WO2007119308A1

WO2007119308A1 - Method of recovering silicon-containing material

Info

Publication number: WO2007119308A1
Application number: PCT/JP2007/054198
Authority: WO
Inventors: Kimihiko Kajimoto; Yoshiyuki Hojo; Masaya Tanaka; Katsumi Takahashi
Original assignee: Sharp Kabushiki Kaisha; Ihi Compressor And Machinery Co., Ltd.
Priority date: 2006-03-17
Filing date: 2007-03-05
Publication date: 2007-10-25
Also published as: TW200804181A; JP2007246366A

Abstract

A method by which a silicon-containing material from which a coolant has been removed is recovered. The method of recovering a silicon-containing material is characterized by comprising the steps of: removing beforehand a water-soluble coolant from a spent slurry resulting from a silicon wafer production process which comprises the water-soluble coolant, abrasive grains, and silicon particles to thereby obtain a solid matter; extracting from the solid matter the water-soluble coolant remaining in the solid matter with a low-boiling organic solvent which has compatibility with the water-soluble coolant and has a lower boiling point than the water-soluble coolant; removing by filtration the low-boiling organic solvent used in the extraction; and recovering the solid matter obtained by the filtration.

Description

Specification

Method for recovering silicon-containing material

Technical field

[0001] The present invention is used when a multi-wire saw (hereinafter referred to as "MWS") or a wrapping apparatus is used to manufacture, for example, a polycrystalline silicon for a solar cell or a silicon wafer for a semiconductor device. Used slurry force The present invention relates to a method for recovering silicon-containing materials.

Background art

[0002] As a method of slicing a silicon ingot into a wafer (thin, plate), there is a method using a wire saw, and in that case, a method of supplying a mixture of bullets and coolant called slurry to the cutting site Is common. Slurries are generally used repeatedly, but each time the slicing force is reached, silicon chips and the like are mixed into the slurry, gradually reducing the cutting performance of the chassis.

[0003] The used slurry contains silicon chips. Until now, these silicon scraps have been disposed of without being used, or as disclosed in Patent Document 1, HF and inorganic acids are used. It was recovered after being used and subjected to many treatments such as filtration and drying.

Patent Document 1: Japanese Patent Laid-Open No. 2001-278612

Disclosure of the invention

Problems to be solved by the invention

[0004] However, in the conventional technology for recovering silicon contained in the used slurry, the equipment has a large force and the number of processes is large and laborious. In particular, when mineral oil is used in the slurry, petroleum-based organic solvents such as kerosene and light oil, and inorganic acids such as HF are required, which is very expensive for safety equipment and treatment for environmental pollution prevention. Was becoming necessary. In addition, the cost of the filtration filter has been a factor in increasing costs because a filtration device is required.

For this reason, there has been a demand for an effective treatment method for silicon scrap in the used slurry. Only However, when the used slurry is used as a silicon-containing material, the organic coolant contained in the slurry can cause various problems. Problems include, for example, the generation of organic harmful substances and contamination due to the adhesion of organic substances in the refining furnace. Therefore, in order to use the used slurry as a silicon-containing material, it is important to reliably remove the coolant.

The present invention has been made in view of such circumstances, and provides a method for recovering a silicon-containing material from which coolant has been removed.

Means for Solving the Problems and Effects of the Invention

[0005] The method for recovering a silicon-containing material according to the present invention comprises removing a used slurry force water-soluble coolant in advance in a silicon wafer manufacturing process containing at least a water-soluble coolant, abrasive grains, and silicon particles. The water-soluble coolant remaining in the solid content is extracted from the solid content using a low-boiling organic solvent that is compatible with the water-soluble coolant and has a lower boiling point than the water-soluble coolant. The low-boiling organic solvent used in the process is removed by filtration, and a solid content obtained by filtration is collected.

