Method for recycling metallic silver from waste crystalline silicon battery piece

Abstract

The invention belongs to the technical field of rare and precious metal recovery, and particularly relates to a method for recovering metallic silver from waste crystalline silicon battery pieces, which comprises the following steps: (1) putting the waste crystalline silicon battery pieces into an inorganic alkali aqueous solution for soaking reaction to obtain an aluminum-containing solution and dealuminized crystalline silicon pieces; (2) adding the dealuminized crystal silicon wafer into a mixed solution of organic acid and hydrogen peroxide for soaking reaction, filtering and washing to respectively obtain silver-containing filtrate and a silver-removed silicon wafer; (3) carrying out chlorination precipitation reaction on the silver-containing filtrate and a chlorine source, filtering and drying to obtain silver chloride powder; (4) adding silver chloride powder into an ammonia water solution, heating and stirring to completely dissolve silver chloride to obtain a silver-ammonia solution; (5) adding PVP (Polyvinyl Pyrrolidone) into the silver-ammonia solution, heating and stirring until the PVP is completely dissolved, adding ascorbic acid, and carrying out reduction reaction at room temperature to obtain metal silver powder precipitate; and filtering, washing and drying the precipitate to obtain the spherical silver powder. According to the method, the silver recovery efficiency is high, the spherical nanoscale silver powder can be prepared, and the purity is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of rare and precious metal recovery, and in particular relates to a method for recovering metallic silver from waste crystalline silicon solar cells. Background Art

[0002] With the onset of a wave of photovoltaic retirements, the disposal of spent crystalline silicon cells has become a pressing issue. Silver, a key electrode material, accounts for approximately 0.1%-0.7% of these spent cells, making it a valuable resource for recycling. Traditional methods for recovering silver from spent crystalline silicon cells, mostly using nitric acid and aqua regia, suffer from low efficiency, high pollution levels, and poor quality of the recovered product.

[0003] Nano-scale silver powder, due to its unique physical and chemical properties, has broad application prospects in photovoltaic silver paste, catalysis, antibacterial materials, and other fields, and is in high market demand. Photovoltaic silver paste primarily consists of an organic carrier, silver powder, and glass powder. Silver powder, as the conductive phase, accounts for 80-90% of the total paste mass, with a particle size of 0.1-5μm. Nano-silver powder can significantly improve the conductivity and stability of photovoltaic silver paste. In the field of catalysis, nano-silver powder acts as a highly efficient catalyst, accelerating chemical reaction rates. As an antibacterial material, nano-silver powder exhibits excellent antibacterial properties and is widely used in the medical, hygiene, textile, and other industries.

[0004] Therefore, developing efficient and environmentally friendly waste crystalline silicon cell recycling technology, especially for the recovery of metallic silver and its preparation into high-value-added nano-scale silver powder, can not only reduce resource waste and alleviate dependence on primary silver mine resources, but also meet the market's urgent demand for high-quality silver powder.

[0005] Most existing technologies use hydrometallurgical methods, using leaching liquid to leach silver from waste crystalline silicon solar cells and then reducing the silver to elemental silver powder. For example: Chinese patent document CN106629738A discloses a method for extracting silver from crystalline silicon solar panels. After removing the aluminum layer with a sodium hydroxide solution, the silver is leached with a mixed solution of an organic acid and hydrogen peroxide, and then electrolyzed to produce silver powder. This patent utilizes an electrolytic method to produce silver powder, which results in high energy consumption and equipment investment, making it unsuitable for large-scale industrial application. Chinese patent document CN117926006A discloses a leaching solution and leaching method for dissolving silver. Silver is leached using an aqueous solution of hydrogen peroxide and ammonia under illumination. This patent's process is complex and limited by conditions such as illumination. Chinese patent document CN118109699A discloses a method for recovering aluminum and silver from discarded crystalline silicon cells using ultrasound. The dealuminated crystalline silicon wafers are added to an aqueous solution of ferric chloride and hydrochloric acid, and the silver is removed by ultrasound. The ammonia is then reduced with hydrazine hydrate to produce silver powder. This patent utilizes products such as hydrazine hydrate, which are highly toxic and pose significant risks to humans and the environment. Furthermore, the process is complex and limited by conditions such as ultrasound.

