Method for recovering silver and tungsten from silver-tungsten alloy waste

Abstract

The invention relates to a method for recovering silver and tungsten from silver-tungsten alloy waste, and belongs to the technical field of comprehensive recovery of precious metal secondary resources. According to the method, the silver-tungsten alloy waste is subjected to extrusion forming and placed in a titanium basket to serve as an anode, a stainless steel plate serves as a cathode, a [AgNH3] < + > solution serves as electrolyte, electrolysis is conducted, and silver powder and anode slime are obtained; the preparation method comprises the following steps: finely grinding anode slime, adding pure water and an oxidizing agent, slurrying, oxidizing metal silver particles in slurry into silver peroxide by virtue of oxidation reaction at the temperature of 60-80 DEG C, adding ammonia water to dissolve the silver peroxide, enabling the silver peroxide to form a silver-ammonia complex, enabling the silver-ammonia complex to enter a solution, and carrying out solid-liquid separation, so as to obtain a silver-ammonia complex solution and coarse tungsten powder; sequentially boiling and washing the coarse tungsten powder with a nitric acid solution and pure water, and drying to obtain high-purity tungsten powder; and adding a reducing agent into the silver-ammonia complex solution for reduction, carrying out solid-liquid separation, and washing and drying the solid to obtain reduced silver powder. Compared with a traditional process, the method is short in technological process, small in environmental pollution, high in metal recovery rate, low in cost and high in production efficiency.

Description

Technical Field

[0001] The present invention relates to a method for recovering silver and tungsten from silver-tungsten alloy waste, and belongs to the technical field of comprehensive recovery of secondary precious metal resources. Background Art

[0002] Silver-tungsten alloy materials are widely used in industries such as circuit breakers, power switches, heavy relays, high-temperature resistant materials, and sports equipment due to their good electrical conductivity, weldability, and corrosion resistance. With the development of related industries, the demand is increasing year by year. A large amount of waste silver-tungsten alloy is generated during the processing and use of silver-tungsten alloy materials every year. Its silver content is between 20% - 70%, and its tungsten content is between 30% - 80%. Comprehensive recycling and utilization of it have important economic value.

[0003] The recycling technologies of silver-tungsten alloy are mainly nitric acid dissolution method and electrolysis-nitric acid dissolution method. The most commonly used method is to dissolve silver in the waste material with nitric acid. Metal tungsten is insoluble in nitric acid, so that silver and tungsten are separated in one step, and then silver is recovered from the solution. Some research has proposed a process of recovering silver and tungsten from waste silver-tungsten contacts by nitric acid dissolution for primary silver separation - roasting - nitric acid dissolution for secondary silver separation. First, the waste silver-tungsten contacts are dissolved in 8 mol / L nitric acid, filtered to obtain silver nitrate solution; the insoluble residue is dried, crushed, roasted at 500 °C for 2 h, and then dissolved in 8 mol / L nitric acid for secondary dissolution to obtain silver nitrate solution. The insoluble residue is dissolved in ammonia water, evaporated, crystallized, and calcined to obtain tungsten trioxide powder. The silver nitrate solution is reduced to obtain ultrafine silver powder. The recovery rates of silver and tungsten reach over 99%. The problems of this method are that when dissolved in nitric acid, tungsten will form insoluble tungstic acid, which will coat silver and hinder the further dissolution of silver, resulting in incomplete dissolution of silver, requiring multiple dissolutions, low direct recovery rate of silver, incomplete separation of silver and tungsten, and generating a large amount of acid gas and nitrogen oxides, causing serious environmental pollution. Patent 201610663527.1 proposes a method for recycling silver-tungsten waste. Its technical solution is: sintering the silver-tungsten waste into a silver-tungsten plate as the anode, a titanium plate as the cathode, using an 8 - 15 wt% silver nitrate solution as the electrolyte and adjusting the pH value to 1.5 - 2 with nitric acid, and electrolytically recovering silver powder under the conditions of a current density of 200 - 250 A / m 2 ², a cell voltage of 2.5 - 3 V; after drying and crushing the electrolytic anode mud with a crusher, it is dissolved in 35 - 50% nitric acid. The silver nitrate solution is adjusted to a certain pH value with ammonia water and then reduced to silver powder with hydrazine hydrate; the filter residue is washed, dried, and subjected to high-temperature reduction in a reducing atmosphere to obtain tungsten powder. The problems of this method are that it has poor adaptability to silver-tungsten alloy materials with different silver contents, the process is unstable, and the same phenomenon of tungstic acid coating occurs during secondary nitric acid dissolution, resulting in incomplete dissolution of silver, affecting the recovery rate of silver, and at the same time, there is also pollution of acid gas and nitrogen oxides. Some research has also proposed a study on recovering silver from silver-tungsten alloy by electrolysis method, using S 2 O3 2- -[Ag(S 2 O 3 ) 2 3- The method for electrolytically recovering Ag from Ag-W alloy with an electrolyte system mainly composed of [Ag(S SUMMARY OF THE INVENTION