[0006] In the present invention, by using a low-boiling organic solvent that is relatively easy to evaporate, the water-soluble coolant remaining in the solid content is extracted, and the low-boiling organic solvent used for the extraction is removed by filtration. , Recover the silicon-containing material from which the water-soluble coolant has been removed. The solid content obtained by filtration contains a low-boiling organic solvent, which can be easily removed because it has a relatively low boiling point.

The recovered silicon-containing material contains a large amount of silicon and can be used in various ways, such as as a raw material for the production of hydrogen gas and sodium silicate, or as a raw material for the production of polysilicon. Further, it can be used as a raw material for producing halosilanes by the method disclosed in JP-A-2005-330149.

In addition, since the water-soluble coolant has been removed from this material, it is possible to avoid problems when organic hazardous substances are generated or contamination occurs due to the adhesion of organic substances in the refining furnace.

Brief Description of Drawings FIG. 1 shows a silicon-containing material recovery system according to Example 1 of the present invention.

FIG. 2 shows a modification of the silicon-containing material recovery system according to Example 1 of the present invention.

FIG. 3 shows a modification of the silicon-containing material recovery system according to Example 1 of the present invention.

FIG. 4 shows a modification of the silicon-containing material recovery system according to Example 1 of the present invention. The

FIG. 5 shows a silicon-containing material recovery system according to Example ² of the present invention.

Explanation of symbols

[0008] 1: Used slurry 3a: Liquid content after primary centrifugation 3b: Solid content after primary centrifugation 4: Regenerated barrel 5a: Liquid content after secondary centrifugation 5b: After secondary centrifugation Solid content 6: Regenerated coolant 7: Excess coolant 9a: Liquid content after distillation 9b: Solid content after distillation 11: Distillation coolant 12: Alcohol 15a: Liquid content after filtration 15b: Solid content after filtration 17a: Liquid after washing 17b: Solid after washing 19a: Liquid after drying 19b: Solid after drying 21: Recycled alcohol 23: Silicon-containing material

BEST MODE FOR CARRYING OUT THE INVENTION

[0009] A method for recovering a silicon-containing material according to an embodiment of the present invention includes a method of previously collecting a water-soluble coolant from a used slurry in a silicon wafer manufacturing process, which contains at least water-soluble coolant, abrasive grains, and silicon grains. A water-soluble coolant remaining in the solid content using a low boiling point organic solvent having a solid content obtained by removing the solid content and having a compatibility with the water-soluble coolant and having a boiling point lower than that of the water-soluble coolant. The low-boiling organic solvent used in the extraction is removed by filtration, and the solid content obtained by filtration is recovered.

[0010] Hereinafter, each step will be described in detail.

1. Solid content acquisition process

First, the solid content is obtained by previously removing the water-soluble coolant used in the manufacturing process of silicon weno, which contains at least water-soluble coolant, abrasive grains, and silicon grains.

[0011] The used slurry is a slurry in which silicon particles are mixed.

The slurry is composed of a barrel and a water-soluble coolant that disperses it. There are no limitations on the type of gunshot particles, but for example, SiC, diamond, CBN, and alumina can also be used. Water soluble One run is a coolant that is compatible with water, and the type of water is not limited, but a water-soluble coolant can also be a water-soluble organic solvent such as ethylene glycol, propylene glycol, or polyethylene glycol. The water-soluble coolant may contain about 5% to 15% water. In this case, it can be avoided that this coolant becomes a dangerous material under the Fire Service Law. In addition, a coolant (bentonite) or the like (a few percent) is usually added to the coolant to disperse the granules and Si chips. In this specification, “%” means “% by weight”.

[0012] Examples of steps included in the silicon wafer manufacturing process include a silicon ingot slicing step and a silicon wafer lapping step. Silicon grains are, for example, silicon chips generated when a silicon wafer is formed by slicing a silicon ingot, or polishing chips generated when lapping a silicon wafer. The silicon concentration in the used slurry is, for example, 10% or more.

