KR20060027634A - Permeable reactive barrier and method for removing chlorinated organic contaminants using steel slag/cement paste/ferrous iron - Google Patents

Abstract

The present invention provides a permeation reaction wall consisting of a media system combining steelmaking slag, cement paste and Fe (II) to develop an economical permeation reaction wall (PRB) medium using industrial by-products, and a method for removing chlorine-based organic contaminants using the same. to provide. The media system according to the invention is superior to the ductile iron mainly used as a medium for PRB in removing chlorine-based organic contaminants, especially TCE. The medium system is the best combination for removing 0.25 mM TCE at 6.1 hours of half life with a 70% slag / 30% cement paste with a solid / liquid ratio of 0.1 and Fe (II) of 100 mM. The removal rate increases linearly as the amount of Fe (II) injection increases. Through column tests, it was proved to be suitable to continuously inject Fe (II) in the form of injecting TCE with Fe (II) dissolved in a reaction medium consisting of steelmaking slag and cement paste in the medium system according to the present invention. . The media developed in accordance with the present invention not only can be utilized as a medium for permeation reaction walls for TCE removal, but also have the added advantage of immobilizing heavy metals into the cement matrix over zero iron.

Steelmaking slag, cement paste, divalent iron, TCE, permeation reaction wall (PRB)

Description

PERMEABLE REACTIVE BARRIER AND METHOD FOR REMOVING CHLORINATED ORGANIC CONTAMINANTS USING STEEL SLAG / CEMENT PASTE / FERROUS IRON}

1 schematically shows the configuration of a column test apparatus for carrying out the method according to the invention;

FIG. 2 is a graph showing the change in concentration of TCE with reaction time for five reaction medium systems combining control steelmaking slag, cement paste and Fe (II) in a batch test and control samples, respectively;

3 is a graph showing the change of reaction rate constants according to the ratio of cement paste and steelmaking slag for the five reaction medium systems of FIG. 2, respectively;

FIG. 4 is a graph showing a change in pH with reaction time for each of the five reaction medium systems of FIG. 2;

5 is a graph showing the decomposition behavior of TCE according to the concentration of Fe (II) injection in the steelmaking slag / cement paste / Fe (II) reaction medium system;

FIG. 6 is a graph showing the relationship between the injection concentration of Fe (II) and the reaction rate constant for the steelmaking slag / cement paste / Fe (II) reaction medium system; FIG.

7 is a graph showing the decomposition behavior of TCE over time for a steelmaking slag / cement paste / Fe (II) reaction medium system in a column (continuous reaction) test in which Fe (II) is injected in a pulse type;

FIG. 8 is a graph showing the decomposition behavior of TCE over time for the steelmaking slag / cement paste / Fe (II) reaction medium system in two column (continuous reaction) tests in which different concentrations of Fe (II) are continuously injected. .

<Explanation of symbols for the main parts of the drawings>

1: column

2: spill storage

3: influent reservoir

4: peristaltic pump

5: sampling port

6: teflon tube

The present invention relates to a permeation reaction wall for removing chlorine-based organic contaminants using steelmaking slag, cement paste, and divalent iron, and more particularly, to an optimal combination of steelmaking slag, cement paste, and divalent iron. A method for removing chlorine-based organic contaminants, particularly trichloroethylene by means of a reductive dechlorination reaction using a reaction medium system, and a permeable reaction wall for removing chlorine-based organic contaminants consisting of such a reaction medium system.

According to the 2003 groundwater quality survey conducted by the Ministry of Environment, trichloroethylene (TCE) (hereinafter referred to as "TCE") is the major water quality exceeding standard among 39 issues exceeding water quality standards in the industrial area. ) Accounted for 23 cases, tetrachloroethylene (PCE) (hereinafter referred to as "PCE"), and 2 cases of nitrate nitrogen (NO ^3- ), 19 for urban areas. Eight trichloroethylene cases, eight nitrate nitrogens (NO ^3- ), and tetrachloroethylene accounted for three cases. ^[1] Among those substances that exceed water quality standards, organic compounds such as dCE and PCE, dense non-aqueous phase liquids (DNAPL), whose specific gravity is greater than that of water, are solvents and degreasing agents. Chlorine organic solvent, which is the most representative pollutant and especially toxic carcinogenic substance which is most widely contaminated with soil and groundwater at home and abroad, and is also designated as a major pollutant by the Environmental Protection Agency (EPA). admit. Therefore, these materials are strictly limited in drinking water quality standards, and there is an urgent need to develop a method for effectively removing TCE, which is a carcinogenic chlorine-based organic compound and a hardly decomposable substance.

