Recycling method of precious metal

Abstract

The invention relates to the technical field of precious metal recovery, in particular to a precious metal recovery method. Comprising the following steps: filtering wastewater containing precious metals by using a precious metal recovery composite membrane, and drying the precious metal recovery composite membrane after filtering; then filtering an acidic aqueous solution by using the dried precious metal recovery composite membrane, and then continuously filtering and cleaning by using clear water; the cleaned precious metal recovery composite membrane is put into an N, N-dimethylformamide soaking solution, then ultrasonic oscillation treatment is conducted, the composite membrane is taken out of the soaking solution, then centrifugal treatment is conducted on the soaking solution, precipitates are collected, and the precious metal particles are obtained. The precious metal is recovered by adopting a membrane filtration method, and compared with an impregnation method, a large amount of membrane cost is saved, so that the precious metal recovery cost is reduced, and the method is suitable for industrial metal recovery.

Description

Technical Field

[0001] The present invention relates to the technical field of precious metal recovery, and in particular to a precious metal recovery method. Background Art

[0002] Because of their unique physical and chemical properties, precious metals are widely used in aerospace, nuclear energy technology, medicine, catalysis, fuel cells, metallurgy, electronic devices and other fields. Because of their excellent electrical corrosion resistance and chemical inertness, precious metals are widely used in various control systems in the aerospace field and electrical contact parts in micromotors. Therefore, precious metal materials play an important role in the aerospace field. In the pharmaceutical production industry, precious metals are widely used in medical materials such as acupuncture materials, implantable devices in the body or drugs containing precious metals because of their corrosion resistance, good biocompatibility, non-toxicity and excellent ductility. At present, drugs containing precious metals such as gold, platinum and palladium are used in cancer treatment.

[0003] With the rapid development of industry, a large amount of industrial wastewater containing precious metals is discharged. Most of the precious metal resources in the wastewater can be recovered by using solvent extraction or chemical precipitation. However, the effluent treated by these methods still contains a small amount or even trace amounts of precious metal ions. If these waste liquids are still treated using the above-mentioned traditional processes, it will not only prolong the treatment process, but also increase the treatment cost. If they are discharged, it will cause serious waste of precious resources and environmental pollution.

[0004] Chinese patent publication number CN108503011 discloses a method for recovering precious metals in sewage based on amorphous tungsten oxide / polymer hybrid nanofiber membrane, wherein the amorphous tungsten oxide / polymer hybrid nanofiber membrane is immersed in precious metal wastewater, the precious metals in the sewage are reduced and adsorbed onto the amorphous tungsten oxide / polymer hybrid nanofiber membrane, and then the fiber membrane is dissolved to recover the precious metals, which solves the problem that the prior art cannot directly recover metals from sewage with ultra-low concentration (ppb level) of metal content. However, due to the large amount of industrial wastewater and the need for the hybrid nanofiber membrane to be in full contact with the wastewater, the impregnation method requires a large amount of amorphous tungsten oxide / polymer hybrid nanofiber membrane, and the investment cost is high, which is not suitable for large-scale industrial precious metal recovery. Summary of the invention

[0005] In order to overcome the above problems of the prior art, the present invention provides a method for recovering precious metals. The present invention uses a membrane filtration method to recover precious metals, which saves a lot of membrane costs compared to the impregnation method, thereby reducing the cost of precious metal recovery and is suitable for industrial metal recovery.

[0006] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0007] A method for recovering precious metals comprises the following steps:

[0008] 1) Filtering the wastewater containing precious metals using a precious metal recovery composite membrane, and drying the precious metal recovery composite membrane after filtration;

[0009] 2) using the dried precious metal recovery composite membrane to filter the acidic aqueous solution, and then using clean water to continue filtering and washing;

[0010] 3) The cleaned precious metal recovery composite membrane is placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate to obtain precious metal particles.

[0011] In the prior art, membranes are used to recover low-concentration precious metals in wastewater by membrane impregnation (see the background technology introduction, which will not be repeated here), but the problem is that the impregnation method consumes a large amount of membrane and has a high cost. In order to solve the above technical problems, the present invention adopts a membrane filtration method. During the continuous filtration process, the water body can fully contact the membrane body, and only a small amount of filtration membrane is needed to achieve the recovery of precious metals. Compared with the prior art, the recovery cost can be greatly reduced, and it is suitable for industrial precious metal recovery.

