JP5244500B2 - Silicon purification method and silicon purification apparatus - Google Patents

Description

  The present invention relates to a silicon purification method, a silicon purification apparatus, and recycled abrasive grains.

In the manufacturing process of a thin plate made of silicon single crystal or polycrystal (hereinafter referred to as “silicon wafer”) widely used for IC chips and solar cells, about 60% of the raw material silicon is waste liquid by cutting, chamfering or polishing. It is the silicon powder inside. For this reason, the cost burden on the product and the environmental burden associated with disposal (this waste liquid is generally disposed of in landfill after concentration processing and recovery of some materials) are serious problems.
In particular, in recent years, the production of solar cells has been steadily increasing, and the demand for raw material silicon has been increasing rapidly. For this reason, a shortage of silicon for solar cells has become apparent.
Therefore, a method for recovering silicon from waste liquid generated during the manufacture of silicon wafers such as cutting or polishing is desired. However, since silicon carbide, silicon nitride, diamond and the like, which are components of abrasive grains contained in the waste liquid, are chemically inert, it is difficult to remove them using a chemical reaction. For this reason, it is difficult to reuse silicon contained in the waste liquid generated when machining silicon. Therefore, a method for recovering silicon from waste liquid generated during the manufacture of a silicon wafer, such as cutting or polishing, has been proposed.

For example, in Patent Document 1, while supplying a slurry in which abrasive grains are dispersed in a dispersant, an ingot composed of a single crystal or a polycrystal of silicon is discharged from a waste slurry discharged in a process of cutting with a metal cutting means. A silicon recovery method is disclosed in which abrasive grains are recovered and an organic solvent cleaning step and a separation step are performed. In the organic solvent cleaning step, the sludge from which the dispersant has been removed is used, and this sludge is washed with an organic solvent to remove the dispersant contained in the sludge. In the separation step, the metal, silicon oxide, and abrasive grains are removed from the solid content after the removal of the dispersant to obtain a powder mainly composed of silicon.
That is, in Patent Document 1, although the sludge obtained by removing the dispersant and abrasive grains from the waste slurry is used as a raw material, the abrasive grains are further removed in a separation step by classification.

Patent Document 2 discloses a very complicated process in which abrasives (abrasive grains) used for polishing or cutting are magnetized chemically or colloidally and collected by magnetic separation. Has been.
JP 2001-278612 A JP 2002-292565 A

However, in patent document 1 and patent document 2, in order to remove an abrasive grain from the mixed powder of a silicon powder and an abrasive grain, a complicated process is required. Moreover, in patent document 1, 2 weight% of silicon carbide is contained in the collect | recovered silicon powder.
The present invention has been made in view of such circumstances, and a silicon purification method capable of removing impurities from waste liquid generated when silicon is machined by a simpler method than before, and A silicon purification apparatus that can be preferably used in the present purification method is provided.
Furthermore, the present invention provides regenerated abrasive grains recovered by the silicon purification method of the present invention and having better crystallinity than conventional ones.

Means and effects for solving the problem

  The silicon purification method of the present invention includes a powder separation step of separating powder containing silicon powder having silicon oxide from waste liquid generated when machining silicon, and a heating container under reduced pressure or inert gas atmosphere. The powder is heated to a temperature not lower than the melting point of silicon and not higher than 2000 ° C. to form a molten metal in which silicon is melted, and the high-viscosity silicon oxide adhering to the inner wall or bottom of the heating vessel contained in the molten metal is heated. And a hot water discharge step of leaving the silicon melt having a low viscosity to the cooling container.

  In the present invention, powder containing silicon powder having silicon oxide obtained from waste liquid generated when machining silicon is stored in a heating container by a storing process. Then, it is heated to a temperature not lower than the melting point of silicon and not higher than 2000 ° C. by a melting step to form a molten metal in a heating container. In this molten metal, silicon is a molten silicon melt having a low viscosity. Moreover, the silicon oxide contained in the silicon powder has a high viscosity and is in a water tank shape. When this molten metal is stirred by convection in the heating container, silicon oxide having a high viscosity adheres to the inner wall or bottom of the heating container. As a result, the silicon melt having a low viscosity can be discharged from the heating container to the cooling container while the high-viscosity silicon oxide remains in the heating container. Purified high-purity silicon can be obtained by solidifying the silicon melt in the cooling container.

In the present invention, purified high-purity silicon can also be obtained when the powder contains abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining.
That is, when the powder contains abrasive grains, the molten metal contains abrasive grains. The abrasive grains generated from the fixed abrasive grains or loose abrasive grains are solid in the molten metal and have a density higher than that of the silicon melt. As a result, the abrasive grains adhere to the high-viscosity silicon oxide adhering to the inner wall or bottom of the heating container by convection of the molten metal in the heating container. As a result, in the hot water discharge process, the silicon melt having a low viscosity can be discharged from the heating container to the cooling container while the abrasive grains remain in the heating container together with the silicon oxide having a high viscosity.

In this way, by performing a melting step and a hot water discharge step on the silicon powder containing silicon oxide, or the silicon powder containing silicon oxide and the powder containing abrasive grains, silicon oxide or silicon oxide and It is possible to remove the abrasive grains and refine the silicon. In addition, high-purity silicon that is easily purified to a level that can be preferably used as a silicon material used for solar cells or the like can be obtained. For this reason, the shortage of silicon for solar cells can be solved, and the amount of waste can be further reduced.
Further, by recovering the abrasive grains from the silicon oxide and abrasive grains adhering to the heating container, crystallization is promoted and the strength is high, and regenerated abrasive grains having a particle diameter of about 1 μm or submicron can be obtained.
Hereinafter, various embodiments of the present invention will be exemplified.

The fixed abrasive or the loose abrasive may include silicon carbide, silicon nitride, or diamond.
The machining may be cylindrical grinding, cutting, polishing or wafer slicing of silicon.
The powder separation step includes (1) a method of obtaining a solid portion by capturing and drying the solid content using a filter or a centrifuge, and (2) collecting or heating or distilling the waste liquid. A solid part separation step, which is a step including at least one of a method for obtaining a solid part and (3) a method for obtaining a solid part using a flocculant with respect to the waste liquid, may be included.
The powder separation step may further include a washing step of washing the solid portion obtained by the solid partial separation step using at least one of water, an acid solution, an alkaline solution, and an organic solvent.
You may further provide the residual part collection | recovery process which collect | recovers the residual part which is a part which was not discharged in the said hot water extraction process.
The powder includes abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining, and the residual portion containing the abrasive grains is mixed with an acid solution or an alkali solution to separate the abrasive grains. You may further provide an abrasive grain collection | recovery process.
You may further provide the classification process of sieving or classifying the said abrasive grain obtained by the said abrasive grain collection | recovery process.
The present invention also provides regenerated abrasive grains obtained by the abrasive grain recovery step or the classification step.

