Treatment method of high-salt high-COD silver powder wastewater

Abstract

The invention discloses a treatment method of high-salt and high-COD silver powder wastewater. The treatment method comprises the following steps: step 1, storing silver powder wastewater; step 2, neutralizing caustic soda flakes; step 3, sulfuration and silver deposition; step 4, carrying out nanofiltration to remove PVP (Polyvinyl Pyrrolidone); step 5, MVR simulation evaporation; step 6, carrying out ozone catalytic oxidation on COD; step 7, reverse osmosis separation and impurity removal; and step 8, sludge dewatering. After the wastewater is treated by the method, the water quality can reach the primary standard of Integrated Wastewater Discharge Standard, the indirect discharge standard of Inorganic Chemical Industrial Pollutant Discharge Standard and the like. According to the method, PVP is removed at the front end of the evaporation process, the evaporation efficiency of the MVR evaporator and the operation stability of a wastewater system can be improved, and the silver sulfide product can be efficiently recycled. According to the method, the environmental protection requirement and the economic requirement are met, and resource utilization of silver in the silver powder wastewater is achieved on the basis of guaranteeing stable operation of a wastewater system.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for treating high-salt, high-COD silver powder wastewater. Background Technology

[0002] Ultrafine silver powder is an important precious metal powder material. Due to its excellent electrical and thermal conductivity, it is widely used in photovoltaic, electronic circuits, 5G communication and other fields. In recent years, with the rapid development of the photovoltaic and electronics industries, the preparation of ultrafine silver powder has become a hot topic of research.

[0003] Currently, the liquid phase chemical reduction method is the most commonly used silver powder production method in the industry due to its low investment in process equipment, low production cost, easy control of process conditions, and ease of large-scale production. The wastewater generated during the production of silver powder by the liquid phase chemical reduction method is difficult to treat, and has the characteristics of high acidity, high COD and high salt, while also carrying a small amount of Ag. Direct discharge will cause serious environmental pollution. The traditional treatment method for this type of silver powder wastewater is to neutralize it with caustic soda. After neutralization, the liquid directly enters the MVR equipment to evaporate and remove most of the salt and COD. The condensate is further biochemically treated and discharged after meeting the standards. However, this method has the following three problems: (1) Due to the high COD and PVP of the influent, the evaporation efficiency of the MVR equipment is low, the cleaning cycle is short and the frequency is high, and a large amount of organic hazardous waste is generated; (2) This type of wastewater contains both reducing substances VC and oxidizing substances sodium nitrate. There is a risk of reaction and explosion during the drying process; (3) Valuable substances silver in the wastewater cannot be recovered. Summary of the Invention

[0004] In view of the shortcomings of the existing technology, the present invention aims to provide a method for treating high-salt, high-COD silver powder wastewater.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for treating high-salt, high-COD silver powder wastewater includes the following steps:

[0007] Step 1, Silver Powder Wastewater Preservation: Store the collected silver powder wastewater in a cool, dark place to prevent it from deteriorating and becoming unusable for effective PVP removal by nanofiltration equipment;

[0008] Step 2, Caustic soda neutralization: Add industrial caustic soda to the silver powder wastewater to carry out a neutralization reaction, adjust the pH value of the silver powder wastewater to 5-8, and obtain the neutralized liquid;

[0009] Step 3, Silver Sulfide Precipitation: Add sodium sulfide solution to the neutralized liquid obtained in Step 2 to perform silver sulfide precipitation. After stirring and reacting fully, separate the solid and liquid to obtain filter residue and silver precipitation liquid. Wash the filter residue with distilled water, and dry the washed filter residue in a drying oven to obtain silver sulfide product. The silver precipitation liquid is a mixed solution of VC, PVP and sodium nitrate.

[0010] Step 4, PVP removal by nanofiltration: The silver-precipitated liquid obtained in Step 3 is subjected to PVP removal using a nanofiltration device. The nanofiltration device continuously concentrates the silver-precipitated liquid, and while continuously introducing the silver-precipitated liquid, the nanofiltration concentrate is continuously circulated within the nanofiltration device to gradually increase the concentration factor; PVP is separated into the nanofiltration concentrate; the nanofiltration device finally obtains nanofiltration concentrate and nanofiltration permeate, the main components of which are vitamin C and sodium nitrate.

