A comprehensive treatment method for silver cyanide production wastewater

Abstract

The application discloses a comprehensive treatment method for cyanide silver production wastewater, free cyanide is removed by using a sodium sulfite-air method to break cyanide, and the efficiency of subsequent silver recovery can be improved to a certain extent; then, the silver in the wastewater is recovered and purified by using an electrolysis-melting casting method, high-value resource utilization of the silver in the wastewater is realized; then, the operation energy consumption of MVR is reduced in a manner of combining reverse osmosis pre-concentration and MVR evaporation, so that the operation cost of wastewater desalination is reduced; finally, the reverse osmosis fresh water and the condensed water enter a biochemical system, and the wastewater is treated to reach the discharge standard.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater harmless treatment and resource utilization technology, specifically to a comprehensive treatment method for silver cyanide production wastewater. Background Technology

[0002] Electroplating is a crucial component of modern industry, and silver plating plays a pivotal role, determining the conductivity, thermal conductivity, corrosion resistance, and solderability of silver-plated components. Silver cyanide is a key raw material in this process. Currently, the main preparation processes for silver cyanide include the metallic silver method, metathesis method, silver chloride method, and sodium cyanide reduction method. Among these, the sodium cyanide reduction method has become a new trend in industrial silver cyanide preparation due to its advantages such as high reaction efficiency, high product purity, simple equipment operation, and low operating costs. The wastewater generated during the sodium cyanide reduction process is characterized by strong acidity and high salinity, and contains toxic and harmful substances such as cyanide and heavy metals. Currently, this wastewater is mostly treated using alkaline chlorination to break down cyanide and chemical precipitation to remove heavy metals. While this can treat the wastewater to meet discharge standards, this method suffers from problems such as large reagent consumption, high wastewater system operating costs, and the ineffective utilization of the valuable metallic silver in the wastewater. Therefore, it is of great significance to develop a comprehensive treatment method for silver cyanide production wastewater that has stable treatment effect, significant economic benefits, and can efficiently recover silver from the wastewater. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention aims to provide a comprehensive treatment method for silver cyanide production wastewater. The method employs a comprehensive approach combining sodium sulfite-air cyanide removal, electrolytic melting and silver recovery, reverse osmosis, evaporation, and biochemical treatment. Specifically, it develops sodium sulfite-air cyanide removal and electrolytic melting and silver recovery processes for silver cyanide production wastewater, and integrates these processes with membrane treatment, MVR evaporation, and biochemical treatment. This approach not only achieves low-cost treatment of silver cyanide production wastewater to meet discharge standards but also enables high-efficiency recovery and utilization of silver from the wastewater.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A comprehensive treatment method for silver cyanide production wastewater includes the following steps: S1. Alkalinity Adjustment: The pH value of the silver cyanide production wastewater is adjusted to 10.5 using alkali to obtain the alkali-adjusted solution. S2, Sodium sulfite-air method for cyanide removal: Sodium sulfite is added to the alkaline solution obtained in step S1 and air is introduced. After sufficient aeration and reaction, the cyanide-removed solution is obtained. S3. Electrolytic-casting method for silver recovery and purification: The cyanide-removed liquid obtained in step S2 is passed into an electrolytic cell for primary electrolysis to obtain a primary silver-recovered liquid. Crude silver is obtained from the cathode plate of the electrolytic cell. The obtained crude silver is mixed with flux and placed in a crucible, which is then placed in a high-temperature furnace for melting. The molten silver liquid is sampled at high temperature to remove slag, and then slowly poured into a preheated graphite mold for casting. After cooling, it is demolded to obtain a silver ingot. The silver ingot is dissolved in nitric acid solution and then subjected to secondary electrolysis to obtain a secondary silver-recovered liquid. High-purity silver powder is obtained from the cathode plate of the electrolytic cell. The high-purity silver powder is recycled to the upstream silver cyanide preparation production line. S4. Reverse osmosis pre-concentration: The primary and secondary post-cash liquids obtained in step S3 are mixed to obtain a mixed electrolyte. The pH of the mixed electrolyte is adjusted to 6.5 using sulfuric acid to obtain a neutralized liquid. A portion of the neutralized liquid is pre-concentrated using a reverse osmosis device. The resulting reverse osmosis concentrate is then fed into an evaporation system for further concentration to obtain evaporation mother liquor. The other portion of the neutralized liquid, the reverse osmosis permeate produced by pre-concentration, and the condensate produced by evaporation are transferred to step S6 for processing. S5. Evaporation: The mother liquor obtained in step S4 is dried using a drying device and then sent to the sludge treatment system for further dehydration. S6. Anaerobic-Anoxic-Aerobic Biological System Treatment: The reverse osmosis freshwater, evaporated condensate, and another portion of the neutralized liquid from step S4 are mixed and incorporated into the biological system. In the biological system, the liquid flows sequentially through the anaerobic tank, the anoxic tank, and the aerobic tank. The anaerobic tank contains hydrolytic acidifying bacteria, the anoxic tank contains denitrifying bacteria, and the aerobic tank contains nitrifying bacteria and aerobic heterotrophic bacteria. By utilizing the biochemical action of microorganisms under different operating conditions, denitrification and COD removal are further achieved, ensuring that the effluent meets the discharge standards. S7. Sludge off-site transportation: The sludge discharged from the sludge treatment system in step S5 and the biochemical system in step S6 is periodically transported to the sludge filter press room for filtration and then outsourced for further treatment.

