A green solvothermal method for recovering silver from waste crystalline silicon photovoltaic modules.

Abstract

This invention belongs to the field of photovoltaic module recycling technology, specifically relating to a green solvent hydrothermal method for recovering silver from waste crystalline silicon photovoltaic modules. The method includes the following steps: 1) cutting the waste photovoltaic module into small photovoltaic module pieces without aluminum frames and junction boxes; 2) washing the modules obtained in step 1) with anhydrous ethanol solution; 3) placing the modules obtained in step 2) in an inner container, pouring in a sodium phosphate aqueous solution, and heating at 180–200°C for 0.80–1.2 hours, separating the front EVA layer from the silicon wafer to obtain a front EVA layer with adhered silver grid lines and the remaining module; 4) separating the silver grid lines from the EVA layer to recover the silver grid lines. This invention, based on sodium phosphate solution, can achieve the recovery of most of the silver grid lines (silver silicon) on solar cells.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic module recycling technology, specifically relating to a green solvent hydrothermal method for recovering silver from waste crystalline silicon photovoltaic modules. Background Technology

[0002] The lifespan of photovoltaic modules is generally set at 20 to 25 years, indicating that a large number of used photovoltaic modules will enter the retirement stage in the next few years. These modules contain abundant high-value materials such as silicon, silver, and aluminum. If they cannot be effectively recycled, it will not only be a huge waste, but will also have a significant negative impact on the ecological environment.

[0003] Traditionally, photovoltaic module recycling methods are divided into three main categories: mechanical processing, thermal processing, and chemical processing. While mechanical processing can achieve basic crushing and screening, it is difficult to extract high-purity solar cells. Thermal processing involves high-temperature incineration, which consumes a lot of energy and is accompanied by the emission of harmful gases, increasing the carbon footprint. Although chemical processing has high recycling efficiency, it relies on strong acids, alkalis, or organic solvents, posing environmental pollution and operational safety hazards.

[0004] Although various recycling methods, such as physical, mechanical, and pyrolysis, exist, they each have limitations in terms of efficiency, environmental friendliness, and economic cost. While physical methods are technologically mature, they struggle to guarantee the recovery of high-purity materials. Mechanical methods have made progress in processing large-scale components, but secondary pollution and the separation of composite materials remain challenges. Pyrolysis can recover high-purity metals and silicon, but its high-temperature operation, high energy consumption, and high equipment costs limit its widespread application. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a green solvent hydrothermal method for recovering silver from waste crystalline silicon photovoltaic modules. This method, based on a sodium phosphate solution, effectively separates the EVA film through a gentle processing procedure, enabling the recovery of the vast majority of the silver grid lines (silver silicon) on the solar cells. The use of sodium phosphate not only reduces processing costs but also significantly alleviates the environmental burden. The entire process is simple to operate, highly efficient, and produces no harmful gas emissions, making it extremely environmentally friendly. Compared to traditional methods, the sodium phosphate green solvent method demonstrates significant advantages in environmental friendliness, processing efficiency, and cost-effectiveness.

[0006] The technical solution provided by this invention is as follows:

[0007] A green solvothermal method for recovering silver from waste crystalline silicon photovoltaic modules includes the following steps:

[0008] 1) Cut the waste photovoltaic modules into small photovoltaic modules that do not contain aluminum frames and junction boxes;

[0009] 2) Wash the components obtained in step 1) with anhydrous ethanol solution;

[0010] 3) Place the component obtained in step 2) into the inner liner, pour in sodium phosphate aqueous solution, and heat at 180-200℃ for 0.80-1.2 hours to react. The front EVA layer separates from the silicon wafer, and the front EVA layer with silver grid lines and the remaining component are obtained.

[0011] 4) Separate the silver grid lines from the EVA layer and recycle the silver grid lines.

[0012] In the above technical solution, an aqueous solution of sodium phosphate is used, and heating at a relatively low temperature achieves the following effects:

[0013] The etchable silicon nitride can separate the front-side EVA from the silicon wafer. Since the silver paste is brushed onto the surface of silicon nitride, the silver gate lines automatically separate from the silicon wafer.

