A method for recovering silver from silver-containing waste materials

Abstract

The present invention relates to a method for recovering silver from silver-containing waste. The method uses sodium thiosulfate pentahydrate, potassium citrate, sodium acetate, sodium hydroxide, and sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]) and H2O to prepare an electrolyte solution. In the electrolyte solution, the electrolysis voltage is adjusted to 0.01 - 0.10 V / cm 2 , and electrolysis is carried out for 5 - 60 minutes until the silver and silver alloy layer in the waste are completely electrolyzed. The electrolyzed silver powder is washed with deionized water, filtered, and dried to obtain silver powder. The method of the present invention has a silver recovery rate of up to 99%, solves the problems of easy corrosion of equipment, environmental pollution, and employee injury during electrolysis in strong acid and strong alkali solutions, and also has the advantages of simple and controllable operation and reusability, with good economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the field of waste recycling, and particularly to a method for recovering silver from silver-containing waste. Background Art

[0002] Nowadays, with the development of the economy, electronic products have penetrated into all aspects of human life, bringing convenience to us and promoting the development of human society at the same time. Electronic products contain certain precious metals, which are widely used due to their excellent chemical stability, electrical conductivity and thermal conductivity. As a precious metal cheaper than platinum, rhodium, palladium, gold, etc., silver has a wider range of applications. At the same time, during the manufacturing process of electronic products, some scrap products are often generated. Since they contain a certain amount of precious metal silver, directly throwing them away will cause waste of resources. Therefore, it is necessary to recycle and reuse them.

[0003] Currently, the commonly used silver recovery technologies mainly include pyrometallurgical refining, chemical refining, extraction refining and electrolytic refining. Pyrometallurgical refining is to introduce oxygen at a certain temperature. Since silver has good antioxidant ability and base metals have good affinity for oxygen, oxides are formed to make slag or volatilize. However, pyrometallurgy has high energy consumption, the exhaust gas generated pollutes the environment, and the production site is harsh. Chemical refining generally uses nitric acid for dissolution, then precipitates and separates impurities, and finally uses a reducing agent to reduce to obtain silver powder. A large amount of nitrogen oxides will be generated during the dissolution process of chemical refining using nitric acid, which pollutes the environment greatly, and it is extremely easy to be inhaled into the human body during the production process if the operation is improper, causing great harm to the human body. Extraction refining is generally for waste materials with low silver content, and has special requirements for the recovered products. At the same time, it also needs to be dissolved and then extracted, and has high requirements for the extractant. In contrast, electrolytic refining has greater advantages. The silver powder electrolyzed has a higher purity, the electrolyte used can be recycled, it is friendly to the environment and has less pollution, and only needs to be maintained regularly. However, conventional electrolytic refining uses strong acid for electrolysis, which has high requirements for equipment, is extremely easy to corrode equipment parts, and the acid mist vapor generated is easy to be inhaled into the operator's body, posing a certain safety risk. Patent CN109735710A, a method for electrolytically recovering silver from silver-plated connector waste, uses one or more of thiourea, thiocyanate, aminosulfonate, sodium thiosulfate as stripping silver powder, prepares an electrolyte, places the plated part at the anode, and uses stainless steel or titanium as the cathode for electrolysis, and obtains silver powder through cleaning, smelting and electrolysis. Research on the electrolytic stripping and recovery of silver in lead frames by Ji Chao, prepared stripping silver powder with sodium thiosulfate pentahydrate, disodium ethylenediaminetetraacetate, sodium acetate trihydrate and sodium hydroxide, and carried out electrolysis under different reaction voltages and reaction times to achieve the purpose of purifying and recovering silver.

[0004] In the above method for electrolytic silver recovery, during the electrolysis process, sodium thiosulfate will be over-oxidized and decomposed, and the sulfur and sulfides produced by the decomposition cause the instability of the purity of the product silver, which causes certain difficulties for the subsequent treatment of the product silver. The base copper will also be electrochemically corroded with the prolongation of the electrolysis time and the increase of the voltage, resulting in excessive consumption of reagents, reduced electrolysis efficiency, and difficult disposal of the electrolytic waste liquid generated by the used disodium ethylenediaminetetraacetate, and the treatment of the waste water increases the production input. Summary of the Invention

[0005] The object of the present invention is to provide a method for recovering silver from silver-containing waste materials, with a silver recovery rate of up to 99%. The method has the characteristics of environmental protection, economy, and practicality, solves the problems of easy corrosion of equipment, environmental pollution, and employee injury during electrolysis in strong acid and strong alkali solutions, and also has the advantages of simple and controllable operation and recyclability, with good economic and social benefits.

[0006] The technical solution of the present invention is as follows:

[0007] The method for recovering silver from silver-containing waste materials has the following steps:

[0008] 1) Preparation of the electrolytic solution

[0009] The electrolytic solution is prepared by mixing sodium thiosulfate pentahydrate, potassium citrate, sodium acetate, sodium hydroxide, and sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]) with H2O; wherein,

[0010] The molar ratio of sodium thiosulfate pentahydrate: potassium citrate: sodium acetate: sodium hydroxide: sodium tris(thiosulfato)argentate(I) is 2.5×10 3 ~15×10 3 :0.5×10 3 ~1.5×10 3 :0.5×10 3 ~5×10 3 :0.25×10 3 ~2.5×10 3 :1~2;

[0011] 2) Electrolysis

[0012] The electrolytic solution is loaded into the electrolytic cell, the silver-containing waste material is loaded into the anode frame, the anode is connected to the positive electrode of the power supply, the cathode is connected to the negative electrode of the power supply, the electrolysis voltage is adjusted to 0.01 - 0.10 V / cm 2 , electrolysis is carried out for 5 - 60 minutes. After analyzing by ICP that the silver and silver alloy layer in the waste material are completely electrolyzed, the power supply is turned off, and the remaining copper base material is taken out;

[0013] 3) Recovery of electrolytic silver powder:

[0014] The electrolyzed silver powder is washed with deionized water, filtered, and dried to obtain silver powder.

[0015] The concentration of sodium thiosulfate pentahydrate is 0.05 - 0.3 M, the concentration of potassium citrate is 0.01 - 0.03 M, the concentration of sodium acetate is 0.01 - 0.1 M, the concentration of sodium hydroxide is 0.005 - 0.05 M, and the concentration of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]) is 2×10 -5 -4×10 -5 M.

[0016] In step 2), the anode is a grid plastic frame and the cathode is a grid stainless steel plate.

[0017] Both the anode and the cathode are wrapped with filter cloth.

[0018] In step 2), the electrolysis voltage is less than or equal to 5 V and the current is less than or equal to 10 A.

[0019] The present invention uses sodium thiosulfate pentahydrate as a complexing agent for silver to promote the electrolysis reaction of silver;

[0020] Potassium citrate is used as a stabilizer to reduce the excessive decomposition of sodium thiosulfate pentahydrate and reduce the occurrence of side reactions. The generated wastewater is easy to treat. At the same time, potassium citrate is a complexing agent for copper ions, which can reduce the oxidation ability of the system and protect copper from electrolytic oxidation;

[0021] Sodium acetate is used as a protective agent for the base copper to reduce the electrolysis of copper;

[0022] Sodium hydroxide is used to adjust the pH value to keep the system in a weak alkaline environment;

[0023] Sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]) can reduce the excessive decomposition of sodium thiosulfate pentahydrate and increase the conductivity, while improving the electrolysis efficiency.

[0024] Compared with the prior art, the advantages of the present invention are as follows: The process of this method is simple, economical and practical, has low requirements for equipment, and does not require acid and alkali resistant materials; the electrolyte can be recycled, is environmentally friendly, produces less wastewater, and is easy to treat. At the same time, the consumption of chemical reagents is low, the electrolysis efficiency is relatively high, the silver recovery rate can reach 99%, the corrosion to materials such as copper-based materials is small, the electrolyzed substrate can be directly recycled, and the electrolyzed silver powder can be collected for the next step of refining silver powder, which speeds up the recovery progress of precious metal silver. Specific embodiments

[0025] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention.

[0026] Example 1

[0027] A method for environmentally friendly recycling of silver from silver-containing waste materials includes the following steps:

[0028] 1. Preparation of electrolyte: Prepare a 200 mL solution, conduct a beaker electrolysis experiment, and use a small plastic frame for loading to simulate electrolysis. 2.48 g of sodium thiosulfate pentahydrate, 1.94 g of potassium citrate, 2.17 g of sodium acetate, 0.4 g of sodium hydroxide, 0.003 g of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]), a solution prepared with deionized water, and mix the solution evenly to obtain the electrolyte.

[0029] 2. Electrolysis by power supply: Load the silver-containing waste material into the anode frame, connect the anode to the positive pole of the power supply, connect the cathode to the negative pole of the power supply, turn on the rectifier switch, and calculate the electrolysis voltage according to 0.01 - 0.10 V / cm 2 Calculate according to the actual situation. The voltage is 3 V and the current is 3.2 A. The anode is a grid plastic frame, and the cathode is a grid stainless steel plate. Both are wrapped with filter cloth to facilitate the collection of silver powder and protect the electrolyte. Electrolyze for 60 minutes until the silver on the anode is completely electrolyzed. Turn off the power supply, take out the completely electrolyzed copper base strip, add new silver-containing waste material and supplement the electrolyte to keep the electrolysis process stable, and take it out after the silver electrolyzed at the cathode reaches a certain weight.

[0030] 3. Recovery of electrolytic silver powder: After the electrolytic silver powder accumulates a certain weight, wash it clean with deionized water, filter, and dry it to obtain silver powder.

[0031] Example 2

[0032] A method for environmentally friendly recycling of silver from silver-containing waste materials includes the following steps:

[0033] 1. Preparation of electrolyte: Prepare a 3000 mL solution, conduct a beaker electrolysis experiment, and use a small plastic frame for loading to simulate electrolysis. 133.92 g of sodium thiosulfate pentahydrate, 29.16 g of potassium citrate, 32.64 g of sodium acetate, 1.2 g of sodium hydroxide, 0.038 g of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]), prepare a solution with deionized water, and mix the solution evenly to obtain the electrolyte.

[0034] 2. Electrolysis with power on: Load the silver-containing waste into the anode frame. Connect the anode to the positive pole of the power supply and the cathode to the negative pole of the power supply. Turn on the rectifier switch. The electrolysis voltage is calculated according to 0.01 - 0.10 V / cm 2 Calculate it according to the actual situation. The voltage is 5 V and the current is 5.5 A. The anode is a grid plastic frame and the cathode is a grid stainless steel plate. Both are wrapped with filter cloth to facilitate the collection of silver powder and protect the electrolyte. Electrolyze for 60 minutes until the silver on the anode is completely electrolyzed. Turn off the power supply, take out the completely electrolyzed copper base strip, add new silver-containing waste and replenish the electrolyte to keep the electrolysis process stable. Take it out after the silver electrolyzed on the cathode reaches a certain weight.

[0035] 3. Recovery of electrolytic silver powder: After the electrolytic silver powder accumulates a certain weight, wash it clean with deionized water, filter it, and dry it to obtain silver powder.

[0036] Example 3

[0037] A method for environmentally friendly recovery of silver from silver-containing waste, comprising the following steps:

[0038] 1. Preparation of electrolyte: Prepare a 3000 mL solution and conduct a beaker electrolysis experiment. Use a small plastic frame for loading to simulate electrolysis. 186 g of sodium thiosulfate pentahydrate, 29.16 g of potassium citrate, 32.64 g of sodium acetate, 1.2 g of sodium hydroxide, 0.05 g of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]). Prepare a solution with deionized water, mix the solution evenly to obtain the electrolyte.

[0039] 2. Electrolysis with power on: Load the silver-containing waste into the anode frame. Connect the anode to the positive pole of the power supply and the cathode to the negative pole of the power supply. Turn on the rectifier switch. The electrolysis voltage is calculated according to 0.01 - 0.10 V / cm 2 Calculate it according to the actual situation. The voltage is 5 V and the current is 5.5 A. The anode is a grid plastic frame and the cathode is a grid stainless steel plate. Both are wrapped with filter cloth to facilitate the collection of silver powder and protect the electrolyte. Electrolyze for 60 minutes until the silver on the anode is completely electrolyzed. Turn off the power supply, take out the completely electrolyzed copper base strip, add new silver-containing waste and replenish the electrolyte to keep the electrolysis process stable. Take it out after the silver electrolyzed on the cathode reaches a certain weight.

[0040] 3. Recovery of electrolytic silver powder: After the electrolytic silver powder accumulates a certain weight, wash it clean with deionized water, filter it, and dry it to obtain silver powder.

[0041] Example 4

[0042] A method for environmentally friendly recovery of silver from silver-containing waste, comprising the following steps:

[0043] 1. Electrolyte preparation: Prepare a 3000 mL solution and conduct a beaker electrolysis experiment. Use a small plastic frame for loading materials to simulate electrolysis. Weigh 223.2 g of sodium thiosulfate pentahydrate, 29.16 g of potassium citrate, 32.64 g of sodium acetate, 1.2 g of sodium hydroxide, and 0.038 g of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]). Make a solution with deionized water, mix the solution evenly to obtain the electrolyte.

[0044] 2. Electrolysis by power supply: Load the silver-containing waste onto the anode frame. Connect the anode to the positive pole of the power supply and the cathode to the negative pole of the power supply. Turn on the rectifier switch. Calculate the electrolysis voltage according to 0.01 - 0.10 V / cm 2 Based on actual conditions, the voltage is 5 V and the current is 5.5 A. The anode is a grid plastic frame and the cathode is a grid stainless steel plate, both wrapped with filter cloth to facilitate the collection of silver powder and protect the electrolyte. Electrolyze for 60 minutes until the silver on the anode is completely electrolyzed. Turn off the power supply, take out the completely electrolyzed copper base strip, add new silver-containing waste and supplement the electrolyte to keep the electrolysis process stable. Take out the cathode when the electrolyzed silver reaches a certain weight.

[0045] 3. Recovery of electrolytic silver powder: After the electrolytic silver powder accumulates to a certain weight, wash it clean with deionized water, filter, and dry to obtain silver powder.

[0046] Example 5

[0047] A method for environmentally friendly recovery of silver from silver-containing waste, comprising the following steps:

[0048] 1. Electrolyte preparation: Prepare a 3000 mL solution and conduct a beaker electrolysis experiment. Use a small plastic frame for loading materials to simulate electrolysis. Weigh 223.2 g of sodium thiosulfate pentahydrate, 29.16 g of potassium citrate, 32.64 g of sodium acetate, 1.2 g of sodium hydroxide, and 0.067 g of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]). Make a solution with deionized water, mix the solution evenly to obtain the electrolyte.

[0049] 2. Electrolysis by power supply: Load the silver-containing waste onto the anode frame. Connect the anode to the positive pole of the power supply and the cathode to the negative pole of the power supply. Turn on the rectifier switch. Calculate the electrolysis voltage according to 0.01 - 0.10 V / cm 2 Based on actual conditions, the voltage is 4 V and the current is 4.8 A. The anode is a grid plastic frame and the cathode is a grid stainless steel plate, both wrapped with filter cloth to facilitate the collection of silver powder and protect the electrolyte. Electrolyze for 60 minutes until the silver on the anode is completely electrolyzed. Turn off the power supply, take out the completely electrolyzed copper base strip, add new silver-containing waste and supplement the electrolyte to keep the electrolysis process stable. Take out the cathode when the electrolyzed silver reaches a certain weight.

[0050] 3. Electrolytic silver powder recovery: After the electrolytic silver powder accumulates a certain weight, it is washed clean with deionized water, filtered, and dried to obtain silver powder.

[0051] Table 1 shows the weight of the waste before and after Examples 1-5, the weight of the recovered silver powder, the recovery rate, etc.:

[0052] Table 1

[0053] Example Theoretical silver content in waste (%) Weight of waste before reaction (g) Weight after reaction (g) Weight of silver powder (g) Recovery rate (%) 1 30 33.75 20.56 10.08 99.56 2 30 46.63 31.43 13.88 99.20 3 20 40.82 31.8 8.11 99.34 4 25 31.5 23.28 7.81 99.21 5 28 36.1 24.9 10.05 99.46

[0054] The silver recovery rate of the present invention is >99%, the corrosion to materials such as copper base is relatively small, the electrolyzed substrate can be directly recycled, and the electrolyzed silver powder can be refined into silver powder in the next step, accelerating the silver recovery progress.

Claims

1. A method for recovering silver from silver-containing waste materials, characterized in that, There are the following steps: 1) Electrolyte preparation The electrolyte is prepared by mixing sodium thiosulfate pentahydrate, potassium citrate, sodium acetate, sodium hydroxide and sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]) with H2O; among them, The molar ratio of sodium thiosulfate pentahydrate: potassium citrate: sodium acetate: sodium hydroxide: sodium argentotristhiosulfate(I) is 2.5×10 3 ~15×10 3 :0.5×10 3 ~1.5×10 3 :0.5×10 3 ~5×10 3 :0.25×10 3 ~2.5×10 3 :1~2; 2) Electrolysis The electrolytic cell is filled with the electrolyte solution. The silver-containing waste is loaded into the anode frame. The anode is connected to the positive pole of the power supply, and the cathode is connected to the negative pole of the power supply. The electrolytic voltage is adjusted to 0.01 - 0.10 V / cm 2 , and electrolysis is carried out for 5 - 60 minutes. Through ICP analysis, it is found that the silver and the silver alloy layer in the waste are completely electrolyzed. Then the power supply is turned off, and the remaining copper base strip is taken out; The anode is a grid plastic frame, and the cathode is a grid stainless steel plate. Both the anode and the cathode are wrapped with filter cloth; 3) Recovery of electrolytic silver powder: The electrolytic silver powder is washed with deionized water, filtered and dried to obtain silver powder.

2. The method according to claim 1, wherein: The concentration of sodium thiosulfate pentahydrate is 0.05 - 0.3 M, the concentration of potassium citrate is 0.01 - 0.03 M, the concentration of sodium acetate is 0.01 - 0.1 M, the concentration of sodium hydroxide is 0.005 - 0.05 M, and the concentration of sodium tris(thiosulfato)argentate(I) (Na5[Ag(S2O3)3]) is 2×10 -5 -4×10 -5 M.

3. The method according to claim 1, wherein: In step 2), the electrolysis voltage is less than or equal to 5V, and the current is less than or equal to 10A.