A method for recovering silver from silver-containing waste material

Abstract

This invention relates to a method for recovering silver from silver-containing waste. The method comprises the following steps: placing the silver-containing waste in a reaction solution, heating and stirring it at a first temperature, filtering to obtain a silver leaching solution and filter residue; cooling the silver leaching solution to a second temperature to precipitate a precipitate, filtering to obtain silver chloride and the remaining reaction liquid; the reaction solution comprises at least a variable-valence oxidant and a halide ion ligand; the temperature difference between the first and second temperatures is at least 20°C. This invention solves the problems of existing wet silver recovery processes, such as strong reagent corrosivity, high reagent consumption, unstable efficiency, cumbersome extraction steps, and large waste volume.

Description

Technical Field

[0001] This invention relates to the field of precious metal recycling technology, specifically to a method for recovering silver from silver-containing waste. Background Technology

[0002] Metallic silver is chemically stable and possesses excellent electrical and thermal conductivity, as well as good ductility, making it widely used in various fields such as electronics, jewelry, photosensitive materials, and photovoltaic new energy. In my country, the supply of silver includes mined silver, recycled silver, and other imported concentrate by-products. In recent years, the proportion of recycled silver has gradually increased. Recycled silver is mainly extracted from materials such as photosensitive materials, electronic products, catalysts, and silver jewelry, where silver exists primarily in its elemental metallic form. With the continuous growth in demand for silver from downstream industries, especially the rapid development of the photovoltaic industry, the production of silver from mines can no longer meet the demand, thus necessitating the extraction and recycling of recycled silver from silver-containing materials.

[0003] Silver-containing materials typically undergo pretreatment before entering the silver recovery process. Currently, the main silver recovery processes are pyrometallurgical and hydrometallurgical methods. Pyrometallurgical processes are more suitable for processing materials with high silver content and large-scale operations, such as silver extraction from ore metallurgy. They facilitate silver enrichment and anode plate preparation, laying the foundation for subsequent silver electrolytic refining. However, since most silver-containing waste materials have low silver content, generally below 5%, hydrometallurgical extraction methods are more suitable.

[0004] The wet silver extraction process mainly includes two key steps: leaching silver from the material and extracting silver from the solution. Because silver has a high oxidation potential, there are two strategies for the silver leaching stage. One is to directly oxidize and leach silver using strong oxidants such as nitric acid or chlorate, but this method has problems such as strong corrosiveness, easy generation of toxic gases, and difficult wastewater treatment. The other is to introduce ligands (such as cyanide, thiosulfate, and thiourea) to lower the potential required for silver oxidation, and then use an oxidant with moderate oxidizing power, such as cyanidation. ), thiosulfate process ( ), thiourea method ( While the cyanidation method is highly toxic, the thiosulfate and thiourea methods suffer from problems such as poor ligand stability, easy decomposition and consumption, high cost, and unstable efficiency.

[0005] Methods for extracting silver from silver leaching solutions include sodium chloride precipitation, extraction-back-extraction-reduction, resin adsorption-desorption-reduction, and electrodeposition. Among these, extraction and resin methods are less commonly used due to cost, complex processes, and limited types of silver extractants / adsorbents. Electrodeposition is only suitable for high-concentration silver-containing solutions; its extraction efficiency decreases rapidly as the silver concentration decreases, and it also consumes a lot of energy. Sodium chloride precipitation is currently the most widely used method. The resulting silver chloride precipitate can be further processed into metallic silver through methods such as ammonia leaching-hydrazine hydrate reduction. However, this method still requires an additional sodium chloride precipitation step and generates a large amount of waste liquid.

[0006] In summary, the main problems with existing silver hydrometallurgical recovery processes include: reliance on strong acids and oxidants leading to high corrosivity, high reagent consumption, unstable efficiency, cumbersome extraction steps, and large waste volume. Summary of the Invention

[0007] In view of this, the purpose of this invention is to provide a method for recovering silver from silver-containing waste, so as to solve the problems of strong reagent corrosivity, large reagent consumption, unstable efficiency, cumbersome extraction steps and large waste volume in the existing silver wet recovery process.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for recovering silver from silver-containing waste includes the following steps:

[0010] S1. Place the silver-containing waste in the reaction solution, heat and stir the reaction under the first temperature condition, filter, and obtain silver leaching solution and filter residue;

[0011] S2. Cool the silver leaching solution to a second temperature to precipitate the precipitate, filter, and obtain silver chloride and the remaining reaction solution;

[0012] The reaction solution comprises at least a variable-valence oxidant and a halide ion ligand;

[0013] The temperature difference between the first temperature and the second temperature is at least 20°C.