[0014] The chemical immersion process does not corrode the silver grid lines;

[0015] The chemical immersion process does not corrode or swell EVA, thus avoiding damage to the silicon wafer;

[0016] It can etch the aluminum back electrode, thereby achieving the effect of etching aluminum and recovering silver;

[0017] The etchable silicon nitride can separate the EVA from the silicon wafer.

[0018] One advantage of sodium phosphate is that it does not corrode EVA, an effect that processing solutions such as sodium carbonate do not possess. Furthermore, sodium phosphate has a stronger etching effect on silicon nitride than sodium carbonate.

[0019] Step 4) Physical splitting can be used to separate the silver gate lines from the EVA layer.

[0020] Based on the above technical solution, neither physical disassembly nor chemical soaking steps will corrode the silver grid lines.

[0021] Specifically, in step 3), pour in an aqueous solution of sodium phosphate until the component is submerged.

[0022] Specifically, in step 3), the reaction is heated at 180°C or 200°C.

[0023] Specifically, in step 3), the reaction is heated for 1 hour.

[0024] Specifically, in step 3), the weight percentage concentration of the sodium phosphate aqueous solution is 28–29.5 g / mL.

[0025] Specifically, step 3) also includes the following steps: recovering the sodium phosphate aqueous solution after the reaction.

[0026] Further, after step 3), rinse the remaining components and let the excess water dry naturally before proceeding to the next step.

[0027] Furthermore, it also includes step 5): repeating steps 1) to 4), with step 2) in the repetition using the recovered sodium phosphate aqueous solution.

[0028] Specifically: Step 4) The recovered silver grid lines are complete silver grid lines.

[0029] Specifically: In step 1), an angle grinder is used for cutting.

[0030] The beneficial effects of this invention are:

[0031] 1) All chemical solvents used in this invention are green and pollution-free solvents;

[0032] 2) The chemical solvents used in this invention can be repeatedly recycled, which greatly reduces the cost of the recycling process;

[0033] 3) Compared with existing technologies, the advantages of this invention are that most existing methods for separating silicon and silver involve soaking the EVA film in nitric acid at around 70°C. Because a highly oxidizing and volatile acid is used during the recycling process, some toxic gases are generated. Therefore, using nitric acid to recover silicon and silver from battery cells requires excessive solvent oxidation, resulting in some loss of metallic silver and environmental pollution. The technical solution of this invention does not have this problem.

[0034] 4) This invention utilizes a wet process to separate EVA (with silver grid lines adhering to it) in photovoltaic modules, achieving good purification of silver grid lines. It not only avoids environmental pollution caused by dissolving silver with nitric acid, but also allows for the recycling and reuse of silicon wafers, making it highly practical. Attached Figure Description

[0035] Figure 1 This is a structural diagram of a photovoltaic module.

[0036] Figure 2 These are SEM and EDS images of the front-side EVA film separated in Example 1.

[0037] Figure 3 This is a component diagram of the front EVA film and silver grid lines separated in Example 1. Detailed Implementation

[0038] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0039] Unless otherwise specified, the test methods used in the embodiments are conventional methods; unless otherwise specified, the materials and reagents used are commercially available.

[0040] Example 1

[0041] A green solvothermal method for recovering silver from waste crystalline silicon photovoltaic modules includes the following steps:

[0042] 1) Cutting photovoltaic panels.

[0043] Remove the aluminum frame and junction box from the retired photovoltaic panels, place the remaining photovoltaic panels in an open space, and slowly cut several 2×2cm modules using an angle grinder.

[0044] 2) Preparation of EVA on the positive surface separated by sodium phosphate

[0045] ① Take 28.8g of solid from the anhydrous sodium phosphate using a spatula.

[0046] ② Place 28.8g of anhydrous sodium phosphate solid in a beaker and dilute to volume in a 100mL volumetric flask.

[0047] ③ Place the 2×2cm component processed in step 1) into the PTFE inner liner.

[0048] ④ Pour 25 mL of the sodium phosphate solution prepared in step ② into the inner liner.

[0049] ⑤ Place the inner liner treated in ④ into a hydrothermal reactor with a pressure of less than 3 MPa.

