JP5232059B2 - Wastewater recovery method and wastewater recovery device - Google Patents

Description

  The present invention relates to a method for collecting wastewater, and more particularly to a method for collecting acidic wastewater.

  For example, in a factory for manufacturing a semiconductor, after silicon oxide is wet-etched with hydrofluoric acid, the silicon substrate is cleaned with ultrapure water. Also, hydrofluoric acid is used for cleaning the jig to be used. In addition, other acids such as nitric acid are also used as the acid, and as a result, a large amount of acidic wastewater containing hydrofluoric acid or the like is generated as wastewater.

On the other hand, in order to reduce the amount of drainage discharged to the outside of the factory as much as possible, there is a need to reduce the amount of wastewater discharged to the outside of the factory in order to legally regulate the amount of drainage discharged. For this reason, the generated acid wastewater also needs to be recovered in order to be reused as recovered water.
Here, as a method of recovering acidic wastewater, a technology that removes oxides and organic substances by bringing the acidic wastewater into contact with activated carbon, and then removing hydrofluoric acid and the like by passing water through an anion exchange resin. Exists.

  For example, in Patent Document 1, when passing the semiconductor cleaning wastewater through the activated carbon tower, the activated carbon to be charged in advance is brought into contact with 2 to 4% by weight of dilute hydrochloric acid, and then washed with ultrapure water. A semiconductor cleaning wastewater recovery method is disclosed in which, when applied to an activated carbon tower, when the semiconductor cleaning wastewater is passed through the activated carbon tower, the elution of the cationic substance into the resulting effluent is less likely to occur.

JP-A-8-281256

However, the method in which the activated carbon to be charged in advance is brought into contact with dilute hydrochloric acid and then washed with ultrapure water, and then the activated carbon is applied to the activated carbon tower does not sufficiently suppress the elution of the cation component. Therefore, particularly when the acid concentration of the acidic waste water is high, iron, aluminum, etc. contained in the activated carbon are eluted and cations are easily generated. As a result, the cation is precipitated as a hydroxide in the ion exchange apparatus for removing anions, which is the next step, that is, the pH of the acidic waste water is close to neutral in the ion exchange apparatus for removing anions. In this case, cations are hydroxylated. In this state, the pressure loss in the ion exchange device increases and the ion exchange rate decreases. If so, the purity of the recovered water decreases. Furthermore, when the recovered water after treating the waste water is sent to the pure water production apparatus, the same phenomenon occurs in the pure water production apparatus. As a result, troubles are likely to occur in each device, and the burden of maintenance increases.
In particular, when the cation is an iron ion, the recovered water is colored, and there is a problem that countermeasures are required.
Furthermore, since a large amount of hydrochloric acid or pure water is used, it is uneconomical and the acid waste water must be treated. There is also a problem that it takes time and effort to clean with hydrochloric acid or pure water.

The present invention has been made in view of the above-described problems of conventional techniques.
That is, an object of the present invention is to provide a wastewater recovery method capable of suppressing the elution of a cation component eluted from activated carbon and obtaining highly purified recovered water when treating acidic wastewater. is there.

  Another object of the present invention is to provide a wastewater recovery device that can reduce the burden on maintenance by suppressing the elution of cationic components eluted from activated carbon when treating acidic wastewater. is there.

  Thus, according to the present invention, the first purification step of refining the acidic wastewater using the plant-derived or activated carbon using the resin as the raw material, and the acid wastewater purified by the first purification step is purified by the anion exchanger. There is provided a method for recovering wastewater characterized by comprising two purification steps.

Here, the activated carbon preferably has an ignition residue of 1.5% or less, more preferably coconut shell activated carbon.
The anion exchanger is preferably a weakly basic anion exchange resin. The wastewater recovery method of the present invention can be preferably applied when acidic wastewater is generated in a semiconductor manufacturing process.

  Furthermore, according to the present invention, the first purification means for purifying by using activated carbon using plant-derived or resin as the raw material, and the acidic waste water purified by the first purification means is purified by an anion exchanger. And a second purifying means. A wastewater recovery device is provided.

  Here, the activated carbon is preferably coconut husk activated carbon having an ignition residue of 1.5% or less, and further has a sending means for sending the acidic waste water purified by the second purification means to the pure water production apparatus. It is preferable.

  ADVANTAGE OF THE INVENTION According to this invention, when processing acidic waste_water | drain, the collection | recovery method of the waste_water | drain etc. which can obtain highly purified recovered water can be provided.