[0006] As can be seen, existing technologies for recovering silver from scrapped crystalline silicon cells suffer from environmental concerns, low efficiency, high costs, and demanding process conditions. The industry typically uses a nitric acid system to leach silver, producing nitrogen oxides that pose significant environmental risks. Furthermore, the purity of silver powder produced by existing technologies needs to be improved, and control over its microstructure is lacking.

[0007] In view of this, it is worthwhile to continue developing silver recovery technology from waste crystalline silicon solar cells and improving the purity and yield of silver powder. Summary of the Invention

[0008] The present invention aims to address the problems of low efficiency, poor environmental performance, and the need to improve product purity and microstructure in current silver recovery technologies from waste crystalline silicon solar cells. The present invention provides a method for recovering metallic silver from waste crystalline silicon solar cells. The method has high silver recovery efficiency (a silver recovery rate is stable at over 95%), and can produce spherical nano-scale silver powder with obvious microstructural advantages. The powder has a smooth surface, a regular morphology, a particle size between 50 and 300 nm, and a high purity (over 99.90%). In addition, the silver is leached using a mixed solution of organic acid and hydrogen peroxide (methanesulfonic acid-hydrogen peroxide solution). The mixed solution can be recycled, thereby avoiding the harm to the environment caused by substances such as nitrogen oxides.

[0009] In order to achieve the above object, the present invention provides the following technical solutions: A method for recovering metallic silver from waste crystalline silicon solar cells comprises the following steps: (1) Dealumination: Place the waste crystalline silicon cell into an inorganic alkali aqueous solution and soak it for reaction to obtain an aluminum-containing solution and dealumination crystalline silicon wafers respectively; (2) Desilvering: After washing, the dealuminized silicon wafer is added to a mixed solution of organic acid and hydrogen peroxide for soaking and reaction. After the reaction is completed, the silicon wafer is filtered and washed to obtain a silver-containing filtrate and a desilvered silicon wafer; (3) Chlorination precipitation: contacting the silver-containing filtrate with a chlorine source to carry out a chlorination precipitation reaction, and then filtering and drying the resulting precipitate to obtain silver chloride powder; (4) Generating silver ammonia: adding the obtained silver chloride powder to an ammonia solution and heating and stirring to completely dissolve the silver chloride to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) Reduction: PVP (polyvinyl pyrrolidone) is added to the purified silver ammonia solution, heated and stirred to dissolve. After the PVP is completely dissolved, ascorbic acid, a reducing agent, is added to the system and a reduction reaction occurs at room temperature to obtain a metallic silver powder precipitate; (6) Post-treatment: The obtained metallic silver powder precipitate is filtered, washed, and dried to obtain high-purity spherical silver powder; optionally, it is placed in a vacuum drying oven to dry to obtain spherical silver powder.

[0010] According to the method provided by the present invention, in some embodiments, the waste crystalline silicon solar cells are waste crystalline silicon solar cells without solder ribbons obtained by dismantling discarded photovoltaic panels and separating them from the solder ribbons.

[0011] According to the method provided by the present invention, in some embodiments, the inorganic alkali aqueous solution in step (1) is selected from sodium hydroxide aqueous solution and potassium hydroxide aqueous solution, preferably sodium hydroxide aqueous solution.

[0012] In some embodiments, the concentration of the inorganic base aqueous solution in step (1) is 1-1.5 mol / L (e.g., 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L); In some embodiments, the inorganic base aqueous solution in step (1) is a sodium hydroxide aqueous solution with a concentration of 1-1.5 mol / L (e.g., 1.1 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L).

[0013] The amount of the inorganic alkali aqueous solution used does not need to be particularly limited. For example, the solid-to-liquid ratio of the waste crystalline silicon solar cells to the inorganic alkali aqueous solution can be in the range of 1:10 to 1:60 (unit: g / ml).

[0014] In some embodiments, the soaking reaction time in step (1) is 50-70 min (eg, 55 min, 60 min, 65 min).

[0015] According to the method provided by the present invention, in some embodiments, the concentration of the hydrogen peroxide in step (2) is 20-30 wt%; for example, 22 wt%, 24 wt%, 25 wt%, 26 wt%, 28 wt%.

