A polydopamine / polyimide dioxime composite membrane for gold recovery and a preparation method thereof

Abstract

The application discloses a kind of polydopamine / polyimide dioxime composite membranes for gold recovery and preparation method thereof.The method comprises the following steps: preparing polyimide dioxime solution;Polyimide dioxime solution is added to N,N-dimethylformamide solution to obtain a mixture, then trimethylolammonium solution is added to the mixture, and dopamine is added to the above obtained mixture, and the polydopamine / polyimide dioxime composite membrane can be obtained by standing in air for 24 h.The application also discloses the application of the composite membrane prepared by the method in the recovery of gold in electronic waste.The application obtains an independent self-supporting composite membrane by a simple interfacial polymerization method.The operation is simple, ecological and safe, and easy to mass production and industrial production.The composite membrane in the application can efficiently, quickly and selectively recover gold in electronic waste, improve the utilization rate of scarce resources, and provide a new idea for the design and preparation of subsequent related actual electronic waste adsorbent.

Description

Technical Field

[0001] This invention relates to the field of organic composite materials technology, and in particular to a polydopamine / polyimide dioxime composite membrane for gold recovery and its preparation method. Background Technology

[0002] Gold is a precious metal and an important resource with a wide range of uses. Besides its use in jewelry, gold is also widely used in electronics, medicine, and catalysis due to its excellent corrosion resistance, stability, electrical conductivity, and thermal conductivity. However, with the continuous upgrading of electronic product consumption, traditional gold mining methods can no longer meet market demands. Therefore, developing methods to recover gold from gold-containing waste such as electronic waste is crucial. It is reported that up to 300 tons of gold are used annually in integrated circuits and connectors. The gold content in mobile phone and computer circuit boards is approximately 300-350 gt. -1 and 200-250g t -1 Significantly higher than the typical gold deposit content (3-30 gt). -1 High-gold-content e-waste is a valuable "urban ore" that can be utilized as a secondary gold resource. However, direct processing of e-waste and inappropriate recycling activities have harmful impacts on human health and the environment. Furthermore, recovering gold from e-waste is more economically viable than mining gold directly from primary ore. Therefore, recovering gold from e-waste is of great significance from both economic and environmental perspectives.

[0003] Gold recovery from electronic waste typically requires dissolving it in acidic chlorides. Subsequently, various recovery methods, such as solvent extraction, chemical precipitation, ion exchange, redox reactions, and adsorption, are used to recover gold from electronic wastewater. Among these methods, adsorption is widely used due to its low cost, simplicity, and mild reaction conditions. However, traditional adsorbents such as zeolites or mesoporous silica often encounter limitations in practical adsorption processes, such as low adsorption capacity, lack of selectivity, or slow kinetics. In recent years, novel adsorbents such as metal-organic frameworks, covalent organic frameworks, porous aromatic frameworks, and porous organic polymers have attracted widespread attention due to their abundant active sites, large specific surface area, and suitable pore size distribution. However, these porous materials are usually in powder or granular form, making them difficult to collect and hindering their practical application. Membrane adsorption is a pressure-driven dynamic membrane adsorption process that combines the advantages of adsorption and membrane separation. Compared to traditional pressure-driven membranes that rely primarily on sieving for separation, adsorption membranes utilize more specialized membrane-solute interactions, such as electrostatic interactions, π-π interactions, van der Waals forces, and hydrogen bonding, to achieve high selectivity and rapid separation of target molecules. Furthermore, membrane adsorbents offer several advantages over powder-based adsorbents. First, during membrane adsorption, the solution is forced through the porous membrane, and molecules pass through the pores via convection. This eliminates the long diffusion time required for molecules or ions to reach the adsorption sites within the pores, thus effectively improving adsorption efficiency. Second, membrane adsorbents do not require filters for recovery, avoiding potentially high costs and the introduction of new contaminants into the treated water. Therefore, adsorption membranes have significant advantages in recovering gold from electronic waste. However, existing membrane adsorbents have small specific surface areas and limited adsorption sites, resulting in low adsorption efficiency. Therefore, it is essential to design a novel membrane adsorbent for recovering gold from electronic waste.

