Method for recycling decommissioned crystalline silicon photovoltaic silicon wafer and precious metal silver

Abstract

The invention discloses a method for recovering a silicon wafer and precious metal silver in a decommissioned crystalline silicon photovoltaic panel, which comprises the following steps of: 1, mechanically disassembling and pyrolyzing the decommissioned photovoltaic panel to obtain a crystalline silicon battery piece; 2, preparing molten salt, and heating the molten salt to melt the salt; and step 3, placing the crystalline silicon cell in molten salt, carrying out selective etching separation, taking out the crystalline silicon cell after etching is finished, and washing with water to obtain a silicon wafer and a silver wire. According to the method, the melting temperature of the used fused salt is low, silver and silicon in the photovoltaic panel can be separated in a targeted mode, the fused salt does not react with substrate silicon and silver wires on the surface, the high recovery efficiency of silver and silicon is guaranteed, meanwhile, environmental pollution caused by silver and silicon in the recovery process is reduced, on the basis, silver and silicon can be obtained through one-step separation and recovery, and the method is suitable for industrial production. The method has the advantages of simple operation, short process, environmental friendliness and the like.

Description

Technical Field

[0001] The present invention relates to a method for recovering silicon wafers and precious metal silver in retired crystalline silicon photovoltaics, belonging to the technical field of recovering silicon and precious metal silver in retired crystalline silicon photovoltaic panels. Background Art

[0002] According to the prediction and calculation of the China Photovoltaic Recycling Industry Development Cooperation Center on the scale of retired photovoltaics in China, under the conventional retirement scenario in China, the cumulative retired amounts of photovoltaics in 2030, 2040, and 2050 will reach 1 million tons, 12 million tons, and 55 million tons respectively; under the early retirement scenario, they will reach 4 million tons, 23 million tons, and 66 million tons respectively (including the waste generated during the production process). Among them, crystalline silicon photovoltaic cell modules will be the main types of scrap. Crystalline silicon photovoltaic modules are mainly composed of products such as glass, frames, wires, crystalline silicon, conductive paste (silver / aluminum, etc.), and adhesives. More than 90% of the materials can be recycled. Clean and efficient recovery of retired crystalline silicon photovoltaic modules is a major requirement for realizing resource recycling and the green and sustainable development of the photovoltaic industry.

[0003] However, the methods in the prior art have disadvantages such as high energy consumption, large pollution, and complex processes; therefore, it is necessary to develop a method for recovering silicon and silver in retired crystalline silicon photovoltaic panels with low cost, simple operation, environmental friendliness, and short recovery process. Summary of the Invention

[0004] The present invention designs and develops a method for recovering silicon wafers and precious metal silver in retired crystalline silicon photovoltaics, using molten salt to etch crystalline silicon photovoltaic panels and specifically separating to obtain silicon and silver.

[0005] Another object of the present invention: During the etching process, the etching temperature is low, and by adjusting the temperature of the molten salt, the alloying and loss rate of silver and silicon are inhibited, and the recovery rate is increased.

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

[0007] A method for recovering silicon wafers and precious metal silver in retired crystalline silicon photovoltaics, comprising:

[0008] Step 1: Mechanically disassemble and pyrolyze the retired crystalline silicon photovoltaic panel to obtain crystalline silicon solar cells;

[0009] Step 2: Prepare molten salt and heat it to melt the salt;

[0010] Step 3: Place the crystalline silicon solar cells in the molten salt for selective etching separation. After the etching is completed, take out the crystalline silicon solar cells and wash them with water to obtain silicon wafers and silver wires.

[0011] Preferably, the heating rate of the pyrolysis process is 5 - 20 °C / min, and the pyrolysis temperature is 450 - 700 °C.

[0012] Preferably, the components of the molten salt are sodium chloride and calcium chloride, and the ratio of sodium chloride to calcium chloride is 0.1 - 5:1. The temperature of the molten salt is 450 - 1000 °C.

[0013] Preferably, the etching and separation of the specimen is 60 - 240 s.