[0013] The solid content is obtained by previously removing the used slurry force water-soluble coolant. Although the removal method of a water-soluble coolant is not limited, For example, it is distillation. The distillation method is not limited as long as the water-soluble coolant is evaporated from the used slurry to obtain a solid content. Distillation can be any of atmospheric distillation, vacuum distillation, and vacuum distillation V, but power from the viewpoint of energy saving and safety Vacuum (lOTorr or less) distillation is preferred. The solid content is usually in powder form. The evaporated water-soluble coolant is preferably recovered and used to regenerate the slurry.

[0014] The water-soluble coolant may be removed by centrifugation or filtration in addition to distillation. (1) A combination of centrifugation and distillation. (2) A combination of filtration and distillation. Solids obtained by distillation or centrifugation may be distilled or liquids may be distilled. Only a part of the solid or liquid obtained by distillation or centrifugation may be distilled. Centrifugation or filtration may be primary or multiple.

[0015] The removal of the water-soluble coolant from the used slurry in advance can be performed more specifically, for example, by the following method.

1-1. First method

In the first method, the pre-removal of water-soluble coolant from the used slurry is used. The spent slurry is subjected to primary centrifugation to recover the solids composed mainly of abrasive grains, and the liquid obtained by the primary centrifugation is subjected to secondary centrifugation, so that water-soluble coolant is the main component. This is performed by a method that includes a step of removing a part of the liquid and preliminarily removing the water-soluble coolant by distillation.

[0016] Hereinafter, the steps included in the first method will be described in detail.

(1) Primary centrifugation process

In this process, the above-mentioned used slurry is subjected to primary centrifugation to recover the solid content of the main component of the abrasive grains.

[0017] The primary centrifugation is preferably performed at 100 to 1000G. In the primary centrifugation, the used slurry is separated into the first solid and the first liquid. The first solid content is mainly composed of gunshot particles. Since the barrel generally has a higher specific gravity than the silicon grain, it settles faster than the silicon grain. For this reason, when low-speed centrifugation is performed, the barrels are selectively settled. Since the first solid contains a lot of particles, the first solid can be used to regenerate the slurry. On the other hand, the first liquid contains mainly water-soluble coolant and silicon particles.

[0018] (2) Secondary centrifugation step

In this process, the liquid obtained by the primary centrifugation is secondarily centrifuged to recover a part of the liquid that is mainly composed of water-soluble coolant.

Secondary centrifugation is preferably performed at 2000-5000G. In this way, if centrifugation is performed at a speed higher than that of the primary centrifugation, the solid content that does not settle will also settle in the primary centrifugation. Therefore, by the secondary centrifugation, the first liquid is separated into a liquid mainly composed of water-soluble coolant (second liquid) and sludge that is a solid. The sludge contains silicon particles and cannon particles that did not settle in the primary centrifugation. The second liquid also contains cannonballs and silicon particles. The second liquid is usually used for slurry regeneration, but if the entire amount is used as it is for slurry regeneration, the silicon mass ratio of the regenerated slurry becomes too large, which is not preferable. Therefore, in this method, only a part of the second liquid is collected. The recovered liquid can be used for slurry regeneration.

[0019] (3) Distillation process In this process, a sample consisting of at least one of the remaining liquid and sludge obtained by secondary centrifugation is distilled. The sample to be distilled may be, for example, (1) only the remaining liquid, (2) only sludge, or (3) a mixture of the remaining liquid and sludge. Only a portion of the sludge may be included in the sample. The sludge may be dried before distillation. The drying method is not particularly limited.

[0020] 1-2. Second method

In the second method, the water-soluble coolant is removed from the used slurry in advance by firstly centrifuging the used slurry to collect the solids whose main component is abrasive grains, and then performing the first centrifuge. The sample force which is at least a partial force of the liquid obtained by the above is carried out by a method including a step of previously removing the water-soluble coolant by distillation.

