KR20110034113A - Reclaiming process of abrasive and reclaimed abrasive - Google Patents

Abstract

PURPOSE: A method for recycling abrasives is provided to separate reusable high purity abrasive at inexpensive operation costs without expensive apparatuses. CONSTITUTION: A method for recycling abrasives comprises the steps of: injecting a solvent in waste slurry, stirring the mixture, controlling specific gravity, and separating solid slurry and suspension; and collecting abrasives in solid slurry. The solvent injected in a separating process is single or two or more kinds selected from water, alcohols and ketones.

Description

Reclaiming process of abrasive and reclaimed abrasive

The present invention relates to a method for regenerating an abrasive from waste sludge containing an abrasive used when cutting a silicon ingot with a metallic wise saw and to an abrasive regenerated by this method.

Silicon wafers required for solar cell or semiconductor manufacturing are manufactured through a process of cutting silicon ingots with a metallic wire saw using a lubricant or coolant mixture containing an abrasive such as silicon carbide. In the cutting process, oil-soluble lubricants, which are not easily washed with water, have been used in the past, but recently, ethylene glycols such as polyethylene glycol (PEG), diethylene glycol (DEG) and methyldiethylene glycol (MDG) have various molecular weights which can be easily washed with water. There is a tendency to use a class of water-soluble coolants.

Cutting of the silicon ingot generally proceeds with continuous feeding of a slurry of a well mixed abrasive and coolant at approximately 1: 1 weight ratio to the metal jigsaw.

For this reason, the process of cutting a silicon ingot basically includes a coolant and an abrasive, and waste slurries containing the silicon polished in the silicon ingot and usually components of a metal jigsaw are discharged.

These discharged pessaries have been discarded because they are no longer usable due to the reduction of polishing capacity or wafer contamination due to abrasives and other contaminants that are unsuitable for the process. Was developed one after another.

As a condition for reusing waste slurries, reusable abrasives and physical properties suitable for the characteristics of the cutting process, together with the technology of removing the broken and broken abrasive components and impurities such as silicon and iron powder during the cutting process included in the waste slurries There is a need for a separation technique with unchanged pure coolant.

In the current technology for recycling or reprocessing abrasive waste slurry, water or organic solvents are added to the waste slurry to reduce the viscosity to separate the recyclable abrasive and the unusable waste abrasive using the hydrocyclone method and then distill the solvent. To remove the coolant (European Patent No. 0786317, International Publication No. WO 01/43933, European Patent No. 0791385) or dry the waste slurry under reduced pressure or heat to obtain a waste abrasive powder. Method of separating by dry such as screening (US Patent No. 6010010), heating the waste slurry to lower the viscosity and then separating by hydrocyclone method (European Patent No. 0968801), but these methods Treated regenerated abrasives do not completely remove impurities such as silicon and iron. Of not properly separate the liquid Ingredients using 50% occupied by the coolant, as well as not being purified, and to solve the problems, the coolant is heat-denatured, or decomposition in the process of distillation to obtain a coolant, such as polyethylene glycol.

 Referring to International Patent Publication WO 02/096611, a waste slurry is separated into a portion containing a large amount of solids and a portion containing almost no amount of solids using a filter, and the portion containing a large amount of solids is treated with an alkaline solution to remove silicon and treated with an acid. Although the process of obtaining a polishing compound having a size that can be recycled using a hydrocyclone and then recycling the metal component is introduced, this method also includes a plurality of solid fine particles in the recovered coolant, thereby intact reprocessing and separation method. It is not suitable.

When the silicon ingot is cut using a coolant or abrasive having a fine powder smaller than the appropriate size, the cross section of the cut silicon wafer may be contaminated by the fine powder, resulting in product defects, or the contaminated wafer may be subjected to high pressure cleaning. It causes problems such as having to go through cleaning process.

According to Korean Patent Laid-Open Publication No. 2008-0021110, the waste slurry is separated into a liquid component containing solid and fine solids using a continuous centrifuge and a filter instead of the hydrocyclone of the conventional inventions. The process of treating with alkaline and acid solution, and the fine solid residual liquid part through the vacuum distillation and filter to minimize the thermal deterioration of the lubricant is introduced, but such a method is also expensive centrifuge, filter, vacuum distillation apparatus The initial equipment investment cost is high, and the maintenance cost is also high.

