Resource recycling method for decommissioned crystalline silicon solar cells by using chemical waste salt in PTA (pure terephthalic acid) industry

Abstract

The invention belongs to the technical field of resource recycling, and particularly relates to a resource recycling method for decommissioned crystalline silicon solar cells by utilizing chemical waste salt in the PTA industry. The method comprises the following steps: mixing and heating the PTA industry chemical waste salt and chlorate to obtain high-temperature molten salt; immersing the retired crystalline silicon solar cell into the high-temperature fused salt, and taking out and cooling the retired crystalline silicon solar cell; washing the cooled battery piece with water to separate the silver grid line and the silicon wafer, adding water into the cooled high-temperature fused salt to dissolve to obtain a salt solution, filtering the silver grid line in the salt solution, and washing and drying the silver grid line to obtain a pure silver grid line; placing the silicon wafer in water, adding a salt solution, heating, soaking, performing ultrasonic washing to obtain turbid liquid, filtering filter residues, and drying to obtain aluminum powder; and heating and soaking the silicon wafer after ultrasonic washing in a salt solution, and then washing and drying to obtain a pure silicon wafer. According to the method, waste salt recycling is achieved, the process stability is high, the recovery rate and recovery purity of valuable elements such as silver and silicon are high, and environment friendliness is achieved.

Description

Technical Field

[0001] This invention belongs to the field of resource recycling technology, specifically relating to a method for the resource recycling of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry. Background Technology

[0002] Crystalline silicon photovoltaic cells have a lifespan of approximately 25–30 years. The first batch of photovoltaic modules installed globally is about to enter a period of retirement. The theoretical recycling value of valuable elements such as silver, silicon, and aluminum in the cells can reach up to 45% of the total module price. The traditional "mechanical crushing + acid-alkali wet process" requires sequential processes of NaOH to remove aluminum, HNO3 / HF to dissolve silver, and mixed acid to remove silicon nitride. This process is cumbersome and has the following disadvantages: high silicon wafer breakage rate, making it impossible to remelt and remanufacture cells; high cost due to the large amount of acid and alkali required for recycling; and low silver recovery rate.

[0003] Purified terephthalic acid (PTA) is a core raw material for synthetic polyester, and its capacity expansion has made my country the world's largest producer and consumer. However, in the PTA oxidative refining unit, approximately 50–80 kg of chemical waste salt is generated as a byproduct for every ton of product produced. This solid waste accumulates in large quantities on the plant site, becoming a prominent bottleneck restricting the industry's green development. The waste salt is mainly composed of sodium carbonate (80–97 wt%) and sodium bromide (3–8 wt%), and also contains sodium chloride and trace amounts of insoluble heavy metals such as cobalt and manganese. It is characterized by strong alkalinity, high toxicity, and high salt solubility. Currently, it can only be landfilled or incinerated according to the HW18 category of hazardous waste, with treatment costs as high as 2,500–3,000 yuan per ton. Moreover, it is impossible to recover the economically valuable and scarce sodium carbonate and sodium bromide, resulting in a double waste of "resources and waste". Summary of the Invention

[0004] To address the aforementioned problems, the main objective of this invention is to solve the resource recycling problem of PTA industrial waste salt and decommissioned crystalline silicon solar cells. By using PTA industrial waste salt as a recycling reagent for decommissioned crystalline silicon solar cells, and through steps such as molten salt soaking, water washing, salt solution soaking, and ultrasonication, silver grid lines, aluminum, and silicon wafers are separated. This method achieves high resource recovery rate, low cost, simple operation, and environmental friendliness.

[0005] To achieve the above objectives, a method for the resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry is provided, comprising the following steps: S1. PTA industry chemical waste salt and chloride salt are mixed and heated to a molten state to form high-temperature molten salt; S2. Immerse the retired crystalline silicon solar cell in the high-temperature molten salt, and after soaking, remove the treated cell and cool it. S3. After cooling, the battery cell is washed with water to separate the silver grid lines and silicon wafer. The cooled high-temperature molten salt is dissolved in water to obtain a salt solution. The silver grid lines in the salt solution are filtered out, and the silver grid lines are washed and dried to obtain pure silver grid lines. S4. Place the silicon wafer in water, add the salt solution, heat and soak, then remove the silicon wafer and ultrasonically wash to obtain a turbid liquid. After filtering the residue and drying, aluminum powder is obtained. S5. After ultrasonic cleaning in step S4, the silicon wafer is placed in the salt solution and heated and soaked, then washed and dried to obtain a pure silicon wafer.