[0004] Considering the complexity of electronic wastewater environments and the coexistence of multiple metal ions, membrane adsorbents must possess excellent selectivity and affinity for target gold ions. From this perspective, based on Pearson's hard-soft acid-base principle, amylopectin-based adsorbents with multidentate nitrogen-containing ligands ("soft" Lewis bases) are considered highly suitable for coordination with "soft" Lewis acids (gold). Amylopectins are among the most effective structures for chelating multiple metal ions and can be prepared by reacting nitrile groups with hydroxylamine. Amylopectin-based adsorbents are diverse in form, such as resins, nanofibers, and microporous membranes, all possessing high specific surface areas, layered pore structures, and abundant active sites. However, existing processes for preparing amylopectin-based adsorbents are complex, and the relative hydrophobicity of the amylopectin groups limits their adsorption efficiency. Therefore, the research objective is to effectively utilize the abundant functional groups of amylopectins, improve their hydrophilicity, and achieve the preparation of composite membranes through simple experimental procedures. Summary of the Invention

[0005] To address the aforementioned problems and proposed feasible methods, this invention provides a polydopamine / polyimide dioxime composite membrane for gold recovery and its preparation method. This not only solves the cumbersome post-treatment issues of traditional adsorbents but also simplifies the preparation process, enabling large-scale production and use. The simplified method saves energy, is environmentally friendly, allows for mass industrial production, and achieves the goal of efficient, rapid, highly selective, and multi-cycle removal and recovery of gold from electronic waste.

[0006] This invention is achieved through the following technical solution: A polydopamine / polyimide dioxime composite membrane for gold recovery is prepared by the following steps: First, a polyimide dioxime solution is prepared; then, polyimide dioxime is prepared by the reaction of a nitrile and hydroxylamine. Subsequently, crosslinking of polydopamine and polyimide dioxime is achieved by interfacial polymerization under weakly alkaline conditions to obtain an independent polydopamine / polyimide dioxime membrane.

[0007] A method for preparing a polydopamine / polyimide dioxime composite membrane for gold recovery includes the following steps: (1) Hydroxylamine hydrochloride, sodium hydroxide and polyacrylonitrile were added to N,N-dimethylformamide solution in a mass ratio of (1~2):1:1 and then heated, stirred and centrifuged to prepare polyimide dioxime solution; (2) Add the polyimide dioxime solution obtained in step (1) to the N,N-dimethylformamide solution and stir thoroughly; (3) Add tris(hydroxymethyl)aminomethane solution to the mixture obtained in step (2); (4) Add dopamine to the mixture obtained in step (3), stir to dissolve, and let stand at room temperature for 24 h to obtain polydopamine / polyimide dioxime membrane.

[0008] Further, in step (1), the mass of hydroxylamine hydrochloride is 10-18 g, the mass of sodium hydroxide is 5-15 g, the mass of polyacrylonitrile is 5-15 g, the volume of N,N-dimethylformamide solution is 80-100 mL, and the concentration is 99.5%.

[0009] Further, in step (1), the heating temperature is 70~100 ℃, the stirring speed is 900~1100 rpm, and the stirring time is 10~14 h.

[0010] Furthermore, in step (1), the centrifugation step involves two centrifugation operations at a speed of 8000~10000 rpm for 3~8 min.

[0011] Further, in step (2), the volume ratio of the polyimide dioxime solution to the N,N-dimethylformamide solution is 1:(2-15).

[0012] Further, in step (2), the volume of the polyimide dioxime solution is 1~5 mL, the volume of the N,N-dimethylformamide solution is 10~15 mL, and the concentration is 99.5%.

[0013] Further, in step (3), the tris(hydroxymethyl)aminomethane solution is prepared by dissolving 1-2 g of tris(hydroxymethyl)aminomethane in 200-300 mL of water.

[0014] Further, in step (3), the volume ratio of the tris(hydroxymethyl)aminomethane solution to the mixture obtained in step (2) is 1:(2~3).

[0015] Further, in step (3), the volume of the tris(hydroxymethyl)aminomethane solution is 5-7 mL, and the volume of the mixture obtained in step (2) is 13-18 mL.

[0016] Furthermore, in step (4), the mass of the dopamine is 20-60 mg, and the volume of the mixture obtained in step (3) is 18 mL-25 mL.

[0017] This invention provides an application of a polydopamine / polyimide dioxime composite membrane prepared according to any of the preceding methods in the adsorption and recovery of gold from actual electronic waste.

[0018] Furthermore, the amount of the polydopamine / polyimide dioxime composite membrane used in water is 0.1~0.3 g / L.

[0019] Furthermore, the adsorption treatment time of the adsorbent containing the composite membrane in the water body is 22~26 h, and the pH of the water body is adjusted to 1.0~3.0.

