JP2011157226A - Silicon recovery system and silicon recovery method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recover a silicon sludge having a high content of pure silicon. <P>SOLUTION: A silicon recovery system is structured by using a resin-made or stainless steel pipe to circulate waste water accompanying polishing and/or grinding of a crystal silicon, and disposing a sludge adsorption apparatus to adsorb a silicon sludge to a membrane element immersed in the waste water in a storage tank to store the circulated waste water, and a sludge drying apparatus to dry the adsorbed silicon sludge to obtain dried silicon sludge, wherein the amount of the waste water per unit time circulated in the pipe and the amount of waste water per unit time treated in the sludge adsorption apparatus are determined so that the residence time in which the silicon stays in the state of being contacted with water is made equal to or less than an upper-limit time calculated based on an oxidation coefficient indicating the time change rate of the oxygen concentration in the silicon in such a state and a target value of the oxygen concentration in the silicon recovered. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a silicon recovery system for recovering silicon from wastewater containing silicon, a silicon recovery method, a recovered material, and a compound of the recovered material.

  Conventionally, in a factory for processing silicon ingots and silicon wafers, a large amount of silicon sludge is discharged along with polishing and grinding of silicon. With the recent increase in ecological momentum, various studies have been conducted on the reuse of such silicon sludge.

  For example, Patent Document 1 discloses a technology for collecting silicon waste by adjusting the pH value of waste water containing silicon waste and passing the adjusted waste water through a filter. Patent Document 1 describes that the collected silicon waste is melted and reused as an ingot or reused as a material for cement or concrete.

Japanese Patent No. 3773823

  However, in the technique of Patent Document 1, since the pH adjusting agent is injected into the waste water, there is a possibility that the recovered material to be collected may contain a component of the pH adjusting agent. Moreover, there is a possibility that pure silicon (Si) contained in the waste water is promoted to be transformed into a compound. For this reason, the technique of Patent Document 1 has a problem that the ratio of pure silicon (Si) contained in the recovered material is low.

  And when the technique of patent document 1 is used, the post-processing after collection | recovery is needed in order to raise the ratio of the pure silicon (Si) contained in a collection | recovery thing, and the cost for the reuse increases. There was also. That is, the higher the ratio of pure silicon contained in the recovered material, the higher the reuse value, and thus the higher the pure silicon content, the better. However, if the cost is excessive, it becomes difficult to make a profit.

  By the way, it is known that the silicon sludge including the recovered material of Patent Document 1 has a moisture content of about 60% even after a dehydration step. For this reason, the recovered silicon sludge has a problem that the volume is large and the transportation cost is high.

  For these reasons, how to recover silicon sludge having a high pure silicon content is a major issue.

  The present invention has been made to solve the above-described problems caused by the prior art, and is a silicon recovery system, a silicon recovery method, and a recovered recovery that can recover a recovered material having a high pure silicon content. It is an object to provide a product and a compound of a recovered product.

  In order to solve the above-described problems and achieve the object, the present invention is a silicon recovery system for recovering silicon from waste water containing silicon, and distributes the waste water accompanying polishing and / or grinding of crystalline silicon. A sludge adsorbing means for adsorbing silicon sludge to a membrane element immersed in drainage in a storage tank for storing drainage circulated by the distribution means, and drying by drying the silicon sludge adsorbed by the sludge adsorbing means A sludge drying means for obtaining silicon sludge, and the residence time during which the silicon stays in contact with water is an oxidation coefficient indicating a time change rate of the oxygen concentration in the silicon in the state and a target of the oxygen concentration in the recovered silicon Units distributed by the distribution means so as to be less than or equal to the upper limit time calculated based on the value And wherein the determining the amount of waste water per unit time to be processed by the waste water quantity and the sludge suction unit somewhere between.

  Moreover, the present invention is characterized in that, in the above-mentioned invention, the distribution means is a pipe made of resin or stainless steel.

  Further, the present invention is the above invention, further provided with a concentration means for concentrating waste water provided upstream of the sludge adsorption means, wherein the circulation means are provided respectively upstream and downstream of the concentration means. The sludge adsorption means receives the waste water concentrated by the concentration means via the distribution means.

  Further, the present invention is characterized in that, in the above invention, the sludge adsorbing means is provided in parallel as viewed from the upstream side.

  Further, the present invention is characterized in that, in the above invention, the sludge drying means obtains the dry silicon sludge having a moisture content of 30% or less by drying the silicon sludge.

  Further, the present invention is characterized in that, in the above-mentioned invention, the end point of the residence time is a time point when the moisture content of the dry silicon sludge becomes 30%.

  Further, the present invention is characterized in that, in the above-mentioned invention, the upper limit time is 100 hours or less.

  Further, the present invention is the above invention, wherein the oxidation coefficient is obtained based on a particle size of silicon contained in the wastewater circulated by the circulation means, and the upper limit time is the target value It is calculated by dividing by an oxidation coefficient.

  The present invention also relates to a silicon recovery method for recovering silicon from waste water containing silicon, the distribution step for distributing only the waste water accompanying polishing and / or grinding of crystalline silicon, and the waste water distributed by the distribution step. A sludge adsorption step for adsorbing silicon sludge to a membrane element immersed in the waste water in the storage tank, and drying silicon sludge adsorbed by the sludge adsorption step to obtain dry silicon sludge Sludge drying step, and the residence time in which the silicon stays in contact with water is an oxidation coefficient indicating a time change rate of the oxygen concentration in the silicon in the state and a target value of the oxygen concentration in the recovered silicon. Per unit time distributed by the distribution process so as to be less than or equal to the upper limit time calculated based on And wherein the determining the amount of waste water per unit time to be processed by the amount and the sludge adsorption step of water.

  The present invention is also characterized in that it is a recovered material recovered in the above invention.

  The present invention is also characterized in that it is a compound of the recovered product recovered in the above invention.

