KR20220089121A - Methode for treatment of waste sulfuric acid - Google Patents

Abstract

The method for treating waste sulfuric acid according to an embodiment of the present invention is a method for treating waste sulfuric acid containing metal ions, comprising the steps of: adding a first neutralizing agent to the waste sulfuric acid for primary neutralization; Separating the first sludge, adding a second neutralizing agent to the supernatant from which the first sludge is separated to be secondarily neutralized, and separating the second sludge generated after the second neutralization, wherein the first neutralizing agent is a calcium-based neutralizing agent, and the second neutralizing agent is a hydroxide of an alkali metal or ammonia.

Description

METHODE FOR TREATMENT OF WASTE SULFURIC ACID

The present invention relates to a method for neutralizing waste sulfuric acid, and more particularly, to a method for neutralizing waste sulfuric acid in which sludge generated during treatment of waste sulfuric acid containing metal ions can be recycled.

During the manufacturing process of carbon steel and stainless steel, a pickling process is performed to chemically remove the oxide scale formed on the steel surface. When sulfuric acid is used in such a pickling process, metal ions are dissolved in sulfuric acid. At this time, in the case of carbon steel, iron divalent ions are mainly dissolved, and in the case of stainless steel, iron divalent ions and a small amount of metals such as chromium and nickel are dissolved. . If the metal is continuously dissolved according to the use of sulfuric acid, it is treated with waste acid at the end of its life as a pickling solution. Waste sulfuric acid that has been treated with sulfuric acid is usually neutralized using an alkali neutralizer and then discharged into waste water. The generated sludge is dewatered and landfilled. do. The sludge generated in the neutralization process has slightly different components depending on the type of alkali neutralizer, but as a neutralizing agent, low-cost calcium-based neutralizing agents such as slaked lime, quicklime, and limestone are commonly used. The method of neutralization using

When a calcium-based neutralizer is used, gypsum components are generated as sludge by the neutralization reaction of sulfuric acid as follows, and metal ions react with alkali to form metal hydroxides.

H ₂ SO ₄ (waste sulfuric acid) + Ca(OH) ₂ (slaked lime) → CaSO ₄ (gypsum) + 2H ₂ O (pH 3.0~5.0)

Fe ²⁺ + 2OH ^- → Fe(OH) ₂ (iron hydroxide sludge, pH 5.0 or higher)

On the other hand, when caustic soda is used, soluble sodium sulfate is formed as shown in the following formula, and metal ions also form metal hydroxide.

H ₂ SO ₄ (spent sulfuric acid) + 2NaOH (caustic soda) → Na ₂ SO ₄ (Soluble Maltwort) + 2H ₂ O (pH 3.0~5.0)

Fe ²⁺ + 2OH ^- → Fe(OH) ₂ (iron hydroxide sludge, pH 5.0 or higher)

This process will be described in more detail with reference to FIG. 1 . 1 is a view showing a conventional neutralization process of spent sulfuric acid. As shown in FIG. 1, neutralization proceeds in multiple stages such as 1st or 2nd stage using the 1st neutralization tank 2 and the 2nd neutralization tank 3, but the sludge is generated at once in one settling tank 4 will do That is, in the settling tank 4, the treated water 5 and the dehydrated neutralized cake sludge 6 are separated and discharged. In this case, the generated sludge 6 is mainly composed of hydroxide of metal ions dissolved in sulfuric acid and gypsum component which is calcium sulfate when a calcium-based neutralizing agent is used. In addition, when caustic soda is used as a neutralizing agent, soluble sodium sulfate (sorghum) is formed. However, in the case of soluble sodium sulfate, the salinity of the wastewater is raised to a very high level, which deteriorates the sedimentation property of the generated sludge. Therefore, calcium-based neutralizers are mainly used. In the case of the generated sludge, since gypsum sludge and metal hydroxide sludge are mixed, recycling is difficult, and thus the generated sludge is disposed of.

