JP2002292565A - Magnetic separating system of polishing/cutting work liquid waste using abrasive material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for a liquid waste treatment in which an abrasive material is recovered by magnetic separation from slurry waste liquid occurring in polishing or cutting work using the abrasive material, and a magnetic separating system for the same. SOLUTION: The abrasive material used in polishing or cutting work is mechanically or colloid chemically magnetized for magnetic separation. The abrasives is mechanically or colloid chemically magnetized in advance, and then collected by the magnetic separation after being employed in polishing or cutting work. The abrasive material is magnetized by mechanical action occurring between a working device and an abrasive material during polishing or cutting work in which abrasive material is used, and are collected by the super-conductive magnetic separation. The magnetic separation system comprises a super-conductive magnet, a filter provided in the center, a waste slurry supply part (waste slurry tank, pump and filter slurry tank), an abrasive grain collecting part (reverse washing liquid tank, pump, recovering tank and blender) or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a waste liquid treatment method for recovering an abrasive by magnetic separation from a slurry waste liquid generated by polishing or cutting using an abrasive, and a magnetic separation system therefor.

[0002]

2. Description of the Related Art FIG. 1 shows a cutting process using a wire saw as an example of a polishing or cutting process using an abrasive. The wire saw presses a workpiece such as a silicon block (ingot) against a large number of wires running at a high speed, and supplies a slurry composed of an abrasive (abrasive grains) and a dispersion liquid to a large number of wires at a time. This is a device for cutting into wafers. Since it is cut with a small-diameter wire, it is widely used because of low generation of cutting powder, high yield, and high productivity. As a dispersion,
There are two types, water-based and oil-based, but currently oil-based is the mainstream. The treatment of the waste liquid is performed exclusively by industrial waste treatment companies and is disposed of without reuse. The same applies to a processing apparatus other than a wire saw that performs polishing or cutting processing using an abrasive, and is also applicable to a slurry using an aqueous dispersion.

[0003]

The slurry used for polishing or cutting using an abrasive is usually circulated, so that cutting powder generated when polishing or cutting a workpiece is accumulated in the slurry. You. This cutting powder reduces the processing performance of the processing device and the processing accuracy of the workpiece. For this reason, a part of the slurry is usually discarded periodically and replaced with a new slurry. This increases the running cost of the processing device. It also causes a problem of discharging a large amount of industrial waste (about 200 l / d / unit in the case of a wire saw). On the other hand, as will be described in detail later, the slurry to be discarded is still maintaining a quality that can be used enough if the cutting powder is removed, and discarding it without reusing it is also from the viewpoint of resource saving. Not preferred. From such a background, it is desired to regenerate the slurry or collect the abrasive. Accordingly, an object of the present invention is to provide a waste liquid treatment method for recovering an abrasive by magnetic separation from slurry waste liquid generated by polishing or cutting using an abrasive, and a magnetic separation system therefor.

[0004]

In order to solve the above-mentioned problems, a waste liquid treatment method of the present invention is characterized in that an abrasive used in polishing or cutting is magnetically separated by mechanochemical or colloidal chemical treatment. Consists of For the magnetic separation, a superconducting magnet is used, but a permanent magnet or an electromagnet can also be used depending on the magnetism. The present invention also provides a waste liquid treatment method in which an abrasive is preliminarily mechanochemically or colloidally magnetized, and is used for polishing or cutting, and then recovered by magnetic separation. Further, the present invention provides a method in which a polishing material is magnetized by a mechanochemical action which necessarily occurs between a processing device (for example, a wire saw or a band saw) and the polishing material during polishing or cutting using the polishing material. A wastewater treatment method recovered by superconducting magnetic separation is also presented. In this case, there is no need to perform a separate magnetizing operation. A magnetic separation system for performing the waste liquid treatment method of the present invention includes a superconducting magnet, a filter provided at the center thereof, a waste slurry supply unit that supplies waste slurry containing abrasives to the filter, and the filter. And an abrasive recovering section for recovering the abrasive captured by the apparatus.

The abrasives recovered in the present invention include silica, tungsten carbide, alumina, ceria, zirconia, titania, manganese dioxide, diamond, borazon, and the like, and those exhibiting the same functions as these are also included. . The workpiece to be polished or cut using an abrasive is not limited to a semiconductor material, but includes ceramics, glass, plastic, magnetic materials, metal materials, and composite materials thereof.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As an example of polishing or cutting using an abrasive, cutting of a silicon block by a wire saw using silica as an abrasive will be described below.
The present invention is not limited to this. First, Table 1 shows the results of measurement of the components of the slurry before use and at the time of disposal, and their ratios. Before use, the slurry consists of an abrasive (abrasive grains) and oil, with a specific gravity of about 1.45 and a viscosity of about 100c.
P. However, at the time of disposal, the specific gravity does not change much, but the viscosity is as high as 180 cP, which affects the processing efficiency. This is mainly due to the mixing of silicon cutting powder, and the proportion of silicon reaches as much as 12%. "Others" in the table also includes iron powder from wire saws.

