Method for recycling cyanide silver plating wastewater

Abstract

This invention discloses a method for recycling and reusing cyanide silver plating wastewater. The method includes four steps: separation of silver ions and cyanide, concentration of the silver-containing solution, cyanide concentration, electrolysis and residual liquid recycling, and reuse of reclaimed water. This method achieves the separate recycling and reuse of silver, cyanide, and water. The silver-containing solution is electrolyzed to obtain metallic silver, the cyanide concentrate's main component is sodium cyanide or potassium cyanide solution, and the reclaimed water with a conductivity below 20 μS / cm is reused in the production line. This method not only maximizes resource utilization and reduces wastewater discharge, but also separates most of the cyanide from the silver-containing solution during electrolysis, making the electrolysis process safer. Furthermore, the residual liquid after electrolysis can be recycled multiple times for the separation and concentration of silver ions and cyanide.

Description

Technical Field

[0001] This invention relates to the field of water treatment, and in particular to a method for recycling and reusing cyanide silver plating wastewater. Background Technology

[0002] Cyanide silver plating remains the mainstream process for electroplating silver. The silver plating layer produced by this process still has significant advantages in performance and cost within the industry. However, the wastewater generated by this process contains extremely high concentrations of highly toxic cyanide and a certain amount of silver. Its discharge not only causes serious environmental damage but also results in a significant waste of resources. Currently, many studies and technologies exist for the recycling and reuse of this type of wastewater, but they all have many problems. In particular, it is impossible to separate cyanide from silver before electrolysis, leading to the generation of highly toxic gases such as hydrogen cyanide during electrolysis, posing a safety hazard. Furthermore, the large amount of cyanide consumed during electrolysis also wastes resources, and the electrolysis recovery speed and silver recovery efficiency are not ideal. To address this issue, we provide a method for recycling and reusing cyanide silver plating wastewater. This method not only separates cyanide from silver before electrolysis, but also recycles and reuses silver, cyanide, and water separately. The silver-containing solution is electrolyzed to obtain metallic silver, the cyanide concentrate is mainly composed of sodium cyanide or potassium cyanide solution, and the regenerated water with a conductivity of less than 20 μs / cm is reused in the production line. The residual liquid after electrolysis can also be recycled multiple times for the separation and concentration of silver ions and cyanide. Summary of the Invention

[0003] The purpose of this invention is to provide a method for recycling and reusing cyanide silver plating wastewater, so as to solve the problems mentioned in the background art.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for recycling and reusing cyanide silver plating wastewater includes the following four steps:

[0006] (1) The cyanide silver plating wastewater and the separating agent are simultaneously introduced into the raw water tank for mixing. After the mixture is evenly mixed, the silver ions and the separating agent form a large number of complexes. The mixture is separated from the cyanide by a first-stage nanofiltration system. Most of the cyanide is contained in the product water and enters the nanofiltration product water tank. The complexes formed by the silver ions and the separating agent and a small amount of cyanide are contained in the concentrated water and enter the silver-containing concentration tank. The silver-containing water in the silver-containing concentration tank is further separated and concentrated by a second-stage nanofiltration system. The cyanide continues to enter the nanofiltration product water tank through the product water of the second-stage nanofiltration system. When the total silver content in the concentrated water of the second-stage nanofiltration reaches 600mg / L-1200mg / L, it is pumped into the electrolysis system through the second-stage nanofiltration system.

[0007] (2) The cyanide-containing wastewater in the nanofiltration product water tank is then treated in the primary FO system. The product water of the primary FO system enters the FO product water tank. When the total cyanide in the concentrate of the primary FO system reaches 5g / L-20g / L, it enters the cyanide concentration tank and is finally pumped into the cyanide concentrate storage area for stripping or production recycling.

[0008] (3) Electrolysis begins 24 hours after the electrolysis system solution is collected. Metallic silver is deposited at the cathode. The small amount of cyanide contained in the electrolysis system solution is completely decomposed by electrolysis. When the total silver content in the electrolysis system solution is less than 10 mg / L, the residual liquid of the electrolysis system can be added back to the original water tank as a separating agent for recycling.

[0009] (4) The water produced by the secondary FO system enters the reclaimed water tank. If the conductivity is less than 20 μs / cm, it can be directly reused in the cyanide silver plating production line.

[0010] The separating agent in step (1) is composed of several of the following: sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, 5,5-dimethylhydantoin, sodium thioglycolate, potassium thioglycolate, sodium dodecyl sulfonate, potassium hydroxide, and water.

