A method for recovering polymers from liquid phase reduction silver powder wastewater

Abstract

The present invention discloses a method for recovering polymers from liquid-phase reduced silver powder wastewater. The recovery method comprises the following steps: (1) filtering the liquid-phase reduced silver powder wastewater; (2) pre-recovering the polymers from the liquid-phase reduced silver powder wastewater by a foam adsorption separation method to obtain a foam liquid and a raffinate; (3) defoaming the foam liquid to obtain an enriched liquid containing the polymer; (4) filtering the pre-treated raffinate and recovering the polymers from the raffinate by an ultrafiltration method to obtain a concentrated liquid containing the polymer; (5) mixing the enriched liquid from step (3) and the concentrated liquid from step (4) to obtain a concentrated liquid containing the polymer; and (6) treating the concentrated liquid containing the polymer by a precipitation method to precipitate the polymer from the liquid phase, allowing the polymer to settle or centrifugally separate, and then washing and drying to obtain the polymer. The recovery method proposed by the present invention can achieve efficient recovery of polymers from wastewater, with a recovery rate of more than 90%. At the same time, the method is simple to operate, has a mild process, and is suitable for large-scale production.

Description

Technical field:

[0001] The invention relates to the technical field of silver powder wastewater treatment, and in particular to a method for recovering polymers in liquid phase reduced silver powder wastewater. Background technology:

[0002] Currently, silver powder, as a metallic functional material, is primarily used in microelectronics applications such as conductive pastes, conductive adhesives, and printed circuits. Ultrafine spherical silver powder is typically produced using a liquid-phase reduction method, using silver nitrate as the silver source, ascorbic acid as the reducing agent, and polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) as the dispersant. The silver powder production process produces a large amount of highly concentrated acidic wastewater. This wastewater primarily consists of the silver powder reduction mother liquor and the first two washes of the silver powder. Typical high-concentration wastewater contains silver (less than 20 mg / L), nitric acid (20-30 g / L), ascorbic acid, dehydroascorbic acid (20-40 g / L), and polyvinylpyrrolidone (15-20 g / L). This silver powder production wastewater is difficult to treat due to its high acidity, high nitrogen content, and high COD content. In recent years, with the rapid development of the solar cell industry, the demand for spherical silver powder has increased significantly, leading to a significant increase in silver powder production wastewater.

[0003] Currently, high-concentration silver powder production wastewater is generally treated by evaporation. During pretreatment, nitric acid in the wastewater reacts with sodium hydroxide to form sodium nitrate. During the wastewater evaporation process, polyvinylpyrrolidone (PPY) and nitrates become solid waste. This solid waste is typically outsourced for treatment as hazardous waste, indicating that existing treatment methods do not effectively recover and reuse PPY. PPY is a water-soluble polymer with high economic value and is widely used in materials, new energy, pharmaceuticals, and daily chemicals. Against the backdrop of resource shortages and environmental degradation, the clean treatment and resource utilization of solid waste has become a major trend. Therefore, the recovery of valuable polymers from high-concentration silver powder production wastewater has significant economic value and promising application prospects. Summary of the invention:

[0004] Aiming at the problems of poor economic efficiency and low resource utilization in the existing evaporation treatment of high-concentration silver powder production wastewater, the present invention provides a method for recovering polymers in liquid-phase reduction silver powder wastewater. The method can achieve efficient recovery of polymers in the wastewater with a recovery rate of more than 90%. At the same time, the method is simple to operate, has a mild process, and is suitable for large-scale production.

[0005] The object of the present invention is to provide a method for recovering polymers in liquid phase reduced silver powder wastewater, comprising the following steps:

[0006] (1) filtering the liquid phase reduction silver powder wastewater;

[0007] (2) using a foam adsorption separation method to pre-recover the polymer in the liquid phase reduced silver powder wastewater after the filtration treatment in step (1) to obtain a foam liquid and a raffinate;

[0008] (3) defoaming the foamed liquid in step (2) to obtain an enriched liquid containing a polymer;

[0009] (4) filtering the raffinate obtained in the pretreatment step (2), and recovering the polymer in the raffinate by ultrafiltration to obtain a concentrated solution containing the polymer;

[0010] (5) mixing the enriched solution in step (3) and the concentrated solution in step (4) to obtain a concentrated solution containing a high polymer;

[0011] (6) The concentrated solution containing the polymer is treated by precipitation method to precipitate the polymer from the liquid phase, and the polymer is allowed to settle or separated by centrifugation, and then washed and dried to obtain the polymer.

[0012] The liquid phase reduction silver powder wastewater proposed by the present invention comprises silver powder, ascorbic acid, dehydroascorbic acid and polyvinyl pyrrolidone, and is a difficult-to-treat organic wastewater with high nitrogen and high COD.