Most of the methods mentioned in the above-mentioned inventions are expensive in equipment such as hydrocyclones, centrifuges, high-temperature vacuum distillers, filter equipment, etc., and their efficiency in separating and purifying coolants and abrasives is not very good. The abrasive is also determined by the classifying ability of the classifier, so there is an uneven particle size variation.

The present invention seeks to provide an abrasive regeneration method and a regenerated abrasive which can separate reusable high purity abrasives at a low operating cost and a facility that does not require an expensive device in regenerating waste slurry.

The present invention provides a preferred first embodiment comprising the step of adding a solvent to the waste slurry and adjusting the specific gravity to separate into a suspension; And it provides an abrasive recycling method comprising the step of recovering the abrasive.

In the above embodiment, the solvent added in the separating step may be one, two or more mixed solvents selected from water, alcohols and ketones.

In the above embodiment, the separating may be performed so that the specific gravity of the waste slurry into which the solvent is added is 1.1 to 1.5.

In the above embodiment, the step of separating may be to leave at least 30 minutes after adjusting the specific gravity to separate into a solid slurry and a suspension based on the specific gravity 1.0 ~ 1.2.

In the above embodiment, in the separating step, the solvent may be added to 10 to 1,000% by weight based on the weight of the waste slurry.

In this embodiment, the step of recovering the abrasive may be to recover the abrasive by removing the solution in the solid slurry.

In the above embodiment, the step of recovering the abrasive may be to recover the abrasive by adding a solvent and left to stand for 5 to 20 minutes and removing the supernatant. In this case, the solvent may be one or two or more selected solvents selected from water, alcohols, and ketones, and the solvent may be 10 to 1,000 wt% based on the weight of the solid slurry. In this case, the process of solvent addition, stirring, standing and removing the supernatant may be repeated until the specific gravity of the supernatant becomes (specific gravity of the additionally added solvent) + (0.1 to 0.3).

In the above embodiment, after recovering the abrasive, it may further comprise the step of drying the recovered abrasive.

In the above embodiment, the drying step may be performed in a rotary drying furnace.

The present invention provides, as a second preferred embodiment, a regenerated abrasive obtained by the abrasive regenerating method of the first embodiment.

Regenerated abrasive according to the embodiment may be 99% or more purity.

The present invention provides an initial investment and operating cost by providing a method for reprocessing without expensive equipment such as a hydrocyclone or jet cyclone for separating useful abrasives from solids, or a centrifuge for separating liquid and solids. It is expected to reduce remarkably and to obtain a reproducible product comparable to a new product in terms of performance of recovered solids.

Hereinafter, the present invention will be described in more detail.

The present invention provides a preferred embodiment of the present invention comprising the steps of separating a solid slurry containing impurity particles to be removed by adding a solvent to the waste slurry, adjusting the specific gravity, and a suspension in which the effective solid content is almost removed; And recovering the abrasive by removing unnecessary fine powder and impurities in the solid slurry.

Most waste slurries have a solids content of about 50 to 55% by weight and include fine particles of silicon cut from the silicon ingot cutting process, which have a size not exceeding 2 μm, and the size and amount of the fine silicon particles It may be slightly different depending on the cutting conditions, the discharge state of the slurry, and the like.

Comprising fine metal or metal oxide particles of up to 1 μm level, in particular formed of iron, from metal jig and device parts, which are approximately 0.1% by weight or less of the discharged slurry, the amount depending on the cutting process conditions of the silicon ingot .

The slurry containing the abrasive before use generally contains 50% of particles having a particle size of 8 μm to 10 μm, and particles having a particle size of 3 μm to 19 μm are distributed as a whole. The abrasive in the waste slurry after use has a particle size of 19 µm or less, and contains a large amount of non-reusable abrasive having a particle size smaller than 3 µm.

In order to regenerate the abrasive from such waste slurry, the solid slurry and the suspension must first be separated. The separation of the solid slurry and the suspension containing the impurity particles from the waste slurry can be performed by adding a solvent to the waste slurry to lower the viscosity and specific gravity. This can be separated using specific gravity differences.

The solvent added in the separating step should be well mixed without reacting with the coolant contained in the waste slurry, the lower the viscosity and specific gravity, the lower the boiling point, the better; Alcohols such as methanol, ethanol, propanol, butanol, pentanol and isopropyl alcohol; And ketones such as acetone may be one or two or more selected mixed solvents.

