KR101146785B1 - Method for ex-situ restoration of contaminated soil - Google Patents

Abstract

PURPOSE: A method for ex-situ restoration of contaminated soil is provided to shorten times required for treatment by excavating contaminated soil and oxidizing oil contained in the contaminated soil using hydrogen peroxide and catalyst. CONSTITUTION: Soil contaminated with oil is excavated and spread on the surface of the ground. Otherwise, moisture is supplied to the soil in an excavating place. 100 parts by weight of 5-35% hydrogen peroxide aqueous solution, 0.05-3.0 parts by weight of ferrous chloride or ferrous sulfate, and 0.005-2.0 parts by weight of a promoter are injected into the soil with moisture to be mixed. The mixture is stirred. The promoter is one selected from ethylenediaminetetraacetic acid, N-(2-hydroxyethyl) iminodiacetic acid, S,S''-ethylene diamine disuccinate, and nitrilotriacetic acid.

Description

{Method for Ex-situ Restoration of Contaminated Soil}

The present invention relates to a method for restoring the surface treatment of contaminated soil to purify soil contaminated with various oils, and more specifically, to excavate contaminated soil with an excavator and lay it on the surface or excavate the hydrogen peroxide and the catalyst in the ground. The present invention relates to a method for purifying and restoring contaminated soil by oxidizing oil contained in contaminated soil.

As the modernization and diversification of the industry is accelerating, the consumption of oil as an energy source and raw materials of various chemical products is increasing exponentially. As a result of the increase of oil storage facilities and transportation handling, oil is a secondary problem caused by it. Soil pollution is a serious environmental problem.

   Soil pollution is one of the serious environmental pollution that can cause wide area pollution such as primary pollution of soil itself, secondary pollution to surrounding rivers and groundwater. Currently, 12,917 gas stations and 7,347 oil storage industry facilities in Korea Etc., which are managed as oil-related soil pollution causing facilities. In recent years, however, leaked oil contaminates a significant amount of soil and groundwater due to aging and inadequate handling of these facilities.

   Fuel stored in these facilities is hydrophobic, insoluble in water, and once spilled into the soil, it can form strong adsorption with the soil or remain non-aqueous phase liquids (NAPL) for a long time. In addition, since they are composed of very complex petroleum hydrocarbons and contain a lot of harmful components to human body and soil organisms, it is necessary to properly treat the contaminated soil.

   In Korea, the Soil Environment Conservation Act has been in force since 1996 to classify more than a certain scale of petroleum and toxic substance manufacturing and storage facilities as specific soil contamination facilities, and periodically conduct soil contamination tests within three years. In case of non-compliance, 16 substances including petroleum and toxic substances are regulated and controlled as soil pollution regulations by issuing a corrective order to improve the contaminated soil.

   The technology to purify soil contaminated with oil is classified into In-situ and Ex-situ by treatment location, and physical methods (excavation removal, shielding, pumping, vacuum extraction, Solidification, hydraulic fracturing, pyrolysis, plasma, etc.), chemical methods (oxidation, neutralization, ion exchange, soil washing, surfactant washing, freezing, vitrification, etc.), biological methods (decomposition, aeration, soil cultivation, etc.) are known. Among them, the chemical oxidation method, that is, the technique of using hydrogen peroxide as a representative oxidant and contacting with oil pollutants in the ground to decompose them into carbon dioxide and water, can disintegrate and treat oil pollutants in the home in a short time.

This method is most widely used because it can be easily implemented anywhere, but this method is not economically economical in a wide range and low concentration of contaminated areas, and it is a cost-effective treatment of excessive hydrogen peroxide and iron catalyst. There are disadvantages such as growth and problems that have a big impact on the ecosystem.

   As a specific example of the prior art, Korean Patent Publication No. 10-0476134 (Mar. 14., 2005) discloses a method for restoring soil contaminated soil and groundwater by sequential merging of hydrogen peroxide, ultraviolet rays and oil decomposition microorganisms. This method combines oil permeation by chemical reaction of hydrogen peroxide with biological oil decomposition by microorganisms to take advantage of each method and eliminates the disadvantages that can occur in combination use.However, as the underground treatment technology, the restoration period is long and the process is complicated. There is a problem that management is difficult. In addition, Korean Patent Laid-Open Publication No. 10-2010-0090506 (August 16, 2010) discloses desorption by increasing the solubility and vapor pressure of organic pollutants by heating the soil through steam injection and increasing the moisture content, and steam After removing the contaminants in the soil through extraction, microorganisms are added to the remaining organic contaminants to further decompose and remove them, and finally, heavy metals are removed by acid washing. This long, complex process is difficult to manage.

