Green silver extraction process of solar cell

Abstract

The invention discloses a green silver extraction process of a solar cell. The green silver extraction process comprises the following steps: 1) alkali washing; 2) filtering; 3) drying; 4) separating; 5) screening; and 6) drying. On one hand, on the basis of a mode of firstly performing alkali washing and then performing microwave or ultrasonic treatment (or performing microwave or ultrasonic treatment by taking an alkali solution as a medium), some chemical bonds of a silver paste substance are broken, the cohesiveness is reduced, and meanwhile, the silver paste substance is separated from the surface of a silicon wafer through a cavitation effect generated by electric field oscillation or vibration; and on the other hand, the purity of silver extracted by the wet method can be kept at 98.2% or above, produced waste liquid and tail gas can be treated and recycled, efficient circulation and comprehensive utilization of resources are achieved, in addition, the time needed by silver paste layer separation is short, and the recovery rate of silver can be kept at 97.98% or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of solar cell recycling, and particularly relates to a green silver extraction process for solar cells. Background Art

[0002] As is well known, the service life of general solar cells is about 25 years. With the development and application of solar cells, a large number of photovoltaic modules will enter the scrapping period. Therefore, the photovoltaic industry will face huge pressure in dealing with retired components.

[0003] Currently, the methods for recycling solar modules mainly focus on recycling materials such as silicon, glass, and aluminum. The recycling of precious metals has not attracted much attention. However, heavy metals (especially silver) have considerable value in solar cells. For example, the weight of PERC solar cells is about 12 g / piece, and the Ag content is 60 - 70 mg / piece. And the conductive silver paste is mainly a mechanical mixture slurry composed of silver powder, glass powder, organic carrier, and other additives (auxiliary materials) in a certain proportion. The traditional process for Ag recycling is: pickling (HNO3) - precipitation (AgCl) - Ag reduction.

[0004] Obviously, this method has the following technical defects:

[0005] 1. Nitric acid not only has a high cost but also belongs to dangerous chemicals. It has strong corrosiveness and high oxidizing property, posing high safety risks to equipment, pipelines, and operators, and strict protection is required. In addition, nitric acid requires special permits and management during storage, transportation, and use, increasing the compliance burden of enterprises.

[0006] 2. When nitric acid reacts with silver, harmful gases such as nitrogen oxides (NO2, NO) may be generated, and waste gas denitrification treatment is required.

[0007] 3. The extraction of Ag in this method involves the oxidation-reduction reaction of silver, with cumbersome steps and complex processes. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a brand-new green silver extraction process for solar cells.

[0009] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0010] A green silver extraction process for solar cells, which includes the following steps:

[0011] 1) Alkali washing: Soaking the waste battery chips in an alkali solution;

[0012] 2) Filtration: Separating solid and liquid and rinsing the surface of the solid to remove the alkali solution;

[0013] 3) Drying: Place the solar cells obtained in step 2) in a forced-air drying oven for drying.

[0014] 4) Separation: Place the dried solar cells in a solution tank and perform microwave or ultrasonic treatment to accelerate the reaction and detach the silver paste layer from the surface of the silicon wafer.

[0015] 5) Sieving: Sieve the solids obtained in step 4) to complete the separation of Ag particles and silicon material, and rinse the surface of the solids to remove the alkaline solution.

[0016] 6) Drying: Place the solids in the sieve in a forced-air drying oven for drying.

[0017] According to a specific implementation and preferred aspect of the present invention, in step 1), the mass percentage concentration of the alkaline solution is 20 - 30 wt%, the alkaline solution is preferably sodium hydroxide, and the soaking time is about 5 min. That is, based on sodium hydroxide, the chemical bond layer formed by the chemical reaction between the glass powder and the surface of the silicon wafer during the sintering process can be broken, thereby weakening the bonding ability between the silver paste and the solar cell.

