JP5114436B2 - Metal content removal method and silicon purification method - Google Patents

Description

  The present invention relates to a metal-containing material removal method and a silicon purification method.

  In the manufacturing process of 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 raw material silicon is in waste liquid by cutting, chamfering or polishing. The environmental impact associated with the cost of the product and disposal (this waste liquid is generally disposed of in landfills after concentration or collection of some materials) is a major problem. ing.

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, the shortage of silicon for solar cells has become apparent.
Therefore, conventionally, for example, as disclosed in Patent Document 1 and Patent Document 2, a method of recovering silicon from waste liquid generated during manufacturing of a silicon wafer, such as cutting or polishing of raw material silicon, has been proposed.

  Generally, waste slurry discharged from a process of cutting or polishing a silicon single crystal or polycrystalline ingot using a slurry in which abrasive grains are dispersed in a coolant includes metal components of abrasive grains, cutting blades, and wires. As an impurity, a metal powder, a metal compound of a metal component of a cutting blade or wire (for example, a chloride such as iron chloride or a hydroxide such as iron hydroxide) is included.

  Although the metal component of abrasive grains and wire scraps can be removed by melting the solid content recovered from the waste slurry (hereinafter referred to as silicon recovery solid content) once and solidifying in one direction, In order to remove a certain amount of impurities, it is necessary to perform melting and unidirectional solidification several times.

In addition, phosphorus is generally contained in cutting blades and wires, and once this is not removed and the solid content for silicon recovery is melted, it is very difficult to remove phosphorus in the subsequent steps. Therefore, before melting the silicon recovery solids, the silicon recovery solids must be washed with an acid solution to remove impurities (consisting of metal powder and a modified metal compound). .
That is, it is preferable to remove as many impurities as possible before melting the silicon recovery solids in order to keep the silicon regeneration cost low.

JP 2001-278612 A JP 2008-1105040 A

Most of the metal impurities such as wire scraps can be removed by washing the solid content for silicon recovery with one acid solution. However, it has been found that even if the washing with the acid solution is repeated many times, some impurities remain in the solids for silicon recovery.
This invention is made | formed in view of such a situation, and provides the metal content removal method which has a high impurity removal effect.
Furthermore, the present invention provides a silicon purification method using a solid content containing silicon particles subjected to the metal-containing material removal method of the present invention.

  The metal-containing material removal method of the present invention includes a first washing step of washing a waste slurry obtained by machining silicon and containing silicon particles or a silicon recovery solid separated from the waste slurry with an acidic first washing liquid; A neutralization treatment step of treating the first cleaning liquid containing silicon particles with a base, and a solid content or slurry containing the silicon particles separated from the first cleaning liquid treated with the base is washed with an acidic second cleaning liquid. And a second cleaning step, wherein the metal-containing material resulting from the machining and cannot be removed by the first cleaning step is efficiently removed by the second cleaning step.

As a result of intensive studies, the present inventors have found that a plurality of silicon particles are aggregated in an acid solution for cleaning the solid content for silicon recovery, and the inside of the aggregate is repeatedly washed with an acid solution many times. It was found that sufficient cleaning was not possible.
Furthermore, the present inventors have found that the solid content for silicon recovery is washed with an acid solution and then neutralized with a base solution, thereby promoting the dispersion of aggregated silicon particles. . Further, the solid content for silicon recovery after the neutralization treatment in which the dispersion of the silicon particles is promoted is washed again with the acid solution, thereby the inside of the aggregate of silicon particles that could not be removed by the first washing with the acid solution. The present inventors have found that the impurities can be efficiently removed and the effect of removing impurities can be dramatically improved, and the present invention has been completed.

According to the present invention, by promoting the dispersion of silicon particles, it is possible to wash and remove the metal-containing substances contained in the waste slurry containing silicon particles or the silicon recovery solids separated from the waste slurry with high efficiency. .
Hereinafter, various embodiments of the present invention will be exemplified.

The first cleaning liquid or the second cleaning liquid may include at least one of sulfuric acid, hydrofluoric acid, hydrochloric acid, hydrogen peroxide, hydrobromic acid, nitric acid, boric acid, citric acid, acetic acid, formic acid, oxalic acid, and lactic acid. .
The base may include at least one of an aqueous ammonia solution, an aqueous magnesium hydroxide solution, and an aqueous cupric hydroxide solution.
The 1st washing | cleaning liquid after the said neutralization process process may have pH of 5-10.
At least one of the first cleaning step, the neutralization treatment step, and the second cleaning step may disperse the silicon particles by ultrasonic irradiation.
You may further provide the crushing process of grind | pulverizing the said waste slurry or the said silicon | silicone collection solid content before a 1st washing | cleaning process.
You may further provide the process of isolate | separating solid content from the 2nd washing | cleaning liquid containing the said silicon particle after the 2nd washing | cleaning process, and washing the solid content isolate | separated from the 2nd washing | cleaning liquid.

Furthermore, the present invention also provides a silicon purification method for removing impurities by melting and then solidifying the solid content containing the silicon particles obtained by the metal-containing material removal method of the present invention.
The various embodiments shown here can be combined with each other.

