Acid-resistant triazine ring polyamine nanofiltration membrane as well as preparation method and application thereof

Abstract

The invention discloses an acid-resistant triazine ring polyamine nanofiltration membrane as well as a preparation method and application thereof. The preparation method comprises the following steps: carrying out hydrophilic modification on a cleaned basement membrane; respectively preparing a water-phase reaction solution and an organic-phase reaction solution, and preparing the nanofiltration membrane on the surface of the hydrophilic modified basement membrane through interfacial polymerization reaction and heating in a closed space; the water-phase reaction liquid takes a polyamine compound as a water-phase monomer, and the organic-phase reaction liquid takes a compound containing a triazine ring group as an oil-phase monomer; volatile polyamine is used for secondary gas phase interfacial polymerization. According to the invention, cyanuric chloride reacts with polyamine to form a-C-N-bond and a triazine ring in cyanuric chloride, so that the NF membrane shows excellent acid resistance. Volatile amine is used for secondary IP on an initial NF membrane, the crosslinking degree of the NF membrane is improved, the ion removal rate of the NF membrane is not increased by increasing the thickness, the salt rejection rate of the NF membrane subjected to gas-phase secondary interfacial polymerization is reduced to less than 1% under the static pickling condition, and the separation performance and stability of the NF membrane under the high-acidity condition are improved.

Description

Technical Field

[0001] This invention belongs to the field of nanofiltration membrane preparation, specifically relating to an acid-resistant triazine ring polyamine nanofiltration membrane, its preparation method, and its application. Background Technology

[0002] Nanofiltration (NF), a low-pressure driven, phase-change-free separation process, boasts advantages such as being environmentally friendly, energy-efficient, and highly effective, and is widely used in drinking water treatment, seawater desalination, biopharmaceuticals, and food engineering. Its core separation element is the NF membrane with a pore size range of 0.5-2 nm. By precisely optimizing the pore size range through membrane control methods, the separation of different ions can be achieved. Therefore, NF technology has received widespread attention in the field of resource recovery. Industrial wastewater is an important resource source, and the recovery of valuable metals from it is crucial for achieving "pollution reduction and carbon reduction, and synergistic efficiency improvement" in industrial processes. NF technology will play a significant role in this. Currently, commercially available NF membranes are mainly polyamide (PA) thin-layer separation membranes prepared by interfacial polymerization (IP) of polyamines and polyacrylamide chlorides on a porous support membrane. The PA separation layer is prone to hydrolysis and breakage under strong acid and alkali conditions. Therefore, various manufacturers define the pH tolerance range of their PA NF membranes as 2-11. If operation exceeds this pH range, its separation performance and lifespan will severely deteriorate. However, in the field of industrial resource recovery (such as lithium battery recycling leaching solution treatment, rare earth metal enrichment in mining wastewater, and purification of acid leaching solutions and separation and concentration of valuable metal ions in hydrometallurgical processes), the treatment systems often exhibit strong acidity. PA NF membranes are insufficient for the resource recovery of these industrial waste liquids. Therefore, developing novel NF membranes with strong acid resistance and high ion selectivity has become a crucial technological challenge for promoting the resource utilization of industrial waste liquids.

[0003] The IP (Intense Pulsation) method is a commonly used method for preparing NF (Non-Fluorescent Alternating Current) membranes with ultrathin separation layers, and it holds a significant advantage in the large-scale production of NF membranes. Therefore, synthesizing an acid-resistant separation layer using monomers suitable for IP reactions is crucial for the synthesis of acid-resistant NF membranes. CN107930412 B discloses an acid-resistant poly(amide-triazine-amine) NF composite membrane, which is prepared on a support membrane by reacting an aqueous phase reaction solution of a poly(triazine)amine precursor with an oil phase reaction solution of a polyacrylamide chloride via an IP reaction. Its main stability is achieved by introducing a certain amount of triazine rings into the separation layer structure; however, the presence of the amide structure still reduces its long-term stability. Patent CN 112717712 B uses sulfonyl chloride as an organic phase monomer to prepare an acid-resistant NF membrane; however, its ion selectivity is not high. CN116585914A hydrophilically modifies cyanuric chloride, then adds an aqueous solution of a polyamine polymer as the aqueous phase solution to perform IP with the acrylamide chloride to obtain a composite acid-resistant NF membrane. This method solves the problem of reduced reactivity of chlorine atoms when cyanuric chloride is used as the oil phase monomer, leading to decreased reactivity. However, it suffers from low water flux and poor acid resistance. CN 115738741 B discloses a method for preparing a regenerable acid-resistant composite NF membrane, using polyacrylamide chlorides and compounds containing triazine ring groups as oil phase monomers and phenolic compounds as aqueous phase monomers for IP (infiltration process). This method is complex and has a low removal rate of high-valence ions. CN 109999666 A discloses a high-flux positively charged acid-resistant NF membrane, its preparation method, and its application. The NF membrane is produced by sequentially immersing a microfiltration substrate membrane into the aqueous and oil phases, followed by heat treatment. This invention is simple to prepare and improves the rejection rate of polyvalent cations and the acid permeability. Compared with the above work, the currently disclosed acid-resistant NF membranes still suffer from problems such as low removal rate of high-valence ions, low ion selectivity, and low water flux.