[0021] Hereinafter, steps included in the second method will be described. The primary centrifugation method and distillation method are the same as the first method. In the second method, the sample to be distilled is different from the first method. In the second method, a solid sample is obtained by distilling a sample that has at least a partial force from the primary centrifuge. The sample to be distilled may be, for example, (1) a part of the liquid or (2) the whole of the liquid. If a portion of the liquid is to be distilled, the remaining liquid may be subjected to secondary centrifugation, and the resulting sludge (total or partial) may be included in the sample to be distilled.

[0022] 2. Extraction process

Next, the water-soluble coolant remaining in the solid is extracted from the solid using a low-boiling organic solvent that is compatible with the water-soluble coolant and has a boiling point lower than that of the water-soluble coolant. In this specification, “extraction” means dissolving a water-soluble coolant remaining in the solid content in a low-boiling organic solvent.

[0023] Extraction of the water-soluble coolant can be performed, for example, by adding the low boiling point organic solvent to the solid content and stirring both.

The type of the low-boiling organic solvent is not limited as long as it is compatible with the water-soluble coolant and has a boiling point lower than that of the water-soluble coolant. For example, the number of carbon atoms is 1 to 6 (preferably 1 , 2, 3, 4, 5 and 6 in the range between two alcohols or ketones with a carbon number of up to 6 (preferably in the range between 3, 4, 5 and 6 between the two) It is. like this Specific examples of such alcohols include methanol, ethanol, isopropyl alcohol, and butyl alcohol. A specific example of such a ketone is acetone methyl ketone. The low boiling point organic solvent may be a mixture of a plurality of types of organic solvents. From another point of view, low-boiling organic solvents have boiling points of 50 ° C or higher (preferably 60 ° C or higher, 70 ° C or higher, 80 ° C or higher, 90 ° C or higher, or 100 ° C) than water-soluble coolants. The above is preferable. In this case, the low-boiling organic solvent remaining in the solid content obtained by filtration described below is easily evaporated, and when the low-boiling organic solvent is recovered by distilling the liquid obtained by filtration, distillation is performed. There is an advantage that the purity of the low-boiling organic solvent obtained by the method is increased.

[0024] In order to efficiently dissolve the water-soluble coolant remaining in the solid content in the low boiling point organic solvent, a step of pulverizing the solid content before or during the extraction may be further provided.

[0025] 3. Filtration process

Next, the low-boiling organic solvent used for extraction is removed by filtration. The filtration method and the apparatus used for it are not limited. Filtration is preferably performed using a leaf filter in consideration of efficiency during mass production.

[0026] 4. Cleaning process

After the filtration, it is preferable to provide a step of washing the solid content with a low-boiling organic solvent of the same or different type as the low-boiling organic solvent used for extraction. As a result, the water-soluble coolant remaining in the solid content is more reliably removed. The washing method is not limited, but washing can be performed, for example, by pouring a low-boiling organic solvent over the solid content on the filter paper. Washing is preferably carried out by repeating the step V when the liquid after passing through the solid is poured again from above the solid U. The low boiling organic solvent may be replaced with a new one during repeated washing. Washing is preferably carried out until the transparency of the liquid after washing is below the standard. The transparency of the liquid is an indicator of how much water-soluble coolant is dissolved in the low-boiling organic solvent. If the transparency is below the standard, a sufficient amount of water-soluble coolant is low It can be said that it is indirectly shown that the amount dissolved in the solvent and the solid content is below the standard. Transparency is defined by the factory drainage test method of JIS K 0102, and the standard can be set to 10 mm or 20 mm, for example. [0027] It is preferable to further comprise a step of recovering the low-boiling organic solvent by distilling the liquid obtained by filtration and the liquid after washing. The recovered low-boiling organic solvent can be used again for extraction or washing of residual water-soluble coolant. The distillation of the liquid obtained by filtration and the liquid after washing may be performed together or separately.

[0028] 5. Drying process

Next, it is preferable to provide a step of evaporating the low boiling point organic solvent remaining in the solid content and drying the solid content.