[0013] The recycling method proposed by the present invention has a direct recovery rate of 90% to 95% for polymer powder. The recovered polyvinyl pyrrolidone can be returned to the spherical silver powder reduction preparation process and can also be applied to other fields, thereby realizing the reuse of valuable resources.

[0014] Preferably, the polymer is polyvinyl pyrrolidone. In step (1), the suspended solids in the liquid phase reduction silver powder wastewater are removed by filtration, so as to facilitate the efficient flotation of the polymer by bubbling the wastewater.

[0015] Preferably, the gas-liquid volume ratio of the foam adsorption separation method in step (2) is 10:1 to 30:1, and the separation time is 5 to 30 minutes. The foam adsorption separation method specifically involves blowing air into the wastewater, and the gas is dispersed to form a large number of bubbles, which carry the PVP out of the liquid surface, thereby forming a stable foam layer, and finally obtaining a foam liquid and a raffinate. The gas in the foam adsorption separation method is nitrogen or air, and the gas-liquid volume ratio refers to the volume ratio of the gas to the liquid phase reduced silver powder wastewater after filtration treatment.

[0016] Preferably, the defoaming method in step (3) is ultrasonic defoaming, wherein the ultrasonic power is 25-40 kW and the time is 10-30 minutes. Ultrasonic defoaming mainly utilizes the cavitation and sound pressure of ultrasound to accelerate the drainage to obtain a polymer-enriched solution.

[0017] Preferably, the ultrafiltration method described in step (4) is to use an ultrafiltration membrane for treatment, and the ultrafiltration membrane is an acid-resistant ultrafiltration membrane, and the cut-off molecular weight of the ultrafiltration membrane is greater than 2500Da. The pretreatment function of step (4) is to remove colloids in the raffinate. The ultrafiltration membrane is an acid-resistant ultrafiltration membrane that can adapt to the environment of 0.1-1.0 mol / L nitric acid solution, thereby ensuring the chemical stability of the membrane material. The cut-off molecular weight of the ultrafiltration membrane is greater than 2500Da, and has a good screening effect on polymers.

[0018] Since the average molecular weight of the high polymer polyvinylpyrrolidone PVP-K30 in the liquid phase reduction silver powder wastewater is about 40,000 and the spatial volume is relatively large, the ultrafiltration membrane used in the present invention can effectively intercept and recover PVP in the wastewater.

[0019] More preferably, the operating pressure of the ultrafiltration membrane in step (4) is 0.1 to 0.5 MPa, and the separation time is 10 to 30 min.

[0020] Preferably, the precipitation method in step (6) is specifically an organic solvent precipitation method, the amount of organic solvent used is 1 to 4 times the volume of the concentrated solution containing the polymer, and the working temperature is 0°C to room temperature.

[0021] More preferably, the organic solvent in step (6) is acetone. Since acetone is almost insoluble in PVP, acetone is added to the PVP aqueous solution, and part of the PVP is precipitated with the acetone, thereby achieving separation of polyvinyl pyrrolidone from the liquid phase.

[0022] Preferably, the static sedimentation time in step (6) is 30 to 120 min, the rotation speed of the centrifugal separation is 2000 to 8000 r / min, and the centrifugation time is 10 to 30 min.

[0023] Preferably, the drying method in step (6) is spray drying, the spray drying pressure is controlled at -500 to -1000 Pa, the drying temperature is 140°C to 160°C, and the drying time is 5 to 60 seconds. The polymer detergent is an acetone-ether mixed solvent, and the washing method is a rinsing method for 10 to 30 minutes.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1. The recovery method proposed by the present invention can achieve efficient recovery of polymers in wastewater, with a recovery rate of more than 90%;

[0026] 2. The recycling method proposed by the present invention is relatively environmentally friendly and is a clean recycling method;

[0027] 3. The recovery method proposed by the present invention is simple to operate, has a mild process, and is suitable for large-scale production. Description of the drawings:

[0028] Figure 1 The present invention is a process flow chart of a method for recovering polymers from liquid phase reduction silver powder wastewater. Specific implementation method:

[0029] The following examples are provided to further illustrate the present invention, but are not intended to limit the present invention.

[0030] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are for the purpose of describing specific embodiments only and are not intended to limit the scope of protection of the present invention. Unless otherwise specified, the experimental materials and reagents herein are conventional commercial products in the art.

[0031] In the following examples, the polyvinyl pyrrolidone (PVP) content of the silver powder wastewater is 12-20 g / L, and the pH value is 0.8-1.0.

[0032] Example 1

[0033] 1000L of liquid-phase silver reduction wastewater (polyvinylpyrrolidone (PVP) content 15g / L, pH 0.8) was measured and suspended solids with a particle size greater than 0.1μm were filtered out to obtain clarified wastewater. Air was blown into the wastewater for 15 minutes at a volume ratio of air to liquid-phase silver reduction wastewater of 10:1. The gas dispersed to form a large number of bubbles, which carried the PVP to the liquid surface, forming a stable foam layer. Finally, a foam solution and 850mL of raffinate were obtained.