[0014] The present invention discloses a method for recovering silver from silver-containing waste. First, it uses high-valence metal ions and halide ions as silver extraction reagents to replace highly corrosive, toxic, and unstable chemical reagents such as nitric acid, hypochlorous acid, cyanide, and thiourea. These reagents are more environmentally friendly, stable, and easy to store, prepare, and use. Second, it uses variable metal ions as reactants, where high-valence metal ions undergo electron transfer reactions with silver in the material. The reaction is fast and efficient, generating low-valence metal ions and silver ions. Third, silver leaching and separation can be achieved through simple heating and cooling operations. This method is simple to operate and has a short process flow. It is a green, low-consumption, high-efficiency, and streamlined silver extraction method, effectively solving the problems of strong reagent corrosivity, high reagent consumption, unstable efficiency, cumbersome extraction steps, and large waste volume in existing silver wet recovery processes.

[0015] Preferably, the variable valence oxidant is selected from divalent copper ions (Cu). 2+ ), trivalent iron ions (Fe 3+ ), trivalent cobalt ions (Co 3+ ), tetravalent tin ions (Sn) 4+ ), tetravalent manganese ions (Mn) 4+ ) and hexavalent chromium ions (Cr 6+ At least one of the following.

[0016] Preferably, the halide ion ligand is selected from chloride ions (Cl... - ) and bromide ions (Br - One or two of them.

[0017] Preferably, the concentration of the variable oxidant in the reaction solution is 0.005–2 mol / L.

[0018] Preferably, the concentration of the variable oxidant in the reaction solution is 0.2 to 1 mol / L.

[0019] Preferably, the concentration of the halide ion ligand in the reaction solution is 0.5 mol / L to the saturation concentration.

[0020] Preferably, the concentration of halide ion ligands in the reaction solution is 3.5 mol / L to the saturation concentration.

[0021] Preferably, the reaction solution further comprises a solvent and hydrochloric acid;

[0022] The solvent is selected from water;

[0023] The concentration of hydrochloric acid in the reaction solution is 0.01 mol / L to 5.5 mol / L.

[0024] The actual amount of hydrochloric acid added should be sufficient to prevent the metal ions in the reaction solution from hydrolyzing, and the pH range of the reaction solution should be adjusted to -0.78 to 6.

[0025] Preferably, the pH range of the reaction solution is 0.5 to 3.

[0026] Preferably, the first temperature is 50℃~95℃.

[0027] Preferably, the second temperature is 0℃~30℃.

[0028] Preferably, the solid-liquid ratio of the silver-containing waste to the reaction solution is 1:1 to 1:50.

[0029] Preferably, the stirring rate is 300 rpm to 2000 rpm.

[0030] Preferably, the heating and stirring reaction time is 20 min to 2 h.

[0031] Preferably, the holding time for cooling the silver leaching solution to the second temperature is 1 min to 30 min.

[0032] Preferably, hydrochloric acid is added to the reaction residue, and air is introduced to regenerate the variable oxidant in the reaction residue, which is then used as a reaction solution to achieve recycling.

[0033] The method cleverly and simply involves introducing air to regenerate low-valence metal ions in the reaction residue into high-valence metal ions through a simple single-electron loss reaction, which can then be reused. This greatly reduces reagent consumption and waste liquid generation, lowers the cost of silver extraction, and has the advantages of being green, environmentally friendly, and recyclable, making it suitable for large-scale industrial production.

[0034] Preferably, the number of moles of hydrochloric acid added to the reaction residue is equal to the number of moles of silver in the silver leaching solution, the regeneration temperature is 25℃~70℃, and the air introduction rate is 0.01m. 3 / h~0.2m 3 / h.

[0035] Preferably, the silver-containing waste is selected from at least one of waste electronic components, waste photovoltaic materials, waste catalysts, and anode mud.

[0036] The beneficial effects of this invention are:

[0037] The present invention discloses a method for recovering silver from silver-containing waste. First, it uses high-valence metal ions and halide ions as silver extraction reagents to replace highly corrosive, toxic, and unstable chemical reagents such as nitric acid, hypochlorous acid, cyanide, and thiourea. These reagents are more environmentally friendly, stable, and easier to store, prepare, and use. Second, it uses variable metal ions as reactants, where high-valence metal ions react with silver in the material via electron transfer. This reaction is fast and efficient, generating low-valence metal ions and silver ions. Third, silver leaching and separation can be achieved through simple heating and cooling operations. This method is simple to operate and has a short process flow. It is a green, low-consumption, high-efficiency, and streamlined silver extraction method, effectively solving the problems of strong reagent corrosivity, high reagent consumption, unstable efficiency, cumbersome extraction steps, and large waste volume in existing silver wet recovery processes. The process has a wide range of applications and is valuable for promotion and application in the field of precious metal recovery technology. Attached Figure Description

[0038] Figure 1 For Ag + / Ag and Cu 2+ / Cu + Graph showing the change in electrode potential with chloride ion concentration;

[0039] Figure 2 The graph shows the change in silver ion solubility in a 5.5 mol / L sodium chloride solution with temperature.

