Method for recovering silver
By controlling the molar ratio of silver chloride precipitation and ultrasonic treatment, the problem of neutralization of silver nitrate solution is solved, and efficient recovery of silver and recycling of resources are achieved, which is suitable for industrial application.
Patent Information
- Application Number
- CN202510890047.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-06-30
- Publication Date
- 2025-09-30
AI Technical Summary
In existing silver recovery methods, silver nitrate solution needs to be neutralized into an alkaline environment before electrolysis, resulting in high alkali consumption and waste of resources. In addition, chloride is toxic and difficult to use in mass production.
The method comprises adding chloride to a silver nitrate solution to form a mixed solution, controlling the molar ratio of chlorine to silver to be no greater than 1, filtering and ultrasonically treating the silver chloride precipitate to dissolve it in a thiosulfate and pyrosulfite solution, and electrolyzing and recovering silver in a neutral or alkaline environment.
The method realizes efficient recovery of silver at room temperature, reduces the use of alkali, saves resources, and the filtrate can be recycled, which reduces costs and is suitable for industrial promotion.
Smart Images
Figure CN120719342A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of silver recovery, and particularly relates to a method for recovering silver. Background Art
[0002] The front electrode of crystalline silicon solar cells often uses silver paste (containing about 90% silver) as a conductive material. The high conductivity and stability of silver are crucial to cell efficiency. The cost of silver paste accounts for 10% to 15% of the total cost of solar cells, and is the second largest material cost in photovoltaic modules after silicon. The production of each 1GW of photovoltaic modules consumes about 20 to 30 tons of silver paste (containing about 18 to 27 tons of pure silver), while the annual output of global silver mines is only about 25,000 tons. The proportion of silver used in the photovoltaic industry has increased year by year (exceeding 15% in 2023). Recycling discarded solar cells not only has significant economic benefits, but also benefits environmental protection.
[0003] The silver recovery methods commonly used in the existing technology include physical crushing and chemical recovery. Physical crushing is to separate the silver-containing layer by screening, which has low purity, cannot effectively recover silver, and is time-consuming. Chemical recovery is to dissolve silver in nitric acid or cyanide and then replace or electrolytically recover it. Cyanide is highly toxic and cannot be mass-produced in the process. Therefore, the common recovery method is to dissolve silver in nitric acid for replacement or electrolytic recovery. However, the existing technology usually uses high-concentration nitric acid to dissolve silver, and the silver nitrate solution after the concentrated nitric acid dissolves the silver is used as the source for Ag extraction and recovery. Since the silver nitrate solution contains a large amount of nitric acid in addition to silver nitrate, the pH of the silver nitrate solution is acidic. When electrolytically recovering Ag, it needs to be carried out in a neutral or alkaline environment. Therefore, it is necessary to neutralize the silver nitrate solution with alkali first. This not only consumes a large amount of alkali, but also wastes the remaining nitric acid, resulting in a large amount of resource waste. Summary of the Invention
[0004] The purpose of the present invention is to overcome the defects of the existing method of using silver nitrate solution as the direct source of Ag extraction and recovery, which requires the silver nitrate solution to be neutralized with alkali, which not only consumes a large amount of alkali but also wastes the remaining nitric acid, and further provide a method for recovering silver.
[0005] The present invention provides a method for recovering silver, comprising the following steps:
[0006] (1) dissolving the silver-containing battery cell in nitric acid and filtering to obtain a silver nitrate solution;
[0007] (2) mixing a silver nitrate solution and a chloride salt to form a mixed solution, filtering to obtain a silver chloride precipitate and a filtrate, wherein the molar ratio of the chlorine element to the silver element in the mixed solution is not greater than 1;
[0008] (3) washing the silver chloride precipitate and mixing it with the first solution, subjecting it to ultrasonic treatment to dissolve the silver chloride precipitate in the first solution to form a mixed solution, and electrolyzing the mixed solution to obtain recovered silver; the first solution includes thiosulfate and pyrosulfite.
[0009] The silver recovery method provided by the present invention integrates silver dissolution and electrolytic recovery, making it portable and fast, suitable for industrial application. Recovery can be performed at room temperature, requiring minimal process requirements. Silver can be electrolytically recovered in a neutral or alkaline environment simply by washing and deacidifying the silver chloride. This simplifies the process and conserves alkali. Nitric acid in the unneutralized filtrate can be recycled to dissolve silver, reducing costs. Ultrasonic treatment can rapidly dissolve the silver chloride precipitate, making it possible to use the silver chloride precipitate for electrolytic recovery.
