Ultrafine silver powder based on retired photovoltaic panel silver recovery and preparation method and application thereof

Abstract

The invention relates to the technical field of waste photovoltaic panel silver recovery, in particular to superfine silver powder based on retired photovoltaic panel silver recovery and a preparation method and application of the superfine silver powder. According to the method, the retired photovoltaic panel is used as a silver source, wet extraction and liquid phase reduction are combined, the superfine silver powder uniform in morphology and good in dispersity is prepared, the recovery rate of silver is larger than 99%, the purity of the silver powder is larger than 99.5%, the silver powder can be directly used for preparing high-temperature sintering type conductive silver paste, the sheet resistance of an obtained conductive layer is 2-5 m omega / sq, the national standard requirement is met, and the method is suitable for industrial production. And closed-loop efficient utilization of silver resources in the photovoltaic industry is realized. According to the method, hard aggregation and secondary aggregation of the silver powder are remarkably inhibited, and the core problems that the silver powder recycled from the waste photovoltaic panel is poor in dispersity and low in sintering activity are solved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of waste photovoltaic panel silver recovery, in particular to a kind of ultra-fine silver powder based on retired photovoltaic panel silver recovery and its preparation method and application. BACKGROUND

[0002] Under the background of global warming and energy transformation, the photovoltaic industry is developing rapidly, and the recycling of retired photovoltaic modules has become a key link for sustainable development. Photovoltaic panels contain valuable metals such as silver, and silver, as the core material of conductive silver paste, has important recycling value. Hydrometallurgy is one of the mainstream technologies for photovoltaic silver recovery at present, which can obtain silver powder through leaching, reduction and other steps. However, existing recovery technologies use strong reducing agents such as ascorbic acid, hydrazine hydrate, sodium borohydride in the reduction process, which has a fast reaction rate, making it difficult to control the particle size, morphology, and dispersibility of the silver powder. The obtained silver powder is mostly sponge silver or irregular silver powder, which needs to go through multiple complex processes of secondary dissolution, purification, and reduction to realize the regeneration of silver powder to silver paste, and cannot be directly applied to the preparation of conductive silver paste. Therefore, it is the key to realize the efficient recycling of silver in photovoltaic panels to prepare high-quality ultra-fine silver powder that can be directly applied to high-temperature silver paste in the reduction reaction process, and to shorten the process of silver recovery and regeneration.

[0003] For example, Chinese patent CN120555756A discloses a method for recovering silver from waste crystalline silicon photovoltaic panels. This patent uses a liquid phase reduction method to achieve efficient recovery of silver and can prepare micro-nano spherical silver powder. However, the use of ascorbic acid as a reducing agent results in poor dispersibility and irregularity of the obtained silver powder, which cannot be directly used for high-temperature silver paste preparation. Chinese patent CN107841635A proposes a method for recovering silver from photovoltaic panels. This method uses the strong reducing agent hydrazine hydrate for reduction, and the obtained silver powder is loose sponge silver, which needs to be processed and treated twice, making it difficult to be directly applied to the preparation of high-temperature conductive silver paste. Patent No. CN114749654A discloses a blocky ultra-fine silver powder and its preparation method and use. This method uses sugar as a reducing agent to prepare blocky ultra-fine silver powder, which is limited by the insufficient reducing performance of sugar. The method uses an alcohol aqueous solution as a solvent to obtain silver powder particles at a high temperature of 100-120℃, which severely limits the reaction efficiency and economy. The above existing technologies all have problems such as irregular morphology and poor dispersibility of the silver powder recovered by liquid phase reduction, which cannot be directly used as raw materials for conductive silver paste.

[0004] In summary, it is of great industrial value and significance to develop a short process technology for efficiently recovering silver from retired crystalline silicon photovoltaic panels, preparing high-purity ultra-fine silver powder by liquid phase reduction, and directly applying it to high-temperature conductive silver paste. Based on this, the present application designs a kind of ultra-fine silver powder based on retired photovoltaic panel silver recovery and its preparation method and application. SUMMARY

[0005] The application provides a superfine silver powder based on silver recycling from retired photovoltaic panels and a preparation method and application thereof, and aims to solve the problems in the background art.