  According to the present invention, the silicon sludge is adsorbed to the distribution means for distributing the wastewater accompanying the polishing and / or grinding of the crystalline silicon, and the membrane element immersed in the wastewater in the storage tank for storing the wastewater distributed by the distribution means. The sludge adsorbing means and the sludge drying means for obtaining dry silicon sludge by drying the silicon sludge adsorbed by the sludge adsorbing means, and the residence time in which the silicon stays in contact with water, the oxygen in the silicon in such a state The amount of wastewater per unit time circulated by the circulation means and sludge adsorption so as to be less than the upper limit time calculated based on the oxidation coefficient indicating the rate of change in concentration over time and the target value of oxygen concentration in the recovered silicon Since we decided to determine the amount of wastewater per unit time processed by the means, By collecting only the wastewater containing the coming silicon waste, it is possible to increase the silicon concentration of the recovered material, and it is possible to prevent the oxidation of silicon contained in the wastewater by limiting the residence time. There is an effect. Thereby, there exists an effect that the collection | recovery with a high content rate of pure silicon can be collect | recovered.

  In addition, according to the present invention, since the distribution means is a pipe made of resin or stainless steel, there is an effect that substances derived from the components of the pipe can be prevented from contaminating the waste water. Thereby, there exists an effect that the collection | recovery with a low content rate of an impurity can be collect | recovered.

  In addition, according to the present invention, the apparatus further includes a concentration unit that is provided on the upstream side of the sludge adsorbing unit, and concentrates the waste water, and the distribution unit is provided on the upstream side and the downstream side of the concentration unit, respectively. Since the wastewater concentrated by the concentration means is received via the distribution means, the adsorption efficiency by the sludge adsorption means can be increased and the time required for the sludge adsorption process can be shortened, so the oxidation of silicon contained in the wastewater can be reduced. There is an effect that can be prevented.

  Further, according to the present invention, since the sludge adsorbing means is provided in parallel when viewed from the upstream side, it is possible to easily balance the treatment capacity in the sludge adsorption process and the amount of generated wastewater. Play. Thereby, it is possible to prevent the silicon contained in the waste water from staying and prevent the silicon contained in the waste water from being oxidized.

  According to the present invention, since the sludge drying means obtains dry silicon sludge having a moisture content of 30% or less by drying the silicon sludge, silicon is prevented from being oxidized in the silicon sludge. There is an effect that can be.

  Further, according to the present invention, since the end point of the residence time is the time when the moisture content of the dry silicon sludge becomes 30%, the content of pure silicon in the recovered material is stopped by stopping the oxidation of silicon. There is an effect that the rate can be increased.

  According to the present invention, since the upper limit time is 100 hours or less, there is an effect that silicon contained in the waste water can be efficiently recovered.

  Further, according to the present invention, the oxidation coefficient is obtained based on the particle size of silicon contained in the circulated waste water, and the upper limit time is calculated by dividing the target value by the oxidation coefficient. As a result, there is an effect that flexible operation can be performed according to the target value of the content of pure silicon in the collected material.

FIG. 1 is a diagram showing an outline of a silicon recovery system according to the present embodiment. FIG. 2 is a diagram showing the configuration of the silicon recovery system. FIG. 3 is an explanatory diagram of the oxidation coefficient. FIG. 4 is an explanatory diagram of the residence time. FIG. 5 is a diagram showing the configuration of the membrane element. FIG. 6 is a diagram illustrating a configuration example of the membrane module. FIG. 7 is a diagram illustrating each process executed by the sludge adsorption device. FIG. 8 is an overview of the sludge adsorption device and the sludge drying device. FIG. 9 is a diagram showing an outline of a silicon recovery system according to the prior art.

  Exemplary embodiments of a silicon recovery system, a silicon recovery method, a recovered material, and a compound of the recovered material according to the present invention will be described below in detail with reference to the accompanying drawings.

  In the following, the silicon recovery system according to the prior art will be described with reference to FIG. 9, and then an embodiment of the silicon recovery system to which the silicon recovery method according to the present invention is applied will be described with reference to FIGS. And

  First, an outline of a silicon recovery system according to the prior art will be described with reference to FIG. FIG. 9 is a diagram showing an outline of a silicon recovery system according to the prior art. As shown in the figure, a silicon recovery system 300 according to the prior art includes a BSG (backside grinder) apparatus 101, a D / S (dicing / saw) apparatus 102, a cooling tower 201, a pure water production apparatus 202, and a PKG (package). ) Collected wastewater discharged from various devices such as dicing 203 and collected silicon sludge (hereinafter sometimes simply referred to as “sludge”) from the collected wastewater.

  Here, the BSG apparatus 101 is an apparatus that polishes a wafer obtained by slicing an ingot of pure silicon (for example, single-crystal silicon having a purity of 11 and 9) and processes the wafer into a wafer having a desired thickness, and the D / S apparatus 102 This is an apparatus for grinding the wafer after thickness adjustment and cutting it into a rectangular shape.

  Then, the waste water discharged from the BSG device 101 and the D / S device 102 is guided to the concentration device 301 to collect pure water by filtering, and the concentrated waste water is discharged to the adjustment tank 302.

  In addition, wastewater from various apparatuses such as the cooling tower 201, the pure water production apparatus 202, and the PKG dicing 203 is also collected in the adjustment tank 302. Note that the PKG dicing 203 is an apparatus for cutting a package in which a wafer is sealed with a resin or the like.

  And the waste_water | drain stored in the adjustment tank 302 is guide | induced to the waste water treatment facility 303, and flocculants, such as PAC (Poly Aluminum Chloride: Poly Aluminum Chloride), are added.

  By adding such a flocculant, components such as silicon waste contained in the wastewater are separated from the wastewater as precipitates. The precipitate thus obtained was led to the dehydrator 304, and sludge (silicon sludge) as the final recovered product was obtained through the dehydration process.

  Note that a part of the wastewater collected in the wastewater treatment facility 303 is generally sent back to the adjustment tank 302. For this reason, the silicon waste contained in the waste water stayed in the silicon recovery system 300 with a span of several days.

  As described above, in the silicon recovery system 300 according to the related art, a substance other than silicon scrap derived from pure silicon (for example, a substance derived from a flocculant, a cooling tower 201, a pure water production apparatus 202, and a PKG dicing 203 is derived. Therefore, the content of pure silicon contained in the recovered sludge remained at about 55%.

  Thus, the sludge obtained by the silicon recovery system 300 according to the prior art has a problem that the utility value is low.