The present invention includes a heating container in which a powder containing silicon powder containing silicon oxide, which is separated from a waste liquid generated when machining silicon, is used as a molten metal, heating means for heating the heating container, and the molten metal. A melting furnace having a means for discharging a molten silicon melt, a cooling container for storing and cooling a low-viscosity silicon melt contained in the molten metal, and a high-viscosity silicon oxide adhering to the inner wall or bottom of the heating container A refining part container for containing a remnant part including the melting furnace, the cooling container, and the remnant part container.
The powder may include abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining.
The machining may be cylindrical grinding, cutting, polishing or wafer slicing of silicon.
You may further provide the residual part collection | recovery mechanism which scrapes off the said residual part containing the silicon oxide adhering to the inner wall or bottom of the said heating container by a physical method, and moves to the said residual part container.
The powder includes abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining, and the residual portion containing the abrasive grains is mixed with an acid solution or an alkali solution to separate the abrasive grains. A cleaning mechanism may be further provided.
You may further provide the classification mechanism which sifts or classifies the said abrasive grain isolate | separated by the said washing | cleaning mechanism.
The various embodiments shown here can be combined with each other.

  Hereinafter, an embodiment of the present invention will be described. 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.

FIG. 1 is a flowchart of a silicon purification method according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view of a silicon purification apparatus used in the silicon purification method of one embodiment of the present invention.
In the silicon refining method of one embodiment of the present invention, the powder 3 containing the silicon powder 4 or the powder 3 containing the silicon powder 4 and the abrasive grains 5 is first obtained with respect to the waste liquid 1 generated when silicon is machined. A separation step is performed. In the powder separation step, a solid partial separation step for removing the liquid portion in the waste liquid 1 can be performed, and the solid portion 2 can be obtained by the solid partial separation step. The solid portion 2 may be the same as the powder 3. Moreover, in the powder separation process, a cleaning process for removing metal components and the like of the solid portion 2 can be performed, and the powder 3 including the silicon powder 4 or the powder 3 including the silicon powder 4 and the abrasive grains 5 is obtained by the cleaning process. You can also. Then, the high purity silicon 6 can be obtained by performing a storing process, a melting process, and a tapping process for the powder 3 using the silicon purification device 24. Moreover, the reproduction | regeneration abrasive grain 8 can also be obtained by performing a residual part collection | recovery process, an abrasive grain collection | recovery process, and a classification process.
Hereinafter, this embodiment will be described.

1. 1. Silicon purification method and purification apparatus 1-1. Silicon machining Various machining processes are performed on silicon in a silicon processing process such as a manufacturing process of a thin plate (silicon wafer) made of silicon single crystal or polycrystal. The machining of silicon is not particularly limited, and includes, for example, cylindrical grinding, cutting, polishing, wafer slicing, dicing cutting, and peripheral cutting of silicon. What is used for the machining of these silicon differs depending on the machining, but for example, one or more of water, lubricating oil, cutting blade, wire, loose abrasive and fixed abrasive are used.
The loose abrasive grains are powdery abrasive grains and are generally used in a state of being liberated in water and lubricating oil. Fixed abrasive grains are abrasive grains fixed with a binder or the like.
Further, the loose abrasive grains and the fixed abrasive grains are not particularly limited, but, for example, those containing at least one of silicon carbide, silicon nitride or diamond are used.

The waste liquid 1 obtained by machining these silicons is different depending on each process, but generally includes the following.
(1) Moisture (2) Silicon powder 4 produced by cutting silicon. The silicon powder 4 has an oxide film (silicon oxide) on the surface. The silicon powder 4 has a particle size of 0.001 μm to 99.9 μm. The silicon powder 4 has a high oxide film (SiO _x ) ratio.
(3) Abrasive grains 5 generated from fixed abrasive grains and free abrasive grains used in machining.
(4) Metal component generated from cutting blade, wire, etc. (5) Oil component of lubricating oil

1-2. Powder Separation Step In the powder separation step, powder 3 containing silicon powder 4 or powder 3 containing silicon powder 4 and abrasive grains 5 is obtained from waste liquid 1 generated when silicon is machined. The powder separation step can include a solid partial separation step. Further, the powder separation step can include a washing step.
FIG. 3 is a flowchart of a powder separation process for each machining of silicon according to an embodiment of the present invention.

1-2-1. Solid part separation process The solid part 2 can be obtained from the waste liquid 1 by the solid part separation process. The solid part 2 may be the same as the powder 3. In the solid partial separation step, (1) a method of obtaining the solid portion 2 by capturing and drying the solid content of the waste liquid 1 using a filter or a centrifuge, and (2) collecting and heating or distilling the waste liquid 1. The method includes at least one of a method for obtaining the solid portion 2 by (3) and a method for obtaining the solid portion 2 from the waste liquid 1 using a flocculant.
The solid portion 2 may contain an oil component and a metal component. The solid part 2 may be a powder 3.
The solid partial separation step is not particularly limited, but an example of the solid partial separation step for the waste liquid 1 generated when specific silicon machining is performed will be described below.

1-2-1-1. When silicon peripheral cutting, cutting, and grinding are performed Silicon machining can be performed using, for example, a cylindrical grinder, a band saw, a surface grinder, a rotary grinder, a multi-wire saw, or the like. Water or oil can be used as the lubricant. A solid partial separation step can be performed on the waste liquid 1 generated by machining these silicon. For example, when circulating water or oil, collecting cutting waste by filtering or centrifuging, collecting the cutting waste by squeezing the water or oil after cutting with a filter press, or using a flocculant The solid part 2 can be obtained, for example, by collecting cutting waste.
As the flocculant, for example, anionic and cationic polymer flocculants can be applied. However, it may be necessary to remove the flocculant using an organic solvent that is soluble in the flocculant used in the subsequent step.
When silicon outer peripheral cutting or cutting is performed, metal impurities may be included, and the ratio of the oxide film of the silicon powder 4 may be high.

