A method for resourceful treatment of silver powder wastewater by liquid phase reduction

Abstract

The application discloses a kind of liquid phase reduction silver powder wastewater resource processing method, comprising the following steps: (1) using membrane filtration method to remove suspended solids in silver powder wastewater;(2) using ultrasonic method to irradiate the clear silver powder solution obtained in step (1), obtain the solution containing low molecular weight pollutants;(3) using wet oxidation method to treat the solution containing low molecular weight pollutants obtained in step (2), obtain low COD acidic solution;(4) in the low COD solution obtained in step (3), add lye until pH is 6.0-7.0, prepare sodium nitrate solution;(5) using heavy metal capture agent to purify the sodium nitrate solution obtained in step (4);(6) using evaporation crystallization method to treat the pure sodium nitrate solution obtained in step (5), obtain high-purity sodium nitrate and condensate;Solve the existing liquid phase reduction silver powder wastewater treatment method cannot recover nitrogen resource and process safety is poor.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of silver powder wastewater treatment, in particular to a resourceful treatment method of liquid phase reduction silver powder wastewater. BACKGROUND

[0002] Silver powder has a wide range of applications in the fields of conductive paste, conductive adhesive and printed circuit, etc. At present, ultra-fine spherical silver powder is generally prepared by liquid phase reduction method, using silver nitrate as silver source, ascorbic acid as reducing agent, and polyvinylpyrrolidone (PVP) or polyvinyl alcohol (PVA) as dispersant. A large amount of wastewater is discharged in the process of silver powder preparation. This wastewater contains silver (20 mg / L or less), nitric acid (20-30 g / L), dehydroascorbic acid (20-40 g / L), polyvinylpyrrolidone or polyvinyl alcohol (15-20 g / L). As can be seen, this silver powder production wastewater is a kind of difficult-to-treat industrial wastewater with high acid, high COD and high nitrogen.

[0003] At present, the silver powder production wastewater is generally treated by alkali neutralization-evaporation-biochemical method. This method is simple in operation and high in treatment efficiency, but produces a large amount of mixture of organic solid waste and nitrate. This mixture is a hazardous waste, which needs to be treated by outsourcing at a cost. As can be seen, the conventional treatment method seriously wastes nitrogen resources and does not meet the requirements of clean production. In addition, this method increases the environmental protection cost, which reduces the competitiveness of silver powder. Under the background of resource shortage and carbon peak and carbon neutral, the silver powder production wastewater urgently needs a clean treatment method which is environmentally friendly and high in safety, to adapt to the current industrial and environmental policies. Therefore, the resourceful treatment of liquid phase reduction silver powder wastewater is of great significance for enterprises to reduce cost and increase efficiency, improve operating environment, and even for the sustainable development of silver powder industry. SUMMARY

[0004] The purpose of the present application is to provide a resourceful treatment method of liquid phase reduction silver powder wastewater, which solves the problems of inability to recover nitrogen resources and poor process safety of the existing liquid phase reduction silver powder wastewater treatment method.

[0005] The present application is realized by the following technical solutions:

[0006] A resourceful treatment method of liquid phase reduction silver powder wastewater, comprising the following steps:

[0007] (1) removing the suspended solids in the silver powder wastewater by membrane filtration to obtain a clear silver powder solution;

[0008] (2) irradiating the clear silver powder solution obtained in step (1) by ultrasonic method, the ultrasonic frequency is 20-50 kHz, the average sound intensity is 1.0-2.0 W / cm 2to obtain a solution containing low molecular weight pollutants;

[0009] (3) treating the solution containing low molecular weight pollutants obtained in step (2) by wet oxidation to obtain a low COD acidic solution;

[0010] (4) adding alkali liquor to the low COD solution obtained in step (3) until the pH is 6.0-7.0 to prepare a sodium nitrate solution;

[0011] (5) purifying the sodium nitrate solution obtained in step (4) by using a heavy metal capturing agent to obtain a pure sodium nitrate solution by filtration;

[0012] (6) treating the pure sodium nitrate solution obtained in step (5) by evaporation crystallization to obtain high purity sodium nitrate and condensed water;

[0013] (7) treating the condensed water obtained in step (6) by using a conventional biochemical method to remove the small amount of small molecular organic acid contained therein to achieve standard discharge of the wastewater.

[0014] The silver content of the liquid phase reduction silver powder wastewater is below 20 mg / L, the nitric acid content is 20-30 g / L, the dehydroascorbic acid content is 20-40 g / L, and the polyvinylpyrrolidone or polyvinyl alcohol content is 15-20 g / L.

[0015] Step (1) uses membrane filtration to remove the suspended solids in the silver powder wastewater to facilitate subsequent ultrasonic treatment. The liquid phase reduction silver powder wastewater usually contains some suspended solids and degradation products, which will affect the subsequent degradation process of organic pollutants. The membrane used is a high molecular weight microporous membrane, preferably a hydrophilic polypropylene membrane, with a pore size of less than 0.45 μm.

