KR102079373B1 - Method for neutralizing dredged soil washed with acid - Google Patents

Abstract

A neutralization method is disclosed that neutralizes pickled dredged soil to remove contaminants.
According to the neutralization method, in order to neutralize the purified dredged soil in the solid state, a solid phase neutralizer is added and mixed to the purified dredged soil. In addition, according to the neutralization method, in order to neutralize the used process water in the liquid state used for pickling treatment, a liquid neutralizer is added to the used process water and mixed.

Description

Pickling method of neutralized dredged soil {METHOD FOR NEUTRALIZING DREDGED SOIL WASHED WITH ACID}

The present invention relates to a method for neutralizing pickled dredged soil, and more particularly, to purify the coastal dredged soil contaminated with high concentration by heavy metals through pickling, and to neutralize the dredged soil showing acidity. Washing waste liquid relates to a method of neutralizing and precipitation of heavy metals extracted from soil.

In the case of sediment or foreign matter that flows from the land, such as rivers and harbors, it not only prevents the smooth flow of the river, but also can cause odor due to the congestion of water or increase flooding damage in floods. Because of this possibility of being stranded, the work of periodically dredging the sediment is carried out for the purpose of improving the environment and maintaining the route.

However, due to urbanization and industrial development, various wastewaters are flowing into rivers and seas all over the world, and soils are contaminated by drops of air pollutants such as smoke discharged from factories, waste dumping, and spraying of pesticides and fertilizers. Later, it leads to pollution of groundwater and river water.

As a result, dredged soils may contain not only domestic sewage and factory wastewater but also a large amount of pollutants with high concentrations of heavy metals. In particular, dredged soils are likely to be contaminated with high concentrations of heavy metals, especially when industrial complexes are established nearby.

The problem of dredged soils in rivers and coastal areas is intensifying, but the existing soil purification technology is applied to dredged soils as it is, but the purification efficiency of dredged soils contaminated with heavy metals by heavy metals is low because of its small particle size. There is a need for research and development.

Republic of Korea Patent Publication No. 10-2011-0130052 (published December 5, 2011) discloses a conventional purification method for treating dredged soil. According to this conventional purification method, there is provided a two-step advanced oxidation cleaning method in which ultrasonic and chemical oxidation effective for separating pollutants are applied in two steps simultaneously with washing water (hydrochloric acid and EDTA). As a result, it is possible to treat large amounts of marine dredged soil contaminated with heavy metals with high alkalinity, high organic content, and high fine soils, but the cost is due to the use of neutralizers such as hydrogen peroxide to neutralize the soil washed by strong acids. There was a problem such as increase.

In addition, the use of chemicals for the cleaning and neutralization of contaminated soil can cause environmental problems. For example, when sodium hydroxide (NaOH) is used as a neutralizing agent, OH- ions are consumed for neutralization, and Na + ions remain in the soil, resulting in large white crystals upon drying. The use of such soil can lead to environmental pollution problems caused by excess salt.

Republic of Korea Patent Publication No. 10-2011-0130052 (published 5 December 2011)

The present invention has been made to solve the problems of the prior art, and neutralizes the dredged soil showing acid after the dredged soil purification process to purify the dredged soil contaminated with high concentration by various heavy metals through pickling. It is aimed at providing a method for neutralizing pickled dredged soils, which enables the purified dredged soils to be recycled as effective resources.

In addition, an object of the present invention is to provide a neutralization method that can utilize the fly ash obtained as an industrial by-product from a thermal power plant, etc. as a neutralizing agent for the low cost, eco-friendly neutralization of pickled dredged soil.

In addition, the present invention aims to provide a neutralization method that can be suitably used for neutralization of soil and process water by mixing fly ash with process water and separating it into liquid and solid phase for high efficiency neutralization of pickled dredged soil. .

According to an aspect of the present invention, as a neutralizing method for neutralizing the pickled dredged soil treated to remove contaminants, in order to neutralize the purified dredged soil in the solid state, by adding a solid neutralizing agent to the purified dredged soil, In order to neutralize the used process water in the liquid state used for the pickling treatment, a pickled dredged neutralization method may be provided, in which a liquid neutralizer is added to and mixed with the used process water.

The solid phase neutralizer may be fly ash (CFA) as a byproduct produced by burning coal.

The reaction time in the neutralization step performed by mixing the purified dredged soil and the solid phase neutralizing agent may be 0.5 to 1 hour. The injection amount of the solid neutralizer may be 2 to 6% by weight, and preferably 2 to 3% by weight of the purified dredged soil.