The amount of solvent added to the waste slurry is determined by the degree of addition of solids suspended in the waste slurry. Solids do not have to be settled completely, because solids suspended in a certain gravity of the liquid are too small to use abrasives or are mostly made of low specific gravity silicon or silicon oxide and metal by-products.

The degree of precipitation is determined by the specific gravity and viscosity of the waste slurry. The lower the viscosity, the faster the precipitation rate, and the lower the specific gravity, the lower the content of solids may be advantageous in the post-process. The viscosity and specific gravity can be lowered by adding more than 10 to 1,000% by weight of solvent based on the weight of waste slurries.If the solvent exceeds 1,000% by weight with respect to the weight of waste slurries, the apparatus for separating solids and suspensions becomes large and the process is easy. There is a disadvantage not, less than 10% by weight can be unnecessary fine powder and impurities remain there is a problem that requires more repeat process. In consideration of the fact that all the solvent added for the recovery of the abrasive should be removed, it may be added in an amount of 10 to 300% by weight based on the weight of the waste slurry.

The waste slurry stock solution has a specific gravity of about 1.6 to 1.7, and the solvent is added to adjust the specific gravity to 1.1 to 1.5, and then allowed to stand for 30 minutes or more to separate the solid slurry and the suspension based on the specific gravity of 1.0 to 1.2. The specific gravity of the solid slurry and the suspension is different depending on the specific gravity of the solvent and the coolant to be separated, and the specific gravity of the solid slurry and the suspension of the specific gravity higher than the reference specific gravity and the suspension of specific gravity lower than the specific specific gravity It may be to separate. The specific gravity used as the reference for separating the solid slurry and the suspension is 1.0 to 1.2, at a low specific gravity (= 1.0) when separating a mixture of a relatively low specific gravity solvent and a coolant, and a high specific gravity when separating a high specific gravity mixture ( = 1.2).

In addition to the reusable abrasive, the solid slurry separated as described above contains a small amount of impurity particles to be discarded. The solid slurry contains little silicon, iron powder and residual coolant in the step of separating into a solid slurry and a suspension. Recyclable abrasives can also be recovered in a separation step process. Therefore, the abrasive may be recovered by removing the solution in the solid slurry.

Meanwhile, the solvent may be added to the separated solid slurry again, followed by stirring and spontaneous precipitation to remove the supernatant, thereby recovering a reusable abrasive having higher purity. This is a step that can be carried out as needed to remove the silicon and iron powder and residual coolant remaining in the separated solids. In this case, the step of recovering the abrasive is adding more solvent and repeating the above steps. That is, after the solvent is added and allowed to stand for 5 to 20 minutes to separate the solid slurry and the supernatant based on the specific gravity 1.0 ~ 1.2 to remove the supernatant as a solution. At this time, solvent injection, stirring, standing (natural sedimentation) and supernatant removal may be repeatedly performed until the specific gravity of the supernatant becomes (the specific gravity of the additionally added solvent) + (0.1 to 0.3). Different solvents may be added for each. The supernatant removal is sufficient to repeat within five times.

The solvent that can be used in this case should be well mixed without reacting with the coolant contained in the solid slurry, the lower the viscosity and specific gravity, the lower the boiling point is better, for example water; Alcohols such as methanol, ethanol, propanol, butanol, pentanol and isopropyl alcohol; And ketones such as acetone may be one or two or more selected mixed solvents.

The solvent may be added to 10 to 1,000% by weight relative to the weight of the solid slurry. More specifically, it may be to be added to 10 to 300% by weight. If the solvent exceeds 1,000% by weight of the solids slurry weight, the apparatus for separating the solids and the suspension becomes large, and the process is not easy, and if it is less than 10% by weight, unnecessary fines and impurities may remain. There is a problem that an iterative process may be necessary. In consideration of the fact that all of the solvent added for the recovery of the abrasive should be removed, 10 to 300% by weight based on the weight of the solid slurry may be added.

The finished solid can be obtained with almost completely removed silicon and iron powder and residual coolant, and most of fine particles of 2 탆 or less to be removed in the abrasive.

Thereafter, the step of drying the recovered abrasive may be further roughened. The drying may be any one, such as a heating furnace or a heating oven, as long as it can be heated to 200 ° C. or higher. Loss can be prevented, and a regenerated abrasive can be obtained by drying completely for 1 to 24 hours at a temperature of 200 ° C. or higher. The drying temperature may vary depending on the type of solvent or coolant, but the temperature ranges from 200 to 2,200 ° C, considering that the boiling point of the commonly used coolant or solvent is 200 ° C or less, and 2,200 ° C, which is the sublimation point of abrasive silicon carbide. And, considering the economic aspects 200 ~ 500 ℃ is good, further 250 ~ 350 ℃ may be good.

