JP4700083B2 - In-situ chemical oxidation purification method for underground ground - Google Patents

Description

  In the present invention, soil and / or groundwater containing pollutants such as benzene, volatile chlorinated compounds, oils, etc. left in the ground or deep underground, particularly in factory and gas station sites, In so-called contaminated sites (in-situ environment) including at least one ground in the saturated zone, without digging / removing, provide chemicals that oxidatively decompose the pollutants by means such as injecting them into the place where the pollutants exist It belongs to the technical field of in-situ chemical oxidation purification treatment method (purification method) of underground ground, which is brought into direct contact and chemically oxidatively decomposes the pollutants into innocuous substances.

Recently, the survey by the Ministry of the Environment shows that the number of in-situ purification methods applied to contaminated sites (in-situ environment) containing at least one unsaturated zone or saturated zone in the underground ground is increasing. it can. The number of in-situ purifications (total of bioremediation, chemical oxidation, soil gas suction, and groundwater pumping) in fiscal 2004 was 78, but in the following fiscal 2005, the number increased to 104, approximately 1.3 times. ing. However, there are other cleanup measures voluntarily taken by companies, and if these are included, it is not difficult to imagine that the number of in-situ cleanup treatment methods for cleanup measures has increased considerably.
In the breakdown of the number of implementations of in-situ purification methods, groundwater pumping is more than in other technologies, but the number of applications of chemical oxidation purification methods is increasing. The main oxidizing agents used in the chemical oxidation purification treatment method include permanganate, Fenton's chemical, ozone, and persulfate. Among them, Fenton's drug (hereinafter referred to as F drug) using hydrogen peroxide (H 2 O 2), ferrous sulfate or ferrous chloride that generates monovalent iron [Fe (II)] and a pH adjuster is often used. ing.

The existing Fenton method (sometimes referred to as the in-situ Fenton chemical oxidation purification method) uses a highly oxidative hydroxy radical (.OH) generated from the F agent, so that it is a volatile organic chlorine compound (hereinafter referred to as a volatile organic chlorine compound). , VOC), BTEX (benzene, toluene, ethylbenzene, xylene) and fuel oil (hereinafter referred to as TPH) such as gasoline, light oil, heavy oil, etc., are very good chemical oxidation purification treatment methods.
This chemical oxidation purification treatment method is the most proven Fenton purification method in Japan, and is taken up as one of the oil pollution countermeasure technologies in the Ministry of the Environment's “Oil pollution countermeasure guidelines (May 2006)”.

Therefore, the technical outline of the existing Fenton method is outlined below.
The purification principle uses the reaction of the following formula (i).
Fe (II) + H 2 O 2 → .OH + OH ⁻ + Fe (III)... (I)
The above formula (i) is a reaction in which Fe (II) derived from ferrous sulfate (FeSO 4) decomposes H 2 O 2 into a hydroxyl radical (.OH) and a hydroxyl anion (OH ⁻ ).
Fe (II) is oxidized to Fe (III). (.OH) has a very strong oxidizing power and acts as an oxidizing agent for oxidatively decomposing pollutants {BTEX, TPH, chlorinated VOC, etc.}.
The basic Fenton reaction of the above formula (i) is a condition for maintaining the pH at an acidic condition of 2.0 to 4 to effectively promote the Fenton reaction in order to prevent Fe (II) from becoming iron hydroxide. It is.

The purification agent most used in the implementation of the previous Fenton method is an aqueous solution diluted and prepared to a predetermined concentration for each of the following agents.
Ferrous sulfate is used as the Fe (II) source.
Hydrogen peroxide (H 2 O 2) is used as the oxidant source.
As the pH adjuster, a mineral acid (for example, phosphoric acid) or an organic acid (citric acid) is used.
As a method of providing the above-mentioned purification agent to the pollutant (in-situ environment) in the ground, generally, through a plurality of wells installed in the target contaminated site, or rods inserted into the ground as necessary Inject the purifying drug as follows.
In other words, the general purification drug injection sequence and procedure are as follows. For each injection well, the purification drug is injected in the following three steps as one cycle.
First step: In order to make the reaction environment acidic, a pH adjusting agent is injected.
Second step: An aqueous hydrogen peroxide solution is injected as an oxidant source.
Third step: An aqueous ferrous sulfate solution is injected as an Fe (II) source.
Regarding Fenton drug injection, the reaction between Fe (II) and H2O2 is very fast, so Fenton drug can be injected into separate wells or pulsed for each drug when injected into the same well. It should be noted that it should be injected separately, and it should be noted that it should never be “mixed” mixed together.