[0004] In the construction of various acid-resistant NF membranes, the CN bonds and triazine rings of the triazine ring polyamine NF separation layer form the main chain backbone, exhibiting excellent chemical stability. However, the organic phase monomer cyanuric chloride used to prepare the NF separation layer has low reactivity with the polyamine monomer, resulting in a typically thick NF separation layer with low crosslinking degree, leading to unsatisfactory ion rejection and water flux. Therefore, there is an urgent need to develop a triazine-type acid-resistant NF membrane with high ion rejection, selectivity, and water flux. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies in terms of selective separation precision and poor chemical resistance, the main objective of this invention is to provide an acid-resistant triazine ring polyamine nanofiltration membrane, its preparation method, and its applications. This invention utilizes a first in-phase (IP) reaction between a polyamine monomer and cyanuric chloride (CC) on a porous substrate. Then, a second gas-phase IP process is performed using a volatile polyamine monomer to react with the residual chloride groups from the first IP reaction. This reduces the thickness of the NF layer and increases its crosslinking degree, thereby preparing a triazine ring-type acid-resistant NF membrane with excellent separation performance. This solves the problems of low ion selectivity and permeability, and poor acid resistance in existing nanofiltration membranes.

[0006] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0007] A method for preparing an acid-resistant triazine ring polyamine nanofiltration membrane includes the following steps:

[0008] Step a: The cleaned basement membrane is hydrophilically modified. The hydrophilic modification solution stays on the basement membrane for 10-40 minutes to obtain a hydrophilically modified basement membrane.

[0009] Step b: Prepare aqueous and organic reaction solutions separately, perform interfacial polymerization, heat in a closed space, and prepare a nanofiltration membrane on the surface of the hydrophilic modified substrate membrane described in step a; the aqueous reaction solution uses a polyamine compound as the aqueous monomer, and the organic reaction solution uses a compound containing a triazine ring group as the oil monomer.

[0010] Step c: Place the nanofiltration membrane described in step b into a closed container and perform secondary gas-phase interfacial polymerization using volatile polyamines. The reaction time is 10-30 minutes and the reaction temperature is 50-90℃.

[0011] In step a, the base membrane is selected from one of the following: polysulfone, polyethersulfone, cellulose acetate, polypropylene, polyethylene, polyvinyl chloride, polyacrylonitrile, polyvinylidene fluoride, and polytetrafluoroethylene.

[0012] In step a, the hydrophilic modification solution is selected from one or more of dopamine, tannic acid, diethylenetriamine, and polyvinylpyrrolidone hydrogel.

[0013] The aqueous reaction solution in step b specifically includes a polyamine compound, the acid absorbent NaOH, and the highly efficient nucleophilic catalyst 4-dimethylpyridine.

[0014] In step b, the polyamine compound is polyethyleneimine; the concentration of polyethyleneimine is 0.1~10 wt%.

[0015] The compound containing a triazine ring group in step b is cyanuric chloride with a concentration of 0.1~0.5 w / v%. The solvent of the organic phase reaction solution is selected from one of n-hexane, cyclohexane, heptane, and Isopar G.

[0016] In step b, the heating conditions are 70°C and the time is 7 minutes.

[0017] In step c, the polyamine is selected from one of ethylenediamine, piperazine, diethylenetriamine, triethylenetetramine, tetraethylpentamine, and Tris(2-aminoethyl)amine.

[0018] An acid-resistant triazine ring polyamine nanofiltration membrane prepared by the method described above.

