KR20040057880A - Permeable reactive barriers made of waste foundry sands - Google Patents

Abstract

PURPOSE: A permeable reactive barrier is provided which is formed of reaction medium that is inexpensive and has excellent purification action on underground water contaminated by organic matter or/and inorganic matter. CONSTITUTION: In a permeable reactive barrier for purifying contaminated underground water, the permeable reactive barrier is formed of waste foundry sand comprising 0.1 to 4 wt.% of organic carbon, 0.1 to 12 wt.% of iron and 13 wt.% or less of clay, wherein the contaminated underground water is purified by passing the contaminated underground water through the permeable reactive barrier, wherein content of the clay is 4 to 9 wt.%, and permeability coefficient of the permeable reactive barrier is 10¬-4 to 10¬-2 cm/sec, wherein thickness of the permeable reactive barrier is 0.5 to 2 m, wherein the contaminated underground water contains organic chlorine based compound, and wherein the contaminated underground water is underground water contaminated with zinc.

Description

Permeable reactive barriers made of waste foundry sands}

The present invention relates to a permeation reaction wall for purifying contaminated groundwater, and more particularly, to a permeation reaction wall made of waste foundry sand which is industrial waste.

Groundwater pollution sources are largely divided into organic and inorganic materials. Most organic materials are organochlorine compounds, and inorganic materials include anions and heavy metals.

Heavy metals are not easily broken down and accumulate in the human body. Major sources of heavy metal contamination include abandoned mines, smelting plants and plating plants. In particular, the abandoned mines are located in an area separated from the residential area, which does not attract special attention. In such an isolated area, it is difficult to invest a lot of money for groundwater restoration.

On the other hand, the permeation reaction wall used for groundwater removal is constructed with iron powder and used as a reaction medium.

In purifying contaminated groundwater, permeation reaction walls are installed in the flow path of contaminated groundwater. There are two groundwater permeation reaction walls. One is to install a permeation reaction wall in a direction crossing the flow path of contaminated groundwater as a continuous wall as shown in Fig. 1 (a). Another permeable reaction wall is a gate wall, in which a reaction wall is installed in a direction transverse to a flow path of contaminated ground water and a guide wall capable of inducing contaminants into the ground as shown in FIG.

The continuous wall passes through the wall in a natural state without changing the flow of the groundwater, so there is little possibility that the groundwater will bypass. However, there is a disadvantage that the size of the wall increases. The gate wall can reduce the size of the permeation reaction wall, but in some cases, the construction cost is increased to install the guide wall.

As a related art for the reaction medium of the permeable reaction wall, a technique using iron and iron sulfide is proposed in US Pat. No. 5,575,927. In addition, US Pat. No. 5,543,059 proposes a technique for purifying contaminated groundwater by creating a layered iron wall or column by dividing the iron particles into three zones by size.

As such, iron is basically used as a reaction medium of most permeation reaction walls. Iron is relatively harmless to humans compared to other metals and can be easily purchased. Currently, there is no embodiment of groundwater treatment using iron in Korea, but it is expected to be used in the future in the case of foreign countries. However, given the high price of iron and the difficulty of transporting it to the site, a material is needed to replace it.

The inventors of the present invention devised in the process of studying a new reaction medium of the permeation reaction wall, the object of the present invention is to provide a permeation reaction wall made of a reaction medium which is not only inexpensive but also excellent in purifying contaminated groundwater. The permeation reaction wall of the present invention is applicable to both groundwater contaminated with organic and / or inorganic materials.

1 is an example of the permeation reaction wall for contaminated groundwater purification,

Figure 1 (a) is a continuous reaction wall type

1 (b) is a gate wall type,

2 is a graph of adsorption capacity of TCE according to the amount of organic carbon contained in the foundry sand

3 is a graph showing the effect of permeability coefficient according to the clay content of the waste casting sand

Figure 4 shows the thickness of the permeation reaction wall according to the TCE concentration of the contaminated groundwater and the iron content of the waste casting sand

Is a graph that represents

5 is a graph comparing the TCE resolution of iron components and conventional iron powder of waste foundry;

6 is a graph showing the effect of reducing the TCE movement of waste foundry sand

7 is a graph of the column test results of waste foundry for TCE

Fig. 7 (a) shows normal sand

Figure 7 (b) (c) is a waste foundry sand,

8 is a graph showing the zinc removal pattern of zinc pollution groundwater.

