Waste acid treatment system and waste acid treatment method

Abstract

To provide a waste acid treatment system and a waste acid treatment method capable of neutralizing and solidifying waste acid such as etching waste generated in an etching process of glass and semiconductor substrates to a state that can be properly accepted at final disposal sites while keeping cost down.SOLUTION: A waste acid treatment system 10 includes at least a waste acid reaction tank 12, a slag storage part 42, a lime storage part 40, and an agitator 162. The waste acid reaction tank 16 is configured to contain waste acid to be treated. The slag accommodation part 42 is configured to add steel slag to the waste acid in the waste acid reaction tank 16. The lime accommodation part is configured to add calcium oxide or calcium hydroxide so that the waste acid to which the steel slag is added is neutralized and solidified. The stirrer 162 is configured to stir the waste acid in the waste acid reaction tank 16.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a waste acid treatment system and a waste acid treatment method for treating waste acid such as etching waste liquid generated in etching treatment of glass substrates, semiconductor substrates, etc.

Background Art

[0002] As one of the processing methods for glass substrates, semiconductor substrates, etc., etching treatment that suitably utilizes chemical reactions has been widely adopted conventionally. This etching treatment has become an essential treatment for manufacturing parts of electrical devices such as smartphones and personal computers.

[0003] However, in the etching treatment of glass substrates, semiconductor substrates, etc., a large amount of waste acid containing etching waste liquid and used washing water is generated. Since this waste acid is industrial waste, it is important to properly dispose of it in accordance with laws and regulations.

[0004] Therefore, among the conventional technologies, there is one that neutralizes and solidifies waste acid such as etching waste liquid to such an extent that it can be properly accepted at the final disposal site of industrial waste by utilizing the dehydration action and neutralization action of calcium oxide (see, for example, Patent Document 1). By using such a conventional technology, it has been considered possible to easily perform proper disposal of waste acid.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, with the conventional technology described above, depending on the type of waste acid being treated, solidification may not proceed favorably, and additional costs may be incurred to solidify the material to a state where it can be properly accepted at a final disposal site.

[0007] For example, if the amount of metal components or other substances that precipitate during the neutralization reaction in the waste acid being treated is small, solidification may not proceed favorably, and it may become necessary to add additional chemical substances to promote solidification, resulting in additional costs.

[0008] The object of the present invention is to provide a waste acid treatment system and waste acid treatment method that can neutralize and solidify waste acids, such as etching waste liquids generated during etching processes for glass substrates, semiconductor substrates, etc., to a state that can be properly accepted at final disposal sites while keeping costs down. [Means for solving the problem]

[0009] The waste acid treatment system according to the present invention is for neutralizing and solidifying waste acid, including etching waste liquid generated during the etching process of glass substrates or semiconductor substrates, to a degree that makes it suitable for acceptance at industrial waste final disposal sites.

[0010] This waste acid treatment system comprises at least a waste acid reaction tank, a means for adding steel slag, a means for adding lime, and a stirring means.

[0011] The waste acid reaction tank is configured to contain the waste acids to be treated (etching waste liquid, used substrate cleaning water, etc.).

[0012] The steel slag addition means is configured to add steel slag to the waste acid in the waste acid reaction tank. An example of a steel slag addition means is a silo that can contain steel slag and supply the contained steel slag to the waste acid reaction tank.

[0013] The lime-adding means is configured to add calcium oxide or calcium hydroxide so that the waste acid to which steel slag has been added is neutralized and solidified. An example of a lime-adding means is a silo that can contain lime and supply the contained lime to the waste acid reaction tank.

[0014] In the present invention, neutralization and solidification means bringing the material to a state where it can be accepted as sludge at a final disposal site, with a pH greater than 2.0 and a pH less than 12.5, and a water content of 85% or less.

[0015] The stirring means is configured to stir the waste acid in the waste acid reaction tank. Examples of stirring means include, but are not limited to, a stirrer that is acid-resistant and heat-resistant and functions as a kneading screw.

[0016] In this configuration, steel slag containing a large amount of metal components that precipitate during the neutralization process of waste acid is added, followed by neutralization and solidification with lime. Therefore, even when treating waste acid with a low metal content, proper neutralization and solidification can be achieved. In particular, since steel slag is available at a lower cost compared to commercially available solidification aids, processing costs can also be reduced.

