Method for recovering silicon from solar cell module

Abstract

A method for recovering silicon from a solar cell module is provided by which silicon can be recovered from the solar cell module without requiring much cost or labor. The method comprises: a step (S2) for cutting a solar cell module from which an outer frame member and a glass substrate have been removed and which comprises at least a solar cell containing silicon, a resin sealing material that seals the periphery of the solar cell, and a resin protection sheet that covers the sealing material on the back-surface side of the solar cell; a step (S4) for crushing the solar cell module with an impact crusher including a crushing vessel into which the cut solar cell module is introduced and a rotator that stirs the introduced solar cell module inside the crushing vessel; and a step (S5) for separating and recovering the silicon by sieving from crushed material obtained by crushing by the impact crusher.

Description

Method for recovering silicon from solar cell modules

[0001] The present invention relates to a method for recovering silicon from a solar cell module.

[0002] Generally, a solar panel used for solar power generation is formed by fitting a solar cell module, the surface of which is covered with a glass substrate, into an outer frame member made of aluminum, etc. Here, the solar cell module has solar cells containing silicon, a resin sealing material that seals the periphery of the solar cell, and a resin protective sheet that covers the sealing material on the back side of the solar cell.

[0003] Known techniques for recovering silicon, a valuable resource, from solar cell modules include, for example, removing an outer frame member, separating the glass substrate and protective sheet using a heated cutter, removing the sealant from the solar cell using a solubilization method in which the sealant is chemically dissolved using a chemical solution, and then immersing the remaining portion in molten tin to recover the silicon floating on top of the molten tin (see, for example, Patent Document 1).

[0004] Also known is a technique in which a solar panel from which an outer frame member has been removed is immersed in an aromatic organic solvent, and ultrasonic waves are applied to the solar panel in the aromatic organic solvent to separate the solar cell, the sealant, and the glass substrate, and silicon is recovered from the organic solvent (see, for example, Patent Document 2).

[0005] Furthermore, a technique is known in which high-pressure water is jet-sprayed onto a solar panel to crush the solar cell module including the solar cells, leaving only the glass substrate (see, for example, Patent Document 3).

[0006] JP 2017-34087 A JP 2012-19134 A Japanese Patent No. 7022467 A

[0007] However, the silicon recovery method disclosed in Patent Document 1 requires high-temperature treatment to melt tin, which results in high energy costs. Furthermore, the silicon recovery method disclosed in Patent Document 2 requires a long ultrasonic immersion treatment, which is not suitable for recovering large amounts of silicon. Furthermore, the use of a volatile organic solvent creates a significant environmental burden. Furthermore, the method disclosed in Patent Document 3 makes it possible to separate a solar cell module containing solar cells from a glass substrate, but does not specify a method for separating and recovering the silicon contained in the solar cells.

[0008] The present invention has been made in light of the above-mentioned problems, and aims to provide a method for recovering silicon from solar cell modules, which can recover silicon from solar cell modules without incurring costs or labor.

[0009] In order to achieve the above object, the method for recovering silicon from solar cell modules of the present invention comprises: a first step of cutting a solar cell module from which an outer frame member and a glass substrate have been removed, the solar cell module having at least solar cells containing silicon, a resin sealing material that seals the periphery of the solar cells, and a resin protective sheet that covers the sealing material on the back side of the solar cell; a second step of crushing the solar cell module using a crusher that has a crushing container into which the cut solar cell module is placed and a rotor that stirs the material placed in the crushing container; and a third step of separating and recovering the silicon from the material crushed by the crusher by sieving or air classification.

[0010] As a result, the method of recovering silicon from a solar cell module of the present invention can recover silicon from the solar cell module without incurring additional costs or labor.