In the prior art, a method of reusing the pickling solution as an inorganic coagulant (Korean Patent Laid-Open No. 10-1990-060899) is disclosed, but in order to reuse it as an inorganic coagulant, a large amount of FeSO ₄ must be added to the spent sulfuric acid, and also stainless steel In the case of a strong pickling solution, since it contains components such as Cr and Ni, it is classified as a harmful component. In addition, a method for treating and recycling waste acid, alkali, and sludge (Korean Patent Publication No. 10-2005-0015421) is disclosed, but the main purpose is to reduce the weight by adding an oxidizing agent to the sludge, heating and decomposing it, so it takes cost and energy. It is also disclosed that only reducing the amount of generated sludge, not recycling of the sludge. In addition, a method for recovering iron compounds from acidic wastewater containing iron ions (U.S. v. v. Lok Patent No. 4,497,707) is disclosed, but it is neutralized using magnesium hydroxide (Mg(OH) ₂ ) and oxidized in air to give iron trivalent As a method of recovering only ions, in this case, the content of soluble ions in the wastewater is greatly increased, and the treated water after the waste acid treatment shows rather high salinity, which causes ecotoxicity and makes it difficult to reuse the wastewater.

An object of the present invention is to provide a neutralization treatment method for waste sulfuric acid that can be recycled without a simple landfill treatment of sludge generated during neutralization treatment of waste sulfuric acid containing metal ions.

However, the problems to be solved by the embodiments of the present invention are not limited to the above problems and may be variously expanded within the scope of the technical idea included in the present invention.

The method for treating waste sulfuric acid according to an embodiment of the present invention is a method for treating waste sulfuric acid containing metal ions, comprising the steps of: adding a first neutralizing agent to the waste sulfuric acid for primary neutralization; Separating the first sludge, adding a second neutralizing agent to the supernatant from which the first sludge is separated to be secondarily neutralized, and separating the second sludge generated after the second neutralization, wherein the first neutralizing agent is a calcium-based neutralizing agent, and the second neutralizing agent is a hydroxide of an alkali metal or ammonia.

The first neutralization may be made up to a pH of 4.0 to 5.0.

The secondary neutralization may be made up to a pH of 7.5 to 9.5.

The first neutralizing agent may be at least one selected from slaked lime, quicklime, and calcium chloride.

The second neutralizing agent may be at least one of caustic soda (NaOH), KOH, and NH ₄ OH.

The first sludge may be recycled into gypsum.

The content of metal components other than calcium contained in the first sludge may be less than 3% by weight.

The second sludge may be recycled as a steel material, including hydroxides of metals.

The content of metal components other than calcium contained in the second sludge may be 30% by weight or more.

The spent sulfuric acid may be waste sulfuric acid generated in a process of acid washing with sulfuric acid for at least one of carbon steel and stainless steel.

According to an embodiment of the present invention, since the entire amount of sludge generated during the neutralization treatment of waste sulfuric acid can be recycled, the cost of sludge treatment can be reduced, and the cost of other industries can be reduced by recycling it as a useful resource. . In addition, it is possible to provide a method capable of reusing sludge without requiring much additional cost compared to the conventional method.

Effects of the present invention are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description of the claims.

1 is a view showing a process for treating waste sulfuric acid according to the prior art.
2 is a view showing a process for treating waste sulfuric acid according to an embodiment of the present invention.
3 is a graph showing a neutralization titration curve according to the type of alkali neutralizer.
4 is a graph illustrating a differential value to find an inflection point in FIG. 3 .

The terms first, second and third etc. are used to describe, but are not limited to, various parts, components, regions, layers and/or sections. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Accordingly, a first part, component, region, layer or section described below may be referred to as a second part, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of referring to specific embodiments only, and is not intended to limit the present invention. As used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite. The meaning of "comprising," as used herein, specifies a particular characteristic, region, integer, step, operation, element and/or component, and includes the presence or absence of another characteristic, region, integer, step, operation, element and/or component. It does not exclude additions.

When a part is referred to as being “on” or “on” another part, it may be directly on or on the other part, or the other part may be involved in between. In contrast, when a part is referred to as being "directly above" another part, the other part is not interposed therebetween.

In addition, unless otherwise specified, % means weight %, and 1 ppm is 0.0001 weight %.

Although not defined otherwise, all terms including technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention belongs. Commonly used terms defined in the dictionary are additionally interpreted as having a meaning consistent with the related technical literature and the presently disclosed content, and unless defined, are not interpreted in an ideal or very formal meaning.

Referring to FIG. 2, a process for treating waste sulfuric acid according to an embodiment of the present invention will be described. 2 is a view showing a process for treating waste sulfuric acid according to an embodiment of the present invention.

Referring to FIG. 2 , the method for treating waste sulfuric acid according to an embodiment of the present invention is a method for treating waste sulfuric acid containing metal ions, and a first neutralization tank ( 20), the first neutralization step, the step of separating the first sludge 40 generated after the first neutralization in the first settling tank 30, the second neutralizing agent is added to the supernatant from which the first sludge 40 is separated. Second neutralization in the second neutralization tank (50), and the second sludge (80) generated after the second neutralization is separated from the wastewater (70) in the second settling tank (60). Here, the first neutralizing agent is a calcium-based neutralizing agent, and the second neutralizing agent is a hydroxide of an alkali metal or ammonia.

