JP2011218503A - Method for disposing silicon-containing waste liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for disposing a silicon-containing waste liquid to recover silicon particles from which impurities are effectively removed.SOLUTION: In the method for disposing a silicon-containing waste liquid, a recycled coolant and a recycled silicon ingot are obtained from a waste liquid that is discharged when a silicon ingot is machined, while supplying a water-soluble coolant. The method includes, in order, the steps of: distilling the waste liquid or a concentrate of the waste liquid to separate the recycled coolant from a solid content for recovering silicon; dispersing the solid content for recovering silicon in a cleaning liquid to clean the solid content, and then separating the solid content for recovering silicon from a liquid; dispersing the solid content for recovering silicon in a basic aqueous solution to clean the solid content; and adding an acid aqueous solution to the basic aqueous solution to clean the solid content for recovering silicon in the acid aqueous solution without separating the solid content for recovering silicon from the basic aqueous solution.

Description

  The present invention relates to a silicon-containing waste liquid treatment method.

  In the manufacturing process of a silicon single crystal or polycrystal thin plate (hereinafter referred to as “silicon wafer”) widely used for IC chips and solar cells, about 60% of the silicon mass as a raw material is cut, chamfered or polished. The environmental impact associated with the cost burden on the product and disposal (this waste liquid is generally disposed of in landfills after concentration or collection of some materials). It has become a big problem.

In particular, in recent years, the production of solar cells has been steadily increasing, and there has been a rapid increase in demand for raw materials such as silicon blocks and coolant used for cutting.
Therefore, conventionally, a method for recovering processing slurry and recycled silicon from waste liquid discharged during the production of silicon wafers such as cutting or polishing has been proposed.

  There is known a processing slurry regeneration method in which waste liquid is separated into a dispersion mainly containing abrasive grains and a dispersion mainly containing silicon scraps, and a dispersion medium mainly containing recovered abrasive grains is used (for example, Patent Document 1). reference).

  In addition, the solid content after solid-liquid separation with respect to the waste liquid is washed with an organic solvent, the organic solvent washing step for removing the dispersant contained in the solid content, and the silicon oxide and abrasive grains from the solid content after the organic solvent washing step There is known a method for recovering silicon waste, which includes a separation step of removing powder and obtaining powder containing silicon waste as a main component (see, for example, Patent Document 2).

JP 2003-340719 A JP 2001-278612 A

However, conventional waste liquid processing methods containing silicon scrap cannot recover silicon scrap from which impurities such as iron, phosphorus, and oil components mixed by machining the silicon lump are sufficiently removed, or these Many processes are required to remove the.
This invention is made | formed in view of such a situation, and provides the silicon-containing waste liquid processing method which can collect | recover the silicon | silicone waste from which the impurity was removed effectively.

  The present invention relates to a waste liquid discharged by machining a silicon lump using a metal processing member while supplying a water-soluble coolant containing glycol as a main component or a water-soluble slurry containing the water-soluble coolant, or the waste liquid. A silicon-containing waste liquid treatment method for obtaining a regenerated coolant and a regenerated silicon lump from the concentrated content of the process, wherein the waste liquid or the concentrated content of the waste liquid is separated into the regenerated coolant and the silicon recovery solid content by distillation. , After dispersing and cleaning the silicon recovery solids in a cleaning liquid, and solid-liquid separating the silicon recovery solids and liquids, and dispersing and cleaning the silicon recovery solids in a basic aqueous solution The basic aqueous solution and the solid content for silicon recovery are separated into the basic aqueous solution without subjecting the basic aqueous solution and the solid content for silicon recovery to solid-liquid separation. The addition, to provide a silicon-containing wastewater treatment method characterized by sequentially comprising a step of washing the solids for the silicon recovery in an acidic aqueous solution.

According to the present invention, silicon scrap, water-soluble coolant mainly composed of glycol, and impurities generated by machining using a metal processing member (impurities such as iron and phosphorus mixed from the processing member and water-soluble) By distilling waste liquid that contains a mixture of organic compounds that have reacted with the heat of processing), it can be separated into regenerated coolant and solids for silicon recovery. Can be recovered as a regenerated coolant and easily reused.
Furthermore, according to the present invention, impurities can be sufficiently removed by dispersing and recovering the solid content for silicon recovery contained in the waste liquid in a basic aqueous solution or an acidic aqueous solution. By using this solid content for silicon recovery from which impurities have been sufficiently removed, a regenerated silicon lump can be produced, so that silicon can be purified to high purity with a small number of steps, and a reclaimed silicon lump can be obtained at a low cost. Can do.

Next, according to the present invention, it will be described that impurities contained in the solid content for silicon recovery are sufficiently removed.
First, the silicon recovery solids obtained by distilling waste liquid containing silicon scraps are dispersed and washed in the cleaning liquid, so that most of the water-soluble coolant and impurities contained in the silicon recovery solids are removed. Can be removed.
Thereafter, the silicon recovery solid content obtained by solid-liquid separation of the cleaning liquid is dispersed in the basic aqueous solution and washed, so that it is contained in the silicon recovery solid content before washing in the basic aqueous solution. And the aggregate containing a silicon | silicone waste can be disperse | distributed and the impurity soluble in the basic aqueous solution inside an aggregate can be removed.
Furthermore, an acidic aqueous solution is added to the basic aqueous solution in which the solid content for silicon recovery is dispersed, and the solution in which the solid content for silicon recovery is dispersed is made into an acidic aqueous solution, so that impurities soluble in the acidic aqueous solution inside the aggregate are obtained. Can be removed.

It is explanatory drawing for demonstrating the process of the silicon-containing waste liquid processing method of one Embodiment of this invention. (A) (b) is explanatory drawing for demonstrating the state of the silicon | silicone waste in the process of wash | cleaning the solid content for silicon collection | recovery contained in the silicon-containing waste-liquid processing method of one Embodiment of this invention. It is a particle size distribution figure which shows the result of the particle size distribution measurement performed about solid content for silicon | silicone collection | recovery.

  The silicon-containing waste liquid treatment method of the present invention discharges by machining a silicon lump using a metal workpiece while supplying a water-soluble coolant mainly composed of glycol or a water-soluble slurry containing the water-soluble coolant. A silicon-containing waste liquid treatment method for obtaining a regenerated coolant and a regenerated silicon mass from a waste liquid or a concentrated content of the waste liquid, wherein the regenerated coolant and a solid content for silicon recovery are obtained by distilling the waste liquid or the concentrated content of the waste liquid. A step of separating the solid content for silicon recovery into a cleaning liquid, washing the solid content for silicon recovery into a solid content and a liquid content, and a step of separating the solid content for silicon recovery basic. The step of dispersing and washing in an aqueous solution and the basic aqueous solution and the solid content for silicon recovery are separated without solid-liquid separation. By adding a basic aqueous solution to an acidic aqueous solution, characterized in that it successively comprises a step of washing the solids for the silicon recovery in an acidic aqueous solution.

