Treatment methods for scrapped silver electrolyte

Abstract

The present invention belongs to the field of smelting, and specifically relates to a method for treating scrapped silver electrolyte, comprising the following steps: (1) sodium chloride precipitation of silver; (2) copper replacement; (3) alkali neutralization; and (4) iron powder replacement. In the above scheme, sodium chloride is first used to precipitate silver to precipitate most of the silver ions in the scrapped silver electrolyte; copper replacement is then used. In the early stage, copper plates are used for replacement to reduce the reaction rate of copper with nitric acid in the waste liquid, thereby inhibiting the escape of nitrogen dioxide gas; copper powder is used for replacement in the later stage, which not only increases the replacement speed but also greatly improves the replacement effect, replacing most of the gold, silver, platinum and palladium in the waste liquid; then alkali is added for neutralization to precipitate the copper ions in the waste liquid in the form of copper hydroxide; iron powder and a small amount of copper sulfate are added to the neutralized liquid to further replace the precious metal ions in the waste liquid; the content of metal ions such as copper, gold, silver, platinum and palladium in the finally obtained replacement liquid is extremely low, which effectively recovers valuable resources and reduces environmental pollution.

Description

Technical Field

[0001] The invention belongs to the field of smelting and relates to a method for treating scrapped silver electrolyte, in particular to a method for recovering copper, gold, silver, platinum and palladium from the scrapped silver electrolyte. Background Art

[0002] Electrolysis is the most common silver production method in the prior art, offering advantages such as simple operation, low reagent consumption, a short cash-to-cash cycle, and high product purity. During the electrolysis process, impurity elements such as copper, gold, platinum, and palladium from the anode and cathode plates enter the solution. As the electrolysis time increases, these impurities accumulate to a certain concentration and precipitate at the cathode, affecting the purity of the electrolytic silver powder. Therefore, it is necessary to continuously drain a portion of the silver electrolyte and replenish it with new electrolyte. This discharged silver electrolyte is called spent silver electrolyte and requires purification. This is partly due to the government's strict requirements for wastewater discharge, but also because separating the precious metals from the spent silver electrolyte can generate some economic benefits for the company while also reducing the loss of precious metal resources.

[0003] In the prior art, the treatment of scrapped silver electrolyte generally involves (1) sodium chloride or hydrogen chloride precipitation, (2) copper plate replacement, and (3) alkaline neutralization. However, the precious metal content in the scrapped silver electrolyte treated by these methods remains high, resulting in a large loss of precious metals. Therefore, how to treat scrapped silver electrolyte, separate and cascade the recovery of silver, copper, gold, platinum, and palladium, and reduce the precious metal content and loss in the wastewater has always been a topic of research for those skilled in the art. Summary of the Invention

[0004] The object of the present invention is to provide a method for treating scrapped silver electrolyte, which can separate copper and precious metal elements in the scrapped silver electrolyte to the greatest extent.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a method for treating scrapped silver electrolyte, comprising the following steps:

[0006] (1) Sodium chloride silver precipitation: sodium chloride is added to the scrapped silver electrolyte to react and generate silver chloride precipitate, and the silver chloride precipitate and the silver precipitation liquid are obtained after solid-liquid separation;

[0007] (2) Copper replacement: A copper plate is added to the silver precipitation solution to carry out a replacement reaction for 10-20 hours, and then nitric acid is added to adjust the pH value to 1-2, and copper powder is added and compressed air is introduced. After the reaction, solid-liquid separation is performed to obtain a replacement precipitate A and a replacement solution A, and the replacement precipitate A is treated as a platinum-palladium concentrate;

[0008] (3) Adding alkali for neutralization: adding sodium hydroxide to the replaced liquid A to a pH of 8-9, and after the reaction, separating the solid and liquid to obtain copper hydroxide and the neutralized liquid;

[0009] (4) Iron powder replacement: sulfuric acid is added to the neutralized liquid to adjust the pH value to 5-6, and iron powder and copper sulfate are added to carry out replacement reaction. After the reaction, solid-liquid separation is performed to obtain replacement precipitate B and replacement liquid B. The replacement precipitate B is treated as platinum-palladium concentrate, and the replacement liquid B is sent to the general wastewater treatment system.