(A)-(c) are the (a) 1st washing | cleaning apparatus in a 1st washing | cleaning process of the metal containing material removal method of one Embodiment of this invention, (b) The neutralization processing apparatus in the neutralization treatment process, (c) ) It is a schematic sectional view of a second cleaning device in the second cleaning step. (A), (b) is the schematic cross section of (a) the 1st washing device in the 1st washing process of the metal content removal method of one embodiment of the present invention, and (b) the 2nd washing device in the 2nd washing process. FIG. It is a flowchart in an impurity measurement experiment, a particle size distribution measurement experiment, and a silicon purification experiment in an effect demonstration experiment of the present invention. It is a flowchart of the solid-liquid separation process of the waste slurry in the effect verification experiment of this invention. It is the graph which showed the measurement result of the particle size distribution of the silicon | silicone collection solid content after the grinding | pulverization process in the effect verification experiment of this invention, the 1st washing | cleaning process, and the neutralization process process, or the solid content containing a silicon particle. .

  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.

FIG. 1 shows (a) a first cleaning device in a first cleaning step, (b) a neutralization processing device in a neutralization processing step, and (c) a second cleaning step in the metal-containing material removal method of one embodiment of the present invention. It is a schematic sectional drawing of the 2nd washing | cleaning apparatus in.
In one embodiment of the present invention, the method for removing a metal-containing material includes a waste slurry obtained by machining silicon and containing silicon particles 2 containing silicon particles, or a silicon recovered solid content 1 separated from the waste slurry. A first cleaning step for cleaning with one cleaning liquid 3; a neutralization processing step for processing the first cleaning liquid 3 containing silicon particles 2 with a base; and a solid containing silicon particles 2 separated from the first cleaning liquid 3 treated with the base. A second washing step of washing the minute or slurry with the acidic second washing liquid 11.
The metal-containing material removal method of the present embodiment includes a pulverization step before the first washing step, a first water washing / solid-liquid separation step after the neutralization treatment step, and a second water washing / washing step after the second washing step. You may provide a solid-liquid separation process and a drying process.
This embodiment will be described below.

1. Each component of the metal inclusion removal method First, each component of the metal inclusion removal method of the present embodiment will be described.
1-1. Silicon Particles Silicon particles 2 are particulate silicon. For example, the silicon particles 2 may contain impurities.
The particle size of the silicon particles 2 is not particularly limited, but is, for example, 0.1 to 5000 μm.

1-2. Waste slurry obtained from silicon machining The waste slurry produced by silicon machining is not particularly limited, but, for example, waste slurry produced by cutting or polishing a silicon lump or silicon wafer using a slurry containing abrasive grains and coolant. It is. In silicon machining, for example, a cutting blade, a wire, a polishing wheel, or the like is used.
As an example of silicon machining in this embodiment, silicon machining for cutting a silicon ingot contained in a silicon lump with a multi-wire saw device (hereinafter referred to as “MWS”), and a silicon ingot with a wheel-type polishing device. The waste slurry generated by machining the silicon to be polished will be described.

In MWS, a wire is wound around a plurality of rollers, wound, and a slurry containing abrasive grains and coolant is supplied to the wire to run, and a silicon ingot is pressed against the wire and cut. In the wheel type polishing apparatus, polishing is performed by rotating a wheel in which abrasive grains are fixed with an adhesive and moving a silicon ingot while supplying slurry.
When a silicon ingot is cut or polished using these devices, silicon scraps, crushed abrasive grains and non-pulverized abrasive grains, and metal scraps that are wear pieces of wires and polishing wheels are contained in the slurry. The waste slurry is discharged.

Here, the structure and composition of the slurry used in silicon machining will be described. The slurry is composed of abrasive grains and a coolant that disperses the abrasive grains. The type of abrasive grains is not limited and is made of, for example, SiC, diamond, CBN, alumina, or the like.
The type of the coolant is not limited. For example, an oil-based coolant (oil based on mineral oil), an aqueous coolant (a glycol solvent based on water (for example, ethylene glycol, propylene glycol or polyethylene glycol), surfactant) Or an organic acid added thereto). The coolant is mainly composed of an organic solvent (water-soluble organic solvent) such as ethylene glycol, propylene glycol, or polyethylene glycol, and an additive such as an organic acid, a basic aqueous solution, or bentonite is 10 wt% or less (preferably 3 wt% or less). ) It may be added. Note that the phrase “having an organic solvent as a main component” here means that, for example, the coolant may contain 20 wt% or less (preferably 15 wt% or less) of water.

1-3. Silicon recovered solid content separated from waste slurry Silicon recovered solid content 1 separated from the waste slurry is a solid content obtained by performing solid-liquid separation on the waste slurry or its concentrated content described in “1-2”. The solid content separation method is not particularly limited, and examples thereof include a centrifugal separator, a filtration device, and a distillation device.
A separation method using a solid-liquid separation device will be described as an example of a separation method of solid content from the waste slurry of the present embodiment.

  First, the solid slurry 1 is used to obtain the silicon recovered solid content 1 by solid-liquid separation of the waste slurry or its concentrated content. The configuration of the solid-liquid separation device is not particularly limited as long as it is a configuration capable of solid-liquid separation of the waste slurry or its concentrated component to obtain the silicon recovered solid content 1, and the solid-liquid separation device is, for example, a centrifugal separator. A solid-liquid separation device such as a separator, a filtration device or a distillation device is used alone or in combination of two or more thereof in series. Specific examples of the combination are (1) a centrifuge and a distillation device, (2) a centrifuge and a filtration device, or (3) a filtration device and a distillation device. In (1) to (3), two or more centrifuges, filtration devices, or distillation devices may be included. Each solid-liquid separation device may send either the separated liquid or solid content to the next solid-liquid separation device, a part of liquid and a mixture of solids or a part of solid and liquid. The mixture may be sent to the next solid-liquid separator.