[0017] Furthermore, instead of treating the liquid after the metal components have been precipitated and removed as wastewater, lime is added until the entire volume solidifies, thus eliminating the need for wastewater treatment and solid-liquid separation.

[0018] In the above-described configuration, it is preferable to further include a slag crushing means configured to crush steel slag. An example of a slag crushing means is a crusher that crushes steel slag so that its particle size is approximately 0.5 mm or less.

[0019] Furthermore, the waste acid treatment method according to the present invention is for neutralizing and solidifying waste acid, including etching waste liquid generated during the etching process of glass substrates or semiconductor substrates, to a degree that makes it suitable for acceptance at industrial waste final disposal sites.

[0020] This waste acid treatment method includes at least a steel slag addition step, a lime addition step, and a stirring step.

[0021] In the steel slag addition step, steel slag is added to the waste acid to be treated.

[0022] In the lime addition step, calcium oxide or calcium hydroxide is further added to the waste acid to which steel slag has been added.

[0023] In the stirring step, the waste acid to which lime has been added is stirred until it is neutralized and solidified. By this stirring step, the waste acid becomes sludge with a pH greater than 2.0 and less than 12.5 and a water content of 85% or less.

[0024] As a result, for example, it becomes possible to appropriately treat waste acids such as etching waste liquids without performing multi-step treatments such as removing fluorine with a calcium-based compound, decomposing borofluoride with an aluminum-based compound, and further removing fluorine and boron with a calcium-based compound as in the prior art.

[0025] In the above configuration, it is preferable to further include a slag pulverization step of pulverizing the steel slag in order to enhance the reaction effect of the steel slag before the steel slag addition step.

[0026] Steel slag is available at a low cost, and using steel slag (especially slag that is likely to become waste) also contributes to the recycling and utilization of resources.

[0027] In addition, when there is no problem of harmful substances eluting from the waste acid neutralized and solidified using steel slag, it is also possible to reuse it as a roadbed material, etc., and in this case, the effect of being able to omit the aging treatment of the slag can also be obtained.

Advantages of the Invention

[0028] This invention makes it possible to realize a waste acid treatment system and waste acid treatment method that can neutralize and solidify waste acids, such as etching waste liquids generated during etching processes for glass substrates, semiconductor substrates, etc., to a state where they can be properly accepted at final disposal sites while keeping costs down. [Brief explanation of the drawing]

[0029] [Figure 1] This is a schematic diagram of a waste acid treatment system according to one embodiment of the present invention. [Modes for carrying out the invention]

[0030] A waste acid treatment system 10 according to one embodiment of the present invention will be explained with reference to Figure 1. The waste acid treatment system 10 is connected to an etching apparatus 100 that performs etching on a glass substrate.

[0031] The etching apparatus 100 etches glass substrates using an etching solution containing hydrofluoric acid, and the etching waste liquid discharged from the etching apparatus 100 is properly treated in the waste acid treatment system 10.

[0032] In the following embodiment, an example of treating waste liquid from an etching apparatus 100 that performs etching on a glass substrate is described, but the present invention can also be used when treating waste liquid from an etching apparatus that performs etching on semiconductor wafers or other semiconductor substrates.

[0033] The waste acid treatment system 10 comprises a waste acid storage tank 12, a liquid transfer pump 14, a waste acid reaction tank 16, a sludge storage tank 200, a scrubber 30, a lime storage section 40, and a slag storage section 42. The waste acid treatment system 10 is also equipped with a pH meter, thermometer, and other devices as needed.

[0034] The waste acid storage tank 12 is configured to contain waste acids (etching waste liquid, used cleaning water, etc.) discharged from the etching apparatus 100.

[0035] Examples of waste acids include, but are not limited to, waste hydrofluoric acid, waste nitric acid, waste sulfuric acid, waste hydrochloric acid, waste phosphoric acid, and mixed acid waste liquids containing these.