[0010] After neutralization with sodium hydroxide, the pH value of liquid A is 8-9, and the neutralized liquid still contains trace amounts of precious metal ions. When using iron powder for replacement, the pH is adjusted to 5-6, and the solution becomes weakly acidic. The replaced gold, platinum, and palladium will dissolve back into the solution. Adding copper sulfate to the reaction promotes a more thorough replacement of gold, platinum, and palladium. Taking palladium as an example:

[0011] Iron powder replaces palladium, reaction formula: Fe+Pd 2+ =Pd+Fe 2+ ;

[0012] But palladium reacts with nitric acid, the reaction formula is: 3Pd+8HNO3=3Pd(NO3)2+H2O+NO;

[0013] After adding copper sulfate, iron powder reacts with copper sulfate, reaction formula: Fe+Cu 2+ =Cu+Fe 2+ ;

[0014] Fresh copper powder reacts more easily with nitric acid, the reaction formula is: 3Cu+8HNO3=3Cu(NO3)2+H2O+NO, thus inhibiting the reverse dissolution of palladium;

[0015] The fresh copper powder produced reacts with palladium, the reaction formula is: Cu+Pd 2+ =Pd+Cu 2+ ;

[0016] Under the action of direct current, gold and platinum can dissolve in dilute nitric acid at a rate of tens of milligrams per liter. The principles of replacement and inhibition of reverse dissolution are similar to those of palladium.

[0017] The above scheme first uses sodium chloride to precipitate silver to separate most of the silver ions in the scrapped silver electrolyte; then copper replacement is used. In the early stage, copper plates are used for replacement to reduce the reaction rate of copper with nitric acid in the waste liquid, thereby inhibiting the escape of nitrogen dioxide gas. In the later stage, copper powder is used for replacement and compressed air is used for stirring, which not only increases the replacement speed but also greatly improves the replacement effect, replacing most of the gold, silver, platinum and palladium in the waste liquid. The replacement precipitate A contains more than 40% of precious metals, which is recorded as platinum palladium concentrate 1; then alkali is added for neutralization, and the waste liquid is The copper ions in the waste liquid are precipitated in the form of copper hydroxide, and the copper hydroxide is returned to the copper smelting system to recover copper; iron powder and a small amount of copper sulfate are added to the neutralized liquid to further replace the precious metal ions in the waste liquid. The obtained replacement precipitate B contains about 10% precious metals and is recorded as platinum-palladium concentrate 2; the content of metal ions such as copper, gold, silver, platinum and palladium in the final replacement liquid is extremely low, with Cu, Ag, and Pt all less than 0.5 mg / L, and Au and Pd reaching 0.001 mg / L, thereby efficiently recovering precious resources and reducing environmental pollution.

[0018] Specifically, in step (1), the amount of sodium chloride is 1.0-1.1 times the amount of silver ion in the scrapped silver electrolyte; after the silver chloride precipitate obtained in step (1) is slurried with water, sodium hydroxide is first added to adjust the pH value to alkaline, and then hydrazine hydrate is added. After the reaction is completed, coarse silver powder is obtained.

[0019] In the step (2), the sum of the amounts of the copper plate and the copper powder is 1.5-1.8 times the sum of the amounts of the gold, silver, platinum and palladium ions in the silver-immersion solution; during the copper replacement process, the silver-immersion solution is heated to 70-80°C.

[0020] In the step (3), during the alkali neutralization process, the liquid after substitution is heated to 40-60°C.

[0021] In the step (4), the amount of iron powder is 3-6 times the sum of the amounts of copper, gold, silver, platinum and palladium ions in the neutralized solution, and the iron powder is added in batches multiple times; the amount of copper sulfate added is 3-6 times the sum of the amounts of copper, gold, silver, platinum and palladium ions in the reaction solution, and the copper sulfate is added in the middle of the reaction; during the iron powder replacement process, the neutralized solution is heated to 70-80°C. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is further described in detail below with reference to specific embodiments.

[0023] Example 1: Treatment of scrapped silver electrolyte in the prior art

[0024] Taking the silver electrolysis workshop of Jinlong Copper Industry Co., Ltd. as an example, in the electrolysis process, in order to prevent the copper ion concentration in the silver electrolyte from being too high and affecting the quality of the electrosilver, the copper concentration of the silver electrolyte is controlled within the range of less than 40g / l. Therefore, about 3m3 of copper is extracted every week. 3The silver electrolyte is scrapped. The processing process is as follows:

[0025] 1. Silver is precipitated with sodium chloride in scrapped silver electrolyte at room temperature. Silver chloride is slurried with water and sodium hydroxide to adjust the pH to alkaline. Hydrazine hydrate is added to reduce it to coarse silver powder. The precious metal contents in the solution after sodium chloride precipitation are: Cu 31g / L, HNO3 5.3g / L, Au 30mg / L, Ag 108mg / L, Pt 38mg / L, Pd 1150mg / L.