[0040] Figure 3 This is a process flow diagram for silver extraction when the silver in the silver-containing material is in a metallic or alloy state.

[0041] Figure 4 The X-ray diffraction pattern of the silver chloride product precipitated in Example 1;

[0042] Figure 5 This is a scanning electron microscope image of the silver chloride product precipitated in Example 1;

[0043] Figure 6 This is a scanning electron microscope image of the silver chloride product precipitated in Example 2;

[0044] Figure 7 This is a scanning electron microscope image of the silver chloride product precipitated in Example 3;

[0045] Figure 8 This is a process flow diagram for silver extraction when the silver in the silver-containing material is in the form of silver salt or oxide. Detailed Implementation

[0046] The following description, with reference to preferred embodiments, illustrates the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are merely illustrative of the present invention and not intended to limit the scope of protection of the present invention.

[0047] The present invention aims to disclose a method for recovering silver from silver-containing waste, in order to solve the problems of existing silver wet recovery processes, such as strong reagent corrosivity, large reagent consumption, unstable efficiency, cumbersome extraction steps, and large waste volume.

[0048] A method for recovering silver from silver-containing waste includes the following steps:

[0049] S1. Place the silver-containing waste in the reaction solution, heat and stir the reaction under the first temperature condition, filter, and obtain silver leaching solution and filter residue;

[0050] S2. Cool the silver leaching solution to a second temperature to precipitate the precipitate, filter, and obtain silver chloride and the remaining reaction solution;

[0051] The reaction solution must include at least a variable-valence oxidant and a halide ion ligand.

[0052] The temperature difference between the first temperature and the second temperature is at least 20°C.

[0053] The above-mentioned method for recovering silver from silver-containing waste firstly utilizes high-valence metal ions and halide ions as silver extraction reagents, replacing highly corrosive, toxic, and unstable chemical reagents such as nitric acid, hypochlorous acid, cyanide, and thiourea. These reagents are more environmentally friendly, stable, and easier to store, prepare, and use. Secondly, variable metal ions are used as reactants, where high-valence metal ions react with silver in the material via electron transfer, resulting in a fast and efficient reaction that generates low-valence metal ions and silver ions. Thirdly, silver leaching and separation can be achieved through simple heating and cooling operations, offering advantages such as simple operation and a short process flow. This method is a green, low-consumption, and highly efficient silver extraction method. It effectively solves the problems of existing wet silver recovery processes, such as highly corrosive reagents, high reagent consumption, unstable efficiency, cumbersome extraction steps, and large waste volume.

[0054] The principle behind the dissolution of silver in silver-containing materials upon heating is that the coordination of halide ions lowers the silver oxidation potential, and the higher the halide ion concentration, the lower the silver oxidation potential. The coordination of halide ions increases or almost eliminates the reduction potential of variable-valence oxidants, such as... Figure 1 Ag shown + / Ag and Cu 2+ / Cu+ The electrode potential changes with chloride ion concentration. The coordination of halide ions makes silver more easily oxidized, and the oxidizing power of variable-valence oxidants is enhanced, thus enabling the silver oxidation reaction to occur. Simultaneously, at high chloride ion concentrations and high temperatures, the solubility of silver ions increases without forming silver chloride precipitate, such as... Figure 2 The solubility of silver ions in a 5.5 mol / L sodium chloride solution varies with temperature, as shown in the figure. (Using Cu...) 2+ -Cl - Taking the system as an example, the equation for the temperature-induced dissolution reaction of silver is:

[0055]

[0056] The principle behind the cooling precipitation of silver chloride is that in high-concentration halide ion solutions, the solubility of silver ions varies greatly with temperature. This difference in solubility at high and low temperatures allows for the cooling precipitation of silver chloride. For example, in a 5.5 mol / L chloride ion solution, when the temperature decreases from 75℃ to 25℃, the solubility of silver ions decreases from over 3 g / L to approximately 0.8 g / L, meaning that 73.33% of the silver can precipitate as silver chloride. After more than 5 cycles of silver extraction, the total silver recovery rate exceeds 95%. Increasing the operating temperature difference can further increase the yield per cooling cycle. (The last sentence appears to be incomplete and possibly refers to a specific process involving Cu.) 2+ -Cl - Taking the system as an example, the reaction equation for the precipitation of silver chloride upon cooling is:

[0057]

[0058] In some embodiments, the variable oxidant is selected from divalent copper ions (Cu). 2+ ), trivalent iron ions (Fe 3+ ) and tetravalent tin ions (Sn 4+ At least one of the following.