[0014] Preferably, during the mechanical disassembly process, the glass, aluminum frame, and backsheet in the photovoltaic panel are mechanically removed.

[0015] Preferably, the size of the retired crystalline silicon photovoltaic panel is 1600 mm × 1000 mm, and the size of the crystalline silicon cell is 80 mm × 40 mm.

[0016] The beneficial effects of the present invention are as follows:

[0017] The method for recycling silicon wafers and precious metal silver in retired crystalline silicon photovoltaics provided by the present invention uses retired crystalline silicon photovoltaic panels as raw materials and adopts a molten salt etching method to efficiently separate and recycle silicon wafers and silver wires in the battery panels. The silicon and silver recovered by the present invention have a high recovery rate. Compared with the traditional method, the preparation method of the present invention has the following advantages: (1) short process and simple operation; (2) low energy consumption and cost; (3) high recovery rates of silver and silicon; (4) environmentally friendly, without the use of toxic and harmful chemical reagents. Description of the Drawings

[0018] Figure 1 It is a flow chart of the method for recycling silicon wafers and precious metal silver in retired crystalline silicon photovoltaics of the present invention.

[0019] Figure 2(a) is a diagram of the silicon wafer product obtained by separation and recovery of the present invention.

[0020] Figure 2(b) is a diagram of the silicon and silver products obtained by separation and recovery of the present invention Detailed Embodiments

[0021] The following further describes the present invention in detail with reference to the drawings, so that those skilled in the art can implement it according to the description in the specification.

[0022] As Figure 1 shown in -2, the present invention provides a method for recycling silicon wafers and precious metal silver in retired crystalline silicon photovoltaics. The retired photovoltaic panel is mechanically disassembled and pyrolyzed to obtain crystalline silicon cells; the crystalline silicon cells are placed in a calcium chloride - sodium chloride molten salt for selective chemical etching and separation; then the crystalline silicon cells are immersed in water to separate and obtain silicon wafers and precious metal silver wires, which specifically include:

[0023] Step 1: Physically disassemble and pyrolyze the retired photovoltaic panels to obtain crystalline silicon cells;

[0024] During mechanical disassembly, mechanically remove the glass, aluminum frame, and backsheet in the photovoltaic panels;

[0025] During pyrolysis, the heating rate is 5 - 20 °C / min;

[0026] If the heating rate is less than 5 °C / min, or the pyrolysis temperature is too high or too low, it will result in too long heating time and increased energy consumption; if the heating rate is greater than 20 °C / min, it will cause damage to the heating element.

[0027] The pyrolysis temperature is 450 - 700 °C;

[0028] If the pyrolysis temperature is lower than 450 °C, it will lead to long pyrolysis time, incomplete pyrolysis, and increased energy consumption; if the pyrolysis temperature is higher than 700 °C, it will cause problems such as cracking of the crystalline silicon cells, damage to the furnace body, and melting of the lead-tin alloy in the photovoltaic panels resulting in lead pollution.

[0029] Step 2: Prepare sodium chloride-calcium chloride molten salt according to a ratio and heat it to melt to obtain molten salt;

[0030] The molten salt consists of a mixture of sodium chloride and calcium chloride, and the ratio of sodium chloride to calcium chloride is 0.1 - 5:1. The heating temperature of the molten salt (salt immersion) is 450 - 1000 °C;

[0031] If the heating temperature of the molten salt is lower than 450 °C and the heating time is less than 60 s, it will lead to incomplete melting of the molten salt and reduced separation efficiency;

[0032] If the salt immersion temperature is higher than 1000 °C, it will cause a large amount of energy consumption loss, loss of salt volatilization, and silver-silicon alloying, resulting in loss of silver and silicon.

[0033] Step 3: Fully immerse the crystalline silicon cells in the molten salt for selective etching separation. After the etching is completed, take out the cells and wash them with water to obtain silicon wafers and silver wires;

[0034] The etching time is 60 - 240 s;

[0035] If the etching time is less than 60 s, it will lead to insufficient etching separation;

[0036] If the etching time is higher than 240 s, it will lead to increased energy consumption and cracking of the silicon wafers, and both too high and too low will significantly reduce the recovery rates of silicon and silver.