Solid-liquid separation is to separate a mixture of a solid and a liquid into a solid and a liquid. Solid-liquid separation includes, for example, centrifugation, filtration, distillation and the like.
The solid content is a portion mainly composed of a solid obtained by solid-liquid separation of a mixture of the solid content and the liquid content, and may contain a liquid.
The liquid part is a part mainly composed of a liquid obtained by solid-liquid separation of a mixture of a solid part and a liquid part, and may contain a solid.
Aggregates are those formed by associating particles.
The concentrated portion of the waste liquid refers to a product in which the ratio of a certain component contained in the waste liquid is increased.

In the silicon-containing waste liquid treatment method of the present invention, the solid content for silicon recovery washed in the acidic aqueous solution preferably has an iron concentration of 5 ppm by weight to 20 ppm by weight.
Thus, when the solid content for silicon recovery is purified to form a regenerated silicon lump, the refining cost can be reduced because the iron concentration is low.
In the silicon-containing waste liquid treatment method of the present invention, the basic aqueous solution for washing the solid content for silicon recovery preferably has a pH value of 9 or more and 11 or less.
By this, it can suppress that silicon melt | dissolves in basic aqueous solution, and the aggregate containing a silicon | silicone waste can be disperse | distributed. As a result, impurities can be removed without reducing the silicon recovery rate.
In the silicon-containing waste liquid treatment method of the present invention, the basic aqueous solution for washing the solid content for silicon recovery is preferably an aqueous ammonia solution.
This makes it possible to easily adjust the pH value of the basic aqueous solution for washing the solid content for silicon recovery to a range of 9 or more and 11 or less.

In the silicon-containing waste liquid treatment method of the present invention, the aqueous ammonia solution preferably has an ammonia concentration of 0.001% by mass or more and 1% by mass or less.
Thereby, it can suppress that silicon melt | dissolves in ammonia aqueous solution, and the aggregate containing a silicon | silicone waste can be disperse | distributed. As a result, impurities can be removed without reducing the silicon recovery rate.
In the silicon-containing waste liquid treatment method of the present invention, the solid content for silicon recovery is preferably dispersed and washed in a basic aqueous solution having a weight of 2 to 20 times.
Thus, the impurities contained in the solid for collecting silicon can be sufficiently removed by dispersing and washing the solid for collecting silicon in the basic aqueous solution.

In the silicon-containing waste liquid treatment method of the present invention, the acidic aqueous solution for washing the solid content for silicon recovery preferably has a pH value of 0 or more and 2 or less.
Thereby, impurities soluble in the acidic aqueous solution can be sufficiently removed.
In the silicon-containing waste liquid treatment method of the present invention, the acidic aqueous solution added to the basic aqueous solution is preferably hydrofluoric acid.
Thereby, impurities soluble in hydrofluoric acid can be sufficiently removed.
In the silicon-containing waste liquid treatment method of the present invention, the cleaning liquid for cleaning the solid content for silicon recovery obtained by distillation is preferably water, an acidic aqueous solution, a basic aqueous solution, or an organic solvent.
This makes it possible to remove most of the impurities contained in the solid content for silicon recovery obtained by distillation.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. The configurations shown in the drawings and the following description are merely examples, and the scope of the present invention is not limited to those shown in the drawings and the following description.

Silicon-containing Waste Liquid Treatment Method FIG. 1 is an explanatory diagram for explaining a silicon-containing waste liquid treatment method according to an embodiment of the present invention. FIG. 2 is an explanatory diagram for explaining the steps included in the silicon-containing waste liquid treatment method according to one embodiment of the present invention. FIG. 2 (a) shows a step of dispersing and washing the solid content for silicon recovery in the washing liquid. It is explanatory drawing, (b) is explanatory drawing of the process of disperse | distributing the solid content for silicon | silicone recovery to basic aqueous solution, and wash | cleaning.

  In the silicon-containing waste liquid treatment method of the present embodiment, the silicon lump 1 is machined using a metal working member while supplying a water-soluble coolant 4 mainly composed of glycol or a water-soluble slurry containing the water-soluble coolant 4. A silicon-containing waste liquid treatment method for obtaining a regenerated coolant 5 and a regenerated silicon lump 25 from the waste liquid 3 or the concentrated content of the waste liquid 3 discharged by the process, wherein the regenerated coolant 5 is obtained by distilling the concentrated waste liquid 3 or the concentrated liquid waste 3 And a step of separating the silicon recovery solid content 7 into the cleaning liquid 9 and dispersing the silicon recovery solid content 7 in the cleaning liquid 9, followed by solid-liquid separation into the silicon recovery solid content 15 and the liquid content 12; The step of dispersing and washing the solid content 15 for silicon recovery in the basic aqueous solution 17 and the solid solution separation of the basic aqueous solution 17 and the solid content for silicon recovery. And without, by adding an acidic aqueous solution 19 in the basic aqueous solution 17, characterized in that it comprises a step of washing the solid silicon recovered in an acidic aqueous solution 20 sequentially.

  Hereinafter, the silicon-containing waste liquid treatment method of this embodiment will be described. In addition, since the silicon-containing waste liquid treatment method of the present embodiment uses the waste liquid 3 generated from the machining of the silicon lump 1, an embodiment of the machining of the silicon lump 1 will also be described. In addition, since the silicon recovery solid content obtained by the silicon-containing waste liquid treatment method of the present invention can be regenerated as a regenerated silicon lump 25 through a process such as melting, the silicon recycle method will also be described. The silicon regeneration method may include a melting step and a silicon lump formation step, a post-melt cleaning step, a vacuum melting step, a leaching step, a segregation step, and the like.

1. Machining of silicon lump The silicon lump 1 can be machined by a metal workpiece while supplying a water-soluble coolant 4 based on glycol or a water-soluble slurry containing water-soluble coolant 4. As a result, a waste liquid 3 including silicon scraps 2 and water-soluble coolant 4 generated by cutting the silicon lump 1 is generated. Further, the machining of the silicon lump 1 includes cutting and polishing of the silicon lump 1. In addition, abrasive grains can be used for machining the silicon lump 1, and the abrasive grains may be free abrasive grains contained in the water-soluble slurry, and are fixed to a processing member used for silicon machining. Fixed abrasive grains may also be used.

  Although the silicon lump 1 is not specifically limited, For example, it is a silicon ingot, a silicon wafer, etc. Although the shape of the silicon lump 1 is not particularly limited, in an example, it is a cylindrical shape, a quadrangular prism shape, or a thin plate shape. An example of an apparatus for machining the silicon lump 1 is a multi-wire saw apparatus (hereinafter referred to as “MWS”) that is widely used as a silicon ingot cutting apparatus. In general, MWS is a cutting device that wraps a wire between a plurality of rollers, winds the slurry while supplying a slurry containing coolant and free abrasive grains to the wire, and presses and cuts the silicon lump 1 against the wire. is there. The wire may be either one obtained by drawing a steel material or one obtained by fixing a fixed abrasive such as diamond to the wire.