The waste sulfuric acid 10 to be treated in the present invention is waste acid generated after the pickling process using sulfuric acid for carbon steel or stainless steel. First, a first neutralizing agent is added to the waste sulfuric acid 10 to perform primary neutralization in the first neutralization tank 20 .

The first neutralizing agent used in the primary neutralization is a calcium-based neutralizing agent. Examples of the calcium-based neutralizing agent include slaked lime (Ca(OH) ₂ ), quicklime (CaO), and calcium chloride (CaCl ₂ ). Preferably, slaked lime may be used.

When the primary neutralization is performed using such a calcium-based neutralizing agent, calcium ions contained in the calcium-based neutralizing agent and sulfate ions of spent sulfuric acid react to produce gypsum (CaSO ₄ ). That is, the first sludge 40 containing gypsum as a main component is generated. At this time, the pH is maintained at 4.0 to 5.0. If the pH is less than 4.0, the free acid of the spent sulfuric acid is not sufficiently neutralized, so that the amount of gypsum generated is reduced, and there is a problem in that the consumption of the neutralizing agent is increased during the secondary neutralization. When the pH exceeds 5.0, the metal ions contained in the spent sulfuric acid may react with the hydroxide ions to start to form metal hydroxide, in this case, the metal component in the first sludge may increase to reduce the purity of the gypsum. Not desirable. In addition, if the metal ions are generated as metal hydroxides during the primary neutralization, the metal component in the second sludge obtained during the secondary neutralization is reduced and the efficiency is also lowered, which is not preferable.

In the first neutralization, as shown in FIG. 2, a polymer coagulant may be used together to increase the particle size of the sludge. The kind of polymer flocculant used is not specifically limited, A general-purpose thing can be used.

After the first neutralization, the product is moved to the first settling tank 30 and separated into a supernatant and first sludge 40 . The first sludge 40 is a precipitate neutralized by the first neutralizing agent 20, which is a calcium-based neutralizer, as described above, and mainly contains insoluble gypsum. By forming insoluble gypsum in this way, the amount of ions remaining in the treated final effluent is reduced, and the treated water may cause ecotoxicity due to salinity or may not be disadvantageous in recycling due to its high ion content. Although there are cases where a multi-stage neutralization process has been applied in the prior art, unlike the present invention, when a neutralizing agent such as caustic soda or magnesium hydroxide is used for primary neutralization, there is an advantage in the amount of sludge generated, but these neutralizers are neutralizing agents with high solubility As a result, the salinity of the treated water increases, which can cause ecotoxicity and makes it difficult to reuse wastewater. However, in the present invention, since insoluble gypsum is first generated by using a calcium-based neutralizing agent in the first neutralization, and it is first separated in the first settling tank 30, such a problem can be prevented.

In addition, in the case of the first sludge 40 separated as described above, the pH was maintained at less than 5.0 during the primary neutralization as described above, and almost no metal hydroxide was generated, so the metal hydroxide in the first sludge 40 was This is hardly included, and high-purity gypsum can be included. That is, the metal ions present in the spent sulfuric acid may hardly be contained in the first sludge 40 . For example, the metal component other than calcium may be included in less than 3% by weight. Accordingly, such gypsum can be recycled without additional refining treatment, and it can be used as an auxiliary material such as cement.

Next, with respect to the supernatant from which the first sludge 40 is separated, a second neutralization agent is added to perform secondary neutralization in the second neutralization tank 50 . As the second neutralizing agent used in the secondary neutralization, hydroxide can be used. For example, it may be a hydroxide of an alkali metal or ammonia, and more specifically, it may be at least one of caustic soda (NaOH), KOH, and NH ₄ OH. Preferably, it may be caustic soda.

By neutralizing using such a second neutralizing agent, the metal component remaining in the supernatant reacts with the neutralizing agent to precipitate as metal hydroxide, thereby forming the second sludge 80 .

At this time, the pH is maintained at 7.5 to 9.5. When the pH is less than 7.5, neutralization of spent sulfuric acid and formation of metal hydroxides of metal ions are not sufficiently achieved. When the pH exceeds 9.5, only the consumption of the second neutralizing agent increases, and the wastewater can be discharged only when it is reverse neutralized again, which is disadvantageous in terms of economy.

