KR20150088563A - Persulfate activation using zero-valent iron and soil-groundwater remediation by the activation - Google Patents

Abstract

The present invention relates to a method for decomposing poorly degradable organic compounds comprising a process of decomposing the poorly degradable organic compounds by activating persulfate through a reaction of zero-valent iron and persulfate wherein the method can be useful for remediation of soil and groundwater by effectively eliminating the poorly degradable organic compounds included in soil or groundwater.

Description

Activation of persulfate using zero valence iron and restoration of soil and groundwater contamination using the same

The present invention relates to a method for decomposing a decomposable organic compound, which comprises decomposing a decomposable organic compound by reacting with zero-valent iron and persulfate, more specifically, And a method for effectively treating a refractory organic compound contained in soil, wastewater, ground water or the like by activating persulfuric acid.

Chlorine-based organic compounds, which are known to be harmful to human bodies, and non-degradable substances such as dioxins, that is, refractory harmful substances, are emitted to nature through incineration facilities such as municipal waste and industrial waste, various combustion equipment, and the like.

In the manufacturing process of chemical substances, various organic compounds which unintentionally adversely affect the environment are discharged, which is becoming a serious social problem. The mechanism of formation of chlorinated aromatic compounds such as dioxins, chlorophenol, and chlorobenzene is not clear, but is believed to be produced in the presence of incombustible carbon, air, moisture, inorganic chlorine, etc. in a low temperature waste gas treatment process. Examples of the source of the wastewater containing these compounds include chlorine-based bleaching equipment in the kraft pulp production plant, decomposition facilities for waste PCB or PCB treatment, cleaning facilities for PCB contamination or PCB treatment, melting furnaces for the production of aluminum or aluminum alloy Waste gas cleaning equipment, wet type dust collecting equipment, abandoned light for discharging sewage and the like are known. In other words, it is likely to be produced in a process using chlorine compounds.

In addition, standards for water pollutants have been revised by the EPA, and organic compounds such as trichlorethylene, tetrachlorethylene, and PCB have been newly added to the environmental standards that have been the subject of heavy metals so far.

Conventionally, a technique has been developed that removes refractory harmful substances as much as possible from a water to be treated containing a refractory harmful substance by using a filtration apparatus, a membrane separation method, and the like, , Japanese Patent Laid-Open No. 1999-99395).

Examples of the oxidizing agent used in the in situ chemical oxidation method for removing harmful substances as described above include permanganic acid, hydrogen peroxide, ozone, and persulfuric acid.

However, in the case of permanganic acid, it is an oxidizing agent applied to the restoration method of many polluted areas. There are many cases applied to the field, but it is very stable in the soil, while it is an oxidizing agent which is difficult to apply to various organic pollutants due to low reactivity It has disadvantages. In the case of hydrogen peroxide, hydroxide radicals are produced through catalytic reaction, and thus exhibit very good reactivity and wide applicability. On the other hand, it is very unstable in the soil and is easily decomposed, so that it is difficult to penetrate deeply into the soil. Hydrogen peroxide is required, and the cost is low. In addition, ozone is disadvantageous in that it is difficult to handle owing to its presence in a gaseous phase, and it is difficult to effectively apply to various organic pollutants due to low solubility in water.

However, persulfuric acid has relatively high stability in soil as compared to other oxidants, has wide reactivity to various contaminants, and has recently attracted a great deal of attention as a substitute for conventional oxidants.

In general, an oxidizing agent forms a more reactive radical through an activation reaction than itself, thereby effecting a more effective oxidation reaction. Persulfate also forms radicals through an activation reaction, and in this case, it has a stronger oxidizing power and can effectively decompose contaminants.

However, the conventional activating method using persulfate has not been able to effectively induce the activation of persulfate in the soil due to technical, economic, or environmental problems. The conventional method activates persulfuric acid by using heat, UV, hydrogen peroxide, a base, a transition metal and the like (for example, Korean Patent Publication No. 2005-7014095), and the reaction formula is as follows:

S ₂ O ₈ ^{2 -} + heat ^- > ² SO ^{4 -} (1)

S ₂ O ₈ ^{2 -} + UV ² SO ^{4 -} (2)

S ₂ O ₈ ^{2 -} + Fe ^{2 + -} SO ^{4 -} + SO ₄ ^{2 -} + Fe ^{3 +} (3)

However, in the soil environment, the "heat" activation method requires the entire soil to be heated to 70 ° C or more, which is economically inefficient and has a secondary pollution problem that kills native microorganisms. Activation methods using "UV" can not be implemented in soil because the soil does not transmit light. In addition, some cases of activation using hydrogen peroxide, a base, and a transition metal in the soil have been reported. However, there is a problem that when using "hydrogen peroxide", it is very unstable in the soil and is easily decomposed and consumed. , There is a problem that secondary contamination occurs when the pH of the soil is increased to 10 or more. In the case of "transition metal", there is a problem that the transition metals and persulfuric acid, which are activators, I have.