[0010] In an optional embodiment, the silver-containing cell is a silver grid cell;
[0011] In an optional embodiment, the molar ratio of chlorine element to silver element in the mixed solution in step (2) is (0.85-0.95):1.
[0012] In an optional embodiment, the process further includes recycling the filtrate from step (2) to step (1) for dissolving the silver-containing battery cells. When the filtrate is transported to step (1) to continue dissolving the silver-containing battery cells for recycling, it is ensured that there is sufficient nitric acid in the filtrate to continuously dissolve the silver-containing battery cells; the recycling of the filtrate ensures the continuous dissolution of silver and the continuous generation of silver chloride precipitates.
[0013] In industrial mass production applications, the actual amount of nitric acid input is far in excess of the amount of nitric acid required to dissolve the silver in each batch of silver grid cell sheets. The filtrate treated by the method provided by the present invention still contains nitric acid and can be recycled to the nitric acid tank for reuse. After each batch of cell sheets is treated, the concentration of nitric acid will decrease slightly. After treating multiple batches of cell sheets, new nitric acid will not be needed until the nitric acid concentration in the tank body decreases to a level that can no longer dissolve the silver grid lines on the silver grid cell sheets. The present invention does not specifically limit the amount of nitric acid added and can adopt the conventional selection in this field. The utilization rate of nitric acid is improved by recycling the filtrate, saving costs.
[0014] In an optional embodiment, before the filtrate in step (2) is reused in step (1), the filtrate in step (2) is further subjected to a chloride ion detection step, and the filtrate in step (2) is reused in step (1) after it is determined that the filtrate does not contain chloride ions. The filtrate can be detected by conventional methods in the art to determine whether it does not contain chloride ions. As an example, the following method can be used: the filtrate is added dropwise to a silver nitrate solution, and no precipitate is generated; chloride salt is added to the filtrate, and a precipitate is generated; this indicates that the filtrate does not contain chloride ions;
[0015] In an optional embodiment, the ultrasonic treatment temperature is 20-30°C;
[0016] In an optional embodiment, the ultrasonic treatment frequency is 20 kHz to 40 kHz;
[0017] In an optional embodiment, the ultrasonic treatment time is not less than 1 min; preferably, the ultrasonic treatment time is 1-10 min.
[0018] In an optional embodiment, the washing step in step (3) is performed until no nitric acid residue remains on the surface of the silver chloride precipitate; the absence of nitric acid residue on the silver chloride precipitate after washing can be detected by conventional methods in the art, for example, pH test paper can be used for detection;
[0019] Preferably, washing is performed with water.
[0020] In an optional embodiment, the concentration of nitric acid in step (1) is >20 wt %; preferably, the concentration of nitric acid is 40-70 wt %;
[0021] In an optional embodiment, the addition ratio of metallic silver to nitric acid in the silver-containing battery cell is no more than 1, with the unit being g:ml.
[0022] In an optional embodiment, the chloride salt in step (2) is added in the form of a chloride salt solution, preferably, the chloride salt solution is a saturated chloride salt solution;
[0023] Preferably, the chloride salt is selected from sodium chloride and / or potassium chloride.
[0024] In an optional embodiment, the concentration of AgNO3 in the mixed solution of step (3) is 10-15 g / L, the concentration of thiosulfate is 80-120 g / L, and the concentration of metabisulfite is 20-30 g / L;
[0025] Preferably, the thiosulfate is sodium thiosulfate and / or potassium thiosulfate;
[0026] Preferably, the metabisulfite is sodium metabisulfite and / or potassium metabisulfite.
[0027] In an optional embodiment, the parameters of the electrolysis satisfy at least one of the following (A)-(C):
[0028] (A) The current density of electrolysis is 0.1-1A / dm 2 ;
[0029] (B) electrolysis is performed at a pH of 7-9;
[0030] (C) The electrolysis was carried out at 20-30°C.