[0020] Furthermore, the adsorption treatment time of the adsorbent containing the composite membrane in the electronic waste leachate solution is 22-26 h, and the pH of the electronic waste leachate solution is adjusted to 1.0-3.0.

[0021] The present invention also provides the application of polydopamine / polyimide dioxime composite membrane in the adsorption and recovery of gold and the recovery of gold from actual electronic waste, wherein the amount of polydopamine / polyimide dioxime composite membrane used in water is 0.2 g / L, the adsorption treatment time is 24 h, the pH value of the adsorption water is adjusted to 3, and the pH value of the electronic waste leachate is adjusted to 3.

[0022] As can be seen from the above technical solutions, the beneficial effects of the present invention are: (1) The polydopamine / polyimide dioxime composite membrane provided by this invention is obtained through a highly efficient, rapid, simple, and easily mass-producible room-temperature interfacial polymerization strategy. Polydopamine and polyimide dioxime crosslink at the air interface to form a polydopamine / polyimide dioxime composite membrane. Due to its hierarchical porous structure, abundant functional groups, large surface area, and sufficient active sites, this composite membrane can be used as an adsorbent for gold in electronic waste, achieving efficient, rapid, and selective adsorption and recovery of the scarce metal resource gold in waste. At the same time, the composite membrane has excellent environmental adaptability and can be used in a wide pH range. Furthermore, it can remove gold from electronic waste multiple times, exhibiting good cycle stability and excellent selectivity.

[0023] (2) The polydopamine / polyimide dioxime composite membrane prepared in this invention can achieve a saturated adsorption capacity of 3368 mg / g for gold; 0.6 g / L of adsorbent can reach equilibrium with 10 ppm of gold in 35 min; it can remove gold through multiple cycles, and the separation coefficient for gold in electronic waste is 3.96 × 10⁻⁶. 4 mL / g indicates extremely high selectivity for gold. Attached Figure Description

[0024] To more conveniently and clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 Scanning electron microscope images and physical photographs of the polydopamine / polyimide dioxime composite membrane prepared in this embodiment; Figure 2 Fourier transform infrared spectrum of the polydopamine / polyimide dioxime composite film prepared in this embodiment; Figure 3 This diagram illustrates the adsorption effect of the polydopamine / polyimide dioxime composite membrane prepared in this embodiment on gold, along with the fitting results. Figure 4 This diagram shows the adsorption kinetics of gold on the polydopamine / polyimide dioxime composite membrane prepared in this embodiment at different time points, along with the fitting results. Figure 5 This is a schematic diagram illustrating the adsorption effect of the polydopamine / polyimide dioxime composite membrane prepared in this embodiment on gold in a cyclic experiment.

[0026] Figure 6This is a schematic diagram illustrating the adsorption selectivity of the polydopamine / polyimide dioxime composite membrane prepared in this embodiment for gold in a real electronic waste CPU leaching adsorption experiment. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0028] The following provides a detailed description of the preparation method and performance of a polydopamine / polyimide dioxime composite membrane for gold recovery provided by the present invention. Contents not described in detail in the embodiments of the present invention are prior art known to those skilled in the art.

[0029] Example

[0030] A method for preparing a polydopamine / polyimide dioxime composite membrane includes: first, preparing a polyimide dioxime solution; adding the polyimide dioxime solution to an N,N-dimethylformamide solution to obtain a mixture; then adding a tris(hydroxymethyl)aminomethane solution to the mixture; finally, adding dopamine to the mixture; and allowing it to stand in air for 24 hours to obtain the polydopamine / polyimide dioxime composite membrane. The specific preparation method is as follows: (1) Add 14 g of hydroxylamine hydrochloride, 10 g of sodium hydroxide and 10 g of polyacrylonitrile to 100 mL of N,N-dimethylformamide solution and stir vigorously for 2 h. Then heat and continue stirring for 12 h. Finally, centrifuge to obtain polyimide dioxime solution.

[0031] (2) Add the above 3 mL polyimide dioxime solution to 10 mL N,N-dimethylformamide solution.

[0032] (3) Add 6 mL of tris(hydroxymethyl)aminomethane solution to the above mixture.

[0033] (4) Add 40 mg of dopamine to the above mixture, stir to dissolve, and let stand for 24 hours to obtain polydopamine / polyimide dioxime membrane.