1-2-1-2. When silicon is polished or diced and cut The silicon can be machined using, for example, a polishing apparatus or a dicing saw. Water is often used for the lubricant. A solid partial separation step can be performed on the waste liquid 1 generated by machining these silicon. For example, the solid portion 2 can be recovered by using the waste liquid 1 as a cutting waste using a filter press, a centrifuge, or the like.
In many cases, a polishing pad used for polishing silicon or a dicing blade used for dicing cutting is one in which diamond is dispersed as fixed abrasive grains. For this reason, the recovered solid portion 2 often contains diamond as the abrasive grains 5. Moreover, the ratio of the oxide film of the silicon powder 4 may be large.

1-2-1-3. When a silicon wafer is manufactured Silicon processing can be performed using a multi-wire saw. As the lubricant, water-soluble or oil-based oil is often used. Specifically, a slurry can be produced by mixing free abrasive grains such as silicon carbide and silicon nitride in a lubricant, and cutting can be performed by feeding the silicon while running a metal wire.
For example, the solid portion 2 can be recovered by recovering the slurry after cutting and using the slurry as a cutting waste using a method such as filter pressing or centrifugation.
The solid portion 2 collected by this method often contains abrasive grains 5 such as oil components, metal powder derived from wires, silicon carbide, and silicon nitride. Moreover, the ratio of the oxide film of the silicon powder 4 may be large.
Specifically, using a multi-wire saw, water, water-soluble or oil-based oil is used as the lubricant, and a wire with diamond or other fixed abrasive grains fixed in the metal wire is fed to the silicon to feed it. Can also be cut.
For example, when water or oil is circulated, the solid part 2 is collected by collecting cutting waste by filtering or centrifuging, or by collecting the cutting waste by squeezing the water or oil after cutting with a filter press or the like. Can be obtained.
In many cases, the solid portion 2 collected by this method contains a relatively large amount of abrasive grains 5 such as metal powder and diamond derived from a wire. Moreover, the ratio of the oxide film of the silicon powder 4 may be large. In addition, when water-soluble or oil-based oil is used for the lubricant, an oil component is also included.

1-2-1-4. When water-soluble or oil-based oil is used When water-soluble or oil-based oil is used, considering the reuse of the oil, the slurry after cutting is recovered, distilled, and the solid is recovered. 2 can also be recovered. The solid portion 2 obtained by this method has a relatively low content of oil components. Moreover, the liquid obtained by distillation can also be reused as oil. As a result, the amount of waste can be reduced.

1-2-2. Washing Step In the washing step, the solid portion 2 separated by the solid portion separation step can be washed using at least one of water, an acid solution, an alkaline solution, and an organic solvent. By the washing step, for example, oil components and metal components contained in the solid portion 2 can be removed. Silicon oxide, which is a silicon oxide film, may be removed by acid cleaning, but the oxide film may be formed again in the form of a natural oxide film while being left standing.
Although a washing | cleaning process is not specifically limited, Below, an example of the washing | cleaning process which removed the oil component and the metal component from the solid part 2 is demonstrated.

1-2-2-1. Method of removing oil component from solid part Of the solid part 2 obtained by the solid part separation step, the solid part 2 recovered from the waste liquid 1 of silicon cutting using water-soluble or oily oil has an oil component of 2 In some cases, it remains as a high component of 50% to 50%.
A washing step can be performed to remove this oil component. For example, the oil component of the lubricating oil can be removed by heating the solid portion 2 to the boiling point of the oil or higher. Further, for example, the oil component can be removed by washing the solid portion 2 with an acid solution or an organic solvent.
The method for heating the solid portion 2 to be higher than the boiling point of the oil is not particularly limited. For example, the oil component is reduced to, for example, 1% or less by heating the oil in the vacuum atmosphere or the inert gas atmosphere to the oil boiling point or higher. Can do.
Moreover, the acid solution for washing the solid portion 2 is not particularly limited, and examples thereof include hydrochloric acid and sulfuric acid. Moreover, the organic solvent for washing the solid component 2 is not particularly limited, but is, for example, an organic solvent that has a low molecular weight such as isopropyl alcohol, ethanol, acetone, and is soluble in the oil component.
When a flocculant is used for recovery of the solid portion 2, the solid portion 2 may be washed using an organic solvent that is soluble in the flocculant.

1-2-2-2. Method for removing metal component from solid portion The solid portion 2 obtained by the solid portion separation step may contain a metal component. In particular, the solid portion 2 obtained from the waste liquid 1 generated when a silicon wafer is manufactured may contain a metal component in an amount of 0.01 wt% to 9.9 wt%, for example.
A cleaning step can be performed to remove this metal component. For example, the metal component can be removed by washing the solid portion 2 with an acid solution. Further, the metal component can be removed from the solid portion 2 by segregation or the like.
The acid solution for washing the solid portion 2 is not particularly limited, and examples thereof include hydrochloric acid, sulfuric acid, and hydrofluoric acid. In addition, since the metal component contained in the solid part 2 exists as a single grain, it can be easily removed by washing with an acid solution.
An alloy may be formed when the solid portion 2 containing a metal component at a high concentration is melted at a high temperature. After the alloy is formed, it is often difficult to remove by segregation.

1-2-3. Powder The powder 3 containing the silicon powder 4 or the powder 3 containing the silicon powder 4 and the abrasive grains 5 collected and washed through the solid partial separation process and the washing process has few oil components and metal components, but the silicon powder 4 is oxidized. The proportion of the membrane is large. In general, it often contains abrasive grains 5 made of silicon carbide, silicon nitride, diamond or the like, and as such is not preferable as a silicon material used for solar cells.
When the powder 3 includes the abrasive grains 5, the content of the abrasive grains 5 is not particularly limited, but for example, 1 to 20 wt% (for example, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, Range between any two of 16, 18 and 20 wt%).
The silicon powder 4 has a particle size of 0.001 to 99.9 μm (for example, 0.001, 0.01, 0.05, 0.1, 0.5, 1, 2, 3, 4, 5, 7, 10, 30, 50, 70, and 99.9 μm), and the ratio of the oxide film (SiO _x ) is high. The silicon oxide content in the silicon powder is, for example, 3 wt% to 30 wt% (for example, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 and a range between any two of 30 wt%).
Therefore, the powder 3 containing the silicon powder 4 or the powder 3 containing the silicon powder 4 and the abrasive grains 5 collected and washed through the powder separation process is subjected to a storing process, a melting process and a hot water process using the silicon purifier 24. Therefore, it can be easily purified to a level that can be preferably used as a silicon material used for solar cells and the like.