[0012] Preferably, in step 1), the operating pressure of the composite membrane during the filtration process is controlled at 0.3-5 MPa, and the temperature is controlled at 30-40°C.

[0013] Preferably, in step 2), the acidic aqueous solution is one or more of citric acid aqueous solution, nitric acid aqueous solution or sulfuric acid aqueous solution.

[0014] Preferably, in step 3), the ultrasonic oscillation time is 1-5h.

[0015] Preferably, the method for preparing the precious metal recovery composite membrane comprises the following steps:

[0016] 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve, to obtain an organic phase solution;

[0017] 12) adding polyethyleneimine into deionized water, stirring to dissolve, and obtaining an aqueous phase solution;

[0018] 13) soaking the polyethersulfone base membrane in an aqueous solution, taking out the polyethersulfone base membrane, and then immersing it in an organic solution for interfacial polymerization reaction, taking out the base membrane and performing heat curing treatment to obtain a nanofiltration membrane intermediate;

[0019] 14) adding tungsten hexachloride to the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, spinning the mixed solution into hybrid polyacrylonitrile fibers by electrostatic spinning, drying, performing ultraviolet treatment, and then cutting into hybrid polyacrylonitrile staple fibers;

[0020] 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby obtaining a carboxymethyl chitosan solution;

[0021] 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fibers are covered, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fibers adhere to the nanofiltration membrane intermediate, and the mixture is placed in an oven to dry.

[0022] As mentioned above, in the prior art, amorphous tungsten oxide / polymer hybrid nanofiber membrane is used to realize the recovery of precious metals by impregnating waste liquid, and the membrane cost is relatively high. If the amorphous tungsten oxide / polymer hybrid nanofiber membrane in the prior art is also used to recover precious metals by filtering, the recovery of precious metals cannot be achieved well, because the hybrid nanofiber membrane has a larger pore size structure, and the retention of precious metals in the waste liquid cannot be achieved. During the filtration process, the wastewater will quickly pass through the membrane body, and the precious metal ions will not have time to be reduced and deposited on the surface of the hybrid fiber membrane. In the technical solution of the present invention, the prepared precious metal recovery composite membrane includes a 4-layer structure, the bottom layer is a polyethersulfone base membrane, the polyethersulfone base membrane is covered with a precious metal ion interception layer, the precious metal ion interception layer is coated with a carboxymethyl chitosan layer bonding layer, and the carboxymethyl chitosan layer bonding layer is a hybrid polyacrylonitrile staple fiber layer. The bottom polyethersulfone base membrane plays a supporting and protective role for the membrane body during the filtration process, avoiding the membrane body from being broken and damaged during the filtration process. The noble metal ion retention layer is prepared by interfacial polymerization of polyethyleneimine and trimesoyl chloride. The pore size of the noble metal ion retention layer is nanometer-scale, and the surface is positively charged, which has a good retention effect on noble metal ions. During the filtration process, the noble metal ions in the water are blocked on the upper surface of the membrane, thereby achieving full contact between the noble metal ions and the membrane. The noble metal ions can be fully reduced and deposited on the hybrid polyacrylonitrile staple fibers, realizing full recovery of the noble metals. In the process of precious metal recovery, N,N-dimethylformamide is used to dissolve the polyacrylonitrile staple fibers, so that the precious metal particles deposited on the polyacrylonitrile staple fibers are dispersed in the solution, and finally the precious metals are obtained by centrifugal separation.

[0023] Preferably, the interfacial polymerization reaction time in step 13) is 5-10 min.

[0024] Preferably, in step 13), the heat curing treatment temperature is 60-70° C., and the heat curing treatment time is 30-60 min.

[0025] Preferably, in step 14), aminosilane coupling agent-modified nano-silica is also added to the mixed solution;

[0026] The preparation of the composite nanofiltration membrane also includes a post-treatment step, wherein the post-treatment method is to place the membrane body dried in step 16) in a glutaraldehyde solution for cross-linking treatment, and then take it out and dry it.