[0006] Furthermore, the PTA industry chemical waste salt, by mass fraction, includes: 80-97% sodium carbonate and 3-8% sodium bromide.

[0007] Further, in step S1, the mass ratio of chloride salt and PTA industry chemical waste salt is 1:0.7~0.9, and the chloride salt includes one or more of sodium chloride and potassium chloride.

[0008] Further, in step S1, the process parameters for heating to the molten state are: heating to 500~700℃ at a heating rate of 10 ℃ / min and holding at that temperature for 0.5~1.5h.

[0009] Furthermore, in step S2, the soaking time is 3~15s.

[0010] Furthermore, in step S3, in the step of dissolving the cooled high-temperature molten salt in water to obtain a salt solution, the ratio of high-temperature molten salt to water is 0.2~0.3g:1mL, and the pH value of the salt solution is 13~14.

[0011] Furthermore, in step S4, the temperature for heating and soaking is 40~80℃, and the soaking time is 0.5~1.0h.

[0012] Furthermore, in step S4, the ultrasonic treatment process takes 0.5 to 3 minutes and the ultrasonic frequency is 100 to 1000 Hz.

[0013] Furthermore, in step S5, the heating and soaking treatment temperature is 40~80℃, and the soaking time is 1~2h.

[0014] Furthermore, in steps S3, S4, and S5, the drying process is carried out at a temperature of 40-80°C for 2-5 hours.

[0015] Compared with the prior art, the beneficial effects of the technical solution of the present invention are as follows: (1) This invention uses industrial waste salt as the raw material for treatment, realizing the secondary utilization of waste salt. Compared with pure salt as the raw material, the price of using waste salt is lower. In the recycling process, no protective atmosphere is required, and the requirements for production equipment are lower.

[0016] (2) High recovery rate of materials in decommissioned crystalline silicon solar cells. The passivation layer is completely removed in molten salt, the silver grid lines separate from the silicon wafer and enter the molten salt phase. After cooling, only dissolution and filtration are performed, achieving separation of silver from the silicon wafer and removing the passivation layer at the same time. In addition, silver does not participate in the reaction in the molten salt and solution, so theoretically all silver can be recovered. The aluminum layer and residual impurities are removed in two salt solution immersions. High recovery rate and high purity recovery of silicon are achieved by controlling the concentration and amount of solution added. The molten salt is strongly alkaline after cooling and dissolving in water, which can be used for aluminum leaching. The aluminum backsheet is recovered in the form of metallic aluminum powder. At the same time, the amount of molten salt solution added is small, and the molten salt solution can be recovered and reused as molten salt raw material through evaporation and crystallization.

[0017] (3) This invention uses only waste salt and chloride salt as raw materials, without acid or alkali reagents or organic solvents, thus reducing environmental pollution and waste treatment costs at the source. In addition, the used waste salt can be reused after impurity removal and replenishment. The process is simple, the processing time is short, it is environmentally friendly and pollution-free, and the raw materials are inexpensive, making it suitable for large-scale production. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 A process flow diagram of the method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry provided by this invention; Figure 2 The following are diagrams illustrating the effects of molten salt treatment on the front side of decommissioned crystalline silicon solar cells in the embodiments of the invention: (a) is a front view of the solar cell before treatment, (b) is a front view of the silicon wafer recovered in Example 1, (c) is a front view of Comparative Example 1, and (d) is a front view of Comparative Example 2. Figure 3 The following are examples of the effects of molten salt method on the back side of decommissioned crystalline silicon solar cells in the embodiments of the present invention: (a) is a back side view of the solar cell before treatment, (b) is a back side view of the silicon wafer recovered in Example 1, (c) is a back side view of Comparative Example 1, and (d) is a back side view of Comparative Example 2. Figure 4 The silver grid wire recovered in Implementation Example 1 of this invention; Figure 5 The aluminum powder recovered in Implementation Example 1 of this invention. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0021] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[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] To address both the resource utilization of chemical waste salt from the PTA industry and the recycling of decommissioned crystalline silicon solar cells, such as... Figure 1 As shown, this invention provides a method for the resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry, comprising the following steps: S1. PTA industry chemical waste salt and chloride salt are mixed and heated to a molten state to form high-temperature molten salt. Specifically, the chloride salt and PTA industry chemical waste salt are mixed evenly at a mass ratio of 1:0.7~0.9 to obtain a mixed salt. The chloride salt is one or more chlorides such as sodium chloride and potassium chloride. The mixed salt is then placed in a container and heated in a high-temperature furnace at a heating rate of 10 °C / min to 500–700 °C, and held at this temperature for 0.5~1.5 h to obtain high-temperature molten salt.