[0006] To achieve the above-mentioned purpose, the embodiment of the application provides a preparation method of a superfine silver powder based on silver recycling from retired photovoltaic panels, which comprises the following steps: S1: ball milling and crushing the pretreated retired photovoltaic panel to obtain photovoltaic panel powder with uniform particle size; S2: soaking the photovoltaic panel powder in dilute sulfuric acid according to a specific liquid-solid ratio, stirring, and performing a decontamination reaction, and then filtering, washing and drying to obtain aluminum-removed photovoltaic panel powder; S3: soaking the aluminum-removed photovoltaic panel powder in dilute nitric acid according to a specific liquid-solid ratio, stirring and reacting, and then filtering to obtain a leaching solution containing Ag + ; S4: adding a precipitant to the leaching solution to react, and then filtering, washing and drying to obtain silver chloride powder; S5: adding the silver chloride powder into a complexing agent, stirring, and reacting to obtain a silver complex; S6: adding a dispersant and glucose into the silver complex, adjusting the pH value to 13-14, and reacting at 40-70 DEG C to obtain a suspension, centrifugally separating the precipitate, and then washing, centrifuging and drying to obtain high-purity superfine silver powder with uniform particle size distribution and no agglomeration; The superfine silver powder has a particle size of 0.1-2.0 μm and a purity of greater than 99.5%.

[0007] Preferably, in step S1, the retired photovoltaic panel is a photovoltaic panel without solder strips after physical and chemical dissociation of a crystalline silicon photovoltaic module; the pretreatment process comprises deionized water washing, soaking and 60 DEG C vacuum drying; and the ball milling process is performed by using a planetary ball mill at a grinding speed of 350-600 r / min for 2-8 h.

[0008] Preferably, in step S2, the concentration of the dilute sulfuric acid is 60-90 g / L; the liquid-solid ratio of the dilute sulfuric acid to the photovoltaic panel powder is 10-20:1; and the reaction temperature is 60-80 DEG C.

[0009] Preferably, in step S3, the concentration of the dilute nitric acid is 3-7 mol / L; the liquid-solid ratio of the dilute nitric acid to the aluminum-removed photovoltaic panel powder is 2-16:1; and the reaction temperature is 40-80 DEG C.

[0010] Preferably, in step S4, the precipitant is at least one of sodium chloride, ammonium chloride and hydrochloric acid, and the concentration is 1-6 mol / L; and the volume ratio of the leaching solution to the precipitant is 25-160:1.

[0011] Preferably, in step S5, the complexing agent is ammonia water or thiourea; the ammonia water concentration is 3-8 mol / L; the thiourea concentration is 1-2 mol / L; the liquid-solid ratio of the complexing agent and silver chloride powder is 15-30:1; the stirring rate is 800-1200 r / min; and the reaction temperature is 30-60℃.

[0012] Preferably, in step S6, the dispersant is at least one of polyvinylpyrrolidone, gelatin or gum arabic; the pH value regulator is at least one of sodium hydroxide or potassium hydroxide; the mass ratio of the dispersant to silver in the silver complex is 0.06-0.2:1; and the molar ratio of glucose to silver in the silver complex is 0.5-5:1.

[0013] The embodiment of the present application also provides the ultra-fine silver powder based on the recycled silver from the retired photovoltaic panel, which is prepared by the preparation method.

[0014] The embodiment of the present application also provides the application of the ultra-fine silver powder in high-temperature conductive silver paste, which is prepared by the preparation method.

[0015] Preferably, the ultra-fine silver powder, the glass phase and the organic carrier are mixed according to a specific mass ratio to prepare the silver paste, the paste is printed on a ceramic substrate, and then the silver film is obtained by leveling and high-temperature sintering and cooling.

[0016] The above scheme of the present application has the following advantages: (1) The present application solves the problem that the recycled silver powder from the retired photovoltaic panel cannot be directly used in the industry due to inherent agglomeration. By means of key technical means such as multi-stage purification, surface modification and introduction of crystal growth regulator in the glucose reduction system, the nucleation, growth and surface state of silver particles are effectively controlled. The present application significantly inhibits the hard agglomeration and secondary aggregation of silver powder, and solves the core problems of poor dispersibility and low sintering activity of the recycled silver powder. The high-purity ultra-fine silver powder prepared by the present application is uniformly dispersed and has regular morphology, and can be directly used to prepare high-temperature sintering type conductive silver paste. The prepared silver paste forms a dense conductive film after sintering at 700-800℃, and the square resistance is stably 2-5 mΩ / sq, which fully meets the national standard of photovoltaic conductive silver paste, and realizes the complete resource recycling from the retired photovoltaic panel to high-performance silver paste.