[0011] Step 5, MVR simulated evaporation: The nanofiltration permeate obtained in step 4 is subjected to MVR simulated evaporation to obtain mother liquor and condensate. The condensate is collected and cooled to room temperature.

[0012] Step 6, Ozone catalytic oxidation of COD: O3 and MnO2 catalysts are introduced into the condensate obtained in step 5. Most of the COD in the condensate is removed through an aeration reaction to obtain the oxidized liquid.

[0013] Step 7, Reverse Osmosis Separation and Impurity Removal: The residual COD and NO3 in the oxidized solution obtained in Step 6 are removed using a reverse osmosis system. - Separation and removal are performed to obtain reverse osmosis permeate and reverse osmosis concentrate, and the reverse osmosis permeate is discharged in compliance with standards.

[0014] Step 8, Sludge Dewatering: The nanofiltration concentrate obtained in Step 4, the evaporation mother liquor obtained in Step 5, and the reverse osmosis concentrate obtained in Step 7 are dried to a sludge cake with a solid content of 40-60% using a rotary drum dryer, and then further filtered into general solid waste.

[0015] Further, in step 3, the sodium sulfide solution has a mass concentration of 10%-30%, the mass amount of pure sodium sulfide is 1.5-3 times the theoretical mass amount calculated based on the silver content in the neutralized solution, and the stirring reaction time for silver sulfide precipitation is 1-2.5 h.

[0016] Further, in step 3, the filter residue is washed 2-4 times with distilled water, and the mass ratio of distilled water to filter residue is 3:1-10:1; the drying temperature of the washed filter residue is 40-100℃, and the drying time is 24-48h.

[0017] Furthermore, in step 4, the concentration factor of the nanofiltration device is 5-10 times, the pore size of the nanofiltration membrane in the nanofiltration device is 1-3 nm, and the membrane flux is 5-30 L / m³. 2 ·h.

[0018] Furthermore, in step 4, the nanofiltration device has a PVP rejection rate >90%.

[0019] Furthermore, in step 5, the MVR simulates evaporation by a factor of 5-9, and the boiling point temperature rise ranges from 5℃ to 10℃.

[0020] Furthermore, in step 6, the mass ratio of O3 to COD in the condensate is 3:1-6:1, the amount of MnO2 catalyst is 0.01-0.50 g / L of condensate, and the aeration time is 1-2.5 h.

[0021] Furthermore, in step 7, the reverse osmosis permeate rate is 80%-90%.

[0022] Furthermore, in step 8, the drum dryer must be designed to be explosion-proof, maintain inert gas protection during the drying process, and reduce the oxygen concentration.

[0023] The beneficial effects of this invention are as follows:

[0024] 1) This invention provides a process route and technical method for treating high-salt, high-COD silver powder wastewater. After treatment using this method, the wastewater quality meets the Class I standard of the "Integrated Wastewater Discharge Standard" and the indirect discharge standard of the "Inorganic Chemical Industry Pollutant Discharge Standard." This invention improves the evaporation efficiency of the MVR evaporator and the operational stability of the wastewater system by removing PVP at the front end of the evaporation process. It also effectively recovers silver sulfide products. This invention meets both environmental and economic requirements, achieving the resource utilization of silver in silver powder wastewater while ensuring the stable operation of the wastewater system.

[0025] 2) This invention removes PVP using nanofiltration, which not only has extremely high selectivity for PVP with a rejection rate of >90%, but also has relatively low operating costs compared to other membrane treatment technologies, making it highly promising for development.

[0026] 3) This invention uses a rotary drum dryer as the drying equipment, which avoids the risk of VC and sodium nitrate burning and exploding under low moisture content conditions, and improves the operational stability of the system.

