JP2010082568A - Method of treating waste liquid - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of treating waste liquid for separating solid contents, e.g. a fine powder of silicon, from a cutting waste liquid of a brittle material, e.g. silicon, and recovering main ingredients of the clean cutting liquid for reuse. <P>SOLUTION: The method of treating waste liquid includes carrying out a centrifugal separation treatment of a cutting waste liquid of a brittle material, adding a silicon compound to the recovered liquid and filtrating. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

The present invention relates to a waste liquid treatment method after cutting a brittle material such as silicon.

Cutting of brittle materials such as silicon is performed using a slurry for a wire saw. The slurry is obtained by dispersing abrasive grains in the cutting fluid, and the brittle material is cut while the slurry is supplied to the wire saw during the cutting process.

Conventionally, the slurry waste liquid after cutting silicon can be roughly recovered by centrifuging or the like, but the recovered waste liquid has been discarded because fine chips cannot be removed. Then, since it is expensive and burdens the environment, the reuse of waste liquid is being studied. For example, there is a method of recovering the main component of the cutting fluid by distilling the recovered waste liquid from which the abrasive grains have been removed by centrifugation. On the other hand, Patent Literature 1 describes a slurry waste liquid recycling system in which a slurry waste liquid is subjected to a two-stage centrifugal treatment, and then a flocculant is added to the discharged liquid, followed by centrifugation.
JP-A-2005-7541

However, it is possible to recover the main component of the cutting fluid by distilling the waste fluid, but it is not practical in terms of cost. In addition, off-flavors that are not found in the new liquid may occur from the distillate. On the other hand, in the system of Patent Document 1, since centrifugal separation is used, it is difficult to completely remove silicon fine powder in the effective coolant although abrasive grains and chips can be removed to some extent. An object of the present invention is to provide a method for completely separating a solid fine powder such as silicon from a slurry waste liquid (cutting waste liquid), treating it into a clean coolant (cutting liquid main component), and reusing it.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the waste slurry can be solved by centrifuging and then adding a silicon compound to the recovered liquid and filtering it, resulting in the present invention. It was.

  That is, the processing method of the brittle material cutting waste liquid is characterized in that the cutting waste liquid of the brittle material is subjected to a centrifugal separation process, and then the silicon compound is added to the recovered liquid for filtration.

  Further, in the above waste liquid treatment method, the waste liquid treatment method is characterized in that the silicon compound has a nitrogen atom and a hydroxyl group.

Further, in the above waste liquid treatment method, the waste liquid treatment method is characterized in that the silicon compound is 0.1 to 2.0% by weight based on the total amount of the recovered liquid.
The present invention is a waste liquid treatment method characterized by performing a centrifugal separation process on a cutting waste liquid of a brittle material, adding a silicon compound having a nitrogen atom and a hydroxyl group to the recovered liquid, and then performing a centrifugal separation process.

In the waste liquid processing method of the present invention, fine abrasive grains and solids of cutting chips in the waste liquid can be almost completely removed, so that the main component of the cutting liquid can be recovered in a clean state and can be reused. Is.

The waste liquid treatment method of the present invention is a step of roughly removing abrasive grains by centrifugal treatment of slurry waste liquid after cutting (slicing) silicon or the like, which is a brittle material, with a wire saw. The silicon cutting fluid may be aqueous or oily. In the case of cutting using a wire saw of fixed abrasive grains, a centrifugal separation process is performed because it is necessary to remove solids such as swarf but not a slurry. The cutting waste liquid assumed by the present invention includes both slurry waste liquid and waste liquid without slurry.

Examples of the main component of the aqueous cutting fluid include ethylene glycol, diethylene glycol, propylene glycol, other polyalkylene glycols and polyalkylene glycol monoalkyl ethers (molecular weight: 100 to 2000). The main component of the oil-based cutting fluid is refined mineral oil.

In this centrifugal separation process, normally large abrasive grains and silicon chips can be removed, but fine powder silicon and abrasive grains are still dispersed in the liquid. This centrifugation process may be repeated a plurality of times. For example, coarse abrasive grains are removed at 100 to 1000 G for the first time, and finer dispersed solids are removed at 1000 to 10,000 G for the second time.

Next, it is a step of adding a silicon compound to the recovered waste liquid after the centrifugal separation treatment.

（式中、Ｘは炭素数１〜８のアミノ基含有の炭化水素基、Ｙは酸素原子で二重結合を含む、ｎは１または３の数）で表される化合物またはその縮合物である。
その添加量は、ケイ素化合物が回収液全量に対して０．１〜２．０重量％、好ましくは０．５〜１．５重量％である。 Examples of the silicon compound include silicon-based antifoaming agents and silane coupling agents. Among these, a silane coupling agent is preferable, and a silicon compound having a nitrogen atom and a hydroxyl group is particularly preferable. In particular,

Wherein X is an amino group-containing hydrocarbon group having 1 to 8 carbon atoms, Y is an oxygen atom and contains a double bond, n is a number of 1 or 3, or a condensate thereof. .
The amount of silicon compound added is 0.1 to 2.0% by weight, preferably 0.5 to 1.5% by weight, based on the total amount of the recovered liquid.

The temperature of the recovered waste liquid when adding the silicon compound is room temperature to 70 ° C, preferably 50 ° C to 70 ° C. And after adding a silicon compound, it stirs for about 1 to 60 minutes, and moves to a filtration process.