[0019] Application of the acid-resistant triazine ring polyamine nanofiltration membrane in the recovery of valuable metals from batteries.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] 1. This invention utilizes the reaction between cyanuric chloride and polyamines to prepare NF membranes. The reaction of cyanuric chloride with polyamines forms -CN- bonds and a triazine ring in the cyanuric chloride, giving the NF membrane excellent acid resistance.

[0022] 2. This invention uses volatile amines to perform secondary interfacial polymerization (IP) on the initial NF membrane, which improves the crosslinking degree of the NF membrane and does not increase its ion removal rate by increasing its thickness. Under static acid immersion conditions, the salt rejection rate of the NF membrane after gas-phase secondary interfacial polymerization decreases by less than 1%, thus improving the separation performance and stability of the NF membrane under high acid conditions. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the NF membrane preparation process;

[0024] Figure 2 The full X-ray photoelectron spectrum of the NF film;

[0025] Figure 3 The images show the fine C element X-ray photoelectron spectroscopy (XPS) spectrum, where a is the fine C element XPS spectrum of the NF film after undergoing a gas-phase secondary IP reaction, and b is the fine C element XPS spectrum of the NF film without undergoing a gas-phase secondary IP reaction.

[0026] Figure 4 The images show the fine N-element X-ray photoelectron spectroscopy (XPS) spectrum, where a is the fine N-element XPS spectrum of the NF film after gas-phase secondary IP, and b is the fine N-element XPS spectrum of the NF film without gas-phase secondary IP.

[0027] Figure 5The images are scanning electron microscope (SEM) surface morphology images: a) is a scanning electron microscope surface morphology image of PES basement membrane; b) is a scanning electron microscope surface morphology image of TA-DETA co-deposited hydrophilic modified basement membrane; c) is a scanning electron microscope surface morphology image of polyethyleneimine and cyanuric chloride interfacial polymerized NF membrane; and d) is a scanning electron microscope surface morphology image of diethylenetriamine vapor phase secondary IP NF membrane.

[0028] Figure 6 The images are cross-sectional images obtained by scanning electron microscopy. a is a cross-sectional image of the PES basement membrane, b is a cross-sectional image of the TA-DETA co-deposited hydrophilic modified basement membrane, c is a cross-sectional image of the polyethyleneimine and cyanuric chloride interfacial polymerized NF membrane, and d is a cross-sectional image of the diethylenetriamine gas-phase secondary IP NF membrane. Detailed Implementation

[0029] The present invention will be further described below with reference to specific embodiments. These embodiments are merely exemplary and do not limit the scope of protection of the present invention.

[0030] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0031] This invention uses polyamine compounds as aqueous monomers and triazine ring-containing cyanuric chloride as oil monomers. During the interfacial polymerization film formation process, its high reactivity can be utilized to interfacially polymerize with amine monomers to form a poly(triazine)amine separation layer with chemically stable triazine rings as the main chain. The secondary interfacial polymerization of polyamine compounds reacts again with the low-activity unreacted chlorine on the surface, enhancing the polymer network and even the acid resistance of the film.

[0032] Before demonstrating specific embodiments, the method for evaluating the separation performance of the prepared NF membrane will be described.

[0033] The NF membrane separation performance was evaluated at room temperature through a cross-flow membrane filtration test at an operating pressure of 6 bar. The membrane was initially pre-pressurized with deionized water for at least 30 minutes before permeate collection. The pure water permeability (PWP, LMH) of the membrane was determined according to equation (1):

[0034] (1)

[0035] Where V(L) is the permeate volume collected by Δt(h), and A(m 2 ) represents the effective membrane area of ​​the module.

[0036] Following pure water permeability testing, the retention response of the NF membrane to different salts was evaluated. Seven different salt solutions (MgCl2, MgSO4, NaCl, LiCl, CoCl2, MnCl2, and NiCl2, each at a concentration of 1000 ppm) were used as feed water. Salt removal rate (R, %) was calculated using the following formula:

[0037] (2)

[0038] Where C p (mgL) −1 ) represents the concentration of the permeate, C f (mgL) −1 () is the concentration of the influent solution.

[0039] Example 1: An acid-resistant membrane was prepared by interfacial polymerization of polyethyleneimine and cyanuric chloride on a polyethersulfone support layer, and a schematic diagram of the preparation process of the NF membrane using diethylenetriamine secondary IP is shown below. Figure 1 As shown.