In the past, various processing techniques for removing such TCEs have been proposed. First, a so-called "pump-and-treat" method is known, in which water contaminated with chlorine-based solvents is pumped to the ground, then the solvent is discarded and the water is returned to the aquifer. However, such a method does not go beyond its fundamental limitations in that it merely transfers contaminants elsewhere. In particular, when the soil is not uniform or when a material such as a poorly water-soluble liquid is treated, the treatment efficiency is greatly reduced. Therefore, as an alternative, the research has been conducted to reduce the mobility of contaminants by installing an adsorbent or a reactive barrier that traps the contaminants underground.

Chlorine-based organic compounds, such as TCE, are easily decomposed into harmless carbon dioxide through the action of microorganisms in the soil via ethylene by reductive dechlorination. As described above, in the field of treating chlorine-based organic contaminants by a reductive dechlorination reaction, a permeation reaction wall which is treated in-situ with zero-valent iron (Fe (0)) which dechlorinates TCE in a short time as a reaction medium. Permeable reactive barrier (PRB) (hereinafter referred to as "PRB") is the most widely studied. ^{[2] [3] [4] [5] [6] [7]} Such permeable reaction walls have the advantage that they do not require a separate treatment facility by introducing contaminants into the walls and treating them naturally. Based on this, studies have been actively conducted in Korea to develop a reaction medium for PRB based on Fe (0) and to improve the resolution of chlorine organic pollutants. ^{[8] [9] [10] [11]}

However, since such Fe (0) is expensive as a pure material, there is a disadvantage in that the initial laying cost is very high in the PRB using Fe (0), which can replace Fe (0) which occupies most of the laying cost. The development of effective and economical reaction media is called for.

Recently, research on divalent iron (Fe (II)), which has a merit that it is not only cheaper than Fe (0) but also can be obtained by using waste by-products discharged from a plating factory, has been frequently reported. In particular, there is an interest in using steelmaking slag containing a considerable amount of Fe (II), a zero-valent metal, etc., as a byproduct of the steel industry as another material for removing chlorine-based organic contaminants.

Methods of treating chlorine-based organic contaminants with iron are known from US Pat. No. 5,543,059 and US Pat. No. 5,575,927, but these methods are only those using Fe (0) or Fe (II). It is not disclosed at all.

In addition, although the international application WO 02/40409 discloses the use of blast furnace slag in a PRB system, the reaction medium of the system is based on Fe coated with Pd as its main element, and the blast furnace slag is attached to the PRB. This is only an option to prevent the efficiency of the Pd / Fe system from falling, and the blast furnace slag itself is not the basis of the PRB system. In other words, blast furnace slag does not form a reaction medium for PRB.

Making an auxiliary reaction wall comprising blast furnace slag or steelmaking slag from Korean Patent Registration No. 0432766 and installing it on the front, back, or front and back of the main reaction wall; And removing the contaminant by passing the contaminant through the reaction wall thereof is known. In addition, Korean Patent Application No. 2004-0003377, which is not yet disclosed, uses a system consisting of converter slag and Fe (II) in steelmaking slag as a reaction medium to treat chlorine-based organic contaminants by reductive dechlorination. Disclosed is a method for treating organic contaminants. In addition, it has already been confirmed that steelmaking slag modified with Fe (II) or cement modified with Fe (II) has a resolution comparable to Fe (0) in treating chlorine organic contaminants. ^{[12] [13] [14] [15]}

The above-mentioned documents disclose techniques for using steelmaking slag, steelmaking slag modified with Fe (II), or cement modified with Fe (II) as the reaction medium of PRB, but steelmaking slag, cement paste and Fe (II). Has not been disclosed in terms of the reaction medium of the combined PRB. At home and abroad, no studies on steelmaking slag / cement paste / Fe (II) reaction medium systems have been reported.

Accordingly, it is an object of the present invention to provide a method for the simple and effective removal of chlorine-based organic contaminants, in particular TCE, which is a major contaminant contaminating soil and groundwater, in particular using TCE, an inexpensive steelmaking slag / cement paste / Fe (II) reaction medium system, and the medium It is to provide a PRB composed of a system.

Another object of the present invention is to identify the optimal system for the treatment of chlorine-based organic contaminants, especially TCE, in the steelmaking slag / cement paste / Fe (II) reaction medium system.

It is still another object of the present invention to consider the effects of various parameters on the removal method and the PRB to identify the optimum conditions.

The above-mentioned objects are achieved by a method of removing chlorine-based organic contaminants by reductive dechlorination reaction using a system in which steelmaking slag, cement paste and Fe (II) are granulated and mixed in the process as a reaction medium.

In addition, the above-mentioned objects are achieved by a permeation reaction wall (PRB) consisting of a reaction medium system in which steelmaking slag, cement paste and Fe (II) are granulated and mixed in the PRB.

