A silver recovery method

Abstract

The application discloses a silver recovery method, comprising the following steps: configuring a first eutectic solvent and a second eutectic solvent, and immersing silver-containing waste in the first eutectic solvent; removing the first eutectic solvent after ultrasonic reaction at 70-100 DEG C for 10-15 min, and adding the second eutectic solvent for reaction for 15-60 min, wherein the oxidant comprises copper chloride, peroxide and halogen; separating the mixture to obtain leaching solution, and performing pulse electrodeposition on the leaching solution as electrolyte, with a current density of 200-400 A / m 2 , a pulse duty ratio of 20-60%, and a pulse frequency of 100-1000 Hz; using the electrolyte as the second eutectic solvent to perform leaching reaction on the silver-containing waste; and taking the cathode deposit silver. The application uses the first eutectic solvent and the second eutectic solvent to sequentially leach the silver-containing waste in a segmented manner, can leach base metals in advance, and can obtain silver-containing waste with higher purity. The copper chloride composition is used as the oxidant to cooperate, so that silver ions are massively leached in the second eutectic solvent, and the purity of the silver ions is improved.

Description

Technical Field

[0001] This invention belongs to the field of solid waste recycling and hydrometallurgical technology, and particularly relates to a silver recovery method. Background Technology

[0002] With the rapid development of the electronics and information industry and the accelerated pace of product upgrades, waste electronic devices have become one of the fastest-growing categories of solid waste globally. Statistics show that my country generates over 10 million tons of electronic waste annually, containing a significant amount of precious metal resources. For example, waste circuit boards can contain 1000–3000 g / t of silver, far exceeding the levels found in primary silver ore, making them extremely valuable for recycling.

[0003] Currently, the mainstream technologies for recovering silver from waste electronic devices mainly fall into two categories: pyrometallurgy and hydrometallurgy. Pyrometallurgy involves high-temperature smelting to concentrate precious metals such as silver in crude copper or lead, followed by electrolytic refining. This technology has a large processing capacity and wide applicability, but it suffers from significant problems such as high energy consumption, large equipment investment, and the generation of toxic and harmful gases like dioxins during the smelting process, resulting in considerable environmental pressure. Hydrometallurgy is currently the most widely used method for silver extraction. Its core principle is to use chemical reagents to transfer metallic silver from the solid phase to the liquid phase, and then recover it through precipitation, reduction, or electrolysis.

[0004] Traditional hydrometallurgy typically uses nitric acid or aqua regia as leaching agents, achieving silver leaching rates of over 98%. However, this method is highly corrosive and oxidizing, and the leaching process generates large amounts of acidic waste gas containing nitrogen oxides (NOx) and acidic waste liquid containing heavy metal ions, posing significant environmental risks. Furthermore, in systems containing base metals such as copper, nitric acid exhibits poor selectivity for silver, complicating subsequent separation and purification processes.

[0005] In recent years, researchers have begun to focus on the application of eutectic solvents (DES) in the field of metal recycling. DES is generally composed of hydrogen bond acceptors (such as choline chloride) and hydrogen bond donors (such as ethylene glycol, urea, oxalic acid, etc.) in a certain molar ratio. It has advantages such as low vapor pressure, good thermal stability, biodegradability, and good solubility for metal oxides and salts, and is regarded as a green alternative to traditional organic solvents and strong acid media.