[0037] The water washing separation time is until silver and silicon are completely separated.

[0038] The molten salt used in this method has a relatively low melting temperature, which can specifically separate silver and silicon in photovoltaic panels without reacting with the substrate silicon and the silver wires on the surface, ensuring a high recovery efficiency of silver and silicon. At the same time, it reduces the environmental pollution caused by silver and silicon during the recovery process. Based on this, the present invention can separate and recover silver and silicon in a one-step method, with the advantages of simple operation, short process, and environmental friendliness.

[0039] Example 1

[0040] Step 1: Physically disassemble and pyrolyze the retired photovoltaic panels to obtain crystalline silicon solar cells;

[0041] During the mechanical disassembly process, the glass, aluminum frame, and backplane in the photovoltaic panel are mechanically removed;

[0042] During the pyrolysis process, the heating rate is 5°C / min, and the temperature is raised to 450°C, with a holding time of 60 min to separate the crystalline silicon solar cells;

[0043] Step 2: Configure the molten salt according to the ratio and heat it to melt it to obtain molten salt;

[0044] The molten salt is a mixture of sodium chloride and calcium chloride. The heating temperature of the molten salt (salt immersion) is 450°C, and the ratio of sodium chloride to calcium chloride is 0.1:1;

[0045] Step 3: Place the crystalline silicon solar cells fully in the molten salt and perform selective etching separation at 450°C for 240 s. After the etching is completed, take out the solar cells and wash them with water to obtain pure silicon wafers and silver wires.

[0046] Example 2

[0047] During the mechanical disassembly process, the glass, aluminum frame, and backplane in the photovoltaic panel are mechanically removed;

[0048] During the pyrolysis process, the heating rate is 12°C / min, and the temperature is raised to 550°C, with a holding time of 40 min to separate the crystalline silicon solar cells;

[0049] Step 2: Configure the molten salt according to the ratio and heat it to melt it to obtain molten salt;

[0050] The molten salt is a mixture of sodium chloride and calcium chloride. The heating temperature of the molten salt (salt immersion) is 650°C, and the ratio of sodium chloride to calcium chloride is 2:1;

[0051] Step 3: Place the crystalline silicon solar cells fully in the molten salt and perform selective etching separation at 650°C for 120 s. After the etching is completed, take out the solar cells and wash them with water to obtain pure silicon wafers and silver wires.

[0052] Example 3

[0053] During the mechanical disassembly process, the glass, aluminum frame, and backsheet in the photovoltaic panel are mechanically removed;

[0054] During the pyrolysis process, the heating rate is 20 °C / min, and the temperature is raised to 700 °C, with a holding time of 20 min to separate the silicon crystal cell;

[0055] Step 2: Prepare the molten salt according to the ratio and heat it to melt it to obtain the molten salt;

[0056] The molten salt consists of a mixture of sodium chloride and calcium chloride. The heating temperature of the molten salt (salt immersion) is 1000 °C, and the ratio of sodium chloride to calcium chloride is 5:1;

[0057] Step 3: Immerse the crystalline silicon cell fully in the molten salt and perform selective etching separation at 1000 °C for 60 s. After the etching is completed, take out the cell and wash it with water to obtain a pure silicon wafer and silver wire.

[0058] Comparative Example 1

[0059] During the mechanical disassembly process, the glass, aluminum frame, and backsheet in the photovoltaic panel are mechanically removed;

[0060] During the pyrolysis process, the heating rate is 12 °C / min, and the temperature is raised to 550 °C, with a holding time of 40 min to separate the silicon crystal cell;

[0061] Step 2: Prepare the molten salt according to the ratio and heat it to melt it to obtain the molten salt;

[0062] The molten salt consists of a mixture of sodium chloride and calcium chloride. The heating temperature of the molten salt (salt immersion) is 400 °C, and the ratio of sodium chloride to calcium chloride is 2:1;

[0063] Step 3: Immerse the crystalline silicon cell fully in the molten salt and perform selective etching separation at 650 °C for 120 s. After the etching is completed, take out the cell and wash it with water to obtain a pure silicon wafer and silver wire.