[0005] Furthermore, in step S1, the alkali used is caustic soda flakes.

[0006] Further, in step S2, the amount of sodium sulfite used is 2.0-4.0 g per liter of the alkali-adjusted solution, and the aeration rate is 65-100 L per liter of the alkali-adjusted solution. The TCN and CN content in the cyanide-degrading solution... - The content is less than 0.3 mg / L; the aeration reaction time is 1.5 h.

[0007] Furthermore, in step S3, during the single electrolysis process, the electrolytic cell operates at a temperature of 50-70℃, a voltage of 3-5V, and a current density of 0.1-0.5A / cm³. 2The electrolysis time is 90 min; the temperature of the high-temperature furnace during the crude silver melting and casting process is 800-1050℃, and the temperature is gradually increased to the melting temperature within 0.5 h, with a melting time of 1.0-2.0 h. Borax is used as the flux, and the amount of borax is 0.3% of the crude silver mass. During the secondary electrolysis process, the pH value of the silver nitrate solution is <1, and the operating temperature, voltage, current density, and electrolysis time of the electrolytic cell are the same as those of the primary electrolysis process. The mass concentration of the nitric acid solution is 8%.

[0008] Furthermore, in step S3, the purity of crude silver is ≥90%, the purity of silver ingots is ≥95%, and the purity of high-purity silver powder is ≥99.99%.

[0009] Further, in step S4, the acid used is sulfuric acid; in the reverse osmosis equipment, the reverse osmosis water production rate is 30-50%, the TN removal rate is >85%, and the COD removal rate is >85%; the evaporation system uses an MVR evaporator with an evaporation ratio of 3-5 times and a boiling point temperature rise range of 3℃-6℃; the COD concentration in the condensate produced by evaporation is <150ppm, TN <300ppm, and BOD5 / COD >0.3.

[0010] Furthermore, in step S4, based on the carbon-nitrogen ratio of the influent to the biological system in step S6, 10-25% of the total mass of the neutralized liquid is directly transferred into step S6, where it is mixed with the reverse osmosis freshwater and condensate from step S4 and incorporated into the biological system for treatment.

[0011] Furthermore, in step S6, the sludge return ratio of the biological system is controlled at 100%-150%, the C / N ratio is 5:1-10:1, the carbon source is glucose or flour, and the sludge discharge cycle is 15-20 days.

