A functional membrane for recovering precious metals from wastewater and a preparation method thereof

Abstract

The present invention relates to the technical field of wastewater resource treatment, and particularly relates to a functional membrane for recovering precious metals from wastewater and a preparation method thereof. The specific preparation method is to prepare a polyamide spinning solution, electrospin the spinning solution into a polyamide fiber network, then stably bind hollow mesoporous nano-silica to the fiber network through carboxymethyl chitosan, graft an epoxy group silane coupling agent on the surface of the hollow mesoporous nano-silica, and finally graft adipic dihydrazide on the hollow mesoporous nano-silica through a ring-opening reaction. The present invention uses organic polyamide as a film-forming substance, has low raw material costs, is suitable for large-scale industrial production, has a high recovery rate for precious metal ions, and the membrane itself has good mechanical strength and can operate stably for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater resource treatment, and particularly relates to a functional membrane for recovering precious metals from wastewater and a preparation method thereof. Background Art

[0002] With the rapid development of modern industry, precious metals have been widely used in many fields such as electronics, chemical industry, and medicine. However, during these industrial production processes, a large amount of wastewater containing precious metals is generated. If directly discharged, it will not only cause serious environmental pollution but also lead to a great waste of precious metal resources. Traditional wastewater treatment methods, such as chemical precipitation method, ion exchange method, etc., although they can remove precious metals from wastewater to a certain extent, have many limitations. The chemical precipitation method may produce a large amount of chemical sludge, with high subsequent treatment costs and easy to cause secondary pollution; the resin regeneration process of the ion exchange method is relatively complex, and the treatment effect on high-concentration wastewater is limited. In recent years, membrane technology has shown great application potential in the field of wastewater treatment due to its advantages of high efficiency, energy saving, and simple operation. The membrane recovery technology can achieve the efficient separation and recovery of precious metals from wastewater by selecting appropriate membrane materials and operating conditions, while reducing the impact on the environment, and has significant economic and environmental benefits.

[0003] Chinese Patent Publication No. CN117623445A discloses a functional membrane for recovering precious metal ions from oily wastewater and a preparation method thereof. The method includes the following steps: preparing carbon nanotubes modified with hydrazide functional groups CNTs-PAH; first, grafting acrylic acid onto the surface of carbon nanotubes by graft polymerization to obtain the first-step product CNTs-PAA, and then reacting adipic dihydrazide with carboxyl functional groups to obtain carbon nanotubes modified with hydrazide functional groups (CNTs-PAH); preparing monolayer MXene nanosheets; based on CNTs-PAH and MXene, preparing a CNTs-PAH / MXene composite membrane by vacuum filtration method. This technical solution uses carbon nanotubes and MXene nanosheets as film-forming substances, with relatively high raw material costs and is not suitable for industrial-scale production. Summary of the Invention

[0004] In order to overcome the above prior art problems, the present invention provides a functional membrane for recovering precious metals from wastewater and a preparation method thereof. The present invention uses organic polyamide as the film-forming substance, with low raw material costs, suitable for large-scale industrial production, having a high recovery rate for precious metal ions, and the membrane body itself having good mechanical strength and being able to operate stably for a long time.

[0005] In order to achieve the above invention purposes, the present invention adopts the following technical solutions:

[0006] A preparation method of a functional membrane for recovering precious metals from wastewater, comprising the following steps:

[0007] 1) Prepare a spinning solution by adding polyamide into a solvent, and electrospin the spinning solution into a polyamide fiber web for standby;

[0008] 2) Prepare a carboxymethyl chitosan solution by adding carboxymethyl chitosan into a solvent, add hollow mesoporous nano-silica into the carboxymethyl chitosan solution, and disperse evenly to obtain a mixed solution;

[0009] 3) Immerse the polyamide fiber web into the above mixed solution, add a crosslinking agent, and carry out a crosslinking reaction to obtain a polyamide fiber membrane;

[0010] 4) Add an epoxy group silane coupling agent into a solvent, stir and hydrolyze to obtain a hydrolysis solution, immerse the polyamide fiber membrane into the hydrolysis solution, and heat and react to obtain an epoxy group silane coupling agent grafted and modified polyamide fiber membrane;

[0011] 5) Prepare an adipic dihydrazide solution by adding adipic dihydrazide into a solvent, immerse the epoxy group silane coupling agent grafted and modified polyamide fiber membrane into the adipic dihydrazide solution, heat and react, take it out and carry out a drying treatment to obtain the product.