1-3. Silicon Purification Device Before describing the melting process and the hot water process, the silicon purification device 24 shown in FIG. 2 used in these steps will be described. 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.
A silicon purifying apparatus 24 according to an embodiment of the present invention is a heating vessel that uses a powder 3 containing a silicon powder 4 separated from a waste liquid 1 generated when silicon is machined and containing silicon oxide as a molten metal 21. 10. A cooling furnace 13 having a heating means 11 for heating the heating vessel 10 and a tapping means 12 for tapping the silicon melt contained in the molten metal 21, and a cooling for storing and cooling the low-viscosity silicon melt contained in the molten metal 21. A container 14 and a residual container 15 for storing a residual part containing high-viscosity silicon oxide adhering to the inner wall or bottom of the heating container 10 are provided. The melting furnace 13, the cooling container 14, and the residual container 15 can be decompressed. The inside of the vacuum container 9 is
In addition, the silicon purification apparatus 24 used in the silicon purification method of one embodiment of the present invention may include a residual portion recovery mechanism 20, a transport mechanism 16, a powder storage mechanism 19, a cleaning mechanism, and a sizing mechanism.
Hereinafter, each component of the silicon refiner | purifier 24 of one Embodiment of this invention is demonstrated.

1-3-1. Depressurized container The depressurized container 9 is not particularly limited as long as the melting furnace 13, the cooling container 14, and the residual container 15 can be accommodated therein, and the interior can be depressurized or an inert gas atmosphere. Moreover, when the residual part collection | recovery mechanism 20, the conveyance mechanism 16, the powder storage means 19, etc. are provided, these can be accommodated inside or can be provided. Moreover, it is desirable that the internal pressure of the decompression vessel 9 can be set to 1 to 760 Torr, for example. The inert gas is a gas containing, for example, argon, helium or nitrogen.

1-3-2. Melting furnace The melting furnace 13 includes a heating means 11, a heating container 10, and a tapping means 12.

1-3-2-1. Heating means The heating means 11 is not particularly limited as long as the powder 3 containing the silicon powder 4 or the powder 3 containing the silicon powder 4 and the abrasive grains 5 can be heated to a temperature at which the silicon melted molten metal 21 can be obtained. For example, resistance heater, induction heating, arc melting or plasma melting.

1-3-2-2. Heating container The heating container 10 is not particularly limited as long as it is a container that can make the powder 3 containing the silicon powder 4 or the powder 3 containing the silicon powder 4 and the abrasive grains 5 into the molten metal 21 in which silicon is melted.
The material of the heating container 10 is, for example, carbon, mullite, alumina, magnesia, or a water-cooled copper mold. In addition, the heating container 10 is preferably a water-cooled copper mold when using a heating means 11 to which a locally high temperature is applied, such as arc melting or plasma melting, and when using a resistance heater or induction heating, A carbon crucible is desirable.
Further, the heating container 10 may include a hot water discharge means 12.

1-3-2-3. The hot water discharge means The hot water discharge means 12 is a means for hot water discharge of the silicon melt part 22 contained in the molten metal 21 in the heating container 10. Note that the silicon melt portion 22 is a portion made of a silicon melt contained in the molten metal 21. The hot water discharge means 12 is not particularly limited as long as the silicon melt portion 22 can be discharged. For example, the hot water discharge means 12 is a tilting means that can tilt the heating container 10.
Further, for example, the hot water discharge means 12 can be provided in the heating container 10.
FIG. 4 is a perspective view of the heating container 10 having the hot water discharge means 12 according to one embodiment of the present invention.
For example, as shown in FIG. 4 (a), the hot water discharge means 12 is provided on the upper surface of the heating container 10, or as shown in FIG. 4 (b), the hot water discharge means 12 is placed at an arbitrary position on the side surface / lower surface of the heating container 10. It can also be provided. When providing the hot water means 12 of FIG.4 (b), it is necessary to set it as the structure which can be opened and closed.

1-3-3. Cooling container The cooling container 14 is not particularly limited as long as it can store the silicon melt part 22 contained in the molten metal 21 and can cool the silicon melt part 22, but for example, a silica crucible or sand It is desirable to use an inexpensive disposable material such as a crucible sintered, but the mold may be reused by pouring hot water into a carbon mold or a water-cooled copper mold.

1-3-4. Residual part container The residual part container 15 is not particularly limited as long as it can accommodate the adhesive part 23 adhered to the heating container 10 as the residual part 7. For example, a silica crucible or a crucible obtained by sintering sand is used. Any one of an inexpensive disposable one, a similar one as a cooling container such as a carbon mold or a water-cooled copper mold, or a simple one such as stainless steel or a heat-resistant board may be used. The adhesive portion 23 is a portion where silicon oxide or silicon oxide and abrasive grains 5 contained in the molten metal 21 are adhered to the heating container 10.
In addition, the silicon purification device 24 of the present embodiment may include a transport mechanism 16 that can move the position of the residual container 15 and the position of the cooling container 14. Further, the transport mechanism 16 enables the cooling container 14 and the residual container 15 to be transported using the transport mechanism 16 such as a turntable or a belt conveyor while maintaining the inert gas atmosphere or the decompressed state in the decompression container 9. Thus, it is desirable that the position can be changed, and it is further desirable that the position can be carried out of the decompression container 9.

1-3-5. Powder Storage Mechanism The powder storage mechanism 19 is not particularly limited as long as the powder 3 is charged into the heating container 10 and the powder 3 can be used as the molten metal 21. It is desirable that the powder storage mechanism 19 can supply the powder 3 while maintaining the inert gas atmosphere or the reduced pressure state in the reduced pressure container 9.
The powder storage mechanism 19 is, for example, a powder charging port 17, a rod-shaped body 18, a gas blowing port, and the like included in the decompression container 9. Although the material of the rod-shaped body 18 is not specifically limited, For example, it is a refractory metal such as carbon or molybdenum.

1-3-6. Residual part recovery mechanism The residual part recovery mechanism 20 is not particularly limited as long as it can move the adhesive part 23 adhered to the heating container 10 to the residual part container 15 as the residual part 7. Such as a scraping bar. Moreover, the material of the residual part collection | recovery mechanism 20 will not be specifically limited if the adhesion part 23 adhere | attached on the heating container 10 can be moved to the residual part container 15, For example, it is a refractory metal, such as carbon or molybdenum.