[0040] Step a: Co-deposition of tannic acid (TA) and diethylenetriamine (DETA) for hydrophilic modification:

[0041] DETA (6 g / L) and TA (20 g / L) were dissolved in phosphate-buffered saline (PBS buffer). The polyethersulfone (PES) basement membrane was fixed to the frame with double-sided tape, the solution was poured onto the surface of the membrane, and the membrane was shaken at room temperature for 30 min. The membrane was then washed three times with deionized water and immersed in deionized water.

[0042] Step b: An NF film is formed on the surface of a TA-DETA modified PES substrate membrane by interfacial polymerization of polyethyleneimine (PEI) as an aqueous monomer and cyanuric chloride (CC) as an organic monomer.

[0043] The PEI aqueous solution (1.0 wt%) was prepared by dissolving 1 wt% PEI (Mw = 150000 Da), 1 wt% NaOH, and 0.05 wt% 4-dimethylpyridine in deionized water. NaOH, acting as an acid absorbent, neutralized the reaction byproduct hydrogen chloride, maintaining an alkaline environment, thereby accelerating the reaction, increasing the degree of cross-linking, and forming a denser separation layer to enhance the retention rate. 4-Dimethylpyridine, as a highly efficient nucleophilic catalyst, significantly increased the reaction rate by forming a highly active intermediate, promoting the formation of a thinner, smoother separation layer with fewer defects. A TA-DETA modified PES substrate membrane was placed between a glass plate and a frame, and the substrate membrane and frame were fixed with double-sided tape. The prepared PEI aqueous reaction solution was evenly spread on the surface of the PES substrate membrane for 6 min. Excess liquid was then poured off, and residual droplets were gently blotted dry with filter paper.

[0044] CC (0.15 w / v%) was uniformly dissolved in a hexane solution. The solution was poured onto the membrane surface and reacted for 3 minutes. Then, the residual liquid was removed, and the membrane was heated in a 70°C oven for 7 minutes to obtain an NF membrane.

[0045] Step c: Preparation of acid-resistant triazine ring polyamine nanofiltration membrane by gas-phase secondary interfacial polymerization of diethylenetriamine:

[0046] DETA was dropped into a glass box, and the NF membrane prepared in step b was placed inside the box, supported by a polyester (PET) sheet. The glass box was sealed with a lid to maintain a diethylenetriamine vapor density of 0.1 mmol / cm³. 3 The membrane was placed in an oven at 60°C for 15 minutes. After removal, the membrane was immersed in deionized water to remove any unreacted monomers, yielding an acid-resistant triazine ring polyamine nanofiltration membrane.

[0047] The full X-ray photoelectron spectrum of the NF film is shown below. Figure 2 As shown; the fine C-element X-ray photoelectron spectroscopy spectrum of the NF film after gas-phase secondary interfacial polymerization is as follows. Figure 3 As shown in Figure a, the fine C element X-ray photoelectron spectroscopy spectrum of the NF film without undergoing the gas-phase secondary interfacial polymerization reaction is as follows: Figure 3 As shown in b; the fine N element X-ray photoelectron spectroscopy spectrum of the NF film after gas-phase secondary interfacial polymerization is as follows. Figure 4 As shown in Figure a, the fine X-ray photoelectron spectroscopy (XPS) spectrum of nitrogen element in the NF film without undergoing the gas-phase secondary interfacial polymerization reaction is as follows: Figure 4 As shown in b; the surface morphology of the PES basement membrane as shown in the scanning electron microscope image. Figure 5 As shown in Figure a, the surface morphology of the TA-DETA co-deposited hydrophilic modified basement membrane is obtained using a scanning electron microscope. Figure 5 As shown in b, the surface morphology of the NF film polymerized at the polyethyleneimine-cyanuric chloride interface is obtained using a scanning electron microscope. Figure 5 As shown in c, the surface morphology of the NF film from the secondary interfacial polymerization of diethylenetriamine is obtained by scanning electron microscopy. Figure 5 As shown in d; the cross-sectional morphology of the PES basement membrane as shown in the scanning electron microscope image. Figure 6 As shown in Figure a, the scanning electron microscope cross-sectional morphology of the TA-DETA co-deposited hydrophilic modified basement membrane is as follows. Figure 6 As shown in b, the scanning electron microscope cross-sectional morphology of the NF film produced by the interfacial polymerization of polyethyleneimine and cyanuric chloride is as follows. Figure 6 As shown in c, the cross-sectional morphology of the NF film from the secondary interfacial polymerization of diethylenetriamine is obtained by scanning electron microscopy. Figure 6 As shown in d.