[0027] 4) This invention uses a combination of ozone catalytic oxidation and reverse osmosis to deeply treat the condensate after evaporation. Compared with traditional biochemical systems, it has advantages such as small footprint, stable treatment effect, and high reaction efficiency, and is easy to industrialize. Attached Figure Description

[0028] Figure 1 This is a flowchart of the method in Embodiments 1-2 of the present invention; Figure 2 This is the XRD diffraction pattern of the silver sulfide product in Example 2 of the present invention. Detailed Implementation

[0029] The present invention will be further described below with reference to the accompanying drawings. It should be noted that this embodiment is based on the present technical solution and provides detailed implementation methods and specific operation processes, but the protection scope of the present invention is not limited to this embodiment.

[0030] Example 1

[0031] The main components of the wastewater from a liquid-phase chemical reduction process for silver powder production include: COD 30.50 g / L, TN 10.05 g / L, Ag 16.86 mg / L, conductivity 115.33 mS / cm, and pH = 0.75.

[0032] This embodiment provides a method for treating high-salt, high-COD silver powder wastewater, such as... Figure 1 As shown, the steps are as follows:

[0033] (1) Silver powder wastewater storage: Store the silver powder wastewater collected on the production line in a cool, dark place to prevent the silver powder wastewater from deteriorating and becoming unable to effectively remove PVP through nanofiltration equipment.

[0034] (2) Neutralization with caustic soda: Add industrial caustic soda to the silver powder wastewater to carry out a neutralization reaction. The amount of caustic soda used is 10g / L. Adjust the pH value of the solution to 6 to obtain the neutralized solution.

[0035] (3) Sodium sulfide precipitation of silver: A 20% sodium sulfide solution was added to the neutralized liquid obtained in step 2 for silver precipitation. The amount of pure sodium sulfide used was 9.13 mg / L of the neutralized liquid (1.5 times the theoretical amount). After stirring for 1 hour, the solid and liquid were separated to obtain filter residue and silver precipitation liquid. The filter residue was washed 4 times with distilled water, with the mass of distilled water being 3 times the mass of the filter residue. After washing, it was placed in a drying oven at 40℃ for 24 hours to obtain silver sulfide product. The silver precipitation liquid was a mixed solution of VC, PVP and sodium nitrate.

[0036] (4) Nanofiltration removal of PVP: PVP was removed from the silver-precipitated solution obtained in step 3 using a nanofiltration device. The membrane pore size of the nanofiltration device was 1.8-3.0 nm, and the membrane flux was 10 L / m³. 2 The silver-precipitated solution was concentrated 5 times, and the conductivity of the nanofiltration permeate was reduced to 90 μS / cm. While continuously introducing the silver-precipitated solution, the nanofiltration concentrate was continuously circulated in the system. PVP was separated into the nanofiltration concentrate, and the PVP removal rate was >95%. The main components of the obtained nanofiltration permeate were vitamin C and sodium nitrate.

[0037] (5) MVR simulated evaporation: The nanofiltration permeate obtained in step 4 was subjected to MVR simulated evaporation with an evaporation ratio of 7 times and a boiling point temperature rise of 6.5℃ to obtain mother liquor and condensate. The condensate was collected and cooled to room temperature.

[0038] (6) Ozone catalytic oxidation of COD: O3 and MnO2 are introduced into the condensate obtained in step 5. The mass ratio of O3 to COD in the condensate is 3:1. The amount of MnO2 is 0.1 g / L of condensate. After aeration for 1.5 h, the oxidized liquid is obtained.

[0039] (7) Reverse osmosis separation and impurity removal: The residual COD and NO3 in the oxidized solution obtained in step 6 are removed using a reverse osmosis device. - Thorough separation and removal are achieved, with a water production rate of 88%, and the reverse osmosis permeate meets discharge standards.

[0040] (8) Sludge dewatering: The nanofiltration concentrate obtained in step 4, the evaporation mother liquor obtained in step 5, and the reverse osmosis concentrate obtained in step 7 are dried to a solid content of 60% using a rotary drum dryer, and then further filtered into general solid waste.

[0041] After multiple tests, the rotary drum dryer has been verified to effectively prevent the combustion and explosion of vitamin C and sodium nitrate at low moisture content when using explosion-proof design (such as explosion-proof motor and electrostatic grounding), maintaining inert gas (such as nitrogen) protection during the drying process, and reducing oxygen concentration.