[0011] 1 is a cross-sectional view schematically showing the structure of a solar panel of Example 1. FIG. 2 is a cross-sectional view schematically showing the structure of a solar cell module of Example 1. FIG. 3 is a flowchart showing the steps of the silicon recovery method of Example 1. FIG. 4 is an explanatory view showing an example of a solar cell module piece. FIG. 5 is an explanatory view showing the configuration of an impact crusher used in the silicon recovery method of Example 1. FIG. 6 is an explanatory view showing the configuration of an airflow crusher used in the silicon recovery method of Example 1. FIG. 7 is an explanatory view showing the over-sieve recovered material with a mesh size of 0.8 mm after crushing using an airflow crusher. FIG. 8 is an explanatory view showing the under-sieve recovered material with a mesh size of 0.8 mm after crushing using an airflow crusher. FIG. 9 is an experimental result showing the relationship between the stirring time by an impact crusher and the under-sieve recovered amount of crushed material for each circumferential speed of the rotor. FIG. 10 is an experimental result showing the relationship between the circumferential speed of the rotor of the impact crusher and the silicon recovery amount and recovery rate. FIG. 11 is an experimental result showing the relationship between the circumferential speed of the rotor of the airflow crusher and the silicon recovery amount and recovery rate. 1 is a table showing the analysis results of the under-sieve recovered material after pulverization using an impact pulverizer, an airflow pulverizer, a pin mill, a hammer mill, and a ball mill, and the silicon recovery results. 2 is a table showing the measurement results of the area and mass of a solar cell module piece, and the calculation results of the mass per unit area of ​​the solar cell module piece. 3 is an explanatory diagram showing a microscopic photograph image of a cross section of a solar cell module piece.

[0012] A mode for carrying out the method for recovering silicon from a solar cell module of the present invention will be described below based on Example 1 shown in the drawings.

[0013] The solar cell module 10 of Example 1 is a component of a solar panel 1 that converts light energy such as sunlight into electrical energy. As shown in Fig. 1, the solar panel 1 is formed by fitting a solar cell module 10, the surface of which is covered with a glass substrate 2, into an outer frame member 3 made of aluminum or the like.

[0014] As shown in Figure 2, the solar cell module 10 has a plurality of solar cell cells 11 in the form of a sheet (panel), a metal pattern 12 wired from the solar cell 11, a sealing material 13 that seals the periphery of the solar cell 11, and a protective sheet 14 that covers the sealing material 13 that seals the back side of the solar cell 11.

[0015] The solar cell 11 is formed from a semiconductor containing silicon, such as single crystal silicon, polycrystalline silicon, or amorphous silicon. The crystalline silicon used in the solar cell 11 is highly pure and, if recovered, can be reused for a wide range of purposes. For example, silicon recovered from the solar cell module 10 can be nitrided to form silicon nitride, which can be used for hard insulating bearing materials and tools. Silicon recovered from the solar cell module 10 can also be oxidized to form silica, which can be reused as a filler for sealing resin. Furthermore, high-purity hydrogen gas can be extracted by mechanochemically treating the silicon recovered from the solar cell module 10.

[0016] The metal pattern 12 has surface electrodes provided on the surfaces of the solar cells 11 and bus bar electrodes that electrically connect the plurality of solar cells 11. The metal pattern 12 is formed of, for example, copper or silver.

[0017] The sealing material 13 is made of a resin such as ethylene vinyl acetate copolymer resin (EVA) or polyethylene (PE). The sealing material 13 is filled around the solar cell 11, including the front and back surfaces, and is integrated with the plurality of solar cell 11 and the metal pattern 12 to form a sheet (panel). The sealing material 13 is bonded to the solar cell 11, glass substrate 2, and protective sheet 14 by heating and pressurizing. Since the sealing material 13 is required to have properties such as transparency, flexibility, adhesiveness, tensile strength, and weather resistance, various additives are generally blended into it.

[0018] The protective sheet 14 is formed from a resin such as polyvinyl fluoride (PVF), polyethylene terephthalate (PET), or polyethylene (PE). Because the protective sheet 14 is exposed to the outside air, it desirably has properties such as weather resistance (UV light resistance, moisture resistance, heat resistance, salt damage resistance, etc.), water vapor barrier properties, electrical insulation, mechanical properties (tensile strength, elongation, tear strength, etc.), and chemical resistance. Furthermore, because the protective sheet 14 is required to have properties such as adhesion to the encapsulant 13, it may be formed by laminating multiple film sheets with different properties.

[0019] The sealing material 13 and the protective sheet 14 are both more flexible than the solar cell 11, which contains silicon. That is, the solar cell 11 is harder and more brittle than the sealing material 13 and the protective sheet 14.

[0020] Next, the procedure of the method for recovering silicon from the solar cell module 10 of Example 1 will be described with reference to the flowchart shown in FIG.

[0021] In step S1, the glass substrate 2 and outer frame member 3 are removed from the solar panel 1, and a recovery preparation process is performed to remove the solar cell module 10, after which the process proceeds to step S2. Note that the method for removing the glass substrate 2 and outer frame member 3 from the solar panel 1 is not particularly limited. That is, the glass substrate 2 is removed by, for example, a hot knife method, a roll crushing method, or a shot blasting method. In addition, in the recovery preparation process, it is desirable to also remove as much of the wiring (metal pattern 12) provided on the solar panel 1 as possible.