The liquid neutralizer may be prepared by mixing the solid neutralizer with clean process water and then separating the solid component. The ratio of the solid phase neutralizer and the clean process water mixed to prepare the liquid neutralizer may be 1: 100 by weight.

The solid component separated to prepare the liquid neutralizer can be recycled as a solid phase neutralizer. The ratio of the separated solid component and the liquid neutralizing agent may be 1: 100 by weight.

The reaction time in the neutralization and precipitation steps performed by mixing the process water and the liquid neutralizing agent after the use may be 5 to 10 minutes. The injection amount of the liquid neutralizer may be 90 to 150%, preferably 90 to 120% of the volume of the process water after use.

The pickled dredged soil neutralization method may further include a strength improvement step for increasing the soil strength of the dredged soil after the neutralization step of mixing the purified dredged soil with the solid neutralizer.

In the strength improvement step, the bottom ash (CBA) as a by-product generated by burning coal may be mixed with the dredged soil neutralized in the neutralization step.

The neutralization step performed by mixing the used process water and the liquid neutralizer may include a precipitation step of precipitating contaminants to be disposed of.

As described above, according to the present invention, a neutralization method for neutralizing the purified dredged soil showing acidity while undergoing a purification process by pickling may be used to recycle the purified dredged soil as an effective resource.

In addition, according to the neutralization method of the present invention, by utilizing the fly ash obtained as an industrial by-product in a thermal power plant, etc. as a neutralizing agent, by reducing the cost of the neutralization process of the pickled dredged soil by replacing the existing neutralized chemical with industrial by-products It becomes possible.

In addition, according to the neutralization method of the present invention, a liquid neutralizer and a solid phase neutralizer may be prepared by mixing fly ash with clean process water and separating a liquid and a solid, and thus, an object to be neutralized, that is, soil and process water. According to the appropriate use of the liquid neutralizer and the solid phase neutralizer, it is possible not only to efficiently carry out environmentally neutralization of pickled dredged soil, but also to remove and remove heavy metals from the pickling waste liquid.

1 is a schematic diagram illustrating a pickled dredged soil neutralization method according to an embodiment of the present invention.
2 is a view for explaining a method for producing a solid phase neutralizer and a liquid neutralizer used in the dredged soil neutralization according to an embodiment of the present invention.

In the pickled dredged soil neutralization method according to an embodiment of the present invention, in order to neutralize the soil washed with strong acids, such as sulfuric acid, during the dredged soil purification process to purify the soil contaminated with high concentration by various heavy metals. Can be used.

Hereinafter, the pickled dredged soil neutralization method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

As shown in FIG. 1, the pickled dredged soil neutralization method according to an embodiment of the present invention includes a contaminated dredged soil 1 contaminated at high concentration by various heavy metals, for example, an acid produced by a strong acid such as sulfuric acid. It may be used to neutralize the product pickled through the purification step (S10) to wash with the washing liquid (2), that is, the purified dredged soil 3 and the used process water (4).

Polluted dredged soil (1) contaminated with high concentration is washed to meet the purification criteria through pickling (acid eluting). However, in order to recycle the dredged soil 3, it is necessary to neutralize the dredged soil showing strong acidity. The dredged soil, which has been neutralized, may be subjected to a process of increasing strength as necessary. On the other hand, since the used process water 4 used in the purification step (S10) of the contaminated dredged soil 1 also exhibits strong acidity, it is necessary to neutralize the used process water in order to recycle it.

According to this embodiment, in order to neutralize the purified dredged soil (water content of about 75%) (3) in the process of purifying the contaminated dredged soil (1), fly ash (Coal) which is a by-product generated after burning coal in a thermal power plant, etc. Fly Ash; CFA) is used as a neutralizing agent. Accordingly, the cost for the neutralizer can be reduced. More specifically, the neutralization of the purified dredged soil 3 may be used as a solid neutralizer, such as solid CFA 11.

In addition, according to the present embodiment, it is possible to neutralize not only the purified dredged soil 3 described above, but also the used process water 4 used in the pickling process. For neutralization of the process water 4 after use, a liquid neutralizer such as liquid CFA 12 may be used.