The water-soluble coolant 4 containing glycol as a main component is a cooling solution supplied when the silicon lump 1 is machined. The water-soluble coolant 4 may be used as a water-soluble slurry for processing by mixing with free abrasive grains, a dispersing agent or the like used for processing the silicon lump 1.
The glycol contained in the water-soluble coolant 4 is a water-soluble organic solvent such as ethylene glycol, propylene glycol, diethylene glycol, or polyethylene glycol, and may be a plurality of these. Further, “having glycol as a main component” means containing 70% by mass or more of glycol. In addition, the water-soluble coolant 4 may include additives such as organic acids, basic aqueous solutions, bentonites, and the addition amount is preferably 10% by mass or less of the water-soluble coolant 4. More preferably, it is 3 mass% or less. Further, the water-soluble coolant 4 may contain 20% by mass or less of water of the water-soluble coolant 4, and preferably may contain 15% by mass or less of water of the water-soluble coolant 4.

When using abrasive grains for machining the silicon lump 1, the abrasive grains may be free abrasive grains or fixed abrasive grains. The abrasive grains are, for example, SiC, diamond, CBN, alumina, and the like.
The silicon scrap 2 is generated when the silicon lump 1 is cut by machining the silicon lump 1. The silicon scrap 2 is mainly in the form of particles, and is discharged as a waste liquid 3 from an apparatus for machining the silicon lump 1.

The waste liquid 3 is the waste liquid 3 discharged from an apparatus for machining the silicon lump 1 and is mainly generated from a metal-worked member used for machining the water-soluble coolant 4, the silicon scrap 2, and the silicon lump 1. Metal scraps are included. In addition, it is considered that a component in which the above components are chemically reacted due to frictional heat accompanying machining of the silicon lump 1 is also included. Further, when abrasive grains are used for machining the silicon lump 1, the abrasive grains are also included in the waste liquid 3.
The silicon-containing waste liquid treatment method of the present embodiment collects the solid content for silicon recovery from which the water-soluble coolant 4 and its chemically reacted components and the metal scrap generated from the processed member are sufficiently removed among the components of the waste liquid 3 can do. If these components are not sufficiently removed, in the process of melting the silicon recovery solids to obtain the regenerated silicon lump 25, it reacts with silicon to lower the silicon recovery rate, or an extra step is required. This is because the time is increased, the life of the crucible used for processing is shortened, the removal is difficult, and the quality of the recycled silicon is lowered. For example, if the recovered solid content for silicon recovery contains an organic compound such as the water-soluble coolant 4 or a compound thereof, the silicon scrap 2 and the organic compound easily react in the step of melting the solid content for silicon recovery. As a result, SiC may be formed to reduce the silicon recovery rate.
In addition, abrasive grains may be included in the silicon recovery solid content 22 including the silicon scrap 2 that can be recovered by the silicon-containing waste liquid treatment method of the present embodiment. This is because the abrasive grains can be removed in the step of melting the silicon recovery solids 22 to obtain the recycled silicon lump 25.
The waste liquid 3 may have a solid content, and the ratio of the liquid content and the solid content is not particularly limited.
The concentrated portion of the waste liquid 3 is obtained by increasing the proportion of certain components contained in the waste liquid 3. For example, the ratio of silicon scrap 2 contained in the waste liquid is increased.
In addition, concentration of a waste liquid can be performed using methods, such as a heating, centrifugation, or filtration, for example. Further, the concentration of the waste liquid 3 to increase the ratio of the silicon waste 2 is performed by, for example, centrifugation, a portion mainly composed of the water-soluble coolant 4 and a portion mainly composed of abrasive grains and the silicon waste 2 as a main component. It is possible to carry out by separating it from the parts to be performed.

2. Distillation of waste liquid, etc. Discharged by machining the silicon lump 1 using a metal processing member while supplying a water-soluble coolant 4 mainly composed of glycol or a water-soluble slurry containing the water-soluble coolant 4, and The waste liquid 3 containing the silicon waste 2 or the concentrated content of the waste liquid 3 is distilled to separate the regenerated coolant 5 and the silicon recovery solid content 7 containing the silicon waste 2.
The method for separating the waste liquid 3 or the like into the regenerated coolant 5 and the silicon recovery solid content 7 by distillation is not particularly limited. For example, the waste liquid 3 or the like is distilled under reduced pressure or under vacuum to recover the distillate and the remaining silicon. The solid content can be separated into 7 for use. This distillate mainly contains water-soluble coolant 4 and can be reused as regenerated coolant 5. The remaining solid content 7 for recovering silicon has most of the water-soluble coolant 4 removed by this process, and can be used in the next process to recover the silicon waste 2.
More specifically, the waste liquid 3 or the like can be heated to a boiling point of glycol or higher, for example, 200 ° C., and distilled, for example, under a reduced pressure of 0.1 atm or lower or under vacuum. As a result, oxidation, chemical reaction, and the like of the components contained in the waste liquid 3 can be suppressed.

3. Cleaning with Silicon Cleaning Solid Cleaning Liquid The silicon recovery solid content 7 is dispersed in the cleaning liquid 9 and cleaned. The cleaning liquid 9 is water, an acidic aqueous solution, a basic aqueous solution, or an organic solvent. Further, the silicon recovery solid content 7 can be cleaned by stirring the cleaning liquid 9 in which the silicon recovery solid content 7 is dispersed with the stirring bar 10. It can also be washed while being dispersed by ultrasonic dispersion. Further, by using a basic aqueous solution for the cleaning liquid 9, it is considered that the same effect as the cleaning with the basic aqueous solution 17 described later is obtained, and the effect of removing impurities is high. In this case, it is considered that the impurity removal effect is further enhanced by performing the cleaning with the basic aqueous solution that is the cleaning liquid 9 and the cleaning with the basic aqueous solution 17.
The solid content 7 for silicon recovery can be dispersed and washed while being diluted with the washing liquid 9. The washing time is not particularly limited, but is preferably 30 minutes or more.
Examples of the acidic aqueous solution used as the cleaning liquid 9 include a solution containing an inorganic acidic substance or an organic acidic substance. Examples of the inorganic acidic substance include hydrogen chloride, sulfuric acid, nitric acid, hydrofluoric acid, and hydrogen bromide. Examples of the organic acidic substance include citric acid, acetic acid, formic acid, oxalic acid, and lactic acid. The acidic aqueous solution only needs to contain at least one kind of acidic substance, and may contain both an inorganic acidic substance and an organic acidic substance.

As the basic aqueous solution used as the cleaning liquid 9, for example, an aqueous solution of an alkali metal hydroxide such as sodium hydroxide or calcium hydroxide or an aqueous ammonia solution can be used. This basic aqueous solution is desirably a weak base in order to suppress reaction with silicon, and an aqueous ammonia solution is preferred.
The organic solvent used as the cleaning liquid 9 preferably has a property of dissolving the water-soluble coolant 4 and has a boiling point lower than that of the water-soluble coolant 4. For example, the organic solvent has 1 to 6 carbon atoms (preferably 1, 2 or 2). Alcohol in the range between any two of 3, 4, 5 and 6) or a ketone in the range between any two of 3 to 6 carbon atoms (preferably 3, 4, 5 and 6). . More preferably, the organic solvent is one selected from the group consisting of methanol, ethanol, isopropyl alcohol and acetone, or a mixture of two or more.
The cleaning liquid 9 may use at least one of water, an acidic aqueous solution, and an organic solvent or two or more in combination.