  The best mode for carrying out the present invention (hereinafter, an embodiment of the present invention) will be described in detail below. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention. The drawings used are for explaining the present embodiment and do not represent the actual size.

(Acid drainage)
The acidic wastewater treated in the present embodiment is not particularly limited, but can be preferably applied particularly when it is generated in the semiconductor manufacturing process. In manufacturing a semiconductor, hydrofluoric acid is used to etch silicon oxide as described above. Therefore, the washing waste water contains a large amount of hydrofluoric acid, and its pH is about 2.5-3.

(Activated carbon)
The activated carbon used in the present embodiment is preferably activated carbon using a plant-derived or resin as a raw material. When plant-derived or resin is used as a raw material, activated carbon with fewer impurities is obtained. Therefore, elution of cation components such as iron is less likely to occur when acidic drainage is passed.
Specific examples of plant-derived materials include coconut husk, charcoal, sawdust, and wood chips. Examples of the resin include synthetic resins such as phenol resin, polyvinylidene chloride resin, polyacrylonitrile resin, and polyvinyl alcohol resin. Among these, activated carbon using coconut shell as a raw material, that is, coconut shell activated carbon is particularly preferable.

Further, when viewed from the viewpoint of the amount of impurities contained in the activated carbon, the ignition residue is preferably 1.5% or less. If the ignition residue exceeds 1.5%, elution of cation components such as iron tends to occur excessively when acid wastewater is passed. As a result, the cation component is hydroxylated, so that troubles are likely to occur in each device as described above, and the recovered water is likely to be colored.
For example, when a coal-based material such as lignite, lignite, bituminous coal, anthracite or the like is used as a raw material, or when an oil carbon, coal pitch, petroleum pitch or the like is used, the ignition residue of activated carbon produced is 1.5. % Is often exceeded.
As coconut husk activated carbon satisfying the above conditions, specifically, Daisobu W-10-30 manufactured by Mitsubishi Chemical Calgon Co., Ltd. or WA manufactured by Cataler Co., Ltd. can be used.

Here, the ignition residue is a value measured by a method according to JIS K1474-1991.
That is, the ignition residue can be measured by the following procedure.
(I) Weigh 1 g to 2 g of activated carbon whose residual residue is to be measured, into a porcelain crucible that has been made constant in a constant temperature dryer in advance until 1 mg is reached, and put it in. Here, as the porcelain crucible, a B-type 30 ml stipulated in JIS R1301 was used.
(Ii) A porcelain crucible containing activated carbon is placed in an electric furnace, initially heated weakly, gradually raised in temperature and completely incinerated, and then ignited at 800 ° C. to 900 ° C. for 1 hour.
(Iii) A porcelain crucible is transferred into a desiccator containing silica gel as a desiccant, allowed to cool in the desiccator, and then weighed to determine the residue. And the ignition residue is calculated by the following formula (1).

Moreover, in order to manufacture activated carbon using the said raw material, it can carry out by the following methods, for example.
(I) The raw material is shaped and pulverized as necessary to adjust to a desired particle size. Then, it is steamed (dry distillation) in an oxygen-free state in a muffle furnace or the like, and carbonized at a temperature of 700 ° C. to 800 ° C. to obtain a carbide. In order to make an oxygen-free state, for example, a method of heating in a nitrogen atmosphere can be applied.
(Ii) The obtained carbide is heated to 900 ° C. to 1100 ° C. by a muffle furnace or the like and reacted with steam or carbon dioxide to form fine holes (gas activation method). Alternatively, chemicals such as phosphoric acid and zinc chloride are mixed and baked at 400 ° C. to 600 ° C. to open holes by the dehydration action of the chemicals (chemical activation method).
(Iii) After cooling, it is finally washed with pure water and dried.

(Anion exchanger)
There are various types of anion exchangers. In the present embodiment, it is preferable to use an anion exchange resin as the anion exchanger. Anion exchange resins can be classified into strong base anion exchange resins, weak base anion exchange resins, and the like. In the present embodiment, either of them can be used. However, it is more preferably a weakly basic anion exchange resin.
Specifically, for example, Diaion WA30, WA30C, WA20, WA21 and the like manufactured by Mitsubishi Chemical Corporation can be used as the weakly basic anion exchange resin.
Specific examples of strongly basic anion exchange resins include Diaion SA10A, SA20A, SA21A, PA316, and PA408 manufactured by Mitsubishi Chemical Corporation.