  Further, in the silicon recovery system 300 according to the prior art, silicon waste contained in the wastewater stays in the adjustment tank 302 and the wastewater treatment facility 303 for a long period of time, so that the oxidation of the silicon waste progresses and pure silicon in the recovered sludge It contributed to lowering the content rate. Further, the sludge obtained by the silicon recovery system 300 according to the prior art has a moisture content of about 60%, and there is a problem that the sludge transportation cost is increased.

  Therefore, in the silicon recovery method according to the present invention, a new sludge recovery method was constructed from the following two viewpoints. That is, the first point of view is to prevent wastewater contamination (contamination: hereinafter simply referred to as “contamination”) from substances other than silicon scrap derived from pure silicon (contamination prevention).

  And the 2nd viewpoint is a viewpoint of preventing the oxidation of the silicon | silicone waste in waste_water | drain (antioxidation). Thereby, according to the silicon | silicone collection | recovery method which concerns on this invention, it succeeded in making the content rate of the pure silicon contained in collection | recovery sludge substantially 99% or more.

  Hereinafter, specific contents of the silicon recovery method according to the present invention will be described.

  FIG. 1 is a diagram showing an outline of a silicon recovery system according to the present embodiment. In the figure, the same components as those in FIG. 9 used for explaining the silicon recovery system 300 according to the prior art are denoted by the same reference numerals.

  As shown in FIG. 1, the silicon recovery system 1 according to the present embodiment is configured to discharge wastewater (a BSG device 101 and a D / S device 102 in FIG. 1) that processes pure silicon (“ Only the wastewater A ") was accepted, and the silicon sludge (" sludge A "shown in the figure) was obtained through the accepted wastewater concentration process, sludge adsorption process and sludge drying process.

  Specifically, the silicon recovery system 1 includes a pipe 10, a concentration device 20, and a sludge adsorption / drying device 30. Here, the pipe 10 is a flow path made of resin or stainless steel such as polyvinyl chloride (PVC).

  Thus, the reason for using a resin or stainless steel flow path is to prevent substances derived from the flow path components from contaminating the waste water (contamination prevention). Here, some members constituting the flow path can be made of resin, and other members can be made of stainless steel. For example, if the pipe is made of resin and the joint and valve are made of stainless steel, the cost of the entire pipe 10 can be reduced. In the silicon recovery system 1, the pipe 10 is used for all the channels of the drainage A.

  The concentrator 20 can be the same type as the concentrator 301 shown in FIG. However, the concentration rate of waste water in the concentrator 20 and the amount of waste water treated per unit time are adjusted to match the amount of waste water A per unit time and the amount treated by the sludge adsorption drying device 30. Specific adjustment contents will be described later.

  The sludge adsorption drying device 30 is a device that filters the waste water by immersing a membrane element, which will be described later, in the waste water, and collects the sludge adhered to the surface of the membrane element. Moreover, the sludge adsorption drying apparatus 30 is also an apparatus for obtaining the sludge A by drying the collected sludge.

  In the silicon recovery system 1, when the sludge A is obtained from the wastewater A, the time during which the silicon waste contained in the wastewater A is in contact with water (hereinafter referred to as “residence time”) is equal to or less than a predetermined upper limit time. It was decided to limit to. Then, the amount of the waste water A and the processing capacity of each device for treating the waste water A are adjusted so that the residence time of the silicon waste is less than the upper limit time.

As described above, the reason for limiting the residence time of the silicon scrap is that the longer the time that the silicon scrap is in contact with water, the more the oxidation of silicon (Si) proceeds and the more easily silicon oxide (SiO ₂ ) is generated. Because.

  That is, in the silicon recovery system 1, the ratio of silicon oxide contained in the sludge A is suppressed by restricting the residence time of silicon waste, and the pure silicon content in the sludge A is increased. The oxidation of silicon will be described later with reference to FIG. Details of the residence time of silicon scrap will be described later with reference to FIG.

  And since the sludge A obtained with the silicon | silicone collection | recovery system 1 is obtained through a drying process as mentioned above, while being able to improve the transportability of sludge A, the oxidation of the silicon waste in the sludge A can also be prevented. it can.

  As shown in FIG. 1, the waste water B discharged from the cooling tower 201, the pure water production apparatus 202, the PKG dicing 203 and the like passes through the waste water treatment facility 303 and the dehydrator 304 as in the conventional case. Sludge B will be collected.

  Hereinafter, the configuration of the silicon recovery system 1 will be described in more detail.

  FIG. 2 is a diagram showing the configuration of the silicon recovery system 1. In addition, in the same figure, the case where the sludge adsorption drying apparatus 30 shown in FIG. 1 is separated into a sludge adsorption apparatus 40 and a sludge drying apparatus 50 is shown.

Below, in order to simplify description, the case where the total amount per unit time of the waste_water | drain A discharged | emitted from the BSG apparatus 101 and the D / S apparatus 102 is 100 m < ³ > / h is demonstrated. Moreover, below, the case where the density | concentration of the pure silicon in the waste_water | drain A immediately after discharged | emitted from the BSG apparatus 101 and the D / S apparatus 102 is 200 ppm is demonstrated.

  As shown in FIG. 2, the BSG device 101 and the D / S device 102 and the concentrating device 20 are connected by the pipe 10 described above. Further, the concentrating device 20 and the sludge adsorbing device 40 are also connected by the pipe 10. That is, in the silicon recovery system 1, a device that handles drainage (drainage A) is connected by a pipe 10 dedicated to drainage A (see FIG. 2A).

  Here, since the pipe 10 is made of resin or stainless steel, contamination of the drainage A can be prevented. Further, from the viewpoint of preventing contamination of the drainage A itself, it is preferable that the BSG apparatus 101 or the D / S apparatus 102 does not provide a protective film or the like on the wafer to be processed. Also, inside the BSG device 101 or the D / S device 102, the shape in which the drainage A stays may be removed, or the part that the drainage A contacts may be coated with the same kind of resin as the pipe 10.

  Furthermore, since the silicon recovery system 1 does not require a flocculant that was essential in the silicon recovery system 300 according to the prior art, the waste water A does not include substances derived from the flocculant.