[0059] In some embodiments, the halide ion ligand is selected from chloride ions (Cl... - ) and bromide ions (Br - One or two of them.

[0060] In some embodiments, the concentration of the variable oxidant in the reaction solution is 0.005 mol / L to 2 mol / L.

[0061] In some embodiments, the concentration of the variable oxidant in the reaction solution is 0.2 mol / L to 1 mol / L.

[0062] In some embodiments, the concentration of halide ion ligands in the reaction solution is 0.5 mol / L to the saturation concentration.

[0063] In some embodiments, the concentration of halide ion ligands in the reaction solution is 3.5 mol / L to the saturation concentration.

[0064] In some embodiments, the reaction solution further comprises a solvent and hydrochloric acid;

[0065] The solvent is water;

[0066] The concentration of hydrochloric acid in the reaction solution ranges from 0.01 mol / L to 5.5 mol / L.

[0067] The actual amount of hydrochloric acid added should be sufficient to prevent the metal ions in the reaction solution from hydrolyzing, and the pH range of the reaction solution should be adjusted to -0.78 to 6.

[0068] In some embodiments, the pH range of the reaction solution is 0.5 to 3.

[0069] In some embodiments, the first temperature is 50°C to 95°C.

[0070] In some embodiments, the second temperature is 0°C to 30°C.

[0071] In some embodiments, the solid-liquid ratio of the silver-containing waste to the reaction solution is 1:1 to 1:50.

[0072] In some embodiments, the stirring rate is 300 rpm to 2000 rpm.

[0073] In some embodiments, the heating and stirring reaction time is 20 min to 2 h.

[0074] In some embodiments, the holding time for cooling the silver leaching solution to the second temperature is 1 min to 30 min.

[0075] In some embodiments, hydrochloric acid is added to the reaction residue and air is introduced to regenerate the variable oxidant in the reaction residue, which is then used as a reaction solution to achieve recycling.

[0076] The method cleverly and simply involves introducing air to regenerate low-valence metal ions in the reaction residue into high-valence metal ions through a simple single-electron loss reaction, thus enabling reuse. This greatly reduces reagent consumption and waste liquid generation, lowers silver extraction costs, and has the advantages of being green and environmentally friendly, making it suitable for large-scale industrial production.

[0077] In some embodiments, the number of moles of hydrochloric acid added to the reaction residue is equal to the number of moles of silver in the silver leaching solution, the regeneration temperature is 25°C to 70°C, and the air introduction rate is 0.01 m / s. 3 / h~0.2m 3 / h.

[0078] The principle of residual liquid regeneration is as follows: when silver in silver-containing materials is in a metallic state, the silver leaching reaction is an electron-loss reaction. By using an oxidant with reversible electron gain and loss, i.e., a variable-valence metal ion oxidant, the silver leaching reaction changes from a high-valence state to a low-valence state, and then through an electron-loss reaction changes it from a low-valence state to a high-valence state, thus achieving regeneration and recycling. Cu... 2+ -Cl - Taking the system as an example, the reaction equation for the air regeneration of the solution after the reaction is as follows:

[0079]

[0080] In fact, the entire silver extraction reaction is a silver oxidation leaching reaction with oxygen, Cu 2+ -Cl - It exhibits a catalytic-like effect. The oxygen oxidation leaching reaction of silver is a gas-solid reaction; unless high-temperature, high-pressure oxygen pressure leaching conditions are employed, the reaction rate is slow, making practical applications difficult. The introduction of Cu... 2+ -Cl - It serves as a carrier for redox reactions, greatly improving the efficiency of silver extraction reactions.

[0081] The above mainly addresses the case where silver in silver-containing materials is in its metallic state, which is also the most common chemical form of silver. When the silver in the silver-containing material is a soluble silver salt such as silver nitrate, silver fluoride, silver acetate, or silver sulfate, it can be directly leached using aqueous solution or corresponding anionic acid solution. When the silver in the silver-containing material is a silver salt with low water solubility such as silver chloride, silver bromide, or silver citrate, silver can be extracted directly using a high halide ion concentration solution by heating to dissolve and cooling to precipitate. When the silver in the silver-containing material is a very insoluble silver salt such as silver cyanide or silver iodide, the above methods are difficult to achieve silver extraction. When the silver in the silver-containing material is silver oxide, it may be necessary to increase the acidity of the solution in addition to the heating to dissolve and cooling to precipitate method. The silver chloride product obtained by the above methods can be further processed into metallic silver by roasting or ammonia leaching-hydrazine hydrate reduction.