[0031] The technical solution of the present invention has the following advantages:
[0032] 1. The method for recovering silver provided by the present invention comprises the following steps: (1) dissolving a silver-containing battery cell in nitric acid and filtering to obtain a silver nitrate-containing solution; (2) mixing the silver nitrate-containing solution and a chloride salt to form a mixed solution, filtering to obtain a silver chloride precipitate and a filtrate, wherein the molar ratio of the chlorine element to the silver element in the mixed solution is not greater than 1; (3) washing the silver chloride precipitate and mixing it with a first solution, ultrasonically treating the solution so that the silver chloride precipitate dissolves in the first solution to form a mixed solution, and electrolyzing the mixed solution to obtain recovered silver; the first solution comprises thiosulfate and pyrosulfite.
[0033] The present invention first dissolves silver-containing battery cells in nitric acid and filters to obtain a silver nitrate solution, then mixes the silver nitrate solution with a chloride salt, and filters to obtain a silver chloride precipitate and a filtrate. During the process, the molar ratio of chlorine to silver in the mixed solution in step (2) is controlled to be no greater than 1 to ensure that the filtrate does not contain chloride ions. The obtained filtrate can be reused for dissolving the silver-containing battery cells. The inventors found that if the filtrate contains chloride ions, when the filtrate is used to dissolve the battery cells, the presence of chloride ions will cause silver chloride to adhere to the silver surface on the battery cells, greatly affecting the silver dissolution rate. The method of the present invention controls the molar ratio of chlorine to silver in the mixed solution in step (2) to be no greater than 1 to ensure that the filtrate does not contain chloride ions, so that the filtrate does not affect the reuse of the filtrate. At the same time, unreacted nitric acid in the filtrate can be effectively utilized, saving resources.
[0034] The silver chloride precipitate obtained in step (2) is washed and mixed with the first solution, and then ultrasonically treated. The inventors found in their research that if the silver chloride precipitate and the first solution are directly mixed and stirred, the silver chloride is difficult to dissolve in the first solution. In order to solve this problem, the inventors cleverly added an ultrasonic treatment step after mixing, so that the silver chloride precipitate can be dissolved in the first solution. The mixed solution obtained is then electrolyzed to obtain recovered silver. The present invention uses silver chloride as a direct source of recovered silver, overcoming the problem that silver chloride is difficult to dissolve in the first solution (electrolyte). At the same time, since a silver nitrate solution is no longer directly used as the electrolyte, there is no need to add a large amount of alkali for neutralization, which greatly saves resources.
[0035] The silver recovery method provided by the present invention integrates silver dissolution and electrolytic recovery, is portable and fast in process, and is suitable for industrial promotion; recovery can be carried out at room temperature, and has low process requirements; silver element is recovered by precipitation with silver chloride, and subsequent electrolysis can be carried out only after washing and deacidification of the silver element, which is a simple process and does not require the addition of alkali, and the filtrate can be recycled to continue dissolving silver, or a small amount of nitric acid can be added during the silver dissolution process to achieve continuous dissolution of silver, thereby reducing costs.
[0036] 2. The method for recovering silver provided by the present invention further ensures that the filtrate does not contain chloride ions, thereby affecting the reuse of the filtrate, by controlling the molar ratio of chlorine element to silver element in the mixed solution in step (2) to ((0.85-0.95):1).
[0037] 3. The method for recovering silver provided by the present invention further comprises the step of washing in step (3) until no nitric acid remains on the surface of the silver chloride precipitate; the present invention removes residual acid on the surface of the silver chloride precipitate by washing to prevent the residual acid from partially decomposing the thiosulfate. BRIEF DESCRIPTION OF THE DRAWINGS
[0038] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.
[0039] Figure 1 The silver-containing battery cell in Example 1 of the present invention;
[0040] Figure 2 The silver-containing battery cell after stirring for 1 minute in Example 2 of the present invention;
[0041] Figure 3 This is the thiosulfate system after ultrasonic treatment in Example 2 of the present invention. DETAILED DESCRIPTION
[0042] The following examples are provided for a better understanding of the present invention and are not intended to limit the best mode of implementation. They do not limit the content and scope of protection of the present invention. Any product identical or similar to the present invention obtained by anyone under the guidance of the present invention or by combining the features of the present invention with other prior arts shall fall within the scope of protection of the present invention.
[0043] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in this field can be used. If the manufacturer of the reagents or instruments is not specified, they are all commercially available conventional reagents.