[0048] Following the steps in Example 1, three groups of nanofiltration membranes were prepared in parallel, and their separation performance was evaluated. The results are shown in Table 1.

[0049]

[0050] NF membrane acid test: Following the steps in Example 1, three sets of nanofiltration membranes were prepared in parallel and subjected to acid test. The acid test conditions were immersion in 2M sulfuric acid for 7 days. The pure water flux and salt rejection rate of the NF membranes are compared in Table 2.

[0051]

[0052] The results showed that, compared with the polyamide NF membrane soaked in sulfuric acid for 1.5 h, the salt rejection rate decreased by 70.8%. Under static acid immersion conditions, the salt rejection rate of the NF membrane without gas-phase secondary interfacial polymerization decreased by about 4%, while the salt rejection rate of the NF membrane with gas-phase secondary interfacial polymerization decreased by less than 1%. This proves that the NF membrane of the present invention is more acid-resistant than the conventional polyamide NF membrane, and is more acid-resistant than the NF membrane without gas-phase secondary interfacial polymerization.

[0053] Example 2: An acid-resistant film was prepared by interfacial polymerization of polyethyleneimine and cyanuric chloride on a polyethersulfone support layer, and secondary IP was utilized using diethylenetriamine.

[0054] Step a: Co-deposition of tannic acid (TA) and diethylenetriamine (DETA) for hydrophilic modification:

[0055] DETA (6 g / L) and TA (20 g / L) were dissolved in PBS buffer. The PES basement membrane was fixed to the frame with double-sided tape, the solution was poured onto the surface of the membrane, and the membrane was shaken at room temperature for 40 min. The membrane was then washed three times with deionized water and immersed in deionized water.

[0056] Step b: An NF film is formed on the surface of a TA-DETA modified PES substrate membrane by interfacial polymerization of polyethyleneimine (PEI) as an aqueous monomer and cyanuric chloride (CC) as an organic monomer.

[0057] The PEI aqueous solution (0.1 wt%) was prepared by dissolving 0.1 wt% PEI (Mw = 150000 Da), 1 wt% NaOH, and 0.005 wt% 4-dimethylpyridine in deionized water. A TA-DETA modified PES substrate membrane was placed between a glass plate and a frame, and the substrate membrane and frame were fixed with double-sided tape. The prepared PEI aqueous reaction solution was evenly spread on the surface of the PES substrate membrane for 6 min. Excess liquid was then poured off, and residual droplets were gently blotted dry with filter paper.

[0058] CC (0.1 w / v%) was uniformly dissolved in a hexane solution. The solution was poured onto the membrane surface and reacted for 3 minutes. Then, the residual liquid was removed, and the membrane was heated in a 70°C oven for 7 minutes to obtain an NF membrane.

[0059] Step c: Preparation of acid-resistant triazine ring polyamine nanofiltration membrane by gas-phase secondary interfacial polymerization of diethylenetriamine:

[0060] DETA was dropped into a glass box, the NF membrane prepared in step b was placed in the box, and the membrane was supported by a PET sheet to fix the vapor density of diethylenetriamine at 0.1 mmol / cm³. 3 The glass box was sealed with a lid and placed in an oven at 60°C for 10 minutes. The membrane was then removed and immersed in deionized water to remove any unreacted monomers, yielding an acid-resistant triazine ring polyamine nanofiltration membrane.

[0061] Example 3: An acid-resistant film was prepared by interfacial polymerization of polyethyleneimine and cyanuric chloride on a polyethersulfone support layer, and secondary IP was performed using diethylenetriamine.

[0062] Step a: Co-deposition of tannic acid (TA) and diethylenetriamine (DETA) for hydrophilic modification:

[0063] DETA (6 g / L) and TA (20 g / L) were dissolved in PBS buffer. The PES basement membrane was fixed to the frame with double-sided tape, the solution was poured onto the surface of the membrane, and the membrane was shaken at room temperature for 10 min. The membrane was then washed three times with deionized water and immersed in deionized water.