[0022] In step S2 (first step), following the collection preparation process in step S1, the solar cell module 10 is cut into pieces of a size that can be fed into a crusher (such as the impact crusher 100 or the airflow crusher 200) described below, and the process proceeds to step S3. FIG. 4 shows an example of a solar cell module cut into a predetermined size (hereinafter referred to as "solar cell module pieces"). The size that can be fed into the crusher is determined by the size, capacity, crushing ability, etc. of the crusher, and is approximately 1 to 5 cm square. The method for cutting the solar cell module 10 is not particularly limited.

[0023] In step S3, following cutting of the solar cell module 10 in step S2, the solar cell module pieces are placed in the crushing containers 101, 201 of a crusher (such as the impact crusher 100 or the airflow crusher 200), and the process proceeds to step S4. Here, the crusher used in the silicon recovery method of Example 1 is, for example, the impact crusher 100, the airflow crusher 200, a pin mill, a hammer mill, or the like.

[0024] The impact crusher 100 is a so-called mixer, and as shown in FIG. 5 , it has a crushing container 101 and a rotor 102 that rotates inside the crushing container 101 and stirs the input material (solar cell module pieces in Example 1). The crushing container 101 is, for example, cylindrical with an input port 103 that opens upward, and has a discharge port 104 at the bottom of the side. A discharge valve 104a is attached to the discharge port 104 and is opened and closed as appropriate by the discharge valve 104a. The rotor 102 has a rotation shaft 105 that passes vertically through the bottom surface 101a of the crushing container 101, a lower blade 106 fixed to the rotation shaft 105, and an upper blade 107 that is fixed to the rotation shaft 105 and attached above the lower blade 106. The rotating body 102 has a rotating shaft 105 rotated by a driving device (not shown), and the lower blade 106 and the upper blade 107 rotate integrally with the rotating shaft 105 .

[0025] In the impact crusher 100, the rotor 102 rotates within the crushing vessel 101, causing the lower blade 106 and upper blade 107 to collide with the input material (solar cell module pieces), and the input material is stirred and crushed while shearing, applying an impact force from the lower blade 106 and upper blade 107. Furthermore, in the impact crusher 100, the input material stirred by the rotor 102 is crushed even when it collides or rubs against itself at high speed within the crushing vessel 101. Furthermore, the impact crusher 100 performs so-called batch processing. That is, before crushing, a predetermined amount of solar cell module pieces is loaded into the impact crusher 100, and then the entire amount of solar cell module pieces is stirred for a predetermined period of time, crushed, and removed.

[0026] The airflow pulverizer 200 is a so-called autogenous pulverizer, and as shown in FIG. 6 , it includes a pulverizer container 201 and a rotor 202 that rotates inside the pulverizer container 201 and agitates the input material (solar cell module pieces). The pulverizer container 201 has, for example, a substantially cylindrical shape with its axial direction set horizontally, and an input port 203 and an output port 104 are formed at the top, aligned axially. The periphery of the pulverizer container 201 is formed with a step 201a whose inner diameter decreases from the input port 203 side toward the output port 204 side. A doughnut-shaped classification plate 201b with an open center is detachably attached to the step 201a. By attaching the classification plate 201b to the airflow pulverizer 200, the classification effect of the step 201a can be improved.

[0027] The rotor 202 has a rotary shaft 205 and an impeller 206 attached to the rotary shaft 205. The rotary shaft 205 axially penetrates a side surface 201c on the inlet 203 side of the grinding container 201. The rotary shaft 205 of the rotor 202 is rotated by a driving device (not shown), and the impeller 206 rotates integrally with the rotary shaft 205.

[0028] In the air flow type crusher 200, the rotor 202 rotates inside the crushing vessel 201, generating a powerful swirling air current inside the crushing vessel 201, causing the input materials (photovoltaic module pieces) to collide with each other and crush. Note that, in the air flow type crusher 200, as in the impact type crusher 100, the impeller 206 also directly strikes and crushes some of the input materials. In addition, the air flow type crusher 200 performs so-called one-pass processing. That is, a predetermined input amount of photovoltaic module pieces is fed into the air flow type crusher 200 while the air flow type crusher 200 is running, and the photovoltaic module pieces are stirred in the crushing vessel 201 and then sequentially discharged from the crushed material that has become finer.

