A method for recovering silver and tungsten from silver-tungsten alloy waste

Abstract

The present invention relates to a method for recovering silver and tungsten from silver-tungsten alloy waste, belonging to the technical field of comprehensive recovery of secondary precious metal resources. In the present invention, 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 + a [Ag(NH3)2] solution is used as the electrolyte for electrolysis to obtain silver powder and anode slime; the anode slime is finely ground, pure water and an oxidant are added and slurried, and an oxidation reaction is carried out at a temperature of 60-80 °C to oxidize the metal silver particles in the slurry into silver peroxide. Ammonia water is added to dissolve the silver peroxide so that the silver peroxide forms a silver ammonia complex and enters the solution. Solid-liquid separation is carried out to obtain a silver ammonia complex solution and coarse tungsten powder; the coarse tungsten powder is washed successively with nitric acid solution and pure water and then dried to obtain high-purity tungsten powder; a reducing agent is added to the silver ammonia complex solution for reduction, and solid-liquid separation is carried out. The solid is washed and dried to obtain reduced silver powder. Compared with the traditional process, the process flow of the present invention is short, the environmental pollution is small, the metal recovery rate is high, the cost is low, and the production efficiency is high.

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 precious metal secondary 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, solder resistance, and corrosion resistance. With the development of related industries, the demand is also 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. The silver content is between 20% and 70%, and the tungsten content is between 30% and 80%. Comprehensive recovery 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 can be 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 with 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 with 8 mol / L nitric acid for the second time to obtain silver nitrate solution. The insoluble residue is dissolved with 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 problem with this method is that when dissolved with nitric acid, tungsten will form insoluble tungstic acid, which will wrap silver and hinder the further dissolution of silver, resulting in incomplete dissolution of silver. Multiple dissolutions are required, the direct recovery rate of silver is low, the separation of silver and tungsten is incomplete, and a large amount of acid gas and nitrogen oxides will be generated, causing serious environmental pollution. Patent 201610663527.1 proposes a method for recycling silver-tungsten waste. Its technical solution is: sinter the silver-tungsten waste into a silver-tungsten plate as the anode, a titanium plate as the cathode, use an 8-15 wt% silver nitrate solution as the electrolyte and adjust the pH value to 1.5-2 with nitric acid, and electrolytically recover silver powder under the conditions of a current density of 200-250 A / m 2 ², and a cell voltage of 2.5-3 V; the electrolytic anode mud is dried, crushed by a crusher, and dissolved with 35-50% nitric acid. The silver nitrate solution is adjusted to a 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 with this method are poor adaptability to silver-tungsten alloy materials with different silver contents, unstable process, and the same phenomenon of tungstic acid wrapping during secondary nitric acid dissolution, incomplete dissolution of silver, which affects the recovery rate of silver. 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 S2O3 2--[Ag(S2O3)2] 3- A method for electrolytically recovering Ag from Ag-W alloy with a main electrolyte system of [Ag(S2O3)2] can directly obtain metallic silver with a purity of over 99% and a current efficiency of over 97%. This method still needs to be improved in aspects such as electrolyte circulation and adding organic additives. Moreover, the pH value of the solution has a great influence on the electrolysis process, and the control requirements of electrolysis process parameters are very strict. Summary of the Invention

[0004] In view of the problems in the prior art of low direct silver recovery rate and incomplete separation of silver and tungsten in the process of recovering silver and tungsten from silver-tungsten alloy waste, the present invention proposes 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 [Ag(NH3)2] + solution for the first time to separate a part of silver, qualified silver powder and anode mud are obtained; the anode mud of electrolysis is oxidized into silver peroxide by the oxidant sodium persulfate and then dissolved with ammonia water. After separation, a silver ammonia complex solution and crude tungsten powder are obtained. The silver ammonia complex solution is reduced by a reducing agent to obtain reduced silver powder; the crude 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:

[0006] (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, with a stainless steel plate as the cathode, and [Ag(NH3)2] + solution as the electrolyte, and electrolyzed until the residual anode rate is 25-35% to obtain silver powder and anode mud;

[0007] (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. Pure water is added to the anode mud powder to form a slurry. An oxidant is added to the slurry, and the 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. Excessive ammonia water is added to dissolve the silver peroxide so that the silver peroxide forms a silver ammonia complex and enters the solution. Solid-liquid separation is carried out to obtain a silver ammonia complex solution and crude tungsten powder;

[0008] (3) The crude tungsten powder is boiled and washed with nitric acid solution and then with pure water in sequence, and dried to obtain high-purity tungsten powder;

[0009] (4) A reducing agent is added to the silver ammonia complex solution for reduction reaction, and solid-liquid separation is carried out. The solid is washed and dried to obtain reduced silver powder.