The regenerated abrasive thus obtained has a purity of 99% or more, and it is possible to provide a high-purity abrasive that can be reused at a low cost of equipment and a facility that requires no expensive equipment.

Meanwhile, the separated suspension contains not only a coolant but also a micronized abrasive, a low specific gravity silicon or silicon oxide and a metal by-product, which are not reusable, and may be recovered through a separate treatment.

Hereinafter, examples of the present invention will be described in more detail, but the scope of the present invention is not limited to these examples.

≪ Example 1 >

400 kg of water with a specific gravity control solvent was added to 1,000 kg of waste slurry with a specific gravity of 1.6 kg, in which polyethylene glycol coolant and silicon carbide (silicon carbide) abrasive were mixed at a weight ratio of 1: 1. After the natural sedimentation step for a minute, a specific gravity of 1.2 or more was separated into a solid slurry of 600 kg, most of which is abrasive, and a specific gravity of 1.2 or less, and 800 kg of a suspension of most of the coolant components. In order to remove the silicon, iron powder and residual lubricant contained in the separated solid slurry, the mixture was stirred and mixed with 600 kg of water equal to the weight of the solid slurry, followed by standing for 5 minutes until the specific gravity of the supernatant became 1.1. After the supernatant was removed twice, water was added again, mixed and stirred, and then the supernatant was removed twice until the specific gravity of the supernatant became 1.2.

Most of the removed supernatants were non-reusable abrasives, fine silicon particles, and other impurities together with the residual coolant, and when the particle size of these removed solids was confirmed, most of them were less than 1 μm and some particles less than 2 μm were observed. An impurity-free abrasive was put into a rotary drying furnace and completely dried at a temperature of 300 ° C. or higher to recover 440 kg of a regenerated abrasive, and the recovery was about 88%.

The state of the finally recovered abrasive particles is very clean, as can be seen in FIG. 1, and a particle photograph of the solid content contained in the waste sludge before treatment is shown in FIG. 2 for comparison.

The final particle size was analyzed using a dry particle size analyzer (Laser Particle Analyzer, model: LS13320, manufacturer: beckmancoulter) as shown in FIG. 3, and it can be confirmed that there are few particles having a thickness of 2 μm or less. there was.

X-ray diffraction analysis (XRD) was performed to confirm the purity of the recovered abrasive, and as a result, it showed a purity of 99.6% or more (FIG. 4).

The recovery rate is not significant because it depends on how much abrasive is available for the waste slurry.

<Example 2>

80 kg of diethylene glycol and 20% by weight of methyl diethylene glycol were mixed in a 1: 1 weight ratio of the coolant and silicon carbide abrasive to 20 kg of waste slurry having a specific gravity of 1.66. After the addition and stirring, the specific gravity was adjusted to 1.5, and after 30 minutes of natural sedimentation, the solids were separated into 52 kg of solid content of 1.1 or less and 68 kg of suspension of specific gravity of 1.1 or more.

 In order to remove the silicon, iron powder, and residual lubricant contained in the separated solid slurry, after mixing and stirring with 50 kg of methanol, the supernatant was washed twice for 5 minutes until the specific gravity of the supernatant became 1.0. After removing the mixture, water was added again, mixed and stirred, and the supernatant was removed once until the specific gravity of the supernatant became 1.1. Most of the removed supernatants were non-reusable abrasives, fine silicon particles, and other impurities together with the residual coolant, and when the particle size of these removed solids was confirmed, most of them were less than 1 μm and some particles less than 2 μm were observed. The impurity-free abrasive was put into a rotary drying furnace equipped with a condenser capable of condensing volatile matter and completely dried at a temperature of 300 ° C. or higher to recover 47 kg of regenerated abrasives, mostly particles of 3 to 19 μm, and the recovery rate was about 94%. XRD analysis showed that the purity was 99.8%. Methanol collected in the condenser and methanol used as the cleaning liquid can be reused.