Low boiling organic solvents are relatively easy to evaporate because of their relatively low boiling points. The method for drying the solid content is not limited as long as it can evaporate the low boiling point organic solvent in the solid content. Drying may be natural drying or drying by heating, reduced pressure or a combination of heating and reduced pressure.

The various features shown in the above embodiments can be combined with each other. In the case where a plurality of features are included in one embodiment, one or more of the features can be appropriately extracted and used in the present invention alone or in combination.

Example 1

[0030] Example 1 of the present invention will be described with reference to FIG. Figure 1 shows the silicon-containing material recovery system of this example.

In this example, silicon for solar cells was selected as an object for slicing using slurry. The MWS for solar cells used in this example focuses on production capacity, and in a single calorie, four seri = 3 ingots (125WX 125D X 400U are calored at once, ^: i ^, (125WX 125D X O. 3L) can be processed about 3200 sheets.

[0031] A slurry tank with a size of about 200L is used for processing, and the slurry contained in this tank is barrel (specific gravity: 3.21) and water-soluble coolant (specific gravity: 1). Were mixed at a mass ratio of 1: 1. A water-soluble coolant with a composition of 80% propylene glycol, 15% water, and 5% dispersant was used. About 20 kg of silicon chips are mixed into the solid-state S slurry mainly consisting of silicon chips by one processing.

[0032] 1. Primary and secondary centrifugation steps First, 500 kg (specific gravity: 1.72, 290 L) of used slurry 1 was separated into liquid 3a and solid 3b by decanter-type centrifugal separation (called primary centrifugation, 500G).

Next, the entire amount of liquid 3a was further separated into liquid 5a and sludge 5b by decanter-type centrifugation (referred to as secondary centrifugation, 350 OG).

Solids generated by primary centrifugation (contains a lot of barrels) 3b is recovered as reclaimed barrels 4 and a part (30%) of liquid 5a generated by secondary centrifugation is recovered. Recovered as coolant 6, mixed them, adjusted specific gravity and viscosity, and added new abrasive grains and new coolant to create a regenerated slurry. When slurry regeneration and slicing were repeated, the concentrations of silicon contained in the used slurry and recycled slurry were about 12% and 6%, respectively.

[0033] The amounts of sludge 5b and liquid 5a that were not used as regenerated coolant 6 (surplus coolant) 7 were 100kg and 80kg, respectively. The amount and composition of sludge 5b and surplus coolant 7 were measured. The results are shown in Table 1.

[0034] [Table 1]

2.Distillation process

Next, a sample in which sludge 5b and surplus coolant 7 were mixed was vacuum distilled to obtain liquid 9a and solid 9b. Vacuum distillation was performed using a vacuum distillation apparatus (temperature: 160 ° C, final ultimate vacuum lOTorr). Liquid 9a was used as distillation coolant 11 to regenerate the slurry. The generation amount and components of solid content 9b were measured. The results are shown in Table 2.

[Table 2]

The particle size distribution of solid content 9b was measured. The particle size was measured by first separating particles of 10 mm or more, 1 mm or more, and 0.1 mm or more using a sieve, and then measuring the particle size of the remaining particles using a particle size distribution meter. The results are shown in Table 3. Looking at Table 3, it can be seen that there are many large grains of 1 ~: LOmm. This remains in solids 9b This is thought to be because fine particles are bonded together by the retained coolant, resulting in large particles.

[Table 3]

[0037] 3. Agitation 'powder crushing process

Next, 5 times by weight (490 kg) of isopropyl alcohol (hereinafter referred to as “alcohol”) 12 was added to the solid content 9b and stirred for 1 hour in a ball mill. The ball mill used was a container with a diameter of lm and a length of 1.5 m. 200 spherical 20 mm ceramic balls were placed in the solution and rotated at 20 RPM. The container was coated with a resin coating on the inner surface of the stainless steel container, and nitrogen was circulated around the shaft to collect the alcohol volatiles. According to this method, the solid content 9b and the alcohol 12 are stirred and the solid content 9b is pulverized.