[0044] The following examples and comparative examples are used to detect whether a solution contains chloride ions: 1 ml of the filtrate is added dropwise to 1 ml of a 0.1 mol / L silver nitrate solution; no precipitation is produced; then 1 ml of a new filtrate is added to 1 g of sodium chloride; a precipitation is produced, indicating that the solution does not contain chloride ions.
[0045] Example 1
[0046] This embodiment provides a method for recovering silver, comprising the following steps:
[0047] (1) At room temperature, the mechanically crushed silver grid cell was added to 42 wt% nitric acid, stirred and dissolved for 1 min, and filtered to obtain a silver nitrate solution and cell residue; the addition ratio of the silver grid cell to the nitric acid was 50:500, in units of g:ml; each silver grid cell weighed about 10 g and contained 0.7 wt% silver;
[0048] (2) adding a saturated sodium chloride solution to the silver nitrate solution, stirring and mixing (the molar ratio of chlorine to silver in the mixture is 0.85:1), filtering to obtain a silver chloride precipitate and a filtrate, and detecting whether the filtrate contains chloride ions;
[0049] (3) The silver chloride precipitate was washed with water until no nitric acid residue remained on the surface of the precipitate, and then added to the first solution (the first solution contained 10 g / L AgNO3, 120 g / L Na2S2O3, and 30 g / L K2S2O5) and mixed. The mixture was ultrasonically treated (frequency 40 kHz, 1 min, temperature 25°C) until the silver chloride precipitate was completely dissolved in the first solution to form a mixed solution. The mixed solution (pH of the mixed solution was 7-9) was electrolyzed at a current density of 1 A / dm 2 , the electrolysis temperature is 25℃, and recovered silver is obtained.
[0050] Depend on Figure 1 It can be seen that there is no precipitate in the thiosulfate system after ultrasonic treatment, indicating that the silver chloride precipitate has been completely dissolved.
[0051] Example 2
[0052] This embodiment provides a method for recovering silver, comprising the following steps:
[0053] (1) At room temperature, the mechanically crushed silver grid cell was added to 42 wt% nitric acid, stirred and dissolved for 1 min, and filtered to obtain a silver nitrate solution and cell residue. The addition ratio of the silver grid cell to the nitric acid was 40:600, expressed in g:ml. Each silver grid cell weighed approximately 10 g and contained 0.7 wt% silver.
[0054] (2) adding a saturated potassium chloride solution to a silver nitrate solution, stirring and mixing (the molar ratio of chlorine to silver in the mixture is 0.95:1), filtering to obtain a silver chloride precipitate and a filtrate, and detecting whether the filtrate contains chloride ions;
[0055] (3) The silver chloride precipitate was washed with water until no nitric acid residue remained on the surface of the precipitate, and then added to the first solution (the first solution contained 15 g / L AgNO3, 80 g / L Na2S2O3, and 20 g / L K2S2O5) and mixed. The mixture was ultrasonically treated (frequency 40 kHz, 10 min, temperature 30°C) until the silver chloride precipitate was completely dissolved in the first solution to form a mixed solution. The mixed solution (pH of the mixed solution was 7-9) was electrolyzed at a current density of 0.1-1 A / dm 2 , the electrolysis temperature is 30℃, and recovered silver is obtained.
[0056] (4) At room temperature, add the mechanically crushed silver grid cell and cell residue to the filtrate obtained in step (2), stir and dissolve for 1 minute, filter to obtain a silver nitrate solution and cell residue, and repeat steps (2)-(3). Figure 2-3 It can be seen that the silver grid lines of the silver grid line battery cell are completely dissolved after the filtrate is stirred for 1 minute.
[0057] Comparative Example 1
[0058] Take 100 ml of the filtrate obtained in step (2) of Example 2, and add 10 ml of saturated potassium chloride solution to the filtrate to obtain a chlorine-containing filtrate, that is, the chlorine-containing filtrate contains chloride ions.
[0059] The chlorine-containing filtrate was divided into two equal parts, and two silver grid line battery cells were added into each part. After stirring the chlorine-containing filtrate for 1 minute, silver grid lines were obviously present in one part. The silver grid line battery cell was taken out and dried. After weighing, the mass of the silver grid line battery cell remained almost unchanged. After stirring the chlorine-containing filtrate for 1 hour, the silver grid line battery cell was taken out and dried. After weighing, it was found that the mass of the silver grid line battery cell decreased by 0.05%, and the mass of the silver grid line battery cell decreased slightly. It can be seen from the comparison between Example 2 and Comparative Example 1 that the presence of chloride ions will significantly hinder the dissolution rate of silver.