[0012] Further, in step S6, the temperature of the anaerobic tank is 40℃, the pH value is 7.0-8.0, the dissolved oxygen content is <0.2ppm, and the hydraulic retention time is 1-2h; the temperature of the anoxic tank is 30℃, the pH value is 7.0-8.0, the dissolved oxygen content is 0.2-0.5ppm, and the hydraulic retention time is 2-4h; the temperature of the aerobic tank is 30℃, the pH value is 8.0-8.5, the dissolved oxygen content is 2.0-4.0ppm, and the hydraulic retention time is 6-8h.

[0013] The beneficial effects of this invention are as follows: 1) The wastewater treated by the method of the present invention has stable water quality and significant economic benefits. The water quality meets the Class I standard of the "Integrated Wastewater Discharge Standard", the direct discharge standard of the "Electronic Industry Water Pollutant Discharge Standard", and the indirect discharge standard of the "Inorganic Chemical Industry Pollutant Discharge Standard", etc., and realizes low-cost operation of the wastewater system and high-value resource utilization of silver.

[0014] 2) This invention uses an electrolytic-smelting method to recover silver from wastewater. It can not only recover high-purity silver powder products at low cost from wastewater with high impurity content and low silver content, but also successfully reuse the silver powder in the upstream silver cyanide production line to solve the problem of silver powder sales, resulting in significant economic benefits.

[0015] 3) The sodium sulfite-air process for cyanide removal developed in this invention for silver cyanide production wastewater is an improved version of the Inco process. This process not only overcomes the need for additional Cu addition in the Inco process, but also... 2+ The catalyst issue is also addressed, and the operating cost is significantly reduced compared to the traditional alkaline sodium hypochlorite method. Furthermore, the equipment is simple, the reaction efficiency is high, and it is easy to industrialize.

[0016] 4) This invention utilizes reverse osmosis equipment to pre-concentrate wastewater before MVR evaporation, which can reduce the operating energy consumption of the MVR evaporator and has a significant operating cost advantage in the application scenario of large-scale silver cyanide production wastewater systems.

[0017] 5) This invention solves the problem of low carbon-nitrogen ratio in the biochemical system by directly mixing the partially neutralized liquid with reverse osmosis fresh water and evaporation condensate into the biochemical system. This greatly reduces the use of external carbon sources, ensuring the stable operation of the biochemical system and reducing operating costs.

[0018] 6) This invention combines sodium sulfite-air cyanide removal technology, electrolytic melting and silver recovery technology with traditional reverse osmosis concentration technology, evaporation drying technology, and biochemical denitrification and COD removal technology. This not only simplifies the wastewater process and stabilizes the system operation, but also reduces operating costs and generates significant economic benefits. Therefore, this process is easy to implement in industrial applications. Attached Figure Description

[0019] Figure 1 The flowcharts are for embodiments 1-3 of the present invention. Figure 2 This is the XRD diffraction pattern of the high-purity silver powder obtained in Example 2 of the present invention. Detailed Implementation

[0020] 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.

[0021] Example 1

[0022] The wastewater generated during the preparation of silver cyanide plating materials by a certain company mainly consists of: TCN (CN) - ) 153.10mg / L, COD 89.73mg / L, NH3-N 70.34mg / L, Na 16.38g / L, NO3- 45.48g / L, Ag 4.52mg / L, pH=0.33.

[0023] This embodiment provides a comprehensive treatment method for silver cyanide production wastewater, such as... Figure 1 As shown, the specific steps include the following: S1. Alkalinity Adjustment: The pH of the silver cyanide production wastewater is adjusted to 10.5 using caustic soda flakes at a dosage of 11.36 g / L. 氰化银生产废水 The alkali-adjusted solution was obtained.

[0024] S2, Sodium sulfite-air method for cyanide destruction: Add 2.0 g / L of the alkali-adjusted solution obtained in step S1. 调碱后液 The dosage is sodium sulfite, and 65 L / L is introduced. 调碱后液 After aeration with air for 1.5 hours, the cyanide-decomposed liquid is obtained.