[0004] In view of the problems in the prior art such as low direct recovery rate of silver and incomplete separation of silver and tungsten in the process of recovering silver and tungsten from silver-tungsten alloy waste, the present invention provides a method for recovering silver and tungsten from silver-tungsten alloy waste. By electrolytically separating silver and tungsten from the waste silver-tungsten alloy in [AgNH 3 + solution for the first time to separate a part of silver, qualified silver powder and anode mud are obtained; the anode mud obtained by electrolysis is oxidized to silver peroxide by an oxidant sodium persulfate and then dissolved with ammonia water, and after separation, a silver ammonia complex solution and coarse tungsten powder are obtained; the silver ammonia complex solution is reduced by a reducing agent to obtain reduced silver powder; the coarse tungsten powder is boiled and washed with nitric acid and then with pure water to obtain tungsten powder, realizing the efficient comprehensive recovery of silver and tungsten.

[0005] A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows: (1) First electrolytic separation of silver and tungsten: The silver-tungsten alloy waste is extruded into a shape and placed in a titanium basket as the anode, a stainless steel plate is used as the cathode, and [AgNH 3 + solution is used as the electrolyte, and electrolysis is carried out until the residual anode rate is 25-35%, obtaining silver powder and anode mud; (2) Oxidation and dissolution of anode mud for secondary separation of silver and tungsten: The anode mud is finely ground to obtain anode mud powder, the anode mud powder is slurried with pure water to obtain a slurry, an oxidant is added to the slurry, and an oxidation reaction is carried out at a temperature of 60-80 °C for 60-120 min to oxidize the metal silver particles in the slurry into silver peroxide, and excessive ammonia water is added to dissolve the silver peroxide so that the silver peroxide forms a silver ammonia complex and enters the solution, and solid-liquid separation is carried out to obtain a silver ammonia complex solution and coarse tungsten powder; (3) The coarse tungsten powder is boiled and washed with nitric acid solution and then with pure water, and dried to obtain high-purity tungsten powder; (4) A reducing agent is added to the silver ammonia complex solution for a reduction reaction, solid-liquid separation is carried out, and the solid is washed and dried to obtain reduced silver powder.

[0006] Preferably, the concentration of silver ions in the [AgNH 3 + solution in step (1) is 180-200 g / L.​​​​

[0007] Preferably, the current density of the electrolysis in step (1) is 250-300 A / m 2 , and the electrolysis temperature is 40-50 °C.

[0008] More preferably, in the anode slime powder in step (2), the proportion of particles with a size of less than 100 mesh is not less than 85%, and the solid-liquid mass ratio of the anode slime powder to pure water in the slurry is 3-5:1.

[0009] Preferably, the oxidizing agent in step (2) is sodium persulfate, and the addition amount of the oxidizing agent is 1.2-1.3 times the theoretical amount of silver oxide.