[0011] The separating agent contains sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, 5,5-dimethylhydantoin, sodium thioglycolate, potassium thioglycolate, sodium dodecyl sulfonate, potassium hydroxide, and water in proportions of 0%-6%, 0%-6%, 4-10%, 0-9%, 0-9%, 3-8%, 1-5%, and 62-79%, respectively. The mass of the separating agent added is 12-50 times the mass of the total silver in the cyanide silver plating wastewater.

[0012] In step (1), the first-stage nanofiltration system and the second-stage nanofiltration system have magnesium sulfate removal rates greater than 90% and sodium chloride removal rates less than 30%.

[0013] The operating pressure of the first-stage nanofiltration system and the second-stage nanofiltration system in step (1) is 4-9 bar.

[0014] The primary FO system and the secondary FO system described in steps (2) and (4) are forward osmosis systems composed of composite forward osmosis membranes.

[0015] The residual liquid in the electrolysis system described in step (3) is recycled 4-20 times.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] 1. In this invention, a separating agent is used to generate a stronger complexing effect with silver ions than silver cyanide complexes. Then, nanofiltration is used to retain the complexes and the separating agent to increase the concentration of the complexes and the separating agent in the wastewater. This causes the complexing reaction equilibrium to shift further towards a direction where the separating agent and silver ions are more complexed, thereby separating most of the silver cyanide complexes.

[0018] 2. Silver concentrate containing a separating agent can be electrolyzed at a higher current density. During the electrolysis process, the high current density enables the complete decomposition of the small amount of residual cyanide in the concentrate. The electrolysis process is safe and completely avoids the formation of hydrogen cyanide during electrolysis, which diffuses into the air and causes harm. The silver electrolysis speed is also faster and more thorough.

[0019] 3. The overall recovery rate of cyanide using forward osmosis is greater than 95%. It not only recovers water and silver, but also recovers cyanide, reducing the emission of highly toxic cyanide and creating more economic benefits.

[0020] 4. The main component of the residual electrolyte after electrolysis is the separating agent, which can be reused multiple times as a separating agent. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the steps and process flow of the present invention. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] Comparative Example 1

[0024] The silver content in the cyanide silver plating wastewater is 25 mg / L and the total cyanide content is 120 mg / L. Two-stage reverse osmosis is used to directly remove cyanide and silver into the concentrate. The silver content in the reverse osmosis permeate is 0.5 mg / L and the total cyanide content is 13 mg / L. The permeate is then treated with two-stage reverse osmosis to obtain pure water. Silver is obtained by electrolyzing the concentrate for 36 hours. However, highly toxic gases such as hydrogen cyanide are generated during the electrolysis process, and the cyanide cannot be efficiently reused.

[0025] Example 1

[0026] The silver content in the cyanide silver plating wastewater was 25 mg / L, and the total cyanide content was 120 mg / L. The separating agent consisted of potassium ethylenediaminetetraacetate, 5,5-dimethylhydantoin, potassium thioglycolate, potassium hydroxide, and water in a mass ratio of 6%, 10%, 9%, 8%, 5%, and 62%. The separating agent was added to the raw water tank at a concentration of 600 mg / L and mixed thoroughly. After thorough mixing, silver ions formed a large number of complexes with the separating agent. This mixture was then separated through a first-stage nanofiltration system at a pressure of 8 bar. The silver content in the first-stage nanofiltration product was 0.6 mg / L. The total cyanide content is 105 mg / L when it enters the nanofiltration product tank. The concentrate from the first-stage nanofiltration system enters the silver-containing concentration tank. The silver-containing water in the silver-containing concentration tank is further separated and concentrated by the second-stage nanofiltration system. The cyanide continues to enter the nanofiltration product tank through the product water of the second-stage nanofiltration system. The total cyanide concentration in the nanofiltration product tank can reach 116 mg / L. The magnesium sulfate removal rate of the first-stage nanofiltration system and the second-stage nanofiltration system is 98%, and the sodium chloride removal rate is 27%. When the total silver content in the concentrate from the second-stage nanofiltration system reaches 1000 mg / L, it is fed into the electrolysis system through the second-stage nanofiltration system.

[0027] The cyanide-containing wastewater in the nanofiltration permeate tank is then treated in the primary FO system. The permeate from the primary FO system enters the FO permeate tank. When the total cyanide in the concentrate of the primary FO system reaches 8 g / L, it enters the cyanide concentration tank and is finally pumped into the cyanide concentrate storage area for stripping or production recycling.

