Method for fuse-separating metal silicon and glass

Abstract

To provide a method for fuse-separating metal silicon and a glass for separating silicone from a mixture of silicone derived from a solar cell module included in a silicon-based photovoltaic generation facility, and glass, and selectively collecting silicon.SOLUTION: This method for fuse-separating metal silicon and a glass comprises: a pre-processing step of crushing a solar cell module and recovering a crushed article containing a mixture of silicon and a glass; a fusing step of fusing the mixture of the silicon and the glass at a temperature of 1420°C-1650°C; a holding step of holding a fused article of the silicon and the glass acquired in the fusing step at the temperature of 1420°C-1650°C in contact with a glass component; a cooling step of cooling the fused article; and a separation step of mechanically removing the glass from the mixture of the silicon and the glass coagulated in the cooling step.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a technology for separating and recovering silicon and glass from waste materials from photovoltaic power generation facilities. [Background technology]

[0002] Photovoltaic power generation using crystalline silicon solar cells and amorphous silicon solar cells has attracted attention as a renewable energy source with a small environmental impact because it generates electricity using the clean energy of sunlight, and its use has been rapidly increasing in recent years. Silicon-based solar cell modules used in photovoltaic power generation are composed of various components in addition to solar cells, such as glass substrates, metal electrical circuit forming materials, sealing materials that seal the solar cells, frame members provided around the sealing materials, protective members such as backsheets, and protective glass.

[0003] Until now, solar cell modules have been disposed of after a certain period of use, but in recent years, from the perspective of recycling, there has been a demand for sorting and recovering valuable materials. Solar cell module recycling methods generally include various steps, such as a pretreatment step, a crushing step, a separation step such as a softening step or a combustion step of organic materials, a step of removing electrodes, and a pulverization step. Such conventional recycling of solar cell modules has mainly involved sorting and recovering valuable metals such as gold, silver, and copper.

[0004] For example, Patent Document 1 discloses a method for recycling solar cell modules, which includes a step of crushing silicon solar cell modules or solar cell sheet structures and a step of sorting the crushed material, and the recycling method aims to recover valuable metals by wind sorting the crushed material. Note that the solar cell sheet structure described in Patent Document 1 refers to a structure obtained by removing the glass substrate and frame member from the solar cell module.

[0005] Patent Document 2 discloses a technique for purifying metallic silicon, but does not describe a technique for selectively recovering only silicon from a solar cell module. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-173099 [Patent Document 2] Japanese Patent Application Publication No. 4-338109 Summary of the Invention [Problem to be solved by the invention]

[0007] In addition to the metal elements mentioned above, solar cell modules contain valuable materials such as high-purity silicon, but until now, research into technologies for separating and recovering silicon has not been conducted as much as technologies for physically separating metals. One reason for this is that conventional recycling technologies have not established technologies for physically separating silicon and glass from crushed solar cell modules.

[0008] For example, when physically separating silicon and metal, gravity separation can be performed by utilizing the difference in density between them, or wind separation as described in Patent Document 1 can be performed. Furthermore, physical separation can be performed using magnetic separation or eddy current separation by utilizing the electromagnetic properties of metals, depending on the type of metal element. However, when separating silicon and glass, the following problems have been encountered in the past.

[0009] The density of pure silicon is 2.33 g / cm at room temperature. 3 In contrast, the density of soda-lime glass commonly used in solar cell modules is 2.38 g / cm 3 Generally, the density difference is 1.0 g / cm 3When the density is below this level, physical separation using density differences is difficult. Also, when silicon and glass are combined, physical separation using electromagnetic properties cannot be used.

[0010] One method for selectively recovering silicon from a mixture of silicon and glass is to melt the mixture and separate the glass by floating it up as a slag component. However, in this case, as mentioned above, the density difference between silicon and glass in the molten state is small, so granular metallic silicon is trapped inside the glass, making it impossible to efficiently separate the two. For this reason, the mixture of silicon and glass derived from solar cell modules has often been disposed of as waste, being disposed of by landfill or other methods.