8 (a) is the case where the initial pH of the zinc-contaminated groundwater is 2.6

8 (b) is the case where the initial pH of the zinc contamination groundwater is 3.0

8 (c) is a case where the initial pH of the zinc contamination groundwater is 4.8,

9 is a graph comparing the zinc removal pattern at the initial pH of the zinc soil groundwater,

10 is a graph showing the results of column experiments on zinc contamination groundwater

10 (a) is the case where the initial pH of the zinc-contaminated groundwater is 3.0

Figure 10 (b) is the case where the initial pH of the zinc contamination groundwater is 4.0.

The permeation reaction wall of the present invention for achieving the above object is composed of waste casting sand containing organic carbon: 0.1-4%, iron: 0.1-12%, clay: 13% or less.

Hereinafter, the present invention will be described in detail.

In the analysis of groundwater contaminated by organic substances, most of them are organochlorine compounds, and the representative component is trichloroethylene (hereinafter simply referred to as TCE). In the present invention, attention was paid to the fact that the waste foundry sand has the adsorption and resolution of TCE during the experiment on the adsorption and resolution of TCE. In the foundry sand, the component that influences the adsorption of TCE is organic carbon, and the component that affects the decomposition is iron content. Therefore, foundry sand has the potential to be used as a permeation reaction wall capable of effectively removing organochlorine compounds, particularly TEC, from contaminated groundwater. To this end, the adsorption capacity and resolution of the organic chlorine compound, and the permeability coefficient should be secured, and organic carbon, iron, and clay have a direct influence on it.

In addition, in the present invention, as a result of applying waste foundry sand to groundwater contaminated with an inorganic material, the present invention has been completed by paying attention to the fact that heavy metal is easily adsorbed to the waste foundry sand.

As described above, the present invention is characterized in that the casting sand containing organic carbon, iron, and clay appropriately is made into a permeable reaction wall.

2 shows the adsorption capacity of TCE according to the organic carbon content of the foundry sand. The higher the organic carbon content, the greater the adsorption capacity of TCE. The waste foundry sand used in this experiment examined only the adsorption capacity of TCE with iron removed.

According to the present invention, the content of the organic carbon in the foundry sand is preferably 0.1 to 4%. When the content of organic carbon is 0.1% or more, it is possible to adsorb TCE or inorganic materials. Even if it exceeds 4%, the adsorption characteristics are good, but it is uneconomical because organic carbon should be added to the waste casting sand arbitrarily.

Iron content in the waste foundry sand is preferably 0.1 ~ 12%. Iron directly decomposes pollutants (TCE or inorganic) and removes contaminants by reduction. To do this, the iron content should be more than 0.1%. The higher the iron content than 12%, the better the adsorption capacity, but it is uneconomical because iron must be added to the waste foundry sand.

Clay in the waste foundry sand affects the coefficient of permeability, the relationship of which is shown in FIG. 3. Permeability and clay volume are inversely related. Permeability coefficient of permeation reaction wall should be about 10 times larger than permeability coefficient of surrounding ground. Since the permeability coefficient of the aquifer is usually about 10 ^-5 cm / sec, the permeation coefficient of the permeation reaction wall should be larger than this. To satisfy this, it is possible if the clay content is 13% or less. Preferably, the content of clay is about 4-9%, and the permeability coefficient of the permeation reaction wall is about 10 ^-4 -10 ^-2 cm / sec.

In the present invention, the thickness of the permeation reaction wall is appropriately selected in consideration of the amount of chlorine-based compounds in the contaminated groundwater and the iron content of the waste foundry sand. An example of the calculation formula of the permeable reaction wall is shown in Equation 1 below.