[0012] The functional membrane for recovering precious metals in wastewater of the present invention uses polyamide as the film-forming substance, which has the advantage of low price compared with the film-forming substances in the prior art and can be applied to large-scale industrial production. The functional membrane of the present invention uses polyamide as the film-forming substance, forms a polyamide fiber web through an electrospinning process, and constructs a stable and high specific surface area membrane infrastructure. Crosslinking with carboxymethyl chitosan on the polyamide fiber web firmly binds the hollow mesoporous nano-silica to the surface of the fiber web, providing a good platform for subsequent functional modification. Through the dehydration reaction between the epoxy group silane coupling agent and the hydroxyl groups on the surface of the hollow mesoporous nano-silica, the epoxy group silane coupling agent is successfully grafted, enabling the hollow mesoporous nano-silica to carry epoxy functional groups. Then, by using the ring-opening reaction between the epoxy functional groups and the amino groups on adipic dihydrazide, adipic dihydrazide is grafted onto the surface of the nano-silica, forming an orderly and efficient functionalization construction process.

[0013] The functional groups on adipic dihydrazide have extremely strong complexing ability with noble metal ions in wastewater, and can specifically react with noble metal ions to achieve precise capture of noble metal ions. At the same time, hollow mesoporous nano-silica plays a dual role. On the one hand, as a carrier, it efficiently loads and grafts adipic dihydrazide, increasing the active sites for reaction with noble metal ions; on the other hand, its unique hollow mesoporous structure greatly enhances the adsorption ability of noble metals in wastewater and can adsorb a large amount of noble metal ions from wastewater. The synergistic effect of these two aspects enables the functional membrane of the present invention to exhibit extremely high recovery rate and recovery efficiency when recovering noble metal ions from wastewater, achieving deep purification and recycling of noble metals in wastewater, effectively reducing the cost of wastewater treatment, and improving the recycling rate of resources.

[0014] Preferably, in the step 1), the mass concentration of polyamide in the spinning solution is 15-20%.

[0015] Preferably, cetyltrimethylammonium bromide is further added to the spinning solution in the step 1).

[0016] In the technical solution of the present invention, as described above, hollow nano-silica is fixed on the polyamide fiber web through a carboxymethyl chitosan cross-linking reaction. However, there is a further problem: it is difficult for carboxymethyl chitosan and hollow mesoporous nano-silica to bind well on the surface of the polyamide fiber web and undergo a cross-linking reaction. This problem affects the structural integrity and performance stability of the functional membrane, and limits its recovery effect on precious metals in wastewater. In view of the above problems, the present invention innovatively adds cetyltrimethylammonium bromide to the polyamide spinning solution. As a cationic surfactant, the molecules of cetyltrimethylammonium bromide carry positive charges. In contrast, both the surface of hollow mesoporous nano-silica and carboxymethyl chitosan carry negative charges. When cetyltrimethylammonium bromide is added to the polyamide spinning solution, during the subsequent preparation process, due to the action of electrostatic attraction, the positively charged cetyltrimethylammonium bromide can attract the negatively charged hollow mesoporous nano-silica and carboxymethyl chitosan. This electrostatic attraction acts like a bridge to tightly connect the hollow mesoporous nano-silica and carboxymethyl chitosan to the surface of the polyamide fiber web. Under the action of the cross-linking agent, carboxymethyl chitosan can undergo a self-cross-linking reaction more efficiently on the surface of the polyamide fiber web. At the same time, the hollow mesoporous nano-silica can also be more firmly fixed on the surface of the polyamide fiber web by means of this electrostatic attraction and cross-linking reaction, forming a more stable and tight structure. Compared with the original scheme, by introducing the action of electrostatic attraction, the hollow nano-silica is better combined on the polyamide fiber web, and at the same time, the binding stability of carboxymethyl chitosan and hollow mesoporous nano-silica on the surface of the polyamide fiber web is significantly improved. This enables the functional membrane to have a better recovery effect on precious metal ions during actual application, and can withstand greater water flow impact and chemical environment changes, and is not prone to the situation of functional material shedding, effectively extending the service life of the functional membrane.