[0024] S2. Immerse the decommissioned crystalline silicon solar cells in the high-temperature molten salt. After immersion, remove the treated cells and cool them. Specifically, cut the decommissioned crystalline silicon solar cells into small pieces of 50-55mm × 50-55mm. Immerse the cut decommissioned crystalline silicon solar cells completely in the high-temperature molten salt at a ratio of 1-5mL per piece. Ensure the cells do not come into contact with air, otherwise there is a risk of fire. Remove and cool after immersion for 3-15 seconds.

[0025] S3. After cooling, the solar cells are washed with water to separate the silver grid lines and silicon wafers. The cooled high-temperature molten salt is dissolved in water to obtain a salt solution. The silver grid lines in the salt solution are filtered out, and then washed and dried to obtain pure silver grid lines. The cooled solar cells are covered with molten salt. They are rinsed with water to remove the residual silver grid lines, obtaining silver grid lines and silicon wafers. For the cooled high-temperature molten salt, water is added at a solid-liquid ratio of 0.2~0.3 g / mL, and the solution is filtered to obtain silver grid lines. The silver grid lines obtained twice are collected, washed with water until neutral, and then dried at 40~80℃ for 2~5 hours to obtain pure silver grid lines. The pH value of the salt solution is 13~14.

[0026] S4. Place the silicon wafer in water, add the salt solution, and heat to 40-80℃ for immersion for 0.5-1.0 h. Then remove the silicon wafer and ultrasonically wash it at an ultrasonic frequency of 100-1000 Hz for 0.5-3 min to obtain a turbid liquid. Filter the residue and dry to obtain aluminum powder. During this process, the solution after the molten salt dissolves is alkaline, which can be used to dissolve aluminum trapped in the silver grid lines, improving the purity of silver. It can also be used to soak the silicon wafer and loosen the aluminum on the back of the wafer.

[0027] S5. Place the silicon wafer that has been ultrasonically cleaned in step S4 into the salt solution and heat it to 40~80℃ for 1~2 hours. Then wash it and dry it at 40~80℃ for 2~5 hours to obtain a pure silicon wafer.

[0028] The specific implementation methods of this application have been described above. In order to objectively illustrate the technical effects produced by this application, the following will further illustrate, in conjunction with embodiments, a method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry provided by this invention.

[0029] Example 1 Weigh 20 g of sodium chloride, 22.6 g of potassium chloride, and 34 g of waste salt, and mix them thoroughly to obtain a mixed salt. Pour the mixed salt powder into a corundum crucible, place it in a muffle furnace, and heat it to 600 °C at a heating rate of 10 °C / h. After reaching the target temperature, hold it at that temperature for 0.5 h. Place all 52 mm × 52 mm Al-BSF type decommissioned crystalline silicon solar cells, face down, into the molten salt, ensuring full contact between the cells and the molten salt. After soaking for 10 seconds, remove them and place them in a stainless steel pan. After the cells cool to room temperature, rinse only the front side with water to wash off the molten salt on the front side, ensuring that the molten salt on the front side does not contain silver grid lines. After the molten salt cools, add 300 ml of water to dissolve and filter. The residue is silver grid lines, and the filtrate is an alkaline molten salt solution. Wash and dry the silver grid lines to obtain silver. Figure 4 As shown. After rinsing the front side clean, place the solar cell in a beaker, add 300 ml of deionized water and 5 ml of molten salt solution, and soak at 50 ℃ for 0.5 h. Then, ultrasonically clean the cell at a frequency of 500 Hz for 1 min to obtain a silicon wafer and a suspension. Remove the silicon wafer, filter the ultrasonically cleaned solution, wash and dry the filter residue to obtain aluminum powder, as shown. Figure 5 As shown in the diagram, the silicon wafer was placed back into a beaker with 300 ml of deionized water and 10 ml of molten salt solution, and soaked at 50 °C for 1.5 h. It was then removed, washed, and dried to obtain a pure silicon wafer. The silver recovery rate reached 99%, and the silver purity reached 98%. The silicon recovery rate reached 96%, and the silicon purity reached over 99%.