[0029] Although not shown, the pin mill includes a grinding container and a rotor that rotates inside the grinding container and agitates the input material. The rotor of the pin mill has a pair of circular disks with many pins fixed to them, and the pair of disks are arranged facing each other so that the pins interlock. In a pin mill, the pair of disks rotate in opposite directions, or one disk is fixed and the other is rotated, and the input material is passed between the opposing disks, pulverizing the input material through impact and shear caused by the interlocking pins. Furthermore, the pin mill performs so-called one-pass processing. That is, while the pin mill is operating, a predetermined amount of solar cell module pieces are fed into the pin mill, and the pulverized material is stirred and finely ground in the grinding container and then sequentially discharged.

[0030] Although not shown, the hammer mill has a grinding container and a rotor that rotates inside the grinding container and agitates the input material. The rotor of the hammer mill has a rotating plate equipped with multiple hammers. In the hammer mill, the rotating plate rotates at high speed, and the input material is pulverized by impact and agitation with the hammers. The pulverized material pulverized by the hammer mill is discharged and collected through a screen (mesh opening 2 mm in Example 1) provided at the discharge outlet. The hammer mill also performs so-called one-pass processing. That is, a predetermined amount of solar cell module pieces are fed into the hammer mill while the hammer mill is running, and the pulverized material is stirred and finely divided in the grinding container and then sequentially discharged.

[0031] In step S4 (second step), following the introduction of the solar cell module pieces into a crusher (such as the impact crusher 100 or the airflow crusher 200) in step S3, the introduced solar cell module pieces are crushed in the crusher, and the process proceeds to step S5. Here, the operating conditions of the crusher (such as the mixing time, the amount introduced per unit time, and the peripheral speed of the rotors 102 and 202) are set arbitrarily.

[0032] In step S5 (third step), following the crushing of the solar cell module pieces in step S4, silicon is separated and recovered from the crushed material, and the process proceeds to the end. In Example 1, regardless of which crusher is used, after crushing is completed, the recovered crushed material is passed through a sieve with a predetermined mesh size, and silicon is separated and recovered from the crushed material by sieving to separate the material into oversized and undersized particles. Note that FIG. 7 shows the oversized material recovered on a sieve with a mesh size of 0.8 mm after crushing using the airflow crusher 200, and FIG. 8 shows the undersized material recovered on a sieve with a mesh size of 0.8 mm after crushing using the airflow crusher 200. When the crusher is an airflow crusher, silicon may be separated and recovered by airflow classification, which classifies the crushed material using an airflow generated in the crushing container 201.

[0033] The operation of the method for recovering silicon from the solar cell module 10 of Example 1 will be described below.

[0034] In the silicon recovery method of Example 1, first, at least the glass substrate 2 and the outer frame member 3 are removed from the solar panel 1 to obtain a solar cell module 10 (step S1). Next, the solar cell module 10 is cut into a predetermined size to obtain solar cell module pieces (see FIG. 4) (step S2). This makes it possible to feed the solar cell module 10 into a crusher.

[0035] The solar cell module pieces are then fed into an arbitrary crusher (such as the impact crusher 100 or the airflow crusher 200) (step S3) and crushed by the crusher (step S4). Here, the solar cell 11 containing silicon is harder and more brittle than the sealing material 13 and the protective sheet 14. On the other hand, both the sealing material 13 and the protective sheet 14 are more flexible than the solar cell 11 containing silicon. Therefore, when an impact is applied to the solar cell module pieces by crushing them in the crusher, the solar cell 11 is crushed relatively easily into small pieces, but the sealing material 13 and the protective sheet 14 are difficult to crush and do not easily become small pieces. Therefore, in the silicon recovery method of Example 1, the solar cell module pieces are crushed to remove the solar cell 11 from the sealing material 13 and the protective sheet 14, and the removed solar cell 11 can be crushed into small pieces.

[0036] After the pulverization is completed, the pulverized material is separated by sieving or the like, and the silicon is recovered (step S5). At this time, the sealing material 13 and the protective sheet 14 are difficult to pulverize and do not easily break down into small pieces, so they remain on the sieve, for example (see FIG. 7). In contrast, the brittle and finely pulverized solar cell 11 falls below the sieve, for example (see FIG. 8). Therefore, the silicon recovery method of Example 1 can easily separate the silicon contained in the solar cell 11 from the pulverized material, and can recover silicon from the solar cell module 10 without incurring additional costs or effort. Furthermore, because no organic solvents or the like are used, the environmental impact during silicon recovery can be reduced.