[0017] In addition, the self-cross-linking reaction of carboxymethyl chitosan on the surface of the polyamide fiber web is promoted by the action of electrostatic attraction, making the cross-linking process more sufficient and uniform. This not only helps to improve the mechanical strength of the functional membrane, but also optimizes the microstructure of the membrane, making the distribution of adsorption and complexation sites for precious metal ions in the wastewater more reasonable, thereby enhancing the recovery ability and efficiency of precious metal ions. The stably bound and fully cross-linked hollow mesoporous nano-silica and carboxymethyl chitosan can better play their respective functional advantages, and the adsorption performance of hollow mesoporous nano-silica and the complexation performance brought by the subsequent reaction of carboxymethyl chitosan with adipic dihydrazide are fully guaranteed, so as to achieve a more efficient and accurate recovery of precious metal ions in wastewater, further enhancing the application value of the entire functional membrane in the field of wastewater treatment.

[0018] Preferably, the mass concentration of cetyltrimethylammonium bromide in the spinning solution is 3.0-5.0%.

[0019] In the technical solution of the present invention, precisely regulating the mass concentration of cetyltrimethylammonium bromide in the spinning solution brings significant and diverse technical effects. When the mass concentration of cetyltrimethylammonium bromide is lower than 3%, the charge amount of the polyimide fiber web is too low, making it difficult to build a strong electrostatic attraction with hollow monitoring nano-silica and carboxymethyl chitosan. The lower concentration limit set in the present invention ensures the effective combination of each component, ensuring that the electrostatic attraction in the system can be fully exerted, and making the composite effect of the functional material reach the best state. Therefore, the present invention controls the mass concentration of cetyltrimethylammonium bromide to be higher than 3%.

[0020] However, another problem encountered by the R & D team of the present invention during the research and development process is that the hydrostatic pressure resistance of a part of the prepared functional membranes has dropped significantly. After research by the R & D team of the present invention, it is found that this problem is related to the mass concentration of cetyltrimethylammonium bromide. When the mass concentration of cetyltrimethylammonium bromide exceeds a certain amount, the distribution of cetyltrimethylammonium bromide molecules in the polyamide fiber membrane is too dense. Its presence may interfere with the original intermolecular forces such as hydrogen bonds between polyamide molecular chains. The hydrogen bonds between polyamide molecular chains play an important role in maintaining the mechanical strength of the fiber membrane. Excessive cetyltrimethylammonium bromide molecules may weaken this hydrogen bond effect, resulting in a decrease in the binding force between molecular chains, thereby reducing the mechanical strength and further reducing its hydrostatic pressure resistance. Therefore, the present invention simultaneously controls the mass concentration of cetyltrimethylammonium bromide to be lower than 5% to maintain the hydrostatic pressure resistance of the polyamide membrane, ensuring that the prepared functional membrane maintains stable and reliable performance in the face of complex usage environments, extending the actual service life of the functional membrane, and enhancing the practicality and applicability of the product.

[0021] Preferably, in step 2), the mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica is 2:0.1 - 0.7.

[0022] Preferably, in step 3), the addition amount of the cross-linking agent is 0.5 - 2.0% of the mass of the mixed solution.