Accordingly, the present inventors have solved the problem that it is very difficult to predict the by-products due to oxidative decomposition in the case of the degradable organic materials such as dioxins or highly toxic chlorine-based organic pollutants (for example, TCE) As a result of repeated studies, it has been confirmed that there is an excellent decomposing effect when the zero valent iron and persulfuric acid are used together with the refractory organic pollutants, thereby completing the present invention.

An object of the present invention is to provide a method for decomposing a poorly decomposable organic compound, which comprises decomposing a poorly decomposable organic compound by reacting ferrous sulfate and persulfuric acid.

Another object of the present invention is to provide a method for recovering soil or ground water comprising the step of decomposing a non-degradable organic compound contained in soil or ground water by reacting ferrous iron and persulfuric acid.

In one aspect of the present invention, there is provided a decomposition method of a decomposable organic compound which comprises decomposing a decomposable organic compound by reacting ferrous sulfate and persulfuric acid to activate persulfate.

According to another aspect of the present invention, there is provided a method for restoring soil or ground water comprising decomposing a refractory organic compound contained in soil or ground water by reacting ferrous iron and persulfuric acid to activate persulfuric acid.

Hereinafter, the present invention will be described in detail.

The present invention provides a method for decomposing a decomposable organic compound, which comprises decomposing a decomposable organic compound by reacting with zero-valent iron and persulfate.

Sulfuric acid refers to an ion or a compound containing [SO ₅ ] ^2- or [S ₂ O ₈ ] ^2- , which is an anion, wherein the anion [SO ₅ ] ^2- contains one peroxide group at the center of the sulfur On the other hand, in the case of [S ₂ O ₈ ] ² -, peroxides function to link sulfur atoms.

These persulfates are known to be activated by divalent iron ions. However, it has not been proved that reductive activation by Zero iron has been possible until now. In the present invention, it has been proved that persulfuric acid can be activated reductively by the zero valent iron, and the divalent iron eluted from the zero valent iron surface also contributes to the activation of persulfuric acid. The reduction reaction on the surface of the zero valent iron and the reaction by the eluted divalent iron are somewhat slow to be applied to the high oxidation reaction using the reactor requiring rapid reaction. However, in the restoration of soil and groundwater pollution, It is well suited for the recovery of soil and groundwater because time is allowed and in some cases it takes a long time to flow into the contaminated area of persulfate.

In the present invention, the zero valent iron and persulfuric acid reaction uses a reductive activation method in which zero valent iron is used as a reducing agent, wherein persulfuric acid is directly contacted with the zero valent iron surface or electrons are supplied by the divalent iron eluted from zero valence iron The reaction can be carried out by forming a radical of persulfic acid (see FIG. 3).

The pollutants such as the decomposable organic compounds are oxidatively decomposed by the radicals generated by the reaction between the zero valent iron and the persulfuric acid as described above. Even in the case of the organic pollutants which are stable in the partial oxidation reaction, .

The reaction between the zero valent iron and persulfuric acid begins with the mixture of zero valent iron and persulfuric acid, and such mixing can take many forms. For example, Zero iron has been widely used as a permeable reaction wall material that has been developed and used. Therefore, there is a method of injecting zero valence iron into the form of a permeable reaction wall and then flowing a persulfate solution to induce activation. In addition, when a high degree of contamination is required and rapid restoration is required, there may be a method of simultaneously injecting persulfuric acid and zero valence iron. In this case, zero valence iron can be injected in the form of nanoparticles. May be used.

The reductive activation method using zero valent iron of the present invention converts persulfuric acid into sulfuric acid radical to obtain high oxidizing power. The reaction rate can be controlled by the amount of zero valence iron and the degree of zero valence iron dissolution. Also, as compared with divalent transition metal activation methods, the zero valence iron can induce a stoichiometric triple activation reaction compared to divalent iron, since it is much easier to control:

Fe ^{0 -} > Fe ^{3 +} + 3e ^- (4)

Fe ^{2 + -} > Fe ^{3 +} + e ^- (5)

Furthermore, the reductive activation method using the zero valence iron does not require the use of a stabilizer such as a chelating agent, so that it can be utilized as a more environmentally friendly technique.

