JP2007185647A - Method of treating silicon powder-containing drainage - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of flocculating a fine silicon powder that can speedily sediment a flocculated precipitate and lower the turbidity of treated water obtained. <P>SOLUTION: Provided is a method of treating silicon powder-containing drainage that involves rendering an inorganic flocculant comprised of a silica sol-aqueous metal salt having the molar ratio of silica to metal being 0.05-3.0 to be contained so that the concentration of the inorganic flocculant is 15-300 (mg/L) in terms of metal, and then adding an organic polymer flocculant thereto. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel method for treating wastewater containing silicon powder. More specifically, the present invention relates to a method for treating waste water containing silicon powder having very fine particles such as metal silicon and silicon cutting waste.

  Wastewater containing silicon powder as waste, specifically, wastewater containing fine metal silicon and silicon cutting waste, is discharged from the following places.

  For example, metallic silicon is used for the production of silicon chloride or the like that is used as a raw material of silicon by reacting with hydrogen chloride, and when this silicon chloride is recovered, it contains metal silicon that has been refined by being used in the reaction. Waste water is discharged. In addition, polycrystalline silicon rods, single crystal silicon rods, silicon wafers, etc. made from silicon chloride or the like are processed through cutting and polishing processes, and at that time, waste water containing silicon cutting waste is discharged. . Silicon powder containing wastewater containing such metal silicon and silicon cutting waste is difficult to agglomerate because the silicon powder contained is very fine particles (especially silicon cutting waste), and various treatment methods have been proposed. ing.

  For example, a method has been proposed in which an inorganic flocculant such as aluminum chloride is added to cutting wastewater containing metal silicon cutting powder, the pH is adjusted to 10 or more, and the metal silicon agglomerates are floated and processed. (See Patent Document 1). The above method is an excellent treatment method with a low residual concentration of the cut material in the finally obtained water, but in order to adjust the pH to 10 or more, the metal silicon powder reacts with water to generate hydrogen. There is room for improvement in terms of operability.

  In addition, a method of adding an inorganic flocculant, a flotation aid, and a polymer flocculant to silicon powder-containing wastewater, and treating with pressurized water containing fine bubbles (see Patent Document 2), adjusting pH or oxidizing agent A method of adding and treating by adding an inorganic flocculant (see Patent Document 3) has been proposed.

  However, since the method described in Patent Document 2 is treated with pressurized water containing fine bubbles, the process becomes complicated and there is room for improvement in terms of operability. Moreover, in the method described in Patent Document 3, there is room for improvement because the sedimentation rate of the obtained aggregates is slow or the turbidity of the finally obtained water cannot be sufficiently reduced.

  On the other hand, a water treatment flocculant composed of silica sol-water-soluble metal salt has also been proposed (Patent Document 4). However, in the specific method described in Patent Document 4, only the treatment of water with turbidity is performed, and the treatment of wastewater containing silicon powder that is the subject of the present invention is shown. It has not been.

Japanese Patent Laid-Open No. 10-323675 Japanese Patent Publication No. 3-14516 JP 2004-261708 A Japanese Examined Patent Publication No. 4-75796

  Therefore, the object of the present invention is to improve the operability in the treatment of wastewater containing silicon powder, which is difficult to agglomerate, and the agglomerate sedimentation rate is fast, and the turbidity of water when separating the agglomerates is sufficiently low An object of the present invention is to provide a method for treating wastewater containing silicon powder.

  The present inventors have continued intensive studies to solve the above problems. As a result, it was found that the above object can be achieved by adding a specific silica sol-water-soluble metal salt to the silicon powder-containing waste water, and then adding an organic polymer flocculant, and the present invention has been completed. .

  That is, in the present invention, an inorganic flocculant composed of silica sol-water-soluble metal salt having a silicon to metal molar ratio of 0.05 to 3.0 is added to a waste water containing silicon powder in an amount of 15 to 300 mg / mg in terms of metal. L) is contained so as to have a concentration of L), and then an organic polymer flocculant is added.

  According to the present invention, in the treatment of wastewater containing silicon powder, the cohesiveness is very high, so the sedimentation rate of the aggregate is fast and efficient sedimentation separation is possible.