[0082] When the silver-containing material being processed contains other metals besides silver, such as copper, iron, nickel, tin, palladium, and lead, these metals may also enter the solution. When the concentration of these other metal ions is low, they have almost no impact on the silver extraction efficiency of the method. When the concentration of these other metal ions is high, they may precipitate simultaneously with the cooling of silver chloride, and the amount of hydrochloric acid required for the solution regeneration stage will increase. When the concentration of these other metal ions accumulates to a certain level and affects the silver extraction efficiency, methods are needed to purify the solution, including precipitating lead ions with sodium sulfate and neutralizing and precipitating iron ions.

[0083] In some embodiments, the silver-containing waste is selected from at least one of waste electronic components, waste photovoltaics, waste catalysts, and anode mud.

[0084] To make the technical problems, technical solutions, and beneficial effects solved by this application clearer, the method for recovering silver from silver-containing waste according to the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. Obviously, the specific embodiments described are only some embodiments of this application, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its application. Based on the specific embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0085] Where specific techniques or conditions are not specified in the detailed embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0086] like Figure 3 As shown, a method for recovering silver from silver-containing waste is described. In this embodiment, the silver-containing waste is decommissioned crystalline silicon solar cells. After multiple pretreatment steps such as dismantling and sorting, the decommissioned crystalline silicon solar cells yield silver-containing cell material, which contains 0.7% silver, with the remainder mainly being silicon. The method for recovering silver includes the following steps:

[0087] S1. Preparation of the reaction solution: 1.52 kg of copper chloride dihydrate, 32.14 kg of sodium chloride, 83.33 mL of concentrated hydrochloric acid, and 99.92 L of water were mixed to prepare a halide ion coordination-enhanced regenerable reaction solution; wherein, the concentration of copper ions in the reaction solution was 0.1 mol / L, the concentration of hydrochloric acid was 0.01 mol / L, and the concentration of sodium chloride was 5.5 mol / L;

[0088] S2. The reaction solution obtained in S1 is loaded into a reaction vessel and preheated to 80°C. 50 kg of silver-containing battery cell material is added, and the mixture is stirred at 400 rpm for 10 min to complete the leaching of silver from the battery cell. The mixture is then filtered at 80°C to obtain silver leachate and filter residue. The silver leaching rate is found to be over 98%, and the silver ion concentration in the silver leachate is approximately 3500 mg / L.

[0089] S3. Cool the silver leaching solution obtained in S2 to 20℃ and maintain it for 5 minutes. It can be observed that white silver chloride precipitate is precipitated in the silver leaching solution and settles to the bottom. Filter to obtain silver chloride product and reaction residue. According to the calculation by formula (I), the single silver recovery rate is about 80%.

[0090] S4. Heat the remaining reaction liquid obtained in S3 to 50℃, add 270.4 mL of concentrated hydrochloric acid, and aerate for 10 min at an aeration rate of 0.05 m / s. 3 / h, while evaporating some water to keep the total solution volume at 100L. During aeration and evaporation, the cuprous ions in the remaining reaction liquid are converted back into copper ions, completing the solution regeneration and recycling.

[0091] The above steps constitute one silver extraction cycle. After five cycles, the total silver recovery rate was calculated using formula (II) to reach 96%, and it increased with the further increase in the number of cycles.

[0092] like Figure 3 As shown, a method for recovering silver from silver-containing waste is described. In this embodiment, the silver-containing waste is electrolytic copper anode sludge, representing the extraction of silver from materials containing silver and other metals. The electrolytic copper anode sludge has the following metal composition: 33% tin, 6% lead, 1.5% silver, 1% palladium, and 0.2% gold. Tin and lead exist as tin dioxide and lead sulfate, respectively, while gold, silver, and palladium exist in metallic form. The method for recovering silver includes the following steps:

[0093] S1. Preparation of reaction solution: 2.16 kg ferric chloride hexahydrate, 21.04 kg sodium chloride, 6.67 L concentrated hydrochloric acid and 73.33 L water were mixed to prepare a halide ion coordination enhanced regenerable reaction solution; wherein, in the reaction solution, the concentration of ferric ions was 0.1 mol / L, the concentration of hydrochloric acid was 1 mol / L and the concentration of sodium chloride was 4.5 mol / L.