[0016] Step (2) uses ultrasonic method to cut the linear polyvinylpyrrolidone (PVP) or polyvinyl alcohol in the wastewater. The principle of ultrasonic cutting is that when a liquid is irradiated by ultrasonic waves of a certain frequency and acoustic intensity, cavitation bubbles are generated under the action of the negative pressure phase of the sound wave. The bubbles collapse rapidly under the action of the subsequent positive pressure phase of the sound wave, forming a high temperature and high pressure environment to cut and degrade the linear PVP or polyvinyl alcohol. The macromolecular PVP or polyvinyl alcohol is converted into small molecular organic fragments to reduce its surface activity.

[0017] The ultrasonic frequency in step (2) is preferably 25-45 kHz, and the average acoustic intensity is 1.5-2.0 W / cm 2 for 60-90 min.

[0018] Step (3) is a wet oxidation method based on the use of air (oxygen) to oxidize organic matter into carbon dioxide, water and nitrate at a high temperature of 150-250℃ and a high pressure of 1-4MPa, so as to remove the organic pollutants in water. The organic nitrogen in the organic pollutants PVP is converted into nitrate after oxidation, so as to recycle sodium nitrate subsequently. The gas-liquid ratio is 20-50:1, and the treatment time is 30-120min.

[0019] Preferably, the temperature is 150-200℃, the pressure is 2-4MPa, the gas-liquid ratio is 20-40:1, and the treatment time is 60-90min.

[0020] Step (4) is to neutralize the free acid in the low-COD solution with lye and synthesize sodium nitrate. The lye used is a nearly saturated solution of alkali, and the alkali used is one of sodium hydroxide and sodium carbonate, preferably sodium hydroxide.

[0021] Step (5) is to selectively remove heavy metal impurities such as copper, silver and iron in the sodium nitrate solution based on the chelation of heavy metal capture agents. The heavy metal capture agent used is diethylene triamine ethyl polymer. The ratio of the mass (g) of the heavy metal capture agent used to the volume (L) of the wastewater is 0.5-2.0, preferably 1.0-1.5.

[0022] Step (6) is evaporation, preferably rotary evaporation, which is to evaporate the target product from the aqueous solution through evaporation and mass transfer processes by using high-speed rotation of the rotary cup to make the liquid into a thin film on the cup wall and expand its evaporation area. The temperature used is 60-100℃, the evaporation pressure is negative pressure, and the vacuum degree is 0--0.3MPa.

[0023] The purity of the sodium nitrate obtained in step (6) is more than 99.5%, and the recovery rate of the nitrogen resource is more than 90%.

[0024] Step (7) is to further treat the condensed water in step (6). Since the condensed water contains a small amount of small-molecule organic acids, it can be treated by conventional biochemical methods to meet the discharge standard.

[0025] The beneficial effects of the present application are as follows:

[0026] 1. The nitrogen resource is recovered in the form of sodium nitrate, and both the recovery rate of the nitrogen resource and the purity of sodium nitrate are high.

[0027] 2. The safety of wastewater evaporation can be significantly improved, thereby reducing the cost of safe production.

[0028] 3. The generation amount of hazardous waste can be greatly reduced, which is very friendly to the environment. DETAILED DESCRIPTION

[0029] The following is a further description of the present application, but not a limitation of the present application.

[0030] Example 1

[0031] Take 1000 mL silver powder wastewater (silver content of 20 mg / L, nitric acid content of 20 g / L, dehydroascorbic acid content of 20 g / L, polyvinylpyrrolidone content of 15 g / L, total nitrogen of 4.5 g / L), remove the suspended matter with medium particle size greater than 0.1 μm by filtering with polypropylene film to obtain a clear silver powder solution. Under the conditions of power of 25 kW, acoustic intensity of 1.5 W / cm 2 Under the conditions of power of 25 kW, acoustic intensity of 1.5 W / cm

[0032] Example 2

[0033] Take 500 mL silver powder wastewater (silver content of 18 mg / L, nitric acid content of 22.5 g / L, dehydroascorbic acid content of 40 g / L, polyvinyl alcohol content of 20 g / L, total nitrogen of 5.0 g / L), remove the suspended matter with medium particle size greater than 0.1 μm by filtering with polypropylene film to obtain a clear silver powder solution. Under the conditions of power of 25 kW, acoustic intensity of 2.0 W / cm 2 Under the conditions of power of 25 kW, acoustic intensity of 2.0 W / cm

[0034] Example 3

[0035] Take 1500 mL silver powder wastewater (silver content in 10 mg / L, nitric acid content of 27 g / L, dehydroascorbic acid content of 40 g / L, polyvinyl alcohol content in 18 g / L, total nitrogen 6.0 g / L), remove the suspended particles with medium particle size greater than 0.1 μm by polypropylene membrane filtration to obtain clear silver powder solution. Under the conditions of power of 45 kW, acoustic intensity of 1.5 W / cm 2 irradiate the silver powder solution by ultrasound for 90 min to obtain a solution containing low molecular weight organic pollutants. Oxidize the solution after ultrasonic irradiation under the conditions of temperature of 150 ℃, pressure of 4 MPa and gas-liquid volume ratio of 30 for 60 min to obtain a low COD acidic solution. Slowly add 45% sodium hydroxide solution to the above solution until the solution pH is 6.0 to prepare a sodium nitrate solution. Take 0.80 g diethylenetriamine ethyl polymer and add it to the sodium nitrate solution, and filter to obtain a pure sodium nitrate solution. Evaporate and concentrate under the conditions of temperature of 60 ℃ and vacuum degree of -0.2 MPa to obtain 30.38 g sodium nitrate. Through chemical analysis, the purity of sodium nitrate is 99.7%, and the nitrogen recovery rate is 90.4%. The collected condensate is treated by conventional biochemical method and discharged after reaching the standard.