[0034] Under the condition of ultrasonic power of 25 kW, the foam liquid was defoamed for 15 minutes to obtain 150 mL of enriched liquid.

[0035] The raffinate was filtered to remove the colloidal matter and control its content to less than 10 mg / L. The raffinate was filtered through a hydrophobic ultrafiltration membrane at a pressure of 0.3 MPa and a separation time of 20 min to obtain 80 mL of PVP-containing concentrated solution, which was then mixed with the enriched solution to obtain 230 mL of PVP concentrated solution.

[0036] Add 450 mL of acetone to the PVP concentrate and let it stand for 30 minutes to precipitate the PVP from the liquid phase. Wash with acetone-ether to remove any residual acidic solution on the PVP surface. Prepare a 20% aqueous solution of PVP and spray dry it at a pressure of -1000 Pa and a temperature of 150°C for 10 seconds to obtain 14.2 kg of pure PVP powder. The PVP recovery rate from silver powder wastewater is 90%, with a purity of 95%.

[0037] Example 2

[0038] 5000L of silver powder wastewater (polyvinylpyrrolidone (PVP) content 20g / L, pH 0.9) was measured and suspended solids with a particle size of 0.1μm or larger were filtered out to obtain clarified wastewater. Nitrogen was then added to the liquid phase at a volume ratio of 20:1, and aeration was introduced into the wastewater for 10 minutes. The gas was dispersed to form a large number of bubbles, which carried the PVP to the liquid surface, forming a stable foam layer. Finally, a foam solution and 4400mL of raffinate were obtained.

[0039] Under the condition of ultrasonic power of 30 kW, the foam liquid was defoamed for 15 minutes to obtain 600 mL of enriched liquid.

[0040] The raffinate was filtered to remove the colloidal matter and control its content to less than 10 mg / L. The raffinate was filtered through a hydrophobic PVDF ultrafiltration membrane at a pressure of 0.4 MPa and a separation time of 30 min to obtain 440 mL of PVP-containing concentrated solution, which was then mixed with the enriched solution to obtain 1040 mL of PVP concentrated solution.

[0041] 3000mL of acetone was added to the PVP concentrate and allowed to stand for 30 minutes to precipitate the PVP. The solution was then washed with acetone and ether to remove any residual acidic solution on the PVP surface. The PVP was then prepared into a 25% aqueous solution and spray-dried at a pressure of -1000 Pa and a temperature of 150°C for 30 seconds to yield 93.8kg of pure PVP powder. The recovery rate of PVP from the silver powder wastewater was 92%, with a purity of 98%.

[0042] Example 3

[0043] Measure 2000L of silver powder wastewater (polyvinylpyrrolidone (PVP) content 12g / L, pH 1.0) and filter out suspended solids with a particle size greater than 0.1μm to obtain clarified wastewater. A nitrogen-to-liquid reduction silver powder wastewater volume ratio of 25:1 was used, and aeration was introduced into the wastewater for 15 minutes. The gas dispersed to form a large number of bubbles, which carried the PVP to the liquid surface, forming a stable foam layer. Finally, a foam solution and 1760mL of raffinate were obtained.

[0044] Under the condition of ultrasonic power of 25 kW, the foam liquid was defoamed for 15 min to obtain 240 mL of enriched liquid.

[0045] The raffinate was filtered to remove the colloidal matter and control its content to less than 10 mg / L. The raffinate was filtered through a hydrophobic ultrafiltration membrane at a pressure of 0.5 MPa and a separation time of 20 min to obtain 176 mL of PVP-containing concentrate, which was then mixed with the enriched solution to obtain 410 mL of PVP concentrate.

[0046] 800 mL of acetone was added to the PVP concentrate and allowed to stand for 30 minutes. White PVP precipitated from the liquid phase. The solution was washed with acetone and ether to remove any residual acidic solution on the PVP surface. The PVP was prepared into a 25% aqueous solution and spray-dried at a pressure of -1000 Pa and a temperature of 160°C for 15 seconds to obtain 24 kg of pure PVP powder. The recovery rate of PVP from silver powder wastewater was 95%, with a purity of 95%.

[0047] Example 4

[0048] 4000L of silver powder wastewater (polyvinylpyrrolidone (PVP) content 15g / L, pH 0.8) was measured and suspended solids with a particle size greater than 0.1μm were filtered to obtain clarified wastewater. The silver powder wastewater was reduced to an air-to-liquid ratio of 30:1 by volume, and air was introduced into the wastewater for 20 minutes. The gas dispersed to form a large number of bubbles, which carried the PVP to the liquid surface, forming a stable foam layer. Finally, a foam solution and 3400mL of raffinate were obtained.