[0094] S2. The reaction solution obtained in S1 is loaded into a reaction vessel and preheated to 75°C. 16 kg of electrolytic copper anode mud is added, and the mixture is stirred at 600 rpm for 20 min to complete the leaching of silver from the electrolytic copper anode mud. The mixture is then filtered at 75°C to obtain silver leachate and filter residue. The silver leaching rate is found to be over 97%, and the silver ion concentration in the silver leachate is approximately 3000 mg / L. Simultaneously with the silver leaching, lead and palladium in the anode mud are also leached into the solution, with concentrations of 0.058 mol / L and 0.019 mol / L, respectively.

[0095] S3. Cool the silver leaching solution obtained in S2 to 25℃ and maintain it for 3 minutes. It can be observed that white silver chloride precipitate is formed in the silver leaching solution and settles to the bottom. Filter to obtain silver chloride product and reaction residue. According to the calculation by formula (I), the single silver recovery rate is 73%.

[0096] S4. Heat the remaining reaction liquid obtained in S3 to 60℃, add 310.7 mL of concentrated hydrochloric acid, and aerate for 15 min at an aeration rate of 0.1 m / s². 3 / h, while evaporating some water to keep the total solution volume at 80L, and adding sodium sulfate to precipitate lead ions, generating lead sulfate precipitate which is then filtered out, completing the solution regeneration and recycling.

[0097] If lead sulfate is not precipitated, lead ions in the solution will precipitate as lead chloride during the cooling stage in the subsequent silver extraction process, making it difficult to obtain pure silver chloride product (i.e., Comparative Example 2).

[0098] The above steps constitute a silver extraction cycle. After ten cycles, the total silver recovery rate, calculated using formula (II), exceeds 97%, and the palladium ion concentration in the solution accumulates to 0.19 mol / L. When the palladium ion concentration reaches a high level, palladium is extracted through extraction, displacement, or other methods, and the solution can then be recycled.

[0099] like Figure 8 As shown, a method for recovering silver from silver-containing waste is described. In this embodiment, the silver-containing waste is a chlorination leaching residue, representing the extraction of silver from materials containing silver salts. The silver content in the chlorination leaching residue is 3%, existing in the form of silver chloride.

[0100] Since silver exists in the form of silver salts and does not require an oxidizing agent, variable-valence metal ions do not need to be added to the reaction solution. The method for recovering silver includes the following steps:

[0101] S1. Preparation of reaction solution: 26.3 kg sodium chloride, 83.33 mL concentrated hydrochloric acid and 199.92 L water were mixed to prepare a halide ion coordination enhanced regenerable reaction solution; wherein, the concentration of hydrochloric acid in the reaction solution was 0.01 mol / L and the concentration of sodium chloride was 4.5 mol / L;

[0102] S2. The reaction solution obtained in S1 is loaded into a reaction vessel and preheated to 90°C. 20 kg of chlorination leaching residue is added, and the mixture is stirred at 800 rpm for 5 minutes to complete the leaching of silver salts from the chlorination leaching residue. The mixture is then filtered at 90°C to obtain silver leaching solution and filter residue. The silver leaching rate is found to be over 98%, and the silver ion concentration in the silver leaching solution is approximately 3000 mg / L.

[0103] S3. The silver leaching solution obtained in S2 is cooled to 15℃ and held for 5 minutes. A white silver chloride precipitate is observed to precipitate in the silver leaching solution and settle to the bottom. The silver chloride product and the reaction residue are obtained by filtration. According to the calculation by formula (I), the silver recovery rate in a single reaction is about 83.3%.

[0104] The remaining liquid from the reaction can be directly reused in cycles of heating to dissolve silver and cooling to extract silver, without consuming reagents throughout the process.

[0105] The above steps constitute a silver extraction cycle. After eight cycles, the total silver recovery rate was calculated using Equation (II) to be close to 98%, and it increased with the further increase in the number of cycles.

[0106] like Figure 3As shown, a method for recovering silver from silver-containing waste is described. In this embodiment, the silver-containing waste is a spent silver-containing industrial catalyst, representing the extraction of silver from materials containing silver and other metals. The silver content in the silver-containing catalyst is 10%–20%, with a few cases reaching as high as 40%, and it exists in the form of elemental metallic silver. In this embodiment, the silver content in the spent silver-containing catalyst is 14.8%. The method for recovering silver includes the following steps:

[0107] S1. Preparation of reaction solution: 2.08 kg tin chloride, 21.04 kg sodium chloride, 6.67 L concentrated hydrochloric acid and 73.33 L water were mixed to prepare a halide ion coordination enhanced regenerable reaction solution; wherein, in the reaction solution, the concentration of tin ions was 0.1 mol / L, the concentration of hydrochloric acid was 1 mol / L and the concentration of sodium chloride was 4.5 mol / L.