[0016] In some embodiments, the organic acid in step (2) is selected from methanesulfonic acid and citric acid, preferably methanesulfonic acid.

[0017] In some embodiments, in the mixed solution of step (2), the volume ratio of the organic acid to hydrogen peroxide is (1-5):1; for example, 1.05:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 4.8:1.

[0018] In some embodiments, the organic acid is methanesulfonic acid; the volume ratio of methanesulfonic acid to hydrogen peroxide is (1-5):1; for example, 1.05:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, 4.8:1.

[0019] In some embodiments, the process conditions of the soaking reaction in step (2) include: a reaction temperature of 50-90°C (for example, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C), preferably 60-70°C, and a soaking time of 1 hour or more (for example, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h).

[0020] According to the method provided by the present invention, in some embodiments, the chlorine source in step (3) is selected from sodium chloride, ammonium chloride or hydrochloric acid.

[0021] In some embodiments, in the chlorination precipitation reaction of step (3), the amount of the chlorine source is calculated according to n(Cl - ):n(Ag + ) is 5:1 to 35:1, for example, 6:1, 8:1, 10:1, 12:1, 14:1, 15:1, 16:1, 18:1, 20:1, 22:1, 24:1, 25:1, 28:1, 30:1, 32:1, 34:1.

[0022] In some embodiments, in the chlorination precipitation reaction of step (3), the chlorine source is sodium chloride, and the amount of sodium chloride is calculated according to n(Cl - ):n(Ag + ) is 5:1 to 35:1.

[0023] According to the method provided by the present invention, in some embodiments, the pH value of the ammonia solution in step (4) is 10-12 (e.g., 10.5, 11, 11.5); In some embodiments, the liquid-to-solid ratio of the ammonia solution to silver chloride is (25-30):1 mL / g, for example, 25.5:1 mL / g, 26.5:1 mL / g, 27:1 mL / g, 27.5:1 mL / g, 28:1 mL / g, 29:1 mL / g, 29.5:1 mL / g, and preferably (26-28):1 mL / g.

[0024] In some embodiments, the temperature of the water bath for heating and stirring in step (4) is 25-40°C (e.g., 26°C, 31°C, 32°C, 34°C, 35°C, 36°C, 38°C), preferably 30-35°C.

[0025] According to the method provided by the present invention, in some embodiments, the liquid-to-solid ratio of the silver ammonia solution to PVP in step (5) is (35-50):1 mL / g, for example, 36:1 mL / g, 38:1 mL / g, 41:1 mL / g, 42:1 mL / g, 43:1 mL / g, 44:1 mL / g, 45:1 mL / g, 46:1 mL / g, 48:1 mL / g, preferably (40-45):1 mL / g; In some embodiments, the temperature of the heating and stirring in step (5) is 25-40°C (e.g., 26°C, 28°C, 30°C, 32°C, 34°C, 35°C, 38°C); the stirring speed is 200-300 r / min (e.g., 220 r / min, 250 r / min, 280 r / min).

[0026] In some embodiments, the mass ratio of ascorbic acid to silver chloride in step (5) is (1-1.8):1, for example, 1.1:1, 1.2:1, 1.45:1, 1.5:1, 1.55:1, 1.65:1, 1.7:1, 1.75:1, preferably (1.4-1.6):1.

[0027] In some embodiments, the reduction reaction time in step (5) is 0.5 h or longer, for example, 0.6 h, 0.8 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, or 5 h.

[0028] According to the method provided by the present invention, in some embodiments, the filtration in step (6) is performed using a micron filter membrane. Preferably, the pore size of the micron filter membrane is 0.1-0.3 μm (for example, 0.15 μm, 0.2 μm).

[0029] In some embodiments, the washing in step (6) is to wash the filter residue at least three times using deionized water and anhydrous ethanol respectively.

[0030] In some embodiments, the drying conditions in step (6) include: drying at 60-90°C (eg, 65°C, 70°C, 75°C, 80°C, 85°C) for 5-10 hours (eg, 6 hours, 7 hours, 8 hours, 9 hours).

[0031] According to the method provided by the present invention, the nano-scale spherical silver powder prepared has a smooth surface, regular morphology, a particle size between 50-300 nm (for example, 50-100 nm, 50-200 nm, 50-250 nm, 100-300 nm, 100-200 nm, 100-250 nm, etc.), and a purity of 99.90% or above.