  In this way, the silicon recovery system 1 succeeded in extremely reducing impurities contained in the recovered silicon. Specifically, it was confirmed that impurities such as iron (Fe), aluminum (Al), calcium (Ca), boron (B), and phosphorus (P) contained in the recovered silicon were each 20 ppm or less.

Further, in the silicon recovery system 1, the unit processing amount of each device is adjusted so that the residence time of the silicon waste contained in the waste water A is a predetermined time or less (see FIG. 2B). Specifically, when the waste water A is generated at 100 m ³ / h, the unit processing amount of the concentrating device 20 is adjusted to be 100 m ³ / h or more. When the unit throughput by the single concentrator 20 is insufficient, a plurality of concentrators 20 may be provided in parallel.

  Thus, the reason for adjusting the residence time of the silicon | silicone waste contained in the waste_water | drain A to below predetermined time is as follows. In other words, as a result of experimentally determining an oxidation coefficient indicating the relationship between the residence time, which is the duration of time when the silicon is in contact with water, and the degree to which silicon is oxidized, the residence time depends on the desired oxygen concentration of recovered silicon. This is because it has been confirmed that adjusting the time is useful.

  Here, the oxidation coefficient obtained by experiment will be described with reference to FIG. FIG. 3 is an explanatory diagram of the oxidation coefficient. The vertical axis of the graph shown in the figure is weight% (mass%) of the oxygen concentration in silicon, and the horizontal axis is time (hour) (in the figure, “hour” is represented by “ h ”).

  In FIG. 3, the data when the moisture content is 99.8% is indicated by “◯”, and the data when the moisture content is 30% is indicated by “◇”. Each data shown in FIG. 3 is acquired at neutral, normal temperature and normal pressure, and the silicon particle size is 1 μm center.

  Hereinafter, in order to simplify the description, (100 [mass%] − oxygen concentration [mass%]) is described as “silicon purity”.

  As shown in FIG. 3, it can be seen that the increase rate of the oxygen concentration is large in the initial stage and approaches a constant value as time passes. Since the increase rate is substantially constant until approximately 70 hours in the initial stage, the slope of the curve connecting the data can be regarded as a straight line. The slope of the straight line is called “oxidation coefficient”.

  Here, as shown in FIG. 3, when the moisture content is 99.8%, the oxidation coefficient is 0.18 [mass% / h]. For example, if silicon having a moisture content of 99.8% is left for 10 hours, the oxygen concentration becomes 1.8% (0.18 × 10). In addition, the case where the moisture content is 99.8% corresponds to a state where silicon is in the waste water.

  On the other hand, when the moisture content is 30%, the oxidation coefficient is 0.02 [mass% / h]. Furthermore, it can be seen that when the moisture content is 30%, the oxygen concentration does not exceed 2% even if 500 hours or more have elapsed.

  Thus, by reducing the water content from 99.8% to 30%, the oxidation rate of silicon decreases by an order of magnitude. Further, the oxygen concentration finally reached also decreases by an order of magnitude from 30% to 2%. That is, the progress of oxidation can be almost stopped by reducing the water content to 30%.

  Based on the experimental results, the silicon recovery system 1 calculates an upper limit time for the residence time in accordance with the oxygen concentration required for the recovered silicon, and the silicon residence time of each apparatus is set so that the silicon residence time is less than the upper limit time. The unit throughput was adjusted.

  For example, when the oxygen concentration required for the recovered silicon is 1% or less, that is, when the silicon purity of the recovered silicon is desired to be 99% or more, the upper limit time is calculated as 5.5 h (1 ÷ 0.18). Is done. Thus, when 99% is required as the silicon purity of the recovered silicon, the silicon recovery system 1 adjusts the unit throughput of each device so that the residence time of silicon is 5.5 hours or less.

  When the oxygen concentration required for recovered silicon is 5% or less, that is, when the silicon purity of recovered silicon is desired to be 95% or more, the upper limit time is calculated as 27.7h (5 ÷ 0.18). Is done. Thus, when the silicon purity of the recovered silicon is required to be 95%, the silicon recovery system 1 adjusts the unit throughput of each device so that the residence time of silicon is 27.7 h or less.

  In addition, since the silicon | silicone collection | recovery efficiency by the sludge adsorption | suction apparatus 40 will fall if the oxygen concentration of the silicon | silicone in waste_water | drain raises to about 20%, the maximum value of upper limit time is about 100 hours (111 = 20 ÷ 0.18) or less. It is preferable that

  Thus, in the silicon recovery system 1, the residence time of silicon is adjusted according to the quality required for the recovered silicon. Furthermore, in the silicon recovery system 1, the oxidation of the recovered silicon is prevented from proceeding by reducing the moisture content of the finally recovered silicon to 30% based on the experimental results.

  FIG. 3 illustrates the oxidation coefficient when the silicon particle size is 1 μm center. This is because the particle size of silicon (silicon scrap) handled by the silicon recovery system 1 according to the present embodiment is 1 μm center. It is. However, the present invention is not limited to this, and the silicon coefficient can be obtained similarly in the case of other particle sizes. That is, by performing an experiment similar to the experiment shown in FIG. 3 according to the particle size of silicon to be collected, the oxidation coefficient can be obtained for each particle size of silicon to be collected.

Since the oxidation coefficient (oxidation rate) of silicon scrap is considered to be proportional to the surface area of silicon scrap, for example, assuming that the shape of the silicon scrap is spherical, the oxidation coefficient obtained with a predetermined particle size (for example, 1 μm center) It is good also as estimating the oxidation coefficient of another particle size based on this. For example, when the oxidation coefficient obtained at the 1 μm center is A, the oxidation coefficient B at the 2 μm center can be estimated as B = A / 2 ² .

  Returning to the description of FIG. 2, the concentration device 20 will be described. In the case shown in FIG. 2, the concentrating device 20 concentrates the waste water A received from the upstream 200 times. As a result, wastewater A having a concentration of 40,000 ppm is supplied to the sludge adsorption device 40. Here, the reason why the concentration rate in the concentration device 20 is set to 200 times is to increase the sludge recovery efficiency in the sludge adsorption device 40, which will be described later.