1-4. Metal-containing material The metal-containing material is generated from a cutting blade, a wire, a grinding wheel, or a processing device structural material used for machining silicon, and is contained in the waste slurry or silicon recovery solid content 1. The metal-containing material is, for example, a metal (for example, metal powder or the like) or a metal compound (for example, a chloride such as iron chloride or a hydroxide such as iron hydroxide). Further, for example, the metal-containing material is a substance containing at least one of Al, B, Ca, Cr, Cu, Fe, Ni, P, Ti, and Zn.

1-5. Cleaning Device The cleaning device includes a first cleaning device 7 and a second cleaning device 12. The cleaning device is not particularly limited as long as the first cleaning step or the second cleaning step can be performed. For example, the cleaning device includes a cleaning tank 4, a stirrer 5 provided in the cleaning tank 4, and an ultrasonic transmission device 6. . The first cleaning device 7 and the second cleaning device 12 may be the same or different.

1-6. Neutralization Treatment Device The neutralization treatment device 10 is not particularly limited as long as the neutralization treatment step can be performed. For example, the neutralization treatment tank 8, the stirrer 5 provided in the neutralization treatment tank 8, and the ultrasonic transmission device 6 is composed. Moreover, the neutralization processing apparatus 10 may be the same as the 1st washing | cleaning apparatus 7 or the 2nd washing | cleaning apparatus 12, and may differ.

1-7. Cleaning liquid The cleaning liquid includes the first cleaning liquid 3 and the second cleaning liquid 11. The cleaning liquid is acidic before the first cleaning step or the second cleaning step. The cleaning liquid is not particularly limited as long as it is a solution in which an acidic substance is dissolved in a solvent containing water. Further, the first cleaning liquid or the second cleaning liquid contains at least one of sulfuric acid, hydrofluoric acid, hydrochloric acid, hydrogen peroxide, hydrobromic acid, nitric acid, citric acid, acetic acid, formic acid, oxalic acid, and lactic acid, for example. Can do. The pH of the cleaning liquid may be less than 7, but is preferably 0-4. The pH of the cleaning liquid is, for example, 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, or 4. The pH of the cleaning liquid may be within a range between any two of the numerical values exemplified here.

  The cleaning liquid can also contain an organic solvent if it is acidic before the cleaning step. The organic solvent is preferably compatible with the coolant and has a lower boiling point than the coolant. For example, the organic solvent has 1 to 6 carbon atoms (preferably any one of 1, 2, 3, 4, 5 and 6). Alcohol) or a ketone having 3 to 6 carbon atoms (preferably, a range between any two of 3, 4, 5 and 6). The organic solvent is more preferably one composed of one selected from the group consisting of methanol, ethanol, isopropyl alcohol and acetone, or a mixture of two or more. In this case, it becomes easy to dissolve and remove the residual coolant in the cleaning liquid.

Examples of acidic substances (substances that dissolve in a solvent such as water and release protons) include inorganic or organic acidic substances. Examples of inorganic acidic substances include hydrogen chloride, sulfuric acid, nitric acid, hydrogen fluoride, and hydrogen bromide. Examples of the organic acidic substance include citric acid, acetic acid, formic acid, oxalic acid, and lactic acid. The cleaning liquid only needs to contain at least one kind of acidic substance, and may contain both an inorganic acidic substance and an organic acidic substance. Hereinafter, a cleaning liquid containing only an inorganic acidic substance is called an inorganic acidic cleaning liquid, and a cleaning liquid containing only an organic acidic substance is called an organic acidic cleaning liquid.
The cleaning liquid is preferably composed of an inorganic acidic cleaning liquid. A compound newly generated by the reaction of an impurity contained in silicon recovered solids 1 and the like with an inorganic acid generally has a lower boiling point than a compound generated by a reaction with an organic acid, and may be easily removed. It is.

The cleaning liquid is preferably non-oxidizing with respect to silicon. In the present invention, “non-oxidizing” means that the oxidizing power of silicon is weaker than that of sulfuric acid. When the cleaning liquid is non-oxidizing with respect to silicon, it is possible to suppress a decrease in silicon recovery rate due to silicon oxidation. Examples of inorganic acidic substances that are non-oxidative to silicon include sulfuric acid, hydrofluoric acid, and hydrochloric acid.
The cleaning liquid may contain hydrogen peroxide. In this case, there is an advantage that metal waste can be removed in a short time. The ratio of hydrogen peroxide is, for example, 0.1 to 5 wt%, specifically, for example, 0.1, 0.5, 1, 2, 3, 4, 5 wt%. The ratio of hydrogen peroxide may be in a range between any two of the numerical values exemplified here.
As the second cleaning liquid 11, for example, an inorganic acid solution made of any one of hydrochloric acid, hydrofluoric acid, sulfuric acid, and nitric acid, or a mixture thereof can be used. The solvent of the second cleaning liquid 11 is preferably water.

1-8. A base is a substance that dissolves in a solvent such as water and releases hydroxide ions or becomes a proton acceptor (basic substance) or a base solution 9 in which this substance is dissolved in a solvent such as water. Although it does not specifically limit, For example, they are sodium hydroxide, calcium hydroxide, magnesium hydroxide, etc., or ammonia aqueous solution, magnesium hydroxide aqueous solution, cupric hydroxide aqueous solution, sodium hydroxide aqueous solution, potassium hydroxide aqueous solution etc. In addition, as the base, one type of base may be used, or a mixture of several types of bases may be used.
Further, when a base containing an alkali metal is used, the alkali metal may be mixed into the solid content containing the silicon particles 2, but these alkali metals can be easily removed together with slag in the silicon purification method described later. . The base solution 9 is preferably a weak base, more preferably one or a mixture of two or more selected from the group consisting of an aqueous ammonia solution, an aqueous magnesium hydroxide solution, and an aqueous cupric hydroxide solution. .