[0023] Preferably, in step 4), the epoxy group silane coupling agent is selected from one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

[0024] Preferably, in step 4), the heating reaction temperature is 50 - 60 °C, and the heating reaction time is 3 - 5 h. Preferably, in step 5), the heating reaction temperature is 80 - 90 °C, and the heating reaction time is 4 - 9 h. A functional membrane for recovering precious metals from wastewater is prepared by the method described above.

[0025] The present invention has the following beneficial effects:

[0026] 1) Polyamide with relatively low raw material cost is used as the film-forming substance, significantly reducing the production cost compared with using carbon nanotubes as the film-forming substance in the prior art, and is suitable for industrial production;

[0027] 2) The noble metal recovery functional membrane has a good complexing and recovery effect on noble metal ions, and the membrane body itself has stable structural properties and good mechanical properties.

[0028] Description of the drawings

[0029] Figure 1 It is an electron scanning microscope image of the surface of the functional membrane for recovering noble metals in wastewater prepared by the present invention. Detailed implementation manners

[0030] The following further clearly and detailedly describes the present invention in combination with specific embodiments. Those of ordinary skill in the art will be able to implement the present invention based on these descriptions. In addition, the embodiments of the present invention involved in the following description are usually only a part of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments obtained by those of ordinary skill in the art without creative efforts based on the embodiments of the present invention shall fall within the scope of protection of the present invention.

[0031] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available or raw materials that can be obtained by those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present invention are all methods mastered by those skilled in the art.

[0032] Example 1

[0033] A preparation method of a functional membrane for recovering noble metals in wastewater, comprising the following steps:

[0034] 1) Add polyamide 6 into formic acid (analytical pure) to prepare a spinning solution with a mass concentration of 19%, then add cetyltrimethylammonium bromide, and the mass concentration of cetyltrimethylammonium bromide in the spinning solution is 4.5%. Stir and mix evenly, and electrospin the spinning solution into a polyamide fiber network with an electrospinning voltage set at 20 kV; 2) Add carboxymethyl chitosan into its ionic water to prepare a carboxymethyl chitosan solution with a mass concentration of 1.5%, add hollow mesoporous nano-silica into the carboxymethyl chitosan solution, and the mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica is 2:0.6. Ultrasonically oscillate and disperse evenly to obtain a mixed solution;

[0035] 3) Immerse the polyamide fiber mesh in the above mixed solution at a bath ratio of 1:20, add glutaraldehyde, with the addition amount of glutaraldehyde being 1.5% of the mass of the mixed solution, heat to 50 °C, and carry out cross-linking reaction for 5 h to obtain a polyamide fiber membrane;

[0036] 4) Add γ-glycidoxypropyltrimethoxysilane to the solvent at a mass-to-volume ratio of 1 g / 30 mL. The solvent is a mixture of ethanol and water at a volume ratio of 10:1. Stir and hydrolyze to obtain a hydrolysis solution. Immerse the polyamide fiber membrane in the hydrolysis solution at a bath ratio of 1:20, and react at a temperature of 60 °C for 3 h to obtain an epoxy silane coupling agent graft-modified polyamide fiber membrane;

[0037] 5) Add adipic dihydrazide to deionized water, stir and dissolve to prepare an adipic dihydrazide solution with a mass concentration of 3%. Immerse the epoxy silane coupling agent graft-modified polyamide fiber membrane in the adipic dihydrazide solution at a bath ratio of 1:20, react at a temperature of 90 °C for 4 h, take it out and carry out drying treatment to obtain the product.