  When the concentration performance of the single concentration device 20 is insufficient, a plurality of concentration devices 20 may be provided in series. For example, when a single concentration device 20 has a 10-fold concentration performance, it is possible to obtain a 200-fold concentration performance by connecting 20 concentration devices 20 in series.

Subsequently, the unit treatment amount of the sludge adsorption device 40 that receives the waste water A concentrated 200 times by the concentration device 20 is adjusted to be 0.5 m ³ / h (100 m ³ / h ÷ 200 times) or more. . And the sludge adsorption | suction apparatus 40 collect | recovers the sludge 4 whose moisture content is 60%. In addition, the density | concentration of the sludge 4 is 400,000 ppm.

  When the sludge adsorption performance of the single sludge adsorption device 40 is insufficient, a plurality of sludge adsorption devices 40 may be provided in parallel. Further, even when the single sludge adsorption device 40 is used, the total area of the filtration membrane used by the sludge adsorption device 40 and the amount of drainage to be sucked through the filtration membrane of the wastewater A to be treated per unit time. It may be adjusted to match the amount.

  Subsequently, the sludge drying device 50 that has received the sludge 4 collected by the sludge adsorption device 40 obtains the dried sludge 5 by drying the sludge 4. Here, the moisture content of the dried sludge 5 is 30%, and the concentration of the dried sludge 5 is 700,000 ppm. The sludge 4 may be naturally dried, or may be forcedly dried by blowing cold air or hot air. When hot air is used, the temperature of the hot air is preferably less than 100 ° C. in order to prevent the degeneration of pure silicon contained in the sludge 4.

  When the sludge drying performance of the single sludge drying device 50 is insufficient, a plurality of sludge drying devices 50 may be provided in parallel.

  In FIG. 2, the BSG device 101 and the D / S device 102 are illustrated as the sources of the drainage A, but any type may be used as long as the device processes pure silicon. 2 shows the case where the drainage A is concentrated by the concentrating device 20 and then passed to the sludge adsorption device 40, the concentrating device 20 may be omitted. In the case where the concentration device 20 is omitted, it is necessary to increase the total area of the filtration membrane used in the sludge adsorption device 40 as compared with the case where the concentration device 20 is used.

  Next, the residence time of silicon waste will be described with reference to FIG. FIG. 4 is an explanatory diagram of the residence time. In addition, the silicon | silicone waste 2 and the waste_water | drain 3 are typically shown in the figure.

  As shown in FIG. 4, the residence time of the silicon waste 2 in the waste water 3 is from when the silicon waste 2 enters the waste water 3 (refer to “Starting point” in FIG. 4) until the silicon waste 2 is taken out from the waste water 3 ( Refers to the “end point” in the figure.

  Specifically, in the BSG device 101 and the D / S device 102, polishing and grinding are performed while spraying pure water, and therefore, the point in time when the silicon scrap 2 is generated by polishing and grinding becomes the “starting point”. In addition, the time point when the sludge adsorbed by the sludge adsorption device 40 is pulled up from the waste water 3 is the “end time point”.

  As will be described later, the sludge adsorbing device 40 stores the drainage 3 in the filtration tank and adsorbs the sludge to the membrane element immersed in the drainage 3, so that the retention of the silicon waste 2 in the filtration tank becomes a problem. . For this reason, it is preferable to estimate the unit processing amount by the sludge adsorption apparatus 40 highly.

For example, when the amount of waste water 3 received from the concentrator 20 per unit time is 0.5 m ³ / h, the unit treatment amount of the sludge adsorption device 40 is originally 0.5 m ³ / h. However, considering the residence time of the silicon waste 2 that is not adsorbed to the membrane element and stays in the filtration tank, it is preferable to set it to about three times or more the unit processing amount that is originally required.

That is, when the unit treatment amount required for the sludge adsorption device 40 is 0.5 m ³ / h from the relationship with the unit treatment amount of the concentration device 20, the unit treatment amount of the sludge adsorption device 40 is about 3 times 1 0.5 m ³ / h or more is preferable.

  And the time (residence time) until the sludge adsorbed by the sludge adsorbing device 40 is lifted from the drainage 3 after the silicon waste 2 is generated in the BSG device 101 or the D / S device 102 is approximately 5.5 hours or less. By doing so, silicon having an oxygen concentration of 1% or less can be recovered.

  In addition, although the moisture content of the sludge 4 collect | recovered by the sludge adsorption | suction apparatus 40 is about 60%, if the moisture content of a collection | recovery sludge is 30% or less, the oxidation of the silicon | silicone waste 2 contained in collection | recovery sludge will stop substantially. This was confirmed by experiments (see FIG. 3). Accordingly, the “end point” shown in FIG. 4 may be set as the time when the dried sludge 5 is generated by the sludge drying apparatus 50 and the residence time may be managed.

  For example, the time from when silicon waste 2 is generated in the BSG device 101 or the D / S device 102 until the dry sludge 5 containing the silicon waste 2 is generated is approximately 5.5 hours or less. It is good also as determining the unit processing amount of the concentration apparatus 20, the sludge adsorption apparatus 40, and the sludge drying apparatus 50. FIG.

  Hereinafter, the sludge adsorption device 40 and the sludge drying device 50 will be described in more detail.

  First, the structure of the sludge adsorption | suction apparatus 40 is demonstrated using FIGS. FIG. 5 is a diagram showing the configuration of the membrane element. 5A is an external view of the membrane element 41, FIG. 5B is an internal structure of the membrane element 41, FIG. 5C is a connection block 42, and FIG. Fig. 1 shows the membrane elements 41 connected to each other.

  As shown to (A) of FIG. 5, the membrane element 41 is comprised by affixing the film | membrane 41c on both surfaces of the resin-made filter plates 41a. Here, the membrane 41c is a polymer microfiltration membrane having a pore diameter of 0.25 μm, and can capture fine particles having a size of 0.25 μm or more. However, actually, the cake layer formed of the fine particles captured on the surface of the film 41c forms a finer network, so that fine particles of 0.05 μm or more can be substantially captured.

  The size of the membrane element 41 (the size excluding the ear portion 41b) is, for example, about 150 mm in height, about 500 mm in width, and about 5 mm in thickness.