2. Metal content removal method 2-1. Grinding process Waste slurry or silicon recovered solids 1 obtained from silicon machining can be ground. This is because the cleaning effect of the waste slurry or silicon recovery solid content 1 can be enhanced. The pulverization method is not particularly limited. For example, the silicon recovery solid content 1 may be pulverized to a specific size using a pulverizer. Moreover, in the case of a waste slurry, the agglomerated silicon particles 2 contained in the waste slurry can be dispersed to some extent by this step.

This crushing step may be omitted. Here, the pulverization step refers to all known methods for pulverizing the agglomerated silicon particles 2 contained in the waste slurry or silicon recovery solid content 1 to a specific size, and includes apparatuses such as a ball mill, a jet mill, and a vibration vacuum dryer. Can be used.
As the pulverization conditions, it is preferable that the particle size is as small as possible in order to enhance the cleaning effect. On the other hand, when the particle size is small, contamination from the structural material of the pulverizer increases, and the pulverization cost increases. Since there exists a problem, it is preferable that the average value of the particle diameter after a grinding | pulverization exists in the range of 10 micrometers or more and less than 10 mm from practical use. More preferably, it is in the range of 100 μm or more and less than 1 mm.
In the present specification, “particle size” means a value measured by a method based on JIS R1629. For example, “a powder having a particle size of less than X μm” means a powder in which the particle size of 98% of the particles in the powder is less than X μm. Further, for example, “powder of powder Y μm or more and less than Z μm” means a powder remaining after removing “powder of particle size less than Y μm” from “powder of particle size less than Z μm”.

2-2. First Washing Step The waste slurry containing silicon particles 2 obtained from silicon machining or the silicon recovery solid content 1 separated from the waste slurry is washed with an acidic first washing liquid.
This step can be performed using the first cleaning device 7. Moreover, in order to disperse the silicon particles 2, the first cleaning liquid 3 can be stirred by the stirrer 5. In order to promote the dispersion of the silicon particles 2, the ultrasonic transmission device 6 can irradiate the first cleaning liquid 3 with ultrasonic waves to vibrate the silicon particles 2 and the like. Although the time which performs a 1st washing | cleaning process is not specifically limited, For example, it is 30 second-10 hours.
This step is performed for the purpose of cleaning the silicon particles 2. More specifically, for example, (1) residual organic substances derived from coolant such as glycol solvents and additives used for machining silicon are acid solution. (2) Dissolving and removing metal debris that is a worn piece of the wire in the cleaning liquid, (3) Pretreatment for enhancing the dispersion effect by neutralization, etc. .

2-3. Neutralization treatment process The 1st washing | cleaning liquid containing the silicon particle 2 after a 1st washing | cleaning process is processed with a base.
This step can be performed using the neutralization apparatus 10. Alternatively, the first cleaning device 7 can be used. Further, in order to disperse the silicon particles 2, the first cleaning liquid 3 to which the base solution 9 has been added can be stirred by the stirrer 5. In addition, in order to promote the dispersion of the silicon particles 2, it is possible to oscillate the silicon particles 2 and the like by irradiating the first cleaning liquid 3 to which the base solution 8 has been added with the ultrasonic transmission device 6 with ultrasonic waves. Although the time which performs a neutralization process process is not specifically limited, For example, it is 30 second-1 hour.
The method of treating with a base is not particularly limited, and examples thereof include a method of adding the base solution 9 to the first cleaning liquid 3 and a method of adding a basic substance directly to the first cleaning liquid 3.
In this neutralization treatment step, it is not always necessary to neutralize all of the acidic substances contained in the first cleaning liquid 3, and an extra base solution 9 or the like may be added.
The pH value of the first cleaning liquid 3 after the neutralization treatment step is not particularly limited. For example, the pH value is in the range of 5 or more and less than 10, for example, any of the pH values of 5, 6, 7, 8, 9, 10 Or a range between the two). This is because the dispersion effect of the silicon particles 2 is enhanced when the pH is 5 or more. Moreover, when pH becomes 10 or more, gelatinization of silicon may advance.

  By performing this neutralization treatment step, the dispersion of the silicon particles 2 contained in the first cleaning liquid 3 can be promoted. This will be described with reference to the drawings. 2A is a schematic cross-sectional view of the first cleaning device 7 showing the silicon particles 2 in the first cleaning step, and FIG. 2B is a second view showing the silicon particles 2 in the second cleaning step. 2 is a schematic cross-sectional view of the cleaning device 12. FIG. In the first cleaning step, the silicon particles 2 partially form silicon particle aggregates 13 as shown in FIG. 2A, and the metal-containing material inside the silicon particle aggregates 13 Can not be removed sufficiently. Dispersion of the silicon particles 2 constituting the silicon particle aggregate 13 can be promoted by adding the base solution 9 or the like to the first cleaning liquid 3 containing the silicon particle aggregate 13 and performing neutralization treatment. As a result, as shown in FIG. 2B, the number of silicon particle aggregates 13 is greatly reduced, and the silicon particles 2 are more dispersed. By performing a second cleaning step, which will be described later, in a state where the silicon particles 2 are more dispersed, the metal-containing material inside the silicon particle aggregate 13 that could not be removed in the first cleaning step is removed. Can do.