[0027] In the technical solution of the present invention, the hybrid polyacrylonitrile staple fiber is adhered to the noble metal ion interception layer by carboxymethyl chitosan. However, it is found during the filtration experiment that under the action of water pressure, the hybrid polyacrylonitrile staple fiber part will fall off from the carboxymethyl chitosan layer, thereby affecting the yield of the noble metal. In order to further solve this problem, the present invention modifies the nano-silica by doping the hybrid polyacrylonitrile staple fiber with an aminosilane coupling agent, so that the hybrid polyacrylonitrile staple fiber is negatively charged with amino groups, and the amino groups on the hybrid polyacrylonitrile staple fiber are cross-linked with the amino groups and hydroxyls on the carboxymethyl chitosan under the action of a glutaraldehyde cross-linking agent, thereby combining the hybrid polyacrylonitrile staple fiber with the carboxymethyl chitosan layer by chemical bonding, significantly improving the binding force between the two, thereby solving the problem of the hybrid polyacrylonitrile staple fiber falling off from the carboxymethyl chitosan layer, and improving the yield of the noble metal.

[0028] Preferably, the preparation method of aminosilane coupling agent modified nano-silica comprises the following steps: adding γ-aminopropyltriethoxysilane to a mixed solution of ethanol and water, stirring to form a hydrolyzate, adding nano-silica to the hydrolyzate, heating and stirring to react, centrifuging, washing and drying to obtain aminosilane coupling agent modified nano-silica.

[0029] Preferably, the concentration of the glutaraldehyde solution is 0.5-1.0 wt %.

[0030] The present invention has the following beneficial effects:

[0031] 1) The membrane filtration method only requires a small amount of filtration membrane to achieve the recycling of precious metals, which can greatly reduce the recycling cost compared with the existing technology and is suitable for industrial precious metal recycling;

[0032] 2) The precious metal ion interception layer in the precious metal recovery composite membrane has a good interception effect on precious metal ions. During the filtration process, the precious metal ions in the water body are blocked on the upper surface of the membrane body, thereby achieving full contact between the precious metal ions and the membrane body. The precious metal ions can be fully reduced and deposited on the hybrid polyacrylonitrile staple fibers, achieving full recovery of precious metals;

[0033] 3) The hybrid polyacrylonitrile staple fibers are bonded to the carboxymethyl chitosan layer by chemical bonding, which significantly improves the binding force between the two, improves the stability of the overall structure of the precious metal recovery composite membrane, and solves the problem of the hybrid polyacrylonitrile staple fibers falling off the membrane. DETAILED DESCRIPTION

[0034] The present invention is further described in detail below in conjunction 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 generally only embodiments of a part of the present invention, rather than all embodiments. Therefore, based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work should fall within the scope of protection of the present invention.

[0035] Unless otherwise specified, the raw materials used in the embodiments of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the embodiments of the present invention are all methods known to those skilled in the art. The precious metal wastewater used in the specific embodiments of the present invention is simulated wastewater, which is a 0.1 mol / L HAuCl4 solution.

[0036] Example 1

[0037] A method for recovering precious metals comprises the following steps:

[0038] 1) Install the precious metal recovery composite membrane in the filtration equipment, pour 100L of precious metal wastewater into the feed liquid tank of the filtration equipment, start the filtration equipment for membrane filtration, control the pressure at 4MPa and the temperature at 35°C during the filtration process, take out the precious metal recovery composite membrane from the filtration equipment after the filtration is completed, and place it in an oven at 60°C for drying for 2h;

[0039] 2) The dried precious metal recovery composite membrane is installed again in the filtration equipment, 20L of 0.5wt% citric acid aqueous solution is added to the feed tank, the filtration equipment is turned on for membrane filtration, and the pressure is controlled at 0.5MPa. After the liquid in the feed tank is filtered, 50L of clean water is added to continue filtering and washing until the filtration is completed;

[0040] 3) The precious metal recovery composite membrane is taken out from the filtering device, placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment at a power of 300 W for 4 hours. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate, which is then washed with water and dried to obtain precious metal particles.