[0007]

[Table 1]

FIG. 2 shows the measurement results of the particle size distribution of the particulate matter in the waste slurry. It can be seen that there are many particles in the submicron region of about 15 μm. Particles of about 15 μm are SiC as abrasive grains, and sub-micron particles are silicon cutting powder. Abrasive before processing (GC # 1000)
Has a particle diameter of 4 to 25 μm and an average particle diameter of about 11 μm. From this, it is considered that the abrasive grains in the waste slurry are in a sufficiently usable state. In fact, SEM observation of the abrasive grains in the waste slurry confirmed that the abrasive grains were not crushed and could be used sufficiently. Also, it was confirmed that the oil in the slurry was not oxidized, and there was no problem in reusing. Therefore, if the abrasive grains or oil can be recovered from the waste slurry, the disposal cost and the purchase cost due to the reuse of the abrasive grains and oil can be reduced, which is economical even if a superconducting magnet is introduced.

In this embodiment, the abrasive grains are SiC and the cutting powder is silicon. In general, it is difficult to magnetically separate any of the materials without using a superconducting magnet without magnetizing. Therefore, first, it was attempted to magnetize the abrasive grains and separate them from the waste slurry. This is because it was determined that the abrasive grains were easier to separate because of the larger particle size and the higher mixing ratio. The magnetizing of the abrasive grains was performed by both a colloidal chemistry method and a mechanochemical method.

[0010] The colloidal chemistry method means that the (water) iron oxide ultra-fine particles (for example, potassium hydroxide is reacted with ferrous sulfate to make ferrous hydroxide into water using hydroxyl groups on the surface of the abrasive grains) It is formed by oxidizing with oxygen supplied from water and air, and is considered to have a particle size of about 50 nm.) is there.

FIG. 3 shows the results of recovery of abrasive grains (average particle size of about 12 μm) magnetized by colloid chemistry using a samarium-cobalt permanent magnet. The difference between the black square and the diamond in the figure indicates that the process of producing the (aqueous) iron oxide ultrafine particles is different, the black square is a mixture of FeSO ₄ and KOH, and the diamond is the colloid precipitated. It was mixed as an aqueous solution. The horizontal axis represents the weight fraction of iron (Fe) in the (water) iron oxide ultrafine particles with respect to the abrasive grains (SiC). It can be understood that when properly magnetized, 100% of the abrasive grains can be recovered with about 5% by weight of magnetism. From this, it became clear that when the abrasive grains are colloidally magnetized, they can be recovered from the waste slurry.

On the other hand, the mechanochemical method is a method in which a magnetic metal piece (for example, iron) and inorganic particles are rubbed in a slight solvent to attach the metal pieces to the inorganic particles. FIG.
Fig. 1 schematically shows a conceptual diagram of a mechanochemical magnetizing method (upper figure) and a mechanism of magnetism (lower figure). In the pot mill 5,
The iron wire fragments 7, the iron balls 8 and the abrasive grains 6 are put in, and rotated together with water and alcohol. Then, iron on the surface of the abrasive grain or iron on the surface of the iron ball adheres to the surface of the abrasive grains by mechanical energy. The contact part between the abrasive and the iron ball or between the abrasive and the iron wire is locally 10
It is considered that the temperature has risen to 00 ° C. or higher, and it is considered that not only mechanically adhering but also forming a compound and adhering firmly. Using this mechanochemical technique, about 2% of iron by weight of inorganic abrasive particles could be attached. A magnetic separation of the abrasive grains magnetized by this mechanochemical method was attempted using a 3T superconducting magnetic field. One example of the result is shown in FIG. In FIG. 5, the left bottle contains a suspension of abrasive grains magnetized by a mechanochemical method, and the grains are blackened by the magnetism. The right bottle in FIG. 5 contains the suspension after magnetic separation. As is clear from the photograph in FIG. 5, almost all the magnetized abrasive grains could be recovered. From the above basic experiments, it can be seen that the abrasive grains can be magnetized using either colloidal or mechanochemical magnetizing methods, and that they can be magnetically separated. It was revealed.

[0013] In addition, the S
EM observation and elemental analysis were performed (FIG. 6). FIG. 6 shows an SEM photograph of the abrasive grains and the results of elemental analysis thereof.
It is recognized that iron does not adhere to the part A, but iron adheres to the part B. This is considered to be due to the fact that the wire fragments of the wire saw were attached by a mechanochemical reaction. The possibility of magnetic separation using the attached iron was examined by experiments. Using a filter of about 200 μm, 10
A magnetic field up to T was applied to perform magnetic separation. as a result,
It was confirmed that about 30% of the suspended components could be separated. Further, when the separated suspended components were analyzed by XRD, about 9%
It was confirmed that 5% was abrasive grains. This experiment confirmed that the magnetic separation of the abrasive grains was possible without magnetism.