[0006] However, since waste electronic devices contain a variety of metals and have a low silver content, most of the metals can be leached in eutectic solvents, which makes the separation of silver difficult. Summary of the Invention

[0007] This invention provides a method for recovering silver, comprising the following steps: Silver-containing waste is obtained by crushing and sorting silver-containing waste materials; A first eutectic solvent and a second eutectic solvent are prepared. The silver-containing waste is immersed in the first eutectic solvent and reacted at 70℃~100℃ for 10-15 min under ultrasonic action. After the reaction, the first eutectic solvent is removed, and the second eutectic solvent is added again to continue the reaction for 15 min~60 min. The oxidant in the second eutectic solvent includes copper chloride. The mixture of silver-containing waste and a second, re-added eutectic solvent is separated to obtain a leachate. This leachate is then used as an electrolyte for pulse electrodeposition, where silver metal is deposited on the cathode, and monovalent copper ions in the leachate are oxidized to divalent copper ions. The current density in this process is 200–400 A / m³. 2 The pulse duty cycle is 20-60%, and the pulse frequency is 100-1000 Hz. The electrolyte after pulse electrodeposition was used as a second eutectic solvent to leach silver-containing waste. The deposited material at the cathode during pulse electrodeposition was used to recover silver metal.

[0008] Specifically, silver-containing waste includes one or more of the following: waste crystalline silicon photovoltaic panels, waste circuit boards, and silver-plated waste.

[0009] Specifically, the first eutectic solvent includes at least one of the following: a composition of oxalic acid and a polyol, a composition of oxalic acid and choline chloride, a composition of oxalic acid, choline chloride and toluenesulfonic acid, a composition of choline chloride, urea and a diol, and a composition of choline chloride and a sulfonamide.

[0010] It should be noted that the role of the first eutectic solvent is to initiate the leaching reaction of the silver-containing waste, preferentially leaching out the base metals to achieve a higher purity of silver in the leached waste. Furthermore, the absence of an oxidizing agent in the first eutectic solvent helps retain the more stable silver, preventing its loss.

[0011] In practical applications, silver-containing waste can be tested before recycling to determine the types of metals present, allowing for the selection of a first eutectic solvent. For example, a combination of oxalic acid and polyols is used to leach lithium and cobalt; a combination of oxalic acid and choline chloride is used to leach nickel, cobalt, and manganese; a combination of oxalic acid, choline chloride, and toluenesulfonic acid is used to leach nickel; a combination of choline chloride, urea, and diols is used to leach zinc; and a combination of choline chloride and sulfonamides is used to leach gold and palladium. In some embodiments, the silver-containing waste can be immersed in a first eutectic solvent in sequence according to the metals it contains to remove base metals.

[0012] Specifically, the main purpose of the second eutectic solvent is to directionally leach silver ions from high-purity silver-containing waste. The second eutectic solvent includes: betaine hydrochloride, quaternary ammonium salt, polyol and oxidant, wherein the molar ratio of betaine hydrochloride, quaternary ammonium salt and polyol is 1:(0.5~1)(3-8), preferably 1:(0.6~0.8)(4-6), and more preferably 1:0.7:5.

[0013] It should be noted that betaine hydrochloride has a wider electrochemical stability window and can withstand higher voltages without decomposition. Therefore, during pulse electrodeposition, higher voltages can be applied without damaging the solvent. Simultaneously, betaine hydrochloride exhibits good thermal stability, ensuring stability during high-temperature leaching and long-term cyclic use. Quaternary ammonium salts possess strong coordination ability, providing abundant chloride ions to form stable complexes with leached silver ions. They also exhibit excellent stability, low viscosity, and are biodegradable. Furthermore, they can modulate the overall polarity of the solvent, promoting dissolution.

[0014] Specifically, quaternary ammonium salts include: tetramethylammonium chloride, tetraethylammonium chloride, tetrabutylammonium chloride, and tributyltetradecylphosphonium chloride; polyols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, glycerol, sorbitol, etc.