In one embodiment of the present invention, the refractory organic compound includes, for example, halogenated dibenzodioxins (dioxins), halogenated dibenzofurans, polychlorinated biphenyls (PCBs), halogenated benzenes, alkylphenols, halogenated phenols, But are not limited to, halogenated alkenes, halogenated alkenes, phthalic acid esters, bisphenols, aromatic compounds such as aromatic nitro compounds and aromatic ether compounds, polycyclic aromatic hydrocarbons, and the like.

Examples of the halogenated dibenzodioxins include 2,3,7,8-tetrachlorodibenzo-p-dioxin, 1,2,3,7,8-pentachlorodibenzo-p-dioxin, 1,2, Hexachlorodibenzo-p-dioxin, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, 1,2,3,4,6, Dioxane, and 7,8,9-octachlorodibenzo-p-dioxin. Examples of the halogenated dibenzofurans include 2,3,7,8-tetrachlorodibenzofuran, 1,2,3,7,8-pentachlorodibenzofurane, 2,3,4,7,8- Pentachlorodibenzofuran, 1,2,3,4,7,8-hexachlorodibenzofurane, 1,2,3,6,7,8-hexachlorodibenzofurane, 1,2,3,7, 8,9-hexachlorodibenzofurane, 2,3,4,6,7,8-hexachlorodibenzofurane, 1,2,3,4,6,7,8-heptacrolodibenzofurane, 1 , 2,3,4,6,7,8,9-octachlorodibenzanurane, and the like. Examples of the polychlorinated biphenyls include Coplanar PCBs in which chlorine atoms are substituted in addition to ortho-styrenes. Specific examples thereof include 3,3 ', 4,4'-tetrachlorobiphenol, 3,3', 4 , 4 ', 5-pentachlorobiphenol, 3,3'4,4', 5,5'-hexachlorobiphenol and the like. Examples of the halogenated benzenes include chlorobenzene, dichlorobenzene, trichlorobenzene, tetrachlorobenzene, pentachlorobenzene, and hexachlorobenzene. Examples of the alkylphenol include compounds such as t-butylphenol, nonylphenol, octylphenol and pentylphenol. Examples of the halogenated phenols include chlorophenol, dichlorophenol, trichlorophenol, tetrachlorophenol, pentachlorophenol And the like. Examples of the halogenated alkenes and halogenated alkenes include dichloro propane, trichloroethane, trichlorethylene, tetrachlorethylene and dichloroethylene. Examples of the phthalic acid esters include dibutyl phthalate, butyl Benzyl phthalate, di-2-ethylhexyl phthalate, and the like. Examples of the bisphenols include compounds such as 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) and 1,1-bis (4-hydroxyphenyl) cyclohexane. Examples of the aromatic nitro compound include nitrobenzene and the like. The aromatic ethers include anisole and the like. Examples of the polycyclic aromatic hydrocarbons include benzopyrylene, klysene, benzoanthracene, benzofluorane, and picene.

The organic contaminants that can be decomposed by the radicals generated by the reaction between ferrous iron and persulfuric acid in the present invention are preferably chlorine compounds, aromatic nitro compounds, and aromatic ether compounds.

The chlorinated compounds herein preferably include but are not limited to trichlorethylene (TCE), perchlorethylene (PCE), carbon tetrachloride (CTC), chlorobenzene, and chlorophenol, The material is trichlorethylene (TCE). The reaction in the present invention proceeds by the reductive desalination reaction of the chlorinated compound (see FIG. 1). In the above, the aromatic nitro compound is preferably nitrobenzene. In the above, the aromatic ether compound is preferably anisole.

The present invention also provides a method for recovering soil or ground water comprising the step of decomposing a non-degradable organic compound contained in soil or ground water by reacting ferrous iron and persulfuric acid.

In the present invention, the above-described decomposition method of the decomposable organic compound can be applied to soil or ground water to restore soil and groundwater. It is known that persulfuric acid has the advantage of being relatively stable in environments such as soil and groundwater. However, in order to use it in in situ chemical oxidation method, it is necessary to use an environmentally friendly activation method that can control the speed. Therefore, in the present invention, as described above, the reduction of persulfuric acid by addition of zero valent iron has been developed to solve the problems of the conventional thermal activation method and the basic activation method.