Next, based on the drawings, an acidic wastewater recovery apparatus to which the present embodiment is applied will be specifically described.
FIG. 1 is a diagram illustrating an example of an acidic wastewater recovery device according to the present embodiment.
The waste water recovery apparatus 10 shown in FIG. 1 introduces the acidic waste water generated in the semiconductor manufacturing process and performs the first purification process by using the activated carbon tower 11 as the first purification means, and the activated carbon tower 11 performs the first purification process. An anion exchange resin tower 12 as a second purification means for introducing the acidic waste water after the second purification step and performing the second purification step, and sending the recovered water after the second purification step to the pure water production apparatus And a pump 13 as means.
The activated carbon tower 11, the anion exchange resin tower 12, and the pump 13 are connected in series by a pipe made of stainless steel or the like. In addition, a pipe for introducing the acidic solution into the activated carbon tower 11 and a pipe for sending recovered water from the pump 13 to the pure water production apparatus are provided.

  Hereinafter, a method for treating acidic wastewater by the wastewater recovery apparatus 10 configured as described above will be described.

First, acidic waste water is introduced into the activated carbon tower 11. The acidic waste water is introduced from the upper part of the activated carbon tower 11. The activated carbon tower 11 is filled with coconut husk activated carbon having an ignition residue of 1.5% or less. At this time, organic substances such as a solvent and heavy metal ions contained in the acidic waste water are removed, and the first purification is performed. That is, removal is performed by these components entering into fine pores formed in coconut shell activated carbon and adsorbing inside the pores.
And the acidic waste water which reached the lower part of the activated carbon tower 11 and was subjected to the first purification is extracted from the lower part of the activated carbon tower 11 and introduced into the anion exchange resin tower 12 from the upper part. The introduction to the anion exchange resin tower 12 may use a pump or the like, but may be introduced into the anion exchange resin tower 12 by the residual pressure from the activated carbon tower 11.

The inside of the anion exchange resin tower 12 is filled with a weak base anion exchange resin, and the acid waste water subjected to the first purification is passed through the weak base anion exchange resin, and the anion exchange resin tower 12 12 flows toward the bottom. At this time, the anion contained in the acidic waste water is exchanged with the exchange group of the weakly basic anion exchange resin, whereby the anion in the acidic waste water is removed and the second purification is performed. In this embodiment, an OH-type weakly basic anion exchange resin is used, and hydrogen ions (H ⁺ ) are combined with hydroxide ions (OH ⁻ ) released from the weakly basic anion exchange resin to form water. Since it becomes (H ₂ O), the acidic waste water becomes almost neutral at this point.

  Then, the acidic waste water that reaches the lower part of the anion exchange resin tower 12 and becomes almost neutral by performing the second purification is extracted from the lower part of the anion exchange resin tower 12 and sent to the pump 13. And in order to recycle | reuse as collection | recovery water, it sends to the pure water manufacturing apparatus with the pump 13, for example.

By performing acidic wastewater recovery treatment through the above-described process, when acidic wastewater containing hydrofluoric acid or the like is brought into contact with activated carbon, iron, aluminum, etc., which are cation components contained in the activated carbon, are eluted. It becomes difficult to do. As a result, it is difficult for cations to be generated, so that it is difficult to deposit as hydroxide in the subsequent steps. As a result, the pressure loss in the anion exchange resin tower 12 is unlikely to increase, and the ion exchange rate is unlikely to decrease. Further, troubles are hardly caused not only in the anion exchange resin tower 12 but also in other apparatuses, so that the maintenance burden is reduced. In addition, since iron ions rarely enter as cations, the recovered water is hardly colored.
Since a large amount of hydrochloric acid or pure water is not used as in the prior art, it is economical, and the labor of washing with hydrochloric acid or pure water is eliminated.

  Normally, two-stage purification using the activated carbon tower 11 and the anion exchange resin tower 12 is sufficient, but a cation exchange resin tower is provided between the anion exchange resin tower 12 and the pump 13 for completeness. Ions may be removed.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail using an Example, this invention is not limited by these Examples, unless the summary is exceeded.

Example 1
In this embodiment, the waste water recovery apparatus 10 shown in FIG. 1 is used as the waste water recovery apparatus.
Then, Diasorb W-10-30 manufactured by Mitsubishi Chemical Calgon Co., Ltd., which is coconut shell activated carbon, was used as the activated carbon, and WA30C manufactured by Mitsubishi Chemical Co., Ltd. was used as the weakly basic anion exchange resin. Here, the ignition residue of Diasorb W-10-30 was 1.2%. In addition, an activated carbon tower 11 filled with Diasorb W-10-30 and an anion exchange resin tower filled with WA30C using a hydrofluoric acid (HF) aqueous solution having a concentration of 120 mg / L and pH 2.7 as acidic waste water No. 12 was passed in order to obtain recovered water. The internal volumes of the activated carbon tower 11 and the anion exchange resin tower 12 were 170 mL, and the water flow rate was 850 mL / h.