  Moreover, since the waste water from which the aggregates have been separated can be made to have a turbidity of 10 degrees or less, it can be discharged without being subjected to a secondary treatment, and further to the manufacturing process depending on the dissolved substances contained in the treated water. Reusable. Furthermore, since the separated agglomerates contain aluminum or iron, silica, silicon, etc., they can be used as raw materials for cement, bricks, etc., and can be reused as valuable resources.

  Hereinafter, the present invention will be described in detail.

  This invention is the processing method of the silicon powder containing waste_water | drain which makes the waste_water | drain containing silicon powder contain the inorganic flocculent which consists of a specific silica sol-water-soluble metal salt, and then adds an organic polymer flocculant.

  In the present invention, the silicon powder-containing waste water refers to waste water containing fine silicon powder, and the silicon powder is a suspended substance in the waste water. Specifically, wastewater containing metallic silicon discharged at a silicon chloride manufacturing plant or discharged when processing or cutting polycrystalline silicon, single crystal silicon, wafers, etc. in a plant that manufactures silicon using silicon chloride as a raw material. Waste water containing silicon cutting waste. Further, the silicon powder-containing waste water does not contain powder containing silicon elements other than silicon powder. For example, in a silicon chloride manufacturing plant, silica-containing wastewater produced as a by-product when detoxifying silicon chlorides and wastewater containing silicon powder are combined and not subject to the treatment of the present invention.

  In the present invention, the silicon powder-containing wastewater is not particularly limited, but since silicon powder is contained, it is preferable to control the pH to less than 10. By controlling the pH of the silicon powder-containing wastewater to less than 10, the reaction between the silicon powder and water can be suppressed and the generation of hydrogen can be reduced. In particular, wastewater containing metallic silicon discharged at a silicon chloride manufacturing plant is discharged as an acidic solution. However, since it is difficult to handle it in an acidic state, it is often treated with an alkali. In this case, the pH should be controlled. preferable. The lower limit of the pH is not particularly limited, but the pH is preferably 5 or more in consideration of handling.

  In the present invention, the amount of suspended matter (silicon powder) such as metal silicon and silicon cutting waste contained in the silicon powder-containing wastewater is determined in the silicon powder-containing wastewater when the agglomeration process described in detail later is performed. It is preferable that it is 0.05 mass% or more. When the amount of silicon powder is 0.05% by mass or more, the amount of treated water finally obtained can be reduced, and wastewater can be treated efficiently. The upper limit of the amount of silicon powder is not particularly limited, but is preferably 3% by mass or less. Even when the amount of silicon powder exceeds 3% by mass, the agglomeration treatment of the present invention is possible, but in this case, it is more efficient to perform solid-liquid separation directly with a filter press or the like.

  In the present invention, the silicon powder contained in the silicon powder-containing wastewater has a size in which the silicon powder is present in the wastewater as a suspended substance. In particular, in the agglomeration process described in detail later, since it is possible to perform a high-level process, even very fine particles having an average particle diameter of 0.01 to 30 μm, and further 0.05 to 20 μm should be processed. Can do.

  In the treatment method of the present invention, first, an inorganic flocculant composed of a silica sol-water-soluble metal salt having a silicon-to-metal molar ratio of 0.05 to 3.0 is added to the silicon powder-containing wastewater in terms of metal. It is contained so as to have a concentration of 300 (mg / L). In the present invention, the temperature during the aggregation treatment is not particularly limited, but is preferably 5 to 40 ° C., more preferably 10 to 30 ° C. in view of operability. Moreover, in order to make the said silicon powder containing wastewater contain the inorganic flocculant which consists of a silica sol-water-soluble metal salt of 0.05-3.0, this inorganic agglomeration so that it may become the said range to the said silicon powder containing wastewater. The agent can be added continuously, or the inorganic flocculant can be added in multiple stages.

  In the present invention, the inorganic flocculant comprises a silica sol-water soluble metal salt having a molar ratio of silicon to metal of 0.05 to 3.0, preferably a silica sol-aluminum salt or a silica sol-iron salt. Examples of the water-soluble metal salt of silica sol-water-soluble metal salt include aluminum sulfate, ferric chloride, ferrous sulfate, and polyiron sulfate. In the present invention, by using such a silica sol-water-soluble metal salt, the sedimentation rate of the aggregate after adding the organic polymer flocculant is increased, and the turbidity of the supernatant liquid is set to 10 degrees or less. And suspended matter can be removed to very low concentrations.