In the present invention, the reaction of various reaction medium systems consisting of a combination of steelmaking slag, cement paste and Fe (II) to TCE is tested by batch test to select a reaction medium system suitable for TCE removal, and then to various reaction parameters. The effects of the system were identified to investigate the system characteristics. In addition, the possibility of applying such a reaction medium system as the reaction medium of PRB was evaluated by examining the resolution of TCE while varying the injection of Fe (II) through a column test in which TCE was continuously injected.

As a result of such tests and considerations, the combined reaction medium system of steelmaking slag, cement paste and Fe (II) granulated and mixed is very suitable for the reductive dechlorination of chlorine organic contaminants. It proved effective. At the same time, the use of cement, a binder of solidification / stabilization (S / S), confirmed that even heavy metals could be fixed in the cement matrix and removed.

According to a preferred configuration of the present invention, a method for removing chlorine-based organic contaminants using steelmaking slag / cement paste / Fe (II) comprises preparing a steelmaking slag and pulverizing it to a predetermined particle size; Curing the mortar with cement and water to obtain a cement paste, and then grinding the mortar into a predetermined particle size; Preparing Fe (II) and pulverizing to a predetermined particle size; Placing the pulverized steelmaking slag, cement paste and granules of Fe (II) into a slurry reactor and floating in water to form a reaction medium slurry; Injecting a chlorine-based organic contaminant, in particular a contaminant solution containing TCE, into the reaction medium slurry; Carrying out a reductive dechlorination reaction while stirring the contents of the slurry reactor to allow the reaction to equilibrate; And separating and recovering the reaction product.

In the steps of pulverizing steelmaking slag, cement paste and Fe (II) to a predetermined particle size, it is preferable to set the predetermined particle size to 0.42 to 0.1 mm (140 mesh-40 mesh).

It is also suitable to set the solids / aqueous solution ratio in the reaction medium slurry to 0.1 on a mass basis.

In the step of injecting the contaminated solution containing TCE, it is preferable to seal the slurry reaction tank to minimize volatilization of TCE and oxidation of Fe (II) and to prevent air ingress from the outside. In addition, it is desirable to minimize the head-space of the slurry reactor to prevent partitioning of the TCE.

Moreover, it is preferable to make the initial concentration of TCE in a slurry into 0.25 mM.

In addition, it is desirable to formulate the reaction medium slurry into a reaction medium system combined with 70% steelmaking slag / 30% cement paste / 100 mM Fe (II). In particular, the concentration of Fe (II) is preferably not to exceed 200 mM.

In the step of stirring the contents of the slurry reactor to bring the reductive dechlorination reaction to equilibrium, it is suitable to stir the contents at a rate of about 8 rpm.

In addition, it is preferable to maintain the pH of aqueous solution more than neutral range during reaction.

In another preferred configuration of the present invention, instead of simultaneously mixing steelmaking slag / cement face / Fe (II) to produce a reaction medium slurry, TCE in which Fe (II) is dissolved together in a reaction medium consisting of steelmaking slag and cement paste. Fe (II) is injected continuously in the form of. As such, when Fe (II) is continuously injected, the effect of increasing the reactivity and sustainability of the steelmaking slag / cement paste / Fe (II) reaction medium system is obtained.

On the other hand, the PRB according to the present invention preferably consists of a reaction medium system combined with 70% steelmaking slag / 30% cement paste / 100 mM Fe (II).

Further, the PRB according to the present invention is more preferably made of a steelmaking slag / cement paste / Fe (II) reaction medium system formed to react with steelmaking slag and cement paste while Fe (II) is continuously injected.

Further features, advantages, and specifications of the invention will become apparent from the following description of the dependent claims of the appended claims and the embodiments of the invention.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

In a preferred embodiment of the present invention, various reaction medium systems formed from a suitable combination of steelmaking slag, cement paste, and Fe (II) are tested in a batch test to test their reactivity to TCE to obtain an optimal reaction medium suitable for TCE removal. After identifying the system, the characteristics of the system were discussed by identifying the effects of the reaction parameters on the identified reaction medium system.

In addition, through the column test to explore the possibility of the continuous treatment of the chlorine-based organic contaminant removal method according to the present invention, while changing the Fe (II) injection method was considered the ability to remove the chlorine-based organic contaminants accordingly. Thereafter, such a series of test procedures will be divided and described in more detail.

In the method of manufacturing the steelmaking slag / cement paste / Fe (II) system as the PRB reaction medium, when the steelmaking slag is aggregated and the cement is used as the binder to prepare the permeable concrete, the method of synthesizing the Fe (II) medium is performed. Since the homogeneity and reactivity of the resin are lowered, the cement paste, steelmaking slag, and Fe (II) are respectively granulated and mixed.