  Although the reason why the dispersion of the silicon particles 2 constituting the silicon particle aggregate 13 is promoted by performing this neutralization treatment step is not clear, for example, the surface charge of the silicon particles 2 may change. Further, for example, it is conceivable that a part of the polymer compound contained in the waste slurry or the silicon recovery solid content 1 is easily dissolved by increasing the pH.

2-4. First Water Washing / Solid-Liquid Separation Step Solid-liquid separation treatment and water washing can be performed on the first washing liquid 3 containing the silicon particles 2 after the neutralization treatment step. More specifically, for example, the first cleaning liquid 3 and the solid content can be separated from each other using a water washing / solid-liquid separation device, and washing can be performed with pure water. Thereby, the solid content containing the silicon particles 2 after washing can be obtained. Note that this step may be omitted, and the second cleaning step may be performed on the slurry containing silicon particles separated from the first cleaning liquid 3 containing the silicon particles 2 after the neutralization treatment step. For example, the first cleaning liquid 3 may be evaporated.
The water washing / solid-liquid separation device can be constituted by combining two or more solid-water separation devices such as a centrifugal separator, a filtration device or a distillation device, and two or more pure water supply devices in series.

2-5. 2nd washing | cleaning process The solid content or slurry containing the silicon particle 2 isolate | separated from the 1st washing | cleaning liquid processed with the base in the neutralization process process is wash | cleaned with an acidic 2nd washing | cleaning liquid. As long as this solid content or slurry is after the neutralization treatment step, it may have undergone another step thereafter.
This step can be performed using the second cleaning device 12. Further, in order to disperse the silicon particles 2, the second cleaning liquid 11 can be stirred by the stirrer 5. Further, in order to promote the dispersion of the silicon particles 2, the ultrasonic transmission device 6 can irradiate the second cleaning liquid 11 with ultrasonic waves to vibrate the silicon particles 2 and the like. Although the time which performs a 2nd washing | cleaning process is not specifically limited, For example, it is 30 second-10 hours.
Since the silicon particles 2 contained in the second cleaning liquid 11 have undergone a neutralization treatment step, those constituting the silicon particle aggregate 13 are reduced, and the dispersion of the silicon particles 2 is promoted. As a result, the metal-containing material that could not be removed in the first cleaning step existing in the silicon particle aggregate 13 or the like can be efficiently cleaned and removed. Therefore, the impurity removal effect can be dramatically enhanced by performing the second cleaning step after performing the neutralization treatment step.

2-6. Second Water Washing / Solid-Liquid Separation Step Solid-liquid separation treatment and water washing can be performed on the second washing liquid 11 containing the silicon particles 2 after the second washing step. More specifically, for example, using a water-washing / solid-liquid separation device, solid-liquid separation between the second washing liquid 11 and the solid content can be performed, and the solid content can be washed with pure water. Thereby, the solid content containing the silicon particles 2 after washing can be obtained. Note that this step may be omitted, and the second cleaning liquid 11 may be evaporated in the next drying step, for example.
The water washing / solid-liquid separation device can be constituted by combining two or more solid-water separation devices such as a centrifugal separator, a filtration device or a distillation device, and two or more pure water supply devices in series.

2-7. Drying process The solid content containing the silicon particles 2 after the second washing liquid or the second water washing / solid-liquid separation process containing the silicon particles 2 after the second washing process can be dried. By drying, the cleaning liquid remaining in the solid content including the silicon particles 2, the organic solvent having a low boiling point, and the like can be removed.
Drying can be performed, for example, by heating or reducing the ambient atmosphere.
In addition, you may abbreviate | omit a drying process and heat-dry in the silicon | silicone purification method mentioned later.
Moreover, this process can be performed with a drying apparatus, and the drying apparatus may be a drying and pulverizing apparatus having a function of pulverizing the solid content including the silicon particles 2. Drying and pulverization may be performed at the same time, pulverization may be performed after drying, or vice versa. The solid content can be pulverized using a known apparatus such as a pulverizing apparatus using a pulverizing blade, a ball mill, a jet mill, or a vibration vacuum dryer.

2-8. In addition, when the solid content containing silicon particles is powder, the solid content forming step and the solid content classification / separation step can be incorporated as necessary. The molding process can be performed as a pretreatment for melting to increase bulk specific gravity and increase transport efficiency, or to increase thermal conductivity and facilitate melting, and pressurizes silicon-containing powder to form a plate, An apparatus having any configuration can be used as long as the apparatus granulates in a block shape, a pellet shape, or the like. The classification / separation process includes, for example, classification of particles based on physical parameters such as particle size and density using an inertia classifier or centrifugal classifier, and a method of removing magnetic impurities such as iron using a magnet. is there.

3. Silicon Purification Method A solid content containing the silicon particles 2 obtained by the metal-containing material removal method described in “2.” can be melted and then solidified to remove impurities, thereby obtaining a purified silicon mass. As a method for removing impurities, a known purification method can be used in which the solid content including the silicon particles 2 is melted and then solidified. For example, slag generated during melting is removed, phosphorus is removed under reduced pressure melting. Or removing segregation impurities by unidirectional solidification. More specifically, for example, by melting the solid content containing the silicon particles 2 from below, the silicon is unidirectionally solidified to form a silicon lump, and further, the upper part of the obtained silicon lump. (Metal impurity concentration portion) can be cut and removed to obtain a purified silicon ingot.

  The silicon purification method can be performed using a heating device. For example, the solid content containing the silicon particles 2 is heated and melted using the heating device. Any heating device may be used as long as it can melt the solid content including silicon particles 2 by heating the solid content including silicon particles 2 to a temperature higher than the melting point of silicon, and more preferably 1800 ° C. or higher. What can heat at 2000 degreeC or more is preferable. Moreover, it is more preferable that the heating device can heat and melt the solid content containing the silicon particles 2 in an inert gas.