1-3-7. Cleaning Mechanism The silicon purification apparatus 24 according to an embodiment of the present invention can further include a cleaning mechanism that further mixes the residual portion 7 with an acid solution or an alkaline solution and separates the abrasive grains 5 contained in the residual portion 7. (Not shown). This cleaning mechanism can be used in the abrasive grain recovery process described in “1-6”. This cleaning mechanism is not used when the remaining portion 7 does not include the abrasive grains 5.

1-3-8. Sorting mechanism The silicon purifying apparatus 24 according to an embodiment of the present invention may further include a sorting mechanism for sieving or classifying the abrasive grains separated by the cleaning mechanism (not shown). This sizing mechanism can be used in the classification process described in “1-7”.

1-4. Removal of Silicon Oxide from Silicon or Removal of Silicon Oxide and Abrasive Grains Hereinafter, a method for obtaining high purity silicon 6 by removing silicon oxide or silicon oxide and abrasive grains 5 from powder 3 using silicon purifier 24 will be described.
In addition, this method consists of a melting process and a tapping process. Moreover, the accommodation process can also be provided. In these steps, the atmosphere in the decompression vessel 9 is performed under reduced pressure or an inert gas. Although an inert gas is not specifically limited, For example, it is a gas containing argon, helium, or nitrogen. The internal pressure of the decompression vessel 9 in the decompressed atmosphere is, for example, 1 Torr or more and 760 Torr or less (for example, between any two of 1, 10, 50, 100, 200, 300, 400, 500, 600, 700, and 760 Torr). Range).
By performing under these conditions, higher purity silicon can be obtained.

1-4-1. Storage process In the storage process, the powder 3 containing the silicon powder 4 or the powder 3 containing the silicon powder 4 and the abrasive grains 5 that have undergone the powder separation process can be stored in the heating container 10 in the vacuum container 9 of the silicon purifier 24. . Although the storage method is not particularly limited, the melting furnace 13 can be stored before being placed in the decompression vessel 9. Further, it can be stored using the powder storing means 19.

1-4-2. Melting process In the melting process, the powder 3 in the heating container 10 is heated by the heating means 11 to a melting point of silicon or higher and 2000 ° C. or lower to obtain a molten metal 21 using silicon contained in the powder 3 as a silicon melt. The heating temperature is, for example, 1412 ° C. or more and 2000 ° C. or less (for example, a range between any one of 1412, 1450, 1500, 1550, 1600, 1800, 1900, and 2000 ° C.), preferably 1600 ° C. or more and 1800 ° C. or less. .
Since the silicon powder 4 contains a large amount of silicon oxide as an oxide film, it often takes time to form the molten metal 21 even if the powder 3 is heated to around 1412 ° C., which is the melting point of silicon. For this reason, it is desirable to heat the powder 3 to a temperature of 1600 ° C. or higher. If the heating temperature is raised too much, the evaporation of silicon may be promoted, so that it is preferably 2000 ° C. or lower, preferably 1800 ° C. or lower.
Further, the powder 3 may be additionally stored by the powder storage mechanism 19 in the melting step. Moreover, since the powder 3 tends to float with respect to the silicon melt contained in the molten metal 21, the powder 3 can be physically submerged by, for example, a rod 18 or gas blowing. Thereby, the molten metal 21 in the heating container 10 can be made into a sufficient amount.

FIG. 5 is a schematic cross-sectional view of the heating container 10 having the molten metal 21 according to an embodiment of the present invention.
Silicon resulting from the silicon powder 4 contained in the molten metal 21 melts and exists as a silicon melt.
The molten metal 21 is mainly composed of a silicon melt. However, silicon oxide 25 resulting from the oxide film of silicon powder 4 exists. Moreover, the abrasive grain 5 resulting from a fixed abrasive grain or a loose abrasive grain may exist.
The silicon oxide 25 exists in the molten metal 21 of 1412 degreeC or more and 2000 degrees C or less with the viscosity higher than a silicon melt. The viscosity of the silicon melt generally referred to is 0.5 mPa · s and water, but the viscosity of the silicon oxide 25 is 10 ⁷ to 10 ⁹ mPa · s at 1600 ° C. and 10 ⁶ to 10 at 1800 ° C. ⁸ mPa · s is in a water tank shape, and there is a remarkable difference.
Since the entire molten metal 21 is stirred by convection or the like, the silicon oxide 25 having a high viscosity sticks to the inner wall or bottom of the heating container 10.

  Since the abrasive grains 5 are caused by fixed abrasive grains or loose abrasive grains, they are particles such as silicon carbide, silicon nitride, and diamond. Table 1 shows the density and melting point, boiling point or sublimation point of silicon, silicon carbide, silicon nitride and diamond. Since the temperature of the molten metal 21 is 1412 ° C. or higher and 2000 ° C. or lower, the abrasive grains 5 exist as solid particles in the molten metal 21. In addition, when the abrasive grains 5 are silicon nitride and the temperature of the molten metal 21 is 1900 ° C. or higher, the silicon nitride may be sublimated and not included in the molten metal 21. Moreover, these abrasive grains 5 have a higher density than the silicon melt.

When the abrasive grains 5 are contained in the molten metal 21, the abrasive grains 5 existing in a solid are agitated by convection of the silicon melt. While being agitated, most of the abrasive grains 5 are adhered and trapped on the silicon oxide 25 adhered to the inner wall and bottom of the heating container 10.
The main component of the molten metal 21 is a silicon melt, and the silicon oxide 25 adheres to the inner wall and the bottom of the heating container 10. Further, when the molten metal 21 contains abrasive grains, the abrasive grains further adhere to the silicon oxide 25.
The silicon powder 4 contained in the powder 3 has a particle size of about 0.001 μm to 99.9 μm and a high ratio of oxide film (SiOx). For this reason, it is considered that there is sufficient silicon oxide 25 necessary for all the abrasive grains 5 contained in the molten metal 21 to adhere.

Moreover, after the silicon resulting from the silicon powder 4 contained in the powder 3 is completely melted and the molten metal 21 is formed, the temperature of the molten metal 21 is set to be equal to or higher than the melting point of silicon and equal to or lower than the temperature at which the molten metal 21 is formed. The viscosity of the silicon oxide 25 can be further increased. By increasing the viscosity of the silicon oxide 25, the silicon oxide 25 can be adhered to the inner wall or bottom of the heating container 2. Moreover, when the abrasive grains 5 are contained in the molten metal 21, the abrasive grains 5 can also be adhered by the silicon oxide 25. Moreover, it becomes easy to pour out only the silicon melt part 22 in the pour-out process described later.
In this way, the molten metal 21 is formed from the powder 3 in the heating container 10 and the molten metal 21 is convected to form the silicon oxide 25 adhered to the heating container 10 or the silicon oxide 25 and the silicon oxide 25 adhered to the heating container 10. It can be separated into an adhesive part 23 composed of the adhered abrasive grains 5 and a silicon melt part 22 in which silicon is melted.