[0064] Step b: An NF film is formed on the surface of a TA-DETA modified PES substrate membrane by interfacial polymerization of polyethyleneimine (PEI) as an aqueous monomer and cyanuric chloride (CC) as an organic monomer.

[0065] The PEI aqueous solution (0.75 wt%) was prepared by dissolving 0.75 wt% PEI (Mw = 150000 Da), 1 wt% NaOH, and 0.0375 wt% 4-dimethylpyridine in deionized water. A TA-DETA modified PES substrate membrane was placed between a glass plate and a frame, and the substrate membrane and frame were fixed with double-sided tape. The prepared PEI aqueous reaction solution was evenly spread on the surface of the PES substrate membrane for 6 min. Excess liquid was then discarded, and residual droplets were gently blotted dry with filter paper.

[0066] CC (0.15 w / v%) was uniformly dissolved in a hexane solution. The solution was poured onto the membrane surface and reacted for 3 minutes. Then, the residual liquid was removed, and the membrane was heated in a 70°C oven for 7 minutes to obtain an NF membrane.

[0067] Step c: Preparation of acid-resistant triazine ring polyamine nanofiltration membrane by gas-phase secondary interfacial polymerization of diethylenetriamine:

[0068] A certain amount of DETA was dropped into a glass box, and the NF membrane prepared in step b was placed inside the box, supported by a PET sheet. The glass box was sealed with a lid and placed in an oven at 50°C for 15 minutes to maintain a fixed vapor density of diethylenetriamine at 0.1 mmol / cm³. 3 After removing the membrane, immerse it in deionized water to remove any unreacted monomers.

[0069] Example 4: An acid-resistant film was prepared by interfacial polymerization of polyethyleneimine and cyanuric chloride on a polyethersulfone support layer, and secondary IP was performed using diethylenetriamine.

[0070] Step a: Co-deposition of tannic acid (TA) and diethylenetriamine (DETA) for hydrophilic modification:

[0071] DETA (6 g / L) and TA (20 g / L) were dissolved in PBS buffer. The PES basement membrane was fixed to the frame with double-sided tape, the solution was poured onto the surface of the membrane, and the membrane was shaken at room temperature for 40 min. The membrane was then washed three times with deionized water and immersed in deionized water.

[0072] Step b: An NF film is formed on the surface of a TA-DETA modified PES substrate membrane by interfacial polymerization of polyethyleneimine (PEI) as an aqueous monomer and cyanuric chloride (CC) as an organic monomer.

[0073] The PEI aqueous solution (10.0 wt%) was prepared by dissolving 10 wt% PEI (Mw = 150000 Da), 1 wt% NaOH, and 0.5 wt% 4-dimethylpyridine in deionized water. A TA-DETA modified PES substrate membrane was placed between a glass plate and a frame, and the substrate membrane and frame were fixed with double-sided tape. The prepared PEI aqueous reaction solution was evenly spread on the surface of the PES substrate membrane for 6 min. Excess liquid was then discarded, and residual droplets were gently blotted dry with filter paper.

[0074] CC (0.5 w / v%) was uniformly dissolved in a hexane solution. The solution was poured onto the membrane surface and reacted for 3 minutes. Then, the residual liquid was removed, and the membrane was heated in a 70°C oven for 7 minutes to obtain an NF membrane.

[0075] Step c: Preparation of acid-resistant triazine ring polyamine nanofiltration membrane by gas-phase secondary interfacial polymerization of diethylenetriamine:

[0076] DETA was dropped into a glass box, the NF membrane prepared in step b was placed in the box, and the membrane was supported by a PET sheet to fix the vapor density of diethylenetriamine at 0.1 mmol / cm³. 3 The glass box was sealed with a lid and placed in an oven at 90°C for 30 minutes. After removing the membrane, it was immersed in deionized water to remove any unreacted monomers, yielding an acid-resistant triazine ring polyamine nanofiltration membrane.