[0042] Table 1 shows the water quality of silver powder wastewater before and after treatment, and Table 2 shows the quality of silver sulfide products.

[0043] Example 2

[0044] The composition of the wastewater from a silver powder production process is the same as that in Example 1.

[0045] This embodiment provides a method for treating high-salt, high-COD silver powder wastewater, such as... Figure 1 As shown, the steps are as follows:

[0046] (1) Silver powder wastewater storage: Store the silver powder wastewater collected on the production line in a cool, dark place to prevent the silver powder wastewater from deteriorating and becoming unable to effectively remove PVP through nanofiltration equipment.

[0047] (2) Neutralization with caustic soda: Add industrial caustic soda to the silver powder wastewater to carry out a neutralization reaction. The amount of caustic soda used is 16g / L. Adjust the pH value of the solution to 7 to obtain the neutralized solution.

[0048] (3) Sodium sulfide silver precipitation: A 20% sodium sulfide solution was added to the neutralized liquid obtained in step 2 for silver precipitation. The amount of pure sodium sulfide used was 18.27 mg / L of the neutralized liquid (3 times the theoretical amount). After stirring for 1 hour, the solid and liquid were separated to obtain filter residue and silver precipitation liquid. The filter residue was washed 4 times with distilled water, with the mass of distilled water being 8 times the mass of the filter residue. After washing, it was placed in a drying oven and dried at 60℃ for 24 hours to obtain silver sulfide product. The silver precipitation liquid was a mixed solution of VC, PVP and sodium nitrate.

[0049] (4) Nanofiltration removal of PVP: PVP was removed from the silver-precipitated solution obtained in step 3 using a nanofiltration device. The membrane pore size of the nanofiltration device was 1.8-3.0 nm, and the membrane flux was 20 L / m³. 2 The silver-precipitated solution was concentrated 7 times. While continuously introducing the silver-precipitated solution, the nanofiltration concentrate was continuously circulated within the system. PVP was separated into the nanofiltration concentrate, with a PVP removal rate of >95%. The main components of the obtained nanofiltration permeate were vitamin C and sodium nitrate.

[0050] (5) MVR simulated evaporation: The nanofiltration permeate obtained in step 4 was subjected to MVR simulated evaporation with an evaporation ratio of 7 times and a boiling point temperature rise of 7°C to obtain the mother liquor and condensate. The condensate was collected and cooled to room temperature.

[0051] (6) Ozone catalytic oxidation of COD: O3 and MnO2 are introduced into the evaporation condensate obtained in step 5. The mass ratio of O3 to COD in the evaporation condensate is 5:1. The amount of MnO2 used is 0.1 g / L of evaporation condensate. After aeration reaction for 1.5 h, the oxidized liquid is obtained.

[0052] (7) Reverse osmosis separation and impurity removal: The residual COD and NO3 in the oxidized solution obtained in step 6 are removed using a reverse osmosis device. - Complete separation and removal are carried out, with a water production rate of 90%. The reverse osmosis permeate meets the discharge standards, and the reverse osmosis concentrate is dehydrated and dried by outsourced treatment.

[0053] (8) Sludge dewatering: The nanofiltration concentrate obtained in step 4, the evaporation mother liquor obtained in step 5, and the reverse osmosis concentrate obtained in step 7 are dried at a temperature of 60°C until the solid content is 60%, and then further filtered into general solid waste.

[0054] Table 1 shows the water quality of silver powder wastewater before and after treatment, Table 2 shows the quality of silver sulfide products, and the XRD diffraction patterns of silver sulfide products are shown in the figure. Figure 2 As shown.

[0055] Comparative Example 1

[0056] The composition of the wastewater from a silver powder production process is the same as that in Example 1.

[0057] This comparative example provides a method for treating high-salt, high-COD silver powder wastewater, including the following steps:

[0058] (1) Silver powder wastewater preservation: The silver powder wastewater collected on the production line is placed in a cool, dark place to prevent the silver powder wastewater from deteriorating and becoming unable to effectively remove PVP through nanofiltration equipment.

[0059] (2) Neutralization with caustic soda: Add industrial caustic soda to the silver powder wastewater to carry out a neutralization reaction. The amount of caustic soda used is 14.5 g / L. Adjust the pH value of the solution to 6.5 to obtain the neutralized solution.