By matching the phases of the neutralizing object and the neutralizing agent, the reaction time required for neutralization can be shortened, and the overall treatment time can be shortened. That is, if any of the neutralizing object and the neutralizing agent is a solid material, the reaction time is longer than that of the liquid material, so matching the phases of the reacting materials as much as possible shortens the reaction time required for neutralization. You can. In addition, in the case where the solid phase material and the liquid phase material are mixed and reacted, a solid-liquid separation process for phase separation after the reaction process is completed should be added, so matching the phases of the reacting materials is advantageous in reducing the overall processing time.

Since fly ash, a by-product produced in a power plant or the like, is in the solid state, it can be used as a solid neutralizer, i.e., a solid phase CFA 11.

Also, as shown in FIG. 2, the liquid CFA 12 may be prepared by mixing the solid CFA 11 with clean process water (eg, distilled water) 14 and then separating the solid and the liquid. At this time, the ratio of the mixed solid CFA and the clean process water may vary depending on the pH of the neutralized dredged soil. For example, when the pH of the soil to be neutralized is about 2.8, the ratio of the solid CFA 11 and the clean process water 14 to be mixed may be about 1:90 to 1: 120 in weight ratio. Alternatively, the ratio of the solid CFA 11 and the clean process water 14 may be set to about 1: 100 by weight.

Solid-liquid separation of the solution made by mixing the solid CFA 11 and the clean process water 14, the solid CFA and the liquid CFA (that is, CFA aqueous solution) 12 is obtained, the separated solid CFA can be reused. The solid-liquid separated solid phase CFA and the liquid CFA can each be divided by half the alkalinity. For example, the alkalinity of the solid phase CFA is about 50% (2,417 mg / L CaCO 3) , and the liquid CFA alkalinity of about 50% (2,774 mg / L CaCO 3). The ratio of the solid-liquid separated solid CFA and the liquid CFA may be approximately 1:90 to 1: 120 by weight. Or about 1: 100.

Referring back to FIG. 1, the reaction time in the neutralization step (S20) performed by mixing the purified dredged soil 3 and the solid CFA 11 may be about 0.5 to 1 hour, for example, the soil of the neutralization target soil. When the pH is about 2.8, the injection amount of the neutralizing agent, that is, the solid CFA may be about 2 to 6%, preferably 2 to 3% by weight of the dredged soil. If the reaction time is shorter than 0.5 hours, the neutralization reaction may not be completed and the pH may be continuously increased. If the reaction time is longer than 1 hour, the neutralization reaction may be completed, but the treatment time may be longer, resulting in lower economic efficiency. Not desirable in If the amount of solid CFA injected is less than 2% of the weight of the dredged soil, there is a risk that neutralization of the dredged soil may not be sufficiently performed. . The above values assume that the pH of the dredged soil to be neutralized is about 2.8. The above values may also change as the pH of the dredged soil to be neutralized changes.

Dredged soil neutralized through the neutralization step (S20) may be recycled as it is, or may be recycled after increasing the strength through the strength improvement step (S30). In the strength improvement step (S30), in order to improve the strength of the dredged soil, coal bottom ash (CBA) 13, which is a by-product generated after burning coal in a thermal power plant or the like, may be mixed in the dredged soil. Dredged soils mixed with CBA 13 have increased soil strength and can be recycled for more diverse uses, such as landfills in ports or coastal areas, for example.

In addition, the used process water 4 may be mixed with the liquid CFA 12 and treated through a neutralization and precipitation step (S40). The reaction time in the neutralization and precipitation step () performed by mixing the used water 4 and the liquid CFA 12 may be about 5 to 10 minutes, and the injection amount of the neutralizing agent, that is, the liquid CFA, may be It may be 90 to 150% by volume. If the reaction time is shorter than 5 minutes, the neutralization reaction may not be completed and the pH may be continuously decreased. If the reaction time is longer than 10 minutes, the neutralization reaction is completed, but the treatment time may be longer, resulting in lower economic efficiency. Not desirable in If the injected amount of liquid CFA is less than 90% of the volume of the process water after use, it may not be sufficiently neutralized, and if it is more than 150%, the neutralizing agent may be excessively consumed and the neutralized process water may be alkaline. not.

The neutralized process water through the neutralization and precipitation step (S40) may be recycled, and the precipitate separated and separated may be reprocessed or disposed of. The amount discarded is extremely small (about 0.01% or less) relative to the total treated soil because heavy metals removed from the soil other than dredged soil are transformed into sedimentary forms.

Table 1 shows the characteristics of contaminated dredged soil (1) before pickling, purified dredged soil (3) after pickling, and industrial by-products as solid phase neutralizers used in the neutralization stage, namely, solid CFA (11) and CBA.