[0018] Preferably, in steps 2) and 5), vacuum filtration and multi-layer sieve ultrasonic filtration are respectively used for solid-liquid separation, and the surface of the solids is repeatedly rinsed with deionized water or dilute hydrochloric acid with a mass percentage concentration of 5 - 10 wt%.

[0019] Preferably, the drying time required in steps 3) and 6) is 4 - 5 h. Further, the drying temperature in steps 3) and 6) is 35 ± 2 °C.

[0020] According to another specific implementation and preferred aspect of the present invention, in step 4), the solution in the solution tank is deionized water or sodium hydroxide with a mass percentage concentration of 25 - 30 wt% (or potassium hydroxide with a mass percentage concentration of 25 - 30 wt%). The time for microwave or ultrasonic treatment is about 30 - 180 min. In short, based on the role of the alkali is to react to break some chemical bonds of the silver paste substance and reduce the adhesiveness, and ultrasonic or microwave is to assist in providing energy to accelerate the reaction, that is, to provide energy to make it come down; at the same time, whether it is to excite molecular vibration through electric field oscillation to cause internal heating (the whole material is heated) to separate the silver paste layer, or to generate cavitation effect through mechanical vibration to form external impact (surface or near-surface action) to separate the silver paste layer is all possible.

[0021] In some specific embodiments, in step 5), the sieve used for sieving is a three-layer sieve, and the mesh numbers are 25 - 30, 200 - 250, and 600 - 650 meshes respectively. Generally, 30, 225, and 625 meshes are respectively the best.

[0022] In addition, based on the above process steps, the components of the waste liquid generated include Na[Al(OH)4], Na3[Al(OH)6], and Na2SiO3; the gas discharged is H2. The waste liquid can be appropriately treated and used to remove suspended solids, heavy metal ions, phosphates, etc. from wastewater, and the tail gas can be used as fuel to achieve efficient recycling and comprehensive utilization of resources.

[0023] Another technical solution of the present invention is: a green silver extraction process for solar cell wafers, which includes the following steps:

[0024] 1) Separation: Place the dried cell wafers in a solution tank. The aqueous solution in the solution tank is an alkaline solution. At the same time, perform microwave or ultrasonic treatment on the cell wafers in the solution tank to accelerate the reaction and detach the silver paste layer from the silicon wafer surface. The microwave or ultrasonic treatment time is 45 - 60 min, and the alkaline solution is sodium hydroxide with a mass percentage concentration of 25 - 30 wt% or potassium hydroxide with a mass percentage concentration of 20 - 30 wt%.

[0025] 2) Screening: First, use a multi-stage sieve to screen Ag particles and silicon materials, and repeatedly rinse the solid surface of the Ag particles with deionized water or dilute hydrochloric acid with a mass percentage concentration of 5 - 10 wt% to remove the alkaline solution.

[0026] 3) Drying: Place the solid in step 2) in a blast drying oven at a temperature of 35 ± 2 °C to dry the solid, where the drying time required is 4 - 5 h.

[0027] Due to the implementation of the above technical solutions, the present invention has the following advantages compared with the prior art:

[0028] In the existing methods, silver extraction is mainly accomplished through nitric acid. However, nitric acid not only has a high cost but also belongs to hazardous chemicals, with strong corrosiveness and high oxidizing property, posing relatively high safety risks to equipment, pipelines, and operators, thus requiring strict protection. In addition, nitric acid requires special permits and management during storage, transportation, and use, increasing the compliance burden on enterprises. Meanwhile, harmful gases such as nitrogen oxides (NO2, NO) may be generated when nitric acid reacts with silver, necessitating waste gas denitrification treatment. Moreover, the extraction of Ag in this method involves redox reactions of silver, with drawbacks such as cumbersome steps and complex processes. In contrast, this application conducts an overall design of the silver extraction method, ingeniously solving the deficiencies and defects of the existing technology. After adopting this silver extraction method, first, the discarded battery chips are immersed in an alkali solution, then solid-liquid separation is carried out, and the surface of the solid is rinsed to remove the alkali solution; then the battery chips are placed in a blast drying oven for drying; secondly, the dried battery chips are placed in a solution tank and subjected to microwave or ultrasonic treatment to accelerate the reaction and detach the silver paste layer from the surface of the silicon wafer; finally, screening and filtration are carried out, and the surface of the solid is washed again, and at the same time, the solid is placed in a blast drying oven for drying to complete the separation of Ag particles and silicon materials. Therefore, on the one hand, based on the method of first alkali washing and then microwave or ultrasonic treatment (or carrying out microwave or ultrasonic treatment with an alkali solution as the medium), some chemical bonds of the silver paste substance are broken, reducing the adhesiveness, and at the same time, cavitation effects are generated through electric field oscillation or vibration to make the silver paste substance detach from the surface of the silicon wafer; on the other hand, the wet silver extraction method adopted can keep the purity of silver above 98.2%, and the waste liquid and tail gas generated can be treated and recycled, realizing the efficient recycling and comprehensive utilization of resources. In addition, the time required for separating the silver paste layer is short, and the recovery rate of silver can be kept above 97.98%. Detailed Embodiments

[0029] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be described in detail below in conjunction with specific embodiments. Many specific details are set forth in the following description to fully understand the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0030] Example 1

[0031] The green silver extraction process for solar cell chips involved in this example includes the following steps:

[0032] 1) Alkali washing: Immerse the discarded battery chips in a sodium hydroxide solution with a mass percentage concentration of 20wt%, and the immersion time is about 5 minutes;

[0033] 2) Filtration: Perform solid-liquid separation by vacuum filtration, and repeatedly rinse the surface of the solid with deionized water for multiple times to remove the alkali solution;

[0034] 3) Drying: Place the solar cells obtained in step 2) in a forced-air drying oven for drying, where the drying temperature is 35 ± 2 °C and the drying time is 5 h;

[0035] 4) Separation: Place the dried solar cells in a solution tank, and the aqueous solution in the solution tank is deionized water. At the same time, perform ultrasonic treatment to accelerate the reaction to detach the silver paste layer from the silicon wafer surface, where the ultrasonic treatment time is about 120 min;

[0036] 5) Sieving: Use 30, 225, and 625-mesh sieves for sieving to complete the separation of Ag particles and silicon material. At the same time, repeatedly rinse the surface of the solid Ag particles with deionized water for multiple times;

[0037] 6) Drying: Place the solid obtained in step 5) in a forced-air drying oven for drying, where the drying temperature is 35 ± 2 °C and the drying time is 5 h.

[0038] Example 2

[0039] 1) Alkaline washing: Immerse the waste solar cells in a sodium hydroxide solution with a mass percentage concentration of 20 wt%, and the immersion time is about 5 min;

[0040] 2) Filtration: Perform solid-liquid separation by vacuum filtration, and repeatedly rinse the surface of the solid with deionized water for multiple times to remove the alkaline solution;

[0041] 3) Drying: Place the solar cells obtained in step 2) in a forced-air drying oven for drying, where the drying temperature is 35 ± 2 °C and the drying time is 5 h;

[0042] 4) Separation: Place the dried solar cells in a solution tank, and the aqueous solution in the solution tank is a 25 wt% sodium hydroxide solution. At the same time, perform ultrasonic treatment to accelerate the reaction to detach the silver paste layer from the silicon wafer surface, where the ultrasonic treatment time is about 30 min;

[0043] 5) Sieving: Use 30, 225, and 625-mesh sieves for sieving to complete the separation of Ag particles and silicon material. At the same time, repeatedly rinse the surface of the solid Ag particles with a 10 wt% dilute hydrochloric acid solution to remove the alkaline solution;

[0044] 6) Drying: Place the solid obtained in step 5) in a forced-air drying oven for drying, where the drying temperature is 35 ± 2 °C and the drying time is 5 h.