[0030] Example 2 Weigh 20 g of sodium chloride, 22.6 g of potassium chloride, and 30 g of waste salt, and mix them thoroughly to obtain a mixed salt. Pour the mixed salt powder into a corundum crucible, place it in a muffle furnace, and heat it to 650 °C at a heating rate of 10 °C / h. After reaching the target temperature, hold it at that temperature for 0.5 h. Place all 52 mm × 52 mm Al-BSF type decommissioned crystalline silicon solar cells face down into the molten salt, ensuring full contact between the cells and the molten salt. After soaking for 5 seconds, remove them and place them in a stainless steel pan. After the cells cool to room temperature, rinse only the front side with water. The molten salt on the front side contains a small amount of silver grid lines. Wash off the molten salt from the front side and collect the silver grid lines. After the molten salt cools, add 350 ml of water to dissolve and filter. The filter residue is the silver grid lines, and the filtrate is an alkaline molten salt solution. Wash and dry both portions of the silver grid lines to obtain silver. After rinsing the front side clean, the solar cell wafers were placed in a beaker, and 300 ml of deionized water and 1 ml of molten salt solution were added. The mixture was then soaked at 50 °C for 0.5 h. The wafers were then ultrasonically cleaned at 500 Hz for 1 min, yielding silicon wafers and a suspension. The silicon wafers were removed, and the ultrasonic solution was filtered. The filter residue was washed and dried to obtain aluminum powder. The silicon wafers were then placed back in the beaker, and 300 ml of deionized water and 5 ml of molten salt solution were added. The mixture was soaked at 40 °C for 0.5 h, then removed, washed, and dried to obtain pure silicon wafers. The silver recovery rate reached 98%, and the silver purity reached 99%. The silicon recovery rate reached 98%, and the silicon purity reached over 97%.

[0031] Example 3 Weigh 20 g of sodium chloride, 22.6 g of potassium chloride, and 38 g of waste salt, and mix them thoroughly to obtain a mixed salt. Pour the mixed salt powder into a corundum crucible, place it in a muffle furnace, and heat it to 700 °C at a heating rate of 10 °C / h. After reaching the target temperature, hold it at that temperature for 0.5 h. Place all 52 mm × 52 mm Al-BSF type decommissioned crystalline silicon solar cells face down into the molten salt, ensuring full contact between the cells and the molten salt. After soaking for 5 seconds, remove them and place them in a stainless steel pan. After the cells cool to room temperature, rinse only the front side with water; the molten salt on the front side should not contain silver grid lines. After the molten salt cools, add 300 ml of water to dissolve and filter. The residue is the silver grid lines, and the filtrate is an alkaline molten salt solution. Wash and dry both portions of the silver grid lines to obtain silver. After rinsing the front side clean, place the solar cells in a beaker, add 300 ml of deionized water and 5 ml of the molten salt solution, and soak them at 50 °C for 0.5 h. The solar cells were then ultrasonically cleaned at a frequency of 500 Hz for 1 minute, yielding silicon wafers and a suspension. The silicon wafers were removed, and the ultrasonically cleaned solution was filtered. The filter residue was washed and dried to obtain aluminum powder. The silicon wafers were then placed back into a beaker with 300 ml of deionized water and 5 ml of molten salt solution, and soaked at 50 ℃ for 0.5 h. Afterward, they were removed, washed, and dried to obtain pure silicon wafers. The silver recovery rate reached 99%, the silver purity reached 99%, the silicon recovery rate reached 95%, and the silicon purity exceeded 99%.

[0032] Comparative Example 1 Weigh 20 g of sodium chloride, 22.6 g of potassium chloride, and 34 g of waste salt, and mix them thoroughly to obtain a mixed salt. Pour the mixed salt powder into a corundum crucible, place it in a muffle furnace, and heat it to 600 °C at a heating rate of 10 °C / h. After reaching the target temperature, hold it at that temperature for 0.5 h. Place all 52 mm × 52 mm retired Al-BSF type crystalline silicon solar cells, face down, into the molten salt, ensuring full contact between the cells and the molten salt. After soaking for 10 seconds, remove them and place them in a stainless steel pan. After the cells cool to room temperature, rinse only the front side with water to wash off the molten salt on the front side, ensuring that the molten salt on the front side does not contain silver grid lines. After the molten salt cools, add 300 ml of water to dissolve and filter. The filter residue contains silver grid lines, and the filtrate is an alkaline molten salt solution. Wash and dry the silver grid lines to obtain silver. After rinsing the front side clean, place the solar cell in a beaker, add 300 ml of deionized water and 5 ml of molten salt solution, and soak at 50 ℃ for 0.5 h. Then, ultrasonically clean the cell at a frequency of 500 Hz for 1 min to obtain a silicon wafer and a suspension. Remove the silicon wafer, filter the ultrasonic solution, and wash and dry the filter residue to obtain aluminum powder.