By the way, the following technical problems have been pointed out regarding the above-described Fenton method .
(A) The durability of the chemical oxidation reaction is short (the reaction is completed in a short time).
That is, in the reaction of the above formula (i), Fe (II) and H2O2 existing in the liquid react with each other, so (.OH) is generated at once and the reaction is completed in a short time. Therefore, the sustainability of the degradation effect is short-term.
(B) It is difficult to mix the drug homogeneously in the ground and / or groundwater.
In order to advance the reaction of the above formula (i) to a complicated and non-uniform geological environment in Japan, when the three kinds of drugs described in [0005] are sequentially injected, for example, the three kinds of drugs are contained in one container. Are not mixed uniformly as in the case of mixing, and inhomogeneity occurs in the degree of mixing. As a result, the amount of (.OH) produced is somewhat distributed, and the decomposition effect of the pollutant varies.
(C) The chemical oxidation reaction is intense.
If Fe (II) already exists in the original soil and the soil environment becomes acidic, the Fenton reaction proceeds with the dissolved Fe (II) and the H 2 O 2 aqueous solution injected therein. Furthermore, when ferrous sulfate solution is added, the reaction proceeds rapidly at a time while generating bubbles, and may generate heat. as a result,
(A) The injected drug is ejected to the ground.
(B) The well pipe material for injection made of vinyl chloride is melted by reaction heat.
(C) The generated bubbles block the gaps between the soil particles, preventing the drug solution from penetrating widely.
And so on.
(D) The metal in the soil is eluted.
Since the reaction environment is adjusted to be acidic (pH 2 to 4), the metal contained in the soil may be eluted to cause secondary environmental pollution.
(E) It is necessary to execute three steps as the injection step, which takes time and increases the purification period.

However, as a method for treating pollutants in the in-situ environment, the above-described Fenton method (in-situ Fenton chemical oxidation purification method, hereinafter referred to as F-ISCO) is VOC, It is recognized as a good ISCO purification technology against the decomposition of BTEX, TPH, and the like.
On the other hand, there is a need for reduction in purification costs, and further technological improvements make injection control easier, making mild Fenton reaction, and suppressing metal elution, stable even in neutrality. The realization of the F-ISCO technology is progressing.
Therefore, recently, an improved Fenton method (referred to as the Modified Fenton method in the United States) disclosed in the following Patent Document 1 developed in the United States to meet the above needs has been proposed and transferred to Japan. ing.
Japanese Patent No. 3793084 (Special Table 2003-503197)

Here, first, the technical outline of the improved Fenton method disclosed in Patent Document 1, that is, the invention “Soil and / or Groundwater Improvement Method” according to Japanese Patent No. 3793084 will be outlined and the problems will be described.
The improved Fenton method disclosed in Patent Document 1 prepares an aqueous catalyst solution in which the pH of a solution containing previously chelated iron is adjusted to 5 to 7, and the aqueous catalyst solution is preceded by an aqueous H2O2 solution containing a stabilizer. This is a method of chemically oxidizing and purifying pollutants in the in-situ environment by additionally providing them to the in-situ environment provided.
The purification principle is the same as the previous Fenton method (in-situ Fenton chemical oxidation purification method) in that Fe (II) decomposes H2O2 and uses the generated (.OH) for the decomposition of pollutants. is there. However, the improved Fenton method is characterized in that it is devised to generate (.OH) even in a neutral reaction environment. That is, the Fe (II) source is iron / chelate, and the aqueous solution is used after adjusting the pH to 5-7.

As a specific purification method, as the purification (injection) chemical, the chemicals shown in Table 1 below are used as the most preferable chemical names, and “stabilized oxidant source aqueous solution” and “treatment agent (catalyst treatment agent)” are used. Is prepared.