Test material and method

Material used

The steelmaking slag used for the test was obtained from steelmaking converter slag generated in the steelmaking process of Pohang Steel. Such steelmaking slag was used by grinding to a particle size of 0.42 to 0.1 mm (140 mesh-40 mesh) which is a size commonly taken in Fe (0) which is most often used as a medium of PRB.

The mortar was cured at 50% water / cement ratio (W / C) to produce a cement paste, which was then ground to the same particle size as steelmaking slag and used for testing.

Fe (II) (99.5%, ferrous sulfate; available from Acros Organics) was also used by grinding to the same particle size as slag and cement paste.

Batch Test

The reactor used in the batch slurry test is a vial made of borosilicate glass of about 24 ml in volume, and the silicon bulkhead of the glass bottle cap minimizes the volatilization of TCE and the oxidation of Fe (II) even after prolonged stirring. The lid bottle was triple-sealed by attaching a lead foil tape to the septum and then attaching a Teflon tape to it again.

The ratio of the reaction medium of the slurry to the aqueous solution was 0.1, and the head-space of the reactor was minimized to prevent partitioning of the TCE.

The control of the TCE solution alone was made as a duplicate sample and the reaction sample consisting of the medium and TCE solution as a triple sample to increase the reliability of the test.

TCE made of stock solution was injected into each sample using a gas-tight syringe.

Using a tumbler, the slurry was agitated at a rate of 8 rpm up and down, and during sampling, centrifugation was performed at 1500 rpm for 3 minutes, and then 50 μl of an aqueous solution was added to hexane (high performance liquid chromatography (HPLC) grade. (Obtained from Fisher Scientific)) and analyzed by gas chromatography (GC).

Column Test

1 schematically shows a column test apparatus for investigating the continuous TCE resolution of a steelmaking slag / cement paste / Fe (II) mixed reaction medium according to the present invention.

First, a glass column 1 made of pyrex glass was used as the column 1 in order to suppress the adsorption of organic matter as much as possible, and a Teflon tube 6 was used as the tubing. Column 1 was constructed with dimensions of 40 cm in length, 5 cm in diameter and 785.40 cm 3 in volume.

The sampling port 5 of the column 1 was made of Pyrex glass and Teflon, and a septum was provided in the sampling port 5 to minimize TCE leakage during sampling.

As the pump 4, a peristaltic pump was used to supply a constant flow rate, and a viton tube made of fluororubber was used to obtain high elasticity as a pipe in the pump.

The inlet TCE solution was made by injecting TCE stock solution into a deionized water in a 4 L vessel using a gas tight syringe and then completely dissolved by stirring with a magnetic stirrer for 48 hours. The test was then carried directly to a 4 L teflon collapsible bag to prevent adsorption of organics and to reduce the concentration of TCE by the headspace resulting from solution leakage.

During the test, a gas tight syringe was used to sample slowly so as not to disturb the flow in the column, a different needle was used for each sampling port, and after sampling, washing with methanol followed by N ₂ pursing This ensures that no residual material remains in the syringe and needle.

Since the measurement of pH requires a larger amount than the time of sampling, pH was measured at regular time intervals.

Reference numerals "2" and "3" not described in FIG. 1 designate the effluent reservoir and the influent reservoir, respectively.

Analytical Method

TCE in the slurry sample was analyzed using a gas chromatograph equipped with an electron capture detector (ECD) (Model GC-17A, Shimadzu, Japan).

Analytical conditions of gas chromatography were to maintain the injector at 250 ° C., the detector at 280 ° C., the column at 100 ° C. for 1 minute, and then raise the temperature by 10 ° C. per minute to 150 ° C. The total flow in was 78 ml / min and the split ratio was 25: 1. The gas chromatography column used for TCE analysis was model name AT-502.2 (Alltech, 0.53 mm x 30 m).

The pH was measured immediately after sample extraction using Orion's Model 4120 and 9159BN electrodes.

Batch Test Results and Discussion

Identification of Optimal Solid Ratio

In order to find the optimal solid ratio of steelmaking slag, cement paste and Fe (II) mixed media, the Fe (II) dosage was reduced to 100 mM, which showed effective resolution in previous studies ^{[13] [14] [15])} . 5 weight ratio combinations of 100% steelmaking slag, 70% steelmaking slag / 30% cement paste, 50% steelmaking slag / 50% cement paste, 30% steelmaking slag / 70% cement paste, and 100% cement paste The batch test was carried out. The ratio of reaction medium to aqueous solution was 10% and the initial concentration of TCE was 0.25 mM.

The change in concentration of TCE according to reaction time for each sample is shown in FIG. 2, and the reaction rate and half-life for TCE in each sample are shown in Table 1, respectively.