Filtration may be any of natural filtration, vacuum filtration, and pressure filtration, but pressure reduction or pressure filtration is preferred to increase the filtration rate.

As the filtration device, Nutsche (Buchner funnel) can be used for vacuum filtration, and a filter press, screw press, and belt press can be used for pressure filtration. A filter paper or filter cloth is laid on the Nutsche, and a filter aid may be laid on the filter or added to the silicon compound. The filter aid is diatomaceous earth or white clay.

The collected filtrate is reused as the main component of the cutting fluid.

Another embodiment of the present invention includes a step of performing a centrifugal separation process instead of the above filtration step. Centrifugation here requires a centrifugal force of 100 to 3000 G or more, preferably about 10000 G.

The present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.

After cutting the single crystal silicon ingot using a wire saw, a slurry waste liquid was obtained. In the cutting process, a cutting fluid mainly composed of diethylene glycol containing water was used. The slurry waste liquid was subjected to a centrifugal separation process (3000 G), and separated into abrasive grains and a processing waste layer and a recovered waste liquid layer. Thereafter, this recovered waste liquid was used for treatment. The state of the recovered waste liquid was a gray turbid color. In addition, the additive used in the Example is as follows. Moreover, the yield was calculated | required as follows.

〔Additive〕
Silane coupling agent: 50% aqueous solution of 3-aminopropyltrihydroxysilane condensate (Chiasso Silaace SF-330)
Silicone defoamer: Polyorganosiloxane (FS Antifoam # 544 from Dow Corning Asia)
Flocculant 1 (Comparative Example): Water-soluble polymer flocculant (Marilim AKM-053 made by NOF)
Flocculant 2 (Comparative Example): Oil-soluble polymer flocculant (NOF Mariarim AAB-0851)
〔yield〕
Oil recovery rate = filtrate volume ÷ collection waste liquid volume ÷ oil content ratio ^*
* Amount of oil contained in the waste liquid

[Example 1]
100 g of the collected waste liquid is put in a beaker, heated to 50 ° C., 1% of each additive is added to the total amount of the collected waste liquid, stirred for 30 minutes, and then added to a Nutsche having a diameter of 10.5 cm. The filter paper of No. 2 was placed, and 30 g of diatomaceous earth was laid on top of the filter paper. The pressure was reduced to about 2-3 mmHg with a vacuum pump.

清浄性の評価：◎透明感がある、○透明感には欠けるが濁りは無い、×回収廃液と変わらない
清浄性の評価は以下の実施例２〜４でも同様である。
比較例の収率は、清浄性が×なので出していない。

上記のシランカップリング剤添加の濾液の成分は、ＧＰＣ（ゲル浸透クロマトグラフィー）にて分析を行った結果、ジエチレングリコールが検出された。また、カールフィッシャー法により水分量を測定した結果、水を約７％含有していた。また、臭気はほとんどなかった。

Evaluation of cleanliness: ◎ There is a sense of transparency, ○ A lack of transparency, but there is no turbidity.
The yield of the comparative example is not given because the cleanliness is x.

Diethylene glycol was detected as a result of analysis by GPC (gel permeation chromatography) on the components of the filtrate with the silane coupling agent added. Further, as a result of measuring the water content by the Karl Fischer method, it contained about 7% of water. Moreover, there was almost no odor.

[Example 2]
In Example 1, it observed by changing the addition amount of a silane coupling agent.

Example 3
In Example 1, the stirring temperature of the recovered waste liquid was changed, and 1.0% of a silane coupling agent was added and observed.
However, since a recovered waste liquid different from those in Examples 1 and 2 was used, the numerical values were slightly different even under the same conditions.

Example 4
The silane coupling agent of Example 1 was filtered using a filter cloth instead of filter paper.

Example 5
The recovered effluent was added with a silane coupling agent and centrifuged and observed under the following conditions.

(Condition 1) A high-speed cooling centrifuge (rotating radius: 9.63 cm, centrifugal force: 3000 G, 5000 G, 10000 G) was used. Temperature (25 ° C room temperature), centrifugation time: 10 minutes, sample volume: 50 ml, addition amount of silane coupling agent: 0%, 1%, 2%
(Condition 2) Each sample of Condition 1 was allowed to stand for 5 days.

清浄性の評価：◎透明感がある、○透明感には欠けるが濁りは無い、△透明感には欠け若干の濁りがみられる、×回収廃液と変わらない
(Condition 1) The cleanliness of the liquid after centrifugation was observed.

Evaluation of cleanliness: ◎ There is a sense of transparency, ○ A lack of transparency, but no turbidity, △ A lack of transparency, a slight turbidity is seen, × Same as recovered waste liquid

(Condition 2) The liquid after centrifugation performed under Condition 1 was allowed to stand for 5 days to observe cleanliness.

Claims (4)

After centrifuging the cutting waste liquid of brittle material,
A method for treating a waste liquid, comprising adding a silicon compound to the recovered liquid and performing filtration. The method for treating a waste liquid according to claim 1, wherein the silicon compound has a nitrogen atom and a hydroxyl group. 3. The method for treating a waste liquid according to claim 1, wherein the silicon compound is 0.1 to 2.0% by weight based on the total amount of the recovered liquid. After centrifuging the cutting waste liquid of brittle material,
A method for treating a waste liquid, comprising adding a silicon compound having a nitrogen atom and a hydroxyl group to the recovered liquid and then performing a centrifugal separation process.