[0032] In this invention, nanoscale spherical silver powder is produced by liquid-phase reduction of a silver-ammonia solution. During this process, the microstructure of the silver powder is controlled by adjusting the addition of polyvinyl pyrrolidone (PVP), added to the system during the reduction step as a dispersant and stabilizer, and the amount of PVP used. During the reduction process, PVP, as a dispersant, exhibits excellent solubilization and dispersion properties while maintaining low toxicity. During the silver ion reduction process, PVP adheres to the surface of the resulting silver particles, effectively preventing their aggregation through its steric hindrance effect and acting as a stabilizer, thereby achieving excellent dispersion of the nanoscale silver powder.

[0033] In this invention, a mixed solution of organic acid and hydrogen peroxide (methanesulfonic acid-hydrogen peroxide solution) is used to leach silver instead of the traditional nitric acid system. This mixed solution can be recycled, avoiding the environmental harm of substances such as nitrogen oxides. Ascorbic acid is used as a reducing agent instead of the traditional reducing agent hydrazine hydrate to prepare silver powder, reducing the toxicity of the system.

[0034] Compared with the prior art, the beneficial effects of the present invention are at least: The method of the present invention can prepare spherical nano-scale silver powder with obvious microstructural advantages, a smooth surface, a regular morphology, a particle size between 50 and 300 nm, and a purity of 99.90% or above. At the same time, the method has a high efficiency in recovering silver from waste crystalline silicon solar cells. By adopting a wet recovery process, the silver recovery rate is stabilized at 95% or above. In addition, the method of the present invention can reduce the toxicity of the system and avoid harm to the environment while preparing spherical nano-scale silver powder with excellent quality and high recovery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagrams showing the process flow of some embodiments of the method of the present invention; Figure 2 The SEM photograph of the appearance of the spherical silver powder obtained in Example 1 is shown; Figure 3The SEM photograph of the appearance of the spherical silver powder obtained in Example 2 is shown; Figure 4 The SEM photograph of the appearance of the spherical silver powder obtained in Example 3 is shown; Figure 5 The SEM photograph of the appearance of the spherical silver powder obtained in Example 4 is shown. DETAILED DESCRIPTION

[0036] In order to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the embodiments, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein.

[0037] If no specific conditions are specified in the examples, the reaction was carried out according to conventional conditions or the conditions recommended by the manufacturer. The raw materials used in the examples are understood to be commercially available unless otherwise specified.

[0038] Example 1: Method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells, such as Figure 1 The process diagram shown includes the following steps: (1) Waste crystalline silicon cells without solder strips were selected as raw materials. First, the fly ash on the surface was removed by blowing with compressed air. Then, the cells after deashing were immersed in a 1.2 mol / L sodium hydroxide aqueous solution for 60 minutes. After separation, aluminum-containing solution and dealuminated crystalline silicon wafers were obtained. (2) The dealuminated silicon wafer obtained above was washed with deionized water in an ultrasonic instrument, and then added to a mixture of hydrogen peroxide and methanesulfonic acid, wherein the concentration of hydrogen peroxide was 30% and the volume ratio of methanesulfonic acid to hydrogen peroxide was 3:1. The mixture was reacted at 65°C for 1.5 hours, and the silver-containing filtrate and the desilvered silicon wafer were obtained after separation. (3) According to n(Cl - ):n(Ag + ) is 5:1, sodium chloride is weighed, the silver-containing filtrate is contacted with sodium chloride to perform a chlorination precipitation reaction, and then the obtained precipitate is filtered and dried to obtain silver chloride powder; (4) adding the obtained silver chloride powder into an ammonia solution with a pH of 11.0, wherein the liquid-to-solid ratio of the ammonia solution to the silver chloride is 27:1 mL / g, heating in a water bath at 32°C with stirring until completely dissolved, to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) PVP was added to the purified silver ammonia solution at a liquid-to-solid ratio of 42:1 mL / g. The solution was heated to 32°C and stirred at 250 r / min until dissolved. Ascorbic acid was then added to the system at a mass ratio of ascorbic acid to silver chloride of 1.5:1. The solution was reacted at room temperature for 1 hour to generate a metallic silver powder precipitate. (6) The obtained metallic silver powder precipitate was filtered through a 0.2 μm micron filter membrane, and then washed three times with deionized water and anhydrous ethanol respectively. After drying, it was placed in a vacuum drying oven at 70°C for 8 hours to prevent it from being oxidized, thereby obtaining high-purity nano-scale spherical silver powder; the silver recovery rate was 95.81%.