[0010] Preferably, the concentration of silver ions in the [Ag(NH3)2] + solution in step (1) is 180-200 g / L.

[0011] Preferably, the current density for electrolysis in step (1) is 250 - 300 A / m 2 , and the electrolysis temperature is 40 - 50 °C.

[0012] More preferably, in step (2), the proportion of the anode slime powder with a particle size below 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.

[0013] Preferably, the oxidant in step (2) is sodium persulfate, and the addition amount of the oxidant is 1.2 - 1.3 times the theoretical amount of silver oxide.

[0014] 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.

[0015] Preferably, the mass concentration of the nitric acid solution is 30 - 35%, the boiling time for boiling and washing with the nitric acid solution is 30 - 60 min, and the number of times is 3 - 4 times; the boiling time for boiling and washing with pure water is 30 - 60 min.

[0016] 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.

[0017] The principle of recovering silver and tungsten from silver-tungsten alloy waste in the present invention:

[0018] (1) Primary electrolytic separation of silver and tungsten: The high-melting-point and difficult-to-crush waste silver-tungsten alloy is loaded into a titanium basket as the anode, and a silver ammonia complex ion solution is used as the electrolyte. Stainless steel is used as the cathode for electrolysis. By controlling 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:

[0019] [Ag(NH3)2] + + e→Ag + 2NH3 (1)

[0020] (2) Oxidation and dissolution of the anode slime for secondary separation of silver and tungsten: After the anode slime is finely ground, sodium persulfate as the oxidant is added for oxidation and then dissolved with ammonia water to obtain silver ammonia complex ions and coarse tungsten powder. The silver ammonium complex ions are reduced to obtain a reduced silver powder product; the main reaction formulas are as follows:

[0021] 2Ag + 2Na2S2O8+ 2H2O → Ag2O2+ Na2SO4+ H2SO4 (2)

[0022] 2Ag2O2 + 8NH4OH → 4Ag(NH3)2OH + 6H2O + O2↑ (3)

[0023] 4OH - + N2H4 + 4[Ag(NH3)2] + → 4Ag↓ + 4H2O + 8NH3 + N2 (4)

[0024] 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.

[0025] The beneficial effects of the present invention are as follows:

[0026] (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 formed 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 silver nitrate electrolysis current density is 200 - 250 A / m 2 ; 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;

[0027] (2) The present invention uses sodium persulfate (Na2S2O8) as the oxidant to oxidize metallic silver to form silver peroxide under normal pressure and in a solution state, and uses ammonia water to dissolve silver peroxide. After filtration and washing, silver and tungsten are separated, which can replace the traditional dissolution of silver with nitric acid, without nitrogen oxide emissions, and effectively reduce environmental pollution;

[0028] (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

[0029] 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.

[0030] In the embodiment of the present invention, the raw material waste silver-tungsten alloy contains 70 wt.% Ag and 30 wt.% W.

[0031] Example 1: A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows:

[0032] (1) Primary electrolytic separation of silver and tungsten: 10 kg of silver-tungsten alloy waste is extruded into a shape, with two layers of filter bags inside the titanium basket. The extruded silver-tungsten alloy waste is placed in the titanium basket as the anode, a stainless steel plate is used as the cathode, and [Ag(NH3)2] +A solution (with an Ag ion concentration of 180 g / L) is used as the electrolyte, and electrolysis is carried out at a cathode current density of 250 A / m 2 ², a temperature of 40 °C until the cell voltage reaches 3 V (the residual anode rate is 31.25%), obtaining cathode silver powder (purity 99.96%, mass 3.8981 kg) and anode slime (2.9769 kg), consuming a total of 41.16 kWh of electricity, with a current efficiency of 98.10%. Compared with traditional silver nitrate electrolysis, the electrolysis time is shortened by about 20%, and the current efficiency is increased by more than 1%;