Reaction medium system containing 100 mM Fe (II) ^{a b} k (hr ^-1 ) Half-life (hr) n ^c 100% cement paste 2.74 × 10 ^-3 253 21 30% steelmaking slag / 70% cement paste 7.89 × 10 ^-2 8.79 18 50% Steelmaking Slag / 50% Cement Paste 1.03 × 10 ^-1 6.71 21 70% steelmaking slag / 30% cement paste 1.14 × 10 ^-1 6.08 21 100% steelmaking slag 6.63 × 10 ^-2 10.5 18

A) FeSO ₄ was used as a source of Fe (II).

          b: The initial concentration of TCE was 0.25 mM and the mass ratio of solid to solution was

              0.1.

          c: Number of samples used for nonlinear regression.

As shown in Figure 2, the concentration of the control sample consisting of TCE and deionized water is almost constant during the test it can be seen that there was no decrease by adsorption or volatilization.

Comparing the reaction rates of Table 1, the combined reaction media system of 70% slag / 30% cement paste / 100 mM Fe (II) modified with Fe (II) was a pseudo-first-order reaction. We assume that this is the fastest with a half-life of 6.1 hours. Next, the combined media systems of 50% slag / 50% cement paste and 30% slag / 70% cement paste showed half-lives of 6.7 and 8.8 hours, respectively, and 10.5 even in combination medium systems consisting solely of slag and Fe (II). Half-life of time is shown. In contrast, a combination medium system consisting solely of cement paste and Fe (II) shows significantly lower resolution than other systems. In the previous study ^[15]) , the combined media system of cement and Fe (II) removed more than about 50% of 0.25 mM TCE within 60 hours of reaction time, but in this test, the combined medium of cement paste and Fe (II) It can be seen that the reactivity of the system is very poor. Therefore, it is believed that a large amount of the active ingredient that decomposes TCE is generated in the initial reaction of Fe (II) and cement.

3 is a graph showing the reaction constant (k) for each combined reaction medium. According to Figure 3, when the slag and cement paste is properly combined, the reaction rate is increased than when the slag or cement paste is injected alone, the reaction rate is increased as the slag content is increased. It is believed that this is because the iron content of Fe (II) and Fe (III) is contained in the slag more than the cement paste (about 34%). ^{[14] Although} no clear identification has been made of the degradable materials in the slag / cement / Fe (II) reaction medium system, in light of previous test results ^{[12] [13] [14] [15]} , In the combined reaction medium system of the steelmaking slag / cement paste according to the present invention, Fe ₂ O ₃ , Al ₂ O ₃ , SO ₄ ^2-, and the like as decomposed substances in the steelmaking slag and cement paste are modified by the injected Fe (II). It is judged to have performed.

Reductive dechlorination of TCE is largely categorized into decomposition through the reaction pathways of reductive elimination and hydrogenolysis. During the course of hydrocracking, it is a reaction route that should be avoided because it produces more toxic vinyl chloride and cis-DCE (dichloroethylene), which are more difficult to degrade than TCE. ^{[16] [17])}

TCE decomposition by-products of steelmaking slag / Fe (II) systems ^[14] and cement / Fe (II) systems ^[15] show that 80% or more of TCE decomposition by-products are acetylene and ethylene. In the steelmaking slag / cement paste / Fe (II) system according to the present invention, TCE is not extinguished by adsorption or volatilization, but is reductively dechlorinated by a reaction route of reducing removal. It seems to have been. In particular, decomposition by-products such as acetylene, ethylene, and ethane produced by the reaction path of reducing reduction are harmless to the environment, and the combination medium system of steelmaking slag / cement paste / Fe (II) according to the present invention is used as the reaction medium of PRB. It should be noted that the application is very encouraging.

4 is a graph showing the pH change over the reaction time for five combined reaction medium systems. As can be seen from FIG. 4, in the combination medium system consisting of cement paste and Fe (II) and the combination medium system of 30% slag / 70% cement paste / Fe (II), the pH was reduced from the initial 6 to about 12. While the reaction time is raised to within 2 days, the reaction time is almost maintained in the vicinity of the neutral pH in other combination medium systems. Previous studies on cement media modified with Fe (II) ^{[12] [13] [15]} showed excellent reactivity in the basic region around 12.6 to 12.8 and showed a tendency that the lower the pH, the lower the reactivity. However, this test for the reaction medium containing steelmaking slag shows good reactivity even at neutral pH. In particular, it makes it possible to implement environmentally sound purification methods that, when applied to PRBs in the field, have a similar pH to soil and do not harm the surrounding environment.

Reactivity with Fe (II) Concentration

In order to investigate the reactivity of the combined media system according to the amount of Fe (II) injected, the decomposition reaction test was performed with varying amounts of Fe (II) in the 70% slag / 30% cement paste having the highest resolution. .