In addition, before heating the solid content including the silicon particles 2 to a temperature equal to or higher than the melting point of silicon, it is lower than the melting point of silicon under reduced pressure or in the presence of an inert gas, and higher than the boiling point of the cleaning liquid used in the metal-containing material removal method The solid content containing the silicon particles 2 can also be fired at a high temperature. As a result, the cleaning liquid remaining in the solid content can be removed. For example, this solid content can be heated to a temperature of 300 ° C. or higher and 600 ° C. or lower in an inert gas atmosphere and held for 2 hours or longer to remove impurities.
Further, during the melting of the solid content including the silicon particles 2, the slag generated by melting the solid content can be separated and removed. For example, when an alkali metal hydroxide is used as a neutralizing agent in the neutralization treatment step described in “2-3”, the alkali metal may be eluted in the slag. At this time, the alkali metal can be removed by removing the slag.
The heating device may have a function of purifying silicon using a known purification method.
The silicon lump from which impurities obtained by this silicon purification method are removed can be recovered as purified silicon as it is.

4). Effect Verification Experiment Next, the effect verification experiment of the present invention will be described. Here, an impurity measurement experiment and a particle size distribution measurement experiment in each step of the metal-containing material removal method were performed. Moreover, the silicon refinement | purification experiment using the solid content containing the silicon particle 2 which performed the metal inclusion removal method, and the characteristic evaluation experiment of the solar cell manufactured using the refined | purified silicon were conducted. FIG. 3 is a flowchart in an impurity measurement experiment, a particle size distribution measurement experiment, and a silicon purification experiment. In addition, as a comparative example, a method for removing a metal-containing material without performing a neutralization treatment step was also performed, and an impurity measurement experiment was performed in each step.

4-1. Impurity measurement experiment and particle size distribution measurement experiment 4-1-1. Acquisition of silicon recovery solid content 4-1-1-1. Silicon Machining Polycrystalline silicon was cut using a slurry containing a multi-wire saw and abrasive grains. First, about 15 wt% of water, a dispersant for facilitating dispersion of abrasive grains, and an organic acid as a pH adjuster were added to propylene glycol to adjust the coolant. Further, a slurry was prepared by mixing abrasive grains in this coolant at a weight ratio of 1: 1. Using this slurry and a multi-wire saw, polycrystalline silicon was cut and waste slurry was discharged from the multi-wire saw device.
Here, SiC having a particle size of 10 μm or more and 30 μm or less was used as the abrasive grains. The waste slurry contained about 10 wt% to 12 wt% of cutting waste made of silicon.

4-1-1-2. Solid-liquid separation process Using a solid-liquid separation device, solid waste separation of the waste slurry discharged from the multi-wire saw device was performed, and silicon recovery solid content 1 was obtained.
FIG. 4 is a flowchart in the solid-liquid separation step.
As the solid-liquid separator, a device including a primary centrifuge, a secondary centrifuge and a distillation device was used. Solid-liquid separation was performed by combining primary centrifugation, secondary centrifugation and distillation. Details will be described below.
(1) Primary Centrifugation Step First, waste slurry is put into a primary centrifuge and subjected to primary centrifugation so that the centrifugal force is 500 G (relatively low centrifugal force, generally called “primary separation”). By operating the separator, the abrasive grains were separated into the primary solid content (heavy specific gravity liquid) of the main component and the coolant and chips (mainly containing silicon) into the primary liquid content (low specific gravity liquid) of the main component.
(2) Secondary Centrifugation Step Next, the primary liquid (low specific gravity liquid) is put into a secondary centrifuge, and the centrifugal force is 3500G (relatively high centrifugal force. The secondary centrifuge was operated so that the coolant became the main component, and the coolant was separated into the secondary liquid component and the chips and abrasive grains were separated into the secondary solid component.
(3) Distillation step The secondary liquid was put into a distillation apparatus, and the secondary liquid was subjected to distillation at a final vacuum of 10 Torr and 160 ° C to obtain a silicon recovered solid 1 and a purified coolant. The silicon recovered solid content 1 contained 90 wt% or more of silicon, and the rest were impurities. Among the impurities contained in the silicon recovery solids 1, the content of iron, boron, and phosphorus that strongly affects the characteristics of the semiconductor was measured using an ICP light emitting device. The results are shown in Table 1.

  From this result, it was found that the silicon recovery solid content 1 contained a large amount of iron and a certain amount of boron and phosphorus.

4-1-2. Pulverization process Next, the silicon recovered solid content 1 was pulverized using a pulverizer. The pulverization conditions were adjusted so that the average particle size was 200 μm. Specifically, using a jet mill apparatus, 200 kg of silicon recovered solid content 1 was sent per hour, and 150 L of air was circulated and pulverized.
Using a particle size distribution meter, the particle size distribution of the powder of silicon recovered solid content 1 after the pulverization step was measured. FIG. 5 is a graph showing the measurement results of the particle size distribution of the solid content powder including the silicon recovered solid content 1 or the silicon particles 2 after the pulverization step, after the first washing step and after the neutralization treatment step. When FIG. 5 was seen, it turned out that the thing of the particle size of 1 micrometer or less to 100 micrometers or more is contained in the silicon | silicone collection solid content 1 after a grinding | pulverization process.