[0033] (2) Oxidative dissolution and secondary separation of silver and tungsten from the anode slime: The anode slime is finely ground until 85% of the particle size is below 100 mesh to obtain anode slime powder. Pure water is 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 is 5:1). 1.1 times the theoretical amount of the oxidant sodium persulfate is added to the slurry, and an oxidative reaction is carried out 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, solid-liquid separation is carried out to obtain 3.0188 kg of silver peroxide tungsten slag. Excess ammonia water (ammonia water mass concentration is 15%, and the solid-liquid ratio of silver oxide slag to ammonia water is g:mL = 1:3) is added to the silver peroxide tungsten slag, and silver peroxide is dissolved at a temperature of 50 °C, allowing the silver peroxide to react for 120 min to form a silver ammonia complex and enter the solution. Solid-liquid separation is carried out to obtain a silver ammonia complex solution (12.15 L, concentration 73.43 g / L) and crude tungsten powder (2.09761 kg); Since direct leaching is carried out without oxidation roasting in this section, 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;

[0034] (3) The crude tungsten powder is boiled and washed 3 times with a nitric acid solution with a mass concentration of 35% (each boiling for 30 min), and then boiled and washed with pure water for 30 min, and dried to obtain high-purity tungsten powder (purity 99.55%, mass 2.0349 kg);

[0035] (4) A reducing agent (1.2 times the theoretical amount of hydrazine hydrate (N₂H₄)) is added to the silver ammonia complex solution, and a reduction reaction is carried out at a temperature of 80 °C for 60 min. Solid-liquid separation is carried out, and the solid is washed and dried to obtain reduced silver powder (purity 99.98%, mass 0.8292 kg).

[0036] In this example, the direct recovery rate of silver is 99.54%, and the direct recovery rate of tungsten is 99.77%.

[0037] Example 2: A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows:

[0038] (1)Primary electrolytic separation of silver-tungsten: Extrude 10 kg of silver-tungsten alloy waste into a mold. 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 [Ag(NH3)2] 2 solution (the concentration of Ag ions is 200 g / L) as the electrolyte. Carry out electrolysis at a cathode current density of 300 A / m 2 ² and a temperature of 50 °C until the cell voltage reaches 3.1 V (the residual anode rate is 29.77%). Obtain cathode silver powder (purity 99.97%, mass 3.9820 kg) and anode mud (3.0410 kg). The power consumption is 41.92 kWh, and the current efficiency is 98.41%. Compared with traditional silver nitrate electrolysis, the electrolysis time is shortened by about 20%, and the current efficiency is increased by more than 1%;

[0039] (2)Oxidation and dissolution of anode mud for secondary separation of silver-tungsten: Grind the anode mud to a particle size of less than 100 mesh, with 87% passing through, to obtain anode mud powder. Add pure water to the anode mud powder to form a slurry (the solid-liquid mass ratio of anode mud powder to pure water in the slurry is 3:1). Add 1.2 times the theoretical amount of the oxidant sodium persulfate to the slurry. Carry out an oxidation reaction at a temperature of 80 °C with stirring for 90 min to oxidize the metallic silver particles in the slurry into silver peroxide. After cooling, perform solid-liquid separation to obtain 3.0838 kg of silver peroxide-tungsten slag. Add excessive ammonia water (the mass concentration of ammonia water is 14%, and the solid-liquid ratio of silver oxide slag to ammonia water is g:mL = 1:3.5) to the silver peroxide-tungsten slag. Dissolve silver peroxide at a temperature of 40 °C for 80 min to form a silver ammonia complex and enter the solution. Perform solid-liquid separation to obtain a silver ammonia complex solution (16.58 L, concentration 55.3118 g / L) and coarse tungsten powder (2.1445 kg). In this section, since there is no need for oxidative roasting and direct leaching is carried out, the power consumption is effectively reduced by more than 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 390 g;

[0040] (3)The coarse tungsten powder is 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);

[0041] (4)Add a reducing agent (1.15 times the theoretical amount of hydrazine hydrate (N2H4)) to the silver ammonia complex solution. Carry out a reduction reaction at a temperature of 90 °C for 30 min. Perform solid-liquid separation. The solid is washed and dried to obtain reduced silver powder (purity 99.77%, mass 0.9173 kg);

[0042] In this example, the recovery rate of silver is 99.66%, and the recovery rate of tungsten is 99.85%.