[0060] (3) Sodium sulfide precipitation of silver: A 30% sodium sulfide solution was added to the neutralized liquid obtained in step 2 for silver precipitation. The amount of pure sodium sulfide used was 12.18 mg / L of the neutralized liquid (twice the theoretical amount). After stirring for 1 hour, the solid and liquid were separated to obtain filter residue and silver precipitation liquid. The filter residue was washed 4 times with distilled water, with the mass of distilled water being 5 times the mass of the filter residue. After washing, it was placed in a drying oven and dried at 100℃ for 24 hours to obtain silver sulfide product. The silver precipitation liquid was a mixed solution of VC, PVP and sodium nitrate.

[0061] (4) Nanofiltration removal of PVP: PVP was removed from the silver-precipitated solution obtained in step 3 using a nanofiltration device. The nanofiltration device had a membrane pore size of 1.8-3.0 nm and a membrane flux of 15 L / m³. 2 The silver-precipitated solution was concentrated 6 times, and the conductivity of the permeate was reduced to 78 μS / cm. While continuously introducing the silver-precipitated solution, the nanofiltration concentrate was continuously circulated in the system. PVP was separated into the nanofiltration concentrate, and the PVP removal rate was >95%. The main components of the nanofiltration permeate were vitamin C and sodium nitrate.

[0062] (5) MVR simulated evaporation: The nanofiltration permeate obtained in step 4 was subjected to MVR simulated evaporation with an evaporation ratio of 7 times and a boiling point temperature rise of 7°C to obtain the mother liquor and condensate. The condensate was collected and cooled to room temperature.

[0063] (6) Ozone catalytic oxidation of COD: O3 and MnO2 are introduced into the evaporation condensate obtained in step 5. The mass ratio of O3 to COD in the evaporation condensate is 3:1, and the amount of MnO2 is 0.1 g / L. After aeration for 1.5 h, the oxidized liquid is obtained.

[0064] (7) Sludge dewatering: The nanofiltration concentrate obtained in step 4 and the evaporation mother liquor obtained in step 5 are dried at 60°C to a solid content of 60% using a rotary drum dryer, and then further filtered into general solid waste.

[0065] Table 1 shows the water quality of silver powder wastewater before and after treatment, and Table 2 shows the quality of silver sulfide products.

[0066] Table 1. Influent and effluent water quality of silver powder wastewater (mg / L)

[0067]

[0068] Note: GB8978-1996 is the Integrated Wastewater Discharge Standard, and GB31573-2015 is the Indirect Discharge Standard for Pollutants from Inorganic Chemical Industry.

[0069] Table 2. Product Specifications (%) of Silver Sulfide

[0070] product Ag S TN Na Example 1 87.25 12.73 <0.01％ <0.01％ Comparative Example 1 87.07 12.90 <0.01％ <0.01％ Example 2 87.12 12.85 <0.01％ <0.01％

[0071] Note: Currently, there are no national or industry standards for silver sulfide products; purity is the primary indicator for evaluating product quality.

[0072] The step of treating the oxidized liquid with reverse osmosis equipment was omitted in Comparative Example 1. As shown in Table 1, the effluent quality of the systems in Examples 1 and 2 both meet the Class I standard of the "Integrated Wastewater Discharge Standard" and the indirect discharge standard of the "Inorganic Chemical Industry Pollutant Discharge Standard." However, the TN in Comparative Example 1 is significantly higher than that in Examples 1 and 2, failing to meet the aforementioned discharge standards. Therefore, it is quite necessary to combine reverse osmosis with ozone catalytic oxidation for advanced treatment.

[0073] The silver sulfide products recovered in Examples 1, 2 and Comparative Example 1 are of high purity, free of other impurities, and can be sold externally, thus having economic benefits.

[0074] For those skilled in the art, various corresponding changes and modifications can be made based on the above technical solutions and concepts, and all such changes and modifications should be included within the protection scope of the claims of this invention.