[0015] Because polyols have low viscosity and high conductivity, they can reduce the viscosity of the eutectic flux system. Therefore, although the hydrogen bond acceptor betaine hydrochloride has high viscosity, its combination with quaternary ammonium salt and polyol does not affect the overall conductivity of the solvent, which is beneficial for diffusion during the leaching process and silver electrodeposition. In addition, polyols have low melting points and are not easily decomposed under heating, exhibiting high stability. Therefore, polyols are selected as hydrogen bond donors in this invention. Furthermore, polyols are rich in hydroxyl groups, which can form hydrogen bonds and complexes with metal ions. Alcohols with different chain lengths will change the polarity and surface tension of the eutectic solvent, i.e., affect its affinity for different metal ions. To facilitate silver leaching, ethylene glycol and 1,3-propanediol are more preferably selected as hydrogen bond donors, as they have a strong affinity for silver ions and can more easily selectively leach silver ions. Tetramethylammonium chloride or tetraethylammonium chloride is selected as the quaternary ammonium salt.

[0016] Cu provided by copper chloride in a eutectic solvent 2+Elemental silver can be oxidized to silver ions. Simultaneously, chloride ions form a stable complex with the dissolved silver ions, continuously driving the reaction and ensuring the continuous leaching of silver ions. In practical applications, to promote the decomposition of silver and desulfurize silver-containing waste, this embodiment uses a combination of copper chloride, peroxide, and halogen as the oxidant. The molar ratio of copper chloride, peroxide, and halogen is 1:(0.5~1):(0.05-0.5), preferably 1:(0.6~0.8):(0.1-0.3). Specifically, the peroxide is hydrogen peroxide or potassium persulfate, and the halogen is iodine or N-bromosuccinimide. This embodiment of the invention uses a combination of copper chloride, peroxide, and halogen as the oxidant, which utilizes the strong oxidizing properties of halogen to rapidly leach silver while reducing copper leaching. The combination with peroxide further enhances the oxidizing power.

[0017] Specifically, the present invention utilizes ultrasound to assist the leaching process. The ultrasonic power of the ultrasound assistance is 150-300 W, and the ultrasonic frequency is 25-40 kHz. Preferably, the ultrasonic power is 200-250 W and the ultrasonic frequency is 30-35 kHz. The heating temperature is 70℃-100℃, preferably 80℃-90℃.

[0018] This invention utilizes the ultrasonic cavitation effect to increase the reaction activation energy, enabling metal leaching in a shorter time at temperatures of only 70℃ to 100℃, thus improving leaching efficiency. Preferably, the leaching temperature is 75℃ to 85℃.

[0019] Ultrasonic waves can continuously peel away the passivation layer on the surface of the waste, allowing the eutectic solvent to continuously contact the internal silver particles and utilize copper ions to oxidize elemental silver into silver ions, which then complex with chloride ions. This process is a diffusion process, and the complexation of silver ions promotes the continuous and stable leaching of silver ions. However, other base metals dissolve relatively quickly in the initial stage of leaching, but the reaction rate decreases as their concentration in the leachate increases, eventually reaching a stable state. In this invention, a first eutectic solvent is used for 10-15 minutes in the first stage of the reaction to remove eutectic solvents with higher base metal content. In the second stage, a second eutectic solvent is used to leach silver ions, resulting in purer leached silver ions and improved leaching purity. Specifically, the leaching time in the first stage is 10-15 minutes, preferably 12-14 minutes, and after changing the eutectic solvent, the leaching time in the second stage is 15-60 minutes, preferably 20-30 minutes.

[0020] After leaching, the mixture can be separated by filtration or centrifugation.

[0021] Furthermore, the base metals are extracted from the first eutectic solvent after leaching.

[0022] This invention, by controlling the average current density and pulse duty cycle of pulse electrodeposition, can precisely maintain the cathode potential within the silver deposition potential range (-0.2V to +0.vs. Ag / AgCl), avoiding the deposition of other metals such as copper (below approximately -0.4V). Specifically, the pulse electrodeposition current density is 250~300 A / m. 2 The pulse duty cycle is 30-50%, the pulse frequency is 400-700 Hz, and the temperature is 30-60℃. Preferably, the pulse electrodeposition current density is 270-290 A / m. 2 The pulse duty cycle is 35-45%, the pulse frequency is 500-600 Hz, and the temperature is 40-50℃.