[0036] In this embodiment, the waste acid storage tank 12 is configured to properly accommodate etching waste liquid containing hydrofluorosilicic acid generated after the etching process of a glass substrate. The waste acid storage tank 12 is equipped with a stirrer 122, which allows the contained waste acid to be stirred as needed.

[0037] The liquid transfer pump 14 is configured to send waste acids, such as etching waste liquid, contained in the waste acid storage tank 12 to the waste acid reaction tank 16.

[0038] The waste acid reaction tank 16 is configured to receive waste acids, such as etching waste liquid, from the waste acid treatment tank 12. The waste acid reaction tank 16 is equipped with an acid-resistant and heat-resistant agitator 162 that functions as a mixing screw, and is configured to stir and mix the waste acids in the tank.

[0039] In the waste acid reaction tank 16, a treatment is performed in which steel slag is added to mitigate the acidity of the received etching waste liquid, and a lime addition treatment is performed in which calcium oxide or calcium hydroxide is further added to the waste acid to which the steel slag has been added.

[0040] Furthermore, since the temperature of the etching waste liquid may rise in the waste acid reaction tank 16, generating a large amount of gas, a cooling device such as a chiller or cooling tower (not shown) is placed near the waste acid reaction tank 16.

[0041] The sludge storage tank 200 is configured to contain sludge that has been neutralized and solidified in the waste acid reaction tank 16 and is in a state where it can be accepted as sludge at a final disposal site.

[0042] The scrubber 30 is configured to neutralize the gases generated during the chemical reaction in the waste acid reaction tank 16. Here, the scrubber 30 is positioned to cover the top of the waste acid reaction tank 16, and the gases generated during the chemical reaction in the waste acid reaction tank 16 are neutralized by the scrubber 30 before being discharged into the atmosphere.

[0043] The lime containment section 40 is configured to contain lime (calcium oxide in this embodiment) to be supplied to the waste acid reaction tank 16.

[0044] The slag containment section 42 is configured to contain steel slag that is to be supplied to the waste acid reaction tank 16.

[0045] The slag containment section 42 is connected to a slag crushing device 50, where the steel slag is crushed as needed.

[0046] In the above configuration, the etching waste liquid used in the etching process of the etching apparatus 100 is sent from the etching apparatus 100 to the waste acid containment tank 12 of the waste acid treatment system 10. Then, when it is time for treatment, it is sent from the waste acid containment tank 12 to the waste acid reaction tank 16.

[0047] As described above, in the waste acid reaction tank 16, first, a treatment is performed to add steel slag in order to mitigate the acidity of the received etching waste liquid, etc.

[0048] In the waste acid reaction tank 16, the acidity of the waste acid is mitigated and its viscosity is moderately increased by mixing it with steel slag. To improve processing efficiency, it is preferable that the steel slag is crushed to a particle size of 1 mm or less in the slag crushing device 50, and more preferably to a particle size of 0.5 mm or less.

[0049] While steelmaking slag is preferable as the steel slag, blast furnace slag or electric furnace slag may also be used.

[0050] Furthermore, lime such as CaO (calcium oxide) is added to the waste acid reaction tank 16 and mixed with the agitator 162, thereby neutralizing and solidifying the waste acid to a degree that allows for proper treatment at the final disposal site.

[0051] When CaO (calcium oxide) is added from the lime containment section 40 to the waste acid reaction tank 16, the main reactions that take place in the waste acid reaction tank 16 are, for example, as follows: (Formula) H2SiF6+ 3CaO → 3CaF2+ SiO2+ H2O

[0052] As the reaction described above proceeds in the waste acid reaction tank 16, for example, in the case of glass etching waste liquid, the viscosity of the etching waste liquid increases due to the formation of an SiO2 gel.

[0053] On the other hand, even in cases where the formation of SiO2 gel is small, such as with hydrofluoric acid wastewater, the use of steel slag ensures that solidification is accelerated without any problems.

[0054] Steel slag (especially reducing slag) contains, in addition to its main component, calcium oxide, magnesium (Mg), aluminum (Al), and silica (Si), which have a solidification-promoting effect and readily react with acids to become insoluble substances. If iron (Fe) is also present, a co-precipitation effect can be expected, further accelerating solidification.