[0038] Example 2

[0039] A preparation method of a functional membrane for recovering precious metals from wastewater, comprising the following steps:

[0040] 1) Add polyamide 6 to formic acid (analytical pure) to prepare a spinning solution with a mass concentration of 16%, then add cetyltrimethylammonium bromide, with the mass concentration of cetyltrimethylammonium bromide in the spinning solution being 3.5%. Stir and mix evenly, and electrospin the spinning solution into a polyamide fiber mesh, with the electrospinning voltage set at 20 kV; 2) Add carboxymethyl chitosan to its ionized water to prepare a carboxymethyl chitosan solution with a mass concentration of 1.5%. Add hollow mesoporous nano-silica to the carboxymethyl chitosan solution, with the mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica being 2:0.2. Ultrasonically oscillate and disperse evenly to obtain a mixed solution;

[0041] 3) Immerse the polyamide fiber mesh in the above mixed solution at a bath ratio of 1:20, add glutaraldehyde, with the addition amount of glutaraldehyde being 0.8% of the mass of the mixed solution, heat to 50 °C, and carry out cross-linking reaction for 5 h to obtain a polyamide fiber membrane;

[0042] 4) Add γ-glycidoxypropyltrimethoxysilane to the solvent at a mass-to-volume ratio of 1 g / 30 mL. The solvent is a mixture of ethanol and water at a volume ratio of 10:1. Stir and hydrolyze to obtain a hydrolysis solution. Immerse the polyamide fiber membrane in the hydrolysis solution at a bath ratio of 1:20, and react at a temperature of 50 °C for 5 h to obtain an epoxy silane coupling agent graft-modified polyamide fiber membrane;

[0043] 5) Add adipic dihydrazide to deionized water, stir to dissolve, and prepare an adipic dihydrazide solution with a mass concentration of 3%. Immerse the epoxy group silane coupling agent graft-modified polyamide fiber membrane in the adipic dihydrazide solution according to a bath ratio of 1:20, react at 80 °C for 9 h, take it out and perform drying treatment to obtain it.

[0044] Example 3

[0045] A method for preparing a functional membrane for recovering precious metals from wastewater, comprising the following steps:

[0046] 1) Add polyamide 6 to formic acid (analytical pure) to prepare a spinning solution with a mass concentration of 17%, then add cetyltrimethylammonium bromide, and the mass concentration of cetyltrimethylammonium bromide in the spinning solution is 4.0%. Stir and mix evenly, and electrospin the spinning solution into a polyamide fiber web, with the electrospinning voltage set at 20 kV; 2) Add carboxymethyl chitosan to its ionized water to prepare a carboxymethyl chitosan solution with a mass concentration of 1.5%, add hollow mesoporous nano-silica to the carboxymethyl chitosan solution, and the mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica is 2:0.5. Ultrasonically oscillate and disperse evenly to obtain a mixed solution;

[0047] 3) Immerse the polyamide fiber web in the above mixed solution according to a bath ratio of 1:20, add glutaraldehyde, and the addition amount of glutaraldehyde is 1.0% of the mass of the mixed solution. Heat to 50 °C and carry out a crosslinking reaction for 5 h to obtain a polyamide fiber membrane;

[0048] 4) Add γ-glycidyl ether oxypropyltrimethoxysilane to a solvent according to a mass-volume ratio of 1 g / 30 mL. The solvent is a mixture of ethanol and water in a volume ratio of 10:1. Stir and hydrolyze to obtain a hydrolysis solution. Immerse the polyamide fiber membrane in the hydrolysis solution according to a bath ratio of 1:20, and react at 60 °C for 3 h to obtain an epoxy group silane coupling agent graft-modified polyamide fiber membrane;

[0049] 5) Add adipic dihydrazide to deionized water, stir to dissolve, and prepare an adipic dihydrazide solution with a mass concentration of 3%. Immerse the epoxy group silane coupling agent graft-modified polyamide fiber membrane in the adipic dihydrazide solution according to a bath ratio of 1:20, react at 90 °C for 4 h, take it out and perform drying treatment to obtain it.