  In the present invention, the inorganic flocculant made of silica sol-iron salt is a composite containing silica sol and iron as a polymer, and ferric chloride, ferrous sulfate, and polyiron sulfate are mixed in the silica sol. Can be obtained. Similarly, the inorganic flocculant made of silica sol-aluminum salt is a composite containing silica sol as a polymer and aluminum, and can be obtained by mixing aluminum sulfate with silica sol.

  In the present invention, the inorganic flocculant composed of the silica sol-water-soluble metal salt contains a molar ratio of silicon to metal (more specifically, iron or aluminum) (hereinafter, Si / Fe molar ratio when the metal is iron, metal When Si is aluminum, it is expressed as Si / Al molar ratio.) Is 0.05 to 3.0. When the molar ratio of silicon to metal is 0.05 to 3.0, the turbidity of the supernatant can be further reduced, the sedimentation rate of the aggregates can be increased, and the separation efficiency can be increased. it can. When the molar ratio of silicon to metal is less than 0.05, the sedimentation rate of the aggregates is slow, and the turbidity of the supernatant is increased, which is not preferable. On the other hand, when the molar ratio of silicon to metal exceeds 3.0, the sedimentation rate of the aggregates becomes slow, which is not preferable. Considering the turbidity of the supernatant and the sedimentation rate of the aggregate, the molar ratio of silicon to metal is preferably 0.05 to 1.5. Further, among the inorganic flocculants made of silica sol-water-soluble metal salt, when the inorganic flocculant made of silica sol-aluminum salt is used, the supernatant liquid is not colored, so that the supernatant liquid can be easily reused.

  Hereafter, the manufacturing method of the inorganic flocculent which consists of a silica sol-water-soluble metal salt is demonstrated in detail.

  In the present invention, for example, as a method of preparing an inorganic flocculant composed of a silisol-aluminum salt having a Si / Al molar ratio of 0.05 to 3.0, a reaction between a sodium silicate aqueous solution and a halogen-free mineral acid An example is a method in which silica sol is produced by mixing aluminum sulfate and the like so that the Si / Al molar ratio is 0.05 to 3.0. Similarly, an inorganic flocculant composed of a silica sol-iron salt having a Si / Fe molar ratio of 0.05 to 3.0 also produces a silica sol by a reaction between a sodium silicate aqueous solution and a halogen-free mineral acid, Ferric chloride and the like can be mixed with silica sol so that the Si / Fe molar ratio is 0.05 to 3.0.

  In the present invention, in order that the obtained inorganic flocculant composed of silica sol-water-soluble metal salt exhibits an excellent effect, for example, silica sol was produced by a method as described in JP-A No. 2003-221222. Thereafter, it is preferable to mix aluminum sulfate or ferric chloride with the silica sol.

  That is, using a Y-shaped, T-shaped, etc. reactor such as a sodium silicate aqueous solution and a mineral acid not containing halogen such as sulfuric acid, the mixture obtained by colliding each liquid is aged, and the aged A method of diluting the resulting mixture to form a silica sol and mixing the silica sol with aluminum sulfate or ferric chloride is preferred. The aging means that the polymerization of the silica sol proceeds in a mixture containing the silica sol.

In the present invention, the silica sol - inorganic flocculant made of a water-soluble metal salt, pH is 1.5 to 2.5, and SiO ₂ concentration is in the range of 5 to 25 g / L, pH and the SiO ₂ This is preferable because the concentration is balanced. The viscosity of the silica sol-water-soluble metal salt is preferably 1 to 5 mPa · S.

  An inorganic flocculant composed of a silica sol-water-soluble metal salt that satisfies the above range produces a silica sol having a viscosity of 3 to 6 mPa · S using a Y-shaped or T-shaped reactor, and this silica sol It can be produced by mixing aluminum sulfate and ferric chloride. Further, by using a silica sol having the above viscosity, a silica sol-based inorganic flocculant having a high degree of polymerization and an increased bead-like structure can be efficiently adjusted in a short time.