[0038] Thereafter, the particle size distribution of the particles contained in the mixed liquid after stirring was measured. The particle size was measured using a particle size distribution meter. The results are shown in Table 4. When Table 3 and Table 4 are compared, by adding alcohol 12 to the solid content 9b after distillation and stirring, particles with a particle size of 0.1 mm or more disappear, and the particle size of most particles is 0. You can see that it is less than 02mm. This is probably because the coolant remaining in the solid content 9b after distillation was dissolved in alcohol and the fine particles adhered by the coolant separated.

[Table 4]

4. Filtration process

Next, it filtered using the leaf filter complete filter apparatus. As a result, liquid (filtrate) 15a and solid (cake) 15b were obtained. A leaf filter set is a horizontal disk-shaped leaf placed inside a closed container in layers on a vertical hollow shaft, and the spacing between each leaf is adjusted by a spacer ring. Solid content 15b only on top of leaf The accumulated liquid 15a is discharged through a vertical hollow shaft.

[0040] If a leaf filter set filtration device is used, the solid content 15b can be easily washed. Furthermore, the leaf filter set filtration device is suitably used in a method having a cleaning process using a volatile organic solvent such as alcohol in this embodiment because of the sealed structure. The filter cloth of the leaf filter used was a polypropylene air permeability of 0.11. The treatment of liquid 15a will be described later.

[0041] 5. Washing process

Next, the solid content 15b deposited on the top surface of the leaf was washed with 3 times the amount of alcohol (294 kg). Isopropyl alcohol was used as the cleaning alcohol. Washing is performed by repeating the process of pouring alcohol from the top of the solid content 15b, allowing the solid content 15b to pass through, recovering the alcohol that has passed the solid content 15b, and pouring it again from the top of the solid content 15b. went. This was repeated for 3 hours. As a result, liquid 17a and solid 17b after washing were obtained.

The solid content 17b after washing had a total weight of 111.8 kg and contained 28 kg of alcohol.

[0042] Liquid 15a and liquid 17a were once stored in a collection tank and then distilled together. The distillate was removed as recycled alcohol 21. Recycled alcohol 21 was reused as stirring or cleaning alcohol. Distillation was performed at 90 ° C, and the evaporated liquid was collected using a condenser. To increase the yield, the condenser temperature was set to 0 ° C. The alcohol (isopropyl alcohol) contained in liquid 15a and liquid 17a has a boiling point of 82.4 ° C, and propylene glycol has 187.85 ° C. Therefore, in the distillation at 90 ° C, the propylenic alcohol is hardly evaporated, and high purity alcohol can be recovered by distillation.

The total weight of liquid 15a and liquid 17a was 750kg. The weight of recycled alcohol 21 was 720kg. The solid content remaining after distillation was mainly composed of PG, a coolant component, and contained SiC, Si, metal impurities, and others as minor components.

[0043] 6. Drying process

Next, vacuum drying (40 ° C lOTorr or less) is applied to the solid content 17b, and the liquid content 19a is reduced. The solid 19b was removed by evaporation. The evaporated liquid 19a was collected by a condenser. The condenser conditions were set at 0 ° C at normal pressure. The amount recovered was 25 kg. The recovered liquid 19a was directly used as recycled alcohol 21. The amount and components of solid content 19b were measured. The results are shown in Table 5.

[Table 5]

[0044] Through the above steps, the silicon-containing material 23 substantially free of coolant could be recovered. Silicon-containing material 23 contains a large amount of silicon and can be used as a raw material for the production of polysilicon or halosilane.

[0045] In this example, alcohol was recovered from liquid 15a and liquid 17a, and alcohol evaporated during the drying process was also recovered. Therefore, most of the used alcohol could be recovered and reused.