[0011] In order to solve the above problems, an object of the present invention is to provide a method for melting and separating metallic silicon and glass, which separates and selectively recovers silicon from a mixture of silicon and glass derived from solar cell modules included in silicon-based solar power generation facilities. [Means for solving the problem]

[0012] [1] In order to achieve the above object, in the present invention, The present invention provides a method for melting and separating metallic silicon and glass, the method comprising: a pretreatment step of crushing solar cell modules and recovering crushed material containing a mixture of silicon and glass; a melting step of placing the mixture of silicon and glass in a fire-resistant container whose inner wall is formed from the components of the glass and melting the mixture at a temperature of 1420°C or higher and 1650°C or lower under an inert atmosphere; a holding step of holding the molten mixture of silicon and glass obtained in the melting step in contact with the components of the glass at a temperature of 1420°C or higher and 1650°C or lower under an inert atmosphere; a cooling step of cooling the molten mixture of silicon and glass; and a separation step of mechanically removing the glass from the mixture of silicon and glass solidified by the cooling step. [2] In the method for melting and separating metal silicon and glass according to the above item [1], the refractory container formed from the components of the glass is preferably any one of a quartz glass crucible, an alumina crucible, and a magnesia crucible. [3] In the method for melting and separating metal silicon and glass according to the above item [1], the constituent component of the glass that comes into contact with the molten mixture of silicon and glass may be a constituent component of glass that forms the inner wall of a fire-resistant container that contains the molten mixture of silicon and glass. [4] In the melting and separating method of metal silicon and glass according to the above item [1], the constituent components of the glass that come into contact with the molten mixture of silicon and glass may include quartz glass that is charged into the molten mixture of silicon and glass. [Effects of the Invention]

[0013] By using the method for melting and separating metallic silicon and glass of the present invention, metallic silicon that can be used as a raw material for high-purity polycrystalline silicon can be separated and recovered from waste solar cell modules. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a flowchart showing the procedure of a pretreatment step used in examples and comparative examples of the present invention. [Figure 2] FIG. 1 is a cross-sectional view schematically illustrating the configuration of an experimental device used in an example of the present invention. [Figure 3] 3 is a photograph showing the observation results of cross sections obtained by simultaneously cutting the crucible and the solidified product in Example 1. [Figure 4] 1 is an SEM photograph showing the results of observing a cross section of the solidified material obtained in Example 1 near the interface between the inner wall of the crucible and the glass slug. [Figure 5] 2 is an SEM photograph showing the results of observing a cross section near the interface between metallic silicon and slag-formed glass in the solidified product obtained in Example 1. [Figure 6]1 is an SEM photograph showing the results of observing a cross section of the solidified material obtained in Example 2 near the interface between the inner wall of the crucible and the glass slug. [Figure 7] 1 is an SEM photograph showing the results of observing a cross section of the solidified product obtained in Comparative Example 1. [Figure 8] 1 is an SEM photograph showing the results of observing a cross section of the solidified material obtained in Example 3 near the interface between the inner wall of the crucible and the glass slug. [Figure 9] 1 is an SEM photograph showing the results of observing a cross section of the solidified material obtained in Example 4 near the interface between the inner wall of the crucible and the glass slug. [Figure 10] 1 is an SEM photograph showing the observation results of a cross section of metallic silicon of the solidified product obtained in Example 4. [Figure 11] 1 is a graph showing the composition ratios of the slag layers of the solidified materials obtained in Examples 1, 3, and 4 as a result of EDX analysis. [Figure 12] 1 is a graph showing the composition ratios of the EDX analysis results of the white portions of the solidified metallic silicon obtained in Examples 1, 3, and 4. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Solar cell module] The method for melting and separating metallic silicon and glass of the present invention is intended for silicon-based solar cell modules that use crystalline silicon solar cells or amorphous silicon solar cells as solar cell elements. Note that the term "glass" used here refers not only to soda-lime glass that is commonly used in solar cell modules, but also to glass in the general sense.

[0016] [Pretreatment process] The method for melting and separating metallic silicon and glass of the present invention includes a pretreatment step of crushing solar cell modules in advance and recovering crushed material containing a mixture of silicon and glass, and a pretreatment step of removing solar cell components other than silicon and glass from the resulting mixture, and recovering the mixture of silicon and glass. The solar cell modules to be crushed may be those from which components other than metallic silicon and glass have been removed in advance. Alternatively, they may be those from which some of the glass components have been removed. Known separation methods, such as the method described in Patent Document 1 or the method described in Japanese Patent Laid-Open No. 2011-173099, can be used as the pretreatment method, even though the solar cell elements are CIS-based compound semiconductors. In this case, organic substances such as sealants can be removed by heating and softening them or by burning them off. Metal materials forming electrodes and the like can be separated by physical separation such as gravity separation or eddy current separation, or by dissolving the metal materials in acid.