4-1-3. First Cleaning Step Next, in the first cleaning device 7, the mass ratio of silicon recovered solids 1 and the first cleaning liquid 3 is 1:10 in the cleaning basket 4 using the first cleaning liquid 3 made of 10 wt% hydrochloric acid aqueous solution. And mixed. While stirring using a stirrer 5 rotating at 200 rpm, a high frequency of 38 kHz was further sent using an ultrasonic cleaning device 6 having a high frequency output of 120 W, and stirring and ultrasonic cleaning were performed for 4 hours. Here, a part of the 1st washing | cleaning liquid 3 which disperse | distributed the silicon | silicone collection solid content 1 was extracted, filtered and dried, solid content containing the silicon particle 2 was taken out, and the impurity analysis was performed. Table 2 shows the impurity content contained in this solid content.

  Table 2 shows that iron is greatly reduced but still exists at 400 wtppm or more, and the content of boron and phosphorus is also reduced, but it is still a raw material for solar cells. It was found to have a high content.

  Moreover, the particle size distribution of the powder of the solid content containing the silicon particles 2 after the first cleaning step was measured using a particle size distribution meter. The result is shown in FIG. Referring to FIG. 5, most of the solids including the silicon particles 2 after the first cleaning step have a particle size of 1 μm or more and 10 μm or less, and the particle size is smaller than that after the pulverization step. I understood. The reason why the particle size becomes smaller is, for example, that when the particle size is large, it is considered that the silicon particles 2 are aggregated. In the first cleaning step, the agglomerated silicon particles 2 are dispersed by stirring and ultrasonic cleaning. It is considered that the particle size was reduced due to the promotion.

  Moreover, also about the comparative example which does not perform a neutralization process process, it performed to the 1st washing | cleaning process by the method similar to the above, and analyzed the impurity contained in the solid content contained in the silicon particle 2 by the method similar to the above. Table 3 shows the impurity content contained in the solid content.

  Up to this point, the comparative example has undergone the same steps as the effect verification experiment of the present invention, so the results in Table 3 showed almost the same results as in Table 2.

4-1-4. Neutralization treatment step Next, an aqueous ammonia solution was added to the first washing liquid 3 until the pH of the first washing liquid 3 showed 6 to 8, and neutralization treatment was performed. Thereafter, the stirrer 5 was stirred at 200 rpm for 0.1 hour.
Moreover, the particle size distribution of the powder of the solid content containing the silicon particles 2 after the neutralization treatment step was measured using a particle size distribution meter. The result is shown in FIG. Referring to FIG. 5, most of the solid content including the silicon particles 2 after the neutralization treatment step has a particle size of 0.1 μm or more and 1.0 μm or less, and the particle size compared with that after the first cleaning step. Was found to be smaller. The reason why the particle size is reduced is considered to be that, for example, the dispersion of the silicon particles 2 contained in the silicon particle aggregate 13 is promoted by performing the neutralization treatment process, and the particle size is reduced.

4-1-5. First washing / solid-liquid separation step Next, the first washing solution 3 after the neutralization treatment step is pumped to the washing / solid-liquid separation device and rinsed with 5 times the amount of the first washing solution 3 with pure water. The solid content containing silicon particles 2 was obtained by solid-liquid separation by filtration. Table 4 shows the impurity content contained in this solid content.

  When Table 4 was seen, it turned out that the impurity is increasing by the neutralization process process. The reason is not necessarily clear, but it is thought that the impurities eluted in the cleaning liquid reacted with the basic substance and precipitated as a solid content.

  Moreover, about the comparative example which does not perform a neutralization treatment process, a neutralization treatment process is abbreviate | omitted, the 1st washing | cleaning liquid 3 after a 1st washing | cleaning process is pumped to a water-washing / solid-liquid separation apparatus, and 1st water washing is carried out by said method. -A solid-liquid separation process was performed. Table 5 shows the impurity content contained in the solid content including the silicon particles 2 obtained in this comparative example.

  When Table 5 was seen, compared with Table 3 of the comparative example after a 1st washing | cleaning process, it turned out that content is reducing little by little in iron, boron, and phosphorus. Moreover, it turned out that the comparative example has few impurities compared with Table 4 which showed the impurity content after the neutralization process process of the effect verification experiment of this invention.

4-1-6. Second Cleaning Step Next, in the second cleaning device 12, the solid content containing the silicon particles 2 and the second cleaning liquid 11 in the cleaning basket 4 are 1:10 using the second cleaning liquid 11 made of a 25 wt% sulfuric acid aqueous solution. Mixed by mass ratio. The second cleaning liquid 11 was stirred using a stirrer 5 rotating at 200 rpm, and stirred and washed for 4 hours.

4-1-7. Second Washing / Solid-Liquid Separation Step Next, the second washing solution 11 after the second washing step is pumped to the washing / solid-liquid separation device and rinsed with 5 times the amount of the second washing solution 11 with pure water. The solid content containing silicon particles 2 was obtained by solid-liquid separation by filtration. Table 6 shows the impurity content contained in this solid content.

Looking at Table 6, compared to Table 4, which is the impurity content after the neutralization treatment step, the iron content is significantly reduced, the boron content is less than half, and the phosphorus content is greatly reduced. I understood that. The reason for this is that, for example, the neutralization treatment step promotes the dispersion of the silicon particles 2 contained in the silicon particle aggregates 13, and the particle size of the solids containing the silicon particles 2 is small as shown in FIG. Become. As a result, it is considered that the surface area of the silicon particles 2 in contact with the second cleaning liquid 11 is increased, and the cleaning effect is increased.