[0010] Preferably, the mass concentration of ammonia water in step (2) is 13-15%, the solid-liquid ratio of silver oxide slag to ammonia water is g:mL = 1:3-5; the dissolution temperature is 40-50 °C, and the time is 1-2 h.

[0011] Preferably, the mass concentration of the nitric acid solution is 30-35%, the boiling time of the nitric acid solution for boiling and washing is 30-60 min, and the number of times is 3-4 times; the boiling time of the pure water for boiling and washing is 30-60 min.

[0012] Preferably, the reducing agent in step (4) is hydrazine hydrate, the addition amount of the reducing agent is 1.1-1.2 times the theoretical amount, the reduction reaction temperature is 80-90 °C, and the time is 30-60 min.

[0013] The principle of recovering silver and tungsten from silver-tungsten alloy waste in the present invention: (1) Primary electrolytic separation of silver and tungsten: Load the high-melting-point and difficult-to-crush waste silver-tungsten alloy into a titanium basket as the anode, use a silver-ammonia complex ion solution as the electrolyte, and electrolyze with a stainless steel cathode. Control appropriate electrolysis conditions. Most of the silver in the waste silver-tungsten alloy is first deposited on the cathode to obtain a qualified electrolytic silver powder product, and at the same time, a porous and fragile anode slime containing silver and tungsten is obtained. The reaction is as follows: [Ag(NH 3 ) 2 + +e →Ag + 2NH 3 (1) (2) Oxidation and dissolution of the anode slime for secondary separation of silver and tungsten: After finely grinding the anode slime, add sodium persulfate as the oxidizing agent for oxidation and then dissolve it with ammonia water to obtain silver-ammonia complex ions and coarse tungsten powder. Reduce the silver-ammonium complex ions to obtain a reduced silver powder product; the main reaction formula is as follows: 2Ag + 2Na 2 S 2 O 8 + 2H 2 O → Ag 2 O 2 + Na​2 SO 4 + H 2 SO 4 (2) 2Ag 2 O 2 + 8NH 4 OH → 4Ag(NH 3 ) 2 OH + 6H 2 O + O 2 ↑ (3) 4OH - +N 2 H 4 + 4[Ag(NH 3 ) 2 + →4Ag↓+ 4H 2 O +8NH 3 +N 2 (4) The crude tungsten powder is boiled and washed successively with nitric acid of a specific concentration and pure water to obtain tungsten powder, realizing the comprehensive recovery of silver and tungsten.

[0014] The beneficial effects of the present invention are as follows: (1) The present invention uses silver ammonia complex ion as the electrolyte to replace the traditional silver nitrate + nitric acid system as the electrolyte. Since no tungstic acid precipitate is generated at the anode, the risk of anode passivation can be reduced. The current density during the electrolysis process can be increased by 20% compared with the traditional silver nitrate electrolysis process (the current density of silver nitrate electrolysis is 200 - 250 A / m 2 , and the current density of this process is 250 - 300 A / m 2 ), the current efficiency > 98%, effectively shortening the electrolysis time, reducing the power consumption, and improving the production efficiency; (2) The present invention uses sodium persulfate (Na 2 S 2 O 8 ) as the oxidant to oxidize metallic silver to silver peroxide under normal pressure and in a solution state, and dissolves silver peroxide with ammonia water. After filtration and washing, silver and tungsten are separated, which can replace the traditional nitric acid dissolution of silver, without nitrogen oxide emissions, and effectively reduce environmental pollution; (3) During the process of tungsten extraction, the high-temperature roasting link is reduced, effectively shortening the process flow, reducing the energy consumption, and improving the recovery rate and production efficiency. Specific Embodiments

[0015] The present invention will be further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the content described.

[0016] ​In the embodiment of the present invention, the raw material waste silver-tungsten alloy contains 70 wt.% Ag and 30 wt.% W.