  In addition, ear portions 41b are provided at both ends of the membrane element 41, respectively. Here, one water passage hole 41ba is provided in the central portion of the ear part 41b, and two connection holes 41bb are provided at positions sandwiching the water passage hole 41ba. Note that an O-ring is provided in the water passage hole 41ba to prevent liquid leakage from the joint surface with the connection block 42 shown in FIG.

  As shown in FIG. 5B, the filter plate 41a is provided with a flow path 41aa, and the membrane permeated water that has permeated through the membrane 41c is guided to one ear portion 41b. The membrane permeated water guided to the ear portion 41b is further guided to the water passage hole 41ba. FIG. 5B shows a case where the membrane permeated water is guided to the ear portion 41b shown on the right side of FIG.

  FIG. 5C shows a connecting block 42 used when connecting the membrane elements 41. The connection block 42 is provided with one water passage hole 42 a and two connection holes 42 b at positions corresponding to the ear portions 41 b of the membrane element 41. And the space | interval of the membrane element 41 and the membrane element 41 can be adjusted by using the connection block 42 from which thickness differs. In addition, the thickness (namely, space | interval of the membrane elements 41) of the connection block 42 can be 15 mm, for example.

  FIG. 5D shows the state of the membrane element 41 connected using the connection block 42. FIG. 5D shows a case where the membrane elements 41 shown in FIG. 5B are alternately connected while being reversed left and right.

  In this case, the membrane permeated water of the odd-numbered membrane element 41 from the front is collected through the connection block 42 as shown by 43R shown in FIG. Further, the membrane permeated water of the even-numbered membrane element 41 from the front is also collected like 43L. In addition, although (D) of FIG. 5 showed about the case where filtered water was disperse | distributed and collected to each ear | edge part 41b, it is good also as collecting filtered water only to the ear | edge part 41b of one side.

  Next, a membrane module in which the membrane elements 41 shown in FIG. 5 are connected will be described with reference to FIG. FIG. 6 is a diagram illustrating a configuration example of the membrane module. As shown in FIG. 6, the membrane element 41 and the connection block 42 shown in FIG. 5D are fixed with bolts 44a penetrating the connection hole 41bb and the connection hole 42b. And the membrane module 44 is obtained by fixing the membrane element 41 group fixed with the volt | bolt using the rail 44b.

  FIG. 6 shows an example of a membrane module 44 in which a set of six membrane elements 41 is assembled in two upper and lower stages. However, the number of membrane elements 41 included in each set and the number of steps are arbitrary. Can be a number.

  Next, operation | movement of the sludge adsorption | suction apparatus 40 using the membrane module 44 shown in FIG. 6 is demonstrated using FIG. FIG. 7 is a diagram showing each process executed by the sludge adsorption device 40. 7A shows the filtration step, FIG. 7B shows the backwash preparation step, FIG. 7C shows the backwash step, and FIG. 7D shows the filtration preparation step. ing.

  As shown in FIG. 7, the sludge adsorption device 40 includes a filtration tank 45 that stores concentrated wastewater received from the concentration device 20 via the pipe 10, and a pulling mechanism 46 that pulls up the membrane module 44. ing. Further, the sludge adsorption device 40 is a pump that discharges filtered water obtained by sucking each membrane element 41 included in the membrane module 44 as treated water, or reversely feeds treated water to each membrane element 41. 47 is provided.

  The membrane module 44 is suspended by an arm 46b that rotates about the support shaft 46a of the pulling mechanism 46, and the support shaft 46a is rotated clockwise in FIG. And positioned above the belt conveyor 52. Further, as the support shaft 46a rotates counterclockwise in the figure, the membrane module 44 is immersed in the filtration tank 45 filled with concentrated drainage.

  Here, the belt conveyor 52 is a mechanism for transporting the sludge 4 to the sludge drying device 50, and is inclined so that the sludge drying device 50 side is higher than the sludge adsorption device side 40 side. And the belt conveyor 52 is installed in the position where the edge part by the side of the sludge adsorption apparatus 40 is higher than the filtration tank 45. FIG. Therefore, the waste water flowing out from the sludge 4 on the backwash water or the belt conveyor 52 is collected at the end on the sludge adsorption device 40 side and then flows into the filtration tank 45 by its own weight.

  The tubes 47 a connected to the pump 47 are connected to water passage holes 41 ba of the membrane element 41 located on the forefront of the membrane module 44. FIG. 7 illustrates a membrane module 44 assembled so as to collect filtered water only on one ear 41b (the right side in the figure).

  As shown in FIG. 7A, in the filtration step, the membrane module 44 is immersed in a filtration tank 45 filled with concentrated waste water, and the pump 47 operates to suck each membrane element 41. . Thereby, a cake layer is formed on the surface of the membrane 41c stretched on each membrane element 41. And the sludge adsorption | suction apparatus 40 continues a filtration process until the thickness of a cake layer becomes about 2-5 mm. The duration of the filtration process is approximately 45 minutes.

  Here, the reason for continuing the filtration step until the thickness of the cake layer is about 2 to 5 mm is that if the cake layer is too thin, the peelability of the cake layer is poor and a large amount of backwash water is required. . On the other hand, if the cake layer is too thick, the wastewater treatment speed in the sludge adsorption device 40 is reduced.

  In addition, since the density | concentration of the waste_water | drain in the filtration tank 45 is concentrated to about 40,000 ppm with the upstream concentration apparatus 20, the continuation time of a filtration process can be limited to about 45 minutes. On the other hand, when the concentration of the waste water is about 1,500 ppm, the growth rate of the cake layer is slow, so the duration of the filtration step needs to be about 240 minutes.

  Subsequently, when the thickness of the cake layer becomes an appropriate thickness, the sludge adsorption device 40 operates the pulling mechanism 46 to pull up the membrane module 44 from the filtration tank 45. Then, as shown in FIG. 7B, the pulled up membrane module 44 is positioned above the belt conveyor 52 and then stopped. In this backwash preparation step, the suction by the pump 47 is continued and the dehydration from the cake layer is advanced.

  Here, the time required from lifting the membrane module 44 to positioning it above the belt conveyor 52 is approximately within one minute. Further, the time for which the pump 47 continues to dehydrate from the cake layer is generally within 5 minutes.