The present invention has the advantage that the soil and groundwater contaminated by oil storage facilities and environmental pollution accidents can be effectively restored through the decomposition method of the refractory organic compounds according to the present invention. In particular, It is possible to efficiently solve the problems such as the control of the reaction rate and the possibility of secondary contamination by performing the conventional non-conventional method in the oxidation method.

Fig. 1 is a schematic diagram of the reductive dechlorination reaction (simultaneous reaction) of persulfate activation and chlorinated organic pollutants by zero valence iron.
Fig. 2 is a prediction diagram of the toxicity reduction effect by the oxidation-reduction simultaneous reaction.
Figure 3 shows the possible electron transfer pathways in the activation reaction of persulfuric acid with zero valent iron.
FIG. 4 shows decomposition experiments on nitrobenzene, TCE, and anisole, showing excellent decomposition efficiency (PS / ZVI) when persulfuric acid and zero valent iron are simultaneously injected.
Figure 5 shows the results of an experiment in which the decomposition efficiency of nitrobenzene was measured while changing the concentration of persulfuric acid.
FIG. 6 shows the experimental results of measuring the decomposition efficiency of nitrobenzene while changing the concentration of zero valent iron.
FIG. 7 is a graph showing decomposition efficiency when dinitrogen and zero valent iron are used for decomposing nitrobenzene. FIG.
FIG. 8 is a schematic of a field application using the method of the present invention, (1) and (2): a general processing technique; (3) and (4): Emergency treatment techniques; (5) and (6): Techniques for treating oxidation-reduction reactions for complex contamination.

Hereinafter, the specific structure and function of the present invention will be described in more detail with reference to Examples and Experimental Examples. However, the following examples and experimental examples are only illustrative of the present invention, but are not limited thereto.

In the following experiment, experiments were carried out in aqueous solution conditions to effectively induce the reaction. A 500 mL volume of dark brown bottle and a cap coated with Teflon were used. Sulfuric acid was injected after dissolving sodium persulfate (Na ₂ S ₂ O ₈ ) with high solubility in water in distilled water and zero iron was used without any treatment. In all experiments, the reaction of Zero Iron and Persulfuric acid was performed by injecting persulfate solution and organic contaminants (nitrobenzene, TCE, anisole, respectively) into the prepared reactor and stirring well. Respectively. All experiments were carried out at room temperature (23 ± 2 ° C) with stirring at 200 rpm.

Experimental Example  1: Degradation of decomposing contaminants

1-1: Nitrobenzene decomposition experiment

10 mM persulfuric acid and 2 mM nitrobenzene were injected into the reactor, and the mixture was thoroughly stirred. Then, 2 mM of zero valence iron was injected and the reaction time was 1 hour. The results were compared with those of control group (control), which was not injected with both persulfuric acid and zero valence iron, group injected with persulfate (10 mM) alone, group injected with zero valence iron (2 mM) (2 mM) were injected into both groups.

1-2: TCE  Decomposition experiment

10 mM persulfate and 2 mM TCE were added to the reactor, and 2 mM Zr was injected. The reaction time was 1 hour. The results were compared with those of control group (control), which was not injected with both persulfuric acid and zero valence iron, group injected with persulfate (10 mM) alone, group injected with zero valence iron (2 mM) (2 mM) were injected into both groups.

1-3: Anisol  Decomposition experiment

10 mM persulfate and 1 mM anisole were injected into the reactor, and 2 mM Zr was injected thereinto. The reaction time was 1 hour. The results were compared with those of control group (control), which was not injected with both persulfuric acid and zero valence iron, group injected with persulfate (10 mM) alone, group injected with zero valence iron (2 mM) (2 mM) were injected into both groups.

Experiment result

It can be seen from the above Experimental Examples 1 to 3 that when both persulfuric acid and zero valence iron are injected, the removal rate of nitrobenzene is more than 90% and that of TCE and anisole is about 80% , The removal efficiency is about 5% for nitrobenzene, about 7-8% for TCE, and about 2-3% for anisole, and the removal rate of nitrobenzene , About 2% for TCE, about 5% for TCE, and about 2-3% for Anisole (FIG. 4). As a result, it can be confirmed from the above experiment that the decomposition ratio of organic pollutants is very excellent when persulfuric acid and zero valent iron are used together.