4). Solid / Liquid Separation of Silicon Recovering Solid Content and Liquid Content The cleaning liquid 9 in which the silicon recovering solid content 7 is dispersed is subjected to solid-liquid separation to obtain a silicon recovery solid content 15 containing silicon scraps 2 and a liquid content 12. To separate. Further, along with this separation, solid-liquid separation may be performed while supplying a cleaning liquid or water to the solid content for silicon recovery. Further, the supply of the cleaning liquid or water and the solid-liquid separation may be alternately repeated a plurality of times.
The method of solid-liquid separation is not particularly limited, and examples thereof include centrifugation and filtration.
Through this step, a silicon recovery solid content 15 having an oil content of 1% by mass or less can be obtained.
The apparatus used for cleaning and solid-liquid separation of the silicon recovery solid content 7 with the cleaning liquid 9 may be any apparatus capable of supplying the cleaning liquid and solid-liquid separation. For example, a centrifuge, a filtration apparatus, etc. It is preferable that two or more solid-liquid separation devices and a cleaning agent supply device are combined in series.

By washing the silicon recovery solid content 7 with the cleaning liquid 9 to obtain the silicon recovery solid content 15, most of the impurities contained in the silicon recovery solid content 7 can be removed. The effect of removing impurities by cleaning using the acidic aqueous solution 20 can be further enhanced.
In the solid content 15 for silicon recovery, there are aggregates 27 in which silicon scraps 2 and the like are aggregated, and the water-soluble coolant 4 inside the aggregates 27, the chemically reacted components thereof, and the metal scraps generated from the processed member Etc. are not considered to be removed. The reason why the silicon scrap 2 or the like forms the aggregate 27 is not clear, but, for example, a high molecular organic compound formed by the reaction of an organic component such as the water-soluble coolant 4 by the heat accompanying the machining of the silicon lump 1 is bonded. It is thought that it plays the role of an agent and agglomerates silicon scraps 2 and the like.
FIG. 2 is an explanatory diagram for explaining the aggregate 27. FIG. 2A is a schematic diagram for explaining the state of the silicon scrap 2 in the cleaning liquid 9 in which the solid content 7 for silicon recovery is dispersed. FIG. As shown in FIG. 2A, since the silicon scrap 2 in the cleaning liquid 9 is considered to form an aggregate 27, it is considered that impurities inside the aggregate 27 cannot be sufficiently removed by the cleaning liquid 9. It is done. In addition, when a basic aqueous solution is used for the cleaning liquid 9, it is considered that there is an effect similar to the cleaning with the basic aqueous solution 17 described later. Therefore, it is considered that impurities inside the aggregate 27 that cannot be removed by the cleaning liquid 9 are reduced.

5. Washing with a basic aqueous solution of solids for silicon recovery The solids 15 for silicon recovery are dispersed in a basic aqueous solution 17 and washed. In addition, by stirring the basic aqueous solution 17 in which the solid content 15 for silicon recovery is dispersed with the stirrer 10, the solid content 15 for silicon recovery can be washed. It can also be washed while being dispersed by ultrasonic dispersion. Although the basic aqueous solution 17 will not be specifically limited if it is a basic aqueous solution, For example, they are ammonia aqueous solution and sodium hydroxide aqueous solution. Further, the cleaning time is not particularly limited, but for example, cleaning can be performed for 30 minutes.

  When the solid content 15 for silicon recovery is dispersed in water, the water exhibits a weak acidity with a pH of 5 to 6.5. It is considered that the basic aqueous solution is soluble. For this reason, by washing the solid content 15 for silicon recovery with the basic aqueous solution 17, the aggregate 27 contained in the solid content 15 for silicon recovery can be dispersed and cannot be removed by washing with the cleaning liquid 9. An organic compound or the like that is soluble in a basic aqueous solution can be removed.

  The basic aqueous solution 17 preferably has a pH value of 9 or more and 11 or less. The basic aqueous solution 17 is preferably an aqueous ammonia solution. Since silicon is generally dissolved in a basic aqueous solution, it is considered that the recovery rate of the silicon scrap 2 is reduced by washing the solid content 15 for silicon recovery with the basic aqueous solution. It was confirmed by an experiment described later that when the value is 9 or more and 11 or less, the dissolution of silicon in the aqueous ammonia solution that is the basic aqueous solution 17 is suppressed. The reason for this is not clear, but it is considered that the polymer organic compound or the like attached to the silicon scrap 2 suppresses the reaction between silicon and alkali. Further, by washing the silicon recovery solids 15 with an aqueous ammonia solution, which is a basic aqueous solution having a pH value of 9 or more and 11 or less, the particle size of the particles contained in the silicon recovery solids 15 is reduced by an experiment described later. It was confirmed that From this, it is considered that the aggregate 27 contained in the solid content 15 for silicon recovery is dispersed by washing with the basic aqueous solution 17.

FIG. 2B is an explanatory diagram for explaining the state of the silicon scrap 2 in the basic aqueous solution 17 in which the silicon recovery solid content 15 is dispersed. In the basic aqueous solution 17, it is considered that the silicon scrap 2 forming the aggregate 27 is dispersed as shown in FIG. 2B, and therefore cannot be removed due to the presence of the aggregate 27. Impurities are dispersed in the basic aqueous solution 17, and impurities soluble in the basic aqueous solution are considered to be removed.
Moreover, the pH value of the basic aqueous solution 17 can be easily controlled in the range of 9 or more and 11 or less by using the basic aqueous solution 17 as an aqueous ammonia solution.
The cleaning device used in this step may be any device that can supply a basic aqueous solution and perform solid-liquid separation. In one example, the cleaning device, a stirrer provided in the cleaning device, It is preferable to be configured with a sound wave oscillating device.

6). Washing with Acidic Aqueous Solution The acidic aqueous solution 19 is added to the basic aqueous solution 17 in which the silicon recovery solid content 15 is dispersed, whereby the solution in which the silicon recovery solid content 15 is dispersed is defined as the acidic aqueous solution 20. This makes the solution acidic in a state where the aggregate 27 contained in the solid content 15 for silicon recovery is dispersed in the solution, for example, in a state similar to the state shown in FIG. can do. As a result, it is considered that impurities such as metal scrap soluble in the acidic aqueous solution contained in the aggregate 27 can be removed.
The acidic aqueous solution 19 is not particularly limited as long as it is an acidic aqueous solution. For example, any one of hydrofluoric acid, hydrochloric acid, sulfuric acid, and nitric acid, or an inorganic acid solution of a mixture thereof can be used. Preferably, hydrofluoric acid can be used. This is because hydrofluoric acid is soluble in many impurities such as iron.