[0039] Figure 2 This is a photo of the appearance of the spherical silver powder obtained in Example 1. The spherical silver powder obtained has a smooth surface, regular morphology, a particle size between 100-200 nm, and a purity of 99.91%.

[0040] Example 2: The method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells comprises the following steps: (1) Using waste crystalline silicon cells without solder strips as raw materials, firstly, the fly ash on the surface is removed by blowing with compressed air; then, the cells after deashing are immersed in a 1 mol / L sodium hydroxide aqueous solution for 55 minutes, and then separated to obtain the aluminum solution and the dealuminated crystalline silicon cells; (2) The dealuminated silicon wafer obtained above was washed with deionized water in an ultrasonic instrument, and then added to a mixture of hydrogen peroxide and methanesulfonic acid, wherein the concentration of hydrogen peroxide was 30% and the volume ratio of methanesulfonic acid to hydrogen peroxide was 2:1. The mixture was reacted at 55°C for 2 hours, and the silver-containing filtrate and the desilvered silicon wafer were obtained after separation. (3) According to n(Cl - ):n(Ag + ) is 5:1, sodium chloride is weighed, the silver-containing filtrate is contacted with sodium chloride to perform a chlorination precipitation reaction, and then the obtained precipitate is filtered and dried to obtain silver chloride powder; (4) adding the obtained silver chloride powder into an ammonia solution with a pH of 11.0, wherein the liquid-to-solid ratio of the ammonia solution to the silver chloride is 25:1 mL / g, heating in a water bath at 38°C with stirring until completely dissolved, to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) PVP was added to the purified silver ammonia solution at a liquid-to-solid ratio of 45:1 mL / g. The solution was heated to 38°C and stirred at 250 r / min until dissolved. Ascorbic acid was then added to the system at a mass ratio of ascorbic acid to silver chloride of 1.6:1. The solution was reacted at room temperature for 1.5 hours to generate a metallic silver powder precipitate. (6) The obtained metallic silver powder precipitate was filtered through a 0.2 μm micron filter membrane, washed four times with deionized water and anhydrous ethanol respectively, dried and placed in a vacuum drying oven at 70°C for 8 hours to prevent it from being oxidized, and high-quality nano-scale spherical silver powder was obtained; the silver recovery rate was 95.63%.

[0041] Figure 3 This is a photograph of the appearance of the spherical silver powder obtained in Example 2; the spherical silver powder obtained has a smooth surface, regular morphology, a particle size between 50-200 nm, and a purity of 99.90%.

[0042] Example 3: The method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells comprises the following steps: (1) Using waste crystalline silicon cell powder without solder strips as raw material, soaking it in a 1 mol / L sodium hydroxide aqueous solution for 50 minutes, and then separating to obtain aluminum-containing solution and dealuminated crystalline silicon wafers; (2) The dealuminated silicon wafer obtained above was washed with deionized water in an ultrasonic instrument, and then added to a mixture of hydrogen peroxide and methanesulfonic acid, wherein the concentration of hydrogen peroxide was 30% and the volume ratio of methanesulfonic acid to hydrogen peroxide was 2:1. The mixture was reacted at 55°C for 2 hours, and the silver-containing filtrate and the desilvered silicon wafer were obtained after separation. (3) According to n(Cl - ):n(Ag + ) is 5:1, sodium chloride is weighed, the silver-containing filtrate is contacted with sodium chloride to perform a chlorination precipitation reaction, and then the obtained precipitate is filtered and dried to obtain silver chloride powder; (4) adding the obtained silver chloride powder into an ammonia solution with a pH of 11.0, wherein the liquid-to-solid ratio of the ammonia solution to silver chloride is 28:1 mL / g, heating in a water bath at 38°C with stirring until completely dissolved, to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) PVP was added to the purified silver ammonia solution at a liquid-to-solid ratio of 35:1 mL / g. The solution was heated to 38°C and stirred at 250 r / min until dissolved. Ascorbic acid was then added to the system at a mass ratio of ascorbic acid to silver chloride of 1.6:1. The solution was reacted at room temperature for 1.5 hours to generate a metallic silver powder precipitate. (6) The obtained metallic silver powder precipitate was filtered through a 0.2 μm micron filter membrane, washed four times with deionized water and four times with anhydrous ethanol, dried in a vacuum drying oven at 70°C for eight hours to prevent oxidation, and high-purity nano-scale spherical silver powder was obtained; the silver recovery rate was 96.28%.