1-4-3. Hot water discharge process In the hot water discharge process, the silicon melt part 22 in the heating container 10 is discharged into the cooling container 14. The hot water discharge method is not particularly limited as long as the silicon melt portion 22 is discharged, but the hot water discharge means 12 can also be used. For example, the silicon melt part 22 in the heating container 10 can be discharged into the cooling container 14 by tilting the heating container 10 using a tilting means that is the hot water discharging means 12.
FIG. 6 is a schematic cross-sectional view of the silicon purifier 24 according to one embodiment of the present invention when the heating container 10 is tilted using the tilting means and the silicon melt portion 22 is discharged into the cooling container 14.
Moreover, as shown to Fig.4 (a), the hot_water | molten_metal part 22 in the heating container 10 can also be tapped out by providing the hot water discharge means 12 in the upper surface of the heating container 10. FIG. Moreover, as shown in FIG.4 (b), the silicon | silicone melt part 22 in the heating container 10 can also be tapped out by providing the hot water discharge means 12 in the arbitrary positions of the side surface / lower surface of the heating container 10. FIG. When providing the hot water means 12 of FIG.4 (b), it is necessary to set it as the structure which can be opened and closed.

Since the silicon melt part 22 in the heating container 10 has a low viscosity, the hot water can be easily discharged using the hot water discharge means 12. However, the adhesive portion 23 made of the silicon oxide 25 or the abrasive grains 5 attached to the silicon oxide 25 and the silicon oxide 25 adheres to the heating container 10 and therefore can remain inside the heating container 10 without taking out hot water. .
That is, the silicon melt part 22 discharged from the cooling container 14 is refined by removing the silicon oxide 25 or the silicon oxide 25 as an impurity and the adhesive part 23 made of the abrasive grains 5 from the molten metal 21 formed in the heating container 10. High purity silicon. By cooling the silicon melt portion 22 with the cooling vessel 14, a lump of high purity silicon 6 can be obtained. Since this high-purity silicon 6 can be used as a silicon material used in the production of solar cells, it is possible to eliminate the shortage of silicon for solar cells and to reduce the amount of waste.
Further, the cooling container 14 can be moved out of the decompression container 9 by the transport mechanism 16.
By repeating the above storage process, melting process and tapping process, high purity silicon 6 continuously purified from the powder 3 can be obtained. In addition, in order to repeat this process, it is necessary to collect | recover the adhesion parts 23 from the heating container 10 to the residual part container 15 after the hot water discharge process.

1-5. Residual Portion Recovery Step A residual portion recovery step of recovering a residual portion that is a portion that has not been discharged in the hot water discharge step can be further performed.
FIG. 7 is a schematic cross-sectional view of the silicon purifier 24 according to an embodiment of the present invention when the heating container 10 is tilted and the adhesive part 23 adhered to the heating container 10 is moved to the residual part container 15 as the residual part 7. FIG.
For example, by using the residual portion recovery mechanism 20, the adhesive portion 23 adhered to the heating container 10 and the silicon melt that could not be discharged can be scraped out by a physical method and moved to the residual portion container 15 as the residual portion 7. The remaining portion 7 includes the adhesive portion 23 and a part of the silicon melt.
In addition, the residual container 15 containing the residual part 7 can be moved out of the decompression container 9 by the transport mechanism 16.
The remaining portion 7 includes silicon oxide 25 and silicon, or silicon oxide 25, abrasive grains 5, and silicon. When the residual part 7 includes the abrasive grains 5, the proportion of the abrasive grains 5 is larger than that of the powder 3.
In addition, the inside of the heating container 10 can be made empty or nearly empty by performing the residual part recovery step. For this reason, the said residual part collection | recovery process, an accommodation process, a fusion | melting process, and a tapping process can be repeatedly performed in the lifetime (due to consumption by long-term use) of the heating container 10.

1-6. Abrasive Grain Recovery Step When the abrasive grains 5 are included in the residual portion 7, in the abrasive grain recovery step, the residual portion 7 is dissolved in the residual portion 7 with an acid solution or an alkali solution, and the silicon oxide 25 is dissolved in the abrasive grains 5. Can be separated. For example, the silicon oxide 25 and silicon contained in the residual portion 7 are dissolved and removed with an acid solution such as hydrofluoric acid or nitric acid, or an alkali solution such as sodium hydroxide or potassium hydroxide to recover the abrasive grains 5. it can. For example, the residual part 7 and the acid can be mixed in a ratio of residual part 7: hydrofluoric acid (46%): nitric acid (70%): water = 5: 20: 10: 70. This can be held for 1 hour with stirring. Thereafter, the abrasive grains 5 can be recovered by a centrifuge. The recovered abrasive grains 5 can be reused as recycled abrasive grains 8 in silicon machining or the like. For this reason, cost reduction can be aimed at, and also the amount of waste can be reduced.

1-7. Classification process The classification process which sifts or classifies the abrasive grain 5 obtained by the abrasive grain collection | recovery process can be further provided. The abrasive grains 5 collected by the abrasive grain collecting step include those having various particle diameters. For example, if it was used in the cutting process, the same particle size as that used in the cutting process is included, and the smaller particle size crushed in the cutting process is also included. If this is sieved or classified, regenerated abrasive grains 8 having a desired particle diameter can be obtained. The recycled abrasive grain 8 can be reused for silicon machining suitable for the grain size.

2. Recycled abrasive grains The recycled abrasive grains 8 obtained in the abrasive grain recovery process and classification process are made of, for example, silicon carbide, silicon nitride, diamond, or the like. Further, the regenerated abrasive grains 8 are generated from fixed abrasive grains or loose abrasive grains crushed during silicon machining. For this reason, the regenerated abrasive grains 8 contain many regenerated abrasive grains 8 having a particle diameter of approximately 1 μm and regenerated abrasive grains 8 having a submicron particle diameter (# 10000 or more). Such abrasive grains having a small particle size require much labor for pulverization and the like in normal production. Therefore, the regenerated abrasive grain 8 has an economical advantage because an abrasive grain having a small particle diameter can be obtained.
In the melting step, the abrasive grains 5 are heated to 1412 ° C. or higher to promote crystallization. For this reason, the regenerated abrasive grains 8 have a very large strength that promotes crystallization.