[0060] Comparative Example 2
[0061] This comparative example provides a method for recovering silver. Compared with Example 1, the only difference is that in step (3), stirring for 10 min (temperature 25°C, speed 800 r / min) is used instead of ultrasonic treatment (40 kHz; 1 min, temperature 25°C) in Example 1;
[0062] After stirring for 10 minutes, there was still a precipitate in the thiosulfate system. The precipitate was taken out, dried, and weighed. The mass of the precipitate remained almost unchanged, indicating that the silver chloride precipitate could not be completely dissolved by stirring. The precipitate was re-added to the thiosulfate system and stirred for another hour. The precipitate still clearly existed. The precipitate was taken out, dried, and weighed. The mass of the precipitate decreased by 0.1%. The mass of the precipitate decreased slightly, indicating that the silver chloride precipitate was extremely difficult to dissolve in the thiosulfate system.
[0063] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.
Claims
1. A method for recovering silver, characterized in that: The steps include: (1) dissolving the silver-containing battery cell in nitric acid and filtering to obtain a silver nitrate solution; (2) mixing a silver nitrate solution and a chloride salt to form a mixed solution, filtering to obtain a silver chloride precipitate and a filtrate, wherein the molar ratio of the chlorine element to the silver element in the mixed solution is not greater than 1; (3) washing the silver chloride precipitate and mixing it with the first solution, subjecting it to ultrasonic treatment to dissolve the silver chloride precipitate in the first solution to form a mixed solution, and electrolyzing the mixed solution to obtain recovered silver; the first solution includes thiosulfate and pyrosulfite.
2. The method for recovering silver according to claim 1, wherein: The molar ratio of chlorine element to silver element in the mixed solution in step (2) is (0.85-0.95):
1.
3. The method for recovering silver according to claim 1 or 2, characterized in that: The method also includes recycling the filtrate in step (2) to step (1) for dissolving the silver-containing battery cells.
4. The method for recovering silver according to claim 3, wherein: Before the filtrate in step (2) is recycled to step (1), the method further includes a step of detecting chloride ions on the filtrate in step (2), and recycling the filtrate to step (1) after determining that the filtrate in step (2) does not contain chloride ions.
5. The method for recovering silver according to any one of claims 1 to 4, characterized in that: The ultrasonic treatment temperature is 20-30°C; and / or, The ultrasonic treatment frequency is 20 kHz to 40 kHz; and / or, The ultrasonic treatment time is not less than 1 min; preferably, the ultrasonic treatment time is 1-10 min.
6. The method for recovering silver according to any one of claims 1 to 5, characterized in that: In step (3), the washing step is performed until no nitric acid remains on the surface of the silver chloride precipitate; Preferably, washing is performed with water.
7. The method for recovering silver according to any one of claims 1 to 6, characterized in that: The concentration of nitric acid in step (1) is >20 wt %; preferably, the concentration of nitric acid is 40-70 wt %; and / or, The addition ratio of metallic silver and nitric acid in the silver-containing battery cell is not greater than 1, and the unit is g:ml.
8. The method for recovering silver according to any one of claims 1 to 7, characterized in that: In step (2), the chloride salt is added in the form of a chloride salt solution, preferably, the chloride salt solution is a saturated chloride salt solution; Preferably, the chloride salt is selected from sodium chloride and / or potassium chloride.
9. The method for recovering silver according to any one of claims 1 to 8, characterized in that: The concentration of AgNO3 in the mixed solution of step (3) is 10-15 g / L, the concentration of thiosulfate is 80-120 g / L, and the concentration of pyrosulfite is 20-30 g / L; Preferably, the thiosulfate is sodium thiosulfate and / or potassium thiosulfate; Preferably, the metabisulfite is sodium metabisulfite and / or potassium metabisulfite.
10. The method for recovering silver according to claim 1 or 8, characterized in that: The parameters of the electrolysis satisfy at least one of the following (A)-(C): (A) The current density of electrolysis is 0.1-1A / dm 2 ; (B) electrolysis is performed at a pH of 7-9; (C) The electrolysis was carried out at 20-30°C.