[0108] S2. The reaction solution obtained in S1 is loaded into a reaction vessel and preheated to 75°C. 8 kg of depleted silver-containing catalyst is added, and the mixture is stirred at 600 rpm for 20 min to complete the leaching of silver from the industrial waste catalyst. The mixture is then filtered at 75°C to obtain silver leachate and filter residue. The silver leaching rate is found to be over 98%, and the silver ion concentration in the silver leachate is approximately 5000 mg / L.

[0109] S3. Cool the silver leaching solution obtained in S2 to 20℃ and maintain it for 5 minutes. It can be observed that white silver chloride precipitate is formed in the silver leaching solution and settles to the bottom. Filter to obtain silver chloride product and reaction residue. According to the calculation by formula (I), the single silver recovery rate is 76%.

[0110] S4. Heat the remaining reaction liquid obtained in S3 to 50℃, add 252.5 mL of concentrated hydrochloric acid, and aerate for 5 min at an aeration rate of 0.05 m / s. 3 / h, while evaporating some water to keep the total solution volume at 100L. During aeration and evaporation, the stannous ions in the remaining reaction liquid are converted back into tin ions, completing the solution regeneration and recycling.

[0111] The above steps constitute one silver extraction cycle. After five cycles, the total silver recovery rate was calculated using formula (II) to reach 98%, and it increased with the further increase in the number of cycles.

[0112] Comparative Example 1

[0113] A method for recovering silver from silver-containing waste, wherein the silver-containing waste in this comparative example is waste ceramic capacitors, representing a situation where the content of other metals in the material is much higher than that of silver. The waste ceramic capacitors are composed of barium titanate / lead titanate and various metal electrodes, containing 12.8% nickel, 2% silver, 1.8% copper, 1.57% tin, and 0.4% palladium; the method for recovering silver includes the following steps:

[0114] S1. Prepare a halide ion coordination-enhanced regenerable reaction solution by mixing 2.44 kg of copper chloride dihydrate, 25.71 kg of sodium chloride, 66.67 mL of concentrated hydrochloric acid, and 79.93 L of water; wherein, in the reaction solution, the concentration of copper ions is 0.2 mol / L, the concentration of hydrochloric acid is 0.01 mol / L, and the concentration of sodium chloride is 5.5 mol / L.

[0115] S2. The reaction solution obtained in S1 is loaded into a reaction vessel, and the reaction solution is preheated to 80°C. 16 kg of crushed waste ceramic capacitor powder is added, and the mixture is stirred at 500 rpm for 30 minutes to carry out the leaching reaction. At this time, there are no silver ions in the leachate, and the main component is nickel ions. This is because the nickel content in the raw material is too high, and nickel is more reactive than silver, so it reacts preferentially with the copper ions oxidizing agent in the reaction solution, causing it to be completely consumed.

[0116] Comparative Example 2

[0117] A method for recovering silver from silver-containing waste is disclosed. In this comparative example, the silver-containing waste is electrolytic copper anode sludge, representing the situation where the concentration of other metal ions in the reaction solution is too high after multiple cycles. This comparative example 2 differs from Example 2 in that sodium sulfate is not added to precipitate lead ions during the regeneration stage of the reaction residue. The remaining steps are the same as in Example 2.

[0118] Since sodium sulfate is not added to precipitate lead ions during the regeneration stage of the reaction residue, some lead chloride precipitate is present in the silver chloride precipitate that is cooled and precipitated in the second cycle extraction stage.

[0119] Detection and Analysis

[0120] 1) The white silver chloride precipitate that precipitated in S3 of Example 1 was analyzed by X-ray diffraction and scanning electron microscopy. The results are as follows: Figure 4 and Figure 5 As shown.

[0121] from Figure 4 and Figure 5 The test results show that the precipitated white silver chloride is a pure silver chloride product.

[0122] 2) The white silver chloride precipitate that precipitated in S3 of Example 2 was analyzed by scanning electron microscopy, and the results are as follows: Figure 6 As shown.

[0123] from Figure 6 The test results show that the precipitated white silver chloride is a pure silver chloride product.

[0124] 3) The white silver chloride precipitate that precipitated in S3 of Example 3 was analyzed by scanning electron microscopy, and the results are as follows: Figure 7 As shown.

[0125] from Figure 7 The test results show that the precipitated white silver chloride is a pure silver chloride product.

[0126] 4) Silver recovery rate testing

[0127] The precipitated silver chloride product is weighed, and the mass of silver in the product is calculated using the relative atomic mass ratios of the elements. The recovery rate of silver in a single run can be calculated using the following formula:

[0128]

[0129] In equation (I), M Ag M represents the relative atomic mass of Ag, with units of g / mol; AgCl This represents the relative molecular mass of AgCl, expressed in g / mol; m AgCl The mass of the product AgCl is expressed in grams (g); m 总Ag This indicates the total mass of silver in the sample, expressed in grams; a Ag This indicates the recovery rate of silver per run, expressed in percent.