In the present invention, the inorganic flocculant composed of the silica sol-water-soluble metal salt is composed of nanoparticles. And since it is a nanoparticle, the agglomeration effect | action of the microparticles | fine-particles containing fine silicon powder can be increased. Furthermore, the inorganic flocculant made of silica sol-water-soluble metal salt, for example, when aluminum salt or iron salt is used, the effect of adsorbing fine particles including silicon powder by Al ³⁺ , Fe ³⁺ , fine particles by silica sol, etc. Since the coagulation and precipitation effect of the silica sol and the silica sol and aluminum sulfate or the silica sol and ferric chloride are separately added, the effect can be exhibited.

  Next, the amount of the inorganic flocculant to be included in the silicon powder-containing waste water will be described.

  In the present invention, the inorganic flocculant composed of silica sol-water-soluble metal salt contained in the silicon powder-containing waste water has a concentration of 15 to 300 (mg / L), more preferably 20 to 250 (mg / L) in terms of metal. It is important to make it contain so that it may become the density | concentration of. Specifically, in an inorganic flocculant composed of silica sol-water-soluble metal salt (aluminum salt or iron salt), the concentration of metal (aluminum or iron) contained in the inorganic flocculant is 15 to 300 (mg / L). Thus, what is necessary is just to mix this inorganic flocculant with silicon powder containing waste_water | drain. When the amount of the inorganic flocculant contained in the silicon powder-containing wastewater is less than 15 (mg / L) in terms of metal, the turbidity of the supernatant cannot be sufficiently lowered, which is not preferable. On the other hand, when it exceeds 300 (mg / L), an excessive inorganic flocculant is used, which is not economical, and further, the bulk volume of the agglomerates increases, so that precipitation concentration becomes difficult. Considering the effect of reducing the turbidity of the supernatant liquid, sedimentation concentration and economy, the concentration of the inorganic flocculant composed of silica sol-water-soluble metal salt is preferably 20 to 250 (mg / L) in terms of metal. is there.

  In the present invention, the silicon powder-containing wastewater containing the inorganic flocculant within the above range (hereinafter sometimes referred to as “treatment wastewater”) is not particularly limited, but suppresses the generation of hydrogen. In consideration of the aggregation effect of the inorganic flocculant and the organic polymer flocculant and the release of the treated water finally obtained, it is preferable to control the pH to 5 to 10, preferably 5.5 to 9.

  In the present invention, when the pH of the treated waste water is controlled to 5 to 10, the method is a method of controlling the pH by adding an inorganic flocculant made of silica sol-water-soluble metal salt to the silicon powder-containing waste water, After adding the inorganic flocculant, it is possible to employ a method of controlling by adding an acid or alkali. That is, when the pH of the treated waste water is 5 to 10, the organic polymer flocculant can be added as it is. Furthermore, when the pH of the treated wastewater is outside the range of 5 to 10, an organic polymer flocculant can be added after controlling the pH to 5 to 10 by adding acid or alkali. In addition, when the pH is to be controlled only by adding an inorganic flocculant made of silica sol-water-soluble metal salt to the silicon powder-containing wastewater, the silicon powder is treated in advance so that the pH of the treated wastewater satisfies the above range. The pH of the wastewater contained can also be adjusted.

  In the present invention, an organic polymer flocculant is then added to the treated waste water. By further adding an organic polymer flocculant, the efficiency of the flocculation treatment can be improved. The temperature at which the organic polymer flocculant is added is not particularly limited, and is preferably 5 to 40 ° C., more preferably 10 to 30 ° C. in view of operability.

  The organic polymer flocculant used in the present invention is not particularly limited, and a known flocculant can be used. For example, cationic modification of polyacrylamide, dimethylaminoethyl ester of polyacrylic acid, polydimethylaminoethyl ester of polymethacrylate, polyethyleneimine, cationic polymer flocculant such as chitosan, nonionic polymer flocculant such as polyacrylamide, Use polyacrylic acid, polyacrylamide-based anionic polymer flocculants, for example, copolymers of acrylamide and acrylic acid and / or salts thereof, polyacrylamides with introduced sulfone groups, etc. can do. Among them, it is preferable to use a polyacrylamide anionic polymer flocculant and a nonionic polymer flocculant such as polyacrylamide.

  Moreover, the addition amount of the organic polymer flocculant to be added is appropriately adjusted according to the types and properties of the silicon powder-containing wastewater and the organic polymer flocculant. The concentration is (mg / L), and more preferably 0.5 to 5 (mg / L). When the addition amount of the organic polymer flocculant satisfies the above range, the agglomeration effect can be enhanced, and the separation can be efficiently performed without increasing the separation resistance when separating the aggregated precipitate.