3. Effect Verification Experiment Next, the effect verification experiment of the present invention will be described. Here, an experiment for purifying silicon contained in the waste liquid 1 generated when silicon was cut and an experiment for obtaining the regenerated abrasive grains 25 from the abrasive grains 5 contained in the waste liquid 1 were performed.

3-1. Silicon machining and solid partial separation process Silicon was cut using a multi-wire saw. Water-soluble oil (manufactured by Ochi Chemical Co., Ltd., Luna Coolant) was used as the lubricant, and silicon carbide GC # 1000 (average particle diameter of about 11 μm) made by Shinano was used as the free abrasive grains. Since the waste liquid 1 generated by this cutting process has a large amount of abrasive grains and oil components, it is divided into a high density solid content mainly composed of abrasive grains and iron by a centrifugal separator, and a low density component mainly composed of silicon powder and oil. separated. Thereafter, the solid content was further vacuum distilled at 200 ° C. and 76 Torr. The results of examining the composition of the obtained solid portion 2 are shown in Table 2. The amount of iron powder contained in the solid portion 2 was analyzed by ICP emission analysis. The amount of abrasive grains contained in the solid portion 2 was analyzed by dissolving the solid portion 2 using a mixed solution of hydrofluoric acid and nitric acid and caustic soda, and measuring the weight of the residue. The amount of oil contained in the solid portion 2 was analyzed by measuring a change in weight after heating from room temperature to 500 ° C. using a solid thermogravimetric measuring device.
The solid portion 2 includes silicon powder 4 resulting from the shaving of silicon, iron powder generated from a multi-wire saw, abrasive grains 5 generated from loose abrasive grains, and oil as a lubricant, and iron powder and oil as impurities. It was found that many components were contained.

3-2. Washing Step In order to remove iron powder and oil components from the solid part 2, washing was performed with hydrochloric acid.
First, the solid part 2 and the like were mixed at a ratio of solid part 2: hydrochloric acid (35%): water = 1: 2: 2. Thereafter, the mixture was held for 1 hour with stirring. Then, solid content was collect | recovered using the filter press and the rinse water was poured and the acid was removed. Thereafter, the collected solid content was dried using a vibration drier, and a powder 3 containing silicon powder 4 and abrasive grains 5 was obtained.
Table 3 shows the results of examining the composition of the powder 3 after drying. The measurement method is the same as in Table 2. The oxidized content of the silicon powder was analyzed using fluorescent X-rays made by EDAX.
The powder 3 was mainly composed of silicon powder 4 and contained abrasive grains 5. It was found that iron and oil were almost removed by the washing process.

3-3. Removal of silicon oxide and abrasive grains from the powder Silicon oxide 25 and abrasive grains 5 were removed from the powder 3 by the silicon purifier 24 to refine the silicon. The melting furnace 13 used what can be induction-heated as the heating means 11, and used the carbon crucible as the heating container 10. FIG. The inside of the decompression vessel 9 was an argon gas atmosphere, and the internal pressure was set to 760 Torr.

3-3-1. Storage process The powder 3 obtained in the cleaning process was stored in a heating container 10 inside the decompression container 9. Specifically, the powder 3 was charged into the heating container 10 from the powder inlet 17.

3-3-2. Melting process The heating container 10 and the powder 3 were heated by induction heating. By heating the powder 3 to 1700 ° C., silicon contained in the powder 3 was melted, and the powder 3 became a molten metal 21. Thereafter, the powder 3 was charged at any time through the powder inlet 17 until the inside of the heating container 10 was filled with the molten metal 21. Since the powder 3 tends to float with respect to the molten metal 21, the powder 3 was physically submerged using a carbon rod 18.

3-3-3. Hot water discharge process The heating container 10 after the melting process is tilted by using a tilting means which is the hot water discharging means 12, whereby the silicon melt portion 22 in the heating container 10 is discharged into the cooling container 14 of the carbon mold. High purity silicon 6 could be obtained by cooling the silicon melt part 22 in the cooling container 14.

3-4. Measurement of abrasive grain component and silicon oxide component in high purity silicon The abrasive 5 component and the silicon oxide 25 component of the high purity silicon 6 in the cooling vessel 14 obtained by the above-described hot water process were measured.
Table 4 shows the results of measuring the silicon carbide concentration, which is the five components of abrasive grains in the high-purity silicon 6. The measurement was performed by pre-cleaning high-purity silicon 6 and removing organic substances (carbon impurities other than silicon carbide) on the surface, and then using a solid-in-carbon analyzer EMIA manufactured by Horiba. Thereafter, the measured C concentration was calculated from the molecular weight in terms of SiC. From this result, it was found that the concentration of silicon carbide, which was 5% in the powder 3, decreased to 300 ppm through the storage process, the melting process, and the hot water discharge process.

  Table 5 shows the results of measuring the oxygen concentration in the high purity silicon 6. Measurement was performed using fluorescent X-rays manufactured by EDAX. From this result, it was found that the oxygen concentration which was 5 to 10% in the powder 3 decreased to the detection limit or less (0.1% or less) through the storage process, the melting process and the hot water process. From this result, it was found that the high purity silicon 6 contained almost no silicon oxide.

  From this result, it was found that the obtained high-purity silicon 6 was refined to a level that can be preferably used as a silicon material used for solar cells and the like.

3-5. Residual Portion Recovery Step A residual portion recovery step was performed to recover the residual portion that was not discharged in the hot water discharge step.
First, the adhesive portion 23 composed of the silicon oxide 25 and the abrasive grains 5 remaining in the heating container 10 is physically scraped using a carbon spatula as the residual portion recovery mechanism 20 and remains in the carbon residual portion container 15. Recovered as part 7.

3-6. Abrasive Grain Recovery Step The residual portion 7 recovered in the residual portion container 15 was taken out from the crucible, and the abrasive grains 5 were recovered to obtain regenerated abrasive grains 8.
First, the residual part 7 and sodium hydroxide were mixed in a ratio of residual part 7: sodium hydroxide: water = 5: 20: 80. This was kept at a temperature of about 50 ° C. for 1 hour with stirring. Thereafter, the abrasive grains 5 were collected by a centrifugal separator to obtain regenerated abrasive grains 8.