[0064] Comparative Example 2

[0065] During the mechanical disassembly process, the glass, aluminum frame, and backsheet in the photovoltaic panel are mechanically removed;

[0066] During the pyrolysis process, the heating rate is 12 °C / min, and the temperature is raised to 550 °C, with a holding time of 40 min to separate the silicon crystal cell;

[0067] Step 2: Prepare the molten salt according to the ratio and heat it to melt it to obtain the molten salt;

[0068] The molten salt consists of a mixture of sodium chloride and calcium chloride. The heating temperature of the molten salt (salt immersion) is 1100 °C, and the ratio of sodium chloride to calcium chloride is 2:1;

[0069] Step 3: Place the crystalline silicon cell fully in the molten salt and perform selective etching separation at 650 °C for 120 s. After the etching is completed, take out the cell and wash it with water to obtain pure silicon wafers and silver wires.

[0070] The experimental conditions and results of Examples 1-3 and Comparative Examples 1-2 were statistically analyzed to obtain Table 1.

[0071] Table 1 Experimental Statistics Table

[0072]

[0073] It can be seen from the data in Table 1 that:

[0074] In Comparative Example 1, the temperature of the molten salt was 400 °C, which is lower than the range of 450-1000 °C in Example of the present invention. There are disadvantages such as incomplete melting of the molten salt and low silver recovery efficiency;

[0075] In Comparative Example 2, the temperature of the molten salt was 1100 °C, which is higher than the range of 450-1000 °C in Example of the present invention. There are disadvantages such as a relatively high temperature of the molten salt, easy alloying of silver and silicon, resulting in increased losses and reduced recovery rate.

[0076] In Examples 1-3, the recovered silicon and silver of the invention have a relatively high recovery rate (≥99%), and the process route has the advantages of rich raw materials, low cost, short process flow, low energy consumption, and environmental friendliness.

[0077] Although the embodiments of the present invention have been disclosed as above, it is not limited to the applications listed in the specification and embodiments. It can be fully applied to various fields suitable for the present invention. For those familiar with the field, additional modifications can be easily made. Therefore, without departing from the general concept defined by the claims and the equivalent scope, the present invention is not limited to the specific details and the illustrated examples here.

Claims

1. A method for recovering silicon wafers and precious metal silver from retired crystalline silicon photovoltaics, characterized in that: include: Step 1: Mechanically dismantle and pyrolyze the retired crystalline silicon photovoltaic panels to obtain crystalline silicon solar cells; Step 2: preparing molten salt and heating it to melt the salt; Step three: Place the crystalline silicon cell piece in molten salt and perform selective etching and separation. After the etching is completed, take out the crystalline silicon cell piece and wash it with water to obtain silicon wafers and silver wires.

2. The method for recovering silicon wafers and precious metal silver from retired crystalline silicon photovoltaics according to claim 1, characterized in that: The heating rate of the pyrolysis process is 5-20°C / min, and the pyrolysis temperature is 450-700°C.

3. The method for recovering silicon wafers and precious metal silver from retired crystalline silicon photovoltaics according to claim 2, characterized in that: The components of the molten salt are sodium chloride and calcium chloride, and the ratio of sodium chloride to calcium chloride is 0.1-5:

1. The temperature of the molten salt is 450-1000°C.

4. The method for recovering silicon wafers and precious metal silver from retired crystalline silicon photovoltaics according to claim 3, characterized in that: The etching separation time of the specimen is 60 to 240 seconds.

5. The method for recovering silicon wafers and precious metal silver from retired crystalline silicon photovoltaics according to claim 4, characterized in that: During the mechanical disassembly process, the glass, aluminum frame and back plate in the photovoltaic panel are mechanically removed.

6. The method for recovering silicon wafers and precious metal silver from retired crystalline silicon photovoltaics according to claim 5, characterized in that: The size of the retired crystalline silicon photovoltaic panel is 1600mm×1000mm, and the size of the crystalline silicon cell is 80mm×40mm.

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