[0034] Furthermore, a polydopamine / polyimide dioxime composite membrane was obtained according to the above preparation method.

[0035] Furthermore, this embodiment also provides a polydopamine / polyimide dioxime composite membrane as an adsorbent for direct adsorption of gold. The dosage of this adsorbent in water is 0.2 g / L, and the pH of the water is controlled at 3 during adsorption treatment, with the adsorption time controlled at 24 h. In practical applications, the adsorption performance of the adsorbent provided by this invention for gold in water can be tested using the following methods: Prepare a gold solution of a certain concentration, adjust the temperature and pH of the solution, add the adsorbent provided by this invention, stir continuously, and then determine the gold content using ICP to obtain the adsorption capacity of the adsorbent for gold; Prepare a 10 ppm gold solution, add the adsorbent provided by this invention when the pH and temperature of the mixed solution reach their optimal values, take a certain amount of liquid at regular intervals, and determine the gold content using ICP, which represents the adsorption effect of the polydopamine / polyimide dioxime composite membrane on gold at different adsorption times. The polydopamine / polyimide dioxime composite membrane for adsorbing gold was soaked in a mixed solution of 0.1 M hydrochloric acid and 0.1 M thiourea for 2 h and rinsed multiple times with deionized water to regenerate the adsorbent. A 10 ppm gold solution was prepared and added to the polydopamine / polyimide dioxime composite membrane prepared in this embodiment of the invention. After continuous stirring, the gold concentration was detected by ICP-OES to assess the cyclic performance of the adsorbent. In actual electronic waste adsorption and recycling experiments, excess material from the waste CPU was first removed, and after cleaning, it was leached with aqua regia for 24 h. The leachate was separated and recovered. The pH of the leachate was adjusted to 3.0 using KOH for adsorption experiments. The adsorption treatment time was controlled to 24 h, and the gold content was determined by ICP to obtain the adsorption and recycling performance of the adsorbent for gold in actual waste CPUs.

[0036] Results analysis: The microstructure, composition, and performance of the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention were observed, analyzed, and tested, and the following experimental results were obtained: (1) The polydopamine / polyimide dioxime composite film prepared in the embodiments of the present invention was observed and photographed using a scanning electron microscope (SU8020, Hitachi) and a camera, thereby obtaining the results shown in the attached figure. Figure 1 The image shown; among which, attached Figure 1 Image (a) is a photograph of the polydopamine / polyimide dioxime composite membrane prepared in this embodiment, demonstrating its independent self-supporting characteristics. (See attached image.) Figure 1 (b)-Appendix Figure 1 Image (c) is a scanning electron microscope image of the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention. It can be clearly seen that the obtained membrane has a layered porous structure. Figure 1Figure (c) shows the ultrathinness and uniformity of the polydopamine / polyimide dioxime composite membrane. In summary, this indicates that the polydopamine / polyimide dioxime composite membrane has a hierarchical multi-level porous structure.

[0037] (2) The polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention was analyzed by Fourier transform infrared spectroscopy (NEXUS, Thermo Nicolet) to obtain the compositional results as shown in the attached figure. Figure 2 The Fourier transform infrared spectrum shown is from the attached image. Figure 2 It can be seen that the polydopamine / polyimide dioxime composite membrane exhibits a characteristic peak of polydopamine (1505 cm⁻¹). -1 ) and the characteristic peak of polyimide dioxime (1650 cm⁻¹) -1 and 940 cm -1 The infrared peak positions of the final product prepared in this embodiment of the invention correspond to the characteristic peaks of the functional groups of polydopamine and polyimide dioxime, indicating the successful crosslinking of polydopamine and polyimide dioxime.

[0038] (3) Using the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention as an adsorbent, an adsorption isotherm test for gold was conducted. Specifically: 20 mL of gold solutions with concentrations of 1 ppm, 5 ppm, 10 ppm, 20 ppm, 50 ppm, 100 ppm, 500 ppm, and 1000 ppm were prepared and the pH was adjusted to 3. Then, 4 mg of the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention was added to each solution as an adsorbent, and the mixture was stirred continuously at 25°C for 24 h. A portion of the solution was removed from the solution, and the solution was filtered through a 0.22 μm filter membrane. The filtrate was collected and labeled, and the gold concentration was measured to obtain the following results: Figure 3 The diagram shows the adsorption effect of the adsorbent on gold in water under different gold concentrations. Figure 3 It can be seen that the adsorption capacity of the polydopamine / polyimide dioxime composite membrane provided in this embodiment of the invention increases continuously with the increase of gold concentration when the gold concentration is low; however, after the initial gold concentration exceeds 500 ppm, the adsorption capacity changes very little with the increase of concentration, and finally reaches equilibrium. The Langmuir fitting results show that the gold adsorption process belongs to monolayer chemisorption. According to the Langmuir adsorption model, the maximum removal capacity of gold in water by the polydopamine / polyimide dioxime composite membrane provided in this embodiment of the invention can reach 3368 mg / g, which is higher than that of currently reported adsorbents.