  In the present invention, a known method can be used as a method for separating the aggregated precipitate after adding the organic polymer flocculant. Examples of specific methods include decantation, filter press, centrifugation, belt filter, multiple disk dehydrator, screw press and the like.

  In the present invention, when treating a large amount of silicon powder-containing wastewater, the amount, composition, etc. of suspended substances in the silicon powder-containing wastewater differ depending on the respective wastewater. It is preferable to perform the treatment after finding the treatment conditions, that is, the silicon powder-containing wastewater, the optimum pH of the treatment wastewater, the addition amount of the inorganic flocculant, the addition amount of the organic polymer flocculant, and the like.

  In the present invention, the treated water after the addition of the organic polymer flocculant can make the turbidity of the supernatant liquid 10 degrees or less by the measurement method described later. Therefore, the treated water from which the agglomerates have been separated has low turbidity, so that not only can it be discharged as wastewater without being subjected to secondary treatment, but depending on the composition of dissolved substances contained in the treated water. Can be reused in the manufacturing process.

  In the present invention, the agglomerated aggregate contains silicon, aluminum, iron, and the like, and therefore can be reused as a valuable resource such as a raw material for cement or brick.

  EXAMPLES Hereinafter, examples will be shown to describe the present invention more specifically, but the present invention is not limited to these examples.

  In addition, the measured value published in the Example and the comparative example was measured with the following method.

1) Turbidity (degree: standard substance kaolin)
According to JIS K0101, the turbidity of the supernatant after the aggregation treatment was measured with a spectrophotometer (wavelength: 660 nm, cell length: 10 mm).

2) pH measurement It measured with TOA-HM35V (made by Toa DK Industrial Co., Ltd.).

(Method for producing inorganic flocculant comprising silica-aluminum salt)
Production Examples 1 to 3 of an inorganic flocculant composed of silica sol-water-soluble metal salt, Comparative Production Example 1
Commercially available sodium silicate and sulfuric acid diluted with water, diluted sodium silicate (SiO ₂ : 282.8 g / L, Na ₂ O: 94.1 g / L, MR: 3.10) and diluted sulfuric acid (H ₂ SO ₄ : 199.9 g / L) using a Y-type collision reactor having a size of 40 mm * 40 mm and a sodium silicate flow rate of 6.59 L / min. A flow rate of 15.5 m / sec (nozzle diameter: 3.0 mm) and a dilute sulfuric acid flow rate of 5.65 L / min. The flow rate is 15.3 m / sec. (Nozzle diameter: 2.8 mm), and the flow rate during discharge is 2.6 m / sec. And reacted for 10 minutes to obtain 122.4 L of silica sol (SiO ₂ : 151.8 g / L). Next, this silica sol was aged until the viscosity of the liquid reached 10 mPa · s without stirring, and then diluted with 622.8 L of water to produce a diluted silica sol having a SiO ₂ concentration of 25 g / L. The diluted silica sol had a pH of 1.92 and a viscosity of 3.8 mPa · s.

  This diluted silica sol and aluminum sulfate were mixed at a constant ratio, and used as a flocculant for fumed silica-containing wastewater as an inorganic flocculant composed of a silica sol-aluminum salt.

  Table 1 shows the mixing ratio of the inorganic flocculant composed of silica sol-aluminum salt. Moreover, the Al concentration in the used aluminum sulfate was 56.66 g / L.

Production example 4 of inorganic flocculant composed of silica sol-iron salt
Commercially available sodium silicate and sulfuric acid diluted with water, diluted sodium silicate (SiO ₂ : 280.0 g / L, Na ₂ O: 96.0 g / L, MR: 3.01) and diluted sulfuric acid (H ₂ SO ₄ : 200.1 g / L) using a Y-type collision reactor having a size of 40 mm * 40 mm and a sodium silicate flow rate of 6.59 L / min. A flow rate of 15.5 m / sec (nozzle diameter: 3.0 mm) and a dilute sulfuric acid flow rate of 5.68 L / min. The flow rate is 15.4 m / sec. (Nozzle diameter: 2.8 mm), and the flow rate during discharge is 2.6 m / sec. Then, the reaction was carried out for 10 minutes to obtain 122.7 L of silica sol (SiO ₂ : 150.3 g / L). Next, this silica sol was aged until the viscosity of the liquid reached 10 mPa · s without stirring, and then diluted with 800 L of water to produce a diluted silica sol having a SiO ₂ concentration of 20 g / L. The diluted silica sol had a pH of 1.90 and a viscosity of 3.0 mPa · s.