[0023] Furthermore, this invention utilizes pulse electrodeposition, which allows the depletion layer on the electrode surface to be restored in a timely manner during the pulse off period (Toff), thus alleviating concentration polarization promptly. Silver deposition can be carried out at a slightly higher average current density, effectively suppressing impurity co-deposition and obtaining silver powder with higher purity.

[0024] It should be noted that the cathode used in pulse electrodeposition is porous or mesh titanium or stainless steel, and the anode is graphite or platinum.

[0025] Furthermore, the concentration of silver ions in the electrolyte is monitored during the pulse electrodeposition process. Electrodeposition is stopped when the silver ion concentration reaches below 0.05 g / L, which can prevent base metal deposition and improve the purity of silver recovery.

[0026] Furthermore, after electrodeposition, the cathode is removed, and the silver powder deposited on the cathode surface is scraped off. After washing with deionized water, dehydration with anhydrous ethanol, and vacuum drying, a high-purity silver powder product is obtained. The supernatant after electrodeposition is purified by activated carbon adsorption and dehydrated by molecular sieve drying. Then, 0.1–5% of the lost amount of oxidant and / or eutectic solvent components are added as a eutectic solvent to mix with silver-containing waste for recycling. This invention utilizes electrodeposition to directly remove monovalent copper ions from oxidized silver.

[0027] Specifically, when extracting silver from the cathode, the silver powder scraped from the cathode is acid-washed, dried, and smelted to obtain recovered silver ingots.

[0028] This invention utilizes a first low-eutectic solvent to directionally remove base metals while retaining silver, and a second low-eutectic solvent to extract silver. In other words, the segmented extraction process can minimize the interference of base metals and improve the purity of silver.

[0029] This invention employs an oxidizing agent composition, namely, the synergistic effect of copper chloride, peroxide and halogen, as an eutectic solvent. Under the action of ultrasound, the oxidizing agent continuously oxidizes silver, causing silver ions to form a complex with chloride ions, thus continuously leaching out silver ions.

[0030] With the assistance of ultrasound, this invention controls the leaching time and replaces the eutectic solvent in a timely manner, allowing silver ions to leach out in large quantities in the new eutectic solvent. This improves the purity of silver ions in the leachate and effectively isolates them from base metals.

[0031] This invention utilizes pulse electrodeposition to precisely maintain the cathode potential within the silver deposition potential range by controlling the average current density and pulse duty cycle, thereby accurately depositing silver and further avoiding interference from other base metals, thus improving the purity of silver recovery. Detailed Implementation

[0032] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit this application.

[0033] Example 1 1. Take waste polycrystalline silicon photovoltaic cell sheets, mechanically crush them, and then pyrolyze them at 450°C for 60 minutes to remove the surface EVA film, thus obtaining pretreated silver-containing waste (silver content of about 630 g / t).

[0034] 2. Preparation of the first DES: Oxalic acid and choline chloride are combined in a molar ratio of 1:1.

[0035] The second DES preparation: Betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol were mixed in a molar ratio of 1:0.7:6 and heated and stirred at 100°C until a clear and transparent liquid was formed. An oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) was added, wherein CuCl2·2H2O was added to a concentration of 0.1 mol / L. The mixture was stirred until homogeneous to obtain an oxidized DES leaching system.

[0036] 3. Leaching operation: Add the above silver-containing waste to the first DES system at a solid-liquid ratio of 1:500 (g / mL), place it in an ultrasonic reactor, set the ultrasonic power to 200 W and the frequency to 30 kHz, react at 80℃ for 12 min, remove the original DES, add new DES at a solid-liquid ratio of 1:500 (g / mL) and continue the reaction for 30 min.

[0037] 4. Solid-liquid separation: After the reaction is complete, filter to obtain silver-rich leachate and silver-removed residue.