Even during secondary neutralization, as shown in FIG. 2 , a polymer coagulant may be used together to increase the particle size of the sludge. The kind of polymer flocculant used is not specifically limited, A general-purpose thing can be used.

After the second neutralization, the product is moved to the second settling tank 60 , and separated into wastewater 70 and second sludge 80 . In the secondary neutralization, because no calcium-based neutralizing agent is used, gypsum is not generated, and sludge containing only metal hydroxide is generated. In addition, since the first sludge 40 containing gypsum was first separated in the previous process, that is, the first settling tank 30, sludge containing only metal hydroxide without gypsum in the second sludge 80 can be obtained. have. For example, it may contain 30 weight% or more of metal components other than calcium. Accordingly, it is possible to separate the second sludge 80 containing the metal hydroxide and recycle it as a raw material for manufacturing steel.

In the case of secondary neutralization, unlike the present invention, when a calcium-based neutralizer is used again, gypsum is formed again, and in particular, since sludge mixed with metal hydroxide is generated, recycling of both gypsum and metal hydroxide becomes difficult. In addition, when a neutralizing agent with high solubility such as magnesium hydroxide is used instead of an alkali metal hydroxide, the acid neutralization ability is very insufficient (it is hardly soluble in the alkali region due to its low solubility in water), and the input neutralizing agent is mostly generated as sludge. There is a problem in that it is difficult to form a metal hydroxide. On the other hand, in the present invention, in the first neutralization, insoluble gypsum is first separated using a calcium-based neutralizing agent, and then the remaining metal ions are precipitated as metal hydroxides using a second neutralizing agent that is a hydroxide such as an alkali metal only for the remaining supernatant. , it is possible to separate into sludge containing only metal hydroxide, not sludge mixed with gypsum or neutralizing agent, and thus it is possible to recycle it as a raw material for steel manufacturing.

As described above, according to an embodiment of the present invention, the first sludge containing high-purity gypsum is separated using a calcium-based neutralizing agent during waste sulfuric acid treatment, and a monovalent hydroxide neutralizing agent is used for the remaining supernatant secondarily to separate the second sludge containing the metal hydroxide and recycle each. That is, since the entire amount of sludge generated during the neutralization treatment of waste sulfuric acid can be recycled, the cost of sludge treatment can be reduced, and the cost of other industries can be reduced by recycling it as a useful resource. In addition, it is possible to provide a method capable of reusing sludge without requiring much additional cost compared to the conventional method.

Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present invention may be embodied in several different forms and is not limited to the embodiments described herein.

Experimental Example 1: Determination of an appropriate pH point for separating and recovering sludge

In the conventional neutralization treatment process as shown in FIG. 1, in order to find out what kind of reaction occurs depending on the degree of neutralization, a neutralization titration curve was prepared according to the type of alkali neutralizer. The results are shown in FIG. 3 . As shown in FIG. 3 , the pH increases as the amount of the alkali neutralizer increases. In a certain range, it can be seen that the inflection point increases while the conductivity of the treated water decreases and then increases again. In particular, in neutralization using NaOH, the electrical conductivity decreases to some extent and then increases again. Therefore, if the entire process is neutralized with NaOH, as described above, the salinity of the treated water (conductivity is a value representing salinity) increases, causing a problem. On the other hand, in the case of using slaked lime, it can be seen that the conductivity of the treated water continuously maintains a very low value.

Meanwhile, in the result of FIG. 3 , when the differential value is drawn to find an inflection point with respect to pH, it appears as shown in FIG. 4 . It can be seen that clearly distinct inflection points are occurring near pH 4, 7, and 10. The inflection point near pH 4 is the region where sulfuric acid is neutralized, and it can be considered that the pH is sludged together if trivalent iron is present among some iron ions. It can be viewed as an inflection point. On the other hand, at pH 10 or higher, metal ions are generated while forming a complex, but at pH 9.0 or higher, neutralization is not actually performed, so this area can be regarded as an unnecessary part. Therefore, it can be seen that sludges of different compositions can be secured when the sludge is collected by dividing the pH region by the point where the inflection point occurs.

Experimental Example 2: Analysis of components in sludge by different neutralizing agents

After collecting a sample of spent sulfuric acid, neutralizing it with a neutralizer, collecting the sludge, and confirming its composition. In Comparative Example 1, slaked lime and caustic soda were used in combination as a neutralizing agent, but only one final sludge collection was performed. In Comparative Example 2, only slaked lime was used as a neutralizing agent and then only sludge was collected once. After using only caustic soda, only one sludge collection was performed. In Comparative Example 1-3, the sludge was collected only once, but neutralization was performed firstly to pH4.5 and secondary to pH9.0.