[0017] [Melting process] In the method for melting and separating metallic silicon and glass of the present invention, the mixture of silicon and glass recovered by the above-described method is placed in a refractory container such as a crucible and heated to a temperature of 1420°C to 1650°C in an inert atmosphere of argon, nitrogen, or the like to melt it. The inert atmosphere is used to prevent oxidation of the molten silicon. The heating temperature is 1420°C or higher, which is the melting point of silicon. Glass generally does not exhibit a clear melting point, but the above-described soda-lime glass, etc., is in a molten state at 1420°C. The heating temperature is set to 1650°C or lower because the melting point of the quartz glass that comes into contact with the molten mixture of silicon and glass is 1650°C, and at temperatures above 1650°C, the quartz glass also melts and deforms, mixing into the molten mixture, making it difficult to separate the metallic silicon. The refractory container preferably has at least an inner wall formed from the glass components contained in the mixture of molten silicon and glass. A quartz crucible, an alumina crucible, or a magnesia crucible is preferably used as the refractory container. Quartz is the main component of glass, and alumina and magnesia are substances normally present in the molten glass slag, and are collectively referred to as glass components. The reasons for using such refractory containers will be described later.

[0018] [Holding process] The greatest technical feature of the method for melting and separating metallic silicon and glass of the present invention is the provision of a holding step in which the molten mixture of silicon and glass obtained in the melting step is held in contact with the constituent components of the glass for a predetermined period of time.

[0019] The present inventors discovered a phenomenon in which, when a mixture of molten silicon and glass is held in contact with quartz glass, the molten glass migrates over time to the surface of the glass's constituent components and adheres to that surface, leading to the completion of the present invention. The mechanism by which the molten glass migrates to the surface of the glass's constituent components is currently unknown, but the present inventors believe that this is because the molten glass and the glass's constituent components wet well, and when the solution flows due to convection or other factors during melting, the glass component preferentially adheres to the surface of the glass's constituent components. Furthermore, the glass component is saturated with SiO2 during melting, and coexisting with the glass's constituent components provides thermodynamic stability, thereby maintaining contact. Note that when a graphite crucible or BN crucible is used as the refractory container, the above phenomenon does not occur even when the molten silicon-glass mixture is held. Furthermore, when a material typically contained in slag, such as an alumina crucible or magnesia crucible, is used as the refractory material, trace amounts of aluminum and magnesium are observed to migrate into the slag or metallic silicon. Therefore, it is particularly preferable to use a quartz glass crucible in order to recover metallic silicon with high purity. The quartz glass used here is glass whose main component is SiO2, and the SiO2 purity should be 99% or higher, preferably 99.9% or higher.

[0020] As mentioned above, when a molten mixture of silicon and glass is kept in contact with quartz glass, the silicon and glass separate over time, resulting in a molten mixture of silicon and glass. Therefore, by immersing a silicon seed crystal in the silicon part of the molten mixture and pulling it up while rotating (the CZ method), metallic silicon crystals can be grown and collected.

[0021] In the method for melting and separating metallurgical silicon and glass of the present invention, the time required to hold the molten mixture of silicon and glass varies depending on the type and amount of recovered glass, and therefore may be determined appropriately based on the state of the recovered material.

[0022] In the method for melting and separating metallurgical silicon and glass of the present invention, the following two embodiments for holding the molten mixture of silicon and glass can be mentioned.

[0023] In a first embodiment of the present invention, the inner wall of the refractory container that comes into contact with the molten silicon-glass mixture in the melting step and the holding step is made of the glass. In this case, as described above, it is preferable to use a quartz glass crucible as the refractory container, but the crucible may be a double crucible, with the inner crucible being made of quartz glass. It is also possible to use a refractory container coated with SiO or a refractory material mainly composed of SiO, as described in Patent Document 2.

[0024] In a second embodiment of the present invention, quartz glass is charged into the molten mixture of silicon and glass. In this case, in addition to alumina or magnesia crucibles, graphite or BN crucibles can be used as the refractory container for containing the molten mixture, and the inner wall may also be made of quartz glass. For example, a quartz glass rod can be used as the quartz glass to be charged. In the method for melting and separating metallic silicon and glass of the present invention, the charging position of the quartz glass to be charged is not particularly specified, but it is preferable to charge it into the center of the refractory container.

[0025] [Cooling process] The molten silicon and glass mixture is held for a predetermined time in the holding step, and the silicon and glass are separated from each other in the molten metal, and then cooled and solidified. In this case, for example, in the first embodiment, a solidified product is obtained in which solidified glass adheres to the periphery of the solidified metallic silicon. In this case, the cooling rate may be either slow cooling or rapid cooling.