[0041] The method for preparing the precious metal recovery composite membrane comprises the following steps:

[0042] 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve to prepare a trimesoyl chloride solution with a concentration of 0.5 wt %, to obtain an organic phase solution;

[0043] 12) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 1.5 wt %, to obtain an aqueous phase solution;

[0044] 13) soaking the polyethersulfone base membrane in the aqueous solution for 5 minutes, taking out the polyethersulfone base membrane, and then immersing it in the organic solution for interfacial polymerization for 8 minutes, taking out the base membrane and placing it in an oven at 65° C. for heat curing for 50 minutes to obtain a nanofiltration membrane intermediate;

[0045] 14) adding 2 g of polyacrylonitrile particles into 40 mL of N,N-dimethylformamide solvent and stirring to dissolve to obtain a polyacrylonitrile solution, adding 5 g of tungsten hexachloride and 0.5 g of aminosilane coupling agent-modified nano-silica into the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, and electrospinning the mixed solution into hybrid polyacrylonitrile fibers, wherein the electrospinning voltage is controlled at 15 kV, the temperature is 25 ° C, the electrode distance is 15 cm, and after drying, the mixture is irradiated with an ultraviolet lamp at a power of 100 W for 30 min, and then cut into hybrid polyacrylonitrile staple fibers;

[0046] 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby preparing a carboxymethyl chitosan solution with a concentration of 2 wt %;

[0047] 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fiber is covered, the mass of the hybrid polyacrylonitrile staple fiber used is 20% of the mass of the polyethersulfone base membrane, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fiber adhere to the nanofiltration membrane intermediate, and then the dried membrane is placed in a 0.8wt% glutaraldehyde aqueous solution, and cross-linked at 40°C for 2h. After taking out, it is placed in a drying oven and dried at 60°C for 3h.

[0048] The preparation method of aminosilane coupling agent modified nano-silica comprises the following steps:

[0049] 0.5 g of γ-aminopropyltriethoxysilane was added to a mixed solution of 40 mL of ethanol and 10 mL of water, and the mixture was stirred to form a hydrolyzate. 2 g of nano-silica was added to the hydrolyzate, and the mixture was heated to 50° C. and stirred for reaction for 3 h. After centrifugal separation, washing and drying, aminosilane coupling agent-modified nano-silica was obtained.

[0050] Example 2

[0051] A method for recovering precious metals comprises the following steps:

[0052] 1) Install the precious metal recovery composite membrane in the filtration equipment, pour 100L of precious metal wastewater into the feed liquid tank of the filtration equipment, start the filtration equipment for membrane filtration, control the pressure at 1MPa and the temperature at 35°C during the filtration process, take out the precious metal recovery composite membrane from the filtration equipment after the filtration is completed, and place it in an oven at 60°C for drying for 2h;

[0053] 2) The dried precious metal recovery composite membrane is installed again in the filtration equipment, 20L of 0.5wt% citric acid aqueous solution is added to the feed tank, the filtration equipment is turned on for membrane filtration, and the pressure is controlled at 0.5MPa. After the liquid in the feed tank is filtered, 50L of clean water is added to continue filtering and washing until the filtration is completed;

[0054] 3) The precious metal recovery composite membrane is taken out from the filtering device, placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment at a power of 300 W for 2 h. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate, which is then washed with water and dried to obtain precious metal particles.

[0055] The method for preparing the precious metal recovery composite membrane comprises the following steps:

[0056] 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve to prepare a trimesoyl chloride solution with a concentration of 0.5 wt %, to obtain an organic phase solution;

[0057] 12) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 1.5 wt %, to obtain an aqueous phase solution;

[0058] 13) soaking the polyethersulfone base membrane in the aqueous solution for 5 minutes, taking out the polyethersulfone base membrane, and then immersing it in the organic solution for interfacial polymerization for 6 minutes, taking out the base membrane and placing it in an oven at 65° C. for heat curing for 40 minutes to obtain a nanofiltration membrane intermediate;

[0059] 14) adding 2 g of polyacrylonitrile particles into 40 mL of N,N-dimethylformamide solvent and stirring to dissolve to obtain a polyacrylonitrile solution, adding 5 g of tungsten hexachloride and 0.5 g of aminosilane coupling agent-modified nano-silica into the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, and electrospinning the mixed solution into hybrid polyacrylonitrile fibers, wherein the electrospinning voltage is controlled at 15 kV, the temperature is 25 ° C, the electrode distance is 15 cm, and after drying, the mixture is irradiated with an ultraviolet lamp at a power of 100 W for 30 min, and then cut into hybrid polyacrylonitrile staple fibers;

[0060] 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby preparing a carboxymethyl chitosan solution with a concentration of 2 wt %;

[0061] 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fiber is covered, the mass of the hybrid polyacrylonitrile staple fiber used is 20% of the mass of the polyethersulfone base membrane, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fiber adhere to the nanofiltration membrane intermediate, and then the dried membrane is placed in a 0.6wt% glutaraldehyde aqueous solution, and cross-linked at 40°C for 2h. After taking out, it is placed in a drying oven and dried at 60°C for 3h.