[0046] In the above embodiment, the secondary centrifugation was performed on the total amount of the liquid 3a of the primary centrifugation, but as shown in Fig. 2, only the amount necessary to obtain the regenerated coolant 6 was obtained. Then, perform secondary centrifugation, mix the remainder of liquid 3a with sludge 5b, and distill it. In this case, the load during secondary centrifugation can be reduced.

[0047] Further, in the above embodiment, the sludge 5b is mixed with the excess coolant 7 without drying, but as shown in Fig. 3, the sludge 5b and the excess coolant 7 may be mixed after the sludge 5b is dried. . Even in this case, the same effect as in the above embodiment can be obtained.

[0048] Furthermore, in the above embodiment, primary / secondary centrifugation is performed, but as shown in Fig. 4, only the primary centrifugation may be performed, and the liquid 3a may be used as a sample. In this case, there is an advantage that the equipment cost can be reduced.

Example 2

[0049] Embodiment 2 of the present invention will be described with reference to FIG. This example is different from Example 1 in that distillation is performed on a sample that only has surplus coolant.

[0050] 1. Primary and secondary centrifugation steps

Since this process is the same as in Example 1, the description thereof is omitted. However, sludge 5b is discarded. Only the surplus coolant 7 was used as the sample to be distilled.

[0051] 2. Distillation process

Next, a sample consisting of excess coolant 7 was vacuum distilled to obtain liquid 9a and solid 9b. The vacuum distillation was performed under the same conditions as in Example 1. Liquid 9a was used as the distillation coolant 11 to regenerate the slurry. The generation amount and components of solid content 9b were measured. The results are shown in Table 6.

[Table 6]

The particle size distribution of solid content 9b was measured. The results are shown in Table 7. Looking at Table 7, it can be seen that there are many large grains of about 1 to: LOm m. This is thought to be because fine particles are bonded to each other by the coolant remaining in the solid content 9b and become large particles.

[Table 7]

[0053] 3. Stirring 'grinding process

Next, 5 times by weight (64 kg) of isopropyl alcohol (hereinafter referred to as “alcohol”) 12 was added to the solid content 9b and stirred for 1 hour in a ball mill. Stirring with a ball mill was performed under the same conditions as in Example 1.

Thereafter, the particle size distribution of the particles contained in the mixed liquid after stirring was measured. The results are shown in Table 8. Comparing Table 7 and Table 8, it can be seen that particles with a particle size of 0.1 mm or more have disappeared, and most of the particles have a particle size of less than 0.02 mm.

[Table 8]

[0054] 4. Filtration process Next, it filtered using the leaf filter complete filter apparatus. Filtration was performed under the same conditions as in Example 1.

[0055] 5. Washing process

Next, the solid content 15b deposited on the upper surface of the leaf was washed with 3 times the amount of alcohol (38.4 kg). The solid content 15b was washed under the same conditions as in Example 1.

[0056] The solid content 17b after washing had a total weight of 13 kg and contained 2 kg of alcohol.

[0057] Liquid 15a and liquid 17a were once stored in a recovery tank and then distilled together. The distillate was removed as recycled alcohol 21. Recycled alcohol 21 was reused as stirring or cleaning alcohol. Distillation was performed at 90 ° C, and the evaporated liquid was collected using a condenser. To increase the yield, the condenser temperature was set to 0 ° C.

The total weight of liquid 15a and liquid 17a was 102.4 kg. The weight of recycled alcohol 21 was 95 kg. The solid content remaining after distillation was mainly composed of PG, a coolant component, and contained SiC, Si, metal impurities, and others as trace components.

[0058] 6. Drying process

Next, vacuum drying (40 ° C lOTorr or less) was applied to the solid content 17b, and the solid content 19b was removed by evaporating the liquid content 19a. Vacuum drying was performed under the same conditions as in Example 1.

[0059] The evaporated liquid component 19a was recovered by a condenser. The condenser conditions were set at 0 ° C at normal pressure. The amount recovered was 1.84 kg. The recovered liquid 19a was directly used as recycled alcohol 21. The generation amount and components of the solid content 19b were measured. The results are shown in Table 9.