[0050] Example 4

[0051] A method for preparing a functional membrane for recovering precious metals from wastewater, comprising the following steps:

[0052] 1) Polyamide 6 was added to formic acid (analytical pure) to prepare a spinning solution with a mass concentration of 20%, and then cetyltrimethylammonium bromide was added. The mass concentration of cetyltrimethylammonium bromide in the spinning solution was 5.0%. After stirring and mixing evenly, the spinning solution was electrospun into a polyamide fiber network, and the electrospinning voltage was set at 20 kV; 2) Carboxymethyl chitosan was added to its ionic water to prepare a carboxymethyl chitosan solution with a mass concentration of 1.5%. Hollow mesoporous nano-silica was added to the carboxymethyl chitosan solution. The mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica was 2:0.7. After ultrasonic oscillation and uniform dispersion, a mixed solution was obtained;

[0053] 3) The polyamide fiber network was immersed in the above mixed solution according to a bath ratio of 1:20, and glutaraldehyde was added. The addition amount of glutaraldehyde was 2.0% of the mass of the mixed solution. It was heated to 50 °C and crosslinked for 5 h to obtain a polyamide fiber membrane;

[0054] 4) γ-Glycidoxypropyltrimethoxysilane was added to the solvent according to a mass-volume ratio of 1 g / 30 mL. The solvent was a mixture of ethanol and water in a volume ratio of 10:1. After stirring and hydrolysis, a hydrolysis solution was obtained. The polyamide fiber membrane was immersed in the hydrolysis solution according to a bath ratio of 1:20 and reacted at a temperature of 50 °C for 5 h to obtain an epoxy silane coupling agent grafted and modified polyamide fiber membrane;

[0055] 5) Adipic dihydrazide was added to deionized water, stirred and dissolved to prepare an adipic dihydrazide solution with a mass concentration of 3%. The epoxy silane coupling agent grafted and modified polyamide fiber membrane was immersed in the adipic dihydrazide solution according to a bath ratio of 1:20 and reacted at a temperature of 80 °C for 9 h. After taking it out, it was dried to obtain the product.

[0056] Example 5

[0057] A method for preparing a functional membrane for recovering precious metals from wastewater, comprising the following steps:

[0058] 1) Polyamide 6 was added to formic acid (analytical pure) to prepare a spinning solution with a mass concentration of 15%, and then cetyltrimethylammonium bromide was added. The mass concentration of cetyltrimethylammonium bromide in the spinning solution was 3.0%. After stirring and mixing evenly, the spinning solution was electrospun into a polyamide fiber network, and the electrospinning voltage was set at 20 kV; 2) Carboxymethyl chitosan was added to its ionic water to prepare a carboxymethyl chitosan solution with a mass concentration of 1.5%. Hollow mesoporous nano-silica was added to the carboxymethyl chitosan solution. The mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica was 2:0.1. After ultrasonic oscillation and uniform dispersion, a mixed solution was obtained;

[0059] 3) Immerse the polyamide fiber mesh in the above mixed solution at a bath ratio of 1:20, add glutaraldehyde, with the addition amount of glutaraldehyde being 0.5% of the mass of the mixed solution, heat to 50 °C, and carry out a cross-linking reaction for 5 h to obtain a polyamide fiber membrane;

[0060] 4) Add γ-glycidoxypropyltrimethoxysilane to the solvent at a mass-volume ratio of 1 g / 30 mL. The solvent is a mixture of ethanol and water in a volume ratio of 10:1. Stir and hydrolyze to obtain a hydrolyzate. Immerse the polyamide fiber membrane in the hydrolyzate at a bath ratio of 1:20, and react at a temperature of 60 °C for 3 h to obtain a polyamide fiber membrane graft-modified with an epoxy group silane coupling agent;

[0061] 5) Add adipic dihydrazide to deionized water, stir and dissolve it to prepare an adipic dihydrazide solution with a mass concentration of 3%. Immerse the polyamide fiber membrane graft-modified with an epoxy group silane coupling agent in the adipic dihydrazide solution at a bath ratio of 1:20, react at a temperature of 90 °C for 4 h, take it out and carry out a drying treatment to obtain the product.