[0017] (2) The present application adopts glucose as a core reducing agent, and by adjusting the reaction system to a specific alkaline pH, the glucose is caused to undergo alkaline catalytic isomerization to form an enediol salt intermediate with strong electron-donating ability. The process of reducing silver ions by the intermediate is mild and the rate is gentle, and the controlled nucleation and growth of silver atoms can be realized, thereby effectively overcoming the problems of explosive nucleation and silver powder agglomeration caused by strong reducing agents, and obtaining superfine silver powder with uniform morphology and good dispersity. The reaction process not only increases the reduction yield to more than 99%, but also the solubility of the oxidation product glucose salt in water is extremely high (about 120 times that of the product of ascorbic acid reducing agent), which is not easy to remain on the surface of the silver powder, further reducing the agglomeration induced by impurities, and is conducive to improving the compactness and conductivity of the silver powder after sintering. In addition, glucose is low in price, safe and environmentally friendly, and has more industrialization and economic competitive advantage than reducing agents such as hydrazine hydrate and sodium borohydride. BRIEF DESCRIPTION OF DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0019] Figure 1 is a process flow chart of a superfine silver powder preparation method based on retired photovoltaic panel recycled silver according to an embodiment of the present application; Figure 2 is a superfine silver powder XRD chart of embodiments 1 and 2 of the present application; Figure 3 is a superfine silver powder SEM chart of embodiment 1 of the present application; Figure 4 is a superfine silver powder SEM chart of embodiment 2 of the present application; Figure 5 is a silver powder SEM chart of comparative example 2 of the present application; Figure 6 is a silver powder SEM chart of comparative example 3 of the present application. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and advantages of the present application more clear, the following will be described in detail with reference to the drawings and specific embodiments.

[0021] Unless otherwise defined, all professional terms used in the following have the same meaning as generally understood by those skilled in the art. The professional terms used in this paper are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present application.

[0022] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0023] This invention addresses existing problems by providing an ultrafine silver powder based on the recovery of silver from decommissioned photovoltaic panels, its preparation method, and its application.

[0024] Example 1 This embodiment provides a method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels. The process flow diagram is shown below. Figure 1 As shown, the specific steps include the following: (1) Dismantled and unsold crystalline silicon photovoltaic panels without solder strips were selected as raw materials. First, the panels were washed, soaked, ultrasonicated and dried with deionized water to remove fly ash and insoluble impurities from the surface. Then, the photovoltaic panels were physically crushed and then ground with a planetary ball mill at 550 r / min for 6 hours. The powder was then passed through a 100-mesh sieve to obtain photovoltaic panel powder with uniform particle size distribution. (2) The photovoltaic panel powder was soaked in 80 g / L dilute sulfuric acid at 75 °C with water bath stirring for 80 min, and then filtered, washed and vacuum dried for 6 h to obtain aluminum-free photovoltaic panel powder. (3) According to the liquid-solid ratio (mL:g) of nitric acid to aluminum-removing photovoltaic panel powder being 2:1, the aluminum-removing photovoltaic panel powder was soaked in 6mol / L dilute nitric acid at 60℃ and stirred in a water bath for 100 min. After filtration, Ag-containing powder was obtained. + leachate; (4) Add 5.4 mol / L sodium chloride solution to the leachate at a volume ratio of 150:1 to precipitant to carry out chlorination precipitation reaction. Then filter, wash and vacuum dry at 60°C for 6 h to obtain silver chloride powder. (5) Silver ammonia solution was obtained by dissolving silver chloride powder in 6 mol / L ammonia solution at room temperature, according to the liquid-solid ratio (mL:g) of complexing agent solution and silver chloride solution being 25:1. (6) Add gum arabic to the silver ammonia solution according to a mass ratio of 0.063:1 between the dispersant and the complex, and stir at 400 r / min until completely dissolved. Then, prepare a glucose solution according to a molar ratio of glucose to silver in the silver ammonia solution of 1.5:1, and adjust the pH to 13 by adding 5 mol / L sodium hydroxide solution. Add the glucose solution to the silver ammonia solution and stir at 800 r / min at 50℃ for 10 min to generate silver powder precipitate. Centrifuge, wash, and vacuum dry at 60℃ for 3 h to obtain high-purity ultrafine silver powder with a particle size of 0.26 ± 0.12 μm. The XRD pattern is shown below. Figure 2 As shown, the SEM image is as follows: Figure 3As shown, the silver powder has a uniform morphology, good dispersibility, and basically no agglomeration, with a purity greater than 99.5%.