(Example 2)
Acidic waste water was treated in the same manner as in Example 1 except that WA manufactured by Cataler Co., Ltd., which is coconut shell activated carbon, was used as the activated carbon to obtain recovered water. The ignition residue of WA was 1.5%.

(Comparative Example 1)
Acidic wastewater was treated in the same manner as in Example 1 except that Filtrasorb 400 manufactured by Mitsubishi Chemical Calgon Co., Ltd., which was activated carbon using a coal-based raw material as activated carbon, to obtain recovered water. The ignition residue of Filtrasorb 400 was 2.0%.

(Comparative Example 2)
Acidic waste water was treated in the same manner as in Example 1 except that Diahop 008N manufactured by Mitsubishi Chemical Calgon Co., Ltd., which is activated carbon using a coal-based raw material as activated carbon, to obtain recovered water. The ignition residue of Diahop 008N was 3.5%.

  Table 1 shows the iron ion concentration at the outlet of the activated carbon tower 11 when Examples 1-2 and Comparative Examples 1-2 have a water flow rate of 100 BV. The water flow rate is an amount indicating how many times the volume of the activated carbon filled with the acid waste water has passed. BV (bed volume) is used as a unit.

  Here, the iron ion concentration at the outlet of the activated carbon tower 11 was set to 0.5 ppm as a reference value, and if it was equal to or less than this value, it was considered good. As can be seen from Table 1, the iron ion concentration used activated carbon made from coconut husks and the ignition residue was 1.5% or less, but was within the range of the standard value. As for the activated charcoal that has an ignition residue exceeding 1.5%, the result deviated from the standard value.

Moreover, FIG. 2 is the figure explaining the change of the iron ion density | concentration in the activated carbon tower 11 exit with respect to the amount of water flow in the case of Examples 1-2. FIG. 3 is a diagram for explaining the change in the iron ion concentration at the outlet of the activated carbon tower 11 with respect to the water flow rate in the case of Comparative Example 2.
In FIG. 2 and FIG. 3, the horizontal axis indicates the water flow rate. The vertical axis indicates the iron ion concentration at the outlet of the activated carbon tower 11 in units of ppm. As can be seen from FIG. 2, in the case of Example 1 and Example 2, the iron ion concentration was within the range of 0.5 ppm or less, which is within the reference value, in the range of up to 160 times the water flow rate tested. Yes. However, in the case of Comparative Example 2, the iron ion concentration did not fall below 1 ppm even when the water flow rate was increased to 155, which was outside the standard value.

It is a figure which shows an example of the collection | recovery apparatus of the acidic waste_water | drain by this Embodiment. It is the figure explaining the change of the iron ion density | concentration in the activated carbon tower exit with respect to the water flow amount in the case of Examples 1-2. It is the figure explaining the change of the iron ion concentration in the activated carbon tower exit with respect to the water flow amount in the case of the comparative example 2.

DESCRIPTION OF SYMBOLS 10 ... Waste water collection | recovery apparatus, 11 ... Activated carbon tower, 12 ... Anion exchange resin tower, 13 ... Pump

Claims (5)

A first purification step of refining acidic wastewater with coconut husk activated carbon having an ignition residue of 1.5% or less and an iron ion concentration eluted from the coconut husk activated carbon of 0.5 ppm or less;
A second purification step for purifying the acidic waste water purified by the first purification step with an anion exchanger;
A method for recovering wastewater characterized by comprising: The wastewater recovery method according to claim 1 , wherein the anion exchanger is a weakly basic anion exchange resin. The method for collecting wastewater according to claim 1 or 2 , wherein the acidic wastewater is generated in a semiconductor manufacturing process. A first purification means for refining acidic wastewater with coconut husk activated carbon having an ignition residue of 1.5% or less and an iron ion concentration eluted from the coconut husk activated carbon of 0.5 ppm or less;
A second purification means for purifying the acidic waste water purified by the first purification means by an anion exchanger;
A wastewater recovery device characterized by comprising: The wastewater recovery apparatus according to claim 4 , further comprising a sending means for sending the acidic wastewater purified by the second purification means to a pure water production apparatus.

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