[0050] ⑥ Preferably, the hydrothermal reactor is placed in an oven and kept at 200°C for 1 hour.

[0051] ⑦ Remove the hydrothermal reactor after the reaction in step ⑥, open the tetrafluoroethylene liner, and remove the components with tweezers.

[0052] ⑧ The component removed by tweezers in step ⑦ is the positive EVA film, and the remaining sodium phosphate liquid and remaining components in the inner liner.

[0053] The removed component is washed and placed on a petri dish containing an EVA film (with silver grid lines adhering to it) and a 2×2cm component. The silver grid lines can be separated from the EVA by mechanical peeling, such as manual peeling.

[0054] 3) Recycling components

[0055] ① Pour the liquid from the tetrafluoroethylene liner in step 2) and the battery cells into a beaker.

[0056] ②Use tweezers to pick up the components.

[0057] Figure 1This is a structural diagram of a photovoltaic module.

[0058] Figure 2 These are SEM and EDS images of the front-side EVA film separated in Example 1. The elemental analysis shows that the silver grid lines are attached to the film.

[0059] Figure 3 This is a component diagram of the front EVA film and silver grid lines separated in Example 1.

[0060] pass Figure 2 , 3 As can be seen, the front EVA film (with silver grid lines adhering to it) can be separated.

[0061] Example 2

[0062] Referring to Example 1, the difference is that only anhydrous ethanol was used to separate each EVA layer. The results showed that although the back EVA layer could be separated, the front EVA layer could not be separated.

[0063] Example 3

[0064] Referring to Example 1, the difference is that a sodium carbonate aqueous solution was directly used to separate the EVA layers. The results showed that although the front EVA layer could be separated, the back EVA layer could not be separated, and the EVA was corroded. It's not corrosion; the front EVA undergoes a saponification reaction after being treated with sodium phosphate, causing the film to turn white and rough.

[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A green solvothermal method for recovering silver from waste crystalline silicon photovoltaic modules, characterized in that, It consists of the following steps: 1) Cut the waste photovoltaic modules into small photovoltaic modules that do not contain aluminum frames and junction boxes; 2) Wash the components obtained in step 1) with anhydrous ethanol solution; 3) Place the component obtained in step 2) into the inner liner, pour in sodium phosphate aqueous solution, and heat at 180-200℃ for 0.80-1.2 hours to react. The front EVA layer separates from the silicon wafer, and the front EVA layer with silver grid lines and the remaining component are obtained. The weight percentage concentration of sodium phosphate aqueous solution is 0.28-0.295 g / mL. 4) Separate the silver grid lines from the EVA layer and recycle the silver grid lines.

2. The method for recovering silver from waste crystalline silicon photovoltaic modules using a green solvothermal method according to claim 1, characterized in that, In step 3), pour in an aqueous solution of sodium phosphate until the immersion component is submerged.

3. The method for recovering silver from waste crystalline silicon photovoltaic modules using the green solvothermal method according to claim 1, characterized in that, In step 3), the reaction is heated at 180°C or 200°C.

4. The method for recovering silver from waste crystalline silicon photovoltaic modules using the green solvothermal method according to claim 1, characterized in that, In step 3), the reaction is heated for 1 hour.

5. The method for recovering silver from waste crystalline silicon photovoltaic modules using a green solvothermal method according to claim 1, characterized in that, Step 3) also The process includes the following steps: recovering the sodium phosphate aqueous solution after the reaction.

6. The method for recovering silver from waste crystalline silicon photovoltaic modules using the green solvothermal method according to claim 5, characterized in that, It also includes step 5): repeating steps 1) to 4), and step 2) in the repeating step uses the recovered sodium phosphate aqueous solution.

7. The method for recovering silver from waste crystalline silicon photovoltaic modules using the green solvothermal method according to claim 1, characterized in that: Step 4) The recovered silver grid lines are complete silver grid lines.

8. The method for recovering silver from waste crystalline silicon photovoltaic modules using the green solvothermal method according to claim 1, characterized in that: In step 1), an angle grinder is used for cutting.

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