[0017] Example 1: A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows: (1) Primary electrolytic separation of silver and tungsten: Extrude 10 kg of silver-tungsten alloy waste into a shape. Line the titanium basket with two layers of filter bags. Place the extruded silver-tungsten alloy waste in the titanium basket as the anode, use a stainless steel plate as the cathode, and use a [AgNH 3 + solution (the concentration of Ag ions is 180 g / L) as the electrolyte. Carry out electrolysis at a cathode current density of 250 A / m 2 and a temperature of 40 °C until the cell voltage reaches 3 V (the residual anode rate is 31.25%). Obtain cathode silver powder (purity 99.96%, mass 3.8981 kg) and anode slime (2.9769 kg). A total of 41.16 kWh of electricity is consumed, and the current efficiency is 98.10%. Compared with the traditional silver nitrate electrolysis, the electrolysis time is shortened by about 20%, and the current efficiency is increased by more than 1%; (2) Oxidation and dissolution of anode slime for secondary separation of silver and tungsten: Grind the anode slime to a particle size of less than 100 mesh, with 85% of it meeting this requirement, to obtain anode slime powder. Add pure water to the anode slime powder to form a slurry (the solid-liquid mass ratio of anode slime powder to pure water in the slurry is 5:1). Add 1.1 times the theoretical amount of the oxidant sodium persulfate to the slurry. Carry out an oxidation reaction at a temperature of 60 °C with stirring for 60 min to oxidize the metallic silver particles in the slurry into silver peroxide. After cooling, perform solid-liquid separation to obtain 3.0188 kg of silver peroxide-tungsten slag. Add excessive ammonia water (the mass concentration of ammonia water is 15%, and the solid-liquid ratio of silver peroxide slag to ammonia water is g:mL = 1:3) to the silver peroxide-tungsten slag. Dissolve silver peroxide at a temperature of 50 °C for 120 min to form a silver ammonia complex and enter the solution. Perform solid-liquid separation to obtain a silver ammonia complex solution (12.15 L, concentration 73.43 g / L) and crude tungsten powder (2.09761 kg); In this section, since direct leaching is carried out without oxidation roasting, the power consumption is effectively reduced by >125 kw·h, and the operation time is shortened by 3 - 4 h; Since sodium persulfate is used to dissolve silver instead of nitric acid to dissolve silver, the nitrogen oxide emissions are effectively reduced by about 380 g; (3) Boil and wash the crude tungsten powder with a nitric acid solution with a mass concentration of 35% for 3 times (each boiling for 30 min), then boil and wash with pure water for 30 min, and dry to obtain high-purity tungsten powder (purity 99.55%, mass 2.0349 kg); (4) Add a reducing agent (1.2 times the theoretical amount of hydrazine hydrate (N 2 H 4 ​)) was added to the silver ammonia complex solution, and the reduction reaction was carried out at 80 °C for 60 min. After solid-liquid separation, the solid was washed and dried to obtain reduced silver powder (purity 99.98%, mass 0.8292 kg); The direct recovery rate of silver in this example was 99.54%, and the direct recovery rate of tungsten was 99.77%.