[0025] The application of the ultrafine silver powder to conductive silver paste specifically includes the following steps: The silver paste was prepared by mixing the ultrafine silver powder, glass phase, and organic carrier in a mass ratio of 15:1:4, as detailed in Table 1. The paste was then printed onto an alumina ceramic substrate, leveled for 30 minutes, and then sintered at 700°C for 10 minutes in a resistance furnace. After cooling, a high-temperature conductive silver film with good shape and sheet resistance meeting national standards was obtained, as detailed in Table 2.

[0026] Table 1. Detailed list of conductive silver paste ingredients

[0027] Example 2 The difference between this embodiment and Example 1 is that in step (6), according to the mass ratio of dispersant to silver in the complex solution of 0.126:1, gum arabic is added to the silver ammonia solution and stirred at 400 r / min until completely dissolved. Then, according to the molar ratio of glucose to silver in the complex solution of 0.8:1, a glucose solution is prepared and 5 mol / L sodium hydroxide solution is added to adjust the pH to 13. The glucose solution is added to the silver ammonia solution and stirred at 800 r / min at 45℃ for 15 min to generate silver powder precipitate. After centrifugation, washing, and vacuum drying at 60℃ for 3 h, high-purity ultrafine silver powder is obtained. The particle size of this silver powder is 0.25±0.07 μm, and the XRD pattern is shown below. Figure 2 As shown, the SEM image is as follows: Figure 4 As shown, the silver powder has a uniform morphology, good dispersibility, and basically no agglomeration, with a purity greater than 99.5%.

[0028] The high-temperature conductive silver film obtained after sintering the silver paste has a sheet resistance that meets the national standard requirements. The specific parameters are shown in Table 2.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that the pH was not adjusted in step (6), there was no obvious change after the solution was mixed, the reduction reaction hardly occurred, and no silver powder was produced.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that in step (6), according to the mass ratio of silver in the dispersant to the complex being 0.063:1, gum arabic was added to the silver ammonia solution and stirred at 400 r / min until completely dissolved. Then, according to the molar ratio of ascorbic acid to silver in the silver ammonia solution being 0.8:1, an ascorbic acid solution was prepared and 7.4 mol / L ammonia solution was added to adjust the pH to 12. The ascorbic acid solution was added to the silver ammonia solution and stirred at 800 r / min at room temperature for 10 min to generate silver powder precipitate. After centrifugation, washing, and vacuum drying at 60℃ for 3 h, silver powder was obtained. The SEM image of the silver powder is shown below. Figure 5 As shown in the figure, SEM observation revealed that the silver powder obtained by ascorbic acid reduction did not exist in an independent, discrete state; there was adhesion between the particles, and some particles formed agglomerates, resulting in poor dispersibility. Furthermore, the sheet resistance of the prepared silver paste did not meet the national standard requirements for photovoltaic silver paste; specific parameters are shown in Table 2.

[0031] Comparative Example 3 The difference between this comparative example and Example 1 is that in step (6), according to the mass ratio of silver in the dispersant to the complex being 0.063:1, gum arabic was added to the silver ammonia solution and stirred at 400 r / min until completely dissolved. Then, according to the molar ratio of hydrazine hydrate to silver in the silver ammonia solution being 0.3:1, a hydrazine hydrate solution was prepared and adjusted to pH=13 with 5 mol / L sodium hydroxide solution. The hydrazine hydrate solution was added to the silver ammonia solution and stirred at 800 r / min for 10 min at room temperature to generate silver powder precipitate. After centrifugation, washing, and vacuum drying at 60℃ for 3 h, silver powder was obtained. The SEM image of the silver powder is shown below. Figure 6 As shown, SEM observation revealed that the silver powder obtained from the reduction of hydrazine hydrate exhibited severe agglomeration and extremely poor dispersibility. Furthermore, the resulting paste could not be printed normally through the screen.