[0026] [Separation process] The solidified mixture of silicon and glass obtained in the cooling process is removed from the refractory container, and the solidified glass is removed by mechanical means. In the method for melting and separating metallic silicon and glass of the present invention, the solidified glass is brittle and can be easily removed, for example, with a grinder. The metallic silicon obtained by removing the solidified glass has high purity and can be used, for example, as a raw material for high-purity polycrystalline silicon. [Example]

[0027] [Elemental analysis] A mixture of silicon and glass was melted in a crucible and allowed to cool sufficiently. After cooling, the crucible was cut with a diamond cutter (IMAHASHI, TS-200) to expose the cross section, which was then embedded in resin using a mounting press (Struers, LaboPress-1). The sample was then polished with a polishing machine (Bueher, MetaServ250) to prepare a sample for observation. A JOEL JSM-6510A was used for SEM-EDX analysis.

[0028] [Preprocessing] The pretreatment procedure was as follows: After dismantling the solar power generation equipment and removing the aluminum frames from the solar panels (PV panels), the cover glass was removed (approximately 90%) using a blasting machine (Mirai Sozo Co., Ltd., manual peeler). The solar panels were then crushed using a crusher (Horai Co., Ltd., UHI-35120). The crushed solar panels were sieved through a 250 μm mesh sieve (Kowa Kogyosho Co., Ltd., KFO-800-3D), and coarse powder with a particle size of 250 μm or larger was collected and removed. Powder with a particle size of less than 250 μm was fired in an electric furnace (Koyo Thermo Systems Co., Ltd., small box furnace KBF314N1) at 550 °C in air for 90 min to obtain a silicon-glass mixture sample. Figure 1 shows a flowchart of the pretreatment procedure.

[0029] [Example 1] Five grams of the silicon and glass mixture sample was placed in a double-walled crucible, consisting of an alumina crucible on the outside and a quartz glass crucible on the inside, which served as a fireproof container. The crucible containing the sample was placed in a reaction tube, and while Ar gas was blown in at a flow rate of 0.4 L / min, the temperature was raised to 1500 °C over 4 hours to melt the sample, and the temperature was then maintained for 2 hours. The crucible was then water-cooled to obtain a solidified silicon and glass mixture. A schematic diagram of the experimental apparatus used in this example is shown in Figure 2.

[0030] After the crucible and solidified material had cooled to room temperature, the crucible containing the solidified silicon and glass mixture was removed, and the crucible and solidified material were cut simultaneously without removing the solidified material from the crucible, and the inner wall of the crucible and the cross section of the solidified material were visually observed. Figure 3 shows a photograph of the appearance of the cross section of the cut sample. In the cross-sectional photograph, a blackish substance can be observed between the solidified metallic silicon in the center of the crucible and the inner wall of the crucible, and this blackish substance is slag-like glass (called the slag layer).

[0031] Figure 4 shows a scanning electron microscope (SEM) photograph (magnification 200x) of a cross section near the interface between the inner wall of the crucible and the glass slug. Figure 5 shows a scanning electron microscope (SEM) photograph (magnification 110x) of a cross section near the interface between the metallic silicon and the glass slug. Table 1 shows the results of energy dispersive X-ray fluorescence (EDX) analysis of the slag layer in contact with the silicon (referred to as Slag 1), and Table 2 shows the results of the EDX analysis of the silicon. Note that trace amounts of oxygen were detected in the silicon analysis results, but this is due to surface oxidation of the silicon that occurred during sample preparation. The silicon obtained in this example was metallic silicon with high purity. The solidified slag layer is brittle and can be easily separated from the solidified metallic silicon by mechanical means such as a grinder.

[0032] [Example 2] A solidified mixture of silicon and glass contained in a crucible was obtained using the same procedure as in Example 1, except that air cooling was used as the cooling method. Figure 6 shows an SEM photograph (magnification 50x) of the cross section of the crucible, slag layer, and silicon observed in the same field of view. In this example, the slag layer is a single layer (referred to as slag 2), but it can be seen that it is completely separated from the metallic silicon. The results of EDX analysis of the slag layer and silicon in the solidified mixture of silicon and glass obtained in this example are shown in Tables 1 and 2, respectively. From this example, it was found that in the case of the method for melting and separating metal silicon and glass of the present invention, metal silicon and glass can be separated regardless of the cooling rate.