[0028] Electrolysis begins 24 hours after the solution is collected in the electrolysis system. Metallic silver is deposited at the cathode. The 11 mg / L cyanide in the electrolysis system solution is completely decomposed by electrolysis. When the total silver content in the system solution is less than 10 mg / L after 18 hours of electrolysis, the residual liquid of the electrolysis system is added back to the original water tank as a separating agent and recycled 15 times.

[0029] The water produced by the secondary FO system enters the reclaimed water tank. If the conductivity is less than 20 μs / cm, it can be directly reused in the cyanide silver plating production line.

[0030] Comparative Example 2

[0031] The silver content in the cyanide silver plating wastewater is 36 mg / L and the total cyanide content is 180 mg / L. The separating agent consists only of water. The separating agent is added to the raw water tank at a concentration of 1500 mg / L and mixed evenly. The mixture is then separated through a first-stage nanofiltration system at a pressure of 6 bar. The silver content in the first-stage nanofiltration permeate is 34 mg / L and the cyanide content is 172 mg / L. This permeate enters the nanofiltration permeate tank. The concentrated water from the first-stage nanofiltration enters the silver-containing concentration tank. The water in the silver-containing concentration tank is further separated and concentrated through a second-stage nanofiltration system. The permeate from the second-stage nanofiltration system enters the nanofiltration permeate tank. The magnesium sulfate removal rate of the first-stage and second-stage nanofiltration systems is 92%, and the sodium chloride removal rate is 19%. The total silver content in the concentrated water from the second-stage nanofiltration system is only 170 mg / L, which is not as high as 1200 mg / L. The total silver content is still as high as 34 mg / L. This water is then fed into the electrolysis system through the second-stage nanofiltration system.

[0032] The cyanide-containing wastewater in the nanofiltration permeate tank is then treated in the primary FO system. The permeate from the primary FO system enters the FO permeate tank. When the total cyanide in the concentrate of the primary FO system reaches 10 g / L, it enters the cyanide concentration tank and is finally pumped into the cyanide concentrate storage area for stripping or production recycling.

[0033] After collecting the solution for 24 hours, electrolysis was started at a limited current density. Metallic silver was deposited at the cathode. The 25 mg / L silver in the solution was completely decomposed by electrolysis. When the total silver content in the solution was less than 10 mg / L after 2 hours of electrolysis, the residual liquid of the electrolysis system was discharged. The 34 mg / L silver content in the product water was not effectively recovered.

[0034] The water produced by the secondary FO system enters the reclaimed water tank. If the conductivity is less than 20 μs / cm, it can be directly reused in the cyanide silver plating production line.

[0035] Example 2

[0036] The silver content in the cyanide silver plating wastewater was 36 mg / L, and the total cyanide content was 180 mg / L. The separating agent consisted of sodium ethylenediaminetetraacetate, 5,5-dimethylhydantoin, potassium thioglycolate, sodium hydroxide, and water in a mass ratio of 6%, 10%, 9%, 8%, 5%, and 62%, respectively. The separating agent was added to the raw water tank at a concentration of 1500 mg / L and mixed thoroughly. After thorough mixing, silver ions formed a large number of complexes with the separating agent. This mixture was then separated using a first-stage nanofiltration system at a pressure of 6 bar. The silver content in the first-stage nanofiltration product was 0.8 mg / L. L. The total cyanide content is 163 mg / L. The concentrate from the first-stage nanofiltration system enters the silver-containing concentration tank. The silver-containing water in the silver-containing concentration tank is further separated and concentrated by the second-stage nanofiltration system. The cyanide continues to enter the nanofiltration product tank through the product water of the second-stage nanofiltration system. The total cyanide concentration in the nanofiltration product tank can reach 175 mg / L. The magnesium sulfate removal rate of the first-stage nanofiltration system and the second-stage nanofiltration system is 92%, and the sodium chloride removal rate is 19%. When the total silver content in the concentrate from the second-stage nanofiltration reaches 1200 mg / L, it is fed into the electrolysis system through the second-stage nanofiltration system.

[0037] The cyanide-containing wastewater in the nanofiltration permeate tank is then treated in the primary FO system. The permeate from the primary FO system enters the FO permeate tank. When the total cyanide in the concentrate of the primary FO system reaches 10 g / L, it enters the cyanide concentration tank and is finally pumped into the cyanide concentrate storage area for stripping or production recycling.

