

3. The electro-nanofiltration device according to claim 1 or 2, characterized in that: The outlet of the desalination chamber liquid 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 liquid storage component; Preferably, the outlet of the concentration chamber liquid 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 liquid storage component; 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.

4. The electro-nanofiltration device according to claim 3, characterized in that: A flow rate control unit is arranged at the outlet of the desalination chamber liquid storage component, the outlet of the concentration chamber liquid storage component and the outlet of the electrolyte liquid storage component.

5. The electro-nanofiltration device according to claim 3 or 4, characterized in that: 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; Preferably, the first anion exchange membrane and the second anion exchange membrane are each independently a non-selective anion exchange membrane.

6. A method for separating rare earth and ammonium ions from rare earth wastewater and simultaneously recovering ammonium sulfate using the electro-nanofiltration device according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: The rare earth wastewater is introduced into the desalination chamber, the auxiliary electrolyte solution is introduced into the concentration chamber, and the electrolyte solution is introduced into the anode chamber and the cathode chamber respectively; under the action of the DC electric field, the NH4 + The SO4 in the rare earth wastewater enters the concentration chamber through the electrically driven nanofiltration membrane from the desalination chamber. 2- Enter the anode chamber from the desalination chamber through the first anion exchange membrane, then enter the cathode chamber, and enter the concentration chamber from the cathode chamber through the second anion exchange membrane to separate rare earth and ammonium ions and simultaneously recover ammonium sulfate; 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, wherein the selective separation layer contains a primary amine group and a secondary amine group.

7. The method according to claim 6, characterized in that The rare earth wastewater includes a mixed solution of rare earth sulfate solution and ammonium sulfate solution; Preferably, in the mixed solution of the rare earth sulfate solution and the ammonium sulfate solution, the rare earth sulfate solution includes a lanthanum sulfate solution, a samarium sulfate solution and an ytterbium sulfate solution; Preferably, the concentration of the rare earth sulfate solution is 0.005 mol / L-0.03 mol / L; Preferably, in the mixed solution of the rare earth sulfate solution and the ammonium sulfate solution, the concentration of the ammonium sulfate solution is 0.005 mol / L-0.12 mol / L; Preferably, the auxiliary electrolyte solution comprises an ammonium sulfate solution; Preferably, the concentration of the auxiliary electrolyte solution is 0.005mol / L-0.05mol / L; Preferably, the electrolyte solution comprises sodium sulfate solution and / or potassium sulfate solution; Preferably, the concentration of the electrolyte solution is 0.2 mol / L-0.4 mol / L.

8. The method according to claim 6 or 7, characterized in that: In the method, the operating temperature range is 10°C-30°C; Preferably, the current of the DC electric field is 0.1A-0.3A; Preferably, the voltage of the DC electric field is 1V-10V; Preferably, 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 independently in a state of circulating flow, and the flow rates of the three are the same; Preferably, the flow rate is 10 L / h-30 L / h.

9. The method according to claim 6, characterized in that The method comprises the following steps: The rare earth wastewater is introduced into the desalination chamber of the electro-nanofiltration device, the auxiliary electrolyte solution is introduced into the concentrating chamber of the electro-nanofiltration device, and the electrolyte solution is respectively introduced into the anode chamber and the cathode chamber of the electro-nanofiltration device. The rare earth wastewater in the desalination chamber, the auxiliary electrolyte solution in the concentrating chamber, and the electrolyte solution in the anode chamber and the cathode chamber have the same flow rate, and each flows independently at a flow rate of 10L / h-30L / h. Under the action of a DC electric field at a temperature of 10℃-30℃, a current of 0.1A-0.3A, and a voltage of 1V-10V, NH4 + The SO4 in the rare earth wastewater enters the concentration chamber from the desalination chamber through the electrically driven nanofiltration membrane of the electro-nanofiltration device. 2- Enter the anode chamber from the desalination chamber through the first anion exchange membrane, then enter the cathode chamber, and enter the concentration chamber from the cathode chamber through the second anion exchange membrane to separate rare earth and ammonium ions and simultaneously recover ammonium sulfate; The electrically driven nanofiltration membrane comprises a polyacrylonitrile-based membrane and a selective separation layer located on the surface of the polyacrylonitrile-based membrane, wherein the surface of the selective separation layer contains primary amine groups and secondary amine groups.

10. Use of an electro-nanofiltration device, characterized in that: The use includes using the electro-nanofiltration device as described in any one of claims 1 to 5 to separate rare earth and ammonium ions from rare earth wastewater and simultaneously recover ammonium sulfate.

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