Further, the silicon recovery solid content 15 can be washed by stirring the acidic aqueous solution 20 in which the silicon recovery solid content 15 is dispersed with a stirrer. It can also be washed while being dispersed by ultrasonic dispersion.
As described above, after the solid content 15 for silicon recovery is washed with the basic aqueous solution 17 and then continuously washed with the acidic aqueous solution 20, the impurity removal effect can be dramatically enhanced. As a reason for this, it is presumed that the contact probability between the acidic aqueous solution 20 and the metal impurities is increased and the impurities are reduced because the dispersion of the solids 15 for silicon recovery progressed by washing with the basic aqueous solution 17.
Although pH of the acidic aqueous solution 20 should just be less than 7, 0-2 are preferable. The acidic aqueous solution 20 has a pH of, for example, 0, 0.5, 1, 1.5, or 2. The pH of the acidic aqueous solution 20 may be within a range between any two of the numerical values exemplified here.
Moreover, although the washing | cleaning time by the acidic aqueous solution 20 is not specifically limited, 1 hour or more is preferable.
The cleaning device used in this step may be any device that can supply an acidic aqueous solution and perform solid-liquid separation. For example, the cleaning device, a stirrer provided in the cleaning device, ultrasonic transmission It is preferable to be comprised with an apparatus.

7). Solid-liquid separation and drying of solids for silicon recovery Next, solid-liquid separation is performed on the acidic aqueous solution 20 in which the solids 15 for silicon recovery are dispersed to separate the liquids into solids 22 for silicon recovery including silicon waste 2. To do. Moreover, the solid content 22 for silicon recovery can be dried. As a result, it is possible to obtain the silicon recovery solid content 22 from which impurities are sufficiently removed. Further, along with this separation, solid-liquid separation may be performed while supplying a cleaning liquid or water to the solid content for silicon recovery. Further, the supply of the cleaning liquid or water and the solid-liquid separation may be alternately repeated a plurality of times. Moreover, you may remove the component of the acidic aqueous solution 20 by wash | cleaning the obtained solid content 22 for silicon | silicone collection | recovery with water.
The method of solid-liquid separation is not particularly limited, and examples thereof include centrifugation and filtration. Further, the acidic aqueous solution 20 may be evaporated using a dryer.

  The apparatus used in this step may be any apparatus that can supply water and perform solid-liquid separation. For example, a solid-liquid separation apparatus such as a centrifuge, a filtration apparatus or a distillation apparatus, and pure water Two or more supply devices are combined in series.

8). Melting step and silicon lump forming step Next, the silicon recovery solid component 22 can be melted by placing the silicon recovery solid component 22 in a crucible and heating it. Moreover, a silicon lump can be obtained by tilting the crucible containing the molten silicon, pouring molten silicon into a cooling container and cooling it. Thus, impurities such as abrasive grains can be left in the crucible, and only molten silicon can be discharged, so that a silicon lump from which impurities have been removed can be obtained.
Although the crucible which puts the silicon | silicone collection | recovery solid content 22 is not specifically limited, For example, it is a carbon crucible. Moreover, the temperature at which the solid content for silicon recovery 22 is melted is not particularly limited as long as the temperature is equal to or higher than the melting point of silicon. Further, the furnace for melting the silicon recovery solid content 22 is not particularly limited, and for example, an induction heating device can be used.

9. Cleaning step after melting Next, the obtained silicon lump can be washed with an acidic aqueous solution and a basic aqueous solution, respectively. As a result, it is possible to remove the reattached impurities and remove the metal (iron, aluminum, etc.) and the metal compound (iron silicide, etc.) in the silicon lump. In addition, the silicon lump can be appropriately pulverized (for example, a diameter of 1 cm or more and 10 cm or less) before the post-melting cleaning step. This is because the effect of removing impurities is increased.
Although acidic aqueous solution is not specifically limited, For example, hydrogen fluoride aqueous solution can be used. The basic aqueous solution is not particularly limited, and for example, a sodium hydroxide aqueous solution can be used.

10. Vacuum melting step Next, the silicon lump is charged into a crucible and heated to melt the silicon lump to obtain molten silicon. While stirring the molten silicon, the atmosphere can be reduced in pressure or vacuum. As a result, phosphorus contained in the molten silicon can be removed. Moreover, the silicon lump from which the impurity was removed can be obtained by cooling this molten silicon.
The atmosphere of the molten silicon is not particularly limited as long as it is a pressure capable of removing impurities such as phosphorus, but can be set to about 1 × 10 ⁻² Pa, for example.

11. Leaching step Next, the silicon lump can be pulverized into fine particles and washed in an acidic aqueous solution. Thereby, the heavy metal component deposited on the grain boundary can be removed.

12 Segregation process Next, molten silicon can be obtained by placing silicon fine particles in a crucible and heating. The molten silicon can be solidified in one direction to obtain a silicon mass. As a result, impurities gather in a part of the silicon lump, so that a portion containing a large amount of impurities can be removed and the remaining portion can be used as a silicon raw material for solar cells.
In addition, the order which performs a vacuum melting process, a leaching process, and a segregation process can be changed arbitrarily.

Experiment 1. Recovery experiment and silicon purification experiment of silicon waste using waste liquid generated by machining of silicon ingot using loose abrasive (Example 1)
<Centrifuge and distillation of waste liquid>
First, the silicon ingot was cut using a multi-wire saw and a processing slurry, and the waste liquid generated during the cutting of the silicon ingot was collected. Here, water-soluble oil (Luna Coolant, manufactured by Ochi Chemical Industry Co., Ltd.) is used as the coolant for the processing slurry, and silicon carbide GC # 1000 (average) made from Shinano is used as the free abrasive grains contained in the processing slurry. A particle size of about 11 μm) was used.

Next, the waste liquid 3 generated during the cutting process of the silicon ingot is put into a centrifuge and then centrifuged so that the centrifugal force becomes 500 G, whereby abrasive grains (free abrasive grains) are the main components. The solid content for recovering silicon and the liquid component containing the coolant and silicon waste as main components were separated.
Next, by adding the liquid component mainly composed of the coolant and silicon scrap obtained above to the centrifuge, by performing the centrifugal separation so that the centrifugal force becomes 3500G, Silicon scraps and abrasive grains were separated into the main component of silicon recovery solids.
Next, the solid content for silicon recovery obtained above was placed in an atmosphere having a temperature of 200 ° C. and a pressure of 76 Torr, and was distilled to separate the regenerated coolant 5 and the solid content 7 for silicon recovery. Table 1 shows the results of examining the content (weight) of impurities in the solid content 7 (first solid content) for silicon recovery after drying. In Table 1, ppm is mass ppm, and% is mass%. The same applies to the subsequent tables.