As can be seen from Table 1, when the pickling method was applied to the contaminated dredged soil, the cleaned purified dredged soil met all the purification criteria. According to this embodiment, in order to neutralize the dredged soil that satisfies the purification criteria, an industrial by-product (solid phase neutralizer) having an alkali was used. In the case of industrial by-products, there is no risk of contaminating the dredged soil because the concentration of each substance is below the purification standard. As the purification standard, the Dutch Standard, which is widely used internationally, was used.

Table 2 shows the results of neutralizing the purified dredged soil using the industrial by-products described in Table 1.

Referring to Table 2, it was found that the neutralization capacity is different according to the type of industrial by-products, and the neutralization capacity of the solid phase CFA is superior to that of the solid phase CBA. In addition, when a solid CFA of about 2-3% by weight of the pickled purified dredged soil (slurry) was added, the neutralized dredged soil showed a neutral pH.

Table 3 shows the characteristics of the spent process water (4) used for pickling and the industrial by-products as liquid neutralizers used in the neutralization and precipitation steps, namely liquid CFA (12) and CBA.

As can be seen in Table 3, the pH of the spent process water separated from the pickled dredged soil is approximately 2.83, according to this example, to neutralize the used process water, the liquid CFA having higher neutralization capacity (ie , CFA solution) was used. As in the case of the solid neutralizing agent, the liquid neutralizing agent does not have to worry about contaminating the process water after use because the concentration of each substance is below the purification standard.

Table 4 shows the result of neutralizing the used process water using the industrial by-product (CFA solution) described in Table 3.

Referring to Table 4, the CFA solution (liquid CFA) was used to neutralize the used process water, and precipitate heavy metal contaminants in the used process water to reduce the concentration of the pollutants.

It is apparent to those skilled in the art that the present invention is not limited to the embodiments described above, and that various modifications and changes can be made without departing from the spirit and scope of the present invention. Accordingly, such modifications or variations will have to be belong to the claims of the present invention.

1: Pollution dredged soil
2: pickling liquid
3: purification dredged soil
4: process water after use
11: Solid Coal Fly Ash
12: liquid CFA
13: CBA (Coal Bottom Ash)
14: clean process water

Claims (13)

A neutralization method for neutralizing the purified dredged soil and the used process water, which is a result of pickling through the step of washing the contaminated dredged soil contaminated by heavy metals with pickling liquid,
In order to neutralize the purified dredged soil in the solid state, a solid neutralizer is added to the purified dredged soil and mixed.
In order to neutralize the used process water in the liquid state used for pickling treatment, a liquid neutralizing agent is added to the used process water and mixed,
The solid phase neutralizer is fly ash (CFA) as a by-product produced by burning coal,
The liquid neutralizer is prepared by mixing the solid neutralizer with clean process water and then separating the solid component,
The injection amount of the solid phase neutralizer is 2 to 6% by weight of the purified dredged soil, the injection amount of the liquid neutralizer is 90 to 150% of the volume of the used water, pickled dredged soil neutralization method. delete The method according to claim 1,
The reaction time in the neutralization step performed by mixing the purified dredged soil and the solid phase neutralizer is 0.5 to 1 hour, pickled dredged soil neutralization method. delete delete The method according to claim 1,
The ratio of the solid phase neutralizer and the clean process water mixed to prepare the liquid neutralizer is 1: 90 to 1: 120 by weight ratio, pickled dredged earth neutralization method. The method according to claim 1,
Wherein the solid component separated to produce the liquid neutralizer can be recycled as a solid phase neutralizer. The method according to claim 1,
The ratio of the separated solid component and the liquid neutralizing agent is 1: 90 to 1: 120 by weight ratio, pickled dredge neutralization method. The method according to claim 1,
The reaction time in the neutralization and precipitation step performed by mixing the process water and the liquid neutralizer after use is 5 to 10 minutes, pickled dredged soil neutralization method. delete The method according to claim 1,
After the neutralization step of mixing the purified dredged soil and the solid phase neutralizer, further comprising the step of improving the strength of the dredged soil soil, pickled dredged soil neutralization method. The method according to claim 11,
In the strength improvement step, pickled dredged soil neutralization method of mixing the dredged soil neutralized in the neutralization step, the bottom ash (CBA) as a by-product generated by burning coal. The method according to claim 1,
The neutralization step of mixing the used process water and the liquid neutralizer comprises a precipitation step of precipitating contaminants to be discarded, pickled dredge neutralization method.

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