[0038] 5. Pulse Electrodeposition: A silver-rich leaching solution was used as the electrolyte in a three-electrode electrolytic cell. The cathode was a titanium plate (working area 50 mm × 50 mm), the anode was a graphite plate, and the reference electrode was an Ag / AgCl electrode. Linear scan voltammetry was first performed at a scan rate of 5 mV / s to determine the initial deposition potential of silver as +0.015 V (vs. Ag / AgCl). The pulse electrodeposition parameters were set as follows: average current density 250 A / m². 2 The pulse duty cycle was 40%, and the pulse frequency was 500 Hz. Deposition was carried out under these conditions for 2 hours.

[0039] 6. Silver recovery: After deposition, the cathode product is scraped off, washed with dilute nitric acid (5% by volume), rinsed with deionized water, and vacuum dried to obtain silver powder.

[0040] Comparative Example 1 The difference between Comparative Example 1 and Example 1 lies in the leaching operation in step 3.

[0041] Leaching process: The silver-containing waste was added to the second DES system at a solid-liquid ratio of 1:500 (g / mL), placed in an ultrasonic reactor, and the ultrasonic power was set to 200 W and the frequency to 30 kHz. The reaction was carried out at 80℃ for 42 min.

[0042] The difference between Comparative Examples 2-3 and Example 1 lies in the composition of the second DES in step 2.

[0043] Comparative Example 2 Preparation of the second DES: Mix choline chloride and ethylene glycol in a molar ratio of 1:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0044] Comparative Example 3 Preparation of the second DES: Mix betaine hydrochloride with ethylene glycol in a molar ratio of 1:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0045] Comparative Example 4 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0046] Comparative Example 5 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride and potassium persulfate in a molar ratio of 1:0.7) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0047] Comparative Example 6 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride and N-bromosuccinimide in a molar ratio of 1:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0048] The difference between Examples 2-10 and Example 1 lies in the composition of the second DES.

[0049] Example 2 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.5:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0050] Example 3 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.8:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0051] Example 4 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:1:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0052] Example 5 Preparation of the second DES: Betaine hydrochloride, tetraethylammonium chloride, and ethylene glycol are mixed in a molar ratio of 1:0.7:6 and heated and stirred at 100°C until a clear and transparent liquid is formed. An oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) is added, wherein CuCl2·2H2O is added to a concentration of 0.1 mol / L, and the mixture is stirred until homogeneous.

[0053] Example 6 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.5) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0054] Example 7 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.1) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0055] Example 8 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, potassium persulfate, and N-bromosuccinimide in a molar ratio of 1:0.7:0.3) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0056] Example 9 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, hydrogen peroxide, and N-bromosuccinimide in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0057] Example 10 Preparation of the second DES: Mix betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol in a molar ratio of 1:0.7:6, heat and stir at 100°C until a clear and transparent liquid is formed, add the oxidant composition (copper chloride, hydrogen peroxide, and iodine in a molar ratio of 1:0.7:0.2) and CuCl2·2H2O to a concentration of 0.1 mol / L, and stir until homogeneous.

[0058] The silver powder obtained from the above comparative examples and embodiments was detected by inductively coupled plasma optical emission spectrometry (ICP-OES). The inductively coupled plasma optical emission spectrometer was an Avio 550 Max.

[0059] The purity of silver recovered from the newly configured first and second DES in Examples 1-10 and Comparative Examples 1-6 was tested. The purity of the silver was greater than 99.9%. The first and second DES were cycled 30 times and then used for silver recovery. The purity of the silver was tested again, and the results are shown in Table 1 below: Table 1. Purity of silver recovered from Comparative Examples 1-6 and Examples 1-10

[0060] As shown in Comparative Example 1 and Example 1, the first DES can significantly remove base metals and improve the purity of silver. Comparing Comparative Examples 2 and 3 with Example 1, the lack of betaine hydrochloride and quaternary ammonium salts significantly reduces the purity of silver ions, indicating that the three components in the second DES can work synergistically to improve the leaching purity of silver. Comparing Comparative Examples 4-6 with Example 1, the purity of silver recovered from the three components in the oxidant is significantly better than that from oxidants with only one or two components.