Next, a preferred method for preparing a cleaning (injection) drug is described as follows.
(A) Preparation of Stabilized Oxidant Source After adding phosphoric acid as a stabilizer to the purchased H2O2 aqueous solution, a stabilized oxidant source is prepared by diluting to a concentration of less than 35 wt% with water.
At the time of injection, the 35 wt% solution is further diluted to less than 10 wt%.
(B) Preparation of treatment agent Sodium hydroxide or sodium acetate is added to the aqueous solution in which iron sulfate and EDTA are dissolved, and the pH of the solution is adjusted to 5-7.

Next, a method for providing a purification agent up to a contaminant (in-situ environment) in the ground is described as follows.
(C) Order of injection of the purifying agent The stabilized oxidizing agent source prepared as described above is injected into the in-situ environment in advance, and then the above-described treatment agent is injected.
The most preferred drug injection method provides a stabilized oxidant source to the in situ environment to disperse or move to the contaminated area, and then inject the treatment agent into the contaminated area in situ environment.
(D) A specific injection method (means) is as follows.
For the groundwater, an oxidizing agent source and a treating agent, which are purification agents, are directly injected through a vertical or horizontal hole by a pump.
For the soil, an oxidizing agent source and a treating agent, which are cleaning agents, are injected by a pump through a hole near the contaminated site or an infiltration trench.

About the improved Fenton method disclosed by said patent document 1, the following problem is pointed out as a problem which should be solved.
(Part 1): The reaction of mixing the two solutions in the ground is difficult to be uniform.
If the above three kinds of drugs are injected into a complicated and non-uniform geological environment like Japan, it is hoped that the three kinds of drugs will be mixed evenly, for example, in one container. Therefore, heterogeneity occurs in the actual condition of mixing. As a result, a slight distribution occurs in the amount of (.OH) generated, and the decomposition effect of the pollutant varies, resulting in poor reliability and accuracy.
(Part 2): The preparation procedure and procedure of the injected drug are complicated.
(Part 3): Since the injection process has two steps, it takes time and the construction period is prolonged.
There is a natural need for a contractor who wants to adopt an in-situ chemical oxidation treatment method in which the purification period is shortened as much as possible and the construction cost is low. On the other hand, the person in charge of construction is obliged to observe the construction safely.

Therefore, the first object of the present invention is to ensure that the preparation of the cleaning chemical solution is safe depending on the soil environment of the in-situ environment to be purified, the type of contaminants, the target purification period, and other construction conditions. It is an object of the present invention to provide an in-situ chemical oxidation purification treatment method that can be carried out easily and can improve the certainty, reliability and accuracy of the purification effect.
Another object of the present invention is to provide an in-situ chemical oxidation purification treatment method that can uniformize the contact environment between a contaminant in the in-situ environment to be purified and the chemical solution for purification, and eliminate variations in the purification effect. It is.
It is a further object of the present invention to provide an in-situ chemical oxidation purification process method that can save time for purification work and processes, greatly shorten the purification work period, and save construction costs.

As a means for solving the above-described problem, an in-situ chemical oxidation purification treatment method for an underground ground according to the invention described in claim 1 includes:
In a method for chemically oxidizing a pollutant in an in-situ environment including at least one ground in an unsaturated zone or a saturated zone in an underground ground,
Preparing a mixed aqueous solution in the range of pH 4-7 containing ferrous sulfate, sodium citrate and hydrogen peroxide in a treatment tank prepared on the ground;
Preparation of the mixed aqueous solution in the treatment tank was carried out by changing the molar ratio of ferrous sulfate to divalent iron with respect to sodium citrate to an aqueous solution containing 0.5 to 4.0% by weight of hydrogen peroxide. A pH adjusted to a range of 6 to 7 by mixing a solution adjusted to -2.0,
The mixed aqueous solution is supplied to an in-situ environment, and a pollutant is chemically oxidized to a harmless substance in the in-situ environment including at least one ground of an unsaturated zone or a saturated zone.

The invention described in claim 2 is the in-situ chemical oxidation purification treatment method for underground ground according to claim 1 ,
The mixed aqueous solution is provided to an in-situ environment through an injection well at an elevated pressure.
The invention described in claim 3 is the in-situ chemical oxidation purification treatment method for underground ground according to claim 1 ,
The mixed aqueous solution is provided to an in-situ environment by an injection method using a boring rod at an increased pressure.
The invention described in claim 4 is the in-situ chemical oxidation purification treatment method for underground ground according to claim 1 ,
The mixed aqueous solution is provided to the in-situ environment by a hydrofracture method (hydraulic crushing method) at an increased pressure.