[0043] Figure 4This is a photograph of the appearance of the spherical silver powder obtained in Example 3; the spherical silver powder obtained has a smooth surface, regular morphology, a particle size between 50-300 nm, and a purity of 99.90%.

[0044] Example 4: The method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells comprises the following steps: (1) Using waste crystalline silicon cell powder without solder strips as raw material, soaking it in a 1 mol / L sodium hydroxide aqueous solution for 50 minutes, and then separating to obtain aluminum-containing solution and dealuminated crystalline silicon wafers; (2) The dealuminated silicon wafer obtained above was washed with deionized water in an ultrasonic instrument, and then added to a mixture of hydrogen peroxide and methanesulfonic acid, wherein the concentration of hydrogen peroxide was 30% and the volume ratio of methanesulfonic acid to hydrogen peroxide was 2:1. The mixture was reacted at 55°C for 2 hours, and the silver-containing filtrate and the desilvered silicon wafer were obtained after separation. (3) According to n(Cl - ):n(Ag + ) is 5:1, sodium chloride is weighed, the silver-containing filtrate is contacted with sodium chloride to perform a chlorination precipitation reaction, and then the obtained precipitate is filtered and dried to obtain silver chloride powder; (4) adding the obtained silver chloride powder into an ammonia solution with a pH of 11.0, wherein the liquid-to-solid ratio of the ammonia solution to silver chloride is 30:1 mL / g, heating in a water bath at 32°C with stirring until completely dissolved, to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) PVP was added to the purified silver ammonia solution at a liquid-to-solid ratio of 35:1 mL / g. The solution was heated to 32°C and stirred at 250 r / min until dissolved. Ascorbic acid was then added to the system at a mass ratio of ascorbic acid to silver chloride of 1:1. The solution was reacted at room temperature for 1.5 hours to generate a metallic silver powder precipitate. (6) The obtained metallic silver powder precipitate was filtered through a 0.2 μm micron filter membrane, washed four times with deionized water and anhydrous ethanol respectively, dried in a vacuum drying oven at 70°C for 8 hours to prevent it from being oxidized, and high-purity nano-scale spherical silver powder was obtained; the silver recovery rate was 95.12%.

[0045] Figure 5 This is a photograph of the appearance of the spherical silver powder obtained in Example 4; the spherical silver powder obtained has a smooth surface, regular morphology, a particle size between 50-300 nm, and a purity of 99.90%.

[0046] Comparative Example 1: The method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells is similar to that of Example 1, except that: in step (5), the mass ratio of ascorbic acid to silver chloride is 0.9:1; The remaining steps were the same as those in Example 1. Nano-scale spherical silver powder was obtained; and the silver recovery rate was 91.40%.

[0047] The prepared silver powder has a smooth surface, regular morphology, a particle size between 100-200nm, and a purity of 99.90%.