[0062] The preparation method of aminosilane coupling agent modified nano-silica comprises the following steps:

[0063] 0.5 g of γ-aminopropyltriethoxysilane was added to a mixed solution of 40 mL of ethanol and 10 mL of water, and the mixture was stirred to form a hydrolyzate. 2 g of nano-silica was added to the hydrolyzate, and the mixture was heated to 50° C. and stirred for reaction for 3 h. After centrifugal separation, washing and drying, aminosilane coupling agent-modified nano-silica was obtained.

[0064] Example 3

[0065] A method for recovering precious metals comprises the following steps:

[0066] 1) Install the precious metal recovery composite membrane in the filtration equipment, pour 100L of precious metal wastewater into the feed liquid tank of the filtration equipment, start the filtration equipment for membrane filtration, control the pressure at 2MPa and the temperature at 35°C during the filtration process, take out the precious metal recovery composite membrane from the filtration equipment after the filtration is completed, and place it in an oven at 60°C for drying for 2h;

[0067] 2) The dried precious metal recovery composite membrane is installed again in the filtration equipment, 20L of 0.5wt% citric acid aqueous solution is added to the feed tank, the filtration equipment is turned on for membrane filtration, and the pressure is controlled at 0.5MPa. After the liquid in the feed tank is filtered, 50L of clean water is added to continue filtering and washing until the filtration is completed;

[0068] 3) The precious metal recovery composite membrane is taken out from the filtering device, placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment at a power of 300 W for 3 hours. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate, which is then washed with water and dried to obtain precious metal particles.

[0069] The method for preparing the precious metal recovery composite membrane comprises the following steps:

[0070] 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve to prepare a trimesoyl chloride solution with a concentration of 0.5 wt %, to obtain an organic phase solution;

[0071] 12) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 1.5 wt %, to obtain an aqueous phase solution;

[0072] 13) soaking the polyethersulfone base membrane in the aqueous solution for 5 minutes, taking out the polyethersulfone base membrane, and then immersing it in the organic solution for interfacial polymerization for 7 minutes, taking out the base membrane and placing it in an oven at 65° C. for heat curing for 45 minutes to obtain a nanofiltration membrane intermediate;

[0073] 14) adding 2 g of polyacrylonitrile particles into 40 mL of N,N-dimethylformamide solvent and stirring to dissolve to obtain a polyacrylonitrile solution, adding 5 g of tungsten hexachloride and 0.5 g of aminosilane coupling agent-modified nano-silica into the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, and electrospinning the mixed solution into hybrid polyacrylonitrile fibers, wherein the electrospinning voltage is controlled at 15 kV, the temperature is 25 ° C, the electrode distance is 15 cm, and after drying, the mixture is irradiated with an ultraviolet lamp at a power of 100 W for 30 min, and then cut into hybrid polyacrylonitrile staple fibers;

[0074] 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby preparing a carboxymethyl chitosan solution with a concentration of 2 wt %;

[0075] 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fiber is covered, the mass of the hybrid polyacrylonitrile staple fiber used is 20% of the mass of the polyethersulfone base membrane, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fiber adhere to the nanofiltration membrane intermediate, and then the dried membrane is placed in a 0.7wt% glutaraldehyde aqueous solution, and cross-linked at 40°C for 2h. After taking out, it is placed in a drying oven and dried at 60°C for 3h.

[0076] The preparation method of aminosilane coupling agent modified nano-silica comprises the following steps:

[0077] 0.5 g of γ-aminopropyltriethoxysilane was added to a mixed solution of 40 mL of ethanol and 10 mL of water, and the mixture was stirred to form a hydrolyzate. 2 g of nano-silica was added to the hydrolyzate, and the mixture was heated to 50° C. and stirred for reaction for 3 h. After centrifugal separation, washing and drying, aminosilane coupling agent-modified nano-silica was obtained.