[0026] 2. The solution after sodium chloride silver precipitation is heated to 70-80°C in a reaction tank and replaced with a copper plate for 48 hours to obtain a platinum-palladium concentrate rich in Au, Ag, Pt, and Pd. The precious metal content in the solution after copper replacement is: Cu 40.6g / L, Au 3.8mg / L, Ag 12.7mg / L, Pt 11.1mg / L, Pd 20.8mg / L.

[0027] 3. The copper-displaced liquid is heated to 40-60°C in a reaction tank and neutralized with sodium hydroxide to a pH of 8-9 to produce copper hydroxide containing approximately 50% copper. The precious metal content in the neutralized liquid is: Cu 3.9 mg / L, Au 1.6 mg / L, Ag 7.5 mg / L, Pt 6.9 mg / L, and Pd 14.3 mg / L. The neutralized liquid is discharged to the company's wastewater treatment station. During wastewater treatment, hydrogen sulfide is first introduced to precipitate copper and arsenic, producing sulfide slag. This causes precious metals to enter the sulfide slag of the wastewater treatment system. The sulfide slag contains approximately Au 0.5-2 g / t, Ag 50-150 g / t, Pt 5-10 g / t, and Pd 20-30 g / t, resulting in the dispersion and loss of precious metals.

[0028] Example 2: Treatment of scrapped silver electrolyte in the present invention

[0029] The same batch of scrapped silver electrolyte as in Example 1 was used for treatment, and the specific process was as follows:

[0030] 1. Silver is precipitated with sodium chloride in scrapped silver electrolyte at room temperature. Silver chloride is slurried in water with sodium hydroxide to adjust the pH to alkaline, and then reduced to coarse silver powder with hydrazine hydrate. The precious metal contents of the solution after sodium chloride precipitation are: Cu 32g / L, HNO3 5.2g / L, Au 30mg / L, Ag 110mg / L, Pt 40mg / L, and Pd 1130mg / L.

[0031] 2. The sodium chloride silver precipitation solution was heated to 70-80°C in a reaction tank and replaced with a copper plate for 20 hours. Then nitric acid was added to a pH of 1, copper powder was added, and the solution was stirred with compressed air for 4 hours. The precious metal contents in the solution after copper replacement were: Cu 35g / L, Au 0.05mg / L, Ag 4mg / L, Pt 2mg / L, and Pd 7mg / L.

[0032] 3. The copper-displaced solution is heated to 40-60°C in a reaction tank and neutralized with sodium hydroxide to a pH of 8-9 to produce copper hydroxide containing approximately 50% copper. The precious metal contents in the neutralized solution are: Cu 1.99 mg / L, Au 0.01 mg / L, Ag 9.53 mg / L, Pt 1.62 mg / L, and Pd 9.22 mg / L. Sulfuric acid is added to the neutralized solution to adjust the pH to 5. Iron powder and copper sulfate are added at 70-80°C and reacted for 2 hours. The precious metal contents in the reaction solution are: Cu 0.25 mg / L, Au 0.001 mg / L, Ag 0.05 mg / L, Pt 0.48 mg / L, and Pd 0.001 mg / L. The solution is then discharged to the company's wastewater treatment station.

[0033] Comparing the above two solutions:

[0034] (1) In the prior art, the copper plate replacement time after silver precipitation is long, and the replacement is still not complete even after 48 hours. However, in the technical solution of the present invention, the copper plate is still used for replacement in the early stage, which can inhibit the rapid reaction of copper and nitric acid to produce a large amount of nitrogen dioxide gas, and the risk that the nitrogen dioxide caused by it cannot be recovered by the nitrogen oxide recovery system in time and enters the atmosphere; in the later stage of replacement, because the nitric acid consumption solution is close to neutral, nitric acid is added to adjust the pH to 1-2, and then copper powder is added, and stirred with compressed air, which improves the reaction activity, increases the contact area between the reactants, improves the replacement efficiency, and shortens the replacement time to less than 24 hours; the replacement is more thorough, and the precious metal content of the liquid after copper replacement is reduced to about Cu 30-50g / L, Au 0.5-1mg / L, Ag 2-5mg / L, Pt 2-5mg / L, and Pd 2-10mg / L.