Next, FIG. 7 shows the configuration of a magnetic separation system according to the present invention. This system comprises a superconducting magnet 11, a filter 12 provided at the center thereof, a waste slurry supply unit (a waste slurry tank 13, a pump 17, and a filtration slurry tank 14), and an abrasive recovery unit (a backwash liquid tank 15, a pump 1).
8, a recovery tank 16, and a blending adjuster (not shown)).
The solid line in FIG. 7 shows the processing flow of the waste slurry supply unit. The waste slurry in the waste slurry tank 13 is sent to the superconducting magnet 11 by the pump 17, and the filter 17 mainly captures abrasives (abrasives). The filtered slurry is stored in the filtered slurry tank 14. The dashed line in FIG. 7 indicates the flow of the abrasive recovery section. Filter 12
The abrasive particles caught in the tank are collected in the collection tank 16 by flowing the backwash liquid stored in the backwash liquid tank 15 (optimum oil used for mixing) in a state where the magnetic field is zero. At this time, if the composition of the oil and the abrasive grains is adjusted, the slurry can be reused as it is.

Further, the slurry stored in the filtration slurry tank 14 is passed through the filter 11 again by a method such as performing appropriate magnetism or changing the strength of the magnetic field, so that the remaining slurry in the slurry is removed. The oil can be recovered by entrapping the particles. In the magnetic separation system, the backwash liquid tank 15, the recovery tank 16, the pump 1
8 and the like are provided, and the abrasive is collected each time by the backwashing method. Alternatively, the filter may be replaced with a cassette type filter and replaced each time.

[0016]

According to the present invention, the slurry containing the abrasive used for polishing or cutting can be reused without being discarded, thereby saving resources and preserving the environment, and also reducing the processing cost.

[Brief description of the drawings]

FIG. 1 is an overall schematic view (upper view) and a partially enlarged cross-sectional view (lower view) of a process for cutting a semiconductor or the like using a wire saw.

FIG. 2 shows the particle size distribution of particulate matter in waste slurry.

FIG. 3 shows the results of magnetic separation of abrasive particles colloidally magnetized by permanent magnets.

FIG. 4 is a schematic view of a mechanochemical magnetizing method.

FIG. 5 is a photograph of a suspension of abrasive grains magnetized by a mechanochemical technique (left) and a suspension after magnetic separation (right).

FIG. 6 shows an SEM photograph of abrasive grains in a waste slurry and a result of elemental analysis.

FIG. 7 shows a configuration of a magnetic separation system of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wire 2 Silicon block 3 Slurry 4 Guide 5 Pot mill 6 Abrasive grain 7 Iron wire 8 Iron ball 11 Superconducting magnet 12 Filter 13 Waste slurry tank 14 Filtration slurry tank 15 Backwash liquid tank 16 Recovery tank 17-19 Pump 20-23 Stirrer

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Atsushi Nakahira Matsugasaki Imperial Palace Kaido-cho, Kyoto, Sakyo-ku Kyoto Institute of Technology (72) Inventor Shinichi Takeda 3-1-1 Tsushimanaka, Okayama City Precision Engineering, Okayama University Within the Department of Applied Chemistry (72) Inventor Takefumi Niki 5-16-8 Hagoromo, Takaishi City, Osaka Prefecture Inside Niki Crafts Co., Ltd. F term (reference) 3C011 BB31 3C047 FF06 FF09 GG17 3C058 AA07 AC01 AC04 CB01 CB05 CB06 DA03

Claims (5)

[Claims] 1. A waste liquid treatment method in which an abrasive used for polishing or cutting is mechanochemically magnetized and recovered by magnetic separation. 2. A waste liquid treatment method in which an abrasive used for polishing or cutting is colloidally chemically magnetized and recovered by magnetic separation. 3. A waste liquid treatment method in which an abrasive is preliminarily mechanochemically or colloidally magnetized, and is used for polishing or cutting, and then recovered by magnetic separation. 4. A waste liquid treatment method in which a polishing material is magnetized by a mechanochemical action generated between a processing apparatus and the polishing material during polishing or cutting using the polishing material, and is collected by superconducting magnetic separation. 5. A magnetic separation system for performing the waste liquid treatment method according to claim 1, wherein the superconducting magnet (11) has a filter (1) provided at the center thereof.
2) a waste slurry supply unit (13, 14, 1) for supplying waste slurry containing an abrasive through the filter;
7), and a magnetic separation system comprising an abrasive collecting section (15, 16, 18) for collecting the abrasive caught by the filter.