[0039] (4) Using the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention as an adsorbent, an adsorption kinetics experiment on gold was conducted, and the gold content was detected by ICP to obtain the gold removal rate of the adsorbent. Specifically: 1 L of gold adsorption test solution with a concentration of 10 ppm was prepared; the pH of the adsorption test solution was adjusted to 3 with 0.01 M hydrochloric acid or potassium hydroxide; then 0.6 g of the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention was added to the gold adsorption test solution and the time was set; the mixture was continuously stirred at 25°C, and equal amounts of solution were taken from the solution at time points of 1 min, 3 min, 5 min, 7 min, 9 min, 13 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, and 50 min, respectively, and filtered through a 0.22 μm filter membrane. The filtrate was collected, labeled, and finally the gold concentration in the filtrate at different time points was detected by ICP to obtain the gold removal rate of the adsorbent. Figure 4 The diagram shows the adsorption effect of gold at different adsorption times; where, Figure 4 (a) is the adsorption kinetics curve of gold on the polydopamine / polyimide dioxime composite membrane prepared in the embodiment of the present invention; Figure 4 (b) is a schematic diagram fitted using a pseudo-second-order adsorption kinetic model. Figure 4 It can be seen that the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention has good adsorption performance for gold and high removal efficiency. Moreover, the adsorption of gold by the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention can reach adsorption equilibrium within 35 min, and shows high adsorption efficiency.

[0040] (5) Using the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention as an adsorbent, a cyclic adsorption test was conducted, and the gold content was detected by ICP to obtain the adsorption capacity and cyclic performance of the adsorbent for gold. Specifically: the polydopamine / polyimide dioxime composite membrane adsorbing gold was soaked in 0.1 M hydrochloric acid and 0.1 M thiourea solution for 2 hours and rinsed multiple times with deionized water. Then, 20 mL of a 10 ppm gold solution was prepared, and 4 mg of the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention was added. After 24 hours, the concentration of gold in the solution was measured to obtain the adsorption capacity and cyclic performance of the adsorbent for gold. Figure 5 The diagram shows the adsorption effect of the polydopamine / polyimide dioxime composite membrane on gold in water during a cyclic experiment. Figure 5 It can be seen that the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention still has good adsorption performance in multiple cycles of use.

[0041] (6) Using the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention as an adsorbent, an adsorption selectivity experiment for gold in actual electronic waste CPU leaching solution was conducted, and the gold content was detected by ICP to obtain the adsorption selectivity of the adsorbent for gold. Specifically: the CPU leaching solution was prepared into 30 mL of adsorption test solution. Before adsorption, a portion of the solution was removed from the solution, and then the solution was filtered through a 0.22 μm filter membrane. The filtrate was collected, labeled, and finally the concentration of different metal ions in the filtrate was tested by ICP. In the adsorption experiment, the pH of the adsorption test solution was adjusted to 3 with 0.01 M potassium hydroxide. 0.01 g of the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention was added to the adsorption test solution. After adsorption for 24 h, a portion of the solution was removed from the solution, and then the solution was filtered through a 0.22 μm filter membrane. The filtrate was collected, labeled, and finally the concentration of different metal ions in the filtrate was detected by ICP to obtain the adsorption selectivity of the adsorbent for gold. Figure 6 The diagram illustrates the competitive adsorption effect; the adsorbent achieves a gold removal rate of 99%, significantly higher than that for other metals in the CPU. The calculated separation coefficient for gold is 3.96 × 10⁻⁶. 4 The concentration of gold in the polydopamine / polyimide dioxime composite membrane is 4 to 5 orders of magnitude higher than that of other metal elements, indicating that the polydopamine / polyimide dioxime composite membrane prepared in the embodiments of the present invention can selectively adsorb gold in actual waste CPUs, and has important economic value and practicality.