[0035] (2) In the prior art, the effect of precipitating precious metals by alkali neutralization is not good. After alkali neutralization, the liquid still contains about 2-5 mg / L of Cu, 0.5-2 mg / L of Au, 2-10 mg / L of Ag, 2-10 mg / L of Pt, and 5-20 mg / L of Pd, causing the precious metals to enter the sulfide slag of the wastewater treatment system and be dispersed and lost. In the solution of the present invention, the liquid after alkali neutralization contains only a small amount of gold, silver, platinum, and palladium. After adjusting the pH value, the process of replacing the precious metals with iron powder and a small amount of copper sulfate is added, which can achieve the effect that the liquid after iron replacement contains less than 0.5 mg / L of Cu, Ag, and Pt, and less than 0.01 mg / L of Au and Pd. Copper sulfate promotes the replacement of Pd during the replacement process, preventing Pd from dissolving back in the nitric acid system, and efficiently recovering valuable precious metal resources.

[0036] (3) In the prior art, the neutralized liquid enters the wastewater treatment system, and the system sulfide slag contains a high content of precious metals, about 0.5-2g / t of Au, 50-150g / t of Ag, 5-10g / t of Pt, and 20-30g / t of Pd, resulting in the dispersion loss of precious metals. In the scheme of the present invention, the precious metal content in the final iron-exchanged liquid is extremely low, and it can directly enter the enterprise's ordinary wastewater treatment system, and the precious and base metals are separated (copper and gold, silver, platinum and palladium are precipitated separately). The produced platinum-palladium concentrate contains high grades of Au, Ag, Pt and Pd, and low levels of base metals such as copper, which is convenient for platinum-palladium refining operations. The produced platinum-palladium concentrate can be chlorinated to purify platinum and palladium separately after acid leaching to remove impurities. There is no pretreatment process of roasting, degreasing and copper removal. The main grade of sponge platinum and sponge palladium after refining by the original process is still above 99.95%.

Claims

1. A method for treating scrapped silver electrolyte, comprising the following steps: (1) Sodium chloride silver precipitation: sodium chloride is added to the scrapped silver electrolyte to react and generate silver chloride precipitate, and the silver chloride precipitate and the silver precipitation liquid are obtained after solid-liquid separation; (2) Copper replacement: A copper plate is added to the silver precipitation solution to carry out a replacement reaction for 10-20 hours, and then nitric acid is added to adjust the pH value to 1-2, and copper powder is added and compressed air is introduced. After the reaction, solid-liquid separation is performed to obtain a replacement precipitate A and a replacement solution A, and the replacement precipitate A is treated as a platinum-palladium concentrate; (3) Adding alkali for neutralization: adding sodium hydroxide to the replaced liquid A to a pH of 8-9, and after the reaction, separating the solid and liquid to obtain copper hydroxide and the neutralized liquid; (4) Iron powder replacement: sulfuric acid is added to the neutralized liquid to adjust the pH value to 5-6, and iron powder and copper sulfate are added to carry out replacement reaction. After the reaction, solid-liquid separation is performed to obtain replacement precipitate B and replacement liquid B. The replacement precipitate B is treated as platinum-palladium concentrate, and the replacement liquid B is sent to the general wastewater treatment system.

2. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (1), the amount of sodium chloride is 1.0-1.1 times the amount of silver ion in the scrapped silver electrolyte.

3. The method for treating scrapped silver electrolyte according to claim 1, wherein: The silver chloride precipitate obtained in step (1) is slurried with water, and then sodium hydroxide is added to adjust the pH value to alkaline, and then hydrazine hydrate is added. After the reaction is completed, coarse silver powder is obtained.

4. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (2), the sum of the amounts of the copper plate and the copper powder is 1.5-1.8 times the sum of the amounts of the gold, silver, platinum and palladium ions in the solution after silver precipitation.

5. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (2), during the copper replacement process, the silver-immersed solution is heated to 70-80°C.

6. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (3), during the alkali neutralization process, the liquid after substitution is heated to 40-60°C.

7. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (4), the amount of the iron powder is 3-6 times the sum of the amounts of the copper, gold, silver, platinum and palladium ions in the neutralized solution, and the iron powder is added in batches multiple times.

8. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (4), the amount of copper sulfate added is 3-6 times the sum of the amounts of copper, gold, silver, platinum and palladium ions in the reaction solution, and the copper sulfate is added in the middle of the reaction.

9. The method for treating scrapped silver electrolyte according to claim 1, wherein: In the step (4), during the iron powder replacement process, the neutralized liquid is heated to 70-80°C.