According to the in-situ chemical oxidation purification treatment method of the present invention, since the infusion chemical is prepared in advance in a treatment tank prepared on the ground before injection, the adjustment is easy and reliable. That is, in order to adapt to the given purification conditions and construction conditions, such as the type of pollutants in the in-situ environment, soil environment, target purification period, etc., the chemical solution for purification in advance in the treatment tank 1 prepared on the ground. Preparation and pH adjustment can be performed precisely and uniformly. Since the purification chemical solution thus prepared is provided to the in-situ environment, there is no distribution in the amount of (.OH) generated in the in-situ environment, and evenly permeates and distributes into the soil particle voids. There is no variation in the environment in contact with pollutants and the degradation effect. In other words, the purification effect can be expected to be uniform and uniform, and the construction accuracy and quality will be high.
In addition, in the preparation of the chemical solution for purification in the treatment tank, it can be adapted to the given purification conditions (purification purpose), such as the soil environment in the in-situ environment, the type of contaminants, the target purification period, etc. The certainty and reliability of construction will be high.
Moreover, according to the in-situ chemical oxidation purification treatment method of the present invention, the purification period is greatly shortened, which contributes to a reduction in construction costs. That is, the construction period required for carrying out the in-situ chemical oxidation purification treatment method occupies most of the time required for the injection of the cleaning chemical solution. However, the above-described conventional Fenton method requires a three-step injection process, and the improved Fenton method. However, although a two-step injection process is required, in the present invention, a purification chemical solution prepared in advance and pH-adjusted in a treatment tank prepared on the ground is injected, so a one-step injection process is sufficient. Therefore, the implementation period of the purification treatment method can be reduced by half.

In a treatment tank prepared on the ground, a mixed aqueous solution containing ferrous sulfate, sodium citrate and hydrogen peroxide is prepared in the range of pH 4-7.
More specifically, an aqueous solution containing 0.5 to 4.0% by weight of hydrogen peroxide has a molar ratio of ferrous sulfate to divalent iron of 1.0 to 2. The pH is adjusted to a range of 6 to 7 by mixing the solution adjusted to 0.
The mixed aqueous solution is supplied to the in-situ environment, and the pollutant is chemically oxidized to a harmless substance in the in-situ environment including at least one ground of the unsaturated zone or the saturated zone.
The mixed aqueous solution is provided to the in-situ environment through an injection well at an increased pressure, or to the in-situ environment by an injection method using a boring rod at an increased pressure. Alternatively, it is provided to the in-situ environment by the hydrofracture method (hydraulic fracturing method) at an increased pressure.

(1) Laboratory test for preparation and pH adjustment of purification (injection) drug First, actual soil containing pollutants in the in-situ environment (application site) where the in-situ chemical oxidation purification treatment method of the present invention is carried out Alternatively, groundwater is sampled, and the mixing ratio of each chemical of H2O2, ferrous sulfate and sodium citrate is within the following ranges, and the solution mixed with 3 chemicals is suitable for attenuating and purifying the target pollutant. The mixing ratio of various chemicals and the pH of the solution are obtained through laboratory tests. A so-called treatability test is performed.
The conditions for laboratory tests are as follows.
H2O2 concentration: 0.5-4.0%
Fe (II) / H2O2 (molar ratio) = 1/100 to 1/50
Fe (II) / sodium citrate (molar ratio) = 0.5 to 2.0
Next, in accordance with the solution conditions obtained in the laboratory test, solid sodium citrate is dissolved in an aqueous solution obtained by diluting H2O2 (35 wt%) with water, and after dissolution, ferrous sulfate is added to purify the dissolved solution. Drugs for use.
The above three kinds of cleaning agents chemicals were mixed, pH by blending sodium citrate and ferrous sulfate as the pH of the targeted Ri Do the adjustment (regulation) already, its on Fe (II ) And chelate and Fenton reaction activity in which the generation of hydroxy radical (.OH) proceeds . As described later in paragraph [0025] with reference to FIG. 2, the pH of the aqueous ferrous sulfate solution is acidic, and the pH of the aqueous sodium citrate solution is alkaline. Therefore, a chelate obtained by mixing these two aqueous solutions. The solution pH can be adjusted in the range of 4-7. Since sodium citrate is excellent in chelating power, it is also used as a chelating agent for chelating Fe (II).
Therefore, in the following, the above-mentioned purification agent will be referred to as “chelate-Fenton activation solution”.