[0077] In step a, polysulfone, polyethersulfone, cellulose acetate, polypropylene, polyethylene, polyvinyl chloride, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, and polyamide ultrafiltration membranes are all commonly used alternative substrate membranes in the art. The polyethersulfone used in this application can be replaced with other substrate membranes. Hydrophilic modification methods such as dopamine (PDA), tannic acid (TA), diethylenetriamine (DETA), and polyvinylpyrrolidone (PVP) hydrogels are all commonly used hydrophilic modification methods in the art. The tannic acid (TA) / diethylenetriamine (DETA) used in this application can be replaced with other hydrophilic modification methods. In step b, the solvent for the organic phase reaction solution is selected from one of n-hexane, cyclohexane, heptane, and Isopar G, all of which are commonly used alternative organic solvents in the art. In step c, the polyamine used is diethylenetriamine, which can be replaced with any one of ethylenediamine, piperazine, diethylenetriamine, triethylenetetramine, tetraethylpentamine, or Tris(2-aminoethyl)amine.

[0078] This invention successfully constructs a composite nanofiltration membrane with a highly cross-linked, dense network by primary interfacial polymerization of polyamine polymers and cyanuric chloride on the surface of a main support, followed by secondary gas-phase interfacial polymerization using diethylenetriamine. This membrane exhibits significant comprehensive advantages in the separation of acidic leachate from wet lithium-ion battery recovery: its retention rate for typical divalent metal ions (such as cobalt, nickel, and manganese) remains consistently high at approximately 96%, and it maintains high structural and performance stability even after immersion in extremely acidic conditions (a sulfuric acid system with pH < 1) for 7 days, demonstrating long-term operational reliability not found in ordinary nanofiltration membranes. This characteristic makes the product of this invention particularly suitable for the efficient and stable recovery of valuable metals from strongly acidic leachate, effectively solving the core problem of easy chemical degradation of traditional membrane materials under harsh operating conditions.

[0079] The above embodiments are merely exemplary and do not constitute any limitation on the scope of the present invention. Those skilled in the art should understand that modifications or substitutions can be made to the details and form of the technical solutions of the present invention without departing from the spirit and scope thereof, but all such modifications and substitutions fall within the protection scope of the present invention.

Claims

1. A method for preparing an acid-resistant triazine ring polyamine nanofiltration membrane, characterized in that, Includes the following steps: Step a: The cleaned basement membrane is hydrophilically modified. The hydrophilic modification solution stays on the basement membrane for 10-40 minutes to obtain a hydrophilically modified basement membrane. Step b: Prepare aqueous and organic reaction solutions separately, perform interfacial polymerization, heat in a closed space, and prepare a nanofiltration membrane on the surface of the hydrophilic modified substrate membrane described in step a; the aqueous reaction solution uses a polyamine compound as the aqueous monomer, and the organic reaction solution uses a compound containing a triazine ring group as the oil monomer. Step c: Place the nanofiltration membrane described in step b into a closed container and perform secondary gas-phase interfacial polymerization using volatile polyamines. The reaction time is 10-30 minutes and the reaction temperature is 50-90℃.

2. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 1, characterized in that, In step a, the base membrane is selected from one of the following: polysulfone, polyethersulfone, cellulose acetate, polypropylene, polyethylene, polyvinyl chloride, polyacrylonitrile, polyvinylidene fluoride, and polytetrafluoroethylene.

3. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 1, characterized in that, In step a, the hydrophilic modification solution is selected from one or more of dopamine, tannic acid, diethylenetriamine, and polyvinylpyrrolidone hydrogel.

4. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 1, characterized in that, The aqueous reaction solution in step b specifically includes a polyamine compound, the acid absorbent NaOH, and the highly efficient nucleophilic catalyst 4-dimethylpyridine.

5. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 4, characterized in that, In step b, the polyamine compound is polyethyleneimine; the concentration of polyethyleneimine is 0.1~10 wt%.

6. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 1, characterized in that, The compound containing a triazine ring group in step b is cyanuric chloride with a concentration of 0.1~0.5 w / v%. The solvent of the organic phase reaction solution is selected from one of n-hexane, cyclohexane, heptane, and Isopar G.

7. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 1, characterized in that, In step b, the heating conditions are 70°C and the time is 7 minutes.

8. The method for preparing the acid-resistant triazine ring polyamine nanofiltration membrane according to claim 1, characterized in that, In step c, the polyamine is selected from one of ethylenediamine, piperazine, diethylenetriamine, triethylenetetramine, tetraethylpentamine, and Tris(2-aminoethyl)amine.

9. An acid-resistant triazine ring polyamine nanofiltration membrane prepared by the method of any one of claims 1-8.

10. The application of the acid-resistant triazine ring polyamine nanofiltration membrane of claim 9 in the recovery of valuable metals from batteries.

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