Here, the content of boron, phosphorus and iron in the solid content 7 for silicon recovery after drying is obtained by measuring boron with an ICP mass spectrometer and phosphorus and iron with ICP emission spectrometry (Inductively Coupled Plasma Spectrometry). Value.
In addition, the carbon content in the solid content 7 for silicon recovery after drying is determined by treating the solid content 7 for silicon recovery with a mixed solution of hydrofluoric acid (aqueous hydrogen fluoride) and nitric acid and an aqueous sodium hydroxide solution. It is a value calculated from the weight of the silicon carbide (abrasive grains) measured by measuring the weight of the residue after the treatment used.
The oil content in the silicon recovery solid content 7 is a value obtained by measuring the weight change of the silicon recovery solid content 7 using a suggestion thermobalance device.
Further, the oxygen content in the solid content 7 for silicon recovery is a value obtained by measurement using an energy dispersive X-ray analyzer manufactured by EDAX. The impurity content in the subsequent experiments was also measured in the same manner.

Moreover, it was observed that the external appearance of the solid content 7 for silicon recovery was an aggregate of several mm. In order to elucidate the cause of this aggregation, a solution obtained by dissolving the solid content 7 for silicon recovery in methanol was analyzed by gas chromatography. As a result, it was confirmed that there was an organic compound (hereinafter referred to as a glycol-modified product) in which glycol was considered to be decomposed or polymerized in addition to the main component of oil.
From these results, it was speculated that these organic compounds acted as adhesives to agglomerate silicon scraps, metal scraps, abrasive grains, and the like.
Therefore, the aggregate is an aggregate containing silicon, wire chips, and abrasive grains via an organic compound, and it is difficult to remove the wire chips inside the aggregate unless the glycol-modified product is removed. I found out.

<Cleaning with cleaning solution>
The dried silicon recovery solid content 7 was dispersed in pure water (25 ° C.) as a cleaning liquid, and the pure water was held for 1 hour while stirring.
Thereafter, the pure water in which the solid content for silicon recovery 7 was dispersed was filtered to separate into solid and liquid, and separated into a liquid content and a solid content for silicon recovery 15 (second solid content).
Next, the particle size distribution was measured for the solid content 15 for silicon recovery.
FIG. 3 is a particle size distribution diagram showing the results of the particle size distribution measurement performed on the silicon recovery solid content 15 (second solid content) and the silicon recovery solid content 22 (third solid content). It can be seen from FIG. 3 that the solid content 15 for silicon recovery has a particle size of 1 to 10 mm.
Moreover, when solid content 15 for silicon | silicone collection | recovery was disperse | distributed to water, this water showed weak acidity with a pH of 5-6.5. From this, it is considered that the polymer organic compound that is considered to aggregate silicon scraps is soluble in the basic aqueous solution.

<Washing with basic aqueous solution>
The solid content 15 for silicon recovery is dispersed in a basic aqueous solution 17 in an aqueous ammonia solution of about 1 to 10% by mass (mass ratio of the solid content 15 for silicon recovery and the aqueous ammonia solution 1: 5), and the aqueous ammonia solution is stirred. For 30 minutes.
<Washing with acidic aqueous solution>
Then, 25-50 mass% hydrofluoric acid which is the acidic aqueous solution 19 is added to the aqueous ammonia solution to obtain an acidic aqueous solution 20 having a pH of 1 or more and 2 or less, and the acidic aqueous solution 20 in which the solid content 15 for silicon recovery is dispersed. Was held for 1 hour with stirring.
Then, the acidic aqueous solution 20 in which the solid content 15 for silicon recovery was dispersed was filtered to separate the liquid component and the solid content 22 for silicon recovery. After rinsing off the hydrofluoric acid adhering to the silicon recovery solid content 22 with water, boron, phosphorus, iron, carbon, oxygen and oil in the silicon recovery solid content 22 (third solid content) in the same manner as described above. The content of was measured. The measurement results are shown in Table 1.

As shown in Table 1, it was confirmed that boron, phosphorus, iron and oxygen were removed from the solids for silicon recovery and oil was removed by the cleaning process using pure water, aqueous ammonia solution and hydrofluoric acid. .
Next, the particle size distribution measurement was performed for the solid content 22 (third solid content) for silicon recovery. The measurement results are shown in FIG. From FIG. 3, it was found that the silicon recovery solid content 22 had a particle size of about 1 mm. As compared with the particle size distribution of the silicon recovery solid content 15 (second solid content), it was found that the silicon recovery solid content 22 had a smaller particle size. From this, the silicon recovery solids 22 washed with the basic aqueous solution 17 and the acidic aqueous solution 20 are free from organic compounds that are considered to agglomerate silicon debris and the like, and silicon debris forming aggregates Etc. are estimated to be dispersed.

<Melting step and silicon lump formation step>
After the silicon recovery solid content 22 was put into the carbon crucible, the silicon recovery solid content 22 was melted by heating the carbon crucible to 1800 ° C. with an induction heating device to produce molten silicon.
Then, by tilting the carbon crucible, the molten silicon in the carbon crucible was discharged into a carbon mold cooling vessel. By cooling the molten silicon in the cooling container, the molten silicon was solidified to obtain a silicon lump.
About the silicon lump obtained in this way, the contents of boron, phosphorus, iron, carbon, oxygen and oil were measured in the same manner as described above. The measurement results are shown in Table 1. As shown in Table 1, it was confirmed that carbon and oxygen mainly contained in the abrasive grains (silicon carbide) were removed by the melting step and the silicon lump formation step.

<Post-melt washing step with hydrofluoric acid and aqueous sodium hydroxide>
The silicon lump formed as described above was crushed to a diameter of 1 cm or more and 10 cm or less, washed with hydrofluoric acid, and then washed with a sodium hydroxide solution. This makes it possible to remove the metal (iron, aluminum, etc.) and the metal compound (iron silicide, etc.) in the silicon block simultaneously with the removal of the reattachment impurities.
In the cleaning with hydrofluoric acid, the silicon lump was immersed in a hydrogen fluoride aqueous solution (25 ° C.) having a hydrogen fluoride concentration of about 1% by mass and held for 1 hour while stirring. And the hydrogen fluoride aqueous solution adhering to the silicon lump was washed away with water.
In washing with an aqueous sodium hydroxide solution, the silicon mass after the aqueous hydrogen fluoride solution is washed away with water as described above is placed in an aqueous sodium hydroxide solution (25 ° C.) having a sodium hydroxide concentration of about 3 mass% to 5 mass%. It was immersed in and held for 1 hour with stirring. Thereafter, the aqueous sodium hydroxide solution adhering to the silicon mass was washed away with water.

And about the silicon lump which performed these washing | cleaning, it carried out similarly to the above, and measured content of boron, phosphorus, iron, carbon, oxygen, and oil. The measurement results are shown in Table 1.
As shown in Table 1, a large amount of carbon and oxygen contained in the abrasive grains (silicon carbide) are removed from the silicon lump by the above-described cleaning step using an aqueous hydrogen fluoride solution and the cleaning step using an aqueous sodium hydroxide solution. It was confirmed that iron was also removed slightly.