[0045] Example 3

[0046] The green silver extraction process for the solar cells in this example includes the following steps:

[0047] 1) Separation: Place the dried solar cells in a solution tank. The aqueous solution in the solution tank is an alkaline solution. At the same time, perform ultrasonic treatment on the solar cells in the solution tank to accelerate the reaction and cause the silver paste layer to peel off from the silicon wafer surface. The ultrasonic treatment time is 60 min, and the alkaline solution is sodium hydroxide with a mass percentage concentration of 20 wt%.

[0048] 2) Sieving: First, sieve using 30, 225, and 625 - mesh sieves to complete the separation of Ag particles and silicon materials. At the same time, repeatedly rinse the surface of the solid Ag particles with dilute hydrochloric acid with a mass percentage concentration of 10 wt% to remove the alkaline solution.

[0049] 3) Drying: Place the solid from step 2) in a forced - air drying oven at a temperature of 35 ± 2 °C to dry the solid. The drying time required is 5 h.

[0050] Comparative Example 1

[0051] The silver extraction process for the solar cells in this example includes the following steps:

[0052] 1) Ultrasonic treatment: Place the solar cells in a solution tank, and the aqueous solution in the solution tank is deionized water. At the same time, perform ultrasonic treatment for about 150 min.

[0053] 2) Filtration: Perform solid - liquid separation by vacuum filtration, and repeatedly rinse the surface of the solid with deionized water for multiple times.

[0054] 3) Drying: Place the solid in a forced - air drying oven to dry. The drying temperature is 35 ± 2 °C, and the drying time is 12 h.

[0055] 4) Sieving: Sieve the dried solid using a sieve with about 400 meshes to complete the separation of Ag particles and silicon materials.

[0056] Comparative Example 2

[0057] The silver extraction process for the solar cells in this example (soaking method) includes the following steps:

[0058] 1) Preliminary soaking in nitric acid for 1 hour, dissolving 70% of silver, nitric acid concentration 6.5 mol / L, and filter after the reaction.

[0059] 2) Fine soaking in nitric acid for 1 hour, dissolving 20% of silver, nitric acid concentration 5.5 mol / L, and filter after the reaction.

[0060] 3) Deep dissolution in nitric acid for 30 min, dissolving 10% of silver, nitric acid concentration 5 mol / L, and filter after the reaction.

[0061] 4) Add filtered NaCl or HCl to the filtrates from steps 1), 2), and 3) to obtain AgCl precipitate.

[0062] 5) Filtration: Solid-liquid separation is carried out by vacuum filtration, and the solid is repeatedly rinsed with deionized water for 3 - 5 times.

[0063] 6) Drying: The solid (AgCl) is placed in a forced-air drying oven at 35 ± 2 °C to dry the solid, and the drying time required is 12 h.

[0064] 7) Calcination: The AgCl solid is calcined at a high temperature (800 °C) to obtain pure silver (Ag).

[0065] Based on the above embodiments and comparative examples, the applicant conducted experiments and comparisons on each process, as shown in Table 1.

[0066] Table 1

[0067]

[0068] Based on the above data comparison and analysis, the main differences between this embodiment and the comparative example are as follows:

[0069] 1. Embodiments 1 to 3 of this application have obvious advantages in the time required for silver paste layer separation. At the same time, the waste liquid of this application can be appropriately treated and used to remove suspended solids, heavy metal ions, phosphates, etc. in wastewater, and the tail gas can be used as fuel, realizing the efficient recycling and comprehensive utilization of resources. In addition, there are also comparisons among Embodiments 1 to 3 themselves. Obviously, first alkali-washing with sodium hydroxide, then ultrasonic treatment in sodium hydroxide solution, and then rinsing with dilute hydrochloric acid water have obvious advantages in terms of time, Ag recovery rate, and silver purity.

[0070] 2. The main hazards of sodium hydroxide used in alkali-washing are its strong corrosiveness and exothermic reaction during dissolution. In addition to corrosiveness, nitric acid also has strong oxidizing properties, strong volatility, and may form toxic gases (NO2, NO), which are more likely to cause environmental pollution and health hazards. At the same time, from the perspective of industrial production and laboratory safety, the overall hazard of nitric acid is higher because it has oxidizing and volatile properties and is more likely to cause accidents.