3-7. Classification process The abrasive grains 5 recovered in the abrasive grain recovery process were classified by a classification mechanism to separate the abrasive grains 5 of 0.2 μm or less and 0.3 μm or more. As a result, regenerated abrasive grains 8 having a particle size of 0.2 to 0.3 μm, regenerated abrasive grains 8 of 0.2 μm or less, and regenerated abrasive grains 8 of 0.3 μm or more were obtained.

3-8. Analysis of recycled abrasive grains 3-8-1. Crystallinity of regenerated abrasive grains A photograph of the regenerated abrasive grains 8 obtained by the abrasive grain collecting step was taken. Moreover, as a comparative example, the powder 3 was treated with an alkaline solution under the same conditions as in the abrasive grain collection step, and a photograph of the obtained abrasive grains was taken.
FIG. 8 is a photograph of the regenerated abrasive grain 8 obtained by the abrasive grain collecting step.
FIG. 9 is a photograph of the abrasive grains 5 in which the powder 3 is washed with an alkaline solution and the silicon powder 4 is removed.
From these photographs, the abrasive grains 5 obtained from the powder 3 are not recrystallized, but the regenerated abrasive grains 8 obtained by the abrasive grain recovery process are accelerated by recrystallization by heating in the melting process, It was found that the carbon was made into high strength green carbon (GC).

3-8-2. Particle size distribution of regenerated abrasive grains The particle size distribution of the regenerated abrasive grains 8 obtained by the abrasive grain recovery process was measured.
FIG. 10 is a view showing the particle amount (%) and the relative particle amount (%) of the regenerated abrasive grains 8 of each particle diameter. It was found that the number of regenerated abrasive grains 8 having a particle size of 0.2 μm or more and 0.3 μm or less was the largest.

It is a flowchart of the silicon | silicone purification method of one Embodiment of this invention. It is a schematic sectional drawing of the silicon refinement | purification apparatus of one Embodiment of this invention. It is a flowchart of the powder separation process of one Embodiment of this invention. It is a perspective view of the heating container which has the hot-water means of one Embodiment of this invention. It is a schematic sectional drawing of the heating container which has the molten metal of one Embodiment of this invention. It is a schematic sectional drawing of the silicon refinement | purification apparatus of one Embodiment of this invention. It is a schematic sectional drawing of the silicon refinement | purification apparatus of one Embodiment of this invention. It is the photograph of the reproduction | regeneration abrasive grain obtained by the demonstration experiment of this invention. It is a photograph of the abrasive grain obtained from the powder of the demonstration experiment of this invention. It is a particle size distribution of the reproduction | regeneration abrasive grain obtained from the demonstration experiment of this invention.

Explanation of symbols

  1: Waste liquid 2: Solid part 3: Powder 4: Silicon powder 5: Abrasive grain 6: High-purity silicon 7: Residual part 8: Recycled abrasive grain 9: Depressurized container 10: Heating container 11: Heating means 12: Hot water means 13: Melting furnace 14: Cooling container 15: Residual part container 16: Transfer mechanism 17: Powder storage port 18: Rod-shaped body 19: Powder storage mechanism 20: Residual part recovery mechanism 21: Molten metal 22: Silicon melt part 23: Adhesive part 24: Silicon purification equipment 25: Silicon oxide

Claims (15)

A powder separation step of separating powder containing silicon powder having silicon oxide from waste liquid generated when machining silicon;
A melting step of heating the powder to a temperature not lower than the melting point of silicon and not higher than 2000 ° C. in a heating container under reduced pressure or in an inert gas atmosphere to obtain a molten silicon melted;
Leaving the high viscosity silicon oxide adhering to the inner wall or bottom of the heating vessel contained in the molten metal in the heating vessel, and pouring a low-viscosity silicon melt into a cooling vessel;
A silicon purification method comprising:   The method according to claim 1, wherein the powder includes abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining.   The method according to claim 2, wherein the fixed abrasive or the free abrasive includes silicon carbide, silicon nitride, or diamond.   The method according to claim 1, wherein the machining is cylindrical grinding, cutting, polishing or wafer slicing of silicon.   The powder separation step includes (1) a method of obtaining a solid portion by capturing and drying the solid content using a filter or a centrifuge, and (2) collecting or heating or distilling the waste liquid. 5. The method according to claim 1, further comprising: a solid part separation step which is a step including at least one of a method for obtaining a solid part and (3) a method for obtaining a solid part using a flocculant with respect to the waste liquid. The method according to one.   The method according to claim 5, wherein the powder separation step further includes a washing step of washing the solid portion obtained by the solid partial separation step using at least one of water, an acid solution, an alkaline solution, and an organic solvent. .   The method as described in any one of Claims 1-6 further equipped with the residual part collection | recovery process which collect | recovers the residual part which is a part which was not poured out in the said hot water extraction process.   The powder includes abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining, and the residual portion containing the abrasive grains is mixed with an acid solution or an alkali solution to separate the abrasive grains. The method according to claim 7, further comprising an abrasive recovery step.   The method according to claim 8, further comprising a classification step of sieving or classifying the abrasive grains obtained by the abrasive grain recovery step. A heating container that uses a powder containing silicon powder containing silicon oxide, which is separated from a waste liquid generated when machining silicon, as a molten metal, a heating means for heating the heating container, and a silicon melt contained in the molten metal A melting furnace having a hot water discharge means for discharging hot water;
A cooling container that houses and cools the low-viscosity silicon melt contained in the molten metal;
A remnant container containing a remnant containing high-viscosity silicon oxide that adheres to the inner wall or bottom of the heating container;
The melting furnace, the cooling container, and the residual container are silicon purification apparatuses inside a decompression container that can be decompressed.   The apparatus according to claim 10, wherein the powder includes abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining. The apparatus according to claim 10 or 11, wherein the machining is cylindrical grinding, cutting, polishing or wafer slicing of silicon.   The residual part collection mechanism which scrapes out the residual part containing silicon oxide adhering to the inner wall or bottom of the heating container by a physical method and moves the residual part to the residual part container. The device described.   The powder includes abrasive grains generated from fixed abrasive grains or free abrasive grains used in the machining, and the residual portion containing the abrasive grains is mixed with an acid solution or an alkali solution to separate the abrasive grains. The apparatus according to claim 10, further comprising a cleaning mechanism.   The apparatus according to claim 14, further comprising a sizing mechanism for sieving or classifying the abrasive grains separated by the cleaning mechanism.