[0037] When the airflow type crusher 200 is used as the crusher, the airflow type crusher 200 has a classification function, so the finely crushed solar cell 11 is quickly discharged from the crushing container 201 and recovered, while the uncrushed solar cell module pieces remain in the crushing container 201 and can continue to be crushed. Therefore, the use of the airflow type crusher 200 makes it possible to prevent silicon that has peeled off from the sealing material 13 from adhering again to the resin of the sealing material 13, etc., and to recover the silicon more efficiently than when the impact type crusher 100 is used to crush the solar cell module pieces.

[0038] Furthermore, when the airflow type pulverizer 200 is used as the pulverizer, continuous processing is possible while classifying the material by airflow, so processing can be performed using a low-capacity motor. Therefore, it is fully possible to use renewable energy such as solar power generation or wind power generation as a power source, and it is possible to recover silicon while suppressing carbon dioxide emissions.

[0039] The test results of the method for recovering silicon from the solar cell module 10 of Example 1 will be described below.

[0040] 9 shows the relationship between the agitation time for each circumferential speed of the rotor 102 and the amount of material recovered under the sieve when 63 g of solar cell module pieces cut into approximately 3 cm square pieces are fed into the impact crusher 100, agitated for a certain period of time at a predetermined circumferential speed by the impact crusher 100, and then sorted by passing the pulverized material through a sieve with a mesh size of 0.8 mm. Here, the "circumferential speed" refers to the speed at which the rotor 102 rotates (unit: meters per second (m / s)), and is determined by the length of the lower blade 106 or upper blade 107 (the distance from the rotor shaft 105 to the blade tip) and the rotation speed of the rotor 102 (rotation shaft 105). Specifically, it can be calculated using the following formula (1): Peripheral speed V (m / s)=π×D×N / 1000 (1) D: diameter (mm) of rotor 102 N: rotation speed (rpm) In Example 1, the peripheral speed of rotor 102 was set by the tip speed of lower blade 106 .

[0041] In this case, as shown in Figure 9, the amount of material recovered below the sieve is relatively small at a peripheral speed of 10 m / s, and it can be seen that even if the stirring time is increased, the amount of material recovered below the sieve hardly increases. Note that since silicon is recovered from the material recovered below the sieve, it is estimated that if the amount of material recovered below the sieve is small, the absolute amount of silicon recovered will decrease. Therefore, it is desirable to have as much of the amount of material recovered below the sieve as possible.

[0042] Furthermore, when the peripheral speed is 20 m / s, the amount of under-sieve recovered is greater than when the peripheral speed is 10 m / s, regardless of the mixing time, and it can be seen that the amount of under-sieve recovered increases as the mixing time increases. Furthermore, at a peripheral speed of 35 m / s, the amount of under-sieve recovered at each mixing time is even greater than when the peripheral speed is 20 m / s. However, at a peripheral speed of 40 m / s, the amount of under-sieve recovered is almost the same as when the peripheral speed is 35 m / s, and is only slightly higher. At a peripheral speed of 55 m / s, the amount of under-sieve recovered increases at each mixing time compared to when the peripheral speed is 35 m / s and 40 m / s, but even at a peripheral speed of 72 m / s, the amount of under-sieve recovered remains almost unchanged.

[0043] 9, it was found that in order to ensure a sufficient amount of under-sieve material recovered when a sieve with a mesh size of 0.8 mm is used, it is desirable to set the peripheral speed of the rotor 102 in the crusher (particularly the impact crusher 100) to 20 m / s or more. Furthermore, it was found that a peripheral speed of the rotor 102 of 35 m / s or more is more preferable because it can further increase the amount of under-sieve material recovered.

[0044] 9, it was found that in pulverization using the impact pulverizer 100, the amount of undersize material recovered tends to saturate when the mixing time is about 8 to 9 minutes at a peripheral speed of 35 m / s or more. Therefore, in pulverization using the impact pulverizer 100 at a high peripheral speed, a mixing time of about 10 minutes is considered sufficient.

[0045] FIG. 10 also shows the relationship between the amount of silicon recovered from 1 kg of solar cell module fragments at each peripheral speed of rotor 102, estimated from the material that falls under the sieve when 63 g of solar cell module fragments cut into 3 cm squares are fed into impact crusher 100, agitated by impact crusher 100 at a predetermined peripheral speed for 10 minutes, and sorted by passing the crushed material through a sieve with a mesh size of 0.8 mm, and the silicon recovery rate.