[0032] Comparative Example 4 The difference between this comparative example and Example 1 is that in step (6), the reducing agent glucose was replaced with D-ribose. After mixing the solution, there was no obvious change, the reduction reaction hardly occurred, and no silver powder was produced. Compared with the six-membered ring skeleton of glucose, the five-membered ring structure of D-ribose has low stability. Under strongly alkaline conditions, the enediol salt intermediate generated is prone to degradation reaction, causing the reducing agent to lose its activity.

[0033] Table 2. Shear resistance results of conductive silver film.

[0034] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels, characterized in that, Includes the following steps: S1: The pretreated retired photovoltaic panels are ball-milled to obtain photovoltaic panel powder with uniform particle size; S2: The photovoltaic panel powder is soaked in dilute sulfuric acid at a specific liquid-solid ratio, stirred, and subjected to a purification reaction. After filtration, washing, and drying, aluminum-free photovoltaic panel powder is obtained. S3: The aluminum-removing photovoltaic panel powder is soaked in dilute nitric acid at a specific liquid-solid ratio, stirred and reacted, and then filtered to obtain a product containing Ag. + The leachate; S4: A precipitant is added dropwise to the leachate to react with it. After filtration, washing and drying, silver chloride powder is obtained. S5: Add the silver chloride powder to the complexing agent, stir, and react to obtain a silver complex; S6: Add dispersant and glucose to the silver complex, adjust the pH to 13-14, react at 40℃-70℃ to obtain a suspension, centrifuge to separate the precipitate, and wash, centrifuge and dry to obtain high-purity ultrafine silver powder with uniform particle size distribution and no agglomeration. The ultrafine silver powder has a particle size of 0.1-2.0 μm and a purity greater than 99.5%.

2. The method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels according to claim 1, characterized in that, In step S1, the retired photovoltaic panel is a photovoltaic panel without solder ribbon after physical and chemical dissociation of crystalline silicon photovoltaic modules; the pretreatment process includes washing with deionized water, soaking, and vacuum drying at 60℃; the ball milling process is to grind with a planetary ball mill at 350r / min-600r / min for 2h-8h.

3. The method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels according to claim 1, characterized in that, In step S2, the concentration of dilute sulfuric acid is 60 g / L-90 g / L; the liquid-solid ratio of the dilute sulfuric acid to the photovoltaic panel powder is 10-20:1; and the reaction temperature is 60℃-80℃.

4. The method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels according to claim 1, characterized in that, In step S3, the concentration of dilute nitric acid is 3 mol / L-7 mol / L; the liquid-solid ratio of the dilute nitric acid to the aluminum-removing photovoltaic panel powder is 2-16:1; and the reaction temperature is 40℃-80℃.

5. The method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels according to claim 1, characterized in that, In step S4, the precipitant is at least one of sodium chloride, ammonium chloride, and hydrochloric acid, with a concentration of 1 mol / L to 6 mol / L; the volume ratio of the leachate to the precipitant is 25-160:

1.

6. The method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels according to claim 1, characterized in that, In step S5, the complexing agent is ammonia or thiourea; wherein the concentration of ammonia is 3 mol / L-8 mol / L; the concentration of thiourea is 1 mol-2 mol / L; the liquid-solid ratio of the complexing agent and silver chloride powder is 15-30:1; the stirring rate is 800 r / min-1200 r / min; and the reaction temperature is 30℃-60℃.

7. The method for preparing ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels according to claim 1, characterized in that, In step S6, the dispersant is at least one of polyvinylpyrrolidone, gelatin or gum arabic; the pH adjuster is at least one of sodium hydroxide or potassium hydroxide; the mass ratio of the dispersant to silver in the silver complex is 0.06-0.2:1; and the molar ratio of glucose to silver in the silver complex is 0.5-5:

1.

8. The ultrafine silver powder based on recycled silver from decommissioned photovoltaic panels prepared by the preparation method according to any one of claims 1 to 7.

9. The application of the ultrafine silver powder prepared by the preparation method according to any one of claims 1 to 7 in high-temperature conductive silver paste.

10. The application according to claim 9, characterized in that, The ultrafine silver powder, glass phase, and organic carrier are mixed in a specific mass ratio to prepare silver paste. The paste is then printed onto a ceramic substrate, leveled, sintered at high temperature, and cooled to obtain a conductive silver film.

Images