  Subsequently, the sludge adsorption device 40 reversely feeds the treated water by reversing the pump 47. As a result, the treated water spouts from the inside of the membrane element 41 toward the membrane 41c, so that the cake layer formed on the surface of the membrane 41c peels off from the membrane 41c as shown in FIG. Drops onto 52. In this way, the sludge 4 is obtained. Note that the time required for this backwashing step is generally within one minute.

  In addition, the low pressure of 50 kPa or less is enough for the pressure of the treated water (backwash water) sent back by the pump 47. Thus, the reason why the low water pressure can be used is that there is no support on the outside of the membrane 41c in the sludge adsorption device 40, and the peelability is so good that the cake layer adsorbed on the surface of the membrane 41c falls by its own weight. It is.

  Subsequently, as shown in FIG. 7D, the sludge adsorption device 40 returns the membrane module 44 to the position shown in FIG. 7A so as to return the support shaft 46a (see FIG. 7A). ) Is rotated counterclockwise in the figure. The time required to return the membrane module 44 to the position shown in FIG. 7A is approximately within 1 minute. Moreover, in this filtration preparation process, the treated water (surplus backwash water) collected along the inclination of the belt conveyor 52 is returned to the filtration tank 45 by its own weight.

  And the sludge adsorption | suction apparatus 40 will collect | recover the sludge 4 continuously by repeating the process of (A)-(D) shown to the same figure. Further, the sludge 4 collected by the sludge adsorption device 40 is conveyed to the sludge drying device 50 by the belt conveyor 52 as needed.

  Thus, since the sludge adsorption | suction apparatus 40 collect | recovers silicon sludge without using additives, such as a coagulant | flocculant, it can raise the content rate of the pure silicon contained in the silicon sludge collect | recovered.

  In addition, when the method (filter press method) which wraps the sludge 4 with a filter cloth and forcibly reduces the water content is taken, it is known that the sludge 4 becomes high temperature, and silicon contained in the sludge 4 This is not preferable because the possibility of transformation is increased.

  Next, the configuration of the sludge drying device 50 and an arrangement example of the sludge adsorption device 40 and the sludge drying device 50 will be described with reference to FIG. FIG. 8 is an external view of the sludge adsorption device 40 and the sludge drying device 50. 8A shows a top view of the sludge adsorption device 40 and the sludge drying device 50, and FIG. 8B shows a side view of the sludge adsorption device 40 and the sludge drying device 50, respectively. .

  FIG. 8 also shows two sludge adsorption devices 40 (sludge sludges) sandwiching a belt conveyor 52 provided below a frame-shaped guide 48 (the center portion is hollow from above) that catches the falling sludge 4. The case where the adsorption device 40A and the sludge adsorption device 40B) are provided in parallel is shown. In this case, since the sludge adsorption device 40A and the sludge adsorption device 40B share one belt conveyor 52, the step of moving the membrane module 44 above the belt conveyor 52 ((B) or (C) in FIG. 7). Are adjusted alternately.

  Although FIG. 8 shows the case where one sludge drying device 50 is provided for two sludge adsorption devices 40, the sludge drying device 50 may be provided for each sludge adsorption device 40.

  Here, the belt conveyor 52 is inclined so that the sludge drying device 50 side is higher than the sludge adsorption device 40 side, and the end on the sludge adsorption device 40 side is from the filtration tank 45 of the sludge adsorption device 40. Is also installed at a higher position (see FIG. 8B). With this arrangement, the waste water and backwash water collected by the belt conveyor 52 returns to the filtration tank 45 by its own weight. Since the configuration and operation of the sludge adsorption device 40 have already been described with reference to FIG. 7, the description thereof is omitted here.

  Below, the structure and operation | movement of the sludge drying apparatus 50 are demonstrated. In the present embodiment, the sludge drying apparatus 50 that obtains the dried sludge 5 by blowing hot air is illustrated, but other drying methods may be used. For example, it is good also as spraying cold wind with respect to the sludge 4, or drying the sludge 4 naturally.

  As shown in FIG. 8A, the sludge drying apparatus 50 includes a drying chamber 51 and a belt conveyor 52. The drying chamber 51 is provided with an exhaust port 55 and connected with a hot air introduction pipe 54 that guides hot air from the heater 53 to the drying chamber 51. Here, the heater 53 adjusts so that the temperature of hot air may be less than 100 degreeC.

  Further, the belt conveyor 52 conveys the sludge 4 falling through the guide 48 to the drying chamber 51. Subsequently, hot air is blown to the transported sludge 4 in the drying chamber 51, and the moisture content of the sludge 4 decreases. When the sludge 4 reaches the end of the drying chamber 51 (the right end of the belt conveyor 52 in the figure), the dried sludge 5 having a moisture content of 30% or less is obtained.

  The dried sludge 5 falls when it reaches the right end of the belt conveyor 52 and is stored in a container (not shown).

  Thus, since the sludge 4 adsorbed by the sludge adsorption device 40 is immediately guided to the sludge drying device 50 and processed into the dried sludge 5, the oxidation of silicon in the sludge 4 is prevented from proceeding. be able to.

  Next, the property of the dried sludge 5 obtained by the silicon recovery system 1 and the usage example of the dried sludge 5 will be described.

  Impurities such as iron (Fe), aluminum (Al), calcium (Ca), boron (B), and phosphorus (P) in the dried sludge 5 obtained by the silicon recovery system 1 are each confirmed to be 20 ppm or less. . It should be noted that if the substances derived from the grindstone or cutting saw used in the BSG device 101 or the D / S device 102 that are the sources of silicon scrap are eliminated, the ratio of such impurities can be further reduced. .

  Further, when the unit treatment amount of each device is adjusted so that the residence time of silicon is 5.5 hours or less, the silicon purity in the dried sludge 5 is approximately 99% or more (that is, the oxygen concentration is 1% or less). It has also been confirmed.

  Furthermore, the particle size of the silicon waste contained in the dried sludge 5 obtained by the silicon recovery system 1 is 1 μm center, and the utility value is very high without performing pulverization. Therefore, the dried sludge 5 obtained by the silicon recovery system 1 can be widely used as a raw material for solar cells, a raw material for hard ceramics, a raw material for silicon resins, a raw material for refractories, and the like.