[0046] In this case, as shown in Figure 10, at a peripheral speed of 10 m / s, the amount of silicon recovered is small, but as the peripheral speed increases, the amount of silicon recovered increases and the silicon recovery rate also gradually increases. Furthermore, at a peripheral speed of 35 m / s or more, the amount of silicon recovered is almost the same regardless of the peripheral speed, and it was found that the amount of silicon recovered tends to saturate. However, since the amount of under-sieve recovered increases as the peripheral speed increases (see Figure 9), it is estimated that the amount of resin mixed into the under-sieve recovered material increases in proportion to the peripheral speed.

[0047] 11 shows the relationship between the amount of silicon recovered from 1 kg of solar cell module fragments at each peripheral speed of the rotor 202, estimated from the material that falls below the sieve when a fixed amount of solar cell module fragments cut into approximately 3 cm squares is fed into the air flow crusher 200, agitated at a predetermined peripheral speed by the air flow crusher 200, and sorted by passing the crushed material through a sieve with 0.8 mm openings, and the silicon recovery rate. In Example 1, the peripheral speed of the rotor 202 was set to the tip speed of the impeller 206. The experiment was also carried out with a classification plate 201b attached inside the crushing container 201.

[0048] In this case, as shown in Figure 11, it was found that the amount of silicon recovered increased as the peripheral speed increased. However, when the peripheral speed was increased from 72.2 m / s to 117 m / s, the increase in silicon recovery rate was slight compared to when the peripheral speed was increased from 40 m / s to 72.2 m / s. Therefore, it is estimated that when the peripheral speed of the rotor 202 is too fast (for example, about 117 m / s), the amount of resin mixed in the undersize recovered material increases.

[0049] FIG. 12 shows the analysis results of the under-sieve recovered material and the silicon recovery results when solar cell module pieces cut into pieces approximately 3 cm square are fed into an impact crusher 100, an airflow crusher 200, a pin mill, and a hammer mill, respectively, and solar cell module pieces cut into pieces approximately 5 to 10 mm square are fed into a ball mill, crushed in each crusher, and then passed through a sieve with 0.8 mm openings for separation.

[0050] Here, the "resin contamination rate of the under-sieve recovered material" is a value indicating the amount of resin components contaminated in the under-sieve recovered material. The "silicon content based on X-ray fluorescence analysis of the under-sieve recovered material" is a value indicating the silicon content relative to the mass of the under-sieve recovered material, determined by analyzing the under-sieve recovered material that has been subjected to thermal decomposition treatment using an X-ray fluorescence analyzer and quantitatively analyzing the contained elements. The "silicon content of the under-sieve recovered material" is a value indicating the amount of silicon contaminated in the under-sieve recovered material. The "amount of silicon recovered from 1 kg of solar cell module pieces" is a value indicating an estimated value of the mass of silicon that can be recovered from 1 kg of solar cell module pieces. The "amount of silicon recovered from 63 g of solar cell module pieces" is a value indicating the mass of silicon that can be recovered from 63 g of solar cell module. The "silicon recovery rate from solar cell module pieces" is a value indicating the recovery rate of silicon recovered from solar cell module pieces.

[0051] The "resin contamination rate of the under-sieve collected material" was calculated using the following procedure. First, the mass of the under-sieve collected material was measured. Next, the under-sieve collected material was heated to a high temperature in an electric furnace in an atmospheric atmosphere, and subjected to a thermal decomposition treatment to thermally decompose the resin components contained in the collected material. The mass of the under-sieve collected material after the thermal decomposition treatment was then measured. The mass of the resin components mixed in the under-sieve collected material was then calculated from the difference in mass of the under-sieve collected material before and after the thermal decomposition treatment, and the ratio of this mass to the mass of the under-sieve collected material was calculated to obtain the "resin contamination rate of the under-sieve collected material." In the thermal decomposition treatment of the under-sieve collected material, the material was heated from room temperature to 600°C in an electric furnace in an atmospheric atmosphere over one hour, then maintained at 600°C for four hours, and then naturally cooled.

[0052] The "silicon content of the undersize recovered material" is calculated based on the results of X-ray fluorescence analysis by subtracting the mass of the resin component contained in the undersize recovered material from the mass of the undersize recovered material.