[0055] In this embodiment, by adding CaO, which has high reactivity with water, it becomes possible to evaporate the water from the waste acid using the heat of neutralization. By converting the entire amount into neutralized and solidified sludge with a low water content, it becomes possible to reduce the amount of waste. Evaporation reaction: CaO + H2O → Ca(OH)2 Neutralization reaction: H₂SiF₆ + 3Ca(OH)₂ → 3CaF₂ + SiO₂ + 4H₂O

[0056] According to this embodiment, it becomes possible to reduce the volume of neutral sludge regardless of the state of the etching wastewater, thereby reducing costs. Moreover, since there is no need to separately install equipment to treat the wastewater discharged during the wastewater treatment process, it becomes possible to simplify the wastewater treatment equipment.

[0057] In the embodiments described above, since the steel slag is used for the purpose of mitigating acidity, it is not necessarily required that the steel slag contain more than the number of moles of CaO needed to neutralize the waste acid.

[0058] Rather, it is expected that the steel slag will contain a large amount of metal components that precipitate during the neutralization reaction of waste acid. While such metal components are also present in the waste acid to be treated, even if the amount of metal components in the waste acid to be treated is small, the addition of steel slag will replenish the necessary metal components.

[0059] These metals dissolve as ions in the acid, but as the neutralization reaction progresses, i.e., as the pH increases, they precipitate as hydroxides. Furthermore, since different metals precipitate at different pH ranges, it is preferable to adjust the pH to the appropriate level when adding lime later.

[0060] In the waste acid treatment system 10, instead of precipitating and removing metal components from the received waste acid and discharging it as waste liquid to the next stage, the entire amount is solidified into sludge (pH greater than 2.0 and less than 12.5, with a water content of 85% or less) that can be accepted at the final disposal site, thus eliminating the need for solid-liquid separation treatment.

[0061] To promote the neutralization reaction, it is advisable to pre-crush and sized the steel slag. A particle size of 1 mm or less is desirable, and 0.5 mm or less is preferable. This is because the reaction occurs from the surface, so a larger specific surface area is advantageous. Furthermore, a larger amount of steel slag is also advantageous. The reaction is carried out by dispersing the steel slag in waste acid. During this process, stirring can be used to maintain a uniform reaction.

[0062] Furthermore, as mentioned above, since steel slag contains CaO in various mineral forms, it is effective to reduce it beforehand to increase the amount of free CaO. The method of reduction is not particularly limited.

[0063] The above description of embodiments should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims, rather than by the embodiments described above. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the claims. [Explanation of symbols]

[0064] 10. Waste Acid Treatment System 12-Waste Acid Containment Tank 14. Liquid transfer pump 16. Waste Acid Reactor 20-Sludge storage tank 30-Scrubber 40-Lime Storage Section 42-Slag containment section 50-Slag crushing device 100-Etching device 122,162-Agitator

Claims

1. A waste acid treatment system for neutralizing and solidifying waste acid, including etching waste liquid generated in the etching process of glass substrates or semiconductor substrates, into sludge that can be properly accepted at an industrial waste final disposal site, comprising: a waste acid reaction tank configured to contain the waste acid to be treated; a steel slag adding means for adding steel slag to the waste acid in the waste acid reaction tank; and a lime adding means for adding calcium oxide or calcium hydroxide so that the waste acid to which the steel slag has been added is neutralized and solidified. A waste acid treatment system comprising at least a stirring means for stirring the waste acid in the waste acid reaction tank.

2. The waste acid treatment system according to claim 1, further comprising a slag crushing means configured to crush the aforementioned steel slag.

3. A waste acid treatment method for neutralizing and solidifying waste acid containing etching waste liquid generated in the etching process of glass substrates or semiconductor substrates into sludge that can be properly accepted at an industrial waste final disposal site, the method comprising at least a steel slag addition step of adding steel slag to the waste acid to be treated; a lime addition step of further adding calcium oxide or calcium hydroxide to the waste acid to which the steel slag has been added; and a stirring step of stirring the waste acid to which the lime has been added until it is neutralized and solidified.

4. The waste acid treatment method according to claim 3, further comprising a slag crushing step of crushing the steel slag before the steel slag addition step.

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