[0025] S3. Electrolytic-smelting method for silver recovery and purification: The cyanide-crushed liquid obtained in step S2 is passed into an electrolytic cell for primary electrolysis. The electrolytic cell operates at a temperature of 50℃, a voltage of 3V, and a current density of 0.1A / cm³. 2 After electrolysis for 90 minutes, a primary silver-collected liquid is obtained, and crude silver is obtained from the cathode plate of the electrolytic cell. 0.3% borax by mass is added to the crude silver and then placed in a crucible and melted in an 800℃ high-temperature furnace for 1 hour. The temperature is gradually increased to 800℃ over 0.5 hours. The molten silver liquid is sampled at high temperature to remove slag, and then slowly poured into a preheated graphite mold for casting. After cooling, the silver block is demolded to obtain a silver ingot. The silver ingot is dissolved in 8% nitric acid (pH < 1) and then subjected to secondary electrolysis to obtain a secondary electrolytic liquid. The operation of the electrolytic cell is the same as that of the primary electrolysis. High-purity silver powder is obtained from the cathode plate of the electrolytic cell and is recycled to the upstream silver cyanide preparation production line.

[0026] S4. Reverse osmosis pre-concentration: The primary and secondary post-cash solutions obtained in step S3 are mixed to obtain a mixed electrolyte. The pH of the mixed electrolyte is adjusted to 6.5 using sulfuric acid at a concentration of 12.30 g / L. 混合电解液 The neutralized liquid is obtained, and the reverse osmosis unit pre-concentrates 90% of the neutralized liquid, resulting in a reverse osmosis permeate rate of 30%. The reverse osmosis concentrate is then concentrated by evaporation using an MVR evaporator, with an evaporation ratio of 3 times and a boiling point temperature rise of 3°C. Both the reverse osmosis permeate and the condensate from evaporation are sent to step S6 for biological system treatment. Additionally, 10% of the neutralized liquid is sent to step S6 for biological system treatment.

[0027] S5. Evaporation: The mother liquor from evaporation is dried using a belt dryer and then enters the sludge treatment system for further dehydration.

[0028] S6. Anaerobic-Anoxic-Aerobic Biological System Treatment: The 10% neutralized liquid from step S4, reverse osmosis freshwater, and evaporation condensate are mixed and incorporated into the biological system. The mixture flows sequentially through the anaerobic, anoxic, and aerobic tanks. Further denitrification and COD removal occur through the respiration of hydrolytic acidifying bacteria in the anaerobic tank (temperature 40℃, pH 7.0-8.0, dissolved oxygen <0.2ppm, hydraulic retention time 1h), denitrifying bacteria in the anoxic tank (temperature 30℃, pH 7.0-8.0, dissolved oxygen 0.2ppm, hydraulic retention time 2h), and nitrifying and aerobic heterotrophic bacteria in the aerobic tank (temperature 30℃, pH 8.0-8.5, dissolved oxygen 2.0ppm, hydraulic retention time 6h). The effluent meets discharge standards. The sludge return ratio of the biological system is controlled at 100%, the C / N ratio is 5:1, glucose is selected as the carbon source, and the sludge discharge cycle is 15 days.

[0029] S7. Sludge off-site transportation: The sludge generated by the sludge treatment system in step S5 and the biochemical system in step S6 is periodically transported to the sludge filter press room for filtration and then outsourced for further treatment. The sludge moisture content is 65%.

[0030] Example 2

[0031] The wastewater generated during the preparation of silver cyanide products for silver plating by a certain company has the same composition as in Example 1.

[0032] The comprehensive treatment method for silver cyanide production wastewater in this embodiment specifically includes the following steps: S1. Alkalinity Adjustment: The pH of the silver cyanide production wastewater is adjusted to 10.5 using caustic soda flakes at a dosage of 11.36 g / L. 氰化银生产废水 The alkali-adjusted solution was obtained.