[0062] Comparative Example 1

[0063] The difference between Comparative Example 1 and Example 1 is that:

[0064] The hollow nano-silica is replaced with ordinary nano-silica;

[0065] The remaining operation steps are the same as those in Example 1.

[0066] Comparative Example 2

[0067] The difference between Comparative Example 2 and Example 1 is that:

[0068] In step 1), cetyltrimethylammonium bromide is not added to the spinning solution;

[0069] The remaining operation steps are the same as those in Example 1.

[0070] Comparative Example 3

[0071] The difference between Comparative Example 3 and Example 5 is that:

[0072] The mass concentration of cetyltrimethylammonium bromide in the spinning solution is 2.5%;

[0073] The remaining operation steps are the same as those in Example 5.

[0074] Comparative Example 4

[0075] The difference between Comparative Example 4 and Example 4 is that:

[0076] The mass concentration of cetyltrimethylammonium bromide in the spinning solution is 5.5%;

[0077] The remaining operation steps are the same as those in Example 4.

[0078] Comparative Example 5

[0079] The difference between Comparative Example 5 and Example 4 is that:

[0080] The mass concentration of cetyltrimethylammonium bromide in the spinning solution is 6.0%;

[0081] The remaining operation steps are the same as those in Example 4.

[0082] Performance Test

[0083] 1. Noble metal recovery rate test: Use HAuCl4 solution to simulate noble metal wastewater with a concentration of 60 mg / L. Install the noble metal recovery functional membrane into the membrane evaluation device with an effective membrane area of 12 cm 2 , at an operating pressure of 1 bar and a temperature of 25 °C, stably filter and operate for 1 h, collect the filtrate, and after centrifuging the filtrate, test the concentration of HAuCl4 in the filtrate. Calculate the recovery rate of noble metals through the following formula: R = (C0 - C1) / C0 × 100%;

[0084] Among them, C1 is the concentration of noble metal ions in the filtrate, and C0 is the concentration of noble metal ions in the original solution.

[0085] 2. Mechanical property test: Use a cutter to cut out 5 dumbbell-shaped specimens from the functional membrane. The working part length of the specimens is 25 mm and the width is 4 mm. Use a vernier caliper to measure the width and thickness at a total of three positions in the middle and on both sides of the working part of the specimen, and take the average value as the width and thickness data of the specimen. The measurement accuracy is accurate to 0.02 mm, and record the data. Place the cut specimens into a thermostatic and humidistatic chamber and place them for 48 h under the conditions of a temperature of 23 ± 2 °C and a relative humidity of 50 ± 5% RH to make the specimens reach the moisture absorption equilibrium state. According to the instrument operation manual, calibrate the universal material testing machine to ensure the measurement accuracy of the force sensor and displacement sensor. Set the tensile speed to 10 mm / min, select an appropriate load range to ensure that the force value at the time of specimen fracture is within the range of 20% - 80% of the range. Carefully clamp the specimen in the upper and lower fixtures of the universal material testing machine, ensure that the center line of the specimen coincides with the center line of the fixture, and avoid eccentric tension. The clamping force is moderate to prevent the specimen from slipping or being clamped off during the stretching process. Start the universal material testing machine and start stretching the specimen. Observe the stretching process of the specimen and record the maximum force value (F) at the time of specimen fracture in units of N. Each specimen is tested 3 times repeatedly, and take the average value as the fracture force of the specimen. Calculate the tensile strength of the membrane body according to the following formula: t = F / A0;

[0086] Among them, F is the maximum force value at the time of specimen fracture, and A0 = average value of the specimen width × average value of the specimen thickness.

[0087] Table 1:

[0088]

[0089] From the above test data, it can be obtained that the functional membrane prepared in the example has a high recovery rate for precious metal ions, and the recovery rate reaches more than 96%. However, the recovery rates of the functional membranes of Comparative Examples 1-3 for precious metal ions are significantly lower than those of the example.