[0049] Under the condition of ultrasonic power of 30 kW, the foam liquid was defoamed for 15 min to obtain 600 mL of enriched liquid.

[0050] The raffinate was filtered to remove the colloidal matter and control its content to less than 10 mg / L. The raffinate was filtered through a hydrophobic ultrafiltration membrane at a pressure of 0.4 MPa and a separation time of 20 min to obtain 60 mL of PVP-containing concentrated solution, which was then mixed with the enriched solution to obtain 950 mL of PVP concentrated solution.

[0051] 1800 mL of acetone was added to the PVP concentrate and allowed to stand for 30 minutes to precipitate the PVP. The solution was then washed with acetone and ether to remove any residual acidic solution on the PVP surface. The PVP was then prepared into a 20% aqueous solution and spray-dried at a pressure of -900 Pa and a temperature of 150°C for 20 seconds to yield 56.8 kg of pure PVP powder. The recovery rate of PVP from the silver powder wastewater was 90%, with a purity of 95%.

[0052] Example 5

[0053] The same as Example 4, except that: the volume ratio of air to liquid phase silver powder reduction wastewater is 30:1, and air is added to the wastewater for 5 minutes; the foam liquid is defoamed for 30 minutes under an ultrasonic power of 25 kW; the raffinate is filtered using a hydrophobic ultrafiltration membrane, the pressure is controlled at 0.1 MPa, and the separation time is 30 minutes; the volume of ketone is 1 times the volume of the PVP concentrate.

[0054] Example 6

[0055] The same as Example 4, except that: the volume ratio of nitrogen to liquid phase reduction silver powder wastewater is 10:1, and air is added to the wastewater for 30 minutes; the foam liquid is defoamed for 10 minutes under an ultrasonic power of 40 kW; the raffinate is filtered using a hydrophobic ultrafiltration membrane, the pressure is controlled at 0.5 MPa, and the separation time is 10 minutes; the volume of ketone is 4 times the volume of the PVP concentrate.

[0056] The description of the above embodiments is only used to help understand the technical solution and core ideas of the present invention. It should be pointed out that for those skilled in the art, several improvements and modifications can be made to the present invention without departing from the principles of the present invention. These improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A method for recovering polymers from liquid phase reduced silver powder wastewater, characterized in that: The polymer is polyvinyl pyrrolidone, and the recovery method comprises the following steps: (1) filtering the liquid phase reduction silver powder wastewater; (2) using a foam adsorption separation method to pre-recover the polymer in the liquid phase reduced silver powder wastewater after the filtration treatment in step (1) to obtain a foam liquid and a raffinate, wherein the gas-liquid volume ratio of the foam adsorption separation method is 10:1 to 30:1, the separation time is 5 to 30 minutes, and the gas in the foam adsorption separation method is nitrogen or air; (3) defoaming the foamed liquid in step (2) to obtain an enriched liquid containing a polymer, wherein the defoaming method is ultrasonic defoaming; (4) filtering the raffinate obtained in the pretreatment step (2), and recovering the polymer in the raffinate by ultrafiltration to obtain a concentrated solution containing the polymer, wherein the ultrafiltration method is performed using an ultrafiltration membrane, the ultrafiltration membrane being an acid-resistant ultrafiltration membrane having a molecular weight cutoff greater than 2500 Da; (5) mixing the enriched solution in step (3) and the concentrated solution in step (4) to obtain a concentrated solution containing a high polymer; (6) A precipitation method is used to treat a concentrated solution containing a high polymer, so that the high polymer is precipitated from the liquid phase, and the high polymer is allowed to settle or centrifuged, and then washed and dried to obtain the high polymer. The precipitation method is specifically an organic solvent precipitation method.

2. The recycling method according to claim 1, wherein: During the ultrasonic defoaming in step (3), the ultrasonic power is 25 to 40 kW and the time is 10 to 30 minutes.

3. The recycling method according to claim 1, characterized in that The ultrafiltration membrane operating pressure in step (4) is 0.1 to 0.5 MPa, and the separation time is 10 to 30 minutes.

4. The recycling method according to claim 1, characterized in that The amount of organic solvent used in step (6) is 1 to 4 times the volume of the concentrated solution containing the polymer.

5. The recycling method according to claim 4, characterized in that: The organic solvent in step (6) is acetone.

6. The recycling method according to claim 1, characterized in that The static sedimentation time in step (6) is 30 to 120 minutes, the rotation speed of the centrifugal separation is 2000 to 8000 r / min, and the centrifugal time is 10 to 30 minutes.

7. The recycling method according to claim 1, characterized in that: The drying method described in step (6) is spray drying, the spray drying control pressure is -500 to -1000 Pa, the drying temperature is 140° C. to 160° C., and the time is 5 to 60 seconds.

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