   On the other hand, when biological processes are linked after treatment by chemical methods, microbial growth and oil degradation activity are often inhibited by residual chemicals, and after treatment by biological methods, treatment by chemical methods is linked. In the case of making the initial purification efficiency slightly lowered, such problems remain.

   Therefore, the present inventors have studied a method of effectively linking the chemical method and the biological method applied to the ground treatment technology, unlike the ground treatment technology, to overcome the disadvantages of each unit process and to restore the surface treatment of oil-contaminated soil that can take advantage only. Invented.

 The present invention has been made to solve the above problems, by excavating soil contaminated with various oils with an excavator to spread the surface or supply water in the excavated site and then to the contaminated soil using hydrogen peroxide and catalyst as oxidant An object of the present invention is to provide a method of purifying and restoring contaminated soil from the ground by oxidizing the oil contained therein.

The present invention is a method for restoring contaminated soil by surface treatment,

1) a water supply step of excavating soil contaminated with oil with an excavator and laying it on the surface or supplying water in the excavated site; 2) an oxidation step of injecting hydrogen peroxide and a catalyst into the contaminated soil supplied with moisture in the water supply step; 3) the soil oxidation step of inverting by stirring the soil contaminated with hydrogen peroxide and catalyst in the oxidation step with an excavator; provides a method for restoring contaminated soil surface treatment comprising a.

In the present invention, the hydrogen peroxide is 5 to 35% aqueous solution in the oxidation step, the catalyst is ferrous chloride (FeCl ₂ ) or ferrous sulfate (FeSO ₄ ), the mixing ratio is 100: 0.05 ~ 3.0 parts by weight Provides a method of restoring contaminated soil surface treatment.

   In addition, the present invention provides a method for restoring contaminated soil surface treatment, characterized in that the promoter is further mixed in addition to the catalyst in the oxidation step, the mixing ratio is hydrogen peroxide 100: 0.005 ~ 2.0 parts by weight of the promoter.

   In the present invention, the promoter is ethylenediamine tetraacetic acid (EDTA), N- (2-hydroxyethyl) imino diacetic acid, S, S'-ethylenediaminedisuccinate (SS-EDDS), nitrile It provides a method for restoring contaminated soil surface treatment, characterized in that any one selected from low tri-acetic acid (NTA).

   In another aspect, the present invention provides a method for restoring contaminated soil surface treatment, characterized in that the hydrogen peroxide is mixed with any one oxidant selected from sodium persulfate, calcium peroxide, soda ash (Sodium Carbonate). do.

   Finally, the present invention provides a contaminated soil surface treatment restoration method, characterized in that the mixing ratio of the hydrogen peroxide and the oxidant is 100: 5 parts by weight.

Underground treatment restoration method of contaminated soil according to the present invention is to excavate the contaminated soil with an excavator and spread it on the surface or by oxidizing the oil contained in the contaminated soil using hydrogen peroxide and a catalyst in the excavated ground to purify the contaminated soil. By doing so, unlike the underground treatment method, the treatment period can be remarkably shortened, and the process is simple.

1 is a schematic diagram of a soil oxidation farm according to the present invention.

 The ground treatment restoration method of the contaminated soil according to the present invention will be described in detail with reference to the accompanying drawings.

   The water supply step of supplying water to the soil contaminated with oil, which is the first step of the present invention, is a preparatory step of the present invention, and it is generally known that the water content of the contaminated soil is 5 to 18 wt%. In order to apply the soil surface restoration method, appropriate moisture is required in the soil, and the appropriate moisture content of the contaminated soil is preferably in the range of 20-25 wt%.

   Soils with high moisture content can block the flow of air between the soil pores, disrupting the oxygen supply, and inhibiting the activity of microorganisms when the soil is dry.

In general, the moisture content of the excavated contaminated soil of contaminated soil is less than 18wt%, so the water is slightly lacking in applying the present invention, and water can be solved by spraying water on the contaminated soil with an injector periodically to solve the water shortage. In addition, in case of excessive moisture due to rainfall, installation of rainwater inflow blocking facilities such as houses should be considered in order to reduce treatment efficiency.

   In the second step of the present invention, the oxidation step is a step of injecting hydrogen peroxide and a catalyst into the contaminated soil supplied with moisture in the water supply step, and injecting an aqueous solution of hydrogen peroxide and a catalyst at an appropriate concentration into the contaminated soil to form radicals. This allows them to react with the oil present in the contaminated soil.

The hydrogen peroxide used in the oxidation step is discharged from the hydrogen peroxide tank, diluted to an appropriate concentration, mixed with the catalyst, and then supplied to the contaminated soil to produce radical hydroxide (OH?) As in Scheme 1 below.

H ₂ O ₂ → 2? OH------(Scheme 1)

Radical hydroxide (OH?) Generated from hydrogen peroxide as described above may decompose the oil by reacting with the oil present in the contaminated soil as in Scheme 2 below.