Experimental Example  2: Zero valence iron  And Persulfate  Experiments on decomposition efficiency of nitrobenzene by concentration

The concentration of zero valent iron was fixed at 2 g / L and the decomposition efficiency of nitrobenzene was evaluated by varying the amount of persulfate injected. As a result, the concentration of nitrobenzene was not changed when persulfate was not injected together, but the decomposition efficiency of nitrobenzene was increased as the concentration of persulfate was increased. Especially, (Fig. 5).

In addition, the concentration of persulfate was fixed to 10 mM, and the nitrobenzene decomposition efficiency was evaluated by varying the injection amount of zero valence iron. As a result, there was almost no change in the concentration of nitrobenzene when the zero valence iron was not injected, but the reaction rate was also continuously increased with the increase of the dose of zero valence. Indicating that the zero valence iron acts as a limiting factor in the response (Fig. 6).

Experimental Example  3: Spiritual iron and Two ferrous  Nitrobenzene decomposition efficiency experiment

In order to compare the decomposition efficiency of zero valence iron and divalent iron, when 10 mM persulfuric acid and 2 g / L bivalent iron were injected into nitrobenzene, 10 mM persulfuric acid and 2 g / L bivalent iron were injected into nitrobenzene (Comparative Example), and the case where only 10 mM persulfate was injected into nitrobenzene (control group). As a result, the concentration of nitrobenzene was not changed when persulfate and divalent iron were injected. However, when persulfate and zero valent iron were injected, the concentration of nitrobenzene was rapidly decreased, and persulfate and zero iron were injected together , It was confirmed that nitrobenzene decomposition efficiency was excellent (FIG. 7).

Example  1: Field application experiment

1-1: General practice

Using normal oxidation treatment method, decomposition of the degradation pollutants caused by the injection of persulfuric acid by injecting persulfuric acid into the upper part of the contaminated soil, The restoration of the contaminated area was confirmed (see Fig. 8- (1)). In addition, after zero-valent iron is buried in the direction of the groundwater flow direction, the decomposition of the degradable pollutants caused by the penetration of persulfuric acid into the zero valent iron by injecting persulfuric acid into the entire surface, (See Fig. 8- (2)).

1-2: Implementation when urgent restoration is required

Slurry form of zero valence iron (or nano-zero iron) and persulfuric acid were injected directly into the contaminated area to generate active species immediately in the contaminated area. In this way, it was confirmed that the soil was restored quickly without being greatly affected by the residence time in the soil (see FIGS. 8- (3) and (4)).

1-3: Conduct in multiple areas

A chlorinated organic pollutant or the like, or a complex pollutant having different chemical decomposition characteristics, the method comprising the steps of: (i) treating a zero-valent iron (or nano- And injecting persulfuric acid into the upper part of the contaminated area and ii) filling the slurry form of zero valence iron (or nano-zero iron) into the backside of the groundwater flow in the contaminated area and injecting persulfuric acid in front of the zero valley Can be used. This method induces the respective reactions to the pollutants and persulfate to cause the reduction dechlorination reaction by the zero valence iron and the oxidative decomposition reaction by the persulfate activation simultaneously (Figs. 8- (5) and (6) Reference).

Claims (7)

A method for decomposing a poorly decomposable organic compound, which comprises decomposing a decomposable organic compound by reacting zero-valent iron and persulfate. The method according to claim 1, wherein the reaction between the zero valent iron and the persulfuric acid is performed by direct contact of the surface of zero valent iron with persulfuric acid, or by reacting the divalent iron released from zero valent iron with persulfuric acid, Wherein the decomposition of the decompositionally decomposable organic compound is performed. The method for decomposing a poorly decomposable organic compound according to claim 1 or 2, wherein the refractory organic compound is a chlorine compound. The method according to claim 3, wherein the chlorine compound is trichlorethylene (TCE), perchlorethylene (PCE), carbon tetrachloride (CTC), chlorobenzene, or chlorophenol . The method for decomposing a refractory organic compound according to claim 1 or 2, wherein the refractory organic compound is an aromatic compound. The method according to claim 5, wherein the aromatic compound is nitrobenzene or anisole. Embedding or injecting zero valence iron into a contaminated soil or groundwater containing a refractory organic compound; And
And decomposing the refractory organic compound by injecting persulfuric acid into the soil or ground water in which the zero valence iron is buried or injected.
Methods for restoration of soil or groundwater.

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