FIG. 5 is a graph showing test results for three Fe (II) injection concentrations of 40 mM, 100 mM, and 200 mM. According to FIG. 5, when 40 mM Fe (II) was injected, TEC was 95% degraded after 90 hours, whereas when 200 mM was injected, 0.25 mM TCE was completely removed within 16 hours of reaction time. Decomposed

The half-lives of each combination medium system were 2.9 hours for 200 mM, 6.1 hours for 100 mM, and 24.7 hours for 40 mM. In the case of Fe (0), which has been used as a reaction medium for the existing PRB, the concentration of the half-life of TCE when the injection amount was changed from 28 mM to 4,476 mM was low compared to that of 13.6 to 347 hours ^{[17] [18].} It is clear that even when Fe (II) is injected, it shows superior reaction rate.

In the case of 40 mM, up to 24 hours of reaction, similar primary reactions are well followed, as in 100 mM and 200 mM, but thereafter, they tend to lag somewhat behind the tendency of the first reaction. It is believed that this is because the pH of Fe (II) is reduced compared to the initial stage of the reaction due to the increase in pH after 24 hours and the passage of time.

6 is a graph showing the relationship between the concentration of Fe (II) injection and the reaction constant (k). Looking at Figure 6, it can be seen that the reaction rate increases linearly as the concentration of Fe (II) increases until the injected Fe (II) concentration is 200 mM. The reaction constant k / Fe (II) per unit Fe (II) with respect to the Fe (II) injection concentration is written in the right vertical axis | shaft of FIG. As can be seen, the increment of the reaction constant per unit Fe (II) when the Fe (II) concentration was increased from 40 mM to 100 mM increased when the Fe (II) concentration was increased from 100 mM to 200 mM. It is much larger than the reaction constant increment per Fe (II). That is, although the reaction constant at 200 mM Fe (II) is superior to the reaction constant at 100 mM Fe (II), the reaction constant per unit Fe (II) is linear even if Fe (II) is injected at 200 mM or more. Is not increased. In other words, injecting Fe (II) 200 mM or more may be referred to as overinjection. Therefore, it is preferable to inject Fe (II) at 200 mM or less for the economic and effective application of the reaction medium system according to the present invention to PRB.

Results and discussion of column test

For evaluation as the PRB reaction medium of the combination medium system selected in the batch test, two column tests were conducted, which differed in the method of injecting Fe (II).

First, in the first column test, the three materials remained at the same ratio of media as in the combined reaction medium system of 70% steelmaking slag / 30% cement paste / 100 mM Fe (II), which was the most reactive in the batch test. Were simultaneously filled into the column and TCE was injected to examine the TCE degradation behavior over time. The second column test was conducted by continuously dissolving 40 mM and 100 mM Fe (II) with TCE in a medium of 70% steelmaking slag / 30% cement paste.

The total porosity of the medium was 0.427 in the TCE injection test with the three mediums put together. TCE was fed upwards, and the concentration of TCE was injected at a flow rate of 0.25 ml / min by the peristaltic pump 4 at 0.25 mM as in the batch test. One pore volume is 18 hours.

Figure 7 is a graph showing the decomposition behavior of TCE over time when the TCE is injected after the three media in the column. As can be seen from FIG. 7, no TCE was detected at all up to the initial 8 pore volume, but increased thereafter and remained nearly constant from about 30 pore volume. In the form of a fracture curve or in a typical model, the curve sags along the X axis over time, despite the absence of high reaction constants k and TCE. This is because the reduction ability of Fe (II) decreases with time as compared to the original capacity at the time of initial injection. As the Fe (II) injected as particles dissolves in water and escapes from the column, the resolution decreases. It is estimated to have fallen.

It can be seen that the conversion (C / C ₀ ) of the decomposition reaction is maintained at about 75% and continues until after the 60 pore volume, which is about 9 mg, which is 25% of the TCE injection concentration, not completely exhausted. It can be seen that the TCE of / l is still being decomposed. The TCE injection concentration in this test is 0.25 mM, which is about 30 times higher than the concentration of TCE (1-2 mg / l) contaminated with groundwater. Thus, for low concentrations of TCE contaminated in groundwater, decomposition can continue to be performed up to 60 pore volumes or more, thereby enabling long term reductive decomposition. This also demonstrates that the combination medium system according to the invention is excellent as a reaction medium system for PRB.

In the second column test in which Fe (II) was continuously injected together with TCE, TCE and Fe (II) were put together in a Teflon bag and injected into the column with the initial concentration of TCE fixed at 0.25 mM. In the sampling port located after the injection but not yet introduced into the column, there was almost no change in the concentration of TCE, indicating that the Fe (II) aqueous solution did not react with the TCE.