  Moreover, about the comparative example which does not perform a neutralization process process, solid content containing the silicon particle 2 obtained at the 1st water washing and solid-liquid separation process is a 2nd washing process and 2nd water washing and solid-liquid separation by said method. The process was performed. Table 7 shows the impurity content contained in the solid content including the silicon particles 2 obtained as a result.

  When Table 7 is seen, compared with Table 5 which showed the impurity content of the solid content containing the silicon particle 2 after the 1st water washing and solid-liquid separation process of a comparative example, iron content is about 2/3. Although decreasing, the contents of boron and phosphorus were not decreased. Moreover, it turned out that it has a higher impurity content than iron, boron, and phosphorus compared with Table 6. For this reason, for example, in the comparative example, since the neutralization process is not performed, the impurities inside the silicon particle aggregate 13 contained in the solid content cannot be sufficiently removed, and thus the impurity content is considered to be high.

4-1-8. Next, the solid content containing the silicon particles 2 was dried in a drying apparatus. In this drying, the solid content was heated to 60 ° C. in air at 0.1 atm for 1 hour.

4-2. Silicon refining experiment Using a heating apparatus, solid content including silicon particles 2 obtained in the experiment described in "4-1" was baked, melted, and purified. Specifically, this solid content was put in a graphite crucible and baked at 600 ° C. for 1 hour by resistance heating under a vacuum of 10 Torr, thereby removing trace organic substances slightly remaining in the solid content. Next, the solid content was heated to 1800 ° C. by high-frequency induction heating in an Ar atmosphere to melt silicon contained in the solid content. Thereafter, the temperature was lowered from below the crucible, so that silicon was unidirectionally solidified to obtain a silicon lump. Furthermore, the upper part (concentration part of a metal impurity) of the obtained silicon lump was cut and removed to obtain a purified silicon ingot.
The impurity content contained in the purified silicon ingot is shown in Table 8 together with the impurity content contained in a normal solar cell silicon ingot.

  Referring to Table 8, the silicon ingot purified by the silicon purification experiment of the present invention had an iron content higher than that of a normal solar cell silicon ingot, but was 1 wtppm or less. It was also found that the boron content was the same, and the phosphorus content was slightly higher.

  Next, the solid content containing the silicon particles 2 obtained by the comparative example not performing the neutralization treatment step of the experiment described in “4-1” was subjected to silicon purification by the above method. The impurity content contained in the purified silicon ingot obtained as a result is shown in Table 9 together with the impurity content contained in a normal solar cell silicon ingot.

  When Table 9 was seen, the silicon ingot obtained by the comparative example had clearly many impurities compared with the normal silicon ingot, and was judged to be unsuitable for use as a solar cell material.

4-3. Solar Cell Characteristic Evaluation Experiment A silicon ingot obtained by the silicon refining experiment of the present invention described in “4-2” was cut into a thickness of 250 μm with a multi-wire saw apparatus to obtain a purified silicon wafer (polycrystalline substrate). A solar cell was produced using this purified silicon wafer, and the photoelectric conversion characteristics were measured.
Table 10 shows the characteristics of a solar cell using a purified silicon wafer obtained by the silicon purification experiment of the present invention and a solar cell using a commercially available ordinary silicon wafer for solar cells. Table 10 shows a relative comparison of the characteristics of solar cells using purified silicon wafers, with the characteristics of solar cells using ordinary silicon wafers for solar cells being 100%.

  When Table 10 was seen, it turned out that the solar cell produced using the silicon wafer which refine | purified waste slurry has a substantially equivalent output as the solar cell produced using the normal silicon wafer.

  1: Silicon recovery solid content 2: Silicon particles 3: First cleaning liquid 4: Cleaning tank 5: Stirrer 6: Ultrasonic transmitter 7: First cleaning apparatus 8: Neutralization processing tank 9: Base solution 10: Neutralization processing apparatus 11: Second cleaning liquid 12: Second cleaning device 13: Silicon particle aggregate

Claims (8)

A first washing step of washing silicon waste solids obtained by machining silicon and containing silicon particles or separated from the waste slurry with an acidic first washing liquid;
A neutralization treatment step of treating the first cleaning liquid containing the silicon particles with a base;
A second washing step of washing the solid or slurry containing the silicon particles separated from the first washing liquid treated with the base with an acidic second washing liquid,
A metal-containing material removal method characterized by efficiently removing a metal-containing material resulting from the machining and not removed by the first cleaning step in the second cleaning step.   The first cleaning liquid or the second cleaning liquid contains at least one of sulfuric acid, hydrofluoric acid, hydrochloric acid, hydrogen peroxide, hydrobromic acid, nitric acid, boric acid, citric acid, acetic acid, formic acid, oxalic acid, and lactic acid. The method according to 1.   The method according to claim 1, wherein the base includes at least one of an aqueous ammonia solution, an aqueous magnesium hydroxide solution, and an aqueous cupric hydroxide solution.   The method according to any one of claims 1 to 3, wherein the first cleaning liquid after the neutralization treatment step has a pH of 5 or more and less than 10.   The method according to claim 1, wherein at least one of the first cleaning step, the neutralization treatment step, and the second cleaning step disperses the silicon particles by ultrasonic irradiation.   The method according to any one of claims 1 to 5, further comprising a pulverization step of pulverizing the waste slurry or the silicon recovery solids before the first cleaning step.   The solid content separated from the 2nd washing | cleaning liquid containing the said silicon | silicone particle | grain after the 2nd washing | cleaning process, The process of further washing with water the solid content isolate | separated from the 2nd washing | cleaning liquid was further provided. the method of.   A method for purifying silicon in which impurities are removed by melting and then solidifying the solids containing the silicon particles obtained by the method according to claim 7.

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