[0053] The "amount of silicon recovered from a 1 kg solar cell module piece" is calculated based on the results of the "amount of silicon recovered from a 63 g solar cell module piece" described below.

[0054] The "amount of silicon recovered from 63 g of solar cell module piece" is calculated using the mass of silicon contained in 63 g of solar cell module piece and the "silicon content of the under-sieve recovered material." The "mass of silicon contained in 63 g of solar cell module piece" is determined by the following procedure.

[0055] That is, first, multiple samples of solar cell module pieces are measured, and the mass per unit area (1 cm2) of the solar cell module piece is calculated. Here, as shown in Figure 13, the mass per unit area of ​​the solar cell module piece is set to 0.182 g / cm2, which is the average for solar cell module pieces No. 1 to No. 5. Then, using the calculated "mass per unit area of ​​the solar cell module piece," the "area of ​​the 63 g solar cell module piece" is calculated (i.e., 63 ÷ 0.182 = 346.15 cm2).

[0056] Meanwhile, a micrograph of the cross section of the solar cell module piece (see FIG. 14 ) reveals that the thickness of the crystalline silicon layer contained in the solar cell module piece is approximately 180 μm. Furthermore, the specific gravity of silicon is 2.33 g / cm (known). Therefore, from these figures, it can be seen that the solar cell module piece contains 0.042 g (2.33 × 0.0180) of silicon per unit area (1 cm).

[0057] Then, from the area of ​​the 63 g solar cell module piece (346.15 cm2) and the silicon content of the solar cell module piece per unit area (0.042 g), the mass of silicon contained in the 63 g solar cell module piece is calculated, which in this case is found to be approximately 14.54 g (346.15 x 0.042).

[0058] The "silicon recovery rate from solar cell module pieces" is calculated based on the mass of silicon contained in the undersize recovered material and the "amount of silicon recovered from 63 g of solar cell module pieces" from the results of pyrolysis of the resin and quantitative X-ray fluorescence analysis.

[0059] Furthermore, the results shown in Figure 12 show that silicon can be recovered from solar cell modules regardless of whether the impact crusher 100, air flow crusher 200, pin mill, or hammer mill is used to crush the solar cell module pieces.

[0060] On the other hand, when the solar cell module pieces were crushed using a ball mill, the shape of the solar cell module pieces remained unchanged after 30 minutes of crushing, indicating that they were not crushed. A ball mill is a device that introduces crushing media and the material to be crushed into a crushing container, stirs the mixture, and grinds the material with the crushing media to produce a fine powder. Here, 170 g of zirconia balls with a diameter of 10 mm were added as the crushing media, and 3.8 g of solar cell module pieces cut into approximately 5-10 mm square pieces were added as the material to be crushed. After 30 minutes of crushing, a small amount of black-brown powder believed to be silicon powder was observed, but most of it was coated on the surface of the solar cell module, making it difficult to recover only the powder of the solar cell 11. Therefore, it was found that recovering silicon from the solar cell module 10 is difficult when a ball mill is used as a crusher.

[0061] It was found that when air flow type crusher 200 was used as the crusher and the peripheral speed of rotor 202 was set to 117 m / s (sample number 11), the "silicon recovery rate from solar cell module fragments" reached 87.1%, achieving a high recovery rate. It was also found that when air flow type crusher 200 was used to crush rotor 202 and the peripheral speed was set to 117 m / s (sample number 11), the "amount of silicon recovered from 1 kg of solar cell module fragments" was the highest compared to crushing using other crushers or crushing using air flow type crusher 200 at other peripheral speeds.

[0062] Furthermore, when comparing the cases where the impact crusher 100 and the airflow crusher 200 are used for crushing, with the peripheral speeds of the rotors 102, 202 being the same (sample numbers 6 and 8), it was found that the "silicon recovery rate from solar cell module pieces" was higher when the airflow crusher 200 was used as the crusher. Note that by attaching a screen instead of the discharge valve 104a of the impact crusher 100 and leaving the discharge port open during crushing, it is possible to quickly discharge the crushed material from the crushing container 101. In this case, solar cell module pieces are not crushed unnecessarily, and it is thought that the recovery rate may be improved.

[0063] Furthermore, when pulverization was performed using the airflow pulverizer 200, a comparison was made with the presence or absence of the classification plate 201b (sample numbers 8 and 9), and it was found that the presence or absence of the classification plate 201b did not have a significant effect on the "amount of silicon recovered from 1 kg of solar cell module pieces."