[0078] Example 4

[0079] A method for recovering precious metals comprises the following steps:

[0080] 1) Install the precious metal recovery composite membrane in the filtration equipment, pour 100L of precious metal wastewater into the feed liquid tank of the filtration equipment, start the filtration equipment for membrane filtration, control the pressure at 5MPa and the temperature at 40°C during the filtration process, take out the precious metal recovery composite membrane from the filtration equipment after the filtration is completed, and place it in an oven at 60°C for drying for 2h;

[0081] 2) The dried precious metal recovery composite membrane is installed again in the filtration equipment, 20L of 0.5wt% citric acid aqueous solution is added to the feed tank, the filtration equipment is turned on for membrane filtration, and the pressure is controlled at 0.5MPa. After the liquid in the feed tank is filtered, 50L of clean water is added to continue filtering and washing until the filtration is completed;

[0082] 3) The precious metal recovery composite membrane is taken out from the filtering device, placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment at a power of 300 W for 5 hours. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate, which is then washed with water and dried to obtain precious metal particles.

[0083] The method for preparing the precious metal recovery composite membrane comprises the following steps:

[0084] 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve to prepare a trimesoyl chloride solution with a concentration of 0.5 wt %, to obtain an organic phase solution;

[0085] 12) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 1.5 wt %, to obtain an aqueous phase solution;

[0086] 13) soaking the polyethersulfone base membrane in the aqueous solution for 5 minutes, taking out the polyethersulfone base membrane, and then immersing it in the organic solution for interfacial polymerization for 10 minutes, taking out the base membrane and placing it in an oven for heat curing at 70° C. for 60 minutes to obtain a nanofiltration membrane intermediate;

[0087] 14) adding 2 g of polyacrylonitrile particles into 40 mL of N,N-dimethylformamide solvent and stirring to dissolve to obtain a polyacrylonitrile solution, adding 5 g of tungsten hexachloride and 0.5 g of aminosilane coupling agent-modified nano-silica into the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, and electrospinning the mixed solution into hybrid polyacrylonitrile fibers, wherein the electrospinning voltage is controlled at 15 kV, the temperature is 25 ° C, the electrode distance is 15 cm, and after drying, the mixture is irradiated with an ultraviolet lamp at a power of 100 W for 30 min, and then cut into hybrid polyacrylonitrile staple fibers;

[0088] 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby preparing a carboxymethyl chitosan solution with a concentration of 2 wt %;

[0089] 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fiber is covered, the mass of the hybrid polyacrylonitrile staple fiber used is 20% of the mass of the polyethersulfone base membrane, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fiber adhere to the nanofiltration membrane intermediate, and then the dried membrane is placed in a 1.0wt% glutaraldehyde aqueous solution, and cross-linked at 40°C for 2h. After taking out, it is placed in an oven and dried at 60°C for 3h.

[0090] The preparation method of aminosilane coupling agent modified nano-silica comprises the following steps:

[0091] 0.5 g of γ-aminopropyltriethoxysilane was added to a mixed solution of 40 mL of ethanol and 10 mL of water, and the mixture was stirred to form a hydrolyzate. 2 g of nano-silica was added to the hydrolyzate, and the mixture was heated to 50° C. and stirred for reaction for 3 h. After centrifugal separation, washing and drying, aminosilane coupling agent-modified nano-silica was obtained.

[0092] Example 5

[0093] A method for recovering precious metals comprises the following steps:

[0094] 1) Install the precious metal recovery composite membrane in the filtration equipment, pour 100L of precious metal wastewater into the feed liquid tank of the filtration equipment, turn on the filtration equipment for membrane filtration, control the pressure at 0.3MPa and the temperature at 30°C during the filtration process, take out the precious metal recovery composite membrane from the filtration equipment after the filtration is completed, and place it in an oven at 60°C for drying for 2h;

[0095] 2) The dried precious metal recovery composite membrane is installed again in the filtration equipment, 20L of 0.5wt% citric acid aqueous solution is added to the feed tank, the filtration equipment is turned on for membrane filtration, and the pressure is controlled at 0.5MPa. After the liquid in the feed tank is filtered, 50L of clean water is added to continue filtering and washing until the filtration is completed;

[0096] 3) The precious metal recovery composite membrane is taken out from the filtering device, placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment at a power of 300 W for 1 hour. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate, which is then washed with water and dried to obtain precious metal particles.