[0048] Comparative Example 2: The method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells comprises the following steps: (1) Waste crystalline silicon cells without solder strips were selected as raw materials. First, the fly ash on the surface was removed by blowing with compressed air. Then, the cells after deashing were immersed in a 1.2 mol / L sodium hydroxide aqueous solution for 60 minutes. After separation, aluminum-containing solution and dealuminated crystalline silicon wafers were obtained. (2) The dealuminated silicon wafer obtained above was washed with deionized water in an ultrasonic instrument, and then added to a mixture of hydrogen peroxide and methanesulfonic acid, wherein the concentration of hydrogen peroxide was 30% and the volume ratio of methanesulfonic acid to hydrogen peroxide was 3:1. The mixture was reacted at 65°C for 1.5 hours, and the silver-containing filtrate and the desilvered silicon wafer were obtained after separation. (3) According to n(Cl - ):n(Ag + ) is 5:1, sodium chloride is weighed, the silver-containing filtrate is contacted with sodium chloride to perform a chlorination precipitation reaction, and then the obtained precipitate is filtered and dried to obtain silver chloride powder; (4) adding the obtained silver chloride powder into an ammonia solution with a pH of 11.0, with a liquid-to-solid ratio of the ammonia solution to silver chloride of 27:1 mL / g, heating in a water bath at 32°C with stirring until completely dissolved, to obtain a silver ammonia solution, which was then filtered to obtain a purified silver ammonia solution; (5) PVP was added to the silver ammonia solution of the pure fox, with the liquid-solid ratio of the silver ammonia solution to PVP being 33:1 mL / g. The solution was heated to 32°C and stirred at a speed of 250 r / min until dissolved. Ascorbic acid was then added to the system, with the mass ratio of ascorbic acid to silver chloride being 1.5:1. The solution was reacted at room temperature for 1.0 hour to generate a metallic silver powder precipitate. (6) The obtained metallic silver powder precipitate was filtered through a 0.2 μm micron filter membrane, washed four times with deionized water and anhydrous ethanol respectively, dried in a vacuum drying oven at 70°C for 8 hours to prevent it from being oxidized, and nano-spherical silver powder was obtained; the silver recovery rate was 90.64%.

[0049] The prepared spherical silver powder has a smooth surface, regular morphology, a particle size between 50-200nm, and a purity of 99.89%.

[0050] Comparative Example 3: The method for recovering nano-scale spherical silver powder from waste crystalline silicon solar cells comprises the following steps: (1) Waste crystalline silicon cells without solder strips were selected as raw materials. First, the fly ash on the surface was removed by blowing with compressed air. Then, the cells after deashing were immersed in a 1.2 mol / L sodium hydroxide aqueous solution for 60 minutes. After separation, aluminum-containing solution and dealuminated crystalline silicon wafers were obtained. (2) The dealuminated silicon wafer obtained above was washed with deionized water in an ultrasonic instrument, and then added to a mixture of hydrogen peroxide and methanesulfonic acid, wherein the concentration of hydrogen peroxide was 30% and the volume ratio of methanesulfonic acid to hydrogen peroxide was 3:1. The mixture was reacted at 65°C for 1.5 hours, and the silver-containing filtrate and the desilvered silicon wafer were obtained after separation. (3) According to n(Cl - ):n(Ag + ) is 5:1, sodium chloride is weighed, the silver-containing filtrate is contacted with sodium chloride to perform a chlorination precipitation reaction, and then the obtained precipitate is filtered and dried to obtain silver chloride powder; (4) adding the obtained silver chloride powder into an ammonia solution with a pH of 11.0, wherein the liquid-to-solid ratio of the ammonia solution to the silver chloride is 27:1 mL / g, heating in a water bath at 32°C with stirring until completely dissolved, to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) adding ascorbic acid to the purified silver ammonia solution in a mass ratio of ascorbic acid to silver chloride of 1.5:1, and reacting at room temperature for 1 hour to generate a metallic silver powder precipitate; (6) The obtained metallic silver powder precipitate was filtered through a 0.2 μm micron filter membrane, and then washed three times with deionized water and anhydrous ethanol respectively. After drying, it was placed in a vacuum drying oven at 70°C for 8 hours to prevent it from being oxidized, thereby obtaining irregularly shaped silver particles; the silver recovery rate was 95.87%.

[0051] The irregularly shaped silver particles obtained are aggregated into blocks with a particle size between 1-5 µm and a purity of 99.90%.

[0052] Table 1 Test data of products obtained in various embodiments and comparative examples

[0053] The experimental results show that each embodiment can recover spherical nanosilver with a smooth surface, regular morphology, and a particle size between 50 and 300 nm from waste crystalline silicon cells, and the silver recovery rate and purity are high. In addition, the method of the present invention can not only produce spherical nano-scale silver powder with excellent quality and high recovery rate, but also reduce the toxicity of the system and avoid harm to the environment.