(2) Injection method (method of providing a purification agent to the in-situ environment)
Preparation of infusion drug:
A treatment tank 1 having a capacity corresponding to the site where the in-situ chemical oxidation purification treatment method of the present invention is carried out was prepared (FIG. 1), and the above-described “chelate-Fenton activation solution” was prepared and completed. The “chelate-fenton activation solution” is injected through the injection pump 2 and the injection well 3 or the boring rod prepared in the in-situ environment (application site) in the following manner.
Well injection method:
A well 3 having a slit 3a is installed in the depth range (saturation zone in FIG. 1) of the in-situ environment (application site) to be purified, and the above-mentioned “chelate-Fenton activation solution” Directly into the in-situ environment. The injected “chelate-Fenton activation solution” passes through the slit 3 a of the well 3, and in the unsaturated zone, penetrates into the voids of the soil particles and spreads to the periphery. When injected into the saturation zone, it spreads to the periphery so as to push out the groundwater in the voids of the soil particles, forming chelate-Fenton reaction active regions, respectively.
Boring rod injection method:
A boring rod is driven to the depth range of the in-situ environment (application site) to be purified, and the “chelate / fenton activation solution” is directly injected at an increased pressure by a pump connected to the boring rod. To provide.
Hydrofracture method (hydraulic fracturing method):
Sand slurry is injected into the upper part of the contaminated plume in the ground to artificially create a sand layer with a spread of several centimeters in thickness. Direct injection of the “chemical solution”. The “chelate-fenton activation solution” penetrates the contaminated plume through the sand layer.

The in-situ chemical oxidation purification treatment method of the present invention implemented as described above uniformly distributes the field of direct contact between the “chelate-Fenton activation solution” that is a purification agent and the target contaminant. That is, since the purification agent already in the Fenton reaction active state is directly injected, a uniform field of Fenton reaction activity can be created in the in-situ environment where this is provided, and (.OH) and the pollutant are in easy and reliable contact. This will cause degradation of pollutants.
However, in the present invention as well, the purification principle uses the reaction of the formula (i) described in paragraph [0004] for the above-described Fenton method, but there is no change.
As for shortening the cleaning work period, the majority of the purification construction period and the installation time of such injection wells, a time required for injection of the cleaning agent. In the case of the present invention, the injection process of the purification agent is completed with one injection well per injection well, compared to the purification treatment method that requires two injection steps as in the improved Fenton method described above. By simply calculating, the injection time is halved. In addition, since the time and effort required is reduced accordingly, the construction period can be greatly shortened and the construction cost can be reduced.

Next, the in-situ environment (application site) to be purified is the site of a gas station, where there is benzene contamination of groundwater, and the present invention is applied to purification work mainly for decomposing and removing benzene in groundwater. The case of carrying out the in-situ chemical oxidation purification treatment method will be described below with reference to the drawings.
In general, a large number of wells for injecting the cleaning chemical solution are installed in the construction site according to the contamination range, but FIG. 1 shows a case where there are three injection wells for convenience.
The benzene contamination of the groundwater of this purification work target site exists in the range of 4m to 7m below the surface of the saturated zone groundwater, and the benzene concentration in the groundwater is about 3mg / L. The formation in the injection range of the cleaning chemical solution is sandy, and the cleaning chemical solution is easy to penetrate.
In formulating the construction plan for carrying out the in-situ chemical oxidation purification treatment method according to the present invention, the specifications of the injection well 3 are based on the results of the previous contamination investigation, and the mixing ratio of each chemical constituting the purification chemical is as described above. As explained in Example 1, a laboratory test was conducted in advance using the groundwater at the application site.