OH + M (oil) → decomposition products------(Scheme 2)

However, hydrogen peroxide is a material having an unstable structure, and has a property of reacting with other media in the soil or decomposing itself as shown in Scheme 3 below.

2H ₂ O ₂ + X (soil) → O ₂ + 2H ₂ O------(Scheme 3)

   As described above, part of the hydrogen peroxide injected into the contaminated soil reacts with oil, and another part reacts with other media in the soil. Therefore, in order to effectively decompose the oil, an appropriate amount of hydrogen peroxide is finally considered in consideration of the loss from the reaction with the soil. Adjust the supply of hydrogen peroxide to allow oil to react with the oil. At this time, a method of checking the treatment rate of hydrogen peroxide and contaminated soil is needed to find the optimal injection amount.In general, since the above reaction occurs firstly, a reaction rate constant is obtained by using a first-order reaction equation such as the following Equation 4 and the Optimal conditions are derived by comparing the rate constant versus the dose.

dC / dt = kC------(Scheme 4)

In the above scheme, C is the concentration of contaminated oil.

   In the restoration method of the present invention according to Scheme 4, it is preferable to use hydrogen peroxide aqueous solution in the range of 5 to 35%. When the concentration is less than 5%, the oxidizing power is weak and almost no oxidation occurs, and more than 35%. In this case, the oxidative power may increase, but the stability may be insufficient and an explosion may occur.

At this time, when the hydrogen peroxide is administered to the contaminated soil, it is preferable to use a mixture of hydrogen peroxide and a catalyst rather than to use hydrogen peroxide alone to increase the treatment efficiency. The catalyst is preferably a granular or powdery one as a compound capable of reacting with hydrogen peroxide to generate radicals. Examples of the catalyst include ferrous chloride (FeCl ₂ ) and ferrous sulfate (FeSO ₄ ). Co-catalysts can be used to further increase the oxidizing power, such as ethylenediamine tetraacetic acid (EDTA), N- (2-hydroxyethyl) imino diacetic acid, S, S'-ethylenediaminedistone Cinates (SS-EDDS), nitrilo triacetic acid (NTA).

   Hydrogen peroxide containing the catalyst is directly sprayed on the surface of the contaminated soil and supplied, and when the spraying process is carried out so that it can be spread evenly over the surface of the soil so that the hydrogen peroxide solution naturally flows into the soil contaminated by gravity. . At this time, the mixing of the hydrogen peroxide and the catalyst is preferably in a ratio of 100: 0.05 to 3.0 parts by weight. When the mixing ratio is less than 0.05 parts by weight, the oxidation reaction hardly occurs. Cost increases due to use. In the case of further use of the promoter, it is preferable to mix the hydrogen peroxide and the promoter in a ratio of 100: 0.005 to 2.0 parts by weight. When the mixing ratio is less than 0.005 parts by weight, the oxidation reaction is hardly increased as compared with the use of the catalyst. If it exceeds 2.0 parts by weight, the increase in oxidizing power is less than that in the case of using the catalyst and the cost increases due to the use of the overcatalyst.

Meanwhile, the present invention is a solid oxidizing agent sodium persulfate (Na ₂ S ₂ O ₈ ), calcium peroxide (Calcium Peroxide, CaO ₂ ), calcium carbonate (Calcium Carbonate, Na ₂ CO ₃ ) together with hydrogen peroxide as a liquid One selected may be mixed and used, and the mixing ratio thereof is preferably 100 parts by weight.

   The soil oxidation step, the final step of the present invention, is a step of inverting the contaminated soil in which the hydrogen peroxide and the catalyst are injected in the oxidation step with an excavator, and the contaminated soil accumulated in the soil oxidation farm as shown in FIG. 1 is periodically stirred with the excavator. It is a finishing step to increase the treatment efficiency by promoting the oxidation reaction of contaminated soil by forming a gyrus while flipping over.

Furthermore, the soil oxidation cultivation site needs additional sites to install the barriers and access roads to prevent the spread of additional pollutants, and the layout of the soil oxidization cultivation site is located at the shortest distance from the excavation site and the excavation area It can be located and installed in single and plural depending on the purification period. The cultivation cycle of the contaminated soil is determined by the time required per one time based on the removal rate derived through the removal efficiency test of the pollutants. The cultivation frequency is determined by the total purification period and the cultivation cycle. Decide For example, if the total purification period is within 48 hours and the tilling cycle is 12 hours, the number of tillages is four. Separately, even in the case of treating soil contaminated with highly volatile oil species, it is not necessary to install an exhaust gas treatment device using a volatile organic compound in a soil oxidation farm.