[Relationship 1]

Where C _ss is the concentration of TCE

C is the initial TCE concentration,

L is the thickness of the reaction wall,

v is the penetration rate of groundwater,

u is the reaction constant

D is dispersion coefficient

When the TCE concentration of the contaminated groundwater is 400 mg / L, the result of calculating the thickness of the permeation reaction wall for treatment according to the drinking water standard from Equation 1 is shown in FIG. 4. In FIG. 4, when the groundwater penetration rate is 0.01 m / day, the x axis represents the amount of iron contained in the foundry sand, and two parallel lines represent a general TCE contamination range. And the y-axis shows the TCE concentration after treatment at the wall thickness change for a given iron content. Referring to Figure 3, the minimum iron content to meet the drinking water standards is 0.8% when the thickness is 0.5m, 0.3% for 1.0m, 0.2% for 1.5m.

Therefore, when considering the TCE pollution concentration of groundwater and the iron content of the waste foundry, the thickness of the permeation reaction wall is usually about 0.5 ~ 2m.

When the waste foundry sand of the present invention is applied to the groundwater contaminated with zinc as an inorganic material, the adsorption capacity of heavy metals depends on the initial pH of the contaminated groundwater. The higher the initial pH of the contaminated groundwater, the higher the adsorption capacity of heavy metals, resulting in better removal efficiency. Therefore, it is possible to determine the persistence of adsorption of the waste foundry to the contaminated ground water as the initial pH of the contaminated ground water. In addition, by actively controlling the pH of the contaminated groundwater can be utilized to increase the adsorption efficiency. In this case, the initial pH of the heavy metal contaminated ground water is 2.6 or more, preferably 3.0 or more, and more preferably 4.8 or more.

Hereinafter, the present invention will be described in more detail with reference to Examples.

The composition of the waste foundry sand used in the experiment of the present invention is shown in Table 1 below.

division Composition (% by weight) clay Organic Carbon (TOC) iron sand Waste casting sand 1 5.1% 1.5% 2.83% Remainder Waste Foundry Sand 2 7.0% 2.6% 0.15% Remainder Waste casting sand 4 10.5% 0.5% 0.29% Remainder Waste casting sand 5 8.4% 1.8% 0.14% Remainder Waste casting sand 10 4.7% 2.5% 0.14% Remainder Waste casting sand 11 13% 4.0% 0.18% Remainder Waste casting sand 12 4.7% 2.4% 11.26% Remainder

Example 1

In consideration of the characteristics of the groundwater, the TCE solution was completely removed with nitrogen to dissolve dissolved oxygen, and the TCE solution was dissolved to the desired concentration. After injection of the TCE solution into the column using a pump, the desired adsorption capacity and resolution were determined using the ADRE (advection-dispersion-reaction equation).

Adsorption capacity of the waste foundry sand is shown in FIG. The waste casting sand used here was tested for adsorption capacity only by removing iron.

As shown in Figure 2, the adsorption capacity has a linear relationship with the amount of organic carbon contained in the foundry sand.

5 shows the results of the resolution experiment. Here, iron contained in the waste foundry sand was separated using a magnet, washed several times with methanol, dried and used in an experiment. As shown in FIG. 5, the resolution has a linear relationship with the SSA-specific surface area, which represents the content of the aqueous solution of iron.

Figure 6 shows the TCE migration inhibition effect of the organic carbon contained in the foundry sand.

Example 2

7 shows the results of the column experiments.

Figure 7a is the case of the general sand, Figure 7b and Figure 7c is for the waste foundry sand. The waste casting sand 1 of FIG. 7B and the waste casting sand 12 of FIG. 7C.

They were tested by injecting TCE solution after filling the column without special treatment, and the model and experimental conditions using ADRE are shown in FIG. 7. Two types of experiments (constant head, constant flow rate) were performed in parallel.

PVE is the pore volume of effluent divided by the pore volume between the foundry sands filled in the column. In general, the column experiment results are expressed in PVE, not in time. For example, if the PVE is 100, it can be interpreted that the experiment has been conducted for a time corresponding to 100 times the volume of the casting sand voids.

As can be seen in Figure 7 it can be seen that the movement of TCE is inhibited as the content of organic carbon, clay increases. For reference, in the case of the torpedo sand, the concentration of TCE is rapidly increased compared to the foundry sand (FIG. 7A). In addition, it can be seen that the TCE is not removed at all in the general sand. On the contrary, foundry sands 1 and 12 had TCE removal ability, and foundry sand 12 showed greater removal ability because it contained more iron (Fig. 7b, c).