[0064] Furthermore, when pulverization was performed using the airflow pulverizer 200, a comparison was made under different conditions of the supply amount of solar cell module pieces (sample numbers 9 and 10). It was found that when the rotor 202 was set to the same circumferential speed and the supply amount was increased, the "silicon recovery rate from the solar cell module pieces" decreased and the "resin contamination rate in the under-sieve recovered material" increased compared to when the supply amount was smaller.

[0065] It was also found that when the solar cell module fragments were crushed using a pin mill as a crusher, although some small resin fragments were mixed in with the under-sieve recovered material, most of the resin fragments were recovered above the sieve, and the crushed silicon was contained in the under-sieve material. However, when comparing crushing using the impact crusher 100 and crushing using the airflow crusher 200 under different conditions of the circumferential speed of the rotor (sample numbers 6, 8, and 12), it was found that the "amount of silicon recovered from 1 kg of solar cell module fragments" was less than half. For this reason, it is considered that using a pin mill as a crusher is less advantageous for recovering silicon than using the impact crusher 100 or the airflow crusher 200.

[0066] Furthermore, when the solar cell module pieces were crushed using a hammer mill as a crusher, most of the resin pieces and uncrushed solar cell module pieces remained in the crushing container. Furthermore, analysis of the crushed material that passed through the screen and was recovered revealed that the "silicon recovery rate from the solar cell module pieces" was lower than when the solar cell module pieces were crushed using other crushers. Furthermore, when comparing the crushing using the impact crusher 100 with the peripheral speed of the rotor as a condition (sample numbers 3 and 13), it was found that the "silicon recovery rate from the solar cell module pieces" was less than half. Therefore, using a hammer mill as a crusher is considered to be less advantageous for recovering silicon than using the impact crusher 100 or the airflow crusher 200.

[0067] The method for recovering silicon from solar cell module 10 of the present invention has been described above based on Example 1. However, the specific configuration is not limited to Example 1, and design changes and additions are permitted as long as they do not deviate from the gist of the invention according to each claim.

[0068] In the silicon recovery method of Example 1, an example is shown in which the crushed material after crushing is passed through a 0.8 mm sieve and silicon is separated by sieving, regardless of the type of crusher. However, the method of separating silicon from the crushed material is not limited to this. For example, when the crusher is an airflow crusher 200, silicon may be separated by airflow classification, which separates silicon according to particle size using an airflow. Furthermore, the mesh size of the sieve used for sieving can be set arbitrarily, and although it is set to 0.8 mm in Example 1, it is not limited to this.

[0069] Examples of pulverization using an impact pulverizer 100, an airflow pulverizer 200, a pin mill, and a hammer mill have been shown. However, the pulverizer is not limited to these, and any pulverizer that pulverizes without using a pulverizing medium, such as a jet mill, may be used. CROSS-REFERENCE TO RELATED APPLICATIONS

[0070] This application claims priority based on Japanese Patent Application No. 2023-127982, filed with the Japan Patent Office on August 4, 2023, the entire disclosure of which is incorporated herein by reference in its entirety.

Claims

1. A method for recovering silicon from solar cell modules, comprising: a first step of cutting a solar cell module from which an outer frame member and a glass substrate have been removed, the solar cell module having at least silicon-containing solar cells, a resin sealing material that seals the periphery of the solar cell, and a resin protective sheet that covers the sealing material on the back side of the solar cell; a second step of crushing the solar cell module using a crusher that has a crushing container into which the cut solar cell module is placed and a rotor that stirs the material placed in the crushing container; and a third step of separating and recovering the silicon from the material crushed by the crusher by sieving or air classification.

2. A method for recovering silicon from a solar cell module as described in claim 1, characterized in that in the second step, the peripheral speed of the rotating body is set to 20 meters per second or more.

3. A method for recovering silicon from a solar cell module as described in claim 2, characterized in that in the second step, the peripheral speed of the rotating body is set to 35 meters per second or more.

4. A method for recovering silicon from solar cell modules as described in any one of claims 1 to 3, characterized in that the crusher is an impact crusher that applies an impact force from the rotor to the input material to shear and stir it.

5. A method for recovering silicon from solar cell modules as described in any one of claims 1 to 3, characterized in that the crusher is an air current type crusher which generates a swirling air current in the crushing container by means of the rotor and causes the input materials to collide with each other to crush them.

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