<Example 3>

80 kg by weight of diethylene glycol and 20% by weight of methyl diethylene glycol, such as those used in Example 2, were mixed in a 1: 1 ratio by weight of silicon carbide abrasive to a waste slurry with a specific gravity of 1.66. 100 kg of ethanol as a specific gravity control solvent was added and stirred to adjust the specific gravity to 1.2, followed by a natural settling step for 30 minutes, and then separated into 50 kg of solid content of 1.1 or less and 150 kg of specific gravity of 1.1 or more.

The separated suspension contains abrasives, fine silicon particles, and other impurities, including the effective part together with the coolant, and analyzed the particle size of the removed solids, which was mostly less than 1 μm but some more than 3 μm. It was confirmed that it is included. 50 kg of the separated solids are put into a rotary drying furnace equipped with a condenser capable of condensing volatiles, and then completely dried at a temperature of 300 ° C. or higher to recover 42 kg of regenerated abrasives having most particles of 3 to 19 μm but some fine particles remain. there was. Compared to the reprocessing of the separated solid slurry, the recovery was 89% and the purity was 99%.

Comparative Example 1

100 kg of the waste slurry as in Example 1 was separated into a 55 kg solid slurry and a 45 kg suspension using a centrifugal separator, and the solid slurry was obtained in the same manner as an abrasive.

The 55 kg of the solid content separated firstly was completely dried in a drying furnace of 300 ° C. or higher to recover 47 kg of powder, and the recovery rate was high as 90% or more. It was confirmed that more than 5% as contained, and XRD analysis was confirmed to contain more than 1% of silicon, iron and iron oxide. That is, the purity of the obtained abrasive was 93% level.

Comparative Example 2

40 kg of the abrasive powder obtained after drying in Comparative Example 1, using a magnetic roller to remove a small amount of iron components, particles of 3 μm or less were separated by using a cyclone classifier, and two times continuous operation to obtain an abrasive.

39.5kg was recovered, and the results of SEM and particle size analysis showed that particles of 2μm or less, which cannot be reused, contained 2% or more as impurities, and XRD analysis contained more than 0.2% of silicon, iron, and iron oxides. Purity was 97.8%.

1 is a photograph of the abrasive particles finally recovered in Example 1,

2 is a particle photograph of the solid content contained in the waste sludge before reprocessing in Example 1,

3 is a particle size analysis data of silicon carbide as an abrasive recovered in Example 1,

4 is XRD data of silicon carbide which is an abrasive recovered in Example 1. FIG.

Claims (14)

Adding a solvent to the waste slurry, stirring and separating specific gravity into a solid slurry and a suspension by adjusting specific gravity; And A method for regenerating abrasives comprising recovering the abrasive in the solid slurry. The method of claim 1, The solvent added in the separating step is an abrasive, characterized in that at least one selected from the group consisting of water, alcohols and ketones or mixed solvents. The method of claim 1, Separation step is abrasive polishing method characterized in that the solvent is added so that the specific gravity of the waste slurry is 1.1 ~ 1.5. The method of claim 1, Separation step is the abrasive regeneration method characterized in that the separation of the solid slurry and the suspension based on the specific gravity 1.0 ~ 1.2 to stand for 30 minutes or more after adjusting the specific gravity. The method of claim 1, In the separating step, the solvent is 10 to 1,000% by weight relative to the weight of the waste slurry, abrasive recycling method characterized in that the input. The method of claim 1, Recovering the abrasive is to recover the abrasive by removing the solution in the solid slurry. The method of claim 1, Recovering the abrasive is an abrasive regeneration method, characterized in that to recover the abrasive by leaving the solvent for 5 to 20 minutes after the addition and stirring of the solvent. The method of claim 7, wherein The solvent is an abrasive regeneration method, characterized in that one or two or more mixed solvents selected from water, alcohols and ketones. The method of claim 7, wherein A solvent is 10 to 1,000% by weight based on the weight of the solid slurry, abrasive recycling method characterized in that. The method of claim 7, wherein A method for regenerating abrasives, characterized in that the process of solvent addition, stirring, standing and removing the supernatant is repeated until the specific gravity of the supernatant becomes (specific gravity of the additionally added solvent) + (0.1 to 0.3). The method of claim 1, And after the recovery of the abrasive, drying the recovered abrasive. The method of claim 11, Drying is an abrasive regeneration method, characterized in that carried out in a rotary drying furnace. The regenerated abrasive obtained by the abrasive regeneration method of any one of Claims 1-12. The method of claim 13, Regenerated abrasive with a purity of at least 99%.

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