[0033] S2, Sodium sulfite-air method for cyanide destruction: Add 3.0 g / L of the alkali-adjusted solution obtained in step S1. 调碱后液 The dosage is sodium sulfite, and 65 L / L is introduced. 调碱后液 After aeration with air for 1.5 hours, the cyanide-decomposed liquid is obtained.

[0034] S3. Silver recovery and purification via electrolysis-smelting: The cyanide-crushed liquid obtained in step S2 is passed into an electrolytic cell for primary electrolysis. The electrolytic cell operates at a temperature of 60℃, a voltage of 5V, and a current density of 0.5A / cm³. 2After electrolysis for 90 minutes, a primary silver-collected liquid is obtained, and crude silver is obtained from the cathode plate of the electrolytic cell. 0.3% borax by weight is added to the crude silver, and the mixture is placed in a crucible and melted in an 850℃ high-temperature furnace for 1.5 hours. The temperature is gradually increased to 850℃ over 0.5 hours. A high-temperature sample of the molten silver is taken to remove slag, and then slowly poured into a preheated graphite mold for casting. After cooling, the silver ingot is demolded to obtain a silver block. The silver block is dissolved in 8% nitric acid (pH < 1) and then subjected to a second electrolysis to obtain a secondary electrolytic liquid. The electrolytic cell operates in the same manner as the primary electrolysis. High-purity silver powder is obtained from the cathode plate of the electrolytic cell and is recycled to the upstream silver cyanide preparation production line. S4. Reverse osmosis pre-concentration: The post-cash liquid obtained in step S3 and the post-electrolysis liquid are mixed to obtain a mixed electrolyte. The pH value of the mixed electrolyte is adjusted to 6.5 using sulfuric acid at a concentration of 12.30 g / L. 混合电解液 The neutralized liquid is obtained, and 85% of its mass is pre-concentrated using a reverse osmosis system, resulting in a reverse osmosis permeate rate of 50%. The reverse osmosis concentrate is then concentrated by evaporation using an MVR evaporator at a 5-fold evaporation ratio and a boiling point temperature rise of 6°C. Both the reverse osmosis permeate and the condensate from evaporation are sent to step S6 for biological system treatment. The remaining 15% of the neutralized liquid is also sent to step S6 for biological system treatment.

[0035] S5. Evaporation: The mother liquor obtained from the evaporation of reverse osmosis concentrate is dried using a belt dryer and then enters the sludge treatment system for further dehydration. The amount of mother liquor is 15% of the influent volume.

[0036] S6. Anaerobic-Anoxic-Aerobic Biological System: The neutralized liquid (15% by mass) from step S4, reverse osmosis freshwater, and evaporation condensate are mixed and fed into the biological system. The mixture flows sequentially through the anaerobic, anoxic, and aerobic tanks. Further denitrification and COD removal occur through the respiration of hydrolytic acidifying bacteria in the anaerobic tank (temperature 40℃, pH 7.0-8.0, dissolved oxygen <0.2ppm, hydraulic retention time 2h), denitrifying bacteria in the anoxic tank (temperature 30℃, pH 7.0-8.0, dissolved oxygen 0.3ppm, hydraulic retention time 2h), and nitrifying and aerobic heterotrophic bacteria in the aerobic tank (temperature 30℃, pH 8.0-8.5, dissolved oxygen 4.0ppm, hydraulic retention time 6h). The effluent meets discharge standards. The sludge return ratio of the biological system is controlled at 120%, the C / N ratio is 7:1, glucose is selected as the carbon source, and the sludge discharge cycle is 15 days.

[0037] S7. Sludge off-site transportation: The sludge generated by the sludge treatment system in step S5 and the biochemical system in step S6 is periodically transported to the sludge filter press room for filtration and then outsourced for further treatment. The sludge moisture content is 65%.

[0038] Example 3

[0039] The wastewater generated during the preparation of silver cyanide products for silver plating by a certain company has the same composition as in Example 1.