  This diluted silica sol and ferric chloride were mixed at a certain ratio and used as a flocculant for fumed silica-containing wastewater as an inorganic flocculant composed of silica sol-iron salt.

  Table 2 shows the mixing ratio of the inorganic flocculant composed of silica sol-iron salt. The Fe concentration in the ferric chloride used was 191.8 g / L.

Example 1
A silicon powder-containing wastewater having an average particle diameter of 12 μm, 0.5% by mass of silicon powder, and a pH of 6.9 discharged during the production of silicon chloride was used. The turbidity of this silicon powder-containing wastewater before the agglomeration treatment was 100 or more. 500 ml of this silicon powder-containing wastewater was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant made of silica sol-aluminum salt shown in Production Example 2 was 0.25 (Al: 2 0.4 g (20 mg-Al / L) of the solution (.51 g / 100 ml) was added. After the addition, the pH dropped to 4.8, so the pH was adjusted to 6.5 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of a 0.2% by mass polyacrylamide anionic polymer flocculant, Cliflock PA331 (product: Kurita Kogyo Co., Ltd.) is added, and the mixture is stirred for 5 minutes at a stirring speed of 40 rpm. Let sit for a minute. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. The volume change rate at this time was 16.0%, and the turbidity of the supernatant was 1.5. The results are shown in Table 3. The volume change rate is defined by the following equation. The smaller the volume change rate, the better the sedimentation efficiency.
Volume change rate after standing for 5 minutes = precipitate interface height / total liquid level × 100 from the bottom after standing for 5 minutes

Example 2
Silicon powder-containing wastewater having a particle size of silicon powder of 5 μm or less, silicon powder 0.2% by mass, and pH 6.7 discharged during cutting of polycrystalline silicon was used. The turbidity of the silicon powder-containing wastewater before the aggregation treatment was 100 or more. 500 ml of this silicon powder-containing wastewater was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio 0.05 (Al: 0) of the inorganic flocculant made of silica sol-aluminum salt shown in Production Example 1 0.5 g / 100 ml) solution was added 0.22 ml (20 mg-Al / L). Since pH fell to 4.8 after addition, it adjusted to pH7.5 with 1N-NaOH, and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the rate of change in volume was high because the sedimentation rate was high, and sedimentation was completed after 5 minutes, and measurement was not possible. The turbidity was 2.1. The results are shown in Table 3.

Example 3
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant composed of silica sol-aluminum salt shown in Production Example 2 was 0.25 (Al : 2.51 g / 100 ml) was added in an amount of 0.4 ml (20 mg-Al / L). After the addition, the pH dropped to 4.6, so the pH was adjusted to 6.9 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the rate of change in volume was high because the sedimentation rate was high, and sedimentation was completed after 5 minutes, and measurement was not possible. The turbidity was 1.9. The results are shown in Table 3.

Example 4
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant made of silica sol-aluminum salt shown in Production Example 3 was 1.0 (Al : 0.95 g / 100 ml) solution was added 1.06 ml (20 mg-Al / L). After the addition, the pH dropped to 4.5, so the pH was adjusted to 6.7 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the rate of change in volume was high because the sedimentation rate was high, and sedimentation was completed after 5 minutes, and measurement was not possible. The turbidity was 2.3. The results are shown in Table 3.

Example 5
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant composed of silica sol-aluminum salt shown in Production Example 2 was 0.25 (Al : 2.51 g / 100 ml) was added in an amount of 2.0 ml (100 mg-Al / L). After the addition, the pH dropped to 4.4, so the pH was adjusted to 7.3 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the rate of change in volume was high because the sedimentation rate was high, and sedimentation was completed after 5 minutes, and measurement was not possible. The turbidity was 1.7. The results are shown in Table 3.