Moreover, since the pure silicon content in the dried sludge 5 obtained by the silicon recovery system 1 is very high as described above, it is also useful as a raw material for silicon compounds. For example, the dried sludge 5 obtained by the silicon recovery system 1 is used as a raw material for silicon compounds such as silicon monoxide (SiO), silicon dioxide (SiO ₂ ), silicon nitride (Si ₃ N ₄ ), and silicon carbide (SiC). be able to.

The generated silicon compound is used, for example, as a semiconductor sealing resin additive for silicon dioxide (SiO ₂ ) and as a circuit board or silicon nitride tool for silicon nitride (Si ₃ N ₄ ), respectively. Can do.

  As described above, in the present embodiment, the resin-made or stainless-steel pipe that circulates the drainage accompanying polishing and / or grinding of crystalline silicon is used, and the inside of the storage tank that stores the circulated drainage is used. A sludge adsorption device that adsorbs silicon sludge to a membrane element immersed in the waste water and a sludge drying device that obtains dry silicon sludge by drying the adsorbed silicon sludge, and the silicon stays in contact with water Units circulated by piping so that the residence time is not more than the upper limit time calculated based on the oxidation coefficient indicating the rate of change of oxygen concentration with time in silicon in such a state and the target value of oxygen concentration in recovered silicon To determine the amount of wastewater per hour and the amount of wastewater per unit time processed by the sludge adsorber It was constructed near-recovery system.

  Therefore, according to the silicon recovery system and the silicon recovery method of the present invention, silicon sludge having a high pure silicon content can be recovered. And the recovered silicon sludge can be widely reused.

  In the embodiment described above, the case where the particle size of silicon scrap to be collected is 1 μm center has been described. However, the present invention can deal with silicon scraps of various particle sizes. That is, an oxidation coefficient corresponding to the particle size of silicon scrap to be collected may be obtained through experiments and the upper limit value of the residence time may be calculated based on the obtained oxidation coefficient.

  As described above, the silicon recovery system and the silicon recovery method according to the present invention are useful for application to a plant that processes silicon, and are particularly suitable when the recovered silicon is desired to be widely reused.

DESCRIPTION OF SYMBOLS 1 Silicon recovery system 2 Silicon waste 3 Drainage 4 Sludge 5 Dry sludge 10 Piping 20 Concentration device 30 Sludge adsorption drying device 40 Sludge adsorption device 41 Membrane element 41a Filter plate 41aa Flow path 41b Ear part 41ba Water passage hole 41bb Connection hole 41c Membrane 42 Connection block 42a Water passage hole 42b Connection hole 44 Membrane module 44a Bolt 44b Rail 45 Filtration tank 46 Lifting mechanism 46a Support shaft 46b Arm 47 Pump 47a Tube 48 Guide 50 Sludge drying device 51 Drying chamber 52 Belt conveyor 53 Heater 54 Hot air introduction pipe 55 Exhaust port 101 BSG device 102 D / S device 201 Cooling tower 202 Pure water production device 203 PKG dicing 300 Silicon recovery system 301 according to the prior art 301 Concentrator 302 Adjustment tank 303 Wastewater treatment facility 3 04 Dehydrator

Claims (11)

A silicon recovery system for recovering silicon from wastewater containing silicon,
Distribution means for distributing drainage accompanying polishing and / or grinding of crystalline silicon;
Sludge adsorbing means for adsorbing silicon sludge to the membrane element immersed in the wastewater in the storage tank storing the wastewater distributed by the distribution means;
A sludge drying means for obtaining dry silicon sludge by drying the silicon sludge adsorbed by the sludge adsorption means,
The residence time in which the silicon stays in contact with water is equal to or less than the upper limit time calculated based on the oxidation coefficient indicating the time change rate of the oxygen concentration in the silicon in the state and the target value of the oxygen concentration in the recovered silicon. Thus, the silicon recovery system, wherein the amount of waste water per unit time distributed by the distribution means and the amount of waste water per unit time processed by the sludge adsorption means are determined. The distribution means is:
2. The silicon recovery system according to claim 1, wherein the silicon recovery system is made of resin or stainless steel. Provided further upstream of the sludge adsorption means, further comprising a concentration means for concentrating the waste water,
The distribution means is:
Provided upstream and downstream of the concentration means,
The sludge adsorption means is
3. The silicon recovery system according to claim 1, wherein the waste water concentrated by the concentration means is received via the distribution means. The sludge adsorption means is
The silicon recovery system according to claim 1, wherein the silicon recovery system is provided in parallel when viewed from the upstream side. The sludge drying means is
The silicon recovery system according to any one of claims 1 to 4, wherein the dry silicon sludge having a moisture content of 30% or less is obtained by drying the silicon sludge. The end point of the residence time is
The silicon recovery system according to any one of claims 1 to 5, wherein the moisture content of the dry silicon sludge is 30%. The upper limit time is
It is 100 hours or less, The silicon | silicone collection | recovery system as described in any one of Claims 1-6 characterized by the above-mentioned. The oxidation coefficient is
It is obtained based on the particle size of silicon contained in the wastewater circulated by the distribution means,
The upper limit time is
The silicon recovery system according to claim 1, wherein the silicon recovery system is calculated by dividing the target value by the oxidation coefficient. A silicon recovery method for recovering silicon from wastewater containing silicon,
A distribution process for distributing only wastewater associated with polishing and / or grinding of crystalline silicon;
Using a storage tank for storing the wastewater distributed by the distribution process, a sludge adsorption process for adsorbing silicon sludge to the membrane element immersed in the wastewater in the storage tank;
A sludge drying step of obtaining dry silicon sludge by drying the silicon sludge adsorbed by the sludge adsorption step,
The residence time in which the silicon stays in contact with water is equal to or less than the upper limit time calculated based on the oxidation coefficient indicating the time change rate of the oxygen concentration in the silicon in the state and the target value of the oxygen concentration in the recovered silicon. Thus, the silicon recovery method characterized in that the amount of wastewater per unit time distributed by the distribution step and the amount of wastewater per unit time processed by the sludge adsorption step are determined.   A recovered material recovered by the silicon recovery method according to claim 9.   A compound of a recovered product recovered by the silicon recovery method according to claim 9.

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