Example 3

The zinc solution used in the experiment was completely removed by dissolving the dissolved oxygen using nitrogen in consideration of the characteristics of the groundwater, and then dissolved to the desired concentration. In the case of column experiment, the zinc solution was injected into the column using a pump to simulate the phenomenon when applied to the actual site.

It can be seen from Figure 8 that the adsorption capacity and removal ability of the zinc casting sand is different depending on the initial pH of the zinc solution used. The equation used to find the adsorption capacity and the removal capacity at the same time is as follows.

[Relationship 2]

Where C _aq (t) is the concentration of zinc at the time of sampling

C ₀ is the initial zinc concentration,

R is the low-constant constant of zinc adsorbed to foundry sand at the beginning (within 1 minute of experiment start)

K _obs is the removal constant of zinc.

The low constant (R) of relation 2 is expressed by relation 3.

[Relationship 3]

Where ρ _d is the mass of foundry sand used (g)

n is the volume of zinc solution (mL),

K _p is the instantaneous distribution coefficient for the foundry sand of zinc adsorbed within 1 minute of the experiment

As shown in Figure 8, it can be seen that the adsorption to the waste foundry sand increases rapidly as the initial pH increases for all used waste foundry sand. At initial pH 2.6 and 3.0 it can be seen that the adsorption of zinc occurs early in most foundry sands and no further adsorption occurs over time. In exceptional cases, it can be seen that rapid adsorption occurs in the case of the waste casting sand 12 in the case of pH 3.0. In the case of pH 4.8, it can be seen that the initial adsorption and continuous removal occur in all waste foundry sand.

In the case of Fig. 8 (a) and (b), the relational expression 2 could not be applied because no further zinc was removed after the initial adsorption. Could be saved. An example of applying relation 2 is shown in FIG. 9.

The instantaneous distribution coefficient and the removal capacity thus obtained are influenced by the pH of the components and the solution contained in the foundry sand, which is expressed by Equation 4 below.

[Relationship 4]

Log K _p = -2.30 + 0.48 pH + 0.048 C

Where C is the amount of clay contained in the waste foundry sand (%),

In addition, the removal ability is expressed by the relational expression (5).

[Relationship 5]

K _obs = -0.0852 + 0.00138 + 0.00277 TOC + 0.00126 I + 0.0163 pH

Where TOC is the amount of organic carbon contained in the foundry sand (%),

I is the amount of iron in the foundry sand (%)

The column test results for evaluating the applicability to the actual site are shown in FIG. 10. In FIG. 10, the PVE displayed on the x-axis represents pore volume of effluent, and is calculated by Equation 6 as follows.

[Relationship 6]

Where Q is the flow rate (mL / hr),

T is the time (hr),

V is the void volume of the foundry sand filled in the column (mL)

As shown in FIG. 10, after 50 PVE in the aqueous solution, the detection of zinc began, and the zinc concentration rapidly increased, showing similar values to the initial concentration. Here, the meaning of 50 PVE indicates that the movement of zinc is about 50 times slower than when there is no foundry sand. For reference, in the general sand, zinc is detected after about 1 PVE.

As described above, in the present invention, by recycling the waste foundry sand, which is defined as waste, as an alternative to iron used as a reactant of the permeation reaction wall, there is a useful effect of reducing the landfill space and purifying the contaminated groundwater at low cost. .

Claims (5)

In the permeation reaction wall to purify the contaminated groundwater, Permeation reaction wall made of waste casting sand composed of waste casting sand containing organic carbon: 0.1-4%, iron: 0.1-12%, and clay: 13% or less. According to claim 1, wherein the clay content of 4 to 9% and the permeability coefficient of the permeation reaction wall is permeability reaction wall of feju water, characterized in that 10 ^-4 ~ 10 ^-2 cm / sec. The permeation reaction wall of the waste casting sand according to claim 1, wherein the permeation reaction wall has a thickness of 0.5 to 2 m. The permeation reaction wall of the waste foundry of claim 1, wherein the contaminated groundwater contains an organochlorine compound. The water permeation reaction wall of claim 1, wherein the contaminated groundwater is groundwater contaminated with zinc.