[0043] Example 3: A method for recovering silver and tungsten from silver-tungsten alloy waste, the specific steps are as follows:

[0044] (1) Primary electrolytic separation of silver and tungsten: Extrude 10 kg of silver-tungsten alloy waste into a mold. 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 + [Ag(NH3)2] 2 solution (the concentration of Ag ions is 200 g / L) as the electrolyte. Carry out electrolysis at a cathode current density of 280 A / m

[0045] and a temperature of 50 °C until the cell voltage reaches 3.05 V (the residual anode rate is 33.58%). Obtain cathode silver powder (purity 99.98%, mass 3.7660 kg) and anode mud (2.8760 kg). A total of 39.73 kWh of electricity is consumed, and the current efficiency is 98.22%. 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%;

[0046] (2) Oxidation and dissolution of anode mud for secondary separation of silver and tungsten: Grind the anode mud to a particle size of less than 100 mesh, with 90% passing through, to obtain anode mud powder. Add pure water to the anode mud powder to form a slurry (the solid-liquid mass ratio of anode mud powder to pure water in the slurry is 8:1). Add 1.3 times the theoretical amount of the oxidant sodium persulfate to the slurry. Carry out an oxidation reaction at a temperature of 70 °C with stirring for 100 min to oxidize the metallic silver particles in the slurry into silver peroxide. After cooling, perform solid-liquid separation to obtain 3.0058 kg of silver peroxide-tungsten slag. Add excessive ammonia water (the mass concentration of ammonia water is 13%, and the solid-liquid ratio of silver oxide slag to ammonia water is g:mL = 1:5) to the silver peroxide-tungsten slag. Dissolve silver peroxide at a temperature of 50 °C for 60 min to form a silver ammonia complex and enter the solution. Perform solid-liquid separation to obtain a silver ammonia complex solution (19.54 L, concentration 44.0483 g / L) and crude tungsten powder (2.2550 kg). In this section, since direct leaching is carried out without oxidation roasting, the power consumption is effectively reduced by more than 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 360 g;

[0046] (3) The crude tungsten powder is 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);

[0047] (4) Add a reducing agent (1.2 times the theoretical amount of hydrazine hydrate (N2H4)) to the silver ammonia complex solution. Carry out a reduction reaction at a temperature of 85 °C for 40 min. Perform solid-liquid separation. The solid is washed and dried to obtain reduced silver powder (purity 99.88%, mass 0.8606 kg);

[0048] In this embodiment, the recovery rate of silver is 99.51%, and the recovery rate of tungsten is 99.72%.

[0049] The specific embodiments of the present invention have been described in detail above. However, 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-tungsten: The silver-tungsten alloy waste is extruded into a shape and placed in a titanium basket as the anode, with a stainless steel plate as the cathode, and [[Ag(NH3)2]] + solution as the electrolyte, and electrolysis is carried out until the residual anode rate of the anode is 25-35% to obtain silver powder and anode slime; (2) Oxidative dissolution and secondary separation of silver and tungsten from anode slime: The anode slime is finely ground to obtain anode slime powder. The anode slime powder is slurried with pure water to obtain a slurry. An oxidant is added to the slurry, and an oxidative 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. An excessive amount of ammonia water is added to dissolve the silver peroxide, so that the silver peroxide forms a silver ammonia complex and enters the solution. Solid-liquid separation is carried out to obtain a silver ammonia complex solution and coarse tungsten powder; the oxidant is sodium persulfate; (3) The coarse tungsten powder is boiled and washed with a nitric acid solution and then boiled and washed with pure water in sequence, and then dried to obtain high-purity tungsten powder; (4) A reducing agent is added to the silver ammonia complex solution for a reduction reaction, and solid-liquid separation is carried out. The solid is washed and dried 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) [Ag(NH3)2] + The concentration of Ag ions in the solution is 180 - 200 g / L.

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

4. The method for recovering silver and tungsten from silver-tungsten alloy waste according to claim 3, characterized in that: In step (2), the proportion of the particle size of the anode slime powder below 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.

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

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 for boiling and washing with the nitric acid solution is 30-60 min, and the number of times is 3-4 times; the boiling time for boiling and washing with 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 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.