[Table 9]

[0060] Further, the particle size distribution of the solid content 19b was measured. The results are shown in Table 10.

[Table 10]

0.001 mm or more 0.02 mm or more 0.1 mm or more 1 mm or more 10 mm or more Solid content 90% 1 0% 0% 0% 0% [0061] Through the above steps, the silicon-containing material 23 substantially free of coolant could be recovered.

Example 3

[0062] Example 3 was performed under the same conditions as in Example 2. The weight of the coolant contained in the solid content 9b after distillation, the solid content 15b after filtration, the solid content 17b after washing, and the solid content 19b after drying was measured. The residual coolant weight was measured by heating each solid to 100 ° C to remove the low-boiling organic solvent, then heating at 300 ° C to remove the coolant, and then measuring the weight again. The weight change before and after heating at 300 ° C was taken as the weight of the residual coolant. The results are shown in Table 11. As can be seen from Table 11, it can be seen that the weight of the residual coolant was significantly reduced by filtration and washing.

[Table 11]

Example 4

[0063] Example 4 was performed under the same conditions as Example 2 except that the washing step was repeated twice. The weight of the coolant contained in the solid content 15b after filtration, the solid content after the first washing, the solid content after the second washing, and the solid content 19b after drying was measured. The results are shown in Table 12. As is clear from Table 12, the weight of the residual coolant was reduced by repeated washing.

[Table 12]

[0064] This application claims priority to Japanese application No. 2006-75164 (Application IV: March 17, 2006), the contents of which are incorporated herein by reference.

Claims

The scope of the claims

[1] A solid content is obtained by previously removing water-soluble coolant from the used slurry in the silicon wafer manufacturing process, which contains at least water-soluble coolant, cannon and silicon particles.

From the solid content, the water-soluble coolant remaining in the solid content is extracted using a low-boiling organic solvent that is compatible with the water-soluble coolant and has a boiling point lower than that of the water-soluble coolant. A method for recovering a silicon-containing material, comprising a step of removing a boiling organic solvent by filtration and recovering a solid content obtained by filtration.

[2] Used slurry force Removing water-soluble coolant in advance

The used slurry is subjected to primary centrifugation to recover the solid content of abrasive grains as the main component, and the liquid obtained by the primary centrifugation is subjected to secondary centrifugation to obtain a water-soluble coolant as the main component. Collect a portion of the liquid,

The method according to claim 1, wherein the method is performed by a method comprising a step of previously removing a water-soluble coolant by distillation from a sample having at least one of the remaining liquid content and sludge obtained by secondary centrifugation.

[3] Used slurry force Removing water-soluble coolant in advance

The used slurry is subjected to primary centrifugation to recover the solids composed mainly of abrasive grains, and the water-soluble coolant is removed beforehand by sample force distillation consisting of at least part of the liquid obtained by primary centrifugation. The method according to claim 1, wherein the method is performed by a method comprising the steps of:

[4] The method according to claim 1, wherein the low boiling point organic solvent comprises an alcohol having 1 to 6 carbon atoms or a ketone having 3 to 6 carbon atoms.

5. The method according to claim 1, wherein the low-boiling organic solvent comprises methanol, ethanol, isopropyl alcohol, or acetone.

[6] The method according to claim 1, wherein the low boiling point organic solvent has a boiling point of 50 ° C or more lower than that of the water-soluble coolant.

7. The method according to claim 1, further comprising the step of washing the solid content obtained by filtration with a low-boiling organic solvent of the same type or different from the low-boiling organic solvent used for extraction after the filtration.

[8] The method according to claim 7, wherein the washing is repeated until the transparency of the liquid after washing is below a reference value.

[9] The method according to claim 1, further comprising a step of pulverizing the solid content before or during the extraction of the remaining water-soluble coolant.

[10] The method according to claim 1, further comprising a step of recovering the low-boiling organic solvent by distilling the liquid obtained by filtration.