[Preparation for experiment]

From the site where the oil storage tank was located, excavated 100㎥ of contaminated soil with an excavator up to about 2m in depth of about 50m2, and collected 500g of it and measured the moisture of the contaminated soil. It was confirmed that, after spraying water on the contaminated soil with an injector, the moisture was measured and found to contain 23% by weight of water was used as a sample.

[Component Analysis of Soil Contamination]

  Analyze the content of benzene, toluene, ethylbenzene, xylene, total petroleum hydrocarbon (TPH) by soil process test using gas chromatography (HP 6890 Plus) to analyze the contaminated soil component of the sample. The results are shown in Table 1 below.

 Analysis of ingredients before treatment of contaminated soil pollutant benzene toluene Ethylbenzene xylene TPH Concentration (ppm) 0.019 0.018 0.009 0.048 573

In this example, 750 kg of 17% hydrogen peroxide aqueous solution and 20 kg of ferrous sulfate (FeSO ₄ ) 7H ₂ O, which are catalysts, were mixed in an soil 10 laid on a soil oxidation farm in advance and mixed by an excavator. Thereafter, the oxidized soil of the soil cultivation plant was stirred four times with an excavator and turned over, while hydrogen peroxide oxidized the contaminated soil for 48 hours, and 500 g of contaminated soil was recovered and sampled.

A sample was obtained after the contaminated soil restoration work was carried out in the same manner, except that 10 kg of ethylenediamine tetraacetic acid (EDTA), a promoter, was added to the ferrous sulfate as a catalyst. .

In Example 1, instead of ferrous sulfate as a catalyst, 37.5 kg of calcium peroxide (Calcium Peroxide, CaO ₂ ) was added and mixed with hydrogen peroxide. A sample was obtained.

A sample was obtained after performing contaminated soil restoration work in the same manner except that 30 kg was added instead of 20 kg of ferrous sulfate as a catalyst in Example 1.

In Example 2, instead of additionally adding 10 kg of ethylenediamine tetraacetic acid (EDTA) as a promoter, the sample was obtained by performing the same method as the contaminated soil except that 20 kg was added.

In Example 3, instead of adding 37.5 kg of calcium peroxide (Calcium Peroxide, CaO ₂ ), except that 30 kg was added, the sample was obtained by performing the restoration process of contaminated soil.

[Component Analysis after Treatment of Polluted Soil]

In order to analyze the contaminated soil components of the samples collected in Examples 1 to 6, benzene, toluene, ethylbenzene, xylene, and petroleum-based hydrocarbons (TPH) were analyzed by soil process test using gas chromatography (HP 6890 Plus). ) The results of analyzing the content are shown in the following [Table 2], and compared with the analysis results before the treatment of contaminated soil.

benzene toluene Ethylbenzene xylene TPH Reduction rate (%) Before processing 0.019 0.018 0.009 0.048 573 - Example 1 0.007 0.011 0.006 0.020 203 64.6 Example 2 0.005 0.008 0.005 0.009 153 73.3 Example 3 0.006 0.009 0.005 0.010 104 82.8 Example 4 0.011 0.015 0.006 0.017 253 55.2 Example 5 0.016 0.014 0.006 0.019 239 58.3 Example 6 0.008 0.013 0.007 0.021 274 52.2

Examples 1 to 3, which fall within the numerical limits of the present invention from Table 2, are significantly reduced than those of Examples 4 to 6 before the treatment of the contaminated soil or outside the numerical limits of the present invention. When the hydrogen peroxide and calcium peroxide were used as the oxidizing agent of 3, the reduction rate and the like were remarkably improved compared with the case of using the hydrogen peroxide and ferrous sulfate as a catalyst.

Claims (6)

delete delete As a method of restoring contaminated soil by surface treatment,
1) a water supply step of excavating soil contaminated with oil with an excavator and laying it on the surface or supplying water in the excavated site;
2) a catalyst and a promoter comprising 100 parts by weight of aqueous solution of 5 to 35% hydrogen peroxide, 0.05 to 3.0 parts by weight of ferrous chloride (FeCl ₂ ) or ferrous sulfate (FeSO ₄ ) in the contaminated soil supplied with moisture in the moisture supplying step. An oxidation step of oxidizing by mixing injection of 0.005 to 2.0 parts by weight;
And 3) soil oxidation step of inverting the soil by mixing the hydrogen peroxide aqueous solution, catalyst and cocatalyst in the oxidation step with an excavator and inverting the soil.
The method of claim 3,
The promoters are ethylenediamine tetraacetic acid (EDTA), N- (2-hydroxyethyl) imino diacetic acid, S, S'-ethylenediaminedisuccinate (SS-EDDS), nitrile triacetic Surface treatment restoration method of contaminated soil, characterized in that any one selected from acid (NTA).

delete delete

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