8 is a graph showing the change in TCE concentration over time when Fe (II) is continuously injected at 40 mM and 100 mM. As can be seen from FIG. 8, both 40 mM Fe (II) and 100 mM Fe (II) effectively decompose TCE up to the initial 5 pore volume and then increase the TCE concentration from the 5 pore volume to 40 mM. In the 15 pore volume, the highest TCE concentration was increased, and in the case of 100 mM, the TCE concentration was increased the highest in the 17 pore volume. In addition, since the concentration of TCE was decreased again from then on, the conversion rate (C / C ₀ ) was maintained at about 0.16 in the case of 40 mM, and the concentration of TCE was also decreased in the case of 100 mM, so that TCE was not detected from the 35 pore volume. .

In the case of 40 mM Fe (II) and 100 mM Fe (II), the concentration of TCE was gradually increased and then decreased again, showing a uniform pattern. It is presumed to be due to the improved resolution of TCE as the active ingredients of slag and cement paste modified with Fe (II) gradually failed to fully decompose. Comparing the TCE resolution of the column injected with 40 mM Fe (II) and 100 mM Fe (II), the highest peak of TCE concentration in the column injected with 40 mM Fe (II) was injected with 100 mM Fe (II). It was about 50% higher than in the column, and the time at which the peak peak appeared was about 2 voids faster. In the column injected with 100 mM Fe (II), 0.25 mM TCE was continuously degraded to reach equilibrium below the detection limit. Therefore, it can be seen that increasing the amount of Fe (II) can improve the resolution of the medium as in the batch test results.

Fig. 7 shows the result of the first column test in which Fe (II) was injected into the column with slag and cement paste, and Fig. 2 shows the result of the second column test in which Fe (II) was dissolved together with TCE and continuously injected. Comparing 8, it appears that in Figure 7, the loss due to the outflow or oxidation of Fe (II) did not maintain the same fast resolution as in the batch test. However, in FIG. 8 in which Fe (II) was continuously injected with TCE, there was a peak of TCE in the beginning, but the sustaining force was superior to that in FIG. 7 by continuously injecting Fe (II) to maintain the reducing power. It can be seen that it is reactive with. That is, in the slag / cement paste / Fe (II) reaction medium system, Fe (II) is considered to act as an effective reaction medium system when reacted with slag and cement paste while continuously injecting with the reduction ability maintained. .

The column test results show that the slag / cement paste / Fe (II) system effectively removes TCE close to about 30 times the TCE concentration in the average groundwater, effectively decomposing TCE for much longer than the test period when actually installed in underground PRBs. Could be. In addition, steel slag, cement paste and Fe (II) used as reaction medium in this test are obtained as industrial by-products, and thus have great advantages in terms of resource recycling and economics compared to Fe (0), which is a conventional medium. The slag / cement paste / Fe (II) system could be applied as an economical and effective PRB reaction medium.

From the above test results and considerations, the following conclusions can be drawn:

1) The optimal resolution for the combination of steelmaking slag and cement paste when Fe (II) is fixed at 100 mM is the best with half-life 6.1 hours when the steelmaking slag is 70% and the cement paste is 30%. In combination with, the reaction rate increases as the amount of steelmaking slag increases.

2) In the 70% slag / 30% cement paste, the optimal combination of selected slag and cement paste, the decomposition rate increases with increasing Fe (II) concentration, but increases linearly within 200 mM. When Fe (II) is injected, the reaction rate can be increased, but the reaction constant per unit Fe (II) does not increase linearly. Therefore, Fe (II) below 200 mM is required for the development of economic PRB reaction medium. It is appropriate to inject.

3) As a result of testing the combination medium system according to the present invention in two column tests, when Fe (II) was injected simultaneously with slag and cement paste, the same fast resolution as in the batch test was not maintained, but the slag and When Fe (II) is continuously injected into the cement paste, TCE can be effectively decomposed for a long time. Therefore, when Fe (II) is continuously injected and modified into slag and cement paste, sufficient reactivity and durability can be ensured.

4) The steelmaking slag / cement paste / Fe (II) reaction medium system according to the present invention showing effective TCE resolution can be obtained by using industrial by-products. It has a big advantage in economics.