[0033] Comparative Example 2 Weigh 20 g of sodium chloride, 22.6 g of potassium chloride, and 34 g of waste salt, and mix them thoroughly to obtain a mixed salt. Pour the mixed salt powder into a corundum crucible, place it in a muffle furnace, and heat it to 600 °C at a heating rate of 10 °C / h. After reaching the target temperature, hold it at that temperature for 0.5 h. Place all Al-BSF type decommissioned crystalline silicon solar cells (52 mm × 52 mm) face down into the molten salt, ensuring full contact between the cells and the molten salt. After soaking for 10 seconds, remove them and place them in a stainless steel pan. After the cells cool to room temperature, rinse only the front side with water to wash off the molten salt, which should not contain silver grid lines. After the molten salt cools, add 300 ml of water to dissolve and filter. The filter residue contains silver grid lines, which are then washed and dried to obtain silver. Subsequently, the cells are ultrasonically cleaned at a frequency of 500 Hz for 1 min to obtain silicon wafers and a suspension.

[0034] The processing results of the battery cells in Example 1 are as follows: Figure 2 As shown, the results of processing Examples 1 and 2 are as follows: Figure 2 As shown in the figure, after molten salt immersion, the blue passivation layer on the front of the solar cell has been completely removed, and the silicon wafer surface appears grayish-white. From Comparative Examples 1 and 2, it can be seen that molten salt solution immersion can make the silicon wafer surface cleaner, but excessive immersion will also lead to a decrease in silicon recovery rate.

[0035] like Figure 3 As shown, in Comparative Example 1, since only one molten salt solution immersion was performed, although most of the aluminum was removed and recovered, a small amount of aluminum still adhered to the silicon wafer, resulting in a decrease in the purity of the recovered silicon wafer. In Comparative Example 2, since no molten salt solution immersion was performed, most of the aluminum remained on the back of the silicon wafer, and the aluminum was not successfully recovered. The recovered silicon wafer also had a decrease in purity due to the presence of aluminum residue.

[0036] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the inventive concept, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for the resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry, characterized in that, Includes the following steps: S1. PTA industry chemical waste salt and chloride salt are mixed and heated to a molten state to form high-temperature molten salt; S2. Immerse the retired crystalline silicon solar cell in the high-temperature molten salt, and after soaking, remove the treated cell and cool it. S3. After cooling, the battery cell is washed with water to separate the silver grid lines and silicon wafer. The cooled high-temperature molten salt is dissolved in water to obtain a salt solution. The silver grid lines in the salt solution are filtered out, and the silver grid lines are washed and dried to obtain pure silver grid lines. S4. Place the silicon wafer in water, add the salt solution, heat and soak, then remove the silicon wafer and ultrasonically wash to obtain a turbid liquid. After filtering the residue and drying, aluminum powder is obtained. S5. After ultrasonic cleaning in step S4, the silicon wafer is placed in the salt solution and heated and soaked, then washed and dried to obtain a pure silicon wafer.

2. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, The PTA industry chemical waste salt, by mass fraction, includes: 80-97% sodium carbonate and 3-8% sodium bromide.

3. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S1, the mass ratio of chloride salt and PTA industry chemical waste salt is 1:0.7~0.9, and the chloride salt includes one or more of sodium chloride and potassium chloride.

4. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S1, the process parameters for heating to the molten state are: heating to 500~700℃ at a heating rate of 10 ℃ / min and holding at that temperature for 0.5~1.5h.

5. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S2, the soaking time is 3~15 seconds.

6. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S3, the ratio of the cooled high-temperature molten salt to water is 0.2~0.3g:1mL, and the pH value of the salt solution is 13~14.

7. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S4, the temperature for heating and soaking is 40~80℃, and the soaking time is 0.5~1.0h.

8. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S4, the ultrasonic treatment process takes 0.5 to 3 minutes and the ultrasonic frequency is 100 to 1000 Hz.

9. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In step S5, the heating and soaking treatment temperature is 40~80℃, and the soaking time is 1~2h.

10. The method for resource recovery of decommissioned crystalline silicon solar cells using chemical waste salt from the PTA industry according to claim 1, characterized in that, In steps S3, S4, and S5, the drying process is carried out at a temperature of 40-80°C for 2-5 hours.

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