[0033] [Table 1]

[0034] [Table 2]

[0035] [Comparative Example 1] In this comparative example, a graphite crucible was used as the fireproof container instead of the double crucible used in the examples. Five grams of the test sample of the silicon and glass mixture obtained by the pretreatment method described above was placed in the graphite crucible, and the temperature was raised to 1500°C over 2.5 hours while blowing nitrogen gas at a flow rate of 5 L / min to melt the test sample, which was then held at that temperature for 1 hour. The crucible was then air-cooled to obtain a solidified silicon and glass mixture.

[0036] Figure 7 shows the results of observation of a cross section of the solidified mixture of silicon and glass according to this comparative example. A digital microscope (KYENCE VHX-7000) was used for the observation. Figure 7 shows that in this comparative example, the metallic silicon and glass do not separate clearly, and a region is formed in which metallic silicon particles are encapsulated in the solidified glass of the silicon and glass mixture.

[0037] [Example 3] In this example, an alumina crucible was used as the refractory container. 10 g of the silicon and glass mixture sample was placed in the alumina crucible, which was then placed in a reaction tube. Ar gas was blown into the crucible at a flow rate of 0.4 L / min while the temperature was raised to 1500°C over 4 hours to melt the sample, which was then maintained at that temperature for 1 hour. The crucible was then water-cooled to obtain a solidified silicon and glass mixture.

[0038] Figure 8 shows an SEM photograph (magnification: 50x) of the cross section of the crucible, slag layer, and silicon observed in the same field of view. In this example, the slag layer is a single layer, but it is completely separated from the metallic silicon. The results of EDX analysis of the slag layer of the solidified mixture of silicon and glass obtained in this example are shown in Table 3, along with the data for Examples 1 and 4. A graph corresponding to Table 3 is shown in FIG. Furthermore, for the solidified mixture of silicon and glass obtained in this example, the results of EDX analysis of the white portion in the silicon are shown in Table 4 together with the data for Examples 1 and 4. A graph corresponding to Table 4 is shown in FIG. When an alumina crucible was used as the refractory container, it was possible to separate the slag layer and the metallic silicon, but an increase in the concentration of the aluminum component was confirmed in the white portions of the slag and the metallic silicon compared to Example 1. This is thought to be due to aluminum derived from the refractory container.

[0039] [Example 4] In this example, a magnesia crucible was used as the refractory container. A solidified mixture of silicon and glass was obtained in the same manner as in Example 3.

[0040] An SEM photograph (magnification: 50x) of the slag layer is shown in Figure 9, and an SEM photograph of the metal silicon portion is shown in Figure 10. In this example, the slag layer is also a single layer, but it is clear that it is completely separated from the metal silicon. The results of EDX analysis of the slag layer of the solidified mixture of silicon and glass obtained in this example are shown in Table 3, along with the data for Examples 1 and 3. FIG. 11 shows a graph corresponding to Table 3. Furthermore, for the solidified mixture of silicon and glass obtained in this example, the results of EDX analysis of the white portion in the silicon are shown in Table 4, along with the data for Examples 1 and 3. FIG. 12 shows a graph corresponding to Table 4. When a magnesia crucible was used as the refractory container, it was possible to separate the slag layer and the metallic silicon, but an increase in the concentration of magnesium components was confirmed in the white portions of the slag and the metallic silicon compared to Example 1. This is thought to be due to magnesium derived from the refractory container.

[0041] [Table 3]

[0042]

Table 4

Claims

1. a pre-processing step of crushing the solar cell modules and recovering crushed material containing a mixture of silicon and glass; a melting step of placing the silicon and glass mixture in a refractory container whose inner wall is formed from the components of the glass and melting the mixture at a temperature of 1420°C or higher and 1650°C or lower under an inert atmosphere; a holding step of holding the molten mixture of silicon and glass obtained in the melting step in contact with the constituent components of the glass at a temperature of 1420°C or higher and 1650°C or lower in an inert atmosphere; a cooling step for cooling the melt of the silicon and glass mixture; a separating step of mechanically removing the glass from the silicon and glass mixture solidified by the cooling step; The method for melting and separating metallurgical silicon and glass comprises the steps of:

2. 2. The method for melting and separating metallic silicon and glass according to claim 1, wherein the refractory container formed from the glass components is any one of a quartz glass crucible, an alumina crucible, and a magnesia crucible.

3. 2. The method for melting and separating metallic silicon and glass according to claim 1, wherein the glass component that comes into contact with the molten mixture of silicon and glass is quartz glass that constitutes an inner wall of a refractory vessel that contains the molten mixture of silicon and glass.

4. 2. The method for melting and separating metal silicon and glass according to claim 1, wherein the glass component in contact with the melt of the silicon and glass mixture comprises quartz glass introduced into the melt of the silicon and glass mixture.

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