The steelmaking slag / cement paste / Fe (II) reaction medium system according to the present invention shows superior resolution to chlorine-based organic contaminants compared to Fe (0), which has been widely used as a reaction medium of PRB, and adsorbs or volatilizes TCE. Rather than being removed by means of decomposing, it is decomposed by the reaction route of reducing removal to reduce dechlorination. In particular, decomposition by-products such as acetylene, ethylene, and ethane produced by the reaction path of reductive removal are harmless to the environment, and the reaction medium system of steelmaking slag / cement paste / Fe (II) according to the present invention is used as the reaction medium of PRB. It is very advantageous in application. In addition, the steelmaking slag / cement paste / Fe (II) reaction medium system according to the present invention exhibits excellent reactivity even at neutral pH, especially when it is actually applied to PRB in the field while showing a pH similar to soil, It enables the implementation of environmentally sound purification methods that are harmless. In addition, even when a low concentration of Fe (II) is injected compared to Fe (0) it shows an excellent reaction rate is economically advantageous. When Fe (II) is continuously injected with TCE, Fe (II) is continuously injected to maintain reducing power as it is, and thus shows excellent sustainability and reactivity of TCE removal. The column test results show that the slag / cement paste / Fe (II) system effectively removes TCE close to about 30 times the TCE concentration in the average groundwater, effectively decomposing TCE for much longer than the test period when actually installed in underground PRBs. Can be. In addition, steelmaking slag, cement paste and Fe (II) used as the reaction medium according to the present invention is obtained as an industrial by-product, and thus has a great advantage in terms of resource recycling and economical aspects compared to Fe (0), which is a conventional medium. The slag / cement paste / Fe (II) system can be applied as an economical and effective PRB reaction medium. In addition, the reaction medium system according to the present invention can be removed by fixing even heavy metals in the cement matrix by using cement which is a solidifying / stabilizing binder.                     

references

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[11] Hyun-Hee Cho, Jae-Woo Park, "Study on the Effect of Surfactants and Naturally Dissolved Organics on the Dechlorination of TCE by Zero-Valent Iron (ZVI)," Journal of the Korean Society of Environmental Engineers, 24 (4), 689-696 ( 2002).

[12] Hwang, I. and Batchelor, B., "Reductive Dechlorination of tetrachloroethylene in soils by Fe (II) based degradative solidification / stabilization," Environ. Sci. Technol ., 35 , 3792-3797 (2001).

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Claims (16)

A method for removing chlorine-based organic contaminants, wherein the chlorine-based organic contaminants are removed by a reductive dechlorination reaction using a system in which steelmaking slag, cement paste, and Fe (II) are granulated and mixed as a reaction medium. The method of claim 1 wherein the chlorine organic contaminant is TCE. The method of claim 1 or 2, wherein the method comprises the steps of preparing and milling the steelmaking slag to a predetermined particle size; Curing the mortar with cement and water to obtain a cement paste, and then grinding the mortar into a predetermined particle size; Preparing Fe (II) and pulverizing to a predetermined particle size; Placing the pulverized steelmaking slag, cement paste and granules of Fe (II) into a slurry reactor and floating in water to form a reaction medium slurry; Injecting a chlorine-based organic contaminant, in particular a contaminant solution containing TCE, into the reaction medium slurry; Carrying out a reductive dechlorination reaction while stirring the contents of the slurry reactor to allow the reaction to equilibrate; And And separating and recovering the reaction product. 4. The chlorine-based organic contaminant according to claim 3, wherein the grinding of the steelmaking slag, cement paste and Fe (II) to a predetermined particle size has a predetermined particle size of 0.42 to 0.1 mm (140 mesh-40 mesh). How to remove. 4. The method according to claim 3, wherein the medium / aqueous solution ratio in the reaction medium slurry is 0.1 on a mass basis. The method of claim 3, wherein in the step of injecting the contaminated solution containing TCE, the slurry reaction vessel is sealed to minimize volatilization of TCE and oxidation of Fe (II) and to prevent air ingress from the outside. Way. 4. The method of claim 3 wherein the headspace of the slurry reactor is minimized to prevent separation of TCE. 4. The method of claim 3 wherein the initial concentration of TCE in the slurry is 0.25 mM. The process of claim 3 wherein the reaction medium slurry is formulated in a reaction medium system combined with 70% steelmaking slag / 30% cement paste / 100 mM Fe (II). 4. The method of claim 3 wherein the concentration of Fe (II) is no more than 200 mM. 4. The method according to claim 3, wherein the content is stirred at a rate of about 8 rpm in the step of stirring the contents of the slurry reaction tank to bring the reductive dechlorination reaction to equilibrium. The method of claim 3 wherein the pH of the aqueous solution is maintained above the neutral range during the reaction. The method of claim 3, wherein instead of simultaneously mixing steelmaking slag / cement face / Fe (II) to produce a reaction medium slurry, TCE in which Fe (II) is dissolved in a reaction medium consisting of steelmaking slag and cement paste is injected. A method of removing chlorine-based organic contaminants comprising continuously injecting Fe (II) in the form of Permeation reaction wall (PRB), characterized in that the steelmaking slag, cement paste, and Fe (II) are granulated to form a mixed reaction medium system. 15. The permeation reaction wall (PRB) of claim 14, wherein the PRB consists of a reaction medium system combined with 70% steelmaking slag / 30% cement paste / 100 mM Fe (II). 16. The method according to claim 14 or 15, wherein the PRB consists of a steelmaking slag / cement paste / Fe (II) reaction medium system formed to react with steelmaking slag and cement paste while Fe (II) is continuously injected. Pitcher Reaction Wall.

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