Example 6
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker and stirred at a stirring speed of 150 rpm, while the Si / Fe molar ratio of the inorganic flocculant made of silica sol-iron salt shown in Production Example 4 was 0.25 (Fe : 5.38 g / 100 ml) was added in an amount of 0.2 ml (20 mg-Fe / L). After the addition, the pH dropped to 4.1, so the pH was adjusted to 7.5 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the rate of change in volume was high because the sedimentation rate was high, and sedimentation was completed after 5 minutes, and measurement was not possible. The turbidity was 1.5. The results are shown in Table 3.

Example 7
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant composed of silica sol-aluminum salt shown in Production Example 2 was 0.25 (Al : 2.51 g / 100 ml) was added in an amount of 0.4 ml (20 mg-Al / L). After the addition, the pH dropped to 4.5, so the pH was adjusted to 7.6 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass polyacrylamide nonionic polymer flocculant, Cliflock PN161 (product: Kurita Kogyo Co., Ltd.) was added, and the mixture was stirred at a stirring speed of 40 rpm for 5 minutes. Let sit for a minute. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the rate of change in volume was high because the sedimentation rate was high, and sedimentation was completed after 5 minutes, and measurement was not possible. The turbidity was 2.0. The results are shown in Table 3.

Comparative Example 1
500 ml of waste water similar to Example 2 was collected in a 500 ml beaker, and 0.18 ml (20 mg-Al / L) of aluminum sulfate having an AL concentration of 5.65 g / 100 ml was added while stirring at a stirring speed of 150 rpm. After the addition, the pH dropped to 4.3, so the pH was adjusted to 6.8 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. At this time, the volume change rate partially aggregated and settled, but because the fine particles remained suspended, the sedimentation rate could not be measured. Moreover, the turbidity was 100 or more. The results are shown in Table 3.

Comparative Example 2
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker and stirred at a stirring speed of 150 rpm, while the Si / Al molar ratio of the inorganic flocculant made of silica sol-aluminum salt shown in Comparative Production Example 1 was 5.0 ( 4.5 ml (20 mg-Al / L) of a solution of Al: 0.35 g / 100 ml) was added. After the addition, the pH dropped to 4.1, so the pH was adjusted to 7.6 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. The volume change rate at this time was 83.7%, and the turbidity of the supernatant was 9.2. The results are shown in Table 3.

Comparative Example 3
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant composed of silica sol-aluminum salt shown in Production Example 2 was 0.25 (Al : 2.51 g / 100 ml) solution was added 10 ml (500 mg-Al / L). After the addition, the pH dropped to 4.4, so the pH was adjusted to 6.8 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. The volume change rate at this time was 78.3%, and the turbidity of the supernatant was 5.4. The results are shown in Table 3.

Comparative Example 4
500 ml of waste water similar to that in Example 2 was collected in a 500 ml beaker, and while stirring at a stirring speed of 150 rpm, the Si / Al molar ratio of the inorganic flocculant composed of silica sol-aluminum salt shown in Production Example 2 was 0.25 (Al : 2.51 g / 100 ml) was added in an amount of 0.2 ml (10 mg-Al / L). After the addition, the pH dropped to 4.5, so the pH was adjusted to 6.9 with 1N NaOH and stirred for 5 minutes. Next, 0.5 ml of 0.2% by mass cliff rock PA331 was added, stirred for 5 minutes at a stirring speed of 40 rpm, and allowed to stand for 10 minutes. The volume change rate of the precipitated substance after standing for 5 minutes and the supernatant after 10 minutes of static value were sampled to measure turbidity. The volume change rate at this time was 46.5%, and the turbidity of the supernatant was 12.4. The results are shown in Table 3.

Claims (3)

  In the waste water containing silicon powder, an inorganic flocculant composed of silica sol-water-soluble metal salt having a molar ratio of silicon to metal of 0.05 to 3.0 has a concentration of 15 to 300 (mg / L) in terms of metal. And then adding an organic polymer flocculant to the silicon powder-containing wastewater treatment method.   The method for treating wastewater containing silicon powder according to claim 1, wherein the pH of the wastewater containing silicon powder is less than 10. The silica sol-water-soluble metal salt is a silica sol-aluminum salt, the inorganic flocculant comprising the silica sol-aluminum salt has a pH of 1.5 to 2.5, a SiO ₂ concentration of 5 to 25 g / L, and aluminum. The method for treating wastewater containing silicon powder according to claim 1 or 2, wherein the molar ratio of silicon to is 0.05 to 1.5.