<Vacuum melting process>
Next, after the silicon lump washed with the sodium hydroxide aqueous solution as described above was put into the carbon crucible, the carbon crucible was heated to 1600 ° C. by an induction heating device to melt the silicon lump to produce molten silicon.
Then, while maintaining the carbon crucible containing the molten silicon at 1600 ° C., the pressure in the container in which the carbon crucible was installed was set to about 10 ⁻² Pa, and the molten silicon was held for 3 hours while stirring.

<Leaching process>
After pulverizing the silicon lump after the above-mentioned vacuum melting step so that the silicon powder having a particle size of 1 mm or less has a particle size distribution of 98% or more, 5 mass% It was immersed in hydrofluoric acid (25 ° C.) and held for 4 hours with stirring. Then, hydrofluoric acid adhering to the silicon powder was washed away with water.
In addition, the measurement of particle diameter distribution means what was measured by the method based on JISR1629.

<Segregation process>
The silicon powder after the above leaching process was melted to obtain molten silicon, and then unidirectional solidification was performed. Specifically, 250 kg of silicon is melted and unidirectionally solidified to obtain a silicon block of 680 mm square × 235 mm in height, and the upper 30 mm of the silicon, 10 mm of each side, and 10 mm of the lower part are cut and removed with a band saw. The inner 660 mm square × 195 mm (200 kg) was used as the silicon raw material for solar cells.
Thereafter, in the same manner as described above, the contents of boron, phosphorus, iron, carbon, oxygen, and oil of the silicon raw material for solar cells were measured. The measurement results are shown in Table 1.
As shown in Table 1, it was confirmed that a large amount of carbon and oxygen contained in iron and abrasive grains (silicon carbide) were removed by the segregation process.

2. Example of silicon waste recovery experiment and silicon purification experiment using waste liquid generated by machining of silicon lump using fixed abrasive (Example 2)
<Recovery and distillation of waste liquid>
While applying a coolant mainly composed of propylene glycol using a multi-wire saw device with diamond attached to the wire and a plated wire (fixed abrasive wire) to suppress the peeling of the diamond, Cutting was performed. Solid waste was recovered from the waste liquid recovered from this multi-wire saw apparatus using a distillation apparatus in the same manner as in Example 1 to obtain a solid content 7 for silicon recovery. About this silicon | silicone collection | recovery solid content 7 (1st solid content), content of boron, phosphorus, iron, carbon, oxygen, and oil was measured. The measurement results are shown in Table 2.

  As shown in Table 2, it was found that the solid content 7 for silicon recovery obtained in this experiment had a very large amount of oil components. Moreover, since the fixed abrasive wire was used, it turned out that the content rate of the carbon which is an abrasive grain component is very short compared with the silicon | silicone collection | recovery solid content 7 collect | recovered by Example 1. FIG.

<Cleaning with cleaning solution>
The solid content 7 for silicon recovery after drying was immersed in pure water (25 ° C.) as the cleaning liquid 9, and the pure water was held for 1 hour with stirring. Thereafter, solid-liquid separation was performed by filtration to obtain a solid content 15 for silicon recovery.

<Basic aqueous solution washing process>
The solid content 15 for silicon recovery after washing was immersed in a basic aqueous solution 17 of about 1 to 10% by mass of ammonia aqueous solution (solid-liquid mass ratio 1: 5), and the aqueous ammonia solution was held for 30 minutes while stirring. .
<Acid aqueous solution washing process>
Then, 25-50 mass% hydrofluoric acid which is the acidic aqueous solution 19 was added in the ammonia aqueous solution, and it was set as the acidic aqueous solution 20 whose pH is 1 or more and 2 or less. The solid content 15 for collecting silicon was dispersed in the acidic aqueous solution 20 and held for 1 hour with stirring. The acidic aqueous solution 20 was subjected to solid-liquid separation and washing with water to obtain a silicon recovery solid content 22 (third solid content).

After rinsing the hydrofluoric acid adhering to the silicon recovery solids 22 with water, the boron, phosphorus, iron, carbon, oxygen, and oil of the silicon recovery solids 22 (third solids) in the same manner as described above. The content was measured. The measurement results are shown in Table 2. As shown in Table 2, it was confirmed that boron, phosphorus, iron and oxygen were removed from the solid content for silicon recovery and oil was removed by the cleaning process using pure water, aqueous ammonia solution and hydrofluoric acid. .
Further, the C concentration is about 0.1% by mass, which is considered to be caused by peeling and abrasion of diamond from the slice wire.

  The silicon recovery solid content 7 obtained from the waste liquid obtained by machining the silicon lump using the fixed abrasive has a very high oil ratio of 50% by mass. It was found that the oil component can be almost removed by washing with water and washing with the acidic aqueous solution 20. It was also found that the ability to remove most of the oil component can suppress the formation of SiC in the melting step by the glycol-modified product.

<Melting step and silicon lump formation step>
As described above, after the hydrofluoric acid is washed away with water and dried, the silicon recovery solid content 22 is put into the carbon crucible, and then the carbon crucible is heated to 1800 ° C. by an induction heating device to thereby obtain the silicon recovery solid content 22. Molten silicon was produced by melting.
Then, by tilting the carbon crucible, the molten silicon in the carbon crucible was discharged into a carbon mold cooling vessel. By cooling the molten silicon in the cooling container, the molten silicon was solidified to obtain a silicon lump.
About the silicon lump obtained in this way, the contents of boron, phosphorus, iron, carbon, oxygen and oil were measured in the same manner as described above. The measurement results are shown in Table 2.
As shown in Table 2, it was confirmed that carbon (silicon carbide as abrasive grains) and oxygen were removed by the melting step and the silicon lump formation step.

  As described above, the solid content 7 for silicon recovery obtained from the waste liquid discharged when the silicon lump is cut using the fixed abrasive grains has 0.1% carbon component (abrasive grain component) and free abrasive grains. It was found that the effect of the abrasive grain component was small and the separability between Si and other components was good because it was very small compared to the case of. It was also found that the recovery rate of silicon was high.

<Post-melt washing step with hydrofluoric acid and aqueous sodium hydroxide>
The silicon lump formed as described above was immersed in a hydrogen fluoride aqueous solution (25 ° C.) having a hydrogen fluoride concentration of about 1% by mass and held for 1 hour while stirring. And the hydrogen fluoride aqueous solution adhering to the silicon lump was washed away with water.
Then, the silicon mass after the aqueous solution of hydrogen fluoride is washed away with water as described above is immersed in a sodium hydroxide aqueous solution (25 ° C.) having a sodium hydroxide concentration of about 3% by mass to 5% by mass and stirred. For 1 hour. Thereafter, the sodium hydroxide aqueous solution adhering to the silicon lump was washed away with water, and the contents of boron, phosphorus, iron, carbon, oxygen and oil in the silicon lump were measured in the same manner as described above. The measurement results are shown in Table 2.