[0018] Example 2: A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows: (1) Primary electrolytic separation of silver and tungsten: 10 kg of silver-tungsten alloy waste was extruded into a shape. Two layers of filter bags were lined inside the titanium basket. The extruded silver-tungsten alloy waste was placed in the titanium basket as the anode, a stainless steel plate was used as the cathode, and [AgNH 3 + solution (the concentration of Ag ions was 200 g / L) was used as the electrolyte. Electrolysis was carried out at a cathode current density of 300 A / m 2 and a temperature of 50 °C until the cell voltage reached 3.1 V (the residual anode rate was 29.77%). Cathode silver powder (purity 99.97%, mass 3.9820 kg) and anode slime (3.0410 kg) were obtained. The power consumption was 41.92 kWh, and the current efficiency was 98.41%. Compared with the traditional silver nitrate electrolysis, the electrolysis time was shortened by about 20%, and the current efficiency was increased by more than 1%; (2) Oxidation and dissolution of anode slime for secondary separation of silver and tungsten: The anode slime was finely ground to a particle size of less than 100 mesh, accounting for 87%, to obtain anode slime powder. Pure water was added to the anode slime powder to form a slurry (the solid-liquid mass ratio of anode slime powder to pure water in the slurry was 3:1). 1.2 times the theoretical amount of the oxidant sodium persulfate was added to the slurry. The oxidation reaction was carried out at 80 °C with stirring for 90 min to oxidize the metal silver particles in the slurry into silver peroxide. After cooling, solid-liquid separation was carried out to obtain 3.0838 kg of silver peroxide-tungsten slag. Excess ammonia water (ammonia water mass concentration was 14%, and the solid-liquid ratio of silver peroxide slag to ammonia water was g:mL = 1:3.5) was added to the silver peroxide-tungsten slag. Silver peroxide was dissolved at 40 °C for 80 min to form a silver ammonia complex and enter the solution. After solid-liquid separation, a silver ammonia complex solution (16.58 L, concentration 55.3118 g / L) and crude tungsten powder (2.1445 kg) were obtained. In this section, since there was no need for oxidative roasting and direct leaching was carried out, the power consumption was effectively reduced by more than 125 kw·h, and the operation time was shortened by 3 - 4 h; Since sodium persulfate was used to dissolve silver instead of nitric acid to dissolve silver, the nitrogen oxide emissions were effectively reduced by about 390 g; (3) The crude tungsten powder was boiled and washed with a nitric acid solution with a mass concentration of 32% for 4 times (each boiling for 40 min), and then washed with pure water for 45 min and dried to obtain high-purity tungsten powder (purity 99.83%, mass 2.1037 kg); (4) The reducing agent (1.15 times the theoretical amount of hydrazine hydrate (N 2 ​H 4 )) It was added to the silver ammonia complex solution, and a reduction reaction was carried out at 90 °C for 30 min. After solid-liquid separation, the solid was washed and dried to obtain reduced silver powder (purity 99.77%, mass 0.9173 kg); In this example, the recovery rate of silver was 99.66%, and the recovery rate of tungsten was 99.85%.

[0019] Example 3: A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows: (1) Primary electrolytic separation of silver and tungsten: 10 kg of silver-tungsten alloy waste was extruded into a shape. Two layers of filter bags were lined inside the titanium basket. The extruded silver-tungsten alloy waste was placed in the titanium basket as the anode, a stainless steel plate was used as the cathode, and [AgNH 3 + solution (the concentration of Ag ions was 200 g / L) was used as the electrolyte. Electrolysis was carried out at a cathode current density of 280 A / m 2 and a temperature of 50 °C until the cell voltage reached 3.05 V (the residual anode rate was 33.58%). Cathode silver powder (purity 99.98%, mass 3.7660 kg) and anode mud (2.8760 kg) were obtained, consuming a total of 39.73 kWh of electricity, and the current efficiency was 98.22%. Compared with traditional silver nitrate electrolysis, the electrolysis time was shortened by about 20%, and the current efficiency was increased by more than 1%; (2) Oxidative dissolution of anode mud for secondary separation of silver and tungsten: The anode mud was finely ground to a particle size of less than 100 mesh, accounting for 90%, to obtain anode mud powder. Pure water was added to the anode mud powder to form a slurry (the solid-liquid mass ratio of anode mud powder to pure water in the slurry was 8:1). 1.3 times the theoretical amount of sodium persulfate, an oxidant, was added to the slurry. An oxidation reaction was carried out at 70 °C with stirring for 100 min to oxidize the metallic silver particles in the slurry into silver peroxide. After cooling, solid-liquid separation was carried out to obtain 3.0058 kg of silver peroxide-tungsten slag. An excessive amount of ammonia water (ammonia water mass concentration was 13%, and the solid-liquid ratio of silver peroxide slag to ammonia water was g:mL = 1:5) was added to the silver peroxide-tungsten slag. Silver peroxide was dissolved at 50 °C for 60 min to form a silver ammonia complex and enter the solution. After solid-liquid separation, a silver ammonia complex solution (19.54 L, concentration 44.0483 g / L) and crude tungsten powder (2.2550 kg) were obtained. In this section, since there was no need for oxidative roasting and direct leaching was carried out, the power consumption was effectively reduced by more than 125 kw·h, and the operation time was shortened by 3 - 4 h; Since sodium persulfate was used to dissolve silver instead of nitric acid to dissolve silver, the nitrogen oxide emissions were effectively reduced by about 360 g; (3) The crude tungsten powder was boiled and washed 3 times (each boiling for 50 min) with a 35% nitric acid solution by mass concentration, and then washed with pure water for 50 min and dried to obtain high-purity tungsten powder (purity 99.73%, mass 1.9673 kg); ​(4) Add the reducing agent (hydrazine hydrate (N 2 H 4 ), which is 1.2 times the theoretical amount) into the silver ammonia complex solution, carry out a reduction reaction at 85 °C for 40 min, perform solid-liquid separation, and the solid is washed and dried to obtain reduced silver powder (purity 99.88%, mass 0.8606 kg); In this example, the recovery rate of silver is 99.51%, and the recovery rate of tungsten is 99.72%.