[0042] In summary, this invention presents a simple and rapid strategy for the large-scale preparation of a novel polydopamine / polyimide dioxime composite membrane with a hierarchical porous structure for gold recovery. This composite membrane can effectively, spontaneously, rapidly, and selectively recover precious metals, particularly gold, at room temperature. Abundant active sites result in a high saturation adsorption capacity for gold. The composite membrane is inexpensive to produce and easily scalable, enabling efficient, highly selective, and rapid removal of gold from electronic waste.

[0043] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. The application of a polydopamine / polyimide dioxime composite membrane in the adsorption and recovery of gold from electronic waste, characterized in that, The polydopamine / polyimide dioxime composite membrane is prepared by the following steps: hydroxylamine hydrochloride, sodium hydroxide, and polyacrylonitrile are added to an N,N-dimethylformamide solution to prepare a polyimide dioxime solution; the prepared polyimide dioxime solution is added to the N,N-dimethylformamide solution and stirred thoroughly; a tris(hydroxymethyl)aminomethane solution is added to the prepared mixture; dopamine is added to the prepared mixture, stirred to dissolve, and then allowed to stand at room temperature to obtain the polydopamine / polyimide dioxime membrane.

2. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 1 in the adsorption and recovery of gold from electronic waste, characterized in that: The dosage of the polydopamine / polyimide dioxime composite membrane in water is 0.1~0.3 g / L; the adsorption treatment time of the adsorbent containing the composite membrane in the electronic waste leachate solution is 22~26 h, and the pH of the electronic waste leachate solution is adjusted to 1.0~3.

0.

3. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 1 in the adsorption and recovery of gold from electronic waste, characterized in that, The preparation method of the polydopamine / polyimide dioxime composite membrane includes the following steps: (1) A polyimide dioxime solution was prepared by adding hydroxylamine hydrochloride, sodium hydroxide and polyacrylonitrile to an N,N-dimethylformamide solution and heating, stirring and centrifuging; wherein the mass ratio of hydroxylamine hydrochloride, sodium hydroxide and polyacrylonitrile was (1~2):1:1; (2) Add the polyimide dioxime solution obtained in step (1) to the N,N-dimethylformamide solution and stir thoroughly, wherein the volume ratio of the polyimide dioxime solution to the N,N-dimethylformamide solution is 1:(2-15); (3) Add tris(hydroxymethyl)aminomethane solution to the mixture obtained in step (2), wherein the volume ratio of the tris(hydroxymethyl)aminomethane solution to the mixture obtained in step (2) is 1:(2~3); (4) Add dopamine to the mixture obtained in step (3), stir to dissolve, and let stand at room temperature for 24 h to obtain polydopamine / polyimide dioxime membrane.

4. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 3 in the adsorption and recovery of gold from electronic waste, characterized in that: In step (1), the mass of hydroxylamine hydrochloride is 10-18 g, the mass of sodium hydroxide is 5-15 g, the mass of polyacrylonitrile is 5-15 g, and the volume of N,N-dimethylformamide solution is 80-100 mL with a concentration of 99.5%.

5. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 3 in the adsorption and recovery of gold from electronic waste, characterized in that: In step (1), the heating temperature is 70~100 ℃, the stirring speed is 900~1100 rpm, and the stirring time is 10~14 h; the centrifugation is performed twice, with a speed of 8000~10000 rpm and a time of 3~8 min.

6. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 3 in the adsorption and recovery of gold from electronic waste, characterized in that: In step (2), the volume of the polyimide dioxime solution is 1-5 mL; the volume of the N,N-dimethylformamide solution is 10-15 mL, and the concentration is 99.5%.

7. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 3 in the adsorption and recovery of gold from electronic waste, characterized in that: In step (3), the tris(hydroxymethyl)aminomethane solution is prepared by dissolving 1-2 g of tris(hydroxymethyl)aminomethane in 200-300 mL of water.

8. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 3 in the adsorption and recovery of gold from electronic waste, characterized in that: The volume of the mixture obtained in step (2) is 13~18 mL, and the volume of the tris(hydroxymethyl)aminomethane solution added in step (3) is 5~7 mL.

9. The application of the polydopamine / polyimide dioxime composite membrane as described in claim 3 in the adsorption and recovery of gold from electronic waste, characterized in that: In step (4), the mass of dopamine is 20-60 mg, and the volume of the mixture obtained in step (3) is 18 mL-25 mL.

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