[0071] 3. For the wet silver extraction method used, the purity of silver can be maintained above 98.2%, and the recovery rate of Ag formed can be maintained above 97.98%.

[0072] The above has described the present invention in detail. The purpose is to enable those skilled in this field to understand the content of the present invention and implement it, but it cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit and essence of the present invention should be covered within the protection scope of the present invention.

Claims

1. A green silver extraction process for solar cells, characterized in that: It includes the following steps: 1) Alkaline washing: Soak the discarded battery cells in an alkaline solution; 2) Filtration: solid-liquid separation and washing of the solid surface to remove the alkaline solution; 3) Drying: drying the battery cell in step 2) in a blast drying oven; 4) Separation: Place the dried cell in a solution tank and perform microwave or ultrasonic treatment to accelerate the reaction and remove the silver paste layer from the silicon wafer surface; 5) Screening: The solid in step 4) is screened to separate the Ag particles and the silicon material, and the surface of the solid is rinsed to remove the alkaline solution. 6) Drying: Place the solids in the sieve in a forced air drying oven for drying.

2. The green silver extraction process for solar cells according to claim 1, characterized in that: In step 1), the mass percentage concentration of the alkaline solution is 20-30 wt%.

3. The green silver extraction process for solar cells according to claim 1 or 2, characterized in that: The alkaline solution is sodium hydroxide or potassium hydroxide.

4. The green silver extraction process for solar cell sheets according to claim 3, characterized in that: The soaking time in step 1) is 3-5 minutes.

5. The green silver extraction process for solar cell sheets according to claim 1, characterized in that: In step 2), vacuum filtration is used for solid-liquid separation, and in step 5), multi-stage screens are used for ultrasonic filtration separation, and deionized water or diluted hydrochloric acid with a mass percentage concentration of 5-10wt% is used to repeatedly rinse the solid surface.

6. The green silver extraction process for solar cell sheets according to claim 1, characterized in that: The time required for drying in step 3) and step 6) is 4-5 hours; and / or, the drying temperature in step 3) and step 6) is 35±2°C.

7. The green silver extraction process for solar cell sheets according to claim 1, characterized in that: In step 4), the solution in the solution tank is deionized water or sodium hydroxide with a mass percentage concentration of 25-30wt% or potassium hydroxide with a mass percentage concentration of 25-30wt%; and / or, in step 4), the microwave or ultrasonic treatment time is 30-180min.

8. The green silver extraction process for solar cells according to claim 1, characterized in that: In step 5), three layers of sieves are used for screening, and the mesh numbers thereof are 25-30, 200-250, and 600-650 respectively.

9. The green silver extraction process for solar cell sheets according to claim 1, characterized in that: The components of the waste liquid produced include Na[Al(OH)4], Na3[Al(OH)6], Na2SiO3; and / or the exhausted gas is H2.

10. A green silver extraction process for solar cell sheets, characterized in that: It includes the following steps: 1) Separation: placing the dried cell in a solution tank, wherein the aqueous solution in the solution tank is an alkaline solution, and simultaneously subjecting the cell in the solution tank to microwave or ultrasonic treatment to accelerate the reaction to remove the silver paste layer from the surface of the silicon wafer, wherein the microwave or ultrasonic treatment time is 45-60 minutes, and the alkaline solution is 25-30wt% sodium hydroxide or 20-30wt% potassium hydroxide; 2) Screening: First, Ag particles and silicon materials are screened using a multi-stage screen, and the Ag particles are repeatedly washed with deionized water or diluted hydrochloric acid with a mass percentage concentration of 5-10wt% to remove the alkaline solution; 3) Drying: The solid obtained in step 2) is placed in a forced air drying oven at a temperature of 35±2° C. to dry the solid, wherein the drying time is 4-5 h.

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