In Comparative Example 4, the first sludge was collected after primary neutralization (~pH4.5) using CaCO ₃ as the first neutralizing agent, and secondary neutralization (~ pH9.0) using caustic soda as the second neutralizing agent After that, a second sludge collection was performed.

In Example 1, the first sludge was collected after primary neutralization (~pH4.5) using slaked lime as the first neutralizing agent, and secondary neutralization (~pH9.0) was performed using caustic soda as the second neutralizing agent. After that, a second sludge was collected.

The components were analyzed by observing the sludge obtained in each Comparative Example and Example with an SEM electron microscope.

The results are shown in Table 1 below.

Neutralizer type main ingredient first sludge second sludge Comparative Example 1 Slaked Lime + Caustic Soda - Fe 11% , Ca 17%, S 16%, O 53% Comparative Example 2 slaked lime - Fe 10% , Ca 18%, S 15%, O 55% Comparative Example 3 caustic soda - Fe 17%, Cr 3% , Na 22%, S 14%, O 43% Comparative Example 4 CaCO ₃ + Caustic Soda Fe 2.5% , Cr 1%, Ca 23% , S 21%, O 52% Fe 13% , Cr 2.3%, Ca 17%, S 13%, O 54% Example 1 Slaked Lime + Caustic Soda Fe 2.9% , Ca 19%, S 18%, O 58% Fe 51%, Cr 3% , Ca 2%, S 4%, O 39%

As shown in Table 1, in Comparative Examples 1-3, the sludge was collected and analyzed as a single sludge, and therefore the first sludge was not generated. In this case, although there were some differences in the composition of the second sludge depending on the type of neutralizer, the Fe content was as low as 10~17% and Ca content was high in the range of 17~22%, making it difficult to recycle both iron and gypsum components. there was

In Comparative Example 4, a limestone component was used instead of slaked lime as the first neutralizing agent. The Fe content of the first sludge was lowered and the Ca content was increased, so that high-purity gypsum was generated, so there was a possibility of recycling as gypsum, but in the case of the second sludge, the Fe content This was rather low and the Ca content was still high, so it was an unfavorable condition for recycling metal materials such as iron in the second sludge.

Finally, in Example 1, the first neutralization was performed with slaked lime and the second neutralized with caustic soda. In this case, it can be seen that the first sludge mainly contains CaSO ₄ component, which is a gypsum component, as a main component. It was found that sludge with high metal purity was generated as it mainly contains Fe component and hardly contains Ca component.

Although preferred embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention as defined in the following claims are also provided. is within the scope of the

Claims (10)

A method for treating spent sulfuric acid containing metal ions, comprising:
Primary neutralization by adding a first neutralizing agent to the spent sulfuric acid;
separating the first sludge generated after the first neutralization;
Second neutralization by adding a second neutralizing agent to the supernatant from which the first sludge is separated; and
Separating the second sludge generated after the second neutralization,
The first neutralizing agent is a calcium-based neutralizing agent, and the second neutralizing agent is a hydroxide of an alkali metal or ammonia. The method of claim 1,
The first neutralization is a method of treating spent sulfuric acid in a pH range of 4.0 to 5.0. The method of claim 1,
The second neutralization is a method of treating spent sulfuric acid in the range of pH 7.5 to 9.5. The method of claim 1,
The first neutralizing agent is at least one selected from slaked lime, quicklime, and calcium chloride. The method of claim 1,
The second neutralizing agent is at least one of caustic soda (NaOH), KOH, and NH ₄ OH. The method of claim 1,
The first sludge is a method of treating waste sulfuric acid that is recycled into gypsum. 7. The method of claim 6,
The method of treating waste sulfuric acid wherein the content of metal components other than calcium contained in the first sludge is less than 3% by weight. The method of claim 1,
The method of treating waste sulfuric acid wherein the second sludge is recycled as a steel material, including metal hydroxides. 9. The method of claim 8,
The content of metal components other than calcium contained in the second sludge is 30% by weight or more of the treatment method of waste sulfuric acid. The method of claim 1,
The waste sulfuric acid is a waste sulfuric acid treatment method that is generated in a process of acid washing with sulfuric acid for at least one of carbon steel and stainless steel.

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