[0097] The method for preparing the precious metal recovery composite membrane comprises the following steps:

[0098] 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve to prepare a trimesoyl chloride solution with a concentration of 0.5 wt %, to obtain an organic phase solution;

[0099] 12) adding polyethyleneimine into deionized water, stirring and dissolving to prepare a polyethyleneimine solution with a concentration of 1.5 wt %, to obtain an aqueous phase solution;

[0100] 13) soaking the polyethersulfone base membrane in the aqueous solution for 5 minutes, taking out the polyethersulfone base membrane, and then immersing it in the organic solution for interfacial polymerization for 5 minutes, taking out the base membrane and placing it in an oven at 60° C. for heat curing for 30 minutes to obtain a nanofiltration membrane intermediate;

[0101] 14) adding 2 g of polyacrylonitrile particles into 40 mL of N,N-dimethylformamide solvent and stirring to dissolve to obtain a polyacrylonitrile solution, adding 5 g of tungsten hexachloride and 0.5 g of aminosilane coupling agent-modified nano-silica into the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, and electrospinning the mixed solution into hybrid polyacrylonitrile fibers, wherein the electrospinning voltage is controlled at 15 kV, the temperature is 25 ° C, the electrode distance is 15 cm, and after drying, the mixture is irradiated with an ultraviolet lamp at a power of 100 W for 30 min, and then cut into hybrid polyacrylonitrile staple fibers;

[0102] 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby preparing a carboxymethyl chitosan solution with a concentration of 2 wt %;

[0103] 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fiber is covered, the mass of the hybrid polyacrylonitrile staple fiber used is 20% of the mass of the polyethersulfone base membrane, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fiber adhere to the nanofiltration membrane intermediate, and then the dried membrane is placed in a 0.5wt% glutaraldehyde aqueous solution, and cross-linked at 40°C for 2h. After taking out, it is placed in a drying oven and dried at 60°C for 3h.

[0104] The preparation method of aminosilane coupling agent modified nano-silica comprises the following steps:

[0105] 0.5 g of γ-aminopropyltriethoxysilane was added to a mixed solution of 40 mL of ethanol and 10 mL of water, and the mixture was stirred to form a hydrolyzate. 2 g of nano-silica was added to the hydrolyzate, and the mixture was heated to 50° C. and stirred for reaction for 3 h. After centrifugal separation, washing and drying, aminosilane coupling agent-modified nano-silica was obtained.

[0106] Comparative Example 1

[0107] The difference between Comparative Example 1 and Example 1 is that:

[0108] The precious metal recovery composite membrane is replaced by the amorphous tungsten oxide / polymer hybrid nanofiber membrane prepared in publication number CN108503011.

[0109] The remaining steps are the same as those in Example 1.

[0110] Comparative Example 2

[0111] The difference between Comparative Example 2 and Example 1 is:

[0112] In the preparation process of the precious metal recovery composite membrane, steps 11), 12) and 13) are omitted.

[0113] At the same time, the nanofiltration membrane intermediate appearing in step 16) is replaced with a polyethersulfone-based membrane,

[0114] The remaining steps are the same as those in Example 1.

[0115] Comparative Example 3

[0116] The difference between Comparative Example 3 and Example 1 is that:

[0117] In the preparation process of the precious metal recovery composite membrane, in step 14), the aminosilane coupling agent-modified nano-silica is not added to the mixed solution.

[0118] The remaining steps are the same as those in Example 1.

[0119] Comparative Example 4

[0120] The difference between Comparative Example 4 and Example 1 is that:

[0121] During the preparation of the precious metal recovery composite membrane, the membrane body in step 16) is not subjected to glutaraldehyde cross-linking treatment, and the remaining operation steps are the same as those in Example 1.