[0054] In Comparative Example 1, the mass ratio of reducing agent to silver chloride was not within the appropriate range, and the silver recovery rate decreased.

[0055] In the reduction process of Comparative Example 2, the liquid-to-solid ratio of the silver ammonia solution to the PVP was not within the appropriate range, the silver recovery rate decreased, and the silver purity also decreased slightly.

[0056] In the reduction process of Comparative Example 3, PVP was not added and the reducing agent was directly added for reaction, resulting in silver particles agglomerated into blocks with irregular shapes.

[0057] While various embodiments of the present invention have been described above, the above description is intended to be illustrative, not exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for recovering metallic silver from waste crystalline silicon solar cells, characterized in that: The following steps are involved: (1) Dealumination: Place the waste crystalline silicon cell into an inorganic alkali aqueous solution and soak it for reaction to obtain an aluminum-containing solution and dealumination crystalline silicon wafers respectively; (2) Desilvering: After washing, the dealuminized silicon wafer is added to a mixed solution of organic acid and hydrogen peroxide for soaking and reaction. After the reaction is completed, the silicon wafer is filtered and washed to obtain a silver-containing filtrate and a desilvered silicon wafer; (3) Chlorination precipitation: contacting the silver-containing filtrate with a chlorine source to carry out a chlorination precipitation reaction, and then filtering and drying the resulting precipitate to obtain silver chloride powder; (4) Generating silver ammonia: adding the obtained silver chloride powder to an ammonia solution and heating and stirring to completely dissolve the silver chloride to obtain a silver ammonia solution, which is then filtered to obtain a purified silver ammonia solution; (5) Reduction: PVP is added to the purified silver ammonia solution, heated and stirred to dissolve. After the PVP is completely dissolved, ascorbic acid, a reducing agent, is added to the system and a reduction reaction occurs at room temperature to obtain a metallic silver powder precipitate; (6) Post-treatment: The obtained metallic silver powder precipitate is filtered, washed, and dried to obtain high-purity spherical silver powder.

2. The method according to claim 1, characterized in that The waste crystalline silicon solar cells are waste crystalline silicon solar cells without soldering strips that are obtained by dismantling discarded photovoltaic panels and separating the soldering strips.

3. The method according to claim 1, characterized in that The inorganic alkali aqueous solution in step (1) is selected from a sodium hydroxide aqueous solution and a potassium hydroxide aqueous solution; The concentration of the inorganic alkali aqueous solution in step (1) is 1-1.5 mol / L; The soaking reaction time in step (1) is 50-70 min.

4. The method according to claim 1, wherein The concentration of the hydrogen peroxide in step (2) is 20-30wt%; The organic acid in step (2) is selected from methanesulfonic acid and citric acid; In the mixed solution of step (2), the volume ratio of organic acid to hydrogen peroxide is (1-5):1; The process conditions of the soaking reaction in step (2) include: a reaction temperature of 50-90° C. and a soaking time of 1 h or more.

5. The method according to claim 1, wherein The chlorine source in step (3) is selected from sodium chloride, ammonium chloride or hydrochloric acid; In the chlorination precipitation reaction of step (3), the amount of the chlorine source is calculated according to n(Cl - ):n(Ag + ) is 5:1 to 35:

1.

6. The method according to claim 1, characterized in that The pH value of the ammonia solution in step (4) is 10-12; The liquid-to-solid ratio of the ammonia solution to silver chloride is (25-30): 1 mL / g.

7. The method according to claim 1, characterized in that The water bath temperature for heating and stirring in step (4) is 25-40°C.

8. The method according to claim 1, wherein The liquid-to-solid ratio of the silver ammonia solution to PVP in step (5) is (35-50): 1 mL / g; The temperature of the heating and stirring in step (5) is 25-40°C; the stirring speed is 200-300 r / min.

9. The method according to claim 1, characterized in that The mass ratio of ascorbic acid to silver chloride in step (5) is (1-1.8):1; The reduction reaction time is 0.5h or longer.

10. The method according to any one of claims 1 to 9, characterized in that The filtration in step (6) is performed using a micron filter membrane; The washing in step (6) is to use deionized water and anhydrous ethanol to wash the filter residue at least 3 times respectively.

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