[0036] Example 4

[0037] Take 2000 mL silver powder wastewater (silver content in 15 mg / L, nitric acid content of 22.5 g / L, dehydroascorbic acid content of 30 g / L, polyvinylpyrrolidone 15 g / L, total nitrogen 6.5 g / L), remove the suspended particles with medium particle size greater than 0.1 μm by polypropylene membrane filtration to obtain clear silver powder solution. Irradiate the silver powder solution by ultrasound for 120 min under the conditions of power of 25 kW, acoustic intensity of 2.0 W / cm 2 obtain a low COD acidic solution. Slowly add 45% sodium hydroxide solution to the above solution until the solution pH is 6.0 to prepare a sodium nitrate solution. Take 1.20 g diethylenetriamine ethyl polymer and add it to the sodium nitrate solution, and filter to obtain a pure sodium nitrate solution. Evaporate and concentrate under the conditions of temperature of 80 ℃ and vacuum degree of -0.1 MPa to obtain 39.88 sodium nitrate. Through chemical analysis, the purity of sodium nitrate is 99.6%, and the nitrogen recovery rate is 96.3%. The collected condensate is treated by conventional biochemical method and discharged after reaching the standard.

Claims

1. A method for resourceful treatment of silver powder wastewater from liquid phase reduction, characterized in that, The silver content of the liquid phase reduction silver powder wastewater is below 20 mg / L, the nitric acid content is 20-30 g / L, the dehydroascorbic acid content is 20-40 g / L, and the polyvinylpyrrolidone or polyvinyl alcohol content is 15-20 g / L. The method comprises the following steps: (1) removing the suspended solids in the silver powder wastewater by membrane filtration to obtain a clear silver powder solution; (2) irradiating the clear silver powder solution obtained in step (1) with ultrasound at a frequency of 20 to 50 kHz and an average acoustic intensity of 1.0 to 2.0 W / cm2 for a period of 30 to 120 minutes to obtain a solution containing low molecular weight contaminants; 2 , time is 30-120 min, obtain the solution containing low molecular weight contaminant; (3) treating the solution containing low molecular weight pollutants obtained in step (2) by wet oxidation to obtain an acid solution with low COD; (4) adding lye to the low COD solution obtained in step (3) until the pH is 6.0-7.0 to prepare a sodium nitrate solution; (5) purifying the sodium nitrate solution obtained in step (4) by using a heavy metal capturing agent to obtain a pure sodium nitrate solution by filtration; (6) treating the pure sodium nitrate solution obtained in step (5) by evaporation crystallization to obtain high-purity sodium nitrate and condensed water; (7) treating the condensed water obtained in step (6) by using a conventional biochemical method to remove the small amount of small molecular organic acids contained therein to achieve standard discharge of the wastewater.

2. The method of claim 1, wherein, The membrane used is a high molecular weight microporous membrane.

3. The method of claim 2, wherein, The membrane used is a hydrophilic polypropylene membrane with a pore size of less than 0.45 μm.

4. The method of claim 1, wherein, Step (2) ultrasonic frequency is 25-45 kHz, average sound intensity 1.5-2.0 W / cm 2 , time is 60-90 min.

5. The method of claim 1, wherein, The wet oxidation method of step (3) is based on the oxidation of organic matter into carbon dioxide, water and nitrate by oxygen in air at a high temperature of 150-250 ℃ and a high pressure of 1-4 MPa, with a gas-liquid ratio of 20-50:1 and a time of 30-120 min.

6. The method of claim 5, wherein, The temperature is 150-200 ℃, the pressure is 2-4 MPa, the gas-liquid ratio is 20-40:1, and the time is 60-90 min.

7. The method of claim 1, wherein, The lye used in step (4) is a nearly saturated solution of an alkali, and the alkali used is one of sodium hydroxide and sodium carbonate.

8. The method of claim 1, wherein, The heavy metal capturing agent used in step (5) is diethylene triamine ethyl polymer, and the mass / volume ratio of the heavy metal capturing agent added to the wastewater is 0.5-2.0 g / L.

9. The method of claim 7, wherein, The mass / volume ratio of the heavy metal capturing agent added to the wastewater is 1.0-1.5 g / L.

10. The method of claim 1, wherein, The evaporation in step (6) is rotary evaporation, and the temperature used is 60-100 ℃, the evaporation pressure is negative pressure, and the vacuum degree is 0 to -0.3 MPa.