(1) Specification of injection well Total length of well: 7m
Screen length (perforated range): 4m
(2) Mixing ratio of each chemical for purification H2O2 wt%: 0.5% (35 wt% H2O2 diluted)
Fe (II) / H2O2 (molar ratio) = 1/50
Sodium citrate / Fe (II) = 1
(3) Preparation Procedure for Purification Chemical Solution In the treatment tank 1 prepared on the ground as shown in FIG. 1, the purification chemical solution (chelate / fenton activation solution) is prepared by the following steps a) to d). Prepared.
a) Dilute H2O2 with a concentration of 35 wt% with tap water to prepare a predetermined amount of H2O2 aqueous solution.
b) An aqueous ferrous sulfate solution having a concentration of 10% is prepared.
c) A 10% aqueous sodium citrate solution is prepared.
d) A 10% sodium citrate aqueous solution is mixed with the H2O2 aqueous solution of a) so as to achieve the blending ratio of (2) , and finally a 10% ferrous sulfate aqueous solution is mixed.
Thus, a cleaning chemical solution for injection (chelate / Fenton activation solution) is completed.

(4) Purification Chemical Solution Injection Process The purification chemical solution injection process will be described with reference to FIG.
The cleaning chemical solution is injected into the in-situ environment (application site) through the injection well 3 under the pressure increased by the injection pump 2 connected to the treatment tank 1. The injected cleaning chemical solution 4 penetrates into the ground around the injection well from the screen 3a of the injection well 3 while being in the chelate-Fenton reaction active state. Benzene is decomposed when the infiltrated cleaning chemical solution 4 comes into contact with benzene in the groundwater.
The above is a description of the basic injection operation in one injection well 3, and the injection process is carried out for each injection well in a sequential order.
However, the step of injecting the cleaning chemical solution can be performed at the same time into a plurality of injection wells 3 instead of the unit for each injection well. In that case, a header pipe following the infusion pump 2 is installed and connected to a plurality of injection wells 3... And a method of distributing and injecting the cleaning chemical solution to the plurality of injection wells through the header pipe is performed. .
The above injection process is repeated several times at intervals of 1 to 2 weeks. Therefore, as the number of injection wells increases, the in-situ chemical oxidation purification treatment method of the present invention increases the effect of shortening the injection time, and has a great effect on shortening the purification work period and consequently reducing the purification work cost. To do.
The effect of decomposition and removal of benzene by the above purification work will be confirmed by monitoring the water in the injection well after injection and the benzene concentration in the observation well.

(Effect of implementation)
Below, the test result in a laboratory is demonstrated about the attenuation | damping effect of benzene or kerosene, and the elution property of lead (pb) using the chemical | medical agent for purification | cleaning of this invention using the groundwater contaminated with benzene or kerosene.
(1) The pH of the reaction system can be adjusted by changing the composition of the cleaning agent.
Two types of solution, ferrous sulfate aqueous solution and sodium citrate aqueous solution, are mixed with the aqueous solution adjusted to 0.5% H2O2 by changing the molar ratio of Fe (II) and sodium citrate. The pH of the drug solution (chelate-Fenton activation solution) can be adjusted.
FIG. 2 shows that when the molar ratio of sodium citrate and Fe (II) is 2.0, the pH can be adjusted to about 7 as indicated by the black square, and the molar ratio becomes 1.0. In the case of such a formulation, the pH can be adjusted to about 6 as indicated by the ▲ mark. When the molar ratio is 0.5, the pH can be adjusted to about 4 as indicated by the mark ● .

(2) The chelate-Fenton reaction is effective even under neutral conditions.
(Part 1): Attenuation of benzene in groundwater As a condition of chemical composition of the chemical solution for purification with respect to groundwater contaminated with benzene, H2O2 is 0.5%, and the molar ratio of Fe (II) / H2O2 is 1. As shown in FIG. 3, the initial concentration of 3 mg / L is obtained by adding a cleaning chemical solution (chelate-Fenton activation solution) in which the molar ratio of sodium citrate / Fe (II) is set to 1. The amount of benzene was 0.001 mg / L after 8 hours.
(Part 2) Attenuation effect of kerosene in groundwater The left figure A of Fig. 4 is based on the conventional general-purpose Fenton method, and the right figure B shows the degradation effect of kerosene when the chemical solution for purification of the present invention is used. Yes.
That is, with respect to groundwater containing kerosene, the composition conditions of the purifying agent are as follows: H2O2 is 1.0%, Fe (II) / H2O2 molar ratio is 1/50, and sodium citrate / Fe (II) is 1 When a cleaning chemical solution (chelate-Fenton activation solution) set to 0.0 is added, the initial 1200 mg / L of kerosene becomes 320 mg / L after 8 hours. It was about 320 mg / L based on the existing general-purpose Fenton method.
Therefore, it turns out that the chemical | medical agent solution for purification | cleaning of this invention exhibits the decomposition | disassembly effect equivalent to or more compared with the thing by the past general purpose Fenton method.