As shown in Table 2, carbon (abrasive silicon carbide) and oxygen are removed from the silicon lump by the above-described cleaning step using an aqueous hydrogen fluoride solution and the cleaning step using an aqueous sodium hydroxide solution. Was also confirmed to be slightly removed.
In addition, since the solid content for silicon recovery contained in the waste liquid 3 generated by cutting the silicon lump using the fixed abrasive wire is washed with the cleaning liquid 9, the basic aqueous solution 17, and the acidic aqueous solution 20, respectively, the C and O concentrations are low. The post-melting cleaning step may be omitted.

<Vacuum melting process / Segregation purification / Leaching>
The silicon lump after the post-melting cleaning step was remelted and held at a temperature of 1650 ° C. or higher at a pressure of 1 Torr or lower for 10 hours to reduce phosphorus in the silicon.
Furthermore, in order to remove metal impurities, unidirectional solidification using segregation was performed.
When performing unidirectional solidification, if the concentration of C (SiC) and O is high, solidification starting from C (SiC), which has a particularly high melting point, may occur. May be.
Since the silicon lump obtained from the silicon recovery solid content 22 has a low C concentration, it is easy to remove metal impurities by segregation.
Further, in order to remove metal impurities, the silicon lump is finely pulverized to a particle size of about 0.1 to 2 mm, and the metal impurities precipitated at the grain boundaries are washed with hydrofluoric acid or a mixed solution of hydrofluoric acid and nitric acid. The leaching process was performed.
Thereafter, the content of boron, phosphorus, iron, carbon, oxygen, and oil was measured for the silicon fine particles after the leaching step in the same manner as described above. The measurement results are shown in Table 2.

3. First comparative experiment As a first comparative experiment, in the same manner as the above-mentioned step of “1. Silicon scrap recovery experiment and silicon purification experiment using waste liquid generated by machining a silicon ingot using loose abrasive grains” Silicon purification experiments were performed. However, cleaning using the aqueous ammonia solution that is the basic aqueous solution 17 of the silicon recovery solid content 15 was not performed, and cleaning using the hydrofluoric acid that was the acidic aqueous solutions 19 and 20 was performed on the silicon recovery solid content 15. .
Table 3 shows the results of measurement of the contents of boron, phosphorus, iron, carbon, oxygen and oil performed in this experiment.

Table 1 compares the content of each impurity in the solid content for silicon recovery 22 (third solid content) in Table 1 with the content of each impurity in the solid content for silicon recovery 22 (third solid content) in Table 3. It was found that Fe, P, and oil components were removed more effectively in Example 1 of the present invention, which was washed with the basic aqueous solution 17 shown in FIG.

4). Second comparative experiment As a second comparative experiment, in the same manner as the above-mentioned process of “2. Retrieval experiment of silicon waste and waste silicon refining experiment using waste liquid generated by machining silicon lump using fixed abrasive” Silicon purification experiments were performed. However, cleaning using the aqueous ammonia solution that is the basic aqueous solution 17 of the silicon recovery solid content 15 was not performed, and cleaning using the hydrofluoric acid that was the acidic aqueous solutions 19 and 20 was performed on the silicon recovery solid content 15. .
Table 4 shows the results of measurement of boron, phosphorus, iron, carbon, oxygen and oil contents performed in this experiment.

Table 2 compares the content of each impurity in the solid content for silicon recovery 22 (third solid content) in Table 2 with the content of each impurity in the solid content for silicon recovery 22 (third solid content) in Table 4. It was found that Fe, P, and oil components were removed more effectively in the example of the present invention in which washing was performed with the basic aqueous solution 17 shown in FIG.

  From these results, it was found that Fe, P, and oil components can be effectively removed according to the silicon-containing waste liquid treatment method of the present invention. Moreover, in the silicon purification using the silicon recovery solid content 22 obtained by the silicon-containing waste liquid treatment method of the present invention, if the segregation purification treatment is performed, the crucible life of the segregation purification can be increased. Furthermore, in the silicon purification using the silicon recovery solid content 22 obtained by the silicon-containing waste liquid treatment method of the present invention, when performing the vacuum melting treatment, the vacuum melting treatment time can be reduced. That is, when the silicon-containing waste liquid treatment method of the present invention is used, the cost of refining and reusing silicon waste can be reduced.

  The present invention makes it possible to recycle coolant used for manufacturing silicon wafers for solar cells, for example, by obtaining recycled coolant and recycled silicon from waste fluid discharged by silicon processing, and solar cells from waste fluid that has been discarded in the past. The polycrystalline silicon raw material can be recycled.

    1: Silicon lump 2: Silicon scrap 3: Waste liquid 4: Water-soluble coolant 5: Recycled coolant 7: Solid content for silicon recovery (first solid content) 9: Cleaning liquid 10: Stirrer 12: Liquid content 15: Solid for silicon recovery Minute (second solid content) 17: Basic aqueous solution 19: Acidic aqueous solution 20: Acidic aqueous solution 22: Solid content for silicon recovery (third solid content) 23: Liquid content 25: Recycled silicon mass 27: Aggregate

Claims (9)

Recycled from waste liquid or concentrated liquid waste discharged by machining silicon lump using metal processing member while supplying water-soluble coolant mainly composed of glycol or water-soluble slurry containing water-soluble coolant A silicon-containing waste liquid treatment method for obtaining a coolant and a regenerated silicon mass,
Separating the recycled liquid and the solid content for silicon recovery by distilling the waste liquid or a concentrated content of the waste liquid;
After the solid content for silicon recovery is dispersed and washed in a cleaning liquid, and then solid-liquid separation into the solid content for silicon recovery and the liquid content;
Dispersing and washing the solids for silicon recovery in a basic aqueous solution;
A step of sequentially washing the solids for recovering silicon in an acidic aqueous solution by adding an acidic aqueous solution to the basic aqueous solution without performing solid-liquid separation of the basic aqueous solution and the solids for recovering silicon. A silicon-containing waste liquid treatment method comprising:   The method according to claim 1, wherein the solid content for silicon recovery washed in the acidic aqueous solution has an iron concentration of 5 ppm by weight to 20 ppm by weight.   The method according to claim 1 or 2, wherein the basic aqueous solution for washing the solid content for silicon recovery has a pH value of 9 or more and 11 or less.   The method according to any one of claims 1 to 3, wherein the basic aqueous solution for washing the solid content for silicon recovery is an aqueous ammonia solution.   The method according to claim 4, wherein the aqueous ammonia solution has an ammonia concentration of 0.001% by mass or more and 1% by mass or less.   The method according to any one of claims 1 to 5, wherein the solid content for silicon recovery is dispersed and washed in the basic aqueous solution having a weight of 2 to 20 times.   The method according to any one of claims 1 to 6, wherein the acidic aqueous solution for washing the solid content for silicon recovery has a pH value of 0 or more and 2 or less.   The method according to claim 1, wherein the acidic aqueous solution added to the basic aqueous solution is hydrofluoric acid.   The method according to any one of claims 1 to 8, wherein the cleaning liquid for cleaning the solid content for silicon recovery is water, an acidic aqueous solution, a basic aqueous solution, or an organic solvent.

Images