Claims

1. A method for treating high-salt, high-COD silver powder wastewater, characterized in that, Includes the following steps: Step 1, Silver Powder Wastewater Preservation: Store the collected silver powder wastewater in a cool, dark place to prevent it from deteriorating and becoming unusable for effective PVP removal by nanofiltration equipment; Step 2, Caustic soda neutralization: Add industrial caustic soda to the silver powder wastewater to carry out a neutralization reaction, adjust the pH value of the silver powder wastewater to 5-8, and obtain the neutralized liquid; Step 3, Silver Sulfide Precipitation: Add sodium sulfide solution to the neutralized liquid obtained in Step 2 to perform silver sulfide precipitation. After stirring and reacting fully, separate the solid and liquid to obtain filter residue and silver precipitation liquid. Wash the filter residue with distilled water, and dry the washed filter residue in a drying oven to obtain silver sulfide product. The silver precipitation liquid is a mixed solution of VC, PVP and sodium nitrate. Step 4, PVP removal by nanofiltration: The silver-precipitated liquid obtained in Step 3 is subjected to PVP removal using a nanofiltration device. The nanofiltration device continuously concentrates the silver-precipitated liquid, and while continuously introducing the silver-precipitated liquid, the nanofiltration concentrate is continuously circulated within the nanofiltration device to gradually increase the concentration factor; PVP is separated into the nanofiltration concentrate; the nanofiltration device finally obtains nanofiltration concentrate and nanofiltration permeate, the main components of which are vitamin C and sodium nitrate. Step 5, MVR simulated evaporation: The nanofiltration permeate obtained in step 4 is subjected to MVR simulated evaporation to obtain mother liquor and condensate. The condensate is collected and cooled to room temperature. Step 6, Ozone catalytic oxidation of COD: O3 and MnO2 catalysts are introduced into the condensate obtained in step 5. Most of the COD in the condensate is removed through an aeration reaction to obtain the oxidized liquid. Step 7, Reverse Osmosis Separation and Impurity Removal: The residual COD and NO3 in the oxidized solution obtained in Step 6 are removed using a reverse osmosis system. - Separation and removal are performed to obtain reverse osmosis permeate and reverse osmosis concentrate, and the reverse osmosis permeate is discharged in compliance with standards. Step 8, Sludge Dewatering: The nanofiltration concentrate obtained in Step 4, the evaporation mother liquor obtained in Step 5, and the reverse osmosis concentrate obtained in Step 7 are dried to a sludge cake with a solid content of 40-60% using a rotary drum dryer, and then further filtered into general solid waste.

2. The processing method according to claim 1, characterized in that, In step 3, the sodium sulfide solution has a mass concentration of 10%-30%, the mass amount of pure sodium sulfide is 1.5-3 times the theoretical mass amount calculated based on the silver content in the neutralized solution, and the stirring reaction time for silver sulfide precipitation is 1-2.5 hours.

3. The processing method according to claim 1, characterized in that, In step 3, the filter residue is washed 2-4 times with distilled water, and the mass ratio of distilled water to filter residue is 3:1-10:

1. The drying temperature of the washed filter residue is 40-100℃, and the drying time is 24-48h.

4. The processing method according to claim 1, characterized in that, In step 4, the concentration factor of the nanofiltration equipment is 5-10 times, the pore size of the nanofiltration membrane in the nanofiltration equipment is 1-3 nm, and the membrane flux is 5-30 L / m³. 2 ·h.

5. The processing method according to claim 1, characterized in that, In step 4, the nanofiltration device has a PVP rejection rate of >90%.

6. The processing method according to claim 1, characterized in that, In step 5, the MVR simulates evaporation by a factor of 5-9, and the boiling point temperature rise ranges from 5℃ to 10℃.

7. The processing method according to claim 1, characterized in that, In step 6, the mass ratio of O3 to COD in the condensate is 3:1-6:1, the amount of MnO2 catalyst is 0.01-0.50 g / L of condensate, and the aeration time is 1-2.5 h.

8. The processing method according to claim 1, characterized in that, In step 7, the reverse osmosis permeate rate is 80%-90%.

9. The processing method according to claim 1, characterized in that, In step 8, the drum dryer must be designed to be explosion-proof, maintain inert gas protection during the drying process, and reduce the oxygen concentration.

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