(3) Suppresses elution of lead (pb).
The existing general-purpose Fenton method requires that the reaction environment be acidic, so even if the pollutants on the purification target can be decomposed and removed, the metals contained in the soil are eluted in the acidic environment. New contamination may occur.
Since lead (pb) is the most frequent metal that is found to be contaminated, it is easy to elute pb in the conventional general-purpose Fenton and the case where the purification agent according to the present invention is added to the soil containing lead. Compared.
In the case where the purification agent of the present invention was added as a condition for the pb elution test, 1/50 mol of Fe (II) and Fe (II) of 1/50 mol of H2O2 were added to an aqueous solution of 1.0% H2O2 per soil weight. A cleansing chemical solution (chelate Fenton activation solution) mixed with equimolar sodium citrate was added to the soil.
In the case of the conventional general-purpose Fenton, which is a comparison object, ferrous sulfate is added to the soil so that H2O2 is 1.0% and 1/50 mol of Fe (II) of H2O2 with respect to the soil adjusted to be acidic with citric acid. Added to the sample.
The immersion time of the soil and the reactive agent solution was 24 hours, and then centrifugation was performed to measure pb in the separated water.

As a result, the pb concentration in the separated water of the reaction system is 23 mg / Kg in the conventional general-purpose Fenton, but 0.07 mg / Kg in the case where the purification agent of the present invention is added, and the elution concentration is very small. Was confirmed. It is recognized that the purifying agent of the present invention has a high effect of suppressing elution of pb.
Table 2 below shows the elution suppression effect when the test object described above is added with the same amount of the mineral water not containing the drug as the drug volume of the reaction system.

Although the present invention has been described above together with the embodiments, the present invention is not limited to the embodiments. Without departing from the purpose and spirit of the present invention, it adds to what has been said for the precaution that is intended to encompass the technical idea of design changes and applications deformation called person skilled in the art when necessary.

It is the conceptual diagram which showed the point which enforces the in-situ chemical oxidation purification processing method by this invention. It is a correlation diagram which shows the relationship between the ratio of sodium citrate and Fe (II) and pH in a purification agent. It is a correlation diagram showing the attenuation effect of benzene by the chemical | medical agent for purification | cleaning of this invention. When A is based on the conventional general-purpose Fenton method, B is a comparative view showing the decomposition effect of kerosene by the purification agent of the present invention.

Explanation of symbols

1 treatment tank 2 injection pump 3 injection well 4 injected chemical solution for purification

Claims (4)

In a method for chemically oxidizing a pollutant in an in-situ environment including at least one ground in an unsaturated zone or a saturated zone in an underground ground,
Preparing a mixed aqueous solution in the range of pH 4-7 containing ferrous sulfate, sodium citrate and hydrogen peroxide in a treatment tank prepared on the ground;
Preparation of the mixed aqueous solution in the treatment tank was carried out by changing the molar ratio of ferrous sulfate to divalent iron with respect to sodium citrate to an aqueous solution containing 0.5 to 4.0% by weight of hydrogen peroxide. A pH adjusted to a range of 6 to 7 by mixing a solution adjusted to -2.0,
Providing the mixed aqueous solution to an in-situ environment, and chemically oxidizing the pollutant into a harmless substance in the in-situ environment including at least one ground in an unsaturated zone or a saturated zone. In-situ chemical oxidation purification method. 2. The in-situ chemical oxidation purification method for underground ground according to claim 1, wherein the mixed aqueous solution is supplied to an in-situ environment through an injection well at an increased pressure. The in-situ chemical oxidation purification method for underground ground according to claim 1, wherein the mixed aqueous solution is provided to the in-situ environment by an injection method using a boring rod at an increased pressure. The in-situ chemical oxidation purification method for underground ground according to claim 1, wherein the mixed aqueous solution is provided to an in-situ environment by a hydrofracture method (hydraulic crushing method) at an increased pressure.

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