[0130] The silver recovery rate after multiple cycles can be calculated using the following formula:

[0131]

[0132] In equation (II), M Ag M represents the relative atomic mass of Ag, expressed in g / mol; AgCl This represents the relative molecular mass of AgCl, expressed in g / mol; m i-AgCl This indicates the mass of AgCl produced after each cycle, in grams (g); m 总Ag This indicates the total mass of silver in the sample, expressed in grams. Ag This represents the overall silver recovery rate, expressed as a percentage (%).

[0133] In summary, the method for recovering silver from silver-containing waste of the present invention has at least the following advantages: (1) High-valence metal ions and halide ions are used as silver extraction reaction reagents to replace highly corrosive, toxic, and unstable chemical reagents such as nitric acid, hypochlorous acid, cyanide, and thiourea. The reagents are more green, environmentally friendly, stable, and easy to store, prepare, and use. (2) Compared with silver extraction process routes such as acid leaching-sodium chloride precipitation, leaching-adsorption-desorption-electrolysis, the present invention can achieve silver leaching and separation with simple heating and cooling operations. The operation is simple and the process flow is short. By designing an alternating parallel reaction process, heat exchange can be carried out between a heating silver leaching section and another cooling silver precipitation section, which can significantly reduce the overall process energy consumption. (3) Variable metal ions are used as reactants. High-valence metal ions undergo electron transfer reactions with silver in the material. The reaction speed is fast and the efficiency is high, generating low-valence metal ions and silver ions. Low-valence metal ions can be regenerated into high-valence metal ions through a simple single-electron loss reaction for reuse, which greatly reduces reagent consumption and waste liquid generation, lowers silver extraction costs, has a wide range of applications, and has promotion and application value in the field of precious metal recycling technology. It is suitable for industrial promotion in the field of photovoltaic module recycling technology.

[0134] The above embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention.

Claims

1. A method for recovering silver from silver-containing waste, characterized in that, Includes the following steps: S1. Place the silver-containing waste in the reaction solution, heat and stir the reaction under the first temperature condition, filter, and obtain silver leaching solution and filter residue; S2. Cool the silver leaching solution to a second temperature to precipitate the precipitate, filter, and obtain silver chloride and the remaining reaction solution; The reaction solution consists of a variable-valence oxidant, a halide ion ligand, hydrochloric acid, and water. The temperature difference between the first temperature and the second temperature is at least 20°C; The silver-containing waste is electrolytic copper anode sludge, and the metal composition of the electrolytic copper anode sludge is: 33% tin, 6% lead, 1.5% silver, 1% palladium, and 0.2% gold. Among them, tin and lead exist in the form of tin dioxide and lead sulfate, respectively, while gold, silver, and palladium exist in the metallic state. The obtained reaction residue is heated to 60°C, hydrochloric acid is added to the reaction residue, and sodium sulfate is added to precipitate lead ions. The precipitate of lead sulfate is filtered out, and air is introduced to regenerate the variable valence oxidant in the reaction residue. Then it is used as a reaction solution to achieve recycling. The variable valence oxidizing agent is selected from at least one of divalent copper ions (Cu 2+ ), trivalent iron ions (Fe 3+ ), trivalent cobalt ions (Co 3+ ), tetravalent tin ions (Sn 4+ ), tetravalent manganese ions (Mn 4+ ), and hexavalent chromium ions (Cr 6+ ). The concentration of the variable oxidant in the reaction solution is 0.005–2 mol / L; The concentration of halide ion ligands in the reaction solution is 0.5 mol / L to the saturation concentration; The concentration of hydrochloric acid in the reaction solution is 0.01 mol / L to 5.5 mol / L.

2. The method for recovering silver from silver-containing waste according to claim 1, characterized in that, The halide ion ligand is selected from chloride ions (Cl). - ) and bromide ions (Br - One or two of them.

3. The method for recovering silver from silver-containing waste according to claim 1, characterized in that, The first temperature is 50℃~95℃; And / or, the second temperature is 0℃~30℃.

4. The method for recovering silver from silver-containing waste according to claim 1, characterized in that, The solid-liquid ratio of the silver-containing waste to the reaction solution is 1:1 to 1:

50.

5. The method for recovering silver from silver-containing waste according to claim 1, characterized in that, The stirring speed is 300 rpm to 2000 rpm; And / or, the heating and stirring reaction time is 20 min to 2 h.

Images