[0040] The comprehensive treatment method for silver cyanide production wastewater in this embodiment specifically includes the following steps: S1. Alkalinity Adjustment: The pH of the silver cyanide production wastewater is adjusted to 10.5 using caustic soda flakes at a dosage of 11.36 g / L. 氰化银生产废水 The alkali-adjusted solution was obtained.

[0041] S2, Sodium sulfite-air method for cyanide removal: Add 4.0 g / L of the alkali-adjusted solution obtained in step S1. 调碱后液 Add sodium sulfite and purge with 100 L / L 调碱后液 After aeration with air for 1.5 hours, the cyanide-decomposed liquid is obtained.

[0042] S3. Silver recovery and purification via electrolysis-smelting method: The cyanide-crushed liquid obtained in step S2 is passed into an electrolytic cell for primary electrolysis. The electrolytic cell operates at a temperature of 70℃, a voltage of 5V, and a current density of 0.5A / cm³. 2 After electrolysis for 90 minutes, a primary silver-collected liquid is obtained, and crude silver is obtained from the cathode plate of the electrolytic cell. 0.3% borax by mass is added to the crude silver and then placed in a crucible and melted in a high-temperature furnace at 1050℃ for 2 hours. The temperature is gradually increased to 1050℃ over 0.5 hours. The molten silver liquid is sampled at high temperature to remove slag, and then slowly poured into a preheated graphite mold for casting. After cooling, the silver block is demolded to obtain a silver ingot. The silver ingot is dissolved in 8% nitric acid (pH < 1) and then subjected to a second electrolysis to obtain a secondary electrolytic liquid. The operation of the electrolytic cell is the same as that of the primary electrolysis. High-purity silver powder is obtained from the cathode plate of the electrolytic cell and is recycled to the upstream silver cyanide preparation production line.

[0043] S4. Reverse osmosis pre-concentration: The primary and secondary electrolytes obtained in step S3 are mixed to obtain a mixed electrolyte. The pH of the mixed electrolyte is adjusted to 6.5 using sulfuric acid at a concentration of 12.30 g / L. 混合电解液 After obtaining the neutralized liquid, the reverse osmosis unit pre-concentrates 75% of the neutralized liquid, achieving a reverse osmosis permeate rate of 50%. The reverse osmosis concentrate is then concentrated by evaporation using an MVR evaporator, with an evaporation ratio of 5 times and a boiling point temperature rise of 6°C. Both the reverse osmosis permeate and the condensate from evaporation are sent to step S6 for biological system treatment. Additionally, the remaining 25% of the neutralized liquid is sent to step S6 for biological system treatment.

[0044] S5. Evaporation: The mother liquor produced by the evaporation of reverse osmosis concentrate is dried using a belt dryer and then enters the sludge treatment system for further dehydration.

[0045] S6. Anaerobic-Anoxic-Aerobic Biological System: 25% of the neutralized liquid from step S4, reverse osmosis freshwater, and evaporation condensate are mixed and fed into the biological system. The mixture flows sequentially through the anaerobic, anoxic, and aerobic tanks. Further denitrification and COD removal occur through the respiration of hydrolytic acidifying bacteria in the anaerobic tank (temperature 40℃, pH 7.0-8.0, dissolved oxygen <0.2ppm, hydraulic retention time 2h), denitrifying bacteria in the anoxic tank (temperature 30℃, pH 7.0-8.0, dissolved oxygen 0.5ppm, hydraulic retention time 4h), and nitrifying and aerobic heterotrophic bacteria in the aerobic tank (temperature 30℃, pH 8.0-8.5, dissolved oxygen 4.0ppm, hydraulic retention time 8h). The effluent meets discharge standards. The sludge return ratio of the biological system is controlled at 150%, the C / N ratio is 10:1, glucose is selected as the carbon source, and the sludge discharge cycle is 20 days.