[0038] Electrolysis begins 24 hours after the solution is collected in the electrolysis system. Metallic silver is deposited at the cathode. The 9 mg / L cyanide in the electrolysis system solution is completely decomposed by electrolysis. When the total silver content in the system solution is less than 10 mg / L after 22 hours of electrolysis, the residual liquid of the electrolysis system is added back to the original water tank as a separating agent and recycled 19 times.

[0039] The water produced by the secondary FO system enters the reclaimed water tank. If the conductivity is less than 20 μs / cm, it can be directly reused in the cyanide silver plating production line.

[0040] Example 3

[0041] The silver content in the cyanide silver plating wastewater is 58 mg / L, and the total cyanide content is 216 mg / L. The separating agent consists of sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, 5,5-dimethylhydantoin, sodium thioglycolate, potassium thioglycolate, sodium dodecyl sulfate, potassium hydroxide, and water in a mass ratio of 3%, 3%, 4%, 5%, 4%, 3%, 1%, and 77%. The separating agent is added to the raw water tank at a concentration of 750 mg / L. After thorough mixing, silver ions and the separating agent form a large number of complexes. This mixture is then separated through a nanofiltration system at a pressure of 4 bar. The silver content in the filtration permeate is 0.9 mg / L and the total cyanide content is 198 mg / L. It enters the nanofiltration permeate tank. The concentrate from the first-stage nanofiltration system enters the silver concentration tank. The silver-containing water in the silver concentration tank is further separated and concentrated by the second-stage nanofiltration system. The cyanide continues to enter the nanofiltration permeate tank through the permeate from the second-stage nanofiltration system. The total cyanide concentration in the nanofiltration permeate tank can reach 212 mg / L. The magnesium sulfate removal rate of the first-stage nanofiltration system and the second-stage nanofiltration system is 91%, and the sodium chloride removal rate is 14%. When the total silver content in the concentrate from the second-stage nanofiltration system reaches 700 mg / L, it is fed into the electrolysis system through the second-stage nanofiltration system.

[0042] The cyanide-containing wastewater in the nanofiltration permeate tank is then treated in the primary FO system. The permeate from the primary FO system enters the FO permeate tank. When the total cyanide in the concentrate of the primary FO system reaches 18 g / L, it enters the cyanide concentration tank and is finally pumped into the cyanide concentrate storage area for stripping or production recycling.

[0043] Electrolysis begins 24 hours after the solution is collected in the electrolysis system. Metallic silver is deposited at the cathode. The 16 mg / L cyanide in the electrolysis system solution is completely decomposed by electrolysis. When the total silver content in the system solution is less than 10 mg / L after 16 hours of electrolysis, the residual liquid of the electrolysis system is added back to the original water tank as a separating agent and recycled 5 times.

[0044] The water produced by the secondary FO system enters the reclaimed water tank. If the conductivity is less than 20 μs / cm, it can be directly reused in the cyanide silver plating production line.

[0045] Example 4

[0046] The silver content in the cyanide silver plating wastewater is 50 mg / L, and the total cyanide content is 210 mg / L. The separating agent consists of sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, 5,5-dimethylhydantoin, sodium thioglycolate, potassium thioglycolate, sodium dodecyl sulfate, potassium hydroxide, and water in a mass ratio of 2%, 2%, 6%, 8%, 6%, 5%, 2%, and 69%. The separating agent is added to the raw water tank at a concentration of 750 mg / L. After thorough mixing, silver ions and the separating agent form a large number of complexes. This mixture is then separated through a nanofiltration system at a pressure of 4 bar. The silver content in the filtration permeate is 0.8 mg / L and the total cyanide content is 186 mg / L. It enters the nanofiltration permeate tank. The concentrate from the first-stage nanofiltration system enters the silver concentration tank. The silver-containing water in the silver concentration tank is further separated and concentrated by the second-stage nanofiltration system. The cyanide continues to enter the nanofiltration permeate tank through the permeate from the second-stage nanofiltration system. The total cyanide concentration in the nanofiltration permeate tank can reach 208 mg / L. The magnesium sulfate removal rate of the first-stage nanofiltration system and the second-stage nanofiltration system is 90%, and the sodium chloride removal rate is 13%. When the total silver content in the concentrate from the second-stage nanofiltration system reaches 700 mg / L, it is fed into the electrolysis system through the second-stage nanofiltration system.