[0122] Precious Metal Recovery Test

[0123] HAuCl4 solution was used to simulate precious metal wastewater, the concentration of HAuCl4 solution was 50 mg / L, the volume was 100 L, and the gold content in the wastewater was calculated to be 2.90 g. Gold was recovered from precious metal wastewater by the methods in the examples and comparative examples, and the precious metal particles finally obtained were weighed and the data were recorded, as shown in Table 1:

[0124] Table 1:

[0125] Example 1 Example 2 Example 3 Example 4 Example 5 Mass(g) 2.78 2.73 2.76 2.81 2.70 Yield (%) 95.9 94.1 95.2 96.9 93.1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 Mass(g) 1.53 1.76 2.38 2.45 Yield (%) 52.8 60.7 82.1 84.5

[0126] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for recovering precious metals, characterized in that: The following steps are involved: 1) Filtering the wastewater containing precious metals using a precious metal recovery composite membrane, and drying the precious metal recovery composite membrane after filtration; 2) using the dried precious metal recovery composite membrane to filter the acidic aqueous solution, and then using clean water to continue filtering and washing; 3) The cleaned precious metal recovery composite membrane is placed in an N,N-dimethylformamide soaking solution, and then subjected to ultrasonic oscillation treatment. The composite membrane is taken out from the soaking solution, and then the soaking solution is centrifuged to collect the precipitate to obtain precious metal particles.

2. A method for recovering precious metals according to claim 1, characterized in that: In the step 1), the operating pressure of the composite membrane during the filtration process is controlled at 0.3-5 MPa, and the temperature is controlled at 30-40°C.

3. A method for recovering precious metals according to claim 1, characterized in that: In the step 2), the acidic aqueous solution is one or more of a citric acid aqueous solution, a nitric acid aqueous solution or a sulfuric acid aqueous solution.

4. A method for recovering precious metals according to claim 1, characterized in that: In the step 3), the ultrasonic oscillation time is 1-5h.

5. A method for recovering precious metals according to claim 1, characterized in that: The method for preparing the precious metal recovery composite membrane comprises the following steps: 11) adding trimesoyl chloride into n-hexane solvent, heating and stirring to dissolve, to obtain an organic phase solution; 12) adding polyethyleneimine into deionized water, stirring and dissolving to obtain an aqueous phase solution; 13) soaking the polyethersulfone base membrane in an aqueous solution, taking out the polyethersulfone base membrane, and then immersing it in an organic solution for interfacial polymerization reaction, taking out the base membrane and performing heat curing treatment to obtain a nanofiltration membrane intermediate; 14) adding tungsten hexachloride to the polyacrylonitrile solution, stirring evenly to obtain a mixed solution, spinning the mixed solution into hybrid polyacrylonitrile fibers by electrostatic spinning, drying, performing ultraviolet treatment, and then cutting into hybrid polyacrylonitrile staple fibers; 15) adding the carboxymethyl chitosan solution into deionized water and stirring to dissolve, thereby obtaining a carboxymethyl chitosan solution; 16) The carboxymethyl chitosan solution is evenly coated on the upper surface of the nanofiltration membrane intermediate, and then the hybrid polyacrylonitrile staple fibers are covered, and a flat plate is used to apply downward pressure to make the hybrid polyacrylonitrile staple fibers adhere to the nanofiltration membrane intermediate, and the mixture is placed in an oven to dry.

6. A method for recovering precious metals according to claim 5, characterized in that: The interfacial polymerization reaction time in step 13) is 5-10 min.

7. A method for recovering precious metals according to claim 5, characterized in that: In the step 13), the heat curing treatment temperature is 60-70° C., and the heat curing treatment time is 30-60 min.

8. A method for recovering precious metals according to claim 5, characterized in that: In the step 14), aminosilane coupling agent-modified nano-silica is also added to the mixed solution; The preparation of the composite nanofiltration membrane also includes a post-treatment step, wherein the post-treatment method is to place the membrane body dried in step 16) in a glutaraldehyde solution for cross-linking treatment, and then take it out and dry it.

9. A method for recovering precious metals according to claim 8, characterized in that: The preparation method of the aminosilane coupling agent modified nano-silica comprises the following steps: Adding gamma-aminopropyltriethoxysilane to a mixed solution of ethanol and water, stirring to form a hydrolyzate, adding nano-silica to the hydrolyzate, heating and stirring to react, centrifugally separating, washing and drying to obtain aminosilane coupling agent modified nano-silica.

10. A method for recovering precious metals according to claim 8, characterized in that: The concentration of the glutaraldehyde solution is 0.5-1.0 wt %.