[0046] S7. Sludge transportation: The sludge from the sludge treatment system in step S5 and the biochemical system in step S6 is periodically transported to the sludge filter press room for filtration and then outsourced for further processing. The sludge moisture content is 65%.

[0047] Table 1 shows the influent water quality and aerobic tank effluent water quality of silver cyanide production wastewater in Examples 1-3. Table 2 shows the product indicators of crude silver, silver ingots, and high-purity silver powder in step S3. The XRD diffraction pattern of the high-purity silver powder obtained in Example 3 is shown in Table 2. Figure 2 As shown.

[0048] Table 1. Influent water quality and aerobic tank effluent water quality (mg / L)

[0049] Note: GB8978-1996 is the Integrated Wastewater Discharge Standard, GB39731-2020 is the Water Pollutant Discharge Standard for the Electronic Industry, and GB31573-2015 is the Indirect Pollutant Discharge Standard for the Inorganic Chemical Industry.

[0050] Table 2 Product Indicators (%) of Crude Silver, Silver Ingots and High-Purity Silver Powder

[0051] Note: High-purity silver powder is the same as ordinary silver powder, used in the upstream silver cyanide preparation production line. Ordinary silver powder is mainly characterized by purity, without special standard references or morphology requirements.

[0052] As can be seen, the effluent quality of Examples 1, 2, and 3 all meet the Class I standard of the "Integrated Wastewater Discharge Standard," the direct discharge standard of the "Electronic Industry Water Pollutant Discharge Standard," and the indirect discharge standard of the "Inorganic Chemical Industry Pollutant Discharge Standard," indicating that the methods of Examples 1-3 can effectively treat silver cyanide wastewater to meet discharge standards. The ordinary high-purity silver powder recovered in Examples 1, 2, and 3 not only has a purity ≥99.99%, but also a silver recovery rate >97% from the wastewater, indicating that Examples 1-3 have high resource utilization efficiency and certain economic benefits.

[0053] 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 comprehensive treatment method for silver cyanide production wastewater, characterized in that, Includes the following steps: S1. Alkalinity Adjustment: The pH value of the silver cyanide production wastewater is adjusted to 10.5 using alkali to obtain the alkali-adjusted solution. S2, Sodium sulfite-air method for cyanide removal: Sodium sulfite is added to the alkaline solution obtained in step S1 and air is introduced. After sufficient aeration and reaction, the cyanide-removed solution is obtained. S3. Electrolytic-casting method for silver recovery and purification: The cyanide-removed liquid obtained in step S2 is passed into an electrolytic cell for primary electrolysis to obtain a primary silver-recovered liquid. Crude silver is obtained from the cathode plate of the electrolytic cell. The obtained crude silver is mixed with flux and placed in a crucible, which is then placed in a high-temperature furnace for melting. The molten silver liquid is sampled at high temperature to remove slag, and then slowly poured into a preheated graphite mold for casting. After cooling, it is demolded to obtain a silver ingot. The silver ingot is dissolved in nitric acid solution and then subjected to secondary electrolysis to obtain a secondary silver-recovered liquid. High-purity silver powder is obtained from the cathode plate of the electrolytic cell. The high-purity silver powder is recycled to the upstream silver cyanide preparation production line. S4. Reverse osmosis pre-concentration: The primary and secondary silver-collected solutions obtained in step S3 are used to obtain a mixed electrolyte. The pH value of the mixed electrolyte is adjusted to 6.5 using sulfuric acid to obtain a neutralized solution. A portion of the neutralized solution is pre-concentrated using a reverse osmosis device. The resulting reverse osmosis concentrate is then fed into an evaporation system for further concentration to obtain evaporation mother liquor. The other portion of the neutralized solution, the reverse osmosis permeate produced by pre-concentration, and the condensate produced by evaporation are transferred to step S6 for processing. S5. Evaporation: The mother liquor obtained in step S4 is dried using a drying device and then sent to the sludge treatment system for further dehydration. S6. Anaerobic-Anoxic-Aerobic Biological System Treatment: The reverse osmosis freshwater, evaporated condensate, and another portion of the neutralized liquid from step S4 are mixed and incorporated into the biological system. In the biological system, the liquid flows sequentially through the anaerobic tank, the anoxic tank, and the aerobic tank. The anaerobic tank contains hydrolytic acidifying bacteria, the anoxic tank contains denitrifying bacteria, and the aerobic tank contains nitrifying bacteria and aerobic heterotrophic bacteria. By utilizing the biochemical action of microorganisms under different operating conditions, denitrification and COD removal are further achieved, ensuring that the effluent meets the discharge standards. S7. Sludge off-site transportation: The sludge discharged from the sludge treatment system in step S5 and the biochemical system in step S6 is periodically transported to the sludge filter press room for filtration and then outsourced for further treatment.