[0047] The cyanide-containing wastewater in the nanofiltration permeate tank is then treated in the primary FO system. The permeate from the primary FO system enters the FO permeate tank. When the total cyanide in the concentrate of the primary FO system reaches 16 g / L, it enters the cyanide concentration tank and is finally pumped into the cyanide concentrate storage area for stripping or production recycling.

[0048] Electrolysis begins 24 hours after the solution is collected in the electrolysis system. Metallic silver is deposited at the cathode. The 15 mg / L cyanide in the electrolysis system solution is completely decomposed by electrolysis. When the total silver content in the system solution is less than 10 mg / L after 16 hours of electrolysis, the residual liquid of the electrolysis system is added back to the original water tank as a separating agent and recycled 5 times.

[0049] The water produced by the secondary FO system enters the reclaimed water tank. If the conductivity is less than 20 μs / cm, it can be directly reused in the cyanide silver plating production line.

Claims

1. A method for recycling cyanide silver plating wastewater, comprising four steps of silver ion and cyanide separation, silver-containing solution concentration, cyanide concentration, electrolysis and residual liquid recycling, and the specific steps are as follows: (1) cyanide silver plating wastewater and a separation agent are simultaneously mixed in a raw water tank, the separation agent is composed of several components in sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, 5.5-dimethyl hydantoin, sodium thioglycolate, potassium thioglycolate, sodium dodecyl sulfonate, potassium hydroxide and water, after uniform mixing, a large amount of complex is formed by silver ion and the separation agent, the mixed solution is separated by a first nanofiltration system to separate silver ion and cyanide, most of the cyanide is contained in the produced water and enters a nanofiltration produced water tank, the complex formed by silver ion and the separation agent and a small amount of cyanide are contained in the concentrated water and enter a silver-containing concentrated tank, the silver-containing concentrated tank is further separated and concentrated by a second nanofiltration system, the cyanide continues to pass through the produced water of the second nanofiltration system and enters the nanofiltration produced water tank, when the total silver content in the concentrated water of the second nanofiltration system reaches 600 mg / L-1200 mg / L, the concentrated water is punched into an electrolysis system through the second nanofiltration system; (2) the cyanide-containing wastewater in the nanofiltration produced water tank is further treated by a first FO system, the produced water of the first FO enters an FO produced water tank, when the total cyanide in the concentrated water of the first FO system reaches 5 g / L-20 g / L, the concentrated water enters a cyanide concentration tank, and finally is punched into a cyanide concentrated liquid storage for stripping or production recycling; (3) after the electrolysis system solution is collected for 24 hours, electrolysis is started, metallic silver is deposited on the cathode, a small amount of cyanide contained in the electrolysis system solution is completely decomposed, and when the total silver content in the electrolysis system solution is less than 10 mg / L, the residual liquid of the electrolysis system can be added again into the raw water tank as a separation agent for recycling; (4) the produced water of a second FO system enters a regenerated water tank, and when the conductivity is less than 20 μs / cm, the produced water can be directly recycled to a cyanide plating production line. The composition ratio of sodium ethylenediaminetetraacetate, potassium ethylenediaminetetraacetate, 5.5-dimethyl hydantoin, sodium thioglycolate, potassium thioglycolate, sodium dodecyl sulfonate, potassium hydroxide and water in the separation agent is 0%-6%, 0%-6%, 4-10%, 0-9%, 0-9%, 3-8%, 1-5% and 62-79% respectively. The mass of the separation agent added is 12 times to 50 times the total silver mass in the cyanide plating wastewater. The magnesium sulfate removal rate of the first nanofiltration system and the second nanofiltration system is greater than 90%, and the sodium chloride removal rate is less than 30%. The working pressure of the first nanofiltration system and the second nanofiltration system is 4-9 bar.

2. The method according to claim 1, wherein the cyanide silver plating wastewater is recovered and reused. The first FO system and the second FO system are forward osmosis systems composed of composite forward osmosis membranes.

3. The method according to claim 1, wherein the cyanide silver plating wastewater is recovered and reused. The recycling times of the residual liquid of the electrolysis system is 4-20 times.

4. The method according to claim 1, wherein the cyanide silver plating wastewater is recovered and reused. ​ 5. The method according to claim 1, wherein the cyanide silver plating wastewater is recovered and reused. ​ 6. The method according to claim 1, wherein the cyanide silver plating wastewater is recovered and reused. ​ 7. The method according to claim 1, wherein the cyanide silver plating wastewater is recovered and reused. ​

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