[0061] As shown in Examples 1-4, the highest purity was achieved in Example 1 when betaine hydrochloride, tetramethylammonium chloride, and ethylene glycol were mixed in a molar ratio of 1:0.7:6.

[0062] As can be seen from Examples 1 and 5, tetraethylammonium chloride in Example 5 has the highest purity.

[0063] As can be seen from Examples 1, 6-8, the purity in Examples 1, 7, and 8 is significantly higher than that in Example 6. As can be seen from Examples 9 and 10, the purity was lower than that of Example 1 when hydrogen peroxide was used instead of potassium persulfate and iodine was used instead of N-bromosuccinimide.

[0064] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

[0065] The above description is only a partial embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for recovering silver, characterized in that, Includes the following steps: Silver-containing waste is obtained by crushing and sorting silver-containing waste materials; A first eutectic solvent and a second eutectic solvent are prepared. The silver-containing waste is immersed in the first eutectic solvent and reacted at 70℃~100℃ for 10-15 min under ultrasonic action. After the reaction, the first eutectic solvent is removed, and the second eutectic solvent is added to continue the reaction for 15 min~60 min. The oxidant composition in the second eutectic solvent includes copper chloride, peroxide, and halogen. The mixture of silver-containing waste and a second eutectic solvent is separated to obtain a leachate. This leachate is then used as an electrolyte for pulse electrodeposition, where silver metal is deposited on the cathode, and monovalent copper ions in the leachate are re-oxidized to divalent copper ions. The current density is 200–400 A / m³. 2 The pulse duty cycle is 20-60%, and the pulse frequency is 100-1000 Hz. The electrolyte after pulse electrodeposition was used as a second eutectic solvent to leach silver-containing waste. The deposited material at the cathode during pulse electrodeposition was used to recover silver metal.

2. The recycling method according to claim 1, characterized in that, The first eutectic solvent includes at least one of the following: a composition of oxalic acid and a polyol, a composition of oxalic acid and choline chloride, a composition of oxalic acid, choline chloride and toluenesulfonic acid, a composition of choline chloride, urea and a diol, and a composition of choline chloride and a sulfonamide.

3. The recycling method according to claim 2, characterized in that, The second eutectic solvent includes: betaine hydrochloride, quaternary ammonium salt and polyol; The molar ratio of betaine hydrochloride, quaternary ammonium salt and polyol is 1:(0.5~1)(3-8).

4. The recycling method according to claim 1, characterized in that, The molar ratio of copper chloride, peroxide and halogen in the oxidant is 1:(0.5~1):(0.05-0.5), and the concentration of copper chloride is 0.08~0.15 mol / L.

5. The recycling method according to claim 1, characterized in that, The current density of pulse electrodeposition is 250–300 A / m 2 The pulse duty cycle is 30-50%, the pulse frequency is 400-700 Hz, and the temperature is 30-60℃.

6. The recycling method according to claim 1, characterized in that, Also includes: During pulse electrodeposition, the concentration of silver ions in the electrolyte is monitored, and electrodeposition is stopped when the concentration of silver ions reaches below 0.05 g / L.

7. The recycling method according to claim 6, characterized in that, Also includes: The base metals are recovered from the leachate of the first eutectic solvent.

8. The recycling method according to claim 6, characterized in that, The cathode used in pulse electrodeposition is porous or mesh titanium or stainless steel, and the anode used in pulse electrodeposition is graphite or platinum.

9. The recycling method according to claim 1, characterized in that, The ultrasonic power of the ultrasound-assisted ultrasound system is 150–300W, and the ultrasonic frequency is 25–40 kHz.

10. The recycling method according to claim 1, characterized in that, The silver powder scraped from the cathode is acid-washed, dried, and then melted and cast to obtain recovered silver ingots.

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