2. The method according to claim 1, characterized in that, In step S1, the alkali used is caustic soda flakes.

3. The method according to claim 1, characterized in that, In step S2, the dosage of sodium sulfite is 2.0-4.0 g per liter of the alkali-adjusted solution, and the aeration rate is 65-100 L per liter of the alkali-adjusted solution. The concentrations of TCN and CN in the solution after cyanide destruction are... - The content is less than 0.3 mg / L; the aeration reaction time is 1.5 h.

4. The method according to claim 1, characterized in that, In step S3, during the single electrolysis process, the electrolytic cell operates at a temperature of 50-70℃, a voltage of 3-5V, and a current density of 0.1-0.5A / cm³. 2 The electrolysis time is 90 min; the temperature of the high-temperature furnace during the crude silver melting and casting process is 800-1050℃, and the temperature is gradually increased to the melting temperature within 0.5 h, with a melting time of 1.0-2.0 h. Borax is used as the flux, and the amount of borax is 0.3% of the crude silver mass. During the secondary electrolysis process, the pH value of the silver nitrate solution is <1, and the operating temperature, voltage, current density, and electrolysis time of the electrolytic cell are the same as those of the primary electrolysis process. The mass concentration of the nitric acid solution is 8%.

5. The method according to claim 1, characterized in that, In step S3, the purity of crude silver is ≥90%, the purity of silver ingots is ≥95%, and the purity of high-purity silver powder is ≥99.99%.

6. The method according to claim 1, characterized in that, In step S4, the acid used is sulfuric acid; in the reverse osmosis equipment, the reverse osmosis water production rate is 30-50%, the TN removal rate is >85%, and the COD removal rate is >85%; the evaporation system uses an MVR evaporator with an evaporation ratio of 3-5 times and a boiling point temperature rise range of 3℃-6℃; the COD concentration in the condensate produced by evaporation is <150ppm, TN <300ppm, and BOD5 / COD >0.

3.

7. The method according to claim 1, characterized in that, In step S4, based on the carbon-nitrogen ratio of the influent to the biological system in step S6, 10-25% of the total mass of the neutralized liquid is directly transferred into step S6, where it is mixed with the reverse osmosis freshwater and condensate from step S4 and incorporated into the biological system for treatment.

8. The method according to claim 1, characterized in that, In step S6, the sludge return ratio of the biological system is controlled at 100%-150%, the C / N ratio is 5:1-10:1, glucose or flour is selected as the carbon source, and the sludge discharge cycle is 15-20 days.

9. The method according to claim 1, characterized in that, In step S6, the temperature of the anaerobic tank is 40℃, the pH value is 7.0-8.0, the dissolved oxygen content is <0.2ppm, and the hydraulic retention time is 1-2h; the temperature of the anoxic tank is 30℃, the pH value is 7.0-8.0, the dissolved oxygen content is 0.2-0.5ppm, and the hydraulic retention time is 2-4h; the temperature of the aerobic tank is 30℃, the pH value is 8.0-8.5, the dissolved oxygen content is 2.0-4.0ppm, and the hydraulic retention time is 6-8h.

Images