[0090] The reason why the recovery rate of the functional membrane of Comparative Example 1 for precious metal ions is lower than that of the example is that ordinary nano-silica has no adsorption effect on precious metal ions, thus affecting the complexation of adipic dihydrazide with precious metal ions. The reason why the recovery rate of the functional membrane of Comparative Example 2 for precious metal ions is lower than that of the example is that cetyltrimethylammonium bromide is not added in Comparative Example 2, the membrane is not positively charged, and the gravitational effect on carboxymethyl cellulose and hollow mesoporous silica is lacking, resulting in relatively less hollow mesoporous silica bound to the polyamide fiber membrane, and further resulting in insufficient adipic dihydrazide loaded on the polyamide fiber membrane for complexation with precious metal ions.

[0091] The above is only the preferred embodiment of the present invention. It should be noted that the above preferred embodiment should not be regarded as a limitation of the present invention, and the protection scope of the present invention should be subject to the scope defined by the claims. For those of ordinary skill in the art of this technology, without departing from the spirit and scope of the present invention, several improvements and retouches can also be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A method for preparing a functional membrane for recovering precious metals in wastewater, characterized in that: The following steps are involved: 1) adding polyamide and hexadecyltrimethylammonium bromide into a solvent to prepare a spinning solution, wherein the mass concentration of hexadecyltrimethylammonium bromide in the spinning solution is 3.0-5.0%, and electrospinning the spinning solution into a polyamide fiber web for later use; 2) adding carboxymethyl chitosan into a solvent to prepare a carboxymethyl chitosan solution, adding the hollow mesoporous nano-silica into the carboxymethyl chitosan solution, dispersing the hollow mesoporous nano-silica uniformly, and obtaining a mixed solution; 3) immersing the polyamide fiber web in the mixed solution, adding a crosslinking agent, and performing a crosslinking reaction to obtain a polyamide fiber membrane; 4) adding an epoxy silane coupling agent to a solvent, stirring and hydrolyzing to obtain a hydrolyzate, immersing the polyamide fiber membrane in the hydrolyzate, heating and reacting, and obtaining an epoxy silane coupling agent grafted modified polyamide fiber membrane; 5) Add adipic acid dihydrazide to a solvent to prepare an adipic acid dihydrazide solution, immerse the epoxysilane coupling agent grafted modified polyamide fiber membrane in the adipic acid dihydrazide solution, heat to react, take out and dry to obtain the membrane.

2. The method for preparing a functional membrane for recovering precious metals in wastewater according to claim 1, characterized in that: In the step 1), the mass concentration of polyamide in the spinning solution is 15-20%.

3. The method for preparing a functional membrane for recovering precious metals in wastewater according to claim 1, characterized in that: In the step 2), the mass ratio of carboxymethyl chitosan to hollow mesoporous nano-silica is 2:0.1-0.

7.

4. The method for preparing a functional membrane for recovering precious metals in wastewater according to claim 1, characterized in that: In the step 3), the amount of cross-linking agent added is 0.5-2.0% of the mass of the mixed solution.

5. The method for preparing a functional membrane for recovering precious metals in wastewater according to claim 1, characterized in that: In the step 4), the epoxysilane coupling agent is selected from one or more of γ-glycidyloxypropyltrimethoxysilane, γ-glycidyloxypropyltriethoxysilane, and β-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.

6. The method for preparing a functional membrane for recovering precious metals in wastewater according to claim 1, characterized in that: In the step 4), the heating reaction temperature is 50-60° C. and the heating reaction time is 3-5 h.

7. The method for preparing a functional membrane for recovering precious metals in wastewater according to claim 1, characterized in that: In the step 5), the heating reaction temperature is 80-90° C. and the heating reaction time is 4-9 hours.

8. A functional membrane for recovering precious metals from wastewater, characterized in that: The method is prepared by the method described in any one of claims 1 to 7.

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