[0020] The specific embodiments of the present invention have been described in detail above, but the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. A method for recovering silver and tungsten from silver-tungsten alloy waste, characterized in that: The specific steps are as follows: (1) Primary electrolytic separation of silver and tungsten: The silver-tungsten alloy waste is extruded into a shape and placed in a titanium basket as an anode, and a stainless steel plate is used as a cathode to separate silver from tungsten. + The solution is an electrolyte, and electrolysis is performed until the residual electrode rate of the anode is 25-35%, thereby obtaining silver powder and anode mud; (2) Secondary separation of silver and tungsten by oxidation and dissolution of anode mud: Grind the anode mud to obtain anode mud powder, add pure water to the anode mud powder to obtain slurry, add oxidant to the slurry, and perform oxidation reaction at a temperature of 60-80°C for 60-120 minutes to oxidize the metallic silver particles in the slurry into silver peroxide, add excess ammonia water to dissolve the silver peroxide so that the silver peroxide forms a silver ammonia complex that enters the solution, and separate the solid and liquid to obtain a silver ammonia complex solution and crude tungsten powder; (3) The crude tungsten powder is boiled in nitric acid solution and then in pure water, and then dried to obtain high-purity tungsten powder; (4) Adding a reducing agent to the silver ammonia complex solution to carry out a reduction reaction, separating the solid and the liquid, and washing and drying the solid to obtain reduced silver powder.

2. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 1, characterized in that: Step (1) [AgNH3] + The concentration of Ag ions in the solution is 180~200g / L.

3. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 1, characterized in that: Step (1) The current density of electrolysis is 250~300A / m 2 , the electrolysis temperature is 40~50℃.

4. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 3, characterized in that: In step (2), the anode mud powder has a particle size of less than 100 mesh and accounts for no less than 85%, and the solid-liquid mass ratio of the anode mud powder to pure water in the slurry is 3-5:

1.

5. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 1, characterized in that: In step (2), the oxidant is sodium persulfate, and the amount of the oxidant added is 1.2 to 1.3 times the theoretical amount of silver oxide.

6. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 1, characterized in that: In step (2), the mass concentration of ammonia water is 13-15%; the dissolution temperature is 40-50°C, and the reaction time is 1-2h.

7. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 1, characterized in that: In step (3), the mass concentration of the nitric acid solution is 30-35%, the boiling time of the nitric acid solution is 30-60 min, and the number of times is 3-4 times; the boiling time of the pure water is 30-60 min.

8. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 1, characterized in that: In step (4), the reducing agent is hydrazine hydrate, the amount of reducing agent added is 1.1 to 1.2 times